The field of silicon photonics has experienced widespread adoption in the datacoms industry over the past decade, with a plethora of other applications emerging more recently such as light detection and ranging (LIDAR), sensing, quantum photonics, programmable photonics and artificial intelligence. As a result of this, many commercial complementary metal oxide semiconductor (CMOS) foundries have developed open access silicon photonics process lines, enabling the mass production of silicon photonics systems. On the other side of the spectrum, several research labs, typically within universities, have opened up their facilities for small scale prototyping, commonly exploiting e-beam lithography for wafer patterning. Within this ecosystem, there remains a challenge for early stage researchers to progress their novel and innovate designs from the research lab to the commercial foundries because of the lack of compatibility of the processing technologies (e-beam lithography is not an industry tool). The CORNERSTONE rapid-prototyping capability bridges this gap between research and industry by providing a rapid prototyping fabrication line based on deep-UV lithography to enable seamless scaling up of production volumes, whilst also retaining the ability for device level innovation, crucial for researchers, by offering flexibility in its process flows. This review article presents a summary of the current CORNERSTONE capabilities and an outlook for the future.

We study the role of topological singularities like Bound States in a Continuum (BICs) or Circularly Polarized States (CPSs) in determining ellipticity of the far-field polarization in dielectric metasurfaces. Using finite-difference time-domain as well as rigorous coupled-wave analysis simulations, we determine the behavior of the Stokes parameter S₃ in the whole k space above the light cone, with special regard to the region close to the singularities. Moreover, we clarify the relation between the topological singularities and the circular dichroism in reflectivity.

Semiconductor nanowire ordered arrays represent a class of bi-dimensional photonic crystals that can be engineered to obtain functional metamaterials. Here is proposed a novel approach, based on a particle swarm optimization algorithm, for using such a photonic crystal concept to design a semiconductor nanowire-based two-dimensional diffraction grating able to guarantee an in-plane coupling for light trapping. The method takes into account the experimental constraints associated to the bottom-up growth of nanowire arrays, by processing as input dataset all relevant geometrical and morphological features of the array, and returns as output the optimised set of parameters according to the desired electromagnetic functionality of the metamaterial. A case of study based on an array of tapered GaAs-AlGaAs core–shell nanowire heterostructures is discussed.

Recent advances in the nanofabrication and modeling of metasurfaces have shown the potential of these systems in providing unprecedented control over light–matter interactions at the nanoscale, enabling immediate and tangible improvement of features and specifications of photonic devices that are becoming always more crucial in enhancing everyday life quality. In this work, we theoretically demonstrate that metasurfaces made of periodic and non-periodic deterministic assemblies of vertically aligned semiconductor nanowires can be engineered to display a tailored effective optical response and provide a suitable route to realize advanced systems with controlled photonic properties particularly interesting for sensing applications. The metasurfaces investigated in this paper correspond to nanowire arrays that can be experimentally realized exploiting nanolithography and bottom-up nanowire growth methods: the combination of these techniques allow to finely control the position and the physical properties of each individual nanowire in complex arrays. By resorting to numerical simulations, we address the near- and far-field behavior of a nanowire ensemble and we show that the controlled design and arrangement of the nanowires on the substrate may introduce unprecedented oscillations of light reflectance, yielding a metasurface which displays an electromagnetic behavior with great potential for sensing. Finite-difference time-domain numerical simulations are carried out to tailor the nanostructure parameters and systematically engineer the optical response in the VIS-NIR spectral range. By exploiting our computational-methods we set-up a complete procedure to design and test metasurfaces able to behave as functional sensors. These results are especially encouraging in the perspective of developing arrays of epitaxially grown semiconductor nanowires, where the suggested design can be easily implemented during the nanostructure growth, opening the way to fully engineered nanowire-based optical metamaterials.

We report the first experimental characterizations of the coupling efficiencies of a series of e-beam fabricated focusing non-uniform grating couplers interfaced with a horizontal fiber coupling-scheme and designed for multiple Silicon-On-Insulator thicknesses, spanning between the 220 and 340 nm standard platforms. The design of nonuniform grating couplers is tackled either from an engineering perspective focused on to the optimization of the structures for this particular coupling-scheme; and a physics perspective related to the investigation of the scattering process of each structure for a complete comprehension of its performance in support to the experimental findings. Measured coupling efficiencies, up to 83% for the 340 nm platform at 1550 nm, are reported showing to be in excellent agreement with the theoretical findings. The physics behind the scattering process of each structure is investigated taking advantage of the Finite Difference Time Domain method to obtain a deeper understating of the coupling efficiencies. Consequently, a new parameter, the integrated leakage factor, together with the variation of the effective refractive index, across the local pitches, are calculated. Our belief is that any coupling structure for grating coupling can benefit from the proposed designed approach, as a widely applicable technique.

We compare the simulated optical insertion-losses and fabrication-tolerances of a micro-optical bench (MOB) for laser hybrid-integration on the 220nm Silicon-on-Insulator (SOI) photonic-platform to standard fiber-to-grating coupling. Our millimeter-scale two-dimensional finite difference time domain (2D-FDTD) simulation captures (i) aberration, (ii) reflection, (iii) diffraction, and (iv) wave-guiding effects in a single-shot and completely self-consistent way, indicating that light from a laser-diode can be coupled to the SOI photonic integrated circuit (PIC) with a 2.8dB insertion-loss at 1550nm. This insertion loss is just 1.0dB higher than for a standard Fiber-to-PIC grating-coupler, and is due to a combination of interface-reflections and aberration-effects from the micro-optical elements in the MOB. We use further 2D-FDTD simulations to investigate the alignment and manufacturing tolerances of the MOB, and show that these are compatible with practical photonic-packaging processes for mass-manufacture.