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Optical microresonators are a versatile platform for studying fundamental sciences. They are also highly promising candidates for a wide range of industrial applications. The Precision Measurement Group is exploring microresonators, either based on millimetre-scale crystalline whispering gallery mode resonators or integrated waveguides, to develop cutting-edge optical and photonic technologies for sensing and metrology.

Projects:

• Microresonator Frequency Comb Generation
• Radiofrequency sensing and detection based on electrooptic conversion in microresonators
• Microresonator-based terahertz (THz) generation for THz telecommunication and radar applications

Owing to the strong light confinement, microresonators can generate stable broadband optical frequency combs [1,2] with a variety of linear and nonlinear effects such as the Kerr effect, the Raman effect, the second harmonic generation, the optical parametric oscillation, and the electro-optic effect. This project aims at developing microresonator frequency combs (microcombs) with new structures and semiconductor laser pumping schemes [3] to improve the energy efficiencies and to engineer the comb spectral profiles. Multiple applications, including gas sensing, Lidar, and free-space frequency standard transfer, will be carried out.

Ìý

[1] Kippenberg, T. J., Gaeta, A. L., Lipson, M. & Gorodetsky, M. L. Dissipative Kerr solitons in optical microresonators. Science 361, eaan8083 (2018)

[2] Diddams, S. A., Vahala, K. & Udem, T. Optical frequency combs: coherently uniting the electromagnetic spectrum. Science 369, eaay3676 (2020)

[3] Weng, W. et al. Gain-switched semiconductor laser driven soliton microcombs. Nat. Commun. 12, 1–9 (2021)

With applied electrical fields, the electrooptic effect can be utilised to change the frequency of the laser light trapped in microresonators [1]. With optical techniques, the newly generated frequency components can be detected with an ultralow noise level and measured with an ultrahigh precision. For this project, ultrahigh-quality-factor microresonators that have been utilised in precision thermometry [2,3] will be used to develop electrical field sensors to detect radiofrequency and terahertz signals. In addition, we will explore the possibility of combining electrooptic effect with other nonlinear effects to test novel designs based on synthetic dimensions and parity-time symmetry breaking.

Ìý

Ìý[1] Matsko A. B., Strekalov D. V., & Yu N. Sensitivity of terahertz photonic receivers. Phys. Rev. A 77, 043812 (2008)

[2] Weng, W. et al. Nano-Kelvin thermometry and temperature control: beyond the thermal noise limit. Phys. Rev. Lett. 112, 160801 (2014)

[3] Weng, W., Light, P. S., & Luiten A. N. Ultra-sensitive lithium niobate thermometer based on a dual-resonant whispering-gallery-mode cavity. Opt. Lett. 42, 1281-1284 (2017)

Microresonator frequency combs can produce laser pulse trains with high repetition rates in the THz frequency range (0.3´1012 Hz to 3´1012 Hz) [1,2]. With proper photomixing technologies, the laser pulse trains can be converted into low-noise THz waves that are highly desired in telecommunication, medical and space applications. In collaboration with the Terahertz Engineering Laboratory ( ) led by A/Prof Withawat Withayachumnankul, we are working on the development of microresonator-based THz generators with high conversion efficiency and low phase noise. The generated THz waves will be employed in wireless telecommunications and space ranging systems.

Ìý

[1] Zhang, S. et al. Terahertz wave generation using a soliton microcomb. Opt. Express 27, 35257–35266 (2019)

[2] Weng, W. et al. Coherent terahertz-to-microwave link using electro-optic-modulated Turing rolls. Phys. Rev. A 104, 023511 (2021)