2008 Vol. 29, No. 4

Optoelectronic Engineering
Vision calibration algorithm for object tracking and positioning
LI Liang-fu, CHEN Wei-dong, FENG Zu-ren, ZHENG Bao-zhong
2008, 29(4): 481-487.
An important task for object tracking and positioning is camera calibration, whose purpose is to estimate the internal and external parameters of cameras. A exact mathematical model, which could provide a fast method to obtain the camera centre, was established based on a strict geometric constraint relationship. The other parameters of the camera was acquired in a resonable resolving sequence to guarantee the parameter accuracy of the camera. The pixel position in a distorted image is corrected based on the computed calibration parameters to recover the original space relationship between pixels, then the accurate and undistorted images are obtain. After the position of the spot on the calibration template is computed based on camera calibration parameters, the computed spot position is compared with its real position for verifing its accuracy. The experiments to check the image correction effect and accuracy indicates that the calibration parameters obtained by the algorithm are accrate and reliable, the accuracy is effectively improved, and the accuracy requirement for the position estimation of the target in moving-target tracking can be satisfied.
Determination of entry and exit points in alt-azimuth zenith blind region by three-axis electro-optical tracker
LIU Xing-fa
2008, 29(4): 488-492.
A three-axis electro-optical tracking system can be used to track any space target in all azimuth. It can rapidly and accurately track the target in the altazimuth zenith blind region by rotating X axis. Several determinant methods to track the targets in the alt-azimuth zenith blind region by the three-axis electro-optical tracking system were introduced, such as target range determinant method, Z axis angular speed determinant method, preset blind region determinant method and so on. Determinant methods to track targets in the blind region at zenith have a directly effect on the tracking accuracy of the electro-optical tracking system with three-axis gimbal. Analysis and simulation results prove that the determination of the entry and exit points in the alt-azimuth zenith blind region with maximum angular velocity of Z axis could help three axes trackers to achieve better tracking accuracy and smooth transfer of tracking mode.
Improvement of positioning algorithm for four-quadrant optoelectronic detection system
YU Feng, HE Ye, LI Song, ZHANG Ji-tao
2008, 29(4): 493-497.
Under the same hardware conditions, the systematic characteristics such as the linear area and the responsivity of a four-quadrant optoelectronic detector changes as the algorithm changes. The common algorithms for laser spot positioning were analyzed. The correction curves for the displacement of Gauss laser spot were deduced with two-dimensional numerical integration and curve fitting, and a high-precision digital four-quadrant optoelectronic position detection system was designed and fabricated. The theoretically deduced result was verfied by the detection system.
Best ellipse description method of target area
ZHANG Heng, LI Li-chun, LI You
2008, 29(4): 498-502.
Since the best description of the target is very important to the target feature, the target tracking and the target contour acquisition, a new ellipse description method is proposed. The target area was determined by the method according to the variance between the target and the background, and then the best ellipse description of the target was calculated based on the scale space theory. The experimental results show that the new method can effectively and accurately determine the demension and direction of the target area.
Optical correlation image recognition technology to resist scale distortion
SHAO Jun, HUA Wen-shen, ZHOU Zhong-liang, GAN Hou-ji
2008, 29(4): 503-507.
A concept of multi-complex matched filter is introduced to improve the recognition of optical correlation image and the resistance of distortion, and a new way for the recognition is discussed. The synthetic discriminant function(SDF)was combined with K-L transform as a classical concept to effectively expand the dynamic range of single matched filter. Therefore, the scale distortion was restrained and the recognition efficiency of the optical pattern recognition (OPR) system was significantly improved. The simulation indicates that the concept can increase the update speed of filtering by a factor of 5, compared with that of the ordinary filtering, in the case of the distortion of half scale. The algorithm proved valid and feasible.
Off-axis use of Cassegrain telescope in heterodyne detection system
MAO Hong-min, XU Jing, ZHEN Sheng-lai, MA Yu-fen, YU Ben-li
2008, 29(4): 508-511.
The effect of off-axis use of Cassegrain telescope with different objectives on heterodyne detection probability is studied. In the non-cooperative target heterodyne detection system, when light is off-axially emitted from Cassegrain telescope, the emitted energy is increased while detection probability is declined. In cooperation target heterodyne detection system, the emitted energy is increased by 30%, detection probability is also increased greatly. The detection probabilities for the scattering object and mirror measured at laboratory are 17% and 85% respectively. It verifies that off-axis Cassegrain telescope can be used for achieving better performance in cooperation target heterodyne detection system.
Reflex light-tube in azimuth pointing system of missile
2008, 29(4): 512-517.
The expression between reflex light-tube installation error and emergent beam axis, as well as the calculation formula of the luminous energy loss was derived based on theoretical analysis for the light transmission characteristic of the reflex light-tube in the azimuth pointing system of missiles. The selection principle of the reflex light-tube structure version was summarized. The theoretical foundation for the reflex light-tube applied in the azimuth pointing systems of missiles is provided.
Imaging properties of 5×5 array composed of square GRIN lens
WANG Feng, LIU De-sen, JIANG Xiao-ping, ZHOU Su-mei
2008, 29(4): 518-521.
The 5×5 square GRIN lens array was manufactured with the ion-exchanging technique and precision processing technology. The imaging properties of the array were studied. The results show that, compared with circular aperture GRIN lens array, the square aperture GRIN lens array can effectively increase the filling coefficient and active optical area, and its multiple image and synthetic image have better imaging quality. The reasons of the multiple image′s deflection and synthetic image′s deformation are analyzed. The solution for the problem is presented.
Investigation of electro-optic modulator based on guide mode resonance
YUAN Wen, NIE Yi-you, SANG Ming-huang, LIU Guo-dong
2008, 29(4): 522-525.
A guide-mode resonance based electro-optic modulator, which consists of a coupling prism with 4 layers of film coated, was developed. These 4 layers are metal layer, poled polymer, buffer polymer, bottom electrode. The polymer waveguide electro-optic modulator capable of attenuating total reflection was tested in the transmission of the video. A new method was proposed to stabilize mode angle with the static bias voltage. The effect of the laser noise on the analog signal modulation during the video modulation is eliminated by monitoring of incident laser beam. The operation stability was improved. The experiment results show that the electro-optic modulator has fine linearity and high sensitivity.
Study on micro-jet on ultra-high speed shadow photography
WANG Wei, LI Zuo-you, LI Xin-zhu, LI Jian, SHANG Chang-shui
2008, 29(4): 526-529.
Based on ultra high speed rotating mirror framing camera, a high speed shadow photography was designed and set up. Micro-jet and its wavefront was observed on the Tin free surface loaded explosive which existed a strip of rectangle groove and three small blind holes. The shape of jet、velocity of shock wavefront and ejecta head were obtained through shadow images.
Determination of optimum penetration wavelength for fog lights
LV Zheng, XU Tao
2008, 29(4): 530-532.
The reason of using yellow lights as fog lights is that it has better penetration power than any other single color lights. The wavelength range of yellow light is about 15nm. A method to generate man-made fog is presented. The reason that dry ice is not suitable for making the man-made fog is described. The factors for selecting the wavelength ranges to be measured are considered. The experiment equipment is introduced, with six key issues stressed, radiant power of light source should be higher, width of the I/O slits of the monochromator should be reasonable and both of them should be adjusted to an equal width, the focal length of the convergent lens should be longer, the exit of humidistat should be square, the function of vacuum pump and fog collecting hood is important, and the wavelength adjustment of the monochromator and the auto-record of the measuring signal should be controlled by a micro-computer. It is found that the optimal wavelength of LED taken as fog lights is 578nm.
Test method of life-time and reliability evaluation for high-power LED
HE Wei-li, GUO Wei-ling, GAO Wei, SHI Chen, CHEN Xi, WU Juan, CHEN Jian-xin
2008, 29(4): 533-536.
The development history of the light-emitting diode (LED) is introduced. Several factors influencing LED reliability are put forward, among which the material defectiveness of LED and the heat dissipation during packaging are the main factors. The reliability evaluation of LED is analyzed by testing the LED lifetime, which is usually derived from the accelerated test. The testing methods to evaluate LED lifetime according to the accelerated stress (single and composite accelerated stresses) are listed and introduced. The reliability of high-power LEDs was tested and several mathematical models of the LED lifetime were derived under different accelerated stresses. The mathematical formula for deriving the LED lifetime is given based on some examples.
Optical Design
Design of wide-angle depolarization flat-plate light-splitting film for three wavelengths
WANG Wen-liang, XIONG Sheng-ming, ZHANG Yun-dong
2008, 29(4): 537-541.
Since the light-splitting film is always tilted, the separation between s- and p-component is inevitable. The separation has become a difficult problem to be solved in many applications. The material and structure of original film system were selected according to Costich and Thelen theories. A wide-angle depolarization flat-plate light-splitting film for three wavelengths (532nm, 633nm and 1315nm) was designed with all-dielectric materials by Needle synthesis method and Conjugate graduate refine method. The variation range of the incident angle in the air is 45°±5°. The design and analysis results show that the polarization separation of the film system in the spectral range of (532±10)nm, (633±10)nm and (1315±10)nm can meet the requirement of the depolarization in the wide-angle range.
Optimal design of antireflective films based on genetic algorithms
WU Su-yong, LONG Xing-wu
2008, 29(4): 542-547.
A film design method based on genetic algorithms was proposed and the genetic algorithms for the design of film system were programmed in order to research the global optimization methods of the optical film system design. It was applied to the optimal design of various kinds of antireflective films. The results show that the antireflective films obtained by genetic algorithms are better than or equal to those published previously in spectral characteristics and overall performance. The optimal coating design with genetic algorithms can set the thickness limit and the number of layers without providing any initial film system. All the features are very favorable in both design and deposition of films. Furthermore, the method can be easily applied to the design of other optical coatings by changing the target reflectance values.
MTF and imaging quality of axially symmetrical optical systems with synthetic aperture
SUN Jiang-qin, QIAN Lin, WU Quan-ying
2008, 29(4): 548-552.
The mechanical and imaging characteristics of the synthetic aperture systems were analyzed and compared. By the aid of numerical simulation, the configurations and the modulation transfer functions (MTF) of axially symmetrical synthetic aperture systems with single ring and with dual rings were studied. The imaging qualities of these systems were evaluated and compared. A new axially symmetrical synthetic aperture system with 4+2 dual rings configuration was discussed. Its imaging characteristics were described in detail. The images produced by the new system were processed with Wiener filter to retrieve a better imaging effect.
Dynamic data exchange between Zemax and Matlab
ZHANG Wen-jing, LIU Wen-guang, LIU Ze-jin
2008, 29(4): 553-556.
In order to successfully combine Zemax′s functions of the optical system design and analysis with Matlab′s powerful ability on the matrix calculation and data analysis, the communication technique of DDE(dynamic data exchange) between the two softwares was researched and applied to the numeric simulation process of the computer-aided resonator alignment. The control of Matlab to Zemax was implemented through DDE and the data transmission between the two softwares was realyzed. In other words, under the cantrol of Matlab, the structure of the optical system can be rectified, and it is easy to get a series of values of Zernike polynomial coefficients of the output beam. So it is convenient for the following data process. In the same way, the calculation results can be sent to Zemax as a feedback of the optical system optimization. Data reliability and work efficiency can be improved in this way. DDE technique between Zemax and Matlab is very helpful in the field of optical system design and optimization.
Night Vision
Method for eliminating thickness non-uniformity of transmission Cs2Te photocathode
CHENG Hong-chang, SHI Feng, FENG Liu, LIU Hui, SHI Peng-fei
2008, 29(4): 557-561.
To solve the problem of thickness non-uniformity of the transmission mode Cs2Te photocathode, the mechanism producing the problem and the influencing factors were analyzed on the basis of theoretical and experimental research. The factors that influence the thickness non-uniformity include the shape of the evaporator, the relative position of the evaporator with the photocathode substrate, the binding energy needed by the Cs/Te atom to complete the mechanical reaction on the photocathode substrate and the temperature uniformity level of the substrate surface before the fabrication of the photocathode. The experiment proves that the last factor has the most important effect on the thickness non-uniformity of the transmission mode Cs2Te photocathode. By changing the heating program, optimizing the warm preservation time and balancing the temperature gradient of the photocathode substrate and pallet, the thickness non-uniformity of the transmission Cs2Te photocathode was improved from 76.4% to less than 10%.
Optimization for signal-to-noise ratio of low-light-level image intensifier
SHI Feng, CHENG Hong-chang, HE Ying-ping, LIANG Hong-jun
2008, 29(4): 562-564.
In order to improve the luminance gain of microchannel plate image intensifier, an electron multiplier mechanism-microchannel plate (MCP) was used in low light level image intensifier. The noise mechanism in the MCP was analyzed. By adjusting the energy and angle distribution of the incident electrons at MCP and keeping other MCP parameters unchanged, the optimum operation conditions of MCP for best signal-to-noise ratio were found. The best signal-to-noise ratio of the MCP image intensifier was achieved and the brightness gain of MCP image intensifier was improved.
Infrared imaging model based on geometrical optics
ZHANG Hao-su, ZHAO Yan, XU Dong
2008, 29(4): 565-571.
An infrared-imaging model for a CFD turbulence flow field was established with light ray tracing. It uses a “digital picture” to simulate an “actual target” to carry out simulation and calculation. It is concluded that there are blur effects of the wall-attached layer on a hypersonic missile by comparing the original picture with the simulated picture. It provides the missile computer the theoretical support for recovering images. This paper categorized the models into three types, long-distance, critical-distance and short-distance, according to the operation concept of infrared seeker. All these models were discussed respectively. The relationship between the PSF and the blur board used in digital image processing was analyzed.
Algorithm of GVF Snake contour extraction for infrared image
WANG Jian-hua, LIU Chan-lao, ZHENG Yang-guang, WANG Ying
2008, 29(4): 572-575.
To overcome the blurred borders and poor distinction of the infrared images, an automatic object contour extraction method based on the Ostu threshold method and GVF Snake is proposed. The Ostu algorithm is adopted to segment the image. Then the extracted object contour is taken as an initial contour of Snake model for precise segmentation computation. After that, the initial contour is converged to the target borders precisely by utilizing the feature of GVF Snake. With GVF Snake model, the manual operation is reduced during the segmentation of complex images thanks to the advantages of the Ostu algorithm. Experiments show that such algorithm is fast in calculation, it can converge the contour to the target borders rapidly and track a target precisely, and it is immune to noise.
Laser Technology
Design of optical window for photo-detector in ring laser gyro
HU Zhi-qiang, YAO He-bao, JIANG Jun-biao, WANG Song-Wei, ZHU Guan-fang
2008, 29(4): 576-579.
Because there is diffraction effect in laser and the laser intensity distribution is in Gauss form, a big error is introduced in the calculation of optical window size for the photo-detector (PD) when the spacing between the beat frequency fringes is computed with plane wave. Two steps are applied to the design. First, the phase difference of the two signals is detected by a PD. Then, based on Gauss beam, the spacing between the beat frequency fringes of the two beams is calculated to get the ideal size of the optical window. The method was verified with an experiment.
Modeling and theoretical analysis for improving laser polarized active imaging
ZHANG Xu-guo, JIANG Yue-song, LU Xiao-mei, LI Fang
2008, 29(4): 580-584.
An experimental method to improve the laser polarized active imaging is proposed. The schematic diagram of the experimental setup is presented, and the imaging principle of the setup is analyzed. The formulas to calculate the polarization degree and intensity for the improved experimental setup were derived based on the measurement method of Mueller matrix for the target analysis. The errors of the setup and the depolarization phenomenon of the Cassegrain telescope were analyzed. In comparison with the dualrotating retarder technique (DRRT) for the polarization degree and intensity measurement, the accurate requirements for the experiment setup is released, and the measurement speed is increased. The polarization degree and intensity of the scattered light from the target can be obtained in only one measurement by the new method, rather than 16 times of measurement by DRRT.
Application of multi-resolution analysis in extraction of laser micro-Doppler effect features
SHENG Mei-ju, YUAN Shuai, WANG Jian-hua, ZHANG Jun
2008, 29(4): 585-589.
The wavelet transform has an excellent application prospect in the detection of micro-Doppler effect because of its high precision and good noise immunity. The signal was decomposed into the minutia part of every scale with the multi-resolution analysis (MRA) in order to extract the low pass signal which contains the micro-Doppler effect features. The micro-Doppler effect, which was caused by the miniature vibration of the target, was acquired. The comparison studies for the original signal and the result obtained with MRA decomposition were implemented by the frequency analysis and time-frequency domain joint analysis based on the instantaneous frequency (Instfreq). The result indicates that the extractration of the vibrating signal features from the micro-Doppler effect can be more effective if the low-frequency signal is analyzed by the time-frequency analysis after it is processed with MRA. It provides a convenient method for the recognition, classification and detection of the target features.
Influence of background scattering on measurement accuracy of laser radar cross section
BAO Xue-zhi, GAO Wei, JIA Yang-yu, LV Hong-peng
2008, 29(4): 590-594.
To improve the measurement accuracy of laser radar cross section (LRCS), the background scattering existing in the measurement is pointed out. The equation for measuring LRCS is presented. The mechanism for the effects of the background scattering from the ground and supporting frame on the measurement accuracy was analyzed. According to the equation and the mechanism, the methods to reduce the background scattering, which include extinction material coating, multi-contrasting measurement, size matching, are put forward. The method of the extinction material coating was verified by experiment. The experimental results show that the method could effectively reduce the background scattering and improve the measurement accuracy.
Fiber Optics
Investigation into parameters of grating scanning spectrometer
LIU Han-chen, WANG Qiu-ping, ZHANG Chong-hui, WANG An-xiang, JIANG Xue-fang
2008, 29(4): 595-598.
The grating scanning spectrometer has incident and emergence lights with fixed directions. It works when its grating rotates. It′s different from another lightsplitting system in which the grating is fixed, and the direction of the incident light changes. Based on the equation of the grating, the angular dispersive power, line dispersive power and resolving power of the spectrometer testing system whose grating movement was controlled automatically by a computer were calculated theoretically. The parameter formulae of the angular dispersive power, line dispersive power and resolving power of the grating scanning spectrometers were obtained. The calculated result shows that the measurements made by the grating scanning spectrometers are different from those of the spectrometers with fixed grating.
Optical Material
Recent progress in 1.4μm~1.7μm broadband light amplification materials
ZHOU Bo, XIAO Zhi-song, YAN Lu, ZHU Fang, HUANG An-ping, WANG Jin-liang, XU Huai-zhe
2008, 29(4): 599-605.
The broadband amplification is defined as the net amplified gain achieved in the whole lowest loss wavelength band 1.4μm~1.7μm of silicabased fibers. Efficient broadband light amplification materials can meet the needs of large information capacity and optical integration in communications. The materials for this application are mostly oxide-doped rare earth (RE) thin films, glasses and polymers. The former two materials are introduced in terms of band width, photoluminescence (PL) characteristic and PL mechanisms. The methods to improve the PL properties are discussed with the author′s previous results and experiences. It is concluded that there is a great potential for nano-structured RE co-doped materials. Finally, the prospect of the optical amplification is put forward.
Study on surface roughness of ZrO2 thin films
PAN Yong-qiang, WU Zhen-sen, HANG Ling-xia, LUO Ting
2008, 29(4): 606-609.
The surface roughness of Zirconium oxide (ZrO2) thin films with different thickness and substrate roughness, which were deposited with different ion beam auxiliary energy by electron beam evaporation technique,was studied with Taylor Honson coherence correlation interferometer (Talysurf CCI). The influence of surface roughness of substrates, thickness of ZrO2 thin films and ion energy of ion beam assisted deposition (IBAD) on surface roughness of ZrO2 thin films was investigated. The results show that the surface roughness of ZrO2 thin films increases slowly with the increase of substrate roughness when the substrate roughness is less than 10nm, then increases quickly when the roughness is more than 10nm; the surface roughness of ZrO2 thin films decreases and then increases with the increase of both thickness and ion energy.
Optical constant measurement of rough surface alloy steel by ellipsometry
WU Ying-li, WU Zhen-sen
2008, 29(4): 610-613.
The optical constant of alloy steel was measured with ellipsometry when the incidence wavelength was 0.632μm and incidence angle was 50°~80°. Since the surface of the alloy steel was rough, the measured optical constant was corrected with the Ohlidal-Lukes theory. It is founded that the correction of the ellipsometric parameter increases proportional to the incidence angle. The results indicate that the calculated result after correction agrees with the measured one when the incidence angle is in the range of 50°~70°, but differs significantly when the incidence angle is in the range of 70°~85°. Therefore, the accurate optical constant of alloy steel can be obtained by ellipsometry when the incidence angle is less than 70°.
High-precision optoelectronic axis angle measurement in space
ZHANG Fan, TAO Kun-yu
2008, 29(4): 614-618.
In harsh environment, the precision measurement of the axis angle is critical for the development of space system. The factors such as temperature variations and platform vibration severely limit the accuracy and life time of axis angle measurement device in space. The mechanisms to introduce error code and cause the aging of the device in space were analyzed, and a new solution to realize the high precision measurement of axis angle under the complex space environment was proposed based on such analysis. By using a new adaptive technology of encoder signal processing, the shortcomings of traditional processing method used in measuring the axis angle can be overcome. The experiment results show that the resolution of the angle measurement is 0.618″and the peak-to-peak value of the angle measurement error is 6.2″.
Improved method for three-dimensional profile measurement based on grating projection
CHENG Yin, YU De-min, XU Zeng-pu, WANG Yong-qiang
2008, 29(4): 619-624.
The traditional Fourier transform profilometry (FTP) is not applicable to unwrap the wrapped-phase correctly when the depth continuity phase of the detected object is interrupted by its abrupt height change. The problem can be solved by using the two-frequency grating projection. By summarizing the traditional measurement method and the two-frequency grating measurement method, a novel technique based on the color composite grating projection was introduced, which could eliminate the effects of the background spectra and high-order components on the measurement with only one collection, expand the scope of measurement, and solve the problem of phase interruption. The measured results of the three methods were analyzed and compared. It shows that the accuracy of the color composite grating projection method is the best.
Improved algorithm for Sobel edge detection of image
JIN Peng-fei
2008, 29(4): 625-628.
Edge detection is used in image processing and computer vision. The typical Sobel edge detection algorithm in the digital image processing was analyzed. An improved algorithm for the image edge detection based on Sobel algorithm was proposed to overcome the disadvantages, which the obtained edges of the image is thick and sensitive to the noise. The edge types that exist in the real images are described with mathematical models and the models of the continuous edges are regarded as a research subject. A template for detecting the direction of the image edges was rebuilt. The thinning processing for the gradient histograms of images was adopted, to improve the low accuracy of locating the edge position, caused by the traditional Sobel edge detection which was based on oneorder derivative′s maximum value or two-order derivative′s zero-crossing. The simulated result shows that the algorithm has a better immunity to the noise jamming of images and the edge position extracted by the algorithm is accurate.
Banknote recognition technology based on fluorescence spectrum analysis method
HUANG Ying, XIE Yan-hong, YI Xin-jian
2008, 29(4): 629-632.
A banknote recognition photoelectric system based on grating spectrometer was developed, in which aphotomultiplier tube was used as a detector and a computer sampling interface was designed by VC++ language. The fluorescence spectral characteristics of the banknote are analyzed when it is stimulated by a ultraviolet lamp. The optical system, the optoelectronic signal detection and the signal processing system were designed based on fluorescence spectral analysis. The testing results indicate that the fluorescence spectral characteristics of the true banknote are quite different from those of the counterfeit, their peak values appear at 545nm and 525nm respectively. The fluorescence recognition system is sensitive and reliabile.
Theoretical Study
Simulation study on depolarization for imperfect orthogonal mirrors
CHEN Li-gang, HONG Jin, QIAO Yan-li, SONG Zhi-ping, ZHANG Dong-ying, LI Wen-tao, QIU Zhen-wei
2008, 29(4): 633-638.
Depolarization of imperfect metal orthogonal twin mirrors is studied by building a geometric model of the mirrors to change the direction of light ray. The simulation study shows that linear polarization sensitivity of silvered orthogonal twin mirrors is better than that of aluminum or aurum mirrors at the range of 0.4μm~10μm, and the silvered orthogonal twin mirrors have less influence on polarization ratio than those of aluminum and aurum mirrors. Therefore, the silvered orthogonal twin mirrors are recommended to be used in remote sensing of polarization. The influence of the silvered orthogonal twin mirrors on radiance and polarization ratio is very small if the angular error is controlled within 0.5°. The depolarization performance of the mirrors is well enough to satisfy the requirement of scanning polarimeters.
Theoretical study on photonic crystal tunable filter with multiple channels
LIU Qi-neng
2008, 29(4): 639-643.
In order to implement the multi-channel filtering of the photonic crystal, the numerical calculation and theoretical analysis for the one-dimensional photonic crystal were performed. The result indicates that the wavelength of the multi-channel transmission peak presents linear variation with the optical thickness of the air layer, the air layers with different thickness can capture the different numbers of the transmission peaks, and the FWHM of multi-channel transmission peak is decreased with the increase of the photonic crystal refractive index. Based on the results, the one-dimensional photonic crystal three-channel tunable filter, whose filtering channel has a tunable wavelength range of 60nm, a tunable range of FWHM is 1nm~5nm, and a transmission peak is 0.98, was designed.
Planar optical waveguide mode in biosensing
WANG Xue-jun, LU Ya-xiong, WANG Zhi-gang
2008, 29(4): 644-648.
In order to improve the detection sensitivity and increase the response speed of the biosensor, based on the theory of planar waveguide, the zone energies of the evanescent fields in the single mode and multimode of the planar optical waveguide were compared under the same condition by using the principle of the evanescent field applied to the biosensing field. It is proved that the energy of the single mode is higher than that of the multimode by VC and Matlab. The theoretical calculation indicates that the fluorescence efficiency of single mode is 5.83% and multimode is 1.75%. Therefore, the single mode of planar optical waveguide is a better alternative in the application of biosensors and the relative area.
Influence of spatial frequency on diffraction efficiency of transmission hologram
REN Yu-fen, ZHANG La-mei
2008, 29(4): 649-652.
In order to study the relation between the spatial frequency of interference fringes and the diffraction efficiency of transmission holograms, six transmission holograms in which the planar wave was used as reference beam and the spherical wave as object beam were taken under same situation. The diffraction efficiency was measured in the experiment and the spatial frequency was calculated. Moreover, taking the convergent spherical wave as the object beam and the planar wave as the reference beam, another four transmission holograms were made through changing the angle of the incidence light and the focus of the spherical wave, and then the diffraction efficiency was measured and the spatial frequency was calculated. The results show that the diffraction efficiency of transmission holograms made under same situation was determined by the spatial frequency but not by the reference beam or object beam, the spatial frequency changes only with the angle between the reference beam and the object beam, and that the diffraction efficiency changes according to the angle of incidence.
Hybrid input-output algorithm for phase retrieval of 2-D complex image in fractional Fourier domain
CUI Yuan-feng, LIAO Tian-he, GAO Qiong
2008, 29(4): 653-656.
By introducing the hybrid input-output algorithm into classical Fourier domain, the phase retrieval of 2-dimensional complex image in fractional Fourier domain is studied. The implementation of the algorithm is given in detail, and numerical simulation is also done. For fractional Fourier transform, these results reveal that the proposed algorithm works well for the orders between 1/2 and 3/2 in the orders from 0 to 2, but not satisfactory in other orders.
Resonance tunnelling of two-level atom between double single-mode cavity fields
SUN Yu-hang, LUAN Qian-jin
2008, 29(4): 657-660.
The effect of the kinetic energy of the atomic mass-center movement, cavity length and spacing of two cavities on the atomic transmissivity is investigated based on the consideration of a factor that the single two-level atom passes through two spatially separated single-mode cavity fields. The results show that in the case of ultra-cold atom, when the kinetic energy of the atom is high (k/k0>1), the effect of the cavity length and the spacing between the two cavities on the transmissivity is unobvious; when the kinetic energy of the atom is low (k/k0<1), influence of the cavity length and the spacing of two cavities on the transmissivity is obvious.
Propagation characteristics of beam passing through optical system with annular diaphragm
HAN Yong, WU Jian, YANG Chun-ping, HE Wu-guang, XU Guang-yong, YE Zheng-yu
2008, 29(4): 661-664.
An approximately analytical propagation formula of plane wave passing through a system with annular diaphragm was derived with the method of expanding the window function of the annular diaphragm into the product of Fourier series and complex Gaussian functions. The beam propagation through the optical system with the annular diaphragm was numerically simulated with the formula. On-axial and transverse intensity distribution is calculated and analyzed. The numerical simulation results show that the intensity distribution is related to the obstruction ratio of the annular diaphragm.