2015 Vol. 44, No. 3
2015, 44(3): 789-794.
Infrared countermeasure systems and technology have developed for half a century. Several types of infrared countermeasure systems,such as on-board infrared jamming system, infrared decoy and infrared smoke have appeared, and form a huge family of infrared countermeasure systems. In recent years, with the development of advanced infrared imaging guided weapons and technology, the jamming performance of traditional infrared countermeasure systems became more and more dissatisfactory. The technical concept of direct infrared countermeasure (DIRCM) was gradually proposed, which used high-power Xenon lamp or laser as sources of infrared energy. DIRCM has advantageous infrared countermeasure properties, such as the capability of jamming infrared imaging seeker by jamming, dazzling, in-band damaging and out-ofband damaging, etc, the capability of reuse and high jamming efficiency, which makes it suitable for new generation of infrared countermeasure system. The international research on DIRCM systems and technology in recent years was reviewed. And the operational principle, jamming damage mechanism,technology advantage of DIRCM system and the development status abroad were focused. And the research trends of DIRCM system and technology were forecasted in the next years.
2015, 44(3): 795-802.
Compared with the infrared fixed focal length lens and infrared dual-zoom lens, infrared zoom lens which has continuous variational field of view can track targets sequentially, so it is a research direction in infrared imaging technology. With the development of optical process, mechanism process, optical film coating, it is needed for infrared zoom lens not only has high ratio, but also has good athermalized and imaging performance. The configuration and design method of foreign MWIR lens with high ratio including MWIR lens with 20ratio, MWIR lens with 30ratio, MWIR lens with 300ratio were presented. A set of design experience for MWIR lens with high ratio was summarized, which is useful for the application and development of chinese MWIR lens with high ratio.
2015, 44(3): 803-809.
Infrared air-to-air missiles are the most effective close combat destructive weapons, but their working mechanisms are complex, jamming environment are variable, so the simulation missiles are hard to match the real. To simplify the simulation process and improve the accuracy of the simulation results, start from missiles functional simulation and abandon the complicated physics simulation, only concentrate on identification, guidance, control and motion process. Firstly, missile mathematical models were established based on the three degrees of freedom to simplify missiles motion equations. Secondly, the anti-interference method was classified, analysed different anti-interference mechanisms between the seeker entered into anti-interference state and couldn't enter into. Lastly, the simulation platform to the missile models, bait models and aircraft models as the core were established and miss distance, missile trajectories, anti-interference probability were used as evaluation criteria of simulation results. The simulation results show, the simulation infrared air-to-air missile models are simple and easy to implement and anti-interference results are close to the real missiles, also can meet the requirements of combat assessment.
2015, 44(3): 810-815.
An aviation large field of view(FOV) infrared scanning device employs TDI-CCD detector and performs a complete appliance scanning manner, its imaging quality is influenced by aircraft yawing rotation. The scanning device line of sight (LOS) rotation equation and LOS rotation constraint equation were established through kinematic analysis. Thus the aircraft yawing rotation bound was obtained which allowed a distinct image quality. Simulation was carried out on actual flight data, it shows an excellent image quality when aircraft makes a straight flight. The aircraft yawing rotation influence to large FOV scanning is acceptable.
2015, 44(3): 816-820.
With the rapid development of detection technologies, the infrared detectors have gained more and more applications. The internal structure of a miniature infrared detector for fast cooling-down process was numerically simulated and analyzed in this paper. The simulating result shows that the thermal contact resistance has significant effect on the detector module cooling-down process. By adjusting the contact resistance, the cooling-down time of the detector chip from ambient temperature to 90 K are 4-10 s. The effects of the initial ambient temperature and the diaphragm surface emissivity show few influence on the cooling-down process of the chip. While the temperature of the throttling cool head has a great impact on the cooling-down process. The faster the temperature drops, the shorter the startup time of the chip. Therefore, the detector can be improved by optimizing the thermal contact resistance and the throttling cool head, to achieve the higher requirements.
2015, 44(3): 821-826.
Blind pixels of IRFPA consist of fixed bad pixel and random bad pixel, the former is caused by material and manufacture defect, while the latter is mainly caused by temperature drift. Scene-based blind pixel detection and compensation algorithm is the effective method to eliminate these bad pixels and increase image quality. Aiming at the defect that the current filter-based detection methods can't distinguish random blind pixels and weak point targets, the response and noise feature of random blind pixels were first analyzed, and a new adaptive blind pixel detection and compensation algorithm based on fuzzy median and temporal accumulation was proposed. Fuzzy median filter was used to extract the potential blind pixels from scenes, then the exact distribution of fixed and random blind pixels were determined by temporal accumulation, and blind pixel compensation was performed finally. The experiments show that the proposed algorithm can effectively correct bad pixels while avoid misjudging weak point targets.
2015, 44(3): 827-831.
In order to correct the response linearity and non uniformity of infrared sensor, variable temperature and cryogenic infrared target device was developed. The working principle of the developed infrared target device which temperature was variable and cryogenic was discussed. The temperature control system of the blackbody source was analyzed by temperature field simulation based on finite element method in ANSYS software and temperature measurement experiment. The analysis and experimental results show that the cryogenic infrared target device developed is reasonable, and the distribution of simulated temperature field and measured temperature field is consistent, and temperature control precision(0.5 K) and stability(0.2 K) are high, and temperature distribution of the blackbody source is even(0.1 K/min). And the system can meet the test and verification requirement of cryogenic infrared system.
2015, 44(3): 832-836.
In order to improve the precision of wide field of view infrared optoelectronic theodolite, a calibration method based on multiple regression analysis was established, the reasons which effected the precision of wide field of view infrared optoelectronic theodolite were analyzed and the solution was proposed. First, the measurement theory and shipment of wide field of view infrared optoelectronic theodolit were introduced, the relationship between the object and the image in geodetic coordinates was analyzed. Then, the reason which effected the measurement of wide field of view infrared optoelectronic theodolite was the error between optical design, produce and machining, and the effect must be resolved after installation and adjustment. Lastly, a method based on multiple regression analysis was proposed, the calibration mode was established in all field of view by multiple regression analysis, after that, when measurement, the measurement data will be revised by the calibration multiple regression analysis mode. Experimental results indicate that the precision of the system in horizontal and vertical are improved from 21.44and 26.81to 7.62and 6.38. This method improves the measurement precision effectively.
2015, 44(3): 837-844.
Identification of inner heat source based on surface temperature measurement can find many applications such as in thermographic nondestructive defection, in microbial fermentation and in ammunition and food storage fields. Genetic algorithm was used to study the identification problem of the heat source term. The factors affecting the identification results were analyzed. Numerical examples proved that the method can provide a good solution to the parameter identification problem of inner point heat source. The identification results of position and strength are accurate when multiple point heat sources are identified simultaneously. Only the identification result of the position has a deviation when the point heat source is far from the unique temperature measurement boundary. The identification results of positions and strengths of point heat sources are accurate when the standard deviation of the temperature measurement error does not exceed 1.0℃.
2015, 44(3): 845-851.
Due to the fact that the characteristic peaks of multi-component of mixed gases have overlapping problem, it was hard to implement feature selection for each target gas. To solve this problem, a novel feature selection method was introduced. First, by making full use of the parallel mechanism, dissimilation operator of mind evolutionary computation and local search ability of bat algorithm, the mind evolutionary bat algorithm was designed. Two different mixed gases databases werecollected to validate the performance of proposed method. Then, from the aspects of convergence speed and characteristic peaks, the comparison with basic bat algorithm, genetic algorithm, particle swarmoptimization and parallel glowworm swarm optimization algorithm was investigated. Finally, the influence of combination with uninformative variable elimination method was discussed. Experimental results show that the characteristic peaks of carbon monoxide include 2 090-2 110 cm-1 and 2 115-2 125 cm-1, which total have 32 wavelength points while the characteristic peaks of nitrogen oxide were in range from 2 225 to 2 250 cm-1, which total have 26 wavelength points. Considering the concentration retrieve model established with the selected characteristic peaks, the root mean squared error of prediction set was 0.155, and the determined coefficient can reach as high as 0.908. Experimental results show that the proposed method has the advantage of rapid convergence speed and well global search ability, which was adaptable to do the feature selection for those mixed gases with overlapping problem.
2015, 44(3): 852-856.
The effects of surface plasmon polariton (SPP) propagation on the physical properties of cavities in the MIM) structure was studies. Theory methods were drawed using waveguide mode, resonance, reflection coefficient, and phase. The effects of relevant parameters were discussed, including length and thickness, on cavities in SPP propagation. Moreover, the electromotive force (EMF) of Metal-Insulator-Metal (MIM) waveguide and the effect of structure by varying cavity length and reflection coefficient were simulated, etc. Results show that EMF, which is in the SPP propagation, becomes relatively larger than 1 V, and the energy field can be amplified. Moreover, the effective power increases with increased cavity length, and the cavity length has a similar effect on SPP propagation in different cavity thicknesses, with the propagation coefficient reaching a maximum value in the near field. In general, analysis and discussion of this text are significant in studies on nonlinear THz spectroscopy, nanophotoelectric detection, generation of SPP mode, and strong local field.
2015, 44(3): 857-862.
The method to obtain the intensity distribution of laser beam after propagation through practical optical systems was proposed by combining the Collins formula and the Zernike polynomials for aberrations. The simulations were given to prove the correctness of the theory. Using this theory, the statistical change of the focus spots of Gaussian beams affected by the tolerance aberrations was presented. As a result, it shows that the spot radii increase with the RMS wave front aberrations and the detail forms of tolerance aberrations are important for the issue of laser beam focusing. Detail analysis of a practical system demonstrates that the spot radius is 1.520 mm without the tolerance aberrations. After the tolerance is introduced, the spot radius has an average of 1.700 mm, a standard deviation of 0.238 mm and it is smaller than 2.085 mm with a probability of 90%.
2015, 44(3): 863-866.
Experimental system for laser-induced acoustic signals was built. Acoustic signal was induced by pulsed laser focusing into water. A hydrophone was used to convert acoustic signals into electric signals. The mathematic model for laser-induced acoustic signals in time domain was analyzed. Energy distribution of laser-induced acoustic signals in frequency domain was studied. The modulation method for communication based on laser-induced acoustic signal was theoretically studied and proved by experiments. The results are as follows: Pulse width of laser-induced acoustic signal is about 20s. The laser-induced acoustic signals have most of their energy concentrated within 200 kHz, where half of that is between 100 kHz and 200 kHz. Magnitude modulation and frequency modulation are effective methods in communication based on laser-induced acoustic signal.
2015, 44(3): 867-871.
A high-power diode-side-pumped 1 110 nm Nd:GGG laser and a laser at 555 nm based on intracavity frequency doubling of 1 110 nm laser were demonstrated for the first time. A simple straight cavity scheme was employed to achieve a compact configuration and all the coatings were designed specially. A 25.5 W 1 110 nm laser continuous wave output was achieved under the incident pump power of 168 W. A LiB3O5 (LBO)crystal was used for second harmonic generation of the laser. As a result, at the pump power of 168 W, the maximum power of the frequency-doubled output at 555 nm was found to be 3.1 W with a pulse repetition rate of 10 kHz, corresponding to an optical-to-optical conversion efficiency of about 1.8%. And the pulse width of 555 nm wave was 176 ns. The M2 factors are measured to be 19.6 and 21.3 in the horizontal and vertical directions, respectively.
2015, 44(3): 872-878.
Sulfur dioxide (SO2) is one of the most common and important pollutant in the atmosphere. Differential absorption lidar (DIAL) measurement of SO2 has the advantages of high space-time resolution and high precision. Two laser beams, produced by two dye lasers pumped by two Nd:YAG lasers, were frequency doubled by two second-harmonic crystals, respectively. The dual wavelengths of on =300.05 nm and off=301.5 nm were selected to probe atmospheric SO2. One beam of light was achieved by merging two laser beams via several mirrors, and this laser beam was expanded sixfold with a beam expander and then transmitted vertically into the atmosphere. Backscattered radiation of both wavelengths was received by the telescope and acquired by data acquisition unit. Based on the storage data, the vertical concentration profiles of SO2 can be inversion. Preliminary result during experiment shows that SO2 concentration is roughly from 0 to 14 ppb at altitude ranging from0.3 kmto 1.6 kmover Dongpu island, west suburb of Hefei city. At last, four major measurement errors of this SO2DIAL were analyzed and estimated.
The ambient pressure is one of the basic factors determining cavitation. In order to investigate the influence of ambient pressure on properties of lase-induced cavitation bubble collapse sound waves, besides analysing the influence of ambient pressure on properties of lase-induced cavitation bubble oscillation, the experimental investigation of the lase-induced cavitation bubble callapse in liquids with different ambient pressure was done with hig-speed video, the cavity sound waves generated by the cavitation bubble was detected with the hig-frequency hydrophone. The pressure inside the tank was accurately controlled by an air pump. The results show that the ambient pressure has obvious influence on the bubble oscillation, but has no influence on sound intensity and spectrum. The radiation frequency range is 0-50 kHz, the radiation sound wave energy is 0-20 kHz, and have two obvious frequency peak value at 2 kHz and 8 kHz.
2015, 44(3): 884-887.
Nd:LuVO4, has attracted much attention because its larger absorption and emission cross sections than Nd:YVO4 and Nd:GdVO4. A more efficient pumping method was presented and researched, which was to pump the Nd3+ ions directly into the 4F3/2 upper lasing level to improve the laser parameters such as decreasing the threshold and increasing the slope efficiency and reduce the amount of heat generated by the nonradiative processes. In this paper, the report a quas-thre-level Nd:LuVO4 laser which is directly pumped by a laser diode at 888 nm. Achieved an output power of 2.5W at 916 nm for an incident pump power of 18.6W. The incident pump power at threshold of laser oscillation was 4.7 W, corresponding to the slope efficiency with respect to the incident pump power was 17.8%. For the same incident pump power, a maximum blue output power was 743 mW. The stability of the blue output power was better than 3%. The beam quality M2 value is 1.12.
2015, 44(3): 888-892.
The cloud lidar, with the character of high precision and good stability, is an effective way to detect the cloud height. Pulse diode laser (PLD), as an essential part of the lidar system, needs the triggering pulse. In this paper, the emitting part of the lidar was studied, including the simulation of the backscatter SNR, choosing of PLD and design of trigging circuit to drive the 905 nm PLD with the consideration of the optical system. A circuit for trigging the laser pulse with adjustable power and pulse width was contrived. Then the software Systemview was used to emulate the design and finally the making of PCB was finished. The results show whatever the parameters of the pulse, namely trigging pulse width, the rising edge, dithering, all these can be qualified to be in use in practice and enjoys the merits of low cost and convenience. The emitting module operates well.
2015, 44(3): 893-896.
Diamond array was braze welded on the stainless steel substrate which was processed applying femtosecond and nanosecond laser pulses with pulse duration 40 fs and 5 ns, respectively. The threshold of diamond processed using femtosecond and nanosecond laser pulses was deduced by measuring the relationship between fabricated area and laser power. The processing results show that the threshold of diamond processed by femtosecond laser pulses is lower compared with that processed by nanosecond laser pulses. The morphology of the processed region using differentkinds of laser sources was also compared with microscope. The processing of diamond applying femtosecond was confirmed more effective than that using nanosecond pulses.
2015, 44(3): 897-900.
For the linewidth measurement of the narrow linewidth laser, the resolution of the traditional spectrometer and the F-P interferometer is obviously insufficient to meet the requirement of linewidth measurement. In the experiment, a test platform was built using a spectrum analyzer based on the delay self-heterodyne method. Opportune parameters of the spectrum analyzer was set to distinguish noise suppression, using 20 km delay optical fiber based on the result of the calculation, 80 MHz acousto-optic frequency shifter(AOM)and 50:50 fiber coupler, achieve the photoelectric conversion by the photodetector.Optimally set the visual bandwidth(RBW), resolution bandwidth(VBW) and the scan range. Without reducing the testing sensitivity, the analyzer will distinguish overlapping signals and do not filter out too much high frequency to be distorted. Lorenz curve fitting was carried to the linewidth power spectrum peaks. Then it is achieved that the linewidth of the tunable wavelength fiber laser (1520-1570 nm) is about 161 kHz. It provides a reference to optimize the spectrumanalyzer parameter settings and calibrate the linewidth parameter of the narrow linewidth fiber laser.
2015, 44(3): 901-905.
In order to capture accurate data of lase-driven fusion test, diagnostic instruments (DI) which are mounted onto diagnostic instrument manipulator (DIM) should align the target with tight tolerance. Traditional alignment methods have problems of time consumption and error large. An accurate automatic alignment method was introduced, which based on visual servoing according to the virtue of DIM and DI. First, a 3D alignment vector was constructed to estimate the target deviation in the stereo vision system. Under narrow field of view, estimated value was close to true deviation. Second, a 3 DOF pose adjusting mode was founded to promote motion accuracy. Finally, a visual servo controller based on the alignment vector and pose adjustment mode was designed. The process of alignment needs offline calibration only once. Through the three steps, DI can automatic align the target with high accuracy. Test indicates that alignment accuracy (RMS) is 11m in x direction and 12m in y direction. Laser shot test with X-ray framing camera show that the automatic align method can satisfy the project requirements.
2015, 44(3): 906-910.
Measuring the half-wave voltage with high accuracy and a simple setup is an important issue for the applications of the electro-optical phase modulator. A new method was proposed which was based on the principal of beam steering in the laser phased array. The relationship between the offset of central beam in far field and the half-wave voltage was formulated by theoretical analysis. The setup of the 12 all-fiber laser phased array system was built and the half-wave voltage of the LiNbO3 waveguide phase modulator was measured. Several far-field intensity distributions with different loading voltages were recorded and the measuring error was decreased by taking average of the multiple results. What's more, the curve of phase modulation characteristic was obtained according to the multiple far-field intensity distributions. The experimental results show that the proposed method is simple with high accuracy and has important applications in engineering. Meanwhile, the phase modulation linearity can be analyzed.
2015, 44(3): 911-916.
In order to achieve the high-precision measurement of glass internal stress, a new method of magneto-optical modulation was proposed, and the system of internal stress measurement based on the magneto-optical modulation was established. First, measurement model of the system was derived according to the Mueller matrix description method of polarized light, by using separation of the direct current, fundamental frequency and the second harmonic component of detected signals, and normalized approach, the impact of the light source intensity fluctuation on the measurement result was eliminated. The direction of glass internal stress and the size of stress birefringence values were received by processing the respective signal components. By measuring the glass at different positions, the validity of the method is verified, and the measurement accuracy of internal stress direction is 5, the measurement accuracy of stress birefringence value is below 0.5 nm/cm. This system has high stability and high accuracy.
2015, 44(3): 917-922.
The stray light characteristics of different catadioptric ground-based photoelectric detection system were analyzed. The relevant stray light suppression ways were discussed. Based on structure with middle image surface and the other one without middle image surface, two different suppression schemes for the stray light were provided respectively. Besides, the thermal radiation for the long wave infrared system was analyzed. The results show that adding out baffle to the catadioptric system without middle image surface can do well obviously in reducing stray light with large off-axis angles. However, adding stops and the inner baffle of primary mirror to the catadioptric system with middle image surface can reduce the outer stray light obviously. This can reduce the length and weight greatly. If the thermal radiation demand can be satisfied, the miniaturization and lightweight design had been realized.
2015, 44(3): 923-928.
With the rapid development of relative technologies, the aero-cameras are developing in the direction of high resolution and large field of view. The existing CCDs cannot meet the requirement of large field of view． So, high-precision, multi-degree of freedom stitching technology has become an urgent demand for the current development． By comparing existing stitching technology, a multiple degrees of freedom mechanical interleaving stitching method which was different from traditional mechanical stitching and optical stitching methods were designed. The multiple degrees of freedom stitching machine with three points of cam was used to replace the traditional way of adjusting shims. So stitching can be adjusted in real time online. The analysis result shows that the method has a stitching error of less than 2m, a coplanar error of less than 5m． It can meet the imaging requirement of the camera. Modal simulation and modal experiment show that the resonant frequency of the structure of the first order is greater than 390 Hz, it can meet the requirements.
2015, 44(3): 929-933.
In order to specify the ripple of the large reflecting optical item in different scale, the algorithm based on the structure function was investigated. Firstly, the concrete steps of the algorithm were presented. Secondly, the error composition character was discussed in theory. Furthermore, the method proposed here was applied to the mirror figure data of a 1.23 meter mirror, making the conclusion that the simplification was correct and application was feasible. Lastly, the application to the thirty meter telescope tertiary mirror was processed, the ripple of the mirror figure in different levels was specified. This work will guide the way to the large flat mirror specification.
2015, 44(3): 934-940.
The tunneling breakdown electric field, avalanche breakdown electric field, multiplication region width depend on exceed breakdown voltage of InGaAs/InP SPAD was researched as a key point. The calculated method of exceed breakdown voltage was presented. The basic performance of single photon avalanche diode(SPAD) depends on their excess bias, multiplication region width, working temperature, electric-field distribution and quantum efficiency has been analyzed. According to these analysis, a designed solution of InGaAs/InP SPAD has been presented, and then the device was manufactured later. Under the conditions of-40℃ and exceed breakdown voltage over 2 V, the InGaAs/InP SPAD of 200m diameter exhibits dark count rates(DCR) below 20 kHz and photon detection efficiency(PDE) of 20%(1 500 nm). Under the conditions of-40 ℃ and exceed breakdown voltage over 2.5 V, the InGaAs/InP SPAD of 50m diameter exhibits dark count rates(DCR)below 2 kHz and photon detection efficiency(PDE) of 23%(1 550 nm). Finally, the experimental results were analyzed.
2015, 44(3): 941-946.
In order to design a high frame,large array driver circuit which supports electronic image motion compensation funcition, meet the fuction of image motion compensation.First,the basicdriver circuit of the large array CCD FTF5066M was given,and added an image motion compensation timing generator whick worked together with the main timing generator SAA8103 was added to achieve the electronic image motion compensation. Then the internal structure of the image motion compensation timing generator was given ,the additonal image motion compensation timing generator was only used to produce the vertical transfer drive timing, timing signals and tranfer the timing sigals produces by SAA8103. The FPGA as the image motion compensation timing generator was selected, and the timing simulation was done. In the end, indoor experiment of image motion compensation was given to test the driver circuit designed.The good compensation effect was achieved. The driving circuit system supported a maximum frame rate up to 2.7 F/s, signal to noise ratio reached 66 dB. This driver-circuit can conveniently select output channel number and output mode, the camera is suitable for different occasions.
2015, 44(3): 947-950.
A 0.17 THz Schottky varactors frequency doubler for 0.34 THz wireless communication system was presented in this paper, which can supply the low phase noise and low spurions of local oscillator (LO) signal. The doubler was based on quartz microstrip circuit integrated in waveguide cavity and with the Schottky varactor diodes constituting anti-parallel pairs as the key part. The modeling and simulation for the diodes were accomplished by combining the knot parameter model with three-dimensional electromagnetic model. Two ways were found to achieve a matching circuit for the optimal doubler design and a 0.17 THz doubler was fabricated and tested according to these simulating results. The test results indicate that, at the 80-86 GHz driving frequency and 20 dBm driving power, the maximum output power of the doubler is 12.21 mW with the efficiency up to 11% at 163 GHz, and it can reach to 21.41 mW while the input power at the saturation terminal.
2015, 44(3): 951-954.
Dry etching and wet etching were usually used in the mesa etching process of InAs/GaSb SLs. Three kinds of etch atmosphere(Cl2 based, Ar based and CH4 based)were studied in inductively coupled plasma(ICP) dry etching. The results show that the CH4 based atmosphere give much more smooth surface and less etch pits according to the SEM measurement. Then wet etching was introduced to eliminate the etching damage of ICP dry etching, tartaric acid based etchant and phosphoric acid based etchant, were studied. It was found that the phosphoric acid based etchant gave better result to remove etching damage, and provide a more stable etching rate. InAs/GaSb SLs photodiodes by standard photolithographic procedures were fabricated using this etching recipe. The diodes exhibits a high breakdown voltage and low leakage current, the measurement result reveals a dynamic impedance values of R0A =1.98104 cm2 at 77 K.
2015, 44(3): 955-958.
According to the especial requirement for optical coating in fiber communication passive devices, complicated wavelength division multiplexing(WDM) filter coating was demanded on optical fiber pigtail, in view of the difficulty about the coating deposition on optical fiber pigtail, an initial quarter film was given by resolution method by using TFCalc formula design software, then gradient optimization method was combined to partly optimize the initial formula, and the layer sensitivity of the formula was analysed by combining deposition equipment to assess the robustness and the deposition feasibility, then the formula of wavelength division multiplexing(WDM) filter coating on optical fiber pigtail was obtained with good spectral properties. The internal structure and deposition technology of LEYBOLD APS1104 deposition machine made in Germany was improved to deposit the designed formula by using ion assistant deposition with low temperature, the wavelength division multiplexing filter coating on the optical fiber pigtail with good performance was acquired.
2015, 44(3): 959-963.
Amorphous silicon(a:Si) films were annealed by KrF excimer laser to realize the influence of different power density and different pulse counts. The analysis of a:Si thin film microstructure and surface morphology was conducted using X-ray diffractometer(XRD) and scanning electron microscope (SEM). In the range of 1 Hz, the results show that the polycrystalline silicon structure has been achieved from amorphous silicon by excimer laser annealing when the energy density reaches about 180 mJ/cm2. When the energy density is from the energy density threshold 180 mJ/cm2 to the energy density 230 mJ/cm2, the crystallization effect gets better with the increase of the energy density. The effect of crystallization is best and the gain size is the biggest while the energy density is 230 mJ/cm2. The maximum average size of the grain reaches 60 nm and the polycrystalline silicon film grows preferentially along the crystallographic(111) orientation. The influence of pulse counts are not remarkable if the pulse counts are over 50 times.
2015, 44(3): 964-968.
Spectral hole depth dependence on optical length in Tm3+ :YAG was theoretically and experimentally investigated. A novel model was proposed to analyze the spectral hole depth dependence on optical length. With the proposed model, the spectral hole depth dependence on optical length had been derived theoretically. According to the theoretic result, when temperature was higher than 4K, the maximum spectral hole depth could be found by choosing the optimum optical length. The theoretical analysis were experimentally tested using spectral hole burning in Tm3+:YAG for a couple of configurations and sizes of the beams.
2015, 44(3): 969-973.
Terahertz CT setup was designed and constructed by backward wave Oscillator which has been used to perform computed tomography of 3D objects. However, the imaging quality is affected by strong refraction from materials with the refractive index greater than 1.5 in objects. At first, the cross section image of a teflon modal was reconstructed from the projection dataset by the filtered backprojection algorithm , then high refraction effects were analyzed. Finally, a human tooth sample was scanned and the cross section images were reconstructed to reveal its internal structures. However, the accuracy and resolution of the images were still limited owing to the high refraction effects. And the terahertz transmission depth in teeth was seriously affected by the thickness of enamel. The results in paper are helpful to improve the imaging quality of THz-CT and promote its applications especially in biomedical imaging of human bones like human tooth.
2015, 44(3): 974-978.
Most of terahertz (THz) systems and their application require THz modulator to modulate THz signals. Photoelectric modulators at present are made and producted by semiconductor-based, such as GaAs, materials. But unfortunately, due to their limited response to THz wave, these modulators based on traditional semiconductors are not suitable for THz systems. To overcome the limitation on modulation bandwidth and depth, a new scheme of THz wave intensity modulation system was proposed, which was based on all optically tuned graphene on silicon(GOS). This new modulation system was realized by photo-induced free carrier, which can absorb THz waves. By controlling light intensity which incident on modulator, photo-induced carrier density could be tuned, and even transmitted THz wave intensity was modulated. In this work, the fundamental properties of this THz intensity modulator was theoretically and experimentally studied , such as modulation depth and bandwidth. Our experiment results also show that it has a wide modulation bandwidth, which can modulate efficiently THz wave in THz-TDS of frequency range from 0.1 to 2.5 THz, and the typical modulation depth is 12 % at an optical pump fluence of 18 mW/mm2. what's more, the modulation depth increases with increasing optical pump fluence.
2015, 44(3): 979-984.
Terahertz waves have unique properties and applications, but there are physical limitations such as atmospheric attenuation and so on. Since the main attenuation of terahertz transmission in the atmosphere comes from water vapor, terahertz tim-domain spectroscopy was used to conduct terahertz tim-domain spectroscopy measurements in different air humidity at the frequency range of 0.1-2.0 THz by building terahertz tim-domain spectroscopy system with different stroke (0.5 m, 1 m, 2 m, 3 m), respectively. 25 absorption of water and 10 windows of THz waves were obtained. The results show that: with the increase of transmission itinerary or humidity, absorption band is broadened and terahertz window is compressed. The study provides the basis for the potential applications of ultr-broadband terahertz waves.
2015, 44(3): 985-989.
For study the characteristics of terahertz radar scattering cross section, by building a low-frequency terahertz radar test system, and with the help of standard target method, experiments and research work about terahertz radar scattering cross section of rough aluminum plate were carried out. The experimental results show that: In the small angle scattering, terahertz radar scattering cross section changes much obviously with the increase of the scattering angle; But when the scattering angle is more than 5, terahertz radar scattering cross section varies with the scattering angle tends to be slow; And when the scattering angle is more than 12, the detection signal strength attenuation cannot be measured. The phenomenon that microwave radar scattering cross section size changes with the angle of scattering while acuteness oscillation does not appear in the testing of terahertz radar scattering cross section. Comparison of the test results with the same size of microwave and laser radar cross section, it can be the concluded:In the vicinity of 0, the magnitude of terahertz radar scattering cross section is two orders lower than the same size microwave radar scattering cross section, but is an order higher than the same size laser radar scattering cross section.
Cascaded optical parametric processes in terahertz parametric oscillator with a noncollinear phas-matching scheme based on bulk lithium niobate were observed. The spectra of the first-, second-, and thir-order Stokes waves were observed. By analyze the spectra of the first-, second-, and thir- order Stokes waves it is found that the frequency difference between adjacen-order Stokes waves is approximately equivalent, which means that the hig-order cascaded parametric processes have realized. With hig-order cascaded terahertz parametric processes one pump photon can generate several THz photons, which means that the quantum conversion efficiency can be enhanced.
2015, 44(3): 996-1007.
Terahertz (THz) radiation from femtosecond photo-induced gas plasmas was explored. Given that THz wave is of great importance in safety inspection and national defense, it was summarized and analyzed that physical mechanism, which covers theory model, polarization characteristic and angle distribution of far field, and control technologies consisting of control of THz intensity, polarization and waveform to meet application requirements was discussed. It shows that there are many ways to generate, explain and control THz radiation from laser-induced plasmas. Among them theory models mainly include four wave mixing model and photocurrent model, and high energy of THz emission could be radiated from two-color femtosecond laser-induced filament in air or generated in laser-induced air plasma on the external electric field.
2015, 44(3): 1008-1014.
A polymer straight tapered fiber collimation system with a fiber plano-convex lens coupled directly into the front-end was developed. We demonstrate that the cone angle and taper length of polymer straight tapered fiber have remarkable effects on the collimation performance based on the theory of rays propagation and geometrical optics. We show that the collimation accuracy improves obviously with small cone angle of long straight tapered fiber. In addition, the cone angle and taper length are further optimally designed so that both the coupling efficiency and collimation accuracy are well balanced and maximized in the collimating process. This study can benefit the collimation of the emitted laser beam in free space optical communication systems.
2015, 44(3): 1015-1019.
A novel technique for end-pumped fiber combiner fabrication by multi-step process was reported. The mould, heat-shrinkable tube and filament were used to combine and fix the fibers. The combined input fiber beam can form a whole fiber without turning around before tapering, and was compatible with the commercial cut knife and welding machine. The fabricated 71-type fiber combiner had a endurable power of 1 400 W and the pump coupling loss was under 0.1 dB. The temperature distribution of the packaged fiber combiner was measured and analyzed. It shows that the polymer layer has a big temperature rise and limits the endurable power of the fiber combiner.
2015, 44(3): 1020-1023.
Long period fiber grating is transmission spectrum grating,which is fiber core basic model coupling with cladding modes, and resonance wavelength and amplitude of long period fiber grating is very sensitive to the change of external environment, long period fiber grating has better sensing properties than traditional FBG in temperature, stress, bending, distortion, lateral load, refractive index, and so on. Because the long period fiber grating was sensitive to two or more parameters, when optical fiber grating for sensing measurement, it was difficult to distinguish the change of the measured caused by the various parameters respectively, and cross-sensitivity problem of long period fiber grating was more serious than that of the fiber Bragg grating. The cross-sensitivity was the key problem of fiber grating sensors. Based on analysis of the current typical ideas and solutions, one idea and solution of relation was proposed in this paper, and solves cross-sensitivity between stress and temperature in the long period fiber grating temperature sensing measurement. This idea makes full use of the cross-sensitivity phenomenon of the temperature and strain of LPFG and turns the negative interference of the strain on the temperature to positive sensitization.
2015, 44(3): 1024-1027.
Fiber Bragg grating(FBG) has been widely used in many fields for temperature, stress and other parameters measurement, but it has cross-sensitivity problem with temperature and stress. A dual cladding radius fiber Bragg grating sensor was presented, the FBG was divided into two halves which have different cladding radiuses, the cladding radius of one half(FBG1) was unchanged, and the cladding radius of the other half(FBG2) was decreased from 62.5 m to 40 m. Experimental results show that, FBG2 and FBG1 have same temperature sensitivities which are 10.4 pm/℃, but FBG2 and FBG1 have different stress sensitivities which are 1.12 pm/ue and 3.89 pm/ue respectively, the stress sensitivity of FBG2 is higher than FBG1 nearly 3.24 times. The initial single Bragg reflection peak split into two reflection peaks which respectively sensitive to temperature and stress, the wavelength difference between these two peaks only impact on stress. Through this sensor, it can distinguish center reflection wavelength shift caused by temperature and stress. The sensor has simple structure, small size, low-cost, and simple fabrication,and it be can widely used in various fields to achieve simultaneous measurement of temperature and stress.
2015, 44(3): 1028-1033.
Proceed from the detected optical field's quantum statistics model of the Avalanche Photo Diode (APD) photoelectric detection receivers, an accurate realize method of Intensity-Modulation/Direct-Detection (IM/DD) Free Space Optical Communication (FSOC) fit Low Density Parity Check(LDPC)Codes decoding algorithm was investigated. This scheme, which was based on APD receivers' output statistical model(Webb-Gaussian Model), derivated the accurate calculating method of the original value of the likelihood ratio in LDPC decoding arithmetic over M-PPM demodulation. A detailed decoding process was given at the same time. By taking theoretical analysis and simulations, a result has been proved that:comparing with the most frequent used asymmetric Gaussian approximation model of APD receivers, the scheme introduced in this paper could get a gain of 1-2 dB in the decoding performance while in the same SNR. This gives the theoretical support in order to improve the performance of FSOC system further more.
2015, 44(3): 1034-1041.
Near-field optical tweezers is a new technology based on the near-field optical theory, which can stably trap particles. Compared with conventional far-field optical tweezers based on the single-beam gradient force, near-field optical tweezers which overcomes the diffraction limitation of near-field light optical resolution, thermal effects and many other disadvantages, can achieve the capture on particles in nano order, and have aroused much attention in the field of physics, cell engineering, biomedicine, and so on. Firstly, the model of near-field optical tweezers based on evanescent field and the basic principles of trapping were described. Secondly, the development of total reflection prism optical tweezers, probe type optical tweezers, nano-pore optical tweezers, focused evanescent field optical tweezers, micro-nano fiber optical tweezers, and micro-resonator coupling structure type near-field optical tweezers was introduced. In the end, the applications of optical tweezers in the field of biomedicine were mainly introduced.
2015, 44(3): 1042-1047.
In space-borne laser altimeter system, the range between satellite and target was calculated by the weak received signal which was transmitted from laser device and reflected by earth surface, and the accurate location and elevation of laser footprint was acquired by combining satellite precise orbit with attitude data. The elevation error was mainly affected by the device noise, the environment and the target parameters, and there is no complete analyzing model of location and elevation error for spaceborne laser altimetry system. The error model of laser ranging for solid surface was simplified and improved. Meanwhile, the location and elevation error analysis model of laser footprint was established in this paper. Utilizing airborne lidar data with better spatial resolution and elevation accuracy, the elevation deviation of GLAS data were evaluated, and the result was consistent with the error model. It is proved that on the flat surface of ice sheets the elevation accuracy of GLAS system can meet its design value of approximate 15 cm. This research is instructive for elevation error assessment and system parameters designing of laser altimeter system.
2015, 44(3): 1048-1052.
Studying more precise and efficient measuring-method for determining optical parameters of thin films plays a guiding role in improving design and optimizing preparation process of optical thin films. Several traditional measuring-methods were introduced briefly in this paper, and a new measuring-method was deduced combined envelope with the full spectrum inversion method fitting. In this method, optical parameters of a single layer were calculated approximately with envelope method, and according to the results, the upper and lower limits of the optical parameters were estimated for the full spectrum inversion method fitting firstly. Then, the physical model of the new method was established. After that, the optical parameters of thin films were solved by choosing a comprehensive optimization algorithm. Finally, the validity of the new method was validated through measuring of TiO2、SiO2 single-layer and G|0.5HLHL0.5H|A(H-TiO2,L-SiO2) multilayer. Besides, the measurement accuracy, efficiency and stability of the new method were also analyzed.
A calibration method based on the principle of a non parallel ranging model was presented to obtain the parameters of the binocular stereo vision device. The ranging error caused by the non parallel optical axis and the measurement error of optical center distance were decreased. In order to slove the problem that there were lots of error matching pixels and target recognition rate was low under low illumination in the binocular stereo vision, the threshold selection method which combined the maximum entropy and change of light intensity was proposed to extract significant object, the recognition rate was improved. Finally, the significant target recognition system was build. The results show that the binocular stereo vision device, utilizing the method of camera calibration and threshold selection proposed in this paper, has a higher target recognition rate and ranging precision under low illumination.
2015, 44(3): 1061-1067.
Axis detection resolution was divided into two sections, the first being the inherent optical resolution of the case and the second the case subdivided accuracy, however, atmospheric channel secondary modulation can directly introduced into detection error, and moreover, influence detection precision. In order to reduce sensitive degree of axis detection system for atmospheric interference, firstly, CCD system and 4QD system as two typical axis detection models were analyzed; the relationship among resolution and inherent optical resolution and subdivided accuracy and beam length was deduced. Afterwards, based on the example of 4QD axis detection system, through the analysis of restricted constraint condition of four-quadrant electro-optical inspection model in atmospheric channel,SNR of distortions and axis offset are two main technical parameters to affect electro-optical inspection system. Finally, the point, subdivided accuracy of axis detection was sensitive to atmospheric interference and inherent optical resolution was little influenced by atmospheric interference. Therefore, changing beam length can improve sensitive degree of axis detection system for atmospheric interference.
2015, 44(3): 1068-1072.
The Zernike polynomial is a widely used analytical technique in optics. Because of the discrete sampled measurement data and widely used non-circle aperture system in modern optical engineering, Zernike polynomial fitting can not satisfy a requirement completely. A kind of non-circle aperture discrete sampled orthogonal polynomial based on Zernike polynomial was proposed. The orthogonal basis was obtained using matrix QR decomposition method for discrete samples. Zernike polynomial and orthogonal polynomial were used for fitting 150 mm90 mm rectangular grating wave-front. The differences of PV and RMS between two methods are 0.013 waves and less than 0.001 waves respectively for the residual wave-front. Comparison of different order fitting of the orthogonal polynomial and Zernike polynomial coefficients, indicate that the orthogonal polynomial coefficients are independent of each other. And the corresponding Seidel aberrations were calculated by the orthogonal polynomial coefficients. Orthogonal polynomial coefficients can be solved one by one. This method can significantly improve the solution speed.
2015, 44(3): 1073-1079.
To solve the problem that infrared polarization and intensity image fusion algorithm is not optimal selection along with the change of difference characteristics, a method of establishing the set-valued mapping between difference characteristics set and fusion algorithms set was presented. Different characteristics set was formed with difference characteristics which was obtained by the analysis and extraction of image characteristics, and fusion algorithm set consisted of typical fusion algorithms. Fusion effective measure of each characteristic corresponding to fusion algorithms was calculated by data envelopment analysis and then constructed to be a distribution. Multi-group fusion effective measure distributions were synthesized in order to establish the set-valued mapping of difference characteristics and fusion algorithms set. Experimental results show that the set-valued mapping can select the optimal fusion algorithm, and have the highly complementary characteristics fused effectively.
2015, 44(3): 1080-1084.
Images of roads captured by visual surveillance system are usually degraded by scattering due to atmospheric particles such as haze, fog and mist, which could frequently bring great difficulties to the transportation. In this paper, a novel method was proposed based on weighted least squares(WLS) to remove fog from a single input image. The proposed algorithm begins with estimation of atmospheric light and white balance. Then, through the constraint from the road environment, the weighted least squares(WLS) framework was constructed to estimate atmospheric veil, and restore the fog image by inverting the atmospheric scattering model. The experimental results demonstrates that, compared with the existing algorithm, the proposed method can remove the fog effectively, eliminate the Halo effects, obtain good restoration of distant scene details, and thus realize the improvement of traffic image visibility.
2015, 44(3): 1085-1091.
In order to solve the problems that SIFT(Scale Invariant Feature Transform, SIFT) descriptor may result in a lot mismatches when an image has many similar structures and its high dimensions will consume much time in image matching. This paper presents a compressive sensed SIFT descriptor which is mixed with relative geometry location. At first,this method centers on feature point,and transforms the information of relative geometry location related to around key points into a RGL(Relative Geometrical Location, RGL) descriptor, which is invariant to scale and rotation. Secondly, CS-SIFT(Compressive Sense SIFT, CS-SIFT)descriptor is formed by reducing dimensions of SIFT descriptor using the theory of compressive sense. At last, two descriptors form a RGL-CS-SIFT descriptor(descriptor mixed with RGL and CS-SIFT, RGL-CS-SIFT). The results indicate that the RGL-CS-SIFT increases the matching speed and improves the ratio of image matching significantly, compared with SIFT and PCA-SIFT(Principal Component Analysis SIFT, PCA-SIFT) descriptors.
2015, 44(3): 1092-1097.
Hyperspectral unmixing based on sparsity is a research hotspot in recent years. This paper studies the hyperspectral unmixing algorithms based on L1 regularization. First we analyzed three unmixing models, including unconstrained model, non-negative constraint model and full-constrained model. And then the corresponding algorithms are presented. In the end, both simulated and real hyperspectral data sets are used to compare and evaluate the proposed three hyperspectral unmixing algorithms. Experimental results demonstrate that three models all have good high-precision. The full constrained model achieves the best unmixing precision(SRE). The non-negative constrained model is better. And the unconstrained model is worst. In particular, the fully constrained model achieves the higher SRE under the low signal to noise ratio and a large amount of endmembers situation.
2015, 44(3): 1098-1102.
The compute of pBRDF model is very complex in most cases. In order to get the contrast of degree of linear polarization(DOLP) between camouflaged target and background accurately and conveniently, the distribution function of microfacet and shadowing function in the Maxwell-Beard BRDF model was simplified with the method of idealization and specific values. The distribution function of microfacet become more accurate than Torrance-Sparrow model and easier than Maxwell-Beard model. According to the property that there are differences between the rate of s component and the p component in Fresnel reflection, the Muller matrix which record the process of reflection was got. Then a polarimetric BRDF model was established by physical theoretical analysis. To cope with in-plane reflection, the pBRDF model was simulated by MATLAB and the results show it can describe the reflecting properties of rough surfaces. The model has theoretical and practical significance for the study of the influencing factors of the reflection by rough surface and polarimetric camouflaged target detecting.
