26th Australian Institute of Physics Congress and the Australian and New Zealand Conference on Optics and Photonics

Digitally-enhanced offset-frequency locking across across tens‑of‑GHz wavelength separations

Not scheduled

20m

Belinda Hutchinson Building (The University of Sydney )

Contributed Oral ANZOS | Photonics and Optics (ANZCOP)

Speaker

Jacob Bos (The Australian National University)

Description

The ability to control two lasers at different wavelengths such that their relative frequency difference remains consistent is a desirable trait for continuous variable and twin-field quantum key distribution systems, and stable terahertz signal generation through photomixing. A standard approach for this is to use an optical frequency comb, which provides a phase stable optical reference spanning ranges on the THz scale.

The cost and complexity of comb systems makes them presently inaccessible for many applications. Alternative technologies for providing stable offset optical frequencies such as RF offset locking cannot reach comparable separations due to limited photo-detection and radio-frequency processing bandwidths. Digitally Enhanced Homodyne Interferometry (DEHoI) is an optical interferometry phase measurement technique that has been applied to fibre-frequency reference laser stabilisation [1]. By augmenting the technique presented in [2] with the multiplexing capability of DEHoI we present a method to offset-frequency lock a scalable number of lasers at large separations.

At a frequency separation of $85.42$ GHz we achieve out of loop measurements of an Allan deviation of $7\times{10}^{-12}$ at $1$ s. Further, we show continuous operation over $3.5$ days with a maximum deviation of the relative frequency of $\pm 300$ kHz, without wavelength dependent corrections. This talk outlines the initial experimental results and discusses ongoing efforts in distributed control and remote frequency stabilisation.

[1] Y. Zhang, C. P. Bandutunga, T. G. McRae, M. B. Gray, and J. H. Chow, “A thermal-noise-limited fiber frequency reference with 0.1 Hz/√Hz stability,” in Proc. 9th Symp. Frequency Standards and Metrology, J. Phys.: Conf. Ser., vol. 2889, 012052, 2024, doi: 10.1088/1742-6596/2889/1/012052.
[2] N. Bourbeau Hébert, A. N. Luiten, A. P. Hilton, and P. S. Light, “Hertz-level frequency comparisons between diverse color lasers without a frequency comb,” Opt. Lett., vol. 45, no. 15, pp. 4196–4199, Aug. 2020, doi: 10.1364/OL.394572.