Broadband ultrasound response in a gas environment of a DBR fiber laser sensor

Conventional ultrasonic transducers generally exhibit narrow operating bandwidths centered at specific resonance frequencies, which limit their capability for broadband ultrasonic measurements, especially in airborne or gaseous sensing scenarios. This paper presents an in-depth investigation of the ultrasonic response characteristics of a distributed Bragg reflector (DBR) fiber laser sensor. The phase shift of the fiber laser sensor induced by ultrasonic waves transmitted across a water–air interface is analyzed using mechanical–optical transformation modeling, laser wavelength shift simulation, and non-equilibrium interferometric demodulation. Both theoretical and experimental results demonstrate that the phase response has a linear relationship with the applied sound pressure across a broadband frequency range from 25 kHz to 1 MHz, with a stable and nearly frequency-independent sensitivity of approximately 0.06–0.08 rad/Pa. These results indicate that the fiber laser sensor is well-suited for broadband ultrasonic sensing, particularly in scenarios where conventional airborne ultrasonic transducers are limited.