Abstract
Nulling interferometry is an important technique under development for the
DARWIN planet finding mission which enables the detection of the weak
infrared emission lines of an orbiting planet. This technique requires the
use of single mode optical fibers transmitting light as far as possible in
the infrared. Tellurium based glasses transmit infrared light far beyond the
second atmospheric window but are usually not stable enough toward
crystallisation to be drawn into optical fiber. It was recently shown that
the GeTe<sub>4</sub> initial glass composition could be stabilized by the introduction
of few percents of Se. In this paper, we report the development and the
optical characterisation of far-infrared transmitting step index optical.
The evolution of the refractive index of the glass versus the ratio Se/Te
was measured in order to design a multi mode step index fiber. Its core
diameter was 200 µm therefore permitting to easily characterise its optical
properties. This multimode fiber transmitted light from 4 to about 15 µm with losses near 20 dB.m<sup>-1</sup>. Despite these significant losses, the fiber was efficiently used
to detect the broad absorption band of the CO<sub>2</sub> located at 15 µm. These results are very promising in the context of the DARWIN
mission of the European Space Agency.
© 2010 IEEE
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