Semiconductor ring lasers suitable for monolithic integration in optoelectronic circuits may be formed of curved waveguide (or by a ring of etched mirrors), and fabrication depends on high- quality lithography and etching. Very small devices may be made if the r.i. contrast is sufficiently high, and devices down to 10 micrometers in diameter have been realized. The quality of the dry-etched sidewalls is more critical in curved than in straight waveguides, and wall roughness, together with high r.i. contrast, leads to severe optical scattering loss. Wall roughness has been reduced markedly by high-definition e-beam lithography and optimized dry etching, and the effect of damage has been reduced by nitride passivation. In small ring lasers, directional output couplers are not practicable, and Y-junctions have been used, which cause additional scattering loss. MMI couplers show promise. If strip-loaded or buried rib waveguiding is employed to avoid degradation of the exposed active layer, much larger bend radii must be accepted. Larger structures show promise as actively or passively modelocked sources operating around 10 GHz. Feedback into the laser through the output coupler remains a problem, although a reduced coupling fraction can provide some degree of isolation.

Use of electrically variable couplers and etched facet mirrors in a coupled guide cross point switching and routing array is examined. Theoretical analysis, and experimental results of carrier injection into double heterojunction semiconductor rib waveguide electrically variable couplers, together with effect on modal reflectivity at an etched facet mirror, are presented. Results demonstrate that carrier injection is a viable and efficient method for reducing the effective index beneath the guide rib leading to both detuning of a coupled guide structure, and for effectively `destroying' the guiding ability of one guide. The importance of the diffusion contrast on the operational efficiency of such devices is shown to be significant. Etched mirrors prove theoretically to be viable structures for changing the waveguide direction in this material. Reflectivity is shown not to vary with carrier injection for the proposed guides.

A 2D thermal simulator and a model to evaluate high power lasers characteristics have been developed. With these models it was possible to optimize cavity length of InGaAs/GaAs (Multiple) Quantum Well 980 nm lasers realized both with Al-based and Al-free confining layers. A comprehensive experimental investigation of the influence of cavity length and temperature on the laser emission wavelength has been performed. This allows a fine trimming of the devices to match the Erbium doped fiber absorption bandwidth.

Polarization control photonic functional devices based on quantum well structures for application to advanced fiber communications are described. Two promising techniques are discussed: compositional disordering and strained-layer structures. TE/TM mode selective waveguides were successfully fabricated using polarization dependent index changes induced by the cap annealing. Enhancement of TM mode optical gain with tensile-strain enabled realization of high performance polarization-insensitive semiconductor optical amplifiers and superluminescent diodes.

In this work we have investigated the effect of various implantation schemes on In(0.2)GaAs/GaAs/AlGaAs Single Quantum Well, where the implanted species are Argon and Helium, with doses in the range 1E12 to 1E14 at cm^2, at energy spanning 270 - 400 KeV and 30 to 50 KeV for Ar and He, respectively. Repetitive annealing processes were carried out between 735 and 870 degree(s)C and the interdiffusion was deduced by photoluminescence measurements. A maximum of 20 nm shift from He ion implanted Quantum Well with an high degree of reconstruction has been recorded, thus allowing the application of this disordering scheme for the realization of optoelectronic devices.

A comprehensive, time dependent model of a semiconductor laser/amplifier is applied to such a device, inhomogeneously pumped, operating near Fabry-Perot resonance to produce wavelength conversion. The model includes spontaneous emission as a function of wavelength and carrier density, with photon density and carrier density functions of cavity length. Results indicate theoretical operating range for signal wavelengths and powers and comparison is made with experimentally obtained data.

A combination of Raman spectroscopy and second-harmonic generation techniques was used in the investigation of porous silicon structure. The Raman spectra evidence that our samples consist of microcrystals with the size about (3 - 4) nm. The nonlinear optical data show that there is not appreciable crystal cell distortion in the silicon nanoclusters of porous layer.

Results of experimental investigation of photostimulated effects in porous silicon are presented. Some conclusions about the dissipation of a nonequilibrium charge carrier energy in this material are made.

In this work, we discuss recent research activities towards the development of optical waveguiding devices based on quantum-confined structures, with particular reference to the application for telecommunications. We describe experimental results concerning both device physics and device applications in the 1.55 micrometers wavelength range, specifically addressing linear and nonlinear optical properties of InGaAs/InP multiple-quantum well structures grown by Chemical Beam Epitaxy, along with their role in applications such as modulators and optical switches.

A theoretical model is presented to describe the spectral and modulation characteristics of tunable DBR lasers with two active and two passive sections, by taking into account the actual frequency dependence of the Bragg reflector, the nonlinear gain compression effect, the possibility of laser operation away from gain maximum, and the distribution of the spontaneous emission along the laser cavity. General expressions are derived for the intensity and frequency modulation response, frequency noise spectrum, spectral linewidth, effective linewidth enhancement factor, and spontaneous emission rate. The dependence of the linewidth and of the FM efficiency on the nonuniform injection currents to the active sections and on the tuning currents to the passive sections is particularly investigated.

The electroluminescent properties of various porous silicon pn junction devices have been investigated. Devices were fabricated by constant current anodization method as well as a novel method developed for anodizing heavily doped pn junctions. The constant current anodized devices show electroluminescence only under reverse bias condition. The light emission mechanism in these devices is believed to be similar to the hot electron relaxation mechanism observed in a surface-treated crystalline silicon pn junction diode at breakdown. The pn junctions fabricated by the novel anodization technique show electroluminescence under forward bias condition. The light emission mechanism in these devices is believed to be due to electron-hole injection in the silicon quantum wires.

The problem of optical wave propagation in dielectric waveguide structures with large refractive-index discontinuities and abrupt transitions that give rise to backreflections of the propagating wave is addressed. A set of `transmission-line equations' for the dominant transverse components of electric and magnetic fields in a semivectoral approximation is derived. The wave propagation is described by eigenmode expansion into both forward and backward waves in longitudinally discretized uniform sections using mode matching between the sections. Although the theory is valid for a general class of 3D structures (i.e., channel waveguides), the computer code for numerical calculations presented here was written for 2D (planar) structures only. Examples of wave propagation and reflection from waveguide discontinuities are given, and some problems evoked by the application of a reduced set of eigenmodes for the calculation are briefly discussed.

A numerical model of bulk electroabsorption modulators has been developed. It consists of a quasi-2D representation based on a drift-diffusion approach and includes the presence of heterostructures and Fermi statistics for the carriers. The non-linear behavior of this type of device, essentially related to the pile-up and the space-charge effects, has been analyzed. Simulations results have been compared with laboratory measurements on a fabricated device that presents an abrupt heterojunction, obtaining a good agreement. Two other types of structures have been simulated, one obtained with the inclusion of a thin quaternary layer and the other with a graded heterojunction, which eliminate the hole pile-up at the InGaAsP-InP heterointerface. The paper demonstrates that it is possible to approach the optimum behavior of the modulator using both the alternatives considered here. Finally, non linear effects in short modulators has been investigated.

A 3D waveguide simulation technique is presented. The technique combines the finite- difference-time-domain (FDTD) and mode-propagation-by-Fourier-expansion (MPFE) methods for guided-wave device simulation. The algorithm consists of dividing the device into a series of small sections in which the FDTD method is employed to simulate for very complete wave characteristics. In particular, the wave characteristics around abrupt junctions of the device are simulated comprehensively by this algorithm. At the end of each section, the MPFE method is applied to simulate for optical modes and their profiles. These modes and profiles are used to extract mode parameters from the FDTD results for individual mode analysis. The modes and extracted parameters are further served as inputs to the next section for continued FDTD simulation. Thus, one can simulate arbitrarily shaped and optically large devices for very complete wave characteristics by using these two methods iteratively. The technique, together with well established semiconductor process and device simulators, presents a well-rounded methodology for semiconductor integrated-optic device simulation. This simulation methodology is illustrated by simulation and analysis of a variety of silicon based electro-optic modulators and branching waveguide structures.

We have added to our very general, user friendly simulator for integrated optical circuits the capability to analyze structures made with semiconductor materials whose characteristics are controlled with current injection. The simulator is interfaced with the optical layout generator SIGRAPH^TM-Optik (by Siemens-Nixdorf) and it is based on a finite difference BPM with transparent boundary conditions. Some examples of applications are presented; they show the agreement with the results reported in the literature and the potentiality of the simulator.

In this work the modeling of multifrequency acoustooptic interaction in guiding structure is presented. This model, based on a generalized coupled mode theory, allows us to evaluate the Bragg diffraction efficiency when a multifrequency signal is applied to the interdigited transducer. The dependence of diffraction efficiency of the output orders and of the intermodulation factors among the same orders on both the applied voltage amplitudes and transducer driving radiofrequencies has been extensively investigated. Planar waveguide structures on lithium niobate have been considered under monomodal propagation condition.

After the arm width of an asymmetric Mach-Zehnder interferometer is used to adjust the phase delay at the end, a three-wavelength demultiplexer can be made by cascading two such interferometers. Three wavelengths, 0.98 micrometers , 1.31 micrometers , and 1.55 micrometers are taken as an example. The device is about 1.5 cm long and demonstrated high extinction ratios for all three wavelengths by BPM simulations.

The soliton emission phenomenon can be exploited to design ultrafast switches to be used in all-optical processing systems. When very high speed switching is required and unless high optical power is used, there are needed switching devices very short in length. The propagation characteristics of the soliton emission from a nonlinear interface is simulated using the Beam Propagation Method. The effects of the interaction between two solitons emitted from two different nonlinear interfaces and propagating in a common nonlinear substrate are examined. Based on these principles, new all-optical switching elements can be designed, which exhibit many important advantages on the classical electro-optical devices.

Integrated optical elements with gyrotropic magnetooptic materials are of large interest for the realization of optical isolators and circulators in integrated optical devices. We present a finite- difference scheme for the calculation of nonreciprocal effects in such structures. The method is applied to the numerical simulation of nonreciprocal couplers. These devices are based on the direction dependent coupling of modes between two neighboring magnetooptic waveguides. From the calculated results some guidelines for the optimization of such couplers are derived.

Lithium Niobate is a material almost transparent in the visible and in the near IR range with a fairly high thermo-optical coefficient (5.3 X 10^-5 degree(s)C^-1). Relaying on the above properties, we have designed dielectric multistrate mirrors with supergaussian reflectivity profile whose parameters can be easily varied through the control of the border temperature. In fact, if one of the dielectric layers (active layer) is made up by a thermo-optical material, keeping the border temperature of the mirror above the environmental one, a temperature gradient is created along the radius. This gradient induces a refractive index modulation in the active layer which, in turn, give rise to a tapering of the reflection coefficient. This tapering fits very well a supergaussian profile.

Merged ELO (MELO) technology, which is an extension of Selective Epitaxial Growth and Epitaxial Lateral Overgrowth (ELO), was used to develop the c-Si Fabry-Perot cavity fabrication which is compatible with the well developed conventional integrated circuit fabrication techniques. Increased finesse of the Fabry-Perot cavity was accomplished with multi-dielectric layers as high reflection mirrors. Polycrystalline silicon produced from amorphous Si (a-Si) and SiO₂ were then chosen as the high and low index dielectric materials so that fewer number of dielectric pairs are needed to obtain a high reflectance. An optical intensity modulator using MELO technique, was fabricated and evaluated. The maximum modulation depth was measured to be 40% under an injection current density of 16 A/cm². The current density can be made at even lower if the finesse (calculated to be 19.26) of the cavity is further increased. The measured value was 6.8 but if measured with Fourier transform IR spectrometers or by using laser as the lightsource, it could be larger.

We present a novel optical guided-wave resonator configuration which is based on a single ring and three directional couplers. It has a free spectral range double that of a conventional double-coupler ring resonator (DCRR) with same curvature radius. Moreover, it features higher transmission at resonance and better extinction ratio than a DCRR with same values of waveguide propagation loss and finesse. Transmission characteristics and optimum design parameters are presented. A close comparison with an equivalent DCRR is carried out in terms of transmission at resonance and extinction ratio.

In the conventional waveguiding concept the coupling distance between two waveguides is limited in order to ensure a sufficient overlap of the evanescent tails of the modal field profiles. The Anti-Resonant Reflecting Optical Waveguide (ARROW) scheme provides modal fields exhibiting an oscillating nature in the coupling region too, thus allowing for remote coupling. The design of low-loss and loss-free rib ARROW couplers is demonstrated. In order to give precise predictions of the coupling length, the computation of the propagation constants demands full vectorial numerical methods for solving the wave equation. In a SiO_xN_1-x configuration the coupling over a spacing distance up to 93 micrometers between two rib ARROW's has been demonstrated experimentally. Experimental and theoretical results are compared and discussed.

Light coupling to planar lightwave circuits by means of directional coupling between D-fiber and buried rectangular waveguide is indicated as a viable mean of reducing alignment tolerances in the fiber-pigtailing procedure for integrated optical devices. The geometry involved is that of a circular fiber core vertically coupled to a rectangular buried waveguide. An accurate analysis by a vectorial formulation of the finite element method is presented of such a coupling geometry in collinear configuration. The structure is analyzed for symmetric and antisymmetric cladding configurations. The power coupling efficiency is investigated in terms of waveguide dimensions and refractive index steps.

In the report, we explain how the quasi-velocity-matched electrooptic (EO) modulator using domain inversion can generate extreme wide sideband. The quasi-matching between the phase velocity of microwave and the group velocity of light was established by using periodic domain inversion of an EO crystal LiTaO₃ at a frequency of 9.35 GHz. Long effective interaction length was also obtained at such a high modulation frequency. As a result, we obtained modulation index 22.5 rad and extended the sidebands up to 420 GHz.

In order to obtain an N X N Multistage Interconnection Network capable of passing all the N supplementary stages must be added to the standard ones. In this paper we prove that the completeness property of such networks is preserved even if some switching element suffers from a stuck-at fault. The critical stage is the central one which must be set in a fixed configuration, depending on the desired permutation. This problem is easily overcome if one additional stage is included. Moreover, the static full access capability is preserved in a complete network because of the redundancy of source to destination paths.

Index profiles of Ti:LiNbO₃ waveguides can efficiently be reconstructed by measuring the near-field patterns for different waveguide widths. By this, bending losses of curved waveguides can accurately be predicted. The validity of this method is verified by comparing calculated bending losses with those measured for fabricated semicircular waveguides of different bending radii.

In this paper we present the theoretical study and design of a GaAs-based guided-wave grating device for uniform out-coupling of optical power, to be detected on an external 2D plane. The model of diffraction is based on the exact solution of the relevant boundary-value problem. The device is formed by a number of cascaded gratings, each of them having different geometric characteristics. Simulations have been carried out at different values of grating thickness and number of cascaded gratings, in order to obtain the best performance in terms of diffraction efficiency and device transmissivity. Uniform distribution of the out-coupled power on a 2D region has been achieved by varying the groove depth of each cascaded gratings. This device can be successfully used to obtain uniform illumination of coupled-charge-devices in optical computing and signal processing applications, such as image restoring in synthetic aperture radar systems, spectral analysis, matrical multiplication, and so on.

In this paper we present the design approach and measurements of an optical receiver suited for IM-DD systems operating up to 2.5 Gbit/s bit-rate. The receiver is composed by a Ga-As MMIC transimpedance amplifier and a commercially available pin photodiode. The MMIC amplifier has been fabricated and it has been measured on wafer, showing a -3 dB cut- off frequency of 2.6 GHz, stability and low sensitivity to bias variations.

A systematic study of the optical parameters and electrooptical coefficient r₃₃ of optical waveguides fabricated by proton exchanged in LiTaO₃ substrates has been carried out. Results of direct measurements of the electrooptical coefficient r₃₃ on both as fabricated and annealed planar waveguides are presented. The samples have been annealed in the 265 - 420 degree(s)C range at different cooling rate. It has been found that quick (20 degree(s)C/min) cooling rate leads to different values of refractive index change and r₃₃ coefficient in the exchanged layers than the slow one (1 - 2 degree(s)C/min).

A simple fabrication process for multilayer antiresonant reflecting optical waveguides based entirely on the sol-gel process is presented. Solutions of methyltrimethoxysilane are used to fabricate layers with thicknesses in the range 1 - 20 micrometers , necessary for the core and second cladding. An experimental model has been developed to describe both the process time and the final film thickness with respect to the process parameters. Titanium(iv)propoxide is used to derive the high index layer of the device, all films being deposited via the spin casting technique. Simulation has shown that both the fabrication tolerances and the transmission loss can be controlled via the refractive index of this first cladding layer. Dyes have been successfully incorporated into the porous core material and we have identified possible applications in optical chemical sensing.

The possibility of recording second-order nonlinear susceptibility in commercial and specially synthesized lead-silicate glasses was investigated. Effective photoinduced SHG in glasses with lead content from 10 to 40 mol% was found. Optical waveguides by ion-exchange were made in these glasses. Optimal content of Na₂O in lead-silicate glasses for optical waveguides was found.

Indium tin oxide (ITO) films have been deposited onto glass substrates by rf magnetron sputtering without in-situ substrate heating. The as-deposited films have an electrical resistivity of approximately 5 X 10^-4 (Omega) -cm, visible transmittance of about 85%, and IR reflectance of above 80% at 5 micrometers . The effect of sputtering parameters on the deposition rate and the electrical and optical properties of ITO films are investigated. Loss of transmittance or blackening for ITO films prepared at high sputtering power are observed and explored.

The influence of ion exchange processing on spectral-luminescence properties of surface layers was investigated for neodimium doped silicate and phosphate glasses. It was found that ion exchange resulted in 10 - 15% decrease of luminescence life-time T. The annealing of samples produced increase of T up to values corresponding to substrate glass. These effects has been explained by simultaneous action of two mechanisms--luminescence quenching in surface layer by O-H groups and variation of radiative probabilities for neodymium ions as a result of mechanical diffusion stresses which range up to 1 GPa.

A method to determine the lattice parameters of proton-exchanged (PE) lithium tantalate solid solutions by examining the PE processes on rotated (Okl)LiTa03 cuts is proposed. It has been shown that, depending on exchange and annealing conditions and crystal cuts, the five phases a-, ~-, 7-, o- and ~-HxLi1-xTaQ3 can exist in single crystal H:LiTa03 layers. The relationships between the lattice parameters and the index change in a-, ~-, ~- and o - unstrained HxLi1-xTaQ3 solid solutions has been experimentally determined. The regularities of proton exchange in lithium tantalate crystals under different exchange and annealing conditions are studied and various specific features are explained.

Optical waveguides in lithium tantalate crystals prepared by nonisovalent ion exchange have been characterized. We found that the waveguides can be formed by ion exchange reactions Me²⁺ yields 2Li⁺ (Me: Ni, Mn, Fe, Co) in the salt melts at the temperatures below the Curie point of lithium tantalate. The fabrication and properties of optical waveguides formed in LiTaO₃ by simultaneous processing of nonisovalent and proton exchange have been also described. A surface increase of the refractive index up to 0.14 was observed for the extraordinary polarization and up to 0.11 for the ordinary polarization. The birefringence and index change of such waveguides can be controlled by varying the melt concentrations. The dynamics of the process is discussed. Rare-earth doping of LiTaO₃ by ion exchange reactions Er³⁺ yields 3Li⁺ and Nd³⁺ yields 3Li⁺ have been obtain at the temperature below the Curie point.

A scheme of an all-optical adder realized in a nonlinear planar waveguide is presented. The scheme is based on soliton's interaction properties.

An evanescent field integrated optics amplifier for 1,07-1,34 μm spectral band have been proposed and demonstrated. The amplifier is a silicon oxide thin - film waveguide on an laser active LiF:F2- color center crystalline substrate. The measured gain was - 1 OdB for the mode propagating length 2 cm. Solid state integrated optics lasers and amplifiers, whose rapid development was inspired by successes in waveguide lasers and amplifiers, have several important features that can make them preferable in various applications. The possibility to incorporate these components into integrated optics circuits, developed technology for crystal growth and processing, simple pumping schemes (including by laser diodes), flexibility in using different active ions to achieve the desired goals make them attractive for many . researches. Currently these lasers/amplifiers are usually made by in-diffusion of active ions into crystalline materials and glasses, as well as by ion implantation and epitaxial growth 1. We propose a rather new concept of integrated optics amplifier, which employs a passive waveguide on a substrate of active material. When light propagates through the waveguide, part of it propagates in the substrate as an evanescent field. The portion is defined by the waveguide parameters, the wavelength and the mode index. Using a standard pumping scheme one can amplify the portion that propagates in the active substrate and, therefore, the entire mode. The advantage of this amplifier is relatively simple planar fabrication technology and the possibility to utilize various pumping sources and schemes.

Langmuir films are 2D ordered arrays of amphiphilic molecules that form at an air water interface and can be transferred to a variety of surfaces to give Langmuir-Blodgett (LB) films. LB films are promising materials for building organized structures for molecular electronics and integrated optics. Many non-centrosymmetric LB films, including polymer films, show nonlinear properties (SHG, parametric amplification, electrooptic effect). For use as non- linear materials, LB films usually need to be more than 100 bilayers thick, i.e. > ca 0.4 micrometers . We have investigated the attenuation of light in such films. As the films become thicker surface and bulk inhomogeneities may cause an increase in the attenuation. We have investigated polymeric films samples of various thicknesses, both prepared by LB method and by spin coating, by SEM, Talystep, ellipsometry and we make some theoretical estimation about the influence of these factors on the attenuation of the films.

This paper reports on the operation of lithium niobate electro-optic waveguide modulators at temperatures down to 15 degree(s)K. Commercial and laboratory fiber pigtailed devices have successfully been cooled without any increases in insertion loss from temperature induced stresses in device packaging. Three x-cut devices exhibited a linear increase in V_pi voltage of 8% +/- 1% when cooled from room temperature to approximately 20 degree(s)K. The broadband frequency response improved at lower temperatures. A velocity-matched experimental modulator has shown increased bandwidth when cooled to liquid nitrogen temperature.