Polarization-insensitive σ-COEO based on active mode-locking technology for pulse microwave signal generation

• Published in: Optics communications Vol. 569; p. 130833
• Main Authors: Li, Deqi, Wang, Tianshu, Li, Baoqun, Wang, Sunde, Zhang, Jingkai, Yang, Qiaochu, Chen, Junda
• Format: Journal Article
• Language: English
• Published: Elsevier B.V 15.10.2024
• Subjects: Actively mode-locking; Coupled optoelectronic oscillator; Microwave pulse generation; σ-shaped fiber ring; Coupled optoelectronic oscillator; Actively mode-locking; Microwave pulse generation; σ-shaped fiber ring
• ISSN: 0030-4018; 1873-0310
• DOI: 10.1016/j.optcom.2024.130833

We propose a polarization-insensitive σ-shaped coupled optoelectronic oscillator (σ-COEO) based on an active mode-locking technique and demonstrate that it can generate microwave pulse trains with tunable repetition frequencies. Mode-locking in the time domain is achieved by injecting an external microwave signal with an integral multiple of the frequency of the COEO’s free spectral range, which is used as a bias for the modulator to control the loss in the COEO cavity. In addition, the σ-shaped fiber ring structure is cleverly utilized in COEO to ensure the high Q value of the system while eliminating the polarization perturbation caused by long fibers. The experiment demonstrates that, under the current scheme, the phase noise of various higher order harmonics generated by different carriers is better than −114 dBc/Hz at a frequency offset of 10 kHz. This is a positive finding as it effectively suppresses the phase noise deterioration caused by higher order harmonics. The potential applications of the proposed σ-COEO are significant, spanning fields such as metrology, hybrid communications, and radar systems. •The proposed COEO an directly adjustable center frequency and time duration of pulsed microwave signal, breaking the limitation that current COEO research is still conducted in the frequency domain.•The σ-shaped fiber ring structure is skillfully utilized in COEO to limit the spurious noise, the harmonic mode locking of different orders can be easily realized, and the phase noise of the system does not deteriorate significantly.•The value and potential of microwave pulses generated by COEO for practical applications in radar communications are detailed.