Direct-Modulation Optoelectronic Oscillator for Optical Frequency Comb and Pulse Generation

Opto-electronic oscillators (OEOs) are able to produce low phase noise radio-frequency signals thanks to their high-quality-factor resonator that includes a km-long optical delay line [1]. While the main use of OEOs is the synthesis of ultra-pure electrical signals and optical clock distribution, it is also possible to generate short optical pulses with low timing jitter, using for instance nonlinear compression in the OEO fiber [2], for applications such as optical sampling, remote sensing (RADAR, LiDAR), frequency comb generation and so forth. We have recently demonstrated a 10 GHz direct-modulation OEO (DM-OEO) with a phase noise of -135 dBc/Hz at 10 kHz. In this work, we propose to take advantage of the optical output of the DM-OEO in order to broaden the optical spectrum and possibly generate ultra-low jitter optical pulses by nonlinear compression in the long SMF fiber. To this end, we have designed an optoelectronic loop including a phase modulator to positively chirp the laser field, and an Erbium Doped Fiber Amplifier (EDFA) to increase the nonlinear effects in the fiber (see Fig. 1a).