External Cavity Laser for Chip-Scale Atomic Clock

In this paper we report a new coherent population trapping (CPT) atomic clock based on external cavity laser. Unlike usual CPT atomic clocks, where used the vertical cavity surface emitting laser (VCSEL), we combine the external cavity laser (ECL) with CPT atomic clock to improve the stability. Compared with VCSEL, the ECL has higher laser power of 10 mW and narrower linewidth of 0.8 MHz, meaning that the signal-to-noise ratio of clock can be further improved.