Reconfigurable Multifunctional Operation Using ... - Semantic Scholar
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JOURNAL OF LIGHTWAVE TECHNOLOGY, VOL. 27, NO. 15, AUGUST 1, 2009
Reconfigurable Multifunctional Operation Using Optical Injection-Locked Vertical-Cavity Surface-Emitting Lasers Bo Zhang, Member, IEEE, OSA, Xiaoxue Zhao, Member, IEEE, OSA, Devang Parekh, Member, IEEE, Yang Yue, Student Member, IEEE, Werner Hofmann, Member, IEEE, Markus C. Amann, Fellow, IEEE, Connie J. Chang-Hasnain, Fellow, IEEE, OSA, and Alan E. Willner, Fellow, IEEE, OSA
Abstract—In this paper, we extend the system application of optical injection-locked (OIL) vertical-cavity surface-emitting lasers (VCSELs) to future optical networks by realizing multifunctional operation using a filter-assisted OIL-VCSEL scheme that can be reconfigured. By using a single chirp-adjustable injection-locked VCSEL (either single mode or multimode) followed by a tunable delay line interferometer, we experimentally demonstrate three functions, showing ultra-wide band (UWB) monocycle generation, nonreturn-to-zero (NRZ) to pseudoreturn-to-zero (PRZ) data format conversion, and NRZ-data clock recovery at 10 Gb/s. Index Terms—Clock recovery, data format conversion, optical injection locking (OIL), reconfigurable optical networks, ultrawide band, vertical cavity surface emitting laser (VCSEL).
I. INTRODUCTION
A
DESIRABLE hallmark of optical subsystems is the ability to perform various types of functions by simply adjusting one of the control parameters of a device. As an example, the basic Mach–Zehnder interferometer (MZI) structure has functional utility as an amplitude modulator, phase modulator or optical filter, depending on the bias and structural conditions [1]. Such ability to reconfigure the functionality of an optical module greatly increases its cost effectiveness. Moreover, performing any function at high speed (beyond 10 Gb/s) enhances its value in high-capacity systems. Recent literature has witnessed that optical injection locking (OIL) of a vertical-cavity surface-emitting laser (VCSEL) can produce very high-speed operation, demonstrating 100 GHz of modulation resonance frequency [2]. This structure has also exhibited the ability to produce an adjustable chirp on the output optical signal, such that the magnitude and the polarity (positive or negative frequency deviation) are both controllable [3],
[7]. Very recently, the chirp variability is shown to provide chromatic dispersion precompensation for 10 Gbit/s data signals [3]. On the other hand, ultrawideband (UWB) technology has attracted considerable interest for short-range, high-throughput wireless and sensor networks due to its high data capacity, intrinsic immunity to multipath fading, and low power consumption. UWB overfiber, which offers high data-rate service across different networks, has ignited research interest in generating UWB signal in the optical domain. Photonic generation of UWB signals has been demonstrated using either external phase modulators or semiconductor optical amplifiers via phase-to-intensity conversion, which results in monocycle or doublet pulses [4]. In the mean time, optical data-format conversion and clock recovery have been considered potentially valuable functions for interfacing future optical networks, and are realized using various nonlinear elements [5]. However, to the best of our knowledge, the above three functions have not been reported using the same basic structure in a single device that can be reconfigured. In this paper, we propose and demonstrate multifunctional operation of an injection-locked VCSEL, showing UWB-monocycle generation, data-format conversion, and clock recovery. Both single-mode and multimode VCSELs are shown to be capable of functional reconfiguration. The key mechanism is using a 10 GHz tunable interferometer to selectively filter out the unique time-resolved frequency chirp component after optical injection locking. Polarity-switchable UWB monocycles are generated with a 5.1 GHz center frequency and a fractional bandwidth of 129%. NRZ to pseudo-RZ (PRZ) format conversion is generated from either the rising or falling edge detection. Finally, a 10 GHz clock tone with a 35 dB suppression ratio is also generated from a 10 Gb/s NRZ input data signal. II. CONCEPT
Manuscript received December 09, 2008; revised February 28, 2009, March 09, 2009. Current version published July 22, 2009. This work was supported in part by the NSF ERC CIAN. B. Zhang, Y. Yue, and A. E. Willner are with the University of Southern California, Department of Electrical Engineering-Systems, Los Angeles, CA 90089 USA (e-mail: [email protected]; [email protected]; [email protected]). X. Zhao, D. Parekh, and C. Chang-Hasnain are with the University of California, Berkeley, Electrical Engineering and Computer Science, Berkeley, CA 94720 USA (e-mail: [email protected]). W. Hofmann and M. Amann are with the Walter Schottky Institute, Technical University of Munich, Am Coulombwall 3, D-85749 Garching, Germany (e-mail: [email protected]). Digital Object Identifier 10.1109/JLT.2009.2017926
Optically injection-locked (OIL) VCSEL is locked, both in frequency and in phase, to a master laser by photon injection at adjacent wavelengths. It features significantly reduced adiabatic and transient frequency chirp compared to that of a directly modulated VCSEL, as well as controllable polarity and magnitude of the dominant transient chirp after OIL [3]. This can be understood by the fact that the carrier density change and hence the index variation are greatly reduced or clamped by the injected photon from the master laser. By passing the chirped OIL-VCSEL through a delay-line interferometer (DLI), which
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Fig. 1. Concept of multifunctional generator using optical injection-locked (OIL) VCSEL followed by a delay-line interferometer (DLI). Three unique and reconfigurable functions are achieved by utilizing the adjustable chirp from the OIL-VCSEL and subsequent tunable filtering.
Fig. 2. Since VCSEL exhibits unique transient chirp in both frequency and time domain after optical injection locking, by detuning the delay line interferometer (DLI) to different positions, three unique functions labeled as (1)–(3), corresponding to the functions shown in Fig. 1, can be realized and readily reconfigured.
mainly serves as a tunable optical periodic filter, we propose in Fig. 1 the concept of generating multiple functions by simply reconfiguring the detuned positions of the DLI which selectively filters one or more of the blue-chirped, the red-chirped or the center frequency components of the OIL VCSEL. As shown in Fig. 2, the spectrum of OIL-VCSEL signal along with the associated frequency chirp is depicted. If either the blue or the red chirp is selected while the center frequency component is maintained, labeled as function (1) in blue, polarityswitchable UWB monocycles can be generated, which is envisioned to be useful in future access networks where UWB overfiber and wireless/optical convergence are emerging. If either the blue or the red chirp is selected but the center frequency is suppressed, labeled as function (2) in green, either rising or falling edges of the original data signal are detected and thus NRZ-to-PRZ format conversion can be realized. If both the blue and the red chirp are selected but the center is suppressed, labeled as (3) in red, a strong clock at the data rate can be recovered from the original data signal, which can be used for 3R regeneration or clock and data recovery. III. EXPERIMENTAL SETUP The experimental setup is shown in Fig. 3. A distributed feedback (DFB) laser serves as the master to injection lock a 1.55 mm VCSEL. Both the single-mode (SM) and multimode (MM) BTJ-LW VCSELs, with optimized high-speed design [6], are used. An optical circulator is used for unidirectional locking. The VCSEL is directly modulated at 10 Gb/s, with pseudorandom bit sequence (PRBS) NRZ data or a programmable repeated pattern. The DFB current is adjusted
Fig. 3. Experimental setup of multifunctional generator using a chirp adjustable injection-locked VCSEL followed by a tunable interferometer. A chirp-form analyzer together with a sampling oscilloscope is used to record the chirp and intensity waveforms in the time domain.
to control the power into the VCSEL. A 10 GHz all-fiber delay-line interferometer is placed after the OIL VCSEL serves as a tunable optical filter. The advantest interferometric-based chirp-form analyzer together with a digital sampling oscilloscope is used to obtain the time-resolved chirp and intensity waveforms. A 10 GHz photodiode followed by a radio-frequency spectrum analyzer (RFSA) is used to measure the RF spectrum of various generated functions. IV. TIME-RESOLVED FREQUENCY CHIRP We show in [3] the “data inversion” state that is essential to achieve dispersion tolerance enhancement. Data inversion can be understood from the fact that the locked VCSEL behaves like a gain-clamped narrowband amplifier [7]. This has been modeled and explained in [7] that a minimum reflection power occurs at the cavity transparency where the material gain is equal to the material loss. Biasing above cavity transparency, the device is in the gain regime, whereas biasing below cavity transparency the device is in the loss regime. The electrical-to-optical transfer function reveals that if the VCSEL amplifier is operated in the loss regime with a negative slope, data inversion can be achieved. It is also briefly discussed in [7] that the gain level of an OIL VCSEL amplifier is also dependent on the wavelength detuning between the master DFB and the slave VCSEL under injection locking. By further increasing the power injection ratio and adjusting the detuning value in such a way that the VCSEL amplifier is in between
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Fig. 4. Time-resolved frequency chirp measurement of OIL single-mode VCSEL under the transition state when the VCSEL amplifier is in between the gain and the loss regime. The transition state exhibits residual intensity modulation with magnitude-reduced frequency chirping, which is essential for the realization of multifunctional operation.
the gain and loss regime, we are able to achieve a “transition state” as shown in Fig. 4. This phenomenon can be understood by the fact that by increasing the wavelength detuning, the data pattern gradually goes through an evolution from a noninverted state (gain regime) to a transition state (in between gain and loss) and then to a inversion state (loss regime). As measured by the chirp-form analyzer and shown in the right-Y axis of Fig. 4, the peak-to-peak chirp magnitude is GHz compared with that of the free greatly reduced to running VCSEL, yet with unchanged polarity of the chirp compared with the data inversion state [3], even though a bit of asymmetry exists in positive and negative frequency chirping. The reason why the sign of the chirp transient stays unchanged with the data pattern is attributed to the fact that the frequency deviation follows the change of the carrier density and is only determined by the modulation of the current. We will show in the following section the use of this transient frequency chirp from an OIL VCSEL, assisted with a tunable optical filter, for the realization of reconfigurable multifunctional operation. V. EXPERIMENTAL RESULTS ON RECONFIGURABLE MULTIFUNCTIONAL OPERATION A. Polarity-Switchable UWB-Monocycle Generation The transition state, which manifests itself as having small residual intensity modulation and reduced extinction ratio, is essential for the generation of UWB monocycles. Fig. 5(a) and 5(b) are the electrical input of a 10 Gb/s NRZ data signal and the OIL VCSEL transition state, respectively. By detuning the DLI in such a way that the OIL VCSEL data spectrum is sitting on either the positive or negative slopes of the filter and thus selecting either the blue or red chirp and maintain the center frequency component, polarity-switchable optical differentiators [8] corresponding to the input signal are generated, as shown in Fig. 5(c) and 5(d). Realizing that multimode VCSELs become single mode after injection locking [9], we choose to use a multimode VCSEL with 10 m aperture and three existing transverse modes to demonstrate UWB-monocycle generation in order to
Fig. 5. Polarity-switchable differentiators (c) and (d) from positive or negative slope of the DLI using OIL single-mode VCSEL under the transition state (b).
Fig. 6. Measured polarity-switchable UWB monocycle signals using OIL multimode VCSEL. (a) One polarity UWB signal. (b) The other polarity UWB signal.
show the cost effectiveness with multimode VCSELs as well as the promising UWB overmultimode fiber access network applications [10]. After programming the input data pattern to be repeated “1000000000000000” (one “1” per 16 bits), we obtain one polarity of a UWB-monocycle waveform in Fig. 6(a) when the DLI is blue shifted by 0.04 nm relative to the center frequency of the OIL-VCSEL data signal. The upper full-width at half-maximum (FWHM) is 87 ps, while the lower is 83 ps. Fig. 6(b) shows the other polarity of the UWB monocycle when the DLI is red shifted by 0.04 nm. The 93 ps upper FWHM and 78 ps lower FWHM also exhibit a bit of asymmetry which is mainly due to the asymmetric chirp from the OIL signal, as shown in Fig. 4. Fig. 7 shows the RF spectrum of the monocycle in Fig. 6(a). The center frequency is measured to be 5.1 GHz and the 10 dB bandwidth is about 6.6 GHz (from 0.8 GHz to 7.4 GHz). This means that the generated monocycle pulse has a fractional bandwidth of 129%, which well suits the Federal Communications Commision definition of UWB signals. In addition, the frequency tone spacing is 0.625 GHz, which equals the repetition rate of the input pulse train.
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Fig. 7. RF spectrum of the UWB-monocycle of Fig. 6(a), showing 6.6 GHz bandwidth at 5.1 GHz center frequency, which corresponds to 129% fractional bandwidth. The RF tone spacing of 625 MHz reveals the repetition rate of the input periodic pulse train. Fig. 9. Eye diagrams of NRZ signal and format-converted PRZ signal from the rising-edge detection.
Fig. 8. (a) Rising-edge detection and (b) falling-edge detection of the original data pattern by further detuning the DLI spectrum away from the spectrum of the OIL-VCSEL on either side.
B. NRZ-to-PRZ Format Conversion Optical data format converters have long been considered one of the important signal processing modules for heterogeneous optical networks where edge routers need to exhibit the function to serve as an interface for different incoming modulation formats. In this subsection, we will demonstrate one type of format conversion using the filtering-assisted OIL VCSEL technique. By further detuning away either side of the DLI by 0.06 nm from the center frequency of the OIL data signal, we are able to suppress the center frequency components of the original transition state signal, and further enhance the desired chirped components. In this way, we show in Fig. 8(a) and 8(b) the detection of either the rising edge or the falling edge of the original data signal, respectively. The detected edge signal behaves like a return-to-zero (RZ) format, as compared to the original non-return-to-zero (NRZ) signal. These two types of edge-detected signals do not follow the original data pattern, and are thus called a pseudo-RZ (PRZ) signal. Fig. 9 shows the eye diagram of the original NRZ data signal and the rising-edge-detected PRZ signal, as shown in Fig. 8(a), demonstrating the capability of our proposed multifunctional generator for NRZ-to-PRZ data format conversion. This PRZ type of modulation format is useful in clock tone detection, retiming for 3R regeneration applications, and even has potential for optical logic gating.
Fig. 10. (a) Detection of both the rising and falling edges of the original data pattern by notching out the center frequency component of the OIL VCSEL with detuned DLI. (b) RF spectrum of the both edge-detected signals, showing the recovered 10 GHz clock and the 0.3 MHz tone spacing, which corresponds with the PRBS of the data signal.
C. Clock Recovery Clock recovery is one of the indispensible functions at the receiver side. Recovering the clock in the optical domain before detection has its advantage of data rate transparency and thus very high-speed operation. We will show in this section that the OIL VCSEL can also be reconfigured to achieve clock recovery at 10 Gb/s and has the potential to operate at even higher bit rates.
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Due to the spectral periodicity of the DLI, if the OIL VCSEL signal is placed at the notch of the DLI spectrum, both the blueand red-chirped components are enhanced while the center frequency component is notched out. This way, the detection of both rising and falling edges of the original 10 Gb/s NRZ data is realized and shown in Fig. 10(a). The corresponding RF spectrum is shown in Fig. 10(b), featuring a 10 GHz recovered clock dB suppression ratio and 0.3 MHz tone spacing, with a PRBS. corresponding to the original 10 Gb/s data with a One thing to note here is that the two types of PRZ signal shown in Fig. 8(a) and 8(b) can also be used to recover the clock.
[9] D. Parekh, X. Zhao, W. Hofmann, M. C. Amann, L. A. Zenteno, and C. J. Chang-Hasnain, “Greatly enhanced modulation response of injection-locked multimode VCSELs,” Opt. Exp., vol. 16, pp. 21582–21586, 2008. [10] C. Carlsson, A. Larsson, and A. Alping, “RF transmission over multimode fibers using VCSELs-comparing standard and high-bandwidth multimode fibers,” J. Lightw. Technol., vol. 22, no. 7, pp. 1694–1700, Jul. 2004.
VI. CONCLUSION In conclusion, we have proposed and demonstrated the use of a filter-assisted optical injection-locking scheme for the realization of three reconfigurable networking functions. Both single-mode and multimode VCSELs are used as the objectives for injection locking. By properly detuning the frequency spectrum of a tunable delay line interferometer, which can be simply considered as a periodic optical filter, unique transient chirp components from the OIL VCSEL can be selectively filtered. UWB-monocycle generation, data format conversion, and clock recovery are reconfigurably generated using our proposed technique.
REFERENCES [1] A. H. Gnauck and P. J. Winzer, “Optical phase-shift-keyed transmission,” J. Lightw. Technol., vol. 23, no. 1, pp. 115–130, Jan. 2005. [2] E. K. Lau, X. Zhao, H. Sung, D. Parekh, C. Chang-Hasnain, and M. C. Wu, “Strong optical injection-locked semiconductor lasers demonstrating 100-GHz resonance frequencies and 80-GHz intrinsic bandwidths,” Opt. Exp., vol. 16, pp. 6609–6618, 2008. [3] B. Zhang, X. Zhao, L. Christen, D. Parekh, W. Hofmann, M. C. Wu, M. C. Amann, C. J. Chang-Hasnain, and A. E. Willner, “Adjustable chirp injection-locked 1.55- m VCSELs for enhanced chromatic dispersion compensation at 10-Gbit/s,” in Proc. Conf. Optical Fiber Communications, OSA Technical Digest (CD) (Optical Society of America, 2008), 2008, paper OWT7. [4] J. P. Yao, F. Zeng, and Q. Wang, “Photonic generation of ultra-wideband signals,” J. Lightw. Technol., vol. 25, no. 11, pp. 3219–3235, Nov. 2007. [5] A. D. Ellis, K. Smith, and D. M. Patrick, “All optical clock recovery at bit rates up to 40 Gbit/s,” Electron. Lett., vol. 29, pp. 1323–1324, July 1993. [6] W. Hofmann, M. Gorblich, M. Ortsiefer, G. Bohm, and M. C. Amann, 3 W CW output “Long-wavelength monolithic VCSEL array with power,” Electron. Lett., vol. 42, p. 976, 2006. [7] X. Zhao, B. Zhang, L. Christen, D. Parekh, F. Koyama, W. Hofmann, M. C. Amann, A. E. Willner, and C. J. Chang-Hasnain, “Data inversion and adjustable chirp in 10-Gbps directly-modulated injection-locked 1.55- m VCSELs,” in Conference on Lasers and Electro-Optics/Quantum Electronics and Laser Science Conference and Photonic Applications Systems Technologies, OSA Technical Digest (CD) (Optical Society of America, 2008), paper CMW5. [8] R. Slavík, Y. Park, M. Kulishov, R. Morandotti, and J. Azaña, “Ultrafast all optical differentiators,” Opt. Exp., vol. 14, pp. 10699–10707, 2006.
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Bo Zhang (S’03–M’08) received the B.S. degree from Zhejiang University, China, in 2003, the M.S. degree from the University of Southern California (USC), Los Angeles, in 2005, and the Ph.D. degree from the Department of Electrical Engineering-Systems at USC in 2008. In August 2003, he joined the Optical Communications Laboratory at USC. His research interests include nonlinear optical signal processing using slow light based tunable optical delay lines and semiconductor optical amplifiers (SOAs) based high-speed wavelength converters, enabling techniques for long-haul dense wavelength division multiplexed (DWDM) transmission systems and polarization effects. He has authored and coauthored more than 50 journal and conference papers, including one book chapter and four invited papers. He is now working as a member of technical staff at Opnext subsystems (formally Stratalight Communications). Dr. Zhang is a Member of the IEEE Lasers and Electro-Optics Society (LEOS) and a Member of the Optical Society of America (OSA). He also serves as a reviewer for several IEEE and OSA journals, including Optics Letter, Optics Express, IEEE JOURNAL OF LIGHTWAVE TECHNOLOGY, IEEE PHOTONICS TECHNOLOGY LETTERS and IEEE JOURNAL OF SELECTED TOPICS IN QUANTUM ELECTRONICS. He received a Travel Grant Award from the IEEE LEOS in 2007. He is also one of the three recipients of the Dr. Bor-Uei Chen Memorial Scholarship Award from the Photonics Society of Chinese-Americans (PSC) in 2008.
Xiaoxue Zhao (S’04–M’09) received her B.S. degree in electronics from Peking University, Beijing, P.R. China, in 2003, and her Ph.D. degree in electrical engineering and computer sciences at the University of California, Berkeley in 2008. Her research interests are in high-speed modulation characteristics of diode lasers, optical injection locking of semiconductor lasers, high-speed laser design, optical communication systems and optical networks. She has co-authored more than 40 conference and journal publications, 1 book chapter, and holds 4 US patents. Dr. Zhao has served reviewer for IEEE JOURNAL TECHNOLOGY, IEEE JOURNAL OF SELECTED TOPICS ELECTRONICS, IEEE PHOTONICS TECHNOLOGY LETTERS, and Optical Communications. She is currently a networking engineer at Google Inc.
LIGHTWAVE QUANTUM Optics Express, hardware design OF ON
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Devang Parekh (S’01) received his B.S. in electrical engineering and computer sciences from the University of California, Berkeley in 2003. From 2004 to 2006, he was an electrical engineer at Space and Naval Warfare Systems Center San Diego working on RF photonics. Since 2006, he has been working toward a Ph.D. in electrical engineering and computer sciences at the University of California, Berkeley.
ZHANG et al.: OPTICAL INJECTION-LOCKED VCSELs
Yang Yue (S’07) received the B.S. degree in electrical engineering and the M.S. degree in optics from Nankai University, China, in 2004 and 2007, respectively. He is currently working toward the Ph.D. degree in the Department of Electrical Engineering, University of Southern California, Los Angeles. His current research interests include on-chip optical interconnection, photonic crystal fibers, and optic fiber communications. Mr. Yue is a student Member of the Optical Society of America (OSA).
Werner Hofmann (S’06–M’07) was born in Erlenbach, Germany, in 1978. He received his Dipl.-Ing. (M.S.) degree in electrical engineering and information technology (IT) in 2003 the Dr.-Ing. (Ph.D.) degree in 2009, both from the Technical University of Munich (Technische Universität München), Munich, Germany. Since 2003 he has been with the Walter Schottky Institute, Technical University of Munich, where he was engaged in research on InP-based vertical-cavity surface-emitting lasers (VCSELs) including design, manufacturing and characterization. In 2009 he joined the University of California, Berkeley via a postdoctoral fellowship program granted by the DAAD (German Academic Exchange Service). He has authored or co-authored some 60 articles (including several invited) in scientific journals, conference proceedings and books on long-wavelength VCSELs and their applications. Dr. Hofmann is a member of the Association of German Engineers (VDI), and a member of the IEEE Lasers and Electro-Optics Society.
Markus C. Amann received the Diploma degree in electrical engineering in 1976 and the Dr.-Ing. degree in 1981, both from the Technical University of Munich. During his thesis work, he studied superluminescent diodes and low-threshold laser diodes and developed the AlGaAs-GaAs metal-clad ridge-waveguide laser. From 1981 to 1994 he was with the Corporate Research Laboratories of the Siemens AG in Munich where he was involved in the research on long-wavelength InGaAsP-InP laser diodes. In 1994, he joined the Department of Electrical Engineering at the University of Kassel as a full professor for “Technical Electronics”. Since 1997 he holds the Chair of “Semiconductor Technology” at the Walter Schottky Institute of the Technical University of Munich, where he is currently engaged in the research on tunable laser diodes for the near infrared, quantum cascade lasers, long-wavelength vertical-cavity laser-diodes (VCSELs) and laser diode applications. In 2001, he co-founded VERTILAS GmbH, Garching, commercializing the long-wavelength VCSELs. He authored or co-authored more than 200 articles (including some 40 invited) on semiconductor optoelectronics in scientific journals and conference proceedings, and co-authored two books. In 1981 he was a recipient of the ITG-prize and in 2004 he won the Karl Heinz Beckurts-prize. He is a member of the German Informationstechnische Gesellschaft (ITG), and a Fellow of the IEEE Lasers and Electro-Optics Society.
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Connie J. Chang-Hasnain (M’88–SM’92–F’98) received the B.S. degree from the University of California, Davis in 1982, and the M.S. and Ph.D. degrees from the University of California, Berkeley, in 1984 and 1987, respectively, all in electrical engineering and computer sciences. Currently, she is the John R. Whinnery Chair Professor in the Electrical Engineering and Computer Sciences Department at the University of California, Berkeley. Her research interests include VCSELs, nano-optoelectronic materials and devices She co-authored over 390 research papers in technical journals and conferences, and six book chapters. Prof. Chang-Hasnain was named a Presidential Faculty Fellow, an NSF National Young Investigator, a Packard Fellow, a Sloan Research Fellow, a National Security Science and Engineering Faculty Fellow and a Guggenheim Fellow. She was awarded with the 2000 Curtis W. McGraw Research Award, 2003 William Streifer Scientific Achievement Award, 2005 Gilbreth Lecturer Award, and 2007 OSA Nick Holonyak Jr. Award. She is an Honorary Member of A. F. Ioffe Institute since 2005. She was an Associate Editor of the IEEE JOURNAL OF LIGHTWAVE TECHNOLOGY 2005-2006, and has been the Editor-in-Chief since 2007. She is a Fellow of the IEEE, OSA, and IEE.
Alan E. Willner (S’87–M’88–SM’93–F’04) received the Ph.D. degree in electrical engineering from Columbia University, New York, NY, in 1988. He has worked at AT&T Bell Laboratories and Bellcore. He is currently a Professor of electrical engineering at the University of Southern California (USC), Los Angeles. He has 700 publications, including two books and 24 patents. Prof. Willner has received the National Science Foundation (NSF) Presidential Faculty Fellows Award from the White House, the Packard Foundation Fellowship, the NSF National Young Investigator Award, the Fulbright Foundation Senior Scholars Award, the IEEE LEOS Distinguished Traveling Lecturer Award, the OSA Leadership Award, the USC University-Wide Award for Excellence in Teaching, the Eddy Award from Pennwell for the Best Contributed Technical Article, and the Armstrong Foundation Memorial Prize for the highest ranked EE Master’s degree graduate student at Columbia University. His research is in the area of optical communications. He is a Fellow of the Optical Society of America (OSA) and was a Fellow of the Semiconductor Research Corporation. His professional activities have included the following: President of the IEEE Lasers and Electro-Optics Society (LEOS), Editor-in-Chief of the IEEE/OSA JOURNAL OF LIGHTWAVE TECHNOLOGY, Editor-in-Chief of OSA Optics Letters, Editor-in-Chief of the IEEE JOURNAL OF SELECTED TOPICS IN QUANTUM ELECTRONICS, Co-Chair of the OSA Science and Engineering Council, General Co-Chair of the Conference on Lasers and Electro-Optics (CLEO), Chair of the IEEE TAB Ethics and Conflict Resolution Committee, General Chair of the LEOS Annual Meeting Program, Program Co-Chair of the OSA Annual Meeting, and Steering and Program Committee Member of the Conference on Optical Fiber Communications (OFC).
JOURNAL OF LIGHTWAVE TECHNOLOGY, VOL. 27, NO. 15, AUGUST 1, 2009
Reconfigurable Multifunctional Operation Using Optical Injection-Locked Vertical-Cavity Surface-Emitting Lasers Bo Zhang, Member, IEEE, OSA, Xiaoxue Zhao, Member, IEEE, OSA, Devang Parekh, Member, IEEE, Yang Yue, Student Member, IEEE, Werner Hofmann, Member, IEEE, Markus C. Amann, Fellow, IEEE, Connie J. Chang-Hasnain, Fellow, IEEE, OSA, and Alan E. Willner, Fellow, IEEE, OSA
Abstract—In this paper, we extend the system application of optical injection-locked (OIL) vertical-cavity surface-emitting lasers (VCSELs) to future optical networks by realizing multifunctional operation using a filter-assisted OIL-VCSEL scheme that can be reconfigured. By using a single chirp-adjustable injection-locked VCSEL (either single mode or multimode) followed by a tunable delay line interferometer, we experimentally demonstrate three functions, showing ultra-wide band (UWB) monocycle generation, nonreturn-to-zero (NRZ) to pseudoreturn-to-zero (PRZ) data format conversion, and NRZ-data clock recovery at 10 Gb/s. Index Terms—Clock recovery, data format conversion, optical injection locking (OIL), reconfigurable optical networks, ultrawide band, vertical cavity surface emitting laser (VCSEL).
I. INTRODUCTION
A
DESIRABLE hallmark of optical subsystems is the ability to perform various types of functions by simply adjusting one of the control parameters of a device. As an example, the basic Mach–Zehnder interferometer (MZI) structure has functional utility as an amplitude modulator, phase modulator or optical filter, depending on the bias and structural conditions [1]. Such ability to reconfigure the functionality of an optical module greatly increases its cost effectiveness. Moreover, performing any function at high speed (beyond 10 Gb/s) enhances its value in high-capacity systems. Recent literature has witnessed that optical injection locking (OIL) of a vertical-cavity surface-emitting laser (VCSEL) can produce very high-speed operation, demonstrating 100 GHz of modulation resonance frequency [2]. This structure has also exhibited the ability to produce an adjustable chirp on the output optical signal, such that the magnitude and the polarity (positive or negative frequency deviation) are both controllable [3],
[7]. Very recently, the chirp variability is shown to provide chromatic dispersion precompensation for 10 Gbit/s data signals [3]. On the other hand, ultrawideband (UWB) technology has attracted considerable interest for short-range, high-throughput wireless and sensor networks due to its high data capacity, intrinsic immunity to multipath fading, and low power consumption. UWB overfiber, which offers high data-rate service across different networks, has ignited research interest in generating UWB signal in the optical domain. Photonic generation of UWB signals has been demonstrated using either external phase modulators or semiconductor optical amplifiers via phase-to-intensity conversion, which results in monocycle or doublet pulses [4]. In the mean time, optical data-format conversion and clock recovery have been considered potentially valuable functions for interfacing future optical networks, and are realized using various nonlinear elements [5]. However, to the best of our knowledge, the above three functions have not been reported using the same basic structure in a single device that can be reconfigured. In this paper, we propose and demonstrate multifunctional operation of an injection-locked VCSEL, showing UWB-monocycle generation, data-format conversion, and clock recovery. Both single-mode and multimode VCSELs are shown to be capable of functional reconfiguration. The key mechanism is using a 10 GHz tunable interferometer to selectively filter out the unique time-resolved frequency chirp component after optical injection locking. Polarity-switchable UWB monocycles are generated with a 5.1 GHz center frequency and a fractional bandwidth of 129%. NRZ to pseudo-RZ (PRZ) format conversion is generated from either the rising or falling edge detection. Finally, a 10 GHz clock tone with a 35 dB suppression ratio is also generated from a 10 Gb/s NRZ input data signal. II. CONCEPT
Manuscript received December 09, 2008; revised February 28, 2009, March 09, 2009. Current version published July 22, 2009. This work was supported in part by the NSF ERC CIAN. B. Zhang, Y. Yue, and A. E. Willner are with the University of Southern California, Department of Electrical Engineering-Systems, Los Angeles, CA 90089 USA (e-mail: [email protected]; [email protected]; [email protected]). X. Zhao, D. Parekh, and C. Chang-Hasnain are with the University of California, Berkeley, Electrical Engineering and Computer Science, Berkeley, CA 94720 USA (e-mail: [email protected]). W. Hofmann and M. Amann are with the Walter Schottky Institute, Technical University of Munich, Am Coulombwall 3, D-85749 Garching, Germany (e-mail: [email protected]). Digital Object Identifier 10.1109/JLT.2009.2017926
Optically injection-locked (OIL) VCSEL is locked, both in frequency and in phase, to a master laser by photon injection at adjacent wavelengths. It features significantly reduced adiabatic and transient frequency chirp compared to that of a directly modulated VCSEL, as well as controllable polarity and magnitude of the dominant transient chirp after OIL [3]. This can be understood by the fact that the carrier density change and hence the index variation are greatly reduced or clamped by the injected photon from the master laser. By passing the chirped OIL-VCSEL through a delay-line interferometer (DLI), which
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Fig. 1. Concept of multifunctional generator using optical injection-locked (OIL) VCSEL followed by a delay-line interferometer (DLI). Three unique and reconfigurable functions are achieved by utilizing the adjustable chirp from the OIL-VCSEL and subsequent tunable filtering.
Fig. 2. Since VCSEL exhibits unique transient chirp in both frequency and time domain after optical injection locking, by detuning the delay line interferometer (DLI) to different positions, three unique functions labeled as (1)–(3), corresponding to the functions shown in Fig. 1, can be realized and readily reconfigured.
mainly serves as a tunable optical periodic filter, we propose in Fig. 1 the concept of generating multiple functions by simply reconfiguring the detuned positions of the DLI which selectively filters one or more of the blue-chirped, the red-chirped or the center frequency components of the OIL VCSEL. As shown in Fig. 2, the spectrum of OIL-VCSEL signal along with the associated frequency chirp is depicted. If either the blue or the red chirp is selected while the center frequency component is maintained, labeled as function (1) in blue, polarityswitchable UWB monocycles can be generated, which is envisioned to be useful in future access networks where UWB overfiber and wireless/optical convergence are emerging. If either the blue or the red chirp is selected but the center frequency is suppressed, labeled as function (2) in green, either rising or falling edges of the original data signal are detected and thus NRZ-to-PRZ format conversion can be realized. If both the blue and the red chirp are selected but the center is suppressed, labeled as (3) in red, a strong clock at the data rate can be recovered from the original data signal, which can be used for 3R regeneration or clock and data recovery. III. EXPERIMENTAL SETUP The experimental setup is shown in Fig. 3. A distributed feedback (DFB) laser serves as the master to injection lock a 1.55 mm VCSEL. Both the single-mode (SM) and multimode (MM) BTJ-LW VCSELs, with optimized high-speed design [6], are used. An optical circulator is used for unidirectional locking. The VCSEL is directly modulated at 10 Gb/s, with pseudorandom bit sequence (PRBS) NRZ data or a programmable repeated pattern. The DFB current is adjusted
Fig. 3. Experimental setup of multifunctional generator using a chirp adjustable injection-locked VCSEL followed by a tunable interferometer. A chirp-form analyzer together with a sampling oscilloscope is used to record the chirp and intensity waveforms in the time domain.
to control the power into the VCSEL. A 10 GHz all-fiber delay-line interferometer is placed after the OIL VCSEL serves as a tunable optical filter. The advantest interferometric-based chirp-form analyzer together with a digital sampling oscilloscope is used to obtain the time-resolved chirp and intensity waveforms. A 10 GHz photodiode followed by a radio-frequency spectrum analyzer (RFSA) is used to measure the RF spectrum of various generated functions. IV. TIME-RESOLVED FREQUENCY CHIRP We show in [3] the “data inversion” state that is essential to achieve dispersion tolerance enhancement. Data inversion can be understood from the fact that the locked VCSEL behaves like a gain-clamped narrowband amplifier [7]. This has been modeled and explained in [7] that a minimum reflection power occurs at the cavity transparency where the material gain is equal to the material loss. Biasing above cavity transparency, the device is in the gain regime, whereas biasing below cavity transparency the device is in the loss regime. The electrical-to-optical transfer function reveals that if the VCSEL amplifier is operated in the loss regime with a negative slope, data inversion can be achieved. It is also briefly discussed in [7] that the gain level of an OIL VCSEL amplifier is also dependent on the wavelength detuning between the master DFB and the slave VCSEL under injection locking. By further increasing the power injection ratio and adjusting the detuning value in such a way that the VCSEL amplifier is in between
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Fig. 4. Time-resolved frequency chirp measurement of OIL single-mode VCSEL under the transition state when the VCSEL amplifier is in between the gain and the loss regime. The transition state exhibits residual intensity modulation with magnitude-reduced frequency chirping, which is essential for the realization of multifunctional operation.
the gain and loss regime, we are able to achieve a “transition state” as shown in Fig. 4. This phenomenon can be understood by the fact that by increasing the wavelength detuning, the data pattern gradually goes through an evolution from a noninverted state (gain regime) to a transition state (in between gain and loss) and then to a inversion state (loss regime). As measured by the chirp-form analyzer and shown in the right-Y axis of Fig. 4, the peak-to-peak chirp magnitude is GHz compared with that of the free greatly reduced to running VCSEL, yet with unchanged polarity of the chirp compared with the data inversion state [3], even though a bit of asymmetry exists in positive and negative frequency chirping. The reason why the sign of the chirp transient stays unchanged with the data pattern is attributed to the fact that the frequency deviation follows the change of the carrier density and is only determined by the modulation of the current. We will show in the following section the use of this transient frequency chirp from an OIL VCSEL, assisted with a tunable optical filter, for the realization of reconfigurable multifunctional operation. V. EXPERIMENTAL RESULTS ON RECONFIGURABLE MULTIFUNCTIONAL OPERATION A. Polarity-Switchable UWB-Monocycle Generation The transition state, which manifests itself as having small residual intensity modulation and reduced extinction ratio, is essential for the generation of UWB monocycles. Fig. 5(a) and 5(b) are the electrical input of a 10 Gb/s NRZ data signal and the OIL VCSEL transition state, respectively. By detuning the DLI in such a way that the OIL VCSEL data spectrum is sitting on either the positive or negative slopes of the filter and thus selecting either the blue or red chirp and maintain the center frequency component, polarity-switchable optical differentiators [8] corresponding to the input signal are generated, as shown in Fig. 5(c) and 5(d). Realizing that multimode VCSELs become single mode after injection locking [9], we choose to use a multimode VCSEL with 10 m aperture and three existing transverse modes to demonstrate UWB-monocycle generation in order to
Fig. 5. Polarity-switchable differentiators (c) and (d) from positive or negative slope of the DLI using OIL single-mode VCSEL under the transition state (b).
Fig. 6. Measured polarity-switchable UWB monocycle signals using OIL multimode VCSEL. (a) One polarity UWB signal. (b) The other polarity UWB signal.
show the cost effectiveness with multimode VCSELs as well as the promising UWB overmultimode fiber access network applications [10]. After programming the input data pattern to be repeated “1000000000000000” (one “1” per 16 bits), we obtain one polarity of a UWB-monocycle waveform in Fig. 6(a) when the DLI is blue shifted by 0.04 nm relative to the center frequency of the OIL-VCSEL data signal. The upper full-width at half-maximum (FWHM) is 87 ps, while the lower is 83 ps. Fig. 6(b) shows the other polarity of the UWB monocycle when the DLI is red shifted by 0.04 nm. The 93 ps upper FWHM and 78 ps lower FWHM also exhibit a bit of asymmetry which is mainly due to the asymmetric chirp from the OIL signal, as shown in Fig. 4. Fig. 7 shows the RF spectrum of the monocycle in Fig. 6(a). The center frequency is measured to be 5.1 GHz and the 10 dB bandwidth is about 6.6 GHz (from 0.8 GHz to 7.4 GHz). This means that the generated monocycle pulse has a fractional bandwidth of 129%, which well suits the Federal Communications Commision definition of UWB signals. In addition, the frequency tone spacing is 0.625 GHz, which equals the repetition rate of the input pulse train.
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Fig. 7. RF spectrum of the UWB-monocycle of Fig. 6(a), showing 6.6 GHz bandwidth at 5.1 GHz center frequency, which corresponds to 129% fractional bandwidth. The RF tone spacing of 625 MHz reveals the repetition rate of the input periodic pulse train. Fig. 9. Eye diagrams of NRZ signal and format-converted PRZ signal from the rising-edge detection.
Fig. 8. (a) Rising-edge detection and (b) falling-edge detection of the original data pattern by further detuning the DLI spectrum away from the spectrum of the OIL-VCSEL on either side.
B. NRZ-to-PRZ Format Conversion Optical data format converters have long been considered one of the important signal processing modules for heterogeneous optical networks where edge routers need to exhibit the function to serve as an interface for different incoming modulation formats. In this subsection, we will demonstrate one type of format conversion using the filtering-assisted OIL VCSEL technique. By further detuning away either side of the DLI by 0.06 nm from the center frequency of the OIL data signal, we are able to suppress the center frequency components of the original transition state signal, and further enhance the desired chirped components. In this way, we show in Fig. 8(a) and 8(b) the detection of either the rising edge or the falling edge of the original data signal, respectively. The detected edge signal behaves like a return-to-zero (RZ) format, as compared to the original non-return-to-zero (NRZ) signal. These two types of edge-detected signals do not follow the original data pattern, and are thus called a pseudo-RZ (PRZ) signal. Fig. 9 shows the eye diagram of the original NRZ data signal and the rising-edge-detected PRZ signal, as shown in Fig. 8(a), demonstrating the capability of our proposed multifunctional generator for NRZ-to-PRZ data format conversion. This PRZ type of modulation format is useful in clock tone detection, retiming for 3R regeneration applications, and even has potential for optical logic gating.
Fig. 10. (a) Detection of both the rising and falling edges of the original data pattern by notching out the center frequency component of the OIL VCSEL with detuned DLI. (b) RF spectrum of the both edge-detected signals, showing the recovered 10 GHz clock and the 0.3 MHz tone spacing, which corresponds with the PRBS of the data signal.
C. Clock Recovery Clock recovery is one of the indispensible functions at the receiver side. Recovering the clock in the optical domain before detection has its advantage of data rate transparency and thus very high-speed operation. We will show in this section that the OIL VCSEL can also be reconfigured to achieve clock recovery at 10 Gb/s and has the potential to operate at even higher bit rates.
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Due to the spectral periodicity of the DLI, if the OIL VCSEL signal is placed at the notch of the DLI spectrum, both the blueand red-chirped components are enhanced while the center frequency component is notched out. This way, the detection of both rising and falling edges of the original 10 Gb/s NRZ data is realized and shown in Fig. 10(a). The corresponding RF spectrum is shown in Fig. 10(b), featuring a 10 GHz recovered clock dB suppression ratio and 0.3 MHz tone spacing, with a PRBS. corresponding to the original 10 Gb/s data with a One thing to note here is that the two types of PRZ signal shown in Fig. 8(a) and 8(b) can also be used to recover the clock.
[9] D. Parekh, X. Zhao, W. Hofmann, M. C. Amann, L. A. Zenteno, and C. J. Chang-Hasnain, “Greatly enhanced modulation response of injection-locked multimode VCSELs,” Opt. Exp., vol. 16, pp. 21582–21586, 2008. [10] C. Carlsson, A. Larsson, and A. Alping, “RF transmission over multimode fibers using VCSELs-comparing standard and high-bandwidth multimode fibers,” J. Lightw. Technol., vol. 22, no. 7, pp. 1694–1700, Jul. 2004.
VI. CONCLUSION In conclusion, we have proposed and demonstrated the use of a filter-assisted optical injection-locking scheme for the realization of three reconfigurable networking functions. Both single-mode and multimode VCSELs are used as the objectives for injection locking. By properly detuning the frequency spectrum of a tunable delay line interferometer, which can be simply considered as a periodic optical filter, unique transient chirp components from the OIL VCSEL can be selectively filtered. UWB-monocycle generation, data format conversion, and clock recovery are reconfigurably generated using our proposed technique.
REFERENCES [1] A. H. Gnauck and P. J. Winzer, “Optical phase-shift-keyed transmission,” J. Lightw. Technol., vol. 23, no. 1, pp. 115–130, Jan. 2005. [2] E. K. Lau, X. Zhao, H. Sung, D. Parekh, C. Chang-Hasnain, and M. C. Wu, “Strong optical injection-locked semiconductor lasers demonstrating 100-GHz resonance frequencies and 80-GHz intrinsic bandwidths,” Opt. Exp., vol. 16, pp. 6609–6618, 2008. [3] B. Zhang, X. Zhao, L. Christen, D. Parekh, W. Hofmann, M. C. Wu, M. C. Amann, C. J. Chang-Hasnain, and A. E. Willner, “Adjustable chirp injection-locked 1.55- m VCSELs for enhanced chromatic dispersion compensation at 10-Gbit/s,” in Proc. Conf. Optical Fiber Communications, OSA Technical Digest (CD) (Optical Society of America, 2008), 2008, paper OWT7. [4] J. P. Yao, F. Zeng, and Q. Wang, “Photonic generation of ultra-wideband signals,” J. Lightw. Technol., vol. 25, no. 11, pp. 3219–3235, Nov. 2007. [5] A. D. Ellis, K. Smith, and D. M. Patrick, “All optical clock recovery at bit rates up to 40 Gbit/s,” Electron. Lett., vol. 29, pp. 1323–1324, July 1993. [6] W. Hofmann, M. Gorblich, M. Ortsiefer, G. Bohm, and M. C. Amann, 3 W CW output “Long-wavelength monolithic VCSEL array with power,” Electron. Lett., vol. 42, p. 976, 2006. [7] X. Zhao, B. Zhang, L. Christen, D. Parekh, F. Koyama, W. Hofmann, M. C. Amann, A. E. Willner, and C. J. Chang-Hasnain, “Data inversion and adjustable chirp in 10-Gbps directly-modulated injection-locked 1.55- m VCSELs,” in Conference on Lasers and Electro-Optics/Quantum Electronics and Laser Science Conference and Photonic Applications Systems Technologies, OSA Technical Digest (CD) (Optical Society of America, 2008), paper CMW5. [8] R. Slavík, Y. Park, M. Kulishov, R. Morandotti, and J. Azaña, “Ultrafast all optical differentiators,” Opt. Exp., vol. 14, pp. 10699–10707, 2006.
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Bo Zhang (S’03–M’08) received the B.S. degree from Zhejiang University, China, in 2003, the M.S. degree from the University of Southern California (USC), Los Angeles, in 2005, and the Ph.D. degree from the Department of Electrical Engineering-Systems at USC in 2008. In August 2003, he joined the Optical Communications Laboratory at USC. His research interests include nonlinear optical signal processing using slow light based tunable optical delay lines and semiconductor optical amplifiers (SOAs) based high-speed wavelength converters, enabling techniques for long-haul dense wavelength division multiplexed (DWDM) transmission systems and polarization effects. He has authored and coauthored more than 50 journal and conference papers, including one book chapter and four invited papers. He is now working as a member of technical staff at Opnext subsystems (formally Stratalight Communications). Dr. Zhang is a Member of the IEEE Lasers and Electro-Optics Society (LEOS) and a Member of the Optical Society of America (OSA). He also serves as a reviewer for several IEEE and OSA journals, including Optics Letter, Optics Express, IEEE JOURNAL OF LIGHTWAVE TECHNOLOGY, IEEE PHOTONICS TECHNOLOGY LETTERS and IEEE JOURNAL OF SELECTED TOPICS IN QUANTUM ELECTRONICS. He received a Travel Grant Award from the IEEE LEOS in 2007. He is also one of the three recipients of the Dr. Bor-Uei Chen Memorial Scholarship Award from the Photonics Society of Chinese-Americans (PSC) in 2008.
Xiaoxue Zhao (S’04–M’09) received her B.S. degree in electronics from Peking University, Beijing, P.R. China, in 2003, and her Ph.D. degree in electrical engineering and computer sciences at the University of California, Berkeley in 2008. Her research interests are in high-speed modulation characteristics of diode lasers, optical injection locking of semiconductor lasers, high-speed laser design, optical communication systems and optical networks. She has co-authored more than 40 conference and journal publications, 1 book chapter, and holds 4 US patents. Dr. Zhao has served reviewer for IEEE JOURNAL TECHNOLOGY, IEEE JOURNAL OF SELECTED TOPICS ELECTRONICS, IEEE PHOTONICS TECHNOLOGY LETTERS, and Optical Communications. She is currently a networking engineer at Google Inc.
LIGHTWAVE QUANTUM Optics Express, hardware design OF ON
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Devang Parekh (S’01) received his B.S. in electrical engineering and computer sciences from the University of California, Berkeley in 2003. From 2004 to 2006, he was an electrical engineer at Space and Naval Warfare Systems Center San Diego working on RF photonics. Since 2006, he has been working toward a Ph.D. in electrical engineering and computer sciences at the University of California, Berkeley.
ZHANG et al.: OPTICAL INJECTION-LOCKED VCSELs
Yang Yue (S’07) received the B.S. degree in electrical engineering and the M.S. degree in optics from Nankai University, China, in 2004 and 2007, respectively. He is currently working toward the Ph.D. degree in the Department of Electrical Engineering, University of Southern California, Los Angeles. His current research interests include on-chip optical interconnection, photonic crystal fibers, and optic fiber communications. Mr. Yue is a student Member of the Optical Society of America (OSA).
Werner Hofmann (S’06–M’07) was born in Erlenbach, Germany, in 1978. He received his Dipl.-Ing. (M.S.) degree in electrical engineering and information technology (IT) in 2003 the Dr.-Ing. (Ph.D.) degree in 2009, both from the Technical University of Munich (Technische Universität München), Munich, Germany. Since 2003 he has been with the Walter Schottky Institute, Technical University of Munich, where he was engaged in research on InP-based vertical-cavity surface-emitting lasers (VCSELs) including design, manufacturing and characterization. In 2009 he joined the University of California, Berkeley via a postdoctoral fellowship program granted by the DAAD (German Academic Exchange Service). He has authored or co-authored some 60 articles (including several invited) in scientific journals, conference proceedings and books on long-wavelength VCSELs and their applications. Dr. Hofmann is a member of the Association of German Engineers (VDI), and a member of the IEEE Lasers and Electro-Optics Society.
Markus C. Amann received the Diploma degree in electrical engineering in 1976 and the Dr.-Ing. degree in 1981, both from the Technical University of Munich. During his thesis work, he studied superluminescent diodes and low-threshold laser diodes and developed the AlGaAs-GaAs metal-clad ridge-waveguide laser. From 1981 to 1994 he was with the Corporate Research Laboratories of the Siemens AG in Munich where he was involved in the research on long-wavelength InGaAsP-InP laser diodes. In 1994, he joined the Department of Electrical Engineering at the University of Kassel as a full professor for “Technical Electronics”. Since 1997 he holds the Chair of “Semiconductor Technology” at the Walter Schottky Institute of the Technical University of Munich, where he is currently engaged in the research on tunable laser diodes for the near infrared, quantum cascade lasers, long-wavelength vertical-cavity laser-diodes (VCSELs) and laser diode applications. In 2001, he co-founded VERTILAS GmbH, Garching, commercializing the long-wavelength VCSELs. He authored or co-authored more than 200 articles (including some 40 invited) on semiconductor optoelectronics in scientific journals and conference proceedings, and co-authored two books. In 1981 he was a recipient of the ITG-prize and in 2004 he won the Karl Heinz Beckurts-prize. He is a member of the German Informationstechnische Gesellschaft (ITG), and a Fellow of the IEEE Lasers and Electro-Optics Society.
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Connie J. Chang-Hasnain (M’88–SM’92–F’98) received the B.S. degree from the University of California, Davis in 1982, and the M.S. and Ph.D. degrees from the University of California, Berkeley, in 1984 and 1987, respectively, all in electrical engineering and computer sciences. Currently, she is the John R. Whinnery Chair Professor in the Electrical Engineering and Computer Sciences Department at the University of California, Berkeley. Her research interests include VCSELs, nano-optoelectronic materials and devices She co-authored over 390 research papers in technical journals and conferences, and six book chapters. Prof. Chang-Hasnain was named a Presidential Faculty Fellow, an NSF National Young Investigator, a Packard Fellow, a Sloan Research Fellow, a National Security Science and Engineering Faculty Fellow and a Guggenheim Fellow. She was awarded with the 2000 Curtis W. McGraw Research Award, 2003 William Streifer Scientific Achievement Award, 2005 Gilbreth Lecturer Award, and 2007 OSA Nick Holonyak Jr. Award. She is an Honorary Member of A. F. Ioffe Institute since 2005. She was an Associate Editor of the IEEE JOURNAL OF LIGHTWAVE TECHNOLOGY 2005-2006, and has been the Editor-in-Chief since 2007. She is a Fellow of the IEEE, OSA, and IEE.
Alan E. Willner (S’87–M’88–SM’93–F’04) received the Ph.D. degree in electrical engineering from Columbia University, New York, NY, in 1988. He has worked at AT&T Bell Laboratories and Bellcore. He is currently a Professor of electrical engineering at the University of Southern California (USC), Los Angeles. He has 700 publications, including two books and 24 patents. Prof. Willner has received the National Science Foundation (NSF) Presidential Faculty Fellows Award from the White House, the Packard Foundation Fellowship, the NSF National Young Investigator Award, the Fulbright Foundation Senior Scholars Award, the IEEE LEOS Distinguished Traveling Lecturer Award, the OSA Leadership Award, the USC University-Wide Award for Excellence in Teaching, the Eddy Award from Pennwell for the Best Contributed Technical Article, and the Armstrong Foundation Memorial Prize for the highest ranked EE Master’s degree graduate student at Columbia University. His research is in the area of optical communications. He is a Fellow of the Optical Society of America (OSA) and was a Fellow of the Semiconductor Research Corporation. His professional activities have included the following: President of the IEEE Lasers and Electro-Optics Society (LEOS), Editor-in-Chief of the IEEE/OSA JOURNAL OF LIGHTWAVE TECHNOLOGY, Editor-in-Chief of OSA Optics Letters, Editor-in-Chief of the IEEE JOURNAL OF SELECTED TOPICS IN QUANTUM ELECTRONICS, Co-Chair of the OSA Science and Engineering Council, General Co-Chair of the Conference on Lasers and Electro-Optics (CLEO), Chair of the IEEE TAB Ethics and Conflict Resolution Committee, General Chair of the LEOS Annual Meeting Program, Program Co-Chair of the OSA Annual Meeting, and Steering and Program Committee Member of the Conference on Optical Fiber Communications (OFC).
