Stability Improvement of a Fiber-Based Frequency Reference at $1.5\ \mu \mathrm{m}$ Using an Original Detection Technique for Interference Cancellation

We have developed an optical frequency standard at $1.5\ \mu \mathrm{m}$ based on detecting an acetylene transition by saturation spectroscopy in an absorption cell [1]. With the aim to achieve a compact device combining stability and transportability, the setup is entirely composed of fibered components, except for the acetylene cell. The main limitation to reaching a long-term stability level in the 10 ⁻¹⁴ range is interference fringes [1], [2]. We describe here an original method based on the detection of the error signal at a frequency which is not modulating the interference. We also study the benefit of a multi-pass geometry for the acetylene cell in order to both improve the SNR of the detected signal and reduce the volume.