Light connections

Light channels: oxide wave-gui WHAT microelectronics was to the '70s
and the '80s, optoelectronics promises
to be for the 21st century.
Optoelectronic circuits are finding
increasing use in many diverse areas like
telecommunications, imaging technology and high speed computing.

One of the major areas of research
has been to fabricate optical circuits. A
combination of lasers, optical switches
and other components on a single chip
would offer tremendous advantages
over conventional electronic circuits.
Unlike electrons in micro-circuits, pulses of light are extremely fast and thus
have the potential of improving the performance of devices several-fold. There
has, however, been a minor hiccup -
light cannot be easily made to bend
since the optical wave-guides in use
have a tendency to leak at sharp turns. This mak6 the chips large, thereby limiting their appeal (Science, Vol 268, No 5214).

Now, Michael Krames and his group
at the University of Illinois, Urbana Champaign, have built an efficient
curved wave-guide (the optical equivalent of an electric wire) in a gallium
arsenide-based semiconductor. Gallium
arsenide semiconductors are the staple
material of optoelectronics because,
unlike conventional semiconductors,
they emit -and absorb light easily.

To build the wave-guide, the group
started with a layer of gallium arsenide
sandwiched between layers of aluminium gallium arsenide. The trick is to be
able to etch deep "canyons" in the material which can act as channels for the
light. By masking the crystal and heating
it in a controlled atmosphere, the group
was able to produce a hard oxide material. This material has a lower refractive
index than the original semiconductor
and thus allows the light to be trapped.

The wave-guides have been found to
be far more efficient than the existing
ones in that the leakage losses around
the bends is about 10 times less than that
for the existing wave-guides. What is
more, the technology is coinpatible with
ordinary, existing semiconductor processing and fabrication
techniques, giving it a tremendous commercial edge.

Optical chips will probably
form the core of many of
tomorrow's applications:
whether it is terraflops optical
computers or high speed
switches in telecommunications. With the fabrication of
the optical wave-guide, another hurdle has been overcome
on this technology highway.