Coaxial transmission optical systems can be assembled by optical centering processing and optical centering assembly to eliminate the eccentricity and tilt of each lens, thus ensuring the coaxiality of the lens. Non-coaxial transmission optical systems cannot be assembled by the traditional optical centering method, and this type of system poses a new challenge to the assembly method. Aiming at a non-coaxial transmissive optical system, this paper proposes a precise assembly method based on the spatial coordinate change and the principle of self-collimation imaging. Firstly, we calculate the spatial angle and eccentricity value of different axis mirror groups, and then use two self-collimating theodolites and optical reticle centering tools to construct the spatial angle reference and eccentricity reference for different axis mirror groups. Then, the spatial position of each lens group is determined by the adjustment method of auto-collimation. The article finally carried out the alignment experiment. The wavefront RMS of the optical system after alignment is 0.026λ@632.8nm which meets the design requirements and verifies the effectiveness of the proposed method.
In the field of the active wavefront correction for off-axis telescopes, the sensitivity matrix and damped least squares method are widely employed to calculate the misalignment. Improper selection of the damping coefficient will lead to bad wavefront correction results. Moreover, the calculated misalignment is referenced on the optical coordinate system, which cannot be directly applied as the control quantity. The article has two innovative points to solve these problems. First, an adaptive damping least squares method is proposed. The method considers the mirror surface error, uses Python + Zemax cosimulation to perform closed-loop reverse verification, and selects the optimal damping coefficient. Simulation is carried out for verification. Second, the article deduces the mathematical relationship between the calculated misalignment and the mechanism control quantity. Based on the above research, the wavefront active correction experiment has been completed. The optical component is actively adjusted with the wavefront quickly converging to RMS = 0 . 055λ @ 632 . 8 nm. The results verify the correctness of the proposed method.
As for the conventional off-axis telescope system structure, the primary and secondary mirror are mostly fixed. The alignment process lacks adjustment mechanism. In addition, the off-axis system has no rotational symmetry which increases the difficulty of alignment and makes the cycle longer. In order to solve the above problems, an off-axis telephoto system structure is designed. The primary mirror has a four degree-of-freedom adjustment mechanism can be fine-tuned manually. The secondary mirror is driven by 6-aixs motion hexapod electrically. At the same time, perturbation analysis is carried out for this optical system. The sensitivity matrix between misalignments of second mirror and aberration coefficients is obtained. Based on the matrix, adjustment strategy is proposed [1-9]. Finally, the effectiveness of the designed structure and adjustment strategy is verified by experiments.The detailed process is described below.
Coaxial optical system has a symmetry of revolution. Alignment for this kind of optical system is easy. The desired image quality can be rapidly converged. As for off-axis optical system, traditional optical alignment method can not be used due to the loss of rotational symmetry. Low initial position accuracy makes installation and adjustment more difficult than usual. In this paper, we aim to solve the alignment problem for off-axis optical system with the help of machine learning and its powerful numerical fitting ability. We carried out our research on alignment method for an Gregorian off-axis system. The location of primary mirror is fixed as the optical reference. Alignment process is to adjust posture of secondary mirror to acquire ideal image quality. We use Zemax and Python co-simulation technology to get simulated data. Then multi-layer artificial neural network is utilized to fit the mathematical relationship between misalignments and Zernike coefficients. Given the coefficients, the misalignments can be calculated by the neural network. Finally we conduct alignment experiment to verify the proposed method. The result has proved that this method is a fast and efficient alignment solution for the off-axis optical systems.
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