All-optical clock recovery from advanced modulation formats through injection-locking of fiber laser

The use of advanced modulation formats in optical communication imposes stringent requirements on optical signal to noise ratio (OSNR) and thus, 3R (re-amplification, reshaping and retiming) regeneration is increasingly relevant in long-haul communication links. Clock recovery is a critical functionality for performing the mid-span 3R regeneration and an all-optical implementation is desirable to minimise the number of O-E-O conversions [1]. Injection locking of fiber lasers has proved to be a reliable method that yields improved jitter performance [2]. In this paper, we will explain the working principle of injection locking in an nonlinear polarisation rotation-based passive mode locked laser. We also present the details of clock tone enhancement from non-return-to-zero (NRZ) pulses using a nonlinear SOA. We will further discuss the experimental results of clock recovery for 10 Gbaud NRZ signals, and its resilience to carrier wavelength and modulation formats such as OOK, BPSK, QPSK and 16-QAM.