IEEE PHOTONICS TECHNOLOGY LETTERS, VOL. 11, NO. 1, JANUARY 1999
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`63
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`Reconfigurable 16-Channel WDM DROP Module
`Using Silicon MEMS Optical Switches
`
`C. R. Giles, B. Barber, V. Aksyuk, R. Ruel, Larry Stulz, and D. Bishop
`
`Abstract—A reconfigurable 16-channel 100-GHz spacing wave-
`length-division-multiplexed DROP module for use at 1550 nm
`was demonstrated using silicon microelectromechanical system
`(MEMS) optical switches and arrayed waveguide grating routers.
`Thru-channel extinction was greater than 40 dB and average
`insertion loss was 21 dB. Both drop-and-retransmit of multiple
`channels (11–18 dB contrast, 14–19-dB insertion loss) and drop-
`and-detect of single channels (>20-dB adjacent channel rejection,
`10–14-dB insertion loss) were implemented.
`Index Terms— Fiber-optic communications, MEMS devices,
`micromachines, optical networks.
`
`I. INTRODUCTION
`
`ADVANCED LIGHTWAVE systems utilizing wavelength-
`
`division-multiplexed (WDM) channels are capable of
`supporting functions acting in the optical layer to enhance
`provisioning and protection of the network. Optical wavlength
`add/drop multiplexers (ADM) selectively remove one or more
`WDM channels and replace them with new channels at the
`same wavelengths. Residual leakage of the dropped channels
`must be very small
`to minimize their interference to the
`added channels. This requires low-channel crosstalk through
`the wavelength multiplexers and demultiplexers and high-
`contrast optical switches in a reconfigurable ADM. Integrated
`reconfigurable ADM’s have been demonstrated using silica
`on silicon [1] and InP [2], but their utility is compromised
`by marginal optical performance relative to that needed in
`real applications. A free-space optics ADM having a bulk-
`grating and micromachine mirror array has also been reported,
`with promising performance [3] In this letter, we describe a
`reconfigurable drop module (RDM) implemented as a hybrid
`optical circuit comprised of two 16-channel arrayed waveguide
`grating routers (AWGR) [4], sixteen MEMS optical switches,
`and ancillary optical components. The RDM was designed
`with drop-and-transmit (DT) capability for eight channels such
`that when dropped, they remained combined in a single optical
`fiber, suitable for WDM transport away from the RDM node.
`Eight other channels were configured for drop-and-detect (DD)
`where dropped channels exit on separate fibers, suitable for
`local reception. Channel-add for full ADM functionality may
`be trivially obtained using a final-stage coupler.
`
`Fig. 1. Reconfigurable drop module with channels 1–4 and 13–16 arranged
`for DD and channels 5–12 arranged for DT. Arbitrary reconfiguration of all 16
`channels is obtained using voltage-actuated silicon MEM’s optical switches.
`
`channels and DD capability for the remaining channels. An
`input optical circulator (0.6-dB port-to-port
`insertion loss)
`redirected DT-channels to a transmission fiber and the first
`AWGR demultiplexed the input channels and recombined
`any DT-channels. DT was controlled by reflective MEMS
`optical switches [5]; channels reached the thru-port when
`switches were in the transmit-state and dropped when the
`switches were activated into their reflection state. Channels
`configured for drop-and-detect were divided after the first
`silica-waveguide AWGR using 3-dB passive couplers, result-
`ing in fixed drop-ports and ports that were connected to the
`output AWGR through nonreflective MEMS switches. The
`nonreflective switches were the same as the reflective types
`only their shutter angles were set to reduce reflected light
`coupling back into the fiber. A channel reached the thru-port
`when the corresponding MEMS switch was in the transmit
`state, otherwise it was blocked.
`As seen in the AWGR transmission spectra of Fig. 2,
`the first AWGR had 40-GHz BW gaussian passbands with
`transmission loss varying from 7.1 to 12.4 dB, including the
`3-dB coupler loss of channels 1–4 and 13–16, whereas the
`second AWGR (this router was a “non-wrap-around” design,
`transmitting only one band of 16 channels) with flattened 50-
`GHz passbands had losses ranging from 7.45 to 10.61 dB.
`This combination of two router types was chosen to simplify
`their channel registration while achieving good crosstalk per-
`formance and minimal bandwidth narrowing. Insertion loss of
`1041–1135/99$10.00 © 1999 IEEE
`
`II. RESULTS
`Fig. 1 shows the layout of the 16-channel 100-GHz channel
`spaced RDM configured with DT capability for half of the
`Manuscript received September 24, 1998.
`The authors are with the Lucent Technologies, Holmdel, NJ 07733 USA.
`Publisher Item Identifier S 1041-1135(99)00355-9.
`
`Exhibit 1019, Page 1
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`64
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`IEEE PHOTONICS TECHNOLOGY LETTERS, VOL. 11, NO. 1, JANUARY 1999
`
`Fig. 3. Transmission (solid line) and reflection (dotted line) characteristics
`of a typical MEMS optical switch.
`
`(a)
`
`(b)
`Fig. 2. Transmission spectra of (a) Gaussian passband input AWGR and (b)
`flattened passband output AWGR.
`
`the DD channels from the input of the RDM to their respective
`drop-port ranged from 10.8 to 13.8 dB. The MEMS optical
`switches consisted of a thin, gold-coated silicon shutter that
`was raised in a pivoting action by a voltage applied to a
`moveable capacitor plate on the opposite side of a fulcrum. An
`array of dimples on the underside of the capacitor plate ensured
`that
`it never fully contacted the lower electrode thereby
`preventing the occurrence of stiction. Applying the voltage
`interposed the shutter between two anitreflection-coated fibers
`that were epoxy-bonded to the switches’ silicon substrate.
`Switch losses in the transmit state ranged from 0.8 to 3.3 dB,
`varying because of small alignment errors between the optical
`fibers present during the passive assembly of the switches.
`The return loss of the switches in the reflective state ranged
`from 2.2 to 4.8 dB for those switches having the shutter angle
`aligned for normal incidence. As seen in Fig. 3, most switches
`exhibited high extinction ratios,
`40 dB, achievable with a
`moderate control voltage (20–40 V). Switching time with a
`step drive voltage was approximately 95 s.
`Optical characteristics of
`the assembled reconfigurable
`drop module are summarized in the spectra shown in Fig. 4.
`Fig. 4(a) shows thru-port spectra with all 16 channels either
`
`(a)
`
`(b)
`(a) Optical spectra at the thru-port with all channels transmitted
`Fig. 4.
`and all channels blocked by the MEMS switches. (b) Optical spectra at the
`thru-port (solid line) and the drop-and-transmit port (dotted line) with all DT
`channels (channels 5–12) in the drop state.
`
`transmitted or dropped. Thru-channel loss of the RDM ranged
`from 17–24 dB, including loss from the 3-dB splitters of the
`drop-and-detect channels, and crosstalk through it was below
`40 dB (noise-limited measurement). This crosstalk level
`would cause negligible performance degradation in a digital
`lightwave transmission system. High extinction at the thru-
`port was achieved for all dropped channels, the worst-channel
`extinction was 23 dB, limited by one low-contrast switch,
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`Exhibit 1019, Page 2
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`GILES et al.: RECONFIGURABLE 16-CHANNEL WDM DROP MODULE
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`65
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`while all others exceeded 40 dB. Fig. 4(b) shows spectra at
`the thru-port and the DT port with the RDM set to drop the 8
`drop-and-transmit channels. Losses of the drop-and-transmit
`channels ranged from 14 to 19 dB and their extinction ratios
`from transmit to drop state, 11–18 dB, were limited by weak
`reflections from the fiber gaps in the switches. Low-power
`reflections of the DD channels also appeared in the drop-and-
`continue port, but would have little impact as they would be
`rejected by a demultiplexer before the DT channel receivers.
`Unwanted reflections from the fiber gaps could be greatly
`reduced using angle-cleaved fibers and appropriately orienting
`the MEMS shutter in the gap. These values of extinction,
`loss and crosstalk through the RDM are sufficient for most
`network applications where the RDM is used in conjunction
`with optical amplifiers to compensate the loss. Full channel
`add/drop capability could be implemented by the inclusion of
`a passive combiner after the output port of the RDM.
`
`III. SUMMARY
`We have demonstrated an arbitrarily reconfigurable 16-
`channel 100-GHz spacing drop module using MEMS optical
`
`switches to achieve excellent channel isolation and crosstalk.
`These switches may replace large bulk-optic components to
`make very compact reconfigurable WDM network modules for
`use in advanced lightwave systems. Ultimately, these switches
`might be integrated with passive optical structures including
`WDM routers and cross-connect fabrics, enabling practical
`large-scale WDM network devices.
`
`REFERENCES
`
`[1] K. Okamoto, K. Takiguchi, and Y. Ohmori, “16-channel optical add/drop
`multiplexer using silica based arrayed-waveguide gratings,” Electron.
`Lett., vol. 31, no. 9, pp. 723–724, 1995.
`[2] C. G. M. Vreeburg, T. Uitterdijk, Y. S. Oei, M. K. Smit, F. H. Groen,
`E. G. Metaal, P. Demeester, and H. J. Frankena, “First InP-based
`reconfigurable integrated add-drop multiplexer,” IEEE Photon. Technol.
`Lett., vol. 9, pp. 188–190, Feb. 1997.
`[3] J. E. Ford, J. A. Walker, V. Aksyuk, and D. J. Bishop, “Wavelength-
`selectable add/drop with tilting micromirrors,” presented at the LEOS
`Annu. Meeting, Nov. 1997, postdeadline paper PD 2.3.
`[4] C. Dragone, “An N  N optical multiplexer using a planar arrangement
`of two star couplers,” IEEE Photon. Technol. Lett., vol. 3, pp. 812–815,
`1991.
`[5] V. Aksyuk, B. Barber, C. R. Giles, R. Ruel, L. Stulz, and D. Bishop
`“Low insertion loss packaged and fiber-connectorized MEMS reflective
`optical switch,” Electron. Lett., submitted for publication.
`
`Exhibit 1019, Page 3
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