Optical field trajectory shaping of phase-shift method-based optical BPSK-VSB signal;an experimental study

Abstract

We experimentally studied field trajectory shaping of optical binary phase shift keying-vestigial sideband (BPSK-VSB) signal for optical quadrature phase-shift keying (QPSK)-VSB generation. The field trajectory of the BPSK-VSB signal is an ellipse. In phase-shift method-based optical BPSK-VSB modulation, the ellipticity of the field trajectory can be controlled by manipulating the amplitude response of the Hilbert transformer. When the Hilbert transformer has a high-pass amplitude response, the field trajectory of the optical BPSK-VSB signal reaches a circle with increasing cut-off frequency. We numerically calculated and experimentally demonstrated the achievability of circular field trajectories in BPSK-VSB modulation for cut-off frequencies greater than 20% of the baseband bandwidth.