Investigation On Faraday Anomalous Dispersion Optical Filter

To obtain the weak signal light from the high background light, atomic opticalfilter plays a key role in the field of Free-apace optical communication andUnderwater optical communication. Narrowband optical filters based on theFaraday anomalous dispersion effect have many advantages such asultranarrow-bandwidth transmission, high transmission rate, high backgroundrejection, wide field of view and it will be able to adapt to the demand ofcommunication technology. In this letter, we demonstrate a theoretical andexperimental study on ultra-narrow bandwidth Faraday anomalous dispersionoptical filter (FADOF). The main contents of the dissertation include the followingaspects:Firstly, the filtering mechanism of FADOF was given. It was based on theZeeman effect and Faraday anomalous dispersion effect to realize the function ofthe filter. We use the semi-classical theory to deal the theory analysis of FADOF.And the expression of the transmission for FADOF was given.Secondly, the filter characteristics of FADOF at87Rb D1line were theoreticallyand experimentally investigated. In theory, the characteristic of the filter underdifferent temperatures and different magnetic field intensity was givensystematically. The Faraday anomalous dispersion optical filters have two workingmodes: two side peak transmission and center peak transmission. In experiment, atransmission spectrum narrowed to~220MHz was obtained, and the peaktransmission is about50%.Finally, the ultranarrow tunable passband Faraday atomic filter withElectromagnetically Induced Transparency was studied both in theory and experiment. Through the analysis of the filtering mechanism, the density matrixequation in the semi-classical theory was utilized to deal with the three-level Λatomic system. The system susceptibility was obtained by solving the densitymatrix equation in the steady state. And then the complete filter model wasestablished with associating the filter parameters with the system susceptibility. Inexperiment, two laser beams co-propagate through the sample cell with a smallangle. The experimental transmission spectrum displayed a single peaktransmission of8%with15MHz bandwidth, and the transmission wavelength canbe tuned by changing the coupling light frequency.