We proposed a hybrid transmission system consist of 1Tbit/s Nyquist WDM channels,100Gbit/s PDM-QPSK WDM channels and 10Gbit/s NRZ WDM channels to study whether Terabit Nyquist WDM signal could transmit in the existing hybrid systems with DCM(dispersion compensation module). The simulation results demonstrated the influence of all these three kinds of signals. The 1Tbit/s Nyquist WDM channels introduced 1.5d B Q penalty to the 100Gbit/s PDM-QPSK signals and their influence on the 10Gbit/s NRZ signals was extremely slight. In the hybrid optical system,1Tbit/s Nyquist channel has 5d B Q penalty due to the inline DCM and 2.5d B Q penalty due to the channel interference from existing channels. Therefore,the total Q penalty is 7.5d B caused by strong nonlinear effects at the launch power of 0d Bm. The results have the guiding significance for the design of future backbone system and also support the feasibility of future dynamic optical system.
The compensation effects of fiber nonlinearity in 112 Gb/s polarization division multiplexing（PDM） coherent optical systems by mid-span optical phase conjugation（OPC） based on four wave mixing（FWM） effect are studied. Comparisons of the compensation results between PDM coherent optical-orthogonal frequency division multiplexing（CO-OFDM）system and the single carrier（SC） PDM quadrature phase shift keying（QPSK） system are provided as well. The results demonstrate that nonlinear compensation effect with mid-span OPC in PDM CO-OFDM system is much more obvious than that in SC PDM QPSK system.
In this paper, we proposed a novel modulation format identification method for square M-quadrature amplitude modulation (M-QAM) signals which is based on amplitude histogram space of the incoming data after analog-to-digital conversion, chromatic dispersion com-pensation at the receiver. We demonstrated the identifica-tion of quadrature phase-shift keying (QPSK), 16-QAM, 64-QAM formats with an amplitude histogram space. Simulation results show that it achieve 100% identification accuracy when the incoming signal OSNR is 14 dB to identify the modulation format of QPSK, 16-QAM, and 64-QAM signals in digital coherent systems. The method has low complexity and small delay.
We propose a novel waveguide design of polarization-maintaining few mode fiber(PM-FMF) supporting ≥10non-degenerate modes, utilizing a central circular air hole and a circumjacent elliptical-ring core. The structure endows a new degree of freedom to adjust the birefringence of all the guided modes, including the fundamental polarization mode. Numerical simulations demonstrate that, by optimizing the air hole and elliptical-ring core,a PM-FMF supporting 10 distinctive polarization modes has been achieved, and the effective index difference Δn_(eff) between the adjacent guided modes could be kept larger than 1.32 × 10^(-4) over the whole C +L band. The proposed fiber structure can flexibly tailored to support an even larger number of modes in PM-FMF(14-mode PM-FMF has been demonstrated as an example), which can be readily applicable to a scalable mode division multiplexing system.
