Ultrawide and tunable self-oscillating optical frequency comb generator based on an optoelectronic oscillator
Rahat Ullah, Sibghat Ullah, Gul Zameen Khan, Yaya Mao, Jianxin Ren, Jianye Zhao, Shuaidong Chen, Mingye Li, Jahangir Khan
Abstract
A new mechanism for ultra-wide and tunable self-oscillating optical frequency comb (OFC) based on a novel frequency tunable optoelectronic oscillator (OEO) is proposed using cascaded configuration of optical phase-modulator (PM) and electro-absorption-modulator (EAM). The proposed scheme does not require a dedicated RF source to drive the optical-modulators. The OEO is configured by incorporating the self-oscillation loop with cascaded modulators. A high-speed PIN-photodetector (PD) with a dark current of 10nA, bandwidth of 20 GHz, and responsivity of 1A/W in correspondence with an electrical-amplifier (EA), and bandpass Bessel filter (BPBF) is utilized to convert the optical signal into a microwave signal. The PD detected signal is amplified by the EA. The BPBF is used to extract a 10 Mhz bandwidth from the amplified signal with tunable central frequencies. Part of the extracted OEO signal is directly connected to the PM, whereas, a 180-degree phase-shift is added to the signal before transmitting into the EAM. The PM produces ~19 carrier frequencies, whereas, the generated tunable carriers by the EAM ranges from 85 to 35carrriers with an overall bandwidth of ~1.28THz. The negligible power-fluctuations, good number of generated carriers, and high tone-to-noise-ratio of around 40 dB endorse the applicability of the proposed scheme.