Research of optical short pulse source with tunable repetition rate and ultra-low timing jitter

Abstract

The highly stable optical short-pulse generator with high repetition rate is widely applied in many fields of optical communications, such as optical packet switching systems, high-speed analog-to-digital converter systems, wavelength division multiplexing networks, high-speed optical sampling systems and optical time division multiplexing networks. The optical short-pulse generator which is adopted in such systems mentioned above should possess high stability, low timing jitter, the tunability of the repetition-rate, and narrow pulse width. So far, most of the optical short pulses have been generated from the actively mode-locked lasers and the phase-modulated continuous wave lasers. However, both of the two methods require an additional microwave signal source. Consequently, the stability of such an optical short-pulse generator is strictly limited by the phase noise and stability of the additional microwave signal source. Since the concept of an optoelectronic oscillator which includes the generation of low noise optical pulses together with an ultra-low phase noise microwave signal was proposed by Yao in 1996, the optical short-pulse generator based on the optoelectronic oscillator has attracted much attention in recent years. According to this approach, Lasri demonstrated a novel, self-starting optoelectronic oscillator based on an electro-absorption modulator in a fiber-extended cavity for generating an optical pulse stream with high-rate and ultra-low jitter capabilities in 2003. In the scheme, the repetition rate of the generated optical pulses is 10 GHz, and the phase noise is-115 dBc/Hz at 10 kHz. Devgan demonstrated an optoelectronic oscillator by using a gain-switched vertical-cavity surface-emitting laser in a fiber-feedback configuration in 2006. The structure can generate a 2-GHz optical pulse stream with 750-fs timing jitter (over 100 Hz-10 MHz range). In the present paper, a novel optical short-pulse generator with tunable repetition rate and ultra-low timing jitter based on optoelectronic oscillator is demonstrated. The optoelectronic oscillator system can generate the microwave signal with ultra-low phase noise. The continuous wave light directly modulated by this microwave signal is phase modulated twice, and then the optical pulses with remarkable chirping rate are achieved. By optimizing the length of the dispersion compensating fiber, the optical pulses are further compressed. In this experiment, by utilizing a YIG tunable filter, the high-quality and tunable microwave signal within 8-12 GHz is achieved, which demonstrates the tunability of the repetition rate of the optical pulses. When the frequency of the microwave signal (i.e., the repetition rate of the optical pulses) is 9.6 GHz, the measured pulse width and the phase noise are 3.7 ps and-130.1 dBc/Hz at 10 kHz, respectively. Therefore, the timing jitter of the short optical pulse is calculated to be 60.1 fs (over 100 Hz to 1 MHz).