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Abstract
An all-fiber magnetic field sensor based on whispering-gallery modes (WGM) in a fiber micro-resonator infiltrated with ferronematic liquid crystal is proposed and experimentally demonstrated. The cylindrical microresonator is formed by a 1 cm-long section of a photonic crystal fiber infiltrated with ferronematic materials. Both ferronematics suspensions are prepared based on the nematic liquid crystal 1-(trans-4-Hexylcyclohexyl)-4-isothiocyanatobenzene (6CHBT) doped with rod-like magnetic particles in the first case and with spherical magnetic particles in the second case. WGMs are excited in the fiber microresonator by evanescent light coupling using a tapered fiber with a micron-size diameter. The Q-factor of the microresonator determined from the experimentaly measured transmission spectrum of the tapered fiber was 1.975 × 103. Under the influence of an applied magnetic field the WGM resonances experience spectral shift towards shorter wavelengths. The experimentally demonstrated sensitivity of the proposed sensor was -39.6 pm/mT and -37.3 pm/mT for samples infiltrated with rod like and spherical like ferromagnetic suspensions respectively for a magnetic field range (0-47) mT. Reducing the diameter of the cylindrical micro-resonator by tapering leads to enhancement of the magnetic field sensitivity up to -61.86 pm/mT and -49.88 pm/mT for samples infiltrated with rod like and spherical like ferromagnetic suspensions respectively for the magnetic field range (0-44.7) mT.
Highlights
Optical microresonators are axially symmetric structures that trap light in a small volume in the form of Whispering-Gallery Modes (WGMs)
An all-fiber magnetic field sensor based on whispering-gallery modes (WGM) in a fiber micro-resonator infiltrated with ferronematic liquid crystal is proposed and experimentally demonstrated
The cylindrical microresonator is formed by a 1 cm-long section of a photonic crystal fiber infiltrated with ferronematic materials
Summary
Optical microresonators are axially symmetric structures that trap light in a small volume in the form of Whispering-Gallery Modes (WGMs). This effect occurs when light travels in a dielectric medium of circular geometry. After multiple repeated total internal reflections at the curved boundary, the electromagnetic field can close on itself and give rise to WGM resonances Such microresonators have been investigated for applications in nonlinear optics, quantum electrodynamics, as optical filters, lasers and sensors for several decades [1]. Magnetic fluid strongly absorbes pump light which leads to a resonance shift of the silica microresonator due to the photothermal effect, resulting in tunning sensitivity of 0.15 nm/mW [12]. It has been found that lower order WGMs excited in such a micro resonator are strongly confined within the surface layer of the fiber resonator (in the outer cladding of the PCF), while the higher order modes expand further from the surface and into the body of the micro resonator [1]
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