50-Gb/s silicon quadrature phase-shift keying modulator.

We report the first successful demonstration of quadrature phase-shift keying (QPSK) modulation using two nested silicon Mach-Zehnder modulators. 50-Gb/s QPSK signal is generated with only 2.7-dB optical signal-to-noise ratio penalties from the theoretical limit at a bit-error ratio of 10(-3). This result validates that silicon photonics could be a viable and powerful platform of photonic integrated circuits in coherent optical communications.