Experimental Demonstration of an Angle Laser Sensor Based on an Optical Thinned Microfiber Mach-Zehnder Interferometer

An angle laser sensor based on a Mach-Zehnder interferometer constructed with a thinned microfiber is experimentally demonstrated. The thinned microfiber is a 10-
$\mu \text {m}$
diameter fiber. It is sandwiched between two 125-
$\mu \text {m}$
diameter single-mode fibers (SMFs) connected by conical transitions of 3 mm in length. Two modes are excited and propagated through the microfiber when light from the fundamental core mode is launched to the microfiber via the conical transition. When the length of the microfiber is finished, a phase difference between modes is generated because both modes have different effective refractive indexes. Then, both modes are coupled to the core of an SMF with the second conical transition, and an interference pattern is produced. This interference pattern filters the cavity losses of an optical fiber laser by including the interferometer in a ring cavity laser of an erbium-doped fiber (EDF) laser. When the microfiber is bent with a homemade angle bend station, the filtering properties of the interferometer change, and the wavelength laser emission also changes. Correlating the wavelength emission with the angle position of bending, a bend laser sensor can be produced. Sensitivities in the range from 0.045 to 0.49 nm/(
$\pi /100$
) radian (corresponding to from 0.025 to 0.272 nm/o) were obtained experimentally. The proposed sensor has potential applications for several fields, including engineering for mechanics, robotics, position measurement, and even construction for health monitoring and deformation measurements.