Real-time spectral interferometry enables ultrafast acoustic detection

Abstract

Optical interferometry is a promising alternative for acoustic detection as it records the changes of interference patterns. Apart from interferometric sensor heads, readout systems also play a crucial role in sensing performance. Here, inspired by the soliton molecule vibrations in ultrafast lasers, we introduce an efficient real-time spectral interferometry (RSI) approach to read out the Fabry–Pérot interferometer (FPI) for acoustic detection. Broadband pulses, emitted from an ultrafast fiber laser, are launched into the FPI sensor. Pseudo dual-pulse molecule is constructed by virtue of the equivalent two-beam interference of the FPI and modulated by the diaphragm transducer. The acoustic driven “molecular vibration” conforms to the sound applied on the metal diaphragm. Hence, the acoustic signals can be directly recorded by the successive dual-pulse spectral interferograms, imaged as a spectral encoded “soundtrack.” We experimentally achieve the real-time characterization of both the audible and ultra sounds by retrieving the relative phase evolutions with a phase resolution of 37.6 mrad and preliminarily verifying the feasibility of the RSI in acoustic detection. This approach to wideband acoustic detection highlights an advanced application of ultrafast laser sources and paves an efficient way for interrogating the interferometric fiber sensors.