Three-dimensional mems photonic cross-connect switch ... - IEEE Xplore

IEEE JOURNAL OF SELECTED TOPICS IN QUANTUM ELECTRONICS, VOL. 9, NO. 2, MARCH/APRIL 2003

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Three-Dimensional MEMS Photonic Cross-Connect Switch Design and Performance Xuezhe Zheng, Senior Member, IEEE, Volkan Kaman, Member, IEEE, Shifu Yuan, Senior Member, IEEE, Yuanjian Xu, Member, IEEE, Olivier Jerphagnon, Member, IEEE, Adrian Keating, Member, IEEE, Robert C. Anderson, Henrik N. Poulsen, Bin Liu, Member, IEEE, James R. Sechrist, Chandrasekhar Pusarla, Roger Helkey, Senior Member, IEEE, Daniel J. Blumenthal, Fellow, IEEE, and John E. Bowers, Fellow, IEEE

Abstract—Photonic cross-connects (PXC) play a key role in alloptical transparent networks. In this paper, the optical design and modeling of a three-dimensional microelectromechanical system (3-D MEMS) based optical switch are discussed. Basic design rules and considerations are reviewed and used to determine the optimum configuration for free-space optical switches with more than 300 ports. The optical performance of a 256 256 PXC system, including a 347 347 nonblocking core switch and auxiliary 2 2 optical switches for 1 : 1 protection and optical taps for power monitoring, is presented. The core switch has 1.4-dB median insertion loss, 1.5-dB wavelength dependent loss across a broadband of 1260–1625 nm, and a typical polarization dependent loss of 0.1 dB. Environmental tests including temperature and vibration are described. Index Terms—Optical switches, photonic cross-connects (PXC), three-dimensional microelectromechanical system (3-D MEMS), transparent optical networks.

I. INTRODUCTION

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ITH the need for lower cost and higher capacity long-haul and metro area networks, all-optical (OOO) switching has recently emerged as the alternative to electronic (OEO) switching in realizing OOO networks [1], [2]. This is especially important for metro access networks to achieve bit rate and wavelength transparency for future upgrades as time division (TDM) and wavelength division multiplexing (WDM) technologies are enhanced. In contrast to OEO-based switching nodes utilizing bit rate dependent transponders at the input and output, photonic cross-connects (PXC) are scalable to higher port counts in a more compact footprint with less power consumption and considerably reduced network management and costs. The PXC not only provides optical interconnection between multiple interoffice fiber rings as well as simple wavelength add/drop functions, but also allows for reconfigurable routings and efficient recovery capabilities in mesh architectures [3], [4]. The optical characteristics of the PXC are especially important in an all-optical network where the optical signal needs

Manuscript received October 30, 2002; revised February 3, 2003. X. Zheng, V. Kaman, S. Yuan, Y. Xu, O. Jerphagnon, A. Keating, R. C. Anderson, J. R. Sechrist, C. Pusarla, R. Helkey, D. J. Blumenthal, and J. E. Bowers are with Calient Networks, Goleta, CA 93117 USA (e-mail: [email protected]). H. N. Poulsen and B. Liu were with Calient Networks, Goleta, CA 93117 USA. They are now with the Department of Electrical and Computer Engineering, University of California, Santa Barbara, CA 93106 USA. Digital Object Identifier 10.1109/JSTQE.2003.813321

to be routed through several switching nodes and fiber spans before it reaches its destination for electronic processing. Therefore, a PXC requires low, stable, and uniform insertion loss over a very broad wavelength range under different operating conditions and minimal degradation of the signal-to-noise ratio (SNR) from PDL, return loss, optical crosstalk, group velocity dispersion (GVD), and polarization mode dispersion (PMD). A PXC that can support all of these optical parameters is also transparent to potential future network upgrades, such as operation in different wavelength bands and data formats, and higher bit rates. Recently, large-scale optical switches based on three-dimensional microelectromechanical systems (3-D MEMS) have been proposed as the technology choice for these applications and switch size has surpassed 200 ports [5]–[8]. In this paper, we present a 347 347 nonblocking core switch as well as a 256 256 nonblocking PXC, which consists of the MEMS-based optical core switch module and auxiliary 2 2 optical switches for 1 : 1 protection and optical taps for power monitoring, as shown in Fig. 1(a). Due to the transparency of the core switch and a modular design approach of the PXC, additional functionalities can be implemented by adding modules around the transparent core for different network applications, such as optical performance monitoring, amplification, wavelength multiplexing and demultiplexing, wavelength conversion, and regeneration, without having to replace the core switch. The optical design and modeling of the 3-D MEMS core switch is discussed in Section II. The optical performance and characteristics of the core switch and the PXC will be presented in Section III followed by its environmental performances in Section IV. II. THREE-DIMENSIONAL MEMS-BASED OPTICAL CORE SWITCH DESIGN AND MODELING For low-loss switching of the signal light from one fiber to another, a pair of MEMS mirrors and collimators is required to achieve alignment of the output beam position and angle with the output optical fiber [9]. The light beam from the input fiber is collimated by a lens and incident to the first MEMS mirror, which steers the beam to a second MEMS mirror. The second mirror then adjusts the beam pointing to match the acceptance angle set by the output fiber and its collimating lens. The optical switch design requires careful analysis of the switch geometry, fiber collimator, and MEMS mirror.

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Fig. 1. (a) PXC configuration with core optical switch, 2 2 protection switches, and monitor taps. (b) General model for fiber-to-fiber coupling with MEMS mirrors, where d is the distance from the fiber to the collimator lens, S is distance from the lens and the beam waist, L is the path length, and w is the beam waist after the lens.

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A. General Model for Fiber-to-Fiber Switching In a transparent network, it is likely that an optical signal will traverse a number of switching nodes and optical amplifiers. In order to maintain a high optical signal-to-noise ratio (OSNR), it is imperative to reduce the number of optical amplifiers by minimizing the optical switch loss. Therefore, the overriding design goal for an optical switch is to minimize its optical loss. As shown in Fig. 1(b), a simplified but general configuration can be used to model the insertion loss of any fiber-to-fiber coupling regardless of the real geometric details. In the situation analyzed here, the MEMS mirrors have equal areas and effective location relative to the nearest collimator, although the model allows the areas and distances to be unequal. Since the beam out of a single mode fiber is approximately a Gaussian mode, Gaussian mode theory can be used to calculate beam propagation. Most importantly, the coupling efficiency (or the overlap integral) of the optical field distributions can be calculated at any position between the two fibers by propagating both the input and output fiber modes to that location [10], [11]. Low coupling loss is achieved by matching the beam (propagating in the free-space system) to the mode of the output fiber. The key parameters for low loss are collimator quality, link length uniformity, and sufficiently large mirror size. Assuming negligible beam clipping at both the collimating lens and the MEMS mirrors, the beam propagation in the system can be described by the waist location and beam waist size as follows: (1)

(2)

is the original beam waist radius, is the focal length where of the collimator lens, and is the distance of the original beam waist to the lens. For a symmetric input and output design, the lowest loss occurs when is half of the average lens–lens link length. B. Design Considerations For any given specific lens–lens link length (for an input and output fiber connection), there exists a pair of optimum and values that can always have matched modes and, therefore, achieve low loss. However, in order to perform optical switching, the same output and input fibers are also required to be able to make connections of different link lengths with multiple other input and output fibers. Therefore, the specific connection optimized and pair will not be optimum for other links resulting in higher loss paths. This difference in path lengths produces an inherent loss mechanism, that depends on the switch geometry. Given the same mirror deflection capability, smaller average path length with larger variation is the case for smaller switches such as 16 16, whose losses are more affected by the path length variation. While for larger switches, such as 256 256, the average path length is bigger but its relative variation and its effect on loss becomes smaller. From a link length uniformity point of view, one might conclude that it will have better loss performance by simply using longer focal length to achieve mode matching. Unfortunately, the dominant loss mechanism

ZHENG et al.: 3-D MEMS PHOTONIC CROSS-CONNECT SWITCH DESIGN AND PERFORMANCE

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Fig. 2. Vibration sensitivity of the optical switch with different path lengths. The curve with dot marker shows the lens focal length used for loss calculation. The curves with triangle, rectangle, and diamond markers show the loss variation for mirror deflection angle change of 0.01 , 0.02 , and 0.05 , respectively, due to vibration.

becomes the lens focal length uniformity in this case. In addition, long path lengths make the switch more sensitive to mirror angle and temperature variations. The calculated link loss variation due to vibration-induced MEMS mirror deflection changes (without including clipping losses) is shown in Fig. 2. In these calculations, the lens focal length is the minimum that can achieve beam waist at the middle of the link. Since clipping losses will further increase the loss in longer path lengths, it is evident that the loss change due to vibration-induced mirror deflection changes larger than 0.02 will be significant. Thus, the optimum design point is the minimum lens focal length that produces acceptably low optical loss and the maximum possible mirror deflection to minimize the optical path length. The optimum values of and are found using two-dimensional (2-D) minimization of loss, assuming a 1% lens variation. The collimator lens quality is also critical in minimizing link insertion loss since 1/20th wave of aberration can cause losses as high as 0.5 dB [12]. Even though GRIN lenses have very low aberration, it is difficult to make compact GRIN lens arrays. Diffractive lenses have high chromatic aberration that causes high wavelength-dependent loss and should be used for only narrowband designs. On the other hand, refractive micro lenses are the best choice for large scale and low loss over a broad wavelength range. Both silicon and glass micro lenses can be used for the telecom wavelength range (1260–1650 nm). However, for the same insertion loss target, the lens shape accuracy requirement varies for different materials as a function of their refractive indices. Assuming that at a wavelength of 1.5 m, 0.5-dB insertion loss is allowed, then the lens shape errors are about 150 nm [root mean squared (rms)] and 30 nm (rms) for glass (with refractive index of 1.5) and silicon lenses, respectively [12]. The overlap integral of the optical field at the output fiber with the fiber mode gives the insertion loss of the link. As stated

before, the coupling of a Gaussian mode fiber with the optical field distribution can be calculated anywhere in the path by propagating both the input and output fiber modes to that location. When the mirror effective size is close to the beam size, scalar diffraction modeling is required for accurate modeling. However, a 2-D diffraction beam propagation calculation for every beam propagation step is very lengthy for a path with two lenses and mirrors, especially for the design of a large-port count switch and all the possible link combinations. As discussed briefly in the preceding section, clipping at the MEMS mirror is another loss source and, therefore, the mirrors should be designed as large as possible, so low-loss switches should be designed such that lens clipping and aberration are negligible, which will allow one-step diffraction calculations to be used. With the one-step diffraction method, the optical field distribution at the first MEMS mirror is obtained by propagating the beam from the input fiber through a thin lens using the Gaussian beam parameters of (1) and (2). By applying 2-D diffraction, the beam is propagated to the output MEMS mirror and its optical field distribution is given by

(3) is the distance between the two mirrors and is where the effective aperture of the first MEMS mirror. The coupling efficiency can then be calculated by the overlap integral at the second MEMS mirror

(4)

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Fig. 4. Theoretical loss distribution at 1310 nm of a 300 port nonblocking switch. Fig. 3. Switch configuration using 3-D MEMS.

where is the effective aperture of the output MEMS mirror is the optical field distribution by propagating and and the output fiber mode to the output MEMS mirror, while are the mode distributions for the input and output fibers, respectively. The coupling loss in decibels can then be written as (5) The one-step diffraction method has been found to match a 2-D diffraction beam propagation calculation for lens clipping of 1.5 (defined as lens aperture divided by the beam diameter). C. Optimum Configuration Based on the preceding discussion, the optical switch configuration shown in Fig. 3 was optimized, resulting in excellent optical performance. The switch fabric consists of an input fiber array, an input lens array, two parallel MEMS mirror arrays in 3-D space, an output lens array, and an output fiber array. Each input fiber directs light to a mirror on the input array while the input mirror steers the optical beam to any output mirror, which, in turn, steers the light to an output fiber. Due to the symmetrical design, both input and output mirrors require the same deflection capability. Uniform lens arrays with optimized focal length are used to collimate the beams in and out of the arrays of fibers. A 15 mirror deflection allowed the path length to be kept 4.5 and 5 cm, with an average mirror–mirror separation of 26.9 mm and a lens focal length of 1.71 mm. Greater than 300-port nonblocking switching operation was achieved, with predicted insertion loss less than 1.8 dB at 1310 nm (including measured mirror reflectivity of 91%–95% for different incident angles and 0.5-dB collimator loss), assuming a lens variation %. Fig. 4 shows its theoretical loss distribution with an average loss of 1.3 dB, plotted as a histogram of the loss corresponding to each fiber–fiber connection. The measured optical performance of this 3D-MEMS switch will be described in detail in Section III. III. PXC SYSTEM AND OPTICAL PERFORMANCE For the PXC to present itself as a noninvasive switching solution for optical networks, the transparency of the optical

switch needs to be verified in wavelength and bit rate operation. There are several optical parameters that need to be analyzed, including WDL, PDL, return loss, directivity, optical crosstalk, GVD, and PMD. In this section, the optical performance of the 347-port nonblocking MEMS core switch as well as the 256-port PXC system, which includes the optical core switch and modular input and output line cards, will be discussed. The fundamental optical parameter that needs to be measured is the insertion loss for all the possible input-to-output combinations. As it was discussed in the preceding section, the optical core switch introduces a mean insertion loss of 1.4 dB at 1310 nm [Fig. 5(a)]. A mean loss of 4.3 dB is achieved for the full PXC [Fig. 5(b)]. The extra loss in the PXC is mainly due to the 2 2 protection switches, the optical tap couplers and the connector loss between the modules, as shown in Fig. 1(a). The loss variation at 1.3 or 1.55 m of all connections in the PXC is within 2 dB, and this distribution has been tightened to within 0.5 dB both by employing variable optical attenuators in the interface cards and by tilting the mirrors, which increases loss through the switch by misaligning the mirrors from their optimum angle [13]. The experimental loss is in good agreement with the calculated loss, as the real experimental loss is convolved with a measurement accuracy of about 0.5 dB due to random mate loss of MPX connectors during calibration and measurement. PDL of the PXC system is typically less than 0.1 dB at 1550 nm with a maximum of less than 0.3 dB. The loss distribution of (a) and (b) includes the effect of PDL, as the polarization of the 347 input signals is random, and thus, some of the input signals have polarized in the highest loss polarization states of the switch. In providing an optical switching node capable of operating in the current 1310 nm and C-band WDM networks to the L-band and next generation S-band, it is imperative that the PXC has very low wavelength dependence. The use of metal mirrors for switching allows a wide optical bandwidth from 1260 to 1625 nm (Fig. 6). The wavelength dependent loss variation in this window is less than 1 dB, which is achieved by optimized antireflection coatings of dielectric interfaces within the switch, including the lenses and glass covers sealing each MEMS array. The wavelength dependent loss for different connections due to the angular tilt of the MEMS mirrors is very small. Fig. 6 also


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Fig. 6. Core switch and PXC system wavelength dependent loss.

(a)

Fig. 7. PXC system return loss at 1310 nm for both input and output ports.

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Fig. 5. Measured PXC system insertion loss distribution. (a) 347 347 nonblocking core optical switch loss distribution. (b) 256 256 port PXC system loss distribution including two 2 2 switches for 1 : 1 protection and optical taps for power monitoring.

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shows the wavelength dependence of the whole PXC for a typical path with less than 1.5-dB variation in the same window of operation. The loss peak at 1385 nm and the slightly higher loss variation are a consequence of the OH absorption and wavelength dependent loss in some components added to the core switch. It should be noted that the measured loss variation for the PXC in the 1460–1620-nm window (S, C, and L bands) is less than 0.5 dB. System return loss, directivity, which is defined as the fraction of unwanted power transferred from an input port to any other input port, and optical crosstalk are also important parameters that need to be minimized in order to maintain optical signal integrity. The return loss is dominated by the fiber collimator back reflection and is independent of the connection, which means that only 256 return loss measurements are needed for a 256 256 PXC system. The return loss measured at 1310 nm for the core switch shows all ports performing better than 40 dB (Fig. 7), while the directivity is less than 70 dB. In order to prevent any interference beat noise and degraded OSNR between signals of different paths, it is necessary to achieve very low optical crosstalk, or high-channel isolation. Since the mea-

sured core switch static crosstalk is less than 60 dB, which is primarily dominated by the adjacent ports, optical crosstalk is not an issue even in a system where all the input ports are fully loaded. Dynamic crosstalk of 30 dB has been observed when setting up connections. This dynamic crosstalk is eliminated using the 2 2 protection switches to disable input light when setting up a connection. Finally, bit-rate transparency through the PXC system is desirable since data rate upgrades to 40 Gbit/s or higher is expected in future optical networks. The short length of total optical fiber in the PXC system as well as the core switch design result in negligible GVD ( 0.5 ps/nm) and PMD ( 0.1 ps). Bit error rate (BER) measurements at 40 Gbit/s indicate that no optical power penalty was induced by the PXC (O/O Card and Switch) compared to back-to-back with no PXC for several different connections (Fig. 8), which has been verified for many connections. IV. PXC ENVIRONMENTAL PERFORMANCE The optical path span through the PXC switch fabric is subject to environmental changes such as temperature and vibration. An important requirement of a PXC is its ability to maintain stable optical loss for varying operating conditions, such as external temperature and vibration effects. In order to investigate the effects of temperature, the core switch was placed in a chamber and the temperature was varied from 5 C–50 C over a two-day period. All 32 paths measured showed less than 0.2-dB loss variation while changing temperature conditions

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Fig. 8. PXC performance for 40 Gbit/s RZ signal transmission. (a) BER with (O/O Card and Switch) and without PXC system (Back-to-Back). (b) Eyediagram before (upper) and after (lower) the PXC system.

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(b) Fig. 10. PXC system vibration performance. (a) 0.3-dB loss variation due to 0.1 G operation vibration at the rack resonant frequency 8 Hz. Samples 1, 2, and 3 represent the paths with small, medium and large deflection angles, respectively. (b) PXC connection power drop due to shock impulse at 3 G with 11-ms duration is about 0.3 dB.

Fig. 9. PXC system temperature performance. Thirty-two paths were monitored for 5 C–50 C temperature cycle in a two-day period.

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(Fig. 9) (using closed-loop feedback on the output light to maintain the optimum mirror alignment). The very low temperature sensitivity of the PXC is key for long-term stability under unpredictable operating conditions. Since the optical switching mechanism is based on mechanically actuated mirrors in two planes, the vibration-induced loss stability is another critical issue. Vibration instabilities can be as a result of building vibrations (such as elevators, sliding doors, ventilation systems, etc.) and vibrations within the switch rack itself. External vibrations can range in frequency from fractions of hertz (discrete events, such as line card insertion) up to hundreds of hertz (continuous events, such as ventilation systems). Operation vibration and shock tests based on Telcordia GR-63 were applied to the PXC system to investigate its vibration performance. For office vibration, a 0.1-G amplitude sinusoidal

sweep was applied to all three axes of the PXC from frequencies ranging from 5 to 100 Hz. The sweep rate was 0.25 Hz/s to match the data acquisition rate. The maximum loss variation is found to be at a vibration frequency of 8 Hz, which is the resonant frequency of the rack that holds the core switch, the line cards and other control cards. A subsequent test dwelling at 8 Hz revealed power variations for links with different mirror deflection angles (small, medium and large) in the switch as shown in Fig. 10(a), for 2 small deflection, 8 medium deflection, and 15 large deflection of the mirrors. It shows a maximum power variation of 0.25 dB even for large-deflection-angle paths. The PXC shock performance was also tested with a 3-G and 11 ms duration half-sine shock pulse. A power drop of only 0.3 dB is observed [Fig. 10(b)]. The observed vibration sensitivity is consistent with that predicted for mirror movement, while structural analysis of the package indicates that the mechanical alignment of other optical components does not play a significant role in vibration sensitivity. MEMS shock


reliability was further investigated by shocking the MEMS die three times for all three axes. No mirror failure was found until a 400-G and 3-ms duration shock was applied, which caused one mirror to break at the hinge when the shock was applied perpendicular to the mirror direction. The PXC shows adequate performance to sustain operational vibration at a central office environment. V. CONCLUSION A 3-D MEMS-based 347 347 core switch and a 256 256 PXC system with excellent optical characteristics, including low loss ( 7 dB), low-wavelength dependence ( 1.5 dB within 1260–1625 nm) and bit-rate transparency for all-optical networks is presented. The PXC performance also demonstrated stable operation over a wide range of temperatures and office vibration and shock impulse. REFERENCES [1] M. A. Bourouha, M. Bataineh, and M. Guizani, “Advances in optical switching and networking: Past, present, and future,” in Proc. IEEE SoutheastCon, 2002, pp. 405–413. [2] A. Neukermans, “MEMS technology for optical interconnect and networking applications,” in Proc. LEOS, vol. 2, 2001, pp. 732–733. [3] Y. Liang, H. Dai, J. Pan, X. Wang, and D. Zhang, “Penalty-free 10Gb/s transmission through a cascade of all optical cross-connects,” Proc. SPIE, vol. 4583, pp. 171–177, 2001. [4] R. D. Doverspike, S. Phillips, and A. R. Westbrook, “Future transport network architectures,” IEEE Commun. Mag., vol. 37, pp. 96–101, Aug. 1999. [5] T.-W. Yeow, K. L. E. Law, and A. Goldenberg, “MEMS optical switches,” IEEE Commun. Mag., vol. 39, pp. 158–162, Nov. 2001. [6] V. A. Aksyuk, S. Arney, N. R. Basavanhally, D. J. Bishop, C. A. Bolle, C. C. Chang, R. Frahm, A. Gasparyan, J. V. Gates, R. George, C. R. Giles, J. Kim, P. R. Kolodner, T. M. Lee, D. T. Neilson, C. Nijander, C. J. Nuzman, M. Paczkowski, A. R. Papazian, R. Ryf, H. Shea, and M. E. Simon, “238 238 surface micromachined optical crossconnect with 2 dB maximum loss,” in Tech. Dig. OFC, 2002, postdeadline paper PD-FB9. [7] J. E. Bowers, “Photonic cross-connects,” in Proc. OSA Tech. Dig., Photonics in Switching, 2001, p. 3. [8] R. Helkey, S. Adams, J. Bowers, T. Davis, O. Jerphagnon, V. Kaman, A. Keating, B. Liu, C. Pusarla, Y. Xu, S. Yuan, and X. Zheng, “Design of large scale, MEM’s based photonic switches,” Opt. Photon. News, pp. 40–43, 2002. [9] A. Neukermans and R. Ramaswami, “MEMS technology for optical networking applications,” IEEE Commun. Mag., vol. 39, pp. 62–69, Jan. 2001. [10] H. Kogelnik, “Coupling and conversion coefficients for optical modes,” in Proceedings of the Symposium on Quasi-Optics. ser. Polytechnic Institute Microwave Research Institute Symposia, J. Fox, Ed. Brooklyn, NY: Polytechnic Brooklyn, 1964, vol. 14, pp. 335–347. [11] S. Yuan and N. A. Riza, “General formula for coupling loss characterization of single mode fiber collimators by use of gradient-index rod lenses,” Appl. Opt., vol. 38, pp. 3214–3222, 1999. [12] R. E. Wagner and W. J. Tomlinson, “Coupling efficiency of optics in single-mode fiber components,” Appl. Opt., vol. 21, pp. 2671–2688, 1982. [13] R. Ryf, D. T. Neilson, P. R. Kolodner, J. Kim, J. P. Hickey, D. Carr, V. Aksyuk, D. S. Greywall, F. Pardo, C. Bolle, R. Frahm, N. R. Basavanhally, D. A. Ramsey, R. George, J. Kraus, C. Lichtenwalner, R. Papazian, C. Nuzman, A. Weiss, B. Kumar, D. Lieuwen, J. Gates, H. R. Shea, A. Gasparyan, V. A. Lifton, J. A. Prybyla, S. Goyal, R. Ruel, C. Nijander, S. Arney, D. J. Bishop, C. R. Giles, S. Pau, W. M. Mansfield, S. Jin, W. Y. Lai, D. L. Barr, R. A. Gierlli, G. R. Bogart, K. Teffeau, R. Vella, A. Ramirez, F. P. Klemens, J. Q. Liu, J. M. Rosamilla, H. T. Soh, and T. C. Lee, “Multi-service optical node based on low-loss MEM’s optical cross-connect switch,” in Tech. Dig. OFC, 2002, pp. 410–411.

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Xuezhe Zheng (M’03–SM’03) received the B.S., M.S. and Ph.D. degrees in optical instruments from Tsinghua University, Beijing, China in 1993 and 1997, respectively. His Ph.D. thesis work involved binary optics and diffractive beam shaping technologies for uniform illumination in inertial confinement fusion (ICF). Subsequently, he joined the Electrical and Computer Engineering Department, the University of California, San Diego, as a Researcher, investigating high-speed, high-density free-space optical interconnects. In 1999, he joined Call/Recall Inc., San Diego, where he worked on fast read/write optical data storage technology with two-photon material. He is currently an Optical Designer with Calient Networks, Goleta, CA. His research interests include freespace optical interconnects, optical switching, and dense wavelength division multiplexing transparent networks. Dr. Zheng is a recipient of the Science and Technology Development Award from the National Education Committee of China.

Volkan Kaman (S’97–M’00) received the B.S. degree in electrical engineering from Cornell University, Ithaca, NY, in 1995 and the M.S. and Ph.D. degrees from the University of California at Santa Barbara (UCSB) in 1997 and 2000, respectively. His Ph.D. thesis work involved high-speed electrical and optical TDM systems based on electroabsorption modulators. He is currently an Optical Systems Engineer at Calient Networks, Goleta, CA. His research interests are in high-speed electrical and optical time division and wavelength division multiplexing systems, applications of electroabsorption modulators for optical processing, and optical switching in transparent networks.

Shifu Yuan (M’99–SM’99) received the B.S. degree in applied physics and the M.S. and Ph.D. degrees in optics from Harbin Institute of Technology, Harbin, China, in 1988, 1991, and 1994, respectively. Prior to joining Calient Networks, Goleta, CA, as a Senior Optical Engineer, he was with Corning Incorporated, Corning, NY, where he was a Senior Research Scientist working on optical network research. From 1994 to 1996, he was a Lecturer/Postdoctoral Research Associate and then an Associate Professor in the Department of Precision Instruments, Tsinghua University, Beijing, China. From 1996 to 1998, he was a Postdoctoral Research Fellow with the School of Optics Center for Research and Education in Optics and Lasers (CREOL), University of Central Florida, Orlando. From 1998 to 1999, he was with Chorum Technologies, Richardson, TX, as an Electrooptic Engineer. He has extensive experiences in photonic switching and optical cross-connect, optical information processing, fiber-optic components, and ense wavelength division multiplexing (DWDM) optical networks. His current research interests are in the area of DWDM telecommunication networks. He has published more than 24 papers in technical journals and holds one U.S. patent.

Yuanjian Xu (M’01) was born in Hubei, China. He received the B.S. degree in electrical engineering from the University of Electronic Science and Technology, Chengdu, China, in 1985, the M.S. degree in applied physics from Shanghai Jiao Tong University, Shanghai, China, in 1987, and the Ph.D. degree in applied physics from California Institute of Technology, Pasadena, in 1996. In 1997, he joined Opto Power Corporation, Tucson, AZ, as a Member of Technical Staff, working on high-power semiconductor lasers. In 1999, he joined the Research and Development Lab, Culver City, CA, as a Senior Photonics Engineer, where his research interests shifted to semiconductor optical amplifiers and arranged waveguide gratings. In 2000, he joined Calient Networks, Inc., Goleta, CA, where he works on optical cross-connect switches.

Olivier Jerphagnon (S’99–M’99) received the M.E. degree from the Grenoble Institute of Technology, Grenoble, France, in 1998 and the M.S. degree from the University of California at Santa Barbara in 1999. He was with Alcatel Submairine Networks, Greenwich, U.K., in 1996 and the European Molecular Biology Laboratory, Heidelberg, Germany, in 1997. He has been with Calient Networks, Goleta, CA, since January 2000. He is currently Product Manager and part of the System Architecture group. His focus is the integration and development of photonic switching in DWDM networks. He was instrumental in the development of Calient photonic switching core technology, and he is the technical support of Calient products at Telecom carrier sites around the world. His research work has been on optical communications, high-frequency optoelectronics and instrumentation. Dr. Jerphagnon is a member of the Optical Society of America.

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Adrian Keating (S’94–M’95) received the Ph.D. degree from the Photonics Research Laboratory (PRL), Melbourne, Australia, where he researched wavelength stabilization techniques applied to WDM packet switched networks, in 1995. He subsequently worked at PRL on noise reduction techniques for wavelength division multiplexing spectrum sliced networks. In 1996, he moved to Japan to work for Nippon Telegraph and Telephone NTT, Masashino-shi, Japan, within the Optical Network Systems Laboratory, where he was investigating high-speed time division and wavelength division multiplexing broadcast and select networks. In 1998, he joined the Electrical and Computer Engineering Department, the University of California at Santa Barbara, where he investigated optical pumping, long wavelength VCSELS, free-space transmission systems, and semiconductor-based Terahertz generation. He is currently the Fiber Optical Technology Manager at Calient Networks, Goleta, CA.

James R. Sechrist received the B.S. degree (with high honors and distinction in the major) in mechanical engineering from the University of California at Santa Barbara. He has spent three years with Calient Networks, Goleta, CA, developing MEMS packaging solutions and vibration isolation systems. He has coauthored three papers and has three patents pending.

Robert C. Anderson received the B.S. degree (with honors) in chemistry from the University of California at Santa Barbara in 1989. He was a Senior Physics Engineer with the Santa Barbara Research Center as member of the Technical Staff for ten years, specializing in photolithography and optical thin-film filters utilized in space borne satellite cameras. In November 1999, he joined Calient Networks, Goleta, CA, to provide expertise in design and deposition of thin film coatings. He is currently a Senior Processing Engineer, where he has the responsibility of providing production optical coatings used in free-space optics utilized in fiber-optic switches.

Roger Helkey (M’88–SM’99) received the B.S. degree in engineering from the California Institute of Technology, Pasadena, in 1982 and the M.S.E.E. and Ph.D. degrees from the University of California at Santa Barbara, in 1988 and 1993, respectively. His graduate work was on modelocked semiconductor lasers, where he constructed novel modelocking structures for optical pulse generation. He is currently the Director of Optical Engineering at Calient Networks, Goleta, CA, with projects including the 256-port core photonic switch. From 1982 to 1999, he developed high dynamic range analog optical links and optical A/D conversion systems at Lincoln Laboratory, Massachusetts Institute of Technology, Cambridge, MA, and researched microcavity effects and nonlinear optical switching at the University of Tokyo and Advanced Telecommunications Research Institute, Kyoto, Japan. He has designed RF, microwave, and optical filters, microwave amplifiers, switches, and subsystems, oscillators, phased-locked loops, and CMOS, bipolar, and GaAs integrated circuits. He is coauthor of two book chapters and holds a dozen patents.

Henrik N. Poulsen was born in Copenhagen, Denmark, in 1969. He received the M.Sc.E.E. degree from the Electromagnetics Institute, the Technical University of Denmark, Copenhagen, in 1995. After receiving the degree, he continued his work at Research Center COM, The Technical University of Denmark. His field of interest is high bit rate signal processing in semiconductor devices, in particular all-optical techniques for demultiplexing and add/drop functions, and their applications in telecommunication systems based on combinations of optical time division multiplexing and wavelength division multiplexing. He is currently with the University of California at Santa Barbara.

Bin Liu (S’99–M’00) received the B.S. degree from Zhejiang University, Zhejiang, China, in 1990, the M.S. degree from Shanghai Institute of Optics and Fine Mechanics, Chinese Academy of Science, Shanghai, China, in 1995, and the Ph.D. degree from the University of California at Santa Barbara in 2000. His research interests include the design and fabrication of optical waveguide devices, semiconductor lasers, photonic integrated circuits, and microoptic devices.

Chandrasekhar Pusarla received the Ph.D. degree from the University of Maryland, College Park. He is currently the Optics Technology Manager at Calient Networks, Goleta, CA, where he leads a team of optical engineers in the design of optical switches. He was previously a Senior Associate at Corning, Corning, NY, and a Senior Process Engineer at Tyco, Boston, MA. He has contributed chapters to two books, and has coauthored over 20 papers.

Daniel J. Blumenthal (M’97–SM’97–F’03), photograph and biography not available at the time of publication.

John E. Bowers (M’81–SM’87–F’92) received the M.S. and Ph.D. degrees in applied physics from Stanford University, Stanford, CA. He is the Director of the Multidisciplinary Optical Switching Technology Center (MOST) and a professor in the Department of Electrical Engineering, the University of California, Santa Barbara (UCSB). He is CTO of Calient Networks, Goleta, CA. Before joining UCSB, he was with AT&T Bell Laboratories, Holmedel, NJ, and Honeywell, Minneapolis, MN. He has published five book chapters, over 300 journal papers, over 300 conference papers, and has received 22 patents. Dr. Bowers received the IEEE LEOS William Streifer Award, Sigma Xi’s Thomas F. Andrew prize, and the NSF Presidential Young Investigator Award. He is a Fellow of the American Physical Society.