DPSK Receiver Design - Optical Filtering Considerations - Sponsored Whitepaper

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Abstract: We study via simulation the influence of the DPSK decoder free spectral range (FSR) when strong optical filtering is considered for the NRZ and RZ modulation formats and show that larger FSR can improve performance. ©2007 Optical Society of America OCIS codes: (060.2330) Fiber Optics Communications; (060.5060) Phase Modulation

1. Introduction The differential phase-shift keying (DPSK) modulation format has attracted considerable attention in recent years due to its superior OSNR sensitivity and fiber nonlinearity tolerance compared to on-off keying formats. It has especially attracted attention for higher data rate applications, notably 40 Gbps and beyond. The practical direct detection DPSK receiver architectures considered in this study require two key components, namely a balanced photodetector and a delay-interferometer (DI). These components are quickly reaching a maturity level enabling mass production of DPSK based OC-768/OTU-3 line cards. One critical aspect in any DPSK receiver design is the choice of DI. This choice depends on many factors, including cost, size, control complexity, as well as DWDM system-level considerations such as channel spacing, single or mixed data rates (e.g. 10G + 40G on same platform), impact of terminal equipment filters and ROADMs, channel plan, as well as sparing and manufacturing considerations.

Although DPSK DI performance has been studied extensively for the return-to-zero (RZ) [1-3] and non-return- to-zero (NRZ) [4-6] formats, the effect of strong optical filtering in the DWDM link on DI performance has not been considered. This subject is of high importance for DWDM systems where the DPSK signals must pass through filters whose effective concatenated optical bandwidths approach, or are below, the data rate. Practical examples include deployment of OC-768/OTU-3 DPSK signals over OC-192/OTU-2 systems employing 50 GHz optical filters with ROADMs, and deployment over systems employing a large number of ROADMs, where the concatenated optical bandwidth can quickly go below 50 GHz. In this paper, we study via simulation the impact of the free spectral range (FSR) of the DI as a function of additional optical filtering for both the NRZ and RZ DPSK formats at 43 Gbps. Numerical results are experimentally verified for the NRZ format.
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