In this paper the fabrication of photonic slab heterostructures based on artificial opals is presented. The innovated method combines high-quality thin-films growing of opals and silica infiltration by Chemical Vapor Deposition through a multi-step process. By varying structure parameters, such as lattice constant, sample thickness or refractive index, different heterostructures have been obtained. The optical study of these systems, carried out by reflectance and transmittance measurements, shows that the prepared samples are of high quality further confirmed by Scanning Electron Microscopy micrographs. The proposed novel method for sample preparation allows a high control of the involved structure parameters, giving the possibility of tunning their photonic behavior. Special attention in the optical response of these materials has been addressed to the study of planar defects embedded in opals, due to their importance in different photonic fields and future technological applications. Reflectance and transmission measurements show a sharp resonance due to localized states associated with the presence of planar defects. A detailed study of the defect mode position and its dependance on defect thickness and on the surrounding photonic crystal is presented as well as evidence showing the scalability of the problem. Finally, it is also concluded that the proposed method is cheap and versatile allowing the preparation of opal-based complex structures.

An optical and morphological study has been carried out to understand the role of intrinsic defects in opal-based photonic crystals. The inherent polydispersity in sphere size distribution yields imperfect crystallizations and worsens the photonic properties of these systems. By doping poly-(mehtymethacrylate) thin films opals with polystyrene spheres of larger size it is possible to study the disorder caused by the dopants and the negative influence in the optical response. In addition, it is feasible to grow mixed structures (alloys) with intermediate photonic properties by mixing spheres of different nature and the same size.

The optimization of the procedure to grow accurate amounts of amorphous silicon and germanium by CVD free of con-tamination in opals has been performed. The samples have been optically characterized and results agree with theoretical calculations of band structures. Multilayer systems of both semiconductors have been fabricated. Samples have been optically characterized and observed with a scanning electron microscope. Selective removal of germanium with aqua regia has proven to be possible. Theoretical calculations show that subtle variations of the topography may give rise to important effects (flat bands, pseudogap openings, etc). As an example, a photonic band structure with a complete photonic band gap (cPBG) between the 5th and 6th band has been provided along with a method to obtain it. It would be impossible to discuss all the possible structures that could be obtained from samples with different number of layers and materials forming them. However, there are many interesting topographies that could be fabricated in a relatively straightforward manner following the techniques described here.

The light reflectance in 3-dimensional metal-dielectric photonic crystals assembled from polyelectrolyte-coated latex spheres infiltrated with gold nanoparticles prior or after opal crystallisation has been studied. Strong deviation of the optical reflectance of Au-opals from bare opals has been observed, including flattening of the diffraction resonance dispersion and topology dependence of surface plasmon bands. Depending on whether the infiltration was made before or after opal crystallisation, the plasmon reflectance shows different band central frequencies as well as band positioning as the function of angle. The strong alteration of shape of the reflectance spectrum has been demonstrated in the case of overlapping the diffraction and plasmon resonances.

A heterojunction between two 3-dimensional photonic crystals has been realized by interfacing two opal films of different lattice constants. The interface-related transmission minimum has been observed in the frequency range between two directional lowest-order bandgaps of the hetero-opal constituents. The interface transmission minimum has been modelled numerically and tentatively explained by formation of the standing wave across the photonic hetero-crystal due to matching of group velocities of optical modes in both parts at this frequency.

ZnO infiltration technology was developed by chemical deposition from solution in to a three-dimensional opal lattice, samples of the ZnO - opal composites were prepared with the predominating UV - emission at room temperature. The embedding degree was checked up by the sample weight and by the shift of the spectral position of the reflection maximum (stop band). The both ways were in accordance with one another. The optimal synthesis conditions of the ZnO-filled opals were defined for the maximal intensity of the UV-luminescence. It is shown the use of the "raw" opals and incomplete filling of the pores by semiconducting material increase the edge excitonic emission by several times at room temperature. Angular dependences of the photoluminescence and reflectance spectra of the ZnO-infiltrated opal have been studied. These results can be used to create effective laser light sources in UV spectral range using "photonic crystal" effect.

We describe a simple technique for the selective area modification of the bandgap in planar 3-D photonic crystals (PhC). The PhCs are grown by controlled drying of monosized polystyrene spheres. Uniaxial pressure of 41 MPa can produce a shift in the bandgap of ~90 nm from 230 nm spheres. An unexpected broadening of the bandgap is attributed to the change in topology associated with large necks formed between spheres at pressures greater than 10 MPa.

Holographic techniques have been used for manufacturing multiple band one-dimensional, two-dimensional, and three-dimensional photonic crystals with different configurations, by multiplexing reflection and transmission setups on a single layer of holographic material. The recording material used for storage is an ultra fine grain silver halide emulsion, with an average grain size around 20 nm. The results are a set of photonic crystals with the one-dimensional, two-dimensional, and three-dimensional index modulation structure consisting of silver halide particles embedded in the gelatin layer of the emulsion. The characterisation of the fabricated photonic crystals by measuring their transmission band structures has been done and compared with theoretical calculations.

Periodically structured dielectric media with lattices on a sub-wavelength scale are receiving increased attention as they enable a variety of photonics applications. Fabrication, however, still imposes challenges to the scientific community. This article discusses process modifications in deep X-ray lithography to reduce minimum feature size and eventually allow the fabrication of high aspect ratio photonic crystal slabs with a moderate refractive index. Proximity printing requires an X-ray mask with high contrast and lateral resolution. Electron beam writing exposure doses were optimized to pattern feature sizes down to 400 nm in 3 μm thick resist. The voids were subsequently electroformed with 2 μm gold to generate the absorbers on a suspended silicon nitride membrane. The mask was copied into PMMA films of 5 μm thickness using X-ray lithography at about 0.4 nm. The yield of free standing smallest features is limited by adhesion of the resist to the substrate. Structures with aspect ratios as high as 8 to 12 tend to collapse after dip development. Periodic features are increased on the order of tens of nanometers compared to mask absorbers. Lattice constants need to be slightly reduced at fixed pore diameters before first photonic demonstrators made of PMMA can be fabricated.

We fabricated two-dimensional (2D) polymeric photonic crystals with atoms stretched along a specific direction by using a double exposure with phase modulation.

Materials with a periodically modulated refractive index, with periods on the scale of light wavelengths, are currently attracting much attention because of their unique optical properties which are caused by Bragg scattering of the visible light. In nature, 3d structures of this kind are found in the form of opals in which monodisperse silica spheres with submicron diameters form a face-centered-cubic (fcc) lattice. Artificial opals, with the same colloidal-crystalline fcc structure, have meanwhile been prepared by crystallizing spherical colloidal particles via sedimentation or drying of dispersions. In this report, colloidal crystalline films are introduced that were produced by a novel technique based on shear flow in the melts of specially designed submicroscopic silica-polymer core-shell hybrid spheres: when the melt of these spheres flows between the plates of a press, the spheres crystallize along the plates, layer by layer, and the silica cores assume the hexagonal order corresponding to the (111) plane of the fcc lattice. This process is fast and yields large-area films, thin or thick. To enhance the refractive index contrast in these films, the colloidal crystalline structure was inverted by etching out the silica cores with hydrofluoric acid. This type of an inverse opal, in which the fcc lattice is formed by mesopores, is referred to as a polymer-air photonic crystal.

Detection of light is one of the most fundamental physical processes playing a very important role in both nature and technology. In nature, this process underlies vision, thus providing an opportunity to perceive the world around us. Numerous photodetectors in technology allow the quantification of the detection of optical signals, expanding the spectrum of detected radiation. The problem of detecting optical signals by optical methods themselves was first formulated apparently by Bloembergen [1]. However, this idea has not been adequately developed. In paper [2] it was shown that the signal-to-noise ratio could be improved by using nonlinear radiation detectors in which the signal transformation begins from an absorption transition. It was shown in papers [3] that photocounts appear in conventional photodetectors due to the strong Coulomb instability of a weak electron current produced in the detector by a signal being detected. This suggests that in detectors, instead of free electrons, the electrons that are bound in atoms, ions, or molecules can be used, where they are well stabilized by a strong Coulomb field of nuclei. Below a possible scheme for detecting weak optical signals by laser means is described. At present microcavities are created which can be used in the Bloembergen scheme, providing the passage from spontaneous to stimulated effect, thereby substantially improving the scheme.

We report on the generation of strong surface acoustic wave (SAW) beams on GaAs substrates as well as on their concentration and guiding using acoustic horns and waveguides (WGs). By means of focusing interdigital transducers, we demonstrate the generation of narrow (full width at half maximum of approximately 15 μm), high-frequency (0.5 GHz) SAW beams collimated over distances exceeding 100 μm. The beams can be guided along the surface using narrow (10-μm-wide) WGs of ridge and slot types. The coupling of the SAW into the WGs was achieved using acoustic horns. Coupling power efficiencies of up to 75%, which translates into an eightfold increase of the local acoustic power density within the WG, is demonstrated using slot WGs with a 80-nm-thick aluminum cladding region.

We have investigated the propagation of TM-polarized light through periodic Chromium structures. The fabrication of periodic structures was performed with electron-beam lithography. The Chromium layer covered with Chromium Oxide is opaque. Typical slit widths of the periodic structures are varied between 100nm and 400nm. The periods are ranged between 500nm and 10μm. To analyze these structures we have performed FDTD-modeling for wavelengths in the visible and infrared spectral range. The near field region behind these structures was modeled. The propagation of surface waves was observed. Furthermore spectral measurements on periodic structures with varying periods are carried out. We propose a method for the determination of propagation lengths of surface waves across the interfaces of the metal layer. The experimental findings were compared with FDTD modeling. Resonances of the surfaces waves were also modeled with a RCWA algorithm. A comparison between the numerical findings and the experimentally achieved results will be given.

We review and discuss recent concepts and methods used to detect single fluorescent molecules with sub-wavelength resolution for biological analysis. We start with a brief review of the far field techniques that are able to define an observation volume, which is of the order or smaller than the optical diffraction limit. In a second part, we discuss how photonics structures can be used to shape both the excitation and the emitted optical fields, leading to a better signal to noise ratio and an enhancement of the temporal and spatial resolutions. We show that this 'nano-optical field engineering' can be associated with single molecule detection techniques such as Fluorescence Correlation Spectroscopy. In this framework, we illustrate the potentialities of planar photonic structures for the study of confined molecular diffusion in cells and bacteria.

It is well established that the presence of metallic surfaces or particles in the vicinity of a fluorophore can dramatically increase the radiative decay rate, and consequently the quantum efficiency, of the fluorophore. This effect, which depends on parameters such as metal particle size and fluorophore-particle separation, is manifest as a substantial enhancement in fluorescence emission intensity. This presentation will focus on optimisation strategies to maximise the enhancement for important applications such as fluorescence-based biochip platforms. Ordered arrays of metallic nano-islands were fabricated on a range of substrates by a process of natural lithography using monodisperse polystyrene nanospheres. The metal particle dimensions were tailored in order to match the plasmon resonance wavelength to the spectral absorption of the fluorophore. The fluorophore Cy5 dye, which is widely used in optical immunoassays and has a medium quantum efficiency (~0.3), was used in this study of the plasmonic enhancement effect. The morphology of the metallic arrays was investigated using scanning electron microscope (SEM) and atomic force microscope (AFM). Absorption and emission spectroscopies were used to elucidate the enhancement effect and its dependence on metal island morphology. Results were correlated with existing theoretical models. The applicability of this important technique to sensor platforms, such as fluorescence-based biochips, will be discussed.

Electromagnetic Bloch waves are the standard representation of the optical field in two-dimensional photonic crystals (2D-PhCs). We present an intuitive description of Bloch waves based on their Fourier transform into series of electromagnetic plane waves. The contribution of each plane wave to the global energy and group velocity is detailed and the valid domain of this decomposition is discussed. This approach enables a continuous description of light propagation from the homogeneous medium to the strongly modulated PhC case and resolves inconsistencies that result from band folding. Finally this model provides a clear physical understanding of the negative refraction effects observed in 2D-PhCs.

Standard perturbation theory (PT) and coupled mode theory (CMT) formulations fail or exhibit very slow convergence when applied to the analysis of geometrical variations in high index-contrast optical components such as Bragg fibers and photonic crystals waveguides. By formulating Maxwell's equations in perturbation matched curvilinear coordinates, we have derived several rigorous PT and CMT expansions that are applicable in the case of generic non-uniform dielectric profile perturbations in high index-contrast waveguides. In strong fiber tapers and fiber Bragg gratings we demonstrate that our formulation is accurate and rapidly converges to an exact result when used in a CMT framework even in the high index-contrast regime. We then apply our method to investigate the impact of hollow Bragg fiber ellipticity on its Polarization Mode Dispersion (PMD) characteristics for telecom applications. Correct PT expansions allowed us to design an efficient optimization code which we successfully applied to the design of dispersion compensating hollow Bragg fiber with optimized low PMD and very large dispersion parameter. We have also successfully extended this methodology to treat radiation scattering due to common geometric variations in generic photonic crystals. As an example, scattering analysis in strong 2D photonic crystal tapers is demonstrated.

The temporal coupled mode theory is applied on the design of filters and waveguide crossings that feature a resonator with a high quality factor. To determine the transmission properties of the device we calculate the decay rate of the resonator. The analysis using the decay rates requires far less computational effort than conventional FDTD transmission calculations and therefore the optimum device properties can be determined quickly.

We describe a scattering matrix formalism used to model optical properties of two dimensional photonic crystals slabs. The determination of the scattering matrix poles allows us to simultaneously calculate the band structure and the corresponding losses of the electromagnetic modes, which contributes then to give a complete physical insight of the intrinsic properties of photonic crystal slabs. Using an in-plane supercell approach, a linear defect is also studied, leading to a complete evaluation of photonic crystal slab waveguides performances.

In this work, we show that photonic crystals with geometries of lower symmetry, such as the rectangular geometry, are uniquely suited for applications involving the superprism effect. The extra degree of freedom provided by the anisotropy of the unit cell allows more freedom in searching for suitable iso-frequency curves. Also, the appearance of multiple orders of diffraction allows more than one incident plane wave to couple to the same Bloch mode. This extra degree of freedom is decisive when trying to optimize the transmission. We illustrate this on a particular rectangular configuration which ensures a strong angular superprism effect, a well collimated transmitted beam, and power transmissions of up to 80%. We also study the effect of the incident beam width on the super-prism effect, and propose a possible solution to the problem of beam diffraction at the exit surface.

We use multiple scattering in conjunction with a genetic algorithm to reliably determine the optimized photonic-crystal-based structure able to perform a specific optical task. The genetic algorithm operates on a population of candidate structures to produce new candidates with better performance in an iterative process. The potential of this approach is illustrated by designing a spot size converter that has a very low F-number (F=0.47) and a conversion ratio of 11:1. Also, we have designed a coupler device that introduces the light from the optical fiber into a photonic-crystal-based wave guide with a coupling efficiency over 87% for a wavelength that can be tuned to 1.5 λ.

Modal solutions of photonic crystal fibers with both circular and rectangular air holes are presented by using a rigorous full vectorial finite element-based approach. The effective indices, mode field profiles, spot-sizes, power confinements, modal hybridness, beat lengths and group velocity dispersions are shown for the fundamental and higher order modes of the quasi-TE and TM polarizations.

The synthesis of a narrow band, wide angular aperture 1D grating filter exhibiting close to 100% reflection of a focused beam is developed analytically on the basis of a phenomenological coupled wave representation.

In photonic crystal fiber technique a free choice of microstructure allows flexible design of multicore waveguides. In this paper we study properties of a double-core fiber with square and hexagonal lattices. They can be modified with local changes of a structure. Variable size of the central hole that separates cores influences mode coupling properties. Full-vector mode solver using the biorthonormal basis method is employed to analyze guiding properties of the double-core fiber. In FDTD numerical simulations we study coupling efficiency in fibers with various crystal structures. We present experimental realizations of solid double-core photonic crystal fibers fabricated from multi-component glass. Composition of oxides is chosen to obtain higher refractive index than available in fused silica and relatively low-loss guidance when compared to other silicate glasses. Transmission properties of double-core fibers are measured, inter-core coupling mechanism and possible applications are discussed.

At the present paper the photonic crystal coupler of an optical fiber, which has been made by the adiabatic tapering of the optical fiber based on the photonic crystal is presented. These couplers are characterizing by material refractive index changing in a spatial direction along of the wave propagation direction. In our investigation an effective refractive index model of two-dimensional photonic crystal was used. This model allows analyzing the waveguide structures, which work on the effective index waveguiding in a defect of the photonic crystal. Also this model allows reducing the investigation time by reducing the three-dimensional numerical analysis of the coupler to the two-dimensional consideration. The effective refractive indexes of such couplers were numerically found. Using this model the field distribution in these couplers were investigated and were calculated its losses. It was shown that the couplers with smaller input diameter and the fixed output diameter have smaller losses.

The second-harmonic field generated has been measured in reflection from the surface of one-dimensional and two-dimensional photonic crystals etched into a GaN layer. A very large second-harmonic enhancement is observed when simultaneously the incident beam at the fundamental frequency w excites a resonant Bloch mode and the second-harmonic field generated is coupled into a resonant Bloch mode at 2w. A smaller, but still substantially enhanced, second-harmonic generation level was also observed when the fundamental field was coupled into a resonant mode, while the second-harmonic field was not. By using calculated and experimental equifrequency surfaces, it is possible to identify the geometrical configurations that will allow quasi-phase matching to be satisfied - and observed experimentally in the available wavelength tuning range of the laser. The extended transparency window of III-nitride wide-bandgap semiconductors, coupled with large non linearities, is an appealing feature pointing towards the control and manipulation of light in photonic structures.

We demonstrate ultrafast shifting of a photonic stop band driven by a photoinduced phase transition in vanadium dioxide (VO₂) forming a three-dimensional photonic crystal. An ultrashort 120-fs laser pulse induces a phase transition in VO₂ filling the pores of an artificial silica opal, thus changing the effective dielectric constant of the opal. Consequently, the spectral position of the photonic stop band blue-shifts producing large changes in the reflectivity. The observed switching of the photonic crystal is faster that 350 fs. The demonstrated properties of opal-VO₂ composite are relevant for potential applications in all-optical switches, optical memories, low-threshold lasers, and optical computers.

We report on third-harmonic (TH) generation emitted from 1D photonic slabs etched into Silicon-on-Insulator (SOI) planar waveguides, as compared to the bare waveguide and (100) Silicon bulk responses. 130-fs laser pulses at ~ 810 nm and ~1550 nm have been chosen as a pump to excite TH signals in reflection and diffraction directions. The measured angles of in-plane diffracted third-harmonic beams agree with those predicted by nonlinear diffraction equations. The nonlinear reflectance as a function of the angle of incidence and azimuthal orientation of the structure has been measured. The near-infrared measurements have revealed that, whenever the pump frequency is resonant with a photonic mode, a substantial enhancement of the harmonic signal occurs. This nonlinear mechanism is in principle a very sensitive spectroscopic tool in determining and mapping the photonic band diagram of the system above the light line. The agreement between experimental data and ad hoc simulations of the nonlinear behavior of the system sheds new light on the nonlinear optical response of these nanostructured materials.

We have designed a one-dimensional photonic bandgap crystal to obtain perfect phase-matching conditions for noncollinear type II quadratic processes. The realized sample was 15 periods of Al_(0.3)Ga_(0.7)As/Al₂O₃, for a total length of 3.5um. Noncollinear type II phase-matching was obtained at 1510nm. We have experimentally verified the band structure characteristic as well as its perfect phase-matching for the noncollinear type II parametric process. Indeed, noncollinear type II second harmonic generation was obtained for the first time in a PBG crystal1. The experiment demonstrated that the breaking of symmetry, which is artificially induced in such a structure, and the field resonance effect give rise to a relatively efficient second harmonic generation even using a naturally isotropic material (AlGaAs). In fact, we report a nonlinear effective coefficient of the sample equal to (52±12) pm/V.

We present a new concept for efficient second harmonic generation that is based upon the interference of counter-propagating waves in multilayer structures. We show that phase matching and quasi phase matching are not always necessary conditions to provide optimized nonlinear frequency conversion efficiency.

Silicon on insulator (SOI) substrates provide a naturally good template for the introduction of optics at the microelectronics device level, due to the high refractive index contrast between Si and SiO₂. If one is able to control the propagation of photons in the material, functional devices like, filters, modulators or resonant detectors can be envisioned. One can even imagine to make light emitters since recent progress showed room temperature light emission from doped silicon material or nano-crystalline silicon. This suggests that combining these new materials with low volume optical resonators will allow to make efficient light sources based on Si and opens a route towards CMOS compatible silicon-based light emitters. A promising way to integrate this functions in compact large-scale photonic circuits is to use photonic crystals (PCs). In this work we will present the design, fabrication and optical characterization of SOI based PC resonators engineered to change the emissio rate and/or extraction of photons from the Si layer. Different structures have been studied: vertical microcavities, in-plane 2D hexagonal cavities and defect-less structures and results demonstrating strong light extraction enhancement will be shown together with calculations made by plane wave expansion techniques and FDTD.

Photonic devices based on 2D PCs have so far been principally targeted at operation in a wave-guided configuration and at providing the basic building blocks for Photonic Integration. The problem of optical losses, which are considered as hindering the operation of 2D photonic integrated circuits based on 2D PC, can be approached from a completely different perspective: instead of attempting to confine the light entirely within waveguide structures, the 2D structures can be deliberately opened to the third space dimension by controlling the coupling between wave-guided and radiation modes. It is shown in this paper that interaction of radiative and guided modes through a photonic crystal, especially under conditions where the later correspond to extrema of the dispersion characteristics of the photonic crystal, results in resonance phenomena which can be used practically for the development of new classes of devices, e.g. combining photonic crystal and MOEMS (Micro Opto Electro Mechanical Systems) structures. We present here the general trends for designing and fabricating PC-MOEMS structures and first experimental results on demonstrators which are now under investigations in our group.

We report on the temperature tuning of the optical properties of planar Photonic Crystal (PhC) microcavities. Studies were made on one and two dimensional PhCs that were etched in InP and GaAs vertical waveguides. Two dimensional (hexagonal) and one-dimensional (Fabry-Perot) cavities were optically investigated by an internal light source technique. The samples were mounted on a Peltier-stage which allowed temperature variation from T = 20 °C up to T = 76 °C. A linear dependence of the resonance wavelengths with respect to temperature is observed. A gradient of dλ/dT = 0.09 nm/°C and 0.1 nm/°C for the GaAs and InP based cavities was observed, respectively. These results are in agreement with the theoretical calculations based on the thermal dependence of the refractive index of the PhC semiconductor component.

We present a novel design approach for line-defect waveguides integrated in a photonic crystal slab (PCS) with hexagonal holes in a triangular lattice (aka 'hexagon-type'). Triangular air inclusions are symmetrically added on each side of the waveguide. Size and position of these inclusions are tuning parameters for the band diagram and can be used for minimizing the distributed Bragg reflection (DBR) effect. The waveguides show single-mode behavior with reasonably high group velocity and large transmission window, inside the gap between even-like modes. Qualitative design rules were obtained from 2D calculations based on effective index approximation and full 3D calculations of the band structure were applied for fine-tuning of structural parameters of these high-index contrast systems. Transmission spectra and losses of finite-sized structures were estimated by means of 3D finite-difference time domain (FDTD) calculations. We present a pattern definition technique, which is an integration of optical lithography with focused ion beam (FIB) high-resolution etching. The mask pattern is transferred into the SOI stack by a subsequent reactive ion etching (RIE) process. The combination of moderate resolution optical lithography and FIB etching provides an excellent tool for fast prototyping of PCS-based devices.

We have fabricated and measured 2D photonic crystal Mach-Zehnder device structures using W1 channel waveguides oriented along GK directions in AlGaAs/GaAs epitaxial waveguide material and silicon-on-insulator waveguide material, with operation at wavelengths around 1550 nm. 2D FDTD simulations and experimental results will be shown and compared. The structure has been designed using progressive tapering of the hole diameter in the bend regions, while a 'defect' hole with reduced radius has been placed in the centre of the Y-Junction, giving a substantial improvement in the transmission and bandwidth. The overall length of the photonic crystal Mach-Zehnder structure is typically about 32 um and the structure has been fabricated using a combination of direct-write electron-beam lithography (EBL) and dry-etch processing. Devices were measured using a tunable laser with end-fire coupling. We shall describe the application of such structures for switching and sensing, with deliberate exploitation of the thermo-optic effect via the incorporation of heater electrodes.

We report in this paper the study of a W1 photonic crystal waveguide which supports two Bloch modes having different parity. A monomode ridge waveguide etched in a Silicon-On-Insulator substrate and connecting to the photonic crystal waveguide allows us to excite the even Bloch mode. Transmission measurements, performed on a broad spectral range, evidence the even mode propagation along the defect line and experimental spectrum is discussed in light of band diagram and FDTD calculations. Then spectrally resolved near-field patterns obtained by using a scanning near field optical microscope in collection mode for wavelengths inside and outside the multimode region of the photonic crystal waveguide clearly demonstrate the even mode parity change along the defect line.

We report the spectroscopic characterisation of an integrated microcavity designed for the 1.5μm telecommunication wavelength by using both near- and far-field techniques. We show the establishment of the cavity mode for wavelengths ranging from the photonic band gap to the resonance by using a scanning near-field optical microscope in collection mode. The respective contributions of out of plane losses and evanescent field are clearly identified. Transmission measurements on a broad spectral range are performed and results obtained by the two techniques are in very good agreement.

We fabricated single-mode photonic wires, nanophotonic waveguides confining light by total internal reflection. The structures are defined in silicon-on-insulator using 248nm deep UV lithography, a widely adopted technology for CMOS applications. The crystalline silicon core has a thickness of 220nm and a width of up to 600nm. A 1um thick silica layer serves as the lower cladding. We measured the loss of straight waveguides using the Fabry-Perot interference spectrum of the cleaved samples. A 500nm wide waveguide has a loss as low as 2.4dB/cm at 1550nm wavelength. We measured 90 degree bends to have excess losses of about 1dB. Mirror bends perform comparably. We fabricated symmetrically coupled ring and "racetrack" resonators with small radius. Q-factors higher than 3000 are achieved, leading to low add-drop crosstalk, high finesse and low at-resonance insertion loss. By fitting the theoretical model to the experimental results, we extracted parameters such as the coupling ratio, cavity loss and group index. We analyzed the fabrication tolerances allowed for these resonators to be suitable as a building block for WDM filtering components. The allowed deviation on the waveguide widths and gaps for the coupling ratio to be within specification are within the possibilities of the fabrication method. However, a method to tightly control the optical cavity length is needed as the ring's group index is highly dependent on waveguide width.

Silicon is the basic material for the microelectronics industry. The predicted limits for electrical interconnects in electronic circuits favor the development of alternative solutions such as optical interconnects to transfer information. The silicon-based components are an alternative to realise these interconnections, providing that high speed and high efficiency integrated optoelectronic devices can be realized. In this work, we have fabricated two-dimensional photonic crystal (PC) microcavities on silicon-on-insulator (SOI). The samples contain self-assembled Ge/Si islands deposited in the upper silicon layer by chemical vapor deposition. The silicon layer thickness measures 0.3 mm. The photonic crystals consist of triangular lattices of air holes etched in the upper silicon layer of the SOI substrate. The period lattice measures 0.5 μm and the drilled holes had diameters between 0.3 and 0.45 μm. These structures exhibit a forbidden band around 1.3 - 1.5 μm in TE polarisation. Different photonic crystal hexagonal microcavities were processed and the optical properties are probed at room temperature with the Ge/Si island photoluminescence. Quality factors larger than 200 are measured for hexagonal microcavities. On the one hand, the presence of the PC improves the vertical extraction of light, and on the other hand, we show that a significant enhancement of the Ge/Si island photoluminescence (x 100) can be achieved in the 1.3 - 1.55 μm spectral region using the microcavities. These attractive results should allow to realise efficient light emitting-diodes in the near infrared.

Regular arrays of scatterers like cylinders or spheres which resemble 2D photonic crystals can increase light extraction from organic leds. In a recent SPIE publication we have shown that the scattering of the light emitted from a dipole source by such structures can be effectively modelled by an integral equation which kernel is essentially given by the Green’s tensor of the layered medium constituting the organic led. Here we extend the scope of this method by making use of the fact that the matrix-vector products arising from the discretization of the integral equation via the coupled dipole approximation can be calculated by the fast 3D Fourier transform. In this way the iterative solution of linear systems with millions of unknowns becomes feasible and large finite arrays comprising about 10 by 10 particles and more can be effectively treated. After giving an outline of the algorithms we present the results of calculations for large arrays of spheres and cylinders of circular and quadratic cross section. The influence of particle shape, type of array (quadratic, hexagonal) and refractive index on the efficiency of light extraction and angular distribution is studied. We also investigate the effect of random departures of the scattering elements from their ideal lattice positions.

We demonstrated laser diode pumped quasi-continuous-wave random laser in Nd³⁺ doped YAG nanopower with a one-mirror structure. Beside usual phenomena associated with laser, like threshold behavior and substantially narrowing of emission spectra, chaotic pulsing behavior was observed above a certain pumping level, which is explained as disturbed relaxation oscillation in random cavities. Possible relation between random lasing in such one-mirror structure and coherent backscattering effect, which is also referred as weak localization, is discussed with much interest.

The dispersions and radiative decay rates of polaritons in self-assembling quantum wires have been investigated. This study is based on the analytical solution of the Maxwell's equations in a system presenting a lateral modulated dielectric constant and described by nonlocal periodically susceptibilities. With this generalized theoretical method, we can obtain the polariton energies and their radiative decay rates for any angle θ of incidence. The electromagnetic field confinement along two direction induces guided and diffracted modes which couple to one-dimensional excitonic modes. These interactions enhance strongly the polariton behavior in both S and P polarisations. In addition we have analysed the polariton radiative decay rates where the superlattice of quantum wires SQWW is considered as a resonator.

Organic two-dimensional photonic bandgap structures (2D PBG) have been fabricated by spin-coating a thin polymer film onto a nano-patterned SiO2 circular-grating surface-emitting distributed Bragg reflectors (CG-SE-DBR). When optically pumped and for certain grating parameters, these structures exhibit a peak inside the stop band that leads to lasing with a reduced threshold. An analytical model based on the transfer-matrix method has been developed to investigate the origin of this peak. The theoretical results are in excellent agreement with the experimental findings.

This paper explores the optical characteristics of one-dimensional (1D) and two-dimensional (2D) photonic crystals (PhC) as spectral control components for use in thermophotovoltaic (TPV) systems. 1D PhC are used as optical filters while 2D PhC are used as selective thermal emitters. A Si/SiO2 1D PhC is fabricated using low-pressure chemical vapor deposition (LPCVD). The measurement and characterization of this structure is presented. A 2D hexagonal PhC of periodic holes is fabricated using interference litography and reactive ion etching (RIE) process. Our results predict that a TPV system utilizing a 2D PhC selective emitter and 1D Si/SiO₂ PhC optical filter promises significant performance improvements over conventional TPV system architectures.

The third order nonlinear optical effect called the optical Kerr effect was studied in InP nanoparticles solutions. The synthesized InP nanoparticles have sizes ranging from 1.5 to 3.5 nm and each sample is characterized by its sizes distribution. The Z-scan technique was used to study nonlinear absorption and refraction. Different lasers were used, hence different nonlinear refraction effects were observed at different wavelengths (532, 633 and 1550 nm) and at different time scales (continuous and femtosecond).

We have synthesized nanostructured rare-earth doped silicates by two different methods: combustion flame - chemical vapor condensation (CF-CVC) and sol-gel processing. Substantial rare-earth concentrations (~ 8 wt. %) were achieved with no signs of concentration quenching. We have observed unprecedented spectrally broad/flat fluorescence emissions at 1.55 μm from the Er³⁺-doped materials, which we attribute to their unique nanostructures developed during heat treatments. In depth results of a combined XRD/TEM study monitoring the evolution of the nanostructure will be presented. The role of processing conditions, chemistry, and particle size will also be discussed.

We present a method for mapping the electromagnetic field distribution in the vicinity of noble metal nanoparticles able to sustain localised surface plasmon resonance (LSPR). The field distribution is coded by topographic change in a self-developing photosensitive polymer (PMMA-DR1). Metallic nanostructures are fabricated by e-beam lithography and optically characterised by extinction spectroscopy. Photoinduced topographic changes are checked by means of atomic force microscopy (AFM). The dipolar character of the surface modification around the particles agrees qualitatively with theoretical predictions and a strong correlation between LSPR position and the relief depth is found.

Theoretically investigated oxide-confined and proton-implanted VCSELs with incorporated single-mode defect waveguide in a two-dimensional photonic crystal. It had shown, that such defect establishes single-mode conditions in proton-implanted VCSELs omitting the gain-guidance taking place in these lasers, but same effect can be achieved in oxide-confined VCSELs with oxide layer in anti-node position. In order to check theoretical data, we fabricated a group of proton-implanted VCSELs with two-dimensional photonic crystal, but the photonic crystal did not created single-mode in practical case, probably, because of small etching depth. Experimental researches in process up to now.

Photonic mode behaviors are theoretically investigated for a mechanically driven (rotating) microstructure (microdisk). The present calculation clarifies for the first time the extraordinary behaviors of photonic modes, which are induced by the rotating motion of the microdisk. First, whispering gallery modes with twofold degeneracy in the microdisk at rest split off due to the onset of rotation (Sagnac effect). This rotation also excites a number of extra modes that appear to have developed from vacuum states in the microdisk at rest. These modes reveal anticrossing and mergin-regeneration phenomena in the dispersion curves of photon frequency as the rotation speed increases. The light intensity distributions in the microdisk exhibit a variety of metamorphoses according to the rotation speed variations. All of these phenomena can be explained as being caused by the coupling of photonic modes to the rotating motion of the microdisk and the resultant coupling between different photonic states.

We show that the spontaneous-emission behavior of an emitter-embedded periodic photonic band-gap (PBG) stack, described in general on the basis of the approximation of dipole emission, can be considerably modified if the macroscopic features of the emitter are considered. We have developed a model which takes into account the optical thickness of the emitter in the usual formalism. The extended model is presented in comparison with the classical dipole-emission model. Some numerical results are given and discussed, by using GaAs-embedded SiO2 / TiO2-coated quarter-wave stacks as a specific configuration. Our model provides quantitative arguments for optimization of spontaneous-emission power in terms of radiation frequency and emitter localization. It can be directly applied to optimum design of more complex systems, such as multi-emitter-embedded periodic stacks and any other passive structure.

A novel holographic technique for fabricating three-dimensional photonic crystals (PhCs) by two-beam interference is presented in this paper. The optical setup in this method is much simpler and more flexible compared with other multi-beam interference methods, and large and uniform PhCs are easier to be obtained. In PhCs' fabrication, two coherent laser beams interfere and generate a set of two-dimensional interference fringes, which are recorded on a plate of photosensitive material. One laser beam is incident on the plate in normal direction and the other beam with an angle to the normal. Then with the laser beams maintained in a fixed relative position, the plate is rotated by 120 degrees about an axis through the center of the plate and a second recording is made. This procedure is repeated one more time, producing finally a superposition of three sets of interference fringes at angles of 120 degree to each other. After the chemical treatment, a three-dimensional PhC is fabricated in the material with a particular lattice structure that depends on the detail of the basic interference pattern. PhC with fcc lattice structure was fabricated in the experiment with the angle of 38.9 degrees between the two interference beams, verifying the effectiveness of the technique.

As any lattice-like structure supporting forbidden bands, a discrete periodic network can be considered as a special class of artificial Photonic Crystals (PC). In contrast to usual continuous PC, such a structure can be described exactly in the frame of linear algebra. We investigate theoretically and experimentally Two-Dimensional Discrete Photonic Crystals (2D-DPC) of finite size, made of ideal transmission lines interconnected by reciprocal, lossless and passive four-port networks. The intrinsic spectral responses between any two ports of a DPC (scattering parameters) are defined as its transmission coefficients when all external ports are perfectly matched (antireflection coating). The structure symmetries enable us to accelerate the calculation. In a DPC with arbitrary termination at each port, the spectral responses, including forbidden bands, are quite simply expressed as linear combinations of its intrinsic responses. Extremely sensitive to boundary conditions, they are thus reconfigurable. Since we use normalized units, our results are universally valid at any frequency. We illustrate the concept experimentally in the low microwave band [f < 10 GHz] where, thanks to easier technological control, it is possible to achieve the wanted performance at a given target frequency.

Multi-layer structures, such as Bragg reflectors, rugate filters, and optical microcavities are widely used in optical sensing. They are characterised by a periodical modulation of the refractive index so that they can be classified as 1-D photonic crystals. In this communication, the optical features of such a class of sensors are analyzed from the band structure point of view. This general approach is then applied to the case of vapour sensors based on a porous silicon microcavity. A numerical analysis of the photonic bands, when the porous microcavity is exposed at chemical vapours, is presented and discussed for design optimisation purposes. In particular, we investigate how the photonic band gap changes when a volatile substance condensates in the silicon pores inducing a variation of the refractive indices of the layers forming the microcavity. Results are also compared with those obtained by the usual optical transfer matrix method.

In this work we present optical and structural characterisation of high-quality opal based photonic crystals consisting of polystyrene spheres ordered into a FCC lattice. By means of optical diffraction we orient our samples so that the evolution of its spectral features in reflectivity experiments may be probed along desired directions in reciprocal space. Prior to a comparison with calculated bands, finite size effects in the optical properties of the samples are taken into account. Further, attention is paid to the appearance of spectral features for energies above those where the characteristic Bragg peak is found.

The main laser materials, the most used for optical communication spectral window (~ 1,5 microns), are erbium doped glasses and crystals. The processes of light interaction with gain media essentially change at introduction of ΕΓ3+ ions in mesoporous matrix of various dimensions, in particular, as a result of multiple light scattering and occurrence of new quantum-optical effects. These will allow not only effectively to control a level of spontaneous emission in laser systems, but also to achieve light localization in various waveguide structures. Application of 3D- (volumetric) and 2D- (planar) matrixes (doped by erbium or other rare-earth elements) in systems of optical communication and information processing, in laser technology and optical computers becomes possible. The various approaches to obtain of materials with photonic band gap (photonic crystals) are analyzed. The use of "self-organizing" systems seems to be most perspective. Such, in particular, are 3D- and 2D-structures on the basis of cubic packing SiO2 nanospheres (opal matrixes) and 2D-structures on the basis of porous anodic alumina (PAA). The ΕΓ3+ions can be introduced into these matrixes by various methods (in present work some methods were used: impregnation, sol-gel, magnetron sputtering). As a result, the diverse systems such as "active media - optical matrix" are formed.

Deposition of coinage metals on a crystallographic surface of a colloidal crystal is proposed with the aim of fabricating metal surfaces with a regular relief on a scale of 200-300 nm to get strong surface enhanced Raman scattering (SERS). The approach is implemented through thin gold-film deposition on a surface of a crystal consisting of silica globules. Mitoxantrone, a DNA intercalator, malachite green and methylene blue molecules were used to prove high Raman and fluorescence enhancement efficiency of the structures proposed. Distance dependence measurements of the mitox secondary emission intensity show a long-range character of enhancement effects. As compared to other SERS-active substrates, metal-dielectric colloidal crystal structures possess well-defined surface parameters (globule diameter and film thickness), high stability and reproducibility. These advantages are important for systematic analysis of SERS mechanisms in mesoscopic structures and its application in single-molecule detection.

Chlorine-based inductively coupled plasma etching processes are investigated for the purpose of etching two-dimensional photonic crystals in InP-based materials. Etch rates up to 3.7 mm/min and selectivity’s to the SiN mask up to 19 are reported. For the removal of indiumchloride etch products both the application of elevated temperatures and high ion energy’s are investigated. The reactor pressure is an important parameter, as it determines the supply of reactive chlorine. It is shown, that N2 passivates feature sidewalls during etching, improving the anisotropy. Ions that impact onto the sidewalls, either directly or after scattering with the SiN-mask or hole interior, cause sidewall etching. Highly directional ion bombardment and vertical sidewalls in the SiN-mask are therefore crucial for successful etching of fine high aspect ratio structures.

The basic areas of use the unique characteristics of bacteriorhodopsin are defined by progress in creation of systems with a high degree of such molecules orientation. The maximal range of orientation can be achieved in the self-organized systems of supramolecules of optically active materials. The method of formation such structures is advanced. The structures were created in interstitial voids of cubic packing SiO2 nanospheres with a diameters of 240 - 250 nm (opal matrixes) on various substrates, including crystalline strontium-barium niobate and lithium niobate, which concerning to a class of strong piezoelectrics. The problem of bacteriorhodopsin introduction into opal matrixes is solved. The photoluminescence of the received nanocomposites is investigated under excitation by laser radiation in yellow spectrum range. The influence of substrate materials and temperature on photoluminescence spectra is discussed.

Investigations of polarizations effects in second-harmonic generation of a one-dimensional photonic crystal based on gallium nitride were performed for the fundamental beam incident on the surface of the photonic crystal. The angle of incidence, the azimuthal rotation angle of the photonic crystal, the frequency, and the polarization behaviour for strongly enhanced second-harmonic generation agree well with the identified position and polarization of the resonant Bloch modes. Along the direction, giant enhancements of 7500 times in the second-harmonic conversion have been obtained in the one-dimensional photonic crystal by comparison with the unpatterned GaN layer. The combined role of the resonant coupling of the fundamental field and of the second-harmonic field has been observed as the polarization of the fundamental beam is rotated.

A construction of the polarizing holey fiber was optimized in order to assure maximum single polarization bandwidth. We demonstrated that the polarization bandwidth of the holey fiber can be increased up to 480 nanometers by properly choosing the fiber constructional parameters. A single-polarization operation in the analyzed structure was achieved by introducing a pair of air holes adjacent to the fiber core and having diameters greater than the cladding holes. Similarly to traditional polarizing fibers, the operation principle of the analyzed holey fiber is related to the difference in cut-off wavelengths of the two orthogonally polarized fundamental modes.

We investigated theoretically and experimentally an impact of hydrostatic pressure on phase modal birefringence in birefringent photonic crystal holey fiber of new construction. The birefringence in this fiber is induced by highly elliptical shape of the core, which consists of triple defect in the hexagonal structure. Using finite element method, we first calculated the stress components and deformations induced by hydrostatic pressure in the fiber cross-section. In the second step, the distribution of the stress-related corrections of refractive index were determined. Finally, we calculated the sensitivity of the phase modal birefringence (dB/dp) to hydrostatic pressure versus wavelength. The contribution of the geometrical effects related only to deformation of the holey structure as well as the stress-related contribution to the overall pressure sensitivities were analyzed separately. Our results show that these two factors decrease the phase modal birefringence, which results in negative sign of dB/dp. We also measured the pressure sensitivity for several wavelengths using polarimetric technique. The experimental and theoretical values of dB/dp show very good agreement.

Photonic band gap Crystals (PhC) are usually analyzed using the analogy between photon propagation in artificial periodic structures and electron wave propagation in real crystals. The forbidden band of photons is regarded as equivalent to the energy gap that electrons experience in crystals because of the periodic potential. On the other hand, electron propagation and electromagnetic wave diffraction in periodic solids, respectively developed into band-theory and Dynamical Diffraction Theory (DDT), are formally identical. It appears therefore natural to perform an analysis of the features of an electromagnetic phenomenon, as the PBG, in analogy to the most direct antecedent electromagnetic theory, the DDT, that historically has also represented the direct reference for the derivation of the band-theory of electrons. In this communication, we introduce an analysis of the features of PhCs in analogy with the DDT, underlining the differences between DDT classical application to the x-ray diffraction from real crystals and that from artificial crystals at optical wavelengths. In particular, the high contrast of material refractive indices in PhC makes inapplicable some approximations generally used in x-ray diffraction analysis. Moreover, we discuss in which cases DDT has to be generalized in order to overcome such limitations. The theoretical derivation carried out is validated by the good agreement with the experimental results obtained for very simple 1D photonic crystals, such as porous silicon multilayers and silicon nitride multilayers. The generalization of the proposed approach to the case of 2D and 3D photonic crystals is also discussed.

In this paper we analyze linear and ultrafast non-linear properties of a three-dimensional photonic crystal composed of close-packed SiO₂/Au/SiO₂ core-shell colloidal particles. Strong coupling between incident light and surface plasmon of spherical gold microcavities appears as sharp features in observed reflectivity spectra in the visible. In a single layer of gold-shell particles, a highly directional diffraction pattern was observed with hexagonal symmetry. The non-linear dynamics of the reflectivity has been studied by femtosecond white-light pump-probe experiments. Abrupt changes limited by the instrumental time resolution, were observed in time-resolved reflection spectra while the signal recovers in about 10 ps. Ultrafast changes in reflectivity reach values as high as 20%. The results are compared with theory.

We indicate the ways in which surface plasmon polariton modes may be used to as a means to enhance the emission of light through a thin metallic film. Emitters couple to surface plasmon polariton modes by near-field coupling and microstructure is used to couple the surface plasmon polariton modes to light by Bragg scattering. We discuss both the use of coupled surface plasmon modes and the problems associated with the relative phase of the different scattering mechanisms that can produce radiated light. These concepts are explored in the context of organic light emitting diodes.

We have experimentally realised a tunable photonic crystal microcavity with in-filling holes in silicon-on-insulator waveguide by using thermooptic effect. A thin film nichrome heater has been integrated onto the microcavity where a change in temperature (and consequent change in the refractive index of the silicon core) produced a peak resonance shift at the wavelength region λ = 1530 nm. A peak resonance shift of 5 nm towards longer wavelengths was achieved when the heater was switched on to a current of 1.2 mA - while maintaining high Q-factor value in the microcavity.

Pure, defect-free bulk semiconductor is the foundation of electronics. On its own, however, perfect periodicity does not give rise to useful function. Selective doping and, better yet, heteroepitaxy, are needed for diodes, transistors, resonant tunneling devices, and lasers. Analogously, perfect photonic crystals are a necessary building block, but not an end in themselves, in the implementation of novel, integrable photonic function. Photonic crystal heterostructures, and interfaces between finite photonic crystals and nonperiodic media, are needed to enable in- and out-coupling, guiding, and wavelength selection, to name a few examples. We summarize herein advances in the realization and design of photonic crystal heterostructures and heterointerfaces. In Section 2 we show how bottom-up self-assembly of colloidal crystals can be merged with top-down pattern definition to determine the orientation and placement of finite-sized photonic crystal regions on a planar substrate. In Section 3 we describe the development of a conceptually- and analytically-tractable theory to enable convenient design using combinations of photonic crystals and homogeneous media.

We have demonstrated the feasibility of obtaining intense blue-to-violet electroluminescence (EL) from silicon-based light-emitting structures at room temperature (RT), in line with the need for efficient and inexpensive light sources whose production is compatible with existing silicon device technology. Ion-beam synthesis (IBS) and standard silicon processing have been used to fabricate light-emitting diodes whose active medium is a layer of thermal SiO₂ containing germanium nanocrystals. Extensive research has been carried out in three main directions: optimization of the fabrication process, improvement in the device lifetime, and elucidation of the underlying mechanisms of light emission and charge injection/charge transport. This research effort has resulted in the establishment of a set of optimum conditions for the formation of improved-quality Si-based light emitters. It has been shown that the use of plasma treatement is helpful in increasing device lifetime. Issues related to the nature and the excitation of the light-emitting centers have been considered. Finally, the utility of such light-emitting devices in the development of integrated optoelectronic devices as well as Lab-on-a-Chip, microarray and sensor systems has been outlined.

We demonstrate multifunction operation in a 2D PC slab showing that the same structure may be used for lasing, frequency shifting and switching under appropriate stimulus. Our analytical model, based on a coupled modes nonlinear approach closely describes the main experimental features. The experimental results constitute a first step towards an active reconfiguration of photonic crystal all-optical circuits.