We realize for the first time a forward-looking IR (FLIR) system
using a diffractive optical element (DOE) in its optics made of germanium
in the 8- to 10-?m IR wavelength. We describe the design and
the performance of the DOE optics. The IR diffractive lens made of germanium
is proposed to correct the axial chromatic aberration in optics of
the FLIR system. Compared with conventional optics of an FLIR system
the optics using a DOE singlet instead of ZnSe achromat, we have a
DOE system modulation transfer function (MTF) that is almost equal to
the conventional one. The DOE singlet instead of ZnSe achromat appears
to be enough to compensate for the chromatic aberration of the
optical system. Using the DOE system, the numbers of lens elements,
the mass, and the cost are reduced.