Zhen Ma

The development of high precision carbon fiber composite mirror

Due to low density, high stiffness, low thermal expansion coefficient, duplicate molding, etc., carbon fiber reinforced polymer (CFRP) is one of the potential materials of the optical mirror. The process developed for Φ300mm high precision CFRP mirror described in this paper. A placement tool used to improve laying accuracy up to ± 0.1°.A special reinforced cell structure designed to increase rigidity and thermal stability. Optical replication process adopted for surface modification of the carbon fiber composite mirror blank. Finally, surface accuracy RMS of Φ300mm CFRP mirror is 0.22μm, surface roughness Ra is about 2nm, and the thermal stability can achieve 13nm /°C from the test result. The research content is of some reference value in the infrared as well as visible light applications.

Stray light measurement for point source transmittance of space optical systems

The increased sensitivity of space-based sensors has imposed greater stray light performance goals on telescope design. To meet the demand, a stray light test station for measuring point source transmission (PST) has been built with a lower threshold and higher accuracy. The station is nearly all black with dimensions of 28m long by 8m wide by 9m high. it is coupled with a double cylindrical chamber that reflects the specular light away from the instrument under test. The chamber is a Class 6 cleanroom. The station will allow measuring the instruments with up to a 1 meters diameter, and to perform these measurements at visible and infrared wavelengths. The instrument under test will allow to scan at azimuth angles ±110°, and at elevation ±15°. The tests were performed to estimate stray light characteristics of two optical instruments. Test results demonstrated PST performance below 1×10-7 at visible wavelengths, and 1×10-6 at infrared wavelengths.

The lightweight structure design of a CFRP mirror

The advantage of Carbon Fiber Reinforced Polymer (CFRP) is obvious as a common space material for low density, low thermal expansion coefficient and high specific stiffness characteristics, it is the ideal material choice for space optical reflector. Mirror structure with honeycomb can achieve high rates of lightweight, as well as high specific stiffness. For Φ300mm CFRP mirror, accounting of the actual process properties of CFRP, mirror panels laminated based on thermal stability design, honeycomb fabricated using one innovative inlaying-grafting design method. Finally, lightweight structure design of the CFRP primary mirror completed, the thermal stability result of the Φ300mm CFRP mirror achieved is 10nm°C.

Carbon-fiber-reinforced polymer variable-curvature mirror used for optical zoom imaging: prototype design and experimental demonstration

Abstract. In recent years, optical zoom imaging without moving elements has received much attention. The key to realizing this technique lies in the design of the variable-curvature mirror (VCM). To obtain enough optical magnification, the VCM should be able to change its radius of curvature over a wide range. In other words, the VCM must be able to provide a large sagittal variation, which requires the mirror material to be robust during curvature variation, require little force to deform, and have high ultimate strength. Carbon-fiber-reinforced polymer (CFRP) satisfies all these requirements and is suitable for fabricating such a VCM. Therefore, in this research, a CFRP prototype VCM has been designed, fabricated, and tested. With a diameter of 100 mm, a thickness of 2 mm, and an initial radius of curvature of 1740 mm, this VCM can provide a maximum 23-μm sagittal variation and a minimum and maximum radius of curvature of 1705 and 1760 mm.

Thermal Stability Analysis and Experimental Study of a New Type of Grid-Reinforced Carbon Fiber Mirror

Due to low density, high specific stiffness, and low thermal expansion, carbon fiber reinforced plastic (CFRP) is one of potential materials for high precise components. For high precise structures such as reflectors and optical mirrors, usually strict thermal stability required. In order to ensure rigidity and thermal deformation resistance, carbon fiber mirrors are usually designed as a grid-reinforced sandwich structure. In order to improve the thermal stability of carbon fiber mirrors, a new type of grid-reinforced sandwich structure design is proposed. Finite element method was used to analyze the thermal deformations of the carbon fiber mirror without manufacturing error and with manufacturing error. In order to overcome the effect of moisture absorption deformation, thermal deformation test of the carbon fiber mirror was performed in a vacuum tank. The test results verify the reliability of the finite element analysis results. For Φ100mm center aperture of the Φ150mm carbon fiber mirror, the test results show that the thermal stability is about 4xa0nm/°C, which is enough for optical mirror application, although “grid effect” existed.

Mirrors fabricated with slightly oxidized C/C composites

Up to now, traditional materials, such as glass, metal and SiC ceramic, gradually begin to be unsatisfied development of the future mirrors. Designable carbon fiber reinforced composites became optimized material for large aperture lightweight mirrors. Carbon/carbon composites exhibit low thermal expansion and no moisture-absorption expansion problem, therefore, they get particular attention in the space reflector field. Ni was always employed as optical layer in the mirror, however, the coating behaved poor bond with substrate and often peeled off during optical processing. In order to solve this problem, slight oxidation was carried on the C/C composites before Ni plated. The Ni coating exhibited stronger coherence and better finish performance. Finally, a 100mm diameter plane mirror was successful fabricated.

CFRP variable curvature mirror being capable of generating a large variation of saggitus: Prototype design and experimental demonstration

The key to realize non-moving-element optical zooming lies in VCM (variable curvature mirror). In order to obtain a large optical magnification, VCM should be capable of providing a large center deflection and this requires that the mirror material should be robust enough, require less force to deform and have a high ultimate strength. In this paper, CFRP (carbon-fiber-reinforced-polymer) is selected as the mirror material and a prototype VCM has been fabricated. With diameter of 100mm, thickness of 2mm and initial curvature radius of 1740mm, this VCM can provide a center deflection approaching nearly 23um, which proves the feasibility of CFRP in constructing VCM. Compared with the work reported in [Proc. of SPIE, 8725, 87250W, 2013], the center deflection obtained here becomes even larger.

CFRP variable curvature mirror used for realizing non-moving-element optical zoom imaging

In recent years, how to eliminate moving elements while realizing optical zoom imaging has been paid much attention. Compared with the conventional optical zooming techniques, removing moving elements would bring in many benefits such as reduction in weight, volume and power cost and so on. The key to implement non-moving-element optical zooming lies in the design of variable curvature mirror (VCM). In order to obtain big enough optical magnification, the VCM should be capable of generating a large variation of saggitus. Hence, the mirror material should not be brittle, in other words the corresponding ultimate strength should be high enough to ensure that mirror surface would not be broken during large curvature variation. Besides that, the material should have a not too big Young’s modulus because in this case less force is required to generate a deformation. Among all available materials, for instance SiC, Zerodur and et.al, CFRP (carbon fiber reinforced polymer) satisfies all these requirements and many related research have proven this. In this paper, a CFRP VCM is designed, fabricated and tested. With a diameter of 100mm, a thickness of 2mm and an initial curvature radius of 1740mm, this component could change its curvature radius from 1705mm to 1760mm, which correspond to a saggitus variation of nearly 23μm. The work reported further proves the suitability of CFRP in constructing variable curvature mirror which could generate a large variation of saggitus.

The computer-aided alignment study of three-mirror off-axis field bias optical system

Determine the misalignment of optical element quickly and exactly is the key to the technology of computer-aided alignment (CAA). For alignment a three-mirror off-axis field bias system, the sensitivity matrix method was used to simulate the alignment process. The results of simulation show that the sensitivity matrix method was not convergence. A new CAA method to get misalignment was put forward; the misalignment was obtained by programming the function of optical design software CODE V’s auto-optimization option. The system’s alignment characteristic was analysis and made use of this new method put up a computer simulation. The results of simulation show that the misalignment determined by only once auto-optimization and guidable to alignment of this system. After alignment, the optical system produced a measured wave front error across the all image plane less than 0.08 waves RMS at λ=0.6328μm.