Phase detection of the NIR optical resonances of rectangular glass micro-capillaries

In this work, we propose a spectral interferometric technique for detecting the wavelength position of the resonances of low-cost optical resonators, consisting in rectangular glass micro-capillaries. A detailed theoretical model was developed to calculate the spectral reflectivity of the micro-devices when they are placed at the end of the measuring arm of a Michelson scheme. Using the readout radiation provided by a broadband light source with a flat emission spectrum centered at 1.55 µm and a 2x1 fiberoptic coupler on the common input-output optical path, experimental results were found in good agreement with the expected theoretical behavior. The optical resonances, corresponding to reflectivity minima, of these simple optical resonators are clearly detected by monitoring the positions of steep phase jumps on the interferometric signal recorded as a function of the wavelength.