Patent ID: 8253092

Claim:
Apparatus comprising: an optical module for placement in front of a semiconductor optical image sensor, the optical module comprising a transparent optical die having front and rear parallel surfaces and having a rectangular optically useful zone centered on an optical axis of the semiconductor optical image sensor and a central circular zone within the optically useful zone and also centered on the optical axis, the transparent optical die having a substantially constant refractive index in a first region of the transparent optical die located between the optical axis and an outer edge of the central circular zone, and having a continuously variable refractive index corrective of negative distortion at least in a second region of the transparent optical die located between the outer edge of the central circular zone and an extent of the optically useful zone; wherein the variable refractive index, in an annular peripheral zone lying between a radius Ru enveloping the rectangular optically useful zone and a smaller radius Ro defining the central circular zone, lies between a maximum profile Pmax and a minimum profile Pmin; (a) the maximum profile Pmax being such that between the radius Ro and a radius R 1 , the value of the maximum refractive index is defined, as a function of the distance from the center of the die r, by the formula n = n 2 + ( n 1 - n 2 ) · ( r - R 0 ) 2 ( R 1 - R 0 ) 2 and then that between this radius R 1 and the radius Ru the refractive index is equal to a value n 1 ; (b) the minimum profile Pmin being such that between the radius Ro and a radius R 2 the refractive index is equal to a value n 0 , and then that between this radius R 2 and the radius Ru, the value of the minimum refractive index is defined, as a function of the distance from the center of the die r, by the formula n = n 0 + ( n 3 - n 0 ) · ( r - R 2 ) 2 ( R u - R 2 ) 2 (c) and in which: n 1 is greater than n 0 , n 2 lies between n 0 and n 1 , n 3 lies between n 1 and n 2 , R 1 lies between Ro and Ru, R 2 lies between Ro and Ru.