A Novel Differential Polarization-shift Keying Scheme for Fiber-optic Communication System

The rapid development of fiber-optic communication system requires a increasing transmission data rate and reach. One of the challenge for long-haul high-speed fiber-optic system is how to reduce the impairments and degrading effects from fiber dispersions and nonlinearity. Although the advances of digital signal processor (DSP) make impairment compensation for the coherent systems become possible, the implementation of coherent system is still expensive. Among the direct detection systems, differential phase-shift keying (DPSK) system shows great advantages over other modulation schemes. Although the recent commercial fiber-optic communication systems are based on DPSK, polarization-mode dispersion and fiber nonlinearity are still limiting factors for DPSK systems. In 2004, a differential polarization-phase-shift keying (DPolPSK) system in which information is encoded in both polarization and phase with multi-level direct detection is proposed, and it is found out the DPolPSK system greatly reduces the effect of nonlinear polarization scattering. With the expectation of getting a better nonlinear tolerance than DPSK system, a novel differential polarization-shift keying (DPolSK) system with balanced direct detection receiver is proposed and compared with DPSK system in terms of fiber dispersion and nonlinearity tolerance.