Performance analysis of single-MZM APRZ transmitter

We present the first numerical study of 67%-duty-cycle single-MZM APRZ, comparing it with 33% RZ, 33% APRZ and standard CSRZ. This transmitter is shown to combine CSRZ implementation simplicity with the improved nonlinear tolerance of π/2-APRZ. Introduction A major source of impairments encountered when upgrading 10-Gb/s transmission systems to 40-Gb/s is intra-channel four-wave-mixing (IFWM) [1]. One of the most promising techniques to combat this type of impairments is the alternate-phase return-to-zero (APRZ) modulation format [2], in which neighbouring bits are phase shifted by a value ∆φ with respect to each other. Phase alternation can be imposed by a separate phase modulator [2], but it is also possible to combine pulse carving and phase alternation in a single MZM. This APRZ transmitter is then a modified version of the standard CSRZ transmitter, in which the amplitude and relative delay of the driving voltages can be dynamically tuned to generate APRZ and RZ with 33% duty cycle, as well as APRZ and CSRZ with 67% duty cycle. 33% APRZ thus generated was experimentally studied in [3], whereas 67% APRZ was proposed in [4], although no transmission investigation was carried out. In this paper we present the numerical study of 67% APRZ over a 40-Gb/s, 5×100-km link, in terms of nonlinear, dispersion and filtering tolerance, comparing it with 33% APRZ, 33% RZ, and CSRZ. In particular we study the performance dependence on the duty cycle and the phase shift, ∆φ, for the investigated modulation formats. Furthermore we have discovered a new explanation for CSRZ’s relative non-linear tolerance in terms of linear interference between SPM-broadening and ghost-pulse build up. Transmission analysis The transmission properties of the different modulation formats are evaluated numerically (with VPI TransmissionMaker) on a 500-km link consisting of five spans, each of them containing a 6dBm-output EDFA, 100 km standard single-mode fibre (D = 16 ps/nm/km, S = 0.06 ps/nm/km, γ = 1.32 W−1km−1, α = 0.2 dB/km), a 1-dBm-output EDFA, and 20 km dispersion-compensating fibre (D = −80 ps/nm/km, S = −0.18 ps/nm/km, γ = 2.64 W−1km−1, α = 0.6 dB/km). A 1024-bit data sequence is transmitted by the transmitter in Fig. 1. At the receiver the signal is attenuated to a power level Pr, amplified by an EDFA with 5 dB noise figure, passed through a 150GHz Gaussian filter, and finally detected. Receiver sensitivity is measured as the minimum received power Pr in order to achieve BER = 10−9. MZM