A Compact Rubidium Optical Clock Based on Modulation Transfer Spectrum

A compact rubidium optical clock is presented, incorporating an optical frequency standard, a fiber frequency comb, and associated control electronics. Modulation transfer spectroscopy, devoid of Doppler background and characterized by a high signal-to-noise ratio and sensitivity, is employed to lock the laser frequency to the hyperfine transitions of rubidium atomic lines. The clock exhibits a short-term stability of 4.10 × 10<sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-13</sup> at a 1-second gate time, and the stability remains below 7.27 × 10<sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-13</sup> up to 1000 seconds. These results offer a promising alternative approach for the development of portable optical clocks.