ObjectiveThe 633 nm iodine-stabilized He-Ne laser, based on saturated absorption frequency stabilization, is globally recognized as a national length standard due to its high stability, long lifespan, good wavelength reproducibility, visible wavelength, and compact size. Its laser frequency is used to reproduce the definition of the meter. To meet the demand for portability and intelligence in the field of metrology and to expand the application scenarios of iodine-stabilized He-Ne lasers, this study investigates a digital stabilization method for the wavelength standard of the iodine-stabilized He-Ne laser based on a microprocessor. Digital algorithms are employed to implement key technologies for laser frequency stabilization, and the control system integrates Bluetooth communication, allowing operators to monitor the laser status in real time via host software and adjust optimization parameters as needed for different lasers.The specific algorithm principles are illustrated in
Fig.1,
Fig.2,
Fig.5 and
Fig.9. This method overcomes the cumbersome adjustments, operational difficulties, and limited intelligence of traditional analog technologies, significantly enhancing the portability and intelligence of the 633 nm wavelength standard, laying a solid foundation for industrial applications.
MethodsThis study investigates a digital control method for the iodine-stabilized wavelength standard based on a microcontroller (MCU). Key technologies such as signal modulation, harmonic demodulation, and frequency stabilization are implemented using digital algorithms. By simply adjusting a few parameters, the signal generation frequency can be easily modified, and harmonic signals can be demodulated with a high signal-to-noise ratio, enabling precise identification of absorption peaks and rapid locking of the laser frequency. The reliability of this digital stabilization method is verified through experiments measuring absolute frequency with an optical frequency comb and comparative tests with an analog control system, as shown in
Fig.14 and
Fig.15.
Results and DiscussionsFrequency measurements were conducted between a digitally stabilized unsaturated vapor cell iodine-stabilized laser and a digitally stabilized saturated vapor cell iodine-stabilized laser using a femtosecond laser optical frequency comb. The results show that the short-term and long-term frequency stability closely match the Allan variance results from the analog control system. The maximum frequency fluctuation of the unsaturated iodine-stabilized laser was 13 kHz, yielding a reproducibility of 2.74×10
-11, while the saturated laser exhibited a maximum frequency fluctuation of 4 kHz, resulting in a reproducibility of 1.4×10
-11. Overall, the frequency stability and reproducibility of the saturated laser controlled by the digital method were better compared to those of the unsaturated laser, with both showing performance metrics comparable to lasers using the analog control system. It significantly improves the portability and intelligence of the control system, showing great potential for broader applications.
ConclusionsThis paper introduces a digital stabilization control method for the 633 nm iodine-stabilized wavelength standard, utilizing a self-developed digital control system to implement all functionalities traditionally achieved through analog control. The digital stabilization system can connect the laser control status to a host computer via Bluetooth communication protocol, allowing real-time monitoring of the laser status and supporting on-demand optimization of parameters to accommodate different laser heads. This enhances the system's interactivity and monitoring capabilities, making the entire stabilization control process simpler and further improving portability and intelligence. The stabilization control system is applied to both saturated and unsaturated gas cell 633 nm iodine-stabilized lasers, with their absolute frequencies calibrated using an optical frequency comb. The results show that the stabilization metrics of the digital stabilization laser are comparable to those of the traditional analog circuit stabilization laser. The digital stabilization method developed in this paper effectively controls the iodine-stabilized laser, overcoming the complexities of debugging in analog control systems and the low level of intelligence. It offers a higher level of intelligence and task expansion capability, meeting the new demands of intelligent and digital development in metrology.