Conventional Photonic Crystals Research Articles

Photonic quasi-crystal terahertz lasers.

Quasi-crystal structures do not present a full spatial periodicity but are nevertheless constructed starting from deterministic generation rules. When made of different dielectric materials, they often possess fascinating optical properties, which lie between those of periodic photonic crystals and those of a random arrangement of scatterers. Indeed, they can support extended band-like states with pseudogaps in the energy spectrum, but lacking translational invariance, they also intrinsically feature a pattern of ‘defects’, which can give rise to critically localized modes confined in space, similar to Anderson modes in random structures. If used as laser resonators, photonic quasi-crystals open up design possibilities that are simply not possible in a conventional periodic photonic crystal. In this letter, we exploit the concept of a 2D photonic quasi crystal in an electrically injected laser; specifically, we pattern the top surface of a terahertz quantum-cascade laser with a Penrose tiling of pentagonal rotational symmetry, reaching 0.1–0.2% wall-plug efficiencies and 65 mW peak output powers with characteristic surface-emitting conical beam profiles, result of the rich quasi-crystal Fourier spectrum.

Absolute photonic band gap in 2D honeycomb annular photonic crystals

Abstract Using the plane wave expansion method, we investigate the effects of structural parameters on absolute photonic band gap (PBG) in two-dimensional honeycomb annular photonic crystals (PCs). The results reveal that the annular PCs possess absolute PBGs that are larger than those of the conventional air-hole PCs only when the refractive index of the material from which the PC is made is equal to 4.5 or larger. If the refractive index is smaller than 4.5, utilization of anisotropic inner rods in honeycomb annular PCs can lead to the formation of larger PBGs. The optimal structural parameters that yield the largest absolute PBGs are obtained.

Asymmetric elliptical-hole dual-core photonic crystal fiber with enhanced pressure sensitivity

We propose an asymmetric elliptical-hole dual-core photonic crystal fiber (AE-DC-PCF) for hydrostatic pressure sensing. The transmission spectra of the AE-DC-PCF under hydrostatic pressure and the relationship between pressure sensitivity and the minor axis ratio at different elliptical ratios have been calculated. Our results show that the AE-DC-PCF has higher pressure sensitivity than that of conventional dual-core photonic crystal (DC-PCF) fiber which has the circular-hole. Based on a 10cm fiber, the pressure sensitivity of the AE-DC-PCF as high as 50.6pm/MPa were achieved at 1.55μm, which is higher than the pressure sensitivity obtained from conventional DC-PCF (32.2pm/MPa).

Photonic crystals, amorphous materials, and quasicrystals

Photonic crystals consist of artificial periodic structures of dielectrics, which have attracted much attention because of their wide range of potential applications in the field of optics. We may also fabricate artificial amorphous or quasicrystalline structures of dielectrics, i.e. photonic amorphous materials or photonic quasicrystals. So far, both theoretical and experimental studies have been conducted to reveal the characteristic features of their optical properties, as compared with those of conventional photonic crystals. In this article, we review these studies and discuss various aspects of photonic amorphous materials and photonic quasicrystals, including photonic band gap formation, light propagation properties, and characteristic photonic states.

Study on the anisotropic photonic band gaps in three-dimensional tunable photonic crystals containing the epsilon-negative materials and uniaxial materials

In this paper, the properties of anisotropic photonic band gaps (PBGs) for three-dimensional (3D) photonic crystals (PCs) composed of the anisotropic positive-index materials (the uniaxial materials) and the epsilon-negative (ENG) materials with body-centered-cubic (bcc) lattices are theoretically studied by a modified plane wave expansion (PWE) method, which are the uniaxial materials spheres inserted in the epsilon-negative materials background. The anisotropic photonic band gaps (PBGs) and one flatbands region can be achieved in first irreducible Brillouin zone. The influences of the ordinary-refractive index, extraordinary-refractive index, filling factor, the electronic plasma frequency, the dielectric constant of ENG materials and the damping factor on the properties of anisotropic PBGs for such 3D PCs are studied in detail, respectively, and some corresponding physical explanations are also given. The numerical results show that the anisotropy can open partial band gaps in such 3D PCs with bcc lattices composed of the ENG materials and uniaxial materials, and the complete PBGs can be obtained compared to the conventional 3D PCs containing the isotropic materials. The calculated results also show that the anisotropic PBGs can be manipulated by the parameters as mentioned above except for the damping factor. Introducing the uniaxial materials into 3D PCs containing the ENG materials can obtain the larger complete PBGs as such 3D PCs with high symmetry, and also provides a way to design the tunable devices.

Study on the polarization-insensitive self-collimation behavior in two-dimensional all-solid photonic crystals

Due to unavoidable separation of bands for different polarizations, it is usually difficult to realize polarization-insensitive self-collimation (PISC) from conventional rod-type two-dimensional photonic crystals (PCs). In this paper, we have systematically investigated the band, equi-frequency contours, and transmission properties of a special two-dimensional PC that quite resembles the structure of conventional rod-type PCs. By only replacing the air background in rod-type PCs with dielectric background, the so-called all-solid two-dimensional PC can show much closer bands than conventional rod-type PCs. Such suppressed band feature is quite beneficial to the formation of flat equi-frequency contours for both polarizations at the same frequency, namely a PISC effect. By further comparing the PISC in different all-solid PCs and optimizing the cut-off value at PC terminations, we have obtained some useful rules to control the performance of PISC. Finally, based on the special PISC effect in all-solid PCs, we have also given two specific examples to illustrate the potential ability of all-solid PCs in realizing novel polarization-insensitive functional devices.

The right circular polarized waves in the three-dimensional anisotropic dispersive photonic crystals consisting of the magnetized plasma and uniaxial material as the Faraday effects considered

In this paper, the properties of the right circular polarized (RCP) waves in the three-dimensional (3D) dispersive photonic crystals (PCs) consisting of the magnetized plasma and uniaxial material with face-centered-cubic (fcc) lattices are theoretically investigated by the plane wave expansion method, which the homogeneous anisotropic dielectric spheres (the uniaxial material) immersed in the magnetized plasma background, as the Faraday effects of magnetized plasma are considered (the incidence electromagnetic wave vector is parallel to the external magnetic field at any time). The equations for calculating the anisotropic photonic band gaps (PBGs) for the RCP waves in the first irreducible Brillouin zone are theoretically deduced. The anisotropic PBGs and a flatbands region can be obtained. The effects of the ordinary-refractive index, extraordinary-refractive index, anisotropic dielectric filling factor, plasma frequency, and plasma cyclotron frequency (the external magnetic field) on the properties of first two anisotropic PBGs for the RCP waves are investigated in detail, respectively. The numerical results show that the anisotropy can open partial band gaps in fcc lattices at U and W points, and the complete PBGs for the RCP waves can be achieved compared to the conventional 3D dispersive PCs composed of the magnetized plasma and isotropic material. It is also shown that the first two anisotropic PBGs can be tuned by those parameters as mentioned above. Those PBGs can be enlarged by introducing the uniaxial material into such 3D PCs as the Faraday effects are considered.

Photonic band gap of superconductor-medium structure: Two-dimensional triangular lattice

Based on London theory a general form of wave equation is formulated for both dielectric medium and superconductor. Using the wave equation and applying plane wave expansion, we have numerically calculated the band structures and density of states of a photonic crystal, whose intersection is constructed by a two-dimensional triangular lattice of superconductor padding in dielectric medium. Results indicate a wider band gap in the superconductor-medium photonic crystal than that in conventional photonic crystals. And part of original energy levels are found to be rearranged upon consideration of the superconductivity. The dependence of band gap on penetration length and filling factor is also discussed. Band gap width decreases monotonically with the penetration length, but not with the filling factor. Band gaps can be partially shut down or opened by adjusting filling factor.

Asymmetric light propagation based on semi-circular photonic crystals

A new structure based on a semi-circular photonic crystal is proposed to achieve asymmetric light propagation. The semi-circular photonic crystal structure proposed in this paper is a deformation of a two-dimensional conventional square photonic crystal. Through the directional bandgap of the semi-circular photonic crystal, the light from one direction can transfer to the other side, but the light from the opposite direction cannot. A high contrast ratio is obtained by designing the constitutive parameters of the photonic crystal and choosing the suitable light frequency. This structure promises a significant potential in optical integration and other areas.

Asymmetric Light Propagation Based on Graded Photonic Crystals

This study proposes a novel graded photonic crystal structure that can be used to achieve asymmetric light propagation. This structure is obtained by changing the radius of a conventional square lattice photonic crystal. A higher contrast ratio is obtained by extending the numbers of the periods of the graded photonic crystal in the horizontal direction. The best contrast ratio almost reaches 1. The intensity at the spot where the light propagated forward converges is two orders of magnitude greater than the intensity at the optical axis of the backward transmission. Numerical results are obtained using the finite-difference time domain and plane wave methods. The proposed structure has significant application potential in optical integration.

Omnidirectional reflection from generalized Fibonacci quasicrystals

We determine the optimal thicknesses for which omnidirectional reflection from generalized Fibonacci quasicrystals occurs. By capitalizing on the idea of wavelength- and angle-averaged reflectance, we assess in a consistent way the performance of the different systems. Our results indicate that some of these aperiodic arrangements can largely over-perform the conventional photonic crystals as omnidirectional reflection is concerned.

ChemInform Abstract: Amorphous Photonic Crystals with Only Short‐Range Order

AbstractReview: 55 refs.

Photonic crystal structures for light trapping in thin-film Si solar cells: Modeling, process and optimizations

In this paper, we present our efforts on studying light trapping in thin-film silicon solar cells using photonic crystal (PC) based structures. Specifically, we propose a photonic backside texture combining periodic gratings and a distributed Bragg reflector (DBR). The mechanisms of this integrated photonic design are theoretically studied and compared with conventional PCs. We experimentally fabricate the texture using lithographic and self-assembled method on thin-film single crystalline Si (c-Si) and micro-crystalline Si (μc-Si) cells. We analyze the effects of the photonic textures on different cells and demonstrate the performance improvements. A numerical method is developed to explore the optimal multiscale textured surface and investigate light trapping limits in the wave optics regime. Using a detailed balance analysis, we show that it is possible to reach over 20% efficiency for 1.5μm Si cells through optimal device design and fabrication.

Amorphous Photonic Crystals with Only Short‐Range Order

Distinct from conventional photonic crystals with both short- and long-range order, amorphous photonic crystals that possess only short-range order show interesting optical responses owing to their unique structural features. Amorphous photonic crystals exhibit unique light scattering and transport, which lead to a variety of interesting phenomena such as isotropic photonic bandgaps or pseudogaps, noniridescent structural colors, and light localization. Recent experimental and theoretical advances in the study of amorphous photonic crystals are summarized, focusing on their unique optical properties, artificial fabrication, bionspiration, and potential applications.

Omnidirectional photonic band gaps enhanced by Fibonacci quasiperiodic one-dimensional ternary plasma photonic crystals

An omnidirectional photonic band gap realized by one-dimensional Fibonacci quasiperiodic structure which is composed of plasma and two kinds of isotropic dielectric is theoretically studied. It has been shown that such an omnidirectional photonic band gap is insensitive to the incident angle and the polarization of electromagnetic wave (EM wave). The frequency range and central frequency of omnidirectional photonic band gap cease to change with increasing Fibonacci order, but vary with the thickness and density of the plasma. The bandwidth of omnidirectional photonic band gap can be notably enlarged. The omnidirectional photonic band gap originates from a Bragg gap in contrast to zero-n˜ gap or single negative (negative permittivity or negative permeability) gap. From the numerical results performed by the transfer matrix method (TMM), it has been proved that Fibonacci quasiperiodic one-dimensional ternary plasma photonic crystals have a superior feature in the enhancement of omnidirectional photonic band gap frequency range compared with the conventional ternary plasma photonic crystals. This omnidirectional photonic band gap has potential applications in filters, microcavities, and fibers, etc.

Omnidirectional photonic band gap enlarged by one-dimensional ternary unmagnetized plasma photonic crystals based on a new Fibonacci quasiperiodic structure

In this paper, an omnidirectional photonic band gap realized by one-dimensional ternary unmagnetized plasma photonic crystals based on a new Fibonacci quasiperiodic structure, which is composed of homogeneous unmagnetized plasma and two kinds of isotropic dielectric, is theoretically studied by the transfer matrix method. It has been shown that such an omnidirectional photonic band gap originates from Bragg gap in contrast to zero-n¯ gap or single negative (negative permittivity or negative permeability) gap, and it is insensitive to the incidence angle and the polarization of electromagnetic wave. From the numerical results, the frequency range and central frequency of omnidirectional photonic band gap can be tuned by the thickness and density of the plasma but cease to change with increasing Fibonacci order. The bandwidth of omnidirectional photonic band gap can be notably enlarged. Moreover, the plasma collision frequency has no effect on the bandwidth of omnidirectional photonic band gap. It is shown that such new structure Fibonacci quasiperiodic one-dimensional ternary plasma photonic crystals have a superior feature in the enhancement of frequency range of omnidirectional photonic band gap compared with the conventional ternary and conventional Fibonacci quasiperiodic ternary plasma photonic crystals.

Omnidirectional photonic band gaps enlarged by Fibonacci quasi-periodic one-dimensional ternary superconductor photonic crystals

First two omnidirectional photonic band gaps (OBGs) realized by one-dimensional (1D) Fibonacci quasi-periodic structure which is composed of superconductor and two kinds of isotropic dielectric are theoretically studied by the transfer matrix method (TMM). From the numerical results, it has been shown that such OBGs are insensitive to the incident angle and the polarization of electromagnetic wave (EM wave), and the frequency ranges and central frequencies of OBGs cease to change with increasing Fibonacci order, but vary with the ambient temperature of system and the thickness of the superconductor, respectively. The bandwidths of OBGs can be notably enlarged. The damping coefficient of superconductor layers has no effect on the frequency ranges of OBGs. Those OBGs originate from a Bragg gap in contrast to zero-n˜ gap or single negative (negative permittivity or negative permeability) gap. It has been proved that Fibonacci quasi-periodic 1D ternary superconductor dielectric photonic crystals (SDPCs) have a superior feature in the enhancement of OBGs frequency ranges compared with the conventional binary dielectric photonic crystals (DPCs).

Theoretical studies on transforming a GaN semiconductor into a photonic crystal under a periodic external magnetic field

In this study, the properties of light propagation for a GaN semiconductor when subjected to a periodic external magnetic field were calculated by means of a transfer matrix. The dielectric function which was modulated periodically by the periodic external magnetic field caused changes of photonic band gap (PBG). In the reflection spectra, photons can be localized in the narrow bands. The position and intensity of PBGs can be modulated by changing the periodic external magnetic field and angle of the incident electromagnetic wave. All of these results have shown that a semiconductor has functions similar to conventional photonic crystals subjected to periodic external magnetic field.

Transmission character of general function photonic crystals

In the paper, we present a new general function photonic crystals (GFPCs), whose refractive index of medium is a arbitrary function of space position. Unlike conventional photonic crystals (PCs), whose structure grows from two mediums A and B, with different constant refractive indexes na and nb. Based on the Fermat principle, we give the motion equations of light in one-dimensional GFPCs, and calculate its transfer matrix, which is different from the conventional PCs. We choose the linearity refractive index function for two mediums A and B, and find the transmissivity of one-dimensional GFPCs can be much larger or smaller than 1 for different slope linearity refractive index functions, which are different from the transmissivity of conventional PCs (its transmissivity is in the range of 0 and 1). Otherwise, we study the effect of different incident angles, the number of periods and optical thickness on the transmissivity, and obtain some new results different from the conventional PCs.

Strong light confinement in a photonic amorphous diamond structure

Formation of cavity modes in a recently found unique photonic structure “photonic amorphous diamond (PAD)” has been investigated by finite-difference time domain calculations. A well-confined monopole mode has been found to form when a rod is removed from the structure. The quality (Q) factor and mode volume (Vm) of such a cavity mode in PAD have been evaluated and compared with those in a conventional photonic crystal with a crystalline diamond structure. The two structures have shown nealy the same Q-factor and Vm, leading to the conclusion that strong light confinement is realizable in PAD as well as conventional photonic crystals.