We demonstrate a new type of optical fiber in-line Michelson interferometer, in which an inclined narrow slit inside the single mode fiber, fabricated by femtosecond laser, plays the role of a beam splitter. The inclined narrow slit splits the incident light beam into two parts; one is introduced to the cladding-air interface and reflected back and the other is still guided in the fiber core and reflected at the fiber end. The two reflected beams recombine at the edge of inclined narrow slit and form a Michelson interferometer. Such a device is ultra-compact in size, robust in mechanical strength, and simple in fabrication, and can be used in refractive index and temperature sensing. Moreover, the device has good high temperature sustainability up to 1000 °C.
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