Dual-Drive Mach-Zehnder Modulator-Based Single Side-Band Modulation Direct Detection System Without Signal-to-Signal Beating Interference

Abstract

Kramers-Kronig (KK) receiver based optical single sideband (SSB) direct detection (DD) systems have been extensively investigated to cope with signal-to-signal beating interference (SSBI) for long-reach optical interconnect and 400G ZR. In this paper, we analyze the principle of dual-drive Mach-Zehnder modulator (DDMZM)-based SSB modulation due to its low cost compared with IQ modulator. We find that SSBI does not exist in back-to-back (BTB) after square-law direct detection, and electrical dispersion compensation (EDC) cannot be realized at the transmitter due to the nonlinear modulation of DDMZM. In our proposed scheme, Cartesian to Polar conversion (CPC) is used to achieve the linear modulation of DDMZM, then pre-EDC is achievable. Signal construction operation is applied to generate a target signal avoiding SSBI in DDMZM-based SSB modulation with direct detection, thus KK algorithm is not necessary both in BTB and after fiber transmission with pre-EDC, and the computation complexity of the receiver can be effectively reduced. In the simulation results of 25 GHz SSB Discrete Fourier transform spread discrete multi-tone (DFT-S DMT), the BER of our proposed scheme and conventional DDMZM scheme with optical signal-to-noise ratio (OSNR) of 26 dB are 1.2 × 10−3 and 1.7 × 10−2, respectively, after 80 km standard single mode fiber (SSMF) transmission with pre-EDC. The simulation results show that our proposed scheme is better than conventional DDMZM scheme. Although it is still inferior to the conventional IQ scheme with KK algorithm, the computation complexity of CPC is much lower than KK algorithm as it saves the numbers of adders and multipliers by the factors of 119 and 62, respectively, and reduces the memory size by a factor of 4.3.