Laser Stabilized to a Fiber Interferometer With Close‐To‐Zero Temperature Sensitivity

ABSTRACT Ultra‐stable laser sources typically achieve long‐term frequency stability by locking to a bulky and costly vacuum‐operated Fabry–Perot cavity made of ultra‐low expansion material such as ultra‐low expansion glass (ULE). In this work, we demonstrate that long‐term stability can be achieved with a specially designed fiber interferometer operated at a zero‐temperature‐sensitivity crossing point, a feature typically achieved only with cavities made from zero‐expansion materials. The ultra‐low temperature sensitivity is achieved by using a combination of a hollow‐core optical fiber that provides the required delay and a short segment of a standard single‐mode fiber that provides temperature compensation. Additionally, we placed the interferometer in an airtight aluminum enclosure to mitigate the effect of environmental pressure fluctuations. A laser locked to this interferometer exhibits ±550 kHz peak‐to‐peak frequency variation over 100 h of continuous operation, and a frequency drift below 20 Hz/s. The corresponding Allan deviation reaches 2 × 10 −14 𝜏 (for 𝜏 > 100 s), rivaling the performance of miniature ULE cavities. Compared to previously reported fiber and waveguide‐based systems operating in ambient conditions, our approach offers superior long‐term frequency stability. Owing to its compactness, low cost, and alignment‐free design, this system provides a promising solution for deployable frequency references in applications such as geophysics, field spectroscopy, and space‐based sensing.