Fiber Optic Fabry–Perot Optofluidic Sensor With a Focused Ion Beam Ablated Microslot For Fast Refractive Index and Magnetic Field Measurement

A compact fiber-optic Fabry-Perot interferometric sensor with an embedded microfluidic channel for static magnetic field measurement is proposed and implemented. Fabrication of the Fabry-Perot structure involved cascading two silica capillary tubes with different inner diameters, followed by milling of a microslot directly on the sidewall of the large inner diameter silica capillary tube, by focused ion beam micromachining. The microslot, together with the hollow structure of the small inner diameter silica capillary tubes forms an open Fabry-Perot cavity to function as a microfluidic channel. The microslot was found to improve the response time of the Fabry-Perot sensor to changes in refractive index (RI) of the cavity. Magnetic fluid was introduced in the Fabry-Perot cavity, thereby, enabling implementation of an optofluidics system for magnetic field measurement. The sensing scheme is based on the magnetic field strength induced RI change of the magnetic fluid which in turn modulates the interference spectrum of the sensor. Wavelength shifts were monitored real time for the continuous measurement of magnetic field strength. The sensor calibration curves with respect to magnetic field were plotted and the sensor exhibits a relative high magnetic field sensitivity of ~418.7 pm/Oe relative to the dip wavelength around 1590 nm.