Integrated micro Michelson fiber interferometer with spatial mode beating characteristics for directional discrimination

We demonstrate integrated micro Michelson interferometer with a sphered-end hollow-core fiber attached against the singlemode fiber to serve as a sensing head for discriminating the moving direction of external object. The splicing point between the singlemode fiber and hollow-core fiber can convert the core mode into cladding modes which will be further projected to the external object by a fiber lens. The reflected cladding modes can be captured by fiber lens to interfere with the back-reflected core mode generated at splicing point to produce interferences with spatial mode beating characteristics. This spatial mode beating comes along with multiple foci outside the fiber lens where one of the cladding modes serves as a moving reference for others. The moving direction can thus be discriminated by monitoring the power variations of two neighboring wavelengths at the bilateral side of the wavelength beating node at around 1486 nm or 1504 nm wavelength.