Integrated Transceivers for Optical Wireless Communications

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182 IEEE JOURNAL OF SELECTED TOPICS IN QUANTUM ELECTRONICS, VOL. 11, NO. 1, JANUARY/FEBRUARY 2005Fig. 17.Eye diagram for hybrid integrated link.22 dB, which should be sufficient to allow correct operationwith large variations in link length as well as coverage at aparticular distance. Further variation might be accommodatedby controlling the transmitter power levels using received signalstrength information from the distant transceiver.In order to test the individual components in combination, theCMOS electronics was integrated with the optoelectronics usingwirebonding techniques, within a large IC package. Simple opticswas used at transmitter and receiver, and transmitter andreceiver aligned over a short distance. Fig. 17 shows an eye diagramfrom a hybrid demonstration, showing data link operationat 100 Mb/s.The link uses entirely custom components, and these resultsare the first from such a system. These are excellent results,given the added inductance and shielding problems with theseintegration techniques. We, therefore, expect the integrateddemonstrator to show much improved performance.The link demonstration uses external circuitry to provide thecontrol signals to the driver and receiver circuits, and in this preliminarywork these are set manually. A more advanced systemwould incorporate channel power control, signal strength detection,and other link management functions within the transceiverintegrated circuit. These were beyond the scope of this initialdemonstration, but the use of a commodity CMOS process offersthe possibility of such a high level of integration.IX. CONCLUSIONResults from this work show that high-performance componentswhich are optimized for free-space optical communicationscan be realized using well-developed processes and thatthese when integrated should provide transceivers with goodoverall performance. The receivers are the fastest reported forsuch high-input capacitance and show performance much beyondthat of nonoptimized commercially available components.Similarly, the detectors show lower capacitance than those availablecommercially, and modeling suggests further substantialgains are possible.They also show that there are significant challenges for opticalwireless, perhaps the major one being scalability. As a firstestimate, assuming that each transceiver has a 90 field of view(FOV) in all directions and each cell has a 4.5 FOV, approximately200 channels would be required. This is largely due todetector capacitance and the need to limit this by fabricatingsmall detectors. At present, the receiver circuits that we havedesigned are not scalable, in that the transimpedance amplifiershave a slightly larger area than the detectors, especially when includingspace for the flip-chip bonding pads. The developmentof detectors with lower capacitance per unit area and the use ofa finer feature size CMOS process should allow the fabricationof channel electronics beneath the optoelectronic emitter or detectorfootprint and an increase in the FOV covered with eachchannel. While these represent significant technical challenges,the basic approach that we have taken should allow scaling to thelarge number of channels that an indoor transceiver will require.This work has demonstrated gigabit-per-second operation ofa high-input capacitance receiver, which is far in excess of thatavailable using current wireless LAN standards. As the additional“cost” of an optical channel is small, data rates can beincreased at the cost of detector size, and preliminary simulationsshow that with the further optimization of receivers anddetector structures this approach should be scalable to gigabitper-secondchannel capacities with large numbers of detectors.ACKNOWLEDGMENTThe authors would like to thank G. Hill, C. Roberts,J. Roberts, and C. Button for growing and processing theoptoelectronic devices.REFERENCES[1] A. M. Street, P. N. Stavrinou, D. C. Obrien, and D. J. Edwards, “Indooroptical wireless systems—A review,” Opt. Quantum Electron., vol. 29,pp. 349–378, 1997.[2] J. B. Carruthers and J. M. Kahn, “Angle diversity for nondirected wirelessinfrared communication,” IEEE Trans. Commun., vol. 48, no. 6, pp.960–969, Jun. 2000.[3] J. M. Kahn, R. You, P. Djahani, A. G. Weisbin, B. K. Teik, and A. Tang,“Imaging diversity receivers for high-speed infrared wireless communication,”IEEE Commun. Mag., vol. 36, no. 12, pp. 88–94, Dec. 1998.[4] P. Djahani and J. M. Kahn, “Analysis of infrared wireless links employingmultibeam transmitters and imaging diversity receivers,” IEEETrans. Commun., vol. 48, no. 12, pp. 2077–2088, Dec. 2000.[5] D. Wisely and I. Neild, “A 100 Mbit/s tracked optical wireless telepoint,”in Proc. IEEE Int. Symp. Personal, Indoor and Mobile Radio Communications’97, vol. 3, pp. 964–968.[6] D. O’Brien, G. Faulkner, and F. P. Parand, “A cellular tracked opticalwireless link,” IEE Proc.—J, Optoelectron., vol. 150, pp. 490–496, 2003.[7] D. C. O’Brien, A. M. Street, K. Samaras, D. J. Edwards, G. Faulkner, G.Patry, P. N. Stavrinou, K. H. Tang, C. C. Teo, and M. Whitehead, “Smartpixels for optical wireless applications,” in Spatial Light Modulators,ser. OSA Trends in Optics and Photonics. Washington, DC: Opt. Soc.Amer., 1997, vol. 14, pp. 265–271.[8] F. Mederer, M. Grabherr, F. Eberhard, I. Ecker, R. Jager, J. Joos, C. Jung,M. Kicherer, R. King, P. Schnitzer, H. Unold, D. Wiedenmann, and K.J. Ebeling, “High performance selectively oxidized VCSELs and arraysfor parallel high-speed optical interconnects,” in Proc. Electronic Componentsand Technology Conf. 2000, 2000, pp. 1242–1251.[9] E. F. Schubert, N. E. J. Hunt, R. J. Malik, M. Micovic, and D. L. 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O’BRIEN et al.: INTEGRATED TRANSCEIVERS FOR OPTICAL WIRELESS COMMUNICATIONS 183[11] H. De Neve, J. Blondelle, R. Baets, P. Demeester, P. Van Daele, andG. Borghs, “High efficiency planar microcavity LED’s: Comparison ofdesign and experiment,” IEEE Photon. Technol. Lett., vol. 7, no. 3, pp.287–289, Mar. 1995.[12] D. C. O’Brien, G. E. Faulkner, E. B. Zyambo, K. L. Jim, D. J. Edwards,M. Whitehead, P. N. Stavrinou, G. Parry, J. Bellon, M. J. N.Sibley, V. A. Lalithambika, V. Joyner, R. Samsudin, D. M. Holburn,and R. J. Mears, “High speed integrated optical wireless transceiversfor in-building optical LANs,” Proc. SPIE, Optical Wireless CommunicationsIII, vol. 4124, pp. 104–115, 2000.[13] M. Dixon and J. L. Hokanson, Optical Fiber Communications. NewYork: Academic, 1991.[14] J. Zucker and R. B. Lauer, “Optimization and characterization of highradianceAl,GaAs double-heterostructure LED’s for optical communicationsystems,” IEEE Trans. Electron Devices, vol. ED-25, no. 2, pp.193–198, Feb. 1978.[15] R. H. Dean and C. J. Neuse, “Arefined step-recovery technique for measuringminority carrier lifetimes and related parameters in asymmetricp-n junction diodes,” IEEE Trans. Electron Devices, vol. ED-18, no. 3,pp. 151–158, Mar. 1971.[16] M. Uhle, “The influence of source impedance on the electroopticalswitching behavior of LEDs,” IEEE Trans. Electron Devices, vol.ED-23, pp. 438–441, 1976.[17] D. M. Holburn, V. A. Lalithambika, R. J. Samsudin, V. M. Joyner, R. J.Mears, J. Bellon, and M. J. Sibley, “Integrated CMOS transmitter driverand diversity receiver for indoor wireless links,” Proc. SPIE, OpticalWireless Communications V, vol. 4873, pp. 13–21, 2002.[18] V. A. Lalithambika, V. M. Joyner, D. M. Holburn, and R. J. Mears, “Developmentof a CMOS 310 Mb/s receiver for free-space optical wirelesslinks,” Proc. SPIE, Optical Wireless Communications III, vol. 4214, pp.133–143, 2001.[19] M. Nakamura, N. Ishihara, and Y. Akazawa, “A 156-Mb/s CMOS opticalreceiver for burst-mode transmission,” IEEE J. Solid-State Circuits,vol. 33, no. 8, pp. 1179–87, Aug. 1998.[20] J. B. Carruthers, “Multipath channels in wireless infrared communications:Modeling, angle diversity and estimation,” Ph.D. dissertation,Univ. California, Berkeley, 1997.[21] V. Joyner, “Integrated circuit design for wireless network receivers,”Ph.D. dissertation, Univ. Cambridge, Cambridge, U.K., 2003.[22] D. C. O’Brien, G. E. Faulkner, E. B. Zyambo, D. J. Edwards, P. N.Stavrinou, G. Parry, J. Bellon, M. J. N. Sibley, V. A. Lalithambika, V.Joyner, R. Samsudin, D. M. Holburn, and R. J. Mears, “Flip-chip integratedoptical wireless transceivers,” in Proc. SPIE, Optical WirelessCommunications V, vol. 4873, 2002, pp. 23–29.Dominic C. O’Brien received the M.A. and Ph.D. degrees from theDepartment of Engineering, University of Cambridge, Cambridge, U.K. in1991 and 1993, respectively.He is a currently a Lecturer in engineering science at the University ofOxford, Oxford, U.K., where he leads the Optical Wireless CommunicationsGroup. From 1993 to 1995, he was a NATO Fellow at the OptoelectronicComputing Systems Center, University of Colorado. He is the author orcoauthor of approximately 70 publications or patents in the area of opticsand optoelectronics. His research interests are focused on the field of opticalwireless systems, including integrated transceiver components for high-speednetworks, retroreflecting transceivers, optical channel characterisation, andaspects of optoelectronic component integration.Grahame E. Faulkner received the B.Sc. degree (with honors) in physicsand microelectronics from Oxford Brookes University, Oxford, U.K.He is currently a Research Assistant in the Department of Engineering Science,Oxford University, Oxford. He has coauthored several papers in the fieldof optical wireless communications, optical interconnects, and optoelectronicintegration.Emmanuel B. Zyambo, photograph and biography not available at the time ofpublication.David J. Edwards, photograph and biography not available at the time of publication.Paul Stavrinou, photograph and biography not available at the time of publication.Gareth Parry is a Professor of applied physics at Imperial College, London,U.K. Prior to taking up this appointment, he was the Rank Foundation Chair inElectro-Optic Engineering at Oxford University, Oxford, U.K., and a Professorof electronic engineering at University College London. His research interestsinclude semiconductor optoelectronic devices and their application in communicationand interconnect.He is a Fellow of the IEE, Fellow of Institute of Physics and Fellow of theRoyal Academy of Engineering.Jacques Bellon, photograph and biography not available at the time ofpublication.Martin J. Sibley received the B.Sc.(Hons.) degree in electrical engineeringand the Ph.D. degree from Huddersfield Polytechnic, Huddersfield, U.K., in1981 and 1984, respectively.From 1981-1984, he remained at Huddersfield where he was sponsored byBritish Telecom Research Laboratories to research the design of common-collectorinput preamplifiers for use in optical receivers. This work led to the firstpreamplifier design in ic. He is now a Reader at the University of Huddersfield,where his research interests include pulse position modulation, preamplifier designfor optical receivers, optical wireless LANs ,and free-space optical links.Dr. Sibely was awarded the Marconi Premium from the Institute of Electronicand Radio Engineers for the best engineering paper published in their Proceedingsin1985.Vinod A. Lalithambika received the M.Phil. and Ph.D. degrees from the Universityof Cambridge, Cambridge, U.K. He was a Malaysian CommonwealthScholar at the University of Cambridge from 2001 to 2002.His research interests include opto-electonic integrated circuits, RF circuitdesign, cipolar and CMOS circuit design.Valencia M. Joyner received the S.B. and M.Eng. degrees in electrical engineeringand computer science from the Massachusetts Institute of Technology,Cambridge, MA, in 1998 and 1999, respectively. She is currently working towardthe Ph.D. degree in the Department of Engineering, University of Cambridge,Cambridge, U.K., where her research focus is on the design of highfrequency receiver ICs in CMOS for optical wireless networks.In 1998, she was an intern at Toshiba Corporation, Yokohama, Japan, whereshe worked on sense amplifier architectures for high-speed SRAM chips.Ms. Joyner is a Marshall Scholar and a National Science Foundation GraduateResearch FellowRina J. Samsudin received the B.Sc. degree in electrical engineering fromthe Massachusetts Institute of Technology, Cambridge, MA, in 1999, and theM.Phil. and Ph.D. degrees from Cambridge University, Cambridge, U.K., in2001 and 2004 respectively.David M. Holburn received the B.A. degree in electrical sciences and thePh.D. degree in electrical engineering from the University of Cambridge,Cambridge, U.K., in 1975 and 1979, respectively.From 1979 to 1986, he worked first as a Research Associate in Microelectronics,then as Lecturer in Computer Science at Westfield College, Universityof London, London, U.K., where he has been a Senior Lecturer in the UniversityEngineering Department since January 1986.He is a Member of the Institution of Electrical Engineers and a CharteredEngineer.Kalok Jim, photograph and biography not available at the time of publication.Robert J. Mears, photograph and biography not available at the time ofpublication.
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