Gas flow sensor using a hollow WGM microlaser

Hollow microcapillary and microbubble whispering gallery resonators have the unique feature of allowing a (gain) medium to fill their inner volume as already demonstrated in the case of the dye-filled microbubble laser, capillaries, and on-chip micro fluidic channels [1]. A desired feature of any laser is the ability to tune the frequency of the laser output. Tuning a micron-sized WGR in a fashion that does not add to the footprint of the device or require significant fabrication is a nontrivial task. The main approaches thus far are external heaters, applying stress/strain via an external clamp or aerostatic tuning [2], electric fields or ther-mo-optic tuning [3]. Each of these methods has its own advantages and disadvantages.