We use a scattering matrix approach to simulate the transmission through a hexagonal Photonic Crystal in the vicinity of the Dirac point. If the crystal is oriented so that the propagation direction perpendicular to the surface corresponds to the Gamma-K direction, no oblique transmission is possible for a very long (infinite) structure. For a finite structure with width, W, and length, L, the length dependence of the transmission is given by T_total = Gamma_0 W/L. For T_total all waves with a wavevector parallel to the surface, k_||=n 2pi/W, described by a channel number, n, must be considered. We show the transmission at the Dirac point follows the given scaling law and this scaling law is related to the behavior of the individual channels. This leads to the establishment of a criterion for the maximum length for this scaling behavior when the total transmission reaches a constant value. We also compare this scaling behavior to the results in other frequency regions.
Integrated quantum photonics (IQP) provides a path to practical, scalable quantum computation, communications and information processing. Realization of an IQP platform requires integration of quantum emitters with high quality photonic circuits. However, the range of materials for monolithic platforms is limited by the simultaneous need for a high-quality single photon source, high optical performance and availability of scalable nanofabrication techniques. Here we demonstrate the fabrication of IQP components from the recently emerged quantum material hexagonal boron nitride (hBN), including…
We investigate propagation of light pulses in photonic crystals in the vicinity of the zero-diffraction point. We show that Gaussian pulses due to nonzero width of their spectrum spread weakly in space and time during the propagation. We also find the family of nonspreading pulses, propagating invariantly in the vicinity of the zero diffraction point of photonic crystals.
Ultra-compact topological ring-resonators with chirality are important devices for quantum optics. However, there are limited demonstrations of chiral resonators, especially in the visible region. We proposed a topological photonic ring-resonator based on hexagonal boron nitride (hBN) valley photonic crystal (VPC). The spin-valley locking effect in VPC allows achieving robust unidirectional transmission of edge states in the visible region (600 nm-650 nm). As a result, a high quality factor (679.3) with a free spectral range of 15.2 nm in the visible region can be achieved in a hBN all-pass fi…
We propose and design photonic crystal cavities (PCCs) in hexagonal boron nitride (hBN) for diverse photonic and quantum applications. Two dimensional (2D) hBN flakes contain quantum emitters which are ultra-bright and photostable at room temperature. To achieve optimal coupling of these emitters to optical resonators, fabrication of cavities from monolithic hBN is therefore required, to maximize the overlap between cavity optical modes and the emitters. Here, we design 2D and 1D PCCs using anisotropic indices of hBN. The influence of underlying substrates and material absorption are investiga…
The polarization properties of a magnetophotonic crystal at the frequencies located in the vicinity of ferromagnetic resonance are studied. The investigations are curried out taking into consideration the fact that the magnitude of material losses in ferrite layers at this frequency band is significant. The method is based on obtaining a system of ordinary differential equations and further analyzing the stability of solutions of this system. The electromagnetic properties of the structure under study are found out via the analysis of the eigenvalues of the transfer matrix of the structure per…
Growing interest in devices based on layered van der Waals (vdW) materials is motivating the development of new nanofabrication methods. Hexagonal boron nitride (hBN) is one of the most promising materials for studies of quantum photonics and polaritonics. Here, we report in detail on a promising nanofabrication processes used to fabricate several hBN photonic devices using a hybrid electron beam induced etching (EBIE) and reactive ion etching (RIE) technique. We highlight the shortcomings and benefits of RIE and EBIE and demonstrate the utility of the hybrid approach for the fabrication of su…
In 1964 Bloembergen and Shen predicted that Raman gain could be suppressed if the rates of phonon creation and annihilation (by inelastic scattering) exactly balance. This is only possible if the momentum required for each process is identical, i.e., phonon coherence waves created by pump-to-Stokes scattering are identical to those annihilated in pump-to-anti-Stokes scattering. In bulk gas cells, this can only be achieved over limited interaction lengths at an oblique angle to the pump axis. Here we report a simple system that provides dramatic Raman gain suppression over long collinear path-l…
Adapting optical microscopy methods for nanoscale characterization of defects in two-dimensional (2D) materials is a vital step for photonic on-chip devices. To increase the analysis throughput, waveguide-based on-chip imaging platforms have been recently developed. Their inherent disadvantage, however, is the necessity to transfer the 2D material from the growth substrate to the imaging chip which introduces contamination, potentially altering the characterization results. Here we present a unique approach to circumvent these shortfalls by directly growing a widely-used 2D material (hexagonal…
Integration of solid state quantum emitters into nanophotonic circuits is a critical step towards fully on-chip quantum photonic based technologies. Among potential materials platforms, quantum emitters in hexagonal boron nitride have emerged over the last years as viable candidate. While the fundamental physical properties have been intensively studied over the last years, only few works have focused on the emitter integration into photonic resonators. Yet, for a potential quantum photonic material platform, the integration with nanophotonic cavities is an important cornerstone, as it enables…
Unbalanced CRLH Leaky-wave Antenna With Broadside Radiation Based On Spin Photonic Topological Insulator Featured Hexagonal Configuration In Armchair Arrangement
We have measured the photonic bandgap in the transmission of microwaves through a two-dimensional photonic crystal slab. The structure was constructed by cementing acrylic rods in a hexagonal closed-packed array to form rectangular stacks. We find a bandgap centered at approximately 11 GHz, whose depth, width and center frequency vary with the number of layers in the slab, angle of incidence and microwave polarization.
Development of scalable quantum photonic technologies requires on-chip integration of components such as photonic crystal cavities and waveguides with nonclassical light sources. Recently, hexagonal boron nitride (hBN) has emerged as a promising platform for nanophotonics, following reports of hyperbolic phonon-polaritons and optically stable, ultra-bright quantum emitters. However, exploitation of hBN in scalable, on-chip nanophotonic circuits, quantum information processing and cavity quantum electrodynamics (QED) experiments requires robust techniques for the fabrication of monolithic optic…
A metamaterial with a negative effective index of refraction is made from a three-dimensional hexagonal lattice photonic crystal with a metallic basis embedded in foam. It has been simulated with Ansoft HFSSTM in a frequency range from 7.0 to 12.0 GHz. Simulated results tested experimentally and negative refraction verified in some frequencies. Experimental results are in excellent agreement with simulations.
Hexagonal boron nitride (hBN) is a layered dielectric material with a wide range of applications in optics and photonics. In this work, we demonstrate a fabrication method for few-layer hBN flakes with areas up to 5000 $\rm μm$. We show that hBN in this form can be integrated with photonic microstructures: as an example, we use a circular Bragg grating (CBG). The layer quality of the exfoliated hBN flake on a CBG is confirmed by second-harmonic generation (SHG) microscopy. We show that the SHG signal is uniform across the hBN sample outside the CBG and is amplified in the centre of the CBG.
We report the observations of spontaneous Raman scattering in silicon photonic crystal waveguides. Continuous-wave measurements of Stokes emission for both wavelength and power dependence is reported in single line-defect waveguides in hexagonal lattice photonic crystal silicon membranes. By utilizing the Bragg gap edge dispersion of the TM-like mode for pump enhancement and the TE-like fundamental mode-onset for Stokes enhancement, the Stokes emission was observed to increase by up to five times in the region of slow group velocity. The results show explicit nonlinear enhancement in a silicon…
We demonstrate that photonic and phononic crystals consisting of closely spaced inclusions constitute a versatile class of subwavelength metamaterials. Intuitively, the voids and narrow gaps that characterise the crystal form an interconnected network of Helmholtz-like resonators. We use this intuition to argue that these continuous photonic (phononic) crystals are in fact asymptotically equivalent, at low frequencies, to discrete capacitor-inductor (mass-spring) networks whose lumped parameters we derive explicitly. The crystals are tantamount to metamaterials as their entire acoustic branch,…
We studied the optical properties of a dielectric photonic crystal structure with spirals arranged in a hexagonal lattice. The dielectric constant of the material is 9 and the filling ratio is 15.2%. We found that this kind of structure exhibits a significant polarization gap for light incident along the axis of the spirals. The eigenmodes inside the polarization gap are right-hand (left-hand) circularly polarized depending on the whether the spirals are left-handed (right-handed). The transmission spectrum of a slab of such a structure has been calculated and matches well with the analysis of…
Optical cavities, plasmonic structures, photonic band crystals, interfaces, as well as, generally speaking, any photonic media with homogeneous or spatially inhomogeneous dielectric permittivity (including metamaterials) have local densities of photonic states, which are different from that in vacuum. These modified density of states environments are known to control both the rate and angular distribution of spontaneous emission. In the present study, we ask the question whether the proximity to metallic and metamaterial surfaces can affect other physical phenomena of fundamental and practical…
Polarization-resolved second-harmonic spectra are obtained from the resonant modes of a two-dimensional planar photonic crystal microcavity patterned in a free-standing InP slab. The photonic crystal microcavity is comprised of a single missing-hole defect in a hexagonal photonic crystal host formed with elliptically-shaped holes. The cavity supports two orthogonally-polarized resonant modes split by 60 wavenumbers. Sum-frequency data are reported from the nonlinear interaction of the two coherently excited modes, and the polarization dependence is explained in terms of the nonlinear susceptib…
Two-dimensional hexagonal boron nitride (hBN) that hosts bright room-temperature single-photon emitters (SPEs) is a promising material platform for quantum information applications. An important step towards the practical application of hBN is the on-demand, position-controlled generation of SPEs. Several strategies have been reported to achieve the deterministic creation of hBN SPEs. However, they either rely on a substrate nanopatterning procedure that is not compatible with integrated photonic devices or utilize a radiation source that might cause unpredictable damage to hBN and underlying …
Colour centres in hexagonal boron nitride (hBN) have emerged as intriguing contenders for integrated quantum photonics. In this work, we present detailed photophysical analysis of hBN single emitters emitting at the blue spectral range. The emitters are fabricated by different electron beam irradiation and annealing conditions and exhibit narrow-band luminescence centred at 436 nm. Photon statistics as well as rigorous photodynamics analysis unveils potential level structure of the emitters, which suggests lack of a metastable state, supported by a theoretical analysis. The potential defect ca…
Current quantum cascade lasers based upon conduction band electron transitions are predominantly TM (electrical field normal to the epitaxial direction) polarized. Here we present a study of localized defect modes, with the requisite TM polarization, in connected square and hexagonal lattice two-dimensional (2D) photonic crystals for application as quantum cascade laser resonators. A simple group-theory based analysis is used to produce an approximate description of the resonant modes supported by defects situated at different high symmetry points within the host photonic lattice. The results …
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 origin 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 pre-canceled. The symmetric compatible nature of the off-$Γ$ BICs leads to a trapping of light that can be tuned through continuously varying the wavevector. With the analytical approach, we explain a reported experimen…
A localized defect mode in a photonic-layered structure develops nodal points. Placing a thin metallic layer at such a nodal point results in the phenomenon of induced transparency. We demonstrate that if this nodal point is not a point of symmetry, then even a tiny alteration of the permittivity in the vicinity of the defect suppresses the localized mode along with the resonant transmission; the layered structure becomes highly reflective within a broad frequency range. Applications of this hypersensitive transport for optical limiting and switching are discussed.
The photonic band dispersion and density of states (DOS) are calculated for the three-dimensional (3D) hexagonal structure corresponding to a distributed Bragg reflector patterned with a 2D triangular lattice of circular holes. Results for the Si/SiO$_2$ and GaAs/AlGaAs systems determine the optimal parameters for which a gap in the 2D plane occurs and overlaps the 1D gap of the multilayer. The DOS is considerably reduced in correspondence with the overlap of 2D and 1D gaps. Also, the local density of states (i.e., the DOS weighted with the squared electric field at a given point) has strong v…
A numerical modeling of the radiation emitted from a Luminescent dye embedded in a finite one-dimensional photonic crystal is presented. The Photonic Band Structure and the Photonic Density of States are derived using classical electromagnetic approach, and the Finite Difference Time-Domain formalism is used to calculate the electromagnetic field distribution. It is found that the periodic modulation provides an effective way to control the Spontaneous Emission under certain circumstances. We find the conditions where a large amount of light can be enhanced on the vicinity of a photonic band e…
Single defect centers in layered hexagonal boron nitride (hBN) are promising candidates as single photon sources for quantum optics and nanophotonics applications. However, until today spectral instability hinders many applications. Here, we perform resonant excitation measurements and observe Fourier-Transform limited (FL) linewidths down to $\approx 50$ MHz. We investigate optical properties of more than 600 quantum emitters (QE) in hBN. The QEs exhibit narrow zero-phonon lines (ZPL) distributed over a spectral range from 580 nm to 800 nm and with dipole-like emission with high polarization …
Quantum emitters in hexagonal boron nitride (hBN) are promising building blocks for the realization of integrated quantum photonic systems. However, their spectral inhomogeneity currently limits their potential applications. Here, we apply tensile strain to quantum emitters embedded in few-layer hBN films and realize both red and blue spectral shifts with tuning magnitudes up to 65 meV, a record for any two-dimensional quantum source. We demonstrate reversible tuning of the emission and related photophysical properties. We also observe rotation of the optical dipole in response to strain, sugg…
Color centers in hexagonal boron nitride (hBN) are becoming an increasingly important building block for quantum photonic applications. Herein, we demonstrate the efficient coupling of recently discovered spin defects in hBN to purposely designed bullseye cavities. We show that the all monolithic hBN cavity system exhibits an order of magnitude enhancement in the emission of the coupled boron vacancy spin defects. In addition, by comparative finite difference time domain modelling, we shed light on the emission dipole orientation, which has not been experimentally demonstrated at this point. B…
We report on the formation and development of the photonic band gap in two-dimensional 8-, 10- and 12-fold symmetry quasicrystalline lattices of low index contrast. Finite size structures made of dielectric cylindrical rods were studied and measured in the microwave region, and their properties compared with a conventional hexagonal crystal. Band gap characteristics were investigated by changing the direction of propagation of the incident beam inside the crystal. Various angles of incidence from 0 \degree to 30\degree were used in order to investigate the isotropic nature of the band gap. The…
Progress on two-dimensional materials has shown that valleys, as energy extrema in a hexagonal first Brillouin zone, provides a new degree of freedom for information manipulation. Then valley Hall topological insulators supporting such-polarized edge states on boundaries were set up accordingly. In this paper, a two-dimensional valley photonic crystal composed of six tunable dielectric triangular pillars in unit cells is proposed in the photonic sense of a deformed Su-Schrieffer-Heeger (SSH) model. We reveal the vortex nature of valley states and establish the selection rules for valley polari…
Topological photonics aims to utilize topological photonic bands and corresponding edge modes to implement robust light manipulation, which can be readily achieved in the linear regime of light-matter interaction. Importantly, unlike solid state physics, the common test bed for new ideas in topological physics, topological photonics provide an ideal platform to study wave mixing and other nonlinear interactions. These are well-known topics in classical nonlinear optics but largely unexplored in the context of topological photonics. Here, we investigate nonlinear interactions of one-way edge-mo…
Optical bound state in the continuum (BIC) is characterized by infinitely high quality factor resulting in drastic enhancement of light-matter interaction phenomena. We study the optical response of a one-dimensional photonic crystal slab with Kerr focusing nonlinearity in the vicinity of BIC analytically and numerically. We predict a strong nonlinear response including multistable behaviour, self-tuning of BIC to the frequency of incident wave, and breaking of symmetry protected BIC. We show that all of these phenomena can be observed in silicon photonic structure at the pump power of several…
Germanium self-assembled nanoislands and quantum dots are very prospective for CMOS-compatible optoelectronic integrated circuits but their luminescence intensity is still insufficient for many practical applications. Here, we demonstrate experimentally that photoluminescence of Ge nanoislands in silicon photonic crystal slab with hexagonal lattice can be dramatically enhanced due to the involvement in the emission process of the bounds states in the continuum. We experimentally demonstrate more than two orders of magnitude peak photoluminescence enhancement and more than one order of magnitud…
We create a passive wave splitter, created purely by geometry, to engineer three-way beam splitting in electromagnetism in transverse electric polarisation. We do so by considering arrangements of Indium Phosphide dielectric pillars in air, in particular we place several inclusions within a cell that is then extended periodically upon a square lattice. Hexagonal lattice structures more commonly used in topological valleytronics but, as we discuss, three-way splitting is only possible using a square, or rectangular, lattice. To achieve splitting and transport around a sharp bend we use accident…
A model of an organic solar cell based on a Tamm plasmon polariton localized at the interface between a photonic crystal and a photosensitive layer with an embedded square or hexagonal plasmonic array has been proposed. The spectral properties of the structures have been investigated in the framework of the temporal coupled mode theory and confirmed by the transfer matrix method. It has been shown that the conjugation of a photonic crystal with a photosensitive layer leads to the excitation of a Tamm plasmon polariton at the interface between them and, consequently, to an increase in the integ…
We demonstrate that graphene-based photonic superlattices provide a versatile platform for electrical and all-optical control of photonic beams with deep-subwavelength accuracy. Specifically, by inserting graphene sheets into periodic metallo-dielectric structures one can design optical superlattices that posses photonic Dirac points (DPs) at frequencies at which the spatial average of the permittivity of the superlattice, $\bar{ \varepsilon}$, vanishes. Similar to the well-known zero-$\bar{n}$ bandgaps, we show that these zero-$\bar{\varepsilon}$ DPs are highly robust against structural disor…
The effect of surface termination on the inverse Goos Hanchen (GH) shift of two dimensional (2D) negatively refractive photonic crystal (NRPhC) containing air holes arranged in hexagonal lattice in a dielectric background is investigated for TM polarization. Results show that the magnitude of the inverse GH shift of 2DNRPhC strongly depends on surface termination even for an incident beam with a fixed frequency and incidence angle. Further study by calculating the dispersion of surface mode of 2D-NRPhC as a function of surface termination reveals that 2DNRPhC presents large inverse Goos Hanche…
We present an analytical study of the mode degeneracy in non-Hermitian photonic crystals (PC) with $C_{4v}$ symmetry, from the perspective of the coupled-wave-theory (CWT). The wave couplings and leakages within the non-Hermitian PCs are depicted, and the condition of accidental triple degeneracy is derived which leads to a Dirac-cone like dispersion. We prove that, similar to the real Dirac-cone, the Dirac-cone like band in non-Hermitian PC possesses good linearity and isotropy in the vicinity of the $Γ$ point. Moreover, some topological transit of the band may occur when the parameters adiab…
Combining solid state single photon emitters (SPE) with nanophotonic platforms is a key goal in integrated quantum photonics. In order to realize functionality in potentially scalable elements, suitable SPEs have to be bright, stable, and widely tunable at room temperature. In this work we show that selected SPEs embedded in a few layer hexagonal boron nitride (hBN) meet these demands. In order to show the wide tunability of these SPEs we employ an AFM with a conductive tip to apply an electrostatic field to individual hBN emitters sandwiched between the tip and an indium tin oxide coated glas…
We create hybrid topological-photonic localisation of light by introducing concepts from the field of topological matter to that of photonic crystal fiber arrays. S-polarized obliquely propagating electromagnetic waves are guided by hexagonal, and square, lattice topological systems along an array of infinitely conducting fibers. The theory utilises perfectly periodic arrays that, in frequency space, have gapped Dirac cones producing band gaps demarcated by pronounced valleys locally imbued with a nonzero local topological quantity. These broken symmetry-induced stop-bands allow for localised …
We discover a pair of stable 3D Dirac points, 3D photonic analog of graphene, in all-dielectric photonic crystals using structures commensurate with nano-fabrication for visible-frequency photonic applications. The Dirac points carry nontrivial $Z_2$ topology and emerge for a large range of material parameters in hollow cylinder hexagonal photonic crystals. From Kramers theorem and group theory, we find that only the $C_6$ symmetry lead to point group symmetry stabilized Dirac points in 3D all-dielectric photonic crystals. {The Dirac points are characterized using ${\vec k}\cdot{\vec P}$ theor…
