Strong Light-matter Interaction Research Articles

High-Responsivity Multiband and Polarization-Sensitive Photodetector Based on the TiS3/MoS2 Heterojunction.

Two-dimensional (2D) material photodetectors have received considerable attention in optoelectronics as a result of their extraordinary properties, such as passivated surfaces, strong light-matter interactions, and broad spectral responses. However, single 2D material photodetectors still suffer from low responsivity, large dark current, and long response time as a result of their atomic-level thickness, large binding energy, and susceptibility to defects. Here, a transition metal trichalcogenide TiS3 with excellent photoelectric characteristics, including a direct bandgap (1.1 eV), high mobility, high air stability, and anisotropy, is selected to construct a type-II heterojunction with few-layer MoS2, aiming to improve the performance of 2D photodetectors. An ultrahigh photoresponsivity of the TiS3/MoS2 heterojunction of 48 666 A/W at 365 nm, 20 000 A/W at 625 nm, and 251 A/W at 850 nm is achieved under light-emitting diode illumination. The response time and dark current are 2 and 3 orders of magnitude lower than those of the current TiS3 photodetector with the highest photoresponsivity (2500 A/W), respectively. Furthermore, polarized four-wave mixing spectroscopy and polarized photocurrent measurements verify its polarization-sensitive characteristics. This work confirms the excellent potential of TiS3/MoS2 heterojunctions for air-stable, high-performance, polarization-sensitive, and multiband photodetectors, and the excellent type-II TiS3/MoS2 heterojunction system may accelerate the design and fabrication of other 2D functional devices.

Monolithically integrated mid-infrared sensor with a millimeter-scale sensing range.

On-chip sensors based on quantum cascade laser technology are attracting broad attention because of their extreme compactness and abundant absorption fingerprints in the mid-infrared wavelength range. Recent continuous wave operation microcavity quantum cascade lasers are well suited for high-density optoelectronic integration because their volumes are small and thresholds are low. In this experimental work, we demonstrate a monolithically integrated sensor comprising a notched elliptical resonator as transmitter, a quantum cascade detector as receiver, and a surface plasmon structure as light-sensing waveguide. The sensor structure is designed to exploit the highly unidirectional lasing properties of the notched elliptical resonator to increase the optical absorption path length. Combined with the evanescent nature of the dielectric loaded surface plasmon polariton waveguides, the structure also ensures a strong light-matter interactions. The sensing transmission distance obtained is approximately 1.16 mm, which is about one order of magnitude improvement over the traditional Fabry-Perot waveguide. This sensor opens new opportunities for long-range and high-sensitivity on-chip gas sensing and spectroscopy.

Multiple dipolar resonant silicon-based metamaterials for high-performance optical switching and sensing.

Dielectric nanostructures reinforcing light-matter interactions by manipulating geometric parameters have a sound momentum in optoelectronic applications. Here, we construct and numerically demonstrate a new platform with multiple dipolar resonant behaviors or impressive switching operation and optical sensing with a high sensitivity and figure of merit (FOM) via the graphene-silicon combined metamaterials. Ultra-sharp resonances are excited by introducing broken symmetry in such all-dielectric metamaterials (ADMs) consisting of two silicon trapezoidal bodies on a silica substrate. By analyzing the distributions of the electromagnetic fields and current densities, we find that two types of multipole modes have been excited to support multiple ultra-narrowband resonances in the near-infrared range. The influence of geometers, such as period, thickness, asymmetry parameters, and polarization angle of the incident light, has also been studied. In addition, by adjusting the Fermi levels of graphene, we realize a 95% amplitude modulation efficiency, which manifests perfect capacity for an optical switch. According to the calculated results, the highest sensitivity can reach 447.5 nm/RIU and a large FOM is also up to 1173 RIU-1. This platform not only introduces new insight onto the achievement of high-quality ultra-sharp resonant responses but also offers a distinct possibility for the further development of high-quality related applications in optical sensors, notch filtering, strong light-matter interactions including the nonlinear optics, and multispectral optoelectronics.

Resonant toroidal metasurface as a platform for thin-film and biomaterial sensing.

Toroidal resonances with weak free-space coupling have recently garnered significant research attraction toward the realization of advanced photonic devices. As a natural consequence of weak free-space coupling, toroidal resonances generally possess a high quality factor with low radiative losses. Because of these backgrounds, we have experimentally studied thin-film sensing utilizing toroidal resonance in a subwavelength planar metasurface, whose unit cell consists of near-field coupled asymmetric dual gap split-ring resonators (ASRRs). These ASRRs are placed in a mirrored configuration within the unit cell. The near-field coupled ASRRs support circulating surface currents in both resonators with opposite phases, resulting in excitation of the toroidal mode. In such a way, excited toroidal resonance can support strong light-matter interactions with external materials (analytes to be detected) placed on top of the metasurface. Further, our study reveals a sensitivity of 30GHz/RIU while sensing AZ4533 photoresist film utilizing the toroidal mode. Such detection of thin films can be highly beneficial for the development of sensing devices for various biomolecules and dielectric materials that can be spin coated or drop casted on metasurfaces. Hence, the toroidal mode is further theoretically explored towards the detection of avian influenza virus subtypes, namely, H5N2 and H9N2. Our study reveals 6 and 9GHz of frequency redshifts for H5N2 and H9N2, respectively, in comparison to the bare sample. Therefore, this work shows that toroidal metasurfaces can be a useful platform to sense thin films of various materials including biomaterials.

(Invited, Digital Presentation) Excited State Properties of Low-Dimensional Materials: Insight By Ab-Initio DFT + Mbpt Simulations

The use of emerging low-dimensional materials in technological applications presupposes a detailed knowledge of their chemical and physical properties. In this context ab-initio theoretical methods and simulations are playing a fundamental role.Here I aim to show how the use of parameter-free atomistic simulations can contribute to improve the microscopic understanding of the opto-electronic properties of nanomaterials and to predict new ones. I will show how ab-initio DFT and post-DFT (GW and BSE) calculations, based on Many-Body Perturbation Theory (MBPT), provide a very useful scheme to study i) giant electronic band-gaps renormalization due to low dielectric screening and large quantum confinement ii) strong light-matter interaction iii) fine structure of strongly bound excitons. iv) the influence of electron-phonon interaction on the electronic and optical spectra, v) how doping, molecular functionalization or strain can tune their opto-electronic properties. Main focus will be on different semiconducting 2D materials discovered after graphene, but other dimensionality examples will be discussed.

CMOS-compatible compact optical isolator based on space-time modulated coupled resonators.

This work shows how phase-shifted time-modulations applied to two or more near-field coupled resonators can be engineered to achieve magnet-free optical isolation in a compact footprint. Because of the strong light-matter interaction afforded by high quality factor resonant cavities, only modest modulation amplitudes are required. A coupled mode theory model is developed which is subject to simulated annealing to optimize device performance. Then it is shown via finite-difference time-domain simulation how the device may be implemented in a one dimensional photonic crystal geometry etched in a silicon ridge waveguide. These devices can be implemented in native silicon with standard electrical contacts thereby maintaining CMOS-compatible fabrication without the need for additional specialized materials. Isolation ratios of over 40 dB with insertion loss less than 1 dB using modulation frequencies under 25 GHz are achievable in this device platform.

Visible light metasurface for adaptive photodetection

Semiconductor-based sub-wavelength metasurfaces are promising device platforms for the realization of optically thick and electrically thin photodetectors. Strong light–matter interactions in ultrathin film regions provide an opportunity to achieve near-unity absorption in dimensions comparable with carrier diffusion length and this, in turn, leads to an efficient collection of photogenerated carriers. Moreover, the use of phase change materials can provide real-time active tuning of optical responses of metasurface-based devices. In the first part of this paper, a tunable color filtering device is demonstrated using a metasurface design made of sub-wavelength antimony trisulphide (Sb2S3) grating placed on top of a continuous silver layer. Four distinct optical states can be acquired upon (a) the changes in the incident light polarization and (b) the phase transitions of Sb2S3. Numerical simulations and theoretical modeling data show that Fabry–Perot resonances are the driving phenomena when the proposed design is normally illuminated by an electromagnetic field with transverse electric polarization. In contrast, surface plasmon resonances are excited in transverse magnetic polarization. Furthermore, it is shown that the resonance wavelengths of the proposed design can be dynamically tuned using the geometrical parameters. Later, in the second part of the paper, adaptive photodetection is designed by integrating a nm Sb2S3 layer as a collection layer into the structure. The proposed metasurface design provides light–matter interaction in the Sb2S3 layer and maximizes the photogenerated carriers’ collection efficiency. The optically thick and electrically thin adaptive photodetection offers an opportunity to design efficient active optoelectronic and photonic devices.

SiO2 passivated TaS2 saturable absorber mirrors for the ultrafast pulse generation

Since its inception as the cornerstone of the ultrafast pulse laser, semiconductor saturable absorber mirrors (SESAMs) have attracted considerable interest. Meanwhile, low-dimensional (LD) materials based saturable absorbers (SAs) are gaining popularity in pulsed laser applications due to their high nonlinearity, strong light-matter interaction, and low cost. Here, high-quality LD-SAs have been created by transferring 2 H-TaS 2 onto gold mirrors and covered with plasma-enhanced chemical vapor deposition (PECVD) SiO 2 layers. The non-linear transmission of SiO 2 passivated TaS 2 -SAM was measured using a balanced dual-detector technology. The modulation depth and saturated intensity were ~8.4% and 0.86 MW·cm −2 . Based on the SiO 2 passivated TaS 2 -SAM, Q-switched and mode-locked Erbium-doped (Er 3+ -doped) fiber pulse lasers have been successfully achieved. Stable soliton pulses are obtained in erbium-doped fiber lasers (EDFLs) with pulse width of 1.8 ps, repetition rate of 3.4 MHz and a center wavelength of 1560.6 nm. Moreover, the mode-locking laser exhibited long-term stability with high signal-to-noise ratio of 63 dB. This study serves as a standard for low-dimensional materials research in photonics applications, and the results reveal that TaS 2 -SAM has a wide range of applications in multifunctional all-fiber lasers.

Topological insulator nanoparticles for strong light-matter interaction in the terahertz regime.

We study the spontaneous emission (SPEM) for a quantum emitter (QUEM) near a topological insulator Bi2Se3 nanosphere. We calculate numerically the QUEM Purcell factor near nanospheres of radii between 40 nm and 100 nm, with and without taking into account the topologically protected delocalized states at the surface of the nanosphere. We find exceptionally large Purcell factors up to 1010 at distances between the QUEM and the nanosphere as large as half its radius in the terahertz regime. By computing the SPEM dynamics for a QUEM with transition frequencies in the terahertz and free-space decay rates in the nanosecond to millisecond range, we observe intense reversible dynamics, as well as population trapping effects. This work demonstrates that a Bi2Se3 nanosphere provides the conditions for strong light-matter interaction at the nanoscale in the terahertz regime.

Conformal optical black hole for cavity

Whispering-gallery-mode (WGM) cavity is important for exploring physics of strong light-matter interaction. Yet it suffers from the notorious radiation loss universally due to the light tunneling effect through the curved boundary. In this work, we propose and demonstrate an optical black hole (OBH) cavity based on transformation optics. The radiation loss of all WGMs in the ideal OBH cavity is completely inhibited by an infinite wide potential barrier. Besides, the WGM field in the OBH cladding is revealed to follow 1/r^alpha decay rule based on conformal mapping, which is fundamentally different from the conventional Hankel-function distributions in a homogeneous cavity. Experimentally, a truncated OBH cavity is achieved based on the effective medium theory, and both the Q-factor enhancement and tightly confined WGM fields are measured in the microwave spectra which agree well with the theoretical results. The circular OBH cavity is further applied to the arbitrary-shaped cavities including single-core and multi-core structures with high-Q factor via the conformal mapping. The OBH cavity design strategy can be generalized to resonant modes of various wave systems, such as acoustic and elastic waves, and finds applications in energy harvesting and optoelectronics.

Nonlinear focusing of supercontinuum driven by intense mid-infrared pulses in gas-filled capillaries.

Strong mid-infrared light-matter interactions have attracted extensive attention as they open up new frontiers in nonlinear optics. Here we observe through simulations a novel, to the best of our knowledge, aspect of mid-infrared pulse dynamics in a high-pressure gas-filled capillary, where a pulse with a power well below the critical power for Kerr self-focusing undergoes an astonishing increase of the peak intensity following an extremely efficient spectral broadening. This intensity enhancement is attributed to the Kerr-induced focusing of the supercontinuum. Our study provides an interesting perspective for controlling the laser intensity with possible applications in nonlinear light conversion driven by mid-infrared pulses.

Plasmon resonance of gold and silver nanoparticle arrays in the Kretschmann (attenuated total reflectance) vs. direct incidence configuration

While the behaviour of plasmonic solid thin films in the Kretschmann (also known as Attenuated Total Reflection, ATR) configuration is well-understood, the use of discrete nanoparticle arrays in this optical configuration is not thoroughly explored. It is important to do so, since close packed plasmonic nanoparticle arrays exhibit exceptionally strong light-matter interactions by plasmonic coupling. The present work elucidates the optical properties of plasmonic Au and Ag nanoparticle arrays in both the direct normal incidence and Kretschmann configuration by numerical models, that are validated experimentally. First, hexagonal close packed Au and Ag nanoparticle films/arrays are obtained by air–liquid interfacial assembly. The numerical models for the rigorous solution of the Maxwell’s equations are validated using experimental optical spectra of these films before systematically investigating various parameters. The individual far-field/near-field optical properties, as well as the plasmon relaxation mechanism of the nanoparticles, vary strongly as the packing density of the array increases. In the Kretschmann configuration, the evanescent fields arising from p- and s-polarized (or TM and TE polarized) incidence have different directional components. The local evanescent field intensity and direction depends on the polarization, angle of incidence and the wavelength of incidence. These factors in the Kretschmann configuration give rise to interesting far-field as well as near-field optical properties. Overall, it is shown that plasmonic nanoparticle arrays in the Kretschmann configuration facilitate strong broadband absorptance without transmission losses, and strong near-field enhancement. The results reported herein elucidate the optical properties of self-assembled nanoparticle films, pinpointing the ideal conditions under which the normal and the Kretschmann configuration can be exploited in multiple light-driven applications.

Optical Transparency Induced by a Largely Purcell Enhanced Quantum Dot in a Polarization-Degenerate Cavity.

Optically active spin systems coupled to photonic cavities with high cooperativity can generate strong light-matter interactions, a key ingredient in quantum networks. However, obtaining high cooperativities for quantum information processing often involves the use of photonic crystal cavities that feature a poor optical access from the free space, especially to circularly polarized light required for the coherent control of the spin. Here, we demonstrate coupling with a cooperativity as high as 8 of an InAs/GaAs quantum dot to a fabricated bullseye cavity that provides nearly degenerate and Gaussian polarization modes for efficient optical accessing. We observe spontaneous emission lifetimes of the quantum dot as short as 80 ps (an ∼15 Purcell enhancement) and a ∼80% transparency of light reflected from the cavity. Leveraging the induced transparency for photon switching while coherently controlling the quantum dot spin could contribute to ongoing efforts of establishing quantum networks.

Synergistic effect of hafnium doping in tin diselenide for enhanced photodetection application

For long, photo-sensitive materials of transition metal dichalcogenides (TMDCs) have been explored in the semiconductor industry. TMDCs have superior environmental stability, apart from their strong light-matter interaction. Although Hafnium-based semiconductors capture great interest due to their high carrier mobility at room temperature, their optoelectronic applications are yet to be explored. Herein, we demonstrate the growth of large size HfxSn1-xSe2 (x = 0, 0.05, 0.1, 0.15, 0.2) single crystals by direct vapor transport (DVT) technique and optimized photodetection application. Grown crystals have a highly crystalline nature, attributing to the substitutional doping of Hf4+ on Sn4+-sites. With optimized stoichiometry and improved crystallinity, 5% Hf doped SnSe2 shows the superior photoresponse with the maximum photocurrent 198.28 μA under 120 mW/cm2 blue light intensity. The detector shows photoresponsivity of 16.52 mA/W and specific detectivity 19.44 × 109 Jones owing to the highest crystallite size for 5% HF doped SnSe2. This excellent result shows promising application of HfxSn1-xSe2 (x = 0, 0.05, 0.1, 0.15, 0.2) crystals as high-performance photodetector by improved crystalline nature.

Strong light-matter interaction in hollow-core microfiber for multiplex sensing of environmental hazards

Hollow-core fibers with special micro-geometry have been heralded for years as a supreme medium for data transmission, quantum communications and laser power delivery, owing to their low loss in the air-guiding structure. The recent advances of non-touching hollow core anti-resonant fiber (HARF) have further minimized the loss and improved the modal properties. Here we exploit biochemical sensing performance of HARF. We address hybridization of state-of-the-art HARF with graphene oxide (GO) to achieve strong light-matter interaction and enable ultrasensitive and simultaneous quantification of multiple hazardous antibiotics in environmental samples. The GO-HARF shows a strict light confinement in the core region with 8 dB/km attenuation at 600 nm wavelength via numerical simulation. The broadband transmission (400–1000 nm) of GO-HARF allows simultaneous fluorescence signal acquisition at multiple wavelengths. The operating principle relies on detecting dose-dependent fluorescence changes in GO-HARF when an antibiotics complex is streamed through the fiber channel. Over three-orders-of-magnitude enhancement of sensitivity is achieved with the GO-HARF sensor compared with the limit of detection (LoD) of a microplate reader. GO-HARF offers a unique opportunity to measure picomolar analytes at multiplexed wavelengths in the visible spectral range, holding great potential for fast-response, ultrasensitive and low-cost biomedical analyses.

Polarization-independent tunable terahertz slow light with electromagnetically induced transparency metasurface

Tunable slow light systems have gained much interests recently due to their efficient control of strong light–matter interactions as well as their huge potential for realizing tunable device applications. Here, a dynamically tunable polarization independent slow light system is experimentally demonstrated via electromagnetically induced transparency (EIT) in a terahertz (THz) metasurface constituted by plus and dimer-shaped resonators. Optical pump-power dependent THz transmissions through the metasurface samples are studied using the optical pump THz probe technique. Under various photoexcitations, the EIT spectra undergo significant modulations in terms of its resonance line shapes (amplitude and intensity contrast) leading to dynamic tailoring of the slow light characteristics. Group delay and delay bandwidth product values are modulated from 0.915 ps to 0.42 ps and 0.059 to 0.025 as the pump fluence increases from 0 to 62.5 nJ cm−2. This results in tunable slow THz light with group velocities ranging from 2.18 × 105 m s−1 to 4.76 × 105 m s−1, almost 54% change in group velocity. The observed tuning is attributed to the photo-induced modifications of the optoelectronic properties of the substrate layer. The demonstrated slow light scheme can provide opportunities for realizing dynamically tunable slow light devices, delay lines, and other ultrafast devices for THz domain.

Wavefunction embedding for molecular polaritons.

Polaritonic chemistry relies on the strong light-matter interaction phenomena for altering the chemical reaction rates inside optical cavities. To explain and understand these processes, the development of reliable theoretical models is essential. While computationally efficient quantum electrodynamics self-consistent field (QED-SCF) methods, such as quantum electrodynamics density functional theory, need accurate functionals, quantum electrodynamics coupled cluster (QED-CC) methods provide a systematic increase in accuracy but at much greater cost. To overcome this computational bottleneck, herein we introduce and develop the QED-CC-in-QED-SCF projection-based embedding method that inherits all the favorable properties from the two worlds: computational efficiency and accuracy. The performance of the embedding method is assessed by studying some prototypical but relevant reactions, such as methyl transfer reaction, proton transfer reaction, and protonation reaction, in a complex environment. The results obtained with the new embedding method are in excellent agreement with more expensive QED-CC results. The analysis performed on these reactions indicates that the electron-photon correlation effects are local in nature and that only a small region should be treated at the QED-CC level for capturing important effects due to cavity. This work sets the stage for future developments of polaritonic quantum chemistry methods and will serve as a guideline for the development of other polaritonic embedding models.

Inverse design of broadband, strongly-coupled plexcitonic nonlinear metasurfaces

Hybrid photonic structures of plasmonic metasurfaces coupled to atomically thin semiconductors have emerged as a versatile platform for strong light–matter interaction, supporting both strong coupling and parametric nonlinearities. However, designing optimized nonlinear hybrid metasurfaces is a complex task, as the multiple parameters’ contribution to the nonlinear response is elusive. Here we present a simple yet powerful strategy for maximizing the nonlinear response of the hybrid structures based on evolutionary inverse design of the metasurface’s near-field enhancement around the excitonic frequency. We show that the strong coupling greatly enhances the nonlinear signal, and that its magnitude is mainly determined by the Rabi splitting, making it robust to geometrical variations of the metasurface. Furthermore, the large Rabi splitting attained by these hybrid structures enables broadband operation over the frequencies of the hybridized modes. Our results constitute a significant step toward achieving flexible nonlinear control, which can benefit applications in nonlinear frequency conversion, all-optical switching, and phase-controlled nonlinear metasurfaces.

Epsilon-near-zero substrate-enabled strong coupling between molecular vibrations and mid-infrared plasmons.

As the strong light-matter interaction between molecular vibrations and mid-infrared optical resonant modes, vibrational strong coupling (VSC) has the potential to modify the intrinsic chemistry of molecules, leading to the control of ground-state chemical reactions. Here, by using quartz as an epsilon-near-zero (ENZ) substrate, we have realized VSC between organic molecular vibrations and mid-infrared plasmons on metallic antennas. The ENZ substrate enables sharp mid-infrared plasmonic resonances (Q factor ∼50) which efficiently couple to the molecular vibrations of polymethyl methacrylate (PMMA) molecules with prominent mode splitting. The coupling strength is proportional to the square root of the thickness of the PMMA layer and reaches the VSC regime with a thickness of ∼300 nm. The coupling strength also depends on the polarization of the incident light, illustrating an additional way to control the molecule-plasmon coupling. Our findings provide a new, to the best of our knowledge, possibility to realize VSC with metallic antennas and pave the way to increase the sensitivity of molecular vibrational spectroscopy.

Optically Resonant Bulk Heterojunction PbS Quantum Dot Solar Cell.

We design an optically resonant bulk heterojunction solar cell to study optoelectronic properties of nanostructured p–n junctions. The nanostructures yield strong light–matter interaction as well as distinct charge-carrier extraction behavior, which together improve the overall power conversion efficiency. We demonstrate high-resolution substrate conformal soft-imprint lithography technology in combination with state-of-the art ZnO nanoparticles to create a nanohole template in an electron transport layer. The nanoholes are infiltrated with PbS quantum dots (QDs) to form a nanopatterned depleted heterojunction. Optical simulations show that the absorption per unit volume in the cylindrical QD absorber layer is enhanced by 19.5% compared to a planar reference. This is achieved for a square array of QD nanopillars of 330 nm height and 320 nm diameter, with a pitch of 500 nm on top of a residual QD layer of 70 nm, surrounded by ZnO. Electronic simulations show that the patterning results in a current gain of 3.2 mA/cm2 and a slight gain in voltage, yielding an efficiency gain of 0.4%. Our simulations further show that the fill factor is highly sensitive to the patterned structure. This is explained by the electric field strength varying strongly across the patterned absorber. We outline a path toward further optimized optically resonant nanopattern geometries with enhanced carrier collection properties. We demonstrate a 0.74 mA/cm2 current gain for a patterned cell compared to a planar cell in experiments, owing to a much improved infrared response, as predicted by our simulations.