Long-Haul Transmission of PM-16QAM-, PM-32QAM-, and PM-64QAM-Based Terabit Superchannels Over a Field Deployed Legacy Fiber

Increase in transmission symbol-rate as well as order of quadrature amplitude modulation (QAM) is identified as the most economical way to reduce cost per transmitted bit. In particular, next generation transponders aim at supporting data-rates up to 1 Tb/s employing superchannels due to electrical components' bandwidth limitations. Furthermore, the introduction of a flexible-grid architecture can maximize throughput by minimizing spectral gaps in available optical spectrum. Keeping in view these design options, we conducted several high capacity experiments with tier1 operator Orange using their field deployed standard single mode fiber (SSMF, G.652), having a total length of 762 km, connecting the cities Lyon and Marseille in France. In particular we employed four subcarriers per Tb/s superchannel, each modulated by PM-16QAM, PM-32QAM, and PM-64QAM with per carrier symbol-rates of 41.2 GBd, 33 GBd, and 34 GBd, respectively. The subcarrier spacing was 50 GHz for the PM-16QAM case and 37.5 GHz for both the PM-32QAM and PM-64QAM cases allowing in total 24 × 1.0, 32 × 1.0, and 32 × 1.2 Tb/s superchannels over C-band and resulting in potential C-band capacities of 24.0, 32.0, and 38.4 Tb/s, respectively. After field transmission the maximum available OSNR_{0.1 nm} margin compared to the required OSNR_{0.1 nm} at forward error correction (FEC) threshold was 8.2, 5.4, and 4.2 dB for PM-16QAM, PM-32QAM, and PM-64QAM, respectively. The transmission reach for PM16QAM and PM-32QAM modulated superchannels was extended to ~1571 and ~1065 km using erbium doped fiber amplified SSMF spans of ~101 km length.

I. Introduction

The recent advances in social networking, cloud services and media content quality (4k/8k video) is resulting in exponential growth of data traffic. According to recent forecasts, nearly three fold increase in IP traffic is expected over next five years [1]. Consequently, the forethought limitless capacity of optical fibers is rapidly approaching its limits, leading to a capacity crunch [2]. Using currently deployed coherent polarization multiplexed- (PM-) quadrature phase shift keying (QPSK) systems over 50 GHz spaced standard ITU grid [3], an overall capacity of 10 Tb/s can be achieved over the full C-band spectrum (1528–1566 nm) [4].