Noise Cancellation by an Acousto-optic Modulator in CPT Atomic Clocks

Digital Communication World - - Contents -

Jiang Yi, Liu Ruiyuan, Zhao Jianye

(Department of Electronics, School of Electronics Engineering and

Computer Sciences, Peking University, Beijing, 100871)

Abstract: An approach is presented to suppress noise and improve short-term stability in CPT atomic clocks. In our setup, two divided beams from Aom(acousto-optic modulator) were sent through a same alkali vapor cell. One beam induced CPT by circularly polarized light and another beam induced only absorption by linearly polarized light. Differential algorithm counteracts common-mode noise by subtraction. Also, it is contrastive to switch between traditional CPT detection and differential detection by simply switching AOM radio frequency input off or on. As a result, the noise cancellation scheme improves the short-term stability of the clock by a factor of 1.4 at the second of 100s.

Keywords: Aom(acousto-optic modulator); Noise cancellation; CPT atomic clock

1 引言

原子钟可以提供精确的频率标准,高性能的

[1]

星载原子钟是导航卫星上的重要设备 。卫星技术的不断发展,对于原子钟的体积和功耗提出了更高的要求。基于 CPT 原理[2]的原子钟是一种

成功的小体积、低功耗原子钟生产方案,美国的Symmertricom 公司已经推出了基于 CPT 原理的商业化原子钟。使用 CPT 原理的原子钟与传统铷原子钟相比,由于不需要微波腔,体积可以做到很小。另一方面传统铷原子钟的功耗主要消耗在铷灯的加热上,由于 CPT 原子钟使用体积很小的激光器作为光源,所以消耗的功耗很低[3]。CPT 原子钟在下一代卫星通信、定位导航领域具有广泛的应用前景。

CPT原子钟中,物理光路部分的噪声会对原子

钟稳定度产生明显的影响。本文分析了物理光路部分的噪声来源,提出了一种差分降噪的方案,并进行了具体的实验验证,为CPT原子钟的改进提供了

参考。

2 CPT原子钟的原理及其基本结构

图1 CPT原子钟的结构框图

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