NOVELTY - Optical device includes planar grating layer formed of grating elements. Each grating element has entrance face forming a first angle with a surface normal of the grating layer and a reflection face forming a second angle with the surface normal. The entrance face receives off-axis radiation. The reflection face reflects the off-axis radiation in a direction aligned with the surface normal and under total internal reflection.    USE - The optical device is used in producing optical module useful in vehicle capable of flight e.g. aircraft. It is used in sensing radiation at an off-axis angle of incidence (all claimed).    ADVANTAGE - The inventive optical device is capable of collecting optical radiation at large angles of incidence relative to the surface normal of the first optical element and delivering that optical radiation to an optical sensor located at near-normal incidence relative to the first optical surface.    DETAILED DESCRIPTION - Optical device comprises a planar grating layer formed of grating elements, each has an entrance face forming a first angle with a surface normal of the planar grating layer and a reflection face forming a second angle with the surface normal. The entrance face is positioned for receiving off-axis radiation. The reflection face is positioned to reflect the off-axis radiation in a direction aligned with the surface normal and under total internal reflection. At least one lens (502) is provided for focusing the reflected obliquely incident light onto a focal plane. Photo-detector(s) is positioned to receive the reflected light at the focal plane.    INDEPENDENT CLAIMS are also included for:    (1) optical element (500) comprising a planar grating layer having grating elements disposed to reflect radiation incident upon the grating layer at an off-axis angle of incidence into a normal direction under total internal reflection, and focusing element(s) aligned along the normal direction for focusing the reflected radiation to a focal plane;    (2) optical module comprising a housing having an outer surface, the optical element disposed within the housing and having a grating layer disposed adjacent the outer surface, and photodetector(s) disposed within the housing to detect radiation of the focal plane;    (3) apparatus for use in a vehicle capable of flight, e.g. aircraft comprising an exposed skin defining a recess, and the optical module disposed within the recess of the exposed skin for detecting radiation over an off-axis range of incident angles as measured from an axis defined by the exposed skin;    (4) method of sensing radiation at an off-axis angle of incidence comprising forming grating elements having an entrance face and an internal reflection face, focusing the reflected radiation onto a focal plane; and detecting radiation at the focal plane;    (5) illumination device comprising a light source producing a light energy, a lens positioned to collect the light energy and provide a normal light energy, and a planar grating layer positioned to receive the collected light energy; and    (6) method of providing radiation at an off-axis angle of incidence comprising providing the light source, collecting the light energy, propagating the light energy in a normal direction.    DESCRIPTION OF DRAWING(S) - The figure illustrates a front view of a large angle of incidence optical element.    Optical element (500)    Lens (502)