4 March 2014 Heterodyning cavity-based microlasers to improve sensing performance
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Abstract
Due to their narrow linewidth lasing peaks, microlasers based on whispering gallery mode optical resonators are becoming increasingly useful in sensing applications. Changes in the microlaser’s environment cause the lasing wavelength to shift, enabling detection with high resolution. However, the performance of these devices is often limited by the optical spectrum analyzers used in the detection experiments, which lack the speed and sub-picometer resolution needed to measure small changes in the microlaser’s output. One promising approach to overcome this limitation is heterodyning the microlaser’s output. In the present work, we successfully heterodyne a microlaser sensor based on a neodymium-doped silica toroid platform pumped at 765nm. Combining the microlaser's 1064nm emission with a 1064nm reference laser produces an easily detectable low frequency beat signal. Monitoring the beat frequency on an electrical spectrum analyzer (ESA) enables wavelength shifts to be detected with high speed and subpicometer resolution. As a proof of concept, temperature sensing experiments are performed by tracking the beat frequency as the microlaser is heated. To directly determine the improvement in sensitivity and in signal to noise, comparison experiments are also performed by tracking the resonant wavelength and lasing wavelength. We experimentally show that heterodyning improves the microlaser's detection limit, signal to noise, and time resolution by as much as 50-fold compared to the non-heterodyned laser approaches. Narrowing the microlaser's linewidth and reducing noise could increase this enhancement even further. Therefore, heterodyning will significantly benefit both the performance of microlaser sensors and their many applications.
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Ashley J. Maker, Andrea M. Armani, "Heterodyning cavity-based microlasers to improve sensing performance", Proc. SPIE 8960, Laser Resonators, Microresonators, and Beam Control XVI, 89600T (4 March 2014); doi: 10.1117/12.2035255; https://doi.org/10.1117/12.2035255
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