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`TOPICS IN LIGHTWAVE
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`MEMS Optical Switches
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`Tze-Wei Yeow, K. L. Eddie Law, and Andrew Goldenberg, University of Toronto
`
`ABSTRACT
`
`Leveraging MEMS‘s inherent advantages
`such as batch fabrication technique, small size,
`integratahility, and scalability, MEMS is posi-
`tioned to become the dominant technology in
`optical crossconnect switches. MEMS optical
`switches with complex movable 3D mechanical
`structures, micro—actuators, and micro-optics can
`be monolithically integrated on the same sub-
`strate by using the matured fabrication process
`of the integrated circuit industry. In this article
`we report various popular actuating mechanisms
`and switch architectures of MEMS optical
`switches. The basiCs of surface and bulk micro-
`maehining techniques used to fabricate MEMS
`deviCes will be revievved. Examples of 2D and
`SD approaches to MEMS optical switches will
`be described. The pros and cons of the two
`approaches will be analyzed. In the short term,
`MEMS—bascd optical switches seem to have cap—
`tivated the attention of both the industryr and
`academia. However, there are challenges that
`threaten the long—term survival of this technolo-
`gy. The problems that remain to be fully
`addressed will be discussed.
`
`lNTRODUCTION
`
`Optical switches. The optic switches are used to
`rcconfigurefrcstore the network, increase its relia-
`bility, andlor act as the optical addfdrop multi»
`plexer (OADM). There are,
`indeed, many
`technologies competing to replace the current
`electronic switch fabrics. A successful optical
`switching technology will have to demonstrate
`superiority in the areas of scalability, insertion
`loss, polarization—dependent loss (PDL), wave—
`length dependency, small size, low cost, crosstalk,
`switching speed, manufacturability, serviceability,
`and long-term reliability. Conventional mechani-
`cal switches, which are based on macroscopic bull:
`Optics, utilize the advantages of free-space optics;
`however, they suffer from large size, large mass,
`and slow switching time. On the other hand, guid-
`ed-wave solid state switches have yet to show
`great potential because their high losses and high
`crosstalk limit their scalability. The recent devel—
`opment of free-space optical MEMS technology
`has shown superior performance for this applica-
`tion. MEMS Optical switches not only retained
`their conventional counterparts’ advantages of
`free-Space optics such as low losses and low
`crosstalk, but also included additional ones Such
`as small size, small mass, and submillisecond
`switching times. Furthermorc, MEMS fabrication
`techniques allow integration of micro-optics,
`micro-actuators, complex micromechanical struc-
`tures, and possibly microelectronics on the same
`substrate to realize integrated microsystems.
`
`One of the most promising applications of micro-
`elcctromechanical systems (M EMS) technology
`is in optical communication in general and opti-
`cal cressconnect (OXC) switches in particular.
`The OXC switches in today’s network rely on
`electronic cores. As port count and data rates
`increase, it becomes increasingly difficult for the
`electronic switch fabrics to meet future demands.
`[1' is widely acknowledged that electronic switch
`fabrics are the bottleneck in tomorrow‘s commu—
`nication networks. This bottleneck has stimulat—
`ed intensive research in developing new
`all-optical switching technologies to replace the
`electronic cores. All-optical networks offer many
`advantages compared to conventional opticalnto‘
`electronic and electronic-to-optica] networks,
`including cost-cffcctivcncss, immunity from elec-
`tromagnetic interference, bit ratei'protocol trans-
`This is the most mature and simple microma-
`parency,
`and
`ability
`to
`implement
`chining technology. Bulk micromachining is
`wavelength—division multiplexing (WDM) with
`sometimes called the etchingfsubtraction pro-
`reiativc ease. Therefore, it is desirable to manip—
`cess. It involves the removal of silicon from the
`ulate the data network at the optical level with
`
`
`
`MICROMACHINING TECHNIQUES
`
`MEMS fabrication techniques utilize the mature
`fabrication technology of the Integrated Circuit
`(1C) industry. The fact that silicon is the primary
`substrate material used in the IC circuitry and
`that it also exhibits excellent mechanical proper-
`ties [1] make it the most popular micromachin-
`ing material. The micro-mechanical structures
`used in MEMS optical switching can be fabricat-
`ed using two popular micromachining technolo-
`gies, bulk micromachining, and surface
`micromachining.
`BULK Micaomncumme
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`1.58
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`(1 CID) Surface orientation
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`bulk silicon substrate by etchants. There are two
`types of chemical etchants, anisotropic and
`isotropic. Anisotropic etchants etch different sili-
`con orientation planes at different rates. Figure
`1a shows the silicon planes exposed by using
`anisotropic etchants. Figure lb shows a 3D
`mechanical structure that was fabricated using
`anisotropic etching.
`Isotropic etchants, on the other hand, etch
`the silicon evenly in all directions. Figure 10
`shows the effect of isotropic etches on silicon
`substrate. Note that the mechanical structure
`that canbe created by bulk micromachining is
`not very complex.
`
`SURFACE MICROMACHINING
`
`Surface micromaehining is a more advanced
`fabrication technique. Complex 3D mechanical
`structures can be created using alternate layers
`of sacrificial and structural materials. Sacrificial
`layers act as spacers between structural layers.
`Free-standing 3D mechanical structures will be
`formed when the sacrificial layers are etched
`away during final release. In surface microma—
`chining, thin-film materials are selectively added
`to or removed from the wafer. Thin-film materi-
`al deposited where a free-standing mechanical
`structure is needed is called a sacrificial layer.
`The material that is left after etching of the
`underlying sacrificial layer is called the struc-
`tural material. In surface mieromachining, a
`combination of dry and wet etching, and thin»
`film deposition are essential processes to realize
`micromechanieal structures on silicon. A sacrifi-
`cial layer, such as silicon dioxide, are deposited
`or grown underneath a patterned material for
`later removal. The removal process is usually
`done by chemical etching. After the removal of
`the sacrificial layer, the patterned material is
`left as thin-film free—standing mechanical struc-
`tures as they are suspended over the substrate
`by the thickness of the etched sacrificial layer.
`Figure 2 shows the surface micromaehining pro—
`cess of creating a free-standing mechanical
`structure. An insulation layer has been deposit-
`ed on the silicon substrate, followed by deposi-
`tion of SiOz as the sacrificial
`layer. The
`structural layer is then deposited on the SiOz.
`Openings are etched in the structural layer to
`expose the sacrificial layer. The underlying sac—
`rificial layer is etched away to release the free-
`standing structural layer.
`
`Swurcu ARCHITECTURES
`
`There are currently two popular approaches to
`implement MEMS optical switches:
`- 2D MEMS switches
`' 3D MEMS switches
`
`These two technologies have striking differences
`in terms of how they are controlled and their
`ability to redirect light beams. However. both of
`them have shown promise in finding their niches
`in telecommunication networks.
`
`21) MEMS SWITCHES
`
`Silicon substrate
`Silicon substrate
`
`{100} Surface orientation
`
`(60
`
`{100)
`Surface orientation
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`8 = 54.74”
`
`e111 3» Surface
`orientation
`
`Anisotropically
`etched cavity
`
`
`
`
`(bl
`
`5io2
`
`Silicon substrate
`
`(C)
`
`
`I figure 1 . a) Anisotropicwet etching of(100) and (1 l0) silicon substrate; b)
`deep cavity form in silicon by anisotropic ctchantr; c) isotropic etching ofsilicon
`
`
`
`
`in this architecture mirrors are arranged in a
`I Figure 2. Sudace micromacht'ning process
`crossbar configuration as shown in Fig. 3. Each
`where the sacrificial layer isfirsr deposited or
`mirror has only two positions and is placed at
`grown for later removal. In the process, frec-
`srartdirtg mechanical? structures are released.
`the intersections of light paths between the input
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`3D MEMS Swncnes
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`Most distance path
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`Outputs
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`/ on:
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`Least distance path
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`I Figure 3. A 20 crossbar switchng architecture.
`
`I Figure 4. A ciaseup view oft: WaveStar'"MEMS
`mirror {'2}.
`
`A SD or analog MEMS switch has mirrors that
`can rotate about two axes. Light can be redirect—
`ed precisely in space to multiple angles — at
`least as many as the number of inputs. This
`approach results in only N or 2N mirrors. Cur-
`rently, a majority of commercial 3D MEMS
`switch designs use two sets of N [total of 2N)
`mirrors to minimize insertion loss. Alternatively,
`if only N mirrors were used, port count would be
`limited by insertion loss that results from finite
`acceptance angle of fibersilens. Another advan-
`tage is that differences in free-space propagation
`distances among ports-to-ports switching are
`much less dependent on the sealing of the port—
`count. This architecture can be scaled to thou-
`sands by thousands of ports with high uniformity
`in losses. Inevitably, much more complex switch
`design and continuous analog control are need-
`ed to improve stability and repeatability of the
`mirror angles. Lucent Technologies announced a
`3D optical crossconnect using MEMS mirror
`array called WaveStar'“ LambdaRouter [2]. The
`mirror can rotate on two axes and is continuous-
`ly controllable to tilt greater than 16°. Figure 4
`shows a closeup view of the WaveStar MEMS
`mirror.
`In the first quarter of 2001, Agerc Systems,
`the former Microelectronics Group of Lucent
`Technologies, announced a fully integrated, 3D
`64 X 64 MEMS optical switch component that
`will be marketed to makers of optical network-
`ing systems. The 5200 series MEMS switch mod—
`ule is based on the scalable 3D switching
`architecture developed at Lucent Technologies.
`Amazingly, the switching module has a maxi-
`mum insertion loss of 6 dB and a switching time
`of less than 10 ms. Another notable develop-
`ment in 3D MEMS optical switch is by Nortel
`Networks. Nortel made headlines at Optical
`Fiber Conference {OFC} 2000 by showing the
`first ever all-optical switch, called the X4000, to
`beat the lUOO-port barrier. Following the hype
`created at OFC 2000, Nortel has recently admit-
`ted that only a small portion of the X-lllflil actu-
`ally worked. Nortcl’s 3!) switching architecture is
`illustrated in Fig. 5.
`Nortcl‘s 3D switching architecture utilizes
`two sets of N mirrors for a total of 2N mirrors.
`The first plane of N mirrors redirect light from
`N input fibers to the second plane of N mirrors.
`All the mirrors on the second plane are address-
`able by each mirror on the first plane making
`nonblocking connections. In turn, mirrors on the
`second plane can each be actively and precisely
`controlled to redirect light into desired output
`fibers with minimum insertion loss.
`
`and output ports. They can be in either the ON
`position to reflect light or the OFF position to
`let light pass uninterrupted. The binary nature of
`the mirror positions greatly simplifies the control
`scheme. Typically, the control circuitry consists
`of simple transistor-transistor-logic {T'TL) gates
`and appropriate amplifiers to provide adequate
`voltage levels to actuate mirrors.
`For an N x N-port switch, a total of N2 mir-
`rors is required to implement a strictly non-
`biocking optical switching fabric. For example, a
`16 x l6-port switch will require 256 mirrors. An
`alternative approach to increasing port count is
`to interconnect smaller 2D MEMS switch sub-
`modules to form multistage network architecture
`such as the well-known Clos network. However,
`this cascaded architecture typically requires up
`to thousands of complex interconnects between
`switch submodulcs, thus decreasing scrviccability
`of the overall switching system. In addition, the
`MEMS tilting mirrors alter the free—space propa—
`free-space beam propagation distances among
`gation of light beams by moving into their prop—
`port—to—port switching are not constant; there-
`agation paths, thus achieving their switching
`fore, insertion loss due to Guassian beam propa-
`functionality. In order for MEMS to be a viable
`gation is not uniform for all ports. The minimum
`and maximum insertion losses of OMM’s 2f) 16
`optical switching technology, the actuating mech-
`anisms used to move these mirrors must be
`x16 switching subsystem has a difference of
`small, easy to fabricate, accurate, predictable,
`greater than 5 dB. 2D optical switches find appli*
`cations in areas of communication networks,
`reliable, and consume low power. This section
`which requires smaller port sizes.
`briefly describes three actuating mechanisms
`
`ACTUATtNG MECHANISMS
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`that are being researched extensively in the uni-
`versity laboratories as well as the industry.
`
`Etecrnosrnnc
`Electrostatic forces involve the attraction forces
`
`of two oppositely charged plates. The advantages
`of electrostatic actuation are that it has very well
`researched and understood behavior. Further-
`more, it has very good repeatability. a property
`very important in optical switching. The disadvan-
`tages include nonlinearity in force vs. voltage rela—
`tionship, and requirement of high driving voltages
`to compensate for the low force potential.
`The design usually involves mirrors being
`held in parallel plane (OFF) to the underlying
`electrodes. When an electrode is charged at a
`different voltage level than that of its corre-
`sponding mirror, the mirror will be tilted down
`to its ON position and thereby reflect a light
`beam to a different output fiber. Toshiyoshi and
`Fujita of the University of Tokyo demonstrated
`a 2 x 2 switching matrix using electrostatic actua-
`tion. An optical switching matrix with large isola—
`tion of 60 dB and small crosstalk of —60 dB and
`insertion loss of 7.66 dB are achieved using a
`bulk micromachined torsion mirror [3]. Figure 6
`show; a 2 x 2 switching matrix with collimated
`light beams from input collimated beam fibers
`(CBFs) being reflected off torsion minors, fabri-
`cated at 45° to light beams, into receiving CBFs.
`One of the leading MEMS optical switching
`companies, OMM, has already started shipping
`MEMS switching subsystems, based on electro-
`static actuation. in production quantities since the
`spring of 2000. 2D switching subsystems of sizes 4
`x 4, 8 x 8, and 16 x 16 are hermetically sealed
`and passed Telcordia Technologies’ environmen-
`tal and reliability requirements for carrier-class
`equipment. Passing of the stringent Telcordia
`tests, which include mechanical reliability and
`endurance, will help to facilitate widespread
`acceptance of MEMS—based switching subsystems
`in telecommunication networks. These switches
`have been used to route live data traffic in an
`unmanned central office in Oakland, California,
`with great success. OMM cites insertion loss of
`more than 6 dB, crosstalk of —50 dB, and switch-
`ing time of 13 ms for a 16 x 16 subsystem.
`
`
`
`
`I Figure 5. A schematic illustration ofNortei's 3D switching architecture.
`
`ELECTROMAGNETIC
`
`Electromagnetic actuation involves attraction
`between electromagnets with different polarity.
`The advantages of electromagnetic actuation are
`that it requires low driving voltages because it
`can generate large forces with high linearity.
`Disadvantages such as shielding from other mag-
`netic devices to prevent crosstalk is difficult, and
`it has yet to prove reliable. The California Insti-
`tute of Technology has developed a magnetic 2 x
`2 MEMS fiber optical bypass switch [4]. The
`operation principle of the magnetic MEMS
`switch is illustrated in Fig. 7. The thin double-
`sidcd bulk-mieromachined mirror moves up or
`down in response to changing magnetic field.
`When the mirror moves up, it blocks the optical
`path to opposing optical fibers. [n this case, light
`signal is reflected off the mirror into neighboring
`Optical fibers. When the mirror moves down, it
`moves below the level of the optical fibers, and
`light signal is transmitted to opposing optical
`fibers. Electromagnetic actuation can achieve
`this displacement with less than 100 mW.
`Integrated Micromachines Inc. (IMMI),
`based in Monrovia, California, has developed a
`3D MEMS switching subsystem that has much
`lower loss than its competitors. It claims an
`
`
`Torsion mirror chip
`
`
`
` IflpLIICBF‘l-I .= .M
`
`
`
`
`
`.hSp
`' eke
`lens
`.
`
`
`.. Counter electrode
`
`I Mirror stopper
`‘9.
`
`(shallow dimple}
`gig om‘fitli can,
`Output CBF3
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`I Figure 6. An overall 2 x 2 optical switching matrix design [3}.
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`Magnetic field
`
`
`
`I Figure 7. A schematic illustration of operation
`principle ofthe 2 X 2 bypass fibre optic switch [4].
`
`
`Scratch drive actuator
`
`Translation
`. plate
`
`I Figure 8. A schematic design ofo fies-rotiningfiber optic switch {5}.
`
`SDAs [T]. The translation movement of the
`translation plate by the SDAs is converted to a
`rotation movement of the mirror. Figure 8 shows
`the complete structural design of the FS-MOS.
`The length of the pushrod is 75 um, and the dis-
`tance between the hinges at the bottom of the
`mirror to hinge joint located on the mirror is 70
`pm. This design allows the mirror to be rotated
`up to 45° when the translation plate is moved 2
`pm, and 90" at a translation distance of 22 um.
`The number of bias pulses applied to the SDAs
`determines the plate translation distance, and
`thus the rotation angle.
`The optical switch has shown to have a
`switching time of 700 us for rotating the mirror
`from an OFF position to the ON position. Loss—
`es measured range from a minimum of 3.1 dB to
`a maximum of 3.9 dB. In this design, SDAs have
`been shown to have very fast responses and
`extremely precise translation movement. With
`the presence of the pushrod and binge joints, the
`mirror can be rotated to multiple angles precise-
`ly and reliably. two of the most important
`requirements of 3D MEMS switches. As dis-
`cussed earlier, the current 3D MEMS switches
`require the mirrors to be rotated abriut two axes.
`Novel designs incorporating SDAs to provide
`precise positioning of mirrors about two axes of
`rotation have the potential to reduce needs for
`complex feedback control electronics.
`
`CHALLENGES
`
`In the short term, MEMS appears to be the
`forerunner that has the potential to dominate
`applicati0ns including OXCs, OADMs, and ser-
`vice restoratiom‘protection switches. There
`remain important issues within MEMS technolo-
`gy that need to be addressed before widespread
`acceptanCe in the core transport network.
`Reliability — Like anyr other commercially
`viable products, MEMS switches should function
`reliably in changing and often adverse environ—
`ments. Will the behavior of MEMS switches that
`have been held in the ON position for a few
`months before switching to OFF during network
`rcstorationiprovision be predictable? Or will stic-
`tion between materials restrict the movements of
`the switches? Will switch response times and
`structural integrity of the optical switches
`degrade after millions upon millions of switching
`cycles? Concerns regarding reliability of MEMS-
`based devices and repeatability in terms of per-
`formance need to be well studied in the context
`
`inserti0n loss of 3 dB regardless of switch size. By
`, using electromagnetic actuation instead of the
`weaker electrostatic actuation, IMMI claims that
`the driving voltage does not exceed a maximum
`of 10 V. Low power requirement is a critical crite—
`rion especially when IMMl is looking to develop
`so-calied 1000 >< NOD-port monster switching sub-
`systems. Low insertion loss and low power con-
`sumption bring benefits on both the system and
`economic levels. Now less optically efficient but
`more manageable fiber array connectors can be
`used, thereby reducing servicing time. In addition,
`MEMSicomplementary metal Oxide semiconduc-
`of entire optical systems.
`tor (CMOS) integration, which eliminates tens of
`thousands of individual mirror control wires, is
`Manufacturability — Characteristics of
`MEMS—based devices could fluctuate from one
`possible with lower voltage requirements.
`batch to the next. Repeatability of material
`SCRATCH DRIVE Acrunrorts
`properties and uniformity of processing tech—
`AT&T research labs have demonstrated an 8 x 8
`niques have to be improved to fully address
`these concerns. MEMSiCMOS fabrication pro—
`free-space micromachined optical switch {FS—
`cesses have to be made compatible. The control
`MOS) for the application of restoration and pro-
`electronics and wiring schemes can be fabricated
`visioning in core transport lightwave networks
`in sync with MEMS components, thereby elimi—
`[5]. The mirror and the scratch drive actuators
`nating costly hybrid integrations. Researches
`(SDAs) are monolithically integrated on the sili-
`into novel materials and fabricating processes
`con substrate using surface micromachiniog
`must be ongoing. MEMS should be driven by
`techniques. The rotation of the mirror is
`achieved by connecting the pushrods with the
`technology as well as basic science.
`Serviceability — Matrices of micro—mirrors
`mirror and the translation plate using micro-
`are fabricated using batch fabrication technique.
`hinges [6]. The actuators used are an array of
`
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`When compared
`to their
`
`counterparts.
`
`MEMS optical
`swrtches are
`
`Cheaper because
`of batch
`
`fabrication
`
`techniques.
`
`They are also
`smaller in Size
`
`and lighter in
`mass thus
`
`allowing
`
`high-density
`
`packing on a
`
`single silicon
`substrate.
`
`rior low loss performance allows them to be
`expandable to larger port counts. When com-
`pared to their counterparts, MEMS optical
`switches are cheaper because of batch fabrication
`techniques. They are also smaller in size and
`lighter in mass, thus allowing high~density packing
`on a single silicon substrate. Currently, there is
`much research interest in integrating micro-optics
`and electronics components to MEMS devices to
`realize true integrated optics. Amidst all the hope
`and hype, a MEMS—based optical switch has yet
`to cross major technological hurdles in order to
`fulfill its potential as the preferred optical switch-
`ing technology in the long term.
`
`REFERENCES
`[1] K. E. Petersen. "Silicon As A Mechanical Material." Proc.
`I'EEE. vol. 70. 1982. pp.420—5?.
`{2] \t. A. Aksyuk et at. "Lucent Microstar Micromirror Array
`Technology for Large Optical Crossconnects." Proc.
`SPlE, vol. 41?8. 2000.
`[3] H. Toshiyoshi and H. Fujita. "Electrostatic Micro Torsion
`Mirrors for an Optical Switch Matrix,“ J. Microelec—
`tromech. Sys. vol. 5. no. at. Dec. 1996. pp. 231—31
`[4] RA. Miller at al, ”An Electromagnetic MEMS 2x2 Fiber
`Optic Bypass Switch.” 1997 lnt'l. Conf. Solid-State Sen-
`sors and Actuators (TRANSDUCER ‘97). Chicago.
`IL.
`June 16—19. 199?. pp. 89—92.
`[5] L. Y. Lin, E. Goldstein. and L. M. Lunardi. "Integrated
`Signal Monitoring and Connection Verification in
`MEMS Optical Crossconnects." lEEE Photon. Tech. Left.
`vol. 12. no. 3'. July 2000.
`[6] K. 5. J. Pister at at. "Microfabrtcated Hinges." Sensors
`and Actuators A. vol. 33. 1992, pp. 249—56.
`[‘l'} T. Akiyama and H. Fujita, "A Quantitative Analysis of
`Scratd't Drive Actuator Using Buckling Motion." lEEE Wksp.
`MEMS, Amsterdam. The Netherlands. Jan. 29—Feh. 2. 1995.
`
`BIOGRAPHIES
`TZE—WEI YEow lyeow@mie.utoronto.cal obtained a B.A.Sc.
`degree in electrical and computer engineering and an
`M,A.Sc. in mechanical and industrial engineering from the
`University of Toronto. Ontario. Canada, in 199? and 1999.
`respectively. He is currently pursuing his Ph.D. degree in the
`Robotics and Automation. and Network Architecture Labora‘
`tories at the University of Toronto. His research interests
`include developing novel MEMS devices for biomedical
`imaging and switch architecture for optical crossconnects.
`
`K. L. EooiE LAW (eddie@comm.utoronto.cal received a
`B.Sc.(Eng.) degree in electrical and electronic engineering
`from the University of Hong Kong. an MS. degree in electri-
`cal engineering from Polytechnic University, Brooklyn, New
`York. and a Ph.D. degree in electrical and computer engineer-
`ing from the University of Toronto in Canada. From 1995 to
`1999 he worked in three different groups — — Passport
`Research Group. Next Generation ATM Systems Department.
`and Computing Technology lab — in Nortel Networks.
`Ottawa. Since September 1999 he has been an assistant pro-
`fessor in the Communications Group in the Edward S. Rogers
`Sr. Department of Electrical and Computer Engineering at the
`University of Toronto. His current research interests are active
`networkings. policy-based management on the Internet.
`TCPflP protocol development, and photonic switch design
`
`Will the failure of a single mirror require the
`replacement of the entire optical switch?
`Although the inclusion of redundancy in the
`optical switches will alleviate the problem, it
`remains to be fully explored.
`Scalability — The ability to incorporate more
`port counts when needed is the number one con-
`cern of carriers. The increasing amount of data
`traffic in communication networks, especially for
`long-distance carriers, will demand even more
`wavelengths to be deployed. Therefore, optical
`switches need the capability to Scale in order to
`manipulate the increased number of wave
`lengths. MEMS-based optical Switches must
`incorporate this key feature to gain widespread
`acceptance of the carriers.
`Standardization — There is a lack of techno-
`logical compatibility in the MEMS optical switch
`market. It is shortsighted to rely on a single ven—
`dor for MEMS-based optical switches. However,
`standardization will come with time. Similarly,
`there should be compatibility in the front-end
`MEMS fabricating processes. Ultimately, the-
`MEMS industry should mimic what the integrat-
`ed circuit industry has done. Fabrication of a
`MEMSr‘application-specific integrated circuit
`(ASlC) can be contracted to centralized
`foundries specializing in making MEMS devices.
`To achieve this. standardized fabrication pro-
`cessesllibraries must be defined.
`Packaging — MEMS-based optical switches
`have close interaction with the physical world
`through their mechanical components. How will
`optical switches be packaged so as to minimize
`effects of changing temperature, humidity, vibra—
`tions, and other environmental elements? Pack~
`aging invariably affects the performance of
`MEMS devices. Therefore, it should be included
`in the initial design phase.
`Automation — Assembly of MEMS compo-
`nents, and automatic optoelectronic packaging
`and performance testing of MEMS devices are
`crucial to reducing product cost and cycle time
`while maintaining product quality. issues such as
`self~testing, self—assembly, and automated pack~
`aging remains to be fully explored.
`Competing Technologies -— MEMS—based opti—
`cal switches are facing major challenges from
`other all-optical switch technologies, and the con—
`stantly evolving electronics switching systems. The
`current state-of—the-art electronic switching sys-
`tems offer 512 2.5 Gbr’s ports for a combined
`capacity of over 1 This. It seems that the adoption
`of optical switching technologies are faced with
`fierce resistance from electronic switching systems.
`It should be noted that Lueent’s Lambda Router
`has yet to be commercially successful and is con-
`stantly being outsold by electronic switching sys-
`tems such as Cicna’s CoreDirector. Given the
`current advancement of electronic switching tech-
`nology, switching technologies such as MEMS will
`have a lot more to prove before we can enter the
`era of purely optical switching networks.
`
`ANDREW A. GOLDENBERG [F] (gotden@mie.utoronto.ca)
`received B.A.Sc. and M.A.Sc. degrees from the Technion-
`Israel Institute of Technology. Haifa. lsrael. in 1969 and
`1972. respectively. and a Ph.D. degree from the University
`of Toronto. Ontario, Canada. in 19?6. all in electrical engi-
`neering. From rats to 1981. he was employed by Spar
`Aerospace Ltd.. Toronto. where he worked mainly on con-
`trol, analysis. and design of the space shuttle remote
`manipulator system and satellite controls. Since 198? he
`has been a professor of mechanical engineering at the Uni-
`versity of Toronto. His current research interests are in the
`field of MEMS sensors-actuator-devices with applications in
`MEMS optical switches have been demonstrated
`robotics and industrial automation. He is a former Editor
`to have lower PDL, bit—rate— and protocol~inde-
`of :55? Transactions on Robotics and Automation. He is a
`pendent, lower insertion loss, and lower eroSstalk
`member of the American Society of Mechanical Engineers
`and the Professional Engineers of Ontario.
`than guided-wave solid state switches. Their supe-
`
`
`CONCLUSION
`
`IEEE Communications Magazine - November 2001
`
`163
`
`0006
`0006
`
`