Optical design and simulation
2019, 48(S1): 198-204.
doi: 10.3788/IRLA201948.S118001
In order to reduce the range of movement of multi-node laser communication antennas, improve the motion control accuracy of two-dimensional tip-tilt mirror, avoid changing of mirror surface shape caused by the difference material performance between the mirror and the support, a integrated lightweight tip-tilt mirror with a supporting structure was proposed. Integrated design of tip-tilt mirror and support structure was conducted using material of high volume fraction SiC/Al. The thermal and mechanics stability of the mirror surface shape was improved. It can be mounted directly on the elevation axle seat, and the distance between the tip-tilt mirror rotation axis and the surface was shortened to 20 mm. The result of finite element analysis shows that the eigenfrequency of the tip-tilt mirror was of 1 337 Hz. The peak valley value(PV) of tip-tilt mirror surface shape error was better than 0.121, and root mean square value(RMS) was better than 0.031 in the range of (205)℃. Using ZYGO interference to test the mirror surface shape error, test results show that the peak-valley value of tip-tilt mirror surface shape error is better than 0.163 and root mean square value is better than 0.029 in the ambience of (205)℃ Parameter requirement of laser communication antenna for tip-tilt mirror surface shape error /25(RMS) is satisfied.
2019, 48(S1): 205-210.
doi: 10.3788/IRLA201948.S118002
Surface shape accuracy under gravity is an important aspect of space-based mirror performance. A 3 m aperture space-based mirror was optimized based on the parametric model of mirror structure and support point distribution, taking the surface shape RMS under the action of gravity as the object function. Firstly, the number and location of the support points were determined by using the classical theoretical formula, and the structure of the mirror was designed preliminarily. Secondly, according to the lightweight characteristics of the mirror and the kinematics design of the support system, the parameterized model of the mirror structure and the support points' distribution was established. Finally, the process integration and process automation of mirror component optimization were realized by using Isight software, and the relationship between the shape accuracy under gravity and various parameters was studied. The results show that the RMS value of the optimized mirror is 86.7 nm, which is 66.6% less than that of the preliminary design 259.4 nm, and meets the requirements of the project. The proposed optimization method combines with the kinematic model of the support system, and provides a comprehensive and efficient new approach for the optimization of large aperture mirrors with similar lightweight structure and support schemes.
2019, 48(6): 618001.
doi: 10.3788/IRLA201948.0618001
Panoramic annular optical system have been widely applied in various emerging field like robot sensing. This type system desire a large FOV detection capability while maintaining a small and compact size. According to above requirements a research on the panoramic annular optical system was made, and a two-channel panoramic annular optical system based on the analysis of the panoramic annular lens(PAL) was designed. The system is composed of a marginal FOV channel and a central FOV channel, which correspond to the panoramic annular optical system with entrance pupil preposition and central FOV system respectively. By rational combination, the central FOV of the system is 0-18.5, the marginal FOV of the system is 38-83. In the design process, even-ogive surface was adopted to design the certain surface of the panoramic annular lens of the marginal FOV channel, also an description of how to use the even-ogive surface in the design process was made. Finally both two channels can acquire a good image on the image plane during the working wavelength 0.486-0.656 m, the whole structure of the system is relatively compact, satisfying the demand for application.
2019, 48(6): 618002.
doi: 10.3788/IRLA201948.0618002
Infrared optical systems, facing with complex external environment, are widely used in military, aerospace, civil and other fields. The traditional method for evaluating system performance just by Optical Analysis Software should be improved, and thermal/structural/optical (TSO) integrated analysis is an effective method for synthesizing effects of multiple physical fields, which include optics, mechanics and thermology. The data conversion program between disciplines was compiled after researching Zernike polynomial fitting algorithm. The interface problem of data transmission in optical mechanical and thermal program was solved, and the thermal insensitivity optical system design was carried out using the TSO integrated analysis, as an example. The optical transfer function of infrared system under the high and low temperature environment was obtained by TSO integrated analysis, which provides a theoretical basis for the improvement of system design and performance.
2019, 48(6): 618003.
doi: 10.3788/IRLA201948.0618003
When a laser engraving machine carries out laser engraving, sometimes the laser bursting points are uneven. It is necessary to amplify and analyze the laser explosion points to better control the energy of the laser beam. A zoom microscope objective with long working distance was designed according to the observation requirements of explosion points. The explosion points inside the glass have the viewing range of 9-32 mm. The zoom range of focal length is from 6 mm to 24 mm with optical zoom mechanism. The magnification is 4-16, and the zoom ratio is 4. A 1/2-inch CCD model VA-1MG2 was adopted as the detector with pixel size 5.5 m. The optical system optimization was carried out by using Zemax. The MTF values of all fields are larger than 0.4 at cut-off frequency 91 lp/mm for each configuration. The MTF values for central field and 0.707 field approach to the diffraction limit. The RMS radius of the spot diagram is smaller than the radius of Airy disk. The image quality of the designed system meets the requirements of all technical indicators.
2019, 48(5): 518001.
doi: 10.3788/IRLA201948.0518001
A kind of simultaneous imaging polarimeter with a high spatial resolution for satellite platform environments was designed which was based on an off-axis three-mirror system as front-view telescope system and combined with simultaneous-amplitude polarization imaging technology, and the simultaneous polarization imager was designed to simultaneously acquire the target Stokes parameters to suppress sea surface glare, sea fog, atmospheric radiation and other disturbances. It provided an effective means to improve the contrast of detection targets, and had obvious advantages in dynamic target detection. According to the optical system, the detailed structural design had been finished. Finally, through the laboratory performance test, the working spectrum was 500-700 nm, the FOV was 8.50.1, the spatial resolution was 5 m@500 km, the optical MTF was more than 0.4@71.4 lp/mm, and under the condition of an elevation angle of 30 and a reflectivity of 0.2, the noise ratio was better than 38 dB, the polarization measurement accuracy is better than 1%(P 0.3), the first-order mode of the whole machine was 195 Hz, and it had good strength and stiffness. The overall performance meets the actual use requirements.
2019, 48(5): 518002.
doi: 10.3788/IRLA201948.0518002
Optical fiber image module is one of the key components of large field of view space-based telescope, whose stiffness characteristics of support structure have a crucial impact on the working life of objective lens. In order to ensure the lifetime of objective lens and reduce the weight of the support structure of the optical fiber image transmission module under vibration load, the braced structure of the optical fiber image transmission module was optimized with the inert strength of optical glass and the fundamental frequency of the structure as the optimization constraints on the basis of topological optimization. Firstly, the calculation method of inert strength of optical element was described and the inert strength boundary value of the coupled-fiber monocentric lens was determined. Secondly, the initial braced structure of the optical fiber image transmission module was designed. Finally, on the basis of topology optimization, an integrated optimization model was established with the inertia strength of the monocentric lens and the fundamental frequency of the braced structure as the optimization constraints, and was calculated by using iSIGHT integrated optimization platform. The numerical result of the simulation demonstrates that under the condition of satisfying the optimization constraint, the quality of the optimized support structure is reduced by 11.4%, achieving the obvious weight loss effect. The proposed optimization method provides a reference for the opto-mechanical structure of objective lens coupled with the optical fiber bundle.
2019, 48(5): 518003.
doi: 10.3788/IRLA201948.0518003
In the development of large ground-based telescope technology, the primary mirror support technology is always a key technology. In this paper, a semi-active support method was researched based on a 2 m SiC lightweight primary mirror, which was used to correct some unpredictable low-order wavefront aberration caused by machining error, assembly error and other factors. Firstly, the finite element simulation model was established, and the finite element simulation was carried out. An unit correction moment (1 Nmm) of Mx or My, which were two orthogonal moments, was separately applied to the 6 Tripod soft hinge, so the primary mirror deformations under a total of 12 cases of the situation were respectively analyzed. And then with the linear superposition principle of small deformation, the correction ability of the moment correction method for low order wavefront aberration was analyzed and calculated. It could be seen from the analysis that the moment correction method could correct the tilt and astigmatism very well. The initial mirror RMS value of the tilt and initial astigmatism which were normalized to 1/10(=632.8 nm), could be respectively corrected to 0.687 nm and 2.97 nm, the correction abilities were respectively 98.9% and 95.3%, and the required maximum correction moments were respectively 6.3 Nmm and 19.9 Nmm. Then, according to the whiffletree support structure of the primary mirror, a structure of the moment correction was designed with the leaf spring at the Tripod soft hinge. Finally, the feasibility of the leaf spring correction structure was verified through experiments, and the feasibility of the semi-active support scheme of moment correction was verified further. And a certain degree of engineering experience for the implementation of the moment correction method has been accumulated with high guiding significance.
2019, 48(5): 518004.
doi: 10.3788/IRLA201948.0518004
In order to accurately and easily obtain four wavelength-dependent Stokes parameters, the intensity modulated polarization spectral imaging technology was used. The process of the restoration of polarization spectrum was calculated and derived from polarization spectrum intensity modulation theory and Fourier transform demodulation analysis, and the basic structure of the system was obtained. According to the modular design concept, the forward telescope objective lens and Offner spectral dispersion system of the spectrometer optical system were designed, which achieved a spectral resolution of 1.24 nm in the 400-1 000 nm spectral range. And then the front polarization spectrum modulation module was designed based on spectral system parameter, so a complete design example was given. Finally, the reasonability of the polarization spectrum modulation module design and feasibility of the Fourier transform demodulation method were verified by experiments, which lays the foundation for the recovery of polarization spectrum.
2019, 48(4): 418001.
doi: 10.3788/IRLA201948.0418001
Aiming at the working conditions and working requirements of the fast steering mirrors for space cameras, a lightweight scheme for fast steering mirrors was proposed. Taking the mirror with a diameter of 100 mm as the research object, the lightweight structure based on ribs was designed, and the calculation method of the equivalent thickness of standard circular mirror was proposed. Two supporting methods of the mirror, rear support with three points or rear support with a central point, were designed separately, and the results of the contrastive analysis indicate that mirror supported with a central point can avoid mutual interference between multiple support points, which is caused by inconsistent temperature deformation of the holder and the mirror. The accuracy of the mirror surface is higher, and because of its simple structure, the total mass of the wobble assembly is lighter. In order to achieve the best overall performance of the fast steering mirror structure, a multi-objective optimization of the main structural parameters was executed, the total mass of the wobble assembly and the RMS value of the mirror surface were simultaneously used as the optimization goals. The optimization results showed that the rib height and the adapter thickness contributed the most to the overall performance of the structure. The total mass of the wobble assembly under the optimized scheme is only 95.75 g, and the first-order resonant frequency of the structure is 217 Hz, the RMS of the mirror surface is 7.26 nm under the condition of -8℃ temperature load, which meets the design requirements while achieving a 40.4% reduction in the weight of the mirror.
2019, 48(4): 418002.
doi: 10.3788/IRLA201948.0418002
In order to meet the need of measuring the train groups' three-dimensional coordinates, a 3D laser radar common path zoom optical system was designed. According to the characteristics of laser beam expender, multistage laser amplifiers were carried out by using lens chain. Based on Gauss optics and geometrical optics, the optical structure of the laser emission system based on liquid lens was fully analyzed, and the key parameters of the initial structure of optical system were calculated. Using Zemax optical design software to optimize the simulation, the 3D laser radar transmitting/receiving optical system was designed. The spot diagrams of the transmitting optical system which used a liquid lens to zoom were all less than 20 m/m within the image distance range between 2 m and 30 m, and the spot diagram decreased with the increase of the distance. By minimizing the spot size which was detected by the array detector channel of the receiving system to focus the energy in one point, then the power of liquid lens was the optimal state to make sure the spot diagram in the target was smallest. By optimizing the design, the radius of the 90% energy concentrated area were less than 1.6 m. The optical structure not only improves the system alignment, reducing the external disturbing, but also simplifies the structure of the instrument volume. Using the liquid lens focusing instead of mechanical focusing to avoid the vibration, and the positioning of the laser radar was proved.
2019, 48(4): 418003.
doi: 10.3788/IRLA201948.0418003
Aiming at the problem of small-field, central obscuration and low anergy of reflective optical system, the dual-mode beam positioner optical system of a folded/diffractive co-aperture infrared dual-band positioner was proposed. Based on achromatic theory and MRTD model, the equations of wavelength band achromaticity and action distance were deduced, respectively. With the property of a common focal length in the dual-band optical system, dual-band simultaneous detection and consistency of target information identification were achieved. The parameters of the folded/diffractive co-aperture infrared dual-band positioner optical system were as follows:wavelengths are 3.4-4.8 m and 7.7-9.5 m, pitch/yaw is -26-26. focal length is 115 mm and F number is 2. The results show that thermal difference eliminated in the temperature range of -40-60℃, the optical transfer function is close to the diffraction limit.
2019, 48(4): 418004.
doi: 10.3788/IRLA201948.0418004
In order to ensure the position accuracy and the stiffness of the support system for the 4 m SiC primary mirror, the parameters of hardpoints in a hexapod configuration were analyzed according to the optical indexes of the primary mirror support system. Using the finite element method, the hardpoint positioning mechanism was optimized. The hardpoint distribution radius, positioning angle, axial stiffness and the limit of axial tension and compression were determined by the finite element software. The analysis results show that six hardpoints should be equally distributed at 1 345 mm of the radius on the circumference in the primary mirror backface. When the axial stiffness of the hardpoint reaches 15 000 N/mm, the natural frequency of the primary mirror support system is greater than or equal to 15 Hz. It can meet the design requirements and provide the basis for the following design optimization.
2019, 48(4): 418005.
doi: 10.3788/IRLA201948.0418005
Spectral image information provided by multispectral remote sensing cameras has extremely high application value. In order to break through the limitation of the number of spectral segments of CCD imaging devices and increase the number of spectral segments of a single camera, a two-channel solution was proposed. Starting from the optical system, a high-stability opto-mechanical structure was designed for a dual-channel off-axis multi-spectral remote sensing camera. Firstly, the high stability support of the large-diameter primary mirror was realized by using the four-point spherical support technology, which ensured that the mirror surface shape accuracy met the use requirements under various working conditions. Then, the camera's focal plane component, main frame and vibration isolation system were designed and optimized to ensure that the dual-channel off-axis remote sensing camera had good structural stability while providing eight multi-spectral segments. Finally, the finite element analysis and mechanical environment test of the entire camera show that the camera has high stability and meets the design expectations.
2019, 48(4): 418006.
doi: 10.3788/IRLA201948.0418006
Aiming at the difficulty of searching for physical evidence in complex environments by ordinary unmanned airborne cameras, a method using polarization imaging technology was proposed to conduct physical evidence detection and search. In order to ensure search efficiency and work under low illumination conditions, a large field-of-view and large relative aperture two-speed zoom polarization imaging optical system was designed. The system had a focal length of 11 mm and 22 mm, the F-number of 1.8 and 2.7, an angle of view of 60 and 34, and a reasonable focusing method was given, which can achieve clear imaging at 3 m and 10 m flying height. After simulation analysis, the design results show that the modulation transfers function(MTF) of short focus and long focus is better than 0.45 at 91 lp/mm, and the imaging quality is better. Tolerance analysis shows that tolerances are well designed to meet imaging quality. The system is integrated with the micro-polarizer array detector and equipped with a drone platform, which can perform real-time and efficient physical evidence search on the crime scene in a complex environment, and greatly enhance the ability of cases to crack.
2019, 48(3): 318001.
doi: 10.3788/IRLA201948.0318001
In order to better analyze the integrated installation of ground-based large telescopes' Coude optics system, the error analysis was carried out on three levels, and the Brownian Bridge walk was used to establish the Coude optics system error model. Firstly, based on the equation of light path, the optical fuzzy the Coude optics system under the influence of atmosphere disturbed was analyzed. Secondly, the optical blur caused by dynamic error and the accumulation printing through effect of gravity were analyzed. Finally, using the Brownian Bridge walk, the error model of the focus position of the Coude optics system was established under the full consideration of error chain closure. The results show that even in the temperature gradient of 0.4 ℃/m, atmospheric disturbances can also cause the deviation of about 0.2, equaling to the atmospheric coherent length of 2.3 mm. On the other hand, because the symbols of the refractive compensation were consistent, the effects of atmospheric disturbances cannot be compensated by averaging. According to the improved error model, focus position error of the Coude optics system reduce about 20% compared to the results obtained based on the assumption of independent distribution, that is, the error closure was considered more fully.
2019, 48(3): 318002.
doi: 10.3788/IRLA201948.0318002
A combined non-tracking concentrated optical (CNTCO) system composed of line Fresnel lens (LFL), reflection-type secondary optical element(R-SOE) and total internal reflection prism (TIRP) was proposed due to the high failure rate and high cost of the automatic solar tracking system. Moreover, the principle and design method of each component were discussed. The structure of the system was optimized and simulated in optical design software Zemax. The results show that the average concentration efficiency of the system reaches up to 24.1%, an 18.7% increasement compared with a combined system consisted of LFL and R-SOE (FRS), on the condition that the pitch angle is up to 16. The non-tracking concentrated photovoltaic module based on CNTCO system was integrated and preliminarily tested. The test results indicate that the photoelectric transformation efficiency of the module could be optimized up to 19.6% on non-tracking condition, even still up to 5.9% after 4 hours.
2019, 48(3): 318003.
doi: 10.3788/IRLA201948.0318003
The influence of the position of the sparse aperture mirror hard spot and the layout of the edge sensor on the precision of the relative pose control was studied. Using the geometry characteristic of sparse aperture, a primary mirror model composed of seven circular apertures was established and the control matrix of relative pose among apertures was derived. The generalized least squares method was used to solve this problem, considering the large condition number of control matrix, ridge regression was introduced and the intrinsic bound on the error function of the control matrix was also given. The possible 128 location strategies between edge sensors and hard spots and the effect of geometric distance on the condition number of control matrix were analyzed. The results show that the layout of the hard points and edge sensors is intrinsically linked to the coefficient matrix, the sparse aperture is serious Multi-Collinearity with respect to the coefficient matrix of pose control, and the normal matrix appears seriously ill-conditioned. The condition number of normal matrix are reduced significantly when the distances between the adjacent two edge sensors while the layout is fixed. For the ill-conditioned problem of the normal matrix, the ridge regression is used to effectively suppress the ill-conditioned characteristic by choosing appropriate ridge parameters. Using this method, the redundant edge sensor structure can be effectively used to realize data fusion and ensure the stability and reliability of the measurement system.
In order to solve the evaluation problem of optical system under partially polarized light conditions caused by single ray tracing method, a full-field, full-pupil ray tracing method based on Stokes notation was proposed. The refractive and reflection Mueller matrix expressions were improved. The analytical relationship among the degrees of polarization(DOP) of the incident light, the ray angle and the DOP of the emitting light was analyzed. The analysis results show that when the difference value between the incident angle and the emergence angle was less than 5.7, the influence of the system on the DOP of the light can be reduced effectively. According to the space target polarization imaging requirements, a polarization imaging optical system with micro-polarizer array(MPA) was designed. The resolution was 0.5 m at the distance of 500 km. Dynamic data exchange(DDE) was used to trace the full-field and full-pupil rays for the optimized optical system. Four Stokes vectors and full-field polarization distributions were both calculated and displayed. Due to the DOP of any field of view can be calibrated, the polarization detecting accuracy of the optical system was improved. Therefore, the target can be recognized by matching the DOP of the incident light and the DOP of any field of view.
2019, 48(2): 218001.
doi: 10.3788/IRLA201948.0218001
Epoxy is a key bond material in the mirror assembly of nested conical approximation Wolter-I type focusing telescope which is based on ultra-thin glass. The mechanical properties of the telescope is determined by the bonding strength of the adhesive layer with micron-scale thickness. The bonding strength of ultra-thin glasses-F131 epoxy -graphite bonding structure under different curing environments and surface roughness of graphite was studied. The results show that the bonding strength decreases with the increase of the curing humidity of epoxy and increases with the increase of the surface roughness of the graphite. The peel of the graphite was found to be the main type of failure in bonding structure by comparing the surface peeling area ratio of graphite. Finally, the B basis was introduced as an evaluation of bonding strength to improve the accuracy and reliability of the bonding properties for telescope assembly.
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