Wavelength Selective Property Of Electro-holographic Optical Switch

With the development of AON (All Optical Network), optical switch becomes a core component in optical network communication. Based on holographic techniques by Laser and photorefractive effect in a paraelectric electroholographic crystal, phase gratings was written in to achieve the on-off function. Based on quadratic electro-optic effect, electroholographic switch worked at on-off states by the controlled of external electric field, it has been considered as a promising switch for the combining advantages of high diffraction efficiency and fast electro-optic response time. Paraelectric potassium lithium tantalate niobate (KLTN) crystal has the largest quadratic electro-optic coefficient compared with other crystals, and prominent electro-optic effect near the phase transition temperature. Photorefractive effect was enhanced under external electric field. Due to its excellent properties of KLTN crystal, study on its properties and applications of switch made by paraelectric KLTN crystal would advance the development of all optical network and optical information processing.The Czochralski method was used to grow paraelectric KLTN crystals which phase transition temperature were near room temperature. The space-charge field of paraelectric KLTN crystal was enhanced with several dopant types, so that the photorefractive effect of the crystal was also enhanced. Processing techniques was improved to gained a high quality crystal plate. Two wave mixing setup was designed and built, recording and reading process of Bragg gratings were realized. Based on two wave coupling theory and quadratic electro-optic effect in a paraelectric electroholographic crystal, volume phase Bragg gratings was written in manganese doped potassium lithium tantalate niobate (Mn:KLTN). Diffraction efficiency versus various parameters was discussed at different external voltage. Diffraction efficiency versus read-in time curve and grating erasing curve were given at both 632.8nm and 532nm incident lights. The impact of diffraction efficiency by changing record angle and temperature were also discussed. The abnormal phenomenon of grating diffraction curve was discovered with a high external voltage. The best diffraction qualification was carried out when the related parameters were optimized.Two Bragg gratings were written in a thick paraelectric electroholographic crystal Mn:KLTN, and then both 632.8nm and 532nm signal were diffracted at the same time under electric field controlling. Based on the mechanism of this electro-controlled diffraction, two kinds of switches were designed to accomplish the beam splitting, combining and reading together. Uniformity of the diffractive signal light was also analyzed. The results indicated that the switch made by multiple writing techniques was very suitable to various optical connecting networks, because of its advantages of multifunction, fast response, low cost and low intensity to environment disturbance.Two wave mixing setup was built where the angle of the two recording beams was really tiny. Two-dimensional grating was written in a thin paraelectric electroholographic crystal Mn:KLTN, the Raman-Nath grating was obtained and the high-order diffraction appeared, beam incidence was separated into multi-beam by the controlled of external electric field. At both 632.8nm and 532nm incident lights, the high-order diffraction phenomenon were gained in the way that vertical incidence and oblique incidence contained. Then in the two incident way, the zero-order diffraction was discussed and intercompared. Energy distribution of high-order diffraction was analyzed in the way of oblique incidence. Diffraction efficiency of first order versus incident angle was measured and the conclusion was given. By changing the incident angle and wavelength, the high-order diffraction phenomenon were gained and intercompared. It was proved that Raman-Nath diffraction was insensitivity to the incident angle and wavelength.