We present our work on quantum emitters in silicon nitride (SiN), hexagonal boron nitride (hBN), and aluminum nitride (AlN) for integration with quantum photonic integrated circuits (QPICs). We study properties, fabrication techniques, and photonic structures for tailoring these quantum emitters to optimal functionality within QPICs. Quantum emitters in SiN, discovered by our group, are characterized by exceptional emission brightness and single-photon purity. We have successfully integrated these emitters with SiN waveguides and developed a pathway for large-scale, site-controlled fabrication that is compatible with foundry processes. In hBN platform, we enhanced emission from spin defects through plasmonic cavities and proposed efficient coupling of these emitters to SiN waveguides via inverse design optimized couplers. We also demonstrated the creation of quantum emitters within AlN via heavy ion implantation. Our work sets the stage for the development of next-generation quantum communication, sensing, and computing devices by leveraging the tailored optimization of quantum emitters for QPICs.

The generation of quantum light based on the nondeterministic process of spontaneous parametric down-conversion (SPDC) is usually performed by using bulky conventional nonlinear crystals and waveguides. However, these structures require strict momentum conservation for the involved photons, which strongly limits the versatility of the single photon emission they produce. In addition, the entangled state emission can only be obtained with a certain probability that is usually very small due to the inherent extremely weak nature of nonlinear optical processes. Quantum optical metasurfaces help to overcome these constraints due to their subwavelength thickness leading to relaxed momentum conservation (or phase-matching) requirements and increased optical nonlinear efficiencies. In our talk, we demonstrate compact quantum plasmonic metasurfaces to efficiently generate entangled and correlated single-photon pairs with unprecedently high SPDC generation rates.

Single photon sources play a fundamental role in quantum science and engineering. In the first part of the talk a will present a deterministic quantum light source in silicon based on single emissive centers that emit in the telecom band [1]. In the second part of the talk, I will discuss a probabilistic source based on an interpretable inverse design cavity enhancing the efficiency of on-chip photon pair generation rate through nonlinear processes [2]. I will also discuss how topological disorder can enhance non-linearities on chip [3].

In this work, we present our recent study on coherent random lasing (as opposed to cavity-based lasing) in subwavelength quasi-2D perovskite films. We have studied a quasi-2D metal halide perovskite as a promising light harvesting and emitting media, having high optical absorption and low-threshold amplified spontaneous emission upon optical pumping with femtosecond laser pulses. Initially, we performed statistical analysis of spectral measurements, revealing Lévy-like intensity fluctuations and coherent lasing modes associated with the crystal grain structure of perovskites [1]. Then, to explore the full-wave transient mechanism of random lasing in perovskites, we develop experiment-based time-domain multi-physics models based on population dynamics in multi-level atomic systems coupled to a full-wave electromagnetic solver. The retrieved kinetic parameters of the multi-level system are discussed. The constructed rate equations and dynamic model can be utilized further for other novel mixed halide perovskites for description of lasing in such systems. [1] Fruhling, C., et.al., “Coherent Random Lasing in Subwavelength Quasi‐2D Perovskites,” Laser Photonics Rev., 2200314, 2023.

Solution-processible nanocrystals are attracting a lot of attention as versatile active media to create a wide range of optoelectronics, including sensors, light-emitting diodes, and lasers. Continuous wave on-chip nanolaser is a necessity building block for photonic integrated circuits. However, there is no solution-processed continuous nanolaser yet. In this work, we demonstrate a tunable silicon nanobeam laser integrated with solution processed PbS quantum dots operating at room temperature and optical telecommunication window.

The three-wave equations that describe broadband microresonators with a nearly quartic dispersion are briefly derived. They are then applied to describe recent experimental results in which interleaved frequency combs are generated, from which a single broadband frequency comb can be generated under the right conditions [1,2]. 1. G. Moille, et al., “Kerr-induced synchronization of a cavity soliton to an optical reference,” Nature 624, 267–274 (14 Dec. 2023) [doi: 10.1038/s41586-023-06730-0]. 2. G. Moille, et al., “Ultra-broadband Kerr microcomb through soliton spectral translation,” Nat. Comm. 12, 7275 (2021) [doi: 10.1038/s4146-021-27469-0].

In the realm of terahertz communications and broadband terahertz spectroscopy, practical applications require the development of miniaturized devices that are high-speed, power-efficient, and sensitive. I will discuss the latest advancements, existing challenges, and future prospects concerning hybrid photonic chips for optical-terahertz applications. The presentation will discuss opportunities enabled by integration and miniaturization, aligning with telecom and fiber technologies, to achieve sophisticated terahertz photonics functionalities consolidated onto a single chip.

Nanoplasmonics can serve as a versatile arena for the investigation and utilization of optically excited energetic carriers. This is particularly intriguing when the decay pathways of hot carriers are rationally engineered with purposeful selections of the constituent materials and geometrical symmetries. The generation, transport, and relaxation of hot carriers also provide a novel route to active and nonlinear optical effects with ultrafast response rates. In this talk, we focus on the exploitation of hot carrier dynamics for all-optical modulation, nonlinear optical signal generation, and photoinduced optical chirality in hybrid plasmonic systems.

Controlling near-field in space and time is crucial to applications of high-Q nonlocal metasurfaces, for instance for their use in nonlinear frequency conversion. We discuss near-field interferometric autocorrelation (IAC) measurements that reveal the dynamics of optical fields of quasi-bound states in the continuum (quasi-BICs) in plasmonic-dielectric metasurfaces. Using two-photon excited luminescence (TPEL) from quantum dots as local probes, our IAC measurements probe resonant near-field enhancement. Femtosecond laser pulse excitation of quasi-BICs produces coherent oscillations visible in TPEL, offering insights into resonances and their temporal beating. We discuss application scenarios for frequency-converting nonlinear metasurfaces in XUV generation and wafer metrology, as well as strategies for achieving high metasurface Q factors in metallic and dielectric systems.

Ultrafast control of light is crucial for advancing nonlinear and quantum optics, as well as optical technologies including telecommunication. Tailorable and dynamically tunable materials play a key role, and transparent conducting oxides (TCOs) and transition metal nitrides (TMNs) stand out due to their enhanced light-matter interactions, particularly in their metallic/plasmonic regime and near the so-called epsilon near zero (ENZ) region. We explore the static and dynamic tailorability and tunability of optical properties in TCOs and TMNs, accompanying shifts of their ENZ points. Both homogeneous TCOs and TMNs, as well as structured devices made from them, were investigated for tunability of their nonlinear optical interactions such as harmonic generation and optical modulation. TCO’s potential to realize the emerging and novel idea of photonic time crystals has increased their popularity. To this aspect their ability to be tuned within one optical cycle of light is inspected in ultrafast dynamics studies. This research contributes to understanding novel optical phenomena and holds promise for practical devices with TCOs and TMNs.

We demonstrate a use case for the ENZ region of transparent conducting oxides as a means for compact and phase-matching free pulse characterization for near-infrared beams. We leverage a ‘temporal knife edge’, generated by an off-axis pump to extract the spatial shape and pulse width information of a Gaussian beam using a quadrant cell detector. Operating within the ENZ region enables the use of sub-micron thick films and moderate optical fluences (1-10 GW/cm2) compared to conventional bulk dielectrics or crystals, for compact pulse characterization systems.

A beam’s spatial distribution can be structured in terms of its amplitude and phase, and the transverse and longitudinal distribution can be tailored by an appropriate transmission of orthogonal modes. Interestingly, a space-time wave packet (STWP) with a dynamically varying spatial structure can be produced by simultaneously transmitting multiple lines of an optical frequency comb, such that each frequency line has a tailorable spatial modal combination. This presentation will highlight light fields whose transverse and longitudinal properties can be designed to vary with time and thus have dynamic behavior. Specifically, STWPs can have spatiotemporal evolution that is arbitrarily engineered to occur at any given propagation distance in the transverse dimension as well as at various distances along the longitudinal propagation path. This can be achieved by introducing a 2-D spectrum comprising both temporal and longitudinal wavenumbers, resulting in packets evolving in time and distance. This presentation will discuss various beam properties that can dynamically evolve, including: rotation and revolution, radius, amplitude, phase, polarization, and mode number.

Temporal symmetries (time-reversal and time-translation) and asymmetries (e.g., the one-sided nature of the temporal impulse response, i.e., causality) play a crucial role in the response of natural and engineered materials and in the general behavior of wave physics phenomena. In this talk, I will discuss our recent efforts on probing fundamental limitations and extreme effects in electromagnetics and photonics based on these concepts.

Time-varying media emerged as an exciting platform for novel effects in photonics, including ultra-efficient frequency mixing, non-reciprocity, and light-matter interactions beyond the time-bandwidth limit. Here, we discuss semiconductor metasurfaces—quasi-planar periodic arrays of resonant semiconductor nanoparticles—as time-varying photonic devices. Femtosecond optical pumping in a non-adiabatic regime results in broadband frequency translation, gain, and a dynamically growing quality factor (Q-boosting) that enhances nonlinear and quantum optical phenomena. We conclude with an outlook with non-adiabatic metasurfaces serving as a platform for squeezed state generation, frequency-division multiplexing, and frequency-domain quantum information.

Van der Waals (vdW) interfaces are emerging as a versatile platform to control and investigate electronic, magnetic and optical properties of quantum materials. I will discuss nano-optical studies of charge transfer across an interface of vdW materials with different work functions [Kim et al. Nature Materials 2023]. I will also discuss an interface of two vdW insulators MoO3 and hBN revealing strong polaritonic coupling and negative refraction [Sternbach et al. Science 379, 555 (2023)].

We demonstrate a tuneable nanocube-on-mirror Fabry-Perot cavity that combines the record breaking plasmonic confinement of the nanocube-on-mirror (NCoM) system with the high quality factors and tuneability of microcavity systems. We demonstrate selective addressing of individual molecular vibrational lines with robust SERS enhancements on par with those of the seminal NCoM system, reaching sideband resolved SERS at Q/V values above 1 million inverse cubic wavelengths. We envision this as a platform for sideband-resolved molecular optomechanics, polariton chemistry and vibrational strong coupling.

The possibility of processing information with light has been the driving force behind the quest for all-optical logic gates. Leveraging silicon photonics processing technology, we show optically excited exciton-polariton condensation at ambient conditions in fully integrated metamaterial-based high-index contrast grating microcavities filled with an organic polymer. By coupling two resonators and exploiting seeded polariton condensation, we demonstrate ultrafast all-optical transistor action on a picosecond timescale and cascadability of the device concept. This paves the way for more complex ultrafast all-optical logic circuits operating at room temperature.

Atomically thin materials offer a robust platform for nanoscale light manipulation, featuring a diversity of polaritonic behavior in the form of plasmons in metals, excitons in transition metal dichalcogenides, and phonons in ionic insulators. In this context, we will present recent advances in ultrathin crystalline noble-metal films as promising plasmonic platforms for active nanophotonics. We discuss their optical response characteristics using models ranging from simple phenomenological approaches to a full quantum-mechanical treatment. In addition, we discuss the in/out coupling problem between external light and strongly confined polaritons, which remains a major challenge, and for which we propose innovative solutions based on critical coupling between dipolar scatterers and planar interfaces. We further discuss a disruptive approach to the design of polaritonic materials relying on quantum phase effects, as well as a new mechanism of electron-positron pair production based on the scattering between gamma-rays and surface polaritons.

In the field of optics, we are used to direct light waves with bulky optical components. The development of metasurfaces has recently brought many exciting new ways to manipulate the flow of light. These are essentially flat optical elements comprised of a dense arrays of nanostructures that can scatter light and thereby impart space-varying phases on an incident light wave. The ultimate physical limitations of these optical components can be traced back to the properties of the materials and building blocks that they are constructed from. Current metasurface designs largely employ metallic or high-index nanostructures. They afford strong scattering because of their plasmonic and Mie resonances that enable them to serve as optical antennas. However, emerging metasurface applications in quantum optical communications, augmented reality, non-linear optics, and spatiotemporal light control demand much more than the basic, linear, and typically-static scattering responses provided by such geometrically-shaped antennas. In this presentation, I will ask the question whether the unique quantum properties of atomically-thin quantum can be harnessed to create atomically-thin metasurfaces.

Metasurfaces have received significant attention in the context of non-linear optics, since they allow a dramatic boosting of light-matter interactions, and a corresponding enhancement of non-linear processes. In this talk, I will overview our recent research progress in the area of nonlinear and active metasurfaces, demonstrating opportunities for efficient frequency conversion processes and wave mixing, non-reciprocity, non-linear image processing, and lasing. The integration of 2D materials and polaritonic features, as well as optical pumping, enables the opportunity of accessing low-threshold lasing, polariton condensation and other exotic forms of light manipulation within an ultrathin platform, in which photonic and materials engineering play a pivotal synergistic role.

We discuss aspects of thermal radiation engineering with the use of photonic structures. We show that temporal modulation of the refractive index can be used to create new thermal radiation phenomena, including coherence transfer, and near field radiative heat pump. We also show that the thermal radiation properties can be strongly influenced with unitary transformation of the external modes.

Thermal and blackbody radiations are tightly entangled with the material’s quantum properties for any finite temperature above 0 K. Such radiation is incoherent, both spatially and temporally. However, this characteristic change abruptly in the optical near-field region where it is related to the local density of photonic states (LDOS) [1]. Near-field thermal emission experiences huge amplification close to the epsilon-near-zero (ENZ) spectral region, i.e. at those specific LDOS phonon resonances where the material’s complex dielectric permittivity ε approaches zero. It may lead to narrow-band emission, directionality and coherence properties. Here, we investigate the near-field of anisotropic two-dimensional ENZ materials (Hexagonal boron nitride and α-Molybdenum Trioxide) with Synchrotron Infrared Nano-Spectroscopy and s-SNOM imaging using quantum cascade lasers. Theoretical and numerical investigations confirm the observed enhanced oscillating behaviour of the LDOS around the ENZ frequency. Tuning of the emission properties of 2D ENZ material via external control of the temperature is also demonstrated using a setup for nano-imaging at low temperature.

Heat transfer and closely related (Casimir) phenomena in transdimensional plasmonic film systems are analyzed using the confinement-induced nonlocal electromagnetic response model built on the Keldysh-Rytova electron interaction potential [1,2]. Results are compared to the local Drude model routinely used in plasmonics. The nonlocal response leads to the greater Woltersdorff length in the far-field and larger film thickness at which heat transfer is dominated by surface plasmons in the near-field, to weaken the Casimir attraction force. These findings are crucial for thermal management applications and in general for the development of new quantum materials based on ultrathin metallic films. The latest experiments to confirm this fact will also be reported [3].

The last few years have witnessed significant development in the study of linear and nonlinear optical properties of materials at the nanoscale. This includes metals, semiconductors, conductive oxides, and more recently, time varying media. More often than not, experimental results are reported without the benefit of rigorous theoretical models. I will present a basic hydrodynamic-Maxwell approach that can be used to take into account and simulate all relevant light-matter interactions, depending on the circumstances. For example, simulations in the time domain can simultaneously account for surface and magnetic nonlinearities, linear and nonlinear nonlocal effects and material dispersions beyond the third order, and a phase locking mechanism that makes high harmonic generation possible for semiconductors like silicon deep in the UV range.

By uncovering novel aspects of second harmonic generation, we show that there are unusual, remarkable consequences of resonant absorption, namely an unexpectedly critical role that bound electrons play for light-matter interactions across the optical spectrum, suggesting that a new basic approach is required to fully explain the physics of surface phenomena. By tackling an issue that is never under consideration given the generic hostile conditions to the propagation of light under resonant absorption, we demonstrate through simulations and experimental observations of second harmonic generation from aluminum nanolayers that bound electrons are responsible for a unique signature neither predicted nor observed previously: a hole in the second harmonic spectrum. A hydrodynamic-Maxwell theory developed in other contexts explains these and other findings in metals, semiconductors, and conductive oxides exceptionally well and becomes the basis for renewed studies of surface physics.

As photonic devices become more complex, the need for efficient nonlinear materials and streamlined fabrication methods has increased. Typically, fabrication of compact, integrated, nonlinear photonic devices involve expensive procedures and environments within a cleanroom. Largely due to the need for phase matching constraints, many of these materials and methods have limited nonlinear efficiency. Recently, low-loss 3D printed waveguides have been demonstrated and hence are an attractive alternative that does not require a cleanroom. In this work, second harmonic generation near telecom wavelengths with a very low-cost 3D printed waveguide and nonlinear ENZ material platform is demonstrated with an efficiency exceeding 1.2%.

Lithium niobate (LN) is an excellent nonlinear photonic material due to its large electro-optic (EO) coefficient, second order (χ^((2) )) and Kerr (χ^((3))) nonlinearity, along with a wide optical transparency window. Thanks to the recent advances in nanofabrication technology, monolithic LN waveguides with high optical confinement and ultralow linear loss has been achieved, which was critical to the success of the silicon-based platform in the past decade. Highly efficient and controllable light-matter interactions can be achieved using optical, electrical, or mechanical waves at extremely compact footprints. In this talk, I will review our recent developments of 1) optical frequency combs, 2) generation and measurement of ultrafast optical waveforms. Combination of multiple nonlinearities of LN unlocks ultrabroadband electromagnetic spectrum from microwave to mid-infrared. Lastly, I will discuss the potential of LN photonic platform for scaling up and accelerating classical and quantum technologies in sensing, photonic computing, and communication networks.

We designed and realized nested 3D meta-crystals defined by connectivity. They have scalar-wave-like band dispersions, making the search for photonic topological phases an easier task. Their surface states have skyrmion-like electric field distributions, which have high-Q even inside the light cone continuum. As such, the topological surface states in our 3D nested crystals can be exposed directly to air, making such systems well-suited for practical applications. Our ideas were demonstrated experimentally.

Transmission asymmetry is a characteristic manifestation of non-reciprocal systems incorporating an active bias mechanism e.g. via a non-linear material or an external magnetic field. However, certain design routes to non-reciprocal transmission asymmetry enhancement, such as self-biasing nonlinear routes, can further benefit from having the underlying passive linear reciprocal system exhibiting also an asymmetric transmission. Reciprocal systems can exhibit transmission asymmetry when more than one output channels for light are available. We discuss here an all-dielectric system where additional output channels are provided via higher-order Bragg diffracted beams. We analyze how the structural characteristics of the unit cell building blocks impact the strength of the transmission asymmetry achieved.

Moiré photonics has become a burgeoning research field with many potential applications, one being a new kind of nanoscale, actively tunable semiconductor laser. Stacked bilayer photonic crystal lasers provide possibilities in active tuning using multiple degrees of freedom, including the twist angle and coupling distance between the two layers. Initial demonstrations of moiré photonic crystal lasers with embedded gain material have been shown in devices where the two layers are “merged” into a single layer; however, to fully realize the promise of moiré lasers’ tunability, true bilayer systems must be explored. We demonstrate a fabrication protocol to realize this kind of laser in gallium nitride with embedded indium gallium nitride emitters. We discuss fabrication challenges, including rotational precision, membrane adhesion, and material strain, as well as initial photoluminescent characterization. This research elucidates design questions and limitations that are critical for moving towards novel, tunable, low-threshold lasers in the visible regime.

We will present how to fabricate nanoantennas and metasurfaces in van der Waarls (vdW) materials in a variety of geometries and a range of photonic applications. We observed Mie resonances as well as strong coupling between the excitonic features and anapole modes in the vdW nanoantenna. Due to the weak vdW interactions of the nanoresonators and the substrate, we were able to use an atomic force microscopy cantilever in the repositioning of double-pillar nanoantennas to achieve ultra-small gaps of 10 nm. By employing a monolayer of WS2 as the gain material, we observe room temperature Purcell enhancement of emission as well as low temperature formation of single photon emitters with enhanced quantum efficiencies. More recently, we have also achieved bound states in the continuum ultra-low threshold lasing with these materials, highlighting the vdW materials as a promising platform for optoelectronic devices.

This talk will describe new classes of optical modes that can provide feedback for plasmonic lasing. First, we will discuss how quasi-propagating modes supported by plasmonic nanoparticle lattices can be used to facilitate lasing over a continuous range of discrete angles and wavelengths if the modal gain of the material is high enough. Next, we will discuss the unique lasing beam profiles and polarization states that can emerge from solid-state gain materials combined with Bravais-lattice and moiré-lattice nanocavities. Finally, we will describe prospects for ultra-low threshold lasing at room temperature based on polaritons.

Theoretical and experimental results demonstrating reversible and irreversible regimes of light-metasurface interactions will be described. First, I will describe how all-dielectric metasurfaces can be combined with liquid crystals to develop a new class of electrically-controlled multi-focal metalenses operating at several wavelengths. New design strategies aimed at simplifying metalens fabrication and producing high-NA tunable meta-optics will be discussed. Finally, I will demonstrate how semiconductor metasurfaces enable the strongly-driven regime of laser-metasurface interactions manifested as laser-assisted material nanostructuring using femtosecond mid-infrared laser pulses.

Photonic metacrystals are a class of photonic crystals that leverage deep subwavelength-engineering of the unit cell to synergistically combine metamaterials concepts with on-chip guided-wave photonics. This talk will present design rules for photonic metacrystals, highlighting the additional degrees of freedom in the design space that enable added control of light-matter interactions. Applications that can realize enhanced performance metrics using photonic metacrystals will be discussed, including on-chip modulators, optical biosensors, and optical nanotweezers. Perspectives on scalable foundry fabrication of photonic metacrystals will also be provided.

Iridescent structural color is abundant in nature, arising in the saturated blues of the Morpho butterfly wing or the greens of jeweled beetle shells. At the micrometer scale and smaller, these naturally occurring, three-dimensionally (3D)-architected photonic crystals are composed of ordered, geometrically anisotropic features which exhibit distinct interactions with light at varying angles of incidence or polarization state. Due to their 3D hierarchical architecture, these nature-derived systems are unique sources of polarization-sensitive structural color with high color purity and brightness. Here, we explore the exemplary polarization-sensitive properties of nature-derived photonic crystals and identify their key photonic and optically anisotropic features. We then leverage this knowledge to develop a new class of nature-inspired, 3D-architected colorimetric metasurfaces to enhance polarization-sensitive structural color response beyond what is observed in nature.

In this talk, we discuss recent progress in the field of Mie-resonance-based optical nanostructures, enabling unprecedented control over the amplitude, phase, and polarization of optical fields for the generation of multidimensional light beams with spin and orbital angular momentum in linear and nonlinear media.

Tuning the optical response of metasurfaces can unleash their full potential as compact and reactive optical elements. Here, we present two different approaches to tune the spectral response of a metasurface. In the first approach, a micro-electromechanical system(MEMS)-actuated metasurface is demonstrated in the visible range of the optical spectrum. It consists of an amorphous silicon nanopillar array and a suspended silicon membrane with integrated electrostatic actuators. The second approach utilizes light itself to reconfigure the metasurface by trapping nanoparticles within a templated plasmonic substrate. Optical forces control the position of the nanoparticles, which in turn tune the metasurface spectral response.

Phonon trapping has an immense impact in many areas of science and technology. It usually relies on the mechanical suspension—an approach, while isolating selected vibrational modes, leads to serious drawbacks for interrogation of the trapped phonons, including limited heat capacity and excess noises via measurements. We introduce a novel paradigm of phonon trapping using mechanical bound states in the continuum (BICs) and its experimental realization. Coupling mechanical BICs with optical resonances leads to a new breed of optomechanical systems beyond suspended microcavities, which might mitigate measurement-induced parasitic heating and excess noises. We demonstrate a new breed of optomechanical crystals in two-dimensional slab-on-substrate structures empowered by mechanical BICs at 8 GHz and an optomechanical couplings up to 2.5 MHz per unit cell. We will further show work of merging mechanical BICs for suppression of scattering induced acoustic losses.

We create multi-mode nano-optomechanical networks in which the interactions between mechanical modes are induced and fully reconfigured through time-modulated radiation pressure forces. We study the nonreciprocal and topological states that emerge from controlled breaking of time-reversal symmetry and Hermiticity in such laser-driven optomechanical metamaterials. We demonstrate unidirectional flow of sound and the emergence of the quantum Hall effect in small networks of nanomechanical resonators. We uncover that broken time-reversal symmetry can influence the thermodynamic efficiency of optomechanical refrigeration. Moreover, we realize the bosonic Kitaev chain; the bosonic counterpart of the fermionic model that famously predicts Majorana zero modes. This establishes a non-Hermitian topological phase in which a unique form of directional amplification emerges as a physical phenomenon that links to the chain’s topological nature. This behavior has intriguing implications for signal processing and enhanced sensing performance.

Here, we present Subsurface Controllable Refractive Index via Beam Exposure (SCRIBE), a direct-write lithographic approach that enables fabrication of low-loss volumetric microscale gradient refractive index lenses, waveguides, and metamaterials. The basis of SCRIBE is multiphoton polymerization inside monomer-filled nanoporous silicon and silica scaffolds. Adjusting the laser exposure during printing enables 3D submicron control of the polymer infilling and thus the refractive index over a range of greater than 0.3 and chromatic dispersion tuning. A Luneburg lens operating at visible wavelengths, achromatic doublets, multicomponent optics, photonic nanojets and subsurface 3D waveguides were all formed. Various optical elements were combined to create the building blocks for volumetric photonic integrated circuits.

We proposed recently that the building blocks of metal optics (encompassing plasmonics, metasurfaces, and metamaterials) can be fabricated in existing CMOS foundry processes by repurposing the back-end-of-the-line (BEOL) of the CMOS chip in. We demonstrated a metal-optic liquid crystal modulator using a chip that is fully fabricated in the conventional 65-nm CMOS process. In this talk, we provide an in-depth presentation on the design constrains and post-processing steps required to convert CMOS chips to nano-photonic devices. We will also present recent developments and prospects of CMOS meta-optics and optoelectronics.

Cascaded linear and non-linear operations serve as the backbone of integrated photonic applications, enabling diverse functions from routing to computing. In computing, while incoherent processors have shown excellent speed and parallelization in wavelength, space and time, they require electro-optical components to perform the mathematical operations. Achieving independent modulation and direct summation of multi-wavelength carrier signals within a single waveguide in an entirely optical manner remains a significant challenge. This talk will highlight our recent work in exploiting spatial-degrees-of-freedom of in-plane modes using standing waves, beginning with a wavelength-addressable modulator with non-volatile multi-level operation. I will talk about a recent demonstration of a new photonic framework where the non-local thermo-optic effect is combined, enabling direct addition and all-optical encoding of signals carried in different wavelengths.

I will describe our recent demonstration of perovskite chalcogenides with optical anisotropy far larger than any other known materials. These materials include barium titanium sulfide (BaTiS_3) and strontium titanium sulfide (Sr_9/8TiS_3). Sr_9/8TiS_3 is transparent in the mid- to far-infrared, and is positive uniaxial, with extraordinary refractive index n_e = 4.5 and ordinary index n_o = 2.4. BaTiS_3 has similar optical properties and a smaller, but still giant, birefringence, with n_e ~ 3.3 and ordinary index n_o ~ 2.6. In BaTiS_3, atomic displacements on the order of 0.1 Angstrom (“correlated disorder”) lead to a slight increase in ne and a significant reduction in no compared to what first-principles calculations predict in the absence of these displacements. In Sr_9/8TiS_3, the stable material is Sr rich compared to “stoichiometric” SrTiS_3, resulting in structural modulations and enhance the electronic polarizability along the optical axis, dramatically increasing n_e. We will discuss the implication of these new highly anisotropic materials, including potential applications and how they might be integrated into optical systems.

Here, we show that the precise, non-resonant, subwavelength, dispersion engineering of oxide and phase change chalcogenide glasses, through lithography-free, bottom-up growth techniques, paves the way to the realization of alloys with tunable optical and electronic properties. We show that tunability may be achieved on a material level without the need for stoichiometric changes to chemical composition through oblique angle vapour deposition and oxidation techniques. We also go on to show how metacoatings realized through interlayer nanostructuring can be utilized to realize ultra-compact photonic modulators for emerging integrated computing and telecommunication applications relying on silicon photonics platforms.

This talk discusses a new photonic implementation to perform general discrete linear operations. This is achieved by properly factorizing any arbitrary NxN complex matrix in terms of a prefixed unitary discrete fractional Fourier transform (DFrFT) matrix and complex diagonal matrices. This approach is handy as it allows for an all-optical implementation using N+1 amplitude and N+1 phase modulation layers, interlaced with fixed DFrFT layers implemented via a coupled waveguide array. Numerical optimizations show that target matrices can indeed be represented through this approach by accordingly tunning the phase and amplitude layers. The proposed architecture enables the development of novel families of programmable lossy and lossless photonic circuits for on-chip analog information processing.

This invited talk will discuss various strategies for photonic in-memory computing using nonvolatile optical materials on an integrated silicon photonics platform. Both experimental demonstrations and methods for modeling large scale photonic neural networks will be presented.

We employ the plasmonic Phase-Change Material In3SbTe2 (IST) for direct laser-writing of functional infrared metasurfaces, without the need for cumbersome cleanroom fabrication. We demonstrate rapid prototyping of large area metasurfaces for controlling thermal emission, beam steering, lensing and also create IR holograms into IST films. Additionally, we combine laser-written IST structures with materials hosting surface waves to launch and confine Surface Phonon or Plasmon Polaritons into resonators.

We introduce a scalable platform designed for very-large-scale programmable photonics, achieved through the integration of 300-mm-wafer-scale fabrication processes and in-house phase-change material fabrication. This approach enables reversible electrical tuning capabilities up to 50, 000 switching events. Moreover, we demonstrate a deterministic multilevel scheme capable of achieving 2^N optical levels, offering enhanced control and versatility in programmable photonics applications.

Sb2S3 is currently being developed for programmable photonics applications. It is particularly appealing because it has a relatively large bandgap of 2.05 eV in the amorphous state, which means that it is transparent in the visible spectrum. Moreover, the phase change invokes a large change in refractive index, which means that it can be used to tune photonic resonators. We have used this effect to demonstrate programmable couplers, nano resonator display pixels, and beam steering metasurfaces. In this talk I will discuss these works, and then the challenges and opportunities for Sb2S3 photonics. I will also discuss how it has the potential to revolutionise the fields of communication, information, and health.

Large-scale, electronically reconfigurable photonic integrated circuits (PICs) can enable programmable gate array (PGA) to realize extremely fast, arbitrary linear operations, with potential applications in classical and quantum optical information technology. The basic building blocks of existing PGAs are thermally tunable broadband Mach-Zehnder-Interferometers, which pose several limitations in terms of size, power, and scalability. Chalcogenide-based phase change materials (PCMs), exhibiting large nonvolatile change in the refractive index, can potentially transform these devices, providing at least one order of magnitude reduction in the device size, zero static energy consumption, and minimal cross-talk. In this talk, I will discuss different PCMs that can be used in conjunction with silicon and silicon nitride photonics, to create reconfigurable optical switches for visible and infrared wavelengths. I will also talk about different heaters that are needed to actuate the phase transitions on-chip. Specifically, I will show how using ultrathin graphene as a heater element can provide very high energy-efficiency, close to the fundamental limit set by thermodynamics.

We have developed several strategies for modulating the infrared absorptivity and emissivity of metasurfaces via electrical control signal. These employ such approaches as voltage-induced symmetry breaking and period doubling for controlling the coupling between a guided mode of the metasurface and the continuum. We further describe potential applications in encoding and encrypting light, for development of secure tags.

Metasurfaces and metamaterials emerged as promising nanophotonic material and device platforms to control light-matter interactions at the nanoscale. In such materials, the collective and effective optical response is dictated by individual building blocks and controlled by the geometrical parameters forming the crystal structure. I will introduce DNA-assembly of gold nanoparticles as a fabrication method to realize bottom-up, programmable, and stimuli-responsive nanophotonic hybrid metamaterials and metasurfaces. The ability to control the distance, size, shape, architecture of nanoparticles and overall crystal structure enables access to optical properties that are not accessible readily in nature. I will highlight wide range of functional nanophotonic device architectures including epsilon-near-zero metasurfaces, negative index metamaterials and broadband absorber meta-films. The synthesis of plasmonic NP architectures with structures and stimuli-responsive behavior that are not accessible in lithographically defined plasmonic nanostructures provides an opportunity to design materials with emergent optical properties that offer new fundamental insights.

Spatially controlled photomechanical deformations on the surface of a single photomechanical crystals can be used to actively control light propagation. Single crystals composed of the organic molecules 1,2-bis(2,4-dimethyl-5-phenyl-3-thienyl)-3,3,4,4,5,5-hexafluoro-1-cyclopentene and 4-fluoro-9-anthracenecarboxylic acid are used as reversible beam control elements. This is accomplished by using either electron beam lithography to imprint a fixed pattern with a switchable period, or a digital micromirror array to reversibly imprint an arbitrary pattern ion the crystal surface, which then erases itself due to thermal back-reaction. Both of these approaches allow one light source to control the direction and intensity of a diffracted 633 nm probe laser.

Electrochemistry is a powerful tool to achieve reversible optical property change. The development of new active materials will provide great value to the active photonic platforms, initiating co-design of the atomic/molecular level and the nano/micro-scale structures and coupling. In this talk, I will introduce a few recent research progress of light- and heat-managing metasurfaces based on reversible metal electrodeposition and conjugated polymers.

In this work we study the dynamic modulation characteristics of unconventional silicon photonic circuits with low degrees of spatial symmetry. Specifically, we investigate the electro-optical modulation properties of moiré quasicrystal interferometers realized in a silicon photonics platform with integrated electrically driven thermo-optic heaters. Whereas previously we have studied these devices within the context of physical unclonable functions for hardware security applications, here we focus on the fundamental modulation properties and contrast their behavior with well-known conventional systems such as Michaelson or Mach-Zehnder interferometers and ring resonators – all of which exhibit significant degree of spatial symmetry. Our findings suggest that these unconventional photonic integrated circuits could play a role in future analog information processing, storage, and/or transmission technologies.

We experimentally analyze the simultaneous processes of difference frequency generation (DFG) and second harmonic (SH) generation in multilayer structures exhibiting an effective epsilon-near-zero (ENZ) response and ENZ properties in one of their layers. The structures consist of subwavelength-thin tri-layer periods of 75% ITO, 12.5% Al2O3, and 12.5% BaTiO3, with the total thickness kept near 120 nm. The number of periods and ITO layer thickness (3-30 nm) vary between samples, allowing to tune the effective ENZ wavelength over 1000 nm. We demonstrate that the level of DFG and SH enhancement can be increased by over two orders of magnitude with multilayer composition, with the highest enhancement in samples having 12-15 nm thick ITO layers. The peak enhancement wavelength follows the effective ENZ wavelength, while the relative enhancement levels of DFG and SH depend on sample composition. Our findings are supported by COMSOL simulations, TEM analysis, and ellipsometry data.

Here, we use a novel approach to enhance the visible-light photoresponse in NbN superconducting microwire photon detectors (SMPDs) by integrating them with gap plasmon resonators (GPRs). This talk describes how we observe the plasmonic NbN SMPDs can achieve a 233-fold enhancement in the phonon-electron interaction factor (γ) compared to pristine NbN SMPDs under resonant conditions with illumination at 532 nm. The nonlinear photoresponse in the visible region is attributed to the gap-plasmon resonances that disrupt the Copper pairs that break the superconducting state to normal. In addition, an impressive detection efficiency of 98% was achieved using these plasmonic SMPDs.

We discuss control of thermally-induced focal shifts via engineering the metalens construction and show that metalenses offer additional degree of freedom in controlling the thermal stability of optical systems, compared to standard refractive and diffractive lenses.

Photothermal therapy (PTT) of cancer and bacterial infections is an emerging field that benefits from the light-matter interactions of targeted nanoparticles. Low concentrations of these nanoparticles are desired for low toxicity and low laser excitation power is desired for minimizing proximal tissue damage. Despite earlier experimental success in the PTT with hybrid nanoparticles, a fundamental understanding of concentration-dependence of the photothermal effect is missing. Hence, a computational/theoretical approach must account for the strength of the experimental photothermal effect. Here, we used electromagnetic FDTD simulations and effective medium theory to accurately estimate the in vitro heating behavior of PAA-SPION nanoparticles in water for 640 nm excitation. These nanoparticles were demonstrated to be highly effective in selective killing of prostate cancer cells under near-infrared irradiation (Biomater. Sci., 10, 3951 (2022)). FDTD Solver and EMT using Stack Solver were used to solve for the nanoparticle concentration dependence of their absorption within 450-1000 nm. Our results might pave the way for low-concentration, low power, targeted and drug-loaded PTT.