2013 Vol. 34, No. 2

OE System and Engineering
Analysis and adjustment of aiming axis error for panoramic periscopic system
YANG Hai-cheng, WANG Zhang-li
2013, 34(2): 193-197.
The aiming axis could affect the angle measurement accuracy of panoramic periscopic system. According to the typical opto-mechanical structure of the panoramic periscopic system, the error sources of aiming axis precision were analyzed. The calculation model was established by using the vector reflection theory and rotation principle, and the influence of azimuth axis,pitch axis, optical axis and reflector errors on the aiming axis was provided clearly. Meanwhile, the corresponding adjustment scheme was determined, each control point in the adjusting process was made clearly, and the debugging and testing methods were also determined. The test results show that the aiming axis accuracy is up to 0.1 mrad.
Influence of linear vibration and angular disturbance on image quality of airborne optoelectronic pod
KE Shi-jian, CHEN Ping, LI Jie, ZHANG Yi-jun, WAN Jing-yu, YANG Shao-kang, XI Wei-feng, LIU Tao
2013, 34(2): 198-202.
Taking airborne optoelectronic pod of armed helicopter as an example, the influences of the linear vibration and angular disturbance on the image quality and the stabilization precision were analyzed. Elevation and azimuth of the system occurred disturbance as a result of the coupling vibration, and so the internal television, thermal imaging and other sensor devices occurred disturbance, then the system image dithering occurred. The image quality and stabilization precision of the airborne optoelectronic pod could be improved greatly by installing it properly which means that it can improve the accurate attacking of the armed helicopter.
One kind of high resolution TV guided optical zoom system
SONG Yan-feng, SUN Wei-ping, WANG Guo-li
2013, 34(2): 203-208.
According to the technical requirements of the high resolution TV seeker, the system's optics parameters were calculated and the focusing range was optimized. F number of the optical system was defined. An optical zoom system with focal length of 40 mm ~ 152 mm and the F number of 3.5 was designed. The design results show that throughout the zoom process the values of the MTF at 106 lp/mm reach or close to 0.4, the image plane is stable and the image quality is good.
Design of 6 mm~60 mm megapixel zoom security lens
LUO Chun-hua, ZHANG Qi-yuan, LI Yan-hong
2013, 34(2): 209-214.
A large diameter and megapixels zoom optical imaging lens with CCD image sensor for monitoring system was designed, with the size of CCD at 1/3 inches, and the size of the pixel at 3.75 m. F numbers of lens in the position of short-focus, medium-focus, and long-focus were 1.6, 2.1, and 2.4 respectively. The zoom system was made up of four components, comparing to the traditional zoom system, the 4th component was adopted as compensation group in the zoom system. The initial structure was obtained by using the Gaussian method, the system was optimized by using Zemax software, and it was made up of the spherical lens. The lens field of view on the axis was greater than 0.3 at 133 lp/mm, off-axis 0.7 field of view was greater than 0.2 at 133 lp/mm. Minimum back intercept range of the system was greater than 9 mm, which met the assembly requirements. Finally, the zoom cam curve was mapped out by the method of multi-point fitting.
Miniaturization design of large zoom ratio MWIR zoom optical system
LI Yan, ZHANG Bao, HONG Yong-feng
2013, 34(2): 215-219.
Based on mid-wave infrared (MWIR) (320240) cooled detector, an infrared miniaturization and continuous zoom optical system adopting mechanical compensation method, employing diffractive optical element and folded beam path was designed. Using zoom system principle and Zemax optical design software, the optical design parameters were offered, image quality evaluation was presented and cam curve was solved. The design results show that six lenses are used in system, continuous zoom of 18 mm ~ 360 mm is achieved at band of 3.7 m~4.8 m, and cold optical stop matching is 100%. The value of modulation transfer function is all above 0.5 at the spatial frequency of 16 lp/mm. The system is characterized by large zoom ratio, excellent images, miniaturization and smooth zoom locus. It can be used for airborne electro-optical detection equipments.
Optical design of sunlight fiber coupling system
WEI Dan, WANG Fei, FANG Dan, WANG Xiao-hua
2013, 34(2): 220-225.
A design of sunlight fiber coupling system with long focal length and large aperture was introduced. In order to reduce the spherical aberration and chromatic aberration of the large aperture single-lens during converging sunlight, a method of reducing aberrations optical system added at the back of focusing lens was proposed, and the optical system that was applicable for optical fiber coupling system was designed and optimized by using Zemax software. The radius of spot size was 45.043 m, energy concentration was more than 95%, aperture angle was 9.090 2, and the total length of system was 525.584 mm. The coupling requirements of quartz optical fiber with numerical aperture of 0.22 and core diameter of 1.5 mm were satisfied.
Information automatic acquisition and processing module controlled by flight control system and self-testing
2013, 34(2): 225-229.
A design method based on the interface module of airborne flight control computers, which could realize digital control, real-time acquisition, monitoring and processing of various control signals (including discrete magnitude, analog quantity and serial data), was introduced. Focusing on the engineering application, the design idea and implementation methodology of the module were elaborated, as well as the self-tesing, with the illustration of principle block diagrams and testing process. In the application of a certain air freighter, the module performed the functions of the input and output of 32 interfaces discrete magnitude, the input and output of 16 interfaces analog quantity, the transceiving of 6 interfaces ARINC 429 serial data, and the transceiving of 4 interfaces ARINC 232 serial data, with the coverage of self-testing reaching 100%. The flexibility of the form and the number of the module interface enables the adjustment in accordance with the actual application; therefore the module is featured with evident typicality and generality, which can be used in various types of airborne flight control systems.
Transmission-mode varied-doping GaAs photocathode
CHEN Huai-lin, CHANG Ben-kang, NIU Jun, ZHANG Jun-jü
2013, 34(2): 230-234.
In order to apply varied-doping GaAs material to low-light-level image intensifier, the transmission-mode varied-doping GaAs photocathode experiment was carried out and the transmission-mode varied-doping GaAs photocathodes with two inversion structures were prepared. By testing the carrier concentration change of the GaAs photocathode before and after glass bonding, it is found that the carrier concentration increases after bonding at a high temperature. Moreover, by testing the transmission-mode varied-doping GaAs photocathode of high-temperature activation, result shows that the varieddoping GaAs photocathode still has a high spectral response in the band of 450 nm ~ 550 nm.
Assembly and adjustment technology for tank gunner-sprimary sight optical system
CHEN Qiang, ZHOU Wen-zhe, REN Peng-hui, LIU Yong
2013, 34(2): 235-238.
In order to solve the problems in the integrated assembly and adjustment process for the tank fire-control gunner field stable laser rangefinder collimator optical system, such as the low accuracy of Z axis in image stabilization system, overproof target range, overproof loading list range and different threeaxis parallelism, an integrated assembly and adjustment technology of gun sight optical system was put forward. Using optical auto-collimation method, the lens, high-precision plane-parallel mirror, long-focal-length parallel light tube and zero position instrument were adjusted to establish sighting axis zero reference, and the parallelism of three axes (sighting axis,laser emission axis,laser receiving axis) was up to the standard. The error of photomechanical elements was qualified in benchmark range. The first delivery-check qualified rate was increased from the original 60% to 95%, and the stability and reliability of the products were got promoted, which ensured the first-round hitting probability.
OE Information Acquisition and
Real-time image acquisition and processing system based on NI FlexRIO
YANG Ning, HUO Ju, GONG Sheng-min
2013, 34(2): 239-247.
To solve the problem of real-time image acquisition and processing in visual measurement, a system, based on NI FlexRIO, was developed with virtual instrument technology by using LabVIEW graphical development platform, in which related techniques, such as ping pong operation, pipelining technique, etc, were applied. The system could implement image capture, storage and processing in parallel and real-time. While the accessed image resolution was 1 2801 024 and the sampling rate was 500 f/s, the system worked stably. In the process, the time of image processing was less than 2 ms, and the precision could reach the level of sub-pixel. The system is significant for visual measurement to be implemented in real-time, and it is also highly valuable in other relative fields for its good performance.
OE Information Acquisition and Processing
Histogram extraction method of optical signal features of ship wake
CHEN Ming-rong, CHI Wei, XIE Tian-hua, JIN Liang-an
2013, 34(2): 248-254.
The present optical signal feature extraction methods of ship wake still have a lot of problems such as complex operation and slow processing speed. Histogram extraction method of optical signal feature of ship wake was researched in this paper. As the ship wake image histogram was provided with obvious bimodal characteristic, peak point distribution density and the ratio of pixel gray value were used to characterize the optical signal feature strength of ship wake, and the feature was analyzed by the specialized feature extraction experiment device. Feature extraction experiment results show that the two feature parameters can reliably describe the optical signal feature strength of ship wake, and the advantages of the method are simple and fast. From reading a ship wake image to calculating its value by using Matlab software, computer processing time is approximately 0.07 s.
Real-time moving object detection and tracking by using UAV videos
DONG Jing, FU Dan, YANG Xia
2013, 34(2): 255-259.
A real-time algorithm for detecting and tracking ground moving target by using unmanned aerial vehicle(UAV) video was proposed. Two images were matched based on the correspondence of feature points, and the change detection was proceeded on the basis of the matched images.Then according to the changing and moving information, target was detected and part of false alarm was eliminated. If tracking failed,the target could be correctly relocated to obtain full trace of moving target finally by combining detecting with tracking. The test result of groud vehicle image by UAV implies that the moving target can be detected and tracked at a real-time processing speed of more than 25 f/s by using our algorithm.
Double image encryption system based on principles of interference
QIN Yi, GONG Qiong, LuXiao-dong, MA Mao-fen
2013, 34(2): 260-266.
In this paper a novel virtual optical encryption system was proposed. With the new system two images could be hidden in the three random phase plates. First of all, the two original images were encoded into the amplitude and phase of a complex signal, then the complex signal was transformed into stationary random white noise by using digital holography with the reference wave that generated by random phase plate. Then the white noise was further hided in two random phase plates by using the interference principle. The encryption algorithm for this new method was quite simple and did not require iterative operation. Simulation results prove the encryption effects. The influences of additive parameters on the decryption results are studied, and it is found that the encryption system is highly sensitive to these additive parameters, and the security of the system is further improved.
Modified pyramid algorithm for small FOV star image recognition
LI Hui, WANG An-guo, ZHANG Lei
2013, 34(2): 267-272.
A modified pyramid algorithm is proposed for autonomous star identification of small field-of-view(FOV) star images in the general lost in space case, by selecting outer product of star vectors as characteristic matching quantity, in order to avoid poor discrimination of inner product. The strategy for modification to characteristic matching quantity is analyzed. And the issues related to the modified pyramid algorithm are discussed, involving preprocessing of the original star catalogue, construction of the database of characteristic matching quantity and the K vector, noise reduction and star centroiding, the star identification procedure, and so on. This algorithm is realized by Visual C++ programming. Its performance is tested by simulation. Finally, it is actually applied to star identification for a small FOV star tracker. Experimental results demonstrate that the star identification success rate of the modified pyramid algorithm is 96.7%, the size of data files loaded in memory is about 26.4 MByte, and the average time consumption of star identification is about 131.8 ms. This algorithm meets well the basic requirements of autonomous star identification in the lost in space case, such as high identification success rate, moderate resource consumption, fast identification speed, and strong robustness.
Calculation and application of interference fringe density
MO Wei-dong, FU Zhen-tang, ZHANG Meng, ZHANG Hai-fang, FAN Qi, FENG Ming-de
2013, 34(2): 273-278.
When using optical interferometry to inspect curved optical surfaces, the best technology parameters of light path were always designed in advance and the difficulty of inspection was evaluated in order to ensure the accuracy of inspection. A new way for calculating the interference fringe density was adopted to evaluate the difficulty of inspection for any curved optical surface and to determine the best position of reference spotlight source. Taking the aspheric surface for example, the radius of the best fitting sphere of aspheric surface, the max asphericity and the best position of reference spotlight source were calculated. Result shows the superiority of the new way in choosing the best condition of adjusting the light path of optical interference system. It can provide theoretical basis and analytical guidance for the design of interference inspecting system and the optimization debugging process.
Using Hamming apodization technique to improve spectral beam combining efficiency of volume Bragg grating
BAI Hui-jun, WANG Yue-feng, WANG Jun-zhen, YIN Zhi-yong, LEI Cheng-qiang
2013, 34(2): 279-283.
Spectral beam combining technology of volume Bragg grating is an effective approach to obtain high-power laser output. The side lobe of output spectrum of volume Bragg grating is the main factor which limits the number of spectral beam combining. In this paper, the side lobe of volume Bragg grating was suppressed using Hamming apodization. The theoretical model of the refractive index of the one-dimensional apodized Bragg grating was built, and the diffraction characteristic of the Hamming apodized Bragg grating was analyzed, and the combining efficiency equation of the Hamming apodized Bragg grating was provided. Then the effect of apodized grating on the combining efficiency was analyzed. Numerical analysis shows that the side lobe in diffraction efficiency is suppressed well by using the Hamming apodization. The number of beam in spectral beam combining is increased from 13 to 20 in a total 20 nm bandwidth, and the combining efficiency can reach 75.3% after using Hamming apodized grating, while the output power is 1.5 times of the notapodized output power.
Optical Metrology and Measurement
Study of ultraviolet optical transfer function measurement equipment
YANG Hong, KANG Deng-kui, JIANG Chang-lu
2013, 34(2): 284-288.
The optical transfer function (OTF) is an important parameter of image quality for optical system. As modern OTF measurement equipments just covered visible light and infrared band, the ultraviolet OTF (260 nm~400 nm) measurement equipment was designed. The theory and the components of the testing equipment were introduced. The equipment was calibrated by the OTF standard lens with centric wavelengths of 300 nm and 380 nm. The results show that the errors between theory and measurement of MTF are 0.03 (on-axis) and 0.05 (off-axis). Finally, the uncertainty of equipment measurement is evaluated.
Photoelectric parameters testing system for CCD imaging electronics unit
SUN Jing-xu, LIU Ze-xun, WAN Zhi, LI Xian-sheng, LI Bao-yong, REN Jian-wei
2013, 34(2): 289-294.
According to the testing requirements for photoelectric parameters of CCD imaging electronics unit, as an important part in space optical cameras, the necessity for testing the photoelectric parameters of the CCD imaging electronics unit was introduced, the testing scheme was proposed, and the testing device was designed and developed. The device was debugged and calibrated, and a monochromator wavelength calibration coefficient of 1.003 29 was obtained. Moreover, the stability and the uniformity of the integrating sphere in radiation properties testing of CCD imaging electronics unit were conducted, and the results met the demands. Through the calibration for the detector by the standard detector, the relative spectral responsivity of the detector was got. The whole device met the testing requirements.
Sensitivity analysis of arc light lens-style light screen
NI Jin-ping, ZHAO Jing-yuan, GAO Fen, LIU Lu
2013, 34(2): 295-299.
In order to meet the test requirement of large sensor area light screen indoors, detection sensitivity of a lens-style light screen which is composed of arc light source and sky screen target was analyzed. The composition of this lens-style light screen test system was introduced, the working mechanism of its fan screen was analyzed, and the calculation formulation was put forward. According to the lens imaging principle and the fan screen forming principle, the influence of the light source placed distance R and the lens objective distance l on the detection sensitivity was researched theoretically, and the verified experiment was conducted. The results show that the mentioned lens-style light screen can work normally, its sensitivity is higher than the conventional sky screen target, the experiment results can provide reference for further engineering design.
Measurement of refraction index inhomogeneity of large aperture KDP crystal
WEI Xiao-hong, CHAI Li-qun, GAO Bo, LI Qiang, XU Kai-yuan, HE Yu-hang, LIU Ang
2013, 34(2): 300-303.
The refraction index inhomogeneity of KDP crystal can cause beam phase mismatch in spatial distribution, thus lead to decreasing conversion efficiency of the third-harmonic generation system. In order to obtain the refraction index inhomogeneity of KDP crystal in high precision, the orthogonal polarized interferometry (OPI) was adopted. Using the ZYGO large aperture interferometer, the refraction index inhomogeneity distribution of large size KDP crystal was attained, with the precision as high as 10-7, the effect of crystal surface profile on the testing result was also studied experimentally. The high precision measurement of the refraction index inhomogeneity of crystal provides quantitative measurement references for the improvement of growth and machining technique of large aperture crystal materials.
Distortion measurement with inverse imaging method
GUO Yu, ZHAO Sheng-lu, ZHENG Xue, ZHANG Mei, MA Shi-bang, YANG-Hong, JIANG Chang-lu, KANG Deng-kui
2013, 34(2): 304-307.
According to the definition of relative distortion, a distortion measurement with inverse imaging method was proposed. We first placed the target on the focus surface of the unit-under-test (UUT), put the entrance pupil position of the UUT at the rotation axis position of the precise turntable, and rotated the UUT from the forward maximum field of view (FOV) to the negative maximum FOV, then measured 14 FOV points and finally obtained the distortion value of each FOV. Distortion value of the whole FOV could not be measured unless the entrance pupil position of the UUT was put at the rotation axis position of precise turntable strictly. The accuracy of focal length measurement is 2 m, and the accuracy of relative distortion measurement is 0.5.
Luminance uniformity measurement of integrating sphere using imaging method
Lu Tao, ZHANG Jing-xu, FU Dong-hui, CHEN Xiao-yun, LIU Jie
2013, 34(2): 308-312.
In order to measure the luminance uniformity through the projection lens at the position of the film, an image luminance measurement method was used. The relative brightness distribution of the whole irradiated surface was obtained by using the image luminance measurement method which was more convenient and economical than the traditional method by using light radiometers or photocells. The non-uniformity measured by image luminance measurement method was 4.24%, while the non-uniformity measured by light radiometers was 3.92%, and the relative error was only 8.16%. This method can be applied to solar simulator uniformity measurements and venues uniform illumination detections.
Simulation and design of beam drift measurement with defocus grating
GAO Guo-chang, LONG Chao, SI Lei, JING Chun-yuan
2013, 34(2): 313-318.
Tradition systems of beam drift measurement always need measuring at near field and far field respectively, so they are complex and non-real time. A new theory of drift measurement based on the location change of diffraction spot was proposed, which was not applied. For verifying the theory and building a predigested measurement system, the design of the key elements needed to be simulated. Based on the imaging theory of defocus grating, the model of beam transmission was built by Matlab. The simulation result was consistent with the theory. Finally, the relation between the key parameters of the grating and the maximum drift value was simulated and analyzed. The Results shows that the best design parameters can be obtained while the off-axis value of defocus grating is 15 mm and the focus length ratio of defocus grating to short focus lens is 6 under the condition of the imaging unit 1 cm2 and the focus of short lens 12 cm.
Optical Element and Fabrication
Design of portable multi-band and multi-axis parallel detector
ZHAO Wen-feng, JI Ming, LIU Tao, ZHANG Kui-jia, MENG He-min
2013, 34(2): 319-324.
To meet the requirement of optical axis parallel testing for multi-band and multi-axis observation instrument, the design of portable high-precision optical axis parallel detector was proposed. In order to decrease the volume of the system, Cassegrain system was used as the collimating optical system,and the optical and structural parameters were designed and optimized by using optical design software Zemax. ZnS was used as the reticule glass substrate. Multiband coaxial optical collaboration Target was designed and the photosensitive surface of the CCD was applied to collect the laser spot. The portability and measurement accuracy were improved. The consistency error of the testing instrument was within 15. The experimental results show that the design meets the needs of the optical axis parallel measurement for the observation instrument with high precision and high speed in the outfield.
TIR collimating lens design based on freeform surface
FAN Lu-qing, LI Xiang-ning, WANG Yu, LIU Jie
2013, 34(2): 325-329.
In order to achieve the required lighting in a specific angle range and meet the requirements of various types of LED lighting systems, we put forward a design method for total internal reflection (TIR) compound surface LED lens. According to the principles of non-imaging optics, we determined reflection surface type, calculated the divergence angle, and designed free-form surface lens. We provided the design idea and method, designed a LED lens with emergence half angle of 2.5 degree, and analyzed the influences of error on the actual results.
Performance optimization method of thermal insulating board in space camera
QIAN Jing, SUN Sheng-li, SUN Li-wei
2013, 34(2): 330-335.
The thermal insulating board inside the space camera acts as a role of insulating the internal optic structure from the sunlight radiation which can cause a sharp temperature rise of the board, since it is usually thin and does not add extra cooling components. The difference of increased temperatures on the insulating board can increase interior infrared stray radiance. A full set of thickness optimization method for thermal insulating board was presented. Using the mechanism of bionic optimization, the thickness of the insulating board was optimized according to the temperature gradient difference along the board while keeping the total volume unchanged. Then the Gauss filtering was conducted to make the thickness of insulating board change smoothly and easily for manufacturing. Through comparing the temperature profile and infrared radiance before and after optimization, the result showed that the highest temperature reduced by 3.8℃, and the infrared radiance at the wavelength of 3 m~5 m and 8 m~12 m reduced by 15%. The optimized method could be used to reduce the interior stray radiance by combining with other methods.
Infrared Technology
Precision and identity analysis of target for passive ranging through triple-station IRST system
WANG Dong, ZHAO Wei, LIANG Dong-ming, ZHANG Yan-xiu, YUE Huan-yu
2013, 34(2): 336-340.
Passive ranging measurement of infrared search and track(IRST)system was introduced, the error of ranging was analyzed and the decision condition for the identifying target was presented. Moreover, the precision of passive ranging though triple-station IRST system was analyzed based on combat operation. The result indicates that 2 km site arrangement can guarantee the passive ranging accuracy better than 8% within range of 22 km, and better than 15% within range of 40 km. Omnidirectional, long-distance and high-precision passive ranging could be achieved in this triple-station IRST system.
Simulation technology of dynamic infrared triangle target with decoy
GAO Ze-dong, ZHU Yuan-yuan, GAO Jiao-bo, LI Jun-na, ZHENG Ya-wei, XIE Jun-hu, WANG Jun, CHEN Qing
2013, 34(2): 341-348.
Aiming at the fidelity problem of circular target simulator for simulating the infrared triangle targets such as airplane, missile and so on, a simulation technique of dynamic infrared triangle was studied. Using isosceles triangle geometrical principles ,a novel design method was proposed for isosceles triangle aperture whose size and direction were variable serially and centroid was invariable, and the dynamic triangle target with the size of 0~3and direction of 0~360was achieved. The radiation intensity from 0 to 100% for target or decoy was continuously changed by adopting a combination technique for infrared polarizer with wide spectrum. The decoy-s size and location were variable by using two-dimensional mobile platform and changeable circular aperture. The real-time control technology on Windows operating system was studied, and the main control software including Microsoft foundation class (MFC) process and real-time sub-system (RTSS) process was designed, satisfying the 500 s real-time response of control instruction. The result shows that the dynamic infrared triangle target simulator with a circular decoy can accurately simulate the infrared radiation changing process for attacking airplane or missile and releasing decoy.
Laser Technology
Information fusion method between airborne laser data link and IRST system
XU Qiang, WANG Hai-yan, YANG Hai-yan, WANG Fang, CHEN Xin
2013, 34(2): 349-354.
Aiming at the different characteristics between the detection information of infrared search and track (IRST) system and the radar detection information of friend aircraft transmitted by laser data link system in cooperative air combat, an asynchronous information fusion method based on optimum data compression was put forward to improve the capability of detecting system. The information fusion processes, including time registration, space alignment, data fusion and target tracking, were analyzed. Beside, the observation curve, real contrail and error curve before and after fusion were respectively contrasted and analyzed. The errors of azimuth angle and pitch angle were kept within 2mrad after fusion. Result shows the method can improve the data precision effectively.
LD side-pumped Nd∶GdVO4 electro-optic Q-switched laser with high repetition rate
MAO Xin, SHEN Zhao-guo, FU Jie, TANG Gang-feng, YANG Yi, CHENG Jian-xin
2013, 34(2): 355-358.
To acquire high efficiency middle wave infrared(MWIR) laser of 3 m~5 m,the high repetition rate driving electro-optic Q-switched synchronization technology and LD side-pumped technology were used to get high repetition rate laser output with 1.06 m narrow width. Periodically poled lithium tantalate (PPLT) was pumped to achieve highpower MWIR laser output of 3 m ~5 m. As the input current was 20 A and the Q-switched frequency was 10kHz, the 1.06 m laser with 15 W power was obtained. After pumping PPLT by the laser, the 3.9 m laser with maximum power of 2.6 W was got. The conversion efficiency from 1.06 m to 3.9 m was 17.3%. Experiment results indicate that the high repetition rate driving electro-optical Q-switched technology and LD side-pumped technology can be used to obtain high-repetition narrow-width 1.06 m polarized laser, and pumping PPLT can obtain high-power highefficiency 3.9 m MWIR laser.
Light curtain sensor based on laser reflection
GAO Juan, DONG Tao, NI Jin-ping
2013, 34(2): 359-362.
For the problems of low detection sensitivity, susceptibility to sky brightness and inability to work at night of existing sky screens, a detecting method was put forward which was an active light curtain based on laser reflection. A line laser semiconductor was adopted as the active light source in the design, and the light path detection system consisted of optical lens, slit diaphragm, optical filter and photomultiplier tube. When the flying projectile passed through the light curtain composed of the line laser semiconductor and the optoelectronic detection system, part of the light reflected from the surface of projectile body were received by the optoelectronic detection system. After the process of photovoltaic conversion by photovoltaic detectors and the processing of electrical signal generated by photovoltaic detectors using the subsequent signal processing circuit, the corresponding analog signal and pulse signal indicating the moment when the flying projectile passed through the light curtain were output. Light energy was analyzed and calculated, and finally tested by experiment. The results show that the method can be used at night and the sensitivity is up to more than 200 times of the projectile diameter.
Fiber Sensing and Optical Communication
Adjustable pulse width thulium-doped Q-switched double-clad fiber laser
ZHANG Ling-cong, DU Ge-guo, ZHAO Jun-qing, GUO Chun-yu, RUAN Shuang-chen
2013, 34(2): 363-367.
The peak power is determined by the modulation frequency and pulse width with the average output power of laser settled, thus the tunability of pulse width has its value in practice.The thulium-doped Q-switched double-clad fiber laser was investigated. With optimum transmissivity of 65% the output power of 2 m laser was 3.9 W and the corresponding slope efficiency was 31%. The signal gate width was adjusted from 12 s to 18 s with the external signal generator. Pulse width was measured at modulation frequency of 30 kHz, 40 kHz and 50 kHz, and maximum peak power of 555.6 W was attained. The pulse width varied from 163.4 ns to 207.9 ns. The experiment result shows pulse width of laser can be effectively controlled by using external signal generator.
Full-duplex wireless signal optical transmission system basedon external modulator
LI Hui, ZHAO Qiang, LI Lei, HUANG Wei, GUO Jia, LIANG Dong
2013, 34(2): 368-373.
A full duplex vector signal transmission system based on double parallel Mach-Zehnder modulator was proposed. Traditional optical frequency doubling technology was only suitable for NRZ (not return to zero) that was intensity modulation format and not suitable for MPSK and MQAM vector signal modulation technique in wireless communication. Two sides of optical millimeter wave generated by the traditional multiplier were separated with a filter, and vector signal was modulated in a sideband so that the amplitude information and phase information were properly retained. Bandwidth requirements of optoelectronic device were reduced by using octonary module in the transmission process. Theoretical analysis and simulation results show that after 20 km single-mode optical fiber transmission, the error vector magnitude loss of 625-Msymbol/s 4QPSK signal generated by this method and carried in the carrier of 60 GHz can be neglected.
Using photonic crystal fiber grating sensor to measure temperature, strain and gas concentration simultaneously
PAN Chong-lin, XI Xiao-qiang, ZHANG Fu-mei
2013, 34(2): 374-380.
In order to solve the problem of needing multi-sensor to measure different physical parameters, and enlarge the application of measuring multi-parameters simultaneously, different sensing characteristics of fundamental mode and higher order mode in photonic crystal fiber (PCF) and gas absorption sensing principle were combined. The method to measure temperature, strain and gas concentration simultaneously was discussed based on the experiment of measuring temperature and strain with PCF. Calculation formulas and numerical simulation of the three parameters were offered, and the simple and high cost performance sensing demodulation system was designed at last. Results show that, the temperature sensitivity is more than 0.98 pm/℃ when the temperature is up 0℃, the strain sensitivity of fundamental mode is 1.2 pm/, and the higher order mode is more than 0.83 pm/. The shorter photonic crystal fiber can measure the higher gas concentration. The proposal can decrease the cost of using fiber sensor to measure the three parameters, and can expand the research approach of gas and liquid sensor.
Influence factors for tensile strength of small-diameter liquid-crystalpolymer extruded single-core fiber cable
ZHAN Yi-min, PENG Feng, ZHANG Fan, QIANG Wei, ZHANG Shuan-min, WANG Xiao-ting, CAO Zhan-min
2013, 34(2): 381-384.
This paper theoretically analyzed main factors of tensile strength of liquid-crystal po-lymer (LCP) extruded single-core fiber cable with the diameter of 0.5 mm during the forming process. The factors mainly contained temperature feature of the melted LCP, structure parameters of mold core and die sleeve, space between die sleeve and mold core, and tension stringing and traction speed of optical fiber. Results show linear relationship between tensile strength and strengthened story thickness of small-diameter LCP is not ideal. The liquid-crystal polymer extruded fiber cable has maximum tensile strength within a certain diameter.