Study On The Superprism Effect In The Optical Thin Film Stacks

Superprism effect opens new application to optical thin films, the thin film superprism can spatially separate light with different wavelengths when obliquely placed. It means the thin film superprism can be used as the spatial dispersion device, just as prisms and gratings. Moreover, compared with these conventional dispersion devices, much better spatially demultiplexing effect can be obtained by using the thin film superprism, meanwhile, their small size, integrativity, stability and low cost lead them as the precursor in wavelength demultiplexing field in optical communication system. The research is focus on simulation and corresponding measurement on superprism effect in various of optical thin films. The main contents in this paper are as follows:1. Simulation and calculation on superprism effect. After analyzing the limits of the works presented by predecessor, some new methods on superprism effect and relative calculation are proposed. Firstly, as group delay is a significant ingredient in dispersion system, a novel method based on multi-mirror theory for calculating group delay of multi-cavities filters is presented to simplify the calculation and optimization. Besides the calculation on superprism effect (proportionality technique between temporal and spatial dispersion) proposed by previous works, introducing stationary-phase theory and Gaussian angular spectrum method, which usually used in other fields, to simulate the superprism effect in thin films. Compared with the proportionality technique between temporal and spatial dispersion, the stationary-phase theory is simpler and more accurate. While Gaussian angular spectrum method can not only apply to more situation, such as different profiles of incident light, different thin film structure, but also explain some complex physical phenomena, just as beam splitting effect, beam distortion effect an so on.2. Design and measurement on some novel tunable and multichannel thin film superprism devices. To adapt to the requirement of dense wavelength demultiplexing (DWDM) system in optical communication field, design and optimize some typical superprism thin film systems, including utilizing the superprism effect in Fabry-Perot filter with tunable incident angle and liquid crystal Fabry-Perot filter to realize the tunable spatially demultiplexing effect; then a novel struture of conventional high reflectance (HR) coating sandwiched between two thickness-tapered period thin film stacks is designed to be used as the multichannel spatial demultiplexer; At last, based on the electro-optic property in strontium barium niobate Gires- Tournois interferometer, a novel superprism structure is designed to obtain the step-like spatially dispersive shift with the incident wavelengths. The step-like shift can overcome the limits of linear shift and allow some drifts in the central wavelength of the output channel. This sturcture can also be used in dispersion compenesation system, a compensator to the 50GHz thin film filter is designed as the example. Compared with the prior work, these thin film structures are much simpler for depostion, we fabrication two structures of them, and establish the measurement setup to test the spatial dispersion effect in thin film superprism.3. A novel narrow-band thin film reflection filter is designed and fabricated, and its superprism effect is also studied. A novel thin film reflection filter with hight peak reflectance, narrow bandwidth and deep cutoff is designed for display, colorful, special photography, laser and some other fields which are inclined to reflection system. The requirement on symmetry for reflection filter is not as strict as the conventional transmission filter, so it is much easier for fabrication, and we get approximate agreement between design and depostion. Moreover, we also measure the superprism effect in this filter, compared to the high reflectance coatings and transmission filter, it demonstrate that this structure can double the reflective energy efficiency without decreasing dispersive ability. Ultimately, photonic crystal theroy is introduced to design multichannel reflection filters.4. A dramatic negative spatial shift effect is tested in optical thin film for the first time, analysis and discussion are given on this phenomenon. Negative spatial shift means the beam shift against the propagation direction. We introduce the theroy of beam distortion and superluminal effect to explain this phenomenon. The distribution of the pulse propagate through thin film superprism is analyzed, the relationship between spatially positive/ negative dispersive shift phenomena and temporally fast/ slow light effect is tried to estabilished. This relation may supply a short cut for fast and slow light measurement. Combining the negative and positive shift phenomena, we also frame an enhanced superprism effect to get wider dispersive band and larger dispersive shift.5. Relative measurement setups are built. We establish measurement twice on micro shift for testing superprism effect. And the "thin film gratings" measurement, which we adopt finally, has critically tunable monochroic system, collimated system and exact system for spot detection, realizing detect the micrometer-level shift of reflective and transmissive spots with high sensitivity and precision, and is useful for studies on dispersive device with high resolution. Moreover, owing to the importance of phase properties in dispersion system, we also build a white-light Michelson interferometer to measure the phase properties of thin films. Phase information of single layer is tested in this research. This setup can be not only used to measure superprism effect, but also useful for femtosecond, communication, imaging and some other fields.At last, a summary of this paper is included and the prospect of this research is also given.