A waveguide structure is described. Its propagation losses are evaluated and yield to a world record of 0.2 dB/cm over more than 30 mm propagation length. The study of the active behaviour of the structure exhibits modulation efficiencies close to 4 o /V•mm, about twice as much as in lithium niobate LiNbO 3 , a well known electrooptical material. A figure of merit is thus defined in order to compare modulators based on III-V materials with more «classical» ones

Since III-V material have many applications in the field of optoelectronic components, low loss waveguides and low drive voltage modulators are considered to be key components for many future systems. Up to now, many efforts on material elaboration and technology have led to interesting waveguide characteristics (ref [1], [2], [3]) on ridge structures and on buried ones (ref [4]) with best reported propagation losses on the order of 0.4 dB/cm at 1.55 μm wavelength. Here we report on an improvement of those values (0.18 dB/cm) observed on 30.5 mm long straight waveguides and on the observation of linear and quadratic electrooptic modulation performed with those buried structures.

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.

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.

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.

Traveling-wave Y-fed directional couplers are shown to have a high-frequency bandpass response because of the inherent velocity mismatch between the optical and electrical waves. Furthermore, if their characteristic parameters are suitably chosen, it is possible to achieve an intrinsic resonance by using uniform electrodes. These principles are theoretically investigated and experimentally demonstrated at center frequencies up to 8.5 GHz for titanium indiffused in lithium niobate (Ti:LiNbO3 ) waveguides at 1.3 μm wavelength.

For the time being, Integrated Optics is able to produce a range of devices able of efficiently modulating phase, amplitude and frequency of guided waves in single mode structures implemented at the surface of active materials such as Lithium Niobate. In most of the cases, their basic principle relies on the interference pattern of two guided waves and the classical implementations of such modulators were mainly related to COBRA switch type directional couplers or to MACH ZEHNDER type interferometers. Only very recently a structure combining the coupled waveguides of a COBRA and the Y junction of the MACH ZEHNDER interferometer was designed. This paper is an analysis of the switching characteristics of this Y-fed directional coupler and of its high frequency modulation properties.

Losses as low as 0.4 ± 0.2 dB/cm and electro-optical modulation efficiencies as high as 5°/V/mm have been obtained in single mode waveguides employing a novel buried structure in GaInAsP/InP grown by LPMOCVD and processed by selective chemical etching. Such modulators are potentially excellent candidates for integrated optoelectronics.

Very high speed modulation of guided light has been reported using directional coupler switches (ref. |1, 2|) or Mach-Zehnder interferometers (ref |3, 4, 5, 6|). In some applications base band operation is not necessary and band pass type modulators around a given frequency may be preferred. Such resonance has been predicted in ref |7| where switching diagrams of Y-fed directional couplers have been investigated. A Y-fed coupler as reported in ref |8|, appears to be the combination of a directional coupler switch and of a Y junction through which light is launched. This results in - 3 dB built-in optical bias and makes the device free of any electrical DC drift which is regarded to be a problem in most cases for long term operation. Those considerations lead to consider Y-fed directional couplers as very good candidates for very high speed and band pass operation as it will be discussed in the following.

L'article examine les caracteristiques de modulation d'un coupleur dont la structure combine les guides d'onde couples du coupleur COBRA et la jonction Y de l'interferometre Mach Zehnder

A new technique is analyzed and demonstrated to characterize integrated optical directional couplers. It is based on the locally induced absorption caused by a sliding Mercury drop. This technique works at any wavelength, does not rely on specific material properties, and leads to very fast knowledge of the characteristic parameters of the directional couplers.

Principe de base de la modulation externe en optique integree dans le domaine des hyperfrequences et conception d'un modulateur hyperfrequence