A low phase noise microwave source for high performance CPT Rb atomic clock

TL;DR

This paper presents a low phase noise microwave synthesizer designed for high-stability CPT Rb atomic clocks, achieving superior phase noise performance and improved frequency stability over existing solutions.

Contribution

The work introduces a simple, low-noise microwave synthesizer architecture that significantly enhances phase noise and stability for CPT Rb atomic clocks.

Findings

Phase noise at 1 Hz offset is -55 dBc/Hz

Frequency stability is estimated at 4.7×10^{-14} at 1s

Achieves about half the intermodulation stability of state-of-the-art clocks

Abstract

Phase noise of the frequency synthesizer is one of the main limitations to the short-term stability of microwave atomic clocks. In this work, we demonstrated a low-noise, simple-architecture microwave frequency synthesizer for a coherent population trapping (CPT) clock. The synthesizer is mainly composed of a 100 MHz oven controlled crystal oscillator (OCXO), a microwave comb generator and a direct digital synthesizer (DDS). The absolute phase noises of 3.417 GHz signal are measured to be -55 dBc/Hz, -81 dBc/Hz, -111 dBc/Hz and -134 dBc/Hz, respectively, for 1 Hz, 10 Hz, 100 Hz and 1 kHz offset frequencies, which shows only 1 dB deterioration at the second harmonic of the modulation frequency of the atomic clock. The estimated frequency stability of intermodulation effect is 4.7*10^{-14} at 1s averaging time, which is about half order of magnitude lower than that of the state-of-the-art CPT Rb clock. Our work offers an alternative microwave synthesizer for high-performance CPT Rb atomic clock.