Photonic and Phononic Properties of Engineered Nanostructures XV

Attoseconds: When intense light interacts with a gas of atoms (or a transparent solid), electron wave packets are released. Attosecond pulse formation exploits the correlated electrons and holes, forcing the electron to return. Without the plasma connection, two of the most important strong-field process that accompany attosecond pulse formation—hot electron formation (inverse Bremsstrahlung) and non-sequential double ionization (collisional ionization)—seemed mysterious. These plasma-like processes lead to laser induced electron diffraction and orbital tomography. THz generation: Terahertz pulse formation by ionization has a similar linage. Using PIC codes to describe azimuthally polarized l=4 mm and 2 mm light interacting with a 150 µm thick jet of helium, we calculate THz pulses reaching 8.5 Tesla. But 10 Tesla is not a limit. 30 THz azimuthally polarized beams can be amplified in high-pressure CO2 reaching isolated magnetic fields of 1-gigagauss.

In recent years, topological phenomena in photonic systems have attracted much attention, with their striking features arising from robust states in the energy gaps of spatially periodic media. However, light waves are entities that extend in space as well as time, such that one may ask whether topological effects can also occur in the temporal domain, or even space-time. Intuitively, systems that are periodic in time may be gapped in momentum, leading to topological states localized at time interfaces. However, time - in contrast to space - exhibits a unique unidirectionality often referred to as the “arrow of time”. Inspired by these features, I will present our most recent experiments on topological states residing at temporal interfaces. Moreover, I will discuss the formation of spacetime-topological events and demonstrate unique features such as their limited collapse under disorder and causality-suppressed coupling.

Quantum technologies promise a change of paradigm for many fields of application, for example in communication systems, in high-performance computing and simulation of quantum systems, as well as in sensor technology. However, the experimental realization of suitable system still poses considerable challenges. Current efforts in photonic quantum science target the implementation of practical devices and scalable systems, where the realization of quantum devices and controlled quantum network structures is key for envisioned future technologies. Here we present our progress on the engineering of integrated photonic systems, which can overcome current limitations for the realization of scalable photonic systems. Specifically, our research currently focuses on three different but complementary topics: integrated devices based on lithium niobate circuits, engineering and harnessing the temporal-spectral structure of quantum states of light, and photonic quantum computation.

This talk will describe how; The continuation of Fundamental research in quantum semiconductor technologies that are excited for the generation of, or response to, the light ), illuminating our minds towards the next revolution of understanding ourselves and universe

Dense photonic integration requires miniaturization of materials, devices, circuits and systems, including passive components, active components and integrated circuits. In this talk we will discuss recent progress in developing CMOS compatible nonlinear optical materials as well as examples of foundry enabled silicon photonic circuits and systems. Specifically, we will review silicon photonics-based Fourier transform spectrometer (Si-FTS) that can bring broadband operation and fine resolution to the chip scale. Moreover, taking advantage of nanofabrication we will discuss on-chip spectrometers using stratified waveguide filters and machine learning. Moving forward, we will discuss chip-scale integrated circuit/system that will allow to realize linear algebra accelerators with superior performance in speed, energy consumption and size compared to its electronic counterpart. Such system can be manufactured using monolithic CMOS compatible manufacturing and impact such applications as 5G/6G and beyond wireless MIMO systems as well as deep learning and artificial intelligence.

Recent breakthroughs in photonics design, along with new nanofabrication approaches and heterogeneous integration play crucial roles in building photonics for applications including optical interconnects and quantum technologies. A departure from a traditional photonics design approach can lead to optimal photonics designs that are much better than state of the art in many metrics (smaller, more efficient, more robust). This departure is enabled by development of an inverse design approach and computer software which designs photonic systems by searching through the space of all possible geometries. In fabrication-constrained inverse design in photonics, the full parameter space of fabricable three-dimensional devices is searched, using a variety of optimization algorithms combined with high-speed electromagnetic solvers. This search can be done efficiently by combining fast GPU-based electromagnetic solvers with gradient descent based optimization algorithms. With this approach, novel optoelectronic devices and systems have been designed and demonstrated, including error-free and fast chip-to-chip and on-chip optical interconnects compatible with commercial foundries. Moreover, the approach is material agnostic and fully compatible with quantum photonics platforms in diamond and silicon carbide.

Nano-architected materials are promising for a range of applications due to their unique properties. In this talk, I will present our latest advances in the on-demand manufacturing of nano-architected materials through optothermal manipulation and bubble lithography. These advanced techniques allow for the precise engineering of nano-architectures, enabling in-situ optical measurements that reveal novel photonic behaviors and interactions. Drawing inspiration from nature, we have engineered nano-architected materials with outstanding passive radiative cooling capabilities. By leveraging machine learning, we have significantly accelerated their design, surpassing the constraints of natural evolution and achieving superior cooling efficiency. Furthermore, these materials have been seamlessly integrated into a silicon-based battery, enabling all-season dynamic radiative thermoregulation alongside electrical power generation. This multifunctional device presents a solution for developing energy-efficient buildings and reliable power systems.

Scintillation describes the conversion of high-energy particles into light in transparent media and finds diverse applications such as high-energy particle detection and industrial and medical imaging. This process operates on multiple timescales, with the final radiative step consisting of spontaneous emission, and thus can be controlled and enhanced via nanophotonic effects. However, scintillators that do not obey Lorentz reciprocity have not been explored, even though they represent a novel platform for probing emission which is both nonequilibrium and nonreciprocal in nature. In this work, we harness nonreciprocity to achieve directional control of scintillation emission, granting an additional degree of control over scintillation. We present the design of a nonreciprocal scintillator using a one-dimensional magnetophotonic crystal in the Voigt configuration, demonstrating the potential of controlling nonequilibrium emission such as scintillation by breaking reciprocity and expands the space of nanophotonic design for achieving such control.

We study correlations between the configuration statistics of random metasurfaces and their spectral response. Our metasurfaces consist of a two-dimensional array of silicon nanopillars with widths sampled from a normal distribution placed on a silica substrate. We explore the effect of tuning the parameters characterizing the distribution of nanopillar widths on the wavelength-dependent transmissivity of the random metasurface in the 400 – 800 nm wavelength range. This analysis helps us create a direct mapping between the parameters of the nanopillar width distribution and the spectral responses of the random metasurfaces. We exploit this mapping to design photonic devices encoding spectrally encrypted image data in the visible wavelength range. Our findings offer new insight into the optical properties of random media and provide avenues for developing such systems for a broad range of applications.

Beams carrying Orbital Angular Momentum are produced from multilayered structures upon excitation of surface modes. Such structures are axially-symmetric and exhibit a high Local Density of States to facilitate radiation coupling from localized, possibly individual emitters located on the surface, such as q-dots or defected 2D materials. Polarization-sensitive, free-space diffraction of surface modes is obtained after proper decoration of dielectric multilayers with chiral metasurfaces.

Fabrication of optical metamaterials with chiroptical activity in the visible range is an ongoing research challenge. Our work addresses this challenge by utilising chiral biotemplates decorated with plasmonic gold nanoparticles (AuNPs) via in-situ reduction. The final composite products display chiroptical activity in the LSPR region. Their microstructural analysis confirms the formation of localised helicoidal assemblies of AuNPs. We hypothesise there is an interplay between two governing mechanisms for such optical response: while the molecular-induced chirality may give rise to plasmonic circular dichroism, the chiral spatial deposition of AuNPs also contributes to the overall chiroptical response. This proof-of-concept work showcases a facile and cost-effective fabrication method that can be utilised in the production of metasurfaces with scaleability.

Optical projectors constitute the core component for projection display, structured light, and LiDAR modules. In recent years, metasurfaces have become a strong contender for next-generation optical projection engines offering significant benefits in size, weight, and power consumption. The ability for metasurface to bend optical beams at extreme angles further enables wide-angle beam projection useful for emerging applications such as panoramic sensing and immersive displays. In this talk, we discuss an analytical framework for rational design optimization of wide-angle meta-optical projectors. Guided by the theory, we experimentally demonstrated metasurface-enabled large field-of-view projection display, beam steering engine, and VCSEL-integrated structured light projector.

We design a large aperture, all-silicon meta-optic doublet for unidirectional imaging at a wavelength of 4 μm. When illuminated by a plane wave in the forward mode, our unidirectional imager generates an intense spot on its optic axis at a predefined focal length. In the reverse mode, the imaging performance is significantly reduced, accompanied by a dramatic reduction in light intensity on the focal plane. We envision our devices to provide new avenues for the development of metamaterial imaging platforms for applications in defense and data security.

We propose an imaging platform consisting of an active metasurface coupled to a single-pixel or few-pixel detector and present a theoretical analysis on its resolution, point spread function, and signal-to-noise-ratio (SNR). We show with a computational model which assumes the characteristics of an experimentally realized local metasurface that a 0.2 mm x 0.2 mm aperture can recover ~60,000 image points at a wavelength of 1510 nm with a linear resolution exceeding 1.2 pixel/° across 120° FOV. We study the compatibility of our platform with different sensing bases and edge-detection operations and analyze how the losses and platform modulation rates set the total system acquisition time. Finally, we discuss the impact of active metasurface technological limitations on imaging metrics and propose as a next step to investigate the recovery of phase information in coherent scenes.

To combat climate change, the world needs to reduce greenhouse gas emissions to net zero by 2050. To this end, we need accurate monitoring of greenhouse gases such as CO2. Currently, CO2 is monitored by satellites. While this provides a good global view of CO2 in the atmosphere, it is hard to get data in real-time and of a specific location. Therefore, a small optical system to monitor CO2 that can be put on a drone is desirable. In this work, we provide a first step to this optical system, creating a polychromatic metalens that focuses the light of wavelengths 0.76um, 1.61um, and 2.06um. The smallest wavelength of 0.76um is where O2 absorbs, and the wavelengths 1.61um and 2.06um are where CO2 absorbs.

We present a combined theoretical and experimental study optical microcavity to enhance circular dichroism (CD) signals, with a focus on the fabrication and experimentation of a device. This microcavity is formed by a thin silicon film and a hexagonal array of silicon cylinders on calcium fluoride substrates, resulting in excitation of helicity preserving guided mode resonances which enhance the light-matter interactions. Optimising the microcavity's parameters can amplify CD signals by up to two orders of magnitude. We detail the design and integration of this microcavity into a vibrational circular dichroism (VCD) spectrometer and address experimental challenges. Measurements on both binol and alpha-pinene molecules demonstrate the tunability of the cavity, as these molecules have resonances in very different spectral regions. We finally demonstrate experimental VCD enhancement results on these two molecules.

The incorporation of strategically designed nanostructures within photonic crystal unit cells, including nanoscale shapes that have been used as metamaterial unit cells, can enable enhanced control of light-matter interactions. These structures that combine metamaterial and guided-wave photonic crystal attributes are called photonic metacrystals. The added degrees of freedom in the design space of photonic metacrystals lead to added control of the optical properties of these structures. Design rules and emerging properties of photonic metacrytals will be discussed, along with several applications that can benefit from using photonic metacrystals, ranging from optical modulators to biosensors.

We introduce a novel nanobeam photonic crystal designed for light confinement in an air core, offering an exceptional platform for enhanced light-matter interactions. This design achieves an outstanding quality-to-mode volume (Q/V) ratio with maximum field confinement in air, providing superior performance for applications such as sensing and photon-atom interactions. The presentation will cover the material platform, device engineering, fabrication processes, and potential applications across visible and infrared wavelengths. This advancement opens new possibilities for photonic devices in various fields.

AR demands optical devices transparent to environment light but strongly scattering to specific frequencies. Ideal solutions for simultaneously achieving a large angular bandwidth and a narrow spectral bandwidth are flat photonic bands isolated in frequency space. We develop a coupled-mode model yielding a systematic theory for generating flat bands in the lowest bands of unconventional photonic moiré structures. This enables identification of optimal tradeoffs between frequency isolation and angular bandwidth, and we propose designs that offer strong scattering over more than 80 degrees of angular bandwidth and a narrow spectral bandwidth (< 20 nm in the visible), within a broad band of transparency.

We experimentally demonstrate a new mechanism for broadband nanophotonic light concentration and optical field enhancement by exploiting the suppression of backscattering at the termination of a topological waveguide. We study a silicon topological photonic crystal waveguide that features propagating edge states associated with crystal-symmetry-protected valley degrees of freedom. Using near-field microscopy, we show that light is localized in a small volume when this waveguide is terminated by a photonic crystal with a trivial band gap. The observed field enhancement is ascribed to the delay of backscattering due to near conservation of the valley degree of freedom. This is supported by measurements that prove the large bandwidth of the effect, and that reveal a strong dependence of the localization on the symmetry of the termination.

Controlling a state of material between its crystalline and glassy phase has fostered many real-world applications. Switching between these two different states is particularly interesting if it is accompanied by a significant change of optical properties. Phase change materials provide the interesting property combination of fast switching between these two states which is accompanied by a pronounced property change. For nanophotonic applications it is crucial to tailor the crystallization kinetics, the relevant length scale of the switching processes as well as the optical contrast. In this presentation, we will devise design rules for crystallization and vitrification kinetics, control of the nanostructure as well as the contrast of the corresponding optical properties. We present a clear stoichiometry dependence of optical properties and crystallization speed. The stoichiometry dependence is correlated with material properties, such as the optical properties of the crystalline phase and a bond indicator, the number of electrons shared between adjacent atoms. A quantum-chemical map explains these trends and provides a blueprint to design crystallization kinetics.

This study presents an innovative approach to significantly enhancing asymmetric visibility using reconfigurable metasurfaces, designed to outperform traditional nanosphere-based scattering and absorption methods. By integrating phase-change materials such as VO2 and PEDOT:PSS into the metasurface design, we enable dynamic, real-time control over optical properties, leading to superior asymmetric light management. Unlike the static behavior of classical spherical structures, our metasurfaces allow for adjustable scattering and absorption profiles, achieving lower transmission rates and improved detection performance. Additionally, we incorporate an antenna directly fabricated beneath the metasurface layer, further enhancing the structure’s reconfiguration capabilities. Comparative analyses with conventional configurations, including VO2 and PEDOT:PSS nanospheres, as well as silver-TiO2 and gold-TiO2 nanospheres, underscore the superior performance and versatility of our approach. This work offers a more efficient and adaptable solution for advanced optical applications by optimizing light manipulation and reducing total transmission.

Optical beam steering is crucial for applications like LiDAR and optical communications. Metasurfaces can achieve this by using flat structures with a phase gradient to direct beams. Materials like Ge-Sb-Se-Te (GSST) change their refractive index, enabling beam steering. This study proposes a cross-shaped metasurface structure based on GSST that steers beams 50 degrees in both directions when excited by an infrared plane wave at 1.55 µm. The structure uses unit cells with a constant phase difference to achieve steering when GSST changes between crystalline and amorphous states.

The recent advent of tailorable photonic materials such as plasmonic ceramics including transition metal nitrides (TMNs), MXenes, Weyl semimetals and transparent conducting oxides (TCOs) is currently driving the development of new concepts and devices for IT, communication, sustainable energy and quantum technologies. In addition to great tailorability of their optical properties, strong plasmonic behavior, optical nonlinearities, these materials offer pathways to uncovering new optical and quantum phenomena ranging from epsilon-near-zero behavior to transdimensional photonics and strongly correlated systems. In this talk, we explore novel applications of TMNs (titanium nitride, zirconium nitride) and TCOs for flat optics, all-optical switching, high-harmonic-based XUV generation as well as for demonstrating new physical effects in atomically thin, transdimensional plasmonic films related to strong light confinement and metal-to-insulator transition. Our work paves the way to novel phenomena and device design with ultrafast tunable and tailorable optical materials.

Active optical metasurfaces, capable of dynamically manipulating light in ultra-thin form factors, enable novel interfaces between humans and technology. In such interfaces, soft materials bring many advantages based on their flexibility, compliance, and large stimuli-driven responses. Here, we create electrochemically-mutable, soft metasurfaces that capitalise on the swelling of soft conducting polymers to alter the shape and associated resonant response of metasurface elements. Such geometric tuning overcomes the typical trade-off between achieving significant tuning and low optical loss, intrinsic to dynamic metasurfaces that rely on index-tuning of materials. Using the commercial polymer, PEDOT:PSS, we demonstrate dynamic, high-resolution color-tuning and high-diffraction-efficiency (>19%) beamsteering devices that operate at CMOS compatible voltages (~1.5V). These results highlight how the deformability of soft materials can enable high-performance metasurfaces for body-worn technologies.

Design flexibility in the vertical dimension is a current obstacle hindering the realization of 3D plasmonic arrays, especially for visible wavelengths. We employ focused electron beam-induced deposition (FEBID) – a versatile nanofabrication technique wherein such dimensions can be achieved readily, even in complex geometries – to make scaffold structures with precise control of their 3D shape and position. In our experiment, we demonstrated the ability to fabricate variably structured spheres on posts, coat them in plasmonically active silver, and then measure the resultant spectra.

This study explores the mechanisms of plasmonic photocatalysis using Time-Resolved Infrared Spectroscopy (TRIR) on silver nanoparticles (AgNPs) functionalized with 4-aminothiophenol, biphenylthiol, 1-dodecanethiol, and adenine. These functionalized silver nanoparticles, along with a reference sample of pure silver nanoparticles, are studied by mid-infrared light under visible light excitation. TRIR reveals a broad, non-characteristic photo-induced infrared transient absorption signal in functionalized samples, absent in pure AgNPs, indicating indirect charge transfer from the nanoparticles to the adsorbates. Variations in signal decay times suggest different potential barriers between adsorbates and nanoparticles, inversely correlating with the chemical reactivity of the complexes. Probe frequency-dependent decay times indicate spectral narrowing. These findings underscore TRIR's potential in elucidating charge transfer dynamics and catalytic behavior in plasmonic photocatalysis.

Ultrafast sciences and technologies are founded on the principles of ultrashort-pulse nonlinear optics. Until now, their discrete and bulky nature has hindered the utilization of their vast functionalities for many applications, ranging from sensing to computing and quantum information processing. In the past few years, nanophotonic lithium niobate (LN) has emerged as one of the most promising platforms for integrated photonics, characterized by strong quadratic nonlinearity. In this talk, I will present recent experimental progress in the realization and utilization of ultrafast nonlinear devices in nanophotonic LN, which outperform their table-top counterparts. These advancements include intense optical parametric amplification, ultrafast ultra-low-energy all-optical switching, few-cycle vacuum squeezing, ultrafast laser mode-locking, and ultrabroadband coherent light sources. I will also discuss ongoing efforts toward the miniaturization of ultrafast technologies and the development of chip-scale ultrafast nanophotonic circuits in both the classical and quantum regimes.

We discuss integrated quantum photonics based on our group’s recent discovery of intrinsic quantum emitters in silicon nitride (SiN), which provide bright, high-purity single-photon emission at room temperature and the capability of seamless integration with SiN photonic waveguides. We established methods of deterministic creation of these quantum emitters and performed foundational photophysical studies at room and cryogenic temperatures. Furthermore, we explore the possibility of generating indistinguishable photons at high repetition rates by using plasmonic metamaterials, which may enable broader applications of SiN quantum emitters. Plasmonic speed-up of spontaneous emission rate beyond the rate of detrimental decoherence processes may also enable the generation of indistinguishable photons even. We also demonstrate record-high nonlinearities using avalanche multiplication process and employ it for all-optical modulation at single-photon intensities. This work gives a blueprint for many photonic applications at single-photon level. Finally, we also provide outlook for exciting future developments in the field of integrated quantum photonics based on silicon platform.

Rare-earth ions doped in solid state materials are highly versatile optically addressable spin qubits. In this talk I will give an overview of our latest progress in utilizing both single and ensembles of rare-earths to advance quantum science and technology. Single rare earths coupled to nano-photonic resonators are well suited for establishing remote entanglement in optical quantum networks. At the same time, they couple to other spins in the environment which can be harnessed for local quantum storage and processing as needed for quantum repeater nodes, and to explore highly entangled spin states. Ensembles of rare-earth ions can be used to mediate microwave to optical transduction and to explore quantum many body physics like super-radiance, sub-radiance, and novel types of transparency. I will discuss these research directions that we explored mainly with ytterbium 171 in yttrium orthovanadate.

Color centers in diamond, specifically the group-IV-vacancy centers, have emerged as promising candidates among solid state qubits. Among these, the tin-vacancy (SnV) center features the optimum combination of long spin coherence time and favorable optical properties such as truly lifetime-limited optical linewidths. We here investigate the optical coherence, i.e. emission linewidth and spectral stability, of SnV centers in bulk diamond and photonic nanostructures.

Metasurfaces—structured planarized optical devices with a thickness comparable to the wavelength of light—can shape the optical wavefront either through the independent response of each meta-unit, or through a quasi-bound state in the continuum, which is a collective response over many meta-units. In this talk, I will report experimental demonstration of a few device functionalities: (a) “local” metasurfaces for trapping arrays of ultracold strontium atoms, (b) “nonlocal” metasurfaces based on CMOS-compatible dielectric materials with thermo-optically reconfigurable wavefronts, and (c) nonlinear resonant GaN metasurfaces growth by templated molecular beam epitaxy for efficient second harmonic and sum frequency generation.

While metaphotonics in the linear optical regime have undergone remarkable developments, many exciting research frontiers in the nonlinear regime using metasurfaces, particularly those with low-order nonlinearities, are still emerging. In this talk, we will share the results of our recent endeavors to explore these frontiers. We will introduce an exotic phenomenon called backward phase matching with energy and momentum propagating in opposite directions. We further extend the phase matching from linear to angular momentum in a metasurface that supports bound states in the continuum. Besides the fundamental physics, we will also discuss the application of nonlinear metasurfaces. Specifically, we demonstrate beam steering at gigahertz speed using plasmonic and electro-optic hybrid metasurfaces.

High Q phase gradient metasurfaces are promising candidates for enhancing wavefront shaping and nonlinear technologies but near-field coupling typically forces a trade-off between quality factor and spatial resolution. Here, we show that polarization-based interference can be used to eliminate the trade-off between quality factor and spatial resolution. To show the power of our platform, we simulate high angle beam-splitting (±53o) and beam-steering (33o) with diffraction efficiencies over 90% with index modulation as small as 2×10^-6 and subwavelength pitch of λ/1.6. To experimentally verify our approach, we show that by geometrically sweeping our metasurfaces we can triangulate a decoupling configuration. Also, we show that angle dispersion another symptom of nearfield coupling can be fully suppressed. Our demonstrated platform paves the way for dynamic high-resolution wave-shaping applications requiring small modulation depth.

Resonant metasurfaces exhibit exceptional subwavelength light-trapping capabilities crucial for advanced biochemical sensors and surface-enhanced spectroscopy. While mid-infrared light-matter interactions have predominantly operated in the weak coupling regime, exploring the strong coupling regime—marked by hybrid polariton states—remains underexplored. Notably, low-loss dielectric metasurfaces with quasi bound states in the continuum (q-BIC) offer ideal platforms for coherent energy exchange between their high-Q cavities and molecular resonances. This study delves into q-BIC resonances at mid-infrared frequencies, identifying key parameters governing the transition from weak to strong coupling. We introduce a novel transitional coupling zone where polaritons are challenging to spectrally distinguish. Additionally, we analyze molecules' transition dipole strength, damping rate, and the total number of molecules coupled to a single cavity, offering insights to optimize dielectric metasurfaces for VSC. These findings provide crucial guidelines for enhancing VSC across diverse molecular transitions, anticipating transformative impacts on polaritonic chemistry.

Meta-lenses and meta-surfaces have shown great potential for future optical components. Advantages of meta-lenses over conventional optics rely on the practical aspects (thin/light-weight), free phase profile creation (high NA lenses, holography), specific tailored dispersion engineering, polarization engineering and more. A more overlooked possibility is the angular engineering of meta-atoms. Often simply ignored or stated as angle-independent, angle engineering can be highly interesting for example for wide field of view lenses. As for dispersion engineered meta-atoms, where the phase delay ϕ of a meta-atom can be wavelength dependently defined as ϕ(λ), it is possible to design angular dependent meta-atoms where the meta-atom phase delay is dependent on the incident angle θ, denoted as ϕ(θ). Here we do a thought experiment of creating an idealized perfect collimator, meaning that at any location light from any incident direction comes out perpendicular on the surface. Even if this would be possible for a small area and a small opening angle, etendue would be reduced in the system, which is in direct conflict with the conservation of etendue.

In this talk, we discuss our recent progress on the design, modeling, fabrication and characterization of nonlocal metasurfaces and metastructures, for their use to manipulate and process the optical wavefront both in real and reciprocal space. These nonlocal metastructures hold the promise to enhance light control, reduce the footprint of optical devices, and reduce energy costs in image processing and computing. In the talk, we discuss recent theoretical and experimental results demonstrating space and time nonlocality, involving linear and nonlinear responses, from classical to quantum light waves.

This study presents the design, fabrication, and spectroscopic characterization of a Sn-containing group-IV semiconductor nanowire (NW) metasurface aimed at enhancing light emission at extended short-wave infrared (ESWIR) frequencies. The platform is a two-dimensional Ge/[Ge1-xSnx/SiyGe1-y-zSnz]m core/multishell nanowire array, with m representing the repetition period varied from 1 to 5. Using a low-pressure chemical vapor deposition (CVD) reactor, Au-catalyzed MQWs arrays are grown via vapor-liquid-solid growth. The process includes electron beam lithography and e-beam evaporation for Au-patterns on a Kagome layout. High-resolution transmission electron microscopy (HRTEM) and energy dispersive X-ray spectroscopy (EDX) techniques show Si and Sn contents of 6 at.% and 4 at.%, respectively. Low-temperature infrared photoluminescence spectroscopy quantifies lasing properties and light emission in single MQW nanowires and the fabricated metasurfaces.

We present a novel approach to metasurface design, shifting from traditional meta-atom-based systems to metagrating structures. In this approach, we focus on the phase gradient, recognizing that wave propagation is determined by the phase derivative rather than the absolute phase value. By employing metagratings to diffract light in the desired direction, we simplify the design process while maintaining precise control over wavefront shaping. This method significantly increases the minimum feature size to λ/(3NA) (NA: numerical aperture); e.g., an NA of 0.5 results in feature sizes as large as 2λ/3, making fabrication more straightforward and robust against errors. Using this approach, we demonstrate metalenses that reduce the fabrication requirements compared to conventional metalenses while considerably reducing the sidelobes in the focusing beam profile. Moreover, we present a fully analytical design framework, eliminating the need for time-consuming numerical simulations and complex optimization processes.

In this research, we investigate the achievement of perfect absorption of MIR light using a PbSe metasurface integrated on a metal layer over an Al2O3 substrate. Leveraging the unique properties of the PbSe metasurface, we achieve exceptional absorption efficiency at a single MIR wavelength. This is facilitated by the surface plasmon resonance phenomena, where the interaction between light and matter is specifically tailored to resonate at the desired MIR wavelength. Additionally, we demonstrate bandwidth control by adjusting the parameters of the PbSe metasurface, allowing for tunable absorption characteristics. This enhancement in absorption capabilities is crucial for applications like gas sensing, where detecting changes in the absorption spectrum caused by gas molecules interacting with the metasurface demonstrates promising advancements in sensitive and selective gas detection technologies.

In this talk, we will discuss our efforts in designing and implementing metasurfaces for optical systems intended for advanced imaging, metrology, and additive manufacturing platforms. These concepts utilize the unique capabilities and scalable fabrication capabilities of nanophotonic devices to enable new systems level functionality. First, we will discuss the utilization of freeform spaceplates as aberration correcting elements for imaging systems. We will show how space can be compressed as a function of incidence angle in a customized manner and how aberration correction capabilities can be enhanced with conformal curvilinear spaceplates. Second, we will discuss the utilization of metasurfaces for additive manufacturing, where we parallelize two photon polymerization processes in a scalable manner using large metasurface arrays. Third, we will discuss the implementation of a nanophotonic-enabled snapshot hyperspectral Mueller polarimetry imaging system, in which the combination of nanoscale polarization optics together with machine learning-enabled data processing enables high speed hyperspectral polarimetry functionality.

We present a novel density-based topology optimization method for maximizing or minimizing the power dissipation in lossy dispersive nanostructures. Due to our formulation of a gradient-based optimization in the time domain, it enables the optimization for broadband performance over an arbitrary spectral range. It therefore promises to be computationally more efficient than conventional frequency-based methods. We demonstrate the method on metallic and dielectric nanostructures for enhanced absorption efficiency. Our contribution provides a deeper insight into understanding the interaction of light with 3D nanostructures and holds great potential for applications in a variety of research/engineering fields, such as (thermo-) photovoltaics, broadband absorbers, or photonics devices with a reduced power loss.

We present a novel approach based on physics-informed neural networks (PINNs) for the inverse design of reconfigurable metaphotonic devices for creation of wideband structural colors, spanning the visible spectrum (400–800 nm) by integrating Maxwell’s equations into the loss function of a deep multilayer neural network. Utilizing the optimal design, we demonstrate, for the first time, reconfigurable metaphotonic devices with wideband dynamic color switching between green and blue through phase transition in phase-change materials.

We introduce an efficient open-source python package for the inverse design of three-dimensional photonic nanostructures using the Finite-Difference Time-Domain (FDTD) method. Leveraging a flexible reverse-mode automatic differentiation implementation, our software enables gradient-based optimization over large simulation volumes. Gradient computation is implemented within the JAX framework and based on the property of time reversibility in Maxwells equations. By rapid specification of the desired design properties and quick optimization within the given user constraints, this open-source framework aims to accelerate innovation in photonic inverse design.

4H-silicon carbide (4H-SiC) is gaining prominence as a versatile material platform in integrated and quantum photonics due to its wide bandgap, strong nonlinear optical properties, and ability to host color centers. We have demonstrated, for the first time to our knowledge, self-injection locking (SIL) of an off-the-shelf distributed feedback (DFB) diode laser as well as resonant stimulated Brillouin scattering (SBS) in 4H-SiC microring resonators. The microring, with an optical quality factor of approximately 2×10^6, exhibited multimode behavior, enabling SBS with a pump power threshold below 5 mW. These results demonstrate the versatility of 4H-SiC for turnkey soliton microcomb generation, empowering applications such as optical communications. They furthermore highlight the potential of this CMOS-compatible and quantum-friendly material platform for optomechanical applications.

We design and experimentally demonstrate nonlinear, periodically stacked, all-dielectric metasurfaces, enabling an efficient third harmonic generation not only in the transparent but also in the absorptive wavelength range of the constituent materials. Mie resonance-based silicon metasurfaces were vertically integrated, using the spin-on-glass as the spacer, to generate and control the photonic bandgap formed due to stacking. We developed and optimized the planarization and alignment processes to achieve the predicted performance in laboratory experiments. This work offers a simple and reliable theoretical and experimental approach for three-dimensional integration relying on the synergy of the unique properties of metamaterials and photonic crystals.

We introduce and theoretically demonstrate the performance of a new on-chip device platform for the generation of squeezed light with the potential to achieve a record-high squeezing ratio (SR) exceeding 16 dB, aimed at ultra-low-noise optical detection. Our heterogeneous platforms integrated silicon-carbide integrated photonic devices with an ultra-high-Q (Q: quality factor) whispering-gallery-mode (WGM) microresonator formed in potassium titanyl phosphate (KTP) for second-harmonic generation. Using an interferometric design, the squeezed signal and local oscillator (LO) are mixed with over 99.5% detection efficiency, making this platform a high-performance, CMOS-compatible solution for integrated quantum optics applications.

Despite the undeniable importance of silicon in the semiconductor industry, its nonlinear optical properties have not been fully exploited. We combine the rotational symmetry of the meta-atoms and the Pancharatnam–Berry principle to enable the generation of the fundamental, second, and third harmonics, as well as polarization and wavefront manipulation in silicon metasurfaces. Both the surface and bulk electric field distribution are enhanced, leading to the corresponding enhancement of the surface and bulk contributions of the nonlinear second-order polarization beyond the electric dipole approximation. We experimentally realize the second harmonic and sum-frequency generation in such silicon metasurface in the visible wavelength range.

Over the past decade, the field of special beams, characterized by their self-accelerating and non-diffracting main lobes during propagation, has primarily focused on isotropic media, neglecting anisotropic environments like elliptical or hyperbolic media. We introduce a novel approach for designing special beams in anisotropic settings, exemplified by α-MoO3, a van der Waals crystal that supports mid-infrared surface phonon polaritons. By varying the excitation frequency, the isofrequency contour of α-MoO3 can be adjusted from circular to elliptical or hyperbolic. Our coordinate transformation technique allows for the design of beams tailored to these various contours, with hyperbolic media displaying unique self-focusing characteristics.

The conventional design process for metasurfaces is time-consuming and computationally expensive. To address this challenge, we utilize a deep convolutional generative adversarial network (DCGAN) to generate new nanohole metastructure designs that match a desired transmittance spectrum in the visible range. The trained DCGAN model demonstrates an exceptional performance in generating diverse and manufacturable metastructure designs that closely resemble the target optical properties. The proposed method provides several advantages over existing approaches. These include its capability to generate new designs without prior knowledge or assumptions regarding the relationship between metastructure geometries and optical properties, its high efficiency, and its generalizability to other types of metamaterials. The successful fabrication and experimental characterization of the predicted metastructures further validate the accuracy and effectiveness of our proposed method.

We propose a Deep Q-learning based multi-objective optimization of metasurfaces using Reinforcement Learning and optimized a Si-nano-split-ring with a quality factor of 156,400, sensitivity of 400 nm/RIU, and figure-of-merit of 40,000/RIU suitable for sensing applications.

In this study, we applied the Artificial Bee Colony (ABC) algorithm to the inverse design of Dielectric-Metal-Dielectric (DMD) structures. We implemented the ABC algorithm in conjunction with the transfer-matrix method to maximize the transmittance through DMD structures in the visible window. We assumed a DMD structure comprised of MoO3 (Molybdenum trioxide) / Ag / MoO3 sequentially deposited on top of a soda lime glass substrate. The ABC algorithm reached structures with high, broad, and flat transmittances in the window of interest.

Imagine navigating the world without fully perceiving colors — this is the reality for millions affected by color blindness. There is a lack of research specifically targeting the intersection of color blindness and photonic crystals. While several online platforms offer normal vision users the opportunity to simulate the effects of color blindness digitally, these are limited to static images, preventing a real-time, immersive experience of what it is like to navigate the world with color vision deficiencies. By leveraging the Genetic Algorithm and Transfer Matrix Method (TMM), this paper proposes a one-dimensional photonic crystal structure to solve the issues. This structure is designed with a combination of SiO2, TiO2, defect materials, and a background material, aiming to create a photonic bandgap that transforms normal vision

A new coupling element presented on this poster can be manufactured quickly and is less susceptible to adjustment due to its small footprint of ​​500 µm².

We present a novel metalens design based on a focusing grating coupler concept, addressing the typical limitation of focusing grating couplers capable of focusing light in only one dimension. Our approach features a one-dimensional grating coupler with curved grooves, enabling precise focusing in both the x and y directions. The diffraction of the incoming guided wave follows the grating equation, which governs the groove shapes. By deriving a differential equation for these curves, we achieve fine control over diffraction toward a desired focal point. This design, implemented on CMOS-compatible substrates, incorporates optimized etch depths and duty cycles to maximize asymmetry in scattering, ensuring enhanced upward diffraction. The efficiency can approach unity by employing unidirectional grating couplers with excellent two-dimensional focusing performance.

We introduce a novel approach to achieve scale-invariant waveguides in integrated photonics using a single material. Our design focuses on planar scale-invariance in silicon photonic waveguides, eliminating the need for complex vertical stacking and multiple materials. This innovation provides a uniform field distribution across the planar direction, enhancing the performance and simplifying the fabrication process. The presentation will cover design principles, fabrication methods, and potential applications in high-power optical devices and light-matter interaction. This advancement marks a significant step in the development of more efficient and versatile integrated photonic systems.

We present a heterogeneous platform for realization of high-efficiency transmissive metaphotonic components through integration of dielectrics and phase-change materials. Combined with a new inverse design approach using Gaussian processes, we demonstrate a high-performance beam-steering reconfigurable metasurface in the transmission mode with dynamic switching between grating orders -1 and 1 in the visible spectrum. This device achieves an impressive efficiency of over 90%, setting a new benchmark for beam-steering applications

High-clarity and precision imaging of biological and non-biological samples is critical for applications in healthcare and research, but challenges arise from their small size and low contrast. We introduce a highly efficient, ultra-compact imaging system that integrates multi-modal capabilities, utilizing advanced metasurface optics. The system combines bright-field imaging with edge enhancement by leveraging phase gradient metasurfaces for superior performance. Additionally, a tunable varifocal feature enables precise focus adjustment, while an all-dielectric metasurface ensures high efficiency. With its multifunctional design, ease of fabrication, and cutting-edge optical capabilities, the system opens up new possibilities in healthcare and education.

The trapping of waves in open systems is a fundamental concept extensively explored across fields like optics, acoustics, and quantum physics. Recently, there has been increasing interest in bound states in the continuum (BIC), a unique type of wave mode that remains confined without dissipating energy, even in environments where waves would typically spread out. BICs have shown great potential for applications in areas such as sensors, filters, and lasers. In this work, we explore both the theory and experimental realization of quasi-BIC (QBIC) for ultrasonic waves. This is achieved using a metasurface resonator based on liquid-elastic Fabry-Pérot structures, which efficiently trap ultrasonic waves. Our findings reveal that these QBICs exhibit remarkable stability, maintaining their unique properties even when key parameters are varied, highlighting their robustness. We also provide experimental evidence of an exceptionally high quality factor (Q-factor) of 350 at approximately 1 MHz, significantly outperforming previous fully acoustic underwater systems. This work deepens our understanding of BIC in the realm of acoustics and paves the way for developing highly efficient, ultra-h

Topological waveguide systems have recently emerged as one of the important platforms for the control of electromagnetic/elastic waves due to their unique properties like unidirectionality, robustness, backscattering-free propagation in the presence of structural defects/disorders, etc. Here, we investigate different topological waveguide interfaces using hypersonic phononic crystal structure consisting of patterned plates and exhibiting Dirac gaps in the range of 13-14 GHz. The waveguide structure is formed by using two topologically different valley Hall phononic crystals (VPCs), whose unit cell comprises of two rounded triangles. Our results reveal that the behavior of the topological edge modes is dependent on the configuration of the waveguide interface, from zig zag to bridge shapes. This study could be significant in understanding the behavior of topological egde modes ultimately benefitting in the development of topological waveguides for low loss phononic components.

The study of nanoscale acoustic phonons impacts quantum technologies, data communication, and sensing. GaAs/AlAs Fabry-Perot optophononic micropillar resonators confine near-infrared photons and sub-terahertz phonons, aiding the study of coherent acoustic phonons. The micropillar’s ellipticity splits optical resonance into two orthogonally polarized modes. We present a scheme to manipulate Brillouin scattering polarization rules using elliptical micropillars, accessing frequencies down to tens of GHz and allowing polarization filtering. Polarization states are controlled by the incident laser’s energy and polarization and the micropillar’s ellipticity. Optimal filtering conditions improve polarization-based Brillouin spectroscopy. In pump-probe experiments, phonon generation peaks when the laser wavelength matches the optical cavity resonance, and detection sensitivity is highest at the optical resonance slope. Elliptical optophononic micropillar resonators enhance both generation and detection processes using cross-polarized pump and probe beams, advancing micropillar acoustic resonators as efficient phonon transducers.

Mechanical bound states in the continuum (BICs) have gradually become another popular method, aside from traditional band engineering, for obtaining mechanical resonators with high frequency and high quality factors. In our previous work, we demonstrated symmetry-protected mechanical BICs and coupled them with coexisting optical band-edge modes to achieve release-free optomechanical crystals. However, another important type of BIC — accidental BIC has never been realized in phononic systems. Here, we observe accidental BICs in a high-aspect-ratio gallium arsenide phononic crystal grating, their merging process with symmetry-protected BICs, and the subsequent enhancement of mechanical quality factors. This discovery provides a potential method for enhancing the performance of BIC based optomechanical crystals and can also be applied in fields such as sensing and quantum transduction.

We present novel free-standing Si-membrane mid-infrared (MIR) metasurfaces with strong light-trapping capabilities in accessible air voids. We employ the Brillouin zone folding technique to excite tunable, high-Q quasi-bound states in the continuum (q-BIC) resonances with our highest measured Q-factor of 722. We characterize and outline our metasurface design including their resonance mechanism using simulation and experiment, and demonstrate the Q-factor tunability of our device as a function of asymmetry parameter. Finally, leveraging the strong field localizations in accessible air cavities, we demonstrate vibrational strong coupling (VSC) with multiple numbers of PMMA molecules and the q-BIC modes at various detuning frequencies. Our new approach of fabricating MIR metasurfaces into semiconductor membranes enables scalable manufacturing of MIR photonic devices and provides exciting opportunities for quantum-coherent light-matter interactions, biochemical sensing, and polaritonic chemistry.

An optical pump-probe technique has been widely utilized for the time-resolved two-dimensional imaging of sub-GHz surface acoustic waves. In this measurement, the pump light pulses generate the acoustic waves, and the delayed probe light pulses detect the acoustic field. The technique relies on the synchronization of the pump and probe light pulses. However, such synchronization of the generation and detection is not always possible, especially when the acoustic waves are generated electrically and independently from the probe light pulses. In this paper, the method for the time-resolved imaging in such independent generation case is explained. Then the technique is applied to study the sub-GHz acoustic wave propagation in topological phononic crystal waveguides driven electrically by the interdigital transducer. The topologically protected wave guide mode is clearly observed.

Traditionally investigated in semiconductor superlattices, acoustic phonons in the tens of gigahertz to sub-terahertz range require costly fabrication and lack tunability [1]. Mesoporous materials, with nanoscale pores, present a promising alternative. Mesoporous SiO2 and TiO2-based acoustic resonators support gigahertz-range resonances, and liquid/vapor infiltration can alter their optical and elastic properties. This study proposes open-cavity acoustic resonators using SiO2 mesoporous thin films (MTFs) responsive to ambient humidity. The design includes an acoustic distributed Bragg reflector, a nickel acousto-optical transducer, and an MTF layer. Porosity's influence on acoustic resonances is explored by comparing different pore sizes. Using a transient reflectivity pump-probe setup, where the pump beam induces thermoelastic stress and the probe detects transient reflectivity, these findings advance cost-effective, reconfigurable nanoacoustic devices. [1] P. Priya, Cardozo de Oliveira, E. R., and Lanzillotti-Kimura, N. D., Applied Physics Letters 122, 140501 (2023)

Phononic crystals, elastic analogues of photonic crystals, promise significant advances in controlling elastic energy propagation, crucial for tunable filters, heat management, and acousto-optical devices. By influencing phonon flow, they could control thermal conductivity. Colloidal self-assembly offers a cost-effective method to engineer phononic crystals with desired properties. This study investigates the hypersonic phononic properties of self-assembled two-dimensional colloidal crystals composed of polystyrene (PS) nanospheres on a silicon substrate. We demonstrate tunable hypersonic phononic bandgaps by varying interactions between neighboring PS nanospheres. Ultrafast pump-probe transient reflectivity techniques explore phononic modes across various frequency ranges. Phonon transport analysis via pump-probe methods confirms the phonon-insulating properties. Experimental observations are supported by a finite element method model. These findings underscore the potential of self-assembled colloidal crystals in creating tunable hypersonic phononic insulators, paving the way for advanced phononic applications.

In this study, we present a highly sensitive SAW magnetic field sensor that utilizes phononic crystal structures with Au pillars embedded in a SiO2 guiding layer. The sensor’s sensitivity is considerably enhanced due to increased interactions between the SAW and the magnetostrictive material, facilitated by resonance effects within the PnC structure. Our approach avoids etching the FeCoSiB layer, thereby preserving the magnetostrictive material and maximizing its interaction with the SAW. We achieved an overall sensitivity of 404 °/mT, nearly 23 times higher than that of a continuous delay line of the same dimensions and over 3.6 times greater than the sensitivity achieved with PnC structures composed of FeCoSiB pillars in our previous study. This work demonstrates the significant potential of integrating PnC structures within the guiding layer to enhance the performance of SAW-based magnetic field sensors.

Periodic driving of systems of particles can create crystalline structures in time. Such systems can be used to study solid-state physics phenomena in the time domain. In addition, it is possible to engineer the wave-number band structure of optical systems and to realize photonic time crystals by periodic temporal modulation of the material properties of the electromagnetic wave propagation medium. We introduce here a versatile averaged-permittivity approach which empowers emulating various condensed matter phases in the time dimension in a traveling wave resonator. This is achieved by utilizing temporal modulation of permittivity within a small segment of the resonator and the spatial shape of the segment. The required frequency and depth of the modulation are experimentally achievable, opening a pathway for research into the practical realisation of crystalline structures in time utilising microwave and optical systems.

The rapid technological development in optical telecommunication, high-power laser devices, integrated optics, quantum computing, and communication has increased the demand for novel optical components. Recent developments in metamaterials suggest that conventional optical components could be replaced with metasurfaces to create ultralight and multifunctional optical devices. A metasurface can perform different optical functions by manipulating light’s amplitude, phase, wave vector, and polarization on the subwavelength scale. Perfect absorbers are one of the examples of such metasurface elements. The promising applications of narrowband perfect absorbers include sensing, surface Raman scattering, and nonlinear optics. Split ring resonators (SSR) have been shown to excite magnetic Fano resonances. These resonances can be exploited to construct subwavelength polarization-sensitive absorbers. We studied various materials and designs of the SSR arrays to identify the best design for implementing subwavelength-perfect absorbers in the visible part of the spectrum.

This study presents two innovative anti-reflection coating (ARC) designs for highly anisotropic infrared materials like Sr9/8TiS3, BaTiS3, and BaTiSe3, which enable new compact polarization optics due to their giant birefringence (difference between ordinary and extraordinary refractive index of up to ~2). The first design employs zinc selenide (ZnSe) ridges to create structure-induced anisotropy, suppressing reflection at a particular wavelength and for all polarizations. The second employs a multi-layer planar thin film using yttrium fluoride (YF3) and zinc sulfide (ZnS), showcasing robustness against varying angles of incidence and manufacturing deviations. We experimentally demonstrated the second design, suppressing the reflectance of the BaTiS3/air interface in the long-wavelength IR.

This work presents an all-dielectric metasurface design consisting of coupled nano-disk and nano-bar resonators. This configuration demonstrates double Fano resonances around the telecommunication wavelengths 1.55𝜇m. The first resonance originates from the interference of optically induced electric and magnetic modes within the nano-disk, while the second is primarily driven by the nano-bar with a minor influence from the disk. These unique optical properties provide a direct control over the magnetic and electric modes interference, and, inconsequence, allow for engineering each nano-resonator scattering patterns. Our simulations reveal that increasing the nano-disk radius enhances the backscattering of both resonances. Conversely, varying the nano-bar width selectively influences the forward scattering of the second resonance, leaving the first unaffected. This tailored directionality holds promise for applications in nano-antennas with unidirectional emission.

Quantum photonic circuits face scalability challenges due to the need for single-photon generation and efficient transmission. Silicon is the most scalable material to date for integrating new and existing photonic systems. Recently, bullseye cavities (circular Bragg gratings) have gained attention for their ability to enhance and focus single-photon emission over long distances with precise wavelength selection. Recent studies have analyzed the fundamental properties of single-photon sources in circular Bragg gratings, but achieving high quantum efficiency in silicon-based G-center gratings remains unexplored heretofore. This study explores how the Purcell factor, electric field, and photon collection efficiency are influenced by variables like ring number, numerical aperture, and polarization angle in bullseye cavities at 1279 nm. Optimizing these design parameters is necessary for developing a scalable and highly efficient G-center quantum photonic system.