Photonic Gap Research Articles

Structure of light scattering spectra in opal photonic crystals

Spectra of light losses are studied at a fixed angle of incidence of a collimated beam on the surface of an opal anisotropic photon crystal at various observation angles. It is shown that the structure of the forward-and backscattered light spectra is connected with the existence of several directional photonic forbidden bands. It is demonstrated that back scattering is enhanced and forward scattering is suppressed in the frequency region of photonic forbidden bands. It is suggested that a scattering band associated with photon localization at the photonic gap edge is observed.

Quasiperiodic photonic crystal microcavity lasers

We fabricated a 12-fold symmetric quasiperiodic photonic crystal (QPC) point defect laser, and obtained the lasing action at room temperature. When photopumping a seven-hole-missing defect or a uniform QPC part, the lasing occurred by different modes. The finite-difference time-domain analysis showed that the defect mode is a whispering gallery mode, which is confined by the photonic gap or the boundary reflection. It also indicated that the defect-free mode is an extended but partly localized mode, which cannot be seen in photonic crystals.

Isotropic photonic gaps in a circular photonic crystal.

We investigated the optical properties of a circular photonic crystal (CPC) for which the distance between lattices was systematically distributed. The transmission spectra of CPC composed of alumina cylinders were examined in the frequency region from 0 to 20 GHz. We show that photonic gaps are obtained not only in CPCs but also in phase-shifted CPCs. The isotropic photonic gaps are evidenced by changes in the incident angle of a millimeter wave.

Gap maps and intrinsic diffraction losses in one-dimensional photonic crystal slabs.

A theoretical study of photonic bands for one-dimensional (1D) lattices embedded in planar waveguides with strong refractive index contrast is presented. The approach relies on expanding the electromagnetic field on the basis of guided modes of an effective waveguide, and on treating the coupling to radiative modes by perturbation theory. Photonic mode dispersion, gap maps, and intrinsic diffraction losses of quasi guided modes are calculated for the case of self-standing membranes as well as for silicon-on-insulator structures. Photonic band gaps in a waveguide are found to depend strongly on the core thickness and on polarization, so that the gaps for transverse electric and transverse magnetic modes most often do not overlap. Radiative losses of quasiguided modes above the light line depend in a nontrivial way on structure parameters, mode index, and wave vector. The results of this study may be useful for the design of integrated 1D photonic structures with low radiative losses.

Three absolute photonic gaps from 2d square compound lattices

AbstractThe photonic band structures of two‐dimensional square compound lattices are calculated by the plane‐wave method. Four air hole cylinders drilled in a square dielectric cylinder which locate at each square lattice site are embedded in a background of air. Three absolute photonic band gaps common to E and H polarized waves are created when given proper structure parameters. (© 2004 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Photonic material for designing arbitrarily shaped mirrors and microcavities in two dimensions

Based on the numerical finding of a two-dimensional photonic material which has large complete photonic gaps and structural uniformity, we propose a photonic plate which can be used to design arbitrarily shaped photonic mirrors and microcavities on a wavelength scale. This paper describes a wavelength-sized parabolic mirror that can collect light very efficiently without loss. In addition, we present circular microcavities of tunable resonance frequencies with high values of quality factor Q.

Optical properties of Ga 1− x In x As/GaAs(001) quantum well superlattices: Exciton and polariton dispersion curves

Wannier exciton wavefunctions and energies have been computed in superlattices of strained Ga1−xInxAs/GaAs(001) quantum wells (SLQWs) using Luttinger Hamiltonian and accurate variational envelope functions. Exciton dispersion curves of the SLQWs are then obtained by computing exciton energies for different K-points of the corresponding first Brillouin zone. Photon dispersion curves, due to the background dielectric constant modulation, and the polariton dispersion curves have been computed in the semiclassical self-consistent framework. The results are discussed for the case of exciton energies far from the photonic gaps. (© 2004 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

Polaritonic and photonic gaps in SiO 2/Si and SiO 2/air periodic structures

The one-dimensional (1D) photonic crystals (PhC) Si/SiO 2, SiO 2/Si and SiO 2/air are studied to investigate the coexistence and interaction of polaritonic and structural gaps. Optical multilayer calculations as well as infrared reflectance measurements in the 2.7–12 μm range for relevant cases have been carried out. The samples were prepared by standard chemical vapor deposition (CVD) processes. Satisfactory agreement between experimental and calculated results was obtained without fitting. The calculated results verify the presence of a polaritonic gap for thicknesses much lower than the wavelength for the cases SiO 2/Si and SiO 2/air. Including also the case Si/SiO 2, we find the polaritonic peak can be strengthened, unchanged, or extinguished by the interaction between structural and polaritonic effects. All these predictions have been experimentally verified.

Polaritonic and Photonic Gap Interactions in a Two-Dimensional Photonic Crystal

If an ionic material is used in a photonic crystal, the lattice resonance creates a polaritonic gap in the infrared range. The interaction between a polaritonic gap and the structure gap in a 2D square photonic crystal is studied by transfer matrix photonic band structure calculations. The polaritonic gap appears for a surprisingly low volume density of the ionic material. The TM gaps are larger than the TE gaps, as in the dielectric case. By varying the lattice constant, the structure gaps can be shifted across the polaritonic gap, and the effects of merging the two gaps can be studied.

Microvoid channel polymer photonic crystals with large infrared stop gaps and a multitude of higher-order bandgaps fabricated by femtosecond laser drilling in solid resin

Photosensitive polymer materials are ideally suited for laser-induced micro- and nanostructuring, as structural and compositional changes are achieved already under exposure to moderate intensities of high-repetition rate ultrashort-pulsed light. Photonic crystals with bandgaps in the infrared or the visible spectral region are a particularly interesting application, because highly correlated structural elements at a size of only a few hundred nanometers are required. We fabricated infrared photonic crystals based on microvoid channels inside solid polymer material. Femtosecond-pulsed visible light was focused into UV-cured Norland NOA63 resin by a high numerical aperture objective. In the focal spot microexplosions drive the material out of the center of the focus. Void channels of 0.7–1.3 μm diameter are generated by translating the sample along a preprogrammed pathway. Woodpile structures of void channels at layer spacings of 1.6–2.6 μm and in-plane channel spacings of 1.2–1.3 μm allowed for bandgap-induced suppression of infrared transmission in the stacking direction of as much as 86% by only 20 layers. As these structures are highly correlated and do not contain many imperfections, up to three higher-order stop gaps are observed. Consistent with theory, the number and gapwidth of higher-order gaps strongly increases with the ratio between layer- and in-plane spacing. Due to their low refractive index contrast and the missing interconnectivity of voids our structures do not provide complete photonic bandgaps. However, their manifold of sizable higher-order gaps allows for the engineering of photonic stop gaps down to the near-infrared wavelength region using comparatively large structural dimensions.

Band Gaps of an Amorphous Photonic Materials

A new kind of amorphous photonic materials is presented. Both thesimulated and experimental results show that although the disorder ofthe whole dielectric structure is strong, the amorphous photonicmaterials have two photonic gaps. This confirms that the short-rangeorder is an essential factor for the formation of the photonic gaps.

Larger bandgaps of two-dimensional triangular photonic crystals fabricated by holographic lithography can be realized by recording geometry design

The photonic band gap (PBG) properties of two classes of two-dimensional (2-D) triangular lattice fabricated by holographic lithography are investigated numerically. The effect of intensity threshold on the filling ratio and then the shape of "atoms", and the corresponding photonic gap are comprehensively studied. Our results show that the recording geometry for a given 2-D triangular lattice is not unique, and this fact gives us more freedom in choosing proper recording geometry to obtain larger bandgap.

Theoretical study of the tunable optical filter properties based on photonic crystals

The transmission properties of the one-dimensional photonic crystals with defects were studied using the eigen matrix method, and a new kind of tunable optical filter is proposed in this paper. When the one-dimensional photonic crystals (L1H1)m have defects such as LcH2(L2H2)n, there will be a narrow transmission band in the gap of the photonic crystals, meanwhile the other transmission peak will weaken and disappear with the increase of the periodic number of the cover layer. When the thickness of the couple layer changes, there will be two regions with high transmittivity besides the edges of the photonic crystals gap. The properties of the high transmission band depend on the photonic crystals and the cover layers. When the photonic crystals gap is narrowed, the two regions will come near, which results in a wide transmission region about 150 nm. A new kind of tunable optical filter thus can be fabricated based on this phenomenon by the surface micro-mechanical technology.

Optical Spectroscopy of Silicon-On-Insulator Waveguide Photonic Crystals

AbstractWe report on a complete optical investigation on two-dimensional silicon-on-insulator (SOI) waveguide photonic crystals obtained by electron beam lithography and reactive ion etching. The dispersion of photonic modes is fully investigated both above and below the light-line by means of angle- and polarization-resolved micro-reflectance and attenuated total reflectance measurements.The investigated samples consisted in a) large area (300 × 300 μm2) two-dimensional (2D) triangular lattices of air holes containing repeated line–defects; b) small area triangular lattices of holes with different number of periods and /or line defects integrated in a ridge type waveguide structure.In the case of large area samples, variable-angle reflectance and ATR is measured from the sample surface in a wide spectral range from 0.2 to 2 eV both in TE and TM polarizations. The sharp resonances observed in the polarized reflectance and ATR spectra allow mapping of the photonic dispersion of both radiative and guided modes. Experimentally determined and compared to those calculated by means of an expansion on the basis of the waveguide modes.In the case of ridge type waveguide-integrated photonic crystals, transmission is measured in the 0.9-1.7 eV spectral range by an edge-coupling technique. Transmission spectra exhibit significant attenuation corresponding to the photonic gaps along the Γ–M and Γ–K directions respectively, even when a small number of hole periods is integrated in the ridge waveguide. Good agreement is obtained by comparing the measured transmission spectra with the calculated photonic bands.

Optical and Nanomechanical Characterization of an Omnidirectional Reflector Encompassing 850 nm Wavelength

AbstractWe demonstrate that multilayers composed of nineteen alternating layers of tin sulfide and silica can function as omnidirectional reflectors. These materials exhibit omnidirectional reflectivity for a range of frequencies in the near infra-red (NIR) encompassing the 850 nm wavelength. A refractive index contrast of 2.7/1.46 is achieved, one of the highest values demonstrated until now in NIR photonic bad gaps. In addition, new nanoindentation procedures have been developed to measure mechanical properties of these fine laminate materials, and demonstrate that tin sulfide-silica multilayers are mechanically stable for practical applications.

Efficient Analysis of Via Hole Grounds by Using the Iterative Method

The via hole ground has many applications in the synthesis of microstrip microwave circuits. Indeed, it can be used for the realization of stub, the parallel insertion of lumped element and the photonic gap structures. This paper presents an extension of the iterative method based on the concept of waves combined with the two-dimensional Fast Fourier Transformation algorithm (F.M.T: Fast Modal Transformation) to analyze microstrip microwave distributed circuits including via hole grounds. The results provided by this method are in good agreement with the data determined by MDS's approach.

Localized modes in defect-free dodecagonal quasiperiodic photonic crystals

The transmission property and localization of electromagnetic waves in defect free dodecagonal quasiperiodic photonic crystals (QPCs) are studied. The simulation of total energy flow and the density of states show that the dodecagonal QPC has a photonic gap for TM polarized electromagnetic waves. However, different from the periodic photonic crystals, electromagnetic waves with certain frequencies are localized at some special regions inside a perfect dodecagonal QPC. A corresponding experiment in the microwave region confirms the phenomenon. It is believed that the occurrence of localized modes in QPCs can be attributed to the competition between two spatial structural properties: self-similarity and nonperiodicity.

Depositing light in a photonic stop gap by use of Kerr nonlinear microresonators.

We show theoretically that it is possible to trap light in a microresonator structure by use of four-wave mixing. The efficiency of the parametric process is substantially increased by the high group delay of light inside the structure. The energy that is trapped has a half-life of approximately 500 ps in the presence of both linear and nonlinear loss in the channel waveguides and resonators. We also demonstrate that the energy can be extracted from the cavity with a similar process.

Distribution of density of photonic states in amorphous photonic materials

The density of states (DOS) and local density of states (LDOS) for an amorphous photonic material (APM) with a finite size and constructed by hexagonal basic cells are simulated. It is found that there is a frequency interval in which the total DOS is very small, i.e., a photonic gap exists. Near the gap-center frequency, the LDOS drops rapidly from the edge to the center area of the sample. However, at the gap-edge frequency, some discrete spots with high LDOS spread in the sample and corresponding electric field distributions show the occurrence of localized modes. This phenomenon can be attributed to the disordered distribution of the scatterers.

Optical properties and photonic mode dispersion in two-dimensional and waveguide-embedded photonic crystals

Recent experimental and theoretical work on two-dimensional (2D) and waveguide-embedded photonic crystals is reviewed. The investigated systems are 2D macroporous silicon and photonic crystal slabs based on silicon-on-insulator as well as GaAs/AlGaAs. In all these structures, reflectance at varying angles of incidence allows to determine the dispersion of photonic modes above the light line. For macroporous silicon, reflectance from the side yields a complementary measurement of the photonic gaps. In the GaAs-based system, second-harmonic generation in reflection shows a resonant enhancement when the pump beam is frequency- and momentum-matched to a photonic mode in the slab. A theory of photonic states in waveguide-embedded photonic crystals leads to a determination of mode dispersion and diffraction losses for leaky photonic modes.