WO2010102643A1 - Tunable optical guided-mode filter device - Google Patents
Tunable optical guided-mode filter device Download PDFInfo
- Publication number
- WO2010102643A1 WO2010102643A1 PCT/EP2009/001739 EP2009001739W WO2010102643A1 WO 2010102643 A1 WO2010102643 A1 WO 2010102643A1 EP 2009001739 W EP2009001739 W EP 2009001739W WO 2010102643 A1 WO2010102643 A1 WO 2010102643A1
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- WIPO (PCT)
- Prior art keywords
- filter device
- optical filter
- grating structure
- light field
- grating
- Prior art date
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Classifications
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- G—PHYSICS
- G02—OPTICS
- G02B—OPTICAL ELEMENTS, SYSTEMS OR APPARATUS
- G02B1/00—Optical elements characterised by the material of which they are made; Optical coatings for optical elements
- G02B1/10—Optical coatings produced by application to, or surface treatment of, optical elements
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01J—MEASUREMENT OF INTENSITY, VELOCITY, SPECTRAL CONTENT, POLARISATION, PHASE OR PULSE CHARACTERISTICS OF INFRARED, VISIBLE OR ULTRAVIOLET LIGHT; COLORIMETRY; RADIATION PYROMETRY
- G01J3/00—Spectrometry; Spectrophotometry; Monochromators; Measuring colours
- G01J3/12—Generating the spectrum; Monochromators
- G01J3/18—Generating the spectrum; Monochromators using diffraction elements, e.g. grating
-
- G—PHYSICS
- G02—OPTICS
- G02B—OPTICAL ELEMENTS, SYSTEMS OR APPARATUS
- G02B5/00—Optical elements other than lenses
- G02B5/008—Surface plasmon devices
-
- G—PHYSICS
- G02—OPTICS
- G02B—OPTICAL ELEMENTS, SYSTEMS OR APPARATUS
- G02B5/00—Optical elements other than lenses
- G02B5/18—Diffraction gratings
- G02B5/1809—Diffraction gratings with pitch less than or comparable to the wavelength
-
- G—PHYSICS
- G02—OPTICS
- G02B—OPTICAL ELEMENTS, SYSTEMS OR APPARATUS
- G02B5/00—Optical elements other than lenses
- G02B5/18—Diffraction gratings
- G02B5/1838—Diffraction gratings for use with ultraviolet radiation or X-rays
-
- G—PHYSICS
- G02—OPTICS
- G02B—OPTICAL ELEMENTS, SYSTEMS OR APPARATUS
- G02B5/00—Optical elements other than lenses
- G02B5/18—Diffraction gratings
- G02B5/1861—Reflection gratings characterised by their structure, e.g. step profile, contours of substrate or grooves, pitch variations, materials
-
- B—PERFORMING OPERATIONS; TRANSPORTING
- B82—NANOTECHNOLOGY
- B82Y—SPECIFIC USES OR APPLICATIONS OF NANOSTRUCTURES; MEASUREMENT OR ANALYSIS OF NANOSTRUCTURES; MANUFACTURE OR TREATMENT OF NANOSTRUCTURES
- B82Y20/00—Nanooptics, e.g. quantum optics or photonic crystals
-
- G—PHYSICS
- G01—MEASURING; TESTING
- G01J—MEASUREMENT OF INTENSITY, VELOCITY, SPECTRAL CONTENT, POLARISATION, PHASE OR PULSE CHARACTERISTICS OF INFRARED, VISIBLE OR ULTRAVIOLET LIGHT; COLORIMETRY; RADIATION PYROMETRY
- G01J3/00—Spectrometry; Spectrophotometry; Monochromators; Measuring colours
- G01J3/12—Generating the spectrum; Monochromators
- G01J2003/1213—Filters in general, e.g. dichroic, band
-
- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01S—DEVICES USING THE PROCESS OF LIGHT AMPLIFICATION BY STIMULATED EMISSION OF RADIATION [LASER] TO AMPLIFY OR GENERATE LIGHT; DEVICES USING STIMULATED EMISSION OF ELECTROMAGNETIC RADIATION IN WAVE RANGES OTHER THAN OPTICAL
- H01S3/00—Lasers, i.e. devices using stimulated emission of electromagnetic radiation in the infrared, visible or ultraviolet wave range
- H01S3/10—Controlling the intensity, frequency, phase, polarisation or direction of the emitted radiation, e.g. switching, gating, modulating or demodulating
- H01S3/106—Controlling the intensity, frequency, phase, polarisation or direction of the emitted radiation, e.g. switching, gating, modulating or demodulating by controlling devices placed within the cavity
Definitions
- the present invention relates to an optical filter device, which is adapted for changing parameters of a light field, in particular to a tunable guided-mode resonance filter, which is capable of changing features like an amplitude and/or a wavelength distribution of light waves. Furthermore, the invention relates to a filtering method for changing parameters of a light field, in particular changing the amplitude and/or the wavelength distribution of the light field. The invention also relates to an optical apparatus which is equipped with the optical filter device and which is adapted for conducting the filtering method. The invention can be applied e. g. in the fields of optics, laser technology, spectroscopy, optical measurements, sensor technology and the like.
- the resonance type anomaly is based on the resonance of leaky surface waves guided by the grating (see A. Hessel et al. in “Appl. Optics” vol. 4, 1965, p. 1275-1297; A. Hessel et al. in “Optics Comm.” Vol. 59, 1986, p. 327-330; and R. Magnusson et al. in "Appl. Phys. Lett.” vol. 61, 1992, p. 1022-1024), and the interest in such structures is increasing.
- guided mode resonance filters as sensors, in laser optics, or spectroscopy, as proposed e. g. in the above publication of R. Magnusson et al..
- a tunable guided-mode resonance filter comprising a reflecting grating.
- the reflecting grating is created by a series of parallel grating lines (grooves) formed in a surface of a substrate body.
- a pass band wavelength of the grating can be tuned to target a specific frequency application.
- the grating can be used as a wavelength filter.
- a wavelength shift can be achieved by changing the angle of incidence (AOI) of the in- cident light field, i.e. by a rotation of the grating around an axis parallel to the surface of the grating.
- AOI angle of incidence
- the guided-mode resonance filter described in US 5 126 680 has the following disadvantages. Firstly, in several applica- tions, it is desirable to have a constant AOI. In these cases, a wavelength shift can be obtained with multiple adjustments of an optical setup only. Furthermore, when changing the AOI, the detector system or any other subsequent optical component must also be translated to achieve optimal illumination, e. g. of the sensor at a different angle of detection (AOD) . This requires a complex technical implementation, in particular with several mobile components. In a compact or miniaturized optical system, such mobile or loose components may be problematic.
- Graded-wavelength guided-mode resonance filters have been obtained based on linearly graded TiO 2 thin film deposition along a surface of a photonic crystal (D. W. Dobbs et al. in "Appl. Phys. Lett.” Vol. 89, 2006. p. 1231131-1231133) .
- this optical element has to be translated along the surface by about 3 cm for obtaining a wavelength shift of the resonance mode from 798 nm to 909 nm.
- Compact or even miniaturized optical systems will not accommodate such displacement of optical elements.
- US 7 294 360 B2 discloses a micro-optical element comprising a structured body on a surface of which trenches are formed.
- the surface is functionalized by a thin film, which is formed by atomic layer deposition (ALD) .
- ALD atomic layer deposition
- the micro-optical element is used e. g. as a beam shaper, lens or grating.
- a plurality of parallel, line-shaped trenches can be formed thus creating a one-dimensional linear line grating.
- This grating suffers from the same disadvan- tages as the guided mode resonance filter proposed by R. Mag- nusson et al. as outlined above.
- the objective of the invention is to provide an improved filtering method for changing parameters of an incident light field, which filtering method is capable of avoiding disad- vantages of the conventional techniques and which in particular allows extended applications of guided-mode resonance filtering of electromagnetic waves.
- the objective of the invention is to provide an optical apparatus, which is capable of implementing the filtering method.
- an optical filter device with a guided-mode resonance filter has a grating structure with a refractive coating.
- the grating structure has a two-dimensional periodicity.
- the grating structure includes structure elements having a periodic ar- rangement along two directions in space, in particular along two directions on a plane surface of the guided-mode resonance filter.
- the inventive optical filter device provides an additional degree of freedom for changing parameters of a light field.
- the effect of the guided-mode resonance filter on a light field does not only depend on the angle of incidence (AOI), but also on an azi- muthal angle of a plane of incidence relative to the grating structure on the surface of the guided-mode resonance filter.
- parameters of an incident light field like in particular an amplitude and/or a wavelength distribution thereof can be changed by adjusting the orientation of the grating structure relative to the incident light field. Due to the additional degree of freedom, the adjustment of the optical filter device, in particular a selection of a wavelength distribution can be essentially facilitated. In particular, parameters of the light field can be adjusted without changing the AOI .
- a method of changing parameters of the light field using an optical filter device with a guided-mode resonance filter is provided.
- the guided-mode resonance filter has a grating structure with a two-dimensional periodicity.
- a light field incident light field
- an output light field is created, which is characterized by changed electromagnetic field parameters compared with the incident light field, in particular by a changed wavelength spectrum and/or amplitude.
- the guided-mode resonance filter of the inventive optical filter device generally comprises a solid substrate, on a surface of which the grating structure with the two- dimensional periodicity is formed.
- the grating structure carries a refractive coating.
- the refractive coating is designed for creating the resonance type anomaly for the incident light field as it is known from conventional guided-mode resonance filters.
- the grating structure with the refractive coating can be provided as a free surface exposed to the surrounding environment. Alternatively, a protective transparent coating can be provided on the grating structure.
- the inventive optical filter device is capable of changing parameters of the incident light field.
- the term "light field” generally refers to at least one electromagnetic wave with a wavelength or wavelength distribution in a wavelength range covering UV light (wavelength above 10 nm, in particular above 190 nm, like in the range of 190 nm to 400 nm) , visible light (wavelength in the range of 400 nm to 700 nm) and IR light (wavelength above 700 nm, in particular above 800 nm, up to microwaves) .
- the term “optical filter device” is related not only to filtering incident light fields in the visible wavelength range, but also in the above shorter and longer wavelength ranges.
- the incident light field may include a broad- band wavelength distribution, created e.g. by a white light source, or a narrow band wavelength distribution created e.g. by a laser with a certain centre wavelength.
- the optical filter device is capable of changing both the wavelength distribution and the amplitude of the light field.
- the optical filter device is capable of changing, i.e. switching the amplitude of the incident light.
- the grating structure generally comprises an array of structure elements.
- the array provides the two-dimensional periodicity of the grating.
- Directions of linear periodic arrangements of the structure elements are called here first and second grating directions of the grating structure.
- Each structure element is a local refractive structure of the grating structure preferably having a spot or dot shape.
- Structure elements may comprise e.g. recesses in the surface of the substrate.
- the structure elements comprise pro- jections on the surface of the substrate. Projecting structure elements have particular advantages in terms of available structuring techniques and creating a homogeneous refractive coating.
- equal periods of the grating structure can be provided along the first and second grating directions on the grating surface structure.
- Providing equal grating periods has advantages with regard to the structuring process and the adjustment of the optical filter device.
- different periods along the different grating directions can be provided.
- This embodiment may have advan- tages for adjusting predetermined parameters of the output light field.
- all structure elements may have equal heights above the surface of the substrate, or at least one height gradient can be provided depending on the particular application of the optical filter device.
- the height (s) of the projections is/are preferably selected in the range of 10 nm to 1 ⁇ m, in particular in the range from 10 nm to 300 nm.
- the structure elements comprise nipple, cone-shaped, sinusoidal, square, cylindrical, pyramidal or cube-shaped projections on the surface of the substrate.
- the grating structure comprises a moth-eye nano- structure.
- Moth-eye nanostructures are known as such for providing anti-reflecting surfaces (see above) .
- the inventors have found that moth-eye nanostructures carrying the refractive coating are particularly suitable for creating the guided-mode resonances. While the anti-reflective properties of moth eye nanostructures were well known, the inventors have found new applications of the moth eye nanostructures.
- tunable guided-mode resonance filters based on moth eye nanostructures in polycarbonate (PC) substrates have been proved as efficient wavelength filter.
- the substrates are preferably coated with an AI 2 O 3 and TiO 2 multilayer by atomic layer deposition.
- the substrate and/or at least the grating structure on the surface thereof is made of an optical grade transparent material.
- an optical grade transparent material provides advantages for an efficient wavelength selection or amplitude switching of the incident light field by adjusting the opti- cal filter device.
- Particularly preferred materials comprise glass, fused silica, quartz, MgF 2 , CaF 2 , polycarbonate, polymethylmethacrylate, polycycloolefine, polyamide, polyether- sulfon, polysulfon or fluoropolymer .
- the spatial period of the grating structure is selected depending on the wavelength of the incident light wave. With a centre wavelength ⁇ , the spatial period is preferably selected in the range of ⁇ /4 to ⁇ . With the above pre- ferred wavelength ranges, the spatial period is preferably selected in the range of 25 nm to 5 ⁇ m.
- Various two-dimensional lattices for providing the grating structure are available.
- a hexagonal or a tetragonal lattice structure is provided, which may have advantages in terms of manufacturing the structure elements and positioning the structure elements with a high spatial density.
- the refractive coating on the grating structure comprises one or multiple layers having a refractive index being different from the refractive index of the grating structure, i.e. of the substrate of the optical filter device.
- Preferred materi- als of the refractive coating comprise oxides, e.g. SiO 2 ,
- Al 2 O 3 TiO 2 , Ta 2 O 5 , ZnO, V 2 O 5 , In 2 O 3 , SnO 2 , NiO, MgO, ZrO 2 , FeO, Fe 2 O 3 , a nitride, e.g. AlN, TiN, TaN, a fluoride, e.g. MgF 2 , CaF 2 , AlF 3 , LaF 3 , a sulfide, e.g. ZnS, a metal, e.g. Al, Pt, Ir, Ni, Ag, a semiconductor, e.g. Ge, Si and/or an organic polymer, e.g. polyamides, polyether, polycarboxilate.
- the resonance anomaly of the grating structure is increased if the refractive coating comprises a stack of multiple layers having different refractive indices.
- the refractive coating i.e. the single or multiple refractive layers are made by atomic layer deposition.
- the inventors have found that the atomic layer deposition allows the creation of a homogeneous refractive coating which im- proves the resonance effects of the optical filter device.
- other deposition techniques for creating the refractive coating can be used, like e.g. CVD, PVD, thermal evaporation or the like.
- the grating structure may comprise multiple grating structure components being arranged on the substrate.
- Each of the grating structure components as such may be provided with the above features of the grating structure.
- the period and arrangement of the structures of the grating structure components may be equal or different relative to each other.
- the grating structure components can be arranged on the substrate as follows.
- a first grating structure component is arranged on a first side of the substrate, while a second grating structure component is arranged on a second, opposite side of the substrate.
- a transparent substrate is used.
- the optical filter device is provided with a wavelength tuning device.
- the wavelength tuning device is generally an equipment which is capable of changing a wavelength spectrum of the output light field.
- the wavelength tuning device comprises a first drive unit, which is capable of subjecting the grating structure to a rotation with a rotation axis deviating from the grating structure surface.
- the first drive unit is adapted for rotating the grating structure around an axis normal to the grating structure surface. In this case, a wavelength setting is possible without any change of the AOI.
- the wavelength tuning device may comprise a polarizing filter, which is capable of adjusting a polarization direction of the input light field. In this case, changing of a parameter of the output light field can be obtained without any mechanical adjustment of the optical filter device.
- the wavelength tuning device may comprise a second drive unit, which is capable of tilting the grating surface structure.
- the second drive unit is adapted for changing the AOI of the incident light field.
- the second drive unit may have advantages for adjusting the wavelength spectrum of the output light field in combination with the effect of the first drive unit and/or the polarizing filter.
- a broad field of applications is available for the optical filter device or the method for changing parameters of a light field, respectively.
- the optical filter device can be used for adjusting operation condi- tions of a laser device.
- the optical filter device can be provided in a resonator of a laser device. Due to the facilitated mechanical adjustment of the optical filter device, a wavelength selection can be provided without complex adjustment steps.
- the optical filter device may be used as a part of a sensor device, in a spectroscopic device, as an optical switch, e.g. in an optical data transmission, and/or as a part of a light wave guide.
- an optical ap- paratus which comprises a light source and an optical filter device according to the above first aspect of the invention.
- the optical apparatus is capable of providing an output light field with adjustable light field parameters depending on a setting of the geometrical orientation of the optical filter device relative to the light source.
- the optical apparatus of the invention can be provided with various types of light sources, e.g. with a broadband light source or a laser device with a laser resonator.
- the optical apparatus can be operated with an AOI in the range of nearly 0° to 90°.
- the AOI is selected in the range of 20° to 80°.
- the wavelength selection can be obtained with particular efficiency in this AOI range.
- the optical apparatus can be provided with a detector device being capable of collecting the output light field. The detector device can be arranged for detecting reflected light and/or transmitted light.
- Figure 1 a schematic illustration of a first embodiment of the inventive optical filter device
- Figure 2 an enlarged cross-sectional view of the optical filter device of Figure 1;
- FIGS. 3 to 5 schematic illustrations of further embodiments of the inventive optical filter device
- FIGS 6 and 7 schematic illustrations of wavelength tuning devices used with the inventive optical filter device
- FIGS 8 and 9 schematic illustrations of embodiments of the inventive optical apparatus
- Figure 10 microscopic images showing a moth-eyed structure used according to the invention.
- Figure 11 schematic illustrations of various lattice geometries of the grating structure of an inventive optical filter device
- Figures 12 and 13 experimental results obtained with the inventive optical filter device.
- Embodiments of the invention are described in the following with reference to the preferred implementation using moth-eye structures carrying a refracting coating of multiple refractive layers.
- the invention is not restricted to the illus- trated embodiments, but rather can be implemented with other grating structure designs as outlined in this specification.
- the invention is not restricted to these wavelength ranges, but also applicable in the UV range or in the microwave range.
- the output light field can be obtained in a reflectance mode and/or a transmission mode. In particular in the latter case, a transparent substrate is used.
- the structures shown in the Figures are strongly enlarged for illustrative purposes.
- optical filter devices having a single substrate with a single grating structure or multiple grating structure components on opposite sides of a transparent substrate.
- inventive optical filter device may comprise multiple stacked transparent substrates each carrying a single grating structure or multiple grating structure components.
- Figures 1 and 2 illustrate a first embodiment of the inventive optical filter device 100 with a perspective schematic view ( Figure 1) and an enlarged sectional view ( Figure 2) .
- the optical filter device 100 comprises a guided-mode reso- nance filter 10 with a grating structure 20, which carries a refractive coating 30.
- the guided-mode resonance filter 10 has a substrate 11 on a surface of which structure elements 21 of the grating structure 20 are provided.
- the structure elements 21 can be integrally formed with the substrate 11, e.g. by surface structuring thereof. Alternatively, the structure elements 21 could be deposited on a plane surface of the substrate 11.
- the substrate 11 comprises e.g. a polycarbonate plate with a plane surface, having a thickness of 2 mm and lateral dimensions of 50 mm * 20 mm.
- the height h of the structure elements 21 (Figure 2) is e.g. 100 nm. All structure elements 21 can have the same height h as shown in Figure 2. Alternatively, a height gradient can be provided as schematically illustrated in Figure 4. In this case, the height h changes e.g. in the range from 10 nm to 1000 nm.
- the refractive coating 30 comprises a stack of layers 31, 32 having different refractive indices.
- AI 2 O 3 - and TiO 2 - layers with a thickness of 15 nm to 70 nm are arranged in an alternating manner with a complete thickness of about 180 nm.
- the grating structure 20 extends along the x-y-plane of a Cartesian coordinate system.
- the normal direction on the grating structure 20 is directed to the z-direction.
- the grating structure 20 has a two-dimensional periodicity as schematically shown in Figure 1.
- the first and second grating directions of the grating structure 20 correspond to the x- and y-directions, resp. (indicated with the white arrows in Figure 1) .
- the structure elements are periodi- cally arranged.
- the grating directions span a plane with a lattice geometry of the grating structure.
- a substrate structured onto both sides can been coated onto both sides with grating structure components 20.1, 20.2 as illustrated in Figure 3. This will produce a double filtering guided-mode resonance filter 10.
- Both grating structure components 20.1, 20.2 are illustrates as having equal geometries.
- the structured sides may be exposed to different coating sequences by selectively masking each side of the substrate so that different grating structure components are formed.
- the spatial period of the structure elements 21 is e.g. 50 nm.
- the same spatial period can be provided in both grating directions, i.e. the centre-centre-distances between the structure elements 21 in both grating directions are identical.
- different spatial periods along the grating directions can be provided as schematically shown with the top views of the rectangular lattice and hexagonal grating structures 20 in Figures 5A and 5B.
- the spatial period ⁇ x in the x-direction is 280 nm
- the spatial period ⁇ y in the y-direction is 480 nm.
- the incident light field 1 is directed to the optical filter device 100 with a predetermined angle of incidence (AOI) ⁇ relative to the z-direction. Furthermore, the incident light field 1, in particular the plane of incidence thereof has a certain azimuthal angle ⁇ relative to the grating structure 20, e. g. relative to the x-direction.
- the output light field 2 is reflected on the surface of the grating structure 20. The amplitude and/or the wavelength distribution of the output ' light field 2 is changed, compared to the corresponding parameters of the input light field 1 due to resonance type anomalies mentioned above. Detailed examples of changing the parameters of the output light field 2 are described below with reference to Figures 10 to 12.
- the amplitude and/or wavelength distribution of the incident light field 1 can be changed by changing an orientation of the grating structure 20 relative to the direction of the incident light field 1 and/or by changing a polarization parameter of the incident light field 1.
- the optical filter device is provided with a tuning device 40. Preferred embodiments of the tuning device 40 are illustrated in Figures 6 to 8.
- the tuning device 40 comprises a first drive unit 41, which is capable of rotating the optical filter device 100 around the z-axis.
- the first drive unit comprises e.g. an electric servo motor being arranged on a solid support, like e.g. a mirror support in an optical set-up.
- the optical filter device 100 is connected with the motor shaft. With an operation of the first drive unit 41, the azimuthal angle ⁇ (see Figure 1) can be adjusted.
- the tuning device 40 may comprise a second drive unit 42 as shown in Figure 7.
- the second drive unit 42 is arranged for tilting the optical filter device 100 around an axis parallel to the surface plane thereof, i.e. around an axis in the x-y-plane.
- the second drive unit 42 may comprise at least one second electro servo motor or a pivoting mecha- nism carrying the first drive unit 41 and the optical filter device 100. With the second drive unit 42, the AOI ⁇ can be adjusted.
- the tuning device 40 may comprise a polarizing filter 43.
- the combination of the optical filter device 100 with the polarizing filter 43 is schematically illustrated in Figure 8, which further shows an embodi- ment of an optical apparatus 200 of the invention.
- the optical apparatus 200 comprises the optical filter device 100, optionally with the adjustable polarization filter 43 and/or at least one of the first and second drive units 41, 42 (see above), and a light source 210.
- a detector device 220 can be provided for collecting the output light field 2.
- the light source 210 comprises e.g. a white light source or a laser device.
- the light source 210 can be provided with imaging optics (not shown) for directing the incident light field 1 to the surface of the grating structure 20.
- FIG. 9 illustrates another embodiment of an optical appara- tus 201 according to the invention.
- the optical apparatus 201 comprises a laser resonator with a laser oscillator 211 and resonator mirrors 212.
- One of the resonator mirrors is replaced by the optical filter device 100 according to the invention.
- the optical filter device 100 By adjusting the orientation of the grating struc- ture of the optical filter device 100 relative to the light field circulating in the laser resonator, a wavelength distribution and/or amplitude of the laser light 3 leaving the resonator can be controlled.
- the application of the optical filter device in a laser resonator is not restricted to the optical set-up schematically shown in Figure 9.
- the optical filter device into other resonator geometries, which are known as such from laser technology.
- the following further details of embodiments of the invention demonstrate that in particular 3D nanostructures in polymeric material can be successfully coated with inorganic materials by atomic layer deposition (ALD) .
- the coated nanostructures show guided-mode resonances with narrow reflectance peaks and high sideband transmittance (94%) in the UV-VIS.
- the reflectance peak position can be easily tuned in a broad wavelength range (> 150 nm) through the rotation of the sample around the axis (z-axis) normal to the substrate with- out any change in the optical setup.
- the use of these filters is accentuated by the need to produce optics for ultra- compact, portable, miniaturized equipment.
- strong polarization in the optical transmittance at normal angle of incidence is observed with a rotation of the sample.
- Tunable guided-mode resonance filters based on moth eye nanostructures in polycarbonate (PC) substrates are manufactured as follows. Polycarbonate substrates with moth eye nanostructures in hexagonal ordering is obtained from Fresnel Optics.
- Figure 1OA shows a 3D AFM image of the uncoated moth- eye structure (2.5 x 2.5 ⁇ m 2 ) .
- the moth-eye polycarbonate (PC) nanostructures are coated with five layers consisting of three layers of AI 2 O 3 and two layers of TiC> 2 of varying thicknesses using ALD.
- the ALD process is carried out in a commercial hot-wall flow type ALD reactor (SUNALE R75, Picosun, Finland) .
- Al (CH 3 ) 3 (TMA), Ti(OPr) 4 (TiOP) and 30% H 2 O 2 were used as aluminum, titanium, and oxygen reactant sources, respectively.
- TMA and H 2 O 2 were delivered to the reactor as ambient temperature vapors, whereas the TiOP precursor was heated to 6O 0 C and delivered through a booster system.
- the pulsing times were 0.1 s for TMA, 0.5 s for TiOP, and 2s for H 2 O 2 with N 2 as carrier gas at a flow rate of 200 seem.
- the purging time after each pulse was set to 4 s.
- Purging was done with N 2 gas with a flow rate of 200 seem.
- the substrate temperature reached a maximum of 120 0 C.
- the growth rate of AI 2 O 3 was about 1.30 A per cycle, whereas the TiO 2 growth rate amounts to about 0.75 A per cycle.
- the substrates were exposed to 380 cycles TMA/ H 2 O 2 , 280 cycles TiOP/ H 2 O 2 , 150 cycles TMA/ H 2 O 2 , 880 cycles TiOP/ H 2 O 2 , and 630 cycles TMA/ H 2 O 2 to form a to- tal of five layers onto the substrates. Since ALD film deposition would occur on both sides of the sample, the flat side of the substrate was partially masked. Alternatively, the flat side of the substrate has been concomitantly coated with the sequence mentioned above to form an antireflective coat- ing onto the flat side.
- the chosen film structure corresponds to an antireflective coating on flat BK7 and polycarbonate substrates.
- Figure 1OB shows the multilayer structure in a focused ion beam (FIB) cross section SEM image (a 2 ⁇ m thick conducting carbon paste has been deposited onto the optical element for the FIB processing) .
- the film thicknesses as determined from the SEM image are from bottom (polycarbonate) about 38, 15, 15, 44 and 66 nm, respectively.
- a sharp boundary can be observed between the Al 2 O 3 and TiO 2 layers.
- the moth eye hexagonal nanostruc- tures are perfectly retained after the ALD coating (see Figures IOC and 10D) .
- the grating period of the coated nanos- grappltures is equal to the period of the uncoated substrates; whereas the grating depth decreases with increasing thickness of the coating material.
- the AFM image of the coated sample illustrates the effect of rotation around an axis normal to the surface on the illumination geometry.
- the area in Figures 1OC and 1OD is 1 ⁇ m 2 .
- the black arrow depicts the beam of incident light 1, while the white arrow depicts the rotation of the sample.
- the sample is rotated around the axis perpendicular to the substrate while the light source and detector (see e. g. Figure 8) are kept fixed.
- Figure 1OC corresponds to an azimuthal angle of about 0° rotation, and Figure 1OD to about 90°.
- the incident beam crosses the nanostructures along the diagonal line with a large gap between the struc- ture elements 21 (e. g. cones) .
- the cones are closely packed along the beam direction.
- the rotation of the sample actually leads to a change of the grating periods as it is further illustrated in Figure 11.
- the period pi in the coordinate perpendicular to the incident beam direction is equal to the diameter d of the structure elements 21.
- Adjusting the orientation of the optical filter element comprises setting the grating period for influencing the elec- tromagnetic field parameters of the output light field.
- Figure 12A shows the reflectance with the sample at about 40 to 90° rotation
- Figure 12B the data at about 90 to 130° rotation.
- the rotation angles are indicated above the main peaks.
- the strongest resonances were observed between 60° to 120°.
- the symbols correspond to the data points and the lines are a guide to the eye.
- strong reflection peaks can be ob- served between 390 and 600 nm wavelength.
- the reflectance peaks reach about 20% with narrow bandwidths (FWHM about 4 nm) .
- the peak position shifts by 55 nm between 80° to 100° rotation of the sample.
- the resonances at a fixed AOI can be easily tuned through rotation of the sample and/or rotation of the polari- zation of the incident light.
- the resonance modes observed for p-polarized light can be tuned in a broader range through rotation of the sample, than by changing the angle of incidence.
- circular optical elements of such coatings can be used as components in highly compact, miniaturized laser optics, refractive index sensors, spectrometers, etc. where the element cannot be shifted and/or tilted (see Figure 9) .
- the prime advantage of such tunable filters is that no change in the illumination/detection setup is required for wavelength filtering, reducing the number of mobile parts of the optical instrument.
- tuning the resonances yields an amplitude modulation of the output light.
- the output light With adjusting the optical filter device such that the resonance is tuned to the wavelength of the incident light, the output light can be switched on. With a detuning of the resonance relative to the wavelength of the incident light, the output light can be switched off.
- the wavelength position and intensity of the resonances for a given incidence angle can be shifted by varying the grating period, depth, and film thickness of the GRMG filter. How- ever, this approach is less attractive since an optical element must be produced for each wavelength position.
- the invention is considered to enhance the transmittance/reflectance properties of the optical filter specifically at oblique AOI.
- Increasing the grating depth, in particular of the moth-eye structures, up to the grating period could cause increased measured resonance peaks.
- ultra-narrow bandwidth filters can be provided with the inventive optical filter device.
- a minimal deviation and high thermal stability of the nanostructures is preferred.
- Multilayer structures have been shown theoretically to reduce the FWHM of the ID guided mode resonance grating filters.
- the multilayer coating corresponding to an antireflective coating onto unstructured substrates additionally provides low sideband reflectance (high transmittance) of the optical element in a broad spectral range.
- Additional impact onto the optical properties of the inventive optical filter device has the polarization of the incident light with respect to the moth-eye nanostructure array.
- Polarized reflectance, transmittance and ellipsometry meas- urements were carried out on two different ellipsometers, both from J. A. Woollam Co., Inc..
- the M-2000 ellipsometer equipped with a rotating compensator and the VASE measurement system were used.
- the backside of the substrates was roughened and blackened after the transmittance measurements to avoid perturbing reflections from the uncoated side in the reflectance measurements.
- Cross-polarized transmittance data were recorded with p- and s-polarized incident beams and detection in p- and s-polarization position of the analyzer (Tp P , Tp 3 , T ss , and T S p) . Reflectance data were obtained with p- and s-polarized incident beams.
- the sample was mounted onto a graded circular plate, and the plate was rotated manually from 0° to 180° in 10° steps. An error of about 1 to 2° in the rotation of the plate can be accounted.
- the sample was positioned onto the centre of the plate to ensure that the same region was analyzed. However, additional data obtained at the same rotation angle from dif- ferent sample positions showed very little variation; specifically, 2 to 3% intensity variation at the same wavelength position.
- Polarized reflectance and transmittance measurements identi- fied multiple channels of narrow-band reflections in the ultraviolet-visible range.
- the wavelength position of the reflection peaks can be easily tuned in a broad range (more than 150 nm) through rotation of the optical element around the axis normal to the substrate.
- the transmittance data also indicated rotation dependent polarization probably associated with the birefringence of the substrate material and the form of the nanostructures .
- the spectral shift of the reso- nance modes can be further influenced by adjusting the AOI.
- Experimental results obtained with an angle of incidence between 20° to 60° are illustrated in Figure 13.
- the 0° rotation position of the sample has been chosen for s-polari- zation and the 120° rotation for p-polarization because at these rotations only one intense leaky mode was observed. It can be observed, that the peak position for the s-polari- zation shifts very strongly with the AOI, whereas for p- polarization it shifts only by a few nm.
- the coated moth-eye PC plates act as a polarizer in the near IR and UV spectral region as found by optical meas- urements by the inventors.
- Cross polarized transmission data with s-polarized light and the analyzer in s-polarization (T ss ) at 0° rotation of the sample have been found to be different from the corresponding (T pp ) data.
- T pp 90° rotation the T pp (90°) is equal to T ss (0°) .
- the coupling of the resonance mode to the nanostructures depends on the polarization orientation of the incident light with respect to the moth-eye array (parallel or perpendicular to the nipple chains) .
- the p-polarized incident beam in the near-IR and a narrow UV spectral region becomes s- polarized after passing the optical element.
- the polarization effect is due to the material and form birefringence.
Abstract
An optical filter device (100), being adapted in particular for changing parameters of a light field (1), comprises a guided-mode resonance filter (10) having a grating structure (20) with a refractive coating (30) being formed on at least one surface of a substrate (11), wherein the grating structure (20) has a two-dimensional periodicity. A method of changing parameters of a light field (1), comprises the steps of providing the optical filter device (100), directing the light field (1) to the optical filter device (100), and creating an output light field (2, 3), which compared with the light field (1) has a changed wavelength spectrum and/or amplitude.
Description
Tunable optical guided-mode filter device
Technical field of the invention
The present invention relates to an optical filter device, which is adapted for changing parameters of a light field, in particular to a tunable guided-mode resonance filter, which is capable of changing features like an amplitude and/or a wavelength distribution of light waves. Furthermore, the invention relates to a filtering method for changing parameters of a light field, in particular changing the amplitude and/or the wavelength distribution of the light field. The invention also relates to an optical apparatus which is equipped with the optical filter device and which is adapted for conducting the filtering method. The invention can be applied e. g. in the fields of optics, laser technology, spectroscopy, optical measurements, sensor technology and the like.
Technical background
Optical structures in biology have been an inspiration for scientists and engineers. Mimicking such structures becomes more interesting and important through advances in material science (see L. P. Lee et al. in "Science" vol. 310, 2005, p. 1148-1150) . New or improved analytical tools in combination with developments in material processing techniques allow for laboratory testing and fast industrial implementation of high performance optics resembling biologically inspired systems. Specifically, nano-lithography (see U. Schulz in "Appl . Optics" vol. 45, 2006, p. 1608-1618) and coating technologies (see M. Knez et al. in "Adv. Mater." vol. 19, 2007, p. 3425- 3438) are rapidly advancing so that unconventional three di-
mensional (3-D) nanostructures can cost effectively be created on a large scale.
The anti-reflective property of moth-eye corneal nipple ar- rays has found widespread industrial applications (window panels, cell phone displays, camera lenses, etc.) - The function of such nano-structured surfaces is explained with the refractive index gradient at the air-facet material interface with a period smaller than the wavelength of light (see D. G. Stavenga et al. in "Proc. R. Soc. B" vol. 273, 2006, p. 661- 667) . Additional modifications of the refractive index can lead to so-called Wood's anomalies in the optical properties of structured surfaces (see R. Gordon et al. in "Phys. Rev. Lett." vol. 92, 2004, p. 0374011-0374014; and S. Zhang et al. in "Phys. Rev. Lett." vol. 95, 2004, p. 1374041-1374044) .
These are sharp changes in the transmittance or reflectance intensity with respect to the wavelength or the angle of incidence. The resonance type anomaly is based on the resonance of leaky surface waves guided by the grating (see A. Hessel et al. in "Appl. Optics" vol. 4, 1965, p. 1275-1297; A. Hessel et al. in "Optics Comm." Vol. 59, 1986, p. 327-330; and R. Magnusson et al. in "Appl. Phys. Lett." vol. 61, 1992, p. 1022-1024), and the interest in such structures is increasing. Various practical applications can be envisioned for such guided mode resonance filters as sensors, in laser optics, or spectroscopy, as proposed e. g. in the above publication of R. Magnusson et al..
In US 5 216 680, R. Magnusson et al. have proposed a tunable guided-mode resonance filter comprising a reflecting grating. The reflecting grating is created by a series of parallel grating lines (grooves) formed in a surface of a substrate body. By changing the thickness, periodic structure, permittivity or angle of incidence of an incident light wave, a
pass band wavelength of the grating can be tuned to target a specific frequency application. Accordingly, the grating can be used as a wavelength filter. A wavelength shift can be achieved by changing the angle of incidence (AOI) of the in- cident light field, i.e. by a rotation of the grating around an axis parallel to the surface of the grating.
The guided-mode resonance filter described in US 5 126 680 has the following disadvantages. Firstly, in several applica- tions, it is desirable to have a constant AOI. In these cases, a wavelength shift can be obtained with multiple adjustments of an optical setup only. Furthermore, when changing the AOI, the detector system or any other subsequent optical component must also be translated to achieve optimal illumination, e. g. of the sensor at a different angle of detection (AOD) . This requires a complex technical implementation, in particular with several mobile components. In a compact or miniaturized optical system, such mobile or loose components may be problematic.
Graded-wavelength guided-mode resonance filters have been obtained based on linearly graded TiO2 thin film deposition along a surface of a photonic crystal (D. W. Dobbs et al. in "Appl. Phys. Lett." Vol. 89, 2006. p. 1231131-1231133) . As a disadvantage, this optical element has to be translated along the surface by about 3 cm for obtaining a wavelength shift of the resonance mode from 798 nm to 909 nm. Compact or even miniaturized optical systems will not accommodate such displacement of optical elements.
US 7 294 360 B2 discloses a micro-optical element comprising a structured body on a surface of which trenches are formed. The surface is functionalized by a thin film, which is formed by atomic layer deposition (ALD) . The micro-optical element
is used e. g. as a beam shaper, lens or grating. For the grating application, a plurality of parallel, line-shaped trenches can be formed thus creating a one-dimensional linear line grating. This grating suffers from the same disadvan- tages as the guided mode resonance filter proposed by R. Mag- nusson et al. as outlined above.
Objective of the invention
It is an objective of the present invention to provide an improved optical filter device being capable of changing parameters of a light field and avoiding disadvantages of the conventional techniques. In particular, it is the objective of the invention to provide an optical filter device with an improved light field parameter tuning in terms of tuning ranges and/or complexity of optical structures. Furthermore, the objective of the invention is to provide an improved filtering method for changing parameters of an incident light field, which filtering method is capable of avoiding disad- vantages of the conventional techniques and which in particular allows extended applications of guided-mode resonance filtering of electromagnetic waves. Furthermore, the objective of the invention is to provide an optical apparatus, which is capable of implementing the filtering method.
These objectives are solved with devices or methods comprising the features of the independent claims, respectively. Preferred embodiments and applications of the invention are defined in the dependent claims.
Summary of the invention
According to a first aspect of the invention, an optical filter device with a guided-mode resonance filter is provided.
The guided-mode resonance filter has a grating structure with a refractive coating. According to the invention, the grating structure has a two-dimensional periodicity. The grating structure includes structure elements having a periodic ar- rangement along two directions in space, in particular along two directions on a plane surface of the guided-mode resonance filter. Contrary to the conventional techniques using one-dimensional line gratings only, the inventive optical filter device provides an additional degree of freedom for changing parameters of a light field. The effect of the guided-mode resonance filter on a light field does not only depend on the angle of incidence (AOI), but also on an azi- muthal angle of a plane of incidence relative to the grating structure on the surface of the guided-mode resonance filter.
The inventors have found that parameters of an incident light field, like in particular an amplitude and/or a wavelength distribution thereof can be changed by adjusting the orientation of the grating structure relative to the incident light field. Due to the additional degree of freedom, the adjustment of the optical filter device, in particular a selection of a wavelength distribution can be essentially facilitated. In particular, parameters of the light field can be adjusted without changing the AOI .
According to a second aspect of the invention, a method of changing parameters of the light field using an optical filter device with a guided-mode resonance filter is provided. The guided-mode resonance filter has a grating structure with a two-dimensional periodicity. According to the invention, a light field (incident light field) is directed to the grating structure and an output light field is created, which is characterized by changed electromagnetic field parameters
compared with the incident light field, in particular by a changed wavelength spectrum and/or amplitude.
The guided-mode resonance filter of the inventive optical filter device generally comprises a solid substrate, on a surface of which the grating structure with the two- dimensional periodicity is formed. The grating structure carries a refractive coating. The refractive coating is designed for creating the resonance type anomaly for the incident light field as it is known from conventional guided-mode resonance filters. The grating structure with the refractive coating can be provided as a free surface exposed to the surrounding environment. Alternatively, a protective transparent coating can be provided on the grating structure.
The inventive optical filter device is capable of changing parameters of the incident light field. The term "light field" generally refers to at least one electromagnetic wave with a wavelength or wavelength distribution in a wavelength range covering UV light (wavelength above 10 nm, in particular above 190 nm, like in the range of 190 nm to 400 nm) , visible light (wavelength in the range of 400 nm to 700 nm) and IR light (wavelength above 700 nm, in particular above 800 nm, up to microwaves) . Accordingly, the term "optical filter device" is related not only to filtering incident light fields in the visible wavelength range, but also in the above shorter and longer wavelength ranges.
Advantageously, the incident light field may include a broad- band wavelength distribution, created e.g. by a white light source, or a narrow band wavelength distribution created e.g. by a laser with a certain centre wavelength. In the first case, the optical filter device is capable of changing both the wavelength distribution and the amplitude of the light
field. In the second case of using in particular monochromatic light, the optical filter device is capable of changing, i.e. switching the amplitude of the incident light.
The grating structure generally comprises an array of structure elements. The array provides the two-dimensional periodicity of the grating. Directions of linear periodic arrangements of the structure elements are called here first and second grating directions of the grating structure. Each structure element is a local refractive structure of the grating structure preferably having a spot or dot shape. Structure elements may comprise e.g. recesses in the surface of the substrate. However, according to a preferred embodiment of the invention, the structure elements comprise pro- jections on the surface of the substrate. Projecting structure elements have particular advantages in terms of available structuring techniques and creating a homogeneous refractive coating.
As a further advantage of the invention, there are no particular restrictions with regard to the design of the array of structure elements. According to a first variant, equal periods of the grating structure can be provided along the first and second grating directions on the grating surface structure. Providing equal grating periods has advantages with regard to the structuring process and the adjustment of the optical filter device. Alternatively, according to a second variant, different periods along the different grating directions can be provided. This embodiment may have advan- tages for adjusting predetermined parameters of the output light field. According to further variants, all structure elements may have equal heights above the surface of the substrate, or at least one height gradient can be provided depending on the particular application of the optical filter
device. The height (s) of the projections is/are preferably selected in the range of 10 nm to 1 μm, in particular in the range from 10 nm to 300 nm.
Advantageously, a broad range of structure element shapes is available. Preferably, the structure elements comprise nipple, cone-shaped, sinusoidal, square, cylindrical, pyramidal or cube-shaped projections on the surface of the substrate. According to a particularly preferred embodiment of the in- vention, the grating structure comprises a moth-eye nano- structure. Moth-eye nanostructures are known as such for providing anti-reflecting surfaces (see above) . The inventors have found that moth-eye nanostructures carrying the refractive coating are particularly suitable for creating the guided-mode resonances. While the anti-reflective properties of moth eye nanostructures were well known, the inventors have found new applications of the moth eye nanostructures. In particular, tunable guided-mode resonance filters based on moth eye nanostructures in polycarbonate (PC) substrates have been proved as efficient wavelength filter. The substrates are preferably coated with an AI2O3 and TiO2 multilayer by atomic layer deposition.
According to a further preferred embodiment of the invention, the substrate and/or at least the grating structure on the surface thereof is made of an optical grade transparent material. Using an optical grade transparent material provides advantages for an efficient wavelength selection or amplitude switching of the incident light field by adjusting the opti- cal filter device. Particularly preferred materials comprise glass, fused silica, quartz, MgF2, CaF2, polycarbonate, polymethylmethacrylate, polycycloolefine, polyamide, polyether- sulfon, polysulfon or fluoropolymer .
Preferably, the spatial period of the grating structure is selected depending on the wavelength of the incident light wave. With a centre wavelength λ, the spatial period is preferably selected in the range of λ/4 to λ. With the above pre- ferred wavelength ranges, the spatial period is preferably selected in the range of 25 nm to 5 μm.
Various two-dimensional lattices for providing the grating structure are available. Preferably, a hexagonal or a tetragonal lattice structure is provided, which may have advantages in terms of manufacturing the structure elements and positioning the structure elements with a high spatial density.
According to a further preferred embodiment of the invention, the refractive coating on the grating structure comprises one or multiple layers having a refractive index being different from the refractive index of the grating structure, i.e. of the substrate of the optical filter device. Preferred materi- als of the refractive coating comprise oxides, e.g. SiO2,
Al2O3, TiO2, Ta2O5, ZnO, V2O5, In2O3, SnO2, NiO, MgO, ZrO2, FeO, Fe2O3, a nitride, e.g. AlN, TiN, TaN, a fluoride, e.g. MgF2, CaF2, AlF3, LaF3, a sulfide, e.g. ZnS, a metal, e.g. Al, Pt, Ir, Ni, Ag, a semiconductor, e.g. Ge, Si and/or an organic polymer, e.g. polyamides, polyether, polycarboxilate. The resonance anomaly of the grating structure is increased if the refractive coating comprises a stack of multiple layers having different refractive indices.
According to a particular advantageous embodiment of the invention, the refractive coating, i.e. the single or multiple refractive layers are made by atomic layer deposition. The inventors have found that the atomic layer deposition allows the creation of a homogeneous refractive coating which im-
proves the resonance effects of the optical filter device. However, according to alternative embodiments of the invention, other deposition techniques for creating the refractive coating can be used, like e.g. CVD, PVD, thermal evaporation or the like.
According to further embodiments of the invention, the grating structure may comprise multiple grating structure components being arranged on the substrate. Each of the grating structure components as such may be provided with the above features of the grating structure. In particular, the period and arrangement of the structures of the grating structure components may be equal or different relative to each other.
The grating structure components can be arranged on the substrate as follows. With a first variant, a first grating structure component is arranged on a first side of the substrate, while a second grating structure component is arranged on a second, opposite side of the substrate. In this case, a transparent substrate is used. As an advantage, this way the filter will change the amplitude and/or wavelength distribution of the incident light field twice and a filter with double or multiple bandstop characteristics will be obtained.
With a second variant, a stack of at least two grating structure components each with a separate substrate is arranged on at least one side of the respective substrate. This provides a filtering device unit that will modify the amplitude and/or wavelength distribution of an incident light field multiple times. Furthermore, combinations of both variants are possible.
According to a particularly preferred feature of the invention, the optical filter device is provided with a wavelength tuning device. The wavelength tuning device is generally an equipment which is capable of changing a wavelength spectrum of the output light field. As a main advantage, the combination of the guided-mode resonance filter with the wavelength tuning device allows a precise adjustment (setting) of the wavelength spectrum of the output light field.
According to a preferred embodiment, the wavelength tuning device comprises a first drive unit, which is capable of subjecting the grating structure to a rotation with a rotation axis deviating from the grating structure surface. Particularly preferred, the first drive unit is adapted for rotating the grating structure around an axis normal to the grating structure surface. In this case, a wavelength setting is possible without any change of the AOI.
Alternatively or additionally, the wavelength tuning device may comprise a polarizing filter, which is capable of adjusting a polarization direction of the input light field. In this case, changing of a parameter of the output light field can be obtained without any mechanical adjustment of the optical filter device.
According to a further modification, the wavelength tuning device may comprise a second drive unit, which is capable of tilting the grating surface structure. The second drive unit is adapted for changing the AOI of the incident light field. The second drive unit may have advantages for adjusting the wavelength spectrum of the output light field in combination with the effect of the first drive unit and/or the polarizing filter.
A broad field of applications is available for the optical filter device or the method for changing parameters of a light field, respectively. As a preferred example, the optical filter device can be used for adjusting operation condi- tions of a laser device. The optical filter device can be provided in a resonator of a laser device. Due to the facilitated mechanical adjustment of the optical filter device, a wavelength selection can be provided without complex adjustment steps. As further examples, the optical filter device may be used as a part of a sensor device, in a spectroscopic device, as an optical switch, e.g. in an optical data transmission, and/or as a part of a light wave guide.
According to a third aspect of the invention, an optical ap- paratus is provided, which comprises a light source and an optical filter device according to the above first aspect of the invention. Advantageously, the optical apparatus is capable of providing an output light field with adjustable light field parameters depending on a setting of the geometrical orientation of the optical filter device relative to the light source. The optical apparatus of the invention can be provided with various types of light sources, e.g. with a broadband light source or a laser device with a laser resonator.
Advantageously, there are practically no restrictions with regard to setting the AOI. The optical apparatus can be operated with an AOI in the range of nearly 0° to 90°. According to a preferred embodiment of the optical apparatus, the AOI is selected in the range of 20° to 80°. As an advantage, the wavelength selection can be obtained with particular efficiency in this AOI range.
Additionally, the optical apparatus can be provided with a detector device being capable of collecting the output light field. The detector device can be arranged for detecting reflected light and/or transmitted light.
Brief description of the drawings
Further details and advantages of the invention are described in the following with reference to the attached drawings, which show in:
Figure 1: a schematic illustration of a first embodiment of the inventive optical filter device;
Figure 2: an enlarged cross-sectional view of the optical filter device of Figure 1;
Figures 3 to 5 : schematic illustrations of further embodiments of the inventive optical filter device;
Figures 6 and 7: schematic illustrations of wavelength tuning devices used with the inventive optical filter device;
Figures 8 and 9: schematic illustrations of embodiments of the inventive optical apparatus;
Figure 10: microscopic images showing a moth-eyed structure used according to the invention;
Figure 11: schematic illustrations of various lattice geometries of the grating structure of an inventive optical filter device; and
Figures 12 and 13: experimental results obtained with the inventive optical filter device.
Preferred embodiments of the invention
Embodiments of the invention are described in the following with reference to the preferred implementation using moth-eye structures carrying a refracting coating of multiple refractive layers. The invention is not restricted to the illus- trated embodiments, but rather can be implemented with other grating structure designs as outlined in this specification. Furthermore, reference is made to the preferred application of changing visible or IR light with the optical filter device. The invention is not restricted to these wavelength ranges, but also applicable in the UV range or in the microwave range. While most of the embodiments are described with reference to an optical reflectance filter, the output light field can be obtained in a reflectance mode and/or a transmission mode. In particular in the latter case, a transparent substrate is used. Finally, the structures shown in the Figures are strongly enlarged for illustrative purposes.
Furthermore, exemplary reference is made to optical filter devices having a single substrate with a single grating structure or multiple grating structure components on opposite sides of a transparent substrate. Alternatively, the inventive optical filter device may comprise multiple stacked transparent substrates each carrying a single grating structure or multiple grating structure components.
Figures 1 and 2 illustrate a first embodiment of the inventive optical filter device 100 with a perspective schematic view (Figure 1) and an enlarged sectional view (Figure 2) . The optical filter device 100 comprises a guided-mode reso-
nance filter 10 with a grating structure 20, which carries a refractive coating 30. The guided-mode resonance filter 10 has a substrate 11 on a surface of which structure elements 21 of the grating structure 20 are provided. The structure elements 21 can be integrally formed with the substrate 11, e.g. by surface structuring thereof. Alternatively, the structure elements 21 could be deposited on a plane surface of the substrate 11. The substrate 11 comprises e.g. a polycarbonate plate with a plane surface, having a thickness of 2 mm and lateral dimensions of 50 mm * 20 mm.
The height h of the structure elements 21 (Figure 2) is e.g. 100 nm. All structure elements 21 can have the same height h as shown in Figure 2. Alternatively, a height gradient can be provided as schematically illustrated in Figure 4. In this case, the height h changes e.g. in the range from 10 nm to 1000 nm.
The refractive coating 30 comprises a stack of layers 31, 32 having different refractive indices. As an example AI2O3- and TiO2- layers with a thickness of 15 nm to 70 nm are arranged in an alternating manner with a complete thickness of about 180 nm.
For illustrative purposes it is assumed that the grating structure 20 extends along the x-y-plane of a Cartesian coordinate system. The normal direction on the grating structure 20 is directed to the z-direction. The grating structure 20 has a two-dimensional periodicity as schematically shown in Figure 1. The first and second grating directions of the grating structure 20 correspond to the x- and y-directions, resp. (indicated with the white arrows in Figure 1) . Along the grating directions, the structure elements are periodi-
cally arranged. The grating directions span a plane with a lattice geometry of the grating structure.
In a further embodiment, a substrate structured onto both sides can been coated onto both sides with grating structure components 20.1, 20.2 as illustrated in Figure 3. This will produce a double filtering guided-mode resonance filter 10. Both grating structure components 20.1, 20.2 are illustrates as having equal geometries. Alternatively, the structured sides may be exposed to different coating sequences by selectively masking each side of the substrate so that different grating structure components are formed.
The spatial period of the structure elements 21 is e.g. 50 nm. The same spatial period can be provided in both grating directions, i.e. the centre-centre-distances between the structure elements 21 in both grating directions are identical. Alternatively, different spatial periods along the grating directions can be provided as schematically shown with the top views of the rectangular lattice and hexagonal grating structures 20 in Figures 5A and 5B. As an example, the spatial period Δx in the x-direction is 280 nm, while the spatial period Δy in the y-direction is 480 nm.
The incident light field 1 is directed to the optical filter device 100 with a predetermined angle of incidence (AOI) α relative to the z-direction. Furthermore, the incident light field 1, in particular the plane of incidence thereof has a certain azimuthal angle β relative to the grating structure 20, e. g. relative to the x-direction. The output light field 2 is reflected on the surface of the grating structure 20. The amplitude and/or the wavelength distribution of the output 'light field 2 is changed, compared to the corresponding parameters of the input light field 1 due to resonance type
anomalies mentioned above. Detailed examples of changing the parameters of the output light field 2 are described below with reference to Figures 10 to 12.
According to the invention, the amplitude and/or wavelength distribution of the incident light field 1 can be changed by changing an orientation of the grating structure 20 relative to the direction of the incident light field 1 and/or by changing a polarization parameter of the incident light field 1. For a variable adjustment of the orientation, the optical filter device is provided with a tuning device 40. Preferred embodiments of the tuning device 40 are illustrated in Figures 6 to 8.
According to Figure 6, the tuning device 40 comprises a first drive unit 41, which is capable of rotating the optical filter device 100 around the z-axis. The first drive unit comprises e.g. an electric servo motor being arranged on a solid support, like e.g. a mirror support in an optical set-up. The optical filter device 100 is connected with the motor shaft. With an operation of the first drive unit 41, the azimuthal angle β (see Figure 1) can be adjusted.
Additionally, the tuning device 40 may comprise a second drive unit 42 as shown in Figure 7. The second drive unit 42 is arranged for tilting the optical filter device 100 around an axis parallel to the surface plane thereof, i.e. around an axis in the x-y-plane. The second drive unit 42 may comprise at least one second electro servo motor or a pivoting mecha- nism carrying the first drive unit 41 and the optical filter device 100. With the second drive unit 42, the AOI α can be adjusted.
Alternatively or additionally, the tuning device 40 may comprise a polarizing filter 43. The combination of the optical filter device 100 with the polarizing filter 43 is schematically illustrated in Figure 8, which further shows an embodi- ment of an optical apparatus 200 of the invention.
The optical apparatus 200 comprises the optical filter device 100, optionally with the adjustable polarization filter 43 and/or at least one of the first and second drive units 41, 42 (see above), and a light source 210. As a further option, a detector device 220 can be provided for collecting the output light field 2.
The light source 210 comprises e.g. a white light source or a laser device. The light source 210 can be provided with imaging optics (not shown) for directing the incident light field 1 to the surface of the grating structure 20.
Figure 9 illustrates another embodiment of an optical appara- tus 201 according to the invention. The optical apparatus 201 comprises a laser resonator with a laser oscillator 211 and resonator mirrors 212. One of the resonator mirrors is replaced by the optical filter device 100 according to the invention. By adjusting the orientation of the grating struc- ture of the optical filter device 100 relative to the light field circulating in the laser resonator, a wavelength distribution and/or amplitude of the laser light 3 leaving the resonator can be controlled. The application of the optical filter device in a laser resonator is not restricted to the optical set-up schematically shown in Figure 9. It is rather possible to integrate the optical filter device into other resonator geometries, which are known as such from laser technology.
The following further details of embodiments of the invention demonstrate that in particular 3D nanostructures in polymeric material can be successfully coated with inorganic materials by atomic layer deposition (ALD) . The coated nanostructures show guided-mode resonances with narrow reflectance peaks and high sideband transmittance (94%) in the UV-VIS. Unexpectedly, the reflectance peak position can be easily tuned in a broad wavelength range (> 150 nm) through the rotation of the sample around the axis (z-axis) normal to the substrate with- out any change in the optical setup. The use of these filters is accentuated by the need to produce optics for ultra- compact, portable, miniaturized equipment. Additionally, strong polarization in the optical transmittance at normal angle of incidence is observed with a rotation of the sample.
Tunable guided-mode resonance filters based on moth eye nanostructures in polycarbonate (PC) substrates are manufactured as follows. Polycarbonate substrates with moth eye nanostructures in hexagonal ordering is obtained from Fresnel Optics. Figure 1OA shows a 3D AFM image of the uncoated moth- eye structure (2.5 x 2.5 μm2) .
The moth-eye polycarbonate (PC) nanostructures are coated with five layers consisting of three layers of AI2O3 and two layers of TiC>2 of varying thicknesses using ALD. The ALD process is carried out in a commercial hot-wall flow type ALD reactor (SUNALE R75, Picosun, Finland) . Al (CH3) 3 (TMA), Ti(OPr)4 (TiOP) and 30% H2O2 were used as aluminum, titanium, and oxygen reactant sources, respectively. TMA and H2O2 were delivered to the reactor as ambient temperature vapors, whereas the TiOP precursor was heated to 6O0C and delivered through a booster system. The pulsing times were 0.1 s for TMA, 0.5 s for TiOP, and 2s for H2O2 with N2 as carrier gas at a flow rate of 200 seem. The purging time after each pulse
was set to 4 s. Purging was done with N2 gas with a flow rate of 200 seem. The substrate temperature reached a maximum of 1200C.
Under these conditions, the growth rate of AI2O3 was about 1.30 A per cycle, whereas the TiO2 growth rate amounts to about 0.75 A per cycle. The substrates were exposed to 380 cycles TMA/ H2O2, 280 cycles TiOP/ H2O2, 150 cycles TMA/ H2O2, 880 cycles TiOP/ H2O2, and 630 cycles TMA/ H2O2 to form a to- tal of five layers onto the substrates. Since ALD film deposition would occur on both sides of the sample, the flat side of the substrate was partially masked. Alternatively, the flat side of the substrate has been concomitantly coated with the sequence mentioned above to form an antireflective coat- ing onto the flat side.
The chosen film structure corresponds to an antireflective coating on flat BK7 and polycarbonate substrates. Figure 1OB shows the multilayer structure in a focused ion beam (FIB) cross section SEM image (a 2 μm thick conducting carbon paste has been deposited onto the optical element for the FIB processing) . The film thicknesses as determined from the SEM image are from bottom (polycarbonate) about 38, 15, 15, 44 and 66 nm, respectively. A sharp boundary can be observed between the Al2O3 and TiO2 layers. The moth eye hexagonal nanostruc- tures are perfectly retained after the ALD coating (see Figures IOC and 10D) . The grating period of the coated nanos- tructures is equal to the period of the uncoated substrates; whereas the grating depth decreases with increasing thickness of the coating material.
Surfaces of uncoated and coated moth eye substrates have been studied by an atomic force microscope (AFM, Digital Instruments 5000 microscope) operating in tapping mode. AFM tips
from μMasch (NSC15) were used. Scanning electron microscope (SEM) images of sections cut with the focused ion beam technique were measured with a FEI NovaβOO Nanolab equipment. The samples were coated with a layer of conductive carbon paste of about 2 μm for the FIB processing. The sections were obtained at several probe rotations. The period and grating depth of the nanostructures were determined from the AFM profiles and the SEM images.
The AFM and SEM analysis are in very good agreement. Both techniques have determined a grating period of 280 nm. The grating depth before coating was 65 nm (AFM) // 53 nm (SEM) and reduced to 28 nm (AFM) // 36 nm (SEM data) after ALD deposition. This filling effect is inherent to the ALD tech- nique . The deposited film grows uniformly, perpendicular to the surface of the cones. Hence, eventually the volume between the cones will be filled at a sufficiently high film thickness. The closer look at Figure 1OB reveals that the first 2-3 layers grew conformally onto the structure, whereas the upper AI2O3 layer is affected by the filling effect.
The AFM image of the coated sample (Figures 1OC and 10D) illustrates the effect of rotation around an axis normal to the surface on the illumination geometry. The area in Figures 1OC and 1OD is 1 μm2. The black arrow depicts the beam of incident light 1, while the white arrow depicts the rotation of the sample. The sample is rotated around the axis perpendicular to the substrate while the light source and detector (see e. g. Figure 8) are kept fixed. Figure 1OC corresponds to an azimuthal angle of about 0° rotation, and Figure 1OD to about 90°.
At 0° rotation, the incident beam crosses the nanostructures along the diagonal line with a large gap between the struc-
ture elements 21 (e. g. cones) . At 90° rotation, the cones are closely packed along the beam direction. The rotation of the sample actually leads to a change of the grating periods as it is further illustrated in Figure 11. At 0° rotation (Figure HA) , the period pi in the coordinate perpendicular to the incident beam direction is equal to the diameter d of the structure elements 21. The period in the coordinate along the incident beam is p2 = 31/2 d. However, at 90° rotation (Figure HB) the situation reverses with pi = 31/2 d and p2 = d. Hence, through a continuous change in the rotation of sample, one will obtain a multitude of optical elements of various grating periods with respect to the incidence plane. Adjusting the orientation of the optical filter element comprises setting the grating period for influencing the elec- tromagnetic field parameters of the output light field.
Optical measurements have shown that the properties (reflectance, R and transmittance, T) of the coated nanostructures are extremely sensitive to the rotation of the optical fil- ter. Figure 12 shows polarized reflectance spectra at AOI
55° with p-polarized light. The spectra obtained between 40 and 130° sample rotation are depicted in two sections for clarity (Figure 12A, Figure 12B) . Figure 12A shows the reflectance with the sample at about 40 to 90° rotation, whereas Figure 12B the data at about 90 to 130° rotation. The rotation angles are indicated above the main peaks. The strongest resonances were observed between 60° to 120°. The symbols correspond to the data points and the lines are a guide to the eye. Thus, strong reflection peaks can be ob- served between 390 and 600 nm wavelength. At 55° AOI the reflectance peaks reach about 20% with narrow bandwidths (FWHM about 4 nm) . The peak position shifts by 55 nm between 80° to 100° rotation of the sample. Slight rotation of the sample (2 to 3°) induced a shift of the main reflectance peak of about
8 nm. Around 0 and 180° rotation the peaks vanished or had very low intensity for the p-polarized light. Similar behavior has been observed for s-polarized light; however, the maximum reflections appeared around 0° rotation for s- polarization. A broad spectral range of resonance modes can be obtained through rotation of the sample around the axis normal to the surface.
Corresponding results can be obtained with optical wave- length-dependent measurements of the properties like reflectance or transmittance with a rotation around an axis deviating from any reference plane parallel to the grating structure and/or with a rotation of the polarization direction of the incident light field. Again, with the rotation of the po- larization, various grating periods with respect to the incidence plane can be effectively obtained as described above with reference to Figures 1OC and 1OD. In particular, the coupling of the resonance mode to the nanostructures depends on the polarization orientation of the incident light with respect to the moth-eye array (parallel or perpendicular to the nipple chains) .
Thus, the resonances at a fixed AOI can be easily tuned through rotation of the sample and/or rotation of the polari- zation of the incident light. Specifically, the resonance modes observed for p-polarized light can be tuned in a broader range through rotation of the sample, than by changing the angle of incidence. Hence, circular optical elements of such coatings can be used as components in highly compact, miniaturized laser optics, refractive index sensors, spectrometers, etc. where the element cannot be shifted and/or tilted (see Figure 9) . The prime advantage of such tunable filters is that no change in the illumination/detection setup
is required for wavelength filtering, reducing the number of mobile parts of the optical instrument.
With monochromatic incident light, tuning the resonances yields an amplitude modulation of the output light. With adjusting the optical filter device such that the resonance is tuned to the wavelength of the incident light, the output light can be switched on. With a detuning of the resonance relative to the wavelength of the incident light, the output light can be switched off.
The theoretical analysis of guided mode resonances can be performed through numerical solutions of Maxwell's equations as implemented in the rigorous coupled-wave approach (RCWA, see above publication of R. Magnusson et al. in "Appl. Phys . Lett.") . Subsequent optimization of these optical elements for specific applications based on RCWA calculations can be carried out. Furthermore, the theoretical analysis can be based on publications treating one dimensional (ID) grating systems (see R. Magnusson et al. in "Appl. Optics", vol. 34, 1995, p. 8106-8109; R. Magnusson et al. in "Appl. Optics", vol. 34, 1995, p. 2414-2420; Z. Liu et al. in "Optics Letters", vol. 23, 1998, p. 1556-1558; H. Toyota et al. in "SPIE", vol. 5184, 2003, p. 89-98 ; and L. Li et al. in "Op- tics Letters", vol. 20, 1995, p. 1349-1351) .
The wavelength position and intensity of the resonances for a given incidence angle can be shifted by varying the grating period, depth, and film thickness of the GRMG filter. How- ever, this approach is less attractive since an optical element must be produced for each wavelength position. The inventive moth-eye nanostructure array and similar 2D structures with varying period by rotation, offer an interesting
approach to create tunable filters for a broad range of applications.
According to the invention, it is considered to enhance the transmittance/reflectance properties of the optical filter specifically at oblique AOI. Increasing the grating depth, in particular of the moth-eye structures, up to the grating period could cause increased measured resonance peaks.
Additionally ultra-narrow bandwidth filters can be provided with the inventive optical filter device. For ultra-narrow bandwidths, a minimal deviation and high thermal stability of the nanostructures is preferred. Multilayer structures have been shown theoretically to reduce the FWHM of the ID guided mode resonance grating filters. The multilayer coating corresponding to an antireflective coating onto unstructured substrates additionally provides low sideband reflectance (high transmittance) of the optical element in a broad spectral range.
Additional impact onto the optical properties of the inventive optical filter device has the polarization of the incident light with respect to the moth-eye nanostructure array. Polarized reflectance, transmittance and ellipsometry meas- urements were carried out on two different ellipsometers, both from J. A. Woollam Co., Inc.. The M-2000 ellipsometer equipped with a rotating compensator and the VASE measurement system were used. The backside of the substrates was roughened and blackened after the transmittance measurements to avoid perturbing reflections from the uncoated side in the reflectance measurements. Cross-polarized transmittance data were recorded with p- and s-polarized incident beams and detection in p- and s-polarization position of the analyzer
(TpP, Tp3, Tss, and TSp) . Reflectance data were obtained with p- and s-polarized incident beams.
The sample was mounted onto a graded circular plate, and the plate was rotated manually from 0° to 180° in 10° steps. An error of about 1 to 2° in the rotation of the plate can be accounted. The sample was positioned onto the centre of the plate to ensure that the same region was analyzed. However, additional data obtained at the same rotation angle from dif- ferent sample positions showed very little variation; specifically, 2 to 3% intensity variation at the same wavelength position.
Polarized reflectance and transmittance measurements identi- fied multiple channels of narrow-band reflections in the ultraviolet-visible range. Amazingly, the wavelength position of the reflection peaks can be easily tuned in a broad range (more than 150 nm) through rotation of the optical element around the axis normal to the substrate. The transmittance data also indicated rotation dependent polarization probably associated with the birefringence of the substrate material and the form of the nanostructures .
According to the invention, the spectral shift of the reso- nance modes can be further influenced by adjusting the AOI. Experimental results obtained with an angle of incidence between 20° to 60° are illustrated in Figure 13. The 0° rotation position of the sample has been chosen for s-polari- zation and the 120° rotation for p-polarization because at these rotations only one intense leaky mode was observed. It can be observed, that the peak position for the s-polari- zation shifts very strongly with the AOI, whereas for p- polarization it shifts only by a few nm. Through extrapolation to the 0° incidence, one observes a shift of about 200
nm (from 480 to 660 nm) for the s-polarized light. For the p- polarized light the shift amounts only to about 40 nm (from 480 to 520 nm) . This corresponds to a dispersion of about 3 nm/ degree AOI for s-polarization but less than 1 nm/ degree for p-polarization. Hence, if we consider the FWHM of the element, the wavelength separation is much better for the s- polarization. For s-polarization, the resonance modes measured at 2° AOI difference are well separated. For p- polarization, the separation arises at 10° difference in AOI. In addition, a plateau is reached around 40° AOI for the p- polarized incident light.
Finally, the coated moth-eye PC plates act as a polarizer in the near IR and UV spectral region as found by optical meas- urements by the inventors. Cross polarized transmission data with s-polarized light and the analyzer in s-polarization (Tss) at 0° rotation of the sample have been found to be different from the corresponding (Tpp) data. However, with 90° rotation the Tpp (90°) is equal to Tss (0°) . The coupling of the resonance mode to the nanostructures depends on the polarization orientation of the incident light with respect to the moth-eye array (parallel or perpendicular to the nipple chains) . At about 50° rotation, the p-polarized incident beam in the near-IR and a narrow UV spectral region becomes s- polarized after passing the optical element. The polarization effect is due to the material and form birefringence.
The features of the invention disclosed in the above description, the drawings and the claims can be of significance both individually as well as in combination for the realization of the invention in its various embodiments.
Claims
1. Optical filter device (100), being adapted in particular for changing parameters of a light field (1), comprising:
- a guided-mode resonance filter (10) having a grating structure (20) with a refractive coating (30) being formed on at least one surface of a substrate (11), characterized in that
- the grating structure (20) has a two-dimensional periodicity.
2. Optical filter device according to claim 1, wherein - the grating structure (20) comprises an array of structure elements (21) projecting from a substrate surface (22) .
3. Optical filter device according to claim 2, wherein the array of structure elements (21) has - equal periods along different dimensions on the grating surface structure,
- different periods along different dimensions on the grating surface structure,
- equal heights of all structure elements (21), and/or - at least one height gradient of the structure elements
(21) .
4. Optical filter device according to claim 2 or 3, wherein the structure elements (21) - are at least one of cone-shaped, pyramidal or cube-shaped, and/or
- have a height in the range of 10 nm to 1 μm, preferably of 10 nm to 300 nm.
5. Optical filter device according to one of the foregoing claims, wherein
- the substrate (11) and/or the grating structure (20) is made of optical grade transparent material.
6. Optical filter device according to one of the foregoing claims, wherein
- the grating structure (20) is made of glass, fused silica, quartz, MgF2, CaF2, polycarbonate, polymethylmethacrylate, polycycloolefine, polyamide, polyethersulfon, or polysulfon.
7. Optical filter device according to one of the foregoing claims, wherein the grating structure (20) has
- a periodicity with a period in the range of λ/4 to λ, wherein λ is a wavelength of the light field (1), which preferably is in the range of 100 nm to wavelengths of microwaves, and/or
- a hexagonal or tetragonal structure.
8. Optical filter device according to one of the foregoing claims, wherein
- the refractive coating (30) is made of at least one layer having a refractive index being different from the refractive index of the grating structure (20) .
9. Optical filter device according to claim 8, wherein
- the refractive coating (30) is made of at least one of an oxide, a nitride, a fluoride, a sulfide, a metal, a semiconductor and a polymer.
10. Optical filter device according to one of the foregoing claims, wherein
- the refractive coating (30) comprises multiple layers having varying refractive indices.
11. Optical filter device according to one of the foregoing claims, wherein
- the refractive coating (30) is made of at least one of SiO2, Al2O3, TiO2, Ta2O5, ZnO, V2O5, In2O3, SnO2, NiO, MgO, ZrO2, FeO, Fe2O3, and metal.
12. Optical filter device according to one of the foregoing claims, wherein - the refractive coating (30) is made by atomic layer deposition.
13. Optical filter device according to one of the foregoing claims, further comprising - a tuning device (40) being adapted for tuning an amplitude and/or a wavelength spectrum of an output light field (2, 3) .
14. Optical filter device according to claim 13, wherein the wavelength tuning device (40) comprises: - a first drive unit (41) being adapted for rotating the grating structure (20) around an axis deviating from a reference plane parallel to the grating structure (20), and/or
- a polarizing filter (43) being adapted for setting a polarization parameter of the input light field (1) .
15. Optical filter device according to claim 14, wherein
- the first drive unit (41) is adapted for rotating the grating structure (20) around an axis normal to the grating structure (20) .
16. Optical filter device according to one of the claims 13 to 15, wherein the tuning device (40) further comprises
- a second drive unit (42) being adapted for tilting the grating surface structure.
17. Optical filter device according to one of the foregoing claims, wherein
- the grating structure (20) comprises a moth-eye nanostruc- ture.
18. Optical filter device according to one of the foregoing claims, wherein the grating structure (20) comprises a plurality of grating structure components (20.1, 20.2) arranged on first and second sides of the substrate (11) .
19. Optical filter device according to one of the foregoing claims, comprising at least two stack-wise arranged substrates each carrying at least one grating structure (20) or a plurality of grating structure components (20.1, 20.2) .
20. Method of using the optical filter device according to one of the foregoing claims:
- as an ultra-narrow bandwidth filter, - for adjusting operation conditions of a laser device,
- as a part of a sensor device,
- as a part of a spectroscopic device,
- as a part of an optical switch, and/or
- as a part of a wave guide.
21. Method of changing parameters of a light field (1), comprising the steps of:
- providing an optical filter device (100) having a guided- mode resonance filter (10) with a grating structure (20), which has a two-dimensional periodicity and a refractive coating (30) ,
- directing the light field (1) to the optical filter device (100), and - creating an output light field (2, 3) , which compared with the light field (1) has a changed wavelength spectrum and/or amplitude.
22. Method according to claim 21, comprising the step of:
- adjusting the wavelength spectrum and/or the amplitude of the output light field (2, 3) with a tuning device (40) .
23. Method according to claim 22, wherein the adjusting step comprises:
- rotating the grating structure (20) around an axis deviating from a reference plane parallel to the grating structure (20) , and/or
- setting a polarization parameter of the input light field (1) with a polarizing filter (42) .
24. Method according to one of the claims 21 to 23, wherein
- the light field (1) is directed to the optical filter device (100) with an angle of incidence in the range of 0° to 90°, preferably in the range of 20° to 80°.
25. Optical apparatus (200, 201), comprising
- a light source (210) , and
- an optical filter device (100) according to one of the claims 1 to 20.
26. Optical apparatus according to claim 25, wherein
- the light source (210, 211) is arranged such that the optical filter device (100) is illuminated with an angle of inci- dence in the range of 0° to 90°, preferably in the range of 20° to 80°.
27. Optical apparatus according to one of the claims 25 to
26, further comprising
- a detector device (220) being arranged for detecting light reflected and/or transmitted by the optical filter device (100) .
28. Optical apparatus according to one of the claims 25 to
27, wherein
- the light source is a laser device (211) with a laser reso- nator (212), and
- the optical filter device (100) is arranged in a light path of the laser resonator (212) or on an output side of the laser resonator (212) .
29. Optical apparatus according to one of the claims 25 to
28, wherein
- the light source is a broadband light source, and
- the optical filter device (100) is arranged as a tunable wavelength filter.
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| PCT/EP2009/001739 WO2010102643A1 (en) | 2009-03-11 | 2009-03-11 | Tunable optical guided-mode filter device |
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| PCT/EP2009/001739 WO2010102643A1 (en) | 2009-03-11 | 2009-03-11 | Tunable optical guided-mode filter device |
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| WO2010102643A1 true WO2010102643A1 (en) | 2010-09-16 |
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| CN103620451A (en) * | 2011-04-28 | 2014-03-05 | 巴斯夫欧洲公司 | IR reflectors for solar light management |
| WO2018067147A1 (en) * | 2016-10-05 | 2018-04-12 | Hewlett-Packard Development Company, L.P. | Display control films |
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| WO2018067147A1 (en) * | 2016-10-05 | 2018-04-12 | Hewlett-Packard Development Company, L.P. | Display control films |
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