1：Experimental Design and Method Selection:

The experiment involved designing a micro quasi-Michelson interferometer (QMI) using a fiber-optic taper with a refractive index modification (RIM) region written by a femtosecond laser to improve mode coupling and recoupling. The sensing mechanism is based on interference between recoupled high-order modes and spectral-side band filtering for ultrasonic wave (UW) detection.

2：Sample Selection and Data Sources:

The sensor was fabricated using a single-mode fiber taper with a minimum diameter of 20 μm and length of 300 μm, coated with a gold film for high reflectivity. Seismic-physical models (SPMs) made of organic glass with specific geometries were used for imaging.

3：List of Experimental Equipment and Materials:

Equipment includes a femtosecond laser system (Ti:sapphire laser, 800 nm wavelength, 50 fs pulse length, 1 kHz repetition rate), tunable laser (Santec, 710 model), photodiode (New Focus, 10 MHz bandwidth), function generator for PZT, motorized positioning stages (2 μm resolution), oscilloscope, and a 3D-printed cone-shaped horn for packaging. Materials include optical fibers, gold film for coating, and SPMs.

4：Experimental Procedures and Operational Workflow:

The taper was fabricated using flame-heating technology, coated with gold, and micromachined with the femtosecond laser to create the RIM region. The sensor was packaged with a horn and tested underwater. UW detection involved emitting continuous and pulsed waves from a PZT source, scanning the sensor and source across SPMs with a step size of 1-2 mm, and recording signals with the oscilloscope. Data were reconstructed using inverse time algorithm and log(intensity) transformation.

5：Data Analysis Methods:

Signal analysis was performed using the oscilloscope and spectral-side band filtering. The output power was measured to detect UW-induced strain, and imaging was achieved through data reconstruction.