Frequency-Tunable Microwave Pulse Generation Using a Dual-Drive Active Mode-Locked Optoelectronic Oscillator

We propose an active mode-locked optoelectronic oscillator (AML-OEO) for frequency-tunable microwave pulse generation. In the proposed AML-OEO system, an on-chip dual-drive silicon micro-ring resonator (MRR) is specifically designed with a lateral PN junction and a top-placed metallic micro-heater. When a rectangular signal is used to drive the lateral PN junction, the MRR resonance wavelength is shifted at a high speed and thus the realized OEO has a fast gain modulation. When the repetition rate of the rectangular signal matches with the mode spacing of the OEO, active mode locking is performed and microwave pulse trains can be generated. When a DC voltage signal is applied to the metallic micro-heater, the MRR is driven to have a large resonance wavelength tuning range, which leads to a wide center frequency tuning range for the generated microwave pulse. A dual-drive MRR chip is designed and fabricated, and photonic generation of microwave pulse is experimentally demonstrated with the use of the chip. By controlling the rectangular driving signal applied to the MRR, a microwave pulse with a center frequency of 9 GHz and a phase noise of -105.4 dBc/Hz@10kHz is generated. When the duty cycle of the applied rectangular signal is tuned, the temporal widths of the generated microwave pulses are tuned correspondingly. When the DC voltage signal is changed, the center frequency of the generated microwave pulse can be tuned from 6 to 18 GHz. The key advantage of the proposed system is that a single ultra-compact MRR component is used to perform active mode locking and frequency tuning, which highly simplifies the structure of the AML-OEO system. The proposed AML-OEO holds great potential to be widely used in high-speed multi-carrier communication networks and high-resolution pulsed Doppler radar systems.