Beam steering technology is crucial for radio frequency and infrared telecommunication signal processing. Microelectromechanical systems (MEMS) are typically used for beam steering in infrared optics-based fields but have slow operational speeds. An alternative solution is to use tunable metasurfaces. Since graphene has gate-tunable optical properties, it is widely used in electrically tunable optical devices due to ultrathin physical thickness. We propose a tunable metasurface structure using graphene in a metal gap structure that can exhibit a fast-operating speed through bias control. The proposed structure can change beam steering and can focus immediately by controlling the Fermi energy distribution on the metasurface, thus overcoming the limitations of MEMS. The operation is numerically demonstrated through finite element method simulations.
Wavelength-scale lasers provide promising applications through low power consumption requiring for optical cavities with increased quality factors. Cavity radiative losses can be suppressed strongly in the regime of optical bound states in the continuum; however, a finite size of the resonator limits the performance of bound states in the continuum as cavity modes for active nanophotonic devices. Here, we employ the concept of a supercavity mode created by merging symmetry-protected and accidental bound states in the continuum in the momentum space, and realize an efficient laser based on a finite-size cavity with a small footprint. We trace the evolution of lasing properties before and after the merging point by varying the lattice spacing, and we reveal this laser demonstrates the significantly reduced threshold, substantially increased quality factor, and shrunken far-field images. Our results provide a route for nanolasers with reduced out-of-plane losses in finite-size active nanodevices and improved lasing characteristics.
High quality factor and small mode volume in nanocavities enable the demonstration of efficient nanophotonic devices with low power consumption, strong nonlinearity, and high modulation speed, due to the strong light-matter interaction. In this review, we focus on recent state-of-the-art nanocavities and their applications. We introduce single nanocavities including semiconductor nanowires, plasmonic cavities, and nanostructures based on quasi-bound states in the continuum (quasi-BIC), for laser, photovoltaic, and nonlinear applications. In addition, nanocavity arrays with unique feedback mechanisms, including BIC cavities, parity-time symmetry coupled cavities, and photonic topological cavities, are introduced for laser applications. These various cavity designs and underlying physics in single and array nanocavities are useful for the practical implementation of promising nanophotonic devices.
Integrated photonic circuits provide a versatile toolbox of functionalities for advanced quantum optics applications. Here, we demonstrate an essential component of such a system in the form of a Purcell-enhanced single-photon source based on a quantum dot coupled to a robust on-chip integrated resonator. For that, we develop GaAs monolithic ring cavities based on distributed Bragg reflector ridge waveguides. Under resonant excitation conditions, we observe an over 2-fold spontaneous emission rate enhancement using Purcell effect and gain a full coherent optical control of a QD-two-level system via Rabi oscillations. Furthermore, we demonstrate an on-demand single-photon generation with strongly suppressed multiphoton emission probability as low as 1% and two-photon interference with visibility up to 95%. This integrated single-photon source can be readily scaled up, promising a realistic pathway for scalable on-chip linear optical quantum simulation, quantum computation, and quantum networks.
Hydrogen sensor technologies have been rapidly developing. For effective and safe sensing, we proposed a hydrogen sensor composed of magnesium (Mg), silver (Ag), and palladium (Pd) nano-blocks that overcomes the spectral resolution limit. This sensor exploited the properties of Mg and Pd when absorbing hydrogen. Mg became a dielectric material, and the atomic lattice of Pd expanded. These properties led to changes in the plasmonic gap mode between the nano-blocks. Owing to the changing gap mode, the far-field scattering pattern significantly changed with the hydrogen concentration. Thus, sensing the hydrogen concentration was able to be achieved simply by detecting the far-field intensity at a certain angle for incident light with a specific wavelength.
In this study, we propose a multi-color detector using a simple plasmonic metamaterial structure consisting of a silver and a indium phosphide. The color detector is composed of a metal strip with a periodicity in the x-axis direction on a layer of the dielectric material located on a metal substrate. This color detector can control the spectrum absorbed in the dielectric material layer by changing the thickness of the dielectric material layer or the width of the metal strip. The triangle formed by the three primary colors, namely, red, green, and blue, which are representatively detected by optimizing the color detector using only silver and indium phosphide, covers 44% of the standard Red Green Blue (sRGB) region. Furthermore, the area of the triangle obtained by further optimization, such as changing the material to gold or gallium phosphide or changing the period of the metal stirp, can aid in the detection of a larger number of colors covering 108% of the sRGB area.
The human eye perceives the color of visible light depending on the spectrum of the incident light. Hence, the ability of color expression is very important in display devices. For practical applications, the transmitted color filter requires high transmittance and vivid colors, covering full standard default color spaces (sRGB). In this paper, we propose a color filter with a silver block array on a silica substrate structure with nanoscale air slots where strong transmission is observed through the slots between silver blocks. We investigated the transmitted color by simulating the transmission spectra as functions of various structure parameters. The proposed structure with an extremely small pixel size of less than 300 nm covers 90% of sRGB color depending on the structure and has a narrow angular distribution of transmitted light.
Integrated single photon sources are key building blocks for realizing scalable devices for quantum information processing. For such applications highly coherent and indistinguishable single photons on a chip are required. Here we report on a triggered resonance fluorescence single photon source based on In(Ga)As/GaAs quantum dots coupled to single- and multimode ridge waveguides. We demonstrate the generation of highly linearly polarized resonance fluorescence photons with 99.1% (96.0%) single photon purity and 97.5% (95.0%) indistinguishability in case of multimode (single mode) waveguide devices fulfilling the strict requirements imposed by multi-interferometric quantum optics applications. Our integrated triggered single photon source can be readily scaled up, promising a realistic pathway for on-chip linear optical quantum simulation, quantum computation, and quantum networks.
Upconversion (UC) materials can be used to harvest near-infrared (NIR) light and convert it into visible light. Although this improves optical device operating spectral range and efficiency, e.g., solar cells, typical UC material conversion efficiency is too low for practical devices. We propose a cross-patterned slot waveguide constructed from UC material embedded in a high index semiconductor layer to improve UC. Since the slot waveguide mode is induced in the low index UC slot, NIR absorption (~970 nm) increased 25-fold compared with film structures. Furthermore, the spontaneous emission enhancement rate at 660 nm increased 9.6-fold compared to the reference film due to resonance excited in the UC slot (Purcell effect). Thus, the proposed UC slot array structure improved UC efficiency 240-fold considering absorption and emission enhancements. This double resonance UC improvement can be applied to practical optical devices.
We discuss coupling of site-selectively induced quantum emitters in exfoliated monolayers of WSe2 to plasmonic nanostructures. Gold nanorods of 20 nm-240 nm size, which are arranged in pitches of a few micrometers on a dielectric surface, act as seeds for the formation of quantum emitters in the atomically thin materials. We observe characteristic narrow-band emission signals from the monolayers, which correspond well with the positions of the metallic nanopillars with and without thin dielectric coating. Single photon emission from the emitters is confirmed by autocorrelation measurements, yielding g2(τ = 0) values as low as 0.17. Moreover, we observe a strong co-polarization of our single photon emitters with the frequency matched plasmonic resonances, as a consequence of light-matter coupling. Our work represents a significant step towards the scalable implementation of coupled quantum emitter-resonator systems for highly integrated quantum photonic and plasmonic applications.
A novel method is proposed to detect the horizontal shift of a specific nanoblock relative to a reference nanoblock using surface plasmon modes at nanometer resolution. To accomplish this task, two orthogonal localized surface plasmon resonances were excited within the air gap region between the silver nanoblocks at the respective wavelengths, 890 nm, and 1100 nm. This technique utilized the scattering far-field intensities of the two block nanostructures at the two specific wavelengths at two specific directional spots. The ratio of the scattering intensities at the two spots changed according to the horizontal shift of the block that moved. Correspondingly, this ratio can be used to provide the precise location of the block. This method can be applied to many fields, including label-free bio-sensing, bio-analysis and alignment during nano-fabrication, owing to the high resolution and simplicity of the process.
Sensitive refractive index sensors with small footprints have been studied to allow the integration of a large number of sensors into a tiny chip for bio/chemical applications. In particular, resonant-type index sensors based on various micro/nanocavities, which use a resonant wavelength dependence on the refractive index of the analyte, have been developed. However, the spectral linewidth of the resonance, which becomes the resolution limit, is considerably large in plasmonic cavities due to the large absorption loss of metals. Therefore, there is demand for a new type of plasmonic refractive index sensor that is not limited by the linewidth of the cavity. We propose a new type of plasmonic index sensors consisting of a channel waveguide and a ring cavity. Two emissions from the ring cavity in both directions of the waveguide couple with a reflection phase difference depending on the length of a closed right arm with a reflecting boundary. Therefore, the output power dramatically and sensitively changes as a function of the refractive index of the analyte filling the waveguide.
A Mach-Zehnder interferometer based on a plasmonic channel waveguide is proposed for refractive index sensing. The structure, with a small physical footprint of 20 × 120 µm², achieved a high figure of merit of 294. The cut-off frequency behaviour in the plasmonic channel waveguide resulted in a flat dispersion curve, which induces a 1.8 times larger change of the propagation constant for the given refractive index change compared with previously reported results.
Photon-triggered electronic circuits have been a long-standing goal of photonics. Recent demonstrations include either all-optical transistors in which photons control other photons or phototransistors with the gate response tuned or enhanced by photons. However, only a few studies report on devices in which electronic currents are optically switched and amplified without an electrical gate. Here we show photon-triggered nanowire (NW) transistors, photon-triggered NW logic gates and a single NW photodetection system. NWs are synthesized with long crystalline silicon (CSi) segments connected by short porous silicon (PSi) segments. In a fabricated device, the electrical contacts on both ends of the NW are connected to a single PSi segment in the middle. Exposing the PSi segment to light triggers a current in the NW with a high on/off ratio of >8 × 106. A device that contains two PSi segments along the NW can be triggered using two independent optical input signals. Using localized pump lasers, we demonstrate photon-triggered logic gates including AND, OR and NAND gates. A photon-triggered NW transistor of diameter 25â nm with a single 100â nm PSi segment requires less than 300â pW of power. Furthermore, we take advantage of the high photosensitivity and fabricate a submicrometre-resolution photodetection system. Photon-triggered transistors offer a new venue towards multifunctional device applications such as programmable logic elements and ultrasensitive photodetectors.
Interest in mechanical compliance has been motivated by the development of flexible electronics and mechanosensors. In particular, studies and characterization of structural deformation at the fundamental scale can offer opportunities to improve the device sensitivity and spatiotemporal response; however, the development of precise measurement tools with the appropriate resolution remains a challenge. Here we report a flexible and stretchable photonic crystal nanolaser whose spectral and modal behaviours are sensitive to nanoscale structural alterations. Reversible spectral tuning of â¼26 nm in lasing wavelength, with a sub-nanometre resolution of less than â¼0.6 nm, is demonstrated in response to applied strain ranging from -10 to 12%. Instantaneous visualization of the sign of the strain is also characterized by exploring the structural and corresponding modal symmetry. Furthermore, our high-resolution strain-gauge nanolaser functions as a stable and deterministic strain-based pH sensor in an opto-fluidic system, which may be useful for further analysis of chemical/biological systems.
A tapered plasmonic channel waveguide can be used for index sensing by spatial mapping of the scattering field intensity. A numerical simulation shows that this waveguide reflects the plasmonic channel waveguide mode at various points as the refractive index of an analyte changes, and a strong outgoing scattering wave appears at the reflection point. One can measure the index change by detecting variations in the scattering point. In the case of a unit index change, the scattering point moved 2670 nm, which can be observed by an imaging system. Detection limit of the index change is estimated as 0.12. However, the limit can be further reduced by increasing the tapered length or decreasing the tapered angle of the structure.
Cellulose is one of the most widespread biomolecules in nature and has been exploited in various applications including scaffolding, tissue engineering, and tissue formation. To evaluate the biocompatibility of cellulose film manufactured from Styela clava tunics (SCT-CF), these films were implanted in Sprague-Dawley (SD) rats for various lengths of time, after which they were subjected to mechanical and biological analyses. The cellulose powders (12-268 m) obtained from SCT was converted into films via casting methods without adding any additives. SCT-CF contained about 98 % α-cellulose and very low concentrations of ßß-cellulose. Additionally, the crystallinity index (CrI) of SCT-CF was lower (10.71 %) than that of wood pulp-cellulose films (WP-CF) (33.78 %). After implantation for 90 days, the weight loss and formation of surface corrugations were greater in SCT-CF than that of WP-CF, while the surface roughness was significantly higher in WP-CF than SCT-CF. However, there were no differences in the number of white blood cells between SCT-CF implanted rats and vehicle implanted rats. The level of metabolic enzymes representing liver and kidney toxicity in the serum of SCT-CF implanted rats was maintained at levels consistent with vehicle implanted rats. Moreover, no significant alteration of the epidermal hyperplasia, inflammatory cell infiltration, redness, and edema were observed in SD rats implanted with SCT-CF. Taken together, these results indicate that SCT-CF showed good degradability and non-toxicity without inducing an immune response in SD rats. Further, the data presented here constitute strong evidence that SCT-CF has the potential for use as a powerful biomaterial for medical applications including stitching fiber, wound dressing, scaffolding, absorbable hemostats and hemodialysis membrane.
Absorbable Implants/adverse effects , Cellulose/chemistry , Cellulose/toxicity , Membranes, Artificial , Skin/drug effects , Skin/pathology , Urochordata/chemistry , Animals , Biocompatible Materials/chemistry , Biocompatible Materials/isolation & purification , Biocompatible Materials/toxicity , Cellulose/isolation & purification , Male , Materials Testing , Rats , Rats, Sprague-Dawley , Skin/chemistry , Skin Physiological Phenomena/drug effects
In this review paper, we introduce the unique optical properties of high-quality, fully three-dimensional, subwavelength-scale plasmonic cavities. Surface-plasmon-polaritons excited at dielectric-metal interfaces are strongly confined in such cavities. The field profiles of plasmonic modes, their temperature-dependent quality factors, and subwavelength mode volumes are calculated and analyzed systematically using three-dimensional finite-difference time-domain simulations. Reasonable design of high-quality plasmonic cavities opens an opportunity to demonstrate novel plasmonic lasers enabling the further miniaturization of coherent light sources for use in ultra-compact photonic integrated circuits.
We demonstrate the efficient integration of an electrically driven nanowire (NW) light source with a double-strip plasmonic waveguide. A top-down-fabricated GaAs NW light-emitting diode (LED) is placed between two straight gold strip waveguides with the gap distance decreasing to 30 nm at the end of the waveguide and operated by current injection through the p-contact electrode acting as a plasmonic waveguide. Measurements of polarization-resolved images and spectra show that the light emission from the NW LED was coupled to a plasmonic waveguide mode, propagated through the waveguide, and was focused onto a subwavelength-sized spot of surface plasmon polaritons at the tapered end of the waveguide. Numerical simulation agreed well with these experimental results, confirming that a symmetric plasmonic waveguide mode was excited on the top surface of the waveguide. Our demonstration of a plasmonic waveguide coupled to an electrically driven NW LED represents important progress toward further miniaturization and practical implementation of ultracompact photonic integrated circuits.
We propose a plasmonic whispering-gallery-mode cavity comprising of a dielectric disk with sub-hundred nanometer thickness sandwiched by two silver disks. By reducing radius and thickness carefully based on the investigated resonant wavelength dependencies, the surface-plasmon-polariton cavity mode with a resonant wavelength of 1550 nm can be confined in a disk with a radius of 88 nm and a thickness of 10 nm, where the physical size of the cavity is 0.000064 λ(0) <(3) (λ(0): free space wavelength). The cavity mode has a deep subwavelength mode volume of 0.010 (λ/2n)(3) and a high quality factor of 1900 at 40K, consequently, a large Purcell factor of 1.1 x 10(5).
