This talk is focused on new material and device platforms for realization of reconfigurable metaphotonic devices using materials with a large variation of their optical properties through phase transformation. Volatile and nonvolatile phase-change materials as well as polymer-based materials will be covered. Design, fabrication, and application of this platform for state-of-the-art devices and systems will also be discussed.
In this work, we present an efficient approach based on Bayesian optimization for the design of reconfigurable metaphotonic devices with a considerable reduction in computation for achieving optimal design while reducing the chance of converging to local optimal. The unique features of this approach will be discussed and compared with existing design techniques. To show its practical utility, we will use our approach for designing metasurfaces with reconfigurable absorptance and scattering in a wide wavelength range in the non-volatile, Poly(3,4-ethylenedioxythiophene)/poly (styrenesulfonate) (PEDOT:PSS) as a promising candidate for realization reconfigurable meta-device. Theoretical and experimental results will be presented to further support our claims.
Abstract:
Our study presents an innovative approach to metasurface design, marrying Fourier techniques from image processing with artificial intelligence (AI). Metasurfaces, vital in compact optical system creation, have been a focus. Conventional topological optimization methods show promise but face challenges in computational efficiency, especially with large-scale devices. AI-driven techniques, though effective, are often limited to devices with few design parameters. Our proposed methodology addresses these issues, offering a robust design framework for expansive metasurfaces. We interpret unit cell dimensions as Fourier series coefficients, simplifying design complexities and addressing periodicity concerns. By utilizing AI on the captured Fourier series coefficients, we drastically reduce design parameters, facilitating specialized AI metasurface applications. This fusion of Fourier and AI methodologies promises breakthroughs in metasurface design, enriching optical engineering possibilities.
In this study, we introduce a novel metaphotonic structure using phase-change materials for efficient beam steering through linearly variable refractive index manipulation. Leveraging the unique properties of Sb2Se3, a versatile phase change material, we create a metasurface capable of precisely controlling light propagation. By inducing a linear phase variation in the incident light, our metasurface effectively deflects light in the desired direction, following the principles of the generalized Snell's law. Simulation results demonstrate the development of a highly efficient beam steerer, achieving an impressive redirection range of approximately 10 degrees with an exceptional efficiency exceeding 80% in one material phase. In the other phase, where material loss impacts efficiency, we still achieve rates exceeding 40%. These remarkable levels of efficiency highlight the potential of phase change materials in photonic applications and position our metastructure as a promising candidate for advanced photonic devices and systems, offering precise and efficient beam steering capabilities.
Grating couplers are inevitable building blocks of integrated photonic circuits, so their design and performance are always crucial. We present a straightforward strategy for designing optimal grating couplers by incorporating a photonic bandgap analysis for each element of a grating to achieve better performances. We show that our approach removes unwanted back-scatterings within the grating region. To demonstrate the advantage of our approach, we demonstrated a few important designs for practical applications, especially the design and demonstration of efficient focusing grating couplers with diminished sidelobes at their focal plane.
We present the design and characterization of a novel metasurface absorber utilizing the phase change material, vanadium dioxide (VO2). The absorber demonstrates ultra-wideband performance, exhibiting high absorption across a broad spectrum ranging from 400 nm to 1200 nm. In addition to its spectral versatility, the absorber is designed to function effectively over a wide range of incident angles, maintaining an average absorption of approximately 80% for angles between 0 and 65 degrees. A unique feature of this absorber is its reconfigurability in the infrared regime, particularly in the 1400-1600 nm range. This capability opens up new avenues for dynamic control and optimization of absorption properties in various applications.
Arrayed-waveguide-grating (AWG) devices are among the most popular integrated photonic devices for multi-wavelength operations in several applications like optical communications, spectroscopy, and sensing. Here, we introduce a highly miniaturized (overall size < 1 mm2), yet ultra-wideband (wavelength range: 800 nm-1000 nm), silicon nitride AWG design for spectroscopy applications. The fabrication process of the device is CMOS compatible and hence suitable for mass fabrication. The relative uniformity of the response, the small insertion loss of ~1.07 dB, a wavelength resolution of 5 nm, and cross-talk <-25 dB are among the interesting specifications of this design. Combined with a fine narrowband high-resolution stage formed by a microresonator array, this structure can form a wideband high-resolution spectrometer for sensing applications.
Among all the new cancer treatment modalities, photodynamic therapy (PDT) is a promising method for its lower systemic toxicity, lower side effects, and improved tumor selectivity. PDT is based on activating light-absorbing molecules, often known as photosensitizers (PS). Here we introduce a new zinc-oxide nanowire (ZnONW) hydrogel and transparent wound healing antibacterial patch to treat superficial ulcerating cancer wounds. Active embedded ZnONWs in hydrogel/patch with the band gap of 3.37 eV would absorb ultraviolet radiations, and after a series of photochemical reactions in the aqueous environment of hydrogel/wound would generate ROS. The produced ROS triggers a series of cellular and molecular processes that have an antibacterial effect as well as an impact on the growth cycle of cancer cells. According to our study, using this hydrogel/patch in conjunction with conventional chemotherapy could speed up the healing of malignant wounds by a factor of two.
This talk is dedicated to the use of Fourier techniques for the purpose of designing dielectric metalenses with reduced sidelobes. Metalenses act as submicron scale spatially varying phase plates that apply a quadratic phase shift to a signal, thereby focusing the beam. Abnormalities arise due to the incredibly small scale of the lens; however, spatial filtering techniques, similar to techniques used in optical signal processing, can be applied to counteract these abnormalities. These techniques lead to new strategies in metalens design to remove unwanted effects, such as sidelobes, and a possibility of new functionality for metasurfaces in general.
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