An in-fiber dynamically modulable Mach-Zehnder interferometer derived by ultrasonic waves: Fabrication and sensing property

Interferometers, renowned for their capability to provide extensive spectral information and support various measurement techniques such as wavelength, intensity, phase, frequency, and bandwidth, have become effective tools for applications requiring large dynamic ranges, high precision, and high sensitivity. Traditional optical fiber interferometry systems rely on complex optical path configurations, including reference and measurement arms, to maintain a phase difference. In contrast, in-fiber interferometers offer a more compact and efficient alternative for integration and miniaturization. While conventional fabrication methods, such as misalignment welding, have been widely used, they involve complex processes and inconsistent quality, limiting flexibility and adaptability to different testing environments. This study introduces an in-fiber dynamically modulable Mach-Zehnder interferometer (DMMZI) based on ultrasonic waves. The vibrations induced by ultrasonic waves create a periodic refractive index distribution within the fiber, leading to the formation of long-period gratings (LPGs). The ultrasonic waves propagate axially along the fiber, and the coupling of two waves at specified time intervals resembles the cascading of dynamic LPGs, resulting in the formation of a DMMZI. Theoretical and experimental investigations demonstrate that by adjusting the frequency, duration, and interval of the ultrasound, the characteristics of the interferometer can be effectively tuned. The strain response of the system has also been validated, showing that the DMMZI possesses excellent sensing capabilities and flexibility, making it suitable for various measurement scenarios and target parameters in future applications.