Quantum precision measurement is a method that utilizes the quantum effects and techniques of light-atom interactions to break through the standard quantum limit in order to achieve measurement accuracy, sensitivity and stability that comprehensively surpasses classical measurement means. The key to this disruptive technology is a narrow linewidth laser that realizes fine energy level jumps of atoms and quantum state detection. In addition, the high polarization characteristics of the lasers are also a decisive factor in enhancing the performance of laser frequency stabilization systems and quantum interference systems, and in constraining the accuracy and resolution of the measurements. Therefore, narrow linewidth semiconductor lasers with both narrow linewidth and line polarization have attracted much attention in the field of quantum precision measurements, among which the 852 nm narrow linewidth laser for the preparation of Rydberg states of Cs atoms is a typical representative.
The high-power semiconductor laser research team of Changchun Institute of Optical Precision Machinery and Physics, Chinese Academy of Sciences, under the leadership of academician Wang Lijun and researcher Ning Yongqiang, has carried out research on advanced narrow linewidth semiconductor lasers and key technologies in recent years. Recently, Associate Researcher Chao Chen of the team reported an 852nm narrow linewidth, linearly polarized semiconductor laser based on an external optical feedback structure. By introducing a femtosecond laser-induced birefringent Bragg grating filter and integrating it with a high polarization-correlation semiconductor gain chip hybrid, the laser structure achieves a high line-polarized, narrow-linewidth laser output with a polarization extinction ratio of more than 30 dB and a line-width of as low as 2.58 kHz by utilizing polarization-mode-selective feedback and injection-locking techniques. The laser can be used as a potential atomically pumped light source for quantum precision measurement systems, and based on the previous research in radiation-resistant, narrow linewidth lasers, it is also promising to be used in cold atom quantum experimental systems in space environments, both on-board and off-board.
The research result is entitled "Linear polarization and narrow-linewidth external-cavity semiconductor laser based on birefringent Bragg grating optical feedback", published in Optics and Laser Technology (DOI: https: //doi.org/10.1016/j.optlastec.2023.110211). 110211).
Previously, the research team reported the radiation-resistant narrow-linewidth external cavity semiconductor lasers (DOI: doi.org/10.1016/j.j.optlastec.2023.110211) and high polarization extinction ratio narrow-linewidth hybrid integrated lasers (DOI: https: //doi.org/10.1016/j.optlastec.2023.110211), respectively, in response to the needs of space laser communication and coherent laser detection. laser (results published in Optics Express, DOI: doi.org/10.1364/OE.431341).

Fig. (a) Excitation spectral characteristics of the laser, (b) Polarization extinction ratio with injection current (the inset shows the laser power measured by different waveplate rotation angles), (c) Beat-frequency power spectrum and its fitting curve of delayed self-external difference measurement of the laser linewidth, and (d) Numerical simulation and test results of Lorentzian linewidth.