Simplified Coherent Optics for Passive Optical Networks

Abstract

This chapter discusses the possibility of significantly reducing the optoelectronics hardware complexity of a coherent receiver to facilitate implementation in cost-sensitive applications, such as Passive optical networks (PONs). It explores the digital signal processing (DSP) complexity requirements for coherent receivers operating in PONs. Passive optical networks (PONs) are based on transmission using intensity-modulated lasers and direct-detection receivers as has been the case since their development. The IEEE ethernet PON Working Group 802.3ca is exploring options for advanced, soft-decision, forward error correction (FEC) codes, and discussions are ongoing regarding high-speed avalanche photodiodes, multilevel modulation, external modulation, and even DSP for feed-forward equalization of channel and transceiver impairments. A promising quasi-coherent design, which effectively extends the reach of 10 Gb/s PONs without optical amplification, is depicted. It is shown that the DSP requirements for most PON systems are comparable to the feed-forward equalizers under the consideration for intensity-modulation and direct-detection (IM-DD) PON.