Integrated-optic devices in LiNbO3 are reviewed with emphasis on fabrication technologies (titanium indiffusion, proton exchange) including the critical areas of outdiffusion, fabrication tolerances, and stability, further on fibre coupling, packaging and on the application of these devices in the field of optical communications.

A novel interferometric technique for measurements of optical phase changes in channel waveguides is described. It is based on a simultaneous excitation of two neighbouring channel waveguides with adjustable intensity ratio. Phase changes are deduced from the shift of an interference pattern formed by the superposition of the two collimated output beams. This technique has been applied to measurements of lightinduced refractive index changes (photorefractive effect) in LiNbO3 optical channel waveguides. Systematic investigations on LiNbO3:Ti waveguides show that both the magnitude and the time constant of lightinduced index changes depend characteristically on guided wave power. Light-induced waveguide losses become significant only, when the guided-wave power leads to waveguide cut off. The light-induced processes of index changes can be reduced considerably after the Ti-indiffusion by simple thermal treatments. In channel waveguides, produced by proton exchange (PE) followed by an annealing process, light-induced index changes are smaller, but develope faster than in Ti indiffused waveguides, thus indicating an increased photoconductivity inside the proton exchanged material. At A=B3O nm photorefractive effects are reduced by about one order of magnitude compared to ?=633 nm.

Practical applications of integrated electo-optic devices such as modulators and switches require an optimum design of the optical waveguide and electrode configuration. Due to the anisotropy of LiNbO3 not only the amplitude, phase and frequency of the propagated optical wave, but also its polarization has to be taken into account for an accurate prediction of the device performance. Starting with the physical and geometrical device configuration, a 3-dimensional refractive index profile of the entire device structure can be derived from a technologic data set or from refractive index measurements. In order to reduce the CPU-time consumption of the propagated lightwave simulation (BPM), the 3D-profile is usually reduced to two dimensions by effective index calculations. Electro-optic index changes, caused by applying switching or modulation voltages to the device electrodes, are calculated including dielectric buffer layers. This is achieved by computing the overlap between the electrical and the optical field, which is obtained from the effective index method. The numerical simulation of a propagating lightwave through an electro-optic device on anisotropic substrate requires the solution of the wave equations. BPM-simulations include calculations of axial variations of the index distribution as well as absorption and radiation losses. Taking into account the behaviour of anisotropic substrates, BPM-simulations of polarization splitters and polarization independent devices allow access to a wide area of practical interesting applications. Various examples of BPM-simulations of complex electro-optic devices will be presented together with CADtechniques utilizing a VLSI-editor adapted to integrated optic devices.

An exact statement about single Ti:LiNbO3 waveguide phase-modulators made on Z-cut and X-cut substrates is reported. The optimal placement of the electrodes with respect to the optical channel waveguide is discussed. The optical analysis of channel inhomogeneous anisotropic waveguide is carried-out by the effective refractive index method together with the transformation matrix approach. At the microwaves the analysis is done by conformal mapping and multiple images methods. The results are given in a graphical form.

High-speed electro-optic modulators and switches have important applications in external modulator systems and high-speed instrumentation. Phase-linear switching at high frequencies is accomplished by using balanced bridge interferometric switches with electro-optic tunable X-couplers. The devices are fabricated by titanium indiffusion into X-cut Y-propagating LiNbO3. For high-speed operation, traveling-wave electrodes of aluminium and gold are realized and investigated. Devices with a 3-dB bandwidth of 6.5 GHz using coplanar traveling-wave electrodes with a switching voltage of 7.0 V, an overall insertion loss of 4 dB and -35 dB extinction ratio are realized for ) = I .3 pm. The relations to determine the theoretical maximum 3-dB bandwidth of traveling-wave modulators rely on infinitely thin electrodes and the quasi-TEM approximation, which is not the case in practice. The influence of finite electrode thickness on the frequency response will be discussed. LiNbO3 devices show dc drift effects when applying dc voltages resulting in a temporal change of the output power of optical modulators and switches. Improvements in dc drift stability due to electrodes and buffer layers of indium-tin-oxide are reported. The performance of a new high-speed wavelength selective switch based on two-mode interference will be presented.

We discuss the design, fabrication, and evaluation of high speed integrated optical devices for application to photonics insirumentation systems. Specifically, we have demonstrated integrated optical devices with bandwidths in excess of 25GHz and implemented these devices in single-shot, streak camera based recording schemes.

Virgin and protOn-exchanged LiNbO3 planar waveguldes are investigated by different spectroscopic methods: ir absorption, Raman scattering and luminescence. Absorption spectra in the region of OH-vibrations are used to study the relationship between the refractive index profile and hydrogen content in the exchanged waveguides. An attempt to support the model suggested on the base of ir data is made by waveguide Raman techniques. In some pure and proton-exchanged samples strong luminescence bands in the region 600-650 nm are observed which make difficult the detection of the Raman signals. The appearance of the luminescence features could be connected with the presence of free lithium metal in the crystal lattice. The increased amount of defects in the wavegulde layers (Initially intrinsic Impurities and extrinsic ones produced by the proton-exchanged process) causes disorder effects in the crystal lattice. The disordered state is eflected in the Raman spectrum of the Internal vibrations of LiNbO3 which can be observed In the spectral region with frequency less than 900 cm1.The observed spectrum consists of narrow "crystalline" lines superimposed on a background resembling to phonon density of states, The crystalline component is induced probably by the penetration of guided light in the crystal substrate while the broad band background is characteristic for the "quasi-lattice" of the wavegulde layer.

In the paper a Y-cut Ti--diffused lithium niobate planar waveulde is considered. The field propagates in the direction inclined to the optic axis, so instead of pure TE or TM modes hybrid modes occur. As TE-like modes leak into the substrate we deal with TM-like hybrid modes only. By using WKB method we obtain approximate formulae expressing fields both inside the waveguide and in the substrate. We calculate coefficients of coupling between modes of perturbed and unperturbed area. We analyze transmission characteristic of such modulator and discuss effects playing significant role in device effaciericy.

The reduced directional coupler (RDC) consisted of two titanium diffused lithium niobiate parallel stripe waveguides with a split electrodes configuration and two external X-half fiber couplers is analyzed and compared with devices based on classical directional couplers.

In this paper we introduce the use of normalized parameters to study an electrooptically active Y-Junction, by means of a five-layer model and the step approximation method. In a similar way as it is done for three-layer and four-layer waveguides, we find a set of dimensionless parameters for five-layer waveguides that allows the description of their waveguiding features.

Ultrashort electrical pulses have been generated in LITaO3 and LINbO3 by optical rectification using 50 fs - optical pulses. The propagation of these ultrashort electrical pulses has been studied. Strong damping due to lattice absorption is observed above 2 TH z in LITaO3, which ranges even below 2 TH z in L1NbO3.

In far IR range the reflection and transparency characteristics o semiconductors are determined. by tree carriers plasma, its dielectric permittivity being determined. by pulse relaxation time c. The parameter depends on external electromagnetic flelcls,that allows to control the reflection radiation parameters. It's important,that this method permits one to obtain high mod.ulat ion frequency ( 1 Hz ). Optical coating of semiconductor surface allows to extend essentially the possibilities of such control, e.g. to increase the modulation depth. In this paper conditions o1 the absence o reflection 1or the given T are derived.

The construction and applications of a system for measuring optical birefringence are described. As the system utilizes a photo-elastic modulator for the modulation of incident linearly polarized light, measured data includes not only high resolu- tion of birefringence retardation but also a direction of fast axis of retardation which corresponds to the direction of molecular orientation. The resolution of measured birefringence of this system is i08. As this system is designed for the study of the three-dimensional anisotropic properties and molecular orientation of glass, polymer films and ultra thin organic films such as Langmuir-Brodgett films, some of its applications are discussed.

A nondestructive analysis method for observing the dynamic operation of integrated circuits is described. The operating principle in reflective mode bases on voltage tunable birefringence in homeotropically aligned nematic liquid crystals with negative dielectric anisotropy. The basic principles of the static and dynamic deformation are discussed and theoretical and experimental results treating the voltage and frequency response are presented. A typical application example of a CMOS IC analysis shows the employment of nematic liquid crystals for failure analysis.

The growth of rare earth iron garnet single crystals and epilayers for magneto-optical 45° isolator application is described.

Bi-substitued garnet films with large Faraday rotation and saturation magnetization, low microwave losses and planar anisotropy for a low in-plane saturation field requirement in integrated optics have been investigated. For such a purpose three material composition sets with increasing Bi contents have been grown from L.P.E. on (111)- and (110)- oriented GGG substrates and their magnetic properties analyzed before and after heat treatment under different annealing temperature. Well defined quenching temperatures can be adjusted to obtain either perpendicular or in-plane easy axis or intermediate structure useful for magnetooptical waveguide devices with optimized Faraday or Cotton-Mouton geometry.

Films of pure and (Bi,Al) substituted yttrium iron garnet were grown by liquid phase epitaxy on [110] oriented gadolinium gallium garnet substrates. They will be characterized by a parallel and a perpendicular anisotropy, Lc11 and , according to the direction of the electric field in the film plane and perpendicular to it. Both anisotropies are partly stress induced, due to the mismatch of lattice constants between film and substrate, and partly growth induced. It is mainly the growth induced contribution which can be influenced by annealing. For both groups of garnet films investigated the absolute values of the growth induced contributions to the anisotropies increase with the growth rate. The strongest increase of about 2.5 . 10_2 (im/min)1 has been observed for the perpendicular anisotropy of the (Bi,Al)-YIG films. The crystals were annealed in reducing and oxidizing atmospheres at different temperatures. Annealing in oxygen above 1000° C causes a strong reduction of the growth induced anisotropy and makes the total anisotropy approach the stress induced value. Furthermore, it is shown that phase matching can be achieved by annealing and by choosing a proper direction of mode propagation in the film plane. Nearly 100% TE - TM mode conversion is obtained in agreement with calculations.

Films of yttrium iron garnet, grown by liquid phase epitaxy on [111] oriented gadolinium gallium garnet substrates, are implanted by argon ions at energies of 2.8 and 3.4 MeV and at doses varying from 1012 to 1014 cm2 At these implantation energies the penetration depths of the ions lie at 1 .0 and 1 .4 m, respectively. The implantation induces an increase of the effective mode indices ranging up to 1.7 . 10_2. These changes are equal for TE and TM modes; therefore the induced index variation is isotropic. The refractive index is considered to consist of the original step index superimposed by a Gaussian proffle in order to determine its spatial variation. For this composite proffle the differential equations for TE and TM modes are solved numerically yielding the effective indices of these modes. The height, width and location of the Gaussian profile are then fitted to the experimental values. The location of the maximum of the Gaussian profile agrees well with the penetration depth of the ions. The width of the induced profile is about 1um. The determined profile is verified by removing the garnet film in small steps using a polishing process. On the other hand, the optical damping is increased considerably by ion implantation. However, most of the additional damping can be removed by proper annealing technique without destroying the implantation induced profile of the refractive index.

The eff ect of the Prnesodyrniurn on the growth induced anisotropy has been investigated in garnet films of GdlG : Bi Pr Lu Al : b.KuQ./ YPr = -125. 1o...:· er·I cm·-;'. Dlff erent garnet films have tieen studied f or the st atic tape inspection application V·le have 1jeterrninee! that qual iti f actor Q < 1 are required to obtain good resoluti ons of transf erred domain pattern recorded at short vv·avelengths.

The capabilities of the laser-polarimetric version of Gorter's paramagnetic relaxation technique are considered. The developed method is shDwn to reveal high sensitivity and to enable the study of a number of energy and structural properties of paramagnetic solids unachievable for any other spectroscopic technique.

Recent developments of magneto-optic devices for communications, sensing and data storage are reviewed. Single crystal garnets and sputtered films remain the basic material for nonreciprocal isolators, modulators and field sensors. For waveguide devices the accurate coupling theory for hybrid modes in anisotropic waveguides and the technology of integration into semiconductor chips has to be developed. New concepts which ease the condition for phasematch are emphasized. Magneto-optical recorders are already in use. Improvements involve materials technology of metal alloys with respect to sensitivity, stability, erasure and recording density.

A novel unidirectional mode converter, which has the advantage of a simple magnetization structure, is proposed for an application to a waveguide-type optical isolator. The proposed mode converter is constructed with in-plane magnetization in the whole device, where the magnetization component along a light propagation direction produces a mode conversion between TE0 and TM0 modes, while the magnetization perpendicular to the propagation direction provides a nonreciprocal phase shift to the TM0 mode. The unidirectional mode converter, in which, in the backward direction, 100% TE-TM mode conversion is produced but, in the forward direction, an input TE mode emerges as a TE mode, is realizable by virtue of the nonreciprocal phase shift of the TM0 mode. Design examples are shown by using the (LuBi)3Fe5O12 guiding layer / (YBi)3Fe5O12 cladding layer / Gd3Ga5O12 substrate structure. A typical length of the mode converter is 15.5 mm at the wavelength of 1.152 .tm for the guiding layer thickness of O.575jim and with the magnetization direction tilted by 87 degree from the light propagation direction in the film plane. A relatively large device length is reduced by using a magnetooptic material having a large first-order magnetooptic coefficient.

Today the technical equipment of many optical communication systems is particularly designed to enable extremly high data transmission rates. Unfortunately, the achievable data rates of fiber networks are strongly limited by fluctuating perturbations of the usually used semiconductor laser diode. In practice, these sensitive transmitters must operate with a high degree of spectral stability to avoid degradation of system performance by wavelength fluctuations, modal noise, and insufficient modulation characteristics. In fiber networks the undesired perturbations are caused by light reflected or scattered in the optical system back to the laser diode. To avoid this disadvantageous feedback, the application of an optical isolator is necessary.

Optical nonreciprocal devices, i.e. isolators and circulators, are some of the most important elements in future fiber transmission systems. Today optical communication is realized with extremely high data rates up to some Gbit/s. Therefore a stabilized transmitter is required, in our case a semiconductor laser diode with a linewidth below some hundred kHz. Especially in coherent optical systems the laser has to be protected from undesired reflections caused by splices, couplers or other perturbations. This is the task of an optical isolator. On the other hand an optical circulator will open new aspects in future optical fiber communication, e.g. two way communication or for the application in OTDR's.

Optical waveguide isolators are required in advanced fiber communication systems. The simplest type is the 45°-waveguide-isolator based on magnetooptic channel waveguides. The problem of phase mismatch can be solved simply by choosing a proper angle of preferably 22.5° between the input polarization and the direction of the TE polarization of the waveguide. Mode coupling in this configuration is analysed using "coupling tracks" on the Poincar sphere. First experiments demonstrate that more than 30dB isolation is feasible in practical devices. From these results, design rules for 45°waveguide isolators are obtained.

Magneto-optical garnet materials such as YIG, undoped as well as substituted, exhibit a large Faraday rotation. This fact makes them potentially suitable as sensing elements in fibre optic magnetic field sensor systems. We describe both an intensity based multimode system using bulk materials and a singlemode polarization based system using waveguiding films. A number of different material compositions, such as undoped YIG, (GdGa)- and different Bisubstituted YIG have been used for the sensor elements. Measurement results are presented and discussed. A detection limit in the xT range and a measurement range exceeding 10 have been achieved.

A list of requircments on magnetic films suitable for magneto-optic recording is deduced from a series of test-recorder expeliments with rare-earth transition-metal based disks concerning the write process and the domain stability in dependence on the laser power and the external magnetic field. The most important features are: perpendicular magnetic anisotropy, steep coercivity Hem, medium saturation magneüzation, and a fine microstructwe. The prospects of polycrystalline garnet films to meet these requirements are then discussed with emphasis on how the relevant magneticproperties and the microstructure canbe influenced by the chemical composition and the preparationprocess (pyrolysis and if-sputtering).

In this paper we give an overview of the magnetic and magneto-optical properties of Co/Pt and, to a less extent, Co/Pd multilayers as optimized for magneto-optical storage applications. The Co layers should be very thin, i.e. about 4 A , and the Pt layers about 10-20 A to achieve a 100 % remanent layer with perpendicular magnetic anisotropy and high coercivity (80-100 kA/m). Furthermore, the hysteresis loop becomes rectangular for total film thicknesses below about 20 nm. We measured the optical properties as a function of the wavelength of the light and calculated the figure of merit at three wavelengths (820, 633 and 410 nm) for various disk structures. Optimal figures of merit are obtained for film thicknesses below 20 nm, i.e. thicknesses that are optimum for the magnetic properties. The figure of merit at A. = 820 am for Co/Pt is comparable to that of GdTbFe and increases towards shorter wavelengths which favor higher-density recording. We discuss the recording performance using Lorentz images of the written domain patterns. Very regularly shaped domains can be written at normal writing conditions, i.e. at a laser power of 5-10 mW and fields of 25 kA/m. The highest carrier-to-noise ratio measured for Co/Pt is 51 dB (375 kHz carrier, 1.4 m/s, 10 kHz bandwidth). Aging experiments in dry oxygen-nitrogen atmosphere showed that Co/Pt multilayers are chemically stable up to 1 50 °C . Finally, no change in carrier-to-noise ratio is observed for Co/Pt multilayers with a Curie temperature below 300 °C after 2x104 write/read/erase cycles.

At present the amorphous rare earth-transition metal (RE-TM) films can be considEred, in terms of their properties, the most appropriate media for reversible optical recording of information.1 These films eibit perpendicular magnetic anisotropy within a wide range of compo sitions. Changing the concentration of elements in the films allows to alter both physical and working characteristics of the material, Amorphous state of the films (that is, the absence of polycrystalline ;triicture) allows one to achieve low noise levels in magnetooptical reproduction of signals. In recent years the processes of pulse thermomagnetic recording in RE-TM amorphous films have been intensively studied. 38 However experimental data available in the literature are rather insufficient and often inconsistent. Thus, for example, the dependence of the basic working parameters of magnetooptical carriers (sensitivity,minimum pit size, etc.) on the chemical composition of the magnetic layer is still not clearly understood. Further studies are required to investigate the correlation of pits geometry parameters and pits distortions with magnetic propertices of the carrier as well as with the condi- tions of recording and the subseqent carrier storage. The present paper cliscribes the investigation of the processes of thermomagnetic recording in amorphous TbFe magnetooptical films as WRU ac; the processes of pulse thermal erasure of signals. The results of the experiments on signals degradation during recording media storage at high temperatures ar reported.

In r ec en t year s the amor phous r ar e ear th --t r an si t I on met al ( RE-TM) films have been extensively studied. A combination of structural, mag neti: and magnetooptical properties stimulate their application as media for reversal thermomagnetic recording. Of certain interest ic the investigation of physical properties of the films determining the processes of thermomaçjnetic writing and signal degradation. Investigation of the process of film remagnetiz4ticn is one of the tasks in this direction. It is known that the domain nucleation and th dorain wall moticn appear to be the major mechanisms of remagneti- zation process in thin RE--TM amorphous films'5 It has been shown th&: hcn the external magnetic field value is ncar the coercive force of the film, the magnetic aftereffect is observed, 6)? Since most of th RE-TM films exibit a characteristic feature that the remagnetiza- tion process proceeds due to the domain wall motion from relatively sn311 mourit of nuclei , the magnetic aftereffect was related with a slow domain wall motions The domain wall motion was considered as the thro:tivated process with the temperature dependence of the proba- bility 9 of Arrenius type8)9

The magnetic circular dichroism and optically detected EPR spectra of rareearth ions Er3+, Tm3+, Yb3+ in clusters formed by these ions or by diamagnetic ions Lu3+ or Y are obtained. Thus new paramagnetic states of Er3+,Tm3+ and Yb3' ions in fluorites with nearly tetragonal symmetry of these ions in clusters and coalescence of clusters into grains were established. It is concluded that in the whole range of activator concentrations 0.1-40 mol% the clusters under investigation are similiar in structure to the high symmetry Y6F37 clusters previously observed by X-ray methods in natural mineral of tveitite. The noncentral F ions in clusters are probably responsible for the existence of two-level systems also discovered by our studies in activated fluorites.

This sensor involves the measurement of the amplitude of the Faraday rotation induced by an alternating magnetic field Hm cosQt colinear to the direction of the light beam passing through a thin cell filled with a ferrofluid material (Fe2 Co 04 in dibuthylphtalate or in carbon tetrachiorid) . The peak value of the magnetic field was varied from 0 to 300 gauss, and the frequency f from 10Hz to 40 Khz. Two light beam wavelengths have been tried (1320nm and 1520nm). In AC magnetic fields ( H(t) = Hm cos Qt ) the resultant Faraday rotation is of the form: a(t) = ai cos(Qt+i) a cos(3Qt+3) + a cos(5Qt+45) - . . .etc. We discribe a polarimetric device that gives automaticaly and precisely (0.005°) an angle A of rotation, function of ai , a , a, . . . ,i , Z3 , 'I , ... Accordingly the angle A is only a function of Nm, f, and the ferrofluid cell, then a calibration curve A = f(Hm) can be made. The sensitivity S of this sensor is very high for weak fields (Hm<200 G), obviously depending on the concentration C of the magnetic material (e.g.: C # 5%, A = 1320 nm, S # 180 min/cm.G); a precision of .02 G can be reached. This sensor implements optical polarisaton modulation, thus it is insensible to light beam variations, whether they are due to light source fluctuations, optical misalignment or transmission alteration of some optical component. Furthermore the material is a liquid one, that exhibits no residual birefringence, contrary to most of the solid materials used in usual Faraday modulators. For this reason we think the Fe2 Co 04 ferrofluid material is a good choice for building magnetic fields sensors or polarisation rotators such as those needed in high accuracy polarimetric or ellipsometric devices working on 1320 or 1520nm wavelength. Using ferrofluid materials under longitudinal alternating magnetic field seems more interesting than under the usual dc one [4].

Electro-optic modulators (EOM's) can be used for polarization modulation of light at frequencies up to hundreds of megahertz and are therefore strong candidates for high speed effipsometer systems. The characteristic of this device is the half wave voltage, V ,which is a function of the wavelength of light and the temperature. A description of the particular ADP EOM we are using, and a discussion of the effect of laser linewidth and temperature on the measurement of V,, is presented. For the laser diode wavelength of )t = 830 nm, V, and the extinction ratio are measured at different temperatures.