Study of Light Polarization by Ferrofluid Film Using Jones Calculus

We studied the polarized light patterns obtained using a thin film of ferrofluid subjected to an applied magnetic field. We obtained patterns of polarized light with magnetic field configurations between parallel plates, monopolar, tetrapolar, and hexapolar, and studied how polarized light varies for different intensities and orientations of the applied magnetic field. Using the Jones calculus, we explored the key optical properties of this system and how these properties relate to the applied magnetic field. We have observed general aspects of polarized light obtained by transmission in a Ferrocell using polariscopes and analyzing the resulting Jones vector, such as the formation and rotation of dark bands known as isogyres. We suggest that in a thin film of ferrofluid as in a Ferrocell, two effects occur. The primary effect is dichroism, which is more sensitive to the component of the magnetic field in the direction parallel to the film plane. The secondary effect is the birefringence that can be observed by analyzing the circular polarization of light. Birefringence is related to the thin film thickness of ferrofluid.

Reflective all-fiber magnetic field sensor based on microfiber and magnetic fluid

A kind of reflective all-fiber magnetic field sensor based on a non-adiabatically tapered microfiber with magnetic fluid is proposed and experimentally demonstrated. The modal interference effect is caused by the abrupt tapers, which result in an approximately sinusoidal spectral response. The reflection spectra of the proposed sensor under different magnetic field strengths have been measured and theoretically analyzed. The maximum sensitivity of 174.4 pm/Oe is achieved at wavelength of around 1511 nm. Besides, an intensity tunability of -0.02 dB/Oe is also achieved. Comparing with the traditional sensors operating at transmission mode, the presented sensor in this work owns the advantages of smaller size and higher sensitivity and resolution due to the enhanced extinction ratio. The proposed structure is also promising for designing other tunable all-in-fiber photonic devices.

Magnetic field sensing based on magnetic-fluid-clad fiber-optic structure with taper-like and lateral-offset fusion splicing

A kind of magnetic field sensor composed of magnetic fluid surrounding a segment of singlemode fiber is proposed. The taper-like and lateral-offset fusion splicing techniques are employed. The sensing principle is based on cladding mode interference. The interference valley wavelength or transmission loss of the sensing structure is sensitive to the external magnetic field, which is utilized for magnetic field sensing. The linear response regions are obtained in the range of 38-225 Oe and 250-475 Oe. For the valley-wavelength-shift-type sensing, the sensitivities are 14.1 pm/Oe and 26 pm/Oe at low and high field ranges, respectively. For the transmission-loss-variation-type sensing, the sensitivity of -0.024 dB/Oe is achieved for the magnetic field strength ranging from 250 to 475 Oe.

Magnetic field sensing based on singlemode-multimode-singlemode fiber structures using magnetic fluids as cladding

Magnetic field sensing based on magnetic fluid (MF) and a singlemode-multimode-singlemode (SMS) fiber structure is proposed. The sensitivity of the proposed sensing system can be enhanced by corroding the cladding of the multimode fiber of the SMS fiber structure. The achieved maximum magnetic field sensitivity of our experimental structures is -16.86 pm/Oe as the fiber is corroded for 1680 s. The visibility of the interference dip for the MF-clad SMS fiber structure decreases with corrosion time. Considering the trade-off between sensitivity and visibility, the figure of merit of the sensing system is employed to evaluate the sensing performance comprehensively. In our experiments, the structure corroded for ~1620 s is found to have maximum sensing performance.

Photo-induced electric polarizability of Fe3O4 nanoparticles in weak optical fields

Using a developed co-precipitation method, we synthesized spherical Fe3O4 nanoparticles with a wide nonlinear absorption band of visible radiation. Optical properties of the synthesized nanoparticles dispersed in an optically transparent copolymer of methyl methacrylate with styrene were studied by optical spectroscopy and z-scan techniques. We found that the electric polarizability of Fe3O4 nanoparticles is altered by low-intensity visible radiation (I ≤ 0.2 kW/cm2; λ = 442 and 561 nm) and reaches a value of 107 Å3. The change in polarizability is induced by the intraband phototransition of charge carriers. This optical effect may be employed to improve the drug uptake properties of Fe3O4 nanoparticles. PACS: 33.15.Kr78.67.Bf42.70.Nq.

Magnetic field sensing based on capillary filled with magnetic fluids

A kind of magnetic field sensing system based on capillary tube filled with magnetic fluids is developed in this work. The analytical expressions for the sensing system are derived in detail. The sensitivity and other sensing properties of the system are investigated numerically and experimentally. The focal line position of the emergent light after the capillary is related with the strength of the externally applied magnetic fields and recorded and judged by the CCD to sense the magnetic field indirectly. The sensing mechanism is analyzed and ascribed to the magnetically tunable refractive index of magnetic fluids. This kind of sensing unit has the advantages of miniaturization of device, easy operation, and lower dosage of sensing media.