Dynamic response of magnetic fluid-cladded MMI fiber optic sensor optimized for fourth self-imaging spectral response

Abstract

Even though the dynamic response of the magnetic fluid is well investigated by magnetic means and known for their high frequency response in MHz to GHz range, the same has not been explored as much by optical means in the context of optical fiber sensor platform. The use of magnetic fluid as sensing materials in various fiber optic senor platform is limited to DC magnetic field sensing. In this work, we present the results of magnetic fluid functionalized multimode interferometric fiber optic sensors for their efficacy in measuring the dynamic current induced magnetic field and their limitations to AC frequency response imposed by optical spectrometer as interrogator unit, the response time of the sensing material and the sensor itself. The interferometric structure optimized for unique narrow linewidth spectral response, also known as "fourth self-imaging" in fiber optic platform has demonstrated response time to ~ 15ms enabling sensing of AC magnetic field and measured up to 10 Hz sinusoidal H-field within the peak-to-peak applied H-field of 30 Gauss. By further tailoring of magnetic nanoparticle's concentration in ferrofluid, it is anticipated that the sensors frequency response can be pushed to higher frequencies. The study extends the versatility of these magnetic field sensitive materials for their applications to AC-current and magnetic field sensing.