GB2086168A - Optical Transmission Systems - Google Patents
Optical Transmission Systems Download PDFInfo
- Publication number
- GB2086168A GB2086168A GB8131822A GB8131822A GB2086168A GB 2086168 A GB2086168 A GB 2086168A GB 8131822 A GB8131822 A GB 8131822A GB 8131822 A GB8131822 A GB 8131822A GB 2086168 A GB2086168 A GB 2086168A
- Authority
- GB
- United Kingdom
- Prior art keywords
- optical transmission
- transmission system
- light
- light sources
- displaced
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
- Granted
Links
- 230000005540 biological transmission Effects 0.000 title claims abstract description 26
- 230000003287 optical effect Effects 0.000 title claims description 26
- 238000001228 spectrum Methods 0.000 claims abstract description 19
- 239000013307 optical fiber Substances 0.000 claims abstract description 9
- 238000000295 emission spectrum Methods 0.000 claims abstract description 8
- 238000003491 array Methods 0.000 claims description 8
- 238000003384 imaging method Methods 0.000 claims description 2
- 239000000835 fiber Substances 0.000 description 7
- JBRZTFJDHDCESZ-UHFFFAOYSA-N AsGa Chemical compound [As]#[Ga] JBRZTFJDHDCESZ-UHFFFAOYSA-N 0.000 description 4
- 229910001218 Gallium arsenide Inorganic materials 0.000 description 4
- 238000002955 isolation Methods 0.000 description 3
- 239000000463 material Substances 0.000 description 3
- 230000004075 alteration Effects 0.000 description 2
- 230000003595 spectral effect Effects 0.000 description 2
- 229910005540 GaP Inorganic materials 0.000 description 1
- GYHNNYVSQQEPJS-UHFFFAOYSA-N Gallium Chemical compound [Ga] GYHNNYVSQQEPJS-UHFFFAOYSA-N 0.000 description 1
- XUIMIQQOPSSXEZ-UHFFFAOYSA-N Silicon Chemical compound [Si] XUIMIQQOPSSXEZ-UHFFFAOYSA-N 0.000 description 1
- HCHKCACWOHOZIP-UHFFFAOYSA-N Zinc Chemical compound [Zn] HCHKCACWOHOZIP-UHFFFAOYSA-N 0.000 description 1
- MDPILPRLPQYEEN-UHFFFAOYSA-N aluminium arsenide Chemical compound [As]#[Al] MDPILPRLPQYEEN-UHFFFAOYSA-N 0.000 description 1
- 238000003486 chemical etching Methods 0.000 description 1
- 239000006185 dispersion Substances 0.000 description 1
- 230000000694 effects Effects 0.000 description 1
- 229910052733 gallium Inorganic materials 0.000 description 1
- HZXMRANICFIONG-UHFFFAOYSA-N gallium phosphide Chemical compound [Ga]#P HZXMRANICFIONG-UHFFFAOYSA-N 0.000 description 1
- 239000003365 glass fiber Substances 0.000 description 1
- PCHJSUWPFVWCPO-UHFFFAOYSA-N gold Chemical compound [Au] PCHJSUWPFVWCPO-UHFFFAOYSA-N 0.000 description 1
- 239000010931 gold Substances 0.000 description 1
- 229910052737 gold Inorganic materials 0.000 description 1
- 230000037431 insertion Effects 0.000 description 1
- 238000003780 insertion Methods 0.000 description 1
- LQBJWKCYZGMFEV-UHFFFAOYSA-N lead tin Chemical compound [Sn].[Pb] LQBJWKCYZGMFEV-UHFFFAOYSA-N 0.000 description 1
- 229910052751 metal Inorganic materials 0.000 description 1
- 239000002184 metal Substances 0.000 description 1
- 230000005855 radiation Effects 0.000 description 1
- 229910052710 silicon Inorganic materials 0.000 description 1
- 239000010703 silicon Substances 0.000 description 1
- 239000007787 solid Substances 0.000 description 1
- 229910052725 zinc Inorganic materials 0.000 description 1
- 239000011701 zinc Substances 0.000 description 1
Classifications
-
- G—PHYSICS
- G02—OPTICS
- G02B—OPTICAL ELEMENTS, SYSTEMS OR APPARATUS
- G02B6/00—Light guides; Structural details of arrangements comprising light guides and other optical elements, e.g. couplings
- G02B6/24—Coupling light guides
- G02B6/26—Optical coupling means
- G02B6/28—Optical coupling means having data bus means, i.e. plural waveguides interconnected and providing an inherently bidirectional system by mixing and splitting signals
- G02B6/293—Optical coupling means having data bus means, i.e. plural waveguides interconnected and providing an inherently bidirectional system by mixing and splitting signals with wavelength selective means
- G02B6/29304—Optical coupling means having data bus means, i.e. plural waveguides interconnected and providing an inherently bidirectional system by mixing and splitting signals with wavelength selective means operating by diffraction, e.g. grating
- G02B6/29305—Optical coupling means having data bus means, i.e. plural waveguides interconnected and providing an inherently bidirectional system by mixing and splitting signals with wavelength selective means operating by diffraction, e.g. grating as bulk element, i.e. free space arrangement external to a light guide
- G02B6/29307—Optical coupling means having data bus means, i.e. plural waveguides interconnected and providing an inherently bidirectional system by mixing and splitting signals with wavelength selective means operating by diffraction, e.g. grating as bulk element, i.e. free space arrangement external to a light guide components assembled in or forming a solid transparent unitary block, e.g. for facilitating component alignment
-
- G—PHYSICS
- G02—OPTICS
- G02B—OPTICAL ELEMENTS, SYSTEMS OR APPARATUS
- G02B6/00—Light guides; Structural details of arrangements comprising light guides and other optical elements, e.g. couplings
- G02B6/24—Coupling light guides
- G02B6/26—Optical coupling means
- G02B6/28—Optical coupling means having data bus means, i.e. plural waveguides interconnected and providing an inherently bidirectional system by mixing and splitting signals
- G02B6/293—Optical coupling means having data bus means, i.e. plural waveguides interconnected and providing an inherently bidirectional system by mixing and splitting signals with wavelength selective means
- G02B6/29304—Optical coupling means having data bus means, i.e. plural waveguides interconnected and providing an inherently bidirectional system by mixing and splitting signals with wavelength selective means operating by diffraction, e.g. grating
- G02B6/29305—Optical coupling means having data bus means, i.e. plural waveguides interconnected and providing an inherently bidirectional system by mixing and splitting signals with wavelength selective means operating by diffraction, e.g. grating as bulk element, i.e. free space arrangement external to a light guide
- G02B6/2931—Diffractive element operating in reflection
-
- G—PHYSICS
- G02—OPTICS
- G02B—OPTICAL ELEMENTS, SYSTEMS OR APPARATUS
- G02B6/00—Light guides; Structural details of arrangements comprising light guides and other optical elements, e.g. couplings
- G02B6/24—Coupling light guides
- G02B6/26—Optical coupling means
- G02B6/28—Optical coupling means having data bus means, i.e. plural waveguides interconnected and providing an inherently bidirectional system by mixing and splitting signals
- G02B6/293—Optical coupling means having data bus means, i.e. plural waveguides interconnected and providing an inherently bidirectional system by mixing and splitting signals with wavelength selective means
- G02B6/29379—Optical coupling means having data bus means, i.e. plural waveguides interconnected and providing an inherently bidirectional system by mixing and splitting signals with wavelength selective means characterised by the function or use of the complete device
- G02B6/2938—Optical coupling means having data bus means, i.e. plural waveguides interconnected and providing an inherently bidirectional system by mixing and splitting signals with wavelength selective means characterised by the function or use of the complete device for multiplexing or demultiplexing, i.e. combining or separating wavelengths, e.g. 1xN, NxM
-
- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04B—TRANSMISSION
- H04B10/00—Transmission systems employing electromagnetic waves other than radio-waves, e.g. infrared, visible or ultraviolet light, or employing corpuscular radiation, e.g. quantum communication
- H04B10/50—Transmitters
- H04B10/501—Structural aspects
- H04B10/502—LED transmitters
-
- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04J—MULTIPLEX COMMUNICATION
- H04J14/00—Optical multiplex systems
- H04J14/02—Wavelength-division multiplex systems
Landscapes
- Physics & Mathematics (AREA)
- Engineering & Computer Science (AREA)
- Computer Networks & Wireless Communication (AREA)
- Signal Processing (AREA)
- General Physics & Mathematics (AREA)
- Optics & Photonics (AREA)
- Electromagnetism (AREA)
- Optical Couplings Of Light Guides (AREA)
- Spectrometry And Color Measurement (AREA)
Abstract
A system for multiplexed transmission of different wavelengths of light comprises at least two light sources 12-16 whose images are formed on the end of an optical fibre 32. The images have displaced spectra so that a different part of the spectrum of each light source is imaged on to the end of the optical fibre and each part is transmitted by the optical fibre. The images themselves may be displaced by displacing the light sources, or the images may be coincident, their spectra being displaced by using light sources with emission spectra centred on different wavelengths. <IMAGE>
Description
SPECIFICATION
Optical Transmission Systems
This invention relates to optical transmission systems and more particularly to systems for multiplexed transmission of different wavelengths of light.
In this specification the term "light" also includes light invisible to the human eye, i.e., infra red and ultra-violet radiation.
It is an object of the present invention to provide such an optical transmission system which has a high radiance and efficiency, high degrees of optical isolation between wavelengths and which is rugged and compact.
According to the present invention an optical transmission system for multiplexed transmission of light comprises at least two light sources and means for imaging the emitted light from the at least two sources onto the end of an optical fibre, the images having displaced spectra whereby a different part of the spectrum of each light source is imaged on to the end of the optical fibre.
The light sources may be displaced from one another so that their images and hence their spectra are displaced.
Preferably the light sources are filtered and focussed in a monochromator comprising a lens and a dispersive element such as a prism or a blazed grating.
Alternatively, the light sources may emit different wavelength bands whereby their images are not displaced but their spectra are displaced.
Preferably the at least two light sources comprise light emitting diodes.
The light emitting diodes preferably have emission spectra centred on the same wavelength but they may have emission spectra centred on different wavelengths.
Preferably the light sources comprise an abutting array of light emitting diodes having emission spectra centred on the same wavelength. Several arrays may be provided, each array having emission spectra centred on different wavelengths.
The monochromator may comprise a monolithic structure comprising a concave reflector in place of a lens, and a prism or grating may be used as the dispersive element.
Embodiments of the invention will now be described by way of example only with reference to the accompanying drawings in which:
Figures 1 a and 1 b illustrate schematically the principal of an optical transmission system for multiplexed transmission of light in accordance with the invention.
Figure 2 illustrates a practical arrangement of the transmission system and
Figure 3 is an alternative arrangement to that of Figure 2,
Figure 1 a illustrates a multi-element array 10 of light emitting diodes (LED's), each element 12, 1 4 and 1 6 emitting a broad spectrum in wavelength and each element being centred on the same wavelength. The array 10 is positioned adjacent to a monochromator 1 8 having a wide entrance slit 20. The monochromator 1 8 is illustrated in Figure 2 and comprises a lens 22 and a dispersive element, in this case a blazed grating 24.The light from each element of the
LED array is focussed by the lens 22 onto the grating 24 where it is defracted and reflected back through the lens 22 which focusses an image of the spectrum of each element adjacent to the LED array. Since the elements 12, 14 and 1 6 are located at different positions adjacent to each other, the three resulting spectrum images are siightly displaced from one another but overlap as illustrated in Figure 1 b. Mounted in the side of the monochromator 1 8 is an optical fibre 32 the end of which is located in the area which receives the three overlapping spectrum images.
Thus the optical fibre 32 receives three different channels 40 of each of the three spectrum images as illustrated in Figure 1 b and the fibre then transmits these multiplexed channels. A similar monochromator (not shown) is also used at the other end of the fibre which demultiplexes the signals (the defraction at the grating is proportional to wavelength and the three multiplexed channels are therefore separated) in conjunction with a detector array.
The LED array 10 emits at high radiance and efficiency and the monochromator gives a very high degree of isolation (both optical and electrical) between the parts of the spectra transmitted along the fibre 32.
The monochromator 18 images at the high numerical aperture of multimode fibres ( 0.20.3) with small aberrations and attenuation, has the correct dispersion characteristics and which is fabricated as a compact and rugged component.
The LED multi-element array 10 may be any of several material systems including lead-tin telluride, gallium phosphide, gallium arsenide, gallium arsenide phosphide, gallium-indiumarsenide-phosphide, gallium arsenide, and also double heterostructure gallium aluminium arsenide. The two latter material systems have many attractions for fibre optic applications.
One example of a gallium arsenide array is a zinc diffused surface emitting array comprising eight 25x 100 ,um2 elements with 100 ,um spacing between elements. In this case the individual elements are separated completely by chemical etching to give a very high degree of electrical and optical isolation but positional accuracy is maintained because of a continuous gold integral heatsink pad. Each element emits at radiances around 20 watts/st/cm2 at current drives of 300 mA which corresponds to 1 mw output per element.
Another example is a 16 element edge emitting array which is fabricated in double heterostructure GaAIAs material. This is a lower current device with a power output of 30 ,uw per element at a current of 30 mA. Each emission element is 20 Mm x ,um in size.
The emitting dimensions for each element, and the number of elements for each array can be altered to suit system requirements.
With the correct type of lens 32 in the monochromator 1 8 diffraction limited optics are straight forwardly achieved and a high quality grating 24 used at the blaze angle will reflect at 90% efficiency. Thus low overall insertion loss is achievable with such a monochromator. This optical arrangement is set up in a 1 cm long metal tube and so is rugged and compact as well as optically efficient.
An alternative monolithic structure 26 is illustrated in Figure 3. In this case a concave reflector 28 is used in place of the lens 22 and a grating 29 is used as the dispersive element.
This optical structure consists of three optical parts:
A body part 27, a reflector part 31 having the curved reflector 28 and a small angle prism 30 with a grating 29. This has the advantage of solid geometry, and as all the light rays are optically immersed any aberrations are smaller than for an equivalent free space configuration. This structure can also be made in a thin piate wave-guide form which can be very small and manufactured in large quantities at relatively low cost.
In this case light diverging from each element 12 or 14 of the LED array 10 is collimated into a parallel beam by the reflector 28. It is diffracted at the grating 29 so that a slightly angled parallel beam is reflected towards the reflector 28 and is then re-imaged adjacent to the LED array 10. As before the fibre 32 receives light from the variously displaced elements of the LED array thus launching different sections of the spectrum along the fibre 32 from each element.
The multiplexing scheme of Figure 1 a creates multiple channels 40 shown in Figure 1 b by cutting the spectral emission of each element 12, 14 or 1 6 into sections but various sophistications can be introduced to optimise the launch power.
With a surface emitter array, enhancement of coupled power by a factor of 10-20 can be achieved by fitting each element with a spherical microlens. Alternatively a 3-5 times improvement can be achieved by the use of a cylindrical lens (e.g. a glass fibre) which extends across all of the elements and this can be applied to both the edge and surface types of arrays.
The near gaussian spectral emission of LED's implies a corresponding variations in launch power for the different wavelength channels 40.
This effect can be reduced by 'Element width taiioring' in which the end of the elements 12, 14, 16 of the array 10 are made proportionately wider so that the widths of the different channels 40 is not constant. Alternatively the current drive to the elements can be adjusted to level the launch powers.
Seven elements giving seven channels 40 (a minimum requirement for one specific application) can easily be driven from one LED array and this number can be multiplied by using other similar arrays with emission spectra centred at other wavelengths. A spectrum centred at a different wavelength can provide seven further different channels and LED arrays with wavelengths centred at 0.8 ym, 0.85 ,um 0.9 ,um and 1.05 m each with a bandwidth of 0.1 ,um can be used. The channels can then be 0.80- 0.85, 0.85-0.9, 0.9-0.95 and 0.95-1.0 and used with silicon arrays as detectors.
A further five LED arrays can also be used (GalnAsP/lnP types) if long wavelength detector arrays are utilised. Thus potentially a 7x9-63 channel wavelength multiplex system can be operated over a single fibre.
Claims (13)
1. An optical transmission system for multiplexed transmission of light comprising at least two light sources and means for imaging the emitted light from the at least two sources on to the end of an optical fibre, the images having displaced spectra whereby a different part of the spectrum of each light source is imaged on to the end of the optical fibre.
2. An optical transmission system as claimed in claim 1 in which the light sources are displaced from one another so their images and hence their spectra are displaced.
3. An optical transmission system as claimed in claim 1 in which the light sources emit different wavelength bands whereby their images are not displaced but their spectra are displaced.
4. A optical transmission system as claimed in any preceding claim in which the at least two light sources comprises at least two light emitting diodes.
5. A optical transmission system as claimed in claim 4 in which the at least two light emitting diodes have emissions spectra centred on different wavelengths.
6. An optical transmission system as claimed in claim 4 in which the at least two light sources comprises an abutting array of light emitting diodes having emission spectra centred on the same wavelength.
7. An optical transmission system as claimed in claim 4 in which the at least two light sources comprises a plurality of arrays of light emitting diodes, each array having emission spectra centred on a different wavelength.
8. An optical transmission system as claimed in any preceding claim in which the light sources are filtered and focussed in a monochromator.
9. An optical transmission system as claimed in claim 8 in which the monochromator comprises a lens and a dispersive element.
10. An optical transmission system as claimed in claim 8 in which the monochromator comprises a concave reflector and a dispersive element.
11. An optical transmission system as claimed in claim 9 or claim 10 in which the dispersive element comprises a prism.
1 2. An optical transmission system as claimed in claim 9 or claim 10 in which the dispersive element comprises a grating.
13. An optical transmission system as claimed in any of claims 8 to 12 in which the monochromator comprises a monolithic structure.
1 4. An optical transmission system constructed and adapted to operate substantially as described with reference to Figure 1 and
Figures 2 or 3 of the accompanying drawings.
Priority Applications (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| GB8131822A GB2086168B (en) | 1980-10-23 | 1981-10-22 | Optical transmission systems |
Applications Claiming Priority (2)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| GB8034236 | 1980-10-23 | ||
| GB8131822A GB2086168B (en) | 1980-10-23 | 1981-10-22 | Optical transmission systems |
Publications (2)
| Publication Number | Publication Date |
|---|---|
| GB2086168A true GB2086168A (en) | 1982-05-06 |
| GB2086168B GB2086168B (en) | 1985-03-27 |
Family
ID=26277309
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| GB8131822A Expired GB2086168B (en) | 1980-10-23 | 1981-10-22 | Optical transmission systems |
Country Status (1)
| Country | Link |
|---|---|
| GB (1) | GB2086168B (en) |
Cited By (4)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| FR2530392A1 (en) * | 1982-07-16 | 1984-01-20 | Instruments Sa | OPTICALLY INSULATING DEVICE FOR WAVELENGTH DIVISION MULTIPLEXING OR DEMULTIPLEXING |
| US4622662A (en) * | 1983-03-31 | 1986-11-11 | Instruments S.A. | Wavelength-selective multiplexer-demultiplexer |
| EP0254453A2 (en) * | 1986-07-21 | 1988-01-27 | Polaroid Corporation | Bulk optic grating and device |
| US4926412A (en) * | 1988-02-22 | 1990-05-15 | Physical Optics Corporation | High channel density wavelength division multiplexer with defined diffracting means positioning |
-
1981
- 1981-10-22 GB GB8131822A patent/GB2086168B/en not_active Expired
Cited By (6)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| FR2530392A1 (en) * | 1982-07-16 | 1984-01-20 | Instruments Sa | OPTICALLY INSULATING DEVICE FOR WAVELENGTH DIVISION MULTIPLEXING OR DEMULTIPLEXING |
| EP0102264A1 (en) * | 1982-07-16 | 1984-03-07 | Instruments S.A. | Arrangement for wavelength multiplexing or demultiplexing with optical isolation |
| US4622662A (en) * | 1983-03-31 | 1986-11-11 | Instruments S.A. | Wavelength-selective multiplexer-demultiplexer |
| EP0254453A2 (en) * | 1986-07-21 | 1988-01-27 | Polaroid Corporation | Bulk optic grating and device |
| EP0254453A3 (en) * | 1986-07-21 | 1989-03-29 | Polaroid Corporation | Bulk optic echelon and device |
| US4926412A (en) * | 1988-02-22 | 1990-05-15 | Physical Optics Corporation | High channel density wavelength division multiplexer with defined diffracting means positioning |
Also Published As
| Publication number | Publication date |
|---|---|
| GB2086168B (en) | 1985-03-27 |
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Legal Events
| Date | Code | Title | Description |
|---|---|---|---|
| 732 | Registration of transactions, instruments or events in the register (sect. 32/1977) | ||
| PCNP | Patent ceased through non-payment of renewal fee |
Effective date: 19941022 |