This PDF file contains the front matter associated with SPIE Proceedings Volume 7713, including the Title Page, Copyright information, Table of Contents, and the Conference Committee listing.

We present a new light scattering pattern in low-contrast opal-based photonic crystals (PhCs). The structure of real opals is always imperfect because of the a-SiO₂ particles being inherently inhomogeneous and nonuniform in size and average dielectric permittivity. We found that opals possess all predictable properties of multi-component PhCs, which we define as periodic structures consisting of inhomogeneous or multiple (three or more) components. By theory, by properly tuning the permittivity of one of the components in ordered, low-contrast multi-component PhCs (for instance, of the filler ε_f in an opal), one can produce selective disappearance of any non-resonant (hkl) stop band. A study of transmission spectra of opals revealed that stop bands exhibit different (including resonant) behavior under variation of ε_f. Experiment did not, however, substantiate complete disappearance of stop bands predicted by theory for an ordered PhC. In the region of the predicted disappearance, a new effect has been observed, namely flip-over of the Bragg band, i.e., transformation of the Bragg dip into a Bragg rise. The flip-over effect, which has been studied in considerable detail in the particular example of the (111) stop band, originates from the nonuniformity of a-SiO₂ particles. This nonuniformity leads to additional broad-band light scattering, the character of which is determined by Mie scattering. Thus, Mie scattering is responsible for two components in opal transmission spectra, more specifically, narrow Bragg bands and broad-band background. Their interference gives rise to formation of the Fano resonance, which in opal spectra becomes manifest, first, in a Bragg band asymmetry, and, second, in the flip-over effect, i.e., transformation of a photonic stop band into a photonic pass band.

Recent advances in the comprehension of the growth dynamics of colloidal crystal films opens the door to conscious design of experiments aiming at fabricating lattices in which the density of intrinsic defects is minimized. Since such imperfections have a dramatic effect on scattered light of wavelength smaller than the lattice constant, the evaluation of the experimental optical response at those energy ranges, based on the comparison to rigorous calculations, is identified as the most sensitive guide to accurately evaluate the progress towards the actual realization of defect free colloidal crystals. The importance of the existence of a certain distortion becomes particularly relevant at the above mentioned energy range. We have thoroughly analyzed the effect of fine structural features on the optical response to conclude that, rather than the generally assumed FCC lattice of spheres, opal films are better approximated by a rhombohedral assembly of distorted colloids. Interparticle distance of actual colloidal crystals coincides with the expected diameter for spheres belonging to the same close-packed (111) plane but differs significantly in directions oblique to the [111] one.

Polarization anisotropy of the zero order forward-diffracted and the off-resonance transmitted light in the 3-dimensional thin film opal photonic crystals has been numerically computed and experimentally measured. Studies of the polarization anisotropy as a function of the incidence and azimuth angles of the incoming light have revealed strong anisotropy changes at diffraction resonances and in the ranges of the multiple-band diffraction. The opposite sign of the polarization anisotropy for different diffraction resonances has been observed. The cross-polarization coupling has been measured and identified as one of the reasons for changing the anisotropy sign. The correlation of the lattice ordering and the magnitude of the light polarization anisotropy has been demonstrated.

Building photonic crystals by combination of colloidal ordering and metal sputtering we were able to construct a system sensitive to an electrical field. In corresponding crystals we embedded the Dexter pair (Ir(ppy₃) and BAlq) and investigated the influence of the band gap on the resonant energy transfer when the system is excited by light and by an electric field respectively. Our investigations extend applications of photonic crystals into the field of electroluminescence and LED technologies.

During the last years, much attention has been paid to photonic crystals (PC) for different applications, but only recently they have been proposed and showed useful for applications in solar cells. Little work has been done in the actual manufacture and characterization of a complete solar cell with a two-dimensional photonic crystal (2D-PC) on its front surface, conceived as a periodic distribution of the dielectric constant in the plane (the surface of the solar cell) and involving sub-wavelength motifs. In this case, the photonic crystal effect is different from the one happening in slabs or suspended membranes. Despite the partial vertical confinement, there may be some reasons that can justify the use of photonic crystal front surface with sub-wavelength motifs. Experimental results on actual devices with a photonic crystal nanopatterned layer will be shown, along with reflectivity studies on PC lattices with different symmetries and shapes.

The absorption of thin hydrogenated amorphous silicon layers can be efficiently enhanced through a controlled periodic patterning. Light is trapped through coupling with photonic Bloch modes of the periodic structures, which act as an absorbing planar photonic crystal. We theoretically demonstrate this absorption enhancement through one or two dimensional patterning, and show the experimental feasibility through large area holographic patterning. Numerical simulations show over 50% absorption enhancement over the part of the solar spectrum comprised between 380 and 750nm. It is experimentally confirmed by optical measurements performed on planar photonic crystals fabricated by laser holography and reactive ion etching.

We present a theoretical study of amorphous and crystalline thin-film solar cells with a periodic pattern on a sub-micron scale realized in the silicon layer and filled with silicon dioxide right below a properly designed antireflection coating. The study and optimization of the PV structure as a function of all the photonic crystals parameters allows to identify the different roles of the periodic pattern and of the etching depth in determining an increase of the absorption. From one side, the photonic crystal acts as an impendence matching layer, thus minimizing reflection of incident light over a particularly wide range of frequencies. Moreover a strong absorption enhancement is observed when the incident light is coupled into the quasi guided modes of the photonic slab. We compare the efficiency of this structure to that of PV cells characterized by the sole antireflection coating. We found a substantial increase of the short-circuit current when the parameters are properly optimized, demonstrating the advantage of a wavelength-scale, photonic-crystal based approach.

In this paper we discuss theoretical modelling methods for the design of photonic crystal and photonic quasi-crystal (PQC) LEDs - and apply them to the analysis of the extraction enhancement performance and shaping of the emitted beam profile of PQC-LED structures. In particular we investigate the effect of the pitch of the PQC patterning, and consider the physical mechanisms giving rise to performance improvements. In addition, we examine the relative contributions to performance improvements from effective index reduction effects that alter the conditions for total internal reflection at the device air interface, and from photonic crystal scattering effects that give rise to radically improved extraction performance. Comparisons are made with the performance of recently fabricated devices.

Liquid crystal (LC, Merk 5 CB) is infiltrated into active, InAs quantum dots embedded, InGaAsP membrane type nanocavities to investigate the possible effect of the LC orientation on active cavity tuning. The tuning is demonstrated thermally and thermo-optically. The thermal tuning showed that the cavity modes can be tuned in opposite directions and exhibits a sudden change at the clearing temperature. The mechanism relies on the existence of both ordinary and extraordinary refractive indices of the liquid crystal due to its molecular alignment inside the voids. It shows that the electric field distribution of cavity modes can have a substantial component parallel to the LC director. The average electric field orientation with respect to the LC orientation can be mode dependent, so that different modes can be dominated by either branch of the LCs refractive index. Thermo-optic tuning of the modes is obtained when the power of the excitation laser is increased from 40 μW to 460 μW. A large and a reversible blueshift of more than 10 nm of the cavity modes is observed which is attributed to temperature induced liquid transport. InGaAsP type of nanocavities, without InAs quantum dots were infiltrated with PbSe colloidal quantum dots to obtain a comparison of internal light sources either in the semiconductor or in the holes.

In this work, we demonstrate that the compound mode properties of coupled photonic-crystal cavities can depend critically on the interplay of distance between cavities and their longitudinal shifts. Thus the robust control over the cavity modes can be imposed. The simple coupled-mode theory employed for such systems predicts a peculiar behavior of band dispersion in the slow light regime at the photonic band-edge. In particular, it reveals an interesting effect that the frequency detuning of the fundamental supermodes in the coupled cavities can be reduced down to zero. We anticipate that this property will be generic for side-coupled cavity systems irrespectively of the individual cavity design, e.g. point-defect cavities in a photonic crystal or linear cavities in one-dimensional arrays of elements (rods or holes). We report here about the finite-difference frequency-domain method (FDFD) developed by us to analyze nanocavities with a very high Q-factor. The method is utilized to confirm by simulations the coupled-mode theory predictions. As an example we choose coupled cavities in one-dimensional periodic arrays of holes in dielectric nanowires known also as nanobeams.

By performing an ultrafast pump-probe experiment, we demonstrate the adiabatic frequency conversion of a telecommunications pulse in a silicon photonic crystal waveguide. By using slow-light modes to spatially compress the pulse, a 1.3 ps long pulse is blue-shifted by 0.3 THz with 80% efficiency in a waveguide just 19 μm long. We also present the results of an adiabatic model of the process, which agrees excellently with the experimentally measured data.

Superprism phenomena in planar photonic crystals (PhCs) can be used for the realization of compact demultiplexers. Yet, strong dispersion is most often accompagnied by strong diffraction. The design, fabrication, and experimental characterization of a PhC demultiplexer is presented. A special care is taken to excite the equi-frequency surfaces in dispersive and simultaneously nearly-collimated regions. The structure is fabricated on a SOI substrate using e-beam lithography and RIE etching. With four output channels, its footprint is 2800μm². It is characterized by a -16 dB level of crosstalk around λ = 1550 nm, with 2dB loss.

We report ensemble-average transport characteristics obtained for a series of photonic-crystal waveguides that are supposedly identical and that only differ because of statistical structural fabrication-induced imperfections. In particular, we evidence that, in addition to a smearing of the local density of states, the probability density function of the transmission rapidly broadens in the slow light regime even for group indices as small as n_g≈20 and for practical situations offering tolerable -3dB losses. This brings a severe constraint on the effective use of slow light for on-chip optical information processing. The experimental results are quantitatively supported by theoretical results obtained with a coupled-Bloch-mode approach that takes into account multiple scattering and localization effects.

Flat band slow light with large bandwidth and low GVD in a novel PC waveguide is investigated. By using only one tuning parameter with respect to a simple W1 waveguide, unusual "U" type ng-frequency curves are obtained, enabling a versatile control of light group index and bandwidth. Delay-bandwidth products have been estimated for the proposed waveguide geometry (0.1363 for ng = 211 < DPBs < 0.336 for ng=11) and can be faborably compared with values reported in previous works. The GVD properties of the proposed structure have been also analyzed. It turns out that nearly-zero dispersion waveguiding can be achieved within the constant high ng range. Addtionnaly, the new waveguide allows a versatile control of positive or negative GVD values, opening opportunities for dispersion compensation devices. Finally, the novel simple PC waveguide is relatively easy for fabrication if compared with previously proposed solutions. Possible applications of the proposed δx PC waveguides can be found in optical interconnects, nonlinear optics, or biophotonics.

Based on the previous work of Nishijima [1], the aim of this work is to realize 3D magnetophotonic crystals (MPC) by a sol-gel approach, in order to obtain a magneto-optical material with a large merit factor. These MPC are made by immersion of an opal template of polystyrene spheres in a sol-gel TEOS preparation doped by magnetic nanoparticles. The template can be realized using centrifugation or sedimentation, and it is removed after the solidification of the doped matrix by an immersion in ethyl acetate. Calculations made on 1D structures confirm that a periodic arrangement of a magneto-optical material is a way to increase the Faraday Rotation and the merite factor. The characterization of the samples is made by SEM and UV-VIS spectrophotometry. In virtue of the SEM pictures we can establish that the template is well-structured, what is confirmed by a Photonic Band Gap (PBG) in the spectrophotometry spectral. The central wavelength of the PBG depends on the size of the polystyrene spheres. The final MPC obtained with a silica matrix doped by maghemite nanoparticles has also well-structured areas. Ongoing works concern the study of the Farady rotation as a function of the wavelength.

We have demonstrated numerically that a waveguide formed by the interface of a metal and uniformly magnetized twodimensional photonic crystal fabricated from a transparent dielectric magneto-optic (MO) material possesses a one-way frequency range where only a forward propagating surface plasmon polariton (SPP) mode is allowed to propagate. In contrast to an analogous waveguide proposed by Yu¹ the non-reciprocity at the interface is introduced by the MO properties of the photonic crystal material and not by applying an unrealistically high static magnetic field (up to 1 T) on metal described by free-electron Drude form of the dielectric function. The considered magnetic material is Bismuth Iron Garnet (BIG, Bi₃Fe₅O₁₂), a ferrimagnetic oxide which may be easily magnetically saturated by fields of the order of tens of mT. Therefore, this configuration allows to achieve sizable one-way bandwidth by using significantly smaller values of the external magnetic field which makes such a waveguide favorable for design of diode-like elements in optical integrated circuits. By using a novel MO aperiodic Fourier Modal Method (MO a-FMM) to calculate the band structure of this magneto-plasmonic photonic crystal waveguide we have proven the existence of one-way SPP bands within the optical wavelength.To investigate transport properties of the structures within this frequency range we have implemented two finite-difference time-domain (FDTD) methods, namely ADE² and that based on Z-transforms³ that allow calculating the propagation of EM waves through media with full tensorial magneto-optic permittivity. We provide numerical evidence confirming suppression of disorder-induced backscattering in the one-way waveguide.

We perform a theoretical study on the group velocity for finite thin artificial opal slabs made of a reduced number of layers in the spectral range where the light wavelength is on the order of the lattice parameter. The vector KKR method including extinction allows us to evaluate the finite-size effects on light propagation in the ΓL and ΓX directions of fcc close-packed opal films made of dielectric spheres. The group is index determined from the phase delay introduced by the structure to the forwardly transmitted electric field. We show that for certain frequencies, light propagation can either be superluminal -positive or negative- or approach zero depending on the crystal size and absorption. Such anomalous behavior can be attributed to the finite character of the structure and provides confirmation of recently emerged experimental results.

In this work, we provide experimental and theoretical evidence of negative group delays (NGDs) for pulses reflected on symmetric, linear, and passive microstrip slabs and distributed Bragg reflectors (DBRs) through frequency- and timedomain characterization. These microwave operating devices excellently scale to their analogous structures in the optical range, and confirm recent theoretical predictions on weakly absorbing dielectric slabs. In this context, we demonstrate a simple scaling law for the group delay at the slab's design frequency. In the case of DBRs, we show that, as opposed to transmitted pulses, NGDs do occur for pulses reflected in these linear and periodical one-dimensional (1D) structures. This result sheds light into the still controversial question as whether negative tunneling times are possible in 1D photonic crystals.

A new type of porous-silicon based photonic biosensor is presented. The device is a 1D planar photonic crystal supporting resonant modes that can be excited at normal incidence. The study of theoretical performances demonstrates a high sensitivity with similar performances in air and in aqueous environment. The experimental realization of the sensor is discussed and preliminary biosensing experiments show very promising results.

We demonstrate the synthesis of different types of "intelligent" 1D photonic crystals (PCs), termed Bragg stacks, using hydrothermal or sol-gel procedures followed by spin-coating, which permit a wide range of materials to be included as functional layer materials. Bragg stacks based on the clay mineral Laponite have been realized, whose response to the presence of liquid analytes translates into a shift of the optical stop band position. Clay-based PCs are capable of reversible swelling and accommodating changes in the effective refractive index of the layers by both adsorption and ion-exchange processes, and key issues in chemo-optical sensing such as accessibility, reversibility and selectivity are demonstrated. The utilization of nanoscale particles as active layer components is highlighted by the integration of microporous materials - zeolites - into a photonic crystal backbone. We demonstrate that the sensitivity of the PC to solvents and gases and thus, refractive index changes, can be maximized through the high porous volumes of nanoparticle-based layers.

Laser diodes emitting in the mid-infrared 2-2.7 μm range are of particular interest for spectroscopic applications and especially for trace gas detection due to the presence of strong absorption bands of several species [1] of pollutants. These applications require single-frequency, wavelength tunable lasers. In this perspective, we have studied designs made of two coupled cavities (C²), coupled by an intracavity Photonic Crystal (PhC) mirror as proposed by Happ et al. [2]. The first devices of this type have recently been proposed on GaSb, emitting at 1.9 μm [4]. In this paper, we demonstrate the first coupled cavity (C²) PhC devices operating above 2.3 μm.

While plasmonic nano-antennas typically have a rather basic shape, they still present considerable challenges for numerical simlations. In particular, their small size (compared to the wavelength) and their strong sensitivity to geometrical changes mandates a highly accurate spatial discretization. In this work, we employ a nodal discontinuous Galerkin time-domain technique to investigate the dependence of the fundamental resonance of rod-shaped nano-antennas on a number of geometrical parameters.

We prepared thin film colloidal crystals, namely, opals and Langmuir-Blodgett crystals, of different lattice constants and coated them with 20, 50 and 100 nm thick gold films. Angle-resolved transmission spectra of these hybrid nanostructures were obtained using linear polarized light over a spectral range of a photonic bandgap energy structure of these colloidal photonic crystals. Up to 10 times transmission enhancement has been observed in specific spectral intervals determined by the light coupling to surface plasmon polaritons in the metal film. At the same time these hybrid nanostructures retain transmission attenuation bands inherited from a photonic crystal. The strong crosscorrelation of the photonic bandgap and surface plasmon polariton properties was observed in the transmission spectra of studied hybrids.

Temporal profile distortion of a femtosecond pulse reflected from one-dimensional plasmonic crystal have been studied using time-resolved cross-correlation technique. Spectral dependences of cross-correlation functions show that SPP resonance with Fano-type lineshape strongly disturbs reflected pulse on picosecond timescale.

We show that photonic crystals made of materials with normal dispersion allow simultaneous broad angular range and broad spectral range phase matching in nonlinear wave mixing processes, in particular second harmonic generation. The configuration proposed ensures subdiffractive propagation regimes for both interacting waves and the slopes of the two dispersion curves (for the fundamental and second harmonic waves) at the phase-matching frequencies are similar (at frequencies slightly shifted from the phase-matched one the phase-mismatch remains very small). The numerical simulations confirm both the broad angular range (by the use of narrow beams, with the width of few wavelengths) and the broad spectral range (by the spectral width of the generated second harmonic beam) for the phase matching, showing a significant increasing of the conversion efficiency with respect to the case of plane waves in homogeneous materials.

In this paper we present a reliable process to fabricate GaN/AlGaN one dimensional photonic crystal (1D-PhC) microcavities with nonlinear optical properties. We used a heterostructure with a GaN layer embedded between two AlGaN/GaN Distributed Bragg Reflectors on sapphire substrate, designed to generate a λ= 800 nm frequency downconverted signal (χ⁽²⁾ effect) from an incident pump signal at λ= 400 nm. The heterostructure was epitaxially grown by metal organic chemical vapour deposition (MOCVD) and integrates a properly designed 1D-PhC grating, which amplifies the signal by exploiting the double effect of cavity resonance and non linear GaN enhancement. The integrated 1D-PhC microcavity was fabricate combing a high resolution e-beam writing with a deep etching technique. For the pattern transfer we used ~ 170 nm layer Cr metal etch mask obtained by means of high quality lift-off technique based on the use of bi-layer resist (PMMA/MMA). At the same time, plasma conditions have been optimized in order to achieve deeply etched structures (depth over 1 micron) with a good verticality of the sidewalls (very close to 90°). Gratings with well controlled sizes (periods of 150 nm, 230 nm and 400 nm respectively) were achieved after the pattern is transferred to the GaN/AlGaN heterostructure.

Herein we present a series of self standing, flexible and transferable one-dimensional photonic crystal obtained through infiltration of a polymer solution in a porous stack prepared by alternating deposition of layers of TiO₂ and SiO₂ nanoparticles. Since the mesostructure is uniformly filled by the polymer, it is possible to lift off the hybrid multilayers using an adequate thermal treatment to obtain a multifunctional material that combines the optical properties of the periodic nanoporous multilayer and the structural and physic-chemical characteristics of the polymer used. The use of these hybrid 1DPCs as flexible interference filters, or as 1DPC to any kind of substrate is demonstrated.

Photonic membranes are widely used kind of 2D photonic crystals in signal processing. We develop the approach uniting both in-plane and out-of-plane geometries as well as resonator properties of membrane-like photonic crystals (MPC). The resonator standing modes are excited by an external source through the special inputs and may be controlled due to nonlinear coating. We study typical 1D and 2D photonic membrane resonators of rectangular form with nonlinear inclusions as an important element of logical devices. The drastic change of the reflectivity due to so-called nonlinear band shift effect is investigated and two main signal processing schemes are analyzed for Si/SiO₂ MPC covered with nonlinear doped glasses. General design of alloptical logic gates and adder design are discussed. Novel calculation method based on the analytical basis of resonator's eigenstates is used to obtain dependencies for reflectivity, modal spectrum and field distribution for chosen working frequencies.

A new concept for optical filters for pulse compression in optical communication systems is presented. The effect of filtering is not based on resonances as used in Bragg gratings, but it is achieved by interferences of parts of the optical wave. The filter consists of three strip loaded dielectric waveguides. Besides two amplification regions, there are two herringbone like grating structures. The first grating pair delivers the dispersion behavior of the filter. The second grating pair is a bandpass which should improve the amplitude response of the filter. The gratings can be built up as a single or multi channel filter. Besides a theoretical analysis of the filter, the performance of the structure will be presented. It will be shown that not only high dispersion values can be reached, but additionally a signal amplification is possible.

Nanoparticle based one dimensional photonic crystals are porous optical lattices that display environmentally responsive optical properties. Herein we will demonstrate that they can be used to build optical micro-resonators in which this response is further enhanced. Its versatility is proved by showing their capacity to host different types of light emitters, with irregular shapes, like rare earths based nanophosphors. The effect of the photonic nanostructure on the emission spectra of embedded optically active nanoparticles is studied. Narrow luminescence bands, typical of rare-earth ions, can be enhanced or reduced in selected and tuneable wavelength ranges, by precise control of the spectral features of cavity modes. We will provide experimental evidence of the strong changes of the optical response caused by environmental changes, which allows us to propose these structures as base materials for the optical detection of liquids and gases.

One-dimensional photonic crystals (1DPC) made by sequential deposition of TiO₂ and SiO₂ dense thin films can be used as environmental sensors by incorporating some responsive coating capable of selectively capturing the targeted molecules. The material chosen is a porous TiO₂ mesostructured thin film with a narrow pore size distribution, which endows it with size selectivity adsorption properties. The deposition of such thin layer onto the dense 1D PC produces a modulation in the reflectance spectrum highly sensitive to modifications of the environment. In order to study the evolution of the optical response with the environmental changes both purely dense and hybrid multilayers were introduced into a close chamber and the partial pressure of the solvent was increased. The optical spectrum of the dense 1DPC remains unaltered by the environmental changes, while the same structure coupled to a designed mesoporous thin film displays clear and gradual modifications of the reflectance spectra when the partial vapour pressure is increased. The analysis of these spectra provides well-defined isotherms due to the adsorption and condensation of the vapour onto the pore walls presented in the mesoporous coating. Depending of the size of the pores, which is controlled by synthetic procedures, the condensation of a specific molecule can be prevented, totally different isotherms being attained.

We report on the fabrication of metallodielectric photonic crystals by means of interference (or holographic) lithography and subsequent coating by gold nanoparticles. The grating is realized in a SU-8 photoresist using a He-Cd laser of wavelength 442 nm. The use of the wavelength found within the photoresist low absorption band enables fabricating structures that are uniform in depth. Parameters of the photoresist exposure and development for obtaining a porous structure corresponding to an orthorhombic lattice are determined. Coating of photonic crystals by gold nanoparticles is realized by reduction of chloroauric acid by a number of reductants in a water solution. This research shows that the combination of interference lithography and chemical coating by metal is attractive for the fabrication of metallodielectric photonic crystals.

We study a special 1D periodic structure with alternative high and low refractive index materials. Such a structure shows different equal-frequency contours for different (TE and TM) polarizations. At designed frequencies, for TE polarization, the energy direction of refractive wave will always have the same direction regardless of the incident angle (that is our structure has a fixed optical thickness for all incident angles); while for TM polarization, the refractive angle will change as the incident angle varies. Based on this structure, a compact polarization beam splitter (PBS) is proposed with high transmission for both polarizations, and its performance is improved by introducing total reflection of the side-wall. Furthermore, a broad-angle PBS which working over a large range of incident angle is achieved by stacking two such 1D structures together; and a method is proposed to improve the its working band width.

Photonic crystal as the porous silicon multilayer structure was designed and formed. Such structures can be characterized by increased nonlinear optical response due to the weak light localization and could be used to implement all-optical switching. We showed the possibility of the essential photonic band gap edge shift due to a shift of the photonic bandgap edge in the intense laser radiation field due to light self-action effect. All-optical switching in photonic crystals allows to realize logic gates that can be implemented in photonic devices.

Gallium nitride is an important material for the contemporary optoelectronics. Large electric band gap, high temperature resistivity and environmental resistance make GaN interesting also for sensor applications. However, asymmetric structure of GaN-on-sapphire slab waveguide, grown as a conventional epitaxial heterostructure, poses a problem with achieving high quality (Q) factor resonators. In this paper, issues related to an asymmetric structure of a waveguide and theoretical possibilities to achieve high Q-factor resonator in the GaN planar structures are discussed. Three dimensional (3-D) finite-difference time-domain (FDTD) modeling tools were used. It is shown that the highest Q-factor value of ~ 23 000 is obtained for a symmetrical membrane in L9 (nine points-defect cavity) micro-cavity based on GaN planar waveguide. In reference to the simulation results, we also discuss the technological issues, i.e. fabrication of photonic crystal patterns in GaN layers. New approach presented here included deep RIE etching with use of only single masking layer and conductive polymer usage in e-beam pattering. Possible applications of the micro-resonators for sensor applications are discussed.

A novel dielectric band-pass filter with focusing function is presented. This filter is the cylindrical dielectric mirror composed of one-dimensional photonic crystals. The transmission characteristic of the band-pass filter is investigated using the finite-difference time-domain method. The numerical results show that only when the number of reflection layers is larger than the corresponding least number, an incident beam with frequency located in the omnidirectional reflection band can be reflected and focused efficiently. It is expected to be applied to highly dense photonic integrated circuits after further research.

We present a study on the design, growth and optical characterization of a GaN/AlGaN microcavity for the enhancement of second order non linear effects. The proposed system exploits the high second order nonlinear optical response of GaN due to the non centrosymmetric crystalline structure of this material. It consists of a GaN cavity embedded between two GaN/AlGaN Distributed Bragg Reflectors designed for a reference mode coincident with a second harmonic field generated in the near UV region (~ 400 nm). Critical issues for this target are the crystalline quality of the material, together with sharp and abrupt interfaces among the multi-stacked layers. A detailed investigation on the growth evolution of GaN and AlGaN epilayers in such a configuration is reported, with the aim to obtain high quality factor in the desiderated spectral range. Non linear second harmonic generation experiments have been performed and the results were compared with bulk GaN sample, highlighting the effect of the microcavity on the non linear optical response of this material.

This work deals with the replacement of the reflection layer stacks by sub-wavelength structures, which form the cavity of Fabry-Perot-Interferometer (FPI) infrared filters. Periodically arranged metal ring resonators are investigated regarding reflectivity and sensitivity with respect to polarization angle by Finite Difference Method (FDM) analysis. E-beam lithography is used for the fabrication of arrays of ring resonators made from aluminum on silicon nitride thin film substrate. The wavelength depending reflection coefficient for random polarization and for linear polarization in different directions is measured by Fourier Transform Infrared Spectrometer and compared to the results from theoretical analysis. Fixed wavelength FPI etalons are in the focus of further theoretical and experimental investigations.

Effect of relaxation time on the performance of photonic crystal optical bistable switches based on Kerr nolinearity is discussed. This paper deals with optical pulses with the duration of about 50 ps. In such cases the steady state response of the optical device can be used to approximate the pulse evolution if the nonlinearity is assumed instantaneous, hence analytical solutions such as the coupled mode theory can be used to obtain the time evolution of the electromagnetic fields. However if the relaxation time of the material nonlinear response is also considered, changes in the power levels and in the shape of the hystersis loop is observed. In this case, we use the nonlinear finite difference time domain method (NL-FDTD) to follow the system dynamics and get the bistability hystersis loop. Codes are developed to analyze the instantaneous Kerr materials and the Kerr materials with finite response times. Depending on the material, the relaxation times of the order of 1-10fs should be considered in studying bistability to obtain the right shape of the output pulses. It is observed that the relaxation leads to larger input power and threshold and hence degrades the performance of the switch in pulse shaping.

Photonic quasicrystals (PQCs) have neither true periodicity nor translational symmetry, however they can exhibit symmetries that are not achievable by conventional periodic structures. The arbitrarily high rotational symmetry of these materials can be practically exploited to manufacture isotropic band gap materials, which are perfectly suitable for hosting waveguides or cavities. In this work, formation and development of the photonic bandgap (PBG) in twodimensional 8-, 10- and 12-fold symmetry quasicrystalline lattices of low dielectric contrast (0.4-0.6) were measured in the microwave region and compared with the PBG properties of a conventional hexagonal crystal. Band-gap properties were also investigated by changing the direction of propagation of the incident beam inside the crystal. Various angles of incidence from 0° to 30° were used in order to investigate the isotropic nature of the band-gap.

The paper analyses electromagnetic wave propagation through nonlinear photonic crystal beam-splitters. Different lattice configurations of Y-junction beam-splitters are simulated and propagation properties are investigated with introducing nonlinearity with varying the rod size in crystal lattice. It is seen that nonlinear photonic crystal shows a considerable band-gap even at low refractive contrast. The division of power in both arms of beam-splitters can be controlled by varying the nonlinearity.

All photonic crystal slab designs rely on the accurate control of the sizes of the holes during fabrication - a small error of just a few nanometers can mean a shift of tens of nanometers in the operating wavelength of the device. A key problem is the measurement of the hole size. We have developed an optical method which determines the functional hole diameter with a typical accuracy of 5 nm. We also suggest a way for the nanometre control of the hole diameter.

We present results of numerical modeling of photonic crystal (PhC) structures fabricated in gallium nitride (GaN). GaN is a wide band gap semiconductor material with large refractive index and very good thermal and mechanical properties, so it is considered a valuable candidate for photonic crystal application - in particular for devices exposed to the harsh environment. In this paper are considered the ideal 2D PhC with infinite high for a different lattice structures and calculated optical band gap maps for each. We also calculated air-bridge type slab and "sandwich-type" PhC slabs with finite height. The dependence of transmission and reflection spectra on holes size, width and profile of "sandwich-type" PhC slab structure are investigated. All calculations were performed using plane wave expansion method (PWE) and finite difference time domain method (FDTD).

The results of a simulation of the optical properties of a silicon Fabry-Pérot resonator (with liquid crystal filler in the cavity), operated on the shift of the interference bands in the infrared range are presented. The possibility of tuning the reflection coefficient from 0 to 0.95 (or transmission coefficient from 1 to 0.05) by changing the refractive index by 0.1 in the cavity and using the stop-bands and resonance peaks of high order is demonstrated. The prototype Fabry-Pérot resonators were fabricated by dry and wet etching of (100)Si and (110)Si. Some of the resonators were fabricated on a silicon-on-insulator platform. A superposition of transmission peaks with reflection maxima, predicted from calculations, was confirmed experimentally, using infrared microspectroscopy, with a temperature variation from 20 ^oC to 65 ^oC and an applied electric field from 0V to 10V.

In this study, three-component One-Dimensional (1D) Photonic Crystal (PC) structures were investigated by modeling them as two-component PCs with an additional regular layer. The Gap Map approach and the Transfer Matrix Method were used in order to mathematically describe these structures. The introduction of a third component to a 1D PC allows manipulation of the optical contrast to a high degree of precision by varying the thickness and refractive index of the additional layer. It also partially reduces the area of the photonic band gaps (PBGs) on the gap map, leaving the remainder of the PBG area unchanged from that of the gap map for the original, two-component, PC. Using this approach to decrease the optical contrast in photonic crystals allows omni-directional bands to be obtained in highcontrast periodic structures constructed from, for example, an array of silicon and air.