High-speed optical switches are essential devices to construct next-generation optical networks. We have studied 2 <formula formulatype="inline" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex Notation="TeX">$\,\times\,$</tex></formula> 2 InAlGaAs/InAlAs hybrid-waveguide-type Mach–Zehnder interferometer-type optical switches and demonstrated low-polarization-dependent switching operation with crosstalks of less than <formula formulatype="inline" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex Notation="TeX">${-}{\rm 20}~{\rm dB}$</tex></formula> , injection currents of about 5 mA, and response times of about 3 ns. In this letter, our conventional 2 <formula formulatype="inline" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex Notation="TeX">$\,\times\,$</tex></formula> 2 optical switch was extended to a 4 <formula formulatype="inline" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex Notation="TeX">$\,\times\,$</tex></formula> 4 optical-switch fabric by a cascading approach. As a result, fundamental switching operation was confirmed with low power consumption and low polarization dependence.