I n contrast to the Japanese approach of setting up centres of

excellence with at tendant research workers from participating companies, the goal with ESPRIT has been to stimulate collaboration between research centres. Despite its modest size of around 135 man years in total (Group A: 71, Group B: 64), ESPRIT 263 has made remarkable progress, and has helped to establish the technology being deployed under the RACE initiative by demonstrating some of the key components required for optical broadband communicat ions networks throughout Europe.

Integrated optoelectronics demands precise control of the semiconductor alloys grown in layers to make lasers, detectors and optical waveguides. ESPRIT 263 has strengthened the key technologies in this area, moving from LPE to MOVPE and MBE for growing InP based compounds on InP substrates. Not only has this resulted in large area wafers of reliable composit ion and reproducible thickness, but losses in waveguides have fallen by a factor of ten.

Group A's work on integrated transmitters has explored the fabrication of laser sources operating at two wavelengths separated by 30nm around 1.55~m. Either direct or external modulat ion is used to encode digital information onto these optical carriers, which are combined onto a single fibre using a wavelength division multiplexer. The receiver comprises a wavelength demultiplexer to separate the two optical carriers, together with integrated photodetectors to convert the signal back into electrical form.

In developing the transmitter components , STL and CGE have

Optoelectronics Technology

Matures Under ESPRIT 263

For the past 5 years, ESPRIT 263 has been the f lagship optoelectronics project supported under Europe's IT initiative, ESPRIT. Composed of two groups, the project aims were to develop integrated wavelength multiplexed transmitter and receiver chips (group A) and to integrate lasers and detectors with transistor drivers and pre-amplifiers (group B). The Group A partners are CSELT (pr ime contractor , I ta ly), CGE (France), GEC-Marconi (UK), STL (UK) and Thomson-CSF (France). The Group B partners are STL (prime contractor, UK), SEL (Germany), HHI (Germany) and CNET (France).

improved their narrow linewidth DFB lasers and demonstrated the ability to fabricate sources operating at different wavelengths on the same chip using direct-write e- beam li thography and localised epitaxy. Thomson-CSF has produced integrable modulators and wavelength multiplexers with channel spacing down to 12 nm. All three partners have also integrated laser sources with optical waveguides on the same chip. Using the InGaA1P material system, CSELT have produced demultiplexers with channel spacings close to the required 30 nm and integrated high speed (>4 Gbit/s) detectors.

A focal point of the Group A collaboration has been the optoelectronic device simulation facility, developed by GEC- Marconi largely under this programme. Sophisticated numerical techniques have been harnessed using interactive graphics interfaces to provide user friendly engineering tools, which enable a rapid

convergence towards, and verification of, the required design. Low loss waveguide bends, fabrication-tolerant power splitters and novel wavelength filters and demultiplexers were generated using this unique facility, and many practical problems of integration have been addressed. Excellent agreement has been found with the experimental result.

Group B has concentrated on the development of the two key components required in any optical transmission system, namely the optical transmitter and the optical receiver. The main innovat ion of this work has been the combining of both the optical (laser of photodetector) and electronic (transistor) devices on the same semiconductor chip, an approach which offers the prospect of higher performance, lower cost, reduced size and improved reliability compared with more conventional hybrid components . Excellent progress has been achieved

within the project. Two different approaches to the transmitter integration have been developed. The major thrust has been towards integrating the semiconductor laser with a heterojunct ion bipolar transistor however the most successful approach to date has been the integration of the laser with an insulated gate transistor. Successful operation at 1.12 Gbit/s has been demonstrated for a hybridised module containing an integrated heterojunction bipolar transistor driver circuit and a high speed laser.

The integrated receiver activity within Group B has achieved world record results. The group has fabricated the most sensitive receiver at 560 Mbit/s with a figure of - 32.7 dBm. This circuit comprises an indium gallium arsenide pin photodiode integrated alongside a heterojunct ion field effect transistor. These same devices have also been combined into a full transimpedance receiver design with a state-of-the-art integration level of 17 components and operation at up to 2.4 Gbit/s.

The technology developed under ESPRIT 263 is already being exploited under RACE, where high quality lasers, optoelectronic ICs, low loss waveguides, etc., are being incorporated into a range of exploratory communicat ion systems and optically-switched networks. Beyond this lies a new generation of telecommunications, instrumentat ion and signal processing - at the speed of light. •

George Papageorgiou, CEC, Brussels

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