This PDF file contains the front matter associated with SPIE Proceedings Volume 12431, including the Title Page, Copyright information, Table of Contents, and Conference Committee information.

The hyperbolic plane affords a rich design space, which can be leveraged to create elastic lattices characterized by boundary-dominated vibrational spectra. Such elastic hyperbolic lattices are made by projecting nodes of a regular tessellation of curved hyperbolic space onto a flat space to define lattice sites which are then connected by simple linkages. Dynamically, these systems are useful for the protection of bulk material from boundary-incident perturbations. The lattice achieves this by guiding waves around its dense boundary rather than towards its sparsely populated bulk, accessing modes from its boundary-dominated spectrum to steer vibrations along its perimeter. We confirm the boundary-dominated spectrum and edge-confined wave propagation via numerical simulation and experimental validation. This elastic hyperbolic lattice introduces an experimentally-feasible approach to generating mechanical systems with boundary-dominated states, reminiscent of recent topologically protected edge-states in quantum systems.

The arising 3D printing technologies open new possibilities for the production of optical devices, e.g. of optical waveguides. Using two-photon polymerization (2PP), arbitrary three-dimensional structures with resolution below the diffraction limit can be manufactured, thus allowing for new and versatile applications in photonics. Recent demonstration of phononic metamaterials using 2PP fabrication rely on homogeneous mechanical properties of the photopolymer. Thus, the state of polymerization can be used as process parameter to develop adaptable phononic crystals. Here we demonstrate an optical setup that combines Brillouin- and Raman-scattering experiments to measure the mechanical and chemical characteristics with respect to the polymerization state.

This work presents an on-chip optical sensing system based on phase-shifted Bragg grating. The proposed design could be easily fabricated using ion exchange technology. The sensor geometry has been optimized using a finite difference time domain (FDTD) solver to achieve maximum sensitivity and figure of merit (FOM). FOM of 227.63 and a sensitivity of 343.1nm/RIU have been achieved for the water-based sensing system.

We show that nanophotonics can provide a compact and versatile platform to generate controllable space-time light. We will present three of our recent works: 1. Creating structured 3D linear space-time light bullets in free space using nonlocal metasurface. 2. Creating guided light bullets in a multimode waveguide using photonic interband transitions. 3. Creating spatiotemporal optical vortices with arbitrarily oriented OAM using photonic crystal slabs. Our works illustrate the significant opportunities in creating nontrivial space-time correlations with nanophotonic devices.

We report and elaborate the design of a hexapole mode of an H1 point-defect photonic crystal nanocavity with a theoretical quality (Q) factor over 10⁸. Thanks to the C₆ symmetry of the mode, our design uses only four structural modulation parameters, unlike that for many other ultrahigh-Q nanocavities based on complicated optimizations. Silicon (S_i) planar H1 nanocavity samples prepared with the design exhibit a systematic variation in their resonant wavelengths by the spatial shift of air holes in 1 nm unit. Their maximum loaded Q factor is measured as 1.2 million, and the corresponding cavity’s intrinsic Q factor is estimated as 1.5 million.

Photons play a crucial role in quantum applications due to their ability to encode quantum information in various degrees of freedom and transmit it at the speed of light. The quantum states of photons are exceptionally robust against decoherence since photons interact relatively weakly with matter. However, this weak light-matter interaction also limits the rate of quantum photonic operations such as single photon generation or photon-photon interactions. Plasmonic metamaterials can improve light-matter interaction and dramatically speed up quantum photonic processes. In this work, we give an overview of our research efforts regarding the application of plasmonics for spontaneous emission enhancement to enable high-speed bright quantum emitters. The ultimate goal is to enhance the spontaneous emission rate beyond the dephasing rate typical for solid-state quantum emitters at cryo-free temperatures. This would enable the generation of indistinguishable photons without the need of a cryostat. We report on the engineering of solid-state quantum emitters in material platforms such as hexagonal boron nitride and silicon nitride suitable for coupling with plasmonic metamaterials and integrated quantum photonics.

Nonlinear metasurfaces based on coupling of intersubband transitions in n-doped semiconductor heterostructures with optical modes in nanoresonators provide the largest known second-order nonlinear response in condensed matter systems in the mid-infrared spectral range. However, these giant nonlinearities are only present at relatively low pumping intensities which limits the maximum achievable frequency conversion efficiency. We experimentally investigate a new nonlinear intersubband metasurface design for second harmonic generation based on two-level nonlinear intersubband system that provides high nonlinearity combined with significantly reduced intensity saturation compared to the intersubband metasurfaces based on three-level intersubband systems demonstrated so far.

High transmission efficiency and ultrathin color filter arrays are highly desirable for next-generation display and imaging technologies. Metallic (plasmonic) and all-dielectric metasurfaces can be utilized for structural color generation through the excitation of strong electric and magnetic dipoles resonances at the nanoscale. However, plasmonic metasurfaces experience high ohmic losses and spectrally broad responses, reducing the optical efficiency and saturation of the generated color. All-dielectric metasurfaces exhibit lower field enhancement, a low-quality factor, and cross -talk due to the excitation of multiple spectrally overlapping modes. Hybrid metal-dielectric metasurfaces have recently emerged as a mean to combine the advantages of both plasmonic and all-dielectric metasurfaces, while mitigating their disadvantages. In this work, we present three different colour filters (red, green, blue) based on hybrid metal-dielectric metasurfaces that exhibit high transmission efficiencies (≈80 %). The hybrid filters are composed of nanostructured titanium dioxide atop of aluminium cylinders. Through finite-difference-time-domain simulations, we show that the response arises because of the hybridization of electric-magnetic dipole modes. The hybrid approach reduces high ohmic absorption losses (plasmonic) and low field enhancement (all-dielectric), resulting in higher transmission efficiencies.

Colloidal synthesis of metal nanoparticles (NPs) requires the use of surfactants or other capping agents as stabilisers. These capping agents form monolayers on the NP surface and determine their functionalities. In most cases, the capping agent used for the synthesis does not provide the required properties for the desired applications and must be exchanged in a separate step. NP functionalisation through ligand exchange is a common strategy to alter their chemical and physical properties to expand their applications. Here, we show the functionalisation of 20 nm citrate-capped gold NPs (AuNPs) with perfluorodecanethiol (PFDT) to generate reversible interactions by exploiting the fluorous effect. Ultraviolet-visible (UV-vis) spectrophotometry and zeta potential (ZP) characterization was performed before and after functionalisation to confirm ligand exchange.

Chalcogenide phase change materials (PCMs) are a unique class of compounds whose switchable optical and electronic properties have fueled an explosion of emerging applications in microelectronics and microphotonics. The key to any application is the ability of PCMs to reliably switch between crystalline and amorphous states over a large number of cycles. While this issue has been extensively studied in the case of microelectronic memories, current PCM-based optical devices suffer from much inferior endurance. To understand the failure mechanisms limiting endurance of PCMs specifically in microphotonic devices, we have developed an on-chip resistive micro-heater platform and an automatic multi-modal characterization system to analyze cycling performance of optical PCMs. Reversible switching of large-area PCM devices over 50,000 cycles was demonstrated.

For the inverse design of metagratings and metasurfaces, generative deep learning has been widely explored. Most of the works are based on a conditional generative adversarial network (CGAN) and its variants, however, selecting proper hyper parameters for efficient training is challenging. An alternative approach, an adversarial conditional variational autoencoder (A-CVAE) has not been explored yet for the inverse design of metagratings and metasurfaces, even though it has shown great promise for the inverse design of planar nanophotonic waveguide power/wavelength splitters recently. In this paper, we discuss how A-CVAE can be applied for two-dimensional freeform metagratings, including the training dataset preparation, construction of the network, training techniques, and the performance of the inverse-designed metagratings.

Light guiding properties of the photonic waveguides highly depend on the geometrical parameters once the material platform is decided, such as silicon-on-insulator technology. Uniform index profile can be engineered to obtain Bragg gratings operating in the wavelength or sub-wavelength scales. The standard index modulation of waveguides as in the Bragg gratings gives rise to band gap appearance that provides various types of light filtering features. Besides, the light propagation at the band edges can be tailored to manipulate the group velocity of optical signals. However, highly dispersive nature of band gap edges causes serious pulse distortions. Overcoming this problem by means of limited parameter search and trial-and-error method is a highly challenging design problem since it would be very time consuming to find a suitable structure. To obtain different spectral characteristics for the index guided mode traveling in silicon waveguide and alter the mode’s dispersion property, we propose an inverse design approach based on topology optimization. By appropriately defining figure of merits in the spectral domain, complex index modulation of short length multimode waveguide sections provides sharp filtering features that are ripple-free and accompanied with large group index values (>15.0) over a certain bandwidth at telecom wavelengths (1550 nm). The generated CMOS compatible non-intuitive geometries inside the waveguide structures were fabricated with the standard optical lithography steps and they can be applied to different photonic applications such as optical computing, spectroscopy, and sensing.

Nonlinear organic materials, including small molecules and polymers, have enabled numerous advances in flexible photonics and electronics. However, combining these materials with conventional device architectures is challenging due to incompatibilities between CMOS fabrication methods and the delicate nature of organic materials. In the present work, a combination of top-down and bottom-up fabrication methods are used to fabricate integrated optical devices comprised of conventional and unconventional optical materials. The platform device studied here is the silica ultra-high-quality factor (Q) whispering gallery mode optical cavity. Optical resonant cavities are able to store light in circular orbits for long periods of time, resulting in the build-up of large optical fields. Past work has leveraged these build-up powers to demonstrate low threshold Raman lasers. While the optical field is primarily located within the cavity, a small portion forms an evanescent field, interacting with both device surface and the surrounding environment. Therefore, any molecules located on the device surface will interact with the optical field. In the present work, a monolayer of silanes is grafted onto the surface of the cavity. Due to the orientation of the molecules with respect to the circulating optical field, the vibrational Raman mode is excited enabling surface Raman scattering to occur. This behavior improves the efficiency of Raman emissions from the cavity.

Among the material families used in nanophotonics, the fundamental mode for metal nanostructures is electric, while that for dielectric nanostructures is magnetic. Here, we consider hybrid nanophotonics, an emerging field of research that mixes both materials into one hybrid structure to benefit from the best of both worlds. It is demonstrated that the magnetic dipole in dielectrics can be entirely suppressed for small interparticle distances by the near-field produced by a nearby metal nanostructure. The explanation of the observed effect is given by considering the formation of a standing wave between the incident field and the light scattered from the metal particle. The analytical coupled electric and magnetic dipole method (CEMD) along with the full wave surface integral equation method (SIE) are used to examine this phenomenon. The conditions required for the observation of the magnetic dipole suppression in the visible range for high refractive index dielectric nanoparticles are described. The influence of the effect on the ability to control the directivity of the radiation in the far-field is considered. We further show that the electric and magnetic responses can be enhanced or suppressed by positioning the dielectric particle in the nodes of the standing wave formed by the metallic particle. This controlled near-field interaction provides a handle on the far-field response of the system, with possible applications as optical switches.

In general, the function of a passive nanophotonic device cannot be varied once its geometric and refractive index parameters are fixed. Thus, research on tunable optical nanostructures has been attracting much attention, and phasechange materials, whose optical properties can be actively controlled by thermal stimulus, have widely been utilized and integrated with nanophotonic devices. In this work, we propose a novel optimized design of an active metagrating transmission modulator composed of crossed ridge waveguides made of a VO₂ film. The proposed device can provide not only near-unity modulation depth of the 0^th order transmittance, but also polarization-independent operation with high efficiency and a broad bandwidth in the telecom wavelength region.

The control of light emission from InGaN quantum wells (QWs) is crucial for improving the performance of LEDs in various applications. Resonant plasmonic nanostructures were demonstrated to affect the properties of coupled emitters significantly. Here, we fabricate Al nanodisks on top of a GaN/sapphire wafer to control the angular far-field emission and enhance the collected light. This far-field photoluminescence (PL) emission is characterized by Fourier-imaging microscopy. Furthermore, we study the relationship between the PL and the pumping laser power, which is required to obtain enhancement in the collected light. The collection enhancement is up to a factor 3.2.

Photonic-crystal (PC) surface-emitting lasers in red wavelength range are demonstrated without epitaxial regrowth in this work. Two-dimensional PCs were patterned and circular shaped holes were etched from GaAs contact down to AlInP cladding layers to form the “PC slab-on-substrate” structure. Indium-tin-oxide was then deposited to facilitate both electrical injection and optical transmission. The fabricated devices were characterized by pulsed current source. The lasing wavelength was around 664 nm at designed lattice period of 208 nm. The peak intensity was over 6 mW at peak current of 2.5 A. The far-field pattern exhibited dual lobes separated by 3.5 degree and the beam divergence perpendicular to the lobes was about 1 degree.