This PDF file contains the front matter associated with SPIE Proceedings Volume 12896, including the Title Page, Copyright information, Table of Contents, and Conference Committee information.

From the birth of plasmonics, the generation of hot carriers in nanostructured metals has been recognized as a fundamental challenge towards effectively harnessing light energy stored in sub-diffraction plasmon modes. However, the observation of hot-carrier transport at metal/dielectric Schottky junctions has reframed this challenge as a distinctive opportunity to facilitate precise control over photochemical and photophysical processes in a manner that is both spectrally selective and spatially precise. To further diversify the array of prospective applicationsin this research area, we showcase the generation of terahertz (THz) electromagnetic waves using the ultrafast formation and interfacial transport of plasmonic hot carriers in hybrid metal/dielectric nano-systems. The introduced hot-carrier-based coherent THz sources mitigate stringent materials requirements pertinent to state-of-the-art technologies for producing THz waves.

Fiber-optic microendoscopy imaging systems are actively being researched. They are interesting as they can be designed with a single fiber in conjunction with gradient refractive index (GRIN) micro-lenses. However, these systems face a significant limitation in the form of optical aberrations caused by beam scanning, resulting in reduced resolution at the edges of the imaging field. The current solutions involve bulky refractive optics, combining micro-optics with an aspherical lens that present challenges in fabrication and alignment. To overcome these limitations, we propose the design of a compact metasurface correction element (diameter = 1 mm) that can be seamlessly integrated into the existing optical system alongside the 1 mm diameter GRIN lens. Accurately modeling such a complex system involving nanoscale metasurface and macroscale optics is challenging. We present the interconnection of ray tracing and electromagnetic simulations to simultaneously achieve the desired optical system performance and the required phase profile. In our imaging probe design, the target phase profile of the correction element is optimized using Zemax Optic Studio for multiple beam scan angles to achieve a minimal and uniform spot of 1 μm across the imaging field, which spans approximately 100 μm. The target phase mask obtained from ray tracing simulation and the phase-look-up table obtained from electromagnetic simulation of the unit cell are used to create the metasurface. The simulation of the metasurface of 1mm diameter is performed in Lumerical and the solved near field is propagated in Zemax to assess the imaging system through physical optics propagation and diffraction analysis.

Active tuning has long been a goal for photonic metamaterial devices. Several approaches have succeeded in providing active tuning. These include mechanical deformation, the incorporation of an active liquid crystal layer, electrically induced permittivity modulation, and the use of phase change materials. In this presentation, we describe a novel method of tuning the resonance of a metamaterial in which an optically transparent thin film, referred to here as a “shifter,” is placed in proximity to a dielectric metasurface. The spacing between the metasurface and the shifter is carefully controlled by a piezoelectric transducer. Device designs for the midwave infrared (MWIR) based on chalcogenide glass films are presented. Modelling shows a tuning range of approximately 500 nm in the MWIR for a change in shifter spacing of approximately 700 nm. It is shown that the size and shape of the field at an individual resonator changes significantly based on shifter spacing, resulting in a large tuning range. The piezo shifting method described here represents a new technique for tuning the resonance of a metasurface over a large-area with a large tuning range.

Increasing demand for high density and broadband photonic integrated circuit (PIC) has motivated designs for photonic devices with high performance and compact footprint. However, the number of parameters in traditional photonic device designs is limited by the working principles for such devices, which often results in a perceived trade-off among device performances, such as bandwidth, efficiency, and footprint. Nonlinear optimizations such as direct binary search (DBS) and genetic algorithms (GA) have been explored in photonic designs, yet they have drawbacks such as slow convergence time in the range of 96-140 hours. By contrast, designs based on deep learning model relates device performances (output) and device parameters (inputs) via data-driven methodology, which enables arbitrarily large number of design parameter space that may overcome the perceived trade-off in traditional photonic designs. This work proposes a design methodology based on a combination of deep learning model and gradient descent method for photonic power splitter with arbitrary splitting ratio. Using pixel-based device geometry, a deep learning model relating the geometric parameters and device spectral performance is first established. Afterwards, a figure of merit based on a target splitting ratio is optimized through gradient descent method to yield the corresponding pixel-based device geometry. We demonstrate this method in the design of photonic power splitter with splitting ratio from 0.25 to 10, with insertion loss between 0.5dB to 1.16dB, and device size smaller than 16 μm². In comparison with the genetic algorithm and direct binary search method, our proposed method is much faster in terms of convergence time.

Metasurface presents itself as a method to create flat optical devices that generate customizable wavefronts at the nanoscale. The traditional metasurface design process involves solving Maxwell’s equations through forward simulations and implementing trial-and-error to achieve the desired spectral response. This approach is computationally expensive and typically requires multiple iterations. In this study, we propose a reverse engineering solution that utilizes a deep learning artificial neural network (DNN). The ideal phase and transmission spectrums are inputted into the neural network, and the predicted dimensions which correspond to these spectrums are outputted by the network. The prediction process is less computationally expensive than forward simulations and is orders of magnitude faster to execute. Our neural network aims to identify the dimensions of elliptical nanopillars that will create the ideal phase response with a near unity transmission in a 20 nm wavelength interval surrounding the center wavelength of the spectral response. We have trained such a reverse DNN to predict the optimal dimensions for a birefringent metasurface composed of elliptical nanopillars.

Despite the engineering advancements in the development of very large photonic crystal lasers, there has been very little progress in the development of better physics-based strategies. Our strategy employs an open-Dirac singularity related to an effective zero-index medium, enabling the existence of a flat-envelope mode. The resulting devices, called Berkeley surface-emitting lasers (BerkSELs), are uniquely characterized by this unconventional mode, effectively mitigating the spatial hole burning effect and leading to more robust single-mode emission. The device architecture enabling this new strategy consists of a photonic crystal patterned as a triangular lattice, truncated to a hexagonal shape, thus forming a finite cavity. The parameters of the photonic crystal are tuned to create an accidental degeneracy forming an open-Dirac singularity. We indicate the properties of the linear band structure that are present in the finite system and enable the in-principal scale invariance of the BerkSEL. In conclusion, this work augments our comprehension in the physics of this newly discovered flat-envelope mode in BerkSELs, shedding light on its role in achieving scale-invariant single-mode operation in photonic crystal lasers. The insights gained from our investigation hold considerable promise for transformative progress in laser technology, unlocking diverse applications in optical communication, sensing, and quantum photonics.

We report finite difference time domain simulations of GaAs-Al_0.95Ga_0.05As micropillars containing single quantum dots with SiO₂ microlenses of differing shapes and heights, finding an approximately linear reduction in the numerical aperture and mode field diameter of the outcoupled emissions via the fundamental mode. This opens the possibility of modifying our previously reported direct-write lithography process to leave an amount of hard mask on top of the pillar, which could modify the light emitted from our single photon sources to be more efficiently coupled into an output single mode fibre.

Informing vehicular and robotic devices with vision systems that can distill relative motion in complex social environments is a pressing need. Low resolution imaging has been shown to provide lower level organisms with quick response times. Here, we propose the use of a metasurface-based imaging system to capture several perspective views and image them directly onto one CMOS camera. Given the single camera, and multiple focal perspectives, the lens angles are inherently skewed and thus lead to the design of asymmetric metasurface lens profiles. The design and optimization of these asymmetric metasurfaces, each composed of 640,000 unit cells, are carried out for a series of off-axis lenses in the imaging array, with an operating wavelength of 0.98 µm. By integrating several images at different angles, the system aims to capture auxiliary data about a scene including distance data, like that acquired via stereovision, but in this case using only a single detector.

We report on the development of a metasurface-based infrared sensor using Dolmen plasmonic nanostructures. The metasurface is designed to resonantly enhance the absorption of infrared light at a specific wavelength. The sensor is designed and optimized for high sensitivity and selectivity in the infrared region. This simple metasurface sensor is a promising platform for various applications, such as gas sensing, biosensing, and security. The optimized design is easy to fabricate and compact. The fabrication tolerance is also studied to ensure the good reliability of the sensor. The sensor achieves a sensitivity of 530 nm/RIU.

In this report we will compare Silicon-based Microwave Photonic CMOS with III-V or II-VI Microwave Photonic CMOS. Ultra-low resistance threshold-less LED or laser are in the CMOS drain region, which function with DC voltage sources. Si or SiGe microwave diodes are also in the CMOS drain region, which are operated under DC biases and generate microwaves only with AC signals. There are various types of microwave diodes. Tunnel diode is a very low-resistance, low-noise solution for Millimeter wave Photonic CMOS. Si, SiGe, III-V and II-VI semiconductors can be used to fabricate Microwave Tunnel diodes. Powered Photonic Waveguides are the extended Microwave Photonic CMOS drain regions. This novel approach not only improves the signal transmission efficiency, but also increases the CMOS drive current and switching speed.

Bound states in the continuum (BICs) are a category of localized states that exist within the continuum of radiating modes. The high Q-factor exhibited by these states makes quasi-BICs interesting for enhancing the emission from quantum emitters. Quasi-BICs have been experimentally realized in silicon for applications in the infrared wavelength range. Instead of silicon, hydrogenated amorphous silicon (a-Si:H) has been used for achieving quasi-BIC resonance in parts of visible spectra. Titanium dioxide (TiO₂) has emerged as an alternate material for fabricating dielectric metasurfaces with high Q-factor in the visible spectral range due to its lower absorptive losses and high refractive index. However, the fabrication process for TiO₂ nanostructures presents challenges compared to the well-established fabrication processes in silicon. Our work focuses on the design and fabrication of TiO₂ metasurfaces supporting a quasi-BIC mode around 795 nm, with a theoretical Q-factor of 353. Experimental results reveal a maximum Q-factor of 258 at 791 nm. We discuss encountered fabrication constraints and explore possibilities for improvement in both design and fabrication processes. This study contributes to the understanding of quasi-BIC resonance in TiO₂ metasurfaces, and opens avenues for further exploration in the utilization of TiO₂ for high-Q dielectric metasurfaces, offering insights into the design and optimization of these structures.

In this study, we demonstrate the improvement of quality factors in InP nanobeam cavities using atomic layer deposition (ALD). By depositing a small amount of Al₂O₃ thin films on the cavities, we achieve up to 140% enhancement in quality factors. This advancement in cavity quality factors holds promise for optimizing InP nanobeam cavities when incorporating active materials like quantum dots and quantum wells, enabling widespread utilization across diverse photonic applications.

Structural colors have the advantage of high reflectance for specific wavelengths, and are generally implemented with SiO₂, PE, PS and PMMA. However, existing crystalline structural color films require particle alignment and precise particle uniformity control, making them difficult to manufacture and highly dependent on the viewing angle. Non-close packed structural color films are relatively free of these problems. In this study, based on high refractive index core-shell particles, we propose a mechanochromic strain sensor that can distinguish the direction, position, and degree of deformation. A film was fabricated using silica coated iron oxide core-shell particles having a high refractive index and black color. It has been demonstrated that this film sensor can display a 2D color profile in response to localized weight or strain.

Recent progress in photonics has highlighted the importance of miniaturization, particularly in achieving dielectric bowtie cavities with small mode volumes, which were previously limited to plasmonics. This study presents a novel method that combines top-down nanopatterning and bottom-up self-assembly to fabricate photonic cavities with atomic-scale dimensions. By utilizing surface forces, we demonstrate waveguide-coupled silicon photonic cavities with high quality factors, confining light to atomic-scale air gaps with an aspect ratio above 100, corresponding to mode volumes more than 100 times below the diffraction limit. These cavities exhibit unprecedented figures of merit for enhancing light-matter interaction and enable charting hitherto inaccessible regimes of solid-state quantum electrodynamics.