Reverse tuning of whispering gallery mode microresonators

Whispering Gallery Mode (WGM) microresonators are a class of optical sensors with the ability to trap and confine light under optical resonance conditions. Typically, this resonance is excited inside a WGM resonator using expensive and bulky tunable diode lasers, which can be a limiting factor in low-resource settings and in developing economies. In the manuscript, we describe a method of "reverse tuning"to modify the resonance conditions, paving the way for lower cost WGM excitation and ultimately lower cost sensing. We demonstrate three different methods of reverse tuning the WGM using temperature, pressure, and refractive index in a microbubble resonator (MBR), a subclass of WGM sensors that is particularly well-suited for reverse tuning using the three aforementioned methods. By reducing the cost of the MBR platform through reverse tuning, we can make these ultra-sensitive devices more practical and accessible in low-resource settings.