The authors have designed and demonstrated a 2 x 2 Mach-Zehnder switch in view of polarization independence as well as low propagation loss (a) and absorption change (Delta alpha). To obtain polarization-insensitive refractive index change (Delta n), a lattice-matched InGaAlAs/InAlAs multiple quantum-well (MQW) with a large detuning wavelength was used. Moreover, to reduce the insertion loss difference between polarizations, we applied a multimode-interferometer 3-dB coupler and a deep-etched high-mesa waveguide structure. This switch, therefore, can provide polarization-independent operation about both driving voltage and insertion loss, which is indispensable to practical optical switching applications, We also paid attention to Delta alpha suppression when we decided the value of wavelength detuning and the length of the phase shift region. We also investigated the wavelength dependence of the switch. Within 1530-1560 nm, which is the erbium-doped fiber amplifier (EDFA) gain band, polarization independence in the driving voltage and the crosstalk was maintained. This result shows that the switch is also applicable in wavelength division multiplexing (WDM) applications.
