The Research Of Polymer Liquid Crystal Variable Optical Attenuator

The Variable Optical Attenuator is one of essential optical components in the DWDM optical communication system. It has widespread application and cannot be substituted in OADM equipment, OXC equipment, optical fiber amplifier, optical testing systems. At present, the variable optical attenuator has some insufficient in the cost, response speed, reliability and miniaturization of integrated, and other aspects that can not meet the demand for rapid development of optical communication network requirements. It is a significant research and trends to replace the existing products using some new technologies and new materials and integrated optical attenuator array. They has tremendous market demand.The components in optical network should have high reliability, less power consumption and miniaturization with the optic communication development. The main research of this thesis is to use the unique electro-optical properties of the polymer liquid crystal material and the crystallization characteristics of Si (100) and (110) Crystal, use their anisotropic etching characteristics in KOH solution to make self-aligned positioning groove, liquid crystal micro-box structure. Use RF magnetron sputtering method to make indium tin oxide (ITO) transparent conductive films as the transparent conductive electrode to control the polymer liquid crystal material. Study the core attenuation functions of Variable Optical Attenuator - liquid crystal polymer materials technology and the modulation parameters. Compared with the influence of the electro-optical properties of the polymer under the craft conditions such as different liquid crystal materials, prepolymers, light initiator material ratio, different curing temperature, and other conditions. We use the light scattering effect of polymer liquid crystal under the different electric-field intensity, to change the optical path to achieve energy controllable continuous attenuation. Through the adjustment of polymer disperser liquid crystal modulation craft parameter and the optimization of component structure, we design a new prototype of continuously polymer liquid crystal variable optical attenuator. This technology overcome the shortcoming of the traditional optical attenuator such as bulky, complicated process, not easy to integrate, without polarizer, does not require special orientation processing, has relatively simple structure. They can create conditions for the practical use of technology and development of theory.In this paper, the design of liquid crystal polymer Variable Optical Attenuator structure contains the single crystal silicon substrate, the incident optical fiber coupler channel, filled with the liquid crystal polymer liquid crystal micro-groove. In planning the overall experimental process, and make full use of the characteristics of crystalline silicon and wet etching technology, respectively produced a self-aligned liquid crystal fiber micro-groove in (100) and (110) silicon and compared with two shafts positioning technology and coupling effects.The key structure of polymer liquid crystal variable optical attenuator is the modules of its attenuaor. Using the refractive index of polymer liquid crystal materials can be effectively controlled by electric field to achieve its macro-physical state of change, so the optical performance of polymer liquid crystal played the decisive role to the entire attentuator target. This requires different contrast LCD materials, prepolymers, light initiator material ratio, different curing temperature, and other conditions of the polymer liquid crystal material separation of the electro-optical properties, as well as its impact.Based on the principle of polymer dispersed liquid crystal film, we choose liquid crystal E7, pair of phenol A surrounds oxygen acrylic acid ester, methyl acrylic acid first ester MMA, I - the base benzene base ketone(Irgacure-184 ) of hydroxyl ring to prepare polymer dispersed liquid crystal film by Ultra-violet Induced Phase Separation. Through changing a series of process conditions, such as content of liquid crystal, polymer to dispersant, content of optical initiator, solidification temperature, we have made a large number of contrast test and found out the best process conditions of preparing polymer dispersed liquid crystal film. The best process conditions: content of liquid crystal is 65%, polymer to dispersant is 1:1, content of Irgacure-184 is 3%, solidification temperature is 40℃. Under this condition, the maximum transmittance can be up to 90%, and its characteristic is good. In this way, we prepare good material to fabricate variable optical attenuator.In the experiments, we choose radio frequency magnetron sputtering technology to grow ITO thin films, contrasted the electro-optical properties of ITO films which under the different experimental parameters. We analyzed and optimized the influence of different craft parameter to the electro-optical properties of the ITO thin film, get the ITO conductive thin films that have high transmittance, high conductivity, surface smooth formation and Uniform distribution. Find out the very experimental parameters with which the prepared films'resistivity combines best with the films'transmittance. With the best parameters, we have obtained ITO thin films with thickness as 80nm, resistivity as 6.2×10-4Ωcm, and transmittance above 85% at fiber optic communication wavelength 1550nm.The several main attenuation Performance Parameters of the liquid crystal polymer Variable Optical Attenuator haveinsertion loss, return loss and response time ,we tests the open-voltage for 6 Vrms, the threshold has good properties, driving voltage range of 6 Vrms - 35Vrms; The attenuation device testing by the largest the range of 5.98 dB - 17.4dB; return loss more than 38 dB; the minimum insertion of attenuator loss (IL) 5.38 dBIt is reported abroad using planar wave guide or optic fiber glass capillary structure at present. We adopt the silicon micro machining technology to get self-aligned grooves on (110) or (100) silicon wafer, design liquid crystal little box structure and combine the polymer network liquid crystal technology together to find out the fabrication technology of the prototype device of the attenuator. This research scheme at present not still seen at home and abroad is innovative. The research scheme adopting silicon micro machining technology connects optic fiber coupling structure and decay function part into a whole, making the device architecture easier to integrate. Comparing with other MEMS micro-structure optical attenuators, our designing fabrication process is comparatively simple; comparing with machinery attenuator made by traditional technology, our attenuator has the advantages such as a small and exquisite volume, low costs, being apt to realize many arrays of the devices.Particularly polymer liquid crystal technology compared with ordinary liquid crystal optical attenuator without polarizer, the liquid crystal material without special orientation processing, designed to be simple, will play an important role and has tremendous market potential and broad prospects in WDM optical networks.