  Integral field spectroscopy (IFS) represents a powerful technique for the
detection and characterization of extrasolar planets through high contrast
imaging, since it allows to obtain simultaneously a large number of
monochromatic images. These can be used to calibrate and then to reduce the
impact of speckles, once their chromatic dependence is taken into account. The
main concern in designing integral field spectrographs for high contrast
imaging is the impact of the diffraction effects and the non-common path
aberrations together with an efficient use of the detector pixels. We focus our
attention on integral field spectrographs based on lenslet-arrays, discussing
the main features of these designs: the conditions of appropriate spatial and
spectral sampling of the resulting spectrograph's slit functions and their
related cross-talk terms when the system works at the diffraction limit. We
present a new scheme for the integral field unit (IFU) based on a dual-lenslet
device (BIGRE), that solves some of the problems related to the classical TIGER
design when used for such applications. We show that BIGRE provides much lower
cross-talk signals than TIGER, allowing a more efficient use of the detector
pixels and a considerable saving of the overall cost of a lenslet-based
integral field spectrograph.
