Method for designing hybrid surface optical system

A method for making an off-axis hybrid surface optical system, comprising:

• step (S1), establishing a first initial system, wherein the first initial system comprises a plurality of initial surfaces, and each of the plurality of initial surfaces corresponds to a surface of the off-axis hybrid surface optical system;
• and selecting a plurality of feature rays Ri (i=1, 2 . . . K) from different fields and different aperture positions;
• step (S2), step (S2a), defining a spherical surface of the off-axis hybrid surface optical system to be calculated as a spherical surface “a”, keeping the plurality of initial surfaces unchanged and calculating a plurality of first feature data points (P1, P2, . . . Pm) point by point, wherein m is less than K, and the plurality of first feature data points (P1, P2, . . . Pm) are m first intersection points of the spherical surface “a” and m of the plurality of feature rays Ri (i=1, 2 . . . K);
• and surface fitting the plurality of first feature data points (P1, P2, . . . Pm) to obtain an initial spherical surface Am;
• step (S2b), calculating a (m+1)th first feature data point Pm+1 based on the initial spherical surface Am, wherein a global coordinate system is defined by a primary mirror location, a beam propagation direction is defined as a Z-axis, and a plane perpendicular to the Z-axis is defined as an xy plane;
• a tangent plane Tm at a first feature data point Pm is calculated, the tangent plane Tm intersects with the initial spherical surface Am at an intersection line Lm;
• and in the global coordinate system, a first feature data point located on the intersection line Lm whose x coordinate is the same as an x coordinate of the first feature data point Pm is defined as a intermediate point Gm, and surface fitting the (m+1) first feature data points (P1, P2, . . . Pm, Pm+1) to obtain a spherical surface Am+1 using the intermediate point Gm;
• step (S2c), repeating steps from step (S2a) to step (S2b) until a Kth first feature data point PK is obtained, and surface fitting the first feature data points (P1, P2, . . . PK) to obtain a spherical surface AK, wherein the spherical surface AK is the spherical surface “a”;
• step (S2d), repeating steps from step (S2a) to step (S2c) until all spherical surfaces of the off-axis hybrid surface optical system are obtained, and a spherical surface optical system is obtained;
• step (S3), step (S3a), defining an aspheric surface of the off-axis hybrid optical system to be calculated as an aspheric surface “b”, the spherical surface optical system being a second initial system, keeping all spherical surfaces of the spherical optical system unchanged and calculating a plurality of second feature data points (P′1, P′2, . . . P′K), wherein the plurality of second feature data points (P′1, P′2, . . . P′K) are K second intersection points of the spherical surface “a” and the plurality of feature rays Ri (i=1, 2 . . . K);
• and step (S3b), surface fitting the plurality of second feature data points (P′1, P′2, . . . P′K) to obtain the aspheric surface “b”;
• repeating steps from step (S3a) to step (S3b) until all aspheric surfaces of the off-axis hybrid surface optical system are obtained, and a first hybrid surface optical system is obtained;
• step (S4), step (S4a), defining a freeform surface of the off-axis hybrid optical system as a freeform surface “c”, the first hybrid surface optical system being a third initial system, and keeping all aspheric surfaces of the first hybrid surface optical system unchanged and calculating a plurality of third feature data points (P″1, P″2, . . . P″K), wherein the plurality of third feature data points (P″1, P″2, . . . P″K) are K third intersection points of the aspheric surface “b” and the plurality of feature rays Ri (i=1, 2 . . . K);
• and step (S4b), surface fitting the plurality of third feature data points (P″1, P″2, . . . P″K) to obtain the freeform surface “c”;
• repeating steps from step (S4a) to step (S4b) until all freeform surfaces of the off-axis hybrid surface optical system are obtained;
• and
• step (S5), making a hybrid surface optical system comprising a primary mirror, a secondary mirror and a tertiary mirror based on the spherical surfaces obtained in step (S2), the aspheric surfaces obtained in step (S3) and the freeform surfaces obtained in step (S4).