  SPHERE is an instrument designed and built by a consortium of French, German,
Italian, Swiss and Dutch institutes in collaboration with ESO. The project is
currently in its Phase B. The main goal of SPHERE is to gain at least one order
of magnitude with respect to the present VLT AO facility (NACO) in the direct
detection of faint objects very close to a bright star, especially giant
extrasolar planets. Apart from a high Strehl ratio, the instrument will be
designed to reduce the scattered light of the central bright star and subtract
the residual speckle halo. Sophisticated post-AO capabilities are needed to
provide maximum detectivity and possibly physical data on the putative planets.
The Integral Field Spectrograph (IFS), one of the three scientific channels
foreseen in the SPHERE design, is a very low resolution spectrograph (R~20)
which works in the near IR (0.95-1.35 micron), an ideal wavelength range for
the ground based detection of planetary features. Its goal is to suppress
speckle to a contrast of 10^7, with a goal of 10^8, and at the same time
provide spectral information in a field of view of about 1.5 x 1.5 arcsecs^2 in
proximity of the target star. In this paper we describe the overall IFS design
concept.
