4$\,\times\,$4 InAlGaAs/InAlAs Optical-Switch Fabric by Cascading Mach–Zehnder Interferometer-Type Optical Switches With Low-Power and Low-Polarization-Dependent Operation

High-speed optical switches are essential devices to construct next-generation optical networks. We have studied 2
$\,\times\,$
2 InAlGaAs/InAlAs hybrid-waveguide-type Mach–Zehnder interferometer-type optical switches and demonstrated low-polarization-dependent switching operation with crosstalks of less than
${-}{\rm 20}~{\rm dB}$
, injection currents of about 5 mA, and response times of about 3 ns. In this letter, our conventional 2
$\,\times\,$
2 optical switch was extended to a 4
$\,\times\,$
4 optical-switch fabric by a cascading approach. As a result, fundamental switching operation was confirmed with low power consumption and low polarization dependence.