Stable broadband all-optical pulse generation with 1 Hz phase noise

Abstract

JTh2A.36.pdf CLEO:2015 © OSA 2015 Fig. 1: Experimental setup for all optical microwave generation based gain-induce FWM.Abstract: Feedback-free, RF-free, long-term stable, all optical, short pulse generation utilizing gain-induced FWM is demonstrated. The approach utilizes passive mode-locked (10 MHz) laser injection locking DFBs to provide pulses with a phase noise of 1 Hz.Photonic-based microwave generation techniques using injection locking have been extensively investigated for various applications, and representative examples are given in [1,2]. They allow, not only the widely tunable optically-controlled generation of microwave signals, but also offer a performance that is characterized with high frequency stability. Thus, Injection locking techniques have offered a very promising solution for photonic-based pulse generation which requires stable microwave seed signal [3]. Recently, optical pulse-trains that are generated in using all-optical approaches with no RF bias have been demonstrated. This appraoch is based on gain-induced FWM in SOAs [4]. A unique advantage of this versatile approach is the optical control afforded over the repetition rate, which could be tuned by controlling the frequency difference between the two light sources. However, in that first demonstration, the uncorrelated phase of the two DFB sources results in a less stable performance of the generated pulses. In this work, we drastically improve upon recent all-optical short pulse genertion [4] by using injection locking. Robust and low-phase noise pulse generation ranging from 230 MHz ~ 76 GHz with a line-width ~ 1 Hz is experimentally demonstrated [5]. The technique for achieving short pulses using such low phase noise across the operating range is demonstrated in Fig. 1. The passive mode-locked laser (FFL) is a 10 MHz repetition rate fiber laser centered at a wavelength of 1550 nm. The slave lasers were two linearly polarized single mode distributed feedback semiconductor sources with an output power of 6 dBm. Injection locking was observed by splitting off a portion of the passive mode-locked laser prior to injection and recombining it with the slave laser output. Then the beating signal of the two locked DFB lasers are externally injected into the ring laser cavity directly at the SOA port to modulate the gain of a SOA, at a frequency determined by their beating signal. The main fiber ring cavity is comprised of two SOAs (Kamelian non-linear SOAs & Thorlab BOA): the first SOA functions as the gain and modulation media while the second one changes the net gain of the cavity. The tunable flat-top OBPF has a 3 dB bandwidth of ~6.8 nm centered at ~1560 nm. It is employed to perform wavelength selection of the output and filter the injected beating signal. By fixing one DFB central wavelength and tuning the other central wavelength, 230 MHz to 76 GHz beating signals are generated and monitored. The external beating signal with a power level of 7 dBm is coupled into the cavity. Robust and long-term stable short pulses are generated at...