CA1107106A

CA1107106A - Fiber optic interface for combined signal transmission and detection

Info

Publication number: CA1107106A
Application number: CA311,608A
Authority: CA
Inventors: Malcolm H. Hodge
Original assignee: TRW Inc
Current assignee: Northrop Grumman Space and Mission Systems Corp
Priority date: 1977-09-30
Filing date: 1978-09-19
Publication date: 1981-08-18
Also published as: JPS5474449A; GB2005433B; US4169656A; JPS6158001B2; DE2841970A1; FR2404865A1; BR7806446A; FR2404865B1; GB2005433A

Abstract

ABSTRACT OF THE DISCLOSURE
A fiber optic interface for combined signal trans-mission and detection is provided. The interface enables transmission in two directions over a single optic fiber and includes a housing having an elongated channel extending therethrough. The housing is comprised of a transparent material. A first optic fiber is secured in one end of the channel with the outermost end of the first optic fiber being aligned with a light source. A second optic fiber is secured in the other end of the channel with the innermost end of the second fiber being disposed adjacent the innermost end of the first fiber. The ends of the fibers are mismatched so that there is a loss of light passed from at least the second fiber to the first fiber during a light transmission from the second to the first fiber. A light sensitive device is secured to the housing and is responsive to light escaping at the junction between the first and the second fiber ends. The mismatching of the fiber ends is accomplished in two ways. The first is the provision of a smaller diameter optic fiber which is connected to the light source than the optic fiber connected to the remote light source. In this way substantially all of the light provided by the light source connected to the first optic fiber is passed to the optic fiber connected to a remote light source. However, in a transmission from the remote light source to the local interface, there is a loss of light about the periphery of the first optic fiber which enables the detection device to pick up the signal.

Description

SPECIFICATION
This inven~ion rela~es generally ~o fiber optic couplers and more particularly to a fiber optic interface for combined signal transmission and detection which enables two way transmission over a single optical fiber~ .
In prior systems where data has been transmitted in two directions over optical fibers, at least two optical fibers have been used. In such systems the two optical fibers run parallel to each other with one end of the ~ibers being ~onnected to a light emitter and a light detect~r a~d at the opposite ~nd of the opticàl fibers the optical fiber connected to the l~ght emitter at the fîrst e~d is ~2 .

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connected to a light detector at the opposite end and vice versa fox the second optical fiber.
When the optical fibers are parts of fiber bundles of macroscopic proportions and it is necessary to arrange half of the fibers to be connected to a de-~ec~or and half of the ibers to be connected to a ligh-t emitter at one end and at the opposite end to connect the fibers that are connected to the ligllt emitter to - a detector at the second end and vice versa, not only is there a problem wi-th the large cross-sectional requirement of all of the optical fibers, but there is the further di~ficulty of identifying the fibers in the bundle ~or correct registration.
In many mass applications, the efficiency of light transmission rom th~e light source to the light detector over optical fibers is not required and yet space requirements and registration difficulties represent a great problem and therefore have prevented the utilization of optical fibers for signal transmitting therein~
It is ~herefore an object of the invention to provide an inter~ace which enables combined signal trans~
mission and detection over a single opti~ fiber.
Still another object of ~he invention is to provide a new and improved fiber optic interface ~or a combined signal transmission anA detection which is inexpensive to manuacture.
;~ Yet another object of the invention is to provide a new and improved fiber op~ic interface for combined signal transmission and de~ec~ion w}~ich utilizes light loss at the , ~ ~

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interface between two optic fibers to enable transmission in two directions over a single optical fiber.
These and other objects of the invention are achieved by proviaing a new and improved fiber optic interface for combined signal transmission and detection. The inter-face includes a housing having an elongated channel which extends therethrough. The housiny is preferably comprised o glass or other transparent material and includes a first optic fiber which is secured in one end of the channel with the ou~ermost end of ~he first optic fiber being aligned with a light source. A second fiber is connected in the other end o the channel with the innermost end of the - second fiber being disposed adjacent the innermost end of the first fiber. The ends of the ~iber are mismatched so that *here is a 10s5 of light passed,from at least the second fiber to the first fiber during a light,transm~ssion from the second to the first fiber. A light sensitive device is secured to the housing and is responsive to the light escaping at the junction between the rirst and second fiber ends during a transmîssion from the second to ~he first fiber and~t~ereby enab1es receipt of a signal vver said optical f iber .
More particularly, there is provided:
A fiber optic inter~ace for combined signal trans-mission and detection via first and second optic ~ibers, said interface including a separate housing body having an elongated channel extending~therethrough, a light source and lisht sensi-tive means, sald housing body comprising translucent material, said first optic fiber being secured in one end of said channel 30~ ~with the~outermost end of said first optic fiber being aligned~
with~sald light source, said second optic ~i~er being in the other end of said channel, with the innermost end of said second~fiber belng disposed'adjacent the innermost end of said first fiber~ said light sensitive means being connected t~ said housing body, said ends of said fibers being arranged so that light passes between said first fiber and said second fiber and vice versa, and means for directing a portion of light to said light sensitive means during a light transmission from said second to said first fiber, said light sensi~ive means being responsive to said light portion directed thereto.

- Other objects and many of the attendant advantages of the instant invention will be readily appreciated as the 1~ same becomes better understood by reference to the followin~
detailed description when considered in connection with the accompanyin~ drawing, whereinv Fig. 1 is a perspective view of a fiber ~ptic interface embodying the inventio~;

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Fig. 2 ;s a sectional view taken along the line

2-2 in Fig. l;
Fig. 3 is a sectional view taken along the line

3-3 in Fi~. 2;
Fi~J. 4 is a ~extical sectional view with portions shown in full for purposes of clarity of an alternate fiber optic interface embodying the invention;
Fig. 5 is a front elevational view of the alternate fiber optic interface; and Fig~ 6 is a sectional view taken along lines 6-6 in Fig" 4.
Referring now in greater detail to the various fi~ures o~ the drawing wherein like reference numerals refer to like parts, a fiber optic inter~ace embodying the invention is shown generally at 20~
The interface 20 basically comprises a housing formed of three rods 22, ~4 and 26 which are of generally cylindrical shape and which include tapered ends 28 at each end of the rods.
: : The rods ~2, 24 and 26 are preferabl~ formed of glass and the housing is formed by drawing the heated glass rods whereby the rods are integrally secured to each other at the junctions along their periphery as shown in Fig. 2 at 31.
It should be ~mderstood that the housing may also be made of more than three rods. An interstitial channel 29 i5 ormed between the three rods as shown in Fig. 2.
As best seen in ~igO 3! a first optic fiber 30 is secured in the interstitial channel at one end o the housing formed ~ .
:: by the~rods 22,~ 24 and 26. A second optic . fiber 32 is ~ : - 5 -.

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secured in the other end of the channel 29 with the ends of the optic fibers 30 and 32 being secured adjacent to each other.
As best seen in Fig. 3, the tapered ends 28 of the rods enable a smooth enlarged openin~ at each end of the interstitial channel 29 which facilitates the insertion o~ the opt;c fibers 30 ana 32.
A light emitting diode 34 is secured to the outermost end o~ the opti.c ~iber 30 and the lateral ends of the rods 24, 26 and 280 The light emitking diode is preferably secured by a suitable adhesive with the light emitting diode being closely aligned with the core o the optic fiber 30 to maximize tlle. light transmission to the optic fiber 30 from the light emitting diode 34 A light sensitive device 36 is proviaed which preerably comprises a photodetector~
The photodetector is preferably secured to a : flat side 37 which is provided on the outer periphery of rod~26~ The light sensitive device 36 is provided as close to the junction between the ends of optic fibers 30 and 32 as is possible.
. The light emitting diode 34 is connected via wires 38 to circuitry whiah is utilized or providing signals to the light emitter 34. Similarly, the ligh~ detector 3~;is conne~ted to circuitry ~ia wires 40. As can be seen in Fig. 3 the junction between the ends 42 and.44 is mi~-~atched as a result of the end of optic fiber 30 having an~inclined end 42 whereas the end 44 of optic fibex 32 extends perpendicular to the axis ~f the optic ~iber 32.

, ~Q7~¢~6 Thuss when light is emi~ted from diode 34 and is transmitted into the optic fibex 30 only a portion of the light is transmitted to optical fib~r 32. The remaining portion of the light t~ansmitted in that direc~ion is reflected into the housing formed of rods 24, ~6 and 28 and such light is picked up by the device 36. By suitable electronic circuitry, light sensitive device 36 is disabled when emitter 34 is operating.
That is, by conventional techniques light sensor 36 is turned of each time the light emitting diode 34 is -turned on. Another technique which may be used where simultaneous transmission in both directions is desired is to provide the signal on optic fiber 30 from light emitting diode on a carrier signal at a frequency different than the ~requency that light sensitive device 36 is capable o receiving. This is accomplished by a conventional filter or tuner.
The portion of the signal which is passed from op~ic fiber 32 is transmitted to a remote location by optic fiber 32 which extends thereto.
It should be noted that op~c fibers 30 and 32 . . .
may be made of either plastic or glass and optic fibers 30 and 32 each includes a core 46 and a cladding of a di~ferent refractive ind~x 48. It can therefore he seen that a simple interface is provided which enables signal transmission over a single optic fiber 32~in two direction.
l'he junction at the ends 42 and 44 of the fibers 30 and 32, respectively, causes a considerable amount o light loss thereat which can easily be tolerated in ~: :

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w 7 _ most mass applications of fiber opticsc Thus, considerable savings can be accomplished by enabl.ing simple installation of only a single optic fiber and thus no registration problems are encountered when ins~alling the same. It should be understood that a similar interface is provided at the opposite end of fiber optic 32 which is used to both transmit and receive signa~s at the other end of the optic fiber.
An alternate fiber optic interface embodying the invention is shown at 50 in Fig. 4.
'rhe interface 50 basicaIly comprises a housing 52 which is Preferably comprised of glass and which includes a glass coating 54 which extends about ~he longitudinal periphery thereof. The qlass coating is preferably of a different light refractive .index so that the light is requlred to escape through the lateral end at which a photosensitive device is secured to the housing 52.
: A longitudinally extending opening is provided which extends through the houaing 52. A first fiber optic 56 is secured in said longitudinally extending opening 60 at one end of the housing 52. A second optic fiber 58 is provided at the oppo~ite end of the opening and this optic fiber extends out to a remot~ location and is secured : adjacent to the optic fiber 56.
Opening 60 ~hich extends through the housing 52 is enlarged at the end in which optic fiber 58 is disposed ~o that a larqer diameter optic 'fiber 58 can be used in conjunc~ion with the smaller diameter optic fiber 56.

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~ ' Optic fiber 56 has a first end face 66 which .is aligned with the lateral wall o~ housing 52 and a second end 68 which is abutted against the core of the optic fiber S8. optic fiber 58 has an end wall 70 which abuts the wall 56 in substantially tangential and intimate contact SQ that light emitted through optic fiber 56 and passed through op~ic fiber 58 occasions very little loss at the iunctions therebetween, The housing 52 is pre~erably formed by drawing a glass rod, cutting the rod at a predetermined length and then providing an opening ~0 extending longitudinally through the housing. The end which accommodatesthe larger diameter fiber is dipped into an acid bath, such as hydrofluoxic acid,~o etch away or taper the end o~
the housing ~2. This also causes the open.ing 60 to be enlarged to the diameter at portion 62 thereofO Thus~
the outer diameter of the housing 52 can be seen to be reduced at 72. Also, the opening 60 is flared at 74 to the ~arger diametex portion 62.
At the end 66 of fiber optic 5~ a light emitting diode-76 is secured with the light emittiny portion being aligned with the core of the optic fiber 56 for maximum efficiency of light transmission to the optic fiber 56~
Directly below the light emitting. diode 76 there is provided a light sensitive device which preferably compxises a photodetector 78 which acts to sense the light which is 105t at th~ junction between the optic fiber 56 and optic fiber 58, The photodetector 78 is ~uitably secured to the end wall of the housing 52 adjacent the 73L~ 6 light emitting diode 76 and is suitably securea thereto by an adhesive.
The light emitting dioae 76 is ~onnected to suitable circuitxy via electric lines ~0 and the light sensitive device 78 is connected by suitable electric lines 82 to circuitry.
The optic fiber 56 is preferably secured within the housing by a suitable adhesive between the outer per-phery of the fiber 56 and the surface of opening 60, Similarly, the end of optic fiber 58 is suitably adhesively secured in intimate contact with optic fiber 5~ by suitable adhesive securement of.the optic fiber 58 with the walls of portion 620f:opening 60.
The intimate contact between the optic ibers 56 and 58 causes s~bstantially no transmission loss from fiber 56 to fiber SB. Therefore, by providing in cavity 6.4 a liguid or solid having a strong absorbtion of wave lengths at the infra-red requency at which the signal from light emitter 76i~provided~ little of the lo~s of light from diode 76 is received by light senstive device 78. The light absorbtive material may also be placed between the light sensiti~e device and the lateral wall of the housing 52 to prevent light at a predetermined wave length from being detected by the light sensitive deviceO
In ~he embodiment of Fig. 4, because there is sub-tantially no lo~s in the transmitting direction of light fxom light emitting diode 76 through optic fiber 56 to opti~ ~iber 58 at the j~nction~e~ween the two optic fibexs; by providing a li~uid which has a strong absorbtion of light at mi~rowave lengths in the cavity ~4 surro~nding the junction between . ~ .

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optic fiber 56 and 58, there can be simultaneous transmission in both directions without further electronic switching with respect to the interrelation between ~he 'ight emitting diode and the light sensitive device 78.
For example, by providing a solution oftr-Pthylamine, whi~h acts to absorb wave lengths of 0.9 microns, within cavity 64 and using a 0.9 micron wave length in light emitting diode 76, any leakage at the junction between optic fiber 55 and 58 will be absorbed by the triethylamine solution which prevents the signal from being picked up by the li~ht sensitive device 78. The transmission of ligllt in the opposite dired~ion would not be a~fected if the light source at the remote end whi.ch is transmitted via optic iber 58 is at an infra-red wa~e lenyth of 0.8 microns, the si~nal is not absorbed by the triethylamine solution and is easily passed to the light sensitive device 78.
Similarly, a solution of ethanolamine can be provided in the cavity 64. The ethanolamine has a characteristic of absorbing wave lengths of 0.8 micronsO With the ethanolamine the~light transmitted from light emitting diode 76 would be ht 0.8 microns while the remote light emitting dio~e would transmit at 0.9 mierons since a 0O9 micron wave l~ngth would be easily transmitted through the ethanol~mine and into th~ housing 52 which wpuld be detected by the light se~sitive device 78.
; It can therefore be seen that a new and improved fiber optic!interface for combined signal transmission and detection has~been provided. Both embodiments enable data .

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to be transmitted over a single optic fiber in two directions.
Both embodiments enable the housing to be made from an inexpensive material. Furthermore, in both embodiments the housing is made ~rom a material whose refractive index is tailored for maximum signal coupling.
Moreover, the fa~rication technique of glass drawing which can be utilized for both housings lends itself to high production rates and is extremelysuitable for the intended purpose.
Without further elaboration the foregoing will so fully illustrate my invention that others may, by applying current or future knowledge, readily adapt the same or use under various conditions of service.

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Claims

THE EMBODIMENTS OF THE INVENTION IN WHICH AN EXCLUSIVE PROPERTY
OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:

1. A fiber optic interface for combined signal trans-mission and detection via first and second optic fibers, said interface including a separate housing body having an elongated channel extending therethrough, a light source and light sensi-tive means, said housing body comprising translucent material, said first optic fiber being secured in one end of said channel with the outermost end of said first optic fiber being aligned with said light source, said second optic fiber being in the other end of said channel, with the innermost end of said second fiber being disposed adjacent the innermost end of said first fiber, said light sensitive means being connected to said housing body, said ends of said fibers being arranged so that light passes between said first fiber and said second fiber and vice versa, and means for directing a portion of light to said light sensitive means during a light transmission from said second to said first fiber, said light sensitive means being responsive to said light portion directed thereto.

2. The fiber optic interface of claim 1 wherein the end of said first fiber extends at an angle to the axis thereof and the end of said second fiber is not parallel to the end of said first fiber so that intimate contact between the ends of said fibers is prevented, to thereby direct light into said body and to said light sensitive means.

3. The fiber optic interface of claim 1 wherein said housing body is comprised of a clear material and a coating of a different refractive index is provided about said housing to maximize light retention within the optic fibers reaching the light sensitive means.

4. The fiber optic interface of claim 1 wherein said housing is comprised of glass.

5. The fiber optic interface of claim 1 wherein a material having a light absorptive characteristic is provided between said junction of said first and second fibers and said light sensitive means.

6. The fiber optic interface of claim 1 wherein said housing comprises at least three rods which are secured together in a side-by-side parallel array and form said elongated channel in which said first and second fibers are disposed.

7. The fiber optic interface of claim 5 wherein one of said rods includes a flat surface along a longitudinal side thereof and said photosensitive means is secured thereto adjacent the junction between said first and second fiber.

8. The fiber optic interface of claim 1 wherein said body includes a cavity and wherein the ends of said first and second fibers are disposed in said cavity, said cavity including therein material which absorbs light of a specific wave length to enable light at said wave length escaping from said junction between said optic fibers to be absorbed by said material.

9. The fiber optic interface of claim 8 wherein said body is an elongated member having a first and second end face and wherein said light source and said light responsive means are secured to said first end face.

10. The fiber optic interface of claim 9 wherein said light responsive means encompasses a major portion of said first end face.

11. The fiber optic interface of claim 9 wherein said first fiber has a smaller diameter than said second fiber, said end of said first fiber being in intimate contact and aligned with said second fiber end so that substantially all of said light in said first fiber is transmitted to said second fiber, while a portion of said light in said second fiber is passed to said first fiber and the remainder of said light in said second fiber is passed into said housing and directed to said light sensitive means.