2010 Vol. 31, No. 4

OE System and Engineering
Three optical path coaxial telescope system
WANG Guang-qi, ZHU Jun, JIANG Chao, JIN Di, XU Feng, YU Ben-li
2010, 31(4): 517-520.
In the basic Kepler telescope system, two pieces of coated glass are placed into the optical path at a 45angle with optical axis. One can reflect infrared light at the wavelength of 1550nm, while it transmits the visible and controlling infrared light with central wavelength at 1310nm; the other can reflect the controlling infrared light with central wavelength at 1310nm, while it transmits the visible light. By incorporating the controlling light and signal light paths, the system becomes simple and practical. Cost is reduced. The impact of the plate glass for visible light path is analyzed, and the path deviation falls within allowed error range by changing the thickness of the plate glass. Power loss of the signal light passing through some optical components is measured,the loss ratios for the telescope tube and plate glass measured at laboratory are 1.31% and 2.90% respectively. Transmission coefficient of signal light is deter-mined. Three optical path coaxial telescope system is successfully used in long-distance infrared control audio frequency monitor after many tests.
Mechanical design of zoom lens and analysis of its focal length
QIAO Jian, CAO Li-hua, CUI Shuang, SHI Long, ZHANG Lei
2010, 31(4): 521-524.
Zoom optical systems with mechanical compensation are widely used in all kinds of optical instruments due to its unique advantages. The structures and principle of mechanical compensation zoom optical systems with 3-unit were briefly described. Cam mechanism and guide mechanism to improve the image quality of zoom optical system were discussed. Actual focal length output with changing focal length was analyzed, including implementation of focal length output and some problems. It is shown that proposed methods are feasible for improving the design and adjustment of zoom optical lens, in addition, the accuracy of actual focal length output at different focal length is improved significantly.
Dual band night vision R-C system with wide field of view and large relative aperture
CAI Zhan-en, LIU Zhao-hui, HUANG Jing, NIU Jin-xing
2010, 31(4): 525-528.
Low-level-light color night vision systems are developing from the single band to the multi-band, and information from visible band and long wave infrared (LWIR) band is used to generate fused image and color vision. A dualband optical system is developed, which made of Ritchie-Crtien(R-C) system, correcting lens, and the beam-splitter which reflects in visible region and transmits in the long wave infrared(LWIR) region. Its full field of view and relative aperture are 50 and F/1.7 respectively, the ratio of scondary mirrors central obstruction is 1∶3, and MTF is higher than 0.60 at 50lp/mm in the visible region, higher than 0.30 at 18lp/mm in the LWIR region. The features of the lens are discussed. The aberration curves and MTF curves of the system are presented.
Novel surface plasmon resonance sensor based on intensity detection
LIU Jin, LIU Hai-shan, YANG Hai-ma, CHEN Jun
2010, 31(4): 529-532.
The structrue of surface plasmon resonance sensors based angle measurement is complex and it is difficult to achieve on-line measurement. Based on surface plasmon resonance principle, a method of differential detection for refractive changes with light intensity is presented and two LEDs are used. Reference light path is designed to eliminate the light fluctuation. Theoretical analysis and experimental results show that the sensitivity of this method is twice as that of single-LED light intensity detection method. It is convenient to realize instrument miniaturization. Angle detection device and Spectrometer are not used in the system, and the system is potable and compact.
Friction compensation strategy based on adaptive algorithm for electro-optical rotation table
LIU Jing-li, CHEN Fang-bin, WANG Hong-hong, SONG Xiao-ming
2010, 31(4): 533-536.
Because of friction disturbance, jitter often happens when the table is working at low speed, which terribly influences the tracking precision. Taking the electrooptical rotation table as a plant, based on Lyapunovs law and adaptive control theory, an adaptive friction compensation method is designed to reduce the disturbances of the friction and improve the tracking performance. The simulation results demonstrate that the method can reduce jitter and provide the better stable tracking performance.
Multi-beam maskless lithograph system
SHEN Yi, WU Yi-xu, XING Yan-bing, ZHOU Cheng-gang
2010, 31(4): 537-539.
A multi-beam lithograph system is introduced. The system uses a digital micro-mirror device (DMD) as a spatial light modulator to modulate the 405nm laser. By controlling the zone-plate-array or focusing-element-array to focus on the substrate to form a focusing-lattice, scanning lithograph is achieved with a nanometer moving platform. The setup and principle of the system is introduced and the result of the experiments is given. The experiment proved that multi-beam lithography with resolution of 400nm is achieved using the ordinary blue light and focusing-element-array.
Design of 90° defection polarizing prism with sandwich structure
REN Shu-feng, XU Xing-lei
2010, 31(4): 540-543.
In order to save the rare cryolite, a new type of polarizing prism was developed with the combination of cryolite and glass. The prism is made of ZBaF3 glass, between which is cryolite, and the glue is C10H7Br with a big refractive index. It can provide the polarized output for o light as well as a deflection 90 relative to the incident light. The experiment indicates that the transmittance of the prism is more than 80%, and the extinction ratio is better than 10-3. It is proved that this kind of prism can be used to replace the traditional prism made of pure cryolite.
Aberration analysis for annular pupils by different Zernike polynomials
SHAO Jing, MA Dong-mei, NIE Zhen-wei
2010, 31(4): 544-548.
Due to the orthogonality of every Zernike annular polynomial in the annular field, the error in Seidel coefficients solved by wave front fitting with circular polynomial for annular pupils could be obtained. To accurately compare Seidel coefficients solved by circular polynomial with Zernike annular polynomial, an experiment model was built according to the theory of wave front aberration. The Seidel coefficients solved by wave front fitting for large obscuration pupils with Zernike annular polynomial and Zernike circular polynomial were compared. The result showed that the main relative errors remained in defocus, sphere and coma aberrations, when the Seidel coefficients were solved by Zernike circular polynomials. The Seidel coefficients solved by the 9 circular polynomial terms are more close to the results solved by the annular polynomial rather than the 36 circular polynomial terms. However, when the number of circular polynomial terms decreases to fewer than 9, the error in Seidel coefficients obtained by circular polynomial will increase.
Temperature compensation for Q-MEMS gyro
ZHANG Wan-lin, YIN Jian, GUO Shuan-yun, KANG Zhen, YUAN Xiao, ying, ZHAO Yong-chang
2010, 31(4): 549-552.
Based on a lot of temperature experiments of Q-MEMS gyro, a novel temperature compensation model based on operation time is established according to the experiment data. The compensation prediction is performed to the new experimental data, and the results of compensations show that the bias is reduced to at least one tenth of the original. And the bias stability is also enhanced. The model can meet the requirement of realtime compensation and can be used in the application of Q-MEMS gyro.
Anisotropy absorption and up-conversion spectroscopy of Er/Yb∶KY(WO4)2 crystal
GUO Li-hua, ZHUANG Ren-zhong, YANG Wen-qin, YANG Jun-jie
2010, 31(4): 553-556.
The anisotropy absorption spectroscopy of crystal for 3-axis Nm, Ng, Np were conducted at room temperature. The characteristics of spectroscopy were analyzed and compared. The energy level transition of the absorption cross-sections was calculated. The strongest absorption and biggest absorption cross section parallel to the Np principal axis, which increases the number of accumulation for particles, the transition probability and the fluorescence output. The Yb3+-doped leads to a strong absorption and large half width near 980nm. Under 980nm LD excitation, the up-conversion green and red luminescence was achieved. There is little difference in peak for the up-conversion luminescence of 3-axis Nm, Ng, Np, in which Np is the strongest in the three axes.
Aspherical IOLs design and influence of pupil on optical performance of AIOL
ZHU Hai-feng, ZHANG Ya-ping, LI Shu-guang, HUANG Liu-bin, LIU Yan-min
2010, 31(4): 557-561.
One design method of aspherical intraocular lens (AIOL) was presented. Based on the corneal model of Holladay, the spherical aberration of the cornea was set as the SA value of the AIOL. The optical performances of aspherical and spherical IOL were analyzed comparatively when the IOL moved forward and the pupil diameter changed. As a result, the MTF, contrast sensitivity and off focus MTF of the eye implanted with aspherical IOL designed by this method were better than those of spherical IOL when the implanted position and the pupil diameter were the same. The imaging quality of the eye decreased with the pupil diameter as the IOL moved forward, the MTF of the eyes decreased with the pupil diameter. However, the aspherical IOL still presented more excellent optical performance than traditional spherical IOL.
OE Information Acquisition and Processing
Real-time multi-target infrared image processing system based on double TMS320DM642 processors
YAN Zong-qun, LI Gang, ZHANG Chu, HOU Yong-jia
2010, 31(4): 562-566.
Based on modular design concept, a real-time multi-target infrared image processing system with two TMS320DM642 chip as its core components is proposed. Combing with the field programmable gate array, the real-time acquiring, processing and outputting of the image data stream from the infrared focal plane detector were accomplished. In order to increase the data processing speed, the system adopted a two-stage cascaded model and employed parallel pipelining processing and multi-target image concurrent processing, which improved the real-time performance of image processing. Experiment indicates that the system needs 15ms to process each image with a resolution of 320240 to enable multi-target tracking in real-time.
Imaging characteristic and image reconstruction ofsynthetic aperture optical system
WU Jun, WU Zhen
2010, 31(4): 567-573.
Optical synthetic-aperture imaging is one of the most potential techniques for improving the resolution of system. U-V coverage, PSF and MTF of synthetic-aperture system were analyzed with different fill factors. They were discussed on the basis of Y-4 system. This study also generated image simulation of Y-4 system with the help of Zemax and Matlab.software, and restored the images with noise making use of Wiener filter and the modified Wiener filter. Reconstruction results of Y-4 system with different fill factors were analyzed and compared with the help of PNSR. The factors which affected the image qualities and reconstruction results of synthetic-aperture system were also analyzed. The results show that image restoration could improve the image quality of synthetic-aperture system and increase its definition, its image quantity is equivalent to a single aperture system and it can achieve the same effect as big aperture system, and the results of image restoration are dependent on the array structure of synthetic-aperture system and noise types.
Moving object detection based on mixture Gaussian model
WEI Xiao-hui, LI Liang-fu, QIAN Jun
2010, 31(4): 574-578.
In order to detect moving object in image scene in time, this paper presents a moving object detection method based on mixture Gaussian model. We regard the image pixel value as the synthesized process of the foreground Gauss distribution and the background Gauss distribution, and realize the background estimation and adaptive background update. Through performing multiple object segmentation after background subtraction, we can successfully detect multiple moving objects. The experiments show that when the background of image sequence is changing, the mixture Gaussian model based algorithm can estimate changed background accurately, and through subtraction between scene image and background image, the interested moving object can be detected. The experimental results for real image sequences demonstrate this moving object detection algorithm based on mixture Gaussian model is efficient.
Impact of light source angle on imaging quality of underwater imaging systems
ZHANG Li, SUN Chuan-dong, HE Jun-hua
2010, 31(4): 579-583.
We present our research about the imaging quality of underwater imaging systems based on the angle configuration of the light source. Supposing the distance between the light source and the target is equal to that between the camera and the target, we developed better transfer functions of the contrast degree and the signal-to-noise ratio (SNR). By defining that the distance from camera to the target is invariable, we described the dependence of the contrast and SNR on the angle configuration of the light source, we also gave some curves of this relationship. We analyzed the impact on the imaging quality caused by the hypothesis and the approximate. Experimental results agree with our analysis.
Optimal design of homorphic filter based on Matlab
MA Yan, ZHANG Cheng-yi
2010, 31(4): 584-588.
The basic principle of the homomorphic filter is introduced. A homomorphic filter model and parameter expression was established by using Matlab. On this basis, the homomorphic filtering method was applied to the brightness of color image and image contrast enhancement. It is shown that the method performs well in enhancing the local contrast of an image while maintaining its global appearance, and the expected filter effect is achieved. Experiments prove that the method is suitable for human visual observation to conduct image analysis and judge.
Medical image registration based on wavelet transformand hybrid genetic algorithm
LIANG Jun-ting, DONG You, WANG Ming-quan, ZHAO Yue-ping, FENG Xiao-xia
2010, 31(4): 589-592.
To address the disadvantages of image registration, a new method for image registration is proposed,which combines hybrid genetic algorithm with wavelet multi-resolution analysis strategy. In this method, mutual information is used as the similarity measure and a hybrid genetic algorithm is used as the search technique, and the parameters of genetic algorithm are adapted along with the computation of mutual information and the multi-resolution of the images. The experimental results show that this registration method could efficiently restrain the local maxima of mutual information function and the subvoxel accuracy can be achieved, which demonstrates that the algorithm is accurate, robust and efficient for image registration.
Improved live-wire algorithm for interactive medical image segmentation
ZHANG Wei, CHEN Shu-yue, LI Quan-dong
2010, 31(4): 593-596.
Lung extract is very important for computer-aided diagnosis, and it provides reliable diagnostic data for doctors. This paper presents an interactive lung segmentation method. Firstly, using optimized Gabor odd filter to filter chest X-ray image, and we can get a map of edge response energy. Then, using the edge response energy values to construct livewire cost function, which can segment chest image. Test shows that this algorithm could correctly-distinguish strong and weak edge, and extract the lung's contour quickly and effectively. Compared with the traditional algorithm, it reduces the number of human-computer interactions, which is more robust and efficient.
Optical Metrology and Measurement
Directional spectral emissivity measurement of solid materials and its error analysis
WU Jiang-hui, GAO Jiao-bo, LI Jian-jun
2010, 31(4): 597-601.
In order to meet the spectral emissivity test and evaluation of infrared materials, a directional spectral emissivity measurement apparatus based on a solid material emissivity testing model was developed. Solid materials can be measured in the temperature range of 50℃ to 300℃ and in the spectral range of 1.3m to 14.5m. Some experiments were done under different conditions, spectral emissivity graphs were given. Final errors caused by the difference between sample surface temperature and blackbody cavity temperature were analyzed and error graphs changing with temperature and wavelength were shown when temperature differences were 1℃ and 2℃.
Fast matching algorithm in cartridge module detection
GUO Dong, DONG You, WANG Ming-quan, GAO Yuan-fei
2010, 31(4): 602-605.
In order to quickly, automatically and accurately judge whether the cartridge module is qualified, according to the combustible tight plug cover image of cartridge module and the detection requirements, a fast image matching algorithm based on classical correlation coefficient matching algorithm is used to reduce the correlation coefficient calculation and template matching search scope, and the speed of the image matching is increased without sacrificing the matching accuracy. Field test shows that this method can rapidly and accurately complete target detection, false rate<1%, matching speed increased by 67%, which meet the production requirements.
Measurement and research of the properties of the nonlinear materials by PDLC method
REN Wei-ge, LIU Gui-xiang, HU Yin-can, WANG Fen, TAN Bing-hui, TAO Wei-dong
2010, 31(4): 606-610.
According to the Kurtzs theory and the relation between the transmittance of the polymer dispersed liquid crystal (PDLC) and the applied voltage, for the signal overflow during the testing process,we proposed using PDLC film to modulate the incident fundamental light intensity to control the signal of the second harmonic generation (SHG). The powder samples of potassium iodate, cesium vanadate and rubidium vanadate were tested and analyzed by this method respectively. It can be derived that KIO3 are phase-matchable, CsV2O5 and Rb3V5O14 are not phase-matchable. The signals of CsV2O5 and Rb3V5O14 is 8.13, 1.78 times that of potassium dideuterium phosphate(DKDP). The results show that this method is accurate, and easy to operate. More importantly, when applied to testing SHG coefficient quantitatively, this method can effectively improve measurement accuracy. It demonstrated that this method is feasible to test the non-linear characteristics of crystals.
Fiber Sensing and Optical Communication
Relationship between group velocity and phase velocity of the mode-field on multi-mode fiber
GAO Feng, ZHU Shi-guo
2010, 31(4): 611-616.
To clarify the discussion on ray optics and wave optics on the delay of mode field propagation process in the multimode fiber theoretically, the relationship between phase velocity Vp and group velocity Vg is derived, Vp*Vg=(c/n1)2, according to the relationship between the mode characteristic roots U and the optic fiber normalized frequency R, as well as the weak waveguide approximation theory. Based on the results, it is concluded that phase velocity is slow and group velocity is fast at low-order mode, phase velocity is fast and group velocity is slow at high speed mode. Ray optics and wave optics are used for bandwidth estimation to a given optical fiber, and the consistency of the results of two theoretical calculations confirms the correctness of these relations.
Analysis of coupled precision in characteristic calculation for long period fiber gratings with a rectangular index modulation
WANG Guo-dong, AI Yong-le
2010, 31(4): 617-619.
Based on the coupled-mode theory, the influences on coupled precision in characteristic calculation for different modes in long period fiber grating are analyzed. Calculated results show that for the low order cladding mode, the longitudinal coupling constants between the odd order cladding mode and the first core mode are smaller than that between even order cladding mode and the first core mode. So we can ignore the influence of odd order cladding mode in calculation without reducing the calculation precision. At the same time, we can select the suitable orders of sinusoidal index modulation to reduce the work of calculation according to the arrangement of wavelength and calculation precision.
All fiber online optical power monitor based on side-polished fiber
XIAO Ya-ting, CHEN Zhe, ZHANG Ling-tong, ZHANG Jun, QIN Jia-rong, PAN Hao
2010, 31(4): 620-625.
According to the principle of evanescent wave and the distribution of optical light from the side polished area of side polished fiber, an all fiber online optical power monitor was made by packaging a chip of optoelectronic detector on the side-polished fiber with U shape and suitable depth to detect the leaked light. Using the wheel side-polished fiber machine, side-polished fibers with the special shape and depth of polished area for monitoring optical power in the fiber was manufactured. The measured results show that the optical power monitor features good optical responsivity and its maximum opto-electric transition efficiency reaches 200mA/W. Its wavelength dependent loss is 0.3dB(1520nm~1620nm), polarization dependent loss is 0.07dB. The all fiber optical power monitor has no invasion to the fiber core, no insertion elements and is easy to be connected with the optical system directly.
Physical model of optical system in interferometric fiber-optic gyro
HAN Biao, LIU Ji-fang, MA Lin, SUN Yan-ling
2010, 31(4): 626-631.
The polarization error of optical system limits the accuracy of fiber-optic gyro. The models of optical devices and fused points in fiber-optic gyro are described using coherent matrix and Jones matrix. The physical model of the optical system in interferometric fiber-optic gyro is established. Compared with the former reports, the optical system described in this model is more engineering oriented. A new method is presented to analyze the polarization error caused by optical devices, fused points and the losses through the optical path. This method could analyze the influence of optical system flaws on bias and scale factor effectively, which can be used to evaluate the property of the optical system in interferometric fiber-optic gyro.
Simulation study on the relation between the structural parameters and the transmission spectra of a long period fiber grating
ZHOU Chun-xin, HUANG Ping, ZENG Qing-ke, QIN Zi-xiong
2010, 31(4): 632-635.
Based on the three-layer fiber model, we found that the relation between the structural parameters and the transmission spectra of LPFG is regular variation, and the variation rules of the transmission spectra were presented. This paper only considers the couple between lowest-order cladding modes and the fundamental core mode. When radii and refractive index of fiber core and cladding increase, the resonance wavelengths shift towards shorter wavelength; When grating period increase, the resonance wavelengths shift towards longer wavelength; When grating length increase, the resonance wavelengths have no shift, but its depth decreases. Comprehensive analysis shows that the shift in the resonance wavelengths is clear, but the change of depth doesnt have distinct rules.
Laser Technology
Temperature and thermal stress distribution in thin disk laser end-pumped by LD
LIU Quan-xi, ZHONG Ming
2010, 31(4): 636-640.
For analyzing the thermal effect in thin disk laser, a numerical model of the thin disk laser medium end-pumped by LD was set up. Considering the influence of the temperature correlation of the thermodynamic parameters of the material and the heat transfer coefficient between air and medium, based on the thermal conduction equations and the thermal-elastic equations, the transient distributions of temperature and thermal stress in the medium were calculated by a finite element analysis method. The influence disciplinarian of the pump power and heat transfer coefficient and time on transient distributions of temperature and thermal stress in the medium were analyzed. Simulation results indicate that thermal extendable damage appears on the edge of beam of the anterior surface. The change of the rise time and renew time of the temperature and stress is not obvious as the pumping power increase. With the increase of the heat transfer coefficient, the temperature and stress and rise time and renew time decrease, but this rate of the change decreases to zero slowly. The theoretical results agree with interrelated experiment results and it provides a theoretical reference for the design of solid laser pumped by LD and experimental analysis.
Modeling and analysis of Pound-Drever-Hall method using Multisim
SANG Feng, JIANG Yue-song, XIN Yao, WANG Lin-chun
2010, 31(4): 641-647.
Pound-Drever-Hall(PDH) stabilization involves both optics and electrics parts, and it is difficult to simulate PDH method synthetically. This article is aimed at solving this problem. Firstly, the electrical part of PDH was designed. Then, the model of electric circuit was used to form the optical device after-analyzing the operation principle. Based on these, independent tests of devices and a synthetic simulation were successfully carried out. The Fabry-Prot cavity (F-P cavity) used in simulation has a length of 15cm with a mirror reflectivity of 0.97. The simulation results prove that the model of the device is reasonable. The system outputs a small zero-drift signal while the frequency shift is zero. At the frequency shift of 5MHz, 10MHz and 15MHz, the system has satisfactory outputs respectively. Some discussion on synthetic simulation result and proposals for improvement are given.
Speckle contrast reduction in laser display
LI Xia, KANG Yu-si
2010, 31(4): 648-651.
In laser display system, speckle noise produced by laser coherence has a serious effect on image. The condition for a diffuser to produce the maximum speckle reduction with the minimum number of distinct phase patterns is derived. A binary realization of this optimum diffuser is obtained by mapping the rows or columns of a Hadamard matrix to the phase patterns. The method is experimentally verified by an example of green light. After using the diffuser,speckle contrast is reduced from 8.4% to 2.7%.
Propagation properties of non-paraxial Lorentz beam
ZHANG Yue, DUAN Qi-qiang, CHEN Xian-Ya, DING Gui-Lin
2010, 31(4): 652-656.
Based on the theory of the second intensity moment, the results of the far-field divergence angle, near-field divergence angle, waist width and beam propagation factor of non-paraxial Lorentz beam are derived, and the relationship of them versus the corresponding waist width and the wavelength is studied. The result indicates that, compared with the non-paraxial Gaussian beam, under the condition of satisfying physical mechanism of diode laser, the non-paraxial Lorentz beam is more appropriate with the actual situations of diode laser beam. Accordingly, the non-paraxial Lorentz beam is a more appropriate model to describe laser sources with small size and high divergence such as diode laser.
Optical Element and Fabrication
Dwell time algorithm based on optimization theory for magnetorheological finishing
ZHANG Yun-fei, WANG Yang, WANG Ya-jun, HE Jian-guo, JI Fang
2010, 31(4): 657-662.
Magnetorheological finishing (MRF) is a deterministic polishing technique capable of rapidly converging to the required surface figure. This process can deterministically control the amount of removed material by varying the time to dwell at each particular position on the workpiece surface. The dwell time algorithm is one of the most important key techniques of the MRF. A dwell time algorithm based on matrix equation and optimization theory was presented in this paper. The previous mathematical model of the dwell time was transferred to a matrix equation containing initial surface error and removal function. The required dwell time was just the solution to the large, sparse matrix equation. A new mathematical model of the dwell time based on the optimization theory was established, which aims to minimize the 2-norm or -norm of the residual error. The solution meets almost all the requirements of precise computer numerical control (CNC) without any need for extra data processing, because this optimization model has taken some polishing condition as the constraints. Practical approaches to find a minimal least-squares solution and a minimal maximum solution are also discussed in the paper. Simulations have shown that the proposed algorithm is numerically robust and reliable. With this algorithm an experiment has been performed on the MRF machine developed by ourselves. After 4.7 minutespolishing, the figure error of a flat workpiece with a 50mm diameter is improved by PV from 0.191 to 0.087 and RMS 0.041 to 0.010. This algorithm can be constructed to polish workpieces of all shapes including flats, spheres, aspheres and prisms.
Simulation of a metal ring resonator based filter with EastFDTD
LIU Er-ming, YAO Jia, MIAO Feng
2010, 31(4): 663-665.
Taking the advantages of the localized and non-radiative properties of surface plasmon, we designed a novel filter by electromagnetic simulation software EastFDTD. This new kind of filter is formed by two metal ring resonators,the inner diameters of the two metal ring resonators are 175nm and 145nm respectively, and the wavelengths of surface plasmon meeting the resonance are different. Such characteristic of metal ring resonator results in outputting signals of 1.85m and 1.58m at different ports. The crosstalk between adjacent ports of this filter can reach -19dB with the output port width of 50nm. The result shows that this novel filter has more advantages than traditional filters in filtering performance, size and integration.
Optical Theory
The influence of polarization on Quasi-Phase-Matched linear electro-optic effect
ZHENG Guo-liang, OUYANG Zheng-biao, XU Shi-xiang
2010, 31(4): 666-671.
Quasi-Phase-Matched (QPM) linear electro-optic effect is investigated when the incident light is of different polarization. The study shows the electro-optic coupling is influenced by the polarization remarkably. For the case that the QPM condition is satisfied, when the input light is linearly polarized, the energies of o-ray and e-ray can be coupled to each other totally, and the polarization direction can be rotated at any angle by external electric field; when the input light is of ellipsoidal polarization, the coupling between o-ray and e-ray is not complete while the azimuth angle of ellipsoid can also be rotated at any angle; when the input light is circularly polarized, there is no electro-optical coupling between o-ray and e-ray, and polarization of the output light keeps unchanged. For the case that QPM condition is not satisfied, the light propagating along PPLN is just as propagating along a normal birefringent crystal. The electro-optic effect makes no contribution to the birefringence when the poling duty cycle D is equal to 0.5.
Effect of modulated amplitude on oscillation of population probability
LIU Bi-rui, FU Zhen-xing
2010, 31(4): 672-676.
To explore the physical mechanism induced by a frequency-modulated light field, the phenomenon of the oscillation of population probability in a twolevel system under a frequency-modulated field is analyzed theoretically by means of the density matrix equation and Bloch vector model. The effect of the modulated amplitude on the process of the oscillation is also discussed. The results show that the oscillation of population probability and population transfer is modulated by the modulated amplitude. Increasing the modulated amplitude when the other parameters are fixed, the oscillation of population probability is weakened, and the efficiency of population transfer and the absorption are enhanced. The analysis in Bloch vector model shows that the population oscillation reflects the dynamic transformation process among the population transfer, absorption and polarization in the quantum system.
Gating beam intensity effect on the self-deflection of two-photon bright photovoltaic spatial solitons
SU Yan-li, JIANG Qi-chang, JI Xuan-mang
2010, 31(4): 677-680.
Gating beam intensity effect on the self-deflection of bright photovoltaic spatial solitons in two-photon photovoltaic photorefractive media was numerically investigated based on diffusion effect. Taking the bright photovoltaic solitons as the input solitary beam, the beam propagation equation was numerically solved in which the diffusion term was taken into account. The full width of half maximum (FWHM) of solitons intensity profile increases with gating beam intensity. The distance of self-deflection of solitons increases with gating beam intensity and starts to decrease when gating beam intensity is increased over a specific value. The nonlinear relation between self-deflection distance and gating beam intensity results from the effects of FWHM and diffusion term.