| dc.description.abstract | The improvement on the efficiency of electro-optic (EO) light modulator can be achieved by the optimal design of EO modulating mechanism and the proper selection of EO materials. In this dissertation, two novel high efficiency EO modulators based on multiple surface plasmon resonance (SPR) effects are presented. One of the proposed EO polymeric modulators is based on a novel design in which the degree of coupling of the collimating monochromatic beam into the coupled waveguide-surface plasmon resonance (CWSPR) is electrically varied in order to enhance the modulation efficiency of the device. The other is so called double surface plasmon resonance (DSPR) and based on increasing coupling effect between two surface plasmon resonances via the optimization of the waveguide layer thickness. Both of EO modulators employed the Pockels effect possessed by the poled nonlinear optical organic polymer (NLOP) and the optimization of the thickness of EO thin film. By applying voltage across EO polymer film to vary the refractive index of the EO polymer, the degree of coupling of CWSPR and DSPR is altered and the reflectivity is modulated. The CWSPR EO modulator consists of a high refractive index prism, a thin metal film, a poled polymer layer, and metal electrode. By optimizing the thickness of the EO polymer, the coupling effect of the SPR and the waveguide coupled resonance (WCR) which induced by the Fabry-Perot (F-P) interference within EO polymer can be enhanced. As a result, the CWSPR EO modulator is able to operate with less modulation voltage and achieves better modulation efficiency. The DSPR EO modulator consists of a high refractive index prism, a thin metal film, a poled polymer layer, thin metal electrode, and EO film. In the same way, by optimizing the EO polymer thickness, the coupling effect of the short-range surface plasmon resonance induced at top metal interface and the long-range surface plasmon resonance induced at bottom metal interface will be enhanced and the modulator then yields a better efficiency. The EO polymer light modulator based on SPR-related principles offer the advantage of less insertion loss due to its shorter interaction length.
This dissertation sequentially introduce the principles of SPR, the dispersion relation of multilayer system, the fundamentals of the modulator, the theoretical study and simulation concerning the relationship between the efficiency of modulator and the thickness of EO film. The determination of the refractive indexes and thicknesses for the various films, which is required for the fabrication of EO polymer modulator possessed with multilayer structure, can be achieved by employing the home-made SPR sensing technique and an improved data analysis method. In the similar approach, the SPR sensing technique is also capable of measuring the EO properties of the poled polymer film. This will greatly simplify experimental procedure. Since the NLOPs offer the advantages of having large EO constants, low dielectric constants, the simplicity to be fabricated, low cost, the diversity of synthesis and being compatible with integrated circuits, they are considered to be the most promising materials for the development of EO light modulator. Due to the aforementioned strengths offered by EO polymer, the EO polymers used in this project include two NLOP materials, one nonlinear optical organic polymer is a polymethyl methacrylate polymer (PMMA) side-chained with DANS (4, 4’-aminnonitroazobenzene) chromophore (DANS-PMMA) which synthesized and fabricated by our lab and the other is a side-chained EO polyimide with 2-(N-ethyl-4-(tricyanovinyl)anilino)ethanol chromophore. Based on using the foregoing principles, we have implemented two CWSPR EO modulators with these two NLOP materials. The modulators are characterized, and their performance is tested, in terms of the optical properties of the polymer thin film, the EO coefficient, the insertion loss, and the modulation index. Additionally, the dynamic response of the EO light modulator is also investigated and discussed. | en_US |