Test results of the infrared single-mode fiber for the DARWIN mission

Abstract

Nulling interferometry is the baseline technique for the DARWIN planet finding mission of the European Space Agency. Using this technique it will be possible to cancel, by destructive interference, the light from the bright star and look directly at its surrounding planets and eventually discover life on them. To achieve this goal wavefront errors need to be reduced to a very high degree in order to achieve the required nulling quality. Such a high wavefront quality can only be achieved with adequate wavefront filtering measures. Single mode fibers in general have excellent mode filtering capabilities, but they were not recently available for the broad infrared wavelength region of Darwin (4-20 um). Within an ESA technology development project, TNO has designed and tested an infrared single mode fiber based on chalcogenide glasses that has been manufactured by the University of Rennes. Several tests are carried out to characterize the materials used and the IR single mode fiber. Far field intensity distribution measurement at 10.6 um reveals the single mode operation of the manufactured fiber. Influence of coating, length, light coupling and bending of the fiber are also investigated.

Development of broadband infrared single-mode fibers for the DARWIN mission

“…The first two items are discussed in a previous paper [1]. Single mode operation of different TAS fibers with absorbing coating is presented (See Fig.…”

“…The results of the refractive index measurement of the TAS material were presented earlier [1]. The spectral absorption was determined from the ratio of two transmission spectra, T 1 and T 2 , recorded for samples of different thickness, d 1 and d 2 , using as first estimate for the spectral extinction coefficient K(λ):…”

“…This can be realized by wavefront error filtering before the detection. Single mode fiber is one promising candidate for the wavefront filtering [1]. For the application of the single mode fiber as wavefront filter in DARWIN, a minimal insertion loss is desired (total insertion loss < 1.5 dB).…”

Single mode chalcogenide glass fiber as wavefront filter for the DARWIN planet finding misson

“…The ball is submerged in water and the sample is exposed to a radioactive Co60 source for 53 seconds. During this treatment the samples receive a total radiation dose of 0.1 kGy, simulating the estimated cosmic radiation dose for the DARWIN mission [1]. The optical absorption spectra, measured before and after this radiation treatment are shown in figure 1.…”

“…An important measuring technique under study for the DARWIN planet finding mission, is nulling interferometry [1]. The main goal of this mission is to identify terrestrial planets, orbiting around nearby stars and capable of having an atmosphere, so possibly supporting life.…”