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Fabrication and imaging of the silica sol-gel optical microcavity. (a)The silica sol-gel is spin coated onto the silicon wafer, creating a thinsilica film. (b) After the buffered oxide etch (BOE), XeF2 etch, and the CO2 laser reflow, an array of toroidal cavities is formed. One of the microlaser cavities is shown operating on resonance. (c) A scanning electron micrograph (SEM) of an as-fabricated toroid microlaser.
Schematics of testing setups and representative transmission spectra. (a) Shifts in resonant and laser wavelength are measured with an oscilloscope and optical spectrum analyzer. For heterodyned measurements, the modified testing setup in (b) is used, with a 1064 nm reference laser and electrical spectrum analyzer. Using the setup in (a), representative transmission spectra for microlaser resonant peaks are obtained near (c) 778 nm and (d) 1064 nm. The resulting quality factors are 3.1 × 10 5 and 1.1 × 10 6 near 765 nm and 1064 nm, respectively.
Representative OSA spectrum showing emission near 1067 nm from the Nd 3+-doped toroid microlaser.
Sensing experiments. The temperature change measured by the thermocouple integrated into the heat stage is also plotted on the lower graph, as a control measurement. (a) Resonant wavelength-based sensing. The resonant wavelength increases by 0.0073 nm/ °C as temperature increases. The SNR is 2.7. (b) OSA temperature sensing. The lasing wavelength increases by 0.0086 nm/ °C as temperature increases. The SNR in this measurement is 1.3. (c) Heterodyned temperature sensing. The beat frequency changes (2.1GHz/ °C) as temperature increases. The reduction in noise results in a 50-fold improvement in the SNR as compared to the other methods.
Comparison of sensing parameters for optical microcavities. a
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