Method for designing off-axis three-mirror imaging system with freeform surfaces

Patent metadata

Field	Value
Publication number	US-2016170191-A1
Application number	US-201514814497-A
Country	US
Kind code	A1
Filing date	Jul 30, 2015
Priority date	Dec 11, 2014
Publication date	Jun 16, 2016
Grant date	—

Abstract

A method for designing an off-axis three-mirror imaging system with freeform surfaces is provided. A primary mirror initial structure, a secondary mirror initial structure, and a tertiary mirror initial structure are established. A number of first feature rays are selected, while the primary mirror initial structure and the secondary mirror initial structure unchanged. The first feature rays are forward ray tracked from an object space to an image detector. A number of first feature data points are calculated to obtain a tertiary mirror. A number of fields and a number of second feature rays are selected, while the secondary mirror initial structure and the tertiary mirror unchanged. The second feature rays are reverse ray tracked from the image detector to the object space. A number of second feature data points are calculated to obtain the primary mirror.

First claim

What is claimed is:

1 . A method for designing an off-axis three-mirror imaging system with freeform surfaces, the method comprising:
establishing an initial system, the initial system includes a primary mirror initial structure, a secondary mirror initial structure, and a tertiary mirror initial structure; keeping the primary mirror initial structure and the secondary mirror initial structure unchanged; selecting a plurality of first feature rays, the plurality of first feature rays are forward rays tracked from an object space to an image detector; and calculating a plurality of first feature data points P i (i=1, 2 . . . K) point by point based on an object-image relationship of the plurality of first feature rays, to obtain a tertiary mirror by surface fitting the plurality of first feature data points P i (i=1, 2 . . . K); and keeping the secondary mirror initial structure and the tertiary mirror unchanged; selecting a plurality of fields and a plurality of second feature rays, the plurality of second feature rays are reverse rays tracked from the image detector to the object space; and calculating a plurality of second feature data points P′ i (i=1, 2 . . . K) point by point based on an object-image relationship of the plurality of second feature rays, to obtain a primary mirror by surface fitting the plurality of second feature data points.

2 . The method of claim 1 , further comprising optimizing the off-axis three-mirror imaging system with freeform surfaces.

3 . The method of claim 2 , wherein the off-axis three-mirror imaging system with freeform surfaces is as the initial system for further optimization.

4 . The method of claim 1 , wherein the primary mirror initial structure, the secondary mirror initial structure, or the tertiary mirror initial structure is planar or spherical.

5 . The method of claim 1 , wherein the selecting the plurality of first feature rays comprises: selecting M fields; dividing an aperture of each of the M fields into N equal parts; and P feature rays at different positions in each of the N equal parts are selected, thus, K=M×N×P different first feature rays are selected.

6 . The method of claim 5 , wherein the aperture of each of the M fields is circle, the aperture of each of the M fields is divided into N angles with equal intervals, and P different positions are selected along a radial direction of each of the N angles.

7 . The method of claim 1 , wherein the calculating the plurality of first feature data points comprises:
defining a first intersection of the first feature ray R 1 and the tertiary mirror initial structure as the first feature data point P 1 ; calculating an unit normal vector {right arrow over (N)} 1 at the first feature data point P i (1≦i≦K−1) based on a vector form of Snell's Law after i (1≦i≦K−1) first feature data points are calculated; and making a tangent plane at the first feature data point P i (1≦i≦K−1), thus, (K−i) intersections are obtained by the tangent plane intersecting with remaining (K−i) first feature rays; and the intersection, which is nearest to the first feature data points P i (1≦i≦K−1), is fixed from the (K−i) intersections as the next first feature data point P i+1 (1≦i≦K−1), until all the plurality of first feature data points P i (i=1, 2 . . . K) are calculated.

8 . The method of claim 7 , wherein the first feature ray R 1 is most close to the optical axis of the off-axis three-mirror imaging system with freeform surfaces.

9 . The method of claim 7 , wherein the unit normal vector {right arrow over (N)} i is calculated as follows:

N
→

i

=

r
→

i
′

-

r
→

i



r
→

i
′

-

r
→

i



;

wherein

r
→

i

=

P
i



S
i

→



P
i



S
i

→



is an incident ray direction unit vector of the tertiary mirror;

r
→

i
′

=

E
i



P
i

→



E
i



P
i

→



is an exit ray direction unit vector of the tertiary mirror; S i are intersections of the plurality of first feature rays and the secondary mirror initial structure, and E i are ideal image points on the image detector.

10 . The method of claim 1 , wherein the calculating the plurality of second feature data points P′ i (i=1, 2 . . . K) comprises:
defining a first intersection of the second feature ray R′ 1 and the primary mirror initial structure as the second feature data point P′ 1 ;
calculating an unit normal vector {right arrow over (N)}′ i at the second feature data point P′ i (1≦i≦K−1) based on a vector form of Snell's Law after i (1≦i≦K−1) second feature data points are c

Assignees

• Univ Tsinghua
• Hon Hai Prec Ind Co Ltd

Inventors

• Hou Wei
• Zhu Jun
• Jin Guo-Fan
• Fan Shou-Shan

Classifications

• G02B17/0642 Primary

  off-axis or unobscured systems in which not all of the mirrors share a common axis of rotational symmetry, e.g. at least one of the mirrors is warped, tilted or decentered with respect to the other elements · CPC title

• G02B27/0012 Primary

  Optical design, e.g. procedures, algorithms, optimisation routines · CPC title

• G02B17/0626

  using three curved mirrors (G02B17/0668, G02B17/0694 take precedence) · CPC title