Choosing metasurface building blocks to encircle a singularity following an arbitrarily closed trajectory in parameter space, we engineer topologically-protected full 2𝜋 − phase on a specific reflected polarization channel. The ease of implementation together with its compatibility with other phase-addressing mechanisms bring topological properties into the realm of industrial applications at optical frequencies, and prove that metasurface technology represents a convenient test bench to study and validate topological photonic concepts.

In this paper, we investigate the mode sensitivity (S mode) of subwavelength grating slot (SWGS) waveguides. S mode is an important parameter in various waveguide-based photonic circuits such as sensors, modulators, and thermally-controlled devices. It is a measure of the sensitivity of the waveguide effective index towards the refractive index perturbations in the cladding medium. The SWGS waveguide exhibits high mode sensitivity, as it combines sensitivity enhancement features of both slot and subwavelength grating waveguides. Finite-difference time-domain simulations are performed for the analysis, design, and optimization of the hybrid structure. The SWGS waveguide is incorporated into a Mach-Zehnder interferometer and fabricated on a silicon-on-insulator platform for the experimental estimation of S mode. The measured S mode value of 79% is consistent with the theoretical prediction of 83%.

This work demonstrates an approach for simplifying fiber-to-chip (edge coupling) packaging by virtually eliminating the longitudinal alignment procedure (also increasing compactness and efficiency) through a fiber lens embedded into the structure of the fiber itself. A parabolic lens, fabricated using focused ion beam milling, with a diameter of 15 μm and height of 5 μm, was embedded 6.5 μm (the working distance of the parabolic lens) below the endfacet of the fiber. The lens focuses a 10.4 μm fiber mode into a spot size of 2.6 μm on the surface of an SMF-28e single-mode optical fiber. The properties of the fabricated lens were studied using the three-dimensional finitedifference time-domain numerical method, and the optimal parameters for maximizing the coupling conditions were extracted. The conversion loss of the lens is estimated to be around 0.5 dB. The insertion loss and lateral alignment of the proposed parabolic lens is comparable to a commercial lensed fiber, while directly ensuring the longitudinal alignment, easing the angular alignment, and providing additional mechanical and environmental robustness.

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We demonstrate a gradient-index (GRIN) optofluidic waveguide using polydimethylsiloxane cured with a radial variation of temperature. The waveguide wraps the microfluidic channel and the GRIN profile localizes the light around it, making the device suitable for evanescent sensing applications. The fabricated waveguide shows good light confinement, with a propagation loss of 1.47 dB/cm at a wavelength of 632.8 nm.