CA2119503C - Wavelength division multiplexed optical communication transmitters - Google Patents

Wavelength division multiplexed optical communication transmitters

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Publication number
CA2119503C
CA2119503C CA002119503A CA2119503A CA2119503C CA 2119503 C CA2119503 C CA 2119503C CA 002119503 A CA002119503 A CA 002119503A CA 2119503 A CA2119503 A CA 2119503A CA 2119503 C CA2119503 C CA 2119503C
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Canada
Prior art keywords
transmitter
lasers
modulator
optical
combiner
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 - Lifetime
Application number
CA002119503A
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French (fr)
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CA2119503A1 (en
Inventor
Thomas Lawson Koch
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AT&T Corp
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American Telephone and Telegraph Co Inc
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Application filed by American Telephone and Telegraph Co Inc filed Critical American Telephone and Telegraph Co Inc
Publication of CA2119503A1 publication Critical patent/CA2119503A1/en
Application granted granted Critical
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Anticipated expiration legal-status Critical
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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
    • G02B6/10—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
    • G02B6/12004—Combinations of two or more optical elements
    • 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
    • G02B6/125—Bends, branchings or intersections
    • 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
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01L—SEMICONDUCTOR DEVICES NOT COVERED BY CLASS H10
    • H01L27/00—Devices consisting of a plurality of semiconductor or other solid-state components formed in or on a common substrate
    • H01L27/14—Devices consisting of a plurality of semiconductor or other solid-state components formed in or on a common substrate including semiconductor components sensitive to infrared radiation, light, electromagnetic radiation of shorter wavelength or corpuscular radiation and specially adapted either for the conversion of the energy of such radiation into electrical energy or for the control of electrical energy by such radiation
    • H01L27/144—Devices controlled by radiation
    • H01L27/1443—Devices controlled by radiation with at least one potential jump or surface barrier
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01S—DEVICES USING THE PROCESS OF LIGHT AMPLIFICATION BY STIMULATED EMISSION OF RADIATION [LASER] TO AMPLIFY OR GENERATE LIGHT; DEVICES USING STIMULATED EMISSION OF ELECTROMAGNETIC RADIATION IN WAVE RANGES OTHER THAN OPTICAL
    • H01S5/00—Semiconductor lasers
    • H01S5/02—Structural details or components not essential to laser action
    • H01S5/026—Monolithically integrated components, e.g. waveguides, monitoring photo-detectors, drivers
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01S—DEVICES USING THE PROCESS OF LIGHT AMPLIFICATION BY STIMULATED EMISSION OF RADIATION [LASER] TO AMPLIFY OR GENERATE LIGHT; DEVICES USING STIMULATED EMISSION OF ELECTROMAGNETIC RADIATION IN WAVE RANGES OTHER THAN OPTICAL
    • H01S5/00—Semiconductor lasers
    • H01S5/40—Arrangement of two or more semiconductor lasers, not provided for in groups H01S5/02 - H01S5/30
    • H01S5/4025—Array arrangements, e.g. constituted by discrete laser diodes or laser bar
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01S—DEVICES USING THE PROCESS OF LIGHT AMPLIFICATION BY STIMULATED EMISSION OF RADIATION [LASER] TO AMPLIFY OR GENERATE LIGHT; DEVICES USING STIMULATED EMISSION OF ELECTROMAGNETIC RADIATION IN WAVE RANGES OTHER THAN OPTICAL
    • H01S5/00—Semiconductor lasers
    • H01S5/02—Structural details or components not essential to laser action
    • H01S5/026—Monolithically integrated components, e.g. waveguides, monitoring photo-detectors, drivers
    • H01S5/0265—Intensity modulators
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01S—DEVICES USING THE PROCESS OF LIGHT AMPLIFICATION BY STIMULATED EMISSION OF RADIATION [LASER] TO AMPLIFY OR GENERATE LIGHT; DEVICES USING STIMULATED EMISSION OF ELECTROMAGNETIC RADIATION IN WAVE RANGES OTHER THAN OPTICAL
    • H01S5/00—Semiconductor lasers
    • H01S5/02—Structural details or components not essential to laser action
    • H01S5/026—Monolithically integrated components, e.g. waveguides, monitoring photo-detectors, drivers
    • H01S5/0268—Integrated waveguide grating router, e.g. emission of a multi-wavelength laser array is combined by a "dragon router"
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01S—DEVICES USING THE PROCESS OF LIGHT AMPLIFICATION BY STIMULATED EMISSION OF RADIATION [LASER] TO AMPLIFY OR GENERATE LIGHT; DEVICES USING STIMULATED EMISSION OF ELECTROMAGNETIC RADIATION IN WAVE RANGES OTHER THAN OPTICAL
    • H01S5/00—Semiconductor lasers
    • H01S5/06—Arrangements for controlling the laser output parameters, e.g. by operating on the active medium
    • H01S5/068—Stabilisation of laser output parameters
    • H01S5/06825—Protecting the laser, e.g. during switch-on/off, detection of malfunctioning or degradation
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01S—DEVICES USING THE PROCESS OF LIGHT AMPLIFICATION BY STIMULATED EMISSION OF RADIATION [LASER] TO AMPLIFY OR GENERATE LIGHT; DEVICES USING STIMULATED EMISSION OF ELECTROMAGNETIC RADIATION IN WAVE RANGES OTHER THAN OPTICAL
    • H01S5/00—Semiconductor lasers
    • H01S5/50—Amplifier structures not provided for in groups H01S5/02 - H01S5/30

Abstract

A wavelength-division-multiplexed transmitter has a single modulator modulating the output of an array of individually actuable semiconductor lasers integrated onto the same substrate as the modulator. An optical combiner integrated onto the same substrate between each of the lasers and the single modulator combines the outputs of the lasers. One or more of the lasers are activated as desired for wavelength division multiplexing.

Description

~t ~ ~ ~ 3 W~VE~ n DIVISION MULTIPLEXED OPTICAL CCMMUNICATION
TRAN~Ul-l'~~

FT~r.n OF TU R nNv~NTTo N
This lnvention relates to optical communications, and particularly to wavelength-division multiplexing (WDM) transmitters.

R~ ~ OF 'l-H ~
The use of wavelength division multiplexing affords one the opportunity of raising the transmission capacity of a single fiber without the need to develop higher speed components. In switching or networking environments, wavelength division multiplexing arrangements permits optical routing of si B ls at different wavelengths to different destinations.
Optical sources used in wavelength division multiplexed communications systems must generate light at controlled wavelengths. They require means either to set them permanently to a desired wavelength allocated to a partlcular channel, or to switch them dynamically to different specific wavelengths for routing purposes. In general, the sources must restrict the wavelengths to prescribed spaced values so that signals do not interfere with each other. Such interference may result from the nonlinear transmlssion properties of the fiber itself, or from source wavelength drift and insufficient out-off band rejection in the optical filtering or heterodyning technology used to demultiplex the signals at the receiver.
Discrete fixed-frequency sources have been used in wavelength division multiplexing demonstrations.
However, using such systems on a commercial basis requires _ the storage and maintenance of large numbers of reserve sources such as distributed feedback (DFB) lasers.
Tunable lasers that attempt to cover the entire range of desired wavelengths have hitherto required cumbersome feedback from external references to provide reliable wavelength stability and often have had insufficient tuning range for many applications.
The paper "A 16 x 1 WDM Transmitter with Integrated DBR Lasers and Electroabsorption Modulators" by M.G. Young et al, paper No. IW~3 in Tech. Digest of 1993 - Topical Meeting on Integrated Photonics Research, pp. 414-417, held in Palm Springs, 1993, discloses the use of an array of sixteen independent distributed Bragg reflector (DBR) lasers, each with an integrated electroabsorption modulator, followed by a combiner and an integrated optical booster amplifier, to provide a single fiber pcrt for all 16 wavelength division multiplexed channels. It requires a modulator for each laser. Such an approach demands complex electrical packaging because the arrangement requires a separate high-speed electrical drive capability for each source, either to modulate each laser directly, or to drive each electroabsorption modulator for each laser.
An object of the invention is to improve wavelength-division-multiplexed systems generally.
Another object of the invention is to improve wavelength-division-multiplexed transmitters.
Yet another object of the invention is to overcome the aforementioned difficulties.

~M~ OF TU~ rhV~LION
According to a feature of the invention, these objects are attained, in whole or in part, by merging the output ends of a plurality of individually actuable 5 ~ 3 semiconductor lasers integrated onto a substrate with an optical combiner integrated onto the substrate, and passing the output of the combiner to a single laser modulator also integrated onto the same substrate.
According to another feature of the invention, the lasers are fixed frequency lasers each tuned to a specific frequency.
The invention utilizes but a single modulator to encode any activated one of or several activated ones of the lasers.
In accordance with one aspect of the present invention there is provided a wavelength-division multiplexed transmitter, comprising: a substrate; a plurality of individually actuable lasers integral with said substrate; an optical modulator integral with said substrate; and an optical combiner integral with said substrate and connecting each of said lasers with said modulator; said lasers each defining a different fre~uency exclusive of said combiner.
These and other features of the invention are pointed out in the claims. Other objects and advantages of the invention will become evident from the following detailed description when read in light of the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a perspective, somewhat schematic, and somewhat block diagram of a wavelength division multiplex arrangement embodying features of the invention.
FIG. 2 is a perspective schematic view of a combiner usable according to an embodiment of the invention, in the form of a Y-branch tree.

- 3a - 7r ~ ~ ~ 5 ~ ~
FIG. 3 is a perspective, schematic, and somewhat block diagram of yet another embodiment of the invention shown in FIG. 1.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS
FIG. 1 illustrates a transmitting arrangement with a single-chip monolithic wavelength division multiplexing transmitter TR1 embodying features of the invention.
Here, eight fixed frequency lasers LA1 to LA8 grown, fabricated, or otherwise integrated onto a substrate SU1, operate at respectively different .,_ wavelengths ~1 to 18. The substrate SU1 is preferably InP
but other substrates may be used. Integrated waveguides W1 to W8 grown on, fabricated on, or otherwise integrated onto the substrate SUl pass the outputs of the lasers LAl to LA8 to a 8 x 1 combiner CO1. The optical combiner CO1 passes the outputs of the activated ones of the lasers LAl to LA8 and illuminates a single output waveguide OW1. An amplifier AM1 amplifies the signal appearing on the fiber OW1. An electroabsorption modulator MOD1 modulates the outputs of the amplifier AM1 and passes it to an output OVT .
According to another embodiment of the invention, the modulator MOD1 is a directional coupler modulator, a Mach-Zehnder modulator, or any other suitable optical modulator. According to another embodiment of the invention, the lasers LAl to L~8 are distributed Bragg reflector (DBR) lasers or distributed feedback (DFB) lasers. They may be any other form of optical laser having a controlled emission wavelength.
The combiner CO1 is in the form of a slab waveguide region without lateral confinement of the l to allow diffraction in the plane of the wafer. Each waveguide W1 to W8 entering the free-space region on t~e input sided has a far field that illuminates the output waveguide OW1 on the output side. With one output waveguide, this device is a 1 x 8 power combiner. In a more general form such combiners have more than one output. With N inputs and N outputs the ccmbiner makes an N x N star coupler. In an embodiment of the invention, the combiner CO1 takes the form of an N x N star coupler and uses only one of the output waveguides.
Combiners, such as combiner CO1, are well known and have been disclosed for Si and SiO2 waveguide technology in the article by C. Dragone, entitled "Efficient N X N Star Couplers Using Fourier optics" in the IF~F~ Jou~nal of Lightwave Tech. 7, pp. 479-489 (1989), and for InGaAsP/InP waveguide technology in the article by M. Zirngibl et al, entitled "Efficient 1 X 16 Optical Power Splitter Based on InP", in Electron. Lett. 28, pp.
1212-1213 (1992). Stated otherwise a combiner such as COl is an in-plane diffraction region optically coupled to all the waveguides Wl to W8 and OWl. It can also operate as a splitter. With energy input in one direction from the waveguides Wl to W8 it,behaves as a combiner. With energy input at the waveguide OWl it behaves as a splitter. The combiner COl serves to pass energy from the waveguides Wl to W8 to the output waveguide OWl.
Another structure that can serve as an 1 X 8 combiner appears in Fig. 2. Here eight input,s INl to IN8 to the branches of a Y-branch tree TEl combine into cr.e output branch OBl.
To energize the transmitter TRl, a current source CSl selectively actuates one or more of the elght lasers LAl to LA8 by applying current to the selected laser or lasers. At the same time a signal source SOl external to the substrate SUl furnishes signals to the modulator MODl through a path PAl.
In operation, the current source CSl energizes a laser LAl to LA8, such as laser LA5 at the wavelength A5, and the corresponding integrated waveguide Wl to W8, namely WI5, passes the output light to the combiner COl which illuminates the input of the optical waveguide OWl.
The latter passes the light at the selected wavelength ~5 to the amplifier AMl, and a modulating signal from the source SOl causes the modulator MODl to modulate the output of the amplifier AMl. Suitable means not shown then transmit the modulated signal to a receiver or other device.

v~ 3 .~_ Fig. 3 illustrates another embodiment of the invention. Here, the structure in Fig. 3 corresponds substantially to the structure of Fig. 1. However, in Fig. 3 the modulator MODl precedes the amplifier AMl in the path from the combiner COl to the output OUT. The operation is similar to that of Fig. 1, except that the amplification occurs after modulation.
According to an embodiment of the invention, the elements of Figs. 1 to 3 are integrated onto or into the substrate SUl by known crystal growth, photolithographic, thin film deposition, or etching techniques, or combinations of such techniques. The elements may range over the surface of the resulting integrated circuit or may extend on the surface of the substrate SUl beneath one or more other layers of the integrated circult. An example of structures made with such techniques, with waveguides beneath one or more layers appears in the article by T.L. Koch et al in the IEEE Journal of Çuantum El ectronics, Volume 27, No.3, March 1991, entitled I'Semiconductor Photonic Integrated Circuits". Other examples of such structures appear in the article by U.
Koren et al, in App. Phys. Lett. 54 (21), of 22 May 1989 entitled l'Wavelength Division Multiplexing Light Source with Integrated Quantum Well Tunable Lasers and Optical Amplifiers". However, the invention is not limited to such means and any suitable known means may be used.
According to another embodiment of the inventlon lasers responsive to voltages are used. A suitable external voltage energizes the selected voltage responsive lasers.
The present invention achieves the effect of a tunable laser by using an array of fixed frequency lasers combined to a single output port in a single chip. It achieves tuning simply by activating the desired laser.

-The invention places the modulator after combining the output of each of the lasers in the array in a single combiner COl. Hence, the transmitter package requires only one high speed drive while maintaining access to all wavelength channels. It achieves the stability inherent in non-tunable lasers.~ Where dynamic wavelength switching is desired, the switching time is simply the time required to turn off the current to one laser and turn on the current to the new laser. In the examples shown, an array of eight fixed frequency lasers combine to a single output waveguide OWl where modulation and amplification occur with an integrated modulator and amplifier.
The current source CSl serves merely to energize one or more lasers LAl to LA8 and hence to select the wavelength or wavelengths to be used by activating the appropriate laser. Any source that activates the laser or lasers may replace the current source CSl. Each laser ~Al to LA8 in the array can be independently activated any time, in any sequence, or all at once. T~e laser activation does not contain the high speed coding signal from the source SOl directed to the modulator MODl.
The present invention offers the advantages of regaining the wavelength stability that has been demonstrated for fixed frequency distributed feedback lasers. It penmits fabrication of arrays of fixed frequency sources with well-controlled wavelength spacings using high-throughput photolithographic printing processes.
According to another embodiment of the invention several or all of the lasers LAl to LA8 at corresponding wavelengths Al to A8 are activated. The combiner COl illwminates the waveguide OWl with all the selected wavelengths, and the modulator M modulates the selected wavelengths.

According to still another embodiment of the invention, each of the lasers LAl to LA8 has some degree of tunability to allow adjustment of each laser to its prescribed frequency. Each laser remains at its tuned frequency during normal operation.
According to yet another embodiment of the invention, the current source actuates the lasers LAl to LA8 on a time division basis and the combiner CO1 illuminates the output waveguide OW1 at wavelengths ll to A8 on the same basis. The modulator MOD1 modulates the light at each wavelength on a time division basis with separate signals specific to each wavelength, synchronized in time with the current source CS1. This provides a time-division and wavelength-division multiplex transmitter. In still another embodiment the current source CO1 time division multiplexes one, or any number, of the lasers. The modulator MOD1 modulates the signals in time with the multiplexing of the current source CS1.
The wavelength division multiplexed transmitter TR1 with the architecture according to the invention offers substantial advantages to networks. In a wavelength division multiplexed transmitter network, according to an embodiment of the invention, each transmitter TR1 has a particular wavelength channel allocated to it for to it operation. In the event that one laser fails in a transmitter, that failure affects only the laser corresponding to the wavelength originally allocated to that transmitter. According to an embodiment, the system returns to an operational condition by having the current source CS1 activate another laser so as to reassign that transmitter a new wavelength.
Suitable means, such as the current source CS1, or another current source, assigns the wavelength of the failed laser to another transmitter whose laser at that wavelength has 3~ ~ 3 ,=_ g not failed.
Fabrication techniques for growing or otherwise integrating the individual elements of the transmitter TR1 of Fig. 1 onto a single substrate are well known, for example, from the aforementioned M.G. Young et al paper.
According on embodiment of the present invention, the transmitter TR1 is constructed by using the same growth and fabrication processes, but with a mask layout suitable for realizing the structure of Figs. 1 to 3. Generation of arrays of fixed frequency sources with high-throughput photolithographic printing processes is disclosed by J-M.
Verdiell et al in "8-Wavelength DBR Laser Array Fabricated with a Single-Step Bragg Grating Printing Technique~, in ~ : Phot. Tech. Lett. 5, pp. 619-621 (1993).
Another embodiment of the invention adapts the particular fabricating technique which appears in "Semiconductor Photonic Integrated Circuits" by Thomas ~
Koch et al in IEEE J. Quantum Electron., Vol. QE-27, pp.
641-653 (1991).
The invention overcomes the disadvantages of prior transmission applications using a set of isolate~, discrete, fixed-frequency sources. In such instances ~;~e manufacturer would have had to "bin" the laser transmitters for each channel and provide for means to guarantee a suitable stock of all channels. Similarly, the system manufacturers must ensure maintenance of a stock of each channel and make a full supply of each channel readily available correctly to replace the appropriate channels for failures in the field. This backup need has a significant cost associated therewith.
Furthermore, the invention overcomes the fact that such a prior art approach is not easily extendable to a wavelength division multiplexing switching application since each source can only achieve one wavelength channel.

a ~

The invention also overcomes the deficiencies of a tunable laser, including either a tunable laser that could access all wavelength channels, or a series of tunable lasers whose frequency ranges overlap to cover the desired frequency range. Such lasers lack a simple, reliable, and low cost wavelength stabilization technique.
In these tunable devices, the wavelength is changed by applying a voltage, current, or some other tuning drive to change the optical characteristic of some part of the laser cavity. Once one achieves the means for providing the wavelength excursions larger than those achieved in conventional distributed feedback lasers, then suitable means must ensure that the calibration of wavelength versus the applied tuning drive remains robust against aging.
The invention also overcomes the disadvantages of modulating each laser in an array. Specifically, ~
overcomes the complexity of packaging necessary to pro~ ~e for the high speed drive for each wavelength channel b~, offering a separate, high speed electrical drive capability to each laser or to each modulator. The invention further overcomes the substantial cost in size of such a transmitter module.
The present invention is particularly pertinenc -25 to applications that do not require, or do not regard as desirable, the simultaneous transmission of multiple independent data streams at each wavelength channel from a single module. This is true where the transmitter for a particular wavelength channel is remote from, or on a circuit board different from, a transmitter at a different wavelength channel. The invention recognizes that the difficulties and costs of providing each transmitter with a simultaneous high speed drive for each wavelength can be overcome.

While embodiments of the invention have been described in detail, it will be evident to those skilled in the art that the invention may be embodied otherwise without departing from its spirit and scope.

Claims (18)

1. A wavelength-division multiplexed transmitter, comprising:

a substrate;
a plurality of individually actuable lasers integral with said substrate;
an optical modulator integral with said substrate;
and an optical combiner integral with said substrate and connecting each of said lasers with said modulator;
said lasers each defining a different frequency exclusive of said combiner.
2. A transmitter as in claim 1, wherein said lasers, said modulator, and said optical combiner are grown on said substrate.
3. A transmitter as in claim 1, wherein said substrate is a semiconductor and said lasers, said modulator, and said optical combiner are grown on said substrate.
4. A transmitter as in claim 1, wherein said modulator includes an optical modulator element and an optical amplifier.
5. A transmitter as in claim 1, wherein said modulator includes an optical modulator element and an optical amplifier between said modulator element and said optical combiner.
6. A transmitter as in claim 1, wherein said modulator includes an optical amplifier and an optical modulator element between said amplifier and said optical combiner.
7. A transmitter as in claim 1, wherein said optical modulator includes an electroabsorption modulator element.
8. A transmitter as in claim 3, wherein said optical modulator element is an electroabsorption modulator.
9. A transmitter as in claim 1, wherein said lasers are each fixed frequency lasers for operation at respectively different frequencies.
10. A transmitter as in claim 1, further comprising actuating means connected to each of said lasers for energizing said lasers.
11. A transmitter as in claim 1, wherein said combiner is an in-plane diffraction region integrated in said substrate.
12. A transmitter as in claim 1, wherein said combiner is a waveguide y-branch tree.
13. A transmitter as in claim 1, wherein said lasers are distributed Bragg reflector lasers.
14. A transmitter as in claim 1, wherein said lasers are distributed feedback lasers.
15. A transmitter as in claim 1, wherein said modulator includes a directional coupler modulator element.
16. A transmitter as in claim 1, wherein said modulator includes a Mach-Zehnder modulator element.
17. A transmitter as in claim 1, wherein said combiner is a star coupler.
18. A transmitter as in claim 1, wherein said combiner is an N x 1 star coupler.
CA002119503A 1993-07-27 1994-03-21 Wavelength division multiplexed optical communication transmitters Expired - Lifetime CA2119503C (en)

Applications Claiming Priority (2)

Application Number Priority Date Filing Date Title
US08/097,692 US5394489A (en) 1993-07-27 1993-07-27 Wavelength division multiplexed optical communication transmitters
US097,692 1993-07-27

Publications (2)

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CA2119503A1 CA2119503A1 (en) 1995-01-28
CA2119503C true CA2119503C (en) 1999-02-16

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EP (1) EP0636908B1 (en)
JP (1) JP3490503B2 (en)
CA (1) CA2119503C (en)
DE (1) DE69415599T2 (en)

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