Magnetic fluid-filled microhole in the collapsed region of a photonic crystal fiber for the measurement of a magnetic field.

A method for measurement of a magnetic field by filling a microhole with magnetic fluid (MF) in a photonic crystal fiber (PCF) is presented and experimentally demonstrated. A microhole is created in the collapsed region between the PCF and the single-mode fiber by using femtosecond laser micromachining, and a PCF-based Mach-Zehnder interferometer is formed. The MF is filled into the microhole. Due to the tunable refractive index property of the MF, the mode field diameter of the propagation light is changed with the external magnetic field, and the magnetic field can be detected by measuring the visibility contrast of the white light interferogram. The experimental results show that sensitivity of up to 0.042 dB/Oe is achieved.