2008 Vol. 29, No. 6

Optoelectronic Engineering
Target extracting algorithm for complex scene in vehicle image tracking system
LUO Shi-tu, WANG Yan-ling
2008, 29(6): 837-843.
A new target extracting algorithm for complex scene is proposed. An improved Snake model is presented and applied to the construction of initial template, and the fractal Brown random field model is introduced to work out the possible target region according to the wavelet fractal dimension and fractal fitting error. After that, a new minimum mismatch distance (MMD) similarity measurement is defined, and the correlation matching is made quickly based on the feature region of the target. By accurately constructing initial template and using coarse-to-precise target searching strategy, the algorithm guarantees good extraction precision and reduces the computation greatly.
3-D surface reconstruction based on polarization analysis
YUE Chun-min, YANG Jin-hua, LI Zhi-hong, GU Guo-zhang
2008, 29(6): 844-848.
The principle and implementation method of surface reconstruction by analyzing the polarization images of reflected light to reconstruct the surface shape of a transparent object are presented. The light reflected from an object has some polarization characteristics, and different polarization characteristics correspond to different shapes and reflectance characteristics of objects. The surface shape of an object can be reconstructed by analyzing the polarization distribution of the reflected light from the object surface. The functional relation between polarization ratio and surface normal was derived according to the Fresnel formula. The surface shape of an object under test was reconstructed by processing the polarization gray-images taken by CCD camera. Experiment results show that the proposed method is feasible and efficient.
Optical imaging technology used in thermal deformation detection of resistive brake for metro
CHEN Chao, YU Jian-guo
2008, 29(6): 849-853.
Due to the electrocaloric shock caused by strong transient electric current, the inner resistance sheets in the brake resistors of Shanghai metro cars often deform seriously under the effect of thermomechanical coupling. In the experiment, in order to avoid the temperature field and displacement field being disturbed by contact sensor, non-contact detections are adopted. A far-infrared remote thermometer is used to measure the temperature and a three-dimensional imaging technology based on the digital grating projection and Gray-code is used to measure the thermal deformation. The thermal deformation detection of brake resistors was carried out at thirteen different temperatures, the accuracy of deformation detection reached 0.1mm after system calibration and error control. The application of optical imaging technology in the thermal deformation detection shows a new way for the experimentation of thermal stress.
Application of CCD refrigeration in the miniaturized spectrometer
CHEN Fang, SUN Li-qun, ZHANG En-yao
2008, 29(6): 854-858.
Compared to the traditional spectrometers, the miniature spectrometer is poor in noise and photometric performance. These problems limit its application in the detection of weak light signals. The noise sources of miniature spectrometers were analyzed and different kinds of techniques used for decreasing the noise were introduced. To enhance the capabilities of a selfdeveloped miniature spectrometer, the semiconductor cooling technology was used to decrease the noise. Based on the size of CCD, the structure of refrigerator was designed to improve the cooling efficiency. The noise sources of linear CCD were analyzed and the dark current at different temperatures was tested. The photometric noise and baseline flatness were tested according to the national industry standard. The results show that refrigeration is useful in limiting noise. The photometric noise of the miniature spectrometer is ±0.002Abs, and the baseline flatness is ±0.004Abs.
Nonlinear compensation of in-situ monitoring SO2 concentration in flue gas by DOAS
LU Jian-min, SHAO Li-tang, TANG Guang-hua, WANG Shi-min
2008, 29(6): 859-862.
Nonlinear absorption occurs when the differential optical absorption spectroscopy (DOAS) is used to monitor the flue gas with high SO2 concentration from fixed pollution source. A nonlinear compensation method is put forward, in which the ratio of the pressure component of the actual concentration to the pressure component of the inverted result versus the inversed result is fitted into a compensation function. The compensation function is used to compensate the inverted result nonlinearly. Experimental results show that the effect caused by the non-linear absorption of highconcentration gas can be reduced with the proposed method and it can improve the inversion accuracy of gas concentration.
Ray tracing in outer fluid field of blunted cone flyer
LIU Jian, LI Shu-min, JIN Gang, WANG Shi-qing
2008, 29(6): 863-866.
Since the density distribution of the outer flow field of a blunted cone flyer is inhomogeneous, the beamlet deflection in the far-field target surface occurs and the detection accuracy of the optical device mounted on the flyer is affected. A method of ray tracing in inhomogeneous medium was investigated for tracing a slim laser beam in the steady outer flow field of the blunted flyer in high speed movement. The beamlet path in the outer flow field of a blunted flyer was calculated. The result shows that in the chosen location, the effect of the outer flow field of a blunted flyer on the exit angle of the beam is observable, but not dramatic; the variation of flow field density gradient and the beam deflection of the beam exit angle increase when a cooling source is applied on the surface of the blunted flyer. The result provides a reference for correcting the beam deflection of the optical system mounted on blunted flyer caused by outer fluid field.
Simulation for moving target processing algorithm based on OpenCV
NIE Wei-le, QU Jian-rong
2008, 29(6): 867-869.
A new simulation method for moving target processing algorithm based on Open Source Computer Vision library in Internet is proposed. The characteristics of OpenCV library and the configuration in the context of VC6 are presented. The optical flow field of moving target was obtained by calling video read-write functions in OpenCV, calculation of image features and optical flow functions, and the foundation for the analysis and tracking of the moving target status was provided. It proves that the proposed simulation method is effective and feasible.
Coaxial measurement of axisymmetric aspheric lens
CHEN Qin-fang, XU Chang-jie
2008, 29(6): 870-873.
A method to measure coaxiality of axisymmetric aspheric lens is introduced. A laser beam is incident on the aspheric side of a tested lens through a beam waist conversion lens and the beam reflected by the aspheric surface is received by CCD camera. The position of the aspheric lens is adjusted until the center of the beam waist doesn′t move with the rotation of the tested aspheric lens. It shows that the symmetry axis of the aspheric surface is aligned with the rotation axis. Then the eccentricity of the sphere side of the tested lens is measured according to the principle of the spherical eccentric measurement. The accuracy of the measurement is better than 20″. This method is applicable to the acceptance inspection of aspheric lens and aspheric mirrors, as well as the improvement of aspheric lens process.
Fourier-transform speckle profilometry based on Michelson interference
MA Zhi-fang, GAO Xiu-mei, SUN Ping
2008, 29(6): 874-877.
A method of shape measurement based on ESPI carrier-frequency modulation is presented. In the typical setup of Michelson interferometer, turning the tested object a small angle generates an air wedge between the object plane and the reference plane. The wedge produces equal thickness interference fringes. A carrier fringe pattern containing height information is formed on the object surface. The carrier fringe pattern is captured by a CCD camera. The phase of the object can be derived by Fourier transform and the shape measurement is realized. The principle of the method is described and the experiment results are given. The results indicate that the method has the virtue of high sensitivity because speckle pattern interferometry is used.
Distal location method of interlocking intramedullary nails based on gravity center of light spot
CUI Ju, WANG Hai-tao, CHEN Yong, WAN Min, ZHU Yong-kai, ZHAO Jian-ning
2008, 29(6): 878-883.
A novel distal location method of interlocking intramedullary nails based on gravity center of light spot is presented. The components of the measurement system are described. To measure and position distal lockholes for interlocking intramedullary nails, an image transmission fiber bundle is used to send illuminating beam, as well as receive and deliver the distal image spot of interlocking intramedullary nails to the CCD target surface. A real-time system based on VC++ was exploited to get the gravity center of the light spot. During image processing, a modified threshold transform is used to avoid the defect caused by the binary transform. A circle is drawn directly around the light spot to get the gravity center. It is easy to get the actual position of distal lockholes for interlocking intramedullary nails by computing the change of gravity center of the spot before and after deformation. In addition, a lot of measurement experiments were performed. The quantitative analysis of the result shows that the alignment accuracy is up to 0.1mm. It meets the requirement of the measurement system.
Imaging characteristics for non-coaxial grazing-incidence
ZHAO Ling-ling1, SUN De-lin
2008, 29(6): 884-888.
Since the refractive index of media in the X-ray region is lower than 1 and Xray is strongly absorbed by media, it is very difficult to image objects in the Xray region. Conventional imaging methods are not suitable to X-ray wave band. Generally, the methods of the grazing-incidence reflective imaging and coding aperture imaging are often used. Imaging quality of a single mirror and two mirrors in the case of grazing incidence is discussed. The focal length, field obliquity and diaphragm position of KBA microscope are analyzed. The results show that the field obliquity is the minimum when the grazing-incident angle is half of the angle between the two mirrors, and the imaging quality is better when the diaphragm is placed on the second mirror instead of the first one. The reasonable structure arrangement of KBA microscope is analyzed. The theoretical basis is provided for the design and manufacture of KAB microscope.
Night Vision
Compound algorithm for restoration of infrared turbulence-degraded image
HONG Han-yu
2008, 29(6): 889-894.
Due to the complexity and randomness of image degradation caused by the aero-optics effects,it is difficult for a single restoration algorithm to reach the requirement of restoration. A scheme to construct a compound algorithm to improve the quality of restoration image is proposed, in which some useful algorithms based on different theoretical models and targets are synthesized, and their advantages are combined to make full use of their superiority. Major compound algorithms are given in this paper. The adaptive adjustment and reformation of various algorithm structures as well as the adaptability selection of various parameters, after the combination of statistics theory based MAP restoration algorithms with regularization theory based total variation algorithm, are discussed. The intelligent combination of various algorithm structures is accomplished to achieve their superiority. Some comparisons on restoration were made on microcomputers, and the experiment results show that the proposed compound algorithm improves the overall quality of restored images.
Numerical simulation of MCP dynamic characteristics
CAI Hou-zhi, LIU Jin-yuan, NIU Li-hong, LIAO Hua, ZHOU Jun-lan
2008, 29(6): 895-899.
The transit time and gain characteristics of electrons which travel in the micro-channel plate gated by picoseconds high voltage pulse were simulated. The curves of the transit time versus the voltage pulse width and the voltage amplitude are obtained when the waveforms of the voltage pulse are Gauss, triangle and trapezoid. The variations of the FWHM and peak of the gain curves with width and amplitude of the voltage pulse are obtained when the incident electrons have a gauss distribution. The results indicate that the transit time and gain characteristics of electrons are better when the voltage applied to the MCP is trapezoidal wave, compared to those of triangular wave or Gaussian wave.
Development of high-resolution X-ray image intensifier for inspection of circuit boards
CAO Xi-bin, ZHAO Bao-sheng, SAI Xiao-feng, WEI Yong-lin, LI Wei, ZHAO Fei-fei
2008, 29(6): 900-904.
Because of the traditional inspection system not being able to detect the defects at solder joints and solder bridges in ball grid array (BGA ) as well as the emergence of miniaturized packaging, high-density assembly and various new packaging technologies, a high resolution inspection system is proposed to solve this problem. A new type of high-resolution X-ray image intensifier is introduced. As one of the key devices for circuit board testing and chip packaging detection, its resolution performance has become a bottleneck for the development of X-ray detection system. Its resolution reached 20lp/mm after the improvement of the fabrication process and the use of new window material for vacuum sealing.
Algorithm of centre location of ellipse in optical measurement
ZHANG Hu, DA Fei-peng, XING De-kui
2008, 29(6): 905-911.
A new algorithm for obtaining the centre of ellipse is brought forward. Some information about an ellipse is obtained by the coarse-location, and the edge points are detected by using Canny operator in the region of interest. Then the accurate edge points are acquired by Gauss curve fitting based on the information of the ellipse and the gray-distribution characteristics of the edge points. Finally, the filtering methods based on the curvature filtering and mean-filtering are carried out respectively to filter the isolated points and the noisy points, and the accurate centre of ellipse is obtained by least square method. The result proves that the new algorithm locates the centers of ellipses accurately and meets the need of real-time measurement.
Nondestructive testing by continuous Terahertz imaging system based on backward wave oscillator
YUAN Hong-yang, GE Xin-hao, JIAO Yue-ying, ZHANG Cun-lin
2008, 29(6): 912-916.
A terahertz (THz) imaging system based on a backward-wave oscillator (BWO) is presented. BWO continuous THz wave imaging is a new approach to nondestructive testing. In the experiment, a sample was scanned on an X-Z 2-D translation stage, and the THz intensity information of the sample was picked up by a pyroelectric detector for imaging with a computer. A number of potential imaging applications were demonstrated by using the 0.71THz radiation, including nondestructive real-time testing of fare cards for bus passengers, Campus IC Card and coins in an envelop. The current setup is capable of resolving an object of 1.5mm size. It is concluded that a BWO THz imaging system is very practical and effective tool in nondestructive identification and security inspection.
Measurement and analysis of flux density distribution for spot focused by concentrator
DAI Jing-min, LIU Ying
2008, 29(6): 917-920.
The flux density distributions on focal plane and other defocused planes of parabolic concentrator were measured with an indirect method based on a CCD camera and a Lambert target. The systematic calibration method was investigated and the characteristics of the spot on every plane were analyzed. The experiment results show that the position of real focus can be obtained by comparing the spot characteristics on each plane; the diameter of the spot is increased, the peak value of flux density is reduced and the shape of the spot becomes more irregular when the amount of defocusing on the receiving plane is increased. The research result can be used for the thermal utilization of the concentrator system and the design of the receiver.
Atmospheric temperature measurement with Fabry-Perot airglow interferometer imaging system
LI Hao, ZHANG Yan-ge
2008, 29(6): 921-925.
The system response of Fabry-Perot interferometer (FPI) imaging system to night airglow is discussed. The method to build the mathematical model of the interferometric system is described and the result is given. On this basis, the principle of measuring atmospheric temperature by FPI is elaborated. In addition, based on the analysis of the interferograms from a stabilized He-Ne laser, the system transfer function is derived and the discussion on the transformation of system transfer function at different wavelengths is also performed. The result from analyzing the images indicates that the analytical model and the method of wavelength transformation can be used to express the properties of the interferometric imaging system. The application of system transfer function in measuring night airglow, the temperature shift and the error estimation of the system are also briefly discussed.
Selection of standard LED by luminous intensity distribution curve
LU Zheng, XU Tao
2008, 29(6): 926-930.
Since LED is a convenient transfer standard, it is widely used in metrology. As a standard, the value of LED should be accurate and stable over a long period of time. LED is selected as standard because its luminous intensity distribution curve(LIDC)is close to that of Lambert light source. The concept of LIDC and the distribution photometer for measuring LIDC are introduced. Three typical electric light source options are given. Ten typical LIDCs and three erroneous LIDCs are given when LED is used as standard. The reason for selecting white light LED with good emitting feature as standard LED is elaborated.
Videogrammetry in highway roughness measurement
JIANG Xin, ZHANG Xiao-hu, YU Qi-feng, SHANG Yang
2008, 29(6): 931-935.
A videogrammetry scheme for road roughness measurement is proposed. The formula for road elevation calculation is given. Two marks were included in the scheme. The difference between them was used so as to remove the vibration of the reference platform, instead of measuring the platform vibration by accelerometers in the traditional instruments. Simulation and preliminary experiment indicate that the method can effectively remove the vibration of the reference platform and accurately measure the relative elevation of vertical section. Although it has accumulative errors in the absolute elevation of vertical section, it will not affect international roughness index (IRI) significantly. In conclusion, it reduces the cost by using fewer sensors and overcomes the limitations and shortages caused by the acceleration sensors used in traditional instrument. It was proved to be an effective and robust method for such applications in China.
Optical Design
Optical design of zoom lenses in IR HWIL simulation system
WANG Zhi-le, DAI Jing-min, YANG Di
2008, 29(6): 936-939.
Since the hardware-in-the-loop (HWIL) simulation systems are designed only for one seeker to one simulator, a five-axis turntable simulation scheme with a zoom projection optical system is proposed. The HWIL simulation systems can be applied to the seekers which have different optical parameters, so it is more cost effective. The characteristics of the zoom projection optical lenses in HWIL simulation system are outlined. The infrared zoom system whose diffraction is limited in the wavelength range of 8m~12m is designed. The zoom ratio of the system is 3.0, and the diameter of spot dispersion is less than 50m.
Optical system design of alignment pointer for SG-Ⅲ diagnostics
XIE Zheng-mao, DONG Xiao-na, YAN Ya-dong, HE Jun-hua
2008, 29(6): 940-943.
The method of improving the accuracy of the diagnostics with alignment pointer is introduced. The transmission characteristics of the laser coupled by the single-mode fiber and passing through the optical system of the alignment pointer were analyzed based on the transformation principle of Gaussian beam thin lens. The paraxial magnification is the major factor to affect the spot size in image space of the alignment pointer. The optical system of the alignment pointer for SG-Ⅲ diagnostic package was designed, whose illumination source was a fiber laser, working wavelength was 635nm, total length was less than 100mm, target distance varied from 600mm to 1500mm, and spot was located at the center of the target and its size was 46.2μm~71.9μm. The optical system includes three normal glasses, in which the fixed group is composed of two separate positive-negative glasses, and the zoom group is a negative lens. The quality of the optical system was evaluated by the point spread function and wavefront aberration. The results show that the optical system meets the design specification.
Design of lens for 3 mega-pixel mobile phone camera
LIU Mao-chao, ZHANG Lei, LIU Pei-pei, DI Xing, BAI Jin-tao
2008, 29(6): 944-948.
A mobile phone lens assembly composed of 3 plastic aspheric lenses and an IR filter was designed. This lens assembly has an excellent imaging performance. Considering production and cost, the plastic lens 480R was chosen. The 1/4 in 3 mega-pixel CMOS made by Samsung was taken as the image sensor of the lens assembly, whose pixel size was 1.75μm, limiting resolution was 285lp/mm, F-number was 2.85 and FOV was 62°. Its MTF in the most of FOV at half of Nyquist frequency is higher than 0.5, RMS wavefront error is less than 0.14λ and maximum distortion is -0.2%.
Optical system design for fixed-focus lens of digital camera
LU Jian-hua, WEN Tong-qiang, HUANG Cheng, DING Gui-lin
2008, 29(6): 949-953.
Based on the conventional fixed-focus lens and the aspherical principles, a triplet fixed-focus lens assembly for the digital camera was simulated with the optical system design software CODE V to meet the needs for the compactness, high transmissivity, excellent optical performance and low cost . In the lens assembly, plastic lenses were chosen instead of glass/plastic hybrid or all glass lenses for the cost and production consideration. The back focal length of the digital camera was increased by 0.8116 mm with the lens assembly. Therefore, it can guarantee a better performance for the telecentric beam path. The profiles of the three lenses were designed as aspheric surfaces so as to correct the aberration and ensure the excellent optical performance.
Design and optimization of LED backlight module with single vertex angle structure
ZANG Jin-hao, HOU Yao, WU Zhao-xin
2008, 29(6): 954-956.
Since light emitting diode (LED) has the features such as long lifetime, wide spectrum, low power consumption and environmental friendly, LED is increasingly used to replace CCFL (cold cathode fluorescent lamp, whose light source contains mercury gas) as the light source in the backlight module. A 2inch LED backlight module using the structure of single-source vertex angle incident was designed. Considering that the LED light source usually causes the uneven brightness because it is a point source, the methods of LED incident angle rotation and regional segmentation were adopted, and the phenomenon of uneven brightness existing in the LED crystal backlight module was effectively eliminated. The simulation result shows that the uniformity of the outgoing light reaches 80.06%.
Optical thin film automatic design using adaptive evolutional algorithm
WANG Xia, Lü Kui
2008, 29(6): 957-960.
In the optimization design of the optical film system, the evaluation function based on film system structure is a complicated multi-peak function. Traditional optimization algorithms depend heavily on the initial design of the film systems, and are prone to fall into the local extreme values close to the initial structure. To solve the problem, the global-optimized adaptive evolutional algorithm is applied to the film-system optimization design of optical thin film. In the design process, only the solution code and the fitness function are needed and no additional information such as initial design is required. The evolutional algorithm was compared with the popular film system design methods. The optimization examples of high reflective films and splitting films show that the algorithm can be used to obtain more reasonable film system structure under the same design requirement. The design is flexible and films can be easily prepared.
Laser Technology
Error source and its elimination in phase retardation measurement of wave plate based on laser feedback
LIU Ming, ZHANG Shu-lian, LIU Wei-xin
2008, 29(6): 961-966.
Laser feedback is a new method to measure the phase retardation of wave plate. The wave plate is located between the laser and the feedback mirror, which can make the laser feedback waveform produce 90o rotation of polarization, i.e. polarization flipping. The duty cycle of the two polarizations is related to the phase retardation. The computer will calculate the phase retardation automatically from the cycle duty. Through scanning the feedback mirror forwards and backwards and getting the duty cycle separately, we can eliminate the error caused by the fluctuation of the two polarization states′loss, and improve the long term stability. A repeatability of 0.5 degree is ensured. This device has advantages such as simple structure, high precision of on-line measurement, and can meet the need of industrial production.
Design of 1.064μm semiconductor pulse seed laser
SU Jun, QIU Qi, XIE Jun, LIAO Yun, SHI Shuang-jin
2008, 29(6): 967-969.
A semiconductor seed laser was designed for master optical parameter amplifier(MOPA). A high-speed and high-current driving module and an arbitrary waveform generator were developed. A semiconductor pulse seed laser, whose peak power is more than 200 mW, pulse width is from 1.5ns to 1μs, and pulse frequency is adjustable from 1kHz to 1MHz, was obtained by using a 1.064μm QW-DFB high-power diode laser.
Realization of four-wavelength laser simultaneous output by LD sidepumped Nd∶YAG
LI Cheng-rong, CHEN Xiu-yan, LI Xiu, CHEN Hao-wei, REN Zhao-yu, BAI Jin-tao
2008, 29(6): 970-974.
In order to obtain the four-wavelength laser of 1064nm, 1319nm, 589nm and 660nm simultaneously, two-rod “T”-shaped composite cavity was designed. By simulation and calculation, perfect resonator parameters were chosen to make two fundamental lasers operate stably in large range of pumping current. Taking KTP and LBO crystals as sum-frequency and SHG crystals respectively, when the pumping current is 17A and the repetition rate is 10kHz, the highest average power of 1064nm, 1319nm, 589nm and 660nm is 150mW, 80mW, 2.3W and 1.7W respectively, and the pulse widths of 589nm and 660nm laser are 110ns and 130ns. The result shows that the fourwavelength laser output could be simultaneously obtained by a thermostable “T”-shaped composite cavity.
Wavelength tuning characteristic improvement of external cavity diode lasers
XU Hui-zhen, QIU Yi-shen, XU Bin
2008, 29(6): 975-977.
On the basis of the traditional Littman external cavity diode laser, a novel optical method for wavelength tuning is proposed. A′refractive optical lever′system which consists of a rotating optical wedge prism is employed to reduce the requirement of the rotation mechanism for tuning and improve the accuracy of wavelength selection. By optimizing the vertex angle of the wedge prism and the incident angle of the light ray, the requirement of the rotation mechanism can be reduced by one or two orders of magnitude, and the wavelength selection accuracy can be improved as well. The characteristics of external cavity diode lasers are improved and its sensitivity to the vibration is reduced.
Fiber Optics
Dynamic characteristics of FBG nonlinear switch
SONG Hui-fang, QIU Kun, WU Bao-jian, PENG Yong-jun
2008, 29(6): 978-983.
Based on the nonlinear coupled mode equation governing the pulse evolution in fiber Bragg gratings (FBG), the Bragg wavelength shift near the forbidden band caused by nonlinear optical characteristics was analyzed numerically. A simulation model was established to study the switching performance of FBG for different input powers. The simulation result shows that the Bragg wavelength of the grating moves to longer wavelength, the reflection peak decreases and the bandwidth becomes narrow when the input signal power increases. The characteristics of the all-optical switch based on this effect were investigated. And it shows that the stabilization period of the switch is short and the pulse wave-shape remains undistorted.
Output characteristics of Er-doped fiber super-fluorescent source for fiber gyroscope
LI Ying-juan, LIU Yan-hu, HUANG Hao, GUO Shuan-yun, JIANG Xiao-cun, XUE Feng, JI Cheng-hui
2008, 29(6): 984-989.
The operation principle of Erbium-doped superfluorescent fiber source (SFS) and several configurations of Erbium-doped SFS are analyzed. The singlepass-backward (SPB) SFS was selected as the source of the fiber optic gyroscope in the application. The factors which may affect the output characteristics of SPB SFS were investigated theoretically. The effect of the Erbium-doped fiber length on pump effective, mean wavelength, spectral linewidth and thermal stability of SPB SFS were analyzed in experiments. It is found that there is an optimal value for the Erbium-doped fiber length for SPB SFS. Using the optimal Erbium-doped fiber length, the influence of the pump power on the spectral-line shape was demonstrated. The stability of the output spectrum and power of SFS at -40℃~60℃ was discussed. A source suitable for inertial navigation grade FOG was obtained.
Acoustic emission sensor based on fiber coupler
MA Liang-zhu, CHANG Jun, LIU Tong-yu, HUO Dian-heng
2008, 29(6): 990-994.
An acoustic emission (AE) sensor based on over fused-taper fiber coupler is introduced to detect the acoustic emission signal produced by partial discharge in transformer. The AE sensor detects the AE signal according to the turbulence caused by the acoustic wave, which may change the optical power output of the two coupling arms. The experimental results prove that such kind of sensor has a flat response to AE in 10kHz~250kHz and its typical sensitivity is 5.6×10-6V/Pa with a noise of 1.8Pa at 155kHz.
Analysis of mode-coupling theory on long-period fiber grating
FENG Xian-qun, YE Bin-yuan
2008, 29(6): 995-998.
As a transmissive and passive fiber-optic device, the long-period fiber grating is interested extensively due to its applications in fiber telecommunication and sensing technology. The transmission spectrum was analyzed to acquire the satisfactory fiber grating. The coupling constants between the fundamental mode and the first-order cladding modes were determined by a mode-coupling equation. With given parameters of the fiber grating, the transmission spectrum of the long-period fiber grating was obtained by simulation with Matlab. As a result, the position of the resonant wavelength of the long-period fiber grating is decided by the grating′s period. The attenuation changes with the length and refractive index of the grating.
Optical Processing
Extrusion process for small-diameter fiber cable made of liquid-crystal polymer
ZHAN Yi-min, ZHANG Shuan-min, LI Xiao-rui, PENG Feng, QIANG Wei, ZHANG Fan
2008, 29(6): 999-1003.
A technique for making the small-diameter cable by the extrusion process is proposed. The foundational features of liquid-crystal polymers (LCPs) are described. The results indicate that LCPs are the ideal extrusion materials for optical fiber cables with small diameter. According to the feathers of LCP, extrusion process parameters of small-diameter cable are studied and the process flow is given. A small-diameter cable with outside diameter of 0.45 mm was manufactured with the extrusion process and its properties were analyzed. The test results show that the extrusion process hardly introduces any addition loss to the cable and the addition loss of the cable is almost zero at -60℃ to 80℃.
Fabrication and testing of aspheric silicon carbide mirror
ZHANG Feng, FAN Di, LI Rui-gang, ZHENG Li-gong, GAO Jin-song, ZHANG Xue-jun
2008, 29(6): 1004-1008.
In order to manufacture a precise aspheric silicon carbide (SiC) mirror, the fabrication and testing technologies for the substrate of the SiC mirror and the surface of the modified SiC mirror were studied. The technique of the computer-controlled optical surfacing for manufacturing aspheric mirror and the FSGJ-2 numerically-controlled machine for processing aspheric surface are introduced. The methods of contour testing and null testing were adopted respectively to measure the surface accuracy of aspheric mirror while SiC mirrors were grinded and polished. The surface profile and roughness of the final aspheric SiC mirror were tested with null testing and surface roughness tester. The testing results indicate that all the specifications meet the requirements of design. The surface profile accuracy of the aspheric SiC mirror is 0.016λ RMS and the surface roughness of the mirror is 0.85nm RMS.
Application of sub-aperture stitching technique
LIU Zhi-ying, ZHANG Lei, HU Yuan, GAO Tian-yuan, WANG Zhi-jian
2008, 29(6): 1009-1012.
The test and measurement of large-aperture optical elements can be made by sub-aperture stitching. The wavefront testing for each area of a largeaperture element under test was performed with a small aperture interferometer, and the wavefront of the large-aperture optical element was calculated according to the sub-aperture stitching results. It is more convenient for large-aperture optical elements to be tested with a small aperture interferometer by sub-aperture stitching method. The simulation of the sub-aperture stitching technology was carried out by the optical design software ZEMAX. The simulated result shows that the relative error of the wavefront testing is less than 4.3λ‰. The high-precision testing for the surface profile of a large-aperture optical element was realized with a small aperture interferometer.
High precision angle processing
WANG Song-wei, JIANG Jun-biao, YAO He-bao, ZHU Guan-fang, LIU Bin
2008, 29(6): 1013-1016.
The prism for coupling beam in ring laser gyro has a strict requirement on angle accuracy and its consistency. In order to process optical elements with high-precision angles, a new process is introduced, in which the optical element was processed by the matrix angles copied from the angles of manual repairing matrix. The impact of the goniometer accuracy, the matching error of the surface profiles and parallelism measurement error on angular machining error was analyzed. It is concluded that this process can improve the process efficiency and the machining accuracy by improving the flatness of the optical surface, avoiding local irregularity, controlling the impact of temperature difference effect and reducing the errors of parallelism measurement.