Research On Electro-holographic Optical Switch Based On The Quadratic Electro-optic Effect

Very large scale parallel computer system requires the interior communication network to have very high capacity and speed. However, the traditionary electronic interconnections bring much insurmountable defect simultaneously in some aspects such as bandwidth, interconnection density, clock skew, power attenuation, anti-interference feature, etc. that has been handicapping the capability improvement of the parallel computer system seriously. The optical interconnections transmit the information with light as the carrier, which is a hopeful way to absolutely solve the ubiquitous electronic bottleneck in the high performance computer system and hyper-speed switching system, and to realise the data switching with high capacity, high speed and low power consumption. One of the critical technologies to be overcome in the optical interconnections is photonic switching; and optical switch is the vital device. Because of the virtues of high speed, high stability, high expansibility, etc., the holographic optical switch has a bright future in the applications of optical communication and the high performance computer system. The optical interconnections and photonic switching have been under the intensive research in recent years. According to the application requirement, the electro-holographic optical switch and its control system are researched theoretically and experimentally in this dissertation, and the main achievements are listed as follows:1. The dissertation begins with the reviewing and analyzing the history of optical interconnections and photonic switching, especially the significant development in recent years of the technology of volume holographic storage and thermal fixing, and the device of electro-holographic optical switch. Comparison and analysis of the performance parameters of several typical optical switches are presented.2. According to the technical principle of electro-holographic optical switch, the photorefractive crystal Mn: KLTN (0.25%, mol) in paraelectric phase is selected as the storage medium. The diffraction efficiency of volume holographic phase grating of reflecting-type and transmitting-type is calculated, respectively. The influences on diffraction efficiency from the factors, such as the incident angle of recording beams, the thickness of grating and the applied electric field, are analyzed. It is found that the properly evaluated influencing factors are advantageous to increase the grating diffraction efficiency. A sub-micron volume holographic phase grating was recorded and the tested diffraction efficiency is 90.6%. The strict reading angle selectivity of volume grating is validated in the experiments of grating reading out.3. The finite element method is introduced into researching the photorefractive phenomenon. Considerating the energy coupling between the record beams, the band transport model under large modulation depths is solved with FlexPDE program. The forming of ionic grating is investigated in the process of thermal fixing of the volume holographic grating. The distributions and time evolvement of parameters in the crystal are displayed on real time and dynamically. By comparison with others, the finite element method reduces the difficulty greatly of solving the model.4. By analogy with the dark decay of electronic grating, based on the physical model of ion transporting, a model and analytic expression of the lifetime of thermal fixed volume holograms is established theoretically. The factors, such as grating spacing, temperature and ion density, which may have influences on the storage time of ionic grating are analyzed and discussed. The conclusions accord with the published theory and experimental results well. Experiments have been designed to thermally fix the volume holographic grating and validate the theoretical expression.5. The time response characteristic of the electro-holographic optical switch is investigated theoretically and experimentally. The factors causing time delay to electro-holographic optical switch are analysed theoretically and the edge curves of the light signal that switched by the optical switch system are tested. The results reveal that the response speed of the designed optical switch experiment system can reach 300ns. The analysis figures that there is great room for improvement in the tested speed index compared with the theoretical value.6. Based on the requirements and the time response characteristics of electro-holographic optical switch, a reliable high-voltage fast pulse signal generator was designed, utilizing the multistage Marx generator as well as the bipolar junction transistors operated in avalanche mode. The circuit is simulated with PSPICE program, and the results indicate that the designed circuit could generate kilo-voltage nanosecond pulse control signal that can match the applications requirement of electro- holographic optical switch well. Integrating the electronic control part with the switch module on PCB, a 2×2 system of electro-holographic optical switch is designed preliminarily.