| The development of dense wavelength division multiplexing (DWDM) optical networks is the necessary trend for the development of optical communication systems, and tunable optical filters will be a key device in dense WDM systems. On the other side, researches about the photonic crystals (PCs) have been becoming a new direction in optical fields, so WDM devices of new type can be manufactured by using superprism effect in one-dimensional PCs. In order to meet the requirements for WDM devices in the development of optical networks, this paper makes systemic study on the tunable Fabry-Perot narrow-band Filter based on birefringence of liquid crystal and the demultiplexer based on the superprism effect in multilayer thin film theoretically and experimentally:The thin film structure of the electric tunable Liquid Crystal Fabry-Perot Filter (LCFPF), has influence on the tunable performance of LCFPF. In the continuous tuning process of LCFPF, the phenomenon of the jumping of the transmission peak spectrums is found, when the interference order of Fabry-Perot cavity changes with the big change of the refractive index of liquid crystal. But in the same interference order, the transmission peak wavelength change monotonically with index. The experimental results are in agreement with the numeric simulations. Some approaches are presented in this paper, in order to improve the monotone tuning performance of the device, and the monotone tuning range will cover the whole C Band with the index difference of only 0.05 when the length of the cavity equals to 10n,m. The influence of the phase on reflection on the tuning properties is also analyzed by numeric simulation. At last, experimental estimate of the primary performance parameters is given. And according to this estimation, optimized projects are proposed to decrease the loss or make the band width narrower.By characteristic matrix method used widely in optical thin film theory, the group delay and the shift caused by superprism effect in the quarter-wave thin film stacks are numerically simulated. And more complex thin film superprism structure based on Fabry-Perot cavity is further designed. Experimental equipments to measure the small dispersive shift caused by superprism effect is designed and set up, which obtained the high precision of 3~5um. Both design and experiments show that, in the quarter-wave periodic thin film stacks, shift causedby superprism effect for single reflection is measured out about 22μm, which is decreased with the metal reflector deposited. But metal reflectors enhance reflected power of light greatly, and the shift can also be increased by adding the number of reflections. As for as the thin film stack with Fabry-Perot cavity, spatial shift is achieved 65 um at the wavelength of peak transmittance, which consists well with the designed one. Compared with the conventional grating element and prism, the device has smaller size and higher spatial resolution, which is nearly 3.4°/ nm , and approximate linear shift according to the measurement.Study of this paper shows that, new thin film structures with more novel properties can be constructed by optical thin film technology, and can be used in different optical fields. |
PDF Full Text Request