A research group led by Prof. Zhang Shougang and Prof. Yun Enxue (Peter Yun) from the National Time Service Center (NTSC) of the Chinese academy of sciences (CAS) developed a high-performance and compact coherent population trapping (CPT) atomic clock, which solves the miniaturization problem of high-performance CPT atomic clock.
The current chip-scale atomic clocks (CSAC) based on the CPT occupy volume close to that of a matchbox. It is an ideal choice for the applications which require precise time signals while has tight restrictions on clock size, power consumption and weight, thus it has already been applied to drone cruises, portable satellite receivers, underwater resource exploration, etc.
However, the frequency stability of the present CSAC is limited to the level of 3E-10@1s. There is still much room for its frequency stability to improve for the applications that need higher precision time signal, such as deep space exploration, satellite navigation, high-speed communication, fire and underground search and rescue, and underwater vehicle navigation.
Focus on the issue of high-performance and compact CPT atomic clock, Peter Yun has proposed an original scheme for high-performance CPT atomic clock based on constructive polarization modulation during his post-doctoral research at the LNE-SYRTE. After returned to China, he furtherly proposed a scheme based on direct modulation narrow linewidth distributed Bragg reflector (DBR) laser diode plus a circularly polarized light CPT configuration, and demonstrated an encouraging short-term fractional frequency stability at the level of 3.6 E-13 τ -1/2 (4 ~ 200 s), and goes down to 1.8 E-14 at 200 s averaging time.
The result has been published in Metrologia which entitled with High-performance coherent population trapping atomic clock with direct-modulation distributed Bragg reflector laser.
"The work has merit of novelty to the extent that for the first time it demonstrates state-of-the-art short-term stability based on direct laser modulation, along with the potential to simplify the realization of high-performance CPT vapour-cell clocks!" commented by the reviewer.
This work was partly supported by Emeric de Clercqand and Stéphane Guérandel from LNE-SYRTE, Observatoire de Paris, France, Gu Sihong from Innovation Academy for Precision Measurement Science and Technology, China, and Liu Xiaochi from National Institute of Metrology, China.
Experimental setup for high-performance miniaturized CPT atomic clock and its frequency stability measurement (Image by Peter Yun)