Performance Study Of Tunable-focus Electroholography Lens

With the development of binary optics and integrated optics, the traditionaloptical elements are moving towards integration and performance-controllable. Thefocus tuning of traditional lens system uses mechanical motion mode, is used in thefocus tuning of traditional lens system, resulting in large system, slow tuning speed,and poor stability. So the miniaturization of high-speed zoom lens is the researchfrontier and faces a lot of difficulties. In this thesis we took the advantage ofMn:KNTN crystal for its fast response, high diffraction efficiency and largequadratic electro-optic coefficient, and studied on the electrically tunable focusingholographic lens.Firstly, the basic physical properties of the Mn:KNTN crystals were studied.The crystal was grown by the top seeded solution growth method. The Curietemperature were determined by the dielectric constant-temperature spectrum whichwere measured by the bridge method. The Curie temperature was near the roomtemperature. The dispersion of the refractive index from400nm to900nm weremeasured by the spectroscopic ellipsometry. The quadric electro-optic (QEO)properties of the KNTN crystals were studied systematically. The QEO coefficientswere measured by an dynamic Mach-Zehnder interferometer, and the QEOcoefficients at different temperature were also investigated. The voltage controlleddiffraction efficiencies were measured by the two-wave mixing setup. It is showedthat KNTN crystals were one of the most promising materials in the EH application,due to the excellent voltage controlled photorefractive property.Secondly, tunable-focus electroholography lens were analyzed theoretically. Abeam of plane wave was interferenced with a beam of cylindrical wave, and wasincidented into Mn:KNTN crystal. The Fresnel zone plate was written in the crystal,and the phase difference between adjacent zones was controlled by the interaction ofapplied field and space charge field. With the applied voltage value increasing, thefocus was gradually moved to the multiple foci of original lens.Finally, combined with theoretical analysis, the tunable-focuselectroholography system was established in the experiment. With the appliedvoltage value increasing, the diffraction intensity decreased at the same point.According to diffraction intensity, it is thought that the focal length of the lens waschanged. Therefore, focal length could be varied in tunable-focus electroholographylens based on Mn-doped potassium sodium tantalate niobate crystal. This investigation will contribute to the development of novel informationdevice, and lay theoretical and experimental foundation for performance control ofthe electroholographic lens, and has scientific significance and application value inpromoting the realization of the high-speed zoom lens.