This PDF contains the front matter associated with SPIE Proceedings Volume 6640, including the Title Page, Copyright information, Table of Contents, Introduction, and Conference Committee listing.

We design and characterize a photonic crystal (PhC) based silicon electro-optic modulator. The device is composed of a planar photonic crystal with associated input and output dielectric waveguides and a p-i-n diode to inject free carriers for index modulation. The photonic crystal, which confines light using the self-collimation phenomenon, has two regions of varying air hole diameters forming a defect area in a host self-collimation lattice. At the interface of the defect with the host lattice, an impedance mismatch is formed which is modulated using free carrier injection. With sufficient index modulation the impedance mismatch is large enough to decrease the transmission through the defect region, thus, modulation the overall transmission of the device. Our analysis shows that with a doping concentration in the range of 10²⁰/cm³, the injected free carrier concentration can exceed 2.5*10¹⁹ with a drive voltage of 2.6 V. This free carrier concentration is sufficient to modulate the refractive index, Δn, greater than .05, which in turn produces a modulation depth greater than 75%. A fabricated device produces a modulation depth of 80% with a drive current of 4mA.

We experimentally demonstrate an all-silicon optical transmission controller based on a semiconductor-oxide-semiconductor capacitor embedded in a slot photonic-crystal waveguide. We incorporate a multimode interference-based structure to reduce the coupling loss induced by the waveguide mode mismatch. We perform a detailed DC characterization of the electro-optic device including the DC modulation test and the evaluation of the resistance-capacitance constant. The measured modulation curve is in good agreement with our theoretical analysis. Calculation of the effective index change indicates as much as 30 times efficiency enhancement compared with the slotted silicon rib waveguide. Such a waveguide layer can serve as the active layer for fully embedded optical interconnect architecture with minimum power consumption.

The light harvesting enhancement observed when photonic colloidal crystals are integrated in dye sensitized titanium oxide solar cells is investigated herein. Such absorptance increment is explained in terms of slow photon propagation at certain ranges of wavelengths lying within the photonic pseudogap and partial localization in an absorbing layer placed onto the colloidal lattice. Based on those findings, not only recently reported experiments have been satisfactorily explained, but also new optical designs for the dye-sensitized solar cells (DSSC) are proposed. The new arrangement consists of piling up different lattice constant crystals leading to light harvesting enhancement in the whole dye absorption range. We provide the optimum structural features of such photonic crystal multilayer needed to achieve a photocurrent efficiency enhancement of around 60% with respect to standard dye-sensitized solar cells.

A structural defect was introduced within the helical lattice of cholesteric liquid crystals to realize a tunable photonic defect mode in the selective reflection band, or the polarization sensitive photonic band-gap of the cholesteric liquid crystal. The cholesteric liquid crystal material was locally polymerized via a two-photon polymerization process and a finite unpolymerized region was left between two polymerized layers to act as the structural defect in which the helical pitch is different from the polymerized bulk. The structural defect was functionalized by first of all, rinsing the unpolymerized cholesteric liquid crystal, and then infiltrating a photo-chromic dye-doped cholesteric liquid crystal material into the gap. A defect mode was observed in the selective reflection band of the cholesteric liquid material at a wavelength depending on the contrast between the pitch at the defect and the bulk. The defect mode was tunable by applying heat or irradiating light at λ ~ 400 nm on the sample, which caused the shortening of the helix pitch of the cholesteric liquid crystal at the defect, therefore increasing the pitch contrast between the bulk and the defect. Reversible tuning of the defect mode was realized in an electrode-free cell.

A method to modulate the local optical properties of porous silicon photonic crystals is reported. The porous silicon photonic crystals are fabricated by electrochemical etching in a hydrofluoric acid-based electrolyte. Local oxidation was performed using either a UV lamp or 532 nm laser to irradiate selective regions of the photonic crystal. The sample was then soaked in an alcohol solution. Unmasked regions of the porous silicon photonic crystal exhibited significant spectral degradation and loss of the microcavity resonance. The region of the porous silicon photonic crystal protected by the oxide exhibited no significant changes in the reflectance spectrum. This simple photolithographic technique can be used to fabricate a variety of spatially localized silicon-based structures such as photonic bandgap mirrors, optical filters, waveguides and optical switches.

In this work we report the fabrication of PbTe quantum dots multilayers embedded in SiO₂ by alternatively use of Laser Ablation and Plasma Enhanced Chemical Vapor Deposition techniques. The quantum dots were grown by pulsed laser deposition (PLD) of a PbTe target using the second harmonic of a Q-Switched Quantel Nd:YAG laser in high purity argon atmosphere. The glass matrix was fabricated by PECVD using tetramethoxysilane (TMOS) as precursor. The RF power was supplied by a RF-150 TOKYO HI-Power operating at 13.56 MHz and coupled to the RF electrodes through a matching box. The deposition rates as well as the best growth parameters for both the nanoparticles and the glass matrix were obtained from a previous work. The morphological properties of the nanostructured material were studied by means of igh Resolution Transmission Electron Microscopy(HRTEM), grazing-incidence small-angle X-ray scattering (GISAXS) and X-ray reflectometry . Unlike HRTEM, which extracts information of a submicron region of the sample and only a few thousand particles are observed, GISAXS signal is obtained through an average over orders of magnitude larger number of particles (perhaps 10¹² particles) distributed over an area of tens of square millimeters. This fact means that GISAXS sampling is much more representative of the sample as whole. Finally, multilayers were grown inside a Fabry-Perot cavity. The complete system operates as an optical switching device for the infrared region. The device was characterized by Scanning Electron Microscopy and optical absorption.

We present ultrafast optical switching experiments on 3D photonic band gap crystals. Switching the Si inverse opal is achieved by optically exciting free carriers by a two-photon process. We probe reflectivity in the frequency range of second order Bragg diffraction where the photonic band gap is predicted. We observe a large frequency shift of up to 1.5% of all spectral features including the peak that corresponds to the photonic band gap. We also demonstrate large, ultrafast shifts of stop bands of planar GaAs/AlAs photonic structures. We briefly discuss how our results can be used in future switching and modulation applications.

In an active photonic band gap structure, a control laser can manipulate the probe signal coherently if the probe field satisfies the Bragg condition and is resonant or near resonant with the electronic or excitonic transitions of the constituting material structure. Using coherent effects in the conduction intersubband transitions of an n-doped quantum well, recently, we showed that one could convert a fully transparent waveguide into an active photonic band gap. Such an active photonic band gap was different from those based on superradiant excitons in two main issues: (i) the probe field was near resonant with the conduction intersubband transitions of the quantum well, and (ii) one needed a control field to generate the coherent effects and, thereafter, the band gap. Here we use such coherent processes, which include electromagnetically induced transparency and coherent enhancement of refractive index, to study a one-dimensional functional photonic band gap structure. In the absence of a control laser field such a structure acts as a conventional photonic band gap created by an off-resonant (background) refractive index perturbation. In other words, the probe field does not feel any resonance in this structure and the photonic band gap is passive. In the presence of the control field, the structure is activated and transformed into a resonant structure. Under this condition, the probe field becomes near resonant with the intersubband transitions while still satisfies the Bragg condition. We study how the coherent effects in such transitions can lead to destruction and enhancement of the photonic band gap in a waveguide structure.

We derive a light-intensity-dependent dielectric constant for gain medium based on the conventional rate equation model. A scattering-matrix method in conjunction with an efficient iteration procedure is proposed to simulate photonic crystal lasers (PCLs). The light output vs pumping (L-I) curve, lasing mode profile, and chirping effect of lasing wavelength can be calculated. We check our method in a 1D DBR laser and the L-I curve agrees well with results by the rate equation model. Our method can be extended to 3D systems. More complex 2D and 3D PCLs will be simulated in the future.

Optical localization in a randomly disordered infinite length one-dimensional photonic band gap structure is studied using the transfer matrix formalism. Asymptotically, the infinite product of random matrices acting on a nonrandom input vector induces an invariant probability measure on the direction of the propagated vector. This invariant measure is numerically calculated for use in Furstenberg's master formula giving the upper Lyapunov exponent (localization factor) of the infinite random matrix product. A quarter-wave stack model with one of the bilayer thicknesses disordered is used for simulation purposes. In this plane wave model the invariant measure is rarely a uniform probability density function, as is sometimes assumed in the literature. Yet, the assumption of a uniform probability density function for the invariant measure gives surprisingly good results for a highly disordered system in the UV region.

The equifrequency contours of a two-dimensional square lattice, Photonic Crystal(PhC) composed of an anisotropic cylinder in anisotropic medium are modeled and theoretically studied. The beam group velocity inside the PhC is determined as a function of input angle and from this data a quantitative measure of the self-collimation effect is deduced. The range of input angles for the self-collimation regime are significantly increased above those for a PhC composed of isotropic constituents.

We propose a novel design for a guided-mode resonance (GMR) grating sensor that is optimized for detecting small average index changes in an extended region of space, retaining sensitivity up to several tens of microns away from the grating surface at optical detection frequencies. This kind of sensors has high sensitivity in the half-space above the grating, close to the theoretical limit, together with a controllable - potentially very high - quality factor. It relies on a resonance with a "confined" mode of a sub-wavelength thick grating slab, a mode that is largely expelled from the grating itself. The small thickness assumption allows us to derive analytical expressions for many properties of these sensors, expressions that are then tested numerically using a rigorous coupled-wave analysis (RCWA) method, and in preliminary experiments.

Index-tunable photonic crystals based on ferroelectric materials provide a means for active modulation of optical signals, and hold promises for novel device applications. In this study, (Ba,Sr)TiO₃ (BST)-based planar photonic crystals with different cavity geometries were modeled. Photonic crystals with square-shaped air rod geometry, which can be prepared in a straight-forward manner by interference lithography, were compared with photonic crystals having circular air rods. Calculations were performed on square lattice, with either square or circular air rods, by the plane wave expansion method. Simulation results suggested comparable bandstructures and gap maps for square or circular air rod photonic crystal, if (1) the dimension of the air rod was small compared to the electromagnetic wavelengths inside the photonic crystal being considered, or (2) the frequencies of the electromagnetic waves were less than 0.35(2πc/a). A better correlation in bandstructures and gap maps between the square and circular air rod photonic crystals can be achieved, if we compare them by the volume fractions of the photonic crystals in stead of the characteristic lengths of the rods (i.e. diameter of the circular rod and width of the square rod).

Optical responses of active multi-quantum well photonic band gap structures are mostly determined by the excitonic effects (superradiant excitons) and the contrast between the background refractive indices of the wells and barriers (nonresonant effects). Recently we studied coherent control of such photonic band gaps via infrared dressing of the superradiant excitons. This was done considering an infrared laser field near resonantly coupled such excitons with the excitons associated with the second conduction subbands of the quantum wells. This led to the formation of photonic electromagnetically induced transparency and disentanglement of the excitonic contributions from those associated with the nonresonant effects via destruction of the superradiant modes. Here we study how such a disentanglement process dramatically changes transmissions of the Bragg multiquantum well structures. In particular, we show that when the infrared laser intensity is high, the non-resonant effects form an incomplete passive band gap around the Bragg wavelength. Such a band gap, which is immune against the infrared laser, is flanked by two non-photonic gaps (absorption peaks). These peaks are associated with the large absorption of two dressed exciton states, i.e., Aulter-Townes doublet. Any variation in the intensity of the infrared laser changes the wavelengths of these peaks, making them closer or farther to the passive photonic band gap.