Digital Linearization of Direct-Detection Transceivers for Spectrally Efficient 100 Gb/s/λ WDM Metro Networking

Single-polarization, single-photodiode-based direct-detection (DD) transceivers offer advantages for metro networks due to their simple and low-cost optical hardware structure. Single-sideband Nyquist-pulse-shaped subcarrier modulation (SSB Nyquist-SCM) is a promising signal format to achieve high information spectral density (ISD) in such DD systems. In this paper, we present theoretical and experimental evaluations of a variety of direct-detection SSB Nyquist-SCM system designs, operating at 100 Gb/s per wavelength in wavelength division multiplexing (WDM) metro network scenarios. Through simulations, several receiver-based digital linearization techniques to overcome the effect of signal-signal beat interference were investigated, and their performance compared with alternative approaches, including optical beat-interference cancellation receivers (BICRx) and coherent receivers (both heterodyne and homodyne). Subsequently, experimental assessments of the digitally-linearized DD receivers were carried out. Spectrally efficient (net ISD exceeding 3 b/s/Hz) 4 × 112 Gb/s WDM DD single-sideband 16-QAM Nyquist-SCM transmission over distances of up to 240 km (multi-span links) and 160 km (single-span links without mid-span amplification) were shown to be possible using uncompensated standard single-mode fiber.