Preparation Of ITO Transparent Electrode And Fabrication Of Device Structure Based On PDLC Variable Optical Attenuator

With the development of science and technology, the fiber optic communication has already become an important branch of the communication field. Following the rapid development of the fiber optic communication system, Passive device technology, as the foundation of optical communication, develops rapidly too. Optical attenuator is a kind of device aiming at reducing the light power transmitting in wave guide and can decay the power of the light signal as much as the user expects. It is a kind of very important passive device of fiber optics and has become the most basic optical passive device with connector, coupler, isolator etc. together. With the rapid development of all optic-networks, the optical attenuator is playing an important role in wavelength division multiplexing (WDM) systems, and the market demand increases very swiftly and violently.At present, the components in optical network are in more demand of dealing optical signal with high reliability, power consumption little and miniaturization with the optic communication development. Utilizing the polymer network liquid crystal material, combining body silicon micro machining technology and liquid crystal technology together we are developing a novel polymer dispersed liquid crystal variable optical attenuator. The working mechanism of polymer dispersed liquid crystal variable optical attenuator is shown as below: Liquid crystal molecules are inserted in the middle of two transparent conductive electrodes. If no voltage is applied on the electrodes, molecules arrange the liquid crystal unordered, so the incidence light beam has been affected by scattering and the output optic power is very small. When the voltage is applied on the electrodes, molecules arrange the liquid crystal in order and present the transmission state, so the output optical power can be very heavy. In this process, optical power of transmission alters from minimum to maximum.One problem is to choose and prepare transparent conductive electrodes, which suits the silicon machining technology and can meet the demand of optical communications. It is reported that ITO thin films have high transmittance in the visible light band and high reflectance in infrared light band, while the transmittance at fiber optic communication wavelength of 1550nm is seldom researched. With the tremendous development of fiber optic communication technology, it is of great importance to have a study on the transmittance at fiber optic communication wavelength of 1550nm since ITO thin films are widely applied in this field. Besides, ITO thin films at present are prepared usually on the substrates with large area such as glass and silicon wafer etc. In our project, we need to prepare transparent electrode on the tiny terminal surface of a single mode optic fiber. There is not a report yet in this, which is innovative.In the experiments, we choose radio frequency magnetron sputtering technology to grow ITO thin films, choosing different experimental parameter constantly, trying to find out the rules. Different experimental parameters conclude different degree of vacuum, different sputtering power and different argon flow. 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 87 nm, resistivity as 8.67×10-4?cm, and transmittance above 85% at fiber optic communication wavelength 1550 nm.It 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 (100) silicon wafers, 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. There are very great market potential and wide application prospect.In the paper, we introduced the manufacture of the whole structure of the polymer dispersed liquid crystal (PDLC) variable attenuator. At first we prepared polymer dispersed liquid crystal with polymerization induced phase separation (PIPS). Second, we made the self-aligned grooves on (100) silicon wafers utilizing silicon micro machining technology. We utilized the coupling laboratory bench of optic fiber to test the light power losses when light passing through the whole structure. When testing, each groove was put into two single mode fibers that each of them was sputtered on one terminal surface with ITO thin film. Then we injected PDLC into the LC groves. After ultraviolet curing, we got the PDLC variable attenuator. We tested the devices that the result showed the attenuation range of 5.98-17.4dB, the minimum insertion loss of 5.98dB, and the offset voltage is 6Vrms.