Diffraction effects play a significant role in scene projectors by digital micromirror devices (DMDs) in the long-wave infrared (IR) band (8 to 12 μm). The contrast provided by these projector systems can become noticeably worse because of the diffraction characteristics of the DMD. The actual diffraction characteristics of the DMD deviate significantly from the predictions of scalar diffraction theory in the long-wave IR. To address this issue, we built a vector diffraction-grating model of the DMD; the diffraction grating model is simulated with MATLAB. Furthermore, we analyze the effect of incident angle and polarization, which are the main factors that decrease the contrast of DMD-based scene projectors in the long-wave IR. Finally, an effective method to improve the contrast of the scene projector system is given, and the maximum contrast of the scene projector system is ∼0.7.
It is shown by a prototype experiment that the deformation of a support structure leads to relative deflection of the optical axes of a multiwaveband imaging system and then inconsistency of the fields of view of the subsystems. To solve this issue, a topology optimization method with the objective of minimizing the deflection angles of the optical axes is proposed. The method consists of the establishment of a deflection angle equation, the construction of an objective function, and the achievement of optimization using commercial software. Then, a new optimization structure is extracted from the topology optimization model. The comparative analysis between the original structure and the optimization structure shows that the deflection angles of the optical axes after topology optimization decrease greatly, which proves the effectiveness of the proposed method.
Plasmonic resonances in metallic subwavelength structures have been widely exploited for a broad range of applications including nanoantennas, surface-enhanced Raman spectroscopy, chiral metamaterials, metamagnetism and absorbers. The phenomenon of extraordinary optical transmission (EOT) through subwavelength holes or slits based on the surface plasmon resonance is also extensively studied and has been applied for light harvesting. However, most of work about light harvesting devices suffer from many disadvantages such as narrow operating waveband, sensitive to the polarization state of the incident light, narrow accepting angles at a fixed azimuthal angle, which greatly limit their potential applications to spectroscopic detection and phase imaging. In this work, we present a broadband plasmonic resonant absorber in infrared regime. The plasmonic resonant absorber consists of a three-layer structure, i.e. two-dimensional metallic subwavelength hole arrays/dielectric-spacer/ thick metallic film from top to bottom. The designed plasmonic resonator is found to be polarization insensitive and omnidirectional due to the symmetry of the subwavelength hole array structure. The absorption efficiency of such absorber can be optimized by tuning the geometry of the metallic subwavelength structure and the thickness of the dielectric layer in between the two metallic films. The broadband efficient light absorbing property of the plasmonic resonant absorber can be explained by the synergetic effect of plasmonic resonance and Fabry-Perot (FP) resonance. It is shown that the periodic subwavelength metallic holes interact with the incident light to excite the surface plasmons so that the transmitted light intensity is significantly enhanced. The enhancement of the electric field near the metallic surface leads to an improved absorption. Moreover, FP cavity provides a resonant environment for the excited surface plasmons as well as the diffracted waves. As a result, the efficient light absorbing is achieved over a broad waveband. It should be noted that the proposed absorber can be applied to other working wavebands by carefully tuning the geometry of the metallic subwavelength structure and the thickness of the dielectric layer in between two metallic layers. The designed absorber may find important applications in solar cells, photodetectors, thermo-photovoltaic, and thermal emitters.
Compound telescope is a new type of space optical system. It uses the concept of compound eyes and the property of diffractive lens. With the help of diffractive lens, the diffractive optical system could become lighter weight, lower cost, and looser tolerance. And with the help of compound-eye configuration, the field of view is expanded. A design example of compound diffractive optical system is given. It is composed of many diffractive telescope of F/4, 200mm aperture, 0.1 degrees field of view. It is shown that the whole system can approximately attain the diffraction limit over wide field of view.
A novel design of combination of hybrid system and zoom system in hyperspectral detection imaging is discribed based on the application of harmonic diffractive element (HDE) compared with conventional system. The principles of HDE and infrared zoom hyspectral detection system are presented and the results of a example design are given. It is show that the resolution of this hybrid system is improved and the light power received by Cassegrain system is enlarged. Wavefront aberrations are less than 1/4 wavelength and Modulation Transfer Function in the dual band on each zoom focus location approaches or attains the diffraction limit on 20 cycles/mm.
This Paper analyzes the mathematical character of the extinction efficiency (normalized extinction cross section) and studies the numerical computation of it. The paper discusses the relations of the extinction efficiency and the size parameter x and the relations of the peak value of the ripple structure of the extinction efficiency and the amplitude of Mie scattering an(x, m), bn(x, m). The paper also discusses the relations of the approximate periodicity of the ripple structure and relative refractive indices m. The result shows that relation curve of the extinction efficiency and the size parameter x has ripple structure, which become faint as x is large; when the relative indices m is real and m<=2, the ripple structure has single periodicity, and positions of the peak values of the ripple structure are corresponding to the positions of peak values of Re[an(x, m)]and Re[bn(x, m)]. When m is complex and Im(m)<0.01, the ripple structure also has the same periodicity, however, the oscillation amplitude of the ripple structure becomes weaker. The larger Im(m) is, the weaker the oscillation amplitude of the ripple structure is.
The geometric distortion of infrared image, which was created by the large-sized relative aperture optical system. It could be corrected by the digital image processing technology. The magnitude of distortion would be enlarged quickly with the enlargement of relative aperture. Though the distortion could not impact on the articulation of the image, it would affect geometric location precision of the image directly. In this paper, the distortion correction of uncooled large-sized relative aperture infrared imaging system was discussed and the mathematical model of distortion correction was established. A algorithm of digital image processing was presented and applied based on control points by combining polynomial warping and space variant linear image interpolation. The method of polynomial warping was used to establish the locality relationship between the original image and the distortion ones. The space-variant linear image interpolation provided an efficient way to rebuild the frame of images. The computational costs of the proposed approach are very little and the precision is almost as high as the method of bicubic interpolation when compared to those of state-of-the-art nonlinear interpolation operators
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