We experimentally demonstrate a 16 × 16 reconfigurably nonblocking optical switch fabric using a Benes architecture. The switch fabric consists of 56 2 × 2 Mach–Zehnder interferometer based elementary switches, with each integrated with a pair of waveguide microheaters. The average on-chip insertion loss is ~5.2 dB for both of the “all-cross” and the “all-bar” states, with a loss variation of 1 dB over all routing paths. The cross talk for all switching states is better than -30 d B. The switching time of the switch element is about 22 μs. The switching functionality is verified by transmission of a 40 Gb∕s quadrature phase-shift keying optical signal. The switch fabric consists of 56 2 × 2 Mach-Zehnder interferometer based elementary switches, with each integrated with a pair of waveguide microheaters. The average on-chip insertion loss is ~ 5.2 dB for both of the “all-cross” and the “all-bar” states, with a loss variation of 1 dB over all routing paths. The cross talk for all switching states is better than - 30 d B. The switching time of the switch element is about 22 μs. The switching functionality is verified by transmission of a 40 Gb / s quadrature phase-shift keying optical signal.