Retroreflection defeat filter
An optical system providing reduced retroreflection includes an optical element with an optic aperture. A retroreflection defeat filter has a partially obstructing material configured to absorb or reflect a subset of the optical system waveband while transmitting the rest. The partially obstructing material is arranged to occupy a first portion of the optic aperture being at least half of the optic aperture, and the partially obstructing material does not occupy a second portion of the optic aperture for the remainder of the optic aperture.
1 . An optical system with reduced retroreflection, comprising:
an optical element comprising first and second optic apertures;
first and second retroreflection defeat filters, each comprising a partially obstructing material configured to absorb or reflect a first portion of an optical system waveband while transmitting a second portion of the optical system waveband;
wherein the partially obstructing material of the first retroflection defeat filter is arranged to occupy a first portion of the first optic aperture comprising at least half of the first optic aperture, and the partially obstructing material of the first retroflection defeat filter does not occupy a second portion of the first optic aperture comprising a remainder of the first optic aperture;
wherein the partially obstructing material of the second retroflection defeat filter is arranged to occupy a first portion of the second optic aperture comprising at least half of the second optic aperture, and the partially obstructing material does not occupy a second portion of the second optic aperture comprising a remainder of the second optic aperture; and
wherein the first and second retroflection defeat filters are arranged in opposite orientations.
2 . The optical system of claim 1 , wherein the first and second retroreflection defeat filters further comprise a transmitting material arranged to occupy the second portions of the first and second optic apertures.
3 . The optical system of claim 2 , wherein the transmitting material is attached to the partially obstructing material.
4 . The optical system of claim 1 , wherein the partially obstructing material comprises NIR absorbing glass.
5 . The optical system of claim 4 , wherein the NIR absorbing glass is selected from the group consisting of KG1, KG2, KG3, and KG5.
6 . The optical system of claim 1 , wherein the retroreflection defeat filter is disposed in a stop of the optical element.
7 . A pair of retroreflection defeat filters for reducing retroreflection in an optical system comprising first and second optic apertures, the first retroflection defeat filter comprising:
a partially obstructing material configured to absorb or reflect a first portion of an optical system waveband while transmitting a second portion of the optical system waveband, wherein the partially obstructing material of the first retroflection defeat filter is arranged to occupy a first portion of the first optic aperture comprising at least half of the first optic aperture; and
the second retroflection defeat filter comprising:
a partially obstructing material configured to absorb or reflect a first portion of an optical system waveband while transmitting a second portion of the optical system waveband, wherein the partially obstructing material of the second retroflection defeat filter is arranged to occupy a first portion of the second optic aperture comprising at least half of the first optic aperture; and
wherein the first and second retroflection defeat filters are arranged in opposite orientations.
8 . The pair of retroreflection defeat filters of claim 7 , wherein the pair of retroreflection defeat filters each further comprises a transmitting material arranged to occupy the second portion of the first and second optic apertures.
9 . The retroreflection defeat filter of claim 8 , wherein the transmitting material is attached to the partially obstructing material.
10 . The retroreflection defeat filter of claim 8 , wherein the transmitting material and/or the partially obstructing material further comprises an anti-reflective (AR) coating.
11 . The retroreflection defeat filter of claim 7 , wherein the partially obstructing material comprises NIR absorbing glass.
12 . The retroreflection defeat filter of claim 11 , wherein the NIR absorbing glass is selected from the group consisting of KG1, KG2, KG3, and KG5.
13 . A method for a reduced retroreflection reduction filter for an optical system, comprising the steps of:
providing a first retroflection defeat filter, the first retroflection defeat filter further comprising:
a first portion of partially obstructing material configured to absorb part of an optical system waveband while transmitting another part of the optical system waveband; and
a second portion not occupied by the partially obstructing material;
positioning a first window within a first optic aperture of the optical system, wherein the window comprises the first retroflection defeat filter, and wherein the first portion occupies at least half of the first optic aperture;
providing a second retroflection defeat filter, the second retroflection defeat filter further comprising:
a first portion of partially obstructing material configured to absorb part of an optical system waveband while transmitting another part of the optical system waveband; and
a second portion not occupied by the partially obstructing material;
positioning a second window within a second optic aperture of the optical system, wherein the second window comprises the second retroflection defeat filter, and wherein the first portion occupies at least half of the second optic aperture; and
wherein the first and second retroflection defeat filters are arranged in opposite orientations.