Simultaneous dibit recovery of DQPSK signal using a single Mach-Zehnder interferometer

The dibit recovery of a differential quadrature phase shift keying (DQPSK) signal is demonstrated using a single Mach-Zehnder interferometer, containing a 1-bit delay, and a single balanced receiver. The electrical output levels of the balanced receiver are dependent upon the relative phase delay between the arms of the Mach-Zehnder interferometer. This characteristic is investigated, when the input signal is DQPSK modulated. It is also shown that with a certain amount of phase shift, the DQPSK signal can be converted into four different equally spaced electrical signal levels, with each decoded level representing one of the four possible dibits.