ow-Loss Polarization-Insensitive InGaAsP Optical Space Switc for Fiber Optical Communication

High-performance InP-InGaAsP optical space switches are reported, which in monolithic four switch arrangements reach fiber-to-fiber losses as low as 5 dB. Polarization insensitivity is within 10.5 dB. On-off ratios throughout the 1.53-1.56 pm wavelength range exceed 15 dB. Switch rearrangement times are below 200 ps. I. INTRODUCTION PTICAL space switches for fiber optical communi- cation networks need low overall fiber-to-fiber inser- tion losses, polarization-insensitive operation over wide wave- length ranges, high on-off ratios, and fast switchmg capabil- ities at low operational voltages. Low losses and polarization insensitivity are obtained for waveguide switch matrices in silicon (l) and in polymers (2), but they are normally not suitable for high-speed applications, since they rely on thermo- optic effects, with milliseconds reconfiguration times. Switch matrices in LiNbQ3 (3) and in GaAs-AlGaAs (4) exhibit low losses in the 1.55-pm wavelength range and high switching speeds, but they usually work for one polarization only. Planar optical space switches, realized in the InP-InGaAsP material system are very attractive, since they offer the possibility for integration with optical amplifiers, detectors, and electronic drivers. Space switch matrices based on carrier injection in InP-waveguide structures have been demonstrated (5), (6). While these switches are polarization independent and operate in convenient digital on-off fashion, their switching speeds are limited by carrier dynamics to the nanosecond range. Low-loss and high-speed single digital optical switches in InP-InGaAs? quantum well reach good performances (7), but when building up matrices or connecting them to lensed fibers the losses will increase. The InP-InGaAsP space switches reported by Bachmann et al. (SI using field effects, however, allow high- speed, low-loss and polarization-insensitive operation. These switches consist of Mach-Zehnder waveguide interferometers in a special angular orientation on the (100) InP, that allow the combination of both the linear TE and the Franz-Keldysh TE and TM electrooptic effects to achieve high-speed and polarization-insensitive operation. Switch modules with four switches, integrated waveguide adapters, self aligned input and