Showing papers on "Photonic crystal published in 2014"

Silicon nanostructures for photonics and photovoltaics

Abstract: Silicon has long been established as the material of choice for the microelectronics industry. This is not yet true in photonics, where the limited degrees of freedom in material design combined with the indirect bandgap are a major constraint. Recent developments, especially those enabled by nanoscale engineering of the electronic and photonic properties, are starting to change the picture, and some silicon nanostructures now approach or even exceed the performance of equivalent direct-bandgap materials. Focusing on two application areas, namely communications and photovoltaics, we review recent progress in silicon nanocrystals, nanowires and photonic crystals as key examples of functional nanostructures. We assess the state of the art in each field and highlight the challenges that need to be overcome to make silicon a truly high-performing photonic material.

Photonic Crystals for Chemical Sensing and Biosensing

Abstract: This Review covers photonic crystals (PhCs) and their use for sensing mainly chemical and biochemical parameters, with a particular focus on the materials applied. Specific sections are devoted to a) a lead-in into natural and synthetic photonic nanoarchitectures, b) the various kinds of structures of PhCs, c) reflection and diffraction in PhCs, d) aspects of sensing based on mechanical, thermal, optical, electrical, magnetic, and purely chemical stimuli, e) aspects of biosensing based on biomolecules incorporated into PhCs, and f) current trends and limitations of such sensors.

Total Absorption in a Graphene Monolayer in the Optical Regime by Critical Coupling with a Photonic Crystal Guided Resonance

Abstract: We numerically demonstrate total absorption in graphene in the near-infrared and visible wavelength ranges by means of critical coupling with guided resonances of a photonic crystal slab. In this wavelength range, there is no plasmonic response in undoped graphene, so the critical coupling is entirely controlled by the properties of the photonic crystal resonance. We discuss the general theory and conditions for absorption enhancement and critical coupling in a thin film and give design rules for a totally absorbing system. We present examples in the near-infrared and visible, using both a lossless metallic mirror and a realistic multilayer dielectric mirror.

Atom-Light Interactions in Photonic Crystals

Abstract: The integration of nanophotonics and atomic physics has been a long-sought goal that would open new frontiers for optical physics, including novel quantum transport and many-body phenomena with photon-mediated atomic interactions. Reaching this goal requires surmounting diverse challenges in nanofabrication and atomic manipulation. Here we report the development of a novel integrated optical circuit with a photonic crystal capable of both localizing and interfacing atoms with guided photons. Optical bands of a photonic crystal waveguide are aligned with selected atomic transitions. From reflection spectra measured with average atom number N = 1.1 ± 0.4, we infer that atoms are localized within the waveguide by optical dipole forces. The fraction of single-atom radiative decay into the waveguide is Γ_(1D)/Γ'≃(0.32±0.08), where Γ_(1D) is the rate of emission into the guided mode and Γ' is the decay rate into all other channels. Γ_(1D)/Γ′ is unprecedented in all current atom–photon interfaces.

Hollow-core photonic crystal fibres for gas-based nonlinear optics

Abstract: Hollow-core photonic crystal fibres are attractive because they exhibit pressure-adjustable normal or anomalous dispersion, low-loss guidance, very low nonlinearity and high damage threshold. This Review overviews nonlinear optical phenomena in gas-filled, hollow-core photonic crystal fibres that may lead to a new generation of versatile and efficient pulse-compression devices and gas-based light sources.

Spectrally selective chiral silicon metasurfaces based on infrared Fano resonances

Abstract: Metamaterials and metasurfaces represent a remarkably versatile platform for light manipulation, biological and chemical sensing, and nonlinear optics Many of these applications rely on the resonant nature of metamaterials, which is the basis for extreme spectrally selective concentration of optical energy in the near field In addition, metamaterial-based optical devices lend themselves to considerable miniaturization because of their subwavelength features This additional advantage sets metamaterials apart from their predecessors, photonic crystals, which achieve spectral selectivity through their long-range periodicity Unfortunately, spectral selectivity of the overwhelming majority of metamaterials that are made of metals is severely limited by high plasmonic losses Here we propose and demonstrate Fano-resonant all-dielectric metasurfaces supporting optical resonances with quality factors Q>100 that are based on CMOS-compatible materials: silicon and its oxide We also demonstrate that these infrared metasurfaces exhibit extreme planar chirality, opening exciting possibilities for efficient ultrathin circular polarizers and narrow-band thermal emitters of circularly polarized radiation

Watt-class high-power, high-beam-quality photonic-crystal lasers

Abstract: The applications of surface-emitting lasers, in particular vertical-cavity surface-emitting lasers (VCSELs), are currently being extended to various low-power fields including communications and interconnections. However, the fundamental difficulties in increasing their output power by more than several milliwatts while maintaining single-mode operation prevent their application in high-power fields such as material processing, laser medicine and nonlinear optics, despite their advantageous properties of circular beams, the absence of catastrophic optical damage, and their suitability for two-dimensional integration. Here, we demonstrate watt-class high-power, single-mode operation by a two-dimensional photonic-crystal surface-emitting laser under room-temperature, continuous-wave conditions. The two-dimensional band-edge resonant effect of a photonic crystal formed by metal–organic chemical vapour deposition enables a 1,000 times broader coherent-oscillation area, which results in a high beam quality of M2 ≤ 1.1, narrowing the focus spot by two orders of magnitude compared to VCSELs. Our demonstration promises to realize innovative high-power applications for surface-emitting lasers. Researchers demonstrate a watt-class high-power, single-mode photonic-crystal laser operating continuously at room temperature. A beam quality of M2 ≤ 1.1 is achieved.

Observation of unconventional edge states in ‘photonic graphene’

Abstract: The propagation of light in photonic crystals with a honeycomb structure mirrors the behaviour of charges in graphene, therefore allowing for the investigation of electronic properties that cannot otherwise be accessed in graphene itself. This approach is now used to predict unexpected edge states that localize in the bearded edges of hexagonal lattices.

Large-scale integration of wavelength-addressable all-optical memories on a photonic crystal chip

Abstract: Large-scale densely integrated optical memory on a single photonic crystal chip is demonstrated. The wavelength-division-multiplexing (WDM) capabilities of nanophotonic memories are exploited for optical addressing. This work may enable optical random-access memories and a large-scale WDM photonic network-on-chip.

Integrated flexible chalcogenide glass photonic devices

Abstract: Photonic integration on thinflexible plastic substrates is important for emerging applications ranging from the realization of flexible interconnects to conformal sensors applied to the skin. Such devices are traditionally fabricated using pattern transfer, which is complicated and has limited integration capacity. Here, we report a convenient monolithic approach to realize flexible, integrated high-index-contrast chalcogenide glass photonic devices. By developing local neutral axis designs and suitable fabrication techniques, we realize a suite of photonic devices including waveguides, microdisk resonators, add–drop filters and photonic crystals that have excellent optical performance and mechanical flexibility, enabling repeated bending down to sub-millimetre radii without measurable performance degradation. The approach offers a facile fabrication route for three-dimensional high-index-contrast photonics that are difficult to create using traditional methods.

Coupling surface plasmon resonance of gold nanoparticles with slow-photon-effect of TiO2 photonic crystals for synergistically enhanced photoelectrochemical water splitting

Abstract: The slow photon effect of a photonic crystal (PC) is a promising characteristic for tuning light–matter interactions through material structure designing. A TiO2 bi-layer structure photoanode was constructed by fabricating a TiO2 PC layer through a template-assisted sol–gel process on a TiO2 nanorod array (NR) layer. Gold nanoparticles (Au NPs) with an average size of about 10 nm were deposited in situ into the TiO2 bi-layer structure. The extended photoelectrochemical (PEC) water splitting activity in visible light was ascribed to the energetic hot electrons and holes that were generated in the Au NPs through the excitation and decay of surface plasmons. By alternating the characteristic pore size of the TiO2 PC layer, the slow photon region at the red edge of the photonic band gap could be purposely tuned to overlap with the strong localized surface plasmon resonance (SPR) region of Au NPs. The matching slow photon effect of TiO2 PC (with a characteristic pore size of 250 nm) intensified the SPR responses (central at 536 nm) of Au NPs. Consequently, more hot electrons were generated in the Au NPs and injected into the conduction band of TiO2, resulting in improved PEC water splitting efficiency in the visible light region. Under simulated sunlight illumination, the photoconversion efficiency of the well matching Au/TiO2 photoanode approached 0.71%, which is one of the highest values ever reported in Au/TiO2 PEC systems. The work reported here provides support for designing coupling plasmonic nanostructures with PC-based materials to synergistically enhance PEC water splitting efficiency.

Analytical perspective for bound states in the continuum in photonic crystal slabs.

Abstract: We investigate the formation of photonic bound states in the continuum (BICs) in photonic crystal slabs from an analytical perspective. Unlike the stationary at-Γ BICs which originate from the geometric symmetry, the tunable off-Γ BICs are due to the weighted destructive via the continuum interference in the vicinity of accidental symmetry when the majority of the radiation is precanceled. The symmetric compatible nature of the off-Γ BICs leads to a trapping of light that can be tuned through continuously varying the wave vector. With the analytical approach, we explain a reported experiment and predict the existence of a new BIC at an unrevealed symmetry.

Silicon nanofin grating as a miniature chirality-distinguishing beam-splitter

Abstract: The polarization of light plays a central role in its interaction with matter, in situations ranging from familiar (for example, reflection and transmission at an interface) to sophisticated (for example, nonlinear optics). Polarization control is therefore pivotal for many optical systems, and achieved using bulk devices such as wave-plates and beam-splitters. The move towards optical system miniaturization therefore motivates the development of micro- and nanostructures for polarization control. For such control to be complete, one must distinguish not only between linear polarizations, but also between left- and right-circular polarizations. Some previous works used surface plasmons to this end, but these are inherently lossy. Other works used complex-layered structures. Here we demonstrate a planar dielectric chirality-distinguishing beam-splitter. The beam-splitter consists of amorphous silicon nanofins on a glass substrate and deflects left- and right-circularly polarized beams into different directions. Contrary to intuitive expectations, we utilize an achiral architecture to realize a chiral beam-splitting functionality.

High quality-factor optical nanocavities in bulk single-crystal diamond.

Abstract: Single-crystal diamond, with its unique optical, mechanical and thermal properties, has emerged as a promising material with applications in classical and quantum optics. However, the lack of heteroepitaxial growth and scalable fabrication techniques remains the major limiting factors preventing more wide-spread development and application of diamond photonics. In this work, we overcome this difficulty by adapting angled-etching techniques, previously developed for realization of diamond nanomechanical resonators, to fabricate racetrack resonators and photonic crystal cavities in bulk single-crystal diamond. Our devices feature large optical quality factors, in excess of 10 5 , and operate over a wide wavelength

Realization of dynamic thermal emission control

Abstract: Thermal emission in the infrared range is important in various fields of research, including chemistry, medicine and atmospheric science. Recently, the possibility of controlling thermal emission based on wavelength-scale optical structures has been intensively investigated with a view towards a new generation of thermal emission devices. However, all demonstrations so far have involved the 'static' control of thermal emission; high-speed modulation of thermal emission has proved difficult to achieve because the intensity of thermal emission from an object is usually determined by its temperature, and the frequency of temperature modulation is limited to 10-100 Hz even when the thermal mass of the object is small. Here, we experimentally demonstrate the dynamic control of thermal emission via the control of emissivity (absorptivity), at a speed four orders of magnitude faster than is possible using the conventional temperature-modulation method. Our approach is based on the dynamic control of intersubband absorption in n-type quantum wells, which is enhanced by an optical resonant mode in a photonic crystal slab. The extraction of electrical carriers from the quantum wells leads to an immediate change in emissivity from 0.74 to 0.24 at the resonant wavelength while maintaining much lower emissivity at all other wavelengths.

Surface Impedance and Bulk Band Geometric Phases in One-Dimensional Systems

Abstract: Surface impedance of a photonic material governs how an impinging light wave behaves at its surface, whereas its bulk ``band structure'' determines what wave modes can propagate in it. Is there a surface-to-bulk correspondence? A new study of one-dimensional photonic crystals indeed uncovers a rigorous fundamental relationship between the two.

Multimode One-Way Waveguides of Large Chern Numbers

Abstract: Current experimental realizations of the quantum anomalous Hall phase in both electronic and photonic systems have been limited to a Chern number of one. In photonics, this corresponds to a single-mode one-way edge waveguide. Here, we predict quantum anomalous Hall phases in photonic crystals with large Chern numbers of 2, 3, and 4. These new topological phases were found by simultaneously gapping multiple Dirac and quadratic points. We demonstrate a continuously tunable power splitter as a possible application of multimode one-way waveguides. All our findings are readily realizable at microwave frequencies.

Two-Dimensional Phononic-Photonic Band Gap Optomechanical Crystal Cavity

Abstract: We present the fabrication and characterization of an artificial crystal structure formed from a thin film of silicon that has a full phononic band gap for microwave X-band phonons and a two-dimensional pseudo-band gap for near-infrared photons. An engineered defect in the crystal structure is used to localize optical and mechanical resonances in the band gap of the planar crystal. Two-tone optical spectroscopy is used to characterize the cavity system, showing a large coupling (g_0/2π≈220 kHz) between the fundamental optical cavity resonance at ω_o/2π=195 THz and colocalized mechanical resonances at frequency ω_m/2π≈9.3 GHz.

Graphene-Based Birefringent Photonic Crystal Fiber Sensor Using Surface Plasmon Resonance

Abstract: We propose a graphene-based photonic crystal fiber (PCF) sensor based on surface plasmon resonance. Graphene helps in prevention of oxidation of the silver layer used as a plasmonic active metal. The birefringent nature of the structure allows one component of the core guided mode to be more sensitive. Further, this structure does not need filling of the voids. The structural parameter of PCF and metal thickness has been optimized. The proposed sensor shows high amplitude sensitivity of 860 RIU-1 and has a resolution as high as 4×10-5 RIU. This reported performance is higher than bimetallic (gold on silver) configuration.

25th anniversary article: ordered polymer structures for the engineering of photons and phonons.

Abstract: The engineering of optical and acoustic material functionalities via construction of ordered local and global architectures on various length scales commensurate with and well below the characteristic length scales of photons and phonons in the material is an indispensable and powerful means to develop novel materials. In the current mature status of photonics, polymers hold a pivotal role in various application areas such as light-emission, sensing, energy, and displays, with exclusive advantages despite their relatively low dielectric constants. Moreover, in the nascent field of phononics, polymers are expected to be a superior material platform due to the ability for readily fabricated complex polymer structures possessing a wide range of mechanical behaviors, complete phononic bandgaps, and resonant architectures. In this review, polymer-centric photonic and phononic crystals and metamaterials are highlighted, and basic concepts, fabrication techniques, selected functional polymers, applications, and emerging ideas are introduced.

Fully etched apodized grating coupler on the SOI platform with −0.58 dB coupling efficiency

Abstract: We design and fabricate an ultrahigh coupling efficiency (CE) fully etched apodized grating coupler on the silicon-on-insulator (SOI) platform using subwavelength photonic crystals and bonded aluminum mirror. Fabrication error sensitivity and coupling angle dependence are experimentally investigated. A record ultrahigh CE of −0.58 dB with a 3 dB bandwidth of 71 nm and low back reflection are demonstrated.

Mechano-actuated ultrafast full-colour switching in layered photonic hydrogels

Abstract: Photonic crystals with tunability in the visible region are of great interest for controlling light diffraction. Mechanochromic photonic materials are periodically structured soft materials designed with a photonic stop-band that can be tuned by mechanical forces to reflect specific colours. Soft photonic materials with broad colour tunability and fast colour switching are invaluable for application. Here we report a novel mechano-actuated, soft photonic hydrogel that has an ultrafast-response time, full-colour tunable range, high spatial resolution and can be actuated by a very small compressive stress. In addition, the material has excellent mechanical stability and the colour can be reversibly switched at high frequency more than 10,000 times without degradation. This material can be used in optical devices, such as full-colour display and sensors to visualize the time evolution of complicated stress/strain fields, for example, generated during the motion of biological cells.

Optical broadband angular selectivity.

Abstract: Light selection based purely on the angle of propagation is a long-standing scientific challenge. In angularly selective systems, however, the transmission of light usually also depends on the light frequency. We tailored the overlap of the band gaps of multiple one-dimensional photonic crystals, each with a different periodicity, in such a way as to preserve the characteristic Brewster modes across a broadband spectrum. We provide theory as well as an experimental realization with an all-visible spectrum, p-polarized angularly selective material system. Our method enables transparency throughout the visible spectrum at one angle--the generalized Brewster angle--and reflection at every other viewing angle.

Photonic crystal fiber based surface plasmon resonance chemical sensors

Abstract: Research developments of the photonic crystal fiber based surface plasmon resonance (PCF-SPR) chemical sensors were intensively reviewed Photonic crystal fibers, such as the microstructured optical fiber, the photonic bandgap fiber and the Bragg fiber with various structures were applied to the SPR sensors, including fuse-tapered fiber structure, D-type fiber structure and cladding-off fiber structure Those sensors were classified as three kinds of configurations which were respectively based on the inner metal layer, the metallic nanowire and the outer metal film What's more, the principles, superiorities and problems of the PCF-SPR sensors were also discussed in detail

Photonic crystal lasers using wavelength-scale embedded active region

Abstract: Lasers with ultra-low operating energy are desired for use in chip-to-chip and on-chip optical interconnects. If we are to reduce the operating energy, we must reduce the active volume. Therefore, a photonic crystal (PhC) laser with a wavelength-scale cavity has attracted a lot of attention because a PhC provides a large Q-factor with a small volume. To improve this device's performance, we employ an embedded active region structure in which the wavelength-scale active region is buried with an InP PhC slab. This structure enables us to achieve effective confinement of both carriers and photons, and to improve the thermal resistance of the device. Thus, we have obtained a large external differential quantum efficiency of 55% and an output power of ?10?dBm by optical pumping. For electrical pumping, we use a lateral p?i?n structure that employs Zn diffusion and Si ion implantation for p-type and n-type doping, respectively. We have achieved room-temperature continuous-wave operation with a threshold current of 7.8??A and a maximum 3?dB bandwidth of 16.2?GHz. The results of an experimental bit error rate measurement with a 10?Gbit?s?1 NRZ signal reveal the minimum operating energy for transferring a single bit of 5.5?fJ. These results show the potential of this laser to be used for very short reach interconnects. We also describe the optimal design of cavity quality (Q) factor in terms of achieving a large output power with a low operating energy using a calculation based on rate equations. When we assume an internal absorption loss of 20?cm?1, the optimized coupling Q-factor is 2000.

Control of two-dimensional excitonic light emission via photonic crystal

Abstract: Monolayers of transition metal dichalcogenides (TMDCs) have emerged as new optoelectronic materials in the two dimensional (2D) limit, exhibiting rich spin-valley interplays, tunable excitonic effects, and strong light–matter interactions. An essential yet undeveloped ingredient for many photonic applications is the manipulation of its light emission. Here we demonstrate the control of excitonic light emission from monolayer tungsten diselenide (WSe2) in an integrated photonic structure, achieved by transferring one monolayer onto a photonic crystal (PhC) with a cavity. In addition to the observation of an effectively coupled cavity-mode emission, the suspension effects on PhC not only result in a greatly enhanced (~60 times) photoluminescence but also strongly pattern the emission in the subwavelength spatial scale, contrasting on and off the holes. Such an effect leads to a significant diffraction grating effect, which allows us to redistribute the emitted photons both polarly and azimuthally in the far field through designing PhC structures, as revealed by momentum-resolved microscopy. A 2D optical antenna is thus constructed. Our work suggests a new way of manipulating photons in hybrid 2D photonics, important for future energy efficient optoelectronics and 2D nano-lasers.