Bending sensor with parallel fiber Michelson interferometers based on Vernier-like effect

•A highly sensitive bending sensor has been proposed and demonstrated.•The bending sensor based on an integrated two parallel Michelson interferometer structure.•The structure consists of a dual-core fiber and a fraction of dual-side-hole fiber.•Owing to the Vernier-like effect, we verified a highly sensitivie of bending sensor.•This kind of sensor has significance in the research of structural safety monitoring. A highly sensitive bending sensor based on two parallel fiber Michelson interferometers (MIs) with a Vernier-like effect is proposed and demonstrated. The interferometric structure consists of a dual-core fiber (DCF) spliced with a short section of dual-side-hole fiber (DSHF). The centric core of the DCF is aligned with one air-hole of the DSHF to form a reflective interface. The centric core of the DCF is connected to the core of the DSHF with a little lateral offset to make the light in the centric core couple to both the core and cladding of the DSHF. The light beams reflected by the end of the DSHF and the DCF interfere with each other, forming two parallel MIs. The free spectral range (FSR) difference between the two MIs is very small due to the tiny difference in refractive index (RI) between the core and cladding of the DSHF, which results in a Vernier-like effect. The most novel feature of the mentioned structure is that both MIs are sensitive to bending with the same sensitive direction. Experimental results indicate that the bending sensitivity of the sensor can reach 38.53 nm/m−1. This kind of sensor has far-reaching significance in the research of structural safety monitoring.