Book Chapter

Continuously Tunable 1.5µm Multiple-Quantum-Well InGaAs/InGaAsP Distributed-Bragg-Reflector Lasers

T.L. Koch, U. Koren, R.P. GNALL, C.A. Burrus, and B.I. Miller
Chapter 2.5 in Coherent Lightwave Communications, pp. 87-88, 1990, IEEE PRESS,ISBN 0-87942-262-9; Edited by P.S. Henry and S.D. Personick (Reprint of Paper #32 below)

Magazine Cover

IEEE Circuits and Devices Magazine - "Quantum Well Semiconductor Lasers Are Taking Over"

Amnon Yariv
IEEE Circuits and Devices Magazine, 5(6), Nov 1989



Phase Grating Masks for Photonic Integrated Circuits Fabricated by E-Beam Writing and Dry Etching: Challenges to Commercial Applications

D.M. Tennant, K. Feder, K.F. Dreyer, R.P. GNALL, T.L. Koch, U. Koren, B.I. Miller, M.G. Young
Microelectronic Engineering, 27(1-4) pp. 427-437, Feb 1995;
International Conference on Micro and Nano Engineering (MNE '94), Davos Switzerland, Sep 26 1994
Abstract Near field holography is a method of using grating photomasks in which the m = -1 and m = 0 diffracted beams of a UV source interfere to form a standing wave pattern. This simple hologram can then be used to expose a grating pattern on a process wafer when held in near-contact. This technique is especially attractive for use in OEICs and PICs when fabrication of the grating masks is accomplished with e-beam lithography and dry etching, since the diffractive properties of the mask can be controlled by the physical parameters of the mask. The grating period on masks made in this way can be precisely controlled to produce arrays of lasers each separated by only a small change in frequency (order 100 GHz) as may be required for WDM applications. We review the phenomenology of fused silica phase grating masks and describe work toward establishing characterization criteria, implementing practical printing methods, improving e-beam precision, and demonstrating laser array performance. We discuss principle issues and progress in each of the technical areas.

Advances in Near Field Holographic Grating Mask Technology

D.M. Tennant, K.F. Dreyer, K. Feder, R.P. GNALL, T.L. Koch, U. Koren, B.I. Miller, C. Vartuli, M.G. Young
Journal of Vacuum Science and Technology B, 12(6) pp. 3689-3694, Nov/Dec 1994;
Presented at 38th International Symposium on Electron, Ion, and Photon Beams (EIPB'94), New Orleans LA, May 31 1994
Abstract We report progress on several practical issues of near field holographic (NFH) printing for optoelectronic applications. In particular, we report on the following: adaptation of the mask making process to large area holographically generated grating masks; evaluation of a commercially available UV contact aligner modified to allow routine NFH printing; use of mask copies to avoid excessive wear on original masks; options for reducing the writing time for e-beam generated grating masks; and the application of e-beam generated grating masks to a DFB six-laser array with 200-GHz frequency channel separation.

Monolithic Integration of GaInAs/GaInAsP Strained Quantum Well DFB Laser, Electroabsorption Modulator and Optical Amplifier by Nonplanar MOVPE

F. Koyama, K.-Y. Liou, A.G. Dentai, R.P. GNALL, G. Raybon, H.M. Presby, C.A. Burrus
Proceedings of 1994 Conference on Lasers and Electro-Optics CLEO/IQEC (CLEO '94), 8() pp. 240-241, Anaheim CA, May 8 1994
Abstract We have demonstrated a monolithically integrated electroabsorption (EA) modulator/DFB laser using nonplanar MOVPE. We have also shown an EA modulator/amplifier integrated device with zero net fiber-to-fiber insertion loss. The wavelength dependencies of the modulation voltage and the insertion loss of the integrated EA modulator/amplifier have been investigated by using an external tunable light source. The integration of an optical amplifier enables us to use an operating wavelength close to the bandgap of the modulator, resulting in low modulation voltage and low wavelength-chirp operation.

Monolithically Integrated Distributed Feedback Laser with an Electro-Absorption Modulator and a Monitoring Photodetector

K.-Y. Liou, A.G. Dentai, E.C. Burrows, F. Koyama, R.P. GNALL, G. Raybon, C.A. Burrus
Presented at Integrated Photonics Research Topical Meeting, San Francisco CA, February 17 1994
Abstract We report a monolithic photodetector-DFB laser-EA modulator chip which has been integrated using low loss butt-joint waveguides grown by MOVPE. The InGaAs/InGaAsP multiple quantum well DFB lasers oscillate without facet reflections at 1.54µm wavelength with low threshold currents (~20 mA). The integrated photo-detectors allow on-wafer laser testing, and they are used as laser output power monitors after the wafers were cleaved into individual chips. The modulator output, coupled to a single mode fiber, exhibits 17 dB extinction ratio with 3 V bias to the modulator.

Integrated MQW Optical Amplifier/Noise Filter/Photodetector Photonic Circuit

R.C. Alferness, L.L. Buhl, U. Koren, T.L. Koch, I. Kim, B.I. Miller, M.A. Newkirk, M.G. Young, R.P. GNALL, F. Hernandez-Gil, H.M. Presby, G. Raybon, C.A. Burrus
Photonics Technology Letters, 5(12) pp. 1401-1403, Dec 1993
Abstract A monolithically integrated photonic circuit with an InGaAs/InGaAsP multiple-quantum-well (MQW) traveling-wave optical amplifier, a Bragg reflection grating-folded noise filter, and an MQW photodetector has been demonstrated. This photonic circuit offers potential as a preamplified lightwave receiver.

Multiwavelength Distributed Bragg Reflector Laser Array Fabricated using Near Field Holographic Printing with an Electron-Beam Generated Phase Grating Mask

D.M. Tennant, T.L. Koch, J.M. Verdiell, K. Feder, R.P. GNALL, U. Koren, M.G. Young, B.I. Miller, M.A. Newkirk, B. Tell
Journal of Vacuum Science and Technology B, 11(6) pp. 2509-2513, Nov/Dec 1993;
Presented at International Symposium on Electron, Ion, and Photon Beams, San Diego CA, June 1993
Abstract We describe near optimum near field holography grating masks patterned by e-beam lithography and a distributed Bragg reflector (DBR) multiwavelength laser array fabricated using near field printing with this mask. Grating pitches in the array ranged from 242.861 to 243.750 nm in 0.127 nm steps. Data on the pitch precision and pitch adjustment is presented. Use of a conventional UV source rather than laser illumination both greatly simplified the printing process and eliminated coherent artifacts from the printed gratings. Chemically etched InP test gratings are shown to be extremely ``clean'' in appearance and low in edge roughness. DBR laser arrays designed with 100 GHz frequency separation were processed using the mask described. The measured frequency separation was 99 GHz which could be further adjusted with a tuning section of the four-section laser design. Characterization of a similar grating mask containing 16 wavelengths with similar pitch increments is also described.

InGaAs/InGaAsP Integrated Tunable Detector Grown by Chemical Beam Epitaxy

F.S. Choa, W.T. Tsang, R.A. Logan, R.P. GNALL, T.L. Koch, C.A. Burrus, M.C. Wu, Y.K. Chen, R. Kapre
Applied Physics Letters, 63(13) pp. 1836-1838, Sep 27 1993;
IEEE Integrated Optoelectronics Summer Topical Meeting Digest, pp. B11-B12, Santa Barbara CA, August 5 1992
Abstract By controlling the thickness of the grating depth with chemical beam epitaxy (CBE) growth time, we report in this letter the design and performance of an integrated tunable detector. A carefully designed tunable active filter, which allows only one below threshold Fabry-Perot mode for operation, is integrated with a waveguide detector. The full tuning range of this kind of tunable device can now be utilized for system applications.

8-Wavelength DBR Laser Array Fabricated with a Single-Step Bragg Grating Printing Technique

J.M. Verdiell, T.L. Koch, D.M. Tennant, K. Feder, R.P. GNALL, M.G. Young, B.I. Miller, U. Koren, M.A. Newkirk, B. Tell
Photonics Technology Letters, 5(6) pp. 619-621, June 1993
Abstract An 8-wavelength DBR array for narrow channel wavelength division multiplexing (WDM) has been fabricated with a new technique for printing first-order Bragg gratings using a phase mask and a conventional incoherent source. All the distributed gratings were printed in a single photolithographic step with a slightly modified mask aligner. We demonstrate excellent wavelength control for channels separated by as little as 0.8 nm. Many advanced photonic devices relying on gratings like quarter-wave shifted DFB lasers and WDM components can potentially be manufactured with this technique in a simple and cost-effective way.

An N-frequency Laser Matched to a Fabry-Perot Etalon Frequency Standard

U. Koren, M.A. Newkirk, Y.C. Chung, B.I. Miller, M.G. Young, R.P. GNALL, M.D. Chien
Presented at Integrated Photonics Research Topical Meeting, San Francisco CA, Feb 1994
Abstract We demonstrate that a tunable N-frequency laser can be matched to a Fabry Perot etalon standard which has an absolute frequency calibration. The optical frequency spacing of the laser tuning modes is exactly 1/2 that of the Fabry Perot etalon standard. With this scheme it is possible to obtain fast tuning curves for the laser, and to monitor for errors during frequency switching.

Incoherent Contact-Print Grating Technology for WDM Laser Sources

T.L. Koch, J.M. Verdiell, D.M. Tennant, R.P. GNALL, K. Feder, M.G. Young, B.I. Miller, U. Koren, M.A. Newkirk, B. Tell
Presented at Optical Fiber Conference (OFC '93), San Jose CA, Feb 21 1993
Abstract A new grating fabrication technique is introduced using incoherent illumination in a modified mask aligner geometry with near-field holographic e-beam generated phase masks. This technique offers the full versatility of e-beam lithography in a high-throughput Hg-source contact exposure, and has been used to fabricate eight-element arrays of densely-spaced (0.8nm) DBR lasers.

A Frequency Reference Photonic Integrated Circuit for WDM with Low Polarization Dependence

J.M. Verdiell, M.A. Newkirk, T.L. Koch, R.P.GNALL, U. Koren, B.I. Miller, B. Tell
Photonics Technology Letters, 5(4) pp. 451-454, April 1993;
Presented at Integrated Photonics Research Conference, Palm Springs CA, Mar 1 1993
Abstract A photonic circuit implementing ten frequency reference filters for narrow-channel wavelength division multiplexing (WDM) has been fabricated. A diluted multiquantum-well waveguide structure is shown to yield a very low TE/TM polarization dependence of 1 Å, as well as improved absolute frequency control and reproducibility. A standard deviation in absolute filter wavelength of 3.33 Å is measured on a random set of devices from a 2-in wafer. The ten channels are evenly spaced by 7.2 Å. Such filters can be used to lock tunable lasers to a set of reference frequencies for WDM applications. The demonstrated diluted multiquantum-well waveguide structure with low birefringence and improved absolute wavelength control could potentially be used in other WDM integrated circuits requiring tight wavelength tolerance and polarization insensitivity.

Aspheric Waveguide Lenses for Photonic Integrated Circuits

J. Verdiell, M.A. Newkirk, T.L. Koch, R.P. GNALL, U. Koren, B.I. Miller, L.L. Buhl
Applied Physics Letters, 62(8) pp. 808-810, Feb 22 1993
Abstract We report the fabrication of aspheric waveguide lenses on the InP/InGaAsP material system. A wide aperture (f/5) lens working at 1.5 times the diffraction limit is reported. Insertion loss below 1 dB is also measured. The lens is fabricated by a selective chemical etch of a planar waveguide and has potential applications in InP-based photonic integrated circuits.

Single Step Contact Printing of Bragg Gratings Using a Conventional Incoherent Source and a Phase Mask: Application to a Multi-Wavelength DBR Laser Array

J.M. Verdiell, T.L. Koch, D.M. Tennant, R.P. GNALL, K. Feder, M.G. Young, B.I. Miller, B. Tell, U. Koren, M.A. Newkirk
Bell Labs Technical Memorandum
Abstract A new technique for making Bragg grating photolithographic exposures is presented. Instead of the usual holographic exposure with a UV laser, we will show that a conventional Mercury arc lamp source is good enough to generate a high-contrast grating pattern from a contact printing exposure with a phase mask. Apart from a great simplification of the processing sequence, this technique also allows to print gratings of different pitches in a single exposure. A 8-wavelength DBR laser array fabricated with a one-step "incoherent" exposure for the gratings is demonstrated. Potential advantages also include cost-effective fabrication conventional or lambda/4-shifted DFB lasers and PIC's involving complex grating structures.

Characterization of Near Field Holography Grating Masks for Optoelectronics Fabricated by Electron Beam Lithography

D.M. Tennant, T.L. Koch, P.M. Mulgrew, R.P. GNALL, F. Ostermeyer, J-M. Verdiell
Journal of Vacuum Science and Technology B, 10(6) pp. 2530-2535, Nov/Dec 1992;
Presented at International Symposium on Electron, Ion, and Photon Beams, Orlando FL, May 1992
Abstract Direct write e-beam lithography and reactive ion etching was used to fabricate square-wave gratings in quartz substrates which serve as pure phase masks in the near-field holographic printing of gratings. This method of fabricating these masks extends the flexibility of the printing technique by allowing both abrupt phase shifts as well as multiple grating pitches to be simultaneously printed from a single contact mask. Grating masks with periods in the 235-250 nm range have been produced and measured to be within 0.15 nm of the design period. Transmitted and diffracted beam powers have also been measured for various duty cycles and etch depths and are shown to be important parameters for ``balancing'' these interfering beams. Simple scalar diffraction modeling is used to qualitatively examine the dependence of diffraction on grating parameters, but the need for a more comprehensive modeling is illustrated. Prototype masks have been used to produce grating patterns on InP substrates using two different ultraviolet illumination sources: an argon ion laser and a conventional mercury lamp.

Design, Fabrication, and Performance of a Very High Side-Mode-Suppression-Ratio Distributed-Bragg-Reflector Laser

F.S. Choa, W.T. Tsang, R.A. Logan, R.P. GNALL, U. Koren, T.L. Koch, P.D. Magill, K.C. Reichmann, C.A. Burrus, M.C. Wu, Y. K. Chen, P.F. Sciortino
Paper DLTA6.3 at IEEE Lasers and Electro-Optics Society Annual Meeting (LEOS '92), Boston MA, Nov 16 1992
Abstract A tunable distributed-Bragg-reflector laser with a record high side-mode-suppression-ratio of 58.5 dB is fabricated with wafers grown by chemical-beam-epitaxy. Chirping characteristics of the laser is studied by employing transmission experiments.

Experimental Demonstration of Fiber Transmission of Compressed Digital Video

P. Magill, K.C. Reichmann, B. Desai, T.L. Koch, R.P. GNALL, U. Koren, B.I. Miller, M.G. Young, G. Raybon
Presented at 18th European Conference on Optical Communications (ECOC '92), Berlin Germany, Sep 27 1992
Abstract We experimentally demonstrate fiber transmission of high-quality, DCT-based compressed digital-video. We used a potentially inexpensive photonic-integrated-circuit bi-directional transceiver as might be applicable for loop fiber systems. Visual impairments caused by transmission errors are characterized.

Quantum Well Interferometric Modulator Monolithically Integrated with a 1.55µm Tunable Distributed Bragg Reflector Laser

J.E. Zucker, K.L. Jones, M. Newkirk, R.P. GNALL, B.I. Miller, M.G. Young, U. Koren, C.A. Burrus, B. Tell
Electronics Letters, 28(20) pp. 1888-1889, Sep 24 1992
Abstract The first monolithically integrated laser/interferometric modulator is reported. The total chip length of 2.5 mm includes a 970 µm-long strained InGaAs-InGaAsP quantum well gain section, a 230 µm-long wavelength tuning section containing a distributed Bragg reflector grating, and an 800 µm-long active length Mach-Zehnder modulator based on electrorefractive InGaAsP-InP quantum wells. 4 V push-pull drive voltage produces 12.5 dB modulation depth with -9 dBm optical power coupled into a cleaved fiber.

High-Power Multiple-Quantum-Well Distributed Feedback Laser Arrays and Fabry-Perot Laser Arrays at 1.5µm Wavelength

K.Y. Liou, A.G. Dentai, E.C. Burrows, R.P. GNALL, C.H. Joyner, C.A. Burrus
13th IEEE International Semiconductor Laser Conference Digest, pp. 88 - 89, Takamatsu Japan, Sep 21 1992
Abstract We report on coherent high-power 12-element laser arrays of both the DFB and FP types. Pulsed emission up to 450 mW/facet and CW output to 85 mW are demonstrated with a single-wavelength spectrum for DFB arrays and multi mode output from FP arrays.

Self-Aligned Ridge Guide Lasers, Monolithic Laser Arrays, and Photonic Integrated Circuits

K.Y. Liou, A.G. Dentai, E.C. Burrows, R.P. GNALL, C.H. Joyner and C.A. Burrus
Paper ThB1 at LEOS Summer Topical Meeting on Integrated Optoelectronics, Santa Barbara CA, Aug 5 1992
Abstract A self-aligned-contact ridge waveguide structure has been employed to fabricate low threshold multiple quantum well DFB lasers, high-power laser arrays, and optoelectronic integrated circuits. Our results indicate that the device structure and processing technique are attractive for high density electro-optical integration.

Very High Side-Mode-Suppression-Ratio Distributed-Bragg-Reflector Lasers Grown by Chemical Beam Epitaxy

F.S. Choa, W.T. Tsang, R.A. Logan, R.P. GNALL, U. Koren, T.L. Koch, C.A. Burrus, M.C. Wu, Y.K. Chen, P. F. Sciortino, A.M. Sergent, P.J. Corvini
Electronics Letters, 28(11) pp. 1001-1002, May 21 1992
Abstract The fabrication and performance of InGaAs/InGaAsP multiquantum well distributed-Bragg-reflector lasers grown by chemical beam epitaxy are reported. Use of a long and weak grating, which was made on a thin and uniformly grown quaternary layer has enabled the grating coupling constant kappa to be well controlled. For most of the lasers the measured linewidths are below 10 MHz. A record high sidemode suppression ratio of 58.5 dB was obtained.

Strained Multiple Quantum Well 1.55µm Distributed Feedback Lasers with Polyimide-Buried Self-Aligned-Contact Ridge Guide Structure

K.Y. Liou, A.G. Dentai, C.H. Joyner, R.P.GNALL, E.C. Burrows, C.A. Burrus
Paper CTuA4 at Conference on Lasers and Electro-Optics (CLEO '92), Anaheim CA, May 10 1992
Abstract A strained MQW polyimide-buried ridge guide DFB laser grown by MOVPE has been fabricated by a self-aligned dry-wet etch method. Accurate control of the Bragg wavelength for low threshold oscillation near the MQW gain peak is demonstrated. The self-aligned structure is attractive for large scale photonic integrated circuits.

Efficient Coupling of High-Intensity Sub-Picosecond Laser Pulses into Dilute Solid Targets

M. Murnane, H. Kapteyn, S. Gordon, S. Verghese, J. Bokor, W. Mansfield, R.P. GNALL, E. Glytsis, T. Gaylord, R.W. Falcone
Short Wavelength Coherent Radiation, 11, pp. 281-284, 1991

Efficient Coupling of High-Intensity Sub-Picosecond Laser Pulses into Solid Grating Targets

J. Bokor, W.M. Mansfield, R.P. GNALL, E. Glytsis, T. Gaylord, R. Falcone, M. Murname, H. Kapteyn
Presented at Short Wavelength Coherent Radiation Generation & Application Topical Meeting, Monterey CA, April 8 1991
Abstract We present experimental and theoretical results on coupling 90% of the energy of high-intensity, 150fsec laser pulses into grating targets, with associated high x-ray yield.

Bi-directional Transmission Experiment Using a 1.5µm/1.3µm In-Line Transceiver

K.C. Reichman, A.H. Gnauck, T.L. Koch, U. Koren, G. Raybon, R.P. GNALL, M. Oron, M.G. Young, J.L. deMiguel, B.I. Miller
Bell Labs Technical Memorandum

Balanced Operation of a GaInAs/GaInAsP Multiple-Quantum-Well Integrated Heterodyne Receiver

T.L. Koch, F.S. Choa, U. Koren, R.P. GNALL, F. Hernandez- Gil, C.A. Burrus, M.G. Young, M. Oron, B.I. Miller
Photonics Technology Letters, 2(8) pp. 577-80, Aug 1990
Abstract We describe the balanced operation of a multiple-quantum-well balanced heterodyne receiver photonic integrated circuit (PIC). Using only SMA-connected 50 Ohm commercial electronics, we achieve a free-space beam sensitivity of -42.3 dBm at 108 Mb/s and -39.7 dBm at 200 Mb/s for NRZ FSK reception. This represents a 14 dB improvement over any previous heterodyne receiver PIC sensitivity. In addition to providing the multi-channel benefits of heterodyne reception, this is also the highest sensitivity yet reported for any OEIC receiver.

Tertiarybutylarsine as a substitute for AsH3: Application to InGaAsP/InP Photonic Integrated Circuits

B.I. Miller, M.G. Young, U. Koren, T.L. Koch, M. Oron, R.P. GNALL, F. Hernandez-Gil, J.E. Zucker, K.E. Jones, and J.L. DeMiguel
Proceedings of 2nd International Conference on Indium Phosphide and Related Compounds, pp. 161 - 164, Denver CO, Apr 23 1990
Abstract We have shown that TBA grown bulk layers of InGaAs and InGaAsP have nearly as good electrical and optical properties as AsH3 grown layers. As a consequence, conventional InGaAsP lasers at 1.3 µm were grown by TBA and were found to have properties as good as AsH3 grown lasers. Continuing this work, we present here investigations into other components of PIC circuits grown by using TBA as a substitute for AsH3, ie: multi-quantum-well (MQW) and strained-layer MQW lasers, a 4-port directional coupler optical switch, and quantum-confined Stark Effect modulator structures. Data is also presented showing the difference in spatial uniformity between TBA grown and AsH3 grown material.

Simple In-Line Bi-directional 1.5µm/1.3µm Transceivers

T.L. Koch, U. Koren, A.H. Gnauck, K.C. Reichmann, H. Kogelnik, G. Raybon, R.P. GNALL, M. Oron, M.G. Young, J.L. DeMiguel, B.I. Miller
12th International Semiconductor Laser Conference Digest, pp. 166 - 167, Davos Switzerland, Sep 9 1990
Abstract We propose some simple new single-waveguide in-line photonic integrated circuit (PIC) architectures for 1.3µm/1.5µm WDM bi-directional (duplex) transmission. Using a prototype in-line 1.5µm transmit/1.3µm receive PIC as one station in a 200 Mb/s - 155 Mb/s duplex link, we achieve 10(-9) BER over 28 km of fiber using no electrical cancellation or isolation techniques, and only 50 ohm 6dB noise figure amplifiers connected to the detectors. The design and fabrication simplicity of the new PIC's suggest their potential usefulness in low-cost local-loop applications.

GaInAs/GaInAsP Multiple-Quantum-Well Integrated Heterodyne Receiver

T.L. Koch, U. Koren, R.P. GNALL, F.S. Choa, F. Hernandez-Gil, C.A. Burrus, M.G. Young, M. Oron, B.I. Miller
Electronics Letters, 25(24) pp. 1621-1623, Nov 23 1989;
Paper PD1 at IEEE Lasers and Electro-Optics Society Annual Meeting (LEOS '89), Orlando FL, Oct 19 1989
Abstract We describe the fabrication and performance of the first integrated heterodyne receiver capable of actual heterodyne data reception. Integrating a continuously tunable 1.5 µm MQW-DBR laser with a single-mode directional coupler/switch and zero-bias MQW waveguide photodetectors, we have achieved error-free reception of FSK-modulated pseudorandom digital code at 105 Mbit/s.

Tunable MQW-DBR Laser with Monolithically Integrated InGaAsP/InP Directional Coupler Switch

F. Hernandez-Gil, T.L. Koch, U. Koren, R.P. GNALL, and C.A. Burrus
Electronics Letters, 25(19) pp. 1271-1272, Sep 14 1989;
Paper PD17 at Conference on Lasers and Electro-Optics (CLEO '89), Baltimore MD, 1989
Abstract We report the successful monolithic integration of a GaInAsP/InP single-mode Delta kappa directional coupler switch with a 4-section tunable multiple-quantum-well distributed Bragg reflector laser. We obtain several mW of output power through the switch, with ~10 dB crosstalk either from the internal laser source or with external light injected through the parallel input port.

Demonstration of Multilevel FSK Modulation

P.D. Magill, T.L. Koch, U. Koren, B.I. Miller, R.P. GNALL, and C.A. Burrus
Presented at Optical Fiber Conference (OFC '89), Houston TX, Feb 6 1989
Abstract A serious problem in high speed optical digital communications research today is that, for binary systems, the associated electronic circuits must operate at frequencies comparable to the bit rate. This limitation has slowed the rise in maximum attainable bit rate in recent years. Multilevel signaling offers some relief by using electronics operating only at the symbol rate where each symbol is derived from n bits (n > 1), and is hence n times slower than the effective bit rate. In addition, the reduced symbol rate allows for greater receiver sensitivity by filtering the noise at an n times lower frequency.

Monolithically Integrated InGaAsP/InP Distributed Feedback Laser with Y-Branching Waveguide and a Monitoring Photodetector Grown by Metalorganic Chemical Vapor Deposition

K.Y. Liou, U. Koren, S. Chandrasekhar, T.L. Koch, A. Shahar, C.A. Burrus, and R.P. GNALL
Applied Physics Letters, 54(2) pp. 114-116, Jan 9 1989;
Paper PD13 at 11th IEEE International Semiconductor Laser Conference, Boston MA, Aug 25 1988;
Paper TuCC2-1 at Topical Meeting on Integrated and Guided Wave Optics (IGWO '89), Houston TX, Feb 6 1989
Abstract We have fabricated an integrated 1.5 µm distributed feedback laser (DFB) with a Y-branching waveguide and a monitoring photodetector, grown entirely by metalorganic chemical vapor deposition. The integrated device is designed to resolve the frontface-backface mistracking problem of the DFB laser and to demonstrate monolithic integration of fundamental building blocks for photonic integrated circuits.

Continuously Tunable 1.5µm Multiple-Quantum-Well InGaAs/InGaAsP Distributed-Bragg-Reflector Lasers

T.L. Koch, U. Koren, R.P. GNALL, C.A. Burrus, and B.I. Miller
Electronics Letters, 24(23) pp. 1431-1433, Nov 10 1988;
Paper J:1 at IEEE International Semiconductor Laser Conference, Boston MA, 1988;
Reprinted in Coherent Lightwave Communications, edited by P.S. Henry and S.D. Personick, pp. 87-88, 1990 by IEEE PRESS, ISBN 0-87942-262-9 (see Book Chapter at top);
Cover Photo, IEEE Circuits and Devices Magazine, 5(6), Nov 1989
Abstract We demonstrate improved performance in tunable distributed-Bragg-reflector lasers using GaInAs/GaInAsP multiple-quantum-well active layers. We observe linewidths as low as 1.9 MHz, differential quantum efficiencies as large as 33%/front facet at 1.5 µm, and rapid electronic access to all frequencies throughout a 1000 GHz range.

Very High-Transconductance Heterojunction Field-Effect Transistor (HFET)

G.W. Taylor, M.S. Lebby, T.Y. Chang, R.P. GNALL, N. Sauer, B. Tell, and J.G. Simmons
Electronics Letters, 23(2) pp. 77-9, Jan 16 1987
Abstract A new form of FET has been demonstrated in the GaAs/AlGaAs material system. Designated the HFET, it has shown a transconductance of 500 mS/mm at 300K for a nominal Lg = 2 µm and a drain current of 430 mA/mm. The conduction occurs in an inversion channel at the heterointerface.

A New Heterostructure FET

G.W. Taylor, M.S. Lebby, T.Y. Chang, R.P. GNALL, N. Sauer, B. Tell, D.M. Tennant, J.G. Simmons
1986 International Electron Devices Meeting Technical Digest, pp. 817-821, Los Angeles CA, Dec 7 1986
Abstract A GaAs-AlGaAs heterojunction FET (HFET) structure is developed. The HFET has several novel features which make it attractive for VLSI. The enhancement threshold voltage is established by ion implantation into the active area. The instabilities associated with Schottky barriers are eliminated since ohmic contacts are used for the gates.

A GaAs/AlGaAs Bipolar Inversion Channel Field Effect Transistor (BICFET)

G.W. Taylor, M.S. Lebby, R.P. GNALL, T.Y. Chang, B. Tell, N.J. Sauer, J.G. Simmons
Bell Labs Technical Memorandum, 1986
Abstract A new form of heterostructure bipolar transistor in which the base layer had been replaced by the inversion channel of an FET and the base contact by the source junction of an FET, has been demonstrated in the GaAs/A1GaAs heterosystem. Designated as the BICFET, the concept and theory of the device have previously been published.