IEEE PHOTONICS TECHNOLOGY LETTERS, VOL. 11, NO. 1, JANUARY 1999 63 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 A DVANCED 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. 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. 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