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Ultra-stable lasers are instrumental in fields such as optical atomic clocks, precision spectroscopy, and gravitational wave detection. Their application has been extended to diverse fields such as monitoring earth environment or radio astronomy.
The state-of-the-art ultra-stable lasers are usually housed in research-grade environmentally-controlled laboratories. To extend their application reach beyond the laboratory walls, they need to be made transportable or their signal needs to be distributed to external users.
Both portability and distribution can be addressed by using optical fibres. Optical fibre delay lines are emerging as a potential alternative to optical cavities for stabilizing lasers [1]. Additionally, optical fibres enable the distribution of optical ultra-stable signals to remote places. However, the thermal sensitivity of Single Mode Fibre (SMF) results in frequency drifts substantially higher than those of cavities. When distributing optical signals in SMF, non-linear effects are induced at relatively low injected power levels, limiting the amount of power that can be transferred. This limitation is particularly significant when transferring frequency combs [2].
In hollow-core optical fibres, light propagates through air rather than silica. This results in a 20 times lower thermal sensitivity, 30 dB lower backscattering, and 3-4 orders of magnitude lower non-linear coefficient, with respect to traditional glass-core SMF [3].
In the presentation, we will review the latest hollow core fibre technology and show how this enables ultra-stable laser stabilisation and several advantages in optical frequency distribution, including optical frequency combs, with respect to SMF.
[1] F. Kéfélian, H. Jiang, P. Lemonde, and G. Santarelli, "Ultralow-frequency-noise stabilization of a laser by locking to an optical fiber-delay line," Optics letters, vol. 34, no. 7, 914-916, (2009).
[2] Z. Feng et al., "Stable Optical Frequency Comb Distribution Enabled by Hollow‐Core Fibers," Laser & Photonics Reviews, vol. 16, no. 11, 2200167, (2022).
[3] E. N. Fokoua, S. A. Mousavi, G. T. Jasion, D. J. Richardson, and F. Poletti, "Loss in hollow-core optical fibers: mechanisms, scaling rules, and limits," Advances in Optics and Photonics, vol. 15, no. 1, 1-85, (2023).
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