Abstract
Lasing from whispering-gallery mode (WGM) resonators occurs omnidirectional in azimuthal plane. Most applications of WGM resonators require spectral analysis with off-chip detectors, where in-plane emission and beam divergence hinder efficient detection. We demonstrate redirecting WGM laser emission from all azimuthal angles using a circular micromirror placed around the cavity. By collecting reflections off the micromirror via free-space optics, read-out intensity improved by one order of magnitude. Blocking vertically emitted spontaneous emission and recording reflections off the micromirror only, signal-to-noise ratio improved from 4.6 dB to 15dB. Our read-out concept may be applied to arbitrary WGM cavity geometries without deteriorating the cavity's quality factor.
Highlights
Whispering-gallery mode (WGM) resonators have been demonstrated as highly sensitive detectors for humidity [1], UV light [2], single cells [3], or nanoparticles [4]
In comparison to recording emission from resonator and micromirror simultaneously, the detected fluorescence intensity was reduced by a factor of 3, while the peak intensity was only reduced by a factor of 1.25, yielding a maximum signal-to-noise ratio (SNR) of 15 dB (λ = 623.78 nm)
We have demonstrated enhanced read-out efficiency of WGM lasers using circular micromirrors placed around the cavity
Summary
Whispering-gallery mode (WGM) resonators have been demonstrated as highly sensitive detectors for humidity [1], UV light [2], single cells [3], or nanoparticles [4]. Collection of the WGM laser emission can be achieved via free-space optics positioned on top or at the side of the resonators Efficiency of both techniques is limited by collecting solely a small fraction of the emitted radiation. Circularity of the micromirror allows redirection of the laser emission from all azimuthal angles, enabling efficient collection with an off-chip detector This approach is applicable to arbitrary cavity geometries and does not reduce the cavity’s quality factor. The ratio of the field amplitudes emitted vertical and horizontal to the mode maximum (positions indicated by grey dotted lines) exceeds ten orders of magnitude, verifying that radiation loss from the microgoblet cavity mainly occurs in horizontal direction.
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