Rectangular QPSK for Generation of Optical 8PSK

摘要

Different from the symmetric square-shape constellation generated by a conventional QPSK (quadrature phase-shift keying) transmitter, a QPSK with a rectangular-shape constellation (i.e. rectangular QPSK) is expected to be obtained when driving an in-phase/quadrature (IQ) modulator in an unbalanced manner. It could be applied to generate multilevel modulation format, like eight-ary phase-shift keying (8PSK). In this paper, we propose and experimentally demonstrate an optical 8PSK transmitter using two tandem IQ modulators. A 30-Gb/s 8PSK is successfully generated through cascading a rectangular QPSK and a square QPSK.