Silicon technologies have been developed for both electronics and photonics. Future demands call for further innovation in each field separately, but also depend on our ability to bring the best of both worlds together through integrated solutions. For decades, the pursuit of all-silicon electronic-photonic integration has been hindered by the lack of a native light source due to silicon’s indirect bandgap. Here, we discuss the potential for micro- and nano-scale light sources realized in microelectronic CMOS technology without any modification or postprocessing. High brightness is realized by exploiting the well-passivated silicon surfaces available in CMOS to realize efficient light emission despite the indirect bandgap. NIR emission at the silicon bandgap is demonstrated and exploited to demonstrate chip-to-chip optical links and sensors utilizing only silicon light sources.

Resonant isolated-particle optical lattices are treated rigorously. These structures possess a wealth of interesting properties. We report results on differentiation of local Mie resonance and guided-mode lattice resonance in mediating resonant reflection. We treat a classic 2D periodic array consisting of AR-coated dielectric spheres. Reflectance maps for coated and uncoated spheres demonstrate that perfect reflection persists in both cases. Moreover, we compare local field profiles in periodic assemblies and in isolated particles. When the lateral leaky-mode field profiles approach the isolated-particle Mie field profiles, the resonance locus tends towards the Mie resonance wavelength yielding the concept of Mie modal memory.

Numerical methods for engineered nanostructure design such as the finite difference time domain (FDTD) and finite element methods (FEM) are accurate but slow for large structures. To reduce simulation time, we combined the principle of the coupled dipole method with analytical solutions for light scattered by a dipole near a flat surface to efficiently simulate the light scattered by a range of nanoparticles on substrates. Simulation results shows that our method can provide the same level of accuracy as FDTD in significantly less time. We analyze both low and high index nanoparticles and substrates.

Here, we demonstrate an in situ electrically driven tunable metasurface by harnessing the full potential of a phase-change material (PCM) alloy, Ge2Sb2Te5 (GST), in order to realize non-volatile, reversible, multilevel, fast, and remarkable optical modulation in the near-infrared spectral range. A dynamically reprogrammable hybrid plasmonic-PCM metasurface with record eleven-fold change in the reflectance (absolute reflectance contrast reaching 80%), unprecedented quasi-continuous spectral tuning over 250 nm, and switching speed that can potentially reach a few kHz is presented. Capitalizing on such unique properties, we also demonstrate an actively tunable gradient phase-change metasurface for beam steering with a large beam deflection angle.

We propose gold-vanadium dioxide microstructured emitters for which the difference in thermally radiated power between two predefined temperatures can be made positive, negative or zero via structural design. The emitter geometry is based on incorporating VO2 in a gold-dielectric-gold waveguide. Such a waveguide exhibits a temperature-dependent mode effective index owing to the phase-changing behavior of VO2. This in turn causes our emitters to exhibit a strongly temperature-dependent emissivity. We use our emitters to design a metasurface with a thermally-invertible spatial emission pattern. Such emitters could be useful for several intriguing applications such as remote temperature monitoring and thermoelectric power generation.

We previously demonstrated that the insulator-to-metal transition (IMT) temperature of vanadium dioxide (VO2) can be modified by engineering its defect density via ion implantation. Here, we quantitatively characterize the defect-induced changes to the IMT temperature and optical refractive indices with respect to the ion fluence. We identify an ion-fluence regime in which the IMT temperature can be modified without changes to the optical contrast between the pure phases, which is generally favorable for reconfigurable photonic applications. As a demonstration, we were able to lower the triggering temperature of a VO2-based optical limiter by 18 °C without trading off its transmittance contrast.

We present the design of a transmission filter in mid-infrared and its experimental verification using phase change material GST (Germanium Antimony Telluride). Progressively increasing the annealing temperature of GST controls the crystalline structure, allowing the refractive index to increase significantly in a steady rate. One-dimensional metal dielectric sub-wavelength grating device, such that the dielectric segments are proportioned to decouple any angular-dependent resonance. Incorporating GST between metal gratings allows transmission wavelengths to be actively tuned as annealing increases refractive index. Amorphous and crystalline GST devices show transmission resonances up to 60 degrees indicate that angular-independence is preserved during material excitation.

Recently there has been a growing interest in SiC on oxide integrated photonics platform, due to excellent linear and strong non-linear properties. Due to excellent thermal and mechanical properties, SiC devices are suitable for operations in harsh environments. In this work, we demonstrate the integration of two PCMs Ge2Sb2Te5 (GST) and Ag3In4Sb76Te17 (AIST) on a CMOS compatible amorphous SiC waveguide, grown using low-temperature CVD on oxide. We demonstrate a photonic memory, which can be programmed and accessed optically and we achieve multiple memory levels reliably on these devices. Furthermore, using time-resolved dynamic switching experiments we study the thermo-optical effects and switching speeds.

The rapid advance in understanding of exciton resonances in layered van der Waals materials has now stimulated thinking about active metasurfaces that exploit excitonic modulation phenomena to enable ‘van der Waals active metasurfaces’. As one example, I will describe recent advances in electrically reconfigurable polarization conversion across the telecommunication wavelength range in tri-layer black phosphorus, enabling spectrally broadband polarization conversion over nearly half the Poincaré sphere. We also observe both linear to circular and cross-polarization conversion with voltage, demonstrating dynamic access to polarization diversity. As a second example, we discuss the observed large gate tunability of the complex refractive index and phase in monolayer MoSe2 by Fermi level modulation near the A and B excitonic resonances for temperatures between 4 K to 150K. I will also give a general outlook for the wide range of possibilities for active van der Waals metasurfaces.

I will present different techniques developed to design and fabricate visible and near-infrared metasurface with large dimensions. In particular, I will present metasurface design using adjoint optimization and introduce a novel technique for designing arbitrarily large metasurfaces using optimized smaller metasurfaces. I will also discuss metasurface design using grating averaging and nonlinear optimization. Scalable and low-cost fabrication of large diameter visible metasurfaces using different nanoimprint techniques will also be presented.

Subwavelength nonlinear optical sources with high efficiency have received extensive attention although strong dynamic tunability of these sources is still elusive. Germanium antimony telluride (GST) as a well-established phase-change chalcogenide is a promising candidate for the reconfiguration of subwavelength nanostructures. Here, we design an electromagnetically induced transparency (EIT)-based high-quality-factor (high-Q) silicon metasurface that is actively controlled with a quarter-wave asymmetric Fabry-Perot cavity incorporating GST to modulate the relative phase of incident and reflected pump waves. We demonstrate a multi-level third-harmonic generation (THG) switch with a theoretical modulation depth as high as ~ 70 dB for the fundamental C-band crossing through multiple intermediate states of GST. This study shows the high potential of GST-based dynamic nonlinear photonic switches for a wide range of applications ranging from communications to optical computing.

We propose all dielectric metasurfaces for highly sensitive infrared absorption spectroscopy. The dielectric metasurfaces consisting of silicon microdisk arrays were designed and fabricated, realizing perfect reflection at certain mid-infrared wavelengths. Furthermore, tunable perfect reflection was achieved over the fingerprint region by changing diameter and height of Si disk, and also periodicity of the array, allowing us for molecular specific detection. Our dielectric perfect reflectors are promising for non-invasive molecular detection owing to ultralow heat generation under infrared irradiation.

This Conference Presentation, “Slow-light and mode localization in high quality factor photonic crystal microring resonator,” was recorded at SPIE Photonics West 2022 held in San Francisco, California, United States.

Monolithic High Contrast Gratings (MHCGs) are a special type of high-contrast grating (HCGs). In MHCGs, the stripes and the substrate on which they are implemented are made of the same material. MHCGs provide up to 100% power reflectance and thus are expected to find numerous applications in modern optoelectronics. We present thorough experimental analysis of spectral properties of GaAs MHCG mirrors designed at the wavelength of 1000 nm. Our results show that MHCG mirrors can be high-reflectivity mirrors as well as efficient polarizer and their properties can be modified by variation of lateral parameters of MHCG stripes.

To date, Bound States in the Continuum (BICs) with infinite quality (Q) factor have been observed in vertically symmetric photonic crystal slabs (PCS) sandwiched from top and bottom by low refractive index material. Such configurations are problematic in real life realization. Thus, we present numerical analysis of vertically nonsymmetric PCS, that exhibits BICs when specific conditions are met. We demonstrate that ~10% refractive index contrast between PCS and substrate enables BICs, which is achievable by all-semiconductor configurations. We also present Q-factor analysis of finite size semiconductor-based electrically driven devices exploiting BICs and configurations integrated with metals.

I will present our recent work on determining where the fundamental, or first, photonic band gap can be opened in three-dimensional photonic crystals with spatial and time-reversal symmetry. In particular, I will present a symmetry-based framework for determining the minimum possible band connectivity below the fundamental photonic gap across every space group, as well as the determination of any associated symmetry-identifiable topology. By systematically examining the topology of all possible minimum-connectivity configurations, we find a new, uniquely photonic topological effect, Γ-enforced topology, that obstructs symmetry-allowed gap-openings by requiring the presence of topological nodal lines.

We introduce a nano-optical platform based on Bloch surface waves (BSWs) capable of exploiting the entire cleaved end facet of a multicore optical fiber. Interconnecting various fiber cores with BSWs directly at the end of a multicore fiber opens the perspective of highly compact complex optical functionalities for the design of “lab on fiber” devices. In counterpart, optical fibers provide a unique opportunity to obtain turnkey nano-optical functions addressing a vast application domain ranging from telecommunications to medical sensing. To show the full potential of our platform, we demonstrate a multiplexing function between three fiber cores.

There is an enormous interest in next-generation optical devices that can be programmed or tuned after fabrication. Here I will present our efforts in combining state of the art materials research with advanced optical experiments. The focus is on two different materials platforms, namely low-loss chalcogenide phase change materials using the antimony compounds Sb2S3 and Sb2Se3, and the ultrafast non-volatile phase transitions in W-doped VO2. Antimony-based phase change materials hold potential for opening up truly low loss resonant nanophotonics and metasurface optics, and we are at the beginning of a materials development process to enable these materials in suitable electro-optical-thermal designed applications. Second, a highly controlled method for deposition of W:VO2 has been recently developed in our group using atomic layer deposition. We will show applications of these materials in new devices with tunable thermochromic phase transition down to room temperature.

Herein, we leverage electrically driven tunable all-dielectric reflective/transmittive metasurfaces made of newly emerged classes of low-loss optical phase-change materials (PCMs), e.g., antimony trisulphide (Sb2S3) and antimony triselenide (Sb2Se3), to realize switchable, high-saturation, high-efficiency, and high-resolution dynamic meta-pixels. Exploiting polarization-sensitive building blocks, the presented meta-pixel can generate two different colors when illuminated by either one of two orthogonally polarized incident beams. Such degrees of freedom (i.e., material phase and polarization state) enable a single reconfigurable metasurface with fixed geometrical parameters to generate four distinct wide-gamut colors. We experimentally demonstrate, for the first time, an electrically driven micro-scale dual-view display through the integration of phase-change metasurfaces with an on-chip heater formed by a transparent conductive oxide.

Phase change materials, and other functional nanomaterials typically require energy to be applied to them in order to have tunable properties. Typically, they can be tuned either optically, or electrically. However, a fundamental issue is that the interaction size scales of optics and that of electronics are very different - electronics function efficiently (energy/speed-wise) when dimensions are smaller than the wavelengths of light; unfortunately these are smaller than the typical interaction length-scales for optics. This has meant that efficient electro-optical coupling between electronic and photonic switching has been challenging. In this talk, I will talk about recent work within our group of collaborators to integrate concepts from plasmonics to bridge this length-scale disparity in integrated photonics, and present our recent work in this area. Although applied to phase change materials, these concepts are broadly applicable to other functional materials.

Chiral light-matter interactions have an extremely weak nature, are difficult to be controlled and enhanced, and cannot be made tunable. Here, we experimentally realize and theoretically verify spectrally tunable, extremely large, and broadband circular dichroism by designing new nanohelical metamaterial configurations (U. Kılıç et. al., Advanced Functional Materials 31(20), 2010329, 2021). The currently presented bottom-up fabricated hybrid helical metamaterials can be used in a plethora of diverse emerging classical and quantum optical applications, such as in the design of ultrathin polarization filters, chiral sensors, circular polarized single- or multi-photon radiation sources, and directional spin-dependent nanophotonic waveguides.

We present electrically switchable nanoantennas whose plasmon resonance can be switched on and off electrically and individually. We demonstrate video-rate switching times, hence overcoming the previous speed issues. In order to validate our concept, we combine our electrically switchable plasmonic nanoantennas in functional metasurfaces. In one implementation, we demonstrate beam steering. In another example, we demonstrate a flat metalens whose focusing ability can be switched on and off electrically. Our system can be operated in transmission as well as in reflection geometry. Our approach represents the breakthrough that will ultimately enable spatial light modulators with densities higher than 1000 lp/mm. This is the crucial element to make possible high-angle variable beam steering, electrically adressable zoom metalenses, and, ultimately, wide-angle holographic videos. These devices are key to enable compact augmented and virtual reality devices.

Hot carriers –electrons and holes with energies notably larger than k¬BTroom¬– play a key role in many photon-driven processes ranging from solar energy harvesting to photochemistry. In essence, hot carriers are the natural products of light absorption in plasmonic platforms and often are regarded as an inherent source of loss in subwavelength metallic resonators. In this talk, we present a series of ideas revealing grand optical and opto-electrical opportunities based on the generation and transport of hot carriers. To name a few, we discuss the essential role of hot carries for implementing sub-picosecond optical switches, inducing second-order nonlinear optical effects in centrosymmetric media, and demonstrating the generation of terahertz electronic signals in hybrid nanophotonic platforms.

Optically-induced magnetism has drawn considerable interest in the past years for its ability to speed up magnetic processes. For example, static magnetic fields have been demonstrated to be generated in non-magnetic plasmonic (gold) nanoparticles and nano-apertures. Using a simplified hydrodynamic model of the free electron gas of metal, we theoretically investigate the IFE and resulting optomagnetism in a thin gold film as well as in axis-symmetric plasmonic nanostructures under illumination with various focused light. The resulting static magnetic field is found to be maximum and dramatically confined at the corners and edges of the plasmonic structures, which reveals the ability of metallic discontinuities to concentrate and tailor static magnetic fields on the nanoscale. Plasmonics can thus generate and tune static magnetic fields on the nanoscale, potentially impacting small-scale magnetic tweezing and sensing as well as the generation of magneto-optical effects and spin-waves.

A wide variety of optical applications and techniques require control of light polarization. So far, the manipulation of light polarization relies on components capable of interchanging two polarization states of the transverse field of a propagating wave (e.g., linear to circular polarizations, and vice versa). Here, we demonstrate that an individual helical nanoantenna is capable of locally converting longitudinally-polarized confined near-fields into a circularly polarized freely propagating wave, and vice versa. To this end, the nanoantenna is coupled to cylindrical surface plasmons bound to the top interface of a thin gold layer. Helices of constant and varying pitch lengths are experimentally investigated. The reciprocal conversion of an incoming circularly wave into diverging cylindrical surface plasmons is demonstrated as well. Interconnecting circularly-polarized optical waves and longitudinal near-fields provides a new degree of freedom in light polarization control.

Here, we present a new approach based on manifold learning for inverse design and knowledge discovery in nanophotonics. We present the unique capabilities of manifold learning approaches for reducing the dimensionality of the high-dimensional relationships in photonic nanostructures. We show how this can help to understand the underlying patterns in the responses of such nanostructures. Such a visualization in the low-dimensional space enables knowledge discovery and studying the underlying physics of nanostructures and can facilitate the inverse design. We also use this method to study the role of the design parameters and design a class of nanostructure while reducing the design complexity.

We present a new machine learning (ML)-based approach for efficient inverse design of nanophotonic structures. Generating training data for a ML method is the most computationally expensive step in the ML-based inverse design and knowledge discovery, and it becomes cumbersome when the number of design parameters and the complexity of the structure increase. Here we show how to optimize the training process and considerably reduce the computation requirements without increasing error in order to efficiently model the input-output relationship in a nanophotonic structure and solve the inverse design problem.

We demonstrated a modular design approach for large metasurface-based optical concentrators. In this approach each concentrator is split into a collection of sublens modules. Each sublens module has an off-axis focal point, and this point is located between the concentrator center and the intended detector center. This reduces the necessary deflection angle, thus improving the concentrator design. We designed, fabricated and tested 300-μm-diameter metasurface-based optical concentrators operating in the 3-5 μm MWIR range. The optical concentrators enhanced the measured optical intensity at the intended detector position up to a factor of 6.4, in the future this will improve the signal-to-noise ratio of detectors and increase their operating temperature.

Over the past twenty years flat-optics and metasurfaces emerged as a promising light manipulation technology. One of the challenges is obtaining scalable and highly efficient designs that can withstand the fabrication errors associated with nanoscale manufacturing. This problem becomes more severe in flexible structures. In this work, we present an inverse design platform that enables the fast design of flexible metasurfaces that maintain high performance under deformations. We validate this method by a series of experiments in which we realize broadband flexible light polarizers efficiency of 80% over 200 nm bandwidths.

I will introduce our research progress of the electrochemical tuning device that can dynamically switch between solar heating and radiative cooling. The solar and mid-IR dual-band synergistic tuning results in wider heat management capability for a broad range of thermal environments. In particular, this device can be used as smart building envelopes for all-weather, year-round HVAC energy saving. I will introduce the key challenges and our innovations of the device, including the ultra-wideband transparent electrode, reversible metal electrodeposition, plasmonic nanostructure evolution, and device configuration optimization. In addition to synergistic multispectral dual-band tuning between solar heating and radiative cooling, the device also shows >0.85 mid-IR emissivity contrast, leading to profound performance for space or military applications.

Faraday rotation is a physical phenomenon that results in the rotation of linearly polarized light when it passes through a magneto-optical (MO) material. The angle of rotation is linearly proportional to the product of an applied magnetic field and the distance light travels inside the material. The proportionality constant is called the Verdet constant. EuS is a semiconductor material that poses a very large Verdet constant at low temperatures (~6K) Its room temperature properties have not been studied so far. In this work, we measured a Verdet constant of EuS at room temperature.

The optical efficiency of metalenses is extremely important for practical applications. With only limited efficiency, useful light is lost. This can for example result in reduced sensitivity. Even worse, the light, will appear as straylight that can result in ghost images, reduced resolution, reduced contrast etc. depending on the specific application. Here, metalenses optimized for a wavelength of 940 nm are experimentally demonstrated with an absolute focusing efficiency of up to 94% measured as the optical power transmitted to the focal spot divided by the power incident on the lens element. The function of the highly efficient metalenses is demonstrated in a camera module. The resulting images are sharp, crisp and artefact free.

Quantum optical networks will enable distribution of quantum entanglement at long distances, with applications including interconnects between future quantum computers and secure quantum communications. I will present our recent work on developing quantum networking components based on rare-earth ions such as single optically addressable quantum bits based on ytterbium 171 in yttrium orthovanadate, microwave to optical transducers based on erbium doped crystals coupled to microwave and optical resonators, and on-chip telecom optical quantum memories.

Photophysical detection, identification and characterization of nanoparticles, quantum dots and single emitter are essential to enhance the efficiency of preparation methods as well as their electronic and optical properties. We present a powerful combination of time-resolved photoluminescence microscopy with a spectrometer, which results in a valuable toolbox for researcher. This combination of microscopic (e.g., FLIM, PLIM or antibunching) and spectroscopic methods like wavelength dependent emission scanning enables a deeper understanding for the optimization of properties and efficiencies in practical applications.

Epitaxially-grown quantum dots (QDs) play an essential role in various quantum photonic technologies as on-demand solid-state single-photon sources. However, these QDs often suffer from the adjacent unintentional emitters such as wetting layers and other adjacent QDs, which attribute to the background noise of the QD emission and fundamentally limit the single-photon purity. Here, we develop a nanoscale site-selective luminescence quenching method using focused ion beam (FIB) and demonstrate improved single-photon purity from site-controlled single QD. Moreover, the reduced background noise led to QD emissions at higher temperatures. This nondestructive method retains the photonic structure and quenches the unwanted luminescence simultaneously, thereby indicating its promising potential in quantum emitters integrated with photonic devices.

This Conference Presentation, “Quantum control of photons and phonons in lithium niobate nanodevices,” was recorded at SPIE Photonics 2022 West held in San Francisco, California, United States.

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. We here investigate the generation of indistinguishable single photons from SnV centers and explore the influence of residual spectral diffusion. To improve the photon collection efficiency we fabricate a planar optical antenna based on two silver mirrors coated on a thin (sub-µm) single crystal diamond membrane. We demonstrate its operation at room and cryogenic temperatures and strong enhancement of the collectible photon rate.

In this study, we present a new approach to increase the spectral response of a silicon solar cell by exploiting the size-dependent refractive index of quantum dots. Compared to a conventional luminescent downshifting layer (LDS), our LDS design allows for thicker films and thus a higher optical absorption at the LDS layer while the reflectance is reduced. Our simulations demonstrate that a multi-size QD design outperforms the optimum single-size structure by reducing the average reflectance from 5.85% to 2.63% and increasing the total thickness from 82 nm to 138 nm when compared to the latter.

State-of-the-art plasmonic nanosystems can now be realized with characteristic dimensions commensurate with intrinsic quantum mechanical length-scales associated with the underlying electron gas. Here, we present an original platform for inferring the quantum nonlocal response of metals directly from experimental measurements of EELS and cathodoluminescence. Capitalizing on the fact that free-electrons constitute first-class tunable near-field probes, we demonstrate how our theory can be employed for retrieving the metallic quantum surface-response [specifically, the surface-response functions d⊥(ω) and d∥(ω)], from the nonclassical features imprinted in the loss/emission spectra. We anticipate that such insight ought to be crucial for engineering nanodevices with few-nanometer footprint.

In this presentation, we propose a method to engineer the resonant wavelengths of electric (ED) and magnetic dipoles (MD) with new structure parameters, gap size and position. A low index gap is introduced inside a high index dielectric rectangular block. As the gap size increases and the geometric volume is maintained, the resonant wavelength of MD blue-shifts significantly with keeping the scattering intensity. On the other hand, the resonant wavelength of ED is relatively insensitive to the gap size and position. Our method to introduce low index gap in high index meta-atom can provide new degrees of freedom to engineer the wavelengths of the multipole modes independently and can be utilized to design a metasurface as desired.

Two-dimensional photonic crystals are artificial periodic structures that can be made of a 2-D array of cylindrical nanoholes. Thanks to their unusual dispersion characteristics, photonic crystals may exhibit some peculiar optical properties such as extremely low group velocity. Photonic crystal waveguides can be created by removing a row of holes in a 2-D photonic crystal. In this work, we theoretically demonstrate third-harmonic generation in an air-bridge PhC waveguide based on a highly nonlinear material Al0.18Ga0.82As by exciting a slow-light mode at 1596 nm to match the refractive index of a folded-back refractive index mode at 532 nm.

We propose a method to manipulate multipole interference by combining different dielectric nanoparticles to build a meta-molecule in which each dielectric nanoparticle exhibits the required resonant wavelength and scattering intensity of Mie resonances. In this method, each atom can be designed a geometrical shape to satisfy the required multipole's optical properties independently. So, we design dielectric cylinders to have strong electric, magnetic dipole intensity in each cylinder at the same wavelength, which satisfies the Kerker effect and shows unidirectional scattering. We expect it can be used as a sensor by analyzing the Far-field pattern transformed through various defects and deployments.