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03 Nov 2005
A photonic crystal circuit offers tunable control over the speed of infrared light pulses.
Scientists at IBM have built a silicon chip that uses the combination of built-in miniature heaters and photonic crystal technology to control the speed of light pulses. The silicon waveguide circuit, reported in this week’s issue of Nature (438 65), operates in the popular telecoms window of 1.5 µm and reduced the group velocity of light by a factor of up to 300.
At the heart of the chip is a short (250µm long) silicon photonic crystal waveguide that is etched with a pattern of tiny holes (109 nm diameter) and in close proximity to an electrical contact that acts as a miniature heater. Applying an electrical current to the contact heats up the waveguide, changing its refractive index and tuning the speed of the pulses.
The beauty of the approach is that it is highly compact and provides fast and easy control. For example, in experiments with 1641 nm pulses the IBM team says that application of just 2 mW of electrical power was able to change the group velocity by a factor of three within 100 ns.
To characterise the performance of the design, Yurii Vlaslov and his colleagues from the IBM T.J. Watson Research Center in the US, placed two such waveguides and heaters side-by-side to create a miniature (0.04 mm2 footprint) Mach Zehnder Interferometer (MZI). One arm of the MZI acted as a reference and the other a variable speed arm. This approach allowed the team to make interferometic measurements of group velocity.
The IBM work follows a recent surge in the number papers on the topic of manipulating the speed of light inside custom designed optical chips. In March, scientists from Belgium and Scotland made movies on light pulses travelling through a photonic crystal waveguide (see related story). Last month researchers in Denmark and the US slowed light using a range of semiconductor optical devices (see related story).
Author
Oliver Graydon is editor of Optics.org and Opto & Laser Europe magazine.
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