Showing papers on "Photonic crystal published in 2016"
TL;DR: In this article, the authors demonstrate an integrated platform for scalable quantum nanophotonics based on silicon-vacancy (SiV) color centers coupled to diamond nanodevices.
Abstract: Efficient interfaces between photons and quantum emitters form the basis for quantum networks and enable optical nonlinearities at the single-photon level. We demonstrate an integrated platform for scalable quantum nanophotonics based on silicon-vacancy (SiV) color centers coupled to diamond nanodevices. By placing SiV centers inside diamond photonic crystal cavities, we realize a quantum-optical switch controlled by a single color center. We control the switch using SiV metastable states and observe optical switching at the single-photon level. Raman transitions are used to realize a single-photon source with a tunable frequency and bandwidth in a diamond waveguide. By measuring intensity correlations of indistinguishable Raman photons emitted into a single waveguide, we observe a quantum interference effect resulting from the superradiant emission of two entangled SiV centers.
583 citations
10 Feb 2016
TL;DR: In this paper, an all-Si photonic topological insulator (PTI) was proposed that emulates the quantum-valley-Hall (QVH) effect with backscattering-free edge states.
Abstract: We propose an all-Si photonic topological insulator (PTI) that emulates the quantum-valley-Hall (QVH) effect with backscattering-free edge states. Such QVH-PTI has exotic external coupling property to vacuum and can be utilized for designing random resonant time-delay cavities immune to reflections.
513 citations
TL;DR: In this article, the authors demonstrate an integrated platform for scalable quantum nanophotonics based on silicon-vacancy (SiV) color centers coupled to nanoscale diamond devices.
Abstract: Efficient interfaces between photons and quantum emitters form the basis for quantum networks and enable nonlinear optical devices operating at the single-photon level. We demonstrate an integrated platform for scalable quantum nanophotonics based on silicon-vacancy (SiV) color centers coupled to nanoscale diamond devices. By placing SiV centers inside diamond photonic crystal cavities, we realize a quantum-optical switch controlled by a single color center. We control the switch using SiV metastable orbital states and verify optical switching at the single-photon level by using photon correlation measurements. We use Raman transitions to realize a single-photon source with a tunable frequency and bandwidth in a diamond waveguide. Finally, we create entanglement between two SiV centers by detecting indistinguishable Raman photons emitted into a single waveguide. Entanglement is verified using a novel superradiant feature observed in photon correlation measurements, paving the way for the realization of quantum networks.
435 citations
01 Jan 2016
TL;DR: The optical properties of photonic crystals is universally compatible with any devices to read and is available in the digital library an online access to it is set as public so you can get it instantly.
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307 citations
TL;DR: In this article, a photonic topological crystalline insulator structure is used to topologically protect the resonance frequency to be in the middle of the band gap, and therefore minimize the mode volume of a two-dimensional photonic defect mode.
Abstract: Defect modes in two-dimensional periodic photonic structures have found use in a highly diverse set of optical devices. For example, photonic crystal cavities confine optical modes to subwavelength volumes and can be used for Purcell enhancement of nonlinearity, lasing, and cavity quantum electrodynamics. Photonic crystal fiber defect cores allow for supercontinuum generation and endlessly-single-mode fibers with large cores. However, these modes are notoriously fragile: small changes in the structure can lead to significant detuning of resonance frequency and mode volume. Here, we show that a photonic topological crystalline insulator structure can be used to topologically protect the resonance frequency to be in the middle of the band gap, and therefore minimize the mode volume of a two-dimensional photonic defect mode. We experimentally demonstrate this in a femtosecond-laser-written waveguide array, a geometry akin to a photonic crystal fiber. The topological defect modes are determined by a topological invariant that protects zero-dimensional states (defect modes) embedded in a two-dimensional environment; a novel form of topological protection that has not been previously demonstrated.
293 citations
TL;DR: In this paper, a photonic analogue of a three-dimensional solid-state topological insulator is proposed, where the symmetries may protect single Dirac cones on the surface of a photonics crystal.
Abstract: Crystal symmetries may protect single Dirac cones on the surface of a photonic crystal, creating a photonic analogue of a three-dimensional solid-state topological insulator.
275 citations
TL;DR: In this paper, the authors proposed multilayer heterostructures on a SiO2 substrate, which provides multiple reflective bands with the very high reflective efficiency of nearly up to 100%.
Abstract: Quantum dots (QDs) show great promise for use in nanotechnology, owing to their high quantum efficiency, color tenability, narrow emission, and high luminescence efficiency. As a new generation of light-emitting devices (LEDs), QD-LEDs have attracted a great deal of attention in displays and lighting. To meet the commercial requirements, the brightness of QD-LEDs needs to be further improved. In this work, we propose multilayer heterostructures on a SiO2 substrate, which provides multiple reflective bands with the very high reflective efficiency of nearly up to 100%. Electric field distributes mostly in the superficial layer. The proposed structure provides highly multiband reflection covering the emission peaks of QDs in LEDs; hence, it can eventually enhance QDs' fluorescence and enhance the brightness of QD-LEDs. We investigate four typical emission wavelengths, mainly aiming for red QD-LEDs and infrared QD-LEDs, which correspond to the applications of displays, infrared illumination, optical communication, and so on. The total reflection bands can be adjusted according to practical requirements by tuning the thickness of every layer. One fabrication procedure can be used for different kinds of QDs or the same kind of QD with different sizes without changing their processing properties. The proposed structure has fewer flat layers compared with 1-D photonic crystals, which leads to lower cost and easier fabrications.
274 citations
TL;DR: 3D printing of microoptics can achieve sufficient performance that will allow for rapid prototyping and production of beam-shaping and imaging devices, and finds excellent agreement with numerical calculations.
Abstract: Micro-optics are widely used in numerous applications, such as beam shaping, collimation, focusing and imaging. We use femtosecond 3D printing to manufacture free-form micro-optical elements. Our method gives sub-micrometre accuracy so that direct manufacturing even on single-mode fibres is possible. We demonstrate the potential of our method by writing different collimation optics, toric lenses, free-form surfaces with polynomials of up to 10th order for intensity beam shaping, as well as chiral photonic crystals for circular polarization filtering, all aligned onto the core of the single-mode fibres. We determine the accuracy of our optics by analysing the output patterns as well as interferometrically characterizing the surfaces. We find excellent agreement with numerical calculations. 3D printing of microoptics can achieve sufficient performance that will allow for rapid prototyping and production of beam-shaping and imaging devices.
256 citations
TL;DR: This work designs, fabricates, and characterize a photonic crystal possessing single Weyl points (including type-II nodes) and multiple Weyl Points with topological charges of 2 and 3, and finds nontrivial 2D bulk band gaps for a fixed kz and the associated surface modes.
Abstract: Weyl points, as monopoles of Berry curvature in momentum space, have captured much attention recently in various branches of physics. Realizing topological materials that exhibit such nodal points is challenging and indeed, Weyl points have been found experimentally in transition metal arsenide and phosphide and gyroid photonic crystal whose structure is complex. If realizing even the simplest type of single Weyl nodes with a topological charge of 1 is difficult, then making a real crystal carrying higher topological charges may seem more challenging. Here we design, and fabricate using planar fabrication technology, a photonic crystal possessing single Weyl points (including type-II nodes) and multiple Weyl points with topological charges of 2 and 3. We characterize this photonic crystal and find nontrivial 2D bulk band gaps for a fixed kz and the associated surface modes. The robustness of these surface states against kz-preserving scattering is experimentally observed for the first time.
242 citations
TL;DR: A refractory W-HfO2 metamaterial is demonstrated, which controls thermal emission through an engineered dielectric response function, marking a paradigm shift in thermal engineering approaches.
Abstract: Control of thermal radiation at high temperatures is vital for waste heat recovery and for high-efficiency thermophotovoltaic (TPV) conversion. Previously, structural resonances utilizing gratings, thin film resonances, metasurfaces and photonic crystals were used to spectrally control thermal emission, often requiring lithographic structuring of the surface and causing significant angle dependence. In contrast, here, we demonstrate a refractory W-HfO2 metamaterial, which controls thermal emission through an engineered dielectric response function. The epsilon-near-zero frequency of a metamaterial and the connected optical topological transition (OTT) are adjusted to selectively enhance and suppress the thermal emission in the near-infrared spectrum, crucial for improved TPV efficiency. The near-omnidirectional and spectrally selective emitter is obtained as the emission changes due to material properties and not due to resonances or interference effects, marking a paradigm shift in thermal engineering approaches. We experimentally demonstrate the OTT in a thermally stable metamaterial at high temperatures of 1,000 °C. The ability to control thermal radiation at high temperatures is of interest for thermal photovoltaics. Here, Dyachenko et al. engineer the epsilon-near-zero frequency of a metamaterial and connected optical topological transition to selectively enhance and suppress the thermal emission in the near-infrared spectrum.
236 citations
TL;DR: A 2D surface plasmon photonic crystal (SPPC) is achieved by implanting gold nanorods onto the periodic surface apertures of the poly(methyl methacrylate) opal photonic crystals.
Abstract: A 2D surface plasmon photonic crystal (SPPC) is achieved by implanting gold nanorods onto the periodic surface apertures of the poly(methyl methacrylate) (PMMA) opal photonic crystals. On the surface of the SPPC, the overall upconversion luminescence intensity of NaYF4 :Yb(3+) , Er(3+) under 980 nm excitation is improved more than 10(3) fold. The device is easily shifted to a transparent flexible substrate, applied to flexible displays.
TL;DR: This work demonstrates high degree of temporally and spatially coherent lasing whereby well-defined directional emission is achieved near 788 nm wavelength at optical pumping energy density threshold of 68.5 ± 3.0 μJ/cm(2).
Abstract: Perovskite semiconductors are actively investigated for high performance solar cells. Their large optical absorption coefficient and facile solution-based, low-temperature synthesis of thin films make perovskites also a candidate for light-emitting devices across the visible and near-infrared. Specific to their potential as optical gain medium for lasers, early work has demonstrated amplified spontaneous emission and lasing at attractively low thresholds of photoexcitation. Here, we take an important step toward practically usable perovskite lasers where a solution-processed thin film is embedded within a two-dimensional photonic crystal resonator. We demonstrate high degree of temporally and spatially coherent lasing whereby well-defined directional emission is achieved near 788 nm wavelength at optical pumping energy density threshold of 68.5 ± 3.0 μJ/cm2. The measured power conversion efficiency and differential quantum efficiency of the perovskite photonic crystal laser are 13.8 ± 0.8% and 35.8 ± 5.4%...
TL;DR: In this paper, an all-dielectric photonic crystal structure that supports two-dimensionally confined helical topological edge states is presented, and three-dimensional finite-difference time-domain calculations show these edges to be confined in the out-ofplane direction by total internal reflection.
Abstract: We present an all-dielectric photonic crystal structure that supports two-dimensionally confined helical topological edge states. The topological properties of the system are controlled by the crystal parameters. An interface between two regions of differing band topologies gives rise to topological edge states confined in a dielectric slab that propagate around sharp corners without backscattering. Three-dimensional finite-difference time-domain calculations show these edges to be confined in the out-of-plane direction by total internal reflection. Such nanoscale photonic crystal architectures could enable strong interactions between photonic edge states and quantum emitters.
TL;DR: A computational inverse-design method based on topology optimization is formulated and exploited to demonstrate photonic crystal structures supporting complex spectral degeneracies, finding that SE can be enhanced by a factor of 8 in passive structures, with larger enhancements possible at exceptional points of higher order n.
Abstract: We formulate and exploit a computational inverse-design method based on topology optimization to demonstrate photonic crystal structures supporting complex spectral degeneracies. In particular, we discover photonic crystals exhibiting third-order Dirac points formed by the accidental degeneracy of monopolar, dipolar, and quadrupolar modes. We show that, under suitable conditions, these modes can coalesce and form a third-order exceptional point, leading to strong modifications in the spontaneous emission (SE) of emitters, related to the local density of states. We find that SE can be enhanced by a factor of 8 in passive structures, with larger enhancements ∼sqrt[n^{3}] possible at exceptional points of higher order n.
TL;DR: In this article, an all-dielectric photonic crystal structure that supports two-dimensionally confined helical topological edge states is presented, and three dimensional finite-difference time-domain calculations show these edges to be confined in the out-ofplane direction by total internal reflection.
Abstract: We present an all-dielectric photonic crystal structure that supports two-dimensionally confined helical topological edge states. The topological properties of the system are controlled by the crystal parameters. An interface between two regions of differing band topologies gives rise to topological edge states confined in a dielectric slab that propagate around sharp corners without backscattering. Three dimensional finite-difference time-domain calculations show these edges to be confined in the out-of-plane direction by total internal reflection. Such nanoscale photonic crystal architectures could enable strong interactions between photonic edge states and quantum emitters.
TL;DR: In this paper, the authors studied the valley degree of freedom in all dielectric silicon photonic graphene and revisited the gap opening physics under inversion symmetry breaking by the viewpoint of nonzero valley Chern number.
Abstract: In this paper, we study valley degree of freedom in all dielectric silicon photonic graphene. Photonic band gap opening physics under inversion symmetry breaking is revisited by the viewpoint of nonzero valley Chern number. Bulk valley modes with opposite orbital angular momentum are unveiled by inspecting time-varying electric fields. Topological transition is well illustrated through photonic Dirac Hamiltonian. Valley dependent edge states and the associated valley-protected backscattering suppression around Z-shape bend waveguide have been demonstrated.
TL;DR: It is shown that, without breaking time-reversal symmetry, by tuning the geometry of the core-shell material, a phase transition into the photonic quantum spin Hall insulator can be achieved.
Abstract: A simple core-shell two-dimensional photonic crystal is studied where the triangular lattice symmetry and the C6 point group symmetry give rich physics in accidental touching points of photonic bands. We systematically evaluate different types of accidental nodal points at the Brillouin zone center for transverse-magnetic harmonic modes when the geometry and permittivity of the core-shell material are continuously tuned. The accidental nodal points can have different dispersions and topological properties (i.e., Berry phases). These accidental nodal points can be the critical states lying between a topological phase and a normal phase of the photonic crystal. They are thus very important for the study of topological photonic states. We show that, without breaking time-reversal symmetry, by tuning the geometry of the core-shell material, a phase transition into the photonic quantum spin Hall insulator can be achieved. Here the "spin" is defined as the orbital angular momentum of a photon. We study the topological phase transition as well as the properties of the edge and bulk states and their application potentials in optics.
TL;DR: It is demonstrated that SAPC patterns on a white background are covert under daylight, such that pattern detection can be avoided, but they become overt in a simple manner under strong illumination with smartphone flash light and/or on a black background, showing remarkable potential for anti-counterfeit techniques.
Abstract: Photonic crystal structures can be created to manipulate electromagnetic waves so that many studies have focused on designing photonic band-gaps for various applications including sensors, LEDs, lasers, and optical fibers. Here, we show that mono-layered, self-assembled photonic crystals (SAPCs) fabricated by using an inkjet printer exhibit extremely weak structural colors and multiple colorful holograms so that they can be utilized in anti-counterfeit measures. We demonstrate that SAPC patterns on a white background are covert under daylight, such that pattern detection can be avoided, but they become overt in a simple manner under strong illumination with smartphone flash light and/or on a black background, showing remarkable potential for anti-counterfeit techniques. Besides, we demonstrate that SAPCs yield different RGB histograms that depend on viewing angles and pattern densities, thus enhancing their cryptographic capabilities. Hence, the structural colorations designed by inkjet printers would not only produce optical holograms for the simple authentication of many items and products but also enable a high-secure anti-counterfeit technique.
TL;DR: The operation principles of photonic hydrogel sensors are explained, syntheses of stimuli-responsive polymers are presented, and an overview of qualitative and quantitative readout technologies are provided.
TL;DR: In this article, the photonic crystal unit cell was designed to incorporate deep subwavelength dielectric inclusions to achieve a mode volume commensurate with plasmonic elements while maintaining a quality factor that is characteristic of traditional photonic cavities.
Abstract: The fields of photonic crystals and plasmonics have taken two different approaches to increasing light–matter interaction. Photonic crystal cavities increase temporal confinement of light in a material, as represented by their high quality factor, while plasmonic structures increase spatial confinement, as represented by their low mode volume. However, the inability to simultaneously attain extreme temporal and spatial confinement of light remains a barrier to realizing ultimate control of light in a material and maximum performance in photonic devices. Here, by engineering the photonic crystal unit cell to incorporate deep subwavelength dielectric inclusions, we show that it is possible in a single structure to achieve a mode volume commensurate with plasmonic elements while maintaining a quality factor that is characteristic of traditional photonic crystal cavities. Manipulating the geometric design of the unit cell leads to precise control of the band structure and mode distribution in the photonic cry...
TL;DR: This work presents a novel way to manipulate VO2 photonic structures to modulate light transmission as a function of wavelength at different temperatures.
Abstract: Two-dimensional (2D) photonic structures, widely used for generating photonic band gaps (PBG) in a variety of materials, are for the first time integrated with the temperature-dependent phase change of vanadium dioxide (VO2). VO2 possesses thermochromic properties, whose potential remains unrealized due to an undesirable yellow-brown color. Here, a SiO2/VO2 core/shell 2D photonic crystal is demonstrated to exhibit static visible light tunability and dynamic near-infrared (NIR) modulation. Three-dimensional (3D) finite difference time domain (FDTD) simulations predict that the transmittance can be tuned across the visible spectrum, while maintaining good solar regulation efficiency (ΔTsol = 11.0%) and high solar transmittance (Tlum = 49.6%). Experiments show that the color changes of VO2 films are accompanied by NIR modulation. This work presents a novel way to manipulate VO2 photonic structures to modulate light transmission as a function of wavelength at different temperatures.
TL;DR: This work reports the first experimental demonstration of localized flat-band states in optically induced Kagome photonic lattices and demonstrates a high-fidelity transmission of complex patterns in such two-dimensional pyrochlore-like photonic structures.
Abstract: We report the first experimental demonstration of localized flat-band states in optically induced Kagome photonic lattices. Such lattices exhibit a unique band structure with the lowest band being completely flat (diffractionless) in the tight-binding approximation. By taking the advantage of linear superposition of the flat-band eigenmodes of the Kagome lattices, we demonstrate a high-fidelity transmission of complex patterns in such two-dimensional pyrochlore-like photonic structures. Our numerical simulations find good agreement with experimental observations, upholding the belief that flat-band lattices can support distortion-free image transmission.
TL;DR: In this paper, a novel optical 4 × 2 encoder based on 2D square lattice photonic crystals of silicon rods is proposed, where the main realization of optical encoder is based on the photonic crystal ring resonator NOR gates.
Abstract: The photonic crystals draw significant attention to build all-optical logic devices and are considered one of the solutions for the opto-electronic bottleneck via speed and size. The paper presents a novel optical 4 × 2 encoder based on 2D square lattice photonic crystals of silicon rods. The main realization of optical encoder is based on the photonic crystal ring resonator NOR gates. The proposed structure has four logic input ports, two output ports, and two bias input port. The photonic crystal structure has a square lattice of silicon rods with a refractive index of 3.39 in air. The structure has lattice constant ‘a’ equal to 630 nm and bandgap range from 0.32 to 044. The total size of the proposed 4 × 2 encoder is equal to 35 μm × 35 μm. The simulation results using the dimensional finite difference time domain and Plane Wave Expansion methods confirm the operation and the feasibility of the proposed optical encoder for ultrafast optical digital circuits.
TL;DR: In this article, the authors demonstrate the use of carbon nanotubes as electrically driven high-speed emitters in combination with a nanophotonic cavity that allows for exceptionally narrow linewidths.
Abstract: An important advancement towards optical communication on a chip would be the development of integratable, nanoscale photonic emitters with tailored optical properties. Here we demonstrate the use of carbon nanotubes as electrically driven high-speed emitters in combination with a nanophotonic cavity that allows for exceptionally narrow linewidths. The one-dimensional photonic crystal cavities are shown to spectrally select desired emission wavelengths, enhance intensity and efficiently couple light into the underlying photonic network with high reproducibility. Under pulsed voltage excitation, we realize on-chip modulation rates in the GHz range, compatible with active photonic networks. Because the linewidth of the molecular emitter is determined by the quality factor of the photonic crystal, our approach effectively eliminates linewidth broadening due to temperature, surface interaction and hot-carrier injection. Carbon nanotubes in a nanocavity offer a route to narrow-linewidth on-chip light emitters.
Abstract: Photonic nanostructures, manipulating and confining light on the nanometer scale, provide new opportunities to improve the efficiency of solar energy conversion. Optical microcavities confine light to small volumes by resonant recirculation. Plasmonic metal nanostructures with surface plasmon resonances can act as antennas to localize optical energy and control the location of charge carrier generation. Photonic crystals can enhance the interaction of light with a semiconductor. Integrated photonic crystals and the plasmonic effects of micro-structural materials may have a superposition effect in controlling light. Some applications and practical examples with respect to improving the efficiency of solar energy conversion with photonic nanostructures have been reviewed, demonstrating how such structures can enhance light absorption and improve the generation and separation of photoexcited charge carriers in photocatalytic degradation, solar water splitting, photovoltaic devices and CO2 photoreduction. Distinct from other published reviews, we simultaneously discuss several different types of photonic nanostructures in order to show the similarities and differences of photonic structures for solar energy conversion. Furthermore, the combination of different types of photonic nanostructures for developing more efficient solar energy conversion systems is discussed and explored.
TL;DR: A novel concept of magnetoplasmonic sensor with ultranarrow resonances and high sensitivity based on the combination of a specially designed one-dimensional photonic crystal and a ferromagnetic layer to realize ultralong-range propagating magnetoplasmons and to detect alteration of the environment refractive index via observation of the modifications in the Transversal Magnetooptical Kerr Effect spectrum.
Abstract: Currently, sensors invade into our everyday life to bring higher life standards, excellent medical diagnostic and efficient security. Plasmonic biosensors demonstrate an outstanding performance ranking themselves among best candidates for different applications. However, their sensitivity is still limited that prevents further expansion. Here we present a novel concept of magnetoplasmonic sensor with ultranarrow resonances and high sensitivity. Our approach is based on the combination of a specially designed one-dimensional photonic crystal and a ferromagnetic layer to realize ultralong-range propagating magnetoplasmons and to detect alteration of the environment refractive index via observation of the modifications in the Transversal Magnetooptical Kerr Effect spectrum. The fabrication of such a structure is relatively easy in comparison with e.g. nanopatterned samples. The fabricated heterostructure shows extremely sharp (angular width of 0.06°) surface plasmon resonance and even sharper magnetoplasmonic resonance (angular width is 0.02°). It corresponds to the propagation length as large as 106 μm which is record for magnetoplasmons and promising for magneto-optical interferometry and plasmonic circuitry as well as magnetic field sensing. The magnitude of the Kerr effect of 11% is achieved which allows for detection limit of 1∙10−6. The prospects of further increase of the sensitivity of this approach are discussed.
TL;DR: It is shown that by choosing appropriate values for the width of the resonant cavity, the desired wavelengths can be separated by the novel defective resonant cavities of an eight-channel photonic crystal demultiplexer.
Abstract: In this paper, we used the novel defective resonant cavities to design an eight-channel photonic crystal demultiplexer. We showed that by choosing appropriate values for the width of the resonant cavity, the desired wavelengths can be separated. The proposed platform has a square lattice of dielectric rods immersed in air. The value of transmission efficiency for channels was obtained in 94$$-$$-99 % range. In addition, the maximum value of crosstalk and average quality factor for channels were calculated ---11.2 dB and 2200, respectively.
TL;DR: It is shown how flexible films of stacked polymer nanoparticles can be directly assembled in a roll-to-roll process using a bending-induced oscillatory shear technique, which gives elastomeric photonic crystals termed polymer opals showing extremely strong tunable structural colour.
Abstract: Despite the availability of elaborate varieties of nanoparticles, their assembly into regular superstructures and photonic materials remains challenging. Here we show how flexible films of stacked polymer nanoparticles can be directly assembled in a roll-to-roll process using a bending-induced oscillatory shear technique. For sub-micron spherical nanoparticles, this gives elastomeric photonic crystals termed polymer opals showing extremely strong tunable structural colour. With oscillatory strain amplitudes of 300%, crystallization initiates at the wall and develops quickly across the bulk within only five oscillations. The resulting structure of random hexagonal close-packed layers is improved by shearing bidirectionally, alternating between two in-plane directions. Our theoretical framework indicates how the reduction in shear viscosity with increasing order of each layer accounts for these results, even when diffusion is totally absent. This general principle of shear ordering in viscoelastic media opens the way to manufacturable photonic materials, and forms a generic tool for ordering nanoparticles.
TL;DR: In this paper, a simple core-shell two-dimensional photonic crystal is studied where the triangle lattice symmetry and $C 6v$ rotation symmetry leads to rich physics in the study of accidental degeneracy's in photonic bands.
Abstract: A simple core-shell two-dimensional photonic crystal is studied where the triangle lattice symmetry and $C_{6v}$ rotation symmetry leads to rich physics in the study of accidental degeneracy's in photonic bands. We systematically evaluate different types of accidental nodal points, depending on the dispersions around them and their topological properties, when the geometry and permittivity are continuously changed. These accidental nodal points can be the critical states lying between a topological phase and a normal phase and are thus important for the study of topological photonic states. In time-reversal systems, this leads to the photonic quantum spin Hall insulator where the spin is defined upon the orbital angular momentum for transverse-magnetic polarization. We study the topological phase transition as well as the properties of the edge and bulk states and their application potentials in optics.