A comprehensive study of the noise characteristic in optical balanced receivers in differential phase shift keying (DPSK) systems is performed. The receiver model based on Karhunen-Loève (KL) transform which may include the main transmission impairments in WDM systems is proposed as well as the numerical computation techniques for bit error ratio (BER) assessment. The statistics of the decision current is obtained which shows exact agreement with that of Monte-Carlo simulation, so the analytical result is reliable for accurate estimation of BER. After validated by the time consuming Monte-Carlo error count, the proposed model is adopted in a back-to-back simulation and the 3 dB advantage of DPSK over traditional on-off keying (OOK) is clearly verified.
This paper studies advanced optical phase modulation formats in 40Gb/s Ultra-long-haul systems. As well known, the performance of 40Gb/s Ultra-long-haul systems depends upon the modulation formats. Since DPSK modulation format has higher spectral efficiency and more tolerance to fibre nonlinearity induced impairment, different duty cycle has important impact on result. In this letter, we comprehensively analyzed the transmitting performances of optical phase modulation formats with using the eye-opening penalty (EOP). NRZ-DPSK, full frequency modulated RZ-DPSK (FullRZ-DPSK), half frequency modulated RZ-DPSK (HalfRZ-DPSK) and CSRZ-DPSK modulation formats was numerical simulated within four kinds fiber system: G.652 Fiber, True Wave fiber (TW), True Wave-Reduced Slope fiber (TW-RS) and Large Effective Area Fiber (LEAF). Through modelling and simulation, we compute the EOP of these phase modulation formats, with different average optical input power. The numerical simulation result shows thatCSRZ-DPSK is best performance in all phase modulation, and G.652 outperforms other types of fibers in 40Gb/s Ultra-long-haul systems.
Dense wavelength division multiplexing (DWDM) system is the tendency of optical fiber communication systems because of its high speeds and capacities. DWDM systems with channel data rates of 40 Gbit/s bring us both advantages and challenges. With broader spectrum, the signal suffers more from chromatic dispersion, optical fiber nonlinear effects and polarization mode dispersion (PMD). Simultaneously, the combination of PMD and nonlinear effects results in more complexity. In this paper, amended nonlinear Schrodinger equations, which include group velocity dispersion (GVD), third order dispersion (TOD), self-phase modulation (SPM), cross-phase modulation (XPM), four-wave mixing (FWM) and PMD synthetically, are derived, then the system degradation induced by PMD and nonlinear effects is investigated via numerical simulation. The results show that when the power of input signal is low, PMD has more affection on system comparing with nonlinear effects, and nonlinear effects become dominating with power increasing, but mild PMD may mitigate their impact to some extent. The results in this paper are valid for design and analysis of long haul DWDM systems with high bit rate.
In this paper, a novel method to reproduce the maximum DGD is proposed. In the model different PMD states are obtained by randomly varying the polarization coupling angle between sections. By confining the coupling angles' distribution to a shrinking range, the statistics of DGD will be distorted and the low probability events will be efficiently produced. The relationship between the mean DGD of changed DGD distribution and the angle range is given to make it convenient to choose a suitable angle range at a given maximum DGD and simulating sections.