A brief outline of pioneering works in integrated optics, as well as of main achievements toward the goal of full integration, is presented. Reliability, high performance and low cost of optoelectronic integrated circuits (OEICs) of growing complexity are the keys to a real deployment on a large scale of integrated optics; in any case, however, OEICs will succeed in offering unique and powerful features and will be able to gain some market niches.

A self-consistent finite difference method for the simulation of electron transfer structures is developed and applied to optimize InGaAsP/InP QW structures for fast optical switching devices. Simultaneous solution of Poisson's equation, continuity equation and Schrodinger's equation on a discretized mesh yields a fast and accurate simulation method which may be applied to arbitrary layer structures and which needs no artificial assumptions like space charge layers. With this method we calculate the important physical parameters of Barrier, Reservoir and Quantum Well Electron Transfer Structures.

The electric field of the modes of waveguides with edges, like rectangular guides or rib guides, is known to diverge along the edges of the guide. The divergence makes the design of rapidly converging numerical algorithms for vector mode field computations in such waveguides difficult. Two closely related methods that have overcome the difficulties to some extent are the method of lines and the transverse resonance (mode matching) method. The common merits of these methods are discussed, and some results are presented for mode field distributions in practical rib waveguides, calculated with the transverse resonance method.

A fully vectorial finite difference beam propagation method for 3D waveguide structures, including longitudinally variant structures is presented. The transparent boundary conditions are utilized in the edges of the computational window. Both Gaussian beams and exact fields of the guided modes are launched as the starting field. Propagating fields are calculated and the power attenuation is evaluated. The choice of step size, finite difference scheme parameter and reference propagation constant is discussed. The applicability and accuracy are demonstrated for two particular waveguide structures.

In the proposed method a directional decomposition of the electromagnetic field is made by eliminating the two field components along the propagation direction from the Maxwell equations. This results in a full vectorial two-way wave equation for the forward and backward traveling waves. By a simple manipulation, a set of two coupled one-way wave equations is constructed, which are pseudo-differential equations and contain simple terms for the interaction between the counter-propagating waves. The Green tensors corresponding to the one-way wave equations are expressed in terms of path integrals and can be based either upon the pseudo-differential operator or upon the corresponding left symbol. Using these path integrals a Bremmer coupling series is applied which completes the directional decomposition procedure. This new scheme encompasses all existing BPM-type methods. Some numerical results are given for a new BPM-type algorithm based upon the application of left symbols.

The finite element method is a successful tool to investigate integrated optics devices, both for stationary as well as for wave propagation problems. Despite the fact that different functionals and discretizations are considered in the literature, in practice most of these approaches use piecewise linear basis functions to approximate the true solution. However, in the case of wave propagation these functions may become numerically inefficient. Therefore our proposal is to construct basis functions fitting the local situation better than the linear standard functions. We introduce new basis functions as the product of linear polynomials and local phase functions. These local phases functions are exponential functions characterized by a wave number, which in general changes in space but is assumed to be constant over a single finite element. The closer the a-priori fixed wave number resembles the true local wave number, the more efficient the simulation will be. The multilevel finite element scheme supplies a well-suited frame to determine the local wave number in an adaptive manner.

Optical spatio-temporal pulse propagation in tapered slab waveguides with Kerr or saturable nonlinear cladding that may exhibit relaxed nonlinear response has been analyzed by the time- dependent split-step finite element method. Novel spatially distributed power-controlled demultiplexing of optical pulse trains has been demonstrated.

In this paper the Method of Lines is applied to simulate the electromagnetic field propagation in optical dielectric nonlinear planar waveguides, with saturation of the refractive index. A comparison between the solutions obtained with the Method of Lines and the Beam Propagation Method (which uses paraxial approximation) is performed.

A method to construct modal fields for an arbitrary one- or two-dimensional intensity dependent refractive index structure is described. An arbitrary starting field is propagated along a complex axis using the slowly varying envelope approximation for the Finite Difference Beam Propagation Method. By suitably choosing the complex value of the propagation step, one mode is maximally increased in amplitude. The applicability of the method is discussed and illustrated by a one-dimensional cross section test example with Kerr- type nonlinearity.

For the first time, we show that soliton switching in semiconductor nonlinear directional couplers without the detrimental pulse break up can be achieved by properly tailoring the waveguide configuration. In particular, we exploit the unusual dispersion characteristic of Anti-Resonant-Reflecting-Optical Waveguides to overturn the normal group velocity dispersion in semiconductors below half-the-band-gap. The coupled set of modified Nonlinear Schrodinger equations is derived and solved by using the Beam Propagation Method.

It is demonstrated computationally that enhanced electrorefractive effects can be obtained by engineering the shape of semiconductor quantum wells. This demands either the generation of a unipolar differential absorption spectrum on application of an electric field, or exploitation of the observed quadratic field dependence of refractive index changes in square wells. Two methods of tailoring quantum well profiles are employed: multi-layered quantum well growth and strategic (delta) -doping. Both approaches are shown to be sufficiently robust to be achievable within the limits of current growth technology. The enhanced electrorefractive effects will be beneficial to the operation of the full range of optical modulator devices from electrorefractive asymmetric Fabry-Perot modulators for optical interconnects and optical processing, to ultra-high bandwidth interferometric travelling-wave modulators for microwave optoelectronics.

To develop ordered cluster-dot structures with predetermined optical properties a model which self-consistently allows to define an electrical field induced by a propagating electromagnetic wave has been elaborated. The model takes into account the contribution of two kinds of anisotropy: the anisotropy of the polarizability of the clusters (`shape anisotropy'), and the anisotropy of their dipole interaction (`structure anisotropy') determined by the anisotropy of the spatial arrangement of the cluster-dots. By numerical computer calculations the components of the tensor of dipole sums versus the degree of structural anisotropy were determined, and it was shown that both types of anisotropy can have the same order of magnitude. Depending on the geometrical configuration of the dot-system, the shape and structure anisotropy can compete or corroborate with one another causing an increase or decrease of the local electric field anisotropy, and thus lead to a change of the anisotropy of the refractive index and of the extinction coefficient of the structure. Strong artificial birefringence, as well as the modifications of the optical absorption spectra predicted by the model are discussed and compared with experiment.

The preliminary results of a round-robin test to check the reproducibility of the measurement of the main optical characteristics of gradient-like planar waveguides are reported. The test involves seven research laboratories in Europe and Canada. The effective indexes of a set of planar waveguides produced by K⁺/Na⁺ ion-exchange have been measured in each laboratory and the refractive-index profiles have been reconstructed by various numerical methods. The comparison between the reconstructed profiles and the directly measured one is also shown for one of the waveguides under test.

Ag-containing glass systems are suitable for fabricating waveguiding devices and are good candidates as optical nonlinear structures, owing to the high non-linear response of silver metallic nanoclusters. A methodology for controlling both the formation of silver clusters and the waveguiding properties is discussed, based on the combination of ion-exchanges and heat- treatments.

An analytical modelling of buried waveguides is presented. These waveguides are fabricated by a purely thermal ion back diffusion in glass, which is enhanced by applying an electric field across the substrate. The model is based on an approximation of low ionic concentration with arbitrary variation, in such a way that an approximate nonlinear diffusion equation can be solved under different boundary and initial conditions.

Thermooptic coefficients of the effective refractive index in integrated optical strip waveguides in LiNbO₃ have been measured with high accuracy by Mach-Zehnder and Fabry-Perot interferometer techniques. Titanium indiffused and annealed proton exchanged (APE) strip waveguides were found to have the same value as it is known for the substrate material. Multimode proton exchanged (PE) strip waveguides specially designed for maximum field overlap to the APE guides show a reduction of the thermooptic coefficient to one-fifth with negative sign. Phase shift dependent on temperature was examined in APE strip waveguides containing such a strip-shaped multimode PE segment.

A simple and reliable method for obtaining the index profile and the value of (Delta) n of diffused planar and channel waveguides from the near-field scan data is presented. The method involves fitting of the Hermite-Gauss functions to the near-field scan data; the implicit assumption in case of channel waveguides being the separability of the field in its dependence of the two transverse coordinates (x and y). The coefficients of expansion are then used to obtain two 1D index profiles. These two profiles are then suitably combined to give the index profile and the value of (Delta) n of channel waveguides. The validity of the procedure is first tested on planar waveguides. Our simulations show that the method is very stable with respect random errors up to 15 - 20% in the intensity, and accurate estimated for (Delta) n can be reliably obtained. For diffused channel waveguides also, our simulation studies show that the method yields very good estimates for (Delta) n with typical errors being less than a few percent.

Mode fields of integrated optical waveguides based on Indium Phosphide (InP) have been determined from near-field intensity measurements obtained by scanning the front face of a waveguide two-dimensionally in the focal plane of a microscope lens. Due to diffraction the focal spot size of this microscope lens (NA equals 0.9) is limited to approximately 2 micrometers at (lambda) equals 1550 nm. The original mode field of the integrated waveguide can be restored by deconvolving the measured intensity profile with the effective focal spot of the scanning lens. Therefore the iterative deconvolution algorithms of Jansson (1984) and Gold (1964) have been expanded and optimized for 2D applications. In order to reduce the numerical effort of these 2D algorithms a novel deconvolution algorithm based on one-dimensional Hankel transform instead of two-dimensional Fourier transform has been developed. The numerical evaluation of these deconvolution algorithms shows a rms-error of less than 1% with an assumed signal to noise ratio of 100:1. Applying these algorithms to measured intensity profiles and comparing the deconvolved fields to the numerically calculated Eigenmode field leads to a maximum difference of less than 10%, which may be caused by the fact that neither the geometric dimensions nor the refractive indices of the examined waveguide are known exactly.

The photodeflection method applied to the propagation losses characterization in channel waveguides is discussed using two different set-up configurations. 3D and 1D models are presented in order to calculate the photodeflection angle. The effects on the measurement of set-up misalignments are studied. Different ways for determining the propagation losses are shown. Comparison between theoretical and experimental results for Ti:LiNbO₃ and a glass channel waveguide is also reported. The method has proven suitable to measure losses as low as 0.2 dB/cm.

Both, GaAs-AlAs and Si-SiGe quantum well structures have been considered for applications as infrared detectors, modulators and switching devices. The miniband structure in these systems covers a wide range of energies (e.g. 1 - 400 meV) and offers an opportunity to design optical devices that would operate in the mid-to-far infrared range of wavelengths. An external field and triangular wells have been used to modify the structure of the confined states. This enhances optical nonlinearities (e.g. the second order susceptibility). In this paper we present a full scale evaluation of GaAs-AlAs and Si-SiGe quantum well structures in which the nonlinearity arises due to virtual transitions between valence minibands. We aim at structures which could operate in the 3 - 5 and 10 - 15 micrometer range. We present both the magnitude and the frequency dependence of the second order susceptibility. We show that a judicious choice of controllable material parameters such as layer width and composition can generate a strong second harmonic response in GaAs-AlAs asymmetric superlattices. Also, we report full scale calculations concerning difference-frequency generation in an asymmetric Si- SiGe quantum well structure. We find that the strongest contributions to the second order response originate from regions lying farther from the zone center.

The propagation of light through nonlinear waveguides has stimulated considerable interest. These devices are capable of exhibiting a wide range of complex but very useful phenomena such as soliton emission and photonic switching. Over the last decade there have been many theoretical studies to understand the lightwave propagation through such nonlinear optical waveguides and amongst them the semi-analytical techniques, the beam propagation method and the finite element method can be mentioned. The finite element method has been established as one of the most powerful and versatile methods to characterize a wide range of linear and nonlinear optical waveguides.

We report on the unexpected large influence of facet properties on wavelength shift and wavelength chirp in uncoated and coated distributed feedback (DFB) lasers. A detailed comparison is performed between various experimental laser data (spectra, electronic and thermal wavelength tunability, relative intensity noise, linewidth) and the results of transfer matrix model calculations. From experimental data of different lasers, a set of physical DFB laser parameters was determined. We succeeded in describing all the experimental data of different lasers by the same parameter set. By use of this set we found that the wavelength chirp and the wavelength shift due to electronic effects including spatial hole burning varies considerably for different end facet phases and facet coatings, but otherwise identical DFB lasers.

We have studied the properties of distributed feedback laser diodes with real and complex coupling used as narrowband optic amplifier. The implemented numerical model is based on the transfer matrix method and allows to analyze general multielectrode laser structures. This model takes into account the interaction between optical field and carrier population in the high input power regime, the thermal effect due to current injection, the spectral dependence of optical gain and the photon and carrier density dependence on the longitudinal coordinate. We report an example of application to the study of filter tunability. With regard to complex coupled DFB lasers (CC-DFB) we compare theoretical and experimental results for the spontaneous emission spectra. CC-DFB amplifiers show quite different nonlinear behavior in the high input power regime, depending on the relative phase between index and gain gratings. These results are related to the effective linewidth enhancement factor which depends, for these structures, on both the material and the grating characteristics.

An overview of the development on lossless Er-doped Y-branches and high gain Er-doped waveguide amplifiers is given, and their applications in future prospects are reviewed. A comprehensive model is presented for the integrated Er-doped phosphate silica amplifier, that includes high concentration ion-ion interaction. The model is applied to a rigorous design optimization of high gain amplifiers, where the influence of variations in the launched pump power, the core cross-section, the waveguide length, the Er-concentration, and the background loss are evaluated. Optimal design proposals are given and the process reproducibility of the proposed design is examined. Requirements to process parameter control in the fabrication of the Er-doped waveguide are also set up.

We have presented a novel numerical method for the analysis of leaky and absorbing optical waveguides. We have also given an easy to use computer program using Mathematica^TM.

We analyze 45 degree(s) Self-Aligned Integrated Mirrors (SAIM) with Finite-Difference Beam Propagation Method. For the first time, we compare the intrinsic losses of three self-aligned structures that are used in integrated optics or optical interconnection circuits. We underline trade-off to make between diffraction and part of reflected power in the choice of self-aligned structures. We consider monomode polyimide optical waveguides and propagation in both quasi-TE and quasi-TM polarization modes. Comparisons are also made with semiconductor optical waveguides. It is shown that, in both cases, intrinsic losses of SAIM can be lower than 0.05 dB. This result is promising for the fabrication of future complex photonic circuits including several ten of mirrors.

On technical reasons it is impossible to produce a Y-branch without a truncated wedge. At this truncation reflections and field deformations appear. This leads to unwanted loss. In this paper the losses and reflections are calculated with the MoL-BPM, a beam propagation method based on the Method of Linies.

The design of integrated optical S-bands, power splitters, and directional couplers are described in terms of normalized parameters. These parameters are calculated accurately by a numerical method leading to general design curves for fiber-compatible waveguide devices.

Key results of a benchmark test, initiated in 1992 by the Working Group 2 of COST Project 240 at a modelling workshop in Teupitz, Germany, are presented. A great number of algorithms--FFT-BPM, various types of FD-BPM, wide angle approximations, adaptive FE- BPM and MoL-BPM--are compared. The quasi-analytic character of the benchmark tests provides a deeper insight into the absolute accuracy of algorithms.

An efficient numerical method for the analysis of periodic waveguides has been presented. The method is based on the collocation method which we have earlier developed for propagation of waves through uniform and nonuniform (e.g., tapers) waveguides. In this method, one converts the Helmholtz equation, which is a partial differential equation, into a set of total (ordinary) differential equations. In our method, the wave is to be propagated only through one period of the waveguide, after which analytical solutions for arbitrary lengths can be obtained. We have also presented an example to show the effectiveness of our method.

A method to analyze linear and nonlinear effects in a Bragg-resonant, quasi-phase matched waveguide is described.

A new type of directional coupler with a diffraction grating formed by two external beams interfering in nonlinear material is analyzed. The parameters of the grating depend on the external waves properties and thus can vary during the work of the coupler. As a result an external power controlled coupling of a chosen pair of normally mismatched couplers modes can be realized.

Tunable filters are key components for future transparent WDM networks'. In a wavelength-routed network add and drop functions can be performed in a cross c.onnect module. Electrically tunable filters in combination with direct detection may be an alternative to coherent detection for high density wavelength division multiplexing (HDWDM) systems. Promising device structures for the implementation of filter functions in optoelectronic circuits are grating assisted (meander-type) couplers, both for passive waveguides and for tunable lasers. Such filters are traditionally analysed and designed by using coupled mode theory. The accuracy of this method, however, depends on the choice of basic eigenfunctions2 and is limited to weak guiding and weak coupling structures. Recently, to overcome these problems, a transfer matrix description has been proposed, which exists in a hierachy of different approximations. The method with the highest accuracy, called bidirectional eigenmode propagation method (BEP)3, solves the Helmholtz equation in forward and backward direction by propagation of eigenmodes of the waveguide structure and calculates the energy transfer at interfaces with abrupt changes of the refractive index by mode matching (overlap integrals). Radiation modes are included by using a finite window with metallic or magnetic walls. An unidirectional version which neglects either the forward or backward travelling waves is also possible. Very important for practical applications is a reduction of the eigenmode series expansion to only (guiding) waveguide modes (guided eigenmode matching and propagation method (GEMP)4). This allows an analysis of a grating assisted coupler to be carried out using only 2 eigenmodes (odd and even coupler modes) in the transfer matrix algorithm and calculating 4 overlap integrals and 4 propagation constants. This mode expansion approach leads to a deep understanding of the physical behaviour of the device. In this paper we present the basic formulation of the eigenmode expansion method (B), coupled mode theory (C) and show, in case of resonance, the equivalence of GEMP with simple coupled mode theory on the basis of coupler eigenmodes in the limit of weak coupling (D). It will be shown, that the key parameters arot of GEMP and the coupling coefficient 1 of CMT are correlated and that for practical applications a combination of both methods are advantageous (E). Some results on codirectional grating assisted couplers and the recently published sampled grating structure5, which is the basis of an electro-optically tunable filter, will be discussed in F. A short conclusion is given in G.

Great hope currently lies in the area of organic materials for third order non linear optics in waveguide devices, even if a large uncertainty still exists in this field. Here the activity of the RACE HIPOS is reported which is closely focused on polymer waveguide fabrication, on the insertion of such guides in Integrated Optics circuits and on nonlinear tests.

Photoreversible gratings in photochromic organic guest/host systems are written using uv- radiation (363.8 nm) or in the visible (514.5 nm) with diffraction efficiencies up to 7%. Poly(Methyl MethAcrylate) or polyimide are used as guest polymers, doped with the fulgides Aberchrome 540 or 670. The thickness of the films is between 50 and 100 micrometers , the grating constant is 2 - 3 micrometers . By adjusting an additional light source the diffraction efficiency rises (here 17%) and it can be tuned optically. With uv-radiation a permanent grating is written in a crosslinkable polyimide. Due to this crosslinking a selective in-diffusion of an active dye into not illuminated areas of the polyimide (grating constant: 2 micrometers ) takes place. This latent grating of the distributed fulgide molecules can be optically activated additionally to the permanent grating resulting from the photoreaction. The diffraction efficiency can be tuned by a homogeneous illumination.

This paper presents a study of the nonlinear wave propagation in an adiabatic all-optical switch, which is composed of an asymmetric Y-branch ion-exchanged glass waveguide with a strip of nonlinear polymer loaded on top of one branch. By extending the effective index method to the analysis of the nonlinear waveguides, the nonlinear dispersion curves are calculated at the successive sections to illuminate the evolution of the normal modes in the device. To further demonstrate the nonlinear switching behaviors in the Y-branch waveguide, a beam propagation method is also employed to simulate the optical field propagation. The inputs by three different ports are investigated.

Efficient power transfer between InP/InGaAsP-based optoelectronically integrated circuits (OEICs) and single-mode optical fibers can be realized by appropriate tapered waveguide- structures on the chip itself, so that the fiber can be directly butt-jointed to the chip. First, a simplified sample structure is considered for the purpose of testing a scalar and two different fully vectorial Finite Difference-Beam Propagation Methods (FD-BPM). The sample structure is excited with the eigenmode of the OEIC-chip waveguide and the optical waves propagating through the device are investigated by means of 3D BPM simulation. Starting from three already fabricated prototypes, scalar simulations with modified parameters of geometry are performed to predict performance of the devices in order to achieve an optimized design. Tapered structures with linearly and nonlinearly laterally tapered layers are investigated in order to minimize radiation loss by simultaneously maximizing coupling efficiency. Simulated data will be validated by measured results and numerically optimized structures will be presented.

The excellent performance of Erbium doped fiber amplifiers and lasers in the 1550 nm wavelength region has stimulated increased interest in Erbium doped integrated optic planar waveguide devices (particularly LiNbO₃). This work describes the measurement techniques and the performance evaluation of Er-doped, X-cut and Z-cut Ti:LiNbO₃ waveguides. Waveguide losses have been measured in the 1300 nm and 1550 nm wavelength regions, in both TE and TM polarization states, using the low finesse Fabry-Perot technique. The resonance phenomena has been obtained with two different methods, the thermal cavity tuning and the sweeping in wavelength using a tunable semiconductor laser. The results obtained in this second case are in good agreement with those obtained by the temperature tuning. The second method has also the advantage of avoiding the coupling stability problems inherent to the thermal tuning. Absorption spectra have been evaluated using a white spectral lamp and a semiconductor LED; spontaneous emission spectra have been evaluated pumping with semiconductor laser. A strong absorption was observed around the value of 1530 nm for TE and TM polarization. Using the spectral lamp significant absorption around 980 nm was observed.

A nonblocking integrated holographic space switch has been realized in a lithium niobate channel-planar-channel composite waveguide. Holograms were recorded from above the waveguide using light at 514 nm. Required reconfiguration time for switching between output ports is 0.12 ms.

The spectral transmission properties of a self-similar optical Fabry-Perot resonator are theoretically studied. The considered structure can be realized by alternating two dielectric layers of different refractive index such that the highest refractive layers belong to a triadic Cantor set. The transmission spectrum exhibits localized peaks inside forbidden frequency band gaps. This feature could be very useful in the design of novel filters. Moreover the self- similarity of the structure reflects itself in a weak self-similarity in the transmission spectrum. A comparison with a regular periodic structure is also presented.

A systematic study on integrated wavelength multi/demultiplexers is presented, in which the experimental features of the devices, the theoretical predictions of a simple model, and the results of extensive modelling by a BPM analysis are compared. The components are based on the two-mode interference principle, and are fabricated on soda-lime glass by Ag-Na ion exchange. The modelling is performed by CAOS, a user-friendly general purpose simulator, based on a FD scheme with transparent boundary conditions. The agreement between experimental and simulated spectral characteristics is very good; moreover the proposed analysis procedure allows the determination of the maximum index variation (Delta) n and the diffusion depth D which describe the optical and geometrical characteristics of the waveguides.

We present a theoretical method which makes it possible to analyze 3D integrated optical waveguides with arbitrary refractive index profiles. With this method it is easy to obtain effective indexes, propagation constants and coupling/switching properties of planar and channel optical waveguides. This theoretical approach involves modelling the original optical waveguide by means of an Equivalent Optical Waveguide whose effective index is evaluated by applying a technique that we call the Asymptotic Effective Index Method. The theoretical results show good convergence and accuracy for effectives indexes, propagation constants and coupling/switching characteristics.

Conventional susceptometers based on superconducting quantum interference devices monitor the magnetic moment of a magnetized sample which is moved through a superconducting gradiometer coil. The measuring accuracy of 10^-8 emu (equals 10^-11 Am²) is limited by mechanical degradations and vibrations of the sample holder, its geometrical shape, magnetostrictive phenomena and positioning error of the sample. Also the method of evaluating the magnetic moment of the sample from the depicted magnetic flux is not unique for extended thin layer samples. The l/f-noise from the `static' measuring procedure is commonly compensated by increasing the volume of the magnetized sample and accordingly the signal to noise ratio. However, if thin epitaxial samples of atomic monolayer thickness, quantum well and superlattice structures of semimagnetic constituents on thick diamagnetic substrates (in contrast to ferromagnetically ordered metal superlattices) are investigated, the conventional method fails for an useful analysis. Thus a novel `dynamic' method to modulate selectively the thermal properties of the epi-layer by a light-wave (guided by a magnetically clean glass fiber) is applied. The boundary conditions to find the thermal wave amplitude in the epi-layer are calculated for the extended configuration helium gas- substrate-helium gas-glass fiber. The sample is mechanically fixed. Lock-in technique increases the sensitivity by at least a factor ten. Since the thermal wave modulates the magnetic properties only of the magnetic epi-layer, the dynamic range is enhanced dramatically. The method called thermal wave susceptometry (TWS) is applied to drive an antiferromagnetic phase transition in a 2.5 micrometers EuTe epi-layer on BaF₂ substrate in a normally out-of-detection limited field of 10 Gauss. A ferromagnetic EuTe/PbTe magnetic semiconductor superlattice of 5 monolayers EuTe between 15 diamagnetic PbTe monolayers (repeated 400 times) is also investigated by this novel low-intensity (10 mW/cm²) light- modulated TWS-method.

In this paper, the design of a new magneto-optical device based on the resonant interaction between magnetostatic and light waves in a two-port band-pass filter is proposed for potential applications in optical modulation, and its performances are theoretically predicted. The advantages of a microwave resonating filter with respect to delay lines for the magneto-optical interaction are a more compact geometry, owing to the reduced dimensions, an increased optical modes conversion efficiency and the low microwave input power. As a peculiar result on the configuration proposed, the device allows for a possible interaction between light and microwave signals when surface magnetostatic waves are excited.

A numerical analysis of microwave and optical properties of a polymer-based travelling-wave integrated electro-optic modulator is presented. We propose a new structure with a microwave buffer layer on top of the driving electrode. This buffer layer is added in order to obtain phase velocity matching between the optical field and the microwave modulation field. Employing the Effective Index Method and the 2D Beam Propagation Method the optical properties is investigated and the optical modulation index and the driving voltage is determined. Employing the Spectral Domain Approach we investigate the microwave properties of the new structure in a configuration with a travelling-wave electrode. It is shown that the two characteristics: the microwave mode index and the characteristic impedance, can be varied independently for the proposed structure. From the optical and microwave properties the active characteristics of a Mach-Zehnder interferometer based on the waveguide structure is investigated. We show that with no restrictions on the electrical power consumption, the optical modulation bandwidth can be higher than 100 GHz. This bandwidth will be reduced to 34 GHz, if a restriction on the electrical power from the signal generator is imposed.

We have modelled a two-layer structure consisting of a Ti-waveguide and a thin proton exchanged layer on top using a multilayer stack approximation. Good agreement with previously reported experimental investigations is obtained. Guidelines are proposed for optimizing the sensing properties of the two-layer structure.

Due to their nonreciprocal properties integrated magnetooptical structures are of large interest for optical communication systems. The paper presents a finite-difference beam-propagation algorithm for the numerical analysis of such structures. It is applied to the simulation of nonreciprocal interferometers and couplers. Conclusions are drawn with respect to the experimental realization of integrated optical isolators and circulators.

Within the framework of dynamic holography we present a theoretical model based on geometric optics ideas which is capable to describe two wave mixing and four wave mixing processes with waves of arbitrary shape in photorefractive crystals. The model takes into account the nonplanarity of the waves and optical activity of the crystal materials. In the slowly varying amplitude approximation coupled partial differential equations describing the evolution of the wave amplitude are derived. These equations are solved numerically by introducing the lightpaths as characteristics. We study the influence of the beam properties like amplitude profiles and polarization as well as the geometrical arrangements and crystal properties on the two wave mixing efficiency.

Passive nonreciprocal components, such as isolators or circulators, can only be realized with magneto-optic, hence gyrotropic media. With lateral magnetization, the quasi TM/TE approximation is applicable, and only TM-modes exhibit nonreciprocal propagation. We investigate a waveguide consisting of a multi-layered ridge on top of a multi-layered substrate. Several methods (effective index, finite-difference, spectral index and Galerkin's) for calculating differences of forward and backward propagation constants are discussed. It is shown that a way to increase the nonreciprocal effect is to provide for strongly non- symmetrical structures.

Z-cut proton-exchanged LiTaO₃ optical waveguides have been fabricated using cinnamic acid and characterized optically. The diffusion constant (D_o) and the activation energy (E_A) were found to be 152.4 micrometers ²/h and 0.34 eV, respectively. The diffusion rate is lower than published data for other proton sources. The effect of annealing on waveguide depth increase could be accurately modeled by a power-law relationship, and the surface index change increases initially before decreasing. The maximum surface index increase for a particular exchange temperature was found to be dependent on the exchange temperature, and the higher the exchange temperature the lower the index increase.

Many possibilities are offered to analyze the field in tapered fibers. We have used in this work the bpm method and the coupled-mode theory for a conical fiber. In the second case, it is shown by a length-scale criterion that some geometries should provide a good efficiency. The comparison between the quasi 3D numerical simulation and the local mode method is also performed. The complete resolution procedure is then dependent on certain essential approximations and simplifying hypothesis.

The propagation of light through nonlinear waveguides has stimulated considerable interest. These devices are capable of exhibiting a wide range of complex but very useful phenomena such as soliton emission and photonic switching. Over the last decade there have been many theoretical studies to understand the lightwave propagation through such nonlinear optical waveguides and amongst them the semi-analytical techniques, the beam propagation method and the finite element method can be mentioned. The salient question is whether these wave solutions are stable on propagation and this has been studied recently. In this paper we present for the first time a stability study of consistent modal solutions obtained by using the finite element method.

The paper presents the formulation of nonlinear TE waves guided by waveguides having second order polynomial in the film with nonlinear cover medium. These waveguides are usually obtained in glass by silver-sodium ion exchange technique. It is shown in this paper that the formation leads to an exact dispersion relation and an exact expression for power flow.

We show that remote coupling in rib Antiresonant-Reflecting-Optical-Waveguide couplers can be achieved. It turns out that fully vectorial methods have to be used in order to determine both the field profiles and the propagation constants of the guided modes and to model the evolution of the fields, respectively. A reasonably agreement between theory and experiment has been found.

We study the evolution of solitary waves in inhomogeneous nonlinear arrays of waveguides. We use both a continuous and a discrete approach. For the continuous approximation we find a Lagrangean that permits to change to a set of ordinary differential equations. The evolution of the solitary waves is studied for various inhomogeneous arrays.

The nonlinear directional coupler is analyzed in the presence of asymmetrically distributed and saturable nonlinear refractive index. We make use of the linear supermodes of the structure and phase-space techniques, which allows to obtain the main features of its behavior, without the need of solving the coupled mode equations.

The paper is devoted to the investigation of full losses into the waveguide cavities that are platelet single crystals of semiconductors A₂B₆. Description of character of additional lines appearance in laser generation spectra is presented. It is shown that the section of symmetric waveguide which is the microlaser cavity creates such conditions of propagation and reflection from the facets for some transverse high-order modes that full losses coefficient of these modes at wavelength (lambda) becomes considerably less than the Urbach absorption coefficient at the same wavelength. The experimental researches of CdS single crystal generation spectra have been conducted and the interconnection between full losses and geometrical parameters of cavity have been established.

Anisotropic optical waveguides in some cases can connect between each other external light beams and waveguide optical fields without any additional coupling elements, only due to existing of leaky optical waves in such waveguides. Because of the simplest design anisotropic waveguides with light leakage can be used in many integrated-optical elements including waveguide sensors. Some features of leaky wave excitation in planar waveguides LiNbO₃:Ti and H⁺:LiNbO₃ while total internal reflection of ordinary polarized light beams from a waveguide boundary have been experimentally investigated in this work. Besides, an influence of temperature changing on coupling angle variations at such excitation method has been considered as well with regard to possible applications of similar elements in integrated optics.

Planar polyimide light guides can be used for the optical detection of various vapor concentrations. Therefore the birefringence of the light guide is monitored as a function of the actual vapor pressure. Using this principal several vapor concentrations of n-heptane and n- octane have been determined. Similar dynamic behavior can be observed for both components only differing in time constants. Furthermore the detection of n-heptane in a mixture with iso- octane can be realized. The waveguide sensor shows a sensitivity only to n-heptane and not so iso-octane vapors. The determination of the n-heptane concentration is not affected by the presence of iso-octane.

Rectangular core waveguides for integrated optics have been designed by the mode matching (transverse resonance) method. To achieve good coupling between the waveguides and an optical fiber, the core cross section of the waveguide at the fiber/waveguide interface has been optimized with regard to minimum coupling loss. In calculating the overlap integral between the fundamental mode of the waveguide and the fiber a very accurate fiber model has been used. Calculations of the effective index and the field distribution of the fundamental fiber mode with this model have been compared with analytic results for circular step-index-fibers. The convergence behavior and accuracy of overlap integral calculations with the mode matching method has been investigated. The calculations show that losses as low as 0.16 dB can be reached for waveguides with refractive index contrasts in the whole range 0.5 to 2%.

Outcoupling of guided modes via a high index liquid acting as movable coupling prism allows for the direct detection of guided power versus propagation distance without the drawbacks of the common two prism method. We present a setup based on this principle which is capable of performing precise loss measurements of plane and strip waveguides. Furthermore, excess losses of devices caused by local defects, bending etc. can be distinguished from the fundamental loss background.

Theoretical consideration of lasing regimes of asymmetric semiconductor heterostructures has been made. The conditions for bistable power switching and periodical radiation pulsations have been determined. The efficiency of injection of current carriers into quantum wells has been investigated. Doping levels of the layers forming the asymmetric heterostructure and its band configuration to realize the request inhomogeneous excitation of the quantum wells have been defined. The asymmetric heterostructure waveguide properties have been considered and the optical confinement factor for various lasing modes has been established. Calculations have been performed for the GaAs-Al_xGa_1-xAs system.

Two-beam interaction of waveguide modes in planar waveguide in electro-optic crystal has been considered within the band-transport model, taking into account one photoactive level only. Equations for amplitudes of zero and first spatial harmonics of space-charge field potential have been obtained for interactions in the waveguide with short diffusion length and without of trap saturation. Consideration of a steady-state has been performed for small modulation index of interference light pattern and for case of the dark conductivity is a factor ore the photoconductivity is a factor. For the first case we obtain distributions of space-charge field components for different TE-TE and TM-TM interactions in the waveguide with an arbitrary large increment of refractive index. For the second case we obtain distributions of space-charge field components within waveguide layer only for TE₀-TE₀ and TM₀-TM₀ interactions only in waveguide with step-shaped profile of refractive index. At initial section of the recording the distributions of space-charge field components are the same in distribution at a steady-state for the case of the dark conductivity is a factor. The values of dimensionless overlap factors of space-charge field components with interference light pattern have been calculated for planar waveguide with large increment of refractive index.

We describe, in the present paper, the production and optical characterization of thin noncrystalline waveguiding films of the polar organic polymer poly-phenyl-acetylene. The nonlinear behavior of the grating coupling, due to the third order nonlinear susceptibility of the polymer, has been investigated. We have used laser sources, producing short pulses ((tau) equals 100 ps) at (lambda) equals 1.064 micrometers and ultrashort pulses ((tau) equals 1 ps) at (lambda) equals 610 nm, to study the change in the coupling efficiency with respect to the pulsed beam average input power. In the two cases, the changes are attributed respectively to a thermal and electronic nonlinearity of the refractive index. First theoretical modeling of the obtained data is given in the frame of the coupled mode approach to the nonlinear behavior.

Waveguide lenses continue to attract great attention due to their importance as basic elements of many signal-processing integrated optical circuits and interconnecting devices. Here we analyze a novel diffractive lens structure, namely a waveguide Fresnel lens with phase shifts between neighboring zones which are a multiple value of 2(pi) ; it has been shown that the analog Fresnel lens and the refractive lenses can be considered as limiting cases of this more general lens element. the possibility of varying the phase shift by an integer multplicative factor introduces additional flexibility into the lens design as well as less stringent requirements into the fabrication process. A specific design has been produces of a lens with aperture 2.83 nm and focal length 10 mm, to be fabricated in glass waveguides. A hybrid modeling tool, based on ray tracing and Huygens-Fresnel integral, has been first used to check the performance of such a lens. Our further simulation tests, carried out using a BPM-based computer program, have confirmed that by neglecting the finite length of the lens, one introduces focal shifts and a decrease in the diffraction efficiency; the infinitesimal-length approximation can be tolerated only in the case of optical system with large F-number.

We present the analysis of guiding properties of the 3D three-layer waveguides, taking into account the material's attenuators. The examined waveguide consists of dielectric rod having rectangular cross section, and thin film of greater refractive index than that of a rod, the given film is loaded on the rod. Attention is given mainly to the influence of the surfacing film's parameters on the phase and attenuation of the lightguide's guided modes. Modeling is based on the use of effective refractive index method in complex form. The film's normalized thickness dependences of phase and attenuation constants are computed for multimode waveguide.

Optical and microstructural characteristics of polycrystalline waveguiding ZnO films deposited by RF reactive sputtering has been investigated. The origin of high waveguiding mode propagation losses and spatial inhomogeneity of the sputtered films has been investigated experimentally. A technique allowing to avoid these disadvantages has been proposed. Using this technique free of mechanical stress highly oriented textured ZnO waveguiding films with optical propagation loss less than 1 dB/cm have been deposited.

Among all the simulation techniques currently used in the modeling of integrated optical devices, the group of Beam Propagation Methods is one of the most powerful and flexible. Here, we analyze an 1 X 4 branch coupler fabricated in glass by ion-exchange with the purpose of checking the capabilities of this algorithm and its reliability through different implementations. A comparison is carried out between the simulation results from two software packages developed in house and a commercial program: such results are also compared with the data resulting from the experimental characterization of the coupler.

The paper presents a study of a single-mode Ti and Fe in-diffusion waveguide. We have reported in this letter the experimental observation of diffraction effects due to the formation of a transitory photorefractive grating. The interference of a guided-wave with light scattering inside the waveguide can form a spatial phase grating due to the photorefractive effect, analogous to the storage process of holograms in bulk crystals. The storage mechanism in these materials is based on light induced permanent changes of the refractive index--the photorefractive effect. In this paper some advantages and limitations of this method are discussed.

Tapered waveguides are frequently used to obtain a good matching between the modes of two butt coupled waveguides having different guiding properties. The design of these tapered waveguides is in most cases conservative because of the lack of precise modelling guidelines and accurate modelling tools. This paper discusses in the first place a quantitative approach for taper design by considering the whole taper with arbitrary shape as a succession of short linear taper fragments. As a result that radiation loss per relative thickness reduction as a function of index contrast, taper angle and thickness is obtained. These simulations require a highly accurate beam propagation method (BPM) able of handling large index contrasts and thereby principally exceeding the applicability range of paraxial algorithms. Therefore a novel BPM which solved directly the non-paraxial 2D Helmholtz equation by decomposing an arbitrary input field in local eigenmodes of the waveguide is used.

The combined effects of a large-scale (in comparison with wavelength) longitudinal periodicity and self-focusing on a Gaussian beam propagation through parabolic-index waveguide with Kerr nonlinearity is investigated analytically in the paraxial approximation of the scalar Helmholtz equation using an aberrationless model of self-focusing in which the beam remains Gaussian. The demonstrated possibility of controlling the beam in such waveguides can be useful for generation of temporal solitons and for design of various all-optical components.

In this paper we propose a model of the planar superlattice structure fabricated from linear dielectric materials. Interesting features of such structures are `anomalous' nonlinear and anisotropic optical properties, which can be observed in experiments with planar waveguides. These properties can be explained by the model. The model is based on the proposal, that internal electron structure in the above superlattices can be described by Hamiltonian, which includes periodical 3D potential of a crystal, modulated by 1D periodical superlattice potential, which appears as a result of difference between zone structures of materials forming the superlattice. Full Hamilton operator also includes standard parts: Hartry potential and inter-electron quantum-correlation potential. Besides that in the case of dielectric superlattices we must also consider the deformation potential in layers, caused by static deformation of layers and electron-phonon interaction. In order to describe carrier transportation in the structure it is reasonable to use the `effective mass'-approximation. It is useful to obtain superlattice wave functions by the `modulation' method, where electron wave functions in bulk sample are used as nonperturbated. Therefore, values of effective masses of carriers in bulk samples of materials, width of energy gap, value of Fermi-level, position of energy zones are the initial parameters of the model, the same as thicknesses of layers, value of non-isotropic deformation in layers and other technological parameters. In accordance with the model, new types of dielectric superlattices are proposed, for example constructed from asymmetrically deformated layers of a single dielectric material.

A new method of coherent coupling between individual waveguide lasers using cascaded single-mode Y-junction and X-directional couplers is presented. A laser system containing two Nd³⁺-doped active fiber sections coupled via a X-type coupler is studied experimentally. The coupling efficiency of 95% between lasers is demonstrated.

A system of two radiationally coupled corrugated waveguides is proposed for remote coupling. Coupling is achieved owing to diffraction of the waveguide mode on the corrugated waveguide surface. Using Rayleigh-Fourier-Kiselev method, we calculated the dispersion curves of the system and the coupling length on their basis. Coupling length changes periodically when waveguide separation increases, this fact makes the remote coupling possible. Optimum distances between the waveguides are also determined. It is shown that the coupling length is related to the radiation loss coefficient of the single waveguide.