Abstract
Frequency references are indispensable to radio, microwave and time keeping systems, with far reaching applications in navigation, communication, remote sensing and basic science. Over the past decade, there has been an optical revolution in time keeping and microwave generation that promises to ultimately impact all of these areas. Indeed, the most precise clocks and lowest noise microwave signals are now based on a laser with short-term stability derived from a reference cavity. In spite of the tremendous progress, these systems remain essentially laboratory devices and there is interest in their miniaturization, even towards on-chip systems. Here we describe a chip-based optical reference cavity that uses spatial averaging of thermorefractive noise to enhance resonator stability. Stabilized fibre lasers exhibit relative Allan deviation of 3.9 × 10−13 at 400 μs averaging time and an effective linewidth <100 Hz by achieving over 26 dB of phase-noise reduction.
Highlights
Frequency references are indispensable to radio, microwave and time keeping systems, with far reaching applications in navigation, communication, remote sensing and basic science
Crystalline resonators are advantageous for reduced thermorefractive noise as the dependence of refractive index on temperature is low in comparison with silica[19]
In the absence of resonator noise sources, the rms frequency difference of a locked laser relative to a cavity line center depends upon the optical Q and signal-to-noise ratio (SNR) of the detected laser signal through the following expression[29], Dnrms % Dn0 1⁄4 1
Summary
In the absence of resonator noise sources, the rms frequency difference of a locked laser relative to a cavity line center depends upon the optical Q and signal-to-noise ratio (SNR) of the detected laser signal through the following expression[29], Dnrms % Dn0 1⁄4 1. Given a high enough Q factor and large enough SNR, the stability of the laser locked to the cavity becomes determined by fluctuations in the cavity line centre, itself. Upper-right: 4.5 cm spiral resonator used for studies of Q scaling. Lower right: quarter shown to provide scale.
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