CA1089932A - Wavelength division multiplexer/demultiplexer in optical fiber communication systems - Google Patents
Wavelength division multiplexer/demultiplexer in optical fiber communication systemsInfo
- Publication number
- CA1089932A CA1089932A CA292,383A CA292383A CA1089932A CA 1089932 A CA1089932 A CA 1089932A CA 292383 A CA292383 A CA 292383A CA 1089932 A CA1089932 A CA 1089932A
- Authority
- CA
- Canada
- Prior art keywords
- optical
- fibre
- demultiplexer
- focussing
- light
- 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.)
- Expired
Links
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
- G02B6/42—Coupling light guides with opto-electronic elements
- G02B6/4201—Packages, e.g. shape, construction, internal or external details
- G02B6/4246—Bidirectionally operating package structures
-
- 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
Landscapes
- Physics & Mathematics (AREA)
- General Physics & Mathematics (AREA)
- Optics & Photonics (AREA)
- Optical Couplings Of Light Guides (AREA)
- Optical Communication System (AREA)
Abstract
Abstract of the Disclosure An optical multiplexer/demultiplexer using wavelength division multiplexing comprises a fibre optic port for connection to an optical transmission fibre, a dispersive diffraction element, and an array of alternate light sources and light detectors. One or more focussing and collimating elements direct predetermined spectral components diffracted by the diffraction element from the light sources to the fibre optic port and from the fibre optic port to the light detectors, thereby allowing simultaneous reception and transmission of optical signals in a single unit.
Description
Field of the Invention ~L(~ 932 This inven~ion relates to transmission on optical fibres and more particularly to a system for multiplex transmission on optical fibres.
Background of the Invention . . _ .
The use of optical fibres for the transmission of telecommunication data is increasing rapidly and falls into two principal categories, namely high capacity trunks and medium capacity loops serving subscribersdirectly.
For high capacity trunking applications, the capacity of a slngle fibre is limited by three factors, namely modal dispersion, fibre material dispersion and the modulation characteristics of the light emitting device. For analogue modulation, the third factor dominates due to nonlinearities in the response of light emi~ting diodes (LEDs) and lasers.
For digital systems, instabilities in laser performance make present reliable operation over 2~0 Mbit/s debatable.
However, it is in the second application category, that of medium capacity subscriber loops, that there are major problems to be overcome. Telecommun~cations systems are evolving towards an integrated ~0 network prov~d~ng the subscriber with a range of video, data and telephone s~n~ls. Fibre is a suitable medium to transmit these slgnals to the suhscrlber~ HoweYer, if the subscriber is to have a variety of terminals, ~ther he must have a separate fibre for each ~erminal, or his terminals must ~ncorp~rate elec~ronic analogue or digital frequency or time division ~ul~iplexers (FDM or TDM). The use of separate fibres increases transmission costs; the use of FDM or TDM increases terminal costs.
Summary of the Invention The present invention endeavours to alleviate some of these problems by providing an optical multiplexer/demultiplexer, where the method of optical multiplexing is wavelength division mul~iplexing (WDM).
WDM in the context of the present invention diPfers from . . - - . . , ., .. ~ ; . .. . .. - - -, .... . . -FDM and TDM in that it uses entirely optical signals at different optical wavelengths, which may be electrically modulated with any desired signal.
This allows the subscriber to transmit and receive at baseband if desired.
In comparison with FDM, a WDM system obviates the need i for accurately controlled electronic oscillators, mixers and filters. In comparison with TDM, WDM obviates the need for sampling circuitry, clock pulse generation, and extraction circuitry.
The utilization of WDM in the present invention involves three aspects: firstly, light sources of different spectral composition are individually modulated by independent signals; secondly, the outputs from the light sources are combined optically and transmitted over a common path; thirdly, the transmitted light at the end of the transmission path is separated into its original spectral components. Each of the components is then individually demodulated.
Thus, according to the present invention there is provided an optical multiplexer/demultiplexer comprising a fibre optic port for connection to an optical transmission fibre, a dispersive diffraction element, an array of alternate light sources and light detectors, and focussing and collimating means, the arrangement being such that light ~a From an optlcal transmission fibre connected to said port is colllmated by said focussing and collimating means, divided into predetermined spectral components by said diffraction element, and each spectral component is focused onto a respective one oF the llght detectors by the focussing and collimating means, and predetermined spectral components of light from the light sources are collimated by the focussing and collimating means, combined by the diffraction element, and the combined components are focused by the focussing and collimating means for transmission via an optical transmission fibre connected to said port.
Brief Description of the Drawings ~0 A preferred embodiment of the invention will now be described in conjunction with the accompanying drawings in which: `
Figure 1 is a block diagram of the wavelength division . . ~ ~
!,, ~ g 3 Z
multiplexer/demultiplexer of the inYentionj Figure 2 is a block diagram o~ an alternate arrangement of the invention;
Figure 3 illustrates a second alternate arrangement of the invention in elevationi Figure ~ is a plan view of the arrangement of Figure 3 taken along the line 4-4; and Figure 5 is an end view of the arrangement of Figure 3 taken along the line 5-5.
~escription of the Preferred Embodiment As illustrated in Figure 1, an optical fibre 10 is connected optically into a multiplexer/demultiplexer 90 of the invention. A
collimator 11 serves to collimate the light emitted from the fibre 10 and direct it to a blazed diffraction (re-flection) grating 12. The diffraction by the grating 12 gives a highly peaked light distribution at given wave-lengths in the direction of a plane 14. A lens system 13 serves to focus the light on the plane 14. An array 18 of alternate light detectors 20, 22, 24 and light sources 21, 23, 25 lies in the plane 14. The plane 14 is opt~cally can~ugate to a plane 19 running through an exit Face 15 of the ~n Fibre 10.
The collimator il lies on the axis of the fibre 10. The ~ptlcal axis of the focussing lens 13 lies on a linè such that the angle deFined by the ax~s of the fibre 10 on a line normal to the faces oF the bl~ed grat~n~ 12 equals the angle defined by the optical axis of the focussing lens 13 and said line normal to the faces of the blazed grating 1 2 .
The fibre 10 is connected at its other end to an optical .~
multiplexer/demultiplexer 90' which is complementary to the unit 90 in that :
its array 18' consists of alternate light sources 20', 22', 2~' and light .
detectors 21', 23', 25'. Elements 11', 12', and 13' in the unit 90' are arranged ln the same manner as the elements 11, 12, and 13 in the unit 90. .
Each detector 20, 21', 22, 23', 24, 25' is positioned to ...
~3 :~
~... .
. ~
.. . ... - .. - ... . . ... .. ~ ~ .. ....... - ... ....... .. - .... - . ..
3~3132 detect a signal of a particular wavelength of light, i.e. a predetermined spectral component. Light sources 20', 21, 22~, 23, 24', 25 provide light signals of corresponding wavelengths. The complementary arrangement of light sources and light detectors in the two units 90 and 90' provides for bidirectional transmission between the units.
Light from any other source other than that to which a particular detector is paired, i.e. 20 and 20', is undeslrable and represents crosstalk in the system. To minimize crosstalk each detector 20, 21' 22, 23', 24, 25', is centered at or near the image in plane 14 produced by the source 20', 22', 24', or plane 14' produced by source ~1, 22, 23, to which that detector is paired by illuminating the fibre 10.
For a given system increasing the area of the detector increases both the desired signal strength and the undesirable crosstalk while decreasing .
the detector area has the opposite effect. As well, all internal ports must be coated with anti-reflection coatings to minimize crosstalk caused by internal reflection.
As illustrated in Figure 2, the use of a blazed transmission grating 30 allows the various components to be placed on a single axis 31.
This alternate arrangement provides For easier alignment but is subject to sl-ightly greater losses due to losses -inherent in the transmission gra-ting.
A second alternate arrangement uses a Littrow conFiguration, a~ Is Famillar to those versecl in the art and illustrated in Figures 3, 4 and 5, wherQ -the colllmating ancl Focussing lenses are the same lens 40.
As illustrated in Figures 3, 4 and 5, the face 15 of optical fibre 10 lies in -the same plane 41 as the sources 43, 45, 499 and detectors 44, 46, 48. A blazed reflection grating 42 completes the unit.
The collimator in the preferred embodiment is a lens having an "f" number defined by:
2tanO ' D < tan~ ~ where:
.,'- "", '.': ..
3~
f = focal length, D = d;ameter of lens; and is defined through the numerical aperture (NA) of the fibre;
sin~ = NA, where n is the refractive index of air.
The preferred value is D ~ 2tln~
A value of D beyond the upper limit introduces unacceptable loss.
~ The lens operates in a paraxial mode so that the principal - 10 aberrations of concern are spherical and chromatic aberrations~ These are controlled to give a resolution in the plane containing the fibre which is better than one-tenth the diameter of the fibre core. Larger aberrations result in reduced performance, in the sense that the number ; of different sources which can be resolved with a given crosstalk and signal-to-noise ratio (SNR) performance is reduced.
The minimum focal length for the collimator is determined ; by the minimum "f" number and the minimum diameter of the lens so that the dlffraction limit on the lens resolution is less than 1~% when compared with the Fibre core diameter~
The grating in the preferred embodiment is a blazed reflection grating. The size and angle of blaze are chosen so that a light ray incident on the grating with a wavelength at the centre of the range to be used for communication wlll give rise to a maximum difFract~on intensity. This is a design procedure well known to those ~
versed in the state of the art. `
The size of the grating is such that the diffraction ;
11mitation caused by the projection of the grating along the optic axis of the focussing lens 13 in the figure is less than 10% when compared with the image of the fibre core in the detector-source plane.
The lines on the grating are ruled sufficiently finely that the separation between diffraction maxima of adjaoent wavelength - 5 - ~ ~
' " , ~, .
should be greater than twice the physical diameter o~ the detectors.
However, systems not needing good crosstalk isolation could tolerate wider spacings between lines.
The focal length of the focussing lens f2 is expressed as a multiple R of the focal length of the collimating lens fl which represents the magnification R of the fibre output in the source-detector plane. R is given by: R = f2 .
The focussing lens does not operate in paraxial mode so that the non-isoplanatic and the isoplanatic aberrations have to be corrected to give a resolution better than one-tenth of the fibre core diameter as measured on its image in the detector plane. Corrections o~ chromatic aberrations are not critical since each image is quasi-monochromatic.
The "f" number of the focussing lens is determined from its focal length and the diameter which when projected on the grating covers the whole grating.
The detectors are optical fibre ends. These fibres lead to photodetectors at a point remote from the detector source plane.
However, it is possible to place the photodetectors directly in the plane ~f they are sufficiently small.
The sources are also optical ~ibres connected to laser ~odes or LEDs.
Nume~r~cal Example We assume that the wavelength of 6 sources for this purpose are 800, 825, 850, 87~, 900, 925 nanometers.
Each source has a spectral power distribution of S(~) = Ae ~ ;
where ~ is one of the six values giYen above.
The devices selected have à = ~ that is the power emitted by a source 2 nm from its central wavelength ~i will be - times ;~
the power at Ai. `
.. . . . . .. . . . . .. . . .
3~32 Diameter of the fibre is 75 ~m9 NA of fibre = 0.18 Based on detailed calculations The values of components in the preferred embodiments will be:
Collimator - "f" number = 3 Aberration and diffraction limited resolution on axis 7 ~m, Focal length 1 cm.
Diameter 1/3 cm.
Diffraction grating:
Angle ~ = 10 Spacing of grating - 2000 lines/nm Focal length - 1 cm Diameter = 1/3 cm Aberrations such that resolution at an angle 10 to the axis is at least 7 ~m "f" number 3 .
Size of detectors 100 ~m diameter covered by 60 ~m slit Size oF sources 25 ~m NA 0.2 .
Spacing between sources and detectors .5 mm. ~ `
'' :.
',' .
- 7 - : .
Background of the Invention . . _ .
The use of optical fibres for the transmission of telecommunication data is increasing rapidly and falls into two principal categories, namely high capacity trunks and medium capacity loops serving subscribersdirectly.
For high capacity trunking applications, the capacity of a slngle fibre is limited by three factors, namely modal dispersion, fibre material dispersion and the modulation characteristics of the light emitting device. For analogue modulation, the third factor dominates due to nonlinearities in the response of light emi~ting diodes (LEDs) and lasers.
For digital systems, instabilities in laser performance make present reliable operation over 2~0 Mbit/s debatable.
However, it is in the second application category, that of medium capacity subscriber loops, that there are major problems to be overcome. Telecommun~cations systems are evolving towards an integrated ~0 network prov~d~ng the subscriber with a range of video, data and telephone s~n~ls. Fibre is a suitable medium to transmit these slgnals to the suhscrlber~ HoweYer, if the subscriber is to have a variety of terminals, ~ther he must have a separate fibre for each ~erminal, or his terminals must ~ncorp~rate elec~ronic analogue or digital frequency or time division ~ul~iplexers (FDM or TDM). The use of separate fibres increases transmission costs; the use of FDM or TDM increases terminal costs.
Summary of the Invention The present invention endeavours to alleviate some of these problems by providing an optical multiplexer/demultiplexer, where the method of optical multiplexing is wavelength division mul~iplexing (WDM).
WDM in the context of the present invention diPfers from . . - - . . , ., .. ~ ; . .. . .. - - -, .... . . -FDM and TDM in that it uses entirely optical signals at different optical wavelengths, which may be electrically modulated with any desired signal.
This allows the subscriber to transmit and receive at baseband if desired.
In comparison with FDM, a WDM system obviates the need i for accurately controlled electronic oscillators, mixers and filters. In comparison with TDM, WDM obviates the need for sampling circuitry, clock pulse generation, and extraction circuitry.
The utilization of WDM in the present invention involves three aspects: firstly, light sources of different spectral composition are individually modulated by independent signals; secondly, the outputs from the light sources are combined optically and transmitted over a common path; thirdly, the transmitted light at the end of the transmission path is separated into its original spectral components. Each of the components is then individually demodulated.
Thus, according to the present invention there is provided an optical multiplexer/demultiplexer comprising a fibre optic port for connection to an optical transmission fibre, a dispersive diffraction element, an array of alternate light sources and light detectors, and focussing and collimating means, the arrangement being such that light ~a From an optlcal transmission fibre connected to said port is colllmated by said focussing and collimating means, divided into predetermined spectral components by said diffraction element, and each spectral component is focused onto a respective one oF the llght detectors by the focussing and collimating means, and predetermined spectral components of light from the light sources are collimated by the focussing and collimating means, combined by the diffraction element, and the combined components are focused by the focussing and collimating means for transmission via an optical transmission fibre connected to said port.
Brief Description of the Drawings ~0 A preferred embodiment of the invention will now be described in conjunction with the accompanying drawings in which: `
Figure 1 is a block diagram of the wavelength division . . ~ ~
!,, ~ g 3 Z
multiplexer/demultiplexer of the inYentionj Figure 2 is a block diagram o~ an alternate arrangement of the invention;
Figure 3 illustrates a second alternate arrangement of the invention in elevationi Figure ~ is a plan view of the arrangement of Figure 3 taken along the line 4-4; and Figure 5 is an end view of the arrangement of Figure 3 taken along the line 5-5.
~escription of the Preferred Embodiment As illustrated in Figure 1, an optical fibre 10 is connected optically into a multiplexer/demultiplexer 90 of the invention. A
collimator 11 serves to collimate the light emitted from the fibre 10 and direct it to a blazed diffraction (re-flection) grating 12. The diffraction by the grating 12 gives a highly peaked light distribution at given wave-lengths in the direction of a plane 14. A lens system 13 serves to focus the light on the plane 14. An array 18 of alternate light detectors 20, 22, 24 and light sources 21, 23, 25 lies in the plane 14. The plane 14 is opt~cally can~ugate to a plane 19 running through an exit Face 15 of the ~n Fibre 10.
The collimator il lies on the axis of the fibre 10. The ~ptlcal axis of the focussing lens 13 lies on a linè such that the angle deFined by the ax~s of the fibre 10 on a line normal to the faces oF the bl~ed grat~n~ 12 equals the angle defined by the optical axis of the focussing lens 13 and said line normal to the faces of the blazed grating 1 2 .
The fibre 10 is connected at its other end to an optical .~
multiplexer/demultiplexer 90' which is complementary to the unit 90 in that :
its array 18' consists of alternate light sources 20', 22', 2~' and light .
detectors 21', 23', 25'. Elements 11', 12', and 13' in the unit 90' are arranged ln the same manner as the elements 11, 12, and 13 in the unit 90. .
Each detector 20, 21', 22, 23', 24, 25' is positioned to ...
~3 :~
~... .
. ~
.. . ... - .. - ... . . ... .. ~ ~ .. ....... - ... ....... .. - .... - . ..
3~3132 detect a signal of a particular wavelength of light, i.e. a predetermined spectral component. Light sources 20', 21, 22~, 23, 24', 25 provide light signals of corresponding wavelengths. The complementary arrangement of light sources and light detectors in the two units 90 and 90' provides for bidirectional transmission between the units.
Light from any other source other than that to which a particular detector is paired, i.e. 20 and 20', is undeslrable and represents crosstalk in the system. To minimize crosstalk each detector 20, 21' 22, 23', 24, 25', is centered at or near the image in plane 14 produced by the source 20', 22', 24', or plane 14' produced by source ~1, 22, 23, to which that detector is paired by illuminating the fibre 10.
For a given system increasing the area of the detector increases both the desired signal strength and the undesirable crosstalk while decreasing .
the detector area has the opposite effect. As well, all internal ports must be coated with anti-reflection coatings to minimize crosstalk caused by internal reflection.
As illustrated in Figure 2, the use of a blazed transmission grating 30 allows the various components to be placed on a single axis 31.
This alternate arrangement provides For easier alignment but is subject to sl-ightly greater losses due to losses -inherent in the transmission gra-ting.
A second alternate arrangement uses a Littrow conFiguration, a~ Is Famillar to those versecl in the art and illustrated in Figures 3, 4 and 5, wherQ -the colllmating ancl Focussing lenses are the same lens 40.
As illustrated in Figures 3, 4 and 5, the face 15 of optical fibre 10 lies in -the same plane 41 as the sources 43, 45, 499 and detectors 44, 46, 48. A blazed reflection grating 42 completes the unit.
The collimator in the preferred embodiment is a lens having an "f" number defined by:
2tanO ' D < tan~ ~ where:
.,'- "", '.': ..
3~
f = focal length, D = d;ameter of lens; and is defined through the numerical aperture (NA) of the fibre;
sin~ = NA, where n is the refractive index of air.
The preferred value is D ~ 2tln~
A value of D beyond the upper limit introduces unacceptable loss.
~ The lens operates in a paraxial mode so that the principal - 10 aberrations of concern are spherical and chromatic aberrations~ These are controlled to give a resolution in the plane containing the fibre which is better than one-tenth the diameter of the fibre core. Larger aberrations result in reduced performance, in the sense that the number ; of different sources which can be resolved with a given crosstalk and signal-to-noise ratio (SNR) performance is reduced.
The minimum focal length for the collimator is determined ; by the minimum "f" number and the minimum diameter of the lens so that the dlffraction limit on the lens resolution is less than 1~% when compared with the Fibre core diameter~
The grating in the preferred embodiment is a blazed reflection grating. The size and angle of blaze are chosen so that a light ray incident on the grating with a wavelength at the centre of the range to be used for communication wlll give rise to a maximum difFract~on intensity. This is a design procedure well known to those ~
versed in the state of the art. `
The size of the grating is such that the diffraction ;
11mitation caused by the projection of the grating along the optic axis of the focussing lens 13 in the figure is less than 10% when compared with the image of the fibre core in the detector-source plane.
The lines on the grating are ruled sufficiently finely that the separation between diffraction maxima of adjaoent wavelength - 5 - ~ ~
' " , ~, .
should be greater than twice the physical diameter o~ the detectors.
However, systems not needing good crosstalk isolation could tolerate wider spacings between lines.
The focal length of the focussing lens f2 is expressed as a multiple R of the focal length of the collimating lens fl which represents the magnification R of the fibre output in the source-detector plane. R is given by: R = f2 .
The focussing lens does not operate in paraxial mode so that the non-isoplanatic and the isoplanatic aberrations have to be corrected to give a resolution better than one-tenth of the fibre core diameter as measured on its image in the detector plane. Corrections o~ chromatic aberrations are not critical since each image is quasi-monochromatic.
The "f" number of the focussing lens is determined from its focal length and the diameter which when projected on the grating covers the whole grating.
The detectors are optical fibre ends. These fibres lead to photodetectors at a point remote from the detector source plane.
However, it is possible to place the photodetectors directly in the plane ~f they are sufficiently small.
The sources are also optical ~ibres connected to laser ~odes or LEDs.
Nume~r~cal Example We assume that the wavelength of 6 sources for this purpose are 800, 825, 850, 87~, 900, 925 nanometers.
Each source has a spectral power distribution of S(~) = Ae ~ ;
where ~ is one of the six values giYen above.
The devices selected have à = ~ that is the power emitted by a source 2 nm from its central wavelength ~i will be - times ;~
the power at Ai. `
.. . . . . .. . . . . .. . . .
3~32 Diameter of the fibre is 75 ~m9 NA of fibre = 0.18 Based on detailed calculations The values of components in the preferred embodiments will be:
Collimator - "f" number = 3 Aberration and diffraction limited resolution on axis 7 ~m, Focal length 1 cm.
Diameter 1/3 cm.
Diffraction grating:
Angle ~ = 10 Spacing of grating - 2000 lines/nm Focal length - 1 cm Diameter = 1/3 cm Aberrations such that resolution at an angle 10 to the axis is at least 7 ~m "f" number 3 .
Size of detectors 100 ~m diameter covered by 60 ~m slit Size oF sources 25 ~m NA 0.2 .
Spacing between sources and detectors .5 mm. ~ `
'' :.
',' .
- 7 - : .
Claims (10)
PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:
1. An optical multiplexer/demultiplexer comprising a fibre optic port for connection to an optical transmission fibre, a dispersive diffraction element, an array of alternate light sources and light detectors, and focussing and collimating means, the arrangement being such that light from an optical transmission fibre connected to said port is collimated by said focussing and collimating means, divided into predetermined spectral components by said diffraction element, and each spectral component is focused onto a respective one of the light detectors by the focussing and collimating means, and predetermined spectral components of light from the light sources are collimated by the focussing and collimating means, combined by the diffraction element, and the combined components are focussed by the focussing and collimating means for transmission via an optical transmission fibre connected to said port.
2. An optical multiplexer/demultiplexer as claimed in claim 1 wherein said light sources comprise light emitting diodes.
3. An optical multiplexer/demultiplexer as claimed in claim 1 wherein said light sources comprise lasers.
4. An optical multiplexer/demultiplexer as claimed in claim 1 wherein said dispersive diffraction element comprises a blazed reflection grating having a predetermined angle of blaze, said focussing and collimating means comprising a first refractive element between the fibre optic port and the grating and a second refractive element between the grating and the array of light sources and light detectors.
5. An optical multiplexer/demultiplexer as claimed in claim 4 wherein said light sources and light detectors are arranged in a plane which is optically conjugate to the face of an optical trans-mission fibre connected to said fibre optic port, the first refractive element has an optical axis coincident with an optical axis of the fibre optic port, and the angle between the optical axis of the first refractive element and the normal to said blaze is equal to the angle between said normal to said blaze and an optical axis of the second refractive element.
6. An optical multiplexer/demultiplexer as claimed in claim 1 wherein said dispersive diffraction element comprises a blazed transmission grating, said focussing and collimating means comprising a first refractive element between the fibre optic port and the grating and a second refractive element between the grating and the array of light sources and light detectors, and the first and second refractive elements and the fibre optic port having collinear optical axes.
7. An optical multiplexer/demultiplexer as claimed in claim 1 wherein said focussing and collimating means comprises a single refractive element arranged between said dispersive diffraction element on one side and said fibre optic port and said array of light sources and light detectors on another side.
8. A bidirectional optical transmission system comprising two complementary optical multiplexer/demultiplexers each as claimed in claim 1, 2, or 3 and an optical transmission fibre connected between the fibre optic ports of said optical multiplexer/demultiplexers.
9. A bidirectional optical transmission system comprising two complementary optical multiplexer/demultiplexers each as claimed in claim 4, 5, or 6 and an optical transmission fibre connected between the fibre optic ports of said optical multiplexer/demultiplexers.
10. A bidirectional optical transmission system comprising two complementary optical multiplexer/demultiplexers each as claimed in claim 7 and an optical transmission fibre connected between the fibre optic ports of said optical multiplexer/demultiplexers.
Priority Applications (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CA292,383A CA1089932A (en) | 1977-12-05 | 1977-12-05 | Wavelength division multiplexer/demultiplexer in optical fiber communication systems |
Applications Claiming Priority (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CA292,383A CA1089932A (en) | 1977-12-05 | 1977-12-05 | Wavelength division multiplexer/demultiplexer in optical fiber communication systems |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1089932A true CA1089932A (en) | 1980-11-18 |
Family
ID=4110209
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA292,383A Expired CA1089932A (en) | 1977-12-05 | 1977-12-05 | Wavelength division multiplexer/demultiplexer in optical fiber communication systems |
Country Status (1)
| Country | Link |
|---|---|
| CA (1) | CA1089932A (en) |
Cited By (4)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| WO1982001631A1 (en) * | 1980-10-23 | 1982-05-13 | Carter Andrew C | Optical transmission systems |
| WO1987004862A1 (en) * | 1986-01-30 | 1987-08-13 | Pa Consulting Services Limited | Optical demultiplexer |
| WO1988007216A1 (en) * | 1987-03-13 | 1988-09-22 | Plessey Overseas Limited | Apparatus for optical wavelength division multiplexing |
| FR2650897A1 (en) * | 1989-08-14 | 1991-02-15 | Framatome Sa | Device for wavelength demultiplexing a light signal |
-
1977
- 1977-12-05 CA CA292,383A patent/CA1089932A/en not_active Expired
Cited By (5)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| WO1982001631A1 (en) * | 1980-10-23 | 1982-05-13 | Carter Andrew C | Optical transmission systems |
| WO1987004862A1 (en) * | 1986-01-30 | 1987-08-13 | Pa Consulting Services Limited | Optical demultiplexer |
| WO1988007216A1 (en) * | 1987-03-13 | 1988-09-22 | Plessey Overseas Limited | Apparatus for optical wavelength division multiplexing |
| US4923270A (en) * | 1987-03-13 | 1990-05-08 | Plessey Overseas Limited | Apparatus for optical wavelength division multiplexing |
| FR2650897A1 (en) * | 1989-08-14 | 1991-02-15 | Framatome Sa | Device for wavelength demultiplexing a light signal |
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