2014 Vol. 7, No. 3
This paper reviews recent developments of tunable THz and optical metamaterials and gives insights into the trend of future research in this field as well as the potential applications. It can be expected that tunable metamaterials will remain to be a hot topic in metamaterials and their developments may lead to a revolution in optical devices and systems and make a deep impact on the development of photonic and THz technology.
In this article, we review the favorite target representation in target tracking, and dassify them systematically, then categorize the target tracking methods used at present on the basis of the object and motion representations, provide detailed descriptions of representative methods in each category, and examine their pros and cons. Moreover, we discuss the difficulties and future trend of target tracking.
In this paper, a new 3D surface reconstruction algorithm named IR-SFS(shape from shading for infrared images) for infrared images of space targets is proposed based on the traditional single image SFS(shape from shading) algorithm, in which both external light source and self-radiation of infrared objects are considered. Firstly, the traditional SFS algorithm is described and the features of IR imaging of space targets are then analyzed to build the IR-SFS radiation equation followed by simulation study. Using temperature estimation to get the IR residual gray image, 3D reconstruction models are achieved on the synthetic infrared images of hemi-sphere, hemi-cylinder satellite and the real infrared image of USA STS107(Space Transportation System Program 107) as the experimental targets. The experiment results show that higher peak signal to noise ratio(PSNR) and better visibility at the top of the space shuttle door, the tail, the cabin and the square equipment in the cabin of STS107 can be obtained by using the proposed 3D reconstruction algorithm with optimized parameters. The overall performance is significantly improved compared to the original SFS algorithm.
In order to solve the problem of serious influence of much noise in the phase fringe patterns of digital speckle pattern interferometry on the result and accuracy of phase unwrapping, an effective method of stripe sine/cosine decomposition combined with frequency domain low-pass filtering is introduced in this paper, and the high precision filter of phase fringe patterns of digital speckle pattern interferometry is realized. Basic idea of this method is that phase fringe patterns is mapped into two patterns by the sine/cosine function before the phase image filter processing, and then is synthesized into phase fringe patterns through frequency domain filter. This decomposition frequency domain filtering method can retention phase jump information effectively when filtering. Experimental results show that compared with the traditional image noise reduction method, this method can filter out the speckle noise in images better on the basis of reserving rush image information, and it is simple and effective, which solves the problem of loss from 10% to 40% for phase fringe patterns gray level information when traditional filtering methods are used in stripe phase fringe patterns.
In order to improve the consistency of the assessment result of image fusion with that of Human Visual System, the state-of-the-art image fusion assessment methods are deeply analysed, then a new assessment method is proposed in this paper, which is based on the complex number expression for image structure. The gradient information of luminance layer of color image is used to perform the task. When it is used to describe image structure, more human visual system-sensitive information are contain in the corresponding complex matrix. Due to the calculation problem of mutual information, we perform singular value decomposition on the complex matrix, and the singular value vector of each image block is used to construct the new matrix. Results from experiments show that the proposed method gives evaluation of 3.748 5 and 3.722 2 for pyramid and DWT methods. It improves the consistency of assessment results with those of human visual system.
Because of the inappropriate choose of reference image, double band(midwave infrared and visible) color fusion image based on the color transfer method has low contrast, decreasing image edge details and the infrared target is not prominent. We present a new algorithm based on the Laplacian Pyramid, and the contrast could be adjusted anywhere. We use the Laplacian reconstructed image as the luminance component of the YUV image fusion constructure, the differential image of visible image and infrared image as the U component, and the infrared image as the V component. In the color transfer formula, the adjustable scaling factor is brought in to adjust the contrast of fusion image. Experiments show that by using the improved method, the color fusion image retains meaningful details. The infrared target is prominent and the fusion image has similar color distribution with the reference image. We evaluate the quality of fusion image by using objective methods, and the result shows that evaluation indexes such as the mean, variance, entropy, average gradient and spatial frequency are improved.
Firstly, we introduce the principle of wave-front shaping with stochastic parallel gradient descent(SPGD) algorithm based on Zernike mode for adaptive optics in atmospheric turbulence, and achieve brief expression about Strehl ratio that makes convergence rate of SPGD algorithm be accelerated obviously. Then we construct wave-front shaping system with SPGD algorithm of specific parameters, and mainly make detailed simulations on the laws of convergence rate, shaping capability and shaping effect about distortion wave-front, Zernike order and actuator number of deformable mirror. The qualitative results show that three change laws are similar, and quantitative expressions of shaping capability and shaping effect are achieved by the least square method. And it can be found from discussion that it's better to select 37-unit deformable mirror to shape 3~27(25) order Zernike aberrations of distortion wave-front at the conditions of some shaping effect considering the nature of real-time and simplification of system.
In this work, a new TiO2 nanowire array based interferometric sensor had been developed. At first, TiO2 nanowire array films were prepared on the surface of conductive FTO glass through hydrothermal synthesis method. Then, a new type of interferometric film sensor based on wavelength modulation was constructed by utilizing the compound structure FTO glass with TiO2 nanowire array thin film as the sensing chip and making use of the typical Kretschmann prism coupling structure. Finally, the response performance of the interferometric sensor to ambient refractive index was displayed by employing sodium chloride aqueous solution as the measured liquid media. The results show that the sensor has a preferable response to refractive index over the range of 1.333 5~1.360 4. In the case of TM mode, there is a good linear relationship between reflectometric light intensity and NaCl concentration in the range of 0% to 3% and 3% to 15% quality percentage, respectively. For TE mode, within the range of 0 to 3% NaCl concentration, it shows a negative linear relationship between NaCl concentration and the absorption intensity while the resonant wavelength is basically unchanged; within the range of 3 to 15% NaCl concentration, with the increase of NaCl concentration, the resonant wavelength is gradually red shifted and it exhibits a positive linear relationship between NaCl concentration and resonant wavelength.
Considering the influence of the temperature fluctuation on the detection performance of the biosensor, the athermal biosensor based on three waveguide micro-ring resonators is proposed in this paper. The resonant wavelengths of the three parallel rings are 1 500 nm, 1 550 nm and 1 580 nm respectively. Two of the rings are utilized as the sensing resonator, and the other one is used as the alternate resonator. Because the resonant wavelengths of the three rings are different, the temperature influence term can be eliminated through computation, and as a result, the athermal bio-sensing is realized. Compared to the existing method, the scheme we proposed shows the following advantages:the unlimited use of the fabricated material, a higher integration level and a higher stability due to the introduction of the standby micro-rings which can avoid the case that the biosensor can not work when partial micro-rings work under a disorder.
In this paper, an integrated 4-channels silica optical waveguide delay line array with low cost and low propagation loss was designed and manufactured. BPM software was selected to simulate the associated parameters, including Y splitter and bend loss. In order to reduce the device size and insertion loss, the smallest bending radius of the delay line was selected to be 1 500 m. And the structure of optimizing gradient Y splitter and right angle intersecting waveguide were optimized. The cross waveguide delay line device was manufactured by standard semiconductor manufacturing processes. The output infrared pattern was obtained. The delay time of each channel was 0 ps, 113 ps, 226 ps and 339 ps, respectively. The 4-channels silica waveguide delay line device can achieve an equal interval of delay time between the adjacent channels. It can be integrated with itself for several times to increase delay time. The output waveguide of the device can be integrated with the optical fiber array at the same time.
Lasers with wavelengths of 532 nm, 355 nm and 266 nm are obtained using harmonic generation of a Nd: YAG solid-state laser by nonlinear optical crystal. The relationship between the absorption of single crystal silicon and the laser wavelength and ablation characteristics of single crystal silicon by 3 different wavelength lasers under vacuum condition are studied. The results show that single crystal silicon has a good absorption of ultraviolet laser in the wavelength range of 100- 370 nm, and under the same conditions, the minimum single pulse energy for 532 nm laser ablation of silicon is 30 J and the minimum single pulse energy for 355 nm or 266 nm laser ablation of silicon is 15 J. The ablation threshold values of 532 nm, 355 nm and 266 nm laser ablation of silicon are different, which become smaller with the decrease of wavelength.
The composition of novel chalcogenide infrared glass are introduced in this paper. Compared with other infrared glass, its advantages are analyzed. Mathematical model of relation between the temperature and other parameters in infrared detection imaging system is established. Benefitting from the less index temperature coefficient and low cost of chalcogenide infrared glasses, a refractive mid-wave infrared(MWIR) detection thermalization imaging system is presented. The design results indicate that the system has good imaging quality at the temperature of -40 ℃, 20 ℃ and 60 ℃.The system is compatible with staring focal plane array MWIR detector with 320 pixel256 pixel and pixel pitch of 30 m30 m.
In order to meet the requirement of mobile phone market on the wide-angle and high-pixel mobile phone lens, a wide-angle and 8 mega-pixel mobile phone lens is designed. The mobile phone lens are composed of 4 plastic aspheric lens and an IR filter, and the F-number is 2.45 and FOV is 80. The sensor OV8850 made by Omnivision with 8 mega pixels, maximum resolution of 3 280 pixel2 464 pixel, pixel size of 1.1 m, and Nyquist sampling frequency of 454 lp/mm. The design result shows that the MTF value is larger than 0.48 at 1/2 Nyquist sampling frequency in the 0.7 fields of view(FOV), and the MTF of FOV is larger than 0.38. The MTF value in 0.7 FOV is larger than 0.15 at Nyquist sampling frequency and the distortion is less than 2%.
In order to realize large field laser detecting and tracking, the characteristics of optical system are analyzed. First, based on the requirement of light spots uniformity for four-quadrant detector and system indexes, the premium structure of optical system is selected and the method of aberration correcting is presented. Then the large field optical system for four-quadrant detector is designed by using the ZEMAX software. The light spots quality is evaluated by the spot diagram, footprint and encircled energy while the distribution of the rays illuminance on the quadrant detector is obtained by TRACEPRO software. Finally, manufacture and assembly for the optical system are finished and optical performance is tested based on designing result. Testing results indicate that linear field of laser detection system is 6 degree and precision of angle measurement is less than 0.15 degree. Testing curve is consistent with theoretical curve, which validates correction of the design.
In order to realize the aspheric cylindrical mirror of high precision processing, and solve the difficult problems in this field, the aspheric cylindrical mirror processing and testing methods are deeply researched. Classical and modern processing methods are adopted and odd-form component for beam shaping system are fabricated in this paper, which is composed of aspheric cylindrical mirror and cylindrical mirror. A unique production of polishing disk is proposed aiming at the problem that the surface shape is controlled hardly. Results show that the surface error is 0.848 7m by the profilometer detecting, which can meet the operational requirement of the optical elements.
In order to accurately measure temperature and concentration of sugar solution at the same time, we presented a hybrid fiber grating sensor. Firstly, based on mode coupling theory, hybrid fiber gratings were formed using fiber Bragg grating and long-period fiber grating, which could realize dual-parameters measurement. In this hybrid fiber grating, FBG response to temperature measurement, while LPFG response to simulataneous measurement of sugar solution concentration and temperature. Then, in two linear refractive index ranges, that is, from 1.33 to 1.42 and from 1.42 to 1.44, we calibrated correlation coefficient of temperature and sugar concentration. Finally, two sensitivity coefficient matrixes were constituted to discuss the method of measuring temperature and sugar solution concentration simultaneously. Experimental results indicate that the measuring sensitivity of temperature reaches 117.9 pm/K, and sugar solution concentration reaches 213.5 pm/RIU. Therefore, the modular fiber grating sensor has high sensitivity property as the photochemical sensor.
Aiming at the big measuring error from grating spectrometer caused by the devices' spectral characterics, an error correction method is brought forward and validated. Firstly, the grating spectrometer's principle is analyzed deeply and the theoretical model of error correction is built. Then, the spectral characteristics of key devices, such as grating, detector, mirror etc., are studied and the algorithm of numerical extraction is brought forward to acquire the value of each point on the spectral curve. Finally, the theoretical model and the method of numerical algorithm are used to correct the bromine-tungsten lamp's spectrum which is obtained by the grating spectrometer. The result of the experiment shows that the mean error of the numerical extraction algorithm is only 0.39%, and the corrected spectrum is very close to the standard spectrum, which certifies that the correction method brought forward in this paper can eliminate the errors brought by the devices' spectral characteristics.
The experience of designing strategic laser systems in the previous years and a strong belief in the attainability of the goalthe development of high-power laser weaponshelp to significantly accelerate the pace of work in the field of new technologies. World press has recently published the articles where it was suggested that the anti-missile airborne laser project suffers cost overruns and delays or may fall victim to budget cuts. Just after that mass media immediately reported that the Pentagon refuses to develop combat lasers. As a result, there has appeared an epic set of myths about combat lasers. The task of this paper is to consider the most ridiculous statements and to reject them by sufficient analysis.
This is a tutorial-style paper in which simple explanations are presented to provide qualitative insight into the different physical processes that account for the guidance of light in the broadening spectrum of fibre types. These types include solid-material index-guiding fibres, holey fibres, photonic band-gap fibres and nano-wires.