Recent progresses in flip-chip and monolithic optoelectronic integrated circuits (OEICs) are reviewed. Demonstrations carried out on basic transmit and receive OEICs using both GaAs- and InP-based materials are encouraging and technological challenges are continueing towards the application to future advanced optical systems.

Monolithic integration of a double heterostructure laser butt-coupled to an optical waveguide is demonstrated on GaAs. The flexibility offered by Focused Ion Beam Etching (F.I.B.E.) is used in this work to fabricate Fabry-Perot resonators. The monolithic device exhibits a threshold current of 90 mA in pulsed operation and an optical power output of 7 mW is measured from the waveguide.

The fabrication of integrated ring semiconductor lasers has been simplified by embedding the etched rib waveguide structures in polyimide and overcoating with a gold bonding layer. Structures defined by optical lithography lased successfully, while e-beam defined devices with very narrow rib structures were optically lossy, resulting in increased threshold current and evidence of second quantised state operation.

We have developed a model to study photodetectors monolithically integrated with optical waveguides and we present the feasability of such compact devices. We report the first fabrication of a 7 Ga0.47In0.53 As photoconductor associated with a GaAlAsAiaAs rib waveguide grown on semi-insulating GaAs substrate, which needs only 100μm to detect 90% of the optical signal.

GaAs MESFETs are very promising for the fabrication of the electronic part of long wavelength InP-based optoelectronic integrated circuits. A special growth procedure has been developed for the heteroepitaxial growth of GaAs on InP. This resulted in MESFET performances similar to results obtained on GaAs substrates. A transconductance of 100 mS/mm and a cutt-off frequency of 7 GHz was obtained for 1.5μm gate MESFETs. The monolithic integration of GaAs MESFETs and InP buried waveguides did not influence their performances.

Results of numerical simulation of the spectral evolution, total power build-up and fine-tuning characteristic of a doubly resonant Ti:LiNbO3 integrated optical parametric oscillator are compared to experimental data. A good at least qualitative agreement is observed. Both, theory and experiment show that the development towards single frequency emission and the saturation of the dominant axial eigenmode take a much longer time than the total power build-up of the oscillator emission. The mea-sured output power modulation during pump frequency fine-tuning qualitatively agrees with calculated results.

The use of the largest nonlinear coefficient d33 of LiNbO3 for second harmonic generation (SHG), first demonstrated with a guided wave phase-matched interaction suffering from poor field overlap integrals (1), has been considerably improved by the use of a Cerenkov type configuration : nonlinear polarization having a phase velocity greater than that of light in the waveguide, harmonic radiated into the substrate (2,3). The excellent results obtained by T. Taniuchi and K. Yamamoto (1) demonstrate the interest of second harmonic generation (SHG) in the form of Cerenkov radiation (2) In the first part of this paper, we present a new calculation of the efficiency of this process in step index waveguides. In the second part, the validity of this model is checked by studying second harmonic Cerenkov radiation in planar step index waveguides realized by proton exchange (PE) (5) in LiNbO3. The comparison of computed and measured efficiencies show a good relative agreement for multimode waveguides using the usual value of the non-linear coefficient in the exchanged region.

A four-layer structure is described for characterizing a Langmuir-Blodgett film wave-guide. The waveguide properties of the Langmuir-Blodgett film and of the total structure have been evaluated; in particular, the power percentage travelling in the different layers and the guide losses have been calculated.

The number of advanced coherent optical long haul transmission and subscriber systems is continuously increasing. Generally LiNbO3 devices are employed today in nearly all of these test systems for future network appli-cations. This contribution gives a survey of some more matured integrated optics LiNbO3 devices. Amplitude modulators and phase modulators for external transmitter laser modulation are briefly discussed. As far as standard single mode fibers are used polarization matching devices have to be provided. For this task LiNbO3 devices for polarization control or polarization diversity reception, polarization scrambling, and polarization switching can be employed. In addition an integrated optical 90 ° -hybrid for phase diversity reception in a homodyne system is presented.

A GaAlAs - CSP laser diode has been stabilized to a waveguide ring resonator. Frequency control to three parts in 10¹³ peak-to-peak has been achieved. The simultaneous locking of two such lasers to one resonator has also been demonstrated. The compact laser/resonator module can withstand 60 g RMS vibration over a 2 kHz range and a peak shock level up to at least 3000 g.

We report for the first time on the monolithic integration of a multi/demultiplexer with its 2D confined access waveguides in InGaAsP/InP grown by Low Pressure Chemical Vapor Deposition (LPMOCVD). A channel separation of 26 nm has been achieved close to 1.5 Am wavelength.

We present theoretical and experimental investigations of integrated optical 3x3-couplers on LiNb0,. Since this system hasn't reached much attention as yet, we made extensive numerical calculations on the basis of coupled mode theory and prepared samples with a wide range of design parameters for use at 820 nm wavelength. Results of various optical measurements are compared to theoretical data. Our investigations show that experimental values agree quite well with theoretical calculations. Coupling constants are determined and different interesting applications are examined. Successful use of a 3x3-coupler in a fiber optic Mach Zehnder interferometric sensor with passive signal evaluation is demonstrated.

A wavequide isolator using a 490-wavequide Faraday rotator and two fibre-optic polarizing filters as a polarizer and an analizer are simulated using the anisotropic three-dimensional RPM (beam propagation method). TE-TM-couplinq in a trapezoidal YIG-waveguide including coupling between guided wavequide modes are shown in different propagation planes. Besides the different development of TE-TM-coupling, which can be noticed between 45° to 115° to 45° Faraday rotation, changing of xy-intensity profiles at these points can he seen. The different behaviour of TE- and TM-fields in a fibre-optic polarization filter is calculated and depicted.

The paper deals with the study and numerical simulation of the nonlinear electrical response of a waveguide-type P.I.N. InGaAs photodiode under intense illumination conditions, including the harmonic generation rate calculation. Indeed, significant optical power absorption in a small-sized device (i.e. microwave waveguide-type P.I.N. photodiode) can perturb, by space-charge effects, the electric field which governs the carrier transport, and then induce a nonlinear electrical response. The device depolarization, due to the current flow in the load circuit, also causes a nonlinearity via the internal electric field perturbation. These nonlinearities induce harmonics, and we investigate especially the third-order harmonics creation, which is closely connected to the third-order intermodulation products term in any narrow-band multichannel network.

We present experimental and theoretical results on an optical circuit which includes four intersecting waveguides. Each intersecting waveguide has been modelized using the beam propagation method (BPM). The circuit has been fabricated on InP substrate using double heterostructure GaInAsP/InP rib waveguides. The layers are grown by chloride vapor phase epitaxy and the rib is defined using reactive ion etching. Each intersecting waveguide is a two input-two output device and can he characterized by its transfer 2x2 matrix. The parameters of this matrix have been calculated for various intersecting angles as well as for various lateral confinements, which actually correspond to different etching depths. The calculated and the experimental results are in good agreement. The optical circuit can he used to realize a 1x4 switching matrix. The basic switching element is the total internal reflection (FIR) switch which combines the passive intersecting waveguide and an electrode. The latter activates the switch by carrier injection. The TIR switch has been also modelled using the BPM and important parameters, such as crosstalk, driving current have been derived.

A new model for the calculation of waveguide's facet reflectivity, which is simple, not restricted to a particular waveguide's structure and which can be easily extended to related problems, is presented. The validity of this model, has been confirmed experimentally, with the Fabry-Perot loss-measurement technique, in the case of semiconductor rib waveguides excited by TE and TM waves.

An electro-optical phase modulator is analysed by the Finite Element Method (FEM) taking into account the phase changes due to the linear electro-optical effect and current depletion using full vector optical and semiconductor heterojunction solvers which are run sequentially. Preliminary results are presented and compared with experimental data.

Advances in the area of bistable semiconductor etalons and inhomogeneously pumped laser diodes are reviewed. Results concerning a novel method to fabricate thin AlGaAs etalons that can be thermally stable for 0.5 seconds is presented. The method is based on results from a rigorous numerical model for the temperature rise. Furthermore, results from optical triggering of multisection InGaAsP lasers at 500 MHz repetition rate with less than 1 fJ optical switching energy are reported.

Sets of 2-10 μm wide and 29 mm long rib waveguides have been processed 2" diameter InP/GaInAsP double-heterostructures (DH) grown by Metalorganic Vapor Phase Epitaxy (MOVPE). They exhibit low loss for 1.52 μm propagation : mean value = 0.32 dB/cm for TE and 0.35 dB/cm for TM ; best value = 0.10 dB/cm. The reflection coefficients have been derived from the Fabry-Perot measurement technique. The importance of laser coherence on this method has been determined theoretically and experimentally.

Graded Refractive-index Embedded Core Optical (GRECO) waveguides have been realized in GaAs/GaAlAs by sequential introduction of superlattice periods during OMCVD growth on patterned substrates. This novel technique offers the possibility of synthesising the vertical index profile of the core and provides a built-in index difference for lateral confinement of guided modes. Fully planarized waveguides have been fabricated with propagation losses of 1.5dB/cm at k= 1.52 vim and their field distribution has been analysed using a finite element technique.

Mask generation, etching process and cha-racterization of first-order deep Bragg grating corrugations on InP and InGaAsP compound material is presented. DFB lasers with a side-mode suppression of more than 30 dB were obtained. In addition nine different monolithic grating filters on rib waveguides proved to be valuable for narrow-band wavelength division multiplexing (WDM) applications.

Optical modulators in A1GaAs or GaInAsP are of particular interest since they allow for optoelectronic integration with transistors, semiconductor lasers and photodetectors. Potential applications are, for instance, in space or time division multiplexing for high-speed signal processing in optical communication networks.

We present results showing error-free operation of a novel 4-bit guided-wave analogue-to-digital converter fabricated in GaAs/GaAlAs for the first time. Experimental and modelling results on high-speed operation of the core modulator device indicate the potential for ADC operation beyond lOGHz.

A novel nondestructive technique to measure the intrinsic absorption-loss spectra of TiliNb03- stripe waveguides is demonstrated. The principle of operation is to generate periodic heat waves by light-absorption in a stripe waveguide and to calculate its absorption coefficient from the measured temperature changes in a parallel waveguide resonator. The lowest measured absorption coefficient in the spectral range of 633-730nm was a = 0.002dB/cm at A = 730nm (HE-polarization). A resolution of 10^-4 dB/cm at 700nm and 2.9mW excite power was achieved.

An integrated optical, acoustically tunable wavelength filter, consisting of a combination of TM-TE converter and integrated polarizer in LiNbO3, is demonstrated. The filter bandwidth is 2.8 nm; the center wavelength can be tuned from λ = 1.45 pm to λ = 1.57 pm by adjusting the driving acoustic frequency. Due to the combined acoustical/optical strip guide structure, used in the mode converter, a very low acoustic drive power of only 9 mW is required.

We report the first integration of a GaAs MSM (metal-semiconductor-metal) detector with LiNbO3 and glass optical waveguides. A 250nm thick GaAs detector layer was fabricated using a recently reported lift-off technique [1] and subsequently grafted onto the waveguide chip. Proof of the optical interaction between the waveguide and its grafted detector was provided by the total absorption of 633nm guided light within a distance of 1mm from the leading edge of the GaAs layer and by the presence of a photocurrent at the detector terminals. We project that the grafting technique reported here will prove useful in the design of new and cost effective optoelectronic devices.

Some of the issues surrounding the development of optical technologies for future switched optical networks are discussed. The potential impact of integrated optoelectronic technology in this area is highlighted.

The principle of an integrated optic component providing four optical signals in quadrature is presented. Such an interferometric element has been fabricated by ion-exchange in glass. The effect of various parameters on the quadrature condition have been studied: length of the mixing section, temperature, polarisation. Losses have been characterised. A possible use of this device is illustrated.

Two types of passive integrated optical coupling elements (IOCE) with same functions are proposed and demonstrated on silicon substrate. The elements can be hybridized along with semiconductor laser and coupled to a single intensity modulated optical fiber sensor. The reflective concept of a fiber sensor system is adopted in the designs. The comparison of switching properties of the two devices is made. Preliminary results show that an efficiency (100% back reflected to total signal ratio) of -3.2 dB can be obtained and that back reflected signal intensities lower than 0.34% (-24.7dB) could be observed in on/off-conditions.

The reflectivity measurement of angular polished surfaces of Ti:LiNbO3 waveguides is utilized to determine directly the refractive index profiles of planar and stripe waveguides with an accuracy of dn/n = 10^-4 and a local resolution of < 0.1 μm in depth and < 1 μm in width.

The refractive index profile of single mode integrated optical strip waveguides, fabricated by a field assisted ion exchange process in glass are determined by the refracted near-field technique. Two-dimensional refractive index profiles are directly measured with a precision of Δn = 0.001 and a spatial resolution of 0.8 μm. This technique is nondestructive, and requires minimal sample preparation. Quantitative data of the index profile are obtained, which are the basis for an efficient control of ion exchange processes and a simulation of integrated optical devices. The index profile is scanned automatically yielding the two dimensional index distribution. By the effective index method the depth coordinate of the two-dimensional profile is eliminated and the effective index profile is used for BPM-simulations of devices.

We demonstrated a new type of integrated optical (I0) sensors, viz., output grating couplers on planar waveguides. They respond (1) with submonomolecular sensitivity to the adsorption of molecules out of a gaseous or liquid sample covering the waveguide in the grating region, and (2) to changes in the refractive index of the sample. The working principle of the output grating coupler sensors is reciprocal to that of the input grating coupler sensors demonstrated earlier by our group. The effects (1) and (2) change the effective refractive index N of a guided mode in the coupler region, and to this change aN the sensors respond with a change in direction of the outcoupled beam, which can be sensitively measured with a position-sensitive-detector (PSD). We also devised a method to measure the absolute value N of the effective refractive index in which the outcoupling angles of two counter-propagating modes, coupled into the waveguide from opposite endfaces, are measured with one PSD. In our experiments we used embossed surface relief gratings of 2442 lines/mm on planar about 150 nm thick Si0,-TiO, waveguiding films on glass substrates. The changes in the outcoupling angles of both the TE and TM modes were measured with two PSD's at wavelength A = 632.8 nm. First results are presen?ed on the sensor's response to changes in relative humidity of ambient air, and on its use as a refractometer. We plan to use output grating couplers, with chemo-responsive adlayers on the waveguides as (bio)chemical sensors.

We demonstrated both a novel integrated optical modulator and a microphone. They are based on an input grating coupler on a planar waveguide. Their working principle is as follows: the incoupled power is modulated by varying the width d of the small air gap between an "effective-refractive-index-shifting element E", i.e., a nonabsorbing dielectric plate, and the waveguide in the coupler region. Since d < A, where 1. is the wavelength, the evanescent field of the guided mode penetrates through the air gap into the element E. Because of this interaction, the Ad variations induce changes in the effective refractive index N of the guided mode, and consequently in the incoupling efficiency. Sufficiently high modulations can be achieved with gap width variations Ad of only a few nanometers which, in turn, are effected by external forces, namely by a piezoelectrically generated force in the case of the modulator, and by sound pressure in the case of the microphone. In our experiments, we used thin monomode Si0,-TiO2 waveguides with embossed surface relief gratings of 1200 or 2442 lines/mm. The effettive-refractive-index-shifting element E was a glass plate. Modulation frequencies of up to 480 kHz were reached.

We report the first fabrication and investigation of strongly coupling Bragg reflector gratings in proton exchanged LiNbO₃ stripe waveguides. A filter bandwidth of 2.5 nm centered at 1.504 μm with a transmission drop of -28 dB was achieved for TM polarization in Z-cut material. These grating properties are compared with those of identically fabricated gratings in Ti:LiNbO3 stripe waveguides, where less localized field distributions result in a weaker coupling strength. The Bragg reflector gratings in Ti:LiNbO₃ stripe waveguides were theoretically analyzed using coupled mode theory with numerically (finite element method) calculated field distributions.

A wavelength multi-/demultiplexer for optical wavelength-division-multiplex communication systems has been investigated. A device was designed for 1.30 and 1.55 μm and analyzed by the coupled-mode theory. The wavelength separation of 1.30 and 1.55 μm was successfully demonstrated with a fabricated device.

We discuss the design of Mach-Zehnder waveguide duplexers for 1300 and 1530nm band-centres using InGaAsP/InP strip-loaded waveguides. We show that this device has a high inherent tolerance to fabrication and waveguide parameter variation. Using a novel configuration of concentrically curved waveguides, better than -11.5dB crosstalk has been achieved in both channels. The performance of the constituent waveguide bends and directional couplers will also be discussed.

We report on guided-wave periodic filters fabricated on a semiconductor substrate. The devices, based on an asymmetric Mach-Zehnder interferometer, operate with a channel separation of 19nm in the 1500nm wavelength range. An extinction ratio of 18dB has been measured in a double heterostructure device designed for TE polarized light. Operation with reduced polarization dependence is also demonstrated in a single heterostructure device with extinction ratios of 24.1dB and 22.5dB for TE and TM polarization, respectively.

Though in many applications in optoelectronics light amplitude is the most important parameter for carrying the information flow, in some cases the phase or the polarisation of the guided waves is more relevant (optical sensors, Faraday rotators, coherent telecommunications...). Here we report on a polarisation beam splitter based on a Y-fed directional coupler with propagation along the Z axis of a LiNb03 crystal.

Wavelength demultiplexers, based on the two-mode interference principle, are demonstrated for the first time in the InGaAlAs/InP material system. In this paper theoretical modelling, device fabrication and experimental results are discussed. Wavelength separations between 35 and 100 nm have been achieved in the spectral range of 1.3-1.6 μm with channel isolation as high as 17 dB for unpolarized light.

Integrated optics in LiNbO₃ have been of great interest in recent years, devices such as e. g. modulators and switch matrices have been demonstrated. Most of them have however been polariza-tion dependent, which means that the chips must be excited with light in a specific linear polarization. In common single mode fibers, the state of polarization (SOP) is not constant along the fiber and typically in the end of a long fiber the SOP is varying randomly. One of the reasons for LiNbO3-devices being polarization dependent is that the electrooptic coefficient (r-coefficient) which determines the index change due to the applied electrical field is not equal for the TE- and TM-modes.

DC-stability is one of the most serious problems in Titanium diffused LiNbO3 devices leading to a temporal change of the output power of optical modulators and switches. In this contribution the influence of Indium-Tin-Oxide (ITO) electrodes on the long term (hours) dc stability of Ti:LiNb01 devices is investigated in comparison with metal (aluminium) electrodes directly deposited on the LiNb03. The technology of the ITO-electrodes is described. Interferometric Ti:LiNb03 switches on x-cut substrates have been used as test devices. The drift was characterized by tracing the drive point voltage as a function of time and applied dc bias. Our main result is that the interferometers with aluminium electrodes showed a voltage drift of the operation point of > 10 % over a time period of several hours, whereas the devices with ITO-electrodes only showed a slight initial drift and remained stable afterwords.

The fabrication of a phase modulator using transverse electrodes on a thin z-cut lithium niobate substrate is described. The modulator has an overlap integral of unity, allowing accurate measurement of the electrooptic coefficients and providing a low operating voltage. The device has been tested with both titanium-indiffused and proton-exchanged waveguides and used to estimate the electrooptic coefficients in the guides. The reappearance of the photorefractive effect is also reported in single-mode proton-exchanged waveguides fabricated using a dilute melt and annealing to restore the electrooptic effect.

The performance of LiNb03 waveguide devices, e.g. switches and modulators, is impaired by drift in the output light characteristics when they are subject to temperature changes or DC voltages are applied to the electrodes ^1,2,3,4,5. The latter phenomenon, known as DC drift, arises from free charge carriers present in the crystal, which move in the applied field and change the "effective" electric field experienced by the light. Since the "effective" field will change in time due to charge carrier motion, the light output of the device will be time dependent. The magnitude and time constants of the described behaviour depends on several parameters. Some of them are: the crystal quality and cut, the buffer layer material, the electrode configuration and in general the processing of the chip. As the DC drift will impair the crosstalk of a switch, it is desirable to minimize its magni-tude. Depending on the application, it can also be an advantage to adjust the time constants for the drift to suitable values. All this can be done through careful design and manufacturing of the switch. However, it is difficult to get rid of the DC and temperature drift problems completely that way, and if the application requires extremely low crosstalk values it might be necessary to stabilize the switch with some kind of feed-back control system. A LiNb03 chip that is subject to temperature changes will to some extent alter its characteristics. That is due to electric fields set up through the pyro-electric effect. The described phenomenon will affect the transfer function of a switch, and appear as a temperature drift in the crosstalk characteristic. The parameters that determine the drift magnitude, are related to those of the DC drift. Another important factor is the packaging of the chip, so careful design of the package is required in order to get a small temperature dependence for the packaged switch. The most interesting parameter, when characterizing a LiNb03 switch under various conditions, is the extinction ratio or crosstalk between the output ports. It is shown here how the crosstalk deteriorates due to drift problems (DC and temperature drift), and how to overcome those problems through stabilization by means of feed-back control signals.