Nanophotonic Chip Slows Down Light
In 1999, Danish Harvard professor Lene Hau was famed for reducing the speed of light in a sophisticated experimental setup. Now, a research group at the Technical University of Denmark's Department of Communications, Optics and Material (COM) has repeated the accomplishment, but this time in a silicon nanophotonic integrated chip, fabricated in the DANCHIP clean rooms. The chip makes use of a so-called photonic crystal waveguide. The technology offers new opportunities within optical systems in telecom, data communication, and compact optical sensors.
In the photonic chip, the research group has reduced the light velocity by a factor of 200, compared to that in vacuum. At present, only a few other groups have been able to record comparable low speed of light in photonic crystal waveguides. Theoretically, there is no lower limit for the speed of the light. The key is to design the photonic crystal waveguide such that it facilitates the desired control and manipulation of the light.
Smaller, better, faster
By exploitation of slow light, optical components such as switches, modulators, detectors, and sensors may be miniaturised. By reducing the light speed by a factor of 10-100, the size of the optical component can typically also be reduced by a factor 10-100. This will make it possible to integrate a high number of optical functions on the same chip. And integration of photonic and electronic signal processing on the same chip could be just around the corner. The fact that the research group uses silicon has a large commercial significance. Silicon is the material that is used in most electronic chips, thus, state-of-the-art fabrication technology is readily available for the chip fabrication. The technology may also be exploited in compact laser systems, for efficient reshaping of an optical pulse. What is performed today with the use of a large length of optical fibre could be done in a small, photonic chip which, in addition, also performs signal processing tasks. In the more peculiar department, one can think of delay lines that will delay an optical signal until the signal is needed. And, in a distant future, one may even foresee optical RAM, that is, optical memory.
The work proceeds
There are still challenges to overcome regarding the optical chips. E.g., the optical propagation loss must be further reduced. And the researchers need to increase the span of wavelengths over which the slow light can be utilised. The penalty for exploiting slow light at several wavelengths simultaneously is to make use of a design that provides only moderately slow light. But even so, highly miniaturised components can still be realised.
The PIPE research group on slow light consists of Peter I. Borel, Jacob Fage-Pedersen, Rune Shim Jacobsen, Lars Hagedorn Frandsen, Gaid Moulin, and Andrei Lavrinenko.
SOURCE: English summary of article brought in DTU-Avisen, October 2005