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UP to date, the Michelson interferometers (MI) have been extensively used in scientific and industrial applications to provide high accuracy measurements of displacement with a best spatial resolution of a half wavelength of the input light.The conventional fiber MI comprises a 2×2 coupler with two physically separated lead-out fibers.This fiber MI intrinsically comes along with a deficient characteristic in which the moving direction is left indiscriminate.Sometimes it may cause a problem in moving toward a wrong direction in real applications.The major reason for not being capable of discriminating the moving direction of external object is the lack of extra signal information from the two-beam interference in frequency or wavelength domain.For instance, when a broadband lightsource covering 1.53-1.58 μm is launched into the MI, the spectral responses at the output port of sensing arm here the phase delay between the sensing and reference arms generates the spectral oscillations.However, the moving direction is still indiscriminate.To conquer this problem, the heterodyne technique was proposed to discriminate the moving direction by detecting the derivative signal of beat frequency when light in one of the optical arms is modulated to generate a new frequency closing to the origin for beating prior to the detector.A dithering mirror at one of the reflection ports driven by a piezoelectric ceramic is used to actively control the phase to provide a moving direction reference.However, it is not a favorable price for most industry sectors to afford the commercial MI based on the conventional expensive heterodyne or dithering techniques.Other methods like the MI with an asymmetric structure based on Fabry-Perot/Michelson or a double Michelson configuration had also been proposed to discriminate the moving direction.A highly nonlinear optical-feedback semiconductor laser Michelson interferometer has also been demonstrated to measure the direction of motion unambiguously.However, several expensive elements must be required to provide the reference for discriminating the moving direction in the conventional two-arm MI.In contrast to the above methods, we propose a simple, compact, cost-effective, and monolithic fiber MI based on core-cladding mode interferences by splicing a segment of sphered-end hollow-core fiber (HOF) to a standard singlemode fiber.Fractional amount of the core mode in singlemode fiber (SMF) is converted into the excited cladding modes at the splicing point between the SMF and a short segment (< 350 μm) of HOF.The output end of the HOF is collapsed and shaped into a sphere to focus and to project the residual core and several excited cladding modes at several foci in space.It is very important to note that no matter what the measurand is, a reference of wavelength, polarization, or phase is always necessary to help discriminate the moving direction for MI.In contrast to the conventional MI, the moving reference in this work is based on one of the higher order cladding modes.Wen the core mode is propagating from the SMF toward the HOF, partial of its power is converted into cladding modes due to core size mismatch.The excited cladding modes are then guided by the HOF and projected onto the external object by the fiber lens.They will be subsequently reflected by the external object and are recombined with the reflected core mode at the air interface between HOF and SMF to produce interferences.Since each of the cladding modes propagates along different optical paths so that an envelope over oscillating curves can be generated when the reflected core and cladding modes are superimposed.This phenomenon is called spatial mode wavelength beating.With the help of the envelope from wavelength beating, the real-time moving direction can thus be distinguished by investigating the relative power variations between two specific neighboring wavelengths easily when the external object is moving.This novel integrated micro MI with a structure of using a singlemode fiber and a short lensed HOF is simple, compact, cost-effective, and promising for various sensing applications.