A novel low-cost, compact, assembly-free and sensitive optical fiber curvature sensor is presented. This device consists of an off-axis positive refractive index modified zone (PRIMZ), induced by direct femtosecond laser, written in single mode fiber (SMF) core. The PRIMZ transforms the original SMF section into a few-mode fiber (FMF). As a result, the whole fiber forms an assembly-free “SMF-FMF-SMF” sandwich Mach-Zehnder interferometer. When the device is bent, a direction dependent spectral shift of the interference pattern is produced. The sensitivity of the sensor is up to 2.53 and 2.24nm/m-1 for the 0° and 180° orientations in a wide bend range (from 0-4m-1). In addition, the device is immune to surrounding refractive index and has low temperature crosstalk, which make it very attractive for practical structural monitoring applications.
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Funding: National Natural Science Foundation of China (NSFC) (61775074); National 1000 Young Talents Program, China; 111 Project (No. B07038); Natural Science Foundation of Guangdong Province, China (2015A030313633).
- All-optical devices;
- Optical sensing and sensors;
- Optical design and fabrication;
- Optical devices;