Thermal Defocus Research Articles

Investigation of additively manufactured lattice structures for refractive optical systems based on auxetic properties

This paper reports on a novel concept of thermally stable lattice structures for next-generation refractive optical systems. The aim is to develop a metallic mount for optical lenses based on auxetic structures fabricated by additive manufacturing. Auxetic structures exhibit an effective negative Poisson ratio at the macroscopic level. This property is used to develop a mounting structure that compensates for thermal defocus between refractive optical elements. Numerical and experimental studies of the mechanical behavior of additively manufactured body-centered cubic cells provide the basis for the development of this application-specific mounting structure. Several static load cases are analyzed and deviations between numerical and experimental data are examined to quantify differences in dependence of element type, element size, and manufacturing-related geometrical inaccuracies. These results are used to compare the numerical analysis of the Poisson ratio of an auxetic unit cell with the analytical descriptions. This comparison is then applied to two-dimensional auxetic unit cell compounds. These studies provide the basis for the further development process of an auxetic mounting structure.

Achromatic and Athermal Design of Aerial Catadioptric Optical Systems by Efficient Optimization of Materials.

The remote sensing imaging requirements of aerial cameras require their optical system to have wide temperature adaptability. Based on the optical passive athermal technology, the expression of thermal power offset of a single lens in the catadioptric optical system is first derived, and then a mathematical model for efficient optimization of materials is established; finally, the mechanical material combination (mirror and housing material) is optimized according to the comprehensive weight of offset with temperature change and the position change of the equivalent single lens, and achieve optimization of the lens material on an athermal map. In order to verify the effectiveness of the method, an example of a catadioptric aerial optical system with a focal length of 350 mm is designed. The results show that in the temperature range of -40 °C to 60 °C, the diffraction-limited MTF of the designed optical system is 0.59 (at 68 lp/mm), the MTF of each field of view is greater than 0.39, and the thermal defocus is less than 0.004 mm, which is within one time of the focal depth, indicating that the imaging quality of the optical system basically does not change with temperature, meeting the stringent application requirements of the aerial camera.

Thermal defocus and compensation analysis of glass-plastic hybrid fixed-focus lens

Thermal defocus and compensation analysis of glass-plastic hybrid fixed-focus lens

Temperature‐Robust Learned Image Recovery for Shallow‐Designed Imaging Systems

Imaging systems are widely applied in harsh environments where the performance of shallow‐designed systems may deviate from expectation. As a representative scenario, environmental temperature variation may degrade image quality due to thermal defocus and sensor response, resulting in blur and noise. However, extensive athermalization in optics usually requires a complex design process and is limited by materials. Herein, a multibranch computational imaging scheme is developed, using emerging generative adversarial networks as the postprocessing to compensate for degradation of all kinds caused by thermal defocus and noise. In addition, a temperature controllable data acquisition, division, and mixture scheme is described to facilitate effective datasets for model robustness. Experiments on a vehicle lens and a mobile phone lens reveal that the proposed multibranch learned strategy notably increases image quality in the temperature range of 0–80 °C, and outperforms conventional athermalization in most instances, which is beneficial to lowering the design and manufacturing costs of imaging systems.

Design and manufacture of miniaturized immersed imaging spectrometer for remote sensing.

A miniaturized immersed imaging spectrometer possessing long slit and large relative aperture is proposed. It is integrated monolithically with three concentric optical components. Through the chief ray tracing, we analyzed its astigmatism characteristic and then deduced the anastigmatic condition for long slit. Meanwhile, it is athermal by matching the suitable lens materials to compensate thermal defocus. Based on the anastigmatic and athermal conditions, we have designed a miniaturized VNIR immersed imaging spectrometer and developed the prototype. Its slit is 48 mm long and it is optically fast with an F-number of 2.5. The new form shows about 12 times smaller in volume than the classic Offner-Chrisp imaging spectrometer and weighs only 2 kg, and has excellent thermal adaptability while temperature changes between -40 °C and 60 °C. Meanwhile, fabrication of core elements and gluing process of the immersed imaging spectrometer are presented. Test results of the prototype show superior performance with high imaging quality and small smile and keystone distortions. Such miniaturized immersed imaging spectrometer will greatly improve the performance and reduce the costs of wide swath hyperspectral remote sensing, and is desirable for usage on small plane or satellite platforms.

Achromatic and athermal design using cost-effective glass selection and aberration-corrected point matching on a glass map.

This paper presents a new method for determining a pair of cost-effective optical materials and powers to achromatize and athermalize a lens system, by introducing the material selection index including price level (MSIP). To obtain a relatively low-cost material effectively, we propose, to the best of our knowledge, a novel glass map including the price levels of the glasses. The materials with a small MSIP were selected on the glass map to correct chromatic aberration and thermal defocus easily, along with providing a cost-effective design. Although there are many material combinations, we can rationally identify the best selection of glasses by checking the MSIP index. Finally, the matching of the aberration-corrected point to an available material by redistributing the optical powers yields a good achromatic and athermal design. Using this aberration-corrected point-matching method, we efficiently obtained an achromatic and athermal system with cost-effective material selection, over the specified temperature and waveband ranges.

Athermalization of infrared optical system through wavefront coding

Owing to the thermal effect of optical components, it has been challenging for conventional infrared optical imaging system to work in a large temperature range. Wavefront coding technique has been shown to greatly increase tolerance to manufacturing inaccuracies and various defocus, particularly thermal defocus. In this paper, we develop an entirely new infrared imaging modality in 3.7 ∼4.8μm waveband, realized with a secondary imaging structure, a non-rotationally symmetric phase mask and a cooled infrared focal plane arrays. The proposed system offers the ability to overcome the temperature limitations of conventional infrared system as well as effectively eliminate the thermal aberration. Proof-of-concept results demonstrate significantly our athermalized optical system perform high-quality images in the operation temperature range of −40 °C to 70 °C.

Termohram quality stabilisation by the way of thermal defocus compensation

This article considers the problem of the thermograph lens defocusing under the influence of ambient temperature. The gradient of the external ambient temperature leads to a change of the design parameters of the optical system and, consequently, to thermoresponsive and the emergence of thermobarics image, which cause a sharp deterioration in the frequency and energy characteristics of the lens of the thermograph. One method of solving this problem is to compensate the influence of temperature fields on the image quality of the focusing assemblies operating in the infrared spectral range for the case of uniform heat distribution in the system.Elimination based on the characteristics of the lenses from the temperature is advantageously carried out at the design stage of the optical system by using methods of passive optical termales, which is based on the application schemes termaltake infrared (IR) lens components, made of different optical materials, transparent in the infrared region of the spectrum and have different signs of thermo-optic constants.<p >Based on the proposed method of filling thermograph thermoresponsive lens and further optimization was designed ternary diagram of temperature-compensated infrared lens for use with thermographs modern matrix receivers emitters with a size of 340×240 pixels with a size of one pixel 25x25 mkm.Thanks to this method, and the calculations in the mathematical software Mathcad have been received a number of combinations termaltake triplets infrared spectral range of 8-12 microns. At the same time it was managed to achieve thermal stabilization and system achromatization. However, this approach is only oncovin because was made from absolutely fine components and without taking into account the nonlinearity of the dependence of materials optical parameters from temperature. Therefore, for the design of termaltake working system with good performance requires further optimization of the triplet. It was implemented in the environment of computer-aided design Zemax, which allows to conduct computer modeling with the following factors: nonlinear dependence of characteristics of optical materials from the wavelength of the radiation and temperature; the analysis of passing through focusing system a large number of rays involved in image formation; obtaining a graphical representation of image quality of the optical system.The proposed lens have the following characteristics: relative aperture of 1:1 angular field of view 2ω=20°, focal length f'=38,2 mm. High image quality of the lens is confirmed by the level of modulation transfer function of 50% at a spatial frequency of 20 mm-1 for the edge of the system view field and the level of the function of energy concentration of 66% in the spot size dispersion of 25 mkm for the edge of the system view field.Back focal length of this triplet at variations of temperature in the range from 0 °C to +50 °C changes only by a fraction of a micrometer, which in turn gives the opportunity to obtain thermogram with high resolution. The stability characteristics of the lens make it possible to more accurately determine the temperature gradient adjacent portions of the object surface and the diagnosis when the temperature of the external environment changes.Ref. 11, fig. 1, tabl. 2.

Two-lens afocal compensator for thermal defocus correction of catadioptric system

Subject of Research. Traditionally, afocal compensators, located in parallel or in converging beams, are used to correct the aberrations of mirror systems. The additional property of afocality gives the possibility to ignore practically the selection of materials in the design, since, in this case, the achromatic correction is achieved automatically. A change in the ambient temperature leads to a change in the shape of the mirrors and their mutual arrangement, in addition, the optical characteristics of the compensator material change that leads to defocusing. Main Results. Based on the analysis of paraxial formulas valid for the correction of chromatic aberrations and thermal defocusing, we have obtained formulas that enable to evaluate the characteristics of the materials necessary for passive athermalization, that is, to keep image quality when the ambient temperature changes without using a mechanical offset of the sensor. It is shown that in a two-lens compensator used to correct aberrations of two-mirror lens in a converging beam of rays, it is necessary to use a combination of optical glasses and polymer materials for passive athermalization. Practical Relevance. Based on the theoretical correlations obtained, a two-mirror system with an afocal compensator is calculated with a high image quality maintained over a wide temperature range. The use of obtained formulas in practice made it possible to demonstrate the possibility of creation of athermalized catadioptric lens involving combinations of conventional glasses with modern polymeric materials. The method presented is not universal, but it gives the possibility to select materials for calculating the afocal two-lens systems, compensating the thermal defocusing of the image without active correction methods (mechanical shifts).

Calculating model for equivalent thermal defocus amount in infrared imaging system

The main effect of temperature change on infrared imaging system is the focus shift of infrared lenses. This paper analyzes the equivalent influence on imaging between the temperature change and the defocus at room temperature. In order to quantify the equivalence, we define an equivalent thermal defocus amount (ETDA). The ETDA describes the distance of the photosensitive surface shifting at room temperature, which has the same effect on imaging as the temperature changes. To model the ETDA, the expression of the focal shift as a function of temperature is obtained by solving partial differential equations for the thermal effect on light path firstly with some approximations. Then point spread functions of the thermal effect and defocus at room temperature are modeled based on wave aberration. The calculating model of ETDA is finally established by making their PSFs equal under the condition that the cutoff frequency of infrared imaging systems is much smaller than that of infrared lens. The experimental results indicate that defocus of ETDA at room temperature has the same influence on imaging as the thermal effect. Prospectively, experiments at high/low temperature can be replaced by experiments at room temperature with ETDA.

Wavefront coding technique for controlling thermal defocus aberration in an infrared imaging system

We use a wavefront coding approach to control thermal defocus aberration in an IR imaging system. The design method of athermalized system using a wavefront coding technique is discussed. An athermalized long wave IR optical system, which works at temperatures ranging from -40 °C to 60 °C, is designed by employing a cubic phase mask. Computer simulations and the first experimental demonstration are executed to verify the performance of this wavefront coded athermalized system and to clarify the issues related to its implementation.

Optical design and manufacturing technology for high resolution laser scanning unit

This paper presents optics and fabrication process of key elements in a laser scanning unit for high quality laser beam printers or multi-function printers with over 600dpi optical resolution which today’s commercial system shows. Considering the light sources with different wavelength, optical characteristics in the laser scanning unit which includes a scanning lens and an athermalization element are explained. Also fabrication technologies to realize high resolution laser system such as mold design, core machining and injection molding processes are described. Finally, the hybrid lens as the athermalization element having refractive and diffractive surface is suggested to compensate thermal defocus. The hybrid lens is fabricated and their performance and effect on laser scanning unit are evaluated.