Silica chips produce light continuum

06 Oct 2003

UK-based start-up Mesophotonics says that its chips beat microstructured fiber when it comes to producing white light.

Optical coherence tomography (OCT) and frequency metrology systems could benefit from a tiny waveguide that produces a 600 nm-wide white-light continuum.

UK start-up company Mesophotonics, a spin-off of the reknowned Optoelectronics Research Centre at the University of Southampton, says that its 1 cm-long devices are better than microstructured fibers for continuum generation.

“This is a brand new method of making a continuum that we believe has never been observed, let alone commercialized,” said Mesophotonics’ John Lincoln.

Lincoln’s ‘continuum-generating chips’ (CGCs) produce light from 600 to 1100 nm. The continuum is symmetrical about the central wavelength and is said to have no visible spectral noise.

Some OCT and high-precision frequency metrology systems fire a femtosecond laser pulse at a microstructured fiber to generate the broadband continuum required for both techniques.

However, Lincoln says that these fibers are susceptible to damage from the blue and ultraviolet wavelengths that are created in a continuum. “These fibers degrade and in some cases prematurely fracture if used continuously,” he explained. “This would restrict the lifetime of fiber-based continuum generation in any commercial application such as OCT.”

Lincoln and colleagues have found that by using different materials that are resilient to ultraviolet exposure, the problems can be avoided. “We can…provide a material that has a lifetime suitable for commercial deployment,” said Lincoln. “This will be especially important for clinical OCT applications.”

The waveguides are made by depositing layers of a high-refractive-index material on top of a standard silicon wafer to make a planar waveguide measuring 10  long by 5  wide and just 1 µm thick.

Lincoln says that the CGCs combine the useful properties of fibers and of bulk media like sapphire crystals. Using the waveguide, pulse energies as low as 10 nJ can generate the continuum, a figure similar to that seen in fiber and much lower than is needed with bulk media.

Meanwhile, damage tests show that the waveguides can withstand several watts of blue light – much higher than fiber and comparable to materials such as sapphire.

Lincoln told Optics.org that Mesophotonics is already using the CGCs every day to characterize the two-dimensional photonic crystals that it is developing.

“The development of CGCs will enable continuum generation to move into industrial and clinical applications of which frequency metrology and OCT are just the start,” he said.

Lincoln is hoping to make the chips available commercially by the end of this year. He estimates that they will have a similar cost to microstructured fiber initially, but with the potential to become far cheaper. “As the technology is based on standard silicon wafer production, it is possible to drastically reduce costs for significant volume demand,” he said.

Author
Michael Hatcher is technology editor of Opto & Laser Europe magazine.