Opportunities for optical access network transceivers beyond OOK [invited]

In response to the ever-growing challenge of using conventional direct-modulation/direct-detection transceivers for upgrading passive optical networks, there has recently been a surge in interest in alternative transceiver technologies. Candidate systems include (simplified) coherent receivers, and digital signal processing in combination with direct detection. Beyond these mainstream solutions, other, more esoteric, system designs have been proposed, including networks based on general purpose signal processing hardware, split carrier transmitters, and ultra-wide bandwidth coherent receivers. Herein, we review these techniques and detail an experimental investigation of an ultra-wide bandwidth coherent receiver. It is found that the use of a dual-local oscillator receiver in an ultra-dense wavelength division multiplexed passive optical network (UDWDM-PON) enables the simultaneous detection of multiple upstream channels while efficiently using the complete receiver optoelectronic bandwidth.