关键词:
Frequency stability
摘要:
Objective Ultrastable lasers offer the benefits of ultrahigh-frequency stability and extremely narrow linewidths. They are crucial in atomic clocks, optical-frequency transmission, gravitational-wave detection, Lorentz-invariance testing, and other applications. Typically, an ultrastable laser is created using the Pound-Drever-Hall (PDH) technique to lock the laser frequency to an ultrastable Fabry-Perot (F-P) cavity. Owing to the continuous progress and development of science and technology, the demand for scientific tasks is increasing. Simultaneously, higher requirements are imposed on the stability and long-term locking ability of ultrastable lasers. When the laser frequency is locked, circuits or mechanical disturbances may cause the laser to be unlocked. Once this occurs, the ultrastable laser must be relocked promptly. Analog feedback circuits are commonly used to implement frequency-locked to avoid introducing additional digital noise. However, the conventional analog circuits present some disadvantages, including inconvenient adjustment of locking parameters, difficulty in automatic locking, and necessity for remote control. Hence, this study proposes a universal analog frequency-locked circuit with digital control. Methods A digitally controlled analog frequency-locked circuit was designed to stabilize the frequency of various types of lasers, such as Nd: YAG, fiber, and external-cavity diode lasers. To satisfy the requirements of different lasers and cavities, the proportional-integration-differentiation (PID) parameters of the circuits were adjusted from hundreds of hertz to hundreds of kilohertz. Additionally, a microcontroller, digital switches, and digital potentiometers were integrated into the circuit to enable the digital control of the locking parameters and locking switches. To determine whether the digital chips imposed additional bandwidth limitations to the circuit, the transmission characteristics of the frequency-locked circuit in the open l