CA1108903A - Integrated optical wavelength demultiplexer (iowd) - Google Patents
Integrated optical wavelength demultiplexer (iowd)Info
- Publication number
- CA1108903A CA1108903A CA342,055A CA342055A CA1108903A CA 1108903 A CA1108903 A CA 1108903A CA 342055 A CA342055 A CA 342055A CA 1108903 A CA1108903 A CA 1108903A
- Authority
- CA
- Canada
- Prior art keywords
- integrated optical
- waveguide
- optical wavelength
- wavelength demultiplexer
- 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
- G02B6/4204—Packages, e.g. shape, construction, internal or external details the coupling comprising intermediate optical elements, e.g. lenses, holograms
- G02B6/4215—Packages, e.g. shape, construction, internal or external details the coupling comprising intermediate optical elements, e.g. lenses, holograms the intermediate optical elements being wavelength selective optical elements, e.g. variable wavelength optical modules or wavelength lockers
-
- 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
- G02B6/10—Light guides; Structural details of arrangements comprising light guides and other optical elements, e.g. couplings of the optical waveguide type
- G02B6/12—Light guides; Structural details of arrangements comprising light guides and other optical elements, e.g. couplings of the optical waveguide type of the integrated circuit kind
- G02B6/12007—Light guides; Structural details of arrangements comprising light guides and other optical elements, e.g. couplings of the optical waveguide type of the integrated circuit kind forming wavelength selective elements, e.g. multiplexer, demultiplexer
-
- 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
- G02B6/10—Light guides; Structural details of arrangements comprising light guides and other optical elements, e.g. couplings of the optical waveguide type
- G02B6/12—Light guides; Structural details of arrangements comprising light guides and other optical elements, e.g. couplings of the optical waveguide type of the integrated circuit kind
- G02B6/122—Basic optical elements, e.g. light-guiding paths
- G02B6/124—Geodesic lenses or integrated gratings
- G02B6/1245—Geodesic lenses
-
- 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
- G02B6/29371—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 principle based on material dispersion
- G02B6/29373—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 principle based on material dispersion utilising a bulk dispersive element, e.g. prism
-
- 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
-
- 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
- G02B6/30—Optical coupling means for use between fibre and thin-film device
Landscapes
- Physics & Mathematics (AREA)
- General Physics & Mathematics (AREA)
- Optics & Photonics (AREA)
- Engineering & Computer Science (AREA)
- Microelectronics & Electronic Packaging (AREA)
- Chemical & Material Sciences (AREA)
- Dispersion Chemistry (AREA)
- Optical Couplings Of Light Guides (AREA)
- Optical Integrated Circuits (AREA)
Abstract
INTEGRATED OPTICAL WAVELENGTH DEMULTIPLEXER (IOWD) Abstract of the Disclosure An integrated optical wavelength demulti-plexer has deposited on a waveguide layer a pair of Luneburg lenses, the first for collimating light from an optical fiber, the second for focussing light at an array of photo-detectors formed under the waveguide layer. Between the lenses is the dispersive element, a thin-film prism of a highly dispersive low-loss material such as arsenic trisulfide.
A known integrated optical demultiplexer, which uses a chirped diffraction grating to spatially disperse (rather than angularly disperse) the optical wavelengths, would suffer a greater insertion loss particularly for wavelengths coupled out at a later point in the grating. Demultiplexing with a thin-film prism should also result in the capability to handle a larger number of channels, for a given channel isolation and substrate area.
- i -
A known integrated optical demultiplexer, which uses a chirped diffraction grating to spatially disperse (rather than angularly disperse) the optical wavelengths, would suffer a greater insertion loss particularly for wavelengths coupled out at a later point in the grating. Demultiplexing with a thin-film prism should also result in the capability to handle a larger number of channels, for a given channel isolation and substrate area.
- i -
Description
Ihis inVention relates to an Inteyrated Optical ~avelength Demultiplexer (IOWD~ for use in ~lave-length Division Multiplexed (WDM) optical communications systems.
WDM systems offer a means of combining a number of information channels onto a single optical fiber by transmitting each via a separate optical wave-length carrier. Specifically, each electrical information channel is used to modulate the amplitude of a semiconductor laser which emits a well defined optical wavelength.
The benefits of such a WDM multiplexing scheme are: -- increased information capacity per fiber, - relaxed requirements on other types of multiplexing (i.e. TDM, FDM);
potentially a -low cost means of multi-plexing, - by employing integrated optics techniques, there is potential for lower cost, rugged construction and small size together with high stability and reliability.
Several types of non-integrated optical demultiplexers are known. One, which uses combinations of beam splitters and wavelength dependent filters, suffers greatly from insertion loss as the number of channels is increased. In another demultiplexer a series of GRIN rods are used. These are transparent rods whose composition varies radially with a consequent parabolic variation in refractive index permitting them to be used as lenses to ,- .
.
.
:
achieve a periodic beam position change. The rods used in this demultiplexer are chosen to be ~ pitch in lenyth so that a light bearn inc;dent at the center of the rod will exit near its periphery and vice ve~sa. A ~ilteriny element, which is normal to the rod axis permits a narrow optical waveband to propagate through the rod to a detector.
Other wavelengths are reflected into another, laterally offset, GRIN rod where further filteriny occurs and so on.
Again, this design suffers from insertion loss; in addition, for a large number of channels, the structure is exceedingly complex.
In a third type of demultiplexer, the light from a fiber is collimated at a first lens directed through a discrete prism where dispersion occurs, then through a second lens which focusses individual wavelengths into the ends of an optical fiber array by means of which light is directed to a detector array. Although this type of multiplexer accomodates a large number of channels it requires accurate positioning of the output fibers and is -bulky. In yet another design input light is collimated at a blazed grating from which wavelenghts are directed into appropriately located detectors. Although bulky, this design accomodates a large number of channels.
Compactness and rigidity can be ach;eved by using a GRIN rod in place of a normal collimating lens and applying the grating to a rear face, inclined at the blazed angle, the intervening space fllled by an index ~atching wedge. However, size reduction reduces the number of . , .
.. , . . . , , ~ , : ~ '- ' ., ' :
, ..... . .
'~ ' :. ' ' ,' ', ' ' ' '':
channels some~hat, and meticulous alignment is required.
R.R. Rice~ et al, "Multi~avelength Monolithic Integrated Fiber-Optic Terminal", SPIE, Vol.
176,-page 133, 1979 have proposed the fabrication of an integrated optical wavelength demultiplexer using a chirped diffraction grating formed within the waveguide.
Typically, chirped gratings are made by diffusion into a waveguide although they can be fabricated on a waveguide surface by conventional lithographic techniques. The dynamic range of this device is claimed to be 20dB and about 8 channels can be demultiplexed.
The use of a chirped grating can cause appreciable scattering of the various wavelengths, and so lower the overall dynamic range and increase interchannel crosstalk. In an N channel demultiplexer, the Nth channel suffers considerably greater loss than the first channel since the wavelength of the ~th channel must travel a greater distance along the grating before being difFracted out.
The number of channels that such a demulti-plexer can handle is therefore limited by:
a) the physical distance between the channels along the grating must be large enough to minimize crosstalk.
b) as a result of (a), N is limited to the maximum allowable loss difference between channels (which limits dynamic range).
c~ ~or large N it is necessary to obtain very high quality gratings and a large substrate area is needed~
,. . .
.
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. ~ . .
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.. ~ . .
~8~3 According to the present invention there is provided an integrated optical waveleng~h demultiplexer comprisiny a substrate, a thin film waveguide deposited on ~he substrate, input means for introducing light from an optical fiber into the waveguide,means within the waveguide for collimating the light at a d;spersive element and means w;thin the waveguide for focussing light from the dispersive qlement onto an array of photodetectors formed within the waveguide, the improvement co~prising said dispersive element being a thin-film prism.
An embodiment of the invention will now be described by way of example with reference to the accompanying drawings, in which:-Figure 1 ;s a plan view of an integratedoptical wavelength demultiplexer according to the invention;
Figure 2 is a sectional view, not to scale~
on the line II-II of Figure 1.
Referring to the Figures in detail, the upper surface layer 10 of a 3" silicon wafer substrate 12 is thermally oxidized to form SiO2. Over this layer, which has a refractive index of 1.459, is sputter-deposited
WDM systems offer a means of combining a number of information channels onto a single optical fiber by transmitting each via a separate optical wave-length carrier. Specifically, each electrical information channel is used to modulate the amplitude of a semiconductor laser which emits a well defined optical wavelength.
The benefits of such a WDM multiplexing scheme are: -- increased information capacity per fiber, - relaxed requirements on other types of multiplexing (i.e. TDM, FDM);
potentially a -low cost means of multi-plexing, - by employing integrated optics techniques, there is potential for lower cost, rugged construction and small size together with high stability and reliability.
Several types of non-integrated optical demultiplexers are known. One, which uses combinations of beam splitters and wavelength dependent filters, suffers greatly from insertion loss as the number of channels is increased. In another demultiplexer a series of GRIN rods are used. These are transparent rods whose composition varies radially with a consequent parabolic variation in refractive index permitting them to be used as lenses to ,- .
.
.
:
achieve a periodic beam position change. The rods used in this demultiplexer are chosen to be ~ pitch in lenyth so that a light bearn inc;dent at the center of the rod will exit near its periphery and vice ve~sa. A ~ilteriny element, which is normal to the rod axis permits a narrow optical waveband to propagate through the rod to a detector.
Other wavelengths are reflected into another, laterally offset, GRIN rod where further filteriny occurs and so on.
Again, this design suffers from insertion loss; in addition, for a large number of channels, the structure is exceedingly complex.
In a third type of demultiplexer, the light from a fiber is collimated at a first lens directed through a discrete prism where dispersion occurs, then through a second lens which focusses individual wavelengths into the ends of an optical fiber array by means of which light is directed to a detector array. Although this type of multiplexer accomodates a large number of channels it requires accurate positioning of the output fibers and is -bulky. In yet another design input light is collimated at a blazed grating from which wavelenghts are directed into appropriately located detectors. Although bulky, this design accomodates a large number of channels.
Compactness and rigidity can be ach;eved by using a GRIN rod in place of a normal collimating lens and applying the grating to a rear face, inclined at the blazed angle, the intervening space fllled by an index ~atching wedge. However, size reduction reduces the number of . , .
.. , . . . , , ~ , : ~ '- ' ., ' :
, ..... . .
'~ ' :. ' ' ,' ', ' ' ' '':
channels some~hat, and meticulous alignment is required.
R.R. Rice~ et al, "Multi~avelength Monolithic Integrated Fiber-Optic Terminal", SPIE, Vol.
176,-page 133, 1979 have proposed the fabrication of an integrated optical wavelength demultiplexer using a chirped diffraction grating formed within the waveguide.
Typically, chirped gratings are made by diffusion into a waveguide although they can be fabricated on a waveguide surface by conventional lithographic techniques. The dynamic range of this device is claimed to be 20dB and about 8 channels can be demultiplexed.
The use of a chirped grating can cause appreciable scattering of the various wavelengths, and so lower the overall dynamic range and increase interchannel crosstalk. In an N channel demultiplexer, the Nth channel suffers considerably greater loss than the first channel since the wavelength of the ~th channel must travel a greater distance along the grating before being difFracted out.
The number of channels that such a demulti-plexer can handle is therefore limited by:
a) the physical distance between the channels along the grating must be large enough to minimize crosstalk.
b) as a result of (a), N is limited to the maximum allowable loss difference between channels (which limits dynamic range).
c~ ~or large N it is necessary to obtain very high quality gratings and a large substrate area is needed~
,. . .
.
' .
. ~ . .
: , . ..
.. ~ . .
~8~3 According to the present invention there is provided an integrated optical waveleng~h demultiplexer comprisiny a substrate, a thin film waveguide deposited on ~he substrate, input means for introducing light from an optical fiber into the waveguide,means within the waveguide for collimating the light at a d;spersive element and means w;thin the waveguide for focussing light from the dispersive qlement onto an array of photodetectors formed within the waveguide, the improvement co~prising said dispersive element being a thin-film prism.
An embodiment of the invention will now be described by way of example with reference to the accompanying drawings, in which:-Figure 1 ;s a plan view of an integratedoptical wavelength demultiplexer according to the invention;
Figure 2 is a sectional view, not to scale~
on the line II-II of Figure 1.
Referring to the Figures in detail, the upper surface layer 10 of a 3" silicon wafer substrate 12 is thermally oxidized to form SiO2. Over this layer, which has a refractive index of 1.459, is sputter-deposited
2 uniform thickness waveguide layer 14 of a low-loss, higher index material ~such as Corning [Registered Trade Mark~ 7059 which has a refractive index of ahout 1.57 and loss as low as 0.2dB/cm). The SiO2 layer optically isolates the wave-guide from the Si substrate.
A V~-groove 16 is then etched into the silicon substrate to permit accurate positioning of the end of a fiber 20 with core 17 of the fiber 20 located : - 4 -.
.. . . . . ..
.: . . . . .: . .. - .... : .. . . ..... - . :
.-: . , .. . , . " . ;. . ,: . ............ . . .
. . . . , .. . , . , ,. :
,. . : .
.
immediatel~ above the substrate sur~ace. An overla~ 18 of tantalum pentoxide having a higher re~rackive index (2.1), than the waveguide is then sputter-deposited on the waveguide with a su~ficient thickness to accep~ the full numerical aperture of the fiber 20. The overlay 18 tapers gradually away from the end of the groove to permit low loss coupling of the light into the waveguide.
Collimating and focussing Luneburg lenses 22 are then sputtered as overlay deposits of a higher index material like tantalum pentoxide with refractive index 2.1.
The Luneburg lenses are sputtered with a specific, well defined profile in order to achieve near diffraction-limited performance and low aberration. The larger the lens, the smaller the spot size at the focus so enabling a greater number of channels to be multi-plexed. However, the limitation on the maximum number is then specified by crosstalk requirements, detector spacing and dynamic range. Details of suitable sputtering method may be found in S.K. Yao and D.B. Anderson, "Shadow Sputtering Dif~raction-Limited Waveguide Lunebury Lenses", Appl. Phys. Lett, Vol. 33, p. 307, Aug. 1978.
A thin film prism 24 made of a material exhibiting strong chromatic dispersion and low loss such as arsenic trisulfide (As2S3) having a refractive index of 2.51, is then sputter deposited on the waveguide 14 between the lenses. The profiles of both the lenses and the prism are carefully controlled by using edge-shaped masks during sputter depositlon. Pro~ile is important ;
.
. "..
,. '.'; ' ~ ' .. : .. .
. . . .. . ..
. ~, .. . .
. ....
especially in sin~le mode operation, since light couples from the waveguide 14 into the overla~ 22 or 24 at a position at which the overlay thickness becomes large enough to sustain the guided mode - and, of course, couples out under the converse conditions. At the input and output ends of the lenses and prismatic deposits 22 and 24 coupling occurs at a specific overlay thickness determined by the refractive index differential between the overlay and the waveguide. It is crucial, therefore, to deposit very smooth and well defined tapers to minimize scattering, but at the same time have a well defined coupling edge.
A detector array, shown schematically as line 26, (Figure 1), is then formed in a manner known in the art, for example, as an array of silicon photo-diode detectors on 15~m centres with readout through a two-phase overlapping gate, charge-coupled arrangement (not shown) as described by Boyd and Chen in "An Integrated Optical Waveguide and Charge-Coupled Device Image Array", IEEE
`20 Journal of ~Quantum Electronics, Vol, QE 13, pp. 282-287, April 1977.
In operation, an end part of a 50~m core fiber 20 is accomodated within the groove 16 so that light from the fiber core 17 enters the tapered Ta205 overlay 18 and gradually couples into the waveguide 14.
For the wavelength ranye of interest, (800 to 860 nm) the Corning 7059 glass and the Ta205 overlay l8 and Luneburg lenses 22 exhibit little dispersion, as desired. Light, collimated at the first lens 22a strikes .
- " ,, ' - . ' - ,. ......... . .
'` ' , ', '` ' ' ' ' ', `
the As2S3 prism 24 and is dispersed. Over the stated wavelength range, As2S3 exhibits an index change of 0.66%, having a refractive index of 2 . 5209 at BOO nm and 2. 5042 at 860 nm. Other materials, for example, CdSe exhibit a larger index change than As2S3 but are appreciably more lossy. In order to reduce the beam attenuation, the optical path length through the prism 24 is made as small as possible. The minimum prism size is, however, limited by the size of the optical beam which in turn determines the size of the focussed spot on the detector array.
To minimize reflection losses at the two prism interfaces~ the angle of incidence is made equal to the Brewster angle for TM polarization. At each interface, the dispersive nature of the prism 24 results in a wavelength dependent angle of refraction. The resulting angular spread for a given wavelength spread at each interface is:-rnp(~A) 1 ~G
~ ~. _ 1 _ r np(~B) np _ 2 np(~A) 1 np a ~ r ~ --n G
where a~r = angular spread of refractionnp = index of prism (~ dependent) nG ~ index of thin-film gulde ~A = shortest wavelength ~B = longest wavelength .-. . , :
- . . .. : , , . ~.. :
, . . ~,, :
`' ~.' " ',, '` ' :' ' ' ~ . .
Using lenses hayiny a ~ocal length of about 3cm, a spatial displacement of the order of 4501~m is achieved for a wavelength spread of 60 nm (800 nm to 860 nm). This gives a spacial dispersion of about 7.5~m/nm. which, for a detector array with 15~m center-to-center spacing, permits resolution down to 2 nm. Thus with sources spaced at 2nm intervals, 30 WDM channels c~n be demultiplexed in the range of 800 to B60 nm. With lenses having a diameter of 0.55 cm., the diffraction limited spot size is about 4~m, ~ollowing well within the available detector spacing of 15~m. At the detector array 26~ the SiO2 isolation layer 10 is tapered down gradually to permit the liyht energy guided in the wave-guide 14 to "tunnel" through the layer 10, into the detectrr 26.
. ,~ .
.
:~
.. , : .
,
A V~-groove 16 is then etched into the silicon substrate to permit accurate positioning of the end of a fiber 20 with core 17 of the fiber 20 located : - 4 -.
.. . . . . ..
.: . . . . .: . .. - .... : .. . . ..... - . :
.-: . , .. . , . " . ;. . ,: . ............ . . .
. . . . , .. . , . , ,. :
,. . : .
.
immediatel~ above the substrate sur~ace. An overla~ 18 of tantalum pentoxide having a higher re~rackive index (2.1), than the waveguide is then sputter-deposited on the waveguide with a su~ficient thickness to accep~ the full numerical aperture of the fiber 20. The overlay 18 tapers gradually away from the end of the groove to permit low loss coupling of the light into the waveguide.
Collimating and focussing Luneburg lenses 22 are then sputtered as overlay deposits of a higher index material like tantalum pentoxide with refractive index 2.1.
The Luneburg lenses are sputtered with a specific, well defined profile in order to achieve near diffraction-limited performance and low aberration. The larger the lens, the smaller the spot size at the focus so enabling a greater number of channels to be multi-plexed. However, the limitation on the maximum number is then specified by crosstalk requirements, detector spacing and dynamic range. Details of suitable sputtering method may be found in S.K. Yao and D.B. Anderson, "Shadow Sputtering Dif~raction-Limited Waveguide Lunebury Lenses", Appl. Phys. Lett, Vol. 33, p. 307, Aug. 1978.
A thin film prism 24 made of a material exhibiting strong chromatic dispersion and low loss such as arsenic trisulfide (As2S3) having a refractive index of 2.51, is then sputter deposited on the waveguide 14 between the lenses. The profiles of both the lenses and the prism are carefully controlled by using edge-shaped masks during sputter depositlon. Pro~ile is important ;
.
. "..
,. '.'; ' ~ ' .. : .. .
. . . .. . ..
. ~, .. . .
. ....
especially in sin~le mode operation, since light couples from the waveguide 14 into the overla~ 22 or 24 at a position at which the overlay thickness becomes large enough to sustain the guided mode - and, of course, couples out under the converse conditions. At the input and output ends of the lenses and prismatic deposits 22 and 24 coupling occurs at a specific overlay thickness determined by the refractive index differential between the overlay and the waveguide. It is crucial, therefore, to deposit very smooth and well defined tapers to minimize scattering, but at the same time have a well defined coupling edge.
A detector array, shown schematically as line 26, (Figure 1), is then formed in a manner known in the art, for example, as an array of silicon photo-diode detectors on 15~m centres with readout through a two-phase overlapping gate, charge-coupled arrangement (not shown) as described by Boyd and Chen in "An Integrated Optical Waveguide and Charge-Coupled Device Image Array", IEEE
`20 Journal of ~Quantum Electronics, Vol, QE 13, pp. 282-287, April 1977.
In operation, an end part of a 50~m core fiber 20 is accomodated within the groove 16 so that light from the fiber core 17 enters the tapered Ta205 overlay 18 and gradually couples into the waveguide 14.
For the wavelength ranye of interest, (800 to 860 nm) the Corning 7059 glass and the Ta205 overlay l8 and Luneburg lenses 22 exhibit little dispersion, as desired. Light, collimated at the first lens 22a strikes .
- " ,, ' - . ' - ,. ......... . .
'` ' , ', '` ' ' ' ' ', `
the As2S3 prism 24 and is dispersed. Over the stated wavelength range, As2S3 exhibits an index change of 0.66%, having a refractive index of 2 . 5209 at BOO nm and 2. 5042 at 860 nm. Other materials, for example, CdSe exhibit a larger index change than As2S3 but are appreciably more lossy. In order to reduce the beam attenuation, the optical path length through the prism 24 is made as small as possible. The minimum prism size is, however, limited by the size of the optical beam which in turn determines the size of the focussed spot on the detector array.
To minimize reflection losses at the two prism interfaces~ the angle of incidence is made equal to the Brewster angle for TM polarization. At each interface, the dispersive nature of the prism 24 results in a wavelength dependent angle of refraction. The resulting angular spread for a given wavelength spread at each interface is:-rnp(~A) 1 ~G
~ ~. _ 1 _ r np(~B) np _ 2 np(~A) 1 np a ~ r ~ --n G
where a~r = angular spread of refractionnp = index of prism (~ dependent) nG ~ index of thin-film gulde ~A = shortest wavelength ~B = longest wavelength .-. . , :
- . . .. : , , . ~.. :
, . . ~,, :
`' ~.' " ',, '` ' :' ' ' ~ . .
Using lenses hayiny a ~ocal length of about 3cm, a spatial displacement of the order of 4501~m is achieved for a wavelength spread of 60 nm (800 nm to 860 nm). This gives a spacial dispersion of about 7.5~m/nm. which, for a detector array with 15~m center-to-center spacing, permits resolution down to 2 nm. Thus with sources spaced at 2nm intervals, 30 WDM channels c~n be demultiplexed in the range of 800 to B60 nm. With lenses having a diameter of 0.55 cm., the diffraction limited spot size is about 4~m, ~ollowing well within the available detector spacing of 15~m. At the detector array 26~ the SiO2 isolation layer 10 is tapered down gradually to permit the liyht energy guided in the wave-guide 14 to "tunnel" through the layer 10, into the detectrr 26.
. ,~ .
.
:~
.. , : .
,
Claims (7)
EXCLUSIVE PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:-
1. An integrated optical wavelength demultiplexer comprising a substrate, a thin film waveguide deposited on the substrate, input means for introducing multichromatic light from an optical fiber into the waveguide, collimating means within the waveguide for collimating the light at a wavelength dispersive element in the form of a thin-film prism, and focussing means within the waveguide for focussing specific wavelength components of the light separated by the dispersive element onto specific ones of an array of photodetectors formed underneath the waveguide.
2. An integrated optical wavelength demultiplexer as claimed in claim 1 in which the thin film prism is composed of arsenic trisulphide having a refractive index of about 2.5.
3. An integrated optical wavelength demultiplxer as claimed in claim 1 in which at least one of said collimating means and said focussing means is a Luneburg lens.
4. An integrated optical wavelength demultiplexer as claimed in claim 3 in which the collimating means and the focussing means comprise Luneburg lenses composed of tantalum pentoixde.
5. An integrated optical wavelength demultiplexer as claimed in claim 1 in which said input means comprises a V-groove in the substrate to support an end portion of said fiber and a film of transparent material deposited in alignment with the V-groove and tapering towards said collimating means for directing light from a core of the fiber into the waveguide.
6. An integrated optical wavelength demultiplexer as claimed in claim 5 in which said transparent material is tantalum pentoxide.
7. An integrated optical wavelength demultiplexer as claimed in claim 1 in which the substrate is silicon having an upper oxidized layer over which oxidized layer said waveguide is deposited.
Priority Applications (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CA342,055A CA1108903A (en) | 1979-12-17 | 1979-12-17 | Integrated optical wavelength demultiplexer (iowd) |
Applications Claiming Priority (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CA342,055A CA1108903A (en) | 1979-12-17 | 1979-12-17 | Integrated optical wavelength demultiplexer (iowd) |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1108903A true CA1108903A (en) | 1981-09-15 |
Family
ID=4115845
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA342,055A Expired CA1108903A (en) | 1979-12-17 | 1979-12-17 | Integrated optical wavelength demultiplexer (iowd) |
Country Status (1)
| Country | Link |
|---|---|
| CA (1) | CA1108903A (en) |
Cited By (3)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| EP0081685A1 (en) * | 1981-12-01 | 1983-06-22 | ANT Nachrichtentechnik GmbH | Wave guiding film |
| FR2699269A1 (en) * | 1992-12-10 | 1994-06-17 | Merlin Gerin | Interferrometric measurement device. |
| EP1402294A1 (en) * | 2001-05-17 | 2004-03-31 | Optronix, Inc. | Polyloaded optical waveguide devices |
-
1979
- 1979-12-17 CA CA342,055A patent/CA1108903A/en not_active Expired
Cited By (7)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| EP0081685A1 (en) * | 1981-12-01 | 1983-06-22 | ANT Nachrichtentechnik GmbH | Wave guiding film |
| US4606602A (en) * | 1981-12-01 | 1986-08-19 | Ant Nachrichtentechnik | Selectively dispersive optical waveguide films |
| FR2699269A1 (en) * | 1992-12-10 | 1994-06-17 | Merlin Gerin | Interferrometric measurement device. |
| WO1994014028A1 (en) * | 1992-12-10 | 1994-06-23 | Merlin Gerin | Interferometric measurement device |
| US5710629A (en) * | 1992-12-10 | 1998-01-20 | Schneider Electric S.A. | Interferometric measuring device forming a spacial interference pattern |
| EP1402294A1 (en) * | 2001-05-17 | 2004-03-31 | Optronix, Inc. | Polyloaded optical waveguide devices |
| EP1402294A4 (en) * | 2001-05-17 | 2006-11-02 | Optronx Inc | Polyloaded optical waveguide devices |
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