Porous silicon gives waveguide with low loss

17 Jun 2002

A pan-European research team has developed a self-aligned oxidised porous silicon optical waveguide with reduced loss.

The team, from Belarus, Italy, France and the UK, achieved low optical losses of 1dBcm-1 using a two-stage anodisation of a highly doped n+ silicon wafer.

The resulting waveguides provide three-dimensional optical confinement, but do not require epitaxy or implantation processes, and therefore offer significant processing and cost advantages over other technologies.

Marco Balucani, one of the researchers involved in the work, said: "The anodisation process is cheaper than epitaxy and implantation. It is well-controlled, and thetwo anodisation steps are performed in one process by simply changing the current density. This process can be readily used in mass production."

To provide light confinement and propagation within the waveguide, the guiding region should have a higher refractive index than that of the surrounding cladding regions. Porous silicon is a good candidate for waveguides because the refractive index of the material can be controlled over a wide range by varying the porosity.

Waveguides based on porous silicon and oxidised porous silicon can be directly integrated with active regions of light-emitting devices and photodetectors to minimise coupling losses. According to Balucani, the next challenge is to build active devices such as amplifiers and lasers, by introducing rare-earth elements into the oxidised porous

He said: "The Belarussian group has more than twenty years of experience in poroussilicon and we believe that there is no other group that has so much experience in the world. We have worked with them for the last ten years have studied porous silicon morphology and application such as LED, waveguides and silicon-on-insulator. We will continue to research the use of porous silicon in optoelectronics and we aredeveloping with the English group a technology to electrochemically dope the oxidised waveguide with different elements, in particular, rare-earth ones to use them as optical amplifier and light up-conversion."

Story courtesy of Opto and Laser Europe magazine.