This PDF file contains the front matter associated with SPIE Proceedings Volume 11688

In this paper, we will outline the architectures of light emitting diode using black phosphorus-based van der Waals heterostructures. The demonstrated device can emit mid-infrared light, ranging from 3 to 4 μm, within the technologically important mid-infrared atmospheric window, and its emission is linearly polarized with the degree of polarization ~ 75%. Additionally, the device can perform high quantum efficiency, high bias voltage operation, fast modulation speed as well as long term stability. By leveraging the integrability of van der Waals materials, we further demonstrate our developed black phosphorus-based light emitting diode can be assembled with a mid-infrared silicon waveguide, which promises for midinfrared silicon photonics applications.

We investigated in situ the coupling spectra of a single gold nanorod and monolayer transition metal dichalcogenides (TMDCs) using nanomanipulation technique and single-particle spectroscopy. The resonant scattering peak of the hybrid redshifted, the full width at half maximum of the resonance narrowed, and the scattering intensity increased compared with those of the same nanorod on the glass surface, i.e., before coupling with monolayer TMDCs. Also, the spectral features varied with the distance between the nanorod and TMDCs, and the coupling interaction should be dominated mainly by the resonant energy transfer effect rather than the electron transfer process.

Here we demonstrate a MoTe2-based photodetector featuring a strong photoresponse (responsivity 0.5 A/W) operating at 1,550 nm in silicon photonics enabled by strain engineering the two-dimensional material. Non-planarized waveguide structures show a bandgap modulation of 0.2 eV, resulting in a large photoresponse in an otherwise photoinactive medium when unstrained. Unlike graphene-based photodetectors that rely on a gapless band structure, this photodetector shows an approximately 100-fold reduction in dark current, enabling an efficient noise-equivalent power of 90 pW/Hz^0.5. Such a strain-engineered integrated photodetector provides new opportunities for integrated optoelectronic systems.

Recently, among the prototypical 2-dimensional transition metal dichalcogenide (TMDs) layered materials, WSe₂ emerged as an excellent candidate and has gained tremendous research interest due to its uncanny Physico-chemical properties. The artificial engineering of zero-dimensional defects in TMDs demonstrated the bandgap tunability and a breakthrough to get the composition modulated atomically thin 2D semiconductors for the anticipated application. Herein, by using the first-principles method based density functional theory in conjunction with Boltzmann transport equation, we have investigated the stability, electronic band structures, and electronic transport coefficients of pristine and defective WSe₂ monolayer with the introduction of vacancy, substitutional doping of Niobium (Nb) and Rhenium (Re) at the compositional proportion x (0 ≤ x ≤ 0:125), interstitial carbon (C) atoms and Frenkel defects at 300 K. Our results reveal that the introduction of vacancy defects induces localized states in the bandgap, Niobium (Nb) and Rhenium (Re) behave as p- and n-type dopants, interstitial carbon atom and Frenkel defects behave as iso-electronic dopants and they do not alter the intrinsic nature of the pristine monolayer WSe₂. The calculated bandgap of monolayer pristine WSe₂, vacancy defect, Nb-doped, Re-doped, C-adatom and Frenkel defect is 1.71 eV, 0.55 eV, 1.60 eV, 1.55 eV, 0.11 eV and 0.31 eV respectively. Furthermore, electrical conductivity (σ/Τ) is calculated as a function of chemical potential. At the studied chemical potential range, for the pristine monolayer WSe₂ the achieved maximum electrical conductivity is 0.55×10²⁰ Ω^-1m^-1s^-1. In addition, for vacancy defect, Nb-doped, Re-doped, interstitial C-atom and Frenkel defect case, the achieved maximum electrical conductivities, are 0.3×10²⁰ Ω^-1m^-1s^-1, 0.12×10²⁰ Ω ^-1m^-1s^-1, 0.17×10²⁰ Ω^-1m^-1s^-1, 0.16×10²⁰ Ω ^-1-1s^-1, 0.3×10²⁰ Ω ^-1m^-1s^-1, and 0.11×10²⁰ Ω ^-1m^-1s^-1, respectively. Our contribution provides insights to understand and ensure the rapid progress of the transport properties of 2D WSe₂ based devices, with anticipated potential applications in next-generation integrated optoelectronics.

The next-generation technology poised to revolutionize our society is 3D displays, and tunable nanophotonics is the key. Tunability in optical devices has been achieved in the past by many techniques including electrical doping, chemical doping, mechanical actuation, and optical nonlinearity. However, they all present either fast and small or slow and large tuning response. An unconventional material that can exhibit a large tuning with MHz response is 1T-tantalum disulfide. We observed unity order refractive index change in the visible at room temperature with an in-plane DC bias, AC bias, and moderately intense white light illumination (2.5 Suns). The strong correlations in this material give rise to charge ordering even at room temperatures and result in the large tunability. Using this new optical material, we demonstrate tunable meta-devices operating in the visible.

Polaritonic modes in two-dimensional van der Waals materials display short in-plane wavelengths compared with light in free space. However, such large confinement is accompanied by poor in/out optical coupling, which severely limits the application of polaritons in practical devices. Here, we quantify the coupling strength between light and 2D polaritons in thin films using accurate rigorous analytical methods. In particular, we obtain universal expressions for the cross sections associated with photon−polariton coupling by point and line defects, as well as with polariton extinction and scattering processes. Additionally, we find closed-form constraints that limit the maximum possible values of these cross sections. Our results bear fundamental interest for the development of 2D polaritonics and the design of applications based on these excitations.

In this talk, we discuss our recent efforts in the context of polaritonic metasurfaces formed through nanophotonic engineering of metasurfaces coupled to 2D materials. In particular, we discuss our recent theoretical and experimental results in the context of hyperbolic polariton manipulation, valley exciton control, sorting and steering, and twisted bilayers for polariton canalization and extreme dispersion engineering arising in polaritonic metasurfaces based on TMDs and TMOs. During the talk, we will discuss the highly unusual light-matter interactions and potential opportunities of these systems for nanophotonic devices.

Atomically thin van der Waals (vdW) materials have generated strong interest in the community due to its unusual physical properties and possibility of creating high-performance devices. However, the ultrathin nature of these materials limits the achievable light-matter interaction. One promising way to increase such interaction is via nanophotonic confinement of light. In fact, researchers have demonstrated various nanophotonic devices using such vdW materials, including optically pumped lasing, second harmonic generation, cavity enhanced electroluminescence, and exciton-polaritons. In this talk, I will explore the possibility of going to quantum optical regime using this material system integrated with nanophotonic resonators. I will discuss the role of exciton-phonon interaction in the cavity photoluminescence spectrum and present a quantum optical model of the coupled system in presence of the phonons. I will then report the observation of the exciton-polaritons using TMDs.

Here, we demonstrate a 2D exciton-polariton system by strongly coupling atomically thin tungsten diselenide (WSe2) monolayer to a silicon nitride (SiN) metasurface. Via energy-momentum spectroscopy of the WSe2-metasurface system, we observed the characteristic anti-crossing of the polariton dispersion both in the reflection and photoluminescence spectrum. A Rabi splitting of 18 meV was observed which matched well with our numerical simulation. Moreover, we showed that the Rabi splitting, the polariton dispersion and the far-field emission pattern could be tailored with subwavelength-scale engineering of the optical meta-atoms.

There is interest in studying nonlinear optical properties of monolayer and few-layer 2D materials due to the inherently strong nonlinear optical properties, interesting symmetry properties and polarization dependence. However, the inherent ultrathin 2D material limits the interaction length and efficiency of the nonlinear optical process studied. To overcome this limitation, 2D materials are integrated with resonant photonic structures to increase the overall nonlinear optical interaction strength. Such heterogeneously integrated structures offer the advantage of combining a range of 2D materials exhibiting diverse linear and nonlinear optical properties with prefabricated photonic structures using simple dry-transfer or chemical vapor deposition techniques. Here we will discuss some of the recent progress made in the area of heterogenous integration of 2D materials with dielectric resonant structures. We will also describe some of our recent effort in this direction in the resonant enhancement of second harmonic generation (SHG) from multi-layer Gallium Selenide coupled to silicon twodimensional resonant metasurface to achieve polarization independent SHG enhancement. We find that the designed 2D silicon resonant structures exhibit field depolarization at the resonance wavelength which needs to be accounted for when analyzing the nonlinear polarization. Furthermore, the second-harmonic signal radiated from the structure exhibits higher order diffraction effects with strong incident polarization angle dependence for the higher order diffraction components. Experimental studies on the above structures are also discussed with the observation of resonant enhancement of SHG and similar polarization dependence of the SHG on-/ off- the resonant metasurface when restricting the collection angles to the zeroth order diffracted nonlinear signal.

Over the past decade, excitonic effects in two-dimensional transition metal dichalcogenide semiconductors such as MoS2 and WSe2 have been intensely studied. Currently, there is significant interest in understanding how to control excitons in heterostructures and on-chip optical structures that have potential applications to excitonic and optical information processing devices. In this presentation, I will discuss our recent work exploring the nature of the moiré trapping potential in MoSe2-WSe2 heterostructures, where the interlayer exciton photoluminescence exhibits a strong temperature dependence. I will also discuss our work demonstrating coupling between organic PTCDA molecular excitons and monolayer WSe2 excitons, which manifests as a ~20 times enhancement of the PTCDA Raman scattering efficiency. Finally, I will report on our recent studies on 2D semiconductor plasmonic structures composed of propagating surface plasmon polaritons (SPPs) coupled to monolayer WSe2 excitons. In our new “cross geometry” structures, we are able to explore the nonlinear exciton response of both co- and cross- propagating SPPs. In these devices, we observe a large (near unity) differential transmission response and population pulsation resonances that are dependent on the direction of SPP propagation.

Precisely positioned and scalable single-photon emitters (SPEs) are highly desirable for applications in quantum technology. We present single-photon-emitting atomistic defects in monolayers of MoS2 that can be generated by focused He-ion irradiation with few nanometers positioning accuracy. We discuss the optical properties of the emitters as well as the possibilities to implement them into photonic and optoelectronic devices. We showcase the advantages of the presented emitters with respect to atomistic positioning, scalability, long (microsecond) lifetime, and a homogenous emission energy within ensembles of the emitters. Moreover, we demonstrate that the emitters are stable in energy on a time scale exceeding several weeks, and that temperature cycling narrows the ensembles’ emission energy distribution.

We study the use of propagating plasmons in 1-D graphene nanoribbons by employing rigorous quantum-mechanical simulations that account for nonlocal, quantum finite-size, and edge-termination effects in the optical response. Our simulations reveal a strong dependence on such phenomena for excitation with a high optical momentum component along the direction of transverse symmetry in both the linear and nonlinear optical response, wherein particular second-order nonlinear phenomena are found to manifest with high efficiency due to the breaking of inversion symmetry. These findings are applied to emitters close by which we use to excite and explore the nonlinear dynamics provided by those plasmons in the graphene ribbons.

The generation of single photons with tunable, high spectral and single-photon purity are essential building blocks of quantum photonic technologies. I will discuss our progress on making high-quality single photon sources based on van der Waals materials including monolayers of WSe2 and hBN defects. In WSe2 we show very spectrally clean emission of high-purity single photons at a strain point in the wrinkles of hBN/WSe2 bilayers, cleaner than the single photon emission at substrate-defined nanopillars. We also study dynamic strain via the integration of ion-beam created hBN defects with drumhead mechanical resonators and study their optical properties.

Compact, highly accurate and fast optical systems for three-dimensional image acquisition are becoming increasingly important in various future relevant applications. A special optoelectronic detector that can be used for distance measurement is the Photonic Mixer Device (PMD). We developed a graphene-based PMD, which benefits from the advantages of graphene (high charge carrier mobility and broadband absorption spectrum) and results in a broadband PMD with enhanced depth resolution. Our graphene PMD has a mirror-symmetrical design and combines two photodetectors in such a way that they have a common source contact made of palladium and two separate drain contacts made of titanium. The charge carrier swing, which is the main feature of a standard PMD, is realized via two separate buried gate contacts. Two versions of the graphene PMD, one silicon-substrate based and the other glass-substrate based, were fabricated. The fabrication steps as well as measurements of the electrical behavior and the photocurrent of the manufactured graphene PMDs are presented.

High-performance hybrid graphene photodetectors were prepared with fullerenes and metallofullerenes deposited on graphene using electrophoretic deposition technique. Fullerene C₆₀ which acts as an electron acceptor, and metallofullerene Sc₃N@C₈₀ which act as an electron acceptor and electron donor respectively, were used to decorate the surface of the graphene. Raman spectroscopy analysis of C₆₀ film after electrophoretic deposition and annealing reveals no change in bonding or chemical composition. Both Raman area map and AFM topography scans reveal a continuous film like deposition of C₆₀ between electrodes during electrophoretic deposition. The charge transfer between graphene and fullerene/metallofullerene and consequent photocurrent generation contribute to a high photoresponsivity ℛ in our hybrid graphene detectors. The responsivity ℛ of the C₆₀ - graphene and Sc₃N@C₈₀ – graphene hybrids were measured to be ~ 10⁹ A/W, while the detectivity and external quantum efficiency were also exceptional, ~ 10¹⁵ Jones and ~ 10⁹ %, respectively. The exceptional performance gains achieved with graphene–0D hybrid structures confirm the potential of endohedrals and metallofullerenes to dope graphene for high performance optoelectronic devices using a facile and scalable fabrication process.

We propose and demonstrate the feasibility of employing a tunable graphene nano-ribbon plasmonic network for optically trapping and transporting nano-particles within the network. In contrast to conventional metal-based plasmonic tweezers which require varying the excitation light source to achieve manipulation of trapped objects, our proposed graphene nano-ribbon plamonic network realizes accurately controlled transportation of trapped nano-particles via electrostatically tuning the carrier density distribution in the graphene network. Plane-wave excitation of the plasmonic resonances of graphene nano-ribbons at 1mW per square micrometer intensity level is sufficient to generate a trapping potential larger than 10kT at room temperature for nano-particles with a sub-100nm diameter.

We report enhanced nonlinear optics in complementary metal-oxide-semiconductor (CMOS) compatible photonic platforms through the use of layered two-dimensional (2D) graphene oxide (GO) films. We integrate GO films with silicon-on-insulator nanowires (SOI), high index doped silica glass (Hydex) and silicon nitride (SiN) waveguides and ring resonators, to demonstrate an enhanced optical nonlinearity including Kerr nonlinearity and four-wave mixing (FWM). The GO films are integrated using a large-area, transfer-free, layer-by-layer method while the film placement and size are controlled by photolithography. In SOI nanowires we observe a dramatic enhancement in both the Kerr nonlinearity and nonlinear figure of merit (FOM) due to the highly nonlinear GO films. Self-phase modulation (SPM) measurements show significant spectral broadening enhancement for SOI nanowires coated with patterned films of GO. The dependence of GO’s Kerr nonlinearity on layer number and pulse energy shows trends of the layered GO films from 2D to quasi bulk-like behavior. The nonlinear parameter of GO coated SOI nanowires is increased 16 folds, with the nonlinear FOM increasing over 20 times to FOM > 5. We also observe an improved FWM efficiency in SiN waveguides integrated with 2D layered GO films. FWM measurements for samples with different numbers of GO layers and at different pump powers are performed, achieving up to ≈7.3 dB conversion efficiency (CE) enhancement for a uniformly coated device with 1 layer of GO and ≈9.1 dB for a patterned device with 5 layers of GO. These results reveal the strong potential of GO films to improve the nonlinear optics of silicon, Hydex and SiN photonic devices.

Acoustic-graphene-plasmons (AGPs) are highly confined electromagnetic modes, which carry extreme momentum and low loss in the Mid-infrared (MIR) to Terahertz (THz) spectra. They are therefore enablers of extremely strong light-matter interactions at these long wavelengths. However, owing to their large momentum they are also challenging to excite and detect. Here, we demonstrate a new way to excite AGPs that are confined to nanometric-scale cavities directly from the far-field, via localized graphene-plasmon-magnetic-resonators (GPMRs). This approach enables the efficient excitation of single AGP cavities, which are able to confine MIR light to record-breaking ultra-small mode-volumes, which are over a billion times smaller than their free-space volume.

We propose a gold -based nanostructured design for achieving enhanced absorption in black phosphorus (BP) thin films in the 3 – 5 microns wavelength range. We tune the design parameters to excite strongly localized radiation modes in layers of thicknesses ranging from 5 to 50 nm at 4 microns. In addition, we compute the absorption enhancement factor of these absorbers and compare it against the conventional 4n2 limit. For a BP layer thickness of 5 nm, we are able to achieve an enhancement of around 561 at a wavelength of 4 microns which is significantly greater than the conventional value of 34 for an isolated textured layer.