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H
ealthcare costs are in the spotlight. The US is
wrestling with the proposed introduction of
universal access and many other countries are looking at
the financial burden of their burgeoning state-run systems.
Reducing the cost of diagnosis and improving treatment
efficiency are areas of major focus. One of the largest
increases in costs in recent years has been the use of
diagnostic imaging tools such as ultrasound,
computed tomography (CT) and magnetic
resonance imaging (MRI), access to
which can cost several thousand dollars
per examination. Diagnostic imaging
based on relatively low cost photonics
could be the answer in some applications.
Whilst not a direct replacement for tools like MRI,
near surface photonic imaging techniques can have an
important place within certain diagnostic schemes. Even
for internal imaging where the lack of light penetration can
be an issue, there is much invention to be gained using
optical probes to bring the source light into the region to
be interrogated. Furthermore, if the applications are
intended to be used for diagnosis in vitro rather than in
vivo, these restrictions are considerably relaxed, since
then specimens can be prepared in which penetration
depth is not an issue.
Non-contact near surface imaging of the skin or eye using
Superluminescent
Optical Coherence Tomography (OCT) is an example of a
technique that has become popular both in the lab and in
the clinic. It has gained considerable favour for its
potential to provide two and three-dimensional real-time
diodes have an eye
images of biological tissues with micron-like resolution.
The technique can be described as an optical analog to
ultrasound in which light is used instead to probe the
for diagnosis
variation of reflected light as a function of depth.
Combined with areal scanning it is relatively easy to
obtain useful cross sectional images of skin and tissue.
The basis of OCT is low-coherence interferometry in
which a broadband source illuminates a Michelson
Superluminescent diodes have been the poor relative
interferometer. The system is very easy to implement in
of the photonics toolkit for many years. But Optical
fibre and the ideal sources for such applications are the
edge-emitting superluminescent diodes. The axial
Coherence Tomography promises to change that, and
resolution of such systems is inversely proportional to the
quantum dot superluminescent diodes have the
bandwidth of the source, which explains the strong desire
for broadband sources.
potential to be the ideal technology for this
application, says Mark Hopkinson from the
Aside from fibre optic test equipment, the edge-emitting
superluminescent diode has served relatively few
University of Sheffield, UK.
applications over the years. But this device may well have
found its niche as a broadband source in the near infrared
(800-1300nm), the wavelength range most suited to the
34 www.compoundsemiconductor.net November / December 2009
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