| With the development of science and technology, fiber optic communication has become an important field of communication branch. In the large amount of information transmission, long distance relay, high reliability advantages, fiber optic communication becomes the basis of the information highway. With fiber optic communication systems of the rapid development of optical communication as the basis - optical passive devices technology has developed rapidly. Targets more advanced, feature more new optical passive devices are emerging. Variable optical attenuator is a device aimed at reducing transmission in the optical power. The device can achieve the expected attenuation in accordance with the requirements of users. It is a very important fiber optic passive component with the development of optical communication. Combing with the connector, coupler, isolation, etc, they become the most basic optical passive devices. The market demand growth is very rapid.This paper by the research-based polymer dispersed liquid crystal (PDLC) of micro-electromechanical system (MEMS) based VOA in the study at home and abroad is just at the initial stage. The project combines with requirements of the development of optical communication with the current optical network optical signal processing components of the high reliability, low power consumption and small size, which uses PDLC materials, MEMS technology in silicon micro-processing technology and the development of LC technology to become a new species of PDLC-VOA devices. Through the effective use of PDLC material parameters and to improve components of the structure, the overall performance of the device is improving. In this way, it overcomes the traditional optical attenuator's big volume, high costs, slow response, and other shortcomings. The device is easier to achieve more array, smaller, lower-cost and lower power consumption than traditional. In particular the use of polymer dispersed liquid crystal optical attenuator compared with it of the ordinary liquid crystals', it does not need Polaroid slice, the liquid crystal materials without the direction of special treatment, structural design simple. It will play an important role in fiber optic network.The basic principles of polymer dispersed liquid crystal variable optical attenuator is that polymer dispersed liquid crystal materials be injected into the middle of two transparent conductive electrode. When the voltage is not imposed between the electrodes, the liquid crystal molecules are disorder, the laser beam by scattering and optical power output is small .When the voltage is imposed between the electrodes, the liquid crystal molecules are arranged in an orderly manner and becoming a transmission, and thus power output will be great. While removed imposed voltage, liquid crystal polymer molecule by the role, again Return to the state of disorder. Accordingly, it achieves the optical power transmission from minimum to maximum attenuation and then to the smallest changes.The problems to be resolved in this project is : the performance research on polymer dispersion of liquid crystal materials, the fabrication processing of the VOA and the transparent conductive film ITO and finally, the achievement of the device. In materials aspect, the LC E7, the polymer bisphenol A epoxy acrylic resin (EB648), the light scattered methyl methacrylate (MMA) and the I-hydroxy-phenyl-Central (Irgacure-184) are used as the basic materials. Polymer dispersed liquid crystal film was prepared by UV-induced phase separation method. By changing the process conditions, the optimum processing condition of preparing high performance polymer dispersed liquid crystal film was fished out: the content of E7 is 76 percent, and the ratio of light scattered and polymers is 1:1, the content of light initiator is three percent, LCD box is 8-micron-thick, Curing temperature is room temperature (27-34 oC), and the light source is Philip's ultraviolet light sources of 300 watts'power. The smallest optical transmission of the prepared film is less than 1 percent , the largest optical transmittance is greater than 90 percent, and the open voltage is less than 3 volts, the high performance PDLC film provide a good material for our device realization. In the prototype device aspect, we use the silicon-micro-machining techniques, According to the crystal characteristics of silicon, self-aligned fiber V-groove, which will be used as access of fiber ,was fabricated on (100) orientation by using wet directed etch, and finally ,electrodes was prepared. The detailed processing and its technical parameters are described in chapter IV. In the ITO aspect, we selected RF magnetron sputtering to prepare ITO film, the ITO film's thickness is about 81 nm and its resistive is 10-4 ohm/cm, the light transmittance is 80 percent at 1550 nanometer wavelength of Optical fiber communications.The device to achieve: use of the device precision optical waveguide Alignment System (PAS-1000) to the assembly of the device. The production of good (100) Self-Aligned fiber positioning groove and a sputtering end of the ITO film single-mode optical fiber for assembly and then coupling, reuse UV glue will be fixed in the V-shaped fiber bed. At this point to the LC-tank has been injected by the polymer dispersion liquid crystal materials, then use UV to induce their separation.Leading electrode lines from the electrode point connecting the external electric field, produced 8 * 8 channel PDLC variable optical attenuator. Testing devices by the open voltage is 3.5-6.5 V, and the drive voltage is 3.5-17 V; attenuation be tested to the maximum extent to 3.1 dB-12.6 dB. The minimum insertion loss (IL) of attenuator is 3.1 dB, compared reported in the MEMS optical attenuator insertion loss to the many indicators. From this we can see that the entire device in the design and production process is feasible. Finally, we analysed the device's overall number of issues and put forward some concrete solutions. |
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