Simultaneous multi-channel ultrasound detection via phase modulated pulse interferometry.

In optical detection of ultrasound, resonators with high Q-factors are often used to maximize sensitivity. However, in order to perform parallel interrogation, conventional interferometric techniques require an overlap between the spectra of all the resonators, which is difficult to achieve with high Q-factor resonators. In this paper, a new method is developed for parallel interrogation of optical resonators with non-overlapping spectra. The method is based on a phase-modulation scheme for pulse interferometry (PM-PI) and requires only a single photodetector and sampling channel per ultrasound detector. Using PM-PI, parallel ultrasound detection is demonstrated with four high Q-factor resonators.