Opt Lett. 2023 Apr 15;48(8):2074-2077. doi: 10.1364/OL.486694.
Microwave photonic phase detectors (MPPDs) can extract ultrastable microwaves from a mode-locked laser (MLL), but their frequencies are often limited by the pulse repetition rate. Few works studied methods to break the frequency limitation. Here, a setup based on an MPPD and an optical switch is proposed to synchronize an RF signal from a voltage-controlled oscillator (VCO) to an interharmonic of an MLL and to realize the pulse repetition rate division. The optical switch is employed to realize pulse repetition rate division, and the MPPD is followed to detect the phase difference between the frequency-divided optical pulse and the microwave signal from the VCO, which is then fed back to the VCO via a proportional-integral (PI) controller. Both the optical switch and the MPPD are driven by the signal from the VCO. When the system reaches its steady state, the synchronization and repetition rate division are achieved simultaneously. An experiment is conducted to verify the feasibility. The 80½th, 80⅓rd, and 80⅔rd interharmonics are extracted, and pulse repetition rate division factors of two and three are realized. The phase noises at offset frequency of 10 kHz are improved by more than 20 dB.
微波光子相位探测器（MPPD）可从锁模激光器（MLL）中提取超稳定微波，但它们的频率通常受到脉冲重复率的限制。很少有研究突破频率限制的方法。这里提出了一种基于 MPPD 和光开关的设置，以将压控振荡器（VCO）的射频信号同步到 MLL 的间谐波，并实现脉冲重复率分频。光开关用于实现脉冲重复率分频，随后 MPPD 检测分频光脉冲与 VCO 微波信号之间的相位差，并通过比例积分（PI）控制器将其反馈给 VCO。光开关和 MPPD 均由 VCO 的信号驱动。当系统达到稳定状态时，可同时实现同步和重复率分频。进行了实验验证其可行性。提取了 80½、80⅓rd 和 80⅔rd 间谐波，并实现了 2 和 3 的分频因子。在 10 kHz 偏移频率处的相位噪声提高了 20 dB 以上。
