Simple DQPSK Signal Regenerator Using Electrical Limiting Amplifiers

A simple optoelectronic regenerator for differential quadrature phase-shift keying (QPSK) signals is demonstrated. The regenerator consists of two parallel delay interferometers followed by balanced detectors, limiting and driving amplifiers, and a dual-parallel Mach-Zehnder modulator that regenerates noise-suppressed optical QPSK signals. We experimentally show that the regenerator improves the receiver sensitivity by about 8 dB at an input optical signal-to-noise ratio (OSNR) of 19 dB at a signal speed of 10 Gbaud. Numerical simulation is conducted for higher speed operation at 56 Gbaud to study the impact of the bandwidth of electrical circuits inside the regenerator on the regenerator performance. Electrical power consumption of the regenerator is assessed, and it is shown that the optoelectronic regenerator consumes a similar amount of electrical power as that consumed by an all-optical version of the regenerator using semiconductor optical amplifiers as a nonlinear element.