Wafer processing in the Advanced Plasma Technology Lab at the Communications Research Centre (CRC)

Optical communication systems are all around us in today's "on-demand" society, from transatlantic fiber links supporting telephone service, to systems that bring TV and Internet services to homes, network workplace computers, or allow commercial or individual access to local or metro-area communication networks. In the not-too-distant future, optical technology will replace electrical wires connecting chips and circuit boards, which currently cause a communications "bottleneck," producing a new generation of high-speed super computers and networks. Optical technology will also yield applications that secure confidential data exchange, bringing significant benefits to many areas, including e-commerce, national security and the banking industry.

These increasingly complex applications require, in addition to fiber links, devices that can route, switch, filter, attenuate, amplify and otherwise control the optical signals that carry valuable information. Like most things in a competitive business world, these devices must continually evolve to meet consumer demand for "better, faster, smaller and cheaper" or in other words, greater functionality and bandwidth, at reduced size and cost.

To address these applications, the CRC's Photonics Component Technology (PCT) group is developing a suite of photonic devices based on silica-on-silicon planar lightwave circuit (PLC) technology. Planar layers of silica, the same material used in optical fibers, are deposited from a plasma under high vacuum, heated to high temperatures then patterned into device structures. The fabricated devices have dimensions and material characteristics similar to those of optical fibers, making them compatible with fiber infrastructure.

PCT researchers have access to state-of-the-art facilities to fabricate PLCs in-house and extensive expertise in design, process development and device characterization, advanced through their detailed study of the materials and processes required to build PLCs, conducted over the past few years. Researchers in the group are now exploiting this expertise for several different applications. The group also carries out custom device fabrication for industrial and university partners.

Closing the Gap between Optical and Electrical Signals

The PCT group has developed silica-based PLCs ranging from simple devices for guiding light, to more complex devices for manipulating the wavelength, phase and optical power in networks that employ separate wavelength channels on a single fiber (wavelength division multiplexing or WDM). Current research is focussed on the development of next generation PLCs that, in addition to routing the light, can actually manipulate the bits and packets of information carried on the light beam. This type of all-optical processing is an important step forward in optical network technology as it potentially removes the need to convert optical signals back to the electrical domain to carry out signal processing functions.

Recently, collaboration with researchers at McGill University has resulted in the demonstration of interferometer devices that can increase the pulse repetition rate from 10GHz to 40GHz. By applying electrical currents to selected parts of the device, the phase of the propagating light can be controlled, and specific binary output codes generated. Researchers at McGill and CRC are developing this technology further, envisaging exciting applications, as all-optical signal processing becomes a reality.

The drive towards closer interaction between optical and electrical signals also motivates another research and development project in the PCT group. In order to fully exploit the speed and data capacity of optical interconnects, a technology is required that can interface optical and electrical signals on the same chip. However, there is currently a huge size differential between photonics (micrometers) and silicon electronics ("computer chip technology") (nanometers). The PCT group is working on the development of photonic components based on multilayer structures in which thin metal strips are embedded in glass or polymer materials. These so-called "plasmonic structures" allow light to be guided in unique ways, they can reduce the dimensions of lightguiding components, and they have the potential for electrical connection.

Metal patterns with dimensions less than the wavelength of light create even more possibilities. The group has developed low-cost patterning techniques, enabling the in-house fabrication of nanoscale devices. Collaborators at Clemson University in South Carolina are actively participating in the supply of materials for this project. The work is at a fairly early stage, but this research topic has generated a lot of excitement in the world of photonics, and researchers at CRC hope it will allow them to move a few steps closer to developing an on-chip photonic/electronic interconnect.

For more information on CRC's research in planar lightwave circuit technology contact Claire Callender, Project Leader, Photonic Component Technologies, at 613-998-2726 or claire.callender@crc.ca.