Orad Reshef

• PhD Applied Physics
• PostDoc Position at University of Ottawa

Integrating the large, subpicosecond nonlinear optical response of epsilon-near-zero (ENZ) materials with the broad design freedoms of plasmonic metasurfaces shows potential for creating rapidly modulated optical devices with possible applications in telecommunications, sensing, and reactive beam steering. In this work, we experimentally investigat...

Epsilon-near-zero (ENZ) polaritons in a thin transparent conducting-oxide film exhibit a significant electric field enhancement and localization within the film at frequencies close to their plasma frequency, but do not propagate. Meanwhile, plasmon polariton modes in thin metallic films can propagate for several microns, but are more loosely confi...

Spaceplates are novel flat-optic devices that implement the optical response of a free-space volume over a smaller length, effectively “compressing space” for light propagation. Together with flat lenses such as metalenses or diffractive lenses, spaceplates have the potential to enable the miniaturization of any free-space optical system. While the...

The utility of all parametric nonlinear optical processes is hampered by phase-matching requirements. Quasi-phase-matching, birefringent phase matching, and higher-order-mode phase matching have all been developed to address this constraint, but the methods demonstrated to date suffer from the inconvenience of only being phase matched for a single,...

Multiresonant metasurfaces could enable many applications in filtering, sensing, and nonlinear optics. However, developing a metasurface with more than one high-quality-factor or high-Q resonance at designated resonant wavelengths is challenging. Here, we experimentally demonstrate a plasmonic metasurface exhibiting different, narrow surface lattic...

Conferences disseminate research, grow professional networks and train employees. Unfortunately, they also contribute to climate change and present barriers to achieving a socially sustainable work environment. Here, we analyse the recent impact of transforming in-person conferences into virtual conferences on improving diversity, equity and inclus...

Asymmetric transmission - direction-selective electromagnetic transmission between two ports - is a phenomenon exhibited by two-dimensional chiral systems. The possibility of exploiting this phenomenon in chiral metasurfaces opens exciting possibilities for applications such as optical isolation and routing without external magnetic fields. This wo...

Silicon nitride waveguides were used to experimentally demonstrate third-harmonic generation (THG) in the TM02 mode at 532 nm. Modal phase-matching between the modes TM00 (pump) and TM02 (signal) is achieved.

The development of metasurfaces has enabled unprecedented portability and functionality in flat optical devices. Spaceplates have recently been introduced as a complementary element to reduce the space between individual metalenses, which will further miniaturize entire imaging devices. However, spaceplates necessitate an optical response which dep...

Resonances in optical systems are useful for many applications, such as frequency comb generation, optical filtering, and biosensing. However, many of these applications are difficult to implement in optical metasurfaces because traditional approaches for designing multi-resonant nanostructures require significant computational and fabrication effo...

Multiresonant metasurfaces could enable many applications in filtering, sensing and nonlinear optics. However, developing a metasurface with more than one high-quality-factor or high-Q resonance at designated resonant wavelengths is challenging. Here, we experimentally demonstrate a plasmonic metasurface exhibiting different, narrow surface lattice...

There isn’t one single ‘early career experience’ in physics, and different subfields involve very different opportunities and challenges. Seven early career physicists who work on a range of research topics in different subfields discuss their views on the lessons we can learn from their professional lives.

Asymmetric transmission - direction-selective control of electromagnetic transmission between two ports - is an important phenomenon typically exhibited by two-dimensional chiral systems. Here, we study this phenomenon in chiral plasmonic metasurfaces supporting lattice plasmons modes. We show, both numerically and experimentally, that asymmetric t...

The development of metasurfaces has enabled unprecedented portability and functionality in flat optical devices. Spaceplates have recently been introduced as a complementary element to reduce the space between individual metalenses. This will further miniaturize entire imaging devices. However, a spaceplate necessitates a non-local optical response...

We experimentally investigate the tunable Doppler shift in an 80 nm thick indium-tin-oxide (ITO) film at its epsilon-near-zero (ENZ) region. Under strong and pulsed excitation, ITO exhibits a time-varying change in the refractive index. A maximum frequency redshift of 1.8 THz is observed in the reflected light when the pump light has a peak intensi...

Centuries of effort to improve imaging has focused on perfecting and combining lenses to obtain better optical performance and new functionalities. The arrival of nanotechnology has brought to this effort engineered surfaces called metalenses, which promise to make imaging devices more compact. However, unaddressed by this promise is the space betw...

The nonlinear optical response of materials is the foundation upon which applications such as frequency conversion, all-optical signal processing, molecular spectroscopy, and nonlinear microscopy are built. However, the utility of all such parametric nonlinear optical processes is hampered by phase-matching requirements. Quasi-phase-matching, biref...

Plasmonic nanostructures hold promise for the realization of ultra-thin sub-wavelength devices, reducing power operating thresholds and enabling nonlinear optical functionality in metasurfaces. However, this promise is substantially undercut by absorption introduced by resistive losses, causing the metasurface community to turn away from plasmonics...

We demonstrate that ultra-strongly coupled SPP and ENZ modes in gold and indium tin oxide bi-films are strongly confined, can propagate for several microns, and offer a useful platform for nanophotonics at NIR frequencies.

We experimentally demonstrate an ultra-high Q -factor ( ≈ 2400) surface lattice resonance in a plasmonic metasurface, that can be a great platform for highly-efficient flat optical applications e . g . biosensors, nanolasers, and metalenses.

We present progress in designing high-performance spaceplates, devices that can mimic free propagation to replace space in an imaging system, where we attain a compression factor of R = 11 . 5 with a NA = 0 . 26.

We present a stacked metasurface device with broad bandpass filtering properties in the terahertz region. The design, optimized with numerical simulations and characterized experimentally, features high transmission over a >1 THz spectral range.

We experimentally demonstrate an ultra-high Q -factor ( ≈ 2400) surface lattice resonance in a plasmonic metasurface, a promising platform for highly-efficient biosensors, LiDAR nanolasers, and imaging metalenses.

We present an epsilon-near-zero metamaterial consisting of a subwavelength periodic stack of metal and dielectric layers with enhanced nonlinear optical response in its zero-permittivity wavelength. This ENZ condition can be tuned by adjusting layer thickness.

We demonstrate tightly-confined hybrid-polaritons formed by the strong-coupling of SPP and ENZ modes in gold and indium tin oxide bi-films that can propagate for several microns, and offer a platform for integrating ENZ with waveguides.

We present a design for a plasmonic metasurface based on surface lattice resonances that features multiple pre-defined resonances. The resonance wavelengths are determined using inverse Fourier transforms of the particle positions.

Among many roles, conferences disseminate research, grow professional networks, and train employees. They also significantly contribute to climate change due to their sizable carbon footprint. More recently, additional negative aspects have surfaced. Namely, they present significant barriers to achieving Diversity, Equity, and Inclusion (DEI). Here...

Spontaneous emission, stimulated emission and absorption are the three fundamental radiative processes describing light-matter interactions. Here, we theoretically study the behaviour of these fundamental processes inside an unbounded medium exhibiting a vanishingly small refractive index, i.e., a near-zero-index (NZI) host medium. We present a gen...

We demonstrate ultrafast tuning of a plasmonic spectral filter at terahertz (THz) frequencies. The device is made of periodically spaced gold crosses deposited on the surface of an undoped silicon wafer in which transient free carriers can be optically injected with a femtosecond resonant pulse. We demonstrate the concept by measuring the transmiss...

Rapid advances in high‐resolution chip lithography have accelerated nanophotonic device development on the silicon‐on‐insulator (SOI) platform. The ability to create sub‐wavelength features in silicon has attracted research in photonic band and dispersion engineering and consequently made available a wide array of device functionalities. By drawing...

We demonstrate that a periodic stack of alternating, subwavelength Ag and SiO$_2$ layers can be designed to place its zero-permittivity wavelength anywhere in the visible. We find that such a metamaterial displays strong nonlinear response in its near-zero-permittivity region, with a Kerr coefficient and nonlinear absorption coefficient as large as...

Space-time duality in paraxial optical wave propagation implies the existence of intriguing effects when light interacts with a material exhibiting two refractive indexes separated by a boundary in time. The direct consequence of such time-refraction effect is a change in the frequency of light while leaving the wavevector unchanged. Here, we exper...

Resonant cavities play a crucial role in many aspects of science and engineering. A resonator with a large quality-factor (Q-factor) is essential to many applications in photonics, such as filtering, delay lines and memories, lasing, switching, spectroscopy, sensing, and nonlinear optical processes, among others. Recently, the rapid development of...

Spontaneous emission, stimulated emission and absorption are the three fundamental radiative processes describing light-matter interactions. Here, we theoretically study the behaviour of these fundamental processes inside an unbounded medium exhibiting a vanishingly small refractive index, i.e., a near-zero-index (NZI) host medium. We present a gen...

The first online-only meeting in photonics, held on 13 January 2020, was a resounding success, with 1100 researchers participating remotely to discuss the latest advances in photonics. Here, the organizers share their tips and advice on how to organize an online conference. The first online-only meeting in photonics, held on January 13th 2020, was...

On January 13th 2020, the inaugural Photonics Online Meetup (POM) brought together more than 1100 researchers to discuss the latest advances in photonics. Or rather, it didn't, because the meeting was completely delocalized with the speakers, organizers, and attendees scattered across six continents and hundreds of locations, connected via a video-...

Centuries of effort to improve imaging has focused on perfecting and combining lenses to obtain better optical performance, such as achromatic lenses, and new functionalities, such as microscopy. The arrival of nanotechnology has now enabled thin subwavelength-structured surfaces called metalenses, which promise to make imaging devices more compact...

Nonlinear optical phenomena are paramount in many photonic applications ranging from frequency broadening and generation of ultrashort pulses to frequency comb-based metrology. A recent trend has been to miniaturize photonic components, resulting also in a demand for small scale nonlinear components. This demand is difficult to address by using con...

We theoretically introduce a new optic, a plate that reduces propagation length for image formation. We experimentally demonstrate it advances a beam’s focus and shifts an obliquely incident beam identically to a longer propagation distance.

We experimentally demonstrate self-phase-modulation-induced wavelength silifl of up- to 15 nm in an 80-nm-tliick ITO at a zero-permittivity wavelength of 1550 nm. We also explore tlie effect oftlie pmnp pulse temporal duration on tlie wavelength silift.

We experimentally demonstrate adiabatic wavelength conversion using a time-varying epsilon-near-zero-based metasurface. We observe up to 47-mn redshift with 4-GW/cnr pump peak intensity. The wavelength shift depends on both pump-probe delay time and pmnp peak intensity.

We experimentally demonstrate an unprecedented ultra-high-Q («2400) surface lattice resonance in a metasurface array of periodically arranged plasmonic nanostructures, which can be adopted for highly efficient nanophotonic applications e.g. nano-lasing, sensing, and nonlinear optical processes.

Surface lattice resonances exhibit the highest quality-factors in metasurfaces containing plasmonic nanoparticles. We present our recent results in developing multiresonant high-Q metasurfaces for various nonlinear applications, including efficient harmonic generation and optical-switching.

We experimentally demonstrate omni-directional phase matching via four-wave mixing in zero-index silicon waveguides exhibiting phase-free propagation in the infrared range. This property can be exploited to miniaturize integrated nonlinear devices.

We theoretically demonstrate a zero-refractive index medium (ZIM) based on Dirac cone metamaterials composed of an Al x Ga 1-x As photonic crystal. This design allows us to achieve a waveguide medium with a very small phase advance. We validate our design further by demonstrating ZIM behavior using Snell’s law, such as the perpendicular refraction...

We theoretically introduce a new optic, a plate that reduces propagation length for image formation. We experimentally demonstrate it advances a beam’s focus and shifts an obliquely incident beam identically to a longer propagation distance.

We experimentally demonstrate a metasurface with an ultra-high Q -factor ( ≈ 2400), based on surface lattice resonances. This platform can be adopted for nanopho-tonic applications such as nano-lasing, sensing, and nonlinear optical processes.

We demonstrate sub-cycle tunability of terahertz metasurfaces using a visible pump pulse and phase-locked terahertz probe. Temporal overlap is optimized to dampen resonant plasmonic oscillations, transforming notch filters into neutral filters.

We theoretically introduce a new optic, a plate that reduces propagation length for image formation. We experimentally demonstrate it advances a beam’s focus and shifts an obliquely incident beam identically to a longer propagation distance.

We investigate active tunability of plasmonic filters on silicon with FDTD. Injecting free-charge carriers changes the dielectric properties of the substrate and bleaches the plasmonic resonance while inducing a blueshift and linewidth broadening.

We use machine learning to design a multilayer spaceplate, a device that can mimic free propagation to replace space in an imaging system.

An invisibility cloak should completely hide an object from an observer, ideally across the visible spectrum and for all angles of incidence and polarizations of light, in three dimensions. However, until now, all such devices have been limited to either small bandwidths or have disregarded the phase of the impinging wave or worked only along speci...

Resonant metasurfaces are devices composed of nanostructured sub-wavelength scatterers that generate narrow optical resonances, enabling applications in filtering, nonlinear optics, and molecular fingerprinting. It is highly desirable for these applications to incorporate such devices with multiple, high-quality-factor resonances; however, it can b...

We numerically investigate second-harmonic generation from multiresonant plasmonic metasurfaces by designing an array consisting of L-shaped aluminum nanoparticles that simultaneously supports two surface lattice resonances with relatively high quality factors (). Using an approach based on the nonlinear discrete-dipole approximation, we predict an...

Resonant metasurfaces are devices composed of nanostructured sub-wavelength scatterers that generate narrow optical resonances, enabling applications in filtering, nonlinear optics, and molecular fingerprinting. It is highly desirable for these applications to incorporate such devices with multiple, high-quality-factor resonances; however, it can b...

Materials with vanishingly small dielectric permittivity, known as epsilon-near-zero materials, enable strong ultrafast optical nonlinear responses within a sub-wavelength propagation length. This Review surveys the various observations of nonlinear phenomena in this class of materials.

We experimentally demonstrate a plasmonic surface that supports a series of high-quality-factor (Q ≈ 100) surface lattice resonances. These resonances are enabled by tuning the thickness of the top-cladding layer to confine higher order diffraction-orders.

We report a large and tunable frequency shifting over 14.8 THz bandwidth of an infrared probe beam through time refraction in indium tin oxide (ITO) in its epsilon-near-zero region. The sign of the frequency change can be controlled by adjusting the delay between a pump and the probe.

We experimentally demonstrate a strong-coupling-induced resonance splitting in indium-tin-oxide (ITO) based epsilon-near-zero (ENZ) metasurface with cross-shaped nanoantennas. An ~11-nm blue shift of the carrier wavelength is observed for this metasurface under ~4-GW/cm2 peak-power density.

We report, as a direct consequence of time refraction, an unprecedentedly large and tunable frequency translation of an optical beam over 14.8 THz bandwidth at infrared frequencies using an epsilon-near-zero material of subwavelength thickness.

We design and simulate an integrated optical device that sorts the four lowest-order transverse electric modes of a multi-mode optical waveguide into four separate single-mode waveguides, finding an 84% average sorting efficiency and 2% average inter-channel cross-talk. This design could also be used forefficient sorting of free-space light modes.

This chapter aims to give a practical introduction to some of the techniques of nanofabrication, written by someone who recently completed a PhD using these techniques. It begins by discussing patterning and pattern transfer, and then techniques of deposition by spin coating, evaporation, and chemical vapor deposition (CVD). Techniques of character...

Metamaterials with a refractive index of zero exhibit properties that are important for integrated optics. Possessing an infinite effective wavelength and zero spatial phase change, zero-index metamaterials may be especially useful for routing on-chip photonic processes and reducing the footprint of nonlinear interactions. Zero-index has only been...

Graphene has emerged as one of the most versatile materials ever discovered due to its extraordinary electronic, optical, thermal, and mechanical properties. However, device fabrication is a well-known challenge and requires novel fabrication methods to realize the complex integration of graphene-based devices. Here, we demonstrate direct laser wri...

Polymers are a highly versatile class of materials for micro and nanofabrication. They have been studied for applications in photonics as they can be readily processed, integrated and doped with a wide range of materials, and can be flexible and stretchable providing numerous opportunities such as wearable devices and structures with tunable photon...

Integrated Dirac-cone metamaterials enable effective refractive indices near zero in the standard silicon-on-insulator (SOI) platform. We experimentally demonstrate small-footprint (≈λ/2-wide) zero-index structures in the telecom regime.

We demonstrate silicon waveguides that support phase-free propagation in the telecom regime. These waveguides have smaller footprints and exhibit improved energy transfer capabilities as compared to previous optical waveguides that support phase-advance-free modes. We measure the effective refractive index using on-chip interferometry and observe a...

Zero-index metamaterials (ZIMs) offer unprecedented ways to manipulate the flow of light, and are of interest for wide range of applications including optical cloaking, super-coupling, and unconventional phase-matching properties in nonlinear optics. Impedance-matched ZIMs can be obtained through a photonic Dirac-cone (PDC) dispersion induced by an...

Polycrystalline anatase TiO2 nanoscale waveguides were proposed as a platform for efficient, on-chip generation of triplet photons via third-order spontaneous parametric down-conversion (TOSPDC). TiO2 has a high nonlinear index of refraction (0. 16 × 10¹⁸ m²/W at 1565 nm), a wide transparency window (absorption edge at 400 nm) and negligible two-ph...

We show that standard approximations in nonlinear optics are violated for situations involving a small value of the linear refractive index. Consequently, the conventional equation for the intensity-dependent refractive index, , becomes inapplicable in epsilon-near-zero and low-index media, even in the presence of only third-order effects. For the...

There has been strong interest in the confinement of electromagnetic energy in sub-diffraction limit waveguide configurations. Such an achievement would offer applications in in telecommunications, subwavelength imaging, optical memory storage, and on-chip photonic processes. Materials with a refractive index of zero have been considered as strong...

Propagation losses in micro-ring resonator waveguides can be determined from the shape of individual resonances in their transmission spectrum. The losses are typically extracted by fitting these resonances to an idealized model that is derived using scattering theory. Reflections caused by waveguide boundaries or stitching errors, however, cause t...

We present small-footprint (≈ λ/2-wide) silicon-based waveguides with an effective index of zero at a wavelength near λ = 1630 nm. We characterize the refractive index using on-chip interferometry and measure the propagation loss to be 1.3 dB/μm.