5

Optical Phase Locking

5.1    Overview of Optical Phase Lock Loop

Coherent receivers offer far more efficient detection and sensitivity of optical signals under various phase, amplitude, or frequency modulation scheme techniques as compared to simple direct detection. The critical component of a practical coherent receiver is the phase lock loop (PLL) in the optical domain, the optical PLL (OPLL). The PLL has found widespread applications in the electrical domain. However, the OPLL has yet to reach maturity due to its difficult setup and problems with stability. This chapter thus aims to improve the performance of the OPLL with the development of a novel FPGA-based loop filter, a digital phase locking state loop.

The OPLL and coherent optical ...

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