1296-port MEMS Transparent Optical CrossConnect with
`2.07Petabit/s Switch Capacity
`
`R. Ryf, J. Kim, J. P. Hickey, A. Gnauck, D. Carr, F. Pardo, C. Bolle, R. Frahm , N.
`Basavanhally , C. Yoh, D. Ramsey, R. Boie , R. George, J. Kraus, C. Lichtenwalner, R.
`Papazian, J. Gates, H. R. Shea, A. Gasparyan, V. Muratov, J.E. Griffith, J.A. Prybyla, S.
`Goyal, CD. White, MX Lin , R. Ruel, C. Nijander, S. Arney, D. T. Neilson, D. J. Bishop,
`P. Kolodner, S. Pau, C. Nuzman, A. Weis, B. Kumar, D. Lieuwen, V. Aksyuk, D. S.
`Greywall, T.C. Lee, H.T. Soh, W.M. Mansfield, S. Jin, W.Y. Lai, H.A. Huggins, D.LBarr,
`R.A. Cirelli, G. R. Bogart, K. Teffeau, R. Vella, H. Mavoori, A. Ramirez, N.A.Ciampa,
`F.P. Klemens, M.D. Morris, T. Boone, J.Q. Liu, J.M.Rosamilia, C. R. Giles
`
`Lucent Technologies
`791 Holmdel-Keyport Rd
`Holmdel, NJ 07733
`Email: ryf@lucent.com
`
`Agere Systems
`600 Mountain Ave.
`Murray Hill, NJ07974-0636
`
`Abstract
`insertion loss
`A 1296-port MEMS transparent optical crossconnect with 5.1dB+/-1.1dB
`at 1550nm is reported. Measured worst-case optical crosstalk in a fabric was h38dB
`and nominal switching rise/fall times were 5msec. A 2.07Petabit/s switch capacity was
`verified upon cross-connecting a forty-channel by 40Gb/s DWDM data stream through a
`prototype fabric.
`
`Summary
`Major data communications optical networks are growing in capacity and sophistication
`to accommodate the demand for reconfigurable and reliable Internet data transport.
`Traditional SONET rings can no longer economically manage the data traffic and more
`flexible mesh architectures are looking attractive. Optical crossconnects would then
`manage WDM traffic at major network intersections, redirecting optical channels as
`dictated by provisioning, protection and restoration needs. Hundreds of optical fibers
`with potentially one hundred or more WDM channels may reach a central office,
`necessitating large, scalable optical crossconnects[1-3]. Here we report a 1296-port
`transparent, strictly nonblocking, Micro-ElectroMechanical Systems (MEMS) optical
`crossconnect. The fabric had a mean insertion loss of 5.1dB (1530-1560nm), worst-case
`optical crosstalk of h38dBand nominal connection rise/fall times of 5msec. Single-port
`data capacity of 1.6 Tb/s using forty 40Gb/s DWDM channels was demonstrated in a
`prototype subsystem, which when fully implemented to populate all ports of a 1296-port
`fabric, corresponds to 1296x1.6Tb/s=2.07Petabit/s switch capacity.
`
`This new optical crossconnect was assembled using two integrated 1296-MEMS single-
`crystal silicon mirror arrays and matching lens-fiber arrays [1]. The MEMS-mirrors were
`built as electrostatically actuated gimbal structures capable of 2-axis tilt motion and the
`mirror arrays were sealed behind glass windows in ceramic packages. The MEMS
`mirrors were designed for sustained operation with a maximum electrode voltage of
`200V. Single-mode optical fiber input and output ports were arranged in lens-fiber
`assemblies, comprised of 36x36=1296 square-pitch fiber bundles, having matching
`collimating lenslet arrays. Both diffractive and refractive lenslet arrays were tested, the
`
`FNC 1031
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`diffractive lenses were designed for restricted wavelength operation, the refractive-
`element design extended the fabrici's operating wavelength range to ~1300nm-1600nm.
`
`Figure 1 shows a schematic of switch fabrici's opto-mechanical layout. The figure also
`shows the placement of a retroreflector, enabling the use of one MEMS mirror array and
`lens/fiber array with half of the MEMS mirrors committed to input-ports and the
`remaining committed to output-ports. This folded configuration was used in the DWDM
`signal switching experiments. In operation, prescribed voltages are applied to the input-
`and output-mirror electrodes, steering input optical beams to impinge on the output-
`destination mirrors that are tilted to minimize coupling loss to the output-ports. The
`photographs in figure 2 show front-views of a 1296-port optical switch module and of a
`prototype crossconnect tested in the folded configuration. The prototype shows that the
`majority of the bay area is occupied by optical port connectors, and highlights the density
`of the drive and control electronics.
`
`Figure 1. Optical layout of the 1296-port switch fabric. A gold mirror retroreflector
`placed in the middle of the optical path enables the use of a single MEMS mirror
`array and lens/fiber array to implement a folded-geometry 648-port fabric.
`
`The loss spectrum of the prototype crossconnect was dictated by the optical properties
`of the diffractive lenses in the lens/fiber array, which were designed to match the C-band
`requirements of amplified optical line systems. Connections measured between 60 input
`ports and 60 output ports yielded a mean insertion loss of 5.1dB+/- 1.1 dB. Figure 3(a)
`shows the loss spectrum of a typical connection through the fabric. Optical crosstalk to
`output ports adjacent to an established connection was h58dB,and worst-case crosstalk
`originating during beam scanning was less than -38dB. The mechanical response of the
`MEMS mirror resulted in nominal 5 msec rise/fall times of connections, as shown by the
`output-port signal response in figure 3(b).
`In laboratory-environment tests, connection
`losses were stable to within 1dB over a 1hour period without any active mirror control.
`
`The data capacity and spectral bandwidth of the prototype optical crossconnect was
`verified by switching a forty channel by 40Gb/s DWDM data stream through the fabric
`(PRBS length:231 - 1). The experiment used forty multiplexed DFB lasers on a 100GHz
`channel spacing centered at 1545nm and externally modulated using a single common
`lithium niobate modulator. This DWDM source was connected to one input port of the
`prototype crossconnect and switched to the output ports. The total input optical power
`was 16dBm with OdBm average channel power. DWDM channels were demultiplexed
`after the switch fabric and detected by an optically preamplified receiver having
`-29.5dBm sensitivity at 10E-9 BER. Figure 4 shows the input and output DWDM optical
`spectra of the fabric together with measured bit-error-rate performance of three
`
`

`

`connections at four wavelengths. No noticeable signal degradation was observed and
`error-free transmission through the switch fabric was consistently obtained for all
`connections and channels. These results confirm the potential aggregate switch
`capacity for this transparent optical crossconnect of 1296x40x40Gb/s=2.07Petabit/s.
`This data transparency and the ability to switch DWDM data streams with low optical
`loss, are suitable for cost-effective management of the vast traffic patterns evolving with
`the growth of Internet data.
`
`free-space optical crossconnect with
`In summary, a 1296-port MEMS-based
`2.07petabit/s switch capacity has been described. The low insertion loss (5.1dB), low
`optical crosstalk (-38dB worst-case), and fast switch response (5msec optical rise/fall
`times) enable the practical implementation of a new generation of scalable switch fabrics
`capable of managing diverse optical signals found in complex optical networks.
`
`References
`[1] D. T. Neilson et al; OFCi'2000, March 2000, pd. 12
`[2] J.E. Fouquet et al;LEOSi'98, December 1998, vol.2, pp.169
`[3] A. A. M. Saleh; OFCi'2000, vol. 4, pp62-65
`
`Figure 2. (a)1296-port optical switch module
`and (b) 648-port folded-geometry optical
`crossconnect prototype.
`
`Figure 4. BER of 4 DWDM channels in 3
`connections (baselines=solid symbols). Insets
`show spectra before and after the fabric.
`
`Figure 3. (a) loss spectrum
`of prototype crossconnect
`with diffractive lenslet array
`and (b) output optical signal
`response upon setting up the
`connection.
`
`