Fabrication of a Two-Dimensional Organic Photonic Crystal

A high-quality two-dimensional polystyrene photonic crystal is fabricated by the method of focused ion beam etching. The scanning electron microscopy (SEM) and the transmittance spectrum are used to characterize the properties of the photonic crystal. The measured transmittance spectrum is in agreement with the theoretical one. The influences of the disorders caused by the random perturbations in the diameter or the position of the air holes on the photonic band structure are analysed. It is found that the phtonic bandgap can tolerate less than 10% degree of disorder.     

Band Structure of a two—Dimensional Photonic Crystal with a Triangular Lattice of Anisotropic Elliptic Cylinders

The plane-wave expansion method is used to calculate the band structure of a two-dimensional photonic crystal formed by a triangular lattice of anisotropic elliptic cylinders.After optimizing the parameters of the elliptic cylinders,we find a large bandgap (about 0.0449 ωe,ωe=2πc/α) at high frequencies beside a coexisting large absolute gap(about 0.035ωe) at low frequencies.Numerical results show that the optimal design is very stable under any parameter perturbation.     

Highly Birefringent Honeycomb Photonic Bandgap Fibre

A new structure of highly birefringent honeycomb photonic bandgap fibres （PBGFs）, including an elliptical air hole in its solid core, is proposed and analysed by using full vectorial plane wave expansion method. From the numerical results it is confirmed that the proposed PBGF. has birefringence of the order of 10^-3. Moreover, there are two single-polarization single-mode ranges at varying normalized wavelength, in one of which only the slowaxis mode exists, and in the other only the fast-axis mode exists, which has not been achieved in index-guiding photonic crystal fibres so far.     

Fabrication of Two-Dimensional Photonic Crystals with Triangular Rods by Single-Exposure Holographic Lithography

We demonstrate a single-exposure holographic fabrication of two-dimensional photonic crystal with round- cornered triangular ＇atoms＇ arranged in a triangular lattice. Simulation results show that double absolute photonic band gaps exist in this structure. Our experimental results show that holographic lithography can be used to fabricate photonic crystals not only with various lattice structures but also with various kinds of structures of the atoms, to obtain absolute band gaps or a particular band gap structure. Furthermore, the single-exposure holographic method not only makes the fabrication process simple and convenient but also makes the structures of the atoms more perfect.     

Metallic Photonic Bandgap Resonant Antennas with High Directivity and High Radiation Resistance

A metallic photonic bandgap (MPBG) resonant antenna is introduced,which has novel characteristics (such as high directivity and high radiation resistance for a certain range of frequencies )as compared to conventional MPBG antennas.The linear MPBG resonant antenna is formed by infinitely long metallic rods in vacuum.The numerical results for the radiation pattern and the radiation resistance are presented.By adjusting the structure of the MPBG resonant antenna and its working frequency,an optimal structure is achieved.The physical reasons for the novel characteristics of the MPBG resonant antenna are also explained.     

The Second Order Guided Modes Based on Photonic Bandgap Effects in Air/Glass Photonic Crystal Fibers

We introduce a defect site in the periodic structure of a photonic bandgap fiber, to confine and guide the second order mode by photonic bandgap effects. Based on a high air-filling fraction photonic crystal cladding structure, a simplified model with an equivalent air cladding was proposed to explore and analyze the properties of this second order guided mode.     

A Two-Dimensional Photonic Crystal Slab Mirror with Silicon on Insulator for Wavelength 1.3μm

A concrete two-dimensional photonic crystal slab with triangular lattice used as a mirror for the light at wavelength 1.3μm with a silicon-on-insulator （SOI） substrate is designed by the three-dimensional plane wave expansion method. For TE-like modes, the bandgap in the Г-K direction is from 1087nm to 1559nm. The central wavelength in the bandgap is about 1.3μm, hence the incident light at wavelength 1.3μm will be strongly reflected. Experimentally, such a photonic crystal slab is fabricated on an SOI substrate by the combination of EBL and ICP etching. The measurement of its transmission characteristics shows the bandgap edge in a longer wavelength is about 1540 nm. The little discrepancy between the experimental data and the theoretical values is mainly due to the size discrepancy of the fabricated air holes.     

Gap opening and tuning in single-layer graphene with combined electric and magnetic field modulation

The energy band structure of single-layer graphene under one-dimensional electric and magnetic field modulation is theoretically investigated. The criterion for bandgap opening at the Dirac point is analytically derived with a two-fold degeneracy second-order perturbation method. It is shown that a direct or an indirect bandgap semiconductor could be realized in a single-layer graphene under some specific configurations of the electric and magnetic field arrangement. Due to the bandgap generated in the single-layer graphene,the Klein tunneling observed in pristine graphene is completely suppressed.     

Compact and broadband waveguide taper based on partial bandgap photonic crystals

Partial bandgap characteristics of parallelogram lattice photonic crystals are proposed to suppress the radiation modes in a compact dielectric waveguide taper so as to obtain high transmittance in a large wavelength range. Band structure of the photonic crystals shows that there exists a partial bandgap, The photonie crystals with partial bandgap are then used as the cladding of a waveguide taper to reduce the radiation loss efficiently. In comparison with the conventional dielectric taper and the complete bandgap photonic crystal taper, the partial bandgap photonic crystal taper has a high transmittance of above 85% with a wide band of 170 nm.     

Design of Two-Dimensional Photonic Crystal Edge Emitting Laser for Photonic Integrated Circuits

An edge emitting laser based on two-dimensional photonic crystal slabs is proposed. The device consists of a square lattice microcavity, which is composed of two structures with the same period but different radius of air-holes, and a waveguide. In the cavity, laser resonance in the inner structure benefits from not only the anomalous dispersion characteristic of the first band-edge at the M point in the first Brillouin-zone but also zero photon states in the outer structure. A line defect waveguide is introduced in the outer structure for extracting photons from the inner cavity. Three-dimensional finite-difference time-domain simulations apparently show the in-plane laser output from the waveguide. The microcavity has an effective mode volume of about 3.2（λ/nslab）^3 for oscillation mode and the quality factor of the device including line defect waveguide is estimated to be as high as 1300.     

A simple model for approximate bandgap structure calculation of all-solid photonic bandgap fibre based on an array of rings

A simple model for approximate bandgap structure calculation of all-solid photonic bandgap fibre based on an array of rings is proposed. In this model calculated are only the potential modes of a unit cell, which is a high-index ring in the low-index background for this fibre, rather than the whole cladding periodic structure based on Bloch＇s theorem to find the bandgap. Its accuracy is proved by comparing its results with the results obtained by using the accurate full-vector plane-wave method. High speed in computation is its great advantage over the other exact methods, because it only needs to find the roots of one-dimensional analytical expressions. And the results of this model, mode plots, offer an ideal environment to explore the basic properties of photonie bandgap clearly.     

Modified Spontaneous Emission from Dye Molecules inside a Photonic Crystal Microcavity

We fabricate a photonic crystal microcavity containing Alq3 in a sandwiched structure by the self-assemble method. The angle-dependent photoluminescence （PL） spectra and the variation of the PL lifetime demonstrate the effect of the photonic band gap on the spontaneous emission of Alq3 in the photonic crystals.     

Simulations of Effect of High-Index Materials on Highly Birefringent Photonic Crystal Fibres

Novel highly birefringent photonic bandgap fibres （PBGFs） are obtained by filling of a high index material in the air holes of total internal reflection birefringent photonic crystal fibres. The effect of the filling high index material on the transmission characteristics has been theoretically investigated. The photonic bandgap has been achieved by using plane-wave method. Moreover, the phase and group modal birefringence have been studied by a full-vector finite-element method. Numerical results show that very high group and phase modal birefringence with magnitude of order of 10^-2 and 10^-3 has been respectively acquired, which is much higher than those of the non-filled fibres. Furthermore, strong coupling between surface modes and the fundamental modes has been found in the bandgap of the birefringent PBGFs, whose effect on the birefringence and confinement loss has also been discussed.     

Reduction of Refractive Index Contrast Threshold for Photonic Band-Gap in Square Lattices

The threshold of refractive index contrast （RIG） to open a photonic band gap can be reduced by symmetry breaking. For the case of square lattice composed by dielectric cylinders, the absolute band gap is demonstrated by inserting small rods in the centre of the lattices, and the threshold RIC is reduced to 3.8. As for the square lattices composed by air holes in dielectric, the minimal RIC required for an absolute band gap decreases to 2.20.     

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.     

Negative and Superluminal Group Velocity Propagation with Narrow Pulse in a Coaxial Photonic Crystal

We investigate the propagation of electric signal along a spatially periodic impedance mismatched transmission line group. Anomalous dispersion is caused by the periodically mismatched impedance structure and a forbidden band appears near 8 MHz in transmission. The group velocity of the amplitude-modulated signal is augmented up to infinity, even -3.89c （c the speed of light in vacuum） in the forbidden region with the amplitude of the modulated signal increasing. When the carrier sinusoid signal is modulated in amplitude by the modulating sinusoid signal, of which the peak is superimposed with a narrow pulse at fivefold frequency, the superluminal group velocity also occurs. The experiment failed to show whether the propagation velocity of narrow pulse exceeds c or not.     

A Pseudospectral Time—Domain Algorithm for Calculating the Band Structure of a Two—Dimensional Photonic Crystal

A pseudospectral time-domain (PSTD) method is developed for calculating the band structure of a two-dimensional photonic crystal.Maxwell‘s equations are rewritten in terms of period fields by using the Bloch theorem.Instead of spatial finite differences,the fast Fourier transform is used to calculate the spatial derivatives.To reach a similar accuracy,fewer sample points are required in the present PSTD method as compared to the conventional finite-difference time-domain methods.Our numerical simulation shows that the present PSTD method is an efficient and accurate method for calculating the band structure of a photonic crystal.     

Broadband Frequency Down-Conversion Using Coupled Cavity Structures in One-Dimensional Photonic Crystals

The frequency down-conversion of one-dimensional photonic crystals with the coupled cavity structure is investigated by the nonlinear finite-difference time-domain method. The efficient frequency conversion is obtained by utilizing the advantages of the broad eigenfrequency band, the strong localization and the Bloch phase matching of the coupled cavity structure. More importantly, the signal frequency could be tuned continuously within the whole band of the coupled cavity structure （with a bandwidth to central frequency ratio of 5.4%）, and the gains are homogeneous in the band.     

Characteristics of Photonic Bandgap Fibres with Hollow Core＇s Inner Surface Coated by a Layer Material

Hollow core＇s inner surface coating in a photonic bandgap fibre （PBCF） is investigated by means of finite element method. The coat material and thickness-dependence dispersion curve and group velocity dispersion are numerically studied. The coating with materials of low index or small thickness will rise up the dispersion curve but will not induce surface modes. However, coating with materials of high index or big coat thickness will induce surface modes and avoided-crossings. By varying coat material＇s refractive index and thickness, the appearances of surface modes and avoided-crossings can be changed. It is found that the avoided-crossing can enormously enlarge the negative dispersion which can find applications in dispersion compensation. We numerically achieve a negative dispersion as large as -21416.15ps/nm/km. The results give a physical insight into the propagation properties of PBGFs with the hollow core coated by a layer of material and are of crucial significance in the applications of PBGF coating.     

Nonlinear Response of One-Dimensional Magneto-Optical Photonic Crystals

We numerically investigate the magneto-optical Cotton-Mouton effect in an alternating multilayer structure with a nonlinear dielectric constant. The multistability and polarization of the transmission of electromagnetic field near the edges of the stop gap are studied in detail. The resonant transmission is accompanied by solitons of intensity of the field. This investigation provides a way to select the transmission property with different polarizations since both the amplitude and the phase of the output field can be adjusted by the input power and by the magneto-optical coefficient depending on the external magnetic field.