Advanced Photonic Devices Based On Magnetic Fluids

Magnetic fluid(MF) is a kind of stable colloidal system consisting of surfactant-coated magnetic nanoparticles dispersed in a suitable liquid carrier. It possesses the features of both the magnetic property of solid magnetic materials and the fluidity of liquids. Besides, MF has numerous unique optical properties assigning to that the agglomerations of magnetic nanoparticles will occur when the magnetic field is applied. This dissertation is mainly concerned with the scheme for realizing the threshold-tunable optical limiters and the generation of ring-shaped beams, as well as the magnetic field sensing based on the singlemode–multimode–singlemode(SMS) fiber structure.Due to the strong thermal lens effect of MF, laser beams are converted into a series of toroidal beams after passing through the MF sample. If an aperture is placed behind the MF sample, an optical limiter is easily achieved. The far- field beam patterns after the magnetic fluid sample are simulated. The conclusions that the threshold value of the optical limiting system shifts to high power when the aperture radiuses are increased and the distances between the aperture and the sample are decreased are obtained through theoretical calculations. The linear relationship between the threshold value and the aperture radiuses is also achieved. The threshold value of the optical limiting system decreases with the increase of the absolute value of the magnetic fluid characteristic parameter(f). The results presented in this work may be helpful for designing the magnetic-fluid-based threshold-tunable optical limiters.If we place a ring- limited window instead of the aperture behind the MF sample, a simple method to generate ring-shaped beams is realized. Far- field patterns of ring-shaped beams are simulated after the ring- limited windows. The relationship between the system parameters and the transmission parameters are calculated and analyzed in detail. The results show that each transmission parameter is a lmost independent of one of the system parameters. The influence of magnetic fluid characteristic parameter on the transmission properties is also investigated. The results presented in this work may be very helpful for designing optical devices with high repeatability of performance for specific applications.Magnetic field sensing based on the property of magnetic- field-dependent refractive index of MF and a 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. The visibility of the interference dip for the magnetic- fluid-cladded 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 ~1620s is found to have maximum sensing performance. The above- mentioned scheme of magnetic fluid sensing has several advantages, such as cost effective, simply fabricating and relative high sensitivity.