Morphology-Dependent Resonances and Their Applications to Sensing in Aerospace Environments

This paper reviews recent developments in Morphology—Dependent Resonance (MDR)—based sensors for aerospace applications. The sensor concept is based on the detection of small shifts of optical resonances (also called the whispering gallery modes or WGM) of dielectric spheres caused by external effects. Recent developments in MDR-based micro-optical sensors for temperature, force, pressure and concentration are discussed. In addition to the experimental configurations used in each type of prototype sensor, a brief overview is also given for analytical approaches to describe the sensor principle. Nomenclature F force in Newtons l polar mode number m azimuth mode number n radial mode number n S refractive index of sphere P 0 pressure in Pascals r radial dimension or radial argument in spherical coordinates R S radius of a microsphere t time α thermal expansion coefficient β thermo-optic coefficient λ vacuum wavelength of light Δ n s change in refractive index of a microsphere Δ