Optical MSK long-haul transmission systems

Abstract

ABSTRACT The generation and detection of linear, weakly non-linear and strongly non-linearly optical MSK long-haul transmission systems have been reported. The simulation test-beds based on Matlab Simulink platform have been successfully developed. The following significant results have been achieved: (i) BER of 10 -38 is achieved for an OSNR of 22.2dB; (ii) At BER of 10 -12 , linear MSK is approximately 1 dB more tolerable to nonlinearity than weakly nonlinear MSK and 5.5dB more durable than strongly nonlinear MSK; (iii) (c).The sideband suppression ratio for linear MSK is approximately 22dB. New technique for calculation of performance evaluation implementing expected maximization (EM) theorem is utilized. Keywords: optical communications, continuous-phase modulation, minimum-shift keying direct detection. 1. INTRODUCTION In bandwidth-limited digital communication including wireless and satellite digital transmission, minimum-shift keying (MSK) has been proven as a very efficient modulation format due to its prominent spectral efficiency, high sideband suppression, constant envelop and high energy concentration in the main spectral lobe. In modern high capacity and high performance optical systems, we have witnessed the accelera tion of transmission bit rate approaching 40Gb/s and even to 160 Gb/s. At these ultra-high bit transmission speeds, the essence of efficient modulation formats for long haul transmission is critical. There are several technical published works on advanced modulation techniques for optical transmission, which mostly focus on discrete phase modulation including binary DPSK and DQPSK [1-3] with various pulse carving formats including non-return-to-zero (NRZ) and CS-RZ [2, 4]. However, there is only limited number of works on MSK modulation format [5-8]. The features of MSK, comparing to other modulation formats have prompted researchers to investigate its suitability for high capacity l ong-haul transmission. The side lobes of MSK power spectrum are greatly suppressed giving it good dispersion tolerance and avoiding inter-channel crosstalks. Thus this modulation is of interests for further investigations. Two different proposals of transmitter configurations for generation of linear and non-linear phase optical MSK modulation are reported in another paper in this conference [9]. The brief operation descriptions of these two transmitter configurations are presented in section 2 whereas the dire ct detection techniques for both linear and non-linear optical MSK signals are stated in section 3. Our simulation models for the modulation and system transmission are based on MATLAB Simulink platform [10] with detailed discussions in section 4. In this paper, we have also proven that optical MSK signal is capable of propagating over an optically amplified and fully dispersion compensated fiber multi-span distance of 360 km , 450 km and 540km span length. Not only the performance of conventional MSK format but also that of the weakly and strongly nonlinea r optical MSK sequences are evaluated.