Off-axis three-mirror freeform telescope with a large linear field of view based on an integration mirror

Abstract

We report on the design of an off-axis three-mirror freeform telescope with a large field of view (FOV) based on an integration mirror (IM). This design is the continuation of the authors' previous work. Based on aberration theory, we established a suitable nonrelayed three-mirror-anastigmat initial configuration for integration mirror design. For an optical freeform surface, we analyzed the qualitative aberration correction ability of a x-y polynomial surface that can provide a simple, convenient, and user-friendly relationship between freeform surface term coefficients and aberrations and then applied the x-y polynomial surface on the tertiary mirror to improve the system optimization degrees of freedom. In an example with a focal length of 1200 mm, an F-number of 12, and a FOV of 1°×30°, the tolerance performance was analyzed, and the system presented a good imaging performance. In addition, the IM structure and opto-mechanics support structure were designed and analyzed. The confirmatory design results showed that the integration of the primary mirror and tertiary mirror can improve opto-mechanical properties judged by multiple criteria. In conclusion, the integration of the primary mirror and tertiary mirror not only offers alignment convenience as described previously but also improves system opto-mechanical properties in multiple perspectives. We believe this large linear FOV system based on IM has broad future applications in the optical remote sensing field.

A Method to Increase the Field of View of an Imaging Optical System

“…In order to solve (10), we use the idea of normalization to find the optimal solution. The optimal evaluation criteria can be expressed as follows:…”

“…The field of view of the optical system can be more than 10°in the X-direction. However, because of the off-axis aberration in the Y-direction, it is difficult to make the field of view very large, generally less than 1° [5][6][7][8][9][10]. This requires a linear array detector to receive the image and obtain the rectangular field of view by scanning and swinging [10].…”

“…However, because of the off-axis aberration in the Y-direction, it is difficult to make the field of view very large, generally less than 1° [5][6][7][8][9][10]. This requires a linear array detector to receive the image and obtain the rectangular field of view by scanning and swinging [10]. In order to realize the imaging of an off-axis three-mirror optical system with a rectangular field of view (expanding the field of view in the Y-direction), scientists use free-form surface optical elements in the system to correct off-axis aberrations and increase the field of view [11][12][13][14][15][16][17][18].…”

Combining freeform optics and curved detectors for wide field imaging: a polynomial approach over squared aperture

“…In the considered examples a few mathematical descriptions of the freeform surfaces are applied: ordinary XY-polynomials [1][2][3][4][5][6][7], Zernike polynomials [8,9], non-uniform rational Bsplines (NURBS) [10][11][12] and a few other types of equations, used in [13][14][15][16][17]. Among the latter it is reasonable to note Bernstein polynomials [13] and Legendre/Q-Legendre polynomials [14].…”

Design of image-side telecentric freeform imaging systems based on a point-by-point construction-iteration process

“…As it has been discussed in Refs. [21][22][23], there is a relationship between the freeform surface term coefficients and aberrations. XY polynomial surface up to the fourth order corresponds to primary aberrations (or fourth-order wave aberrations), which are the dominant aberrations in the optical system before aberration correction.…”