The Study of 1D Photonic Crystal Filter Infilled with Liquid Crystal
|School||Harbin Engineering University|
|Keywords||Liquid crystal Photonic crystals Tunable filter Defect layer|
With the development of optical fiber communication technology, dense wavelength division multiplexing (DWDM) optical transmission system has become a key technology. In order to meet the overall development of DWDM, reducing communication photoelectric conversion part, people began to study the practical all-optical communication network, and all-optical tunable filter is indispensable communication devices. Therefore tunable filter requirements are increasingly high requirements with a stable and accurate wavelength, and small size, ease of integration and low loss characteristics. Photonic crystal has a simple structure, good reliability, ease of integration and control, and other advantages, and when the original periodic photonic crystal damage, you can introduce one in the band gap defect states, corresponding to the frequency of defect states with photons are localized defect position, which for the production of tunable optical filter provides the technical foundation. At present, through the introduction of defects in the photonic crystal to achieve the optical signal filtering technology is increasingly cause for concern. Liquid crystal is an anisotropic optical material, electrically controlled birefringence of the liquid crystal birefringence parameters on the outside (electromagnetic fields, temperature, pressure) is sensitive to changes, based on these characteristics to the liquid crystal as a defect photonic crystal tunable filter devices, low cost, low power consumption, tuning range, high precision tuning, repeat performance, real-time control and so on. Therefore, the liquid crystal photonic crystal filter of great significance. Nematic liquid crystal phase and compared cholesteric liquid crystal smectic phase is relatively easy to obtain and its application technology is more mature, with a larger dielectric anisotropy and the refractive index is highly vulnerable to external action of the electric field, magnetic field and temperature, is therefore a good filter tuning material. Fink, who pointed out from theoretical and experimental one-dimensional photonic crystals may have a full range of three-dimensional band structure of one-dimensional photonic crystal materials may be prepared by a two, three-dimensional photonic crystal materials produced by the device, namely a two-dimensional photonic crystal compared , three-dimensional photonic crystal structure is more simple and easy to introduce defects. Therefore, this study is based on nematic liquid crystal defect photonic crystal filter filter characteristics. On the theoretical side, using the transfer matrix method photonic crystal filter gives the LCD transmittance formula and numerical simulation of Matlab software through an LCD filter characteristics of photonic crystal filter and analyze: When the thickness of the liquid crystal defect layer gradually increases, the transmittance peak position with the defective layer thickness increases linearly; crystal defect layer with the voltage increases, the transmission peak wavelength of blue shift. In the experiment, the preparation of the liquid crystal photonic crystal filter, the effective area of ??5mm × 5mm, respectively tester using a spectrophotometer and their transmittance spectra and response time for testing, to obtain a crystal defect layer at different voltages transmission spectra and the liquid crystal response time. When the voltage of the filter within the range of 0V ~ 10V, the transmission peak of the relative change in transmittance between 37% -55%, the band gap of nearly 400nm, the tuning range of about 50nm, the FWHM of transmission peaks of 18nm . The rise time of the device is 1.5ms, fall time of 6.5ms. In addition, since the liquid crystal molecules having birefringence characteristics, so the traditional use of the liquid crystal photonic crystal filter inevitably accompanied by the use of polarizers, the polarizer with the orientation direction of the liquid crystal used. In some applications non-polarized light, the polarizing plate makes the light energy use reduction. This paper gives a non-polarized light transmission spectrum, a detailed analysis of polarization sensitive device characteristics, proposed and designed a polarization non-sensitive liquid crystal photonic crystal. Double crystal defect layer design has played a role in mutual compensation for polarization, making the forbidden band originally two transmission peaks and transmission peaks for a strengthened light intensity, enhanced filtering performance.