Nanophotonic Devices Research Articles

Quantum control in size selected semiconductor quantum dot thin films

Abstract We introduce a novel technique for coherent control that employs resonant internally generated fields in CdTe quantum dot (QD) thin films at the L-point. The bulk band gap of CdTe at the L-point amounts to 3.6 eV, with the transition marked by strong Coulomb coupling. Third harmonic generation (λ 3 = 343 nm, hν = 3.61 eV) for a fundamental wavelength of λ 1 = 1,030 nm is used to control quantum interference of three-photon resonant paths between the valence and conduction bands. Different thicknesses of the CdTe QDs are used to manipulate the phase relationship between the external fundamental and the internally generated third harmonic, resulting in either suppression or strong enhancement of the resonant third harmonic, while the nonresonant components remain nearly constant. This development could pave the way for new quantum interference–based applications in ultrafast switching of nanophotonic devices.

Active Physics-Informed Deep Learning: Surrogate Modeling for Nonplanar Wavefront Excitation of Topological Nanophotonic Devices.

Topological plasmonics combines principles of topology and plasmonics to provide new methods for controlling light, analogous to topological edge states in photonics. However, designing such topological states remains challenging due to the complexity of the high-dimensional design space. We present a novel method that uses supervised, physics-informed deep learning and surrogate modeling to design topological devices for desired wavelengths. By embedding physical constraints in the neural network's training, our model efficiently explores the design space, significantly reducing simulation time. Additionally, we use nonplanar wavefront excitations to probe topologically protected plasmonic modes, making the design and training process nonlinear. Using this approach, we design a topological device with unidirectional edge modes in a ring resonator at specific operational frequencies. Our method reduces computational cost and time while maintaining high accuracy, highlighting the potential of combining machine learning and advanced techniques for photonic device innovation.

Stacking Engineering toward Giant Second Harmonic Generation in Twisted Graphene Superstructures.

The nonlinear optical response in graphene is finding increasing applications in nanophotonic devices. The activation and enhancement of second harmonic generation (SHG) in graphene, which is generally forbidden in monolayer and AB-stacked bilayer graphene due to their centrosymmetry, is of urgent need for nanophotonic applications. Here, we present a comprehensive study of SHG performance of twisted multilayer graphene structures based on stacking engineering. It is found that the modulation of in-plane and out-of-plane SHG susceptibility components by stacking few-layer graphene is essential in producing giant SHG response in twisted multilayer graphene. Giant SHG intensity in twisted multilayer graphene is observed, reaching nearly 10 times that of monolayer MoS2 under 1064 nm excitation, which significantly outperformed graphene structures reported to date. Our findings present a facile and effective approach to enhance SHG in graphene structures, showing promise for future application of graphene in second harmonic nanophotonic devices as well as prospects for the study of SHG among two-dimensional (2D) structures in general.

High performance nanophotonic logic device for performing plasmonic D and T flip flops with 161 Tb/s bit rate

High performance nanophotonic logic device for performing plasmonic D and T flip flops with 161 Tb/s bit rate

Raman scattering from silicon resonant Mie-voids

The influence of Mie resonances on optical scattering processes is one of the key aspects in nanophotonics. This work is devoted to the study of Raman scattering from silicon resonant Mievoids. The enhancement of the Raman scattering signal associated with the presence of multipole resonances in these structures is experimentally shown. The results demonstrate the dependence of the optical characteristics on the geometry of the samples and confirm the potential of using Mievoids in modern nanophotonic devices. The results of numerical simulation performed by the finite element method are in good agreement with the experimental reflectance spectra and help to understand the distribution of electromagnetic fields inside the nanocavities. This study opens up new possibilities for the practical use of these nanostructures in Raman spectroscopy and the development of high-precision optical devices.

Compact on-chip arbitrary ratio power splitters based on an inverse design method

Abstract Beam splitter (BS) is an important element for photonic integrated circuits (PICs). Conventional BSs designed by traditional approaches are too large to be suitable for PICs. An inverse design method which combines the adjoint method with the finite-difference frequency-domain method (FDFD) and the finite-difference time-domain method (FDTD) is proposed, in which the adjoint method is adopted to construct the structures while the FDFD is used to simulate the fields of the structures at the target wavelength, and the FDTD is used to study their fields and spectra at a wider wavelength range. And a series of compact Si-based arbitrary ratio power splitters (ARPSs) with splitting ratios (SRs) ranging from 1:1 to 10:1 on 2.5 μm × 2.5 μm substrates have been designed by this method. Their SRs fully match the design expectation accurately with total transmission efficiencies of more than 90% at the target wavelength of 1550 nm. Multi-channels BSs with 3:4:1 and 4:1:3:2 SRs have been designed by this method as well, and have good performance with footprints of 2.5 μm × 2.5 μm and 3.2 μm × 3.2 μm, respectively. Furthermore, the Si3N4-based ARPSs with footprints of 3.0 μm × 4.0 μm have been designed, and their performance met expectations also. The results of 2:1 and 3:1 Si3N4-based ARPSs have been shown that total transmission efficiencies are 88.14% and 91.48% at the center wavelength of 1400 nm. Benefiting from the high speed of FDFD, this method has high optimization efficiency. And all the results simulated by FDTD agree well with FDFD. It provides a robust means to construct compact ARPSs and other nanophotonic devices.

Multifunctional non-Hermitian metasurface: metalens and holograms.

Exceptional points (EPs) have been the subject of wide concern because of their unique physical properties and have produced many related applications. However, up to now, most non-Hermitian metasurfaces related to EPs focus on realizing a single function. It remains a challenge to integrate multiple functions into a single non-Hermitian metasurface while making it dynamically adjustable. In this work, we investigated how to combine the Pancharatnam-Berry (PB) phase and exceptional topological (ET) phase and used the polarization decoupling property of EPs to design and realize the integration of multiple functions on a metasurface with the assistance of vanadium dioxide (VO2). As an example in applications, the phase-only metalens and dual-channel holograms can be realized and switched by changing states of the VO2 and incident light polarization. This work will open a prospect for researching a multifunctional non-Hermitian metasurface and the design of switchable multifunctional nano-photonic devices.

Electrodeposition-Grown Mixed-Halide Inorganic Perovskite CsPbI3-xBrx Nanowires for Nanolaser Applications.

Exploring new low-cost and controllable synthesis methods for perovskite nanowires plays an important role in achieving their large-scale applications. However, there have been no studies on the synthesis of cesium lead halide nanowires using the electrodeposition method. In this study, the single-crystal mixed-halide W-CsPbI3-xBrx nanowires are first synthesized via a low-cost and controllable electrodeposition method. The growth process of the W-CsPbI3-xBrx nanowires is observed in situ by using a metallurgical microscope. It is found that the W-CsPbI3-xBrx nanowires are grown via the oriented attachment of B-CsPbI3-xBrx nanocubes. More importantly, the mixed-halide W-CsPbI3-xBrx nanowires can transform into single-crystal B-CsPbI3-xBrx nanowires at a moderate annealing temperature. The obtained B-CsPbI3-xBrx nanowires are applied to nanolasers, and two lasing peaks are observed at 679 and 675nm, with a threshold of 277.6µJcm-2. These results can promote the development of growth methods for perovskite nanomaterials, which can broaden the applicability of perovskite nanowires in integrated nanophotonic and optoelectronic devices.

Formation of vanadium dioxide nanocrystal arrays via post-growth annealing for stable and energy-efficient switches

The abrupt and reversible semiconductor-metal phase transition in vanadium dioxide nanocrystals has attracted considerable attention for potential applications in oxide electronics, including neuromorphic systems. This study presents a systematic investigation of post-growth annealing conditions for the formation of single VO2 M-phase nanocrystals arrays from VOx films synthesized by atomic layer deposition. The composition of the initial VOx films and the annealing parameters were found to significantly affect the morphology, phase composition and electrical properties of the obtained single nanocrystal arrays. Our results demonstrate that the formation of VO2 M-phase nanocrystal arrays occurs at annealing temperatures of 650 °C and above, irrespective of the initial film composition. More homogeneous in size nanocrystals are formed from initial VOx films with higher V+4 content. The structures with the initial V+4 content of 60 % annealed at 650 °C for 2 h demonstrates the resistive switching with an energy less than 150 fJ, and a total number of stable switching cycles more than 101⁰. Our results pave the way for the novel energy-efficient nanoelectronic and nanophotonic devices based on VO₂ nanoparticles.

Asymmetric steering of phonon polaritons based on bilayer metagratings.

Polaritons in van der Waals (vdWs) materials enable light-matter interactions at the nanoscale. Polaritonic manipulation is of significance in fundamental physics and various promising nanophotonic applications. Here we study the asymmetric steering of phonon polaritons (PhPs) in hexagonal boron nitride (hBN) based on numerical simulations. Empowered by metagratings, the deflection angle of PhPs can be controlled. Furthermore, by employing the combination of metagrating and uniform grating, asymmetric steering of PhPs not only can be achieved but also can be switched to symmetric steering by tuning the period of grating. More intriguingly, an asymmetric dual-functional polaritonic metalens with the function of convergence/divergence for forward/backward incident PhPs is demonstrated. Our work provides insights into the manipulation of polaritons in vdWs materials and a promising strategy for developing nanophotonic devices.

Numerical investigation on the polarization-dependent light extraction of 275-nm AlGaN based nanowire with bowtie antenna array or passivation layer

Abstract The low light extraction efficiency (LEE) is one of the major factors hindering the application of AlGaN based deep ultraviolet (DUV) light-emitting diodes (LEDs). Here we investigate the LEE of AlGaN based nanowire (NW) DUV LEDs emitting at 275 nm for bare NW, NW integrated with aluminum (Al) bowtie antenna array, and NW with passivation layer under transverse-electric (TE) and transverse-magnetic (TM) polarization. It is observed that by integrating plasmonic Al bowtie antenna array with AlGaN based NW, the LEE up to 83% and 74% can be achieved under TE and TM polarization. In addition, the effect of the three different passivation layer SiO2, SiNx and AlN on the LEE of AlGaN based NW is also analysed, the results suggests that SiO2, which has smaller refractive index than NW core, could extract more photons from the NW and lead to large enhancement of LEE. For SiNx and AlN passivation layer, which has refractive index similar to the NW core, have strong coupling with the NW core, when the thickness of passivation layer satisfy resonance coupling conditions, the LEE could be achieved more than 80% for both TE and TM polarization. These integrated NW/antenna array and NW with passivation layer system can provide guidelines for designing other nano-photonic devices.

Broad Range Tuning of InAs Quantum Dot Emission for Nanophotonic Devices in the Telecommunication Bands.

InAs semiconductor quantum dots (QDs) emitting in the near-infrared are promising platforms for on-demand single-photon sources and spin-photon interfaces. However, the realization of quantum-photonic nanodevices emitting in the telecom windows with similar performance remains an open challenge. In particular, nanophotonic devices incorporating quantum light emitting diodes in the telecom C-band based on GaAs substrates are still lacking due to the relaxation of the lattice constant along the InGaAs graded layer which makes the implementation of electrically contacted devices challenging. Here, we report an optimized heterostructure design for QDs emitting in the telecom O- and C-bands grown by means of molecular beam epitaxy. The InAs QDs are embedded in mostly relaxed InGaAs matrices with fixed indium content grown on top of compositionally graded InGaAs buffers. Reciprocal space maps of the indium profiles and optical absorption spectra are used to optimize In0.22Ga0.78As and In0.30Ga0.70As matrices, accounting for the chosen indium grading profile. This approach results in a tunable QD photoluminescence (PL) emission from 1200 up to 1600 nm. Power and polarization dependent micro-PL measurements performed at 4 K reveal exciton-biexciton complexes from quantum dots emitting in the telecom O- and C-bands. The presented study establishes a flexible platform that can be an essential component for advanced photonic devices based on InAs/GaAs that serve as building blocks for future quantum networks.

Enhanced ultrafast nonlinear optical response in Bi-doped ZnO glass-ceramics

Incorporating plasmonic nanocrystals (NCs) into solid-state electronics is an important step toward realizing nanophotonic devices. However, only a few noble metal-based systems can directly precipitate plasmonic NCs in a solid transparent medium. In contrast, plasmonic metal oxide NCs can exhibit a plasmonic response at infrared energies that noble metal-based systems cannot reach due to their high carrier concentration. Here we demonstrate the precipitation of bismuth-doped ZnO (BZO) NCs in an aluminosilicate glass matrix, demonstrating a robust near-infrared (NIR)-localized surface plasmon resonance. Benefited from the strong resonant absorption by the plasmonic BZO NCs, these glass ceramics (GCs) exhibit enhanced ultrafast nonlinear optical (NLO) response across the NIR optical communication bands, which might be promising for applications such as optical limiting, optical switching, optical modulation, and NIR-nanophotonic devices.

An overview on plasmon-enhanced photoluminescence via metallic nanoantennas

Abstract In the realm of nanotechnology, the integration of quantum emitters with plasmonic nanostructures has emerged as an innovative pathway for applications in quantum technologies, sensing, and imaging. This research paper provides a comprehensive exploration of the photoluminescence enhancement induced by the interaction between quantum emitters and tailored nanostructure configurations. Four canonical nanoantennas (spheres, rods, disks, and crescents) are systematically investigated theoretically in three distinct configurations (single, gap, and nanoparticle-on-mirror nanoantennas), as a representative selection of the most fundamental and commonly studied structures and arrangements. A detailed analysis reveals that the rod gap nanoantenna configuration achieves the largest photoluminescence enhancement factor, of up to three orders of magnitude. The study presented here provides insights for the strategic design of plasmonic nanoantennas in the visible and near-IR spectral range, offering a roadmap for these structures to meet specific requirements in plasmon-enhanced fluorescence. Key properties such as the excitation rate, the quantum yield, the enhanced emitted power, or the directionality of the emission are thoroughly reviewed. The results of this overview contribute not only to the fundamental understanding of plasmon-enhanced emission of quantum emitters but also set the basis for the development of advanced nanophotonic devices with enhanced functionalities.

Phase-transition-driven polarization and intensity modulation in GST metasurfaces

Metasurfaces, especially those employing phase-change materials (PCMs) like Ge2Sb2Te5 (GST), have revolutionized subwavelength light manipulation, promising enhanced reconfigurability in nanophotonic devices. Despite their potential, the limited tunability in terms of states and dimensions has hindered broader applications. Here, we propose a GST-based reconfigurable metasurface capable of simultaneously modulating transmissivity, phase, and polarization. Leveraging the full states of phase transitions from amorphous to crystalline states, the metasurface can elaborately adjust the focal spot's intensity based on amplitude and phase joint regulation. Our design exploits the refractive index shifts during phase transition and phase modulation discrepancies between the two axes of composite nanorods, allowing for dynamic transitions across three polarization states, with each state's transmittance decreasing sequentially. Furthermore, we demonstrate the metasurface's ability to transition from multichannel vectorial holography to near-perfect absorption by eliminating the limitations imposed by intermediate phase states. These advancements represent a new way to multi-dimensional, multi-state tunable photonic systems, broadening the scope for novel optical devices.

Comparative analysis of theories accounting for quantum effects in plasmonic nanoparticles

Understanding and accounting for quantum effects in nanoplasmonics is essential for accurate modeling and design of nanophotonic devices. In this paper, we investigate the influence of such quantum effects as spatial nonlocality and splitting of the wave function of conduction electrons near the surface of plasmonic nanoparticles on the extinction cross-section and the field enhancement factor. We apply the theory of generalized nonlocal optical response (GNOR) to describe the spatial nonlocality of noble metal particles. To consider the behavior of electrons near the metal–dielectric interface, mesoscopic boundary conditions are used, including the surface response functions (SRF) - the Feibelman parameters. We use the discrete source method (DSM), allowing for numerical analysis of the scattering problems taking into account quantum effects in the frame of both theories. The application of both GNOR and SRF approaches leads to a decrease in the amplitude of the plasmon resonance compared to the classical Maxwell theory and its shift to the shorter wavelength region (blue shift). The simulation results demonstrate significant differences between the two theories explaining the quantum effects arising in non-spherical plasmonic nanoparticles located in a dense environment. Specifically, compared with GNOR theory, SRF predicts a larger field enhancement. We found that quantum nonlocal effects are more significant for the enhancement factor at the particle surface than for the extinction cross-section. In addition, it was discovered that a denser environment leads to a significant increase in the blue shift of the plasmonic peak.

Improved inverse design of polarization splitter with advanced Bayesian optimization

As many silicon nanophotonic devices are polarization-dependent, a polarization beam splitter that divides TE and TM modes is an essential component for photonic integrated circuits. Various structures have been proposed for polarization splitters, but it is still challenging to simultaneously achieve low insertion loss, high extinction ratio, compact size and simplicity of fabrication. In this paper, we combine new machine learning methods with the principle of multimode interference to propose a novel design for a polarization beam splitter. Our design has low insertion loss (-0.17dB/-0.42dB) and high extinction ratio (-23.1dB/-23.4dB) at the central wavelength of 1550nm for TE/TM modes, with compact size of 2×19μm2 and fabrication constraints strictly satisfied. Furthermore, our design is a standard 220nm-thick single-layer device for the silicon-on-insulator platform, without any auxiliary structures, making it easy for fabrication. Since our design cannot be optimized by the most commonly used methods, we adopt several specialized techniques to Bayesian optimization for inverse design. In this paper, we also share these skills which are simple but effective, possible to solve much more complicated design problems than others.

Tailoring Second Harmonic Generation via Strong Coupling in a One‐Dimensional Photonic Crystal Heterostructure

Controlling harmonic generation is crucial for nonlinear optics and nanophotonic devices. Herein, a 1D photonic crystal heterostructure is theoretically proposed comprising a metal film, a lithium niobate layer, and a distributed Bragg reflector with a defect layer. The Tamm state and the defect state for dual‐band second‐harmonic generation (SHG) enhancement simultaneously are numerically investigated. Finite‐element method simulations indicate that SHG efficiencies based on Tamm plasmons and the defect state are 6.85 × 10−6 and 3.28 × 10−4, respectively. Intriguingly, the strong coupling between the defect state and Tamm plasmons enables spatial energy exchange, leading to the SHG switching between them. In the strong coupling region with Rabi splitting energy up to 5.5 meV, the SHG conversion efficiency reaching 5 × 10−5 is observed for both two new hybridized states. During the entire anticrossing Rabi splitting process, the SHG efficiency difference between two resonances can be modulated by up to two orders of magnitude. The coupling strength between two resonances is adjusted by varying the position of the defect layer. Simulation results are consistent with the coupled oscillator model. This work not only offers a platform for studying nonlinear frequency conversion but also establishes a new method of using strong coupling to tailor SHG.

Probing plexciton emission from 2D materials on gold nanotrenches

Probing strongly coupled quasiparticle excitations at their intrinsic length scales offers unique insights into their properties and facilitates the design of devices with novel functionalities. In this work, we investigate the formation and emission characteristics of plexcitons, arising from the interaction between surface plasmons in narrow gold nanotrenches and excitons in monolayer WSe2. We study this strong plasmon–exciton coupling in both the far-field and the near-field. Specifically, we observe a Rabi splitting in the far-field reflection spectra of about 80 meV under ambient conditions, consistent with our theoretical modeling. Using a custom-designed near-field probe, we find that plexciton emission originates predominantly from the lower-frequency branch, which we can directly probe and map its local field distribution. We precisely determine the plexcitonʼs spatial extension, similar to the trench width, with nanometric precision by collecting spectra at controlled probe locations. Our work opens exciting prospects for nanoscale mapping and engineering of plexcitons in complex nanostructures with potential applications in nanophotonic devices, optoelectronics, and quantum electrodynamics in nanoscale cavities.

In Situ Solid-State Dewetting of Ag-Au-Pd Alloy: From Macro- to Nanoscale.

Metal alloy nanostructures represent a promising platform for next-generation nanophotonic devices, surpassing the limitations of pure metals by offering additional "buttons" for tailoring their optical properties by compositional variations. While alloyed nanoparticles hold great potential, their scalability and underexplored optical behavior still limit their application. Here, we establish a systematic approach to quantifying the unique optical behavior of the AgAuPd ternary system while providing a direct comparison with its pure constituent metals. Computationally, we analyze their electronic structure and uncover the transition of Pd d states to Pd/Ag hybridized s states in the bulk form, explaining the similar optical properties observed between Pd and AgAuPd. Experimentally, we fabricate pure metal and fully alloyed nanoparticles through solid-state dewetting, a scalable method. During the process, we trace the optical transition in the systems from the initial thin film stage to the final nanoparticle stage with in situ ellipsometry. We reveal the interplay between optical properties influenced by chemical interdiffusion and localized surface plasmon resonance arising from morphological changes with ex situ surface characterizations. Additionally, we analytically implement a metallic layer derived from the ternary system in a trilayer device, resulting in a single-time and irreversible color filter, to demonstrate an application encompassing a lithography-free and cost-effective route for nanophotonic devices.