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'Hybrid' assembly technique connects optical devices precisely

17 May 2006

A hybrid assembly technique, based on tessellating "Lego"-style building blocks, provides a simple and reliable method of integrating optical devices.

A novel, field-proven method of aligning optical devices and associated boards has been developed by the Centre for Integrated Photonics (CIP), based in Ipswich, UK.

It is claimed to cut both the cost and effort of actively aligning devices and provides a means of creating the sophisticated building-blocks required for integrated optical devices.

"Hybrid integration is an optimal way forward for many of the optical functions needed in advanced optical networks, but most of the assembly techniques in mainstream use today rely on highly skilled labour and expensive equipment, and do not scale", says Graeme Maxwell, CIP's VP of Hybrid Research & Development.

"Our technique requires just passive assembly, yet provides very low insertion losses - making it possible to create single-module solutions for applications such as packet switches, signal regenerators and sensors."

The technique integrates by means of plugging silicon daughter boards carrying individual optical components into a planar silica motherboard - each having precision-machined mating faces - somewhat like "Lego" building bricks.

The components themselves also employ simple interface modifications - namely mode expansion and features to support precision cleaving. The result turns hybrid photonic integration into a similar process to that used for assembling electronic PCBs - with the planar silica motherboard providing the equivalent of printed wiring.

"The platform we have developed is a means of aligning single mode optical components, therefore it is beneficial for applications that require precise positioning of optical devices," adds Maxwell.

"So if you consider the sensor market and devices such as optical gyroscopes these are ideal application areas for hybrid integration, such as a combination of a laser source and beam splitter. With hybrid integration, such devices have a smaller form factor than if developed in the conventional way."

10 years in development

The assembly technique has been developed and refined over the past 10 years, and has been optimised for low interface losses and ease of assembly. It does not involve any complex processing or etching. The technique is scalable and applies equally well to two devices or a large subsystem integrating many component elements.

CIP has manufactured numerous devices using the technique, such as its 2R regenerator - a recently-announced commercial device that is attracting a lot of interest from optical network developers.

In this example of its hybrid integration, the component integrates a planar silica Mach-Zehnder interferometer and a monolithic quad semiconductor optical amplifier array to create a dual-channel 2R regenerator with just a 1 dB loss at daughterboard/motherboard interfaces.

CIP is already selling finished devices and partnering on real solution projects. For example, it is integrating optical amplifiers inside interferometric devices, which it says is quite a difficult challenge. Some other optical systems developers employ monolithic integration but it is not possible to design and make every optical device in that way.

One limiting factor is that it is not always possible to integrate every function simultaneously. CIP uses the highest practical level of monolithic integration in the development of sub-devices and then integrates these using the hybrid mounting technique.

The assembly method has evolved from considerable research and development undertaken by CIP staff during the company's history as part of BT, then Corning, and for the past two years as an independent photonic design and manufacturing consultancy.

CIP offers the technology to customers in a variety of forms to suit different applications and users. These include bespoke hybrid integrated solutions, the provision of turnkey hybrid component solutions - such as its multi-channel 2R regenerator, technology consultancy to support design-in and funded joint development programs.

The company's background in telecoms research and development is certainly not limiting the range of potential applications of this development. Other emerging market areas include sensing, biophotonics and metrology.

These application areas are still at the early stages but CIP is partnering with several commercial and academic groups in joint ventures. It is involved in a UK government Department for Trade & Industry-funded program investigating water sensing with Yorkshire Water and also working on an EPSRC (Engineering Physical Sciences Research Council) funded project with Hull University researching DNA testing using advanced microfluidic devices based on hybrid integration.

Another application is in the development of optical logic gates, such as AND and EX-OR gates and optical buffer memories. These hybrid integration designs are also of interest to researchers developing optical interconnects for computers, CIP says.

About CIP

CIP develops and supplies advanced photonic hybrid integrated circuits and indium phosphide based optoelectronic chips, devices and modules for communications, biomedical, defence and industrial markets. CIP also provides technical services and consultancy in the photonics field.

The company's range of competencies are based on advanced world-renowned research, incorporating III-V photonic materials, silicon micromachining, planar silica waveguides and systems measurements expertise.

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