2013 Vol. 34, No. 3

OE System and Engineering
Athermalization of dual field of view infrared system
LI Yan, ZHANG Bao, HONG Yong-feng, ZHAO Chun-lei
2013, 34(3): 385-390.
Based on a 320240 middle-wave infrared cooled detector, a dual field of view infrared system was designed. Using focal shift of optical passive compensation temperature, athermalization design technology was realized. The computation process to obtain structural parameters of the optical system was introduced, and then optimization was applied by using Zemax software. The optical simulation and image evaluation were carried out. The experimental results indicate that the system realize the zoom of 50 mm and 200 mm at the band of 3.7m ~4.8 m by using eight lenses, and cold shield efficiency is 100%. During the temperature range of -20℃~60℃, value of the modulation transfer function is all above 0.5 at the Nyquist frequency.
Athermal design of cooled MWIR optical system
LIU Xiu-jun, ZHANG Jin-wang, ZHANG Hua-wei, LIU Bo
2013, 34(3): 391-396.
The pros and cons of the typical methods of athermal design were compared, and the basic theory of optical passive athermalization was discussed. According to the system requirement temperature range of -60℃ ~ 90℃, based on initial structure in normal temperature, using multi-configuration and automatic thermal analysis function, other temperature structures were added in Zemax software, then thermal and aberration were optimized. Finally a cooled medium wave infrared optical system was designed by using the optical passive athermalization. Detector cold-shield stop was used as system aperture stop, so this optical system could realize a 100% cold-shield-match. Optical materials were Si, Ge and ZnSe, and structure material was Al in the optical system. The MTF value is greater than 0.74, which is close to diffraction limit at the spatial resolution of 17 lp/mm, and the RMS spot diameter is less than single pixel size within -60℃~90℃. Those results show that the optical system has good image quality and athermal effect.
Infrared searching optical system with three-field of view
HU Bo, YANG Zi-jian, HAN Kun-ye, GAO Jing, WANG Ling, ZHANG Xuan-zhi
2013, 34(3): 397-401.
A kind of optical system with three-field of view for practical application was designed. The switch between wide and middle FOV was realized by using lenses group, and the switch between narrow and wide field was actualized by using mirrors. Three-field of view shared secondary imaging lens group, and the secondary imaging technique was used in the system design in order to endure 100% cold shield efficiency and reduce the diameter of the first lens. The technology for aspheric lenses was introduced to improve the imaging quality by correcting spherical aberration and coma. Then the performance of optical system was analyzed by CODE V software. The max spot was less than 11 m and MTF approached to diffraction limit. The results show that the image quality of optical system reaches application requirements. In addition, compact structure and light weight are the features of the system.
Hybrid refractive/diffractive eyepiece for head-mounted display with multilayer diffractive optical element
ZHAO Ya-hui, FAN Chang-jiang, YING Chao-fu, XU Jian-cheng
2013, 34(3): 402-406.
Based on the theory analysis of diffraction efficiency of multilayer diffractive optical element (MDOE), a hybrid diffractive-refractive eyepiece for head-mounted display (HMD) with MDOE was designed. The diffraction efficiency of the system at each field of view (FOV) and in design wave band was lager than 90%, which improved the utilization rate of energy and contrast ratio of image. The exit pupil distance and diameter of 60 FOV eyepiece were 22 mm and 8 mm. The distortion was less than 4.8 % and the maximum lateral color difference was 10 m. The modulation transfer function (MTF) value was more than 0.38 for all FOV at spatial frequency 25 lp/mm. It met the requirement of VGA resolution. The structure of the total system is compact, the length of lens is 26.8 mm, the maximum diameter is 16 mm, and the weight of the entire system is only 8 g. It realizes the miniaturization optical system.
Design and implement of infrared panoramic scanning and tracking imaging system
JIA Jun-tao, TANG Yue-feng, MAO Xin, ZHANG Liang, PAN Xiao-dong, LIU Yu
2013, 34(3): 407-412.
For the different requires of view scene on the processes of full range search and track, using linear array detector, high-speed turntable and high uniformity scanner, a 360 full range search and track imaging system was realized. The experimental results show that the system can successfully realize the 360 panoramic scanning and can be quickly turn to track imaging after search the target within 1.94 s. Its performance reach application requirement.
An ultra-thin eight-mega-pixel mobile phone lens
YANG Zhou, YANG Hui-ming, DING Gui-lin
2013, 34(3): 413-419.
The ultra-thin and high-pixel mobile phone lens is demanded with the development of mobile phone market. Combining the non-spherical principles, an ultra-thin eight-mega-pixel lens system was designed by using optical software CODEV. Four plastic aspheric lenses, an IR cut filter and a sensor cover glass compose the system. From the object side to the image side, the first and the third lenses are positive lenses, the second and the fourth lenses are negative lenses, and aperture stop is located in front of the first lens. The F-number is 2.4, FOV angle is 65.5, the effective focal length and the back focal length are 3.731 5 mm and 0.31 mm, and the length of the total lens group of the optical system is 4.6mm. The MTF values of the most of FOV are more than 0.5 at 1/2 Nyquist sampling frequency, and distortion is less than 2%.
Photoelectric conversion and amplifying circuit for photoelasticmodulated interferometer
HUANG Yan-fei, WANG Zhi-bin, WANG Yan-chao, ZHAO Dong-e, ZHANG Rui, WANG Yao-li
2013, 34(3): 420-424.
The output of detector which receives the interference light that is modulated by photoelastic modulated interferometer is weak electric signal that is of rapid change. Extracting and amplifying this electric signal is crucial to the development of the photoelastic modulator-Fourier transform spectrometer. A photoelectric conversion amplifying circuit with high signal-to-noise ratio and high bandwidth was designed through analyzing the interference light. The circuit consists of power circuit, photoelectric conversion circuit, amplifying circuit and the band-pass filter circuit with the theoretical pass band of 100 kHz ~ 3.5 MHz. The test results indicate that the circuit can amplify the signal from the detector whose maximum frequency is 1.6 MHz to about 670 mV, extract and amplify the output signal effectively from the background noise, and provides reliable data to the subsequent Fourier transform.
Friction torque of dynamic sealing of panoramic electro-optical aiming device
LI Xiao-hang, GUO Xin-sheng, ZHU Hong, DANG Li, NIU Jing, XU Yuan-yuan, LI Hong-guang
2013, 34(3): 425-429.
In order to solve the dynamic sealing of the panoramic electro-optical aiming device, through analysis of three typical kinds sealing principle of the panoramic electro-optical aiming device, the influence of friction torque of dynamic sealing on structure and accuracy of stabilized platform was analyzed. Combining with application of engineering practice, three kinds of sealing corresponding to the friction torque analysis and estimation methods were given, in order to help the follow-stabilized platform system design. Experiments of three kinds of dynamic sealing were analyzed and calculated respectively. Results indicate that magnetic fluid is the better way to solve the problem of dynamic sealing of electro-optical devices.
A new zooming method for projection imaging lithography
RAN Zuo, ZHOU Jin-yun, LEI Liang, ZHOU Ya-mei, DENG Ya-fei
2013, 34(3): 430-435.
In order to study the zooming for large-area laser projection lithography, using Zemax optical design software, the defocusing effect on modulation transfer function (MTF) and optical path difference (OPD) was simulated, the effect of OPD and MTF on the imaging quality of projection imaging lithography was analyzed, and the maximum defocusing range of the system was also provided. A zooming method by using microscope was proposed, the zooming errors of this method was mainly come from the depth of field of microscope. According to the expression of the depth of field and the maximum defocusing value of this system, a microscope whose depth of field was not more than the maximum defocusing amount was chosen to construct the zooming system. The experiment was demonstrated based on the zooming system for lithography. Experiment results illustrate that the new zooming method for project imaging lithography can obtain a good lithography image quality.
OE Information Acquisition and Processing
Real-time registration for long-distance multi-source image fusion system
ZHANG Bao-hui, ZHANG Jun-ju, MIAO Zhuang, CHANG Ben-kang, QIAN Yun-sheng
2013, 34(3): 436-441.
In order to achieve all-weather, multi-band, long-distance and real-time image monitoring, the optical front-end with low light level television, infrared and visible light system was designed, real-time multi-source image registration was investigated. Based on the parallel optical axis, the affine transformation parameters could be obtained by calculating the imaging disparity of the different field, the bilinear interpolation algorithm was used to make up the difference between infrared image and visible image in imaging, the infrared image transformation parameters were made into a look-up table stored in the image processor DM642, the system could quickly register different images through the look-up table and achieve real-time registration and synchronous fusion video. Experimental results indicate that this design can register multi-source images in real-time, the total processing time of image registration, image fusion and pseudo-color transformation is about 24.3 ms, the detection range is greater than 3 km.
Defect detection for resin lenses based on digital image processing technology
YAO Hong-bing, LI Liang-wan, PING Jie, GU Ji-nan, MA Gui-dian, ZENG Xiang-bo, ZHENG Xue-liang
2013, 34(3): 442-446.
The automatic defect detection technology for resin lenses was studied, including its hardware system design and its image processing method. The image difference method was used to remove the edge of the lens image in order to obtain high detecting speed, the effect of dust in lens detection was solved, and an improved normalization method was also proposed to determine the number of defects, which could provide technical support and feasibility for the development of subsequent digital control module of the classifying and sorting system of the whole resin lenses defect detection system. Detection accuracy of the detection system is 0.03 mm, speed is 1 piece/s, and the measuring error is maintained below 5%.
Implement of Fourier transform in real-time infrared spectrum recovery based on FPGA
WANG Xiang-yun
2013, 34(3): 447-451.
In order to obtain the real-time spectrum recovery of spectrum information such as battlefield laser, atmospheric pollutants gases, poisonous gas, etc. the real-time spectrum acquisition and analysis system based on FPGA was designed. The spectral information was abtained by using a Michelson interferometer and HgCdTe detector, and the collected date was transmitted to FPGA. Using hardware language Verilog HDL on the chip of Xilinx FPGA, the system achieved real-time processing of the spectrum data from interference pattern based on FFT. The simulation result indicates that the spectrum distribution information calculated by 1 024-point radix 2-FFT with FPGA is the same as the theoretical calculation result of Matlab, which can meet the requirement for real-time spectral detection.
Zoom-FFT based on Fourier transform spectroscopy
ZHANG Ming-xuan, GAO Jiao-bo, MENG He-min, FAN Zhe, ZHENG Ya-wei, LI Jun-na
2013, 34(3): 452-456.
Based on the analysis of the classical Zoom-FFT, a Zoom-FFT algorithm based on Fourier transform spectroscopy was presented. Both FFT and ZoomFFT were used to process the interferogram with different sampling steps by Matlab simulation software, through the comparison of the inverted and original spectrum curves, it indicated that the spectrum could be inverted by both FFT and Zoom-FFT when the sampling step was less than 20 m; But when the sampling step was greater than 20 m and less than 33.3 m, the spectrum could not be inverted by FFT algorithm, while the spectrum could be inverted by Zoom-FFT.
Optical Metrology and Measurement
Measurement accuracy of out-of-plane displacement forbinocular vision DIC system
FENG Xiu, CHEN Xu, XU Nan, CHEN Fan-xiu, XIE Xin, YANG Lian-xiang
2013, 34(3): 457-462.
Using electronic speckle pattern interferometry measurement system of high accuracy and sensitivity, the measurement accuracy of out-of-plane displacement for binocular vision digital speckle correlation measurement was verified. The maximum out-of-plane displacement was analyzed and compared. The results show that the consistency is good, the difference of two root-mean-square displacements is 2.76 m~3.56 m, the relative error is 4.59%~7.60%. High accuracy can be reached by Q400 when the out-of-plane displacement of measured object is greater than 4 m.
Error analysis of absolute test method of inhomogeneity of optical materials
LI Qiang, LIU Ang, GAO Bo, XU Kai-yuan, CHAI Li-qun
2013, 34(3): 463-468.
Absolute test eliminates the surface errors of reference plane of interferometer, so that the inhomogeneity of optical materials can be measured with high accuracy. A brief review and comparison of several mainstream absolute test methods for inhomogeneity of optical material were given. And influence of the factors, such as the pixel offset, resolution of interference pattern, repetition of interferometer, the sample thickness and the refractive index measurement, etc, on the measurement error of absolute test was analyzed respectively. Experimental results indicate that the measuring accuracy of window-flipping method, transmission method and parallel flat method can reach 10-8 respectively. Repetition of interferometer is the main error in absolute test method of the inhomogeneity of optical materials.
Several critical qualifications in measurement ofatmospheric coherence length
XU Wen-qiang, ZONG Fei, QIANG Xi-wen, SUN Xue-jin
2013, 34(3): 469-472.
In order to ensure the accuracy in measurement of atmospheric coherence length, it is necessary to specify qualifications of measurement. The qualifications of differential image motion monitor are determined through analysis of several critical problems such as sampring frequency, spampling time and exposure time in measurement of atmospheric coherence length, and combining with the result of domestic and foreign research, it is ensured that the sampling frequency should not be lower than 100 Hz, the sampling time should not be shorter than 20 s, the exposure time of single frame image should not be longer than the Greenwood time constant along with the measuring beam path, and the number of samples should not be less than 2 000 frames.
Image measuring system and its calibration of aero engine tip clearance
CHEN Yu-tao, ZHU Mu-cheng, TONG Si-rong, LUO Xian-peng, ZHAO Bi-wu, ZHAO Dong-mei
2013, 34(3): 473-478.
An image measuring system was designed to measure tip clearance when assembling aero engine. Its camera position was precisely controlled through PID controller, which was based on open control system of PC and motion control card. The camera was calibrated through its accurate movement. The blade tip clearance was measured on line. Compared with other image measuring system and traditional feeler gauge, this system has some advantages: first,it is efficient. Its calibration and measuring process is simple and fast; Second, it can achieve the on-line measurement during the assemble process; Third, when the measuring range is within 1 mm, its error is below 20 m.
Principles and simulation of polarized spectrum measurement based on double intensity modulation
ZHANG Rui, WANG Zhi-bin, ZHAO Dong-e, CHEN You-hua, WANG Li-fu
2013, 34(3): 479-484.
Due to single intensity modulated polarization spectrum measurement technology has aliasing phenomenon and effective optical path difference is limited, double intensity modulated polarization spectrum measurement was presented. This method not only has the advantage of a single intensity modulation spectropolarimetry, but also effectively eliminates the aliasing phenomenon and improves the effective optical path difference and the spectral resolution by sum-difference processing of the double intensity modulation interference signal. The sum-difference signal Fourier transform was used to get the polarization spectrum. The interference signal of incident spectrum and Fourier inversion spectrum were simulated by MATLAB. Simulation results show that this method effectively eliminates aliasing and gets double effective optical path difference after the sum-difference treatment. The principle for measuring the spectrum of the Stokes components based on the double intensity modulation spectropolarimetry is deduced in detail and its feasibility is proved by the simulation, which provides the necessary theoretical basis for engineering implementation of this method.
Low LighiI Level Technology
Distribution characteristic measurement of LLL image intensifierbackground noise with photon counting method
SHI Ji-fang, CUI Dong-xu, HE Ying-ping, XIE Qi, LI Hong-guang, SUN Yu-nan, CAO Feng
2013, 34(3): 485-488.
According to the noise characteristic of Low Light Level(LLL) image intensifier, the background noise characteristic of LLL image intensifier theoretically was analyzed. Then the photon counting method was designed, and LLL image intensifier background noise was measured by quasi-point source low light illuminometer. On the signal-to-noise ratio measurement device of the third-generation LLL image intensifier, illuminance produced by 0.2 mm point source on the fluorescent screen was measured using quasi-point source low light illuminometer with no input. For the spatial characteristics, the illuminance value inhomogeneity was less than 1% when the phosphor screen center point acted as the center of the concentric circles. But for the temporal characteristics,after the LLL image intensifiers worked 270 min later, illuminance values of phosphor screen center point could reach a steady state. Distribution characteristic of LLL image intensifier background noise based on the illuminance both in space points and time points was analyzed,and data proof for evaluating noise characteristic of LLL image intensifier was offered.
Stability of transmission GaAs cathode photoemission of3rd generation image intensifier
XU Jiang-tao, CHENG Yao-jin, LIU Feng, LI Min, LIU Bei-bei
2013, 34(3): 489-493.
In order to find the reason of sensitivity degradation in tube body of the third generation low-light-level (LLL) image intensifier, on-line quality detection was carried out by using mass spectrometer and activation process parameters were determined. The acquisition of the cathode atom clean surface, high pure cesium and oxygen source were studied. The online stability for transmission cathode photoemission of GaAs was measured. Results show that the sensitivity (1 500 A/lm) is stable in ultra-high vacuum pressure 10-9 Pa in continuous time of 500 hour. Sensitivity degradation is in connection with the vacuum loss and harmful gas pollution.
Relationship between voltage of MCP and signal-to-noise ratio of UV image intensifier
WU Xing-lin, QIU Ya-feng, QIAN Yun-sheng, LIU Zhao-lu, CHENG Hong-chang
2013, 34(3): 494-497.
Ultraviolet image intensifier has a very broad application prospects in many fields, such as space optical detection, environmental monitoring, strategic defense, and so on. Signal-to-noise ratio measurement system of ultraviolet image intensifier was designed by reference to the test principle of signal-tonoise ratio for UV image intensifier, and its test conditions were provided. The relationship between voltage of MCP and signal-to-noise ratio of UV image intensifier was deeply studied, and its curve is measured by using the development of its own signal-to-noise ratio tester for UV image intensifier. The result shows that in the region of less than 850 V, the output of the signal-to-noise ratio of the ultraviolet image intensifier is increased with the increase of voltage; when the voltage is more than 850 V, the output of the signal-to-noise ratio of the ultraviolet image intensifier is essentially unchanged.
Optical Element and Fabrication
Alignment method of aspheric optical reflector
LI Xiao-yan, FU Xing, WANG Peng, DUAN Xue-ting
2013, 34(3): 498-502.
According to the alignment demand of aspheric mirror with aperture of 230 mm, using the aberrationless surface figure test method, based on the three key processes of experimental research (bonding between the bottom plate and bare mirror; connection of the frame and the bottom plate; calibration of optical center), micro-stress alignment method that could get the minimum variation of the adhesive stress and conduction stress of structure was put forward, and aspheric mirror optical center was calibrated through the optical alignment. Alignment results show that surface shape error of the aspheric mirror with aperture of 230 mm is less than or equal to 0.02, optical center offset is less than or equal to 5 m, the plate was calibrated and the optical axis perpendicularity error is less than or equal to 2.5.
Optical landing aid system simulator
GUO Yu, ZUO Yong, WU Li-peng, CAO Feng, MA Shi-bang
2013, 34(3): 503-506.
When the carrier aircrafts land on the ship, carrier optical landing aid system is required on occasion. The lamp simulator used halogen tungsten light as light source, and a light uniformizer was added beside the light source. Then the beam shaping conical cavity was added according to the distribution of outgoing beam of light source. According to the demand of field angle, a cylinder array optical system was added at a certain distance. Then optical filter and optical attenuator were added at the exit pupil of the simulator. The lamp simulator had red, yellow, green spectrum, the horizontal field angle was 30 degree, the vertical field angle was 20 degree, the light intensity was over 10 000 cd, the uniformity of the lamphouse was better than 8%, and the light intensity was adjustable.
Laser Technology
Monitoring and study of tropospheric aerosol by lidar over Tibet plateau
YANG Hui, LI Xin-jian, CHEN Pei-bin, ZONG Jun-jun, LIU Jian, LIU Wen-qing
2013, 34(3): 507-511.
Qinghai-Tibet plateau is famous for the name of the third pole of the earth. The aerosol vertical scattering ratio profiles and extinction coefficient time-space distribution at Naqu prefecture and Beijing prefecture were shown and compared. The data shows that: the similar multi-layered zigzag vertical structure of aerosol extinction coefficient distribution exists in the day and night time; the layers include close ground layer, mixed layer and troposphere. The maximum value of aerosol scattering ratio remains at 2.0 under cloud-free conditions. Because of the vapor cycle, cumulus is existed over the prefecture most of the time, and presence probability of cumulus in summer is less than in winter.
Illumination distribution of forward paraxial scattering with bubble films
ZHANG Jian-sheng, CHEN Yan, SUN Jian-peng
2013, 34(3): 512-516.
From the Mie scattering theory, using single bubble scattering model, the forward scattering characteristics and the illumination distribution of forward scattering which around the optical axis of the laser were studied. With the wavelength of 632.8 nm, the illumination of scattering laser beam was measured and analyzed in different media under varied pressures. Research results indicate that, the forward scattering light beam of the laser mainly distribute in the range of 0.588 around the optical axis. Along the laser optical axis, illumination is axisymmetric, and the cross-sectional distribution is Gaussian distribution. Considering the scattering of water body itself, the ratio forward scattering illumination is probably accounted 35%, 45% and 55% of the total under the pressures of 0.006 MPa, 0.008 MPa and 0.010 MPa. The results show that the forward scattering light of the laser and pressure were inversely proportional whether the water self-scattering is calculated or not.
Multi-beam pump mid-infrared laser
SHEN Zhao-guo, FU Jie, TANG Gang-feng, MAO Xin, CHENG Jian-xin, YANG Yi, Lv Xin-jie
2013, 34(3): 517-520.
To acquire high power and high efficiency mid-infrared laser output, using double acousto-optic Q-switched crystal, through high repetition rate drive Qswitched synchronization technology and LD-side-pumped two-rod series connection technology, high power and high beam quality 1.06 m laser twoport output was acquired, laser output of four beams was got by exterior polarizer. Using wave-plate polarization rotation principle, consistent polarization laser output of four beams could be realized, PPLT was pumped to get high power 3 m~5 m Mid-IR laser output. As the input current was 30 A and the Qswitched frequency was 10 kHz, the highest out power of 3.9 m laser was 10.6 W, conversion efficiency of 1.06 m ~3.9 m laser was 9.5%. Experiment results indicate that using double acousto-optic Q-switched technology and LD-side-pumped two-rod series connection technology, high repetition 1.06 m polarizer laser output of four beams can be realized, and pumping PPLT can gain high power 3.9 m mid-infrared laser output.
Application of finite impulse response filter in four-frequency differential laser gyro
MA Chong-ze, FANG Zhong-chun, FU Xin, Lv Hang-wei, CHEN Lin-feng, YANG Hong-you
2013, 34(3): 521-526.
In order to overcome the problems of poor reliability and thermal sensitivity for the current optical separation system of four-frequency differential laser gyros, a digital signal demodulating system based on FPGA was presented. After analyzing the demands of signal demodulation for four-frequency ring laser gyro, the low-pass filter was designed in detail and was implemented, which was the key component of digital signal demodulating system. The pass band cutoff frequency and stop band cut-off frequency were calculated on the basis of parameters of four-frequency differential laser gyros. The parameter design of FIR filter was realized by using the FDATool of Matlab software, which is the design and analysis tool of filter. Using the FPGA integrated development environment (ISE), the proposed FIR digital filter was implemented via SOPC architecture. The simulation and experiment results show that the sum frequency component is reduced to -66 dB by designed FIR digital filter, and it meets the requirements of the digital signal demodulating system of fourfrequency differential laser gyros, and it helps to realize the miniaturization and digitization of full digital four-frequency differential laser gyros.
Infrared Technology
Background suppression technology in infrared armor target detection
CHEN Zhi-bin, ZHANG Chao, WANG Wei-ming, LIU Yu-xiang, LIU Bao-hua
2013, 34(3): 527-531.
It is hard to detect the infrared armor target because the background is so complex and the SNR of image is low. Consequently, a new background suppression method is put forward which bases on the wavelet and improved fractal theory. Filtering the low frequency background in image by using wavelet transformation, image with the target and edge clutter can be obtained. Because fractal dimension of target is much more sensitive than that of the edge clutter, so the edge clutter in background can be inhibited by calculating the rate of irregular factor of the image in different scale, so as to achieve a good background suppression effect. Experiment results show that this algorithm can significantly improve image signal-to-noise ratio (GSNR is about 2), and has good inhibition effect on undulate background.
An infrared detection range model based on discrete spectral atmosphere transmittance
MA He, WU Ping, ZHAO Yu
2013, 34(3): 532-536.
Atmosphere transmittance, which is an important factor influencing the operating range of infrared system and couldn-t be described precisely because of its complex changing with the atmospheric environment, wavelength and range etc, becomes one of difficulties for calculating the operating range. The impact of atmospheric transmittance on the effect distance of the infrared system was studied. An infrared detection range model based on discrete spectral transmittance was proposed. The atmospheric transmittance of the 1 cm-1 wave number segments was calculated by the MODTRAN software and was used to calculate transmitting infrared radiation power in the 1 cm-1 wave number segments. The calculated data was used to calculate the operating range of the infrared image system, instead of using a constant or average atmospheric transmittance in traditional method. The presented model is applied to the calculation of Tomahawk cruise missiles. Results indicate that it has a high accuracy and feasibility.
Fiber Sensing and Optical Communication
Properties of resonant wavelength of long period grating in photonic crystal fiber
GUAN Shou-hua, YU Qing-xu
2013, 34(3): 537-541.
With the finite difference method and the coupled mode theory, it was analyzed that photonic crystal fiber (PCF)-s structure parameters affected the adjusting action of long period grating (LPG)-s grating period on the resonant wavelength. The results showed that, for the same kind of PCF, it is feasible to decrease or increase resonant wavelength by increasing or decreasing grating period. If duty cycle f of PCF is increased or decreased, the resonant wavelength can be kept unchanged by decreasing or increasing grating period. If the scale coefficient M of PCF is increased or decreased, the resonant wavelength can be kept unchanged by increasing or decreasing grating period. For the PCF series only with the layer numbers of air hole increased, in the long-wavelength region, the grating period should be increased several ms to keep the resonant wavelength unchanged, while it was just the opposite in the short-wavelength region. The air holes in the inner layers greatly affect the adjusting action of grating period on the resonant wavelength, while the layers outside of the fifth layer affect the action very faintly. Using these regularities, it is portable to choose appropriate grating period, and high-effectively prepare LPG in PCF with appropriate resonant wavelength.
High-sensitive fiber-optic refractometer constructed by core-diameter-mismatch welding
GAO Ping-an, RONG Qiang-zhou, SUN Hao, HU Man-li
2013, 34(3): 542-546.
A high sensitive refractive index (RI) sensor based on Mach-Zehnder interferometer (MZI) is proposed and experimentally demonstrated. The sensing head is formed by a single-mode fiber (SMF) sandwiched between two short sections of thin-core fibers (TCFs), and the length of TCF-SMF-TCF MZI configuration is about 9 mm. A well-defined interference pattern is obtained as the result of fiber-core mismatch and core-cladding modes interference. The selected interference spectrum is extremely sensitive to the response of ambient RI. Using the proposed sensor to measure the glycerine aqueous solution with different RI, results indicate that the RI sensitivity of the sensor is 159 nm/RIU in the ambient RI range of 1.33 RIU~1.38 RIU. The fiber sensor has advantages of low-cost, simple mechanism, easy fabrication, high sensitivity, anti-electromagnetic interference, etc. It has great application potentiality in fields of bio-chemical measurement and environmental monitoring.
Optimization of inter-satellite microwave photonic link modulation mode
LI Xuan, ZHAO Shang-hong, ZHU Zi-hang, HAN Lei, ZHAO Jing
2013, 34(3): 547-552.
To the output signal-to-noise ratio (SNR) optimization of inter-satellite microwave photonic link, the direct intensity modulation detection inter-satellite microwave photonic link based on dual-electrode Mach-Zehnder modulator (DE-MZM) was modeled, the link performance was improved by optimizing the modulation mode. The link output SNR under single-sideband (SSB), double-sideband (DSB) and push-pull modulation was derived by numerical analysis. The minimum optical amplifier gain of the transmitter and the corresponding optical modulator DC bias point with the given output SNR were obtained by curved surface projection method. The results show that, when the input signal power and the optical emission power remain unchanged, the SNR of DSB modulation is 3 dB higher than SSB modulation, and the optimum SNR is obtained with low DC bias of push-pull modulation. When the input signal power is -20 dBm and the output SNR is 17.3 dB, the needed minimum optical amplifier gain is 43.9 dB, and the corresponding DC bias phase is 0.87 .