1 2
of those possible today with hard discs and with a ELECTROPHOTOGRAPHIC OPTICAL MEMORY smaller bit error rate than presently possible. The memSYSTEM ory system should be erasable as well as provide other
advantages. The present invention fulfills these needs, DESCRIPTION 5 and further provides other related advantages.
1. Technical Field 3. Disclosure of the Invention
The present invention relates to computer mass mem- The present invention resides in an optical memory ory devices. system for storage and retrieval of digital data. The
2. Background of the Invention memory system includes a source of writing light havWith the introduction of high speed digital computers 10 ing a first wavelength less than a threshold wavelength,
to business and industry, a problem has developed con- and a source of reading light having a second wavecerning the storage and retrieval of large quantities of length greater than the threshold wavelength. Moduladigital data in a manner which does not significantly tion means are provided for modulating the writing impact the operating speed of the computer and which light by a write digital signal containing the digital data is economic. While many forms of memory devices 15 to be stored. Means are also provided for forming the exist, such as magnetic floppy and hard discs, magnetic writing light into a writing light beam, and means are tapes and optical compact discs, each has its limitation provided for forming the reading light into a reading as to capacity, speed of operation and cost. light beam. The invention further includes means for The primary mass memory storage devices used with deflecting the writing and reading light beams along a computers today, whether they be mainframe, mini- 20 first axis in response to a first control signal, and means computers or microcomputers are magnetic tapes and for deflecting the beams along a second transverse axis discs. Even with a mainframe computer which might at ^ mgie t0 the first axis in response to a second conutilize a bank of 14 inch diameter hard discs, the mem- troi sjgnai. Lens means are included for focusing the ory capacity with 7 such discs is approximately 350 writmg and reading light beams to a focal point with a megabytes. Since a byte has 8 bits, this produces a total 25 focal plane tjjerethrough
memory capacity of slightly less than 3 gigabits. While xhe memory SyStem deludes a stationary medium
this is a substantial amount of memory, the size and cost manufactured of a dry fllm having submicron electri
of the hard discs involved and the equipment necessary call photosensitive micles embedded in a thermo
to operate the disc is substantial. To achieve this quan- ^ , ... Qn a substantiall transparent
My of storage capacity using floppy d,scs would reqmre 30 conducting substrate. The particles are in
over 1,000 discs and is impractical. ... / ,. ...f , r .
While optical compact discs, known as CD-ROMs, T TM ^ TM£ ^ 2^ 8wa^t.d?n the are currently being discussed and can provide storage th'esho!d W/I JlS TM%Pa*ic es *ryn? capacity in the large amounts mentioned above, they barged and the film is sensitive to light after receiving have inherent disadvantages in that the medium used for 35 an imtial surface charge. The uncharged particles according is generally non-erasable or rewritable. Fur- <Julre * char^at !he expense of the surface charge upon thermore, the CD-ROMS have inherent limitations in bem« struck by the writmg light beam. Regions of the accuracy and speed because the CD-ROM uses a platter medlum wlth ,the charSed Partlcles and w* *e un" which must be mechanically rotated much like a record char8ed particles cause differing conditions of the readso that the appropriate portion of the rotating platter 40 mS light beam. Passage of the reading light beam can be read. Read head alignment problems and the through the charged particles corresponds to a retime required for the mechanical operation involved corded information bit of the digital data at one binary slow the read process down and add the chance for lo8ic state and passage through the uncharged particles error and malfunction. Of course, the limitation of being corresponds to a recorded information bit of the digital a read only memory is in itself enough to make a CD- 45 data at the other binary logic state. ROM useless in situations where data must be written to A fixed mask is positioned substantially in the focal storage as the computer is operating. p\ane of the lens means and in juxtaposition with the
As mentioned above, the speed of writing to and medium, between the medium and the lens means. The reading from memory is also a consideration. With mask is substantially opaque to the writing and reading conventional hard discs, the write speed is approxi- 50 light beams with a plurality of apertures substantially mately 20 megahertz. With less expensive floppy disc transparent to the beams. The apertures define the exmemories, the write speed is significantly less. Even at tent of the regions of the medium with the charged and the higher speed, the speed at which today's computers uncharged particles. Each of the apertures has a size to operate and the expected operating speeds of future admit sufficient energy when exposed to the writing generation computers require an increased speed of data 55 light beam for a predetermined time period to exceed a storage and retrieval so that the central processing unit sensitivity threshold value of the medium and charge of "the computer is not forced to wait or to perform the particles in the corresponding region of the medium unnecessary shifts between jobs to more economically to produce charged particles. The apertures are aruse the waiting time while the disc drive head is moving ranged in a plurality of rows aligned with the first axis to the location where the desired information is to be 60 and positioned one row adjacent to the other in the stored or read, and while the writing or reading takes direction of the second axis.
place. The memory system further includes detector means
It will, therefore, be appreciated that there is a signifi- positioned to be exposed to the reading light beam after
cant need for a mass memory system for storing digital passing through the mask apertures and the medium,
data which avoids these problems and disadvantages, 65 The detector means is responsive to the incident ray of
and provides increased storage capacity with a small the reading light beam thereon and insensitive to the
size and low cost memory system. The memory system writing light beam, and detects conditioning of the
should be operable at write and read speeds far in excess reading light beam corresponding to passage through
one of the regions of the medium with the charged particles, and to passage through one of the regions of the medium with the uncharged particles. The detector means further generates a read digital data signal containing the stored digital data from the medium. As such, the binary logic state of a recorded information bit corresponding to one of the regions of the medium is determined.
There is also included means for generating the first control signal to detect the writing and reading light beams to scan along a selected one of the rows of the apertures in the direction of the first axis at a selected scan speed. The selected scan speed for the writing light beam issuch as to expose each of the apertures to the writing light beam for at least the predetermined time period to charge the particles in the corresponding region of the medium to produce charged particles.
The optical memory system further includes means for generating the second control signal to selectively deflect the writing and reading light beams to the selected row of the apertures. The memory system also has means for substantially uniformly charging a surface of the film with the initial charge prior to exposure to the writing light beam.
Other features and advantages of the invention will become apparent from the following detailed description, taken in conjunction with the accompanying drawings.
BRIEF DESCRIPTION OF THE DRAWINGS 3Q
FIG. 1 is a schematic drawing of an optical memory system embodying the present invention.
FIG. 2 is a schematic drawing of a beam deflector used with the memory system of FIG. 1.
FIG. 3 is an enlarged, fragmentary schematic dia- 35 gram showing the storage medium used in the memory system of FIG. 1 while receiving an initial surface charge.
FIG. 4 is a schematic drawing showing the initial surface charged memory medium of FIG. 3 with light 40 impinging thereon to transfer the surface charge in the region struck by light to the photosensitive particles embedded within the medium.
FIG. 5 is an enlarged, fragmentary view of the storage medium used in the memory system of FIG. 1 45 showing an aperture mask bonded to the medium.
BEST MODE FOR CARRYING OUT THE
INVENTION
As shown in the drawings for purposes of illustration, 50 the present invention is embodied in an optical memory system, indicated generally by reference numeral 10, for the storage of digital data. The memory system 10 utilizes an electrophotographic dry film material as a recording medium 12. As best shown schematically in 55 FIGS. 3 and 4, the medium 12 has submicron electrically photosensitive particles 14 embedded in a thermoplastic layer 16 mounted on a substantially transparent electrically conducting substrate 18. With the medium used in the presently preferred embodiment of the in- 60 vention, the particles 14 are insensitive to light with a wavelength greater than 0.480 microns.
The particles 14 are initially uncharged and the medium becomes sensitive to light only after receiving an initial surface charge. To apply the initial surface 65 charge at a surface 20 of the medium 12, a Corona charging device 22 which extends along one length of the medium is moved laterally across the surface of the
medium to apply a uniform charge intensity across the surface, as shown in FIG. 3.
As shown in FIG. 4, when the medium 12 is exposed to light having a wavelength less than .480 microns, the initially uncharged particles 14 acquire a charge at the expense of the surface charge upon being struck by the light. As will be described in more detail below, the light used is a writing light beam modulated with a digital data signal. The thermoplastic layer 14 and conductive substrate 18 are mounted on a transparent glass backing 24. Additional details concerning the operation of the medium 12 with the present invention will be described below. It is noted that unlike when the film material is used as photographic film, the medium is not developed after being exposed to light by being subjected to a vapor, a liquid solvent or heat, and by so keeping the medium in an undeveloped state, the medium can be repeatedly charged, erased and recharged.
The electrophotographic material used in the preferred embodiment as the medium 12 is known as Xerox Dry Microfilm (XDM) and is described in greater detail in U.S. Pat. Nos. 3,357,989; 3,542,545; 3,648,607 3,671,282; 3,720,513; 3,816,118; 3,979,210; 3,982,936: 3,985,560; 4,013,462; 4,014,695; 4,028,101; 4,040,826 4,055,418, which are incorporated herein by reference.
The optical memory system 10 further includes a source 26 of continuous wave monochromatic writing light in the visible light range having a wavelength of less than 0.480 microns. A modulator 28 amplitude modulates the writing light at about a 20 megahertz rate according to a write data input signal on line 30 which embodies the digital data to be stored by the storage medium 12. In the preferred embodiment, the writing light source 26 is a non-coherent mercury lamp operating at a 0.4 micron wave-length. Collimation optics 32 form the modulated writing light into a substantially collimated writing light beam which is projected onto a cube beamsplitter 34 for transmission therethrough.
The write data input signal is provided by an input/output (I/O) device 35a controlled by a central processing unit (CPU) 35b of the computer with which the memory system 10 is operating.
The memory system 10 also includes a source 36 of near infrared, coherent and polarized reading light having a wavelength of greater than 0.480 microns. In the preferred embodiment, the reading light source 36 is a GaAlAs laser operating at a 0.82 micron wavelength. As will be more readily understood from the description provided below, the reading light source 36 may provide constant illumination and need not be switched on and off during operation of the memory system, even when the system is in a writing mode. Additionally, since the medium 12 is photosensitive to only the visible spectrum writing light, the near infrared reading light beam can pass through the medium without altering or modifying the stored charge on the particles 14, thus permitting repeated readings of the stored data.
The reading light produced by the source 36 is projected through collimation optics 38 to form a substantially collimated reading light beam which is projected onto beamsplitter 34. A reflected beam of the reading light beam and the transmitted writing light beam project from the beamsplitter along a single path for both the writing light beam and the reading light beam. A beam stop 40 is positioned to intercept the reading light beam transmitted through the beamsplitter.
As will be described in more detail below, the reading light beam is used only to read information from the
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memory medium 12, and the writing light beam is used correspondingly sized region of the medium 12 which
only to write information to the medium. To accom- may have charged or uncharged particles. The charged
plish this, the writing light beam has a wavelength or uncharged state of the particles is used to indicate
greater than a threshold wavelength for the medium 12 whether the information stored in the region is a binary
above which the medium is photosensitive to light. In 5 "1" or a binary "0", and the state of the particles may be
comparison, the reading light beam has a wavelength detected using the reading light beam. This means that
which is below the threshold, and thus the medium is on a 4.3 inch by 4.3 inch square of medium 12, it is
insensitive to the reading light beam. possible to store 3.0 gigabits of information which is
A horizontal deflector 42 is positioned along the path approximately equal to the storage capacity of seven
to deflect which ever of the writing or reading light 10 conventional 14 inch hard discs,
beam is present along a horizontal axis in response to a The focal plane mask 56 is manufactured using a
horizontal deflector drive signal provided by control diazo material which is developed using a photolitho
circuitry, indicated generally in FIG. 1 by reference graphic technique to form the opaque portions of the
numeral 44. As best shown in FIG. 2, the deflector 42 is mask ^ the transmissive apertures 58. Other suitable
a solid state device having a bimorphic piezoelectric 15 techniques may be used to manufacture the mask,
crystal electronically controlled by a horizontal deflec- By use of the focal plane mask 56 the focusing prob.
tor drive signal provided by the control circuitry 44. lems that have heretofore been encountered are elimi
The deflector dnve signal causes deformation of the nated since the apertures 58 serVe as aperture stops. The
bimorphic crystal and thus causes the writing/reading apertures 58 have a diameter which is preferably
light beam which is incident upon a reflective alumi- 20 f than the wavel th of both the writing n ht
nized surface 46 mounted on one side of the bimorphic ^ readin j. ht moV thr h jt so that nQ defrac.
crystal to scan along a honzontd axis at a selected scan ^ Wems afe encountered. In the tl
speed, n FIG. 2, two light rays A and B are sche- fefr J embodiment of the invention, the writing light
matically shown as«^daB th^alunmuzed surface ^ ^ ... ^ w wavelengths of0A Jd 0*82
a es.,, . t, , „ .. j u microns, respectively, and the apertures have a diame
many possible angles of deflection permitted by the . « ■ ■ * j iV. * i. *
deflector 42. The aligle of change between the reflected ter of TM » » noted that it may be possible to
rays at time "1" and at time "2" is indicated by the mcreaf ^ density of the medium 12 by reducing the doubled headed arrow 48 for both the "A" and the "B» diameter of the apertures or the spacing between aper
30 tures, or both. It has been found that the film medium 12
Also in the path for the writing/reading light beam bem8 usedin *e presently preferred embodiment of the after it is deflected off the horizontal deflector 42 is a f ventlfn has resolution through use of the
vertical deflector 50 of somewhat similar construction focal P^e mask 56 that increased ^formation packing to horizontal deflector 42 except that the writing/read- can be achieved without diffraction problems, ing light beam passes through the bimorphic crystal. 35 ^ apertures 58 of the mask 56 define regions of the The vertical deflector 50 deflects the writing/reading medium 12 whlch have not been struck by the wntlnS light beam along a vertical axis substantially orthogonal h8ht beam and hence have particles 14 which retain to the horizontal axis in response to a vertical deflector their mitial uncharged state or have been struck by the drive signal provided by the control circuitry 44. With writing light beam and hence have particles which have appropriate drive signals to the horizontal deflector 42 40 acquired a charge at the expense of the surface charge and the vertical deflector 50, the writing/reading light on tne medium surface 20. Regions of the medium 12 beam can be caused to scan horizontally or vertically, witb- the charged particles and regions with the unacross any desired portion of the medium 12. charged particles cause differing phase velocities of
After the writing/reading light beam passes through propagation for orthagonal elements of the reading the vertical deflector 50, it passes through a horizontal 45 tight beam which results in angular rotation of the resulcylindrical lens 52 and then through a vertical cylindri- tant electric and magnetic field vectors as it passes cal lens 54 which condition the light beam and focus it through the region. The electric and magnetic fields are to a focal point with a focal plane passing therethrough. rotated upon passing through a region with charged A fixed mask 56 is positioned substantially in the focal particles by a first degree of rotation, and upon passing plane and in juxtaposition with the medium 12. 50 through a region with uncharged particles by a second
The mask 56 is bonded to a side of the medium 12 degree of rotation detectably different from the first which is toward the lenses 52 and 54. The mask is sub- degree of rotation.
stantially opaque to the writing and reading light beams When passing through a region with uncharged partiexcept for a matrix of horizontal rows and vertical col- cles 14, the electric and magnetic fields of the reading umns of substantially transparent light admitting aper- 55 light beam are rotated as a result of the initial charge tures 58 therethrough as is best shown in FIG. 5. In the placed upon the surface 20 of the medium 12. An even presently preferred embodiment of the invention, the greater rotation is realized when the reading light beam apertures 58 are circular transmissive portions one mi- passes through a region which has charged particles, cron (i.e., 1.0X 10~6 meters) in diameter spaced apart This is because the initial surface charge might be at 100 on two micron centers, both along the rows and be- 60 volts while the region which has charged particles tween the rows. With this arrangement, 25 X106 aper- might be at 120 volts. The higher voltage is the result of tures can be positioned in a matrix of 1.0 cm2 in size the additional charge applied by photons impinging having 5,000 rows and 5,000 columns of apertures. As upon the photosensitive particles and imparting addisuch, using a relatively small 4.3 inch by 4.3 inch square tional energy thereto. In the presently preferred emmask 56 over a similar size block of medium 12, which 65 bodiment of the invention, a region with charge partiis equivalent to about 119 cm2 of area, it is possible to cles and the first degree of rotation of the electric and have 3.0 x 109 apertures. As will be described in more magnetic fields of the reading light beam passing theredetail below, each aperture 58 defines the extent of a through correspond to a binary "1", and a region with
uncharged particles and a lesser resulting second degree of rotation correspond to a binary "0".
Because a specific amount of light energy must impinge upon a region of the medium 12 to exceed its sensitivity threshold value and thereby cause the photo- 5 sensitive particles 14 embedded in the thermoplastic layer 16 (see FIGS. 3 and 4) to acquire a charge, each of the apertures 58 in the mask 56 must have a minimum opening size which is related to the time period the writing light beam will impinge on the medium through 10 the aperture. The opening size must be large enough to admit sufficient energy when exposed to the writing light beam to exceed the sensitivity threshold value of the medium. Of course, the time period during which the writing light beam impinges upon the medium de- 15 pends upon the scan rate of the beam, which is controlled by the control circuitry 44 and which will be described in more detail below.
Upon a region of the medium 12 defined by one of the apertures 58 being illuminated by the reading light 20 beam, the reading light beam passes through the medium and then through a spherical lens 60 which focuses the reading light beam onto a light detector 62, which in the preferred embodiment of the invention is a light detecting photodiode having associated light de- 25 tection circuitry, indicated by reference numeral 63. The light detector 62 generates an indicator signal indicating detection of the reading light beam, and provides the indicator signal to a pulse conditioning comparator 66. The photodiode is sensitive to the reading light 30 beam incident thereon, but is insensitive to light at the wavelength of the writing light beam. The light detector 62 and circuitry 63 is a conventional OPIC light detector, such as model number IS006 manufactured by Sharp which includes both a light detecting element 35 and peripheral circuits integrated onto one chip.
Positioned between the light detector 62 and the lens 60, and in the path of the reading light beam, is a Senarmont polarization compensator 64. The compensator 64 includes associated conventional circuitry (not shown). 40 The compensator 64 detects and measures the angular rotation of the electric and magnetic field of the reading light beam by measuring the reading light beam intensity relative to a predetermined reference after passing through one of the regions of the medium 12 defined by 45 one of the apertures 58. The reading light beam intensity will vary as a function of the degree of angular rotation of the electric and magnetic field vectors as predicted by the well-known Malus' law. The reference is based upon the rotation experienced by the reading 50 light beam upon passing through a region of uncharged particles 14. The compensator 64, based upon the sensed phase difference between the reading light beam passing through the charged and uncharged regions, generates a data indicating signal on a line 65 to the light detector 55 circuitry 63.
The data indicating signal effectively modulates the indicator signal amplitude from the light detector 62 and attenuates the indicator signal if a rotation is detected indicative of a recorded information bit of stored 60 digital data at the binary logic state "0". An electronic signal amplitude comparator 66 monitors the indicator signal and by comparing the indicator signal to a predetermined amplitude threshold level, will produce a binary "1" output only when the indicator signal, and 65 hence the detected degree of rotation corresponding to passage of the reading light beam through a region of charged particles, exceeds that predetermined threshold
indicating a recorded information bit of "1". The output of the comparator 66 is a read digital data signal containing the digital data which was stored in the regions of the medium 12 scanned by the reading light beam. The read digital data signal is provided to the computer I/O device 35a
To provide the initial charge to the surface 20 of the medium 12, a Corotron 68 extends the full vertical length of the medium and is selectively movable across the horizontal width of the medium. The Corotron 68 is a Corona charging device (as was the device 22 described with respect to FIG. 3) and has a back deflector 69 which essentially evenly sprays the surface 20 of the medium 18 with electrons to thereby provide a uniform charge intensity across the surface. After the initial charge is provided to the medium prior to any exposure with the writing light beam, the Corotron 68 is moved out of the path of the writing/reading light beam.
The medium 12 used with the invention is sensitive to temperatures elevated above normal ambient temperatures and the memory system 10 includes an erasure conditioner 70 which is a heatable shoe positioned adjacent to the glass backing 24 of the medium 12. The erasure conditioner heats a correspondingly sized selected portion of the medium 12 to a sufficiently elevated temperature to allow the charged particles in the corresponding portion of the medium to yield their charge and resume an uncharged state when subjected to a reversed polarity field. Since glass is used as the backing 24 (see FIGS. 3 and 4), the heat is transmitted primarily transversely through the glass, but not laterally so as to enable isolation of adjacent portions of the medium from the heat.
At present, the erasure conditioner is a 1 cm2 foot which is selectively heated to heat the corresponding portion of the medium 12 to 70° C. or better. At about 70° C, the medium 12 is erased in approximately five seconds, and if the temperature is elevated somewhat, the erasure process can be completed more quickly. In practice, after the medium is heated, the Corotron charging device 68 is passed across the surface 20 of the medium corresponding to the portion heated, and a reverse polarity charge is applied thereto (i.e., reversed compared to that of the initial charge). This effectively removes the charge on the particles in that portion of the medium 12. After the medium has cooled sufficiently, the polarity of the Corotron 68 is changed back to that necessary to apply the initial charge, and an initial charge is applied to the surface of the erased portion of the medium 12 to, render the particles 14 in that portion photosensitive. The erased portion of the medium is now ready for storage of new digital data based upon the writing light beam impinging upon the medium and the photosensitive particles which have been relieved of their prior charge again being charged upon the incident thereon of the writing light beam. Unless erased, once charged, the photosensitive particles 14 retain their charge and establish a charged field in a region of the medium 12 without any physical deformation to the medium. The charge is held by the charge particles for prolonged periods of time and without the need to maintain any electrical power to the system.
By using an erasure conditioner 70 having an area less than the total surface area of the medium 12, the medium can essentially be divided into blocks which can have the regions of charged particles therein corresponding to the apertures of the block simultaneously
9
erased by the erasure conditioner 70. In the preferred embodiment, the erasure conditioner 70 is a square heatable pad which is selectively movable about the surface of the medium 12 for erasure purposes, and then movable out of the writing/ reading light beam when not in 5 use for heating the medium.
As discussed above, the control circuitry 44 provides the horizontal and vertical deflector drive signals to the deflectors 42 and 50 to control the horizontal and vertical scanning of the writing/reading light beam on the 10 medium 12. The control circuitry 44 includes a synchronous controller 72 which controls the overall tuning and operation of the controller circuit. The synch controller 72 provides control signals to two 20 megahertz clocks 74 and 76 which are respectively the clocks for 15 the horizontal scanning circuitry and for the vertical scanning circuitry. Each of the clocks 74 and 76 provides its output to a corresponding horizontal scan counter 78 or a vertical scan counter 80. Each of these scan counters counts from 1 to 5,000 which corresponds 20 to the 5,000 apertures 58 which exist in each row and each column of the focal plane mask 56.
The output of each of the scan counters 78 and 80 is provided to a corresponding horizontal digital-toanalog converter 82 or a vertical digital-to-analog con- 25 verter 84. The digital-to-analog converters convert the digital counter output signal provided at the output of the scan counters to an analog voltage signal which serves as the deflector drive signal provided to the corresponding one of the horizontal or vertical deflec- 30 tors 42 or 50. The analog voltage signal is used to deform the bimorphic piezoelectric crystal portion of the deflectors to cause the beam to scan horizontally or vertically, as desired. In such manner, under the control of the synch controller 72 the memory system 10 can be 35 caused to automatically scan the medium 12.
In conventional fashion, the scan can also be manually controlled in the horizontal or vertical direction by horizontal manual scan circuit 86 and vertical manual scan circuit 88 which are responsive to the user manu- 40 ally inputting the particular information address which the optical memory is to write to or read from. The manual scan circuits 86 and 88 each provide a digital signal to the corresponding digital-to-analog converter 82 or 84, in much the same manner as provided via the 45 automatic scan mode by the scan counters 78 and 80. It should be understood, that conventional scanning techniques may be used to control the scanning so as to provide a left to right horizontal scan of the rows of apertutes, or a left to right and then right to left interlac- 50 ing scan of the rows of apertures. Of course, the medium could be scanned vertically by column rather than by rows.
While the memory system 10 has been described and shown utilizing a beamsplitter 34 which directs the 55 writing light beam and the reading light beam along a single path through a single set of horizontal and vertical deflectors, since the read and write functions are accomplished with different wavelength lights, an optical system with separate horizontal and vertical deflec- 60 tors for each of the writing light beam and reading light beam may be utilized. In such manner the writing and reading functions can occur simultaneously. To do so, scan control circuitry would be provided for each of the sets of horizontal and vertical deflectors. 65
It is noted that with the memory system 10 of the present invention, the system is controlled purely by optics and electronic devices without requiring any
10
mechanical movement except for the slight movement produced by piezoelectric crystal deflectors. There are no mechanical heads which must be moved about and the information recording medium 12 is stationary. Since the medium does not have to be moved about, such as by rotation, and a read/write head does not have to be physically moved relative to the storage medium so as to align the head with the track or sector to be read or written to, the present invention provides a system which can operate at extremely high speeds limited only by the speed of the electronics and optical components involved. Inherently, the speed is substantially more than any system utilizing the mechanical components. Writing speeds significantly greater than 20 megahertz and reading speeds of 3 to 5 gigahertz are possible. This provides an improvement of several thousand times the access speed presently possible with a conventional, magnetic hard disc, while providing the equivalent storage capacity of many large size hard discs. Another benefit of the present invention is that the bit error rate is substantially improved over that possible with a magnetic hard disc and the power consumption is minimal.
As noted above, with the memory system 10 of the present invention, the writing light beam and reading light beam operate at two different frequencies which do not interfere with the operation of the other, and thus with appropriate control circuitry the memory system can be reading from the medium 12 at the same time it is writing to the medium. This arrangement inherently increases the speed of operation of the memory system and provides greatly increased efficiency of operation and speed. When coupled with the fact that the memory system utilizes no moving parts, the speed of operation of this system is greatly increased over anything available today.
It will be appreciated that, although specific embodiments of the invention have been described herein for purposes of illustration, various modifications may be made without departing from the spirit and scope of the invention. Accordingly, the invention is not limited except by the appended claims.
We claim:
1. An optical memory system for storage and retrieval of digital data, comprising: a source of writing light having a wavelength of less
than 0.480 microns; means for amplitude modulating said writing light by
a write digital signal containing the digital data to
be stored;
first lens means for forming said writing light into a substantially collimated writing light beam;
a source of reading light having a wavelength of greater than 0.480 microns;
second lens means for forming said reading light into a substantially collimated reading light beam;
means for directing said writing light beam and said reading light beam along a single path;
first means in said path for deflecting said writing/reading light beam along a first axis generally transverse to said path in response to a first control signal;
second means in said path for deflecting said writing/reading light beam along a second axis generally transverse to said path and substantially orthogonal to said first axis in response to a second control signal;
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