Silicon-on-Insulator Slot Waveguides: Theory and Applications in Electro-Optics and Optical Sensing

This chapter deals with the basic concept of silicon-on-insulator (SOI) slot waveguides, including slot waveguide theory, fabrication steps, and applications. First, in the theory section, a modal field expression and the characteristic equation is derived, which is also valid for higher-order modes. SOI slot waveguide structures are simulated and characteristic values like the effective refractive indices and the field confinement factors are deter- mined. The fabrication section describes typical SOI fabrication steps and the limits of current fabrication techniques. Additionally, developments regarding loss reduction in SOI slot waveguides are given from the fabrication point of view. This is followed by the theory and practice of slot waveguide based electro-optical modulators. Here, the SOI slot waveguide is embedded in an organic nonlinear optical material in order to achieve record-low voltage-length products. In the field of optical sensors, it is shown that slot waveguides enable remarkable waveguide sensitivity for both refractive index sensing and surface sensing. finite element method based mode solver. We have determined field confinement factors for the slot and cladding region for applications as EO modulator and optical sensor, respectively. According to the present simulation study, SOI slot waveguides provide about five times higher field confinement in the cladding region with respect to conventional SOI strip waveguides. These results can be used for design optimizations in order to achieve optimum SOI slot waveguide dimensions for sensing applications. The present study was designed to determine the optical and electro-optical characteristics of SOI slot waveguide-based devices. The presented hybrid-waveguide ring resonator consisting of a slot waveguide implemented in a strip waveguide-based ring resonator has a set of characteristics, which makes it an excellent and unique candidate for low power switches and modulators in the field of optical communication systems. The device was fabricated using CMOS fabrication processes, which enables high integration density and scalable, large-volume manufacturing. One of the more significant findings to emerge from this study is the significantly improved EO response compared to common ring-based modulators making use of the plasma dispersion effect, giving rise to the perspective of sub-femtojoule EO switching. In addition, we have performed intensity modulation at 25 kHz. So far, these characteristics are not combined in any other ring resonator to our knowledge. Moreover, there is still significant room for enhancing the device performance in terms of EO response, for example, by taking advantage of the continuously improving EO polymers. Taken together, the presented results suggest that the slot waveguide-based ring resonators are promising candidates for future EO switches, modulators and tunable filters. Future work should investigate the poling procedure to achieve a larger linear EO effect and therefore, higher modulation frequencies using the same EO polymer. Another limitation is the utilized EO polymer. Using advanced EO polymers indicate that the current results could be further improved. Notwithstanding these limitations, the device performance observed in this study indicate the great promises of using EO polymers which are essential for various hybrid photonic devices particularly for low-power applications. The demonstrated ring resonator opens a new route toward promising applications in the realm of polymer-based non-linear photonics. the use of SOI slot waveguides for optical sensing. As proof of principle, homogeneous sensing of different concentrations of 2-propanol in de-ionized water was performed. This study set out to determine the overall sensitivity, taking into account the optical losses and the ring resonator sensitivity. It turns out that the slot waveguide-based ring resonator has a higher overall sensitivity than most traditional ring resonator sensors based on strip waveguides. Thus, it appears to be promising for a wide range of sensing applications, including biochemical sensors.