Resonant electro-optic phase modulator and photodetector for stabilizing laser frequency and quantum optics
Authors: Tian Long , Zheng Li-Ang , Zhang Xiao-Li , Wu Yi-Miao , Wang Qing-Wei , Qin Bo , Wang Ya-Jun , Li Wei , Shi Shao-Ping , Chen Li-Rong , Zheng Yao-Hui ,   State Key Laboratory of Quantum Optics and Quantum Optics Devices, Institute of Opto-Electronics, Shanxi University, Taiyuan 030006, China,   College of Physics and Electronic Engineering, Shanxi University, Taiyuan 030006, China,   Collaborative Innovation Center of Extreme Optics, Shanxi University, Taiyuan 030006, China
Published: May 2023

Photoelectric functional device with specific optical, electrical and photoelectric conversion effects is one of the most important resources of modern information science and technology. Electro-optic modulator and photodetector are very important photoelectric functional devices, which are key devices in the fields of frequency locking, feedback control, photoelectric information conversion, optical communication, photoelectric information modulation, etc., and play an irreplaceable role in frequency stabilization locking technology of PDH (Pound-Drever-Hall, simply referred to as PDH). The PDH technology is widely used in researches of large scientific devices, quantum optics, optical communication and other fields. Using electro-optical phase modulator to carry out laser phase modulation is the primary process to realize frequency stabilization locking of standard PDH. Photoelectric detection can implement the photoelectric conversion of the carried weak modulation signal and spectral peak signal into electrical signal, and then feedback control through proportional integral and differential circuits, so as to achieve stable locking and frequency stabilization. The resonant electro-optical phase modulation (RPM) with high modulation depth, low power consumption and low half-wave voltage and microwatt resonant photoelectric detection (RPD) functional device with high signal-to-noise (SNR) ratio are invented to meet the demand for extraction and detection of extremely weak signals. The resonant circuit is composed of the single-end wedge-angle lithium niobate crystal, low noise photodiode and low-loss and high-Q electronic components. Low power consumption, high modulation depth electro-optic modulation, and high gain photoelectric detection are realized by the principle of resonant enhancement. When the optimal modulation frequency point is 10 MHz, the bandwidth of RPM is 225 kHz with <i>Q</i> of 44.4, when the modulation depth is 1.435, the RPM requires RF drive voltage of RPM to be 4 V. When the optimal modulation frequency point is 20 MHz, the bandwidth of RPM is 460 kHz with <i>Q</i> of 43.5, the required RF drive voltage of RPM is 6.5 V when the modulation depth is 1.435. The optimal detection frequency point of the self-invent RPD is 20.00 MHz, with a bandwidth of 1 MHz, Q of 20, the gain of 80 dB at 100 μW. With the home-made RPM and RPD in the extraction loop for extremely weak signal, the SNR of error signal is as high as 5.088 at 10 μW, 34.933 at 50 μW and 58.7 at 100 μW. Such a loop improves the performance and stability of the entire feedback control loop by optimizing parameters of proportional integral differential, which provides key devices and technological approaches for preparing a highly stable quantum light source and ultra-stable laser.