It's been a busy 12 months at Pirelli Labs, the research arm of diversified Italian manufacturing concern Pirelli. For starters, the group's scientists and engineers have been hard at it, refining a battery of proprietary production techniques - detailed in FibreSystems back in January (p25) - for nanometre-scale devices and structures such as photonic crystals. Perhaps more significantly, though, the group has just unveiled the first wave of products to emerge from its nanotechnology R&D programme.
"We are designing technologies that process materials with nanometre resolution, in such a way as to modify the characteristics of the material itself," explained Giorgio Grasso, Pirelli Labs' chief executive officer. "This is the essence of what we call nanophotonics - creating optical circuits by modifying the material via mechanical processing, rather than the traditional method of modifying its refractive index via doping."
Photonic-crystal materials exploit lattices of tiny air holes to create photonic bandgaps - structures that can be engineered to provide extremely tight confinement of light within an optical waveguide. Pioneers of the technology, including Pirelli, argue that photonic crystals will help manufacturers to reduce the dimensions of optical circuits from centimetres to millimetres, while at the same time providing a route to low-cost, high-volume production.
Take it to market
The first release based on Pirelli's photonic-crystal technologies is a dynamically tunable laser, the DTL-C13. The laser is a hybrid device with an external cavity, the resonance frequency of which is controlled by a tunable mirror. Specifications include a wavelength range of 1530 to 1565 nm, a frequency accuracy of ±1.5 GHz, an output power of up to 13 dBm and a tuning speed of 10 ms.
The laser has no moving parts and its big selling point, says Grasso, is its simple tuning mechanism. "A reflective structure is written on the surface of the mirror by nanotechnology and its optical characteristics are modified by the application of a voltage," he explained. "The voltage level controls the characteristics of the material and thus there is a change in resonance frequency." This compares favourably with other tunable lasers that have several, often co-dependent, variables (such as different bias currents) that have to be set for every frequency.
"In terms of price, we think that the tunable laser will cost between 5 and 10% more than a standard fixed-wavelength DFB [distributed-feedback] laser," Grasso added. "We have demonstrated it to our customers and they have all told us that the device will be a big step forward if we can manufacture in large volumes."
So how easy is it to mass produce photonic-crystal-based devices? Grasso says that the tunable mirror itself is easily manufactured in volume. "Volume is not a problem - even in our laboratory we have a facility that is able to produce up to 1 million pieces per year," he explained. "The bottlenecks are mounting the external cavity, and the packaging, which require the use of semi-automated asembly lines."
Pirelli is currently working on two other components for optical comms applications. The first is an optical add-drop multiplexer (OADM) that enables add or drop of up to four software-defined wavelengths without affecting the pass-through channels. Scheduled for sampling next June, the OADM uses photonic-crystal technology to ensure a compact footprint.
"Current OADM solutions are very big [rack mounted]. Typically they open a data stream, switch the wavelengths and then recombine them," said Grasso. "Instead, we have a very small planar cavity that is tunable and can extract a single wavelength. The cavity is designed using nanotechnology and is less than 1 mm long, resulting in a highly compact device."