In this paper, the spatial positioning technology of off-axis optical elements is studied for the installation and positioning requirements of the off-axis mirror and the anomalous off-axis ellipsoid mirror in an optical system. In this paper, the assembly coordinate system is established according to the global coordinate system of space optical system. The key optical parameters of the optical system are accurately measured and controlled by the theodolite, laser tracker, interferometer and other instruments, so as to realize the precise positioning of the special-shaped off-axis optical element. Secondly, the optical characteristics of the system are analyzed by computer aided setting technology, and the optical misalignment is calculated according to the system wave aberration detection results. Thirdly, the attitude of optical element is adjusted precisely according to the amount of optical misalignment. After many iterations calculation and precision adjustment, the optical index requirements are finally achieved. The spatial positioning method of large size anomalous off-axis optical elements proposed in this paper provides an effective method for the spatial positioning and system assembly of anomalous off-axis optical elements in large aperture optical systems.
According to the assembly requirements of the space camera's primary and secondary mirror system, this paper proposes the assembly process of carbon fiber truss fuselage's primary and secondary mirror system based on adhesive error compensation technology. The process starts from a system point of view, the adhesive bonding of the truss fuselage was unified with the assembly of the primary and secondary mirror system. The adhesive technology was used to compensate the machining errors of the structural parts, and the adhesive bonding of the truss fuselage and the optical axis consistency assembly of primary and secondary mirror system are realized in the process of one adjustment. According to this assembly process idea, the assembly process of primary and secondary mirror system was designed. Firstly, the optical axis of the primary mirror and the optical axis of the secondary mirror were calibrated by the principle of autocollimation, and the optical axis was guided to the cross reticule as the reference for subsequent installation and adjustment. Secondly, in order to realize this process method, the assembly and adjustment platform of the primary and secondary mirror was designed and built. In addition, the factors that affect the assembly precision of the primary and secondary mirror system are analyzed one by one, and the calculation method of system assembly error is obtained. This assembly method has been successfully applied to a space camera. After assembly, the coaxiality between the optical axis of the primary mirror and the optical axis of the secondary mirror is better than 0.02mm, the Angle between the optical axis is better than 10 ", and the wavefront of the primary and secondary mirror system is close to the optical design index. The assembly method presented in this paper provides a technical reference for the assembly of similar large aperture optical machine system.
With the continuous development of aerospace and aviation, the field of view of the interferometric spectrometer is getting larger and larger, and the field of view of the interferometer also increases. In order to realize the precise adjustment of the interferometer, it is necessary to input the interferometer through a large field of view target to form a large array of interference fringes. In order to improve the measurement accuracy of interference fringes, the large field of view target with small distortion and small chromatic aberration is required to produce interference fringes with a large field of view, so it is necessary to design wide-band collimator with a large field of view to provide an object that meets the above characteristics. In this paper, we designed a collimator whose focal length of the system is 307mm, the field of view is ±12°, the working wavelength is 450nm~900nm,the effective aperture is Φ50mm. The diameter of the diffusion spot in each field of view is smaller than the diameter of the Ellie disk, reaching the diffraction limit, and the distortion correction is better than 2%. The transfer function is almost close to the diffraction limit, meeting the design requirements of the wide-band collimator with large field of view and low distortion.
In order to adapt to the requirement of modern astronomical observation and warfare, the resolution of the space telescope is needed to improve, sub-aperture stitching imaging technique is one method to improve the resolution, which could be used not only the foundation and space-based large optical systems, also used in laser transmission and microscopic imaging. A large aperture main mirror of sub-aperture stitching imaging system is composed of multiple sub-mirrors distributed according to certain laws. All sub-mirrors are off-axis mirror, so the alignment of sub-aperture stitching imaging system is more complicated than a single off-axis optical system. An alignment method based on auto-collimation imaging and interferometric imaging is introduced in this paper, by using this alignment method, a sub-aperture stitching imaging system which is composed of 12 sub-mirrors was assembled with high resolution, the beam coincidence precision is better than 0.01mm, and the system wave aberration is better than 0.05λ.
A Sagnac interferometer whose optical diameter is 80mm and spectral channel is 75 is introduced based on its working principle. The method of precision alignment is introduced in detail, which includes the installation of primary alignment plane, the precise location of splitting prism, the precise adjustment of long-arm and short-arm reflector. Through the installation of alignment reference and the masterly reference transformation, the precise alignment of separated Sagnac interferometer is achieved based on the principle of auto-collimation, whose position accuracy is better than 0.01mm, angle accuracy is better than 1”, primary working plane is better than 1”.
Off-axis optical system has a wide application in space optics and remote detective area. The high surface shape accuracy can be ensured with the development of advanced manufacture technique. So the only condition which limits the wide application of off-axis optical system is how to realize the precise alignment of it. Based on a RC reflective optical system whose diameter is 400mm, the alignment method which combines the high resolution initial placement and computer-aided alignment is introduced. By designing a system which can measure the off-axis fabrication and off-axis angle precisely, the high resolution initial placement of off-axis mirror can be ensured with a measurement accuracy of ±0.05mm and ±10”. The good initial placement can give a good initial state, so the computer-aided model can be converged well. The experiment shows that a system which has a good initial placement could have a good wave aberration of 0.04λ after three times iteration adjustment.
With the development of space and aviation industry, the optical systems with high resolution and better imaging quality are required. According to the alignment technical process, the factors of every step which have big influence to the imaging quality are analyzed. It is detected that the micro-stress assembly of the optical unit and the high co-axial precision of the entire optical system are the two important factors which are supposed to determine how well the imaging quality of the optical system is; also the technical methods are discussed to ensure these two factors from the engineering view. The reflective interference testing method to measure the surface figure and the transitive interference testing method to measure the wave aberration of the optical unit are combined to ensure the micro-stress assembly of the optical unit, so it will not bring astigmatism to the whole system imaging quality. Optical alignment machining and precision alignment are combined to ensure the high co-axial precision of the optical system. An optical lens of high accuracy is assembled by using these methods; the final wave aberration of optical lens is 0.022λ.
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