Ultrahigh polarization-stable narrow-linewidth grating coupled-cavity vertical-cavity surface-emitting laser for atomic clock systems.

Vertical-cavity surface-emitting lasers (VCSELs) demonstrate significant potential for all-optical coherent population trapping (CPT) atomic clocks due to their compact size and high integration capabilities. However, the effectiveness of atomic clocks is significantly limited by the polarization instability and broad linewidth of a VCSEL. Moreover, the discrete phase noise induced by mode competition not only induces polarization instability, but also constitutes the fundamental physical constraint on achieving narrow-linewidth laser output. Therefore, pursuing both narrow linewidth and high polarization stability represents interdependent and mutually reinforcing objectives. In order to address these fundamental constraints, a guide-mode resonant subwavelength grating coupling cavity VCSEL (GC-VCSEL) is proposed in this study, which is different from traditional surface gratings. The design employs a grating waveguide-coupled cavity to selectively amplify transverse electric (TE) modes while suppressing transverse magnetic (TM) modes, coupled with a dual-cavity optical feedback system to compress linewidth in the cold cavity of the VCSEL. Experimental verification confirms that GC-VCSEL can achieve a polarization suppression ratio of nearly 30 dB in high temperature environments. In addition, the device exhibits stable single-mode performance over both temperature and current variations. Even at 80 °C, which is required for chip-scale atomic clocks (CSACs), GC-VCSEL maintains an excellent current wavelength coefficient of 0.33 nm/mA.