Key Engineering Materials Vol. 552

Abstract: In order to satisfy the high－precision technical requirements of static star simulator, according to the optical design characteristics of traditional star simulator, the paper designed a collimating objective optical system with little distortion, flat field apochromatism, made the simulated star chart by parallel light exit, on the entrance of star sensor produced star chart, and realized the static star simulator could simulate star accuracy static star simulator. This system is designed by four lenses, effective aperture is 20mm, and focal distance is 190.84mm. By imaging quality analysis it shows that in the angular field of view 6°×6°, the relative distortion of collimating objective optical system is less than 0.01%, MTF at 40lp/mm reached 0.6, and has higher imaging quality. It proves that the optical system meet the design requirements.

Abstract: IR optical system is much more appropriate to be applied in cluttered and formidable conditions. The change of temperature could degrade image quality of the infrared optical system. So the athermalization becomes the difficult part and key factor in the designing of MWIR optical systems for working under temperature range of -40°C~60°C. In this paper, the infrared telephoto lens is designed; it meets the designing requirements and has good image quality. The effective focal length is 240mm and the F-number is 2.The full field of view is 3.2°. In order to balance the chromatic aberration, an aspherical surface is used in the athermalized infrared optical system. Through carefully selected optical material and reasonable optical power distribution, passive optical athermalization can be realized. The curve of MTF is close to diffraction limit. Within the working temperature, the value of MTF at 30cy/mm is always large than 0.6. The results show that the modulation transfer function (MTF) of optical system in all field of view approaches the diffraction limit at different temperature, and 80% energy concentrates in 1 pixel.

Abstract: A second-order effective medium theory (second-order EMT) and thin film theory have been used to design a polarizing beam splitter (PBS) composed of one-dimensional sub-wavelength metal grating, considering the material of metal to be copper (Cu). It was analyzed by the finite difference time domain method for the wavelength of 1500nm. A high extinction ratio in transmission (>55.71dB) over abroad interval of angles of incidence ([-60o, 60o]) is achieved with the depth and the filling factor of the grating chosen to be 350nm and 0.3762, which are selected to transmit TM polarized light and reflect TE polarized light as much as possible at normal incident. The loss of the TE polarized light for the Cu structures is approximately less than 5.55% due to the absorption of Cu in a large angle range. The desired property will enable this type of polarizing beam splitter to be used in diverging beams. When the PBS needs to transmit approximately 25% of the TE polarized light and as much as possible the TM polarized light, it can be used in magneto-optical data storage head. But the depth of grating has been changed (approximately d=40nm) and TM transmission is only 94.7%. But it can be further improved (from 94.7% to 97.97%) by etching into the substrate.

Abstract: In order to meet the requirement of tank sight and improve the ability of Joint Transform Correlator(JTC) in target detection and recognition, the infrared telephoto system with high image quality and high performance-price ratio is designed for wavelength 8μm～12μm. Initial structure is composed of four refractive lenses. The focal length is 200 mm, the relative aperture is 1:2.6 and image field of view is 1 inch (CCD). Considering the fabrication process, production cost and other factors, the system structure is further improved. First the telephoto which is composed of four lenses is designed with normal spherical surface. Then on the basis of the original spherical structure, an aspheric surface is introduced. The optical system can be reduced into three lenses. The image quality of the whole system becomes much better. The optical system image quality is evaluated with ZEMAX optical design software. The result shows that MTF of each field is close to the diffraction-limited curve at the cut-off frequency 17lp/mm. The spot diagram RMS radiuses are smaller than the radius of Airy disk 25.35μm. The wave front aberrations for all the fields are less than 0.25λ. The telephoto can meet the requirement of target detection. Combining JTC with this infrared telephoto lens, the infrared target at longer distance can be detected and recognized.

Abstract: Due to the possession of advantages of passivity working mode, good disguise, and easy observation, infrared systems are used in a wide variety of applications. This paper using 640×480 uncooled detector designed a long-wave scan optical system with large field and large aperture working at 8.0μm～12μm, the Pixel Dimensions of the detector is 30μm. The F number of this system is 1.4 and focal length is 17mm, FOV is 63.6°, which extended to 143° by adopting dual-wedge prism rotating, the paper also given the extended field theory by the dual-wedge prism. Because there are a limited number of lens materials used in LWIR spectral bands, Germanium material and three aspheric surfaces were adopted to balance sphere aberrations and chromatic aberration. All above mentioned are intending to ensure the system has good imaging quality. The results show that the optical performance approximates to the diffraction limit and the design has better achromatic performance. The modulation transfer function (MTF) is above 0.5 at spatial frequency of 20lp/mm, energy concentration ratio is greater than 70% within the sensing element of the detector and Root Mean Square (RMS) value of spot diameter is smaller than the Pixel Dimensions. The system has advantages of simple structure, large aperture, high image quality etc.

Abstract: The application of diffractive surface in the continuous zoom system is investigated by taking advantage of the negative dispersion characteristics of binary elements. A sample design is presented in this paper using cool 320×240 detector with staring focal plane array and secondary imaging, and a mid-wave optical system using mechanical-compensated with refractive/diffractive hybrid technique is designed. The Pixel Dimensions of the detector is 30μm, and the wavelength between 3.7μm ~4.8μm.The system adopts negative group variable times and positive group of compensation which can realize 18mm～180mm continuous zoom and FOV =36.8°~3.8° , F-number is 2, it consists of 7 lenses including 2 aspheric surface and 1 diffractive surface. The length of this system is 230mm with the reflection mirror to shorten optical path. The results show that the modulation transfer function(MTF) is above 0.6 within the whole focal range at spatial frequency of 17 lp/mm, and Root Mean Square (RMS) value of spot diameter were smaller than the Pixel Dimensions. After the image quality being optimized, the monotonic and smooth cam curve is given and 100% cold shield efficiency is obtained. The curve shows that the imaging plane is stable and the cam is easy to process. The system has advantages of simple structure, high image quality and short zoom path etc.

Abstract: The effects of temperature changes on the focus of IR optical system are described in this paper, and the general methods used for compensation of thermal effects are analyzed. On this basis, the feasibility of athermalization of long focal length IR optical systems by using of hydraulics is studied, and an athermalization design of an uncooled IR optical system with focal length 200mm and F-number 1 is presented. The result shows that within the temperature range from -30 to 50 °C, the defocus of this system is less than the depth of focus.

Abstract: Zoom lens has been widely applied in all kinds of fields, and its cam optimization is the key to actualizing the performance of its optical design and the zooming process, while the smoothness and speediness of zooming movement must be considered for military and civilian use. With the incremental use of environmental requirements, it puts forward higher requests to the cam performance of lens. In order to guarantee that the cam has good stiffness in the case of vibration and shock environment, in the process of cam design, it not only requires curve optimal, but also needs to consider influence on the performance which is caused by reduced cam stiffness of the zoom system. A fine curve can ensure that the cam pressure angle α is smaller, and to ensure the cam follower maintains the uniform velocity and smaller acceleration in zooming process, and make the zoom system produce little impact, and whole zooming process smooth and fluent, it can reduce the zoom systems driving moment M, and can ensure the stability imaging of the zoom system. Good cam stiffness K can make the zoom lens have good stability in vibration environment, and make sure that the image quality. M and K respectively up to the pressure angle α of zoom curve and the rotation angle θ of zoom curve in cam. In the new cam design process, considering the whole influence on the performance that is caused by K and M to cam, we construct the function expressions K = f (α, θ) and M = f (α, θ), and then, build target optimization function with K and M, optimize the relationship between pressure angle α of zoom curve and rotation angle θ, looking for the optimal value for the stiffness K and the cam system driving moment M , and improve overall performance of the zoom cam .

Abstract: Optical lenses act as the important methods for acquire the image information is applied increasingly board ,In accordance with the application environment that require content the precision and the force environment adaptation yet more power, so it is necessary that research on the adaption ability to the big level vibration and shock. In order to stand the bitter force environment put to use the centering assembly technology to ensure the image quality of the optical system. Design the different damping coefficient rubber-bearing isolation that assimilate the big level shock energy. At first, by the Pro/e software establish the three-dimensional model and use the ANSYS software simulate and analysis the result of the design. We want to apple the Sigfit software to simulate the effect that the vibration and shock affect on the MTF of the optical system. After optimize the design theory so as to attain the optimized result. By the experiment test the lenses about the accommodate ability, the result which can meet the shock of5000g.and 20g random vibration, camera can work effectively. This kind of design technology is mature and reliable and live through the examination under all kinds of environment, this design method is provided the reference for the design and development of optical mechanism production.