A model based on the Leaky Mode Propagation Method has been implemented in a computer program to design 1D waveguiding Photonic Band-Gap (PBG) devices. A complete analysis of the propagation characteristics, including the determination of modal propagation constants, electromagnetic field harmonics and total field distribution, transmission and reflection coefficients, total forward and backward power flow in the structure, guided and radiated power, and total losses, can be determined in a few seconds, so enabling the optimized design. The design of a PBG filter and of a resonant device have been carried out to demonstrate the ease of use of our model.
Transmission properties of hollow waveguides utilizing dielectric multilayer are examined by using a photonic bandgap theory. Theoretical results show that, in the waveguide having quarterwave film stack, a large number of films is necessary to obtain low loss property. It is shown that covering the dielectric films with a metal layer is effective to reduce the number of dielectric films. To verify the effect of this design, we fabricate a prototype waveguide with three dielectric layers of SiO2 / Ta2O5 / SiO2 and a silver cover layer. From the loss spectrum of the waveguide, we confirm that, as designed, the waveguide shows wideband low loss at the wavelength of Nd:YAG laser light 1.06 micrometers .
Analytical theory of plane electromagnetic wave reflection from a layer or half-space of a particulate photonic crystal is introduced. The photonic (artificial) crystal is formed by small complex-shaped dielectric or metallic inclusions arranged in the nodes of a regular three-dimensional lattice with parallelepipedal elementary cell of general kind. The dipole model and the local-field approach are used for description of electromagnetic interaction between inclusions. Frequency-dependent polarizabilities are used for description of inclusions polarization. The interaction between adjacent layers is considered using the Floquet representation including evanescent modes. Using an analytical theory of dispersion for the crystals under consideration it becomes possible to make predictions for dipole moments distribution deep inside the layer. Additional corrections for distribution in the surface layers and amplitudes of predicted modes have been found numerically from a linear system of equation. This method needs much less computational time comparing with the same method without prediction of distribution and can be applied for calculation of reflection coefficient for much more thicker layers or for a half space. Also, a simple analytical single mode propagation theory for reflection from layer and half-space of particulate crystal is presented. It does not take into account the surface effects, but it is numerically shown for microwave crystal of loaded wires that this theory gives an excellent correspondence with exact one in the case of single mode propagation.
In this paper a theoretical treatment on guided-wave acousto-optic (AO) Bragg interactions on a spherical waveguide together with new experimental results at significantly higher surface acoustic wave center frequency (500 MHz) using a LiNbO hemisphere block is reported. The theoretical analysis for the optical and the acoustic waves are carried out using the lowest-order asymptotic expansions and the resulting AO Bragg diffraction calculated using Green's function technique. Bragg diffraction experiments using LiNbO3 hemisphere block (3.1 cm Dia) at the optical wavelength of 0.6328 (mu) and the center SAW frequency of 500 MHz involve the physical dimensions that satisfy the assumptions required in the theoretical treatment. Efficient diffraction efficiency and large bandwidth as well as high quality focused spots of both the undiffracted and the Bragg-diffracted light beams obtained suggest potential use of the spherical surface for realization of integrated AO device modules.
Wide energy gap and strong piezoelectric effects in A1GaN-based materials are very attractive for the development of visible-ultraviolet spectral range optoelectronic devices, such as optical waveguides and light modulators. In this paper, we report on the experimental studies ofthe acousto-optical diffraction in GaN-based layered structures grown by low-pressure MOCVD over sapphire substrates. We present the extracted values of the acoustooptic figures of merit and effective photoelastic constants for red (633 nm) and blue (442 nm) wavelengths. Our results demonstrate the potential of GaN-based structures for the development ofblue-ultraviolet acousto-optical devices.
One of the most important applications of acousto-optic spectrum analyzers (AOSA) is providing of the radio air panoramic observation. It is necessary to provide simultaneously wide operation frequency band and good frequency resolving power on a level with high operation rate for this purpose. These demands are contradictory. Their conjugation is possible if the composition of different kinds of AOSA is used in the total device. Application of AOSA with space and time integration has been analyzed. The optimal values of the frequency subbandwidth and integration time have been determined proceeding from the condition of maximum resolving power (both spatial and temporal) and operation rate. The totally observed frequency bandwidth in the optimized device can attain value of 1..2 GHz and observation time - several seconds. On a level with that the frequency resolving power can be less than 1 kHz. The experimental studies of some AOSA compositions have been reported. We have made the devices on the basis of acousto-optic Bragg cells using tellurium dioxide single crystals in which the slow shear acoustic mode was excited. The experimental study of these devices has demonstrated that the parallel connection of AOSA with space and time integration provides more profitable conditions from the point of view of maximum information transmission capability than earlier proposed AOSA with combined space and time integration.
Thermo-optic 1x2 vertical coupler switches (VCSs) using a hybrid polymer/silica integration technology were designed using finite element method and coupled mode method for different refractive index contrasts. The multilayer structures were optimized by thermal analysis. Based on this design and simulation, hybrid polymer/silica thermo-optic 1x2VSCs exhibiting low insertion loss, low crosstalk, low switching power, and polarization independence were demonstrated. Using this 1x2VCS as the building block, a 1x8VCS has been implemented.
The booming telecom market pushes the development towards highly integrated optical devices. For a breakthrough in the increase of packaging densities, a bypass of the limited horizontal dimension of a waveguide chip is necessary. This leads to an introduction of a vertical integration scheme which needs an adapted fabrication method to meet the requirements of integrated optical applications. To this end, a newly developed technology for the stacking of mono-mode waveguides using inorganic-organic hybrid polymers (ORMOCERs) is presented. Besides important advantages concerning an efficient fabrication by UV lithography methods, the stacking process faces several fundamental problems, e.g., broadening of the structures by scattering during UV patterning or the occurrence of index inhomogenities constituted by diffusion effects. Both problems could be solved in the framework of conventional processing techniques, which will be presented. The key points of the new technology, a UV absorber method and a combined UV and thermal curing, are investigated in detail. On the basis of this development the design, fabrication as well as the test of a novel optical fan-out element is discussed. The device consists of four stacked layers of single-mode waveguides, which enables one to accomplish signals from different sources to an output adapted to a single detector. Experimental results as well as the potential for future applications are presented.
Theory and the first experimental results concerned interaction between a traveling acoustic wave and light wave of whispering gallery modes in glass cylinders with variable cross-section along their length are presented. It is shown theoretically that gradual shift of light frequency by tens of percents can be obtained in a frequency converter based on a glass cone.
A novel injector design allows to increase the peak optical power of quantum cascade (QC) lasers with GaInAs/AlInAs superlattice active regions. At wavelengths of 8.4 micrometers peak powers of 2.2 W per facet, corresponding to 88 mW/stage, have been measured at operating temperatures less than 80 K. The laser output power grows steadily above threshold with a slope efficiency of 160 mW/A up to currents 6 times larger than the threshold one, displaying the widest reported dynamic range without any sign of gain saturation. In order to measure the facet temperature profile and the active region thermal resistance, a micro-probe band-to-band photoluminescence technique is developed and tested on GaAs/Al0.33Ga0.67As and GaInAs/AlInAs/InP three-wells QC lasers. Comparison between substrate-side and epilayer-side mounted devices shows the superior thermal dissipation capacity of the latter and explains their better performance with respect to threshold current and maximum operating temperature.
Ion exchange processes in glass have been studied since several decades, and have demonstrated themselves as one of the most convenient technologies to produce integrated optical components and devices. Ion-exchanged waveguides are attractive candidates for photonic components because they exhibit low insertion losses, thanks also to the capability of very good matching to the modal field of an optical fiber, and their fabrication costs are very low in batch production. A brief overview of the main processes and demonstrated applications is presented here.
Polymeric single mode optical waveguides based on a new kind of negative tone epoxy novolak resin (ENR) polymer have been fabricated using electron beam direct writing. This polymer has a high refractive index, high sensitivity and high glass transition temperature (Tg). Contrast curves and saturation dosages of the polymer on different substrate materials were obtained, and the sensitivity of ENR is found to be over a hundred times larger than that of Polymethyl-methacrylate (PMMA). For single mode channel waveguides with upper claddings, the propagation losses measured were 0.22 dB/cm and 0.48 dB/cm at 1330 nm and 1550 nm for TM mode, and 0.9 dB/cm and 1.2 dB/cm for TE mode, respectively.
According to Sellmeier equation, the detailed theoretical study using a computer stimulation on the nonlinear optical properties of CLBO (CsLiB6O10) frequency doubling are presented as compared to that of BBO in type I and type II phase matching (PM). We obtained the advantage of both a large acceptance angle and a small effective nonlinear coefficient of CLBO versus BBO. The curves of the effective nonlinear coefficient, phase matching angle, walk- off angle, permitted angle and wavelength versus the fundamental wavelength and SHG conversion efficiency versus the crystal length are plotted according to the formulas we derived in type I and type II from the PM. The theoretical guiding to experiments band application in CLBO is presented.
Phase change optical recording disks using chalcogenide alloy Ag-Sb-Te have been found to demonstrate long thermal stability of the amorphous recording marks. The crystallization process and nature of Ag-Sb-Te material were studied using Differential Thermal Analysis (DTA) and X Ray Diffraction (XRD) respectively. The films were studied for both the cases: before and after annealing and it was concluded that the alloy (Ag-Gb-Te) can be used as a phase change optical memory material.
In this paper, we measure the dispersion characteristic of chalcogenide fiber. We use phase shift method to measure the dispersion characteristic of single mode As2S3 fiber around 1 .55 im. Measurement show the strong dispersion of about -39 ps/kmnm at communication wavelength of 1 .55 um. Chalcogenide fiber has promising market as dispersion compensation device with such good performance.
We propose a novel method to calculate invariants of colour and multicolour images. It employs an idea of classical and quantum hypercomplex numbers and combines it with the idea of classical and quantum number theoretical transforms over hypercomplex algebras, which reduce the computational complexity of the global recognition algorithm for nD k-multispectral images from O(knNn+1)to O(kNn log N) and to O(kn log N), respectively. Our hypotheses are 1) the brain of primates calculates hypercomplex-valued invariants of an image during recognizing, 2) visual systems of animals with different evolutionary history use different hypercomplex algebras. The main goal of the paper is to show that quantum Clifford algebras can be used to solve pattern recognition in multispectral environment in a natural and effective manner.
Recent advances in bright sources of entangled photons are combined with demonstrations of Electromagnetically Induced Transparency (EIT) to suggest a design model for an optical data link whose propagation delay is distance invariant. Intense entangled photon streams P and P' are directed into a transmitting telescope and an optical delay line respectively. The optical delay line is constructed of an extended region of EIT to reduce the local velocity of light many orders of magnitude, while experiencing no loss. A design example employing Rubidium vapor is presented. The delay line is adjusted so that as the entangled photon stream P is about to arrive at the receiver, the first photon of stream P' emerges from the delay line. A second entanglement operation on P' imposes a polarization on this photon which simultaneously appears as the compliment on the remote entangled photon of stream P. The process continues on remaining photons of both streams. An optical link budget approach is used to calculate required intensities, conversion efficiencies, apertures and received irradiances. Polarization modulation sequences are used in a transponder mode to measure the varying distance between transmitter and receiver iteratively and is used to adjust and track the optical delay line. Application to astronomical distances is considered.
A global and versatile problem of fire and environmental safety is formulated. It is pointed out that one of the main ways to solve this problem is the development of equipment for early fire detection. The results of the development and study of a smoke fiber optic fire detector are presented. Such detector is absolutely explosion-safe and immune to increased radiation level and aggressive chemical environment.
In this paper, we design a novel 2x2 silicon-on-insulator (SOI) wavelength switch photonic crystal included multimode interference waveguide design. With the changes of refractive index of photonic crystal, we can perform the switching function. Applying the configuration of Y branches, the input and output waveguides can be easily laterally separated for direct coupling to fiber without S- bending structure. The 1.55 micrometers wavelength will be switched at different output ports. The output mode patterns and light propagations are simulated by using beam propagation method.
We present a novel design of a two-layer Mach-Zehnder Interference switch using silicon-on-insulator integrated optical technology. According to the design, we can reduce the size of Mach-Zehnder Interference switches with six refractive index adjustment cases by Beam Propagation Method (BPM) simulation. Some cases of better switches are sorted by tuning the phase difference between the two paths of the Mach-Zehnder Interference refractive indexes of the rib bending waveguide. Such a device shows great potential in achieving coarse wavelength division routing devices.
The search for a reliable, low-cost, general-application modeling tool has been assuming a growing importance among integrated optics theoreticians. For example, finite-difference (FD) based algorithms have given rise to commercial photonic CAD software programs that are less expensive, from both financial and computational points of view, than finite-elements (FEM) based ones. On the other hand, the former show some computational drawbacks that do not permit to consider them as of truly general application, while the latter provide extremely reliable modeling tools. Recently, a few numerical techniques (alternative to both FD and FEM methods) have been proposed, mainly in view of an improvement in flexibility and a reduction in computational cost. In particular, methods based on the Galerkin approach and Krylov reduction have proven particularly effective for the solution of the Helmholtz equation in a very wide class of integrated optical structures. Moreover, these methods are very promising from the point of view of reliability and are computationally non-expensive. Here, we present the implementation of one of such numerical techniques, the so-called Arnoldi-Galerkin method, together with that of a home-made FEM software program. A comparison with the results from other algorithms is shown as well.
Highly c-axis oriented SBN films with various compositions were obtained on MgO(100) substrates using sol-gel process. Although the sol-gel process has been developed for ferroelectric thin films, it is known as being hard to fabricate highly oriented films. Thus, the preferential orientation of the films was enhanced by two methods: (1) poling the film by a high dc electric field (greater than Ec) and (2) growing the film on an SBN-seeded MgO substrate. The mechanisms of these methods were discussed. For their optical applications, second-harmonic generation (SHG) effect of SBN films was studied. Fundamental beam of Nd:YAG laser with 1064 nm was used as a pump beam. From Maker fringe measurements with a quartz reference, second- order nonlinear optical (NLO) coefficients d of the films were obtained. The second-order NLO coefficients of the films could be enhanced to considerable extent by applying the electric poling and using a self-seeds layer. These phenomena indicate that the SHG effect is sensitive to crystallographic structure as well as ferroelectric polarization. Mathematical equation was derived to correlate this microstructure to the SHG effect of SBN films.
We report on the investigations of optical and structural properties of ZnO films deposited by pulsed laser deposition technique on silicon (100) p-type, quartz, and glass substrates. The second order nonlinear optical response from films deposited at different ambient pressures ranging from 10 mTorr to 1 Torr of oxygen on glass substrate at room temperature depends on grain size and thickness of the film. The dependence of second harmonic generation on the size of nanocrystallites observed at different pressures is discussed.