Imaging system comprising a Fresnel lens

摘要

The imaging system for imaging field rays comprises a detection surface, a device for focusing the field rays with said detection surface, and a diaphragm. Said device comprises a Fresnel lens comprising a first dioptre, the non-plane surface of which, called the active zone, makes it possible to focus the field rays towards said detection surface, and said diaphragm allows controlled distribution of the field rays over said active zone.

主权项

1. A system for imaging field rays originating from any point in an observed scene, comprising:
a detector; a diaphragm placed upstream of the detector and located at a distance d0 from said any point in the observed scene; and a device for focusing the field rays onto the detector, the focusing device being designed for a working wavelength λ0 comprised in the spectral band of the observed scene, the active dioptre of the focusing device being placed between the diaphragm and the detector: at a distance d1 from the diaphragm minimizing astigmatic aberration at the detector; and at a distance dd from the detector, the distance dd depending on the distance d0 and being the focal distance of said active dioptre,the imaging system wherein:
the focusing device comprises a plate having parallel sides, said plate comprising at least one Fresnel dioptre that is the active dioptre of the focusing device and that supplies most of the optical power of said focusing device, this optical power being generated by phase-continuity zones of said active dioptre, said phase-continuity zones essentially functioning in refractive mode, said optical power being adapted to focus the field rays onto the detector; said active dioptre is designed to the order p for the working wavelength, the order p being greater than or equal to three, in order to obtain many diffraction orders in the spectral band of the observed scene; and the aperture Ld of the diaphragm placed upstream of the active dioptre is smaller than Ldmax=L4·d0/(d0+d1), where L4 is the smallest distance between four consecutive discontinuities of the Fresnel lens, in order on the one hand, to limit to 3 the maximum number of phase-discontinuity zones illuminated by said field rays for a given angle of incidence, and on the other hand, to make allowance for a local correction of aberrations, which correction is adapted to the angle of incidence of said field rays; said active dioptre is designed to make said local correction of aberrations.