Adiabatic frequency conversion driven by the electro-optic response of potassium tantalate niobate mixed crystals
Final Report Abstract
Many are familiar with the following acoustic phenomenon: a guitar string is plucked, and while the sound is still ringing, the length of the string is shortened. As a result, the pitch — that is, the frequency — of the sound increases. Although this effect has been known for centuries, it was only about 20 years ago that researchers began to explore its optical analogue. In this optical counterpart, a resonator is initially filled with light. If the resonance frequency of the cavity is changed on a timescale shorter than its photon lifetime, the frequency of the intracavity light adiabatically follows the resonance shift. In our preliminary work, we have demonstrated that these adiabatic frequency converters can be driven via the linear electro-optic effect. Here, a temporally varying voltage signal applied to the optical resonator is transferred linearly to a temporally varying frequency shift. In this project, we aimed to enhance adiabatic frequency conversion by several orders of magnitude using optical resonators made of potassium tantalate niobate, a material known for its strong electro-optic response. However, in the initial phase, we found that commercially available crystals lacked sufficient homogeneity for reproducible and verifiable results. We therefore shifted our focus to the linearity of electro-optically driven frequency conversion. In particular, we investigated the generation of linear frequency chirps in the sub-microsecond regime and demonstrated the first-ever application of adiabatic frequency conversion for distance measurement using chirps with less than 2 % deviation from perfect linearity. This approach outperformed the state of the art in terms of update rate. Moreover, we identified a previously overlooked limitation: mechanical resonances of the optical resonator in the 10 MHz range fundamentally constrain chirp linearity. To enable electrically driven frequency conversion in the deep ultraviolet, we also studied resonators made from barium magnesium fluoride. While their electro-optic effect is negligible, we discovered a strong piezoelectric response. Finally, we developed an electro-optically driven fiber ring capable of generating linear frequency chirps with a tunable slope ranging from 0.001 to 1 GHz/ns — controlled simply by adjusting the frequency of the sinusoidal driving voltage. Although the initial goal of demonstrating high-efficiency adiabatic conversion in solid resonators could not be fulfilled due to material limitations, the project yielded significant insights. We believe that both the findings on miniaturized barium magnesium fluoride resonators and the fiber-based concept will benefit related fields such as deep-ultraviolet light generation for atomic clocks and digital holography.
Publications
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Potassium Tantalate-Niobate for Electro-Optically Driven Adiabatic Frequency Conversion. 2023 Conference on Lasers and Electro-Optics Europe & European Quantum Electronics Conference (CLEO/Europe-EQEC), 1-1. IEEE.
Mrokon, Alexander; Kirste, Lutz; Buse, Karsten & Breunig, Ingo
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Adiabatic frequency conversion in a lithium niobate microresonator for FMCW-LiDAR. Laser Resonators, Microresonators, and Beam Control XXVI, 12. SPIE.
Mrokon, Alexander; Oehler, Johanna & Breunig, Ingo
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Continuous adiabatic frequency conversion for FMCW-LiDAR. Scientific Reports, 14(1).
Mrokon, Alexander; Oehler, Johanna & Breunig, Ingo
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Electrically induced resonance shifts of whispering gallery resonators made of barium magnesium fluoride. APL Photonics, 10(9).
Mrokon, Alexander; Kraft, Heike; Shin, Dongsung; Tanaka, Hiroki; Herr, Simon J.; Buse, Karsten & Breunig, Ingo
