Recently there has been a growing amount of attention devoted to tuneable photonic crystals (PhCs) where the optical response of PhC structures can be dynamically modified. We will show how infiltrating planar PhCs with a synthetic organic material allows the trimming and tuning of their optical properties. The potential of PhC infiltration will be demonstrated for InP-based planar PhCs consisting of a hexagonal array of air holes (hole diameter = 200 − 400 nm; air filling factor = 0.40-0.50) etched through a planar waveguide in which light emitters (i.e. quantum wells) were embedded to enable optical measurements. The PhC pores were infiltrated with LC-K15 (5CB) nematic liquid crystals (LCs) in a specifically designed vacuum chamber, thereby changing the refractive index contrast between the holes and the semiconductor (trimming). Moreover, the possibility of tuning the optical response of PhCs by an external perturbation (i.e. temperature) was demonstrated. The change of the PhC optical properties due to infiltration and temperature tuning was studied both experimentally and theoretically. Experimental measurements were compared to theoretical calculations in order to obtain information on the in-filling efficiency, the LC refractive index, and the molecule orientation inside the holes. In the first case, optical measurements were performed as a function of temperature, whilst the average LC director configuration was determined by comparing transmission spectra in the transverse electric and magnetic polarization directions.

Silicon-based 2-D photonic bandgap (PBG) structures have an unmatched potential for integration with well-established microelectronic devices and circuits. They can allow for compact optical devices with enhanced functionality and performance. While a number of passive PBG silicon-based devices have already been demonstrated, electrical tuning of their properties has yet to be implemented. PBG tuning can be achieved by replacing the air inside the device with active optical material, for example liquid crystals (LCs) or an electro-optic polymer. The two main requirements necessary for tuning in PBG structures are (i) the electric field of the control signal should be present inside the active optical material to modify its properties, and (ii) the energy of the optical mode of interest should be distributed inside the active material. While the latter condition can be satisfied by proper optical design, the former requirement is difficult to satisfy due to external electric field screening by the conductive silicon walls. In this work, an analysis of this effect is conducted and guidelines to overcome screening and thus allow for switching are suggested. Further, by using LCs as an active optical material, electric field switching in 2-D silicon-based PBG structures is demonstrated for the first time. Results of this work can lead to the development of silicon-based switches, active routers and filters for future optical interconnects.

Variations of the refractive index can be utilized in order to shift the stop band in photonic crystals. Here, two- and three-dimensional structures made of macroporous silicon were filled with liquid crystals. Optical investigations in the infrared wavelength range indicate temperature-induced spectral shifts of the edges of stopbands. In addition, the defect modes corresponding to microcavities within the periodic structure can be thermally controlled. Investigations of the director field within the pores by means of ²H-NMR and confocal microscopy indicate that both parallel and escaped radial director fields can appear, depending on the surface treatment of the substrates. In cylindrical pores with a periodic modulation of the pore diameter, the escaped radial director field is modified thereby showing a regular array of disclination rings.

We demonstrated a novel two-dimensional photonic crystal (PC) based Symmetric-Mach-Zehnder-type all-optical switch (PC-SMZ) with InAs quantum dots (QDs) acting as a nonlinear phase-shift source. The 600-μm-long PC-SMZ with integrated wavelength-selective PC-based directional couplers and other PC components exhibited a 15-ps-wide switching-window with a 2-ps rise/fall time at a wavelength of 1.3μm. Nonlinear optical phase shift in the 500-μm-long straight PC waveguide was also achieved at sufficiently low optical-energy (e.g., π phase shift at ~100-fJ control-pulse energy) due to the small saturation energy density of the QDs, which was enhanced in the PC waveguide, without having to use conventional measures such as SOAs with current-injected gain. These results pave the way to achieving novel PC- and QD-based photonic integrated circuits including multiple PC-SMZs and other novel functional devices.

The real (Kerr) and imaginary (two photon absorption) parts of a third order optical nonlinearity are used to tune the long (1.6μm) and short (1.3μm) wavelength band edges of a stop gap in a two-dimensional silicon photonic crystal. The reflectance of the probe beam reveals information about the rise and fall times of the switching. More detailed investigations show the different time response of reflectance for different optical modes excited by the pump beam. We present a model based on simple "pertubation" formalism that can explain how any mode of photonic crystals is affected by general, weak refractive index pertubations.

We describe the use of high-index-contrast, photonic-crystal wavegides for tunable time delays. The waveguide is designed such that the operating frequency is near a photonic band edge. In this slow light region, a small change in index yields a large change in group velocity, and consequently in time delay. Figures of merit for tunable time delay devices are introduced, including sensitivity, length, and dispersion. We show that a simple quadratic band model is a good predictor of the figures of merit for realistic, 3D, high-index-contrast structures. By cascading two grated waveguides, we can obtain a flat tunable time delay across the operating bandwidth.

We show here that both the Debye poles and Lorentz pole pairs are special cases of complex-conjugate pole-residue pairs, and the general form of such pairs in fact offers us a much more efficient approach of treating real dispersive media in FDTD than the usual ones that are based on Debye poles and Lorentz pole pairs. We first derive a unified formulation of the auxiliary differential equation method for arbitrary dispersive media by using these pairs. We then use this formulation to perform several numerical experiments, including the permittivity of noble metal Ag and the electroabsorption coefficient of semiconductor quantum wells. The result of these experiments clearly demonstrates the feasibility and advantages of using these pairs in treating dispersive media in FDTD.

Demand for a silicon (Si) based optical modulator is becoming more pressing as optical interconnects are starting to be considered seriously as replacement for conventional copper wires in electronic chips. Difficulties in realizing this device in Si are well known as are the stringent requirements on its performance in terms of size (~μm), power (~μW-mW), speed (>1 GHz) and operating voltage (<5 V). Here we present a detailed numerical design and analysis of a compact, high-speed silicon-on-insulator (SOI) waveguide electro-optical modulator. The device operates by tuning the reflection resonance of a microring resonator by means of field-effect generated free carriers in metal-oxide-semiconductor accumulation layers. Electrical and optical analyses are carried out by solution of Poisson's, charge continuity, and Maxwell's equations by finite-element method. Our simulations predict a ~0.5 nm shift in the spectral response of the resonator around 1550 nm. With an appropriate pre-biasing, this leads to ~80% modulation depth switching with voltage swing of 2 V. Field-effect induced generation of free-carriers allows for operating bandwidth >5 GHz while consuming a total dynamic power of < 500 μW. Use of the field effect results in extremely thin charge layers of very high carrier concentration. We show that an appropriate placement of these layers in the modal field of strong-confinement SOI waveguides greatly enhances the charge-field interaction. This enables significant improvements in size and modulation depth and allows the device to operate at CMOS compatible power and voltage levels. Present work adds to the design space explored in the previous works and aims to advance the field-effect based micro-resonator modulator as an active photonic device to be used in future generations of opto-electronic circuits.

The self-assembly of monodispersed colloids into an ordered three-dimensional structure, i. e., an opal (colloidal crystal) structure, is routinely employed to fabricate photonic crystals. In this study, high-quality polystyrene (PS) colloidal crystals in large area were fabricated during 24 hours via the capillary-enhanced process. Then, the tunable photonic crystals were formed by incorporating silica nanoparticles of different concentration into the void space via a dipping process. According to Fick's Law, the interstitial space of opal could be completely filled. Thereby, the monodisperse spheres of opal will form core-shell structure. Moreover, increase of silica nanoparticle concentration will result in an increased refractive index of the opal film. The absorptive peak of pure opal is 445nm as measured in UV-Vis spectrum, and the absorptive peak of core-shell opal is 453nm, 463nm and 469nm for suspensions with different concentration of silica nanoparticles of 0.017, 0.122, and 0.244wt%, respectively. Therefore, by using this dipping process to fill the opal film with colloidal nanoparticles, the characteristic absorption wavelength for opal film can be fine-tuned more easily, efficiently and cost effectively than by traditional methods of constructing opal from monodispersed colloids of different diameter.

The sensitivity of photonic bandgap (PBG) structures to the environment makes them suitable for sensing applications. In this study, we describe how 1-D and 2-D PBG devices can be used for sensing biological matter, from small DNA segments to larger proteins. Our work focuses on using the tunability of silicon PBGs upon binding of the desired target on the internal surface of the air holes. Modeling of the optical response is performed to identify the material nanostructure and device configuration that lead to optimum performance (e.g., sensitivity).

Significant research efforts have been focused on the development of effective means for the optical detection of organic molecules using porous one-dimensional photonic bandgap (PBG) structures. To date, efforts have been focused on porous silicon microstructures, which are typically created using a controlled electrochemical etching process in a hydrofluoric acid solution. Generally, these sensors rely on changes in the optical resonance that occurs when the porous structure is filled by the analyte of interest and allows for simple and effective optical detection schemes. Here, we present a simple method for the production of polymer Bragg reflection gratings containing periodic porous layers, and we demonstrate optical detection of organic solvent vapors using these structures. To create the structures, a pre-polymer syrup containing a monomer, a photoinitiator, a co-initiator, liquid crystals (LC), and a non-reactive solvent (acetone or toluene) is sandwiched between two pieces of glass, and the periodic structure is then formed by applying an optical interference pattern generated using a simple one-beam laser setup. More importantly, we demonstrate that acetone vapor penetrates the porous structure and induces a change in the effective refractive index of these gratings that result in a shift in the reflection wavelength. This shift is pronounced, and can easily be observed by eye, or detected by optical means. We also demonstrate that this shift depends on the particular type of chemical vapor and vapor concentration, and the detection is reversible and repeatable. Finally, the addition of aminosilane to the pre-polymer syrup is shown to improve the stability of the resulting gratings, suggesting that this photopolymer fabrication technique could be used to create structures suitable for biological applications in aqueous environments.

Aegis Semiconductor is developing a diverse family of tunable thin film filters based on the thermo-optic properties of amorphous semiconductors. As thin film Fabry-Perot or multiple cavity filters, these devices have the fundamental structure of tunable 1D photonic crystals. We describe the evolution of our designs and the motivations for extending certain structures to 3D photonic crystals to reduce the device volume. Two different types of tunable thermo-optic devices apply for differing telecom functions at 1.5 µm. Continuously scanned filters for monitor purposes are deposited on solid substrates. Set-and-hold filters intended to be maintained at specific wavelengths must have greater thermal isolation, and so must be membranes. But simple planar membrane filters with metal trace resistive heaters have been shown experimentally to be subject to thermally induced strains causing birefringence. To address these limitations, membrane filters with laterally confined active regions are proposed using 2D photonic crystal mechanisms for waveguiding in the plane of the filter. Various methods are considered to provide this structuring, such as deep RIE holes through the full thickness of the membrane. Alternatively, patterning and etching of single quarter wave thicknesses at or near the spacer will create islands of antiresonant regions in the transverse plane to yield lateral guided-wave confinement. Confinement will permit much smaller devices with spot sizes on the order of 3 µm instead of the minimum of 62 µm available using Gaussian beam optics, and will also enable optical instead of resistive heating of the membrane by delivering green light to the filter, eliminating the distortions caused by metallic heater circuits and reducing the required power from 100 mW possibly to 5 mW.

During the past decade, defect engineering in photonic crystals has successfully miniaturized many optical devices, such as optical filters and lasers, to a sub-wavelength scale. In the field of magneto-optics, previous researches on one-dimensional photonic crystals have demonstrated that magnetic cavities can be used to create Friday rotation in sub-wavelength optical paths, important for integrated optical isolators. In this paper, we study an optical circulator formed of a bismuth-iron-garnet defect infiltrated in a two dimensional silicon photonic crystal. The additional dimension of the field confinement allows further miniaturization and paves the way for monolithic in-plane integration with current integrated optical devices. The magneto-optical defect is constructed to support two doubly-degenerate TE modes and side-coupled to three photonic-crystal waveguides to form a three-port Y-junction circulator. When maximized with geometrically-optimized bismuth-iron-garnet domain, the gyrotropic effects cross couple the two modes and split them into a pair of counter-spinning states. We use the coupled-mode theory to derive the general criterion between the magneto-coupling and resonance decay constant for complete transmission and isolation. Numerical experiments with finite-difference time-domain methods confirmed the coupled mode theory and demonstrate a Y-junction circulator with an isolation ratio greater than 40dB. The design principle for this two dimensional photonic crystal defect can be readily transferred to magneto-optical defects in three dimensional slab photonic crystals. The silicon/air based system has a small footprint of one wavelength squared and good compatibility for integration with other planar optical devices.

We propose new design parameters for index-guiding holey-fiber (IGHF) that can provide flexibility in defect and lattice design as well as adiabatic mode transformation capability. The new defect consists of the central air hole and germanosilicate-ring surrounding it. In this paper, utilizing layers of hollow structure as a defect, we introduce a new IGHFstructure and its optical properties are theoretically analyzed and experimentally demonstrated. The annulus mode intensity profile, effective mode area, chromatic dispersion properties and splicing loss for the single-layered and two-layered defect structure are investigated along with their dependence on the proposed defect parameters using plane wave expansion method and 3D full-vectorial Beam Propagation Method (BPM). Unlike conventional silica defect IGHF, the proposed structure showed an annulus mode profile in the fundamental mode, which can benefit from larger effective area to separate the fiber non-linearity from other unique optical properties of IGHFs. The proposed IGHF also showed low splice loss unlike previous conventional IGHFs with collapsed hole by arc since the newly introduced defect structure, germanosilicate-rings are remained as solid core with high index contrast D. With the new defect parameters we could achieve a large area annulus mode profile, low splice losses to standard fiber, 0.7dB at 1.55 m, and chromatic dispersion with low slope, 0.002ps/km.nm2

We show experimental results of anomalous refraction through a photonic crystal membrane. The membrane layer consists of a thin polymer film suspending a triangular array of silicon pillars. Light is coupled into the photonic crystal (PC) through ridge waveguides etched onto a silicon substrate. By altering the shape of the tip of the input waveguides, we can shape the light that is incident into the PC. In this paper we show that when we shape the field to be quasi point source like, the PC focuses the incident light onto a deflection block placed behind the membrane structure. We experimentally observe focusing of both TE and TM light inside the PC. In the same structure we have previously shown that when we illuminate the PC with a much broader beam incident at an angle, the light negatively refracts through the crystal. We designed the device so that it is capable of being stretched by mechanical actuators, which will stretch the polymer film and silicon lattice and distort the photonic band structure. Mechanical stretching of the dimensions of the flexible PC makes possible a device that can dynamically change its beam steering and focusing properties.

We reported the solid-state laser composed of an Al₂O₃ photonic crystal and an organic gain medium. The photonic crystal was fabricated through the impinging technique and electrochemical process, which do not require any elaborate process used in the lithographic device technology, but they are effortless for transferring the periodic pattern in the photonic crystal and controlling its photonic band gap. When the photonic crystal was infiltrated with the organic gain material, we found a laser emission under optical excitation. The minimum laser-threshold was about 2.4 nJ/pulse, where linewidth of laser emission was as narrowed as 0.09 nm. We explain the laser action as due to the photonic band edge effect, and precise control of the laser mode and oscillation wavelength through the control of the photonic stop band and small change in the refractive index of the gain medium.

We propose the light switching technique by photonic induced carriers injection in a silicon guiding layer. The designed Photonic crystal Bandgap (PBG) waveguide and the 32x32 channel Photonic Multimode Interference structure are utilized to construct the all-optical switching device. The pumping light generates free carrier density to change the silicon local material refractive index, so we simulate light switching by the control of pumping light. In this paper the beam propagation method (BPM) is applied to simulate the wavelength division and the optical signal switching characteristics. The Finite Difference Time Domain Method (FDTD) is used to analyze PBG characteristics. The simulations demonstrate the possibility of achieving an all-optical switching device.

Many useful and interesting optical applications of thin films make use of multilayer stacks of films, or a superlattice. To evaporate multiple layers while maintaining control over both refractive index and individual layer thickness has become a matured technology today. In this work, light scattering in a dielectric superlattice is investigated. The polarization characteristics including the transverse electric (TE) and transverse magnetic (TM) modes are considered in our simulation model. A transfer matrix approach is employed to discretize the dielectric function profile of the dielectric superlattice and the transmission functions are calculated by matching the boundary conditions at each interfaces. In order to solve the dispersion relation, the corresponding band structures are obtained by solving the eigenvalue equations with proper periodic boundary conditions as following the Bloch theorem. The equifrequency surfaces in wave-vector space are employed to facilitate the calculation of the photon density of states (PDOS). The PDOS of the superlattice for the TE and TM modes are obtained, respectively.

In the last years there is a considerable interest in designing integrated optoelectronic or all-optical circuits based on photonic crystals (PhC). A PhC structure possess photonic band gap in which the light with a certain frequency range cannot propagate. However, the existence of linear defects causes dispersion relations in photonic band gaps. Light that satisfies in the dispersion relations decay except linear defects and can exist only in linear defects. Modifying some scatters it is possible to create a waveguide inside the PC. This waveguide have great potential in application for their ability to control light wave propagation and the possibilities of implementing PhC based optical devices. We propose a PhC diplexer based on a square lattice of silicon rods. The demupltiplexing mode is fed exploiting the different dispersion relation of the light in the three braches of a T-junction. A difficult challenge is to realise active PhC devices. In order to achieve tunable photonic band gap devices, we investigate the possibility to use the thermo-optic effect and the Liquid Crystals (LCs). The main feature of LCs is the high sensitivity of their optical response to an applied electrical field. Moreover their ability to be micromanipulated, their low cost and the possibility for integration with silicon circuit technology make LCs particularly attractive in designing photonic devices.