Femtosecond laser inscribed straight waveguide in no-core fiber for in-line Mach-Zehnder interferometer construction.

A new fiber in-line Mach-Zehnder interferometer based on a straight waveguide along the central axis of the no-core fiber sandwiched between single mode fibers is fabricated by a femtosecond laser. The device can be used for high temperature sensing with a sensitivity of -278.86  pm/°C and for bending sensing with a sensitivity of 0.28  nm/m. The high mechanical strength, simple fabrication, and precisely controlled free spectral range make the device attractive for potential applications in high temperature monitoring.