2015 Vol. 36, No. 1

OE System and Engineering
Method of designing linearization double-linkage continuous zoom lens
Yao Duo-shun, Wang Nan-xi, Kang Wen-li
2015, 36(1): 1-8. doi: 10.5768/JAO201536.0101001
A kind of linearization double-linkage continuous zoom lens was proposed. This system utilized the simplified configuration of the conventional doublelinkage continuous zoom optic system with mechanical compensation , its zoom group and compensation group both used linear motion, and the zooming cam mechanism for controlling the curvilinear motion discipline of zoom group was omitted . This configuration had a few image displacement, however, it could not influence the image quality when the image displacement was controlled in allowed range. In addition, the principle and method for designing linearization double-linkage zoom lens were given.
Dynamic viewer system in gunner sight for self-propelled anti-aircraft artillery
Li Qin-xue, He Yu-lan, Wang Tao, Chai Ji-he, Yan Li, Chen Xiu-ping, Qiang Hua, Zhang Ying
2015, 36(1): 9-14. doi: 10.5768/JAO201536.0101002
The servo system of the self-propelled anti-aircraft artillery has the possibility of failures. While working in the emergency state, it has the problems of slow reaction, low precision and large error for lead. To solve these problems, the dynamic cursor circuit was proposed to use for producing the video frequency with a dynamic cursor. Thus, the target data and the lead of artillery could be calculated in real time, so as to control the position of the dynamic cursor. The video frequency signal was shown on the display screen and projected to the reticle surface of the sight lens, enabling the dynamic cursor in the field of view. Therefore, it could guide the user to aim manually and to slew the artillery to the lead position rapidly while working in the emergency state. The use of the dynamic cursor in the sight lens could reduce the operational difficulty and improve the slew rate, facilitating to grasp the fighting chance and increase the probability of hitting. This device was tested with a type of self-propelled anti-aircraft artillery. The results show that it fulfills its intended functions and can attain the predetermined effect.
Design for visual comfort of binocular optical system with large exit pupil
Liu Xiao-dong, Hou Jian-wei, Zhu Jia-li, Qiu Wei-gen, Sun Jian-hua
2015, 36(1): 15-18. doi: 10.5768/JAO201536.0101003
Based on the binocular vision theory, the effects of the convergence angle and the focusing difference of the binocular optical system with large exit pupil were analyzed.Furthermore,the factors and the misunderstanding of design which could influence the visual comfort were also analyzed. It is pointed out that different pupil distances and the condition of nonzero visibility observation instrument should be considered. The result shows that the convergence angle should be controlled between 0~4 m-1 ,and the binocular focusing difference should be 0~2 m-1 which is the smaller,the better.
Development of testing instrument of optical-axial parallelism for multi-axial systems
Huang Xin, Shen Xiang-heng, Ye Lu, Wu Jin, Zhao Yu-yan
2015, 36(1): 19-23. doi: 10.5768/JAO201536.0101004
A high-precision, good-portability testing instrument was designed, which could detect optical axis- parallelism of multi-axial system according to practical needs. The instrument was able to test the nonparallelism of system-s optical axis among visible, infrared and different laser spectrum bands. Compared with similar instruments, the instrument was characterized by utilizing total reflection structure design and did not use infrared optical glass.Meanwhile, through optimization design, the instrument avoided some disadvantageous factors that influenced precision,such as the influence of plane mirror-s wedge angle . Main structure of the instrument used completely symmetric structure design and cordwood assembly way to ensure that the test precision superiored to 5, after temperature cycle test and vibration test. The instrument meets customer requirements.
Design of low-light-level panoramic imaging system
Yang Zi-jian, Hu Bo, Zhang Xuan-zhi, Liu Feng, Yan Lei
2015, 36(1): 24-28. doi: 10.5768/JAO201536.0101005
According to the property of low-light-level (LLL) imaging system, the LLL panoramic imaging system was designed, which was made up of a reflection part and a transmission part. The basic theory for designing the reflection part was expounded, and according to the theory, a imaging system of good performance was designed and optimized. This system has a waveband of 0.4 m~ 0.9 m, an effective focal length of 2.43 mm, a working F-number of 1.5, and a field of view of 30~100. Simulation results show that in the entire field of view, the distortion is less than 6%, the value of the modulation transfer function (MTF) at 24 lp/mm is greater than 0.3. The system can meet the demands for imaging.
Optical design of near infrared fluorescence confocal laser scanning system
Luo Gang-yin, Wang Bi-dou, Miao Peng, Wang Lei, Wang Zhong-zhou, Qian Qing, Qian Jun
2015, 36(1): 29-34. doi: 10.5768/JAO201536.0101006
In order to realize the high resolution scanning for near infrared fluorescence,a laser scanning confocal optical system was designed which worked in the near infrared region.The lighting lens,and emission lens were realized based on simple concave lens and convex lens.The software Zemax was used for the optical design and simulation. Simulation results shows that the focal spot-s size of lighting lens is less than 1 m, and the focal spot-s size is less than 40 m at the lighting pinhole position, which meets the lighting pinhole-s requirement.The focal spot-s size is less than 10 m at the emission pinhole position, which meets the emission pinhole-s requirement.In addition,the cutoff frequency of the lighting lens and emission lens meets the diffraction limit resolution requirement respectively. Therefore, it has high optical transmission efficiency.
Effect of control error of boresight angle on imaging quality of space camera
Wang Zhan, Han Cheng-shan, Li Xiang-zhi, Huang Liang, Yao Chen
2015, 36(1): 35-40. doi: 10.5768/JAO201536.0101007
In order to reduce the influence of boresight angle error on the image quality of the time delay integration charge couple device (TDICCD) space camera during the tilted imaging process, the requirements for the scopes of boresight angle and its control errors were put forward to meet the image quality of space camera. According to the imaging mechanism of space camera, the calculation formula of focal plane image motion speed and that of the matching error of image motion speed caused by boresight angle error were presented, and the effect of boresight angle on the ground pixel resolution was analyzed. Moreover,the ranges of boresight angles for different integration degrees were given under the constraints of modulation transfer function (MTF). From practical calculations, it is concluded that, when the control error of boresight angle is 0.8, the boresight angle should be less than 12.75or if the boresight angle needs to reach 25, the control error should be less than 0.4to satisfy the quality requirements of TDICCD of which the integration degree is 96.
Optical design of large FOV imaging system for AOTF imaging spectrometer
Li Yong-shuai, Wang Zhi-bin, Chen You-hua, Zhang Yu-han
2015, 36(1): 41-45. doi: 10.5768/JAO201536.0101008
In order to obtain the two-dimensional spatial information and one-dimensional spectral information within the field of view (FOV) range of 15 from 400 nm to 900 nm, a kind of system for acousto-optic tunable filter (AOTF) imaging spectrometer was designed. The working principle of AOTF was described. According to the overall plan, the fore-optics and post imaging system were finished. The fore-optic system was utilized the inverted Galileo telescope, and the post had an improved-Cooke triplet-structure. Finally the optic system was completed. The focal length is 19.311 mm and the F number is 12.3. While the spatial frequency is 34 lp/mm, the modulation transfer function (MTF) is 0.5.
Design of optical system for fiber optic spectrometer based on holographic optical elements
Jiang Li-ping, Sui Cheng-hua, Chen Xiao-ming
2015, 36(1): 46-51. doi: 10.5768/JAO201536.0101009
Based on the theory of holographic optics, we analyzed the Gaussian imaging properties of holographic optical elements, including the optical focal power, position of imaging and diffraction efficiency, verified its feasibility to be a grating for the spectrometer. Based on the above theory and the spectrometer work principle,we designed the optical system, and through the simulation, image quality evaluation and optimization with Zemax,the final result was got. The parameters of holographic grating were as follows: the recording wavelength was 575nm,the angle between the recording beams (a planar wave beam and a spherical wave beam)was 100, the focal length was 40mm, the used diffracted light was +1 order , the aperture was 10 mm;The parameters of spectrometer were as follows:the range of work wavelength was 400 nm~800 nm, the volume was 140 mm30 mm40 mm,the width of spectrum was 29.1 mm. Finally,we built the light path on the optical platform, used the circuit system and the spectrometer software that were developed completely to collect mercury lamp spectrum. Testing results show the spectral resolution is better than 8 nm,the mercury spectra obtained are the same with the standard one, indicating that the optical system designed based on holographic optics is feasible.
OE Information Acquisition and
Visual tracking algorithm based on improved Bhattacharyya coefficient and model update strategy
Huang An-qi, Hou Zhi-qiang, Yu Wang-sheng, Liu Xiang
2015, 36(1): 52-57. doi: 10.5768/JAO201536.0102001
In the traditional mean shift tracking algorithm, the Bhattacharyya coefficient is an efficient method in image statistical feature matching;however, due to the influence of background feature, the optimal location obtained by Bhattacharyya coefficient may not be the exact target location. Thus, biased or even wrong location may be got in visual tracking. We presented an improved Bhattacharyya coefficient based on target-background confidence .The new coefficient effectively reduced the influence of background feature and emphasized the importance of target feature, which obviously improved the target matching accuracy compared to the original coefficient. In order to get an effective model update strategy, we synthetically analyzed the similarity of target model and background model, and estimated the reason of the disturbance. We used 4 challenging video sequences to test 5 tracking algorithms. The quantitative experimental analysis shows that the proposed algorithm has good real-time performance, it only takes 75.76 ms to track one frame and exceeds the other trackers in tracking precision. The experimental result shows the proposed algorithm can well restrain background disturbance, while effectively update the model and overcome the problem of model drifting, and the tracking algorithm is effective and robust.
Image quality assessment method based on regional contrast and structural similarity
an Le-le, Li Hui, Qiu Ju-neng, Liang Ping
2015, 36(1): 58-63. doi: 10.5768/JAO201536.0102002
Among numerous image quality assessment(IQA) methods, the structural similarity (SSIM) algorithm is simple, high efficient and accurate. However, it often does not work well when there is regional distortion or cross distortion in the image. To deal with the problem that SSIM algorithm treats the different regions of the image identically, we took human visual characteristics in spatial domain into consideration and put forward an improved IQA method based on regional contrast and structural similarity(RCSSIM). The new algorithm combines regional contrast with structural similarity, weighs and normalizes the original SSIM index to a regional contrast structural similarity metric between the reference image and the distortion image to assess the image quality. The experiment results on LIVE image database show that the Pearson linear correlation coefficient(PLCC) of the new algorithm increases by about 0.015 and the root-mean-square error decreases by about 0.55 compared with the SSIM algorithm. It indicates that the evaluation result of RCSSIM algorithm is more consistent with human visual system(HVS) characteristics and is more effective than the SSIM algorithm.
Single-intensity-recording optical encryption technology based on phase retrieval algorithm
Wang Zhi-peng, Wang Hong-juan, Jiang Hua-long, Qin Yi
2015, 36(1): 64-70. doi: 10.5768/JAO201536.0102003
Based on the traditional double-random phase optical encryption system, a new single-intensity-recording optical encryption technology was proposed. In the encryption process, the original image was placed on the input plane of 4-f system to have a double random phase encryption. Using CCD sensitization devices, only the intensity distribution on the output plane was recorded as ciphertext. The optical encryption process only needed one exposure. In the decryption process, the original image could be retrieved from the ciphertext using phase retrieval algorithm. Since the decryption process used digital method, a variety of digital image processing technology could be introduced in the decryption process to suppress speckle noise, so as to further improve the decrypted image quality. Through a series of simulation experiments, it is proved that the proposed encryption system can be used for binary image and grayscale image encryption. Moreover, it can well resist known plaintext attack and chosen plaintext attack. Theoretical analysis and computer simulations show that this optical encryption system is simple in structure, easy to achieve, invulnerable to various attacks and of high security.
Optical Metrology and Measurement
High-precision hand-eye calibration for automatic stiffness bonder
Ye Su, Ye Yu-tang, Liu Juan-xiu, Liu Lin, Du Chun-lei
2015, 36(1): 71-76. doi: 10.5768/JAO201536.0103001
To eliminate the error of hand-eye calibration caused by installation error associated with the verticality of the camera-s optic axis in the automatic stiffness bonder, we proposed a novel method to calculate the homogeneous coordinate transformation between the camera frame and the robot base frame. The external parameters of camera obtained with the calibration boards, were combined with the conventional 2D calibration model, thereby extending the dimensions of the model to 3 and effectively improving the calculation accuracy. The calculation error of the calibration with the 3D model is less than 0.1m, which decreases by an order of magnitude compared with the 2D model. Using the thin films to modify the value in Z direction in coordinate transformation, the system has high location precision and the error of the calibration is less than 0.015 mm. The mean error is reduced effectively, and the performance of system is significantly improved. The proposed method is capable to obtain the unique solution of calibration equation with the finite degree of freedom system. The 3D calibration model including the whole information associated with the camera pose, has no additional constraints such as camera installation, and can effectively improve the accuracy of hand-eye calibration.
Test method of stabilization accuracy in EO tracking system
Wang Ke-wei, Wang Xiao-yi, Wang Jing, Liu Zhao-qing, Wang Sheng-rang, Zhang Kui-jia
2015, 36(1): 77-81. doi: 10.5768/JAO201536.0103002
For the stability test requirements of precision optical tracking system ,we presented a dynamic testing method of stability accuracy. According to the optical auto-collimation principle,we utilized the CCD array detector combined with the computation for center of image to realize the dynamic test , and we required the test results of stability accuracy by this device. Experiments results show that for the 50 rad level two-axis two-frame system,the tested stability accuracy is up to 48 rad by our method.
Uncertainty evaluation in infrared optical material refractive index homogeneity measurement
Liang Fei, Mai Lyu-bo, Zhou Tao-geng, Wang Lei, Sha Ding-guo
2015, 36(1): 82-87. doi: 10.5768/JAO201536.0103004
Based on the test information from multi-sample and multi-mode instrument, as well as the guide to expression of uncertainty in measurement (GUM) and Monte Carlo method (MCM) , the four-step interferometry measurement range and uncertainty of the infrared optic materials refractive index uniformity were discussed. Although the absolute sensitivity and accuracy of infrared interferometry are lower than that of visible laser interferometer, the four-step interferometry can eliminate the inherent systematic errors of the interferometer and can help achieve high-accuracy measurements of infrared optical refractive index homogeneity. The practical tests show that the measurement range can reach 110-5~510-3 and the relative standard uncertainty can reach 210-1~210-2.
Decoding and compensation technology of turntable angle based on DSP and ADC application
Xie Na, Zhao Chuang-she, Hou Rui, Li Hong-guang, Tan Ming-dong, Liang Ting
2015, 36(1): 88-92.
We designed a high-speed and high-precision resolver-digital converter, sampled the modulated sine-cosine analog output of resolver at each peak through the sinusoidal carrier using the analog digital converter (ADC). After decoding the sample result and other operation with DSP software,we obtained the final angle of two-channel multiple resolver. Then we proposed a method for compensating the gain and phase errors between sine and cosine output of resolver,and presented the calculation of error parameters and the judgment of angle quadrant in detail. Experimental results verify the proposed low-cost decoding system has a high calculation speed and high precision of 0.01 in static condition and 0.05 in dynamic condition.
Optical Element and Fabrication
Reliability of Ge-based MW antireflective films in hygrothermal environment
Chen Fen-gjin, Su Xian-jun, Ma Sheng-xi, Sun Yong-yan, Yan Kai
2015, 36(1): 93-97. doi: 10.5768/JAO201536.0105001
Mid-wave(MW) antireflective films were coated on double-side polished Ge substrate, and the films were experimented in hygrothermal environment for sustaining 24 h,224 h,324 h,424 h,524 h,724 h,,1224 h,respectively. The effects of hygrothermal environment on the reliability including transmittance and adhesion of Gebased MW antireflective films were studied .The results indicate that , the transmittance of MW antireflective films becomes lower gradually after sustained in the hygrothermal environment, and the absorption peak of CO2 and H2O turnes up , resulted from the increase of the content of CO2 and H2O in the films sustained under hygrothermal environment for enough time; The fringe of film becomes desquamated after 1024 h in hygrothermal environment ,and from that time,the average transmittance is lower than 85%.
Fabrication of diffractive grating based on YAG transparent ceramics
Li Hao-wei, Gong Yong-qing, XiaHou -Mingjiu, Xiao Meng-chao, Luo Ning-ning
2015, 36(1): 98-102. doi: 10.5768/JAO201536.0105002
Diffractive grating element based on yttrium aluminum garnet (YAG) transparent ceramics substrate was fabricated and researched. A uniform dense metal chrome film was deposited on YAG transparent ceramics by direct current(DC) reactive magnetron sputtering. The YAG transparent ceramics with hard mask were obtained. The photolithography was accomplished by contact UV-lithography system, and the YAG transparent ceramics sample with diffractive grating was obtained by trial and error. Testing results show the thickness of chrome film is 0.072 m by optical profiler, the details of diffractive grating in the sample are remained perfectly. The feasibility of fabricating diffractive grating by substituting YAG transparent ceramics for traditional photolithography substrate has also been proved by the diffraction pattern of this grating. It is concluded that this research makes possible to use diffractive grating in a more complex environment and has broad prospects in application.
Machine-made bit error mechanism of absolute grating scale in different structures
Wei Qing-hai, Chen Xin, Liu Qiang, Wang hang, Chen Bin, Fang Fei-yu
2015, 36(1): 103-108. doi: 10.5768/JAO201536.0105003
Aiming at the advantages of grating scale has that it can set reset for power outage, has no cumulative error with high accuracy, we established the unsealed and sealed absolute grating experimental systems respectively by using the technology of image identification on the optical vibration isolation platform.Taking the air bearing linear motor ArotechABL1500 for reference,we checked its accuracy by the laser interferometer RENISHAW XL-80, and analyzed the characters and the causes of the bit errors of different-structure absolute grating scale. By the contrast experiment and the analysis, it is proved that the bit error rate of the sealed absolute ruler is higher than that of unsealed, the bit error rate of the sealed absolute ruler is 3% while the unsealed one is 8%.
Reticle pattern process technique of germanium crystal optical code disc
Su Ying, Chen Jun-xia, Zhang Yong, Zhang Cheng-qun, Gong Tao
2015, 36(1): 109-113. doi: 10.5768/JAO201536.0105004
In order to process code disc pattern on the Ge crystal base met the needs , we did the technological experiments, through adopting the positive photoresist and negative photoresist, in the technological ways that coating before exposure and exposure before coating,respectively.We analyzed the measurement results, and came to the conclusion that the optimum matching scheme of reticle pattern processing technology for Ge crystal optical encoder was adopting the negative photoresist in accordance with the exposure before coating. Experimental results show that the finished graphic pattern has obvious contrast, the asymmetry distribution of edge is lower than 0.008 mm. It can be applied to the manufacture of the reticle pattern on Ge base.
Design and analysis of optical system about visible light source target
Wu Wen-bin, Chang Jin-biao, Qiu Ya-feng
2015, 36(1): 114-118. doi: 10.5768/JAO201536.0105005
The evaluation of aircraft reconnaissance system was executed by wild test and laboratory test. We created the visible light target in laboratory, then put it on an two-dimensional turntable to simulate a long-distance target, utilizing halogen lamp, US army target source and optical system. The optical system of visible light target source was designed to meet the required technical indicators. The light beam angle was calculated and the diaphragm hole was designed on the foundation of light path design and temperature field analysis. The temperature variation-s impact on optical lens was analyzed to verify the reliability of the optical design. Results show that the testing requirement of aircraft reconnaissance system could be met.
Laser Technology
Technology of MWIR laser in directed infrared countermeasure systems
Yang Ai-fen, Zhang Jia, Li Gang, Zhang Wan-xia
2015, 36(1): 119-125. doi: 10.5768/JAO201536.0107001
Aiming at the special technique requests of directed infrared countermeasure systems for mid-wave infrared (MWIR) lasers in laser wavelength, power,divergence,repetition frequency and modulation pattern, the technique characteristics and present developing situation of the optically pumped semiconductor disk laser,the quantum cascade laser, the optical-parametric-oscillator-based solid-state laser and fiber laser were analyzed .The characteristics and new developments of the birefringent phase matching and the quasi-phase matching were also summarized. A technique project of MWIR lasers was proposed by using a solid-state laser or a fiber laser with the wavelength of 1 064 nm and high power good beam quality to pump an optical parametric oscillator based on the crystal of periodically poled lithium niobate with MgO-doping(PPMgLN).The converting efficiency above 16% on wavelength could be obtained.
Fiber laser pumped periodically poled crystal dual-band laser
Shen Zhao-guo, Dong Tao, Meng Dong-dong, Ma Jun-ling, Tang Gang-feng, Yang Yi
2015, 36(1): 126-129. doi: 10.5768/JAO201536.0107002
Aiming at the laser directed interference system ,which counteracts two kinds of detectors of 1 m~3 m and 3 m~5 m, needing two corresponding wavebands outputs,we used the high repetition rate driving Q-switched technology and the seed injection magnifying technology to acquire high-power good-quality 1.06 m fiber laser output, the exterior polarizer got two beams laser outputs, the periodically poled lithium tantalate (PPLT) and periodically poled lithium niobate (PPLN) crystals were pumped to get high-power 1 m~3 m and 3 m~5 m laser outputs. As the input current was 60A and the Q-switched frequency was 50 kHz ,the 2 m laser output was obtained with up to 7.5 W power as well as the 3.9 m laser with a 4.2 W max power, the conversion efficiency was 39.5%. Experiment results indicate that using the fiber laser pumped optical parametric oscillator(OPO), the high power 1~3 m and 3~5 m dual-band laser output can be got.
Measurement error for projective angle of spatial out-of-plane hole system in zero-lock laser gyro
Deng Xin, Bai Bo, Li Da-qi, Chen Yong
2015, 36(1): 130-133. doi: 10.5768/JAO201536.0107003
In order to improve the accuracy and stability in the measurement of slightness hole system in zero-lock laser gyro cavity,the main error in the measurement of slightness hole system in out-of-plane zero-lock laser gyro was analyzed. The expression of the effect of inclination error on the projective angle of spatial out-of-plane hole system was built. It was found that the variation of inclination of spatial out-of-plane hole system could change the projective angle , when the inclination was 16 ,30% of the inclination error weighted in the projective angle error,and it was verified by UG software. Moreover, the effect of measuring point error from video measurement instrument on projective angle was analyzed with the method of least square fitting, and it was found that increasing the measuring points from 2 to 10 could reduce the influence of super error by 50%. Results show that this method increases the stability of the zero-lock laser gyro measurement.
Design of laser-s driven circuit based on MCU
Chen Xiao, Jia Hua-yu, Guo Yan
2015, 36(1): 134-139. doi: 10.5768/JAO201536.0107004
In order to more effectively control and adjust the temperature and the power of the laser, we designed a kind of laser driven circuit based on STC11F08XE micro controller unit (MCU),which had the ability of temperature control and power control. The chip ADN8830 and ADN2830 were used to realized the control of temperature and power, respectively .At the same time, the laser output power could be manually changed. The experimental results show that the temperature control module of this system can stably control the laser-s temperature, and make sure the target temperature error less than 0.01 ℃. And the wavelength can be adjusted between 1 535.17 nm~1 563.24 nm. The power control module can implement manual control and make the laser power change between 0 dBm~10 dBm with the error of 0 mW~0.05 mW.
Fiber Sensing and Optical Communication
Optical fiber refractive index sensor with temperature calibration ability
Zhou Jing-hui, Sun Hao, Yang Shen, Hu Man-li, Ye Zeng-liang, Zhou Li-bin, Zhang Xiao-lei, Yuan Liu-tong
2015, 36(1): 140-144. doi: 10.5768/JAO201536.0108001
We proposed a type of optical fiber refractive index(RI) sensor with the temperature calibration ability. The sensing head consisted of two very short lengths of multimode fiber (MMF) and a length of refractivity-insensitive fiber Bragg grating (FBG) fused between them, which had a total length of 14 mm. Here the FBG was used as the temperature calibration component for refractivity measurement. The experimental results show that the RI sensitivity of this sensor is about 126 nm, the temperature sensitivity of the resonance wavelength is 35.09 pm/℃, and the temperature sensitivity of the FBG is 11.14 pm/℃. Compared with the general refractive index sensors, this sensor with a good temperature calibration ability has better application prospect.
Design and analysis of fiber Bragg grating soil pressure sensorwith flexure of sheet structure
Zhao Yan, Zhang Ji-jun, Zou Hong, Chen Zhi-jun, Zhao Yong-mei
2015, 36(1): 145-149. doi: 10.5768/JAO201536.0108002
Based on the matching principle of soil medium and pressure transducer, a circular flat diaphragm with flexure of sheet structure fiber Bragg grating (FBG) soil pressure sensor was designed. By designing two symmetric fix ends on the diaphragm, we could successfully solve the problem that the reflection spectra of the FBG subject to the transverse force split in two main peaks. As the same time, for the strain effect caused by the fix ends-flare angle, the sensor-s pressure sensitivity was enhanced dramatically. By analyzing the sensor-s enhancement effect theoretically, we got the sensor-s pressure sensitivity formula. Computed result showed the sensor-s pressure sensitivity was 1374.3 pm/MPa. ANSYS was used to establish the finite element model for the flexure of sheet structure. By extracting the displacement of fix ends- coordinate point on the fiber-s direction, we got the finite element model-s pressure sensitivity about 1360.8 pm/MPa. ANSYS analysis result has high entropy with theoretical analyis- conclusion and the relative error is 0.98%, which verifies theory design and analysis.
Method for fiber nonlinearity mitigation in coherent optical OFDM systems based on constellation restoration
Leng Dan, HAO Yao-hong
2015, 36(1): 150-154. doi: 10.5768/JAO201536.0108003
Coherent optical orthogonal frequency division multiplexing (CO-OFDM) system is sensitive to nonlinearity because of high peak-to-average power ratio (PAPR) and closely-packed subcarriers, which seriously suppresses the transmission performance.A method for reducing the PAPR was put forward based on constellation restoration, the system model and action mechanism were analyzed. Analyses and simulation results show that, the system Q value of constellation restoration based CO-OFDM system is improved by about 3 dB for 720 km distance at a speed of 10 Gbit/s transmission through standardsingle-mode fiber (SSMF),compared with the CO-OFDM system without nonlinearity suppression. Meanwhile, the clipping factor is strongly influenced by the chromatic dispersion which can decrease the effect of constellation restoration. At the length of 240 km, the clipping factor is 0.9 and 0.8, while the dispersion factor is 12 ps/nmkm and 6 ps/nmkm,respectively.
Design of UV DPIM modulation system based on FPGA
Ma Ning, Li Xiao-yi, Yang Gang, Chen Mou
2015, 36(1): 155-160. doi: 10.5768/JAO201536.0108004
In order to verify the feasibility of digital pulse interval modulation(DPIM)used in ultraviolet(UV) communication, a DPIM modulation and demodulation system was designed based on field programmable gate array (FPGA). The deserialized data was input into the comparator under the control of latch during modulation process, and the DPIM modulation signal was output through comparing with the count value. In the demodulator, the number of free slot between neighbor pulses was detected by counter, and the original data was acquired through recovering under the control of latch. In the case of 16-DPIM, we input a set of serial binary data randomly and output 16-DPIM signal in modulation system. In the same way, we input a 16-DPIM modulation signal randomly and recovered the original data in demodulation system. On the basis of this analysis, a new dual-amplitude fixed-length DPIM modulation which could make up the lack of the DPIM symbol length change was proposed.