This paper presents theoretical and experimental study of ultra-compact Si-wire Optical Directional Couplers (ODCs) on Silicon-on-Insulator wafer for optical signal processing. The presence of the controllable evanescent light strongly confined in the region bounded by the Si nano-wires has a large impact on the optical power coupling between waveguides. The characteristics of coupling length and power transmission in ODCs based on separation, wavelength, light field propagation distance and geometry of waveguides are described in detail by the coupled mode theory, 3-D finite-difference time-domain analysis and beam propagation method, and are confirmed by experiments. The exponential dependency of coupling length on the separation of coupled waveguides and wavelength shows interesting high-sensitivity optical sensing, switching and multiplexing properties. Custom spectral properties can be achieved by the configuration of coupled nano-wire waveguides based on their separation and lengths. We show that optimization of ODCs based on the physics of the coupled waveguides will lead to short optical devices which can be integrated as building blocks within high-density photonic circuits with the desired spectral characteristics. In the end, two new systems based on Mach-Zehnder structure and Micro-Ring Resonators are proposed in which ODCs are implemented as embedded tunable devices resulting in more functional optical sensing and signal processing devices.

In this article the immersed gratings for the ESA Copernicus Sentinel-5 mission are presented. The manufacturing approach is shown and the optical performance of the SWIR-3 immersed gratings as well as the results of the environmental tests are discussed. The immersed gratings show an average efficiency of 60% and a wavefront error of 200 nm rms. The total integrated scatter over the complete stray-light hemisphere excluding ghosts from internal reflections is found to be 0.2% using a conservative estimate. A method for the derivation of the wavefront error from separate surface measurements is presented and the results are compared to measurements with an experimental Shack-Hartmann setup. The immersed gratings are produced by bonding a prism to a wafer with a grating. Environmental tests and testing at operational temperatures show the suitability of this approach for complex space optical components. The article concludes with possible improvements in the optical performance of future immersed gratings.

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Due to copyright restrictions, the access to the full text of this article is only available via subscription.Fabrication and actuation errors of submicron silicon waveguide optical switches are reported to remain within sub-100 nm ranges. These errors cause high loss ruining the optical performance of the switches at the on-state. Elliptical tips with tip angles about the Brewster angle are studied in an attempt to reduce the high-loss of such optical switches. Numerical computations are conducted in 3D Finite Difference Time Domain analysis. Optical performances at various distances both along and perpendicular to the light propagation directions are studied for tips with angles above and below the Brewster angle. Effect of fabrication and actuation errors on the performance of optical switch is reduced using tips with angles greater than Brewster angle. Transmittance of optical switch is calculated to be 94.69% when 1.5 μm-wide and 74º-angled waveguide tip geometry after two cascaded waveguide pairs is utilized