2006 Vol. 27, No. 1
The moon exploration program is a sophisticated multidisciplinary integration systematic engineering project. Its optical detection system plays an important role throughout the different stages of the project. The accurate metrology on all kinds of optical sensors and systems is critical for ensuring the whole project successful. Based on the mission requirements, the facilities and technologies available are described, and the facilities and technologies to be built are also suggested.
Two dimensional atmosphere wireless optical CDMA communication system with Mary PPM(pulse position modulation)signal format is presented and studied．With the factors of multiuser interference，avalanche photodiode (APD) noise and thermal noise taken into account，the influence of atmospheric scintillation on the bit error rate(BER) of two dimensional wireless optical CDMA communication system was analyzed in detail. The results indicate that the atmospheric scintillation is an important factor for the bit error rate of two dimensional wireless optical CDMA systems. High speed communication can be realized in wireless optical CDMA systems if the logarithm variance of the scintillation is small enough (for example，σ2s=0.1). Otherwise，if the logarithm variance is too big(σ2s≥0.2),it will be difficult to communicate with limited receiving power. In this case, some improving methods，such as channel coding technology，need to be used to improve the BER performance of 2D optical CDMA communication system.
A mathematical expression for the optical limiting threshold is derived according to the nonlinear absorption model. Based on the theoretical expression, the influence of optical physics parameters on the optical limiting effect, such as nonlinear absorption parameter, linear transmissivity and effective excitedstate absorption crosssection， were investigated with the experimental data obtained at the wavelength of 532 nm and in the pulse width of 40 ps by means of coordination polymer［Cd(L4)(SO4)(H2O)2］n. The research on the nonlinear optical properties and the optical limiting characteristics of the laser protection material provides the theoretical and experimental bases for preparing the much better optical limiting material.
An infrared image processing solution is proposed. It uses bithreshold method to segment image and enhance the image with segmentation gray scale transform method．For a specific image，two thresholds are selected manually to cut the image into three parts (target area，transition area and background area).Based on the characteristic of each part，different gray scale transforms are designed to carry out image linear enhancement to get the best visual effect for the interested area. The satisfactory result is achieved with the experiment on 16 bit infrared images. The experiment shows that the algorithm is flexible and convenient. It can increase the contrast and decrease the noise while suppressing the background.
Optical correlated recognition is one of the important methods in image recognition applications. For optical correlator, to effectively recognize the peak signal of correlated output plane is the key factor to ensure the accurate image recognition. The traditional threshold method can’t achieve satisfactory results due to the output power fluctuation of lasers, errors from optical systems and noise inherent in SLMs. The author proposed that, in order to effectively classify and recognize the correlated peak signal and noise to improve the performance of the optical system, the output plane of the correlator should be preprocessed, the shape information of correlating signal should be well considered, the ROI (range of interest) should be extracted and the BP neural network should be adopted to calculate the input vector. The result shows that the proposed method can improve the reliability of the correlator and reduce the possibility of misjudgments.
In order to meet real time and tracking reliability requirements for image tracking system installed in modern weapon system, based on the target signatures being tracked by the system, fractal geometry based edge extraction method was adopted in an image tracking system, and a target tracking solution based on moving area and edge image was put forward. The edge extraction method not only extracts the outline of the target, but also keeps the inner details, thus the optimum matching position found by template matching becomes more reliable. Meanwhile, edge extraction is only processed in moving area to reduce computation greatly, especially for longrange tracking. In addition, based on the matching with the edge image, the adaptive template modification is applied in edge image matching to minimize the effect of distortion and illumination variation etc. and make the tracking process more accurate and reliable. Simulation results demonstrate that this method demands much less computation and could meet the realtime requirements of the weapon system.
By adopting doubletail fiber, lens and flat reflector, an innovative scheme, which uses a doublechannel reflecting optical circulator and duplicates the function in comparison with conventional optical circulator with singlefiber tip, is proposed. Typical insertion loss and isolation of the developed reflective circulator are the same as those of the conventional optical circulator. With Jones matrix, the main performances of the reflective circulator are analyzed theoretically. The result shows that the insertion loss may be reduced with antireflective film, the isolation capability depends on the extinction ratio of the crystal it uses, and the performance index of the reflective circulator can meet the requirement of application. In comparison with the conventional circulator, its cost is lower and the volume is smaller.
The optical cross connecter (OXC) plays an important role in dense wavelength division multiplexing (DWDM) network. A new OXC structure based on bidirectional optical circulators (OC) is proposed in this paper. Its basic structure, which called as 2×2 optical cross connecter, is composed of a fiber Bragg grating (FBG) and a bidirectional OC. Based on the basic structure, the required N×N OXC can be designed. In comparison with traditional schemes, the new scheme has several strong points, e.g. more simple and compact structure, smaller volume, lower cost and fewer number of OCs (67% less than the traditional structures). The simulation result shows that its insertion loss is much less than that of the conventional structure.
Since infrared systems have features such as good atmospheric adaptability, passive features, antijamming ability and small volume, light weight and little power consumption, they have found wide applications in navigation, surveillance, guidance and military camouflage target detection. In recent years, the demand for infrared zoom systems is increasing in proportion with the development of infrared technology and its applications. The design of a zoom lens for middle infrared system with a staring focal plane array detector is described in this paper. The operating wavelength of the system is 3～5 μm, and zoom ratio is 20∶1. The image quality achieved with the zoom lens is evaluated with the CODE V optical design software.
Nanometer Ag film is deposited on the interface of surface active agent and electrolyte by electrodeposition process. By comparing the electrodeposition rate and the particlesize of nanometer Ag film prepared by methyl sulfonic acid silver system with those of nanometer Ag film prepared by nitrate silver system under the same conditions, it is found that the particlesize of nanometer Ag film electrodeposited with nitrate silver is smaller and the growth rate of the nitrate silver nanometer film is faster. During the experiment, the silver grain was smaller and the distribution was more uniform in the nitrate silver electrolyte than in the methylsulfic silver electrolyte. That’s the reason why the nitrate silver system is selected as the electrodeposition system. For the nitrate silver electrolyte, the depositing current increases with the increase of concentration and voltage. The effect of cell voltage, concentration and temperature of electrolyte and pH value of the solution on nanometer film preparation has been analyzed. The optimal conditions on which the needed nanometer film was prepared: the concentration of the nitrate silver is 5 mmol/L, the voltage is 4 V, the pH value is 3.0 and the concentration of stearic acid is 0.2 g/L. The experiment indicates that grain diameter of Ag nanometer film deposited under the optimum conditions is about 20 nm on average and the grain shape is roughly spherical. The Ag nanometer film prepared with this method can be used in nonlinear optical material.
In this paper，Al∶ZnO film was prepared on glass substrate with solgel method successfully．The films was annealed at temperatures of 100℃～400℃ in two different conditions, atmosphere and vacuum. The microstructures，electrical and optical properties were analyzed with Xray diffraction (XRD) spectroscopy. The result shows that it has a polycrystalline hexagonal wurtzite structure with highly preferred orientation along the (002) plane. The annealing treatment in vacuum is of benefit to the improvement of the crystalline condition of the thin film，the steep increase of the free carrier concentration and the decrease of the resistivity, and it has no obvious effect on the film transmittance.
The laser warning is the important precondition and basic measure in laser countermeasure. The first technical problem for the laser warning is how to recognize a targeting laser signal from complex background noise and accurately raise the alarm. The relationship between detection probability of laser warning equipment and signaltonoise ratio is analyzed. It can be seen form the relational expression that, the increase of the signaltonoise ratio of laser signal is a precondition for improving the detection probability. In order to ensure the optimization of the system signaltonoise ratio, an adaptive method was proposed to ensure maximum signaltonoise ratio. The algorithm analysis was carried out and the algorithm simplification was made with the matrix transformation. Finally, a simple iterative algorithm suitable for the optimum weight vector solution is given.
The experimental study on Nd∶YAG laser passively Qswitched by Cr∶YAG is carried out. The focus is given to the influence of pumping power, cavity length, the output coupler transmission and initial transmission on the repetition rate, pulse width and output power of laser output. The experiment results were analyzed and discussed. It can be observed from the curve that an increase of pumping power results in an increase of repetition rate and decrease of pulse width，but the impact of cavity length is on the contrary side. There is an optimized output coupler transmission which can maximize the output power. Different initial transmittances have certain effects on the output. The analyses show that the passive Qswitching technology is applicable to DPL.
In this paper，the power coupling efficiency of semiconductor laser passing through a collimating system is discussed. The relational expression for power coupling efficiency of semiconductor laser beam and k (ratio of the aperture radius to the equivalent radius of the laser beam) is given, and the relationship for the power coupling efficiency of semiconductor laser beam and NA (numerical aperture) of the collimating system is also offered according to the laser collimating system. The research will have a significant function for the design of semiconductor laser collimating system.
Two design schemes, diaphragms discharge tube and CuBr hydrogenfilled laser discharge tube, were adopted in the engineering design in order to overcome the nonuniformity of radial temperature in the discharge tube of CuBr laser. The diaphragm structure and the temperature field of the hydrogenfilled CuBr laser discharge tube are analyzed. Based on the heat flow dissipation Poisson equation, a mathematical model of temperature field distribution in the laser discharge tube is set up, an analytic expression for the gas temperature field radial distribution in the laser discharge tube is derived. The relation between the temperature distribution and the input electric power thermal conductivity of the buffer gas is defined. The achieved result agrees with experiment result. A theoretical analysis is provided for the applications of such laser.
In order to analyze the surface deformation of the frame scanning mirror of a certain thermal imager in operation mode, the cause of the 2 KHz resonance was investigated for improving the design basis. The scanning angular velocity and angular acceleration of the frame scanning mirror were calculated based on the moving curves of the frame scanning mirror，the acceleration, deceleration, the surface deformation as well as the first ten orders of the natural modal of the scanning mirror in the process of scanning were calculated with FEA software (IDEAS), and the cause of 2 KHz resonance of the scanning mirror was analyzed in the experiment. Based on the experimental results, the surface deformation and the first 10 orders of the natural modal were calculated, and the structure of the scanning mirror was improved. It was proved that the resonance phenomenon was eliminated. At last, the important details are given in designing the scanning mirror, care shall be given to the deformation of the facet and efforts shall be made to avoid the jitter from driving torquer, which will interfere the natural modal.
Image inverter is a special type of fiberoptic plate, which can directly invert an image by 180° to an image intensifier. The device is making the night vision goggle more compact by integrating the image transfer and image invert function into a phosphor substrate. But due to the image inverter′s special structure, the numerical aperture and luminous flux decrease gradually with the increase of the radial distance from torsion axle centre. Compared with the fiberoptic plate, the image inverter has lower contrast transfer function and lower transmissivity. By improving the glass system to reduce the ion diffusion and interpermeation which may occur to the corecladding interface, the actual numerical aperture of the fiber image inverters can be improved. By means of adjusting EMA absorption, not only the needs of image intensifiers can be reached for the transmissivity of fiber image inverter screens, but also the stray light escaping from the optical fiber can be absorbed to the full extent to improve the contrast. With the selection for a reasonable corecladding ratio, the cladding thickness reduction caused by torsion stretch can be remedied and also the cladding thickness can be increased further more to restrain the light to escape from fibers. The result shows that the innovation mentioned above can improve the contrast transfer characteristics of fiber image inverters.
In this paper, a fiber Bragg grating (FBG) based temperature sensor is presented and its temperature measurement mechanism is explained. A folded MachZehnder interferometer composed of two identical FBGs is employed in the sensing system. One of the gratings is used as a reference arm (local oscillator) and another as a sensing arm. The technology of heterodyne detection is utilized to measure the physical quantity of ambient temperature，since the wavelength of the FBG variates with the temperature .The heterodyne detection is used to detect the output signal frequency difference between the reference arm and sensing arm, which is caused by the temperature variation. The dynamic range and sensitivity of the system are analyzed and presented.
The floatertype measurement devices with their readings recorded manually are still used in many petrochemical enterprises. With regard to their low efficiency, great error and their improbability in implementing automation management and remote control, a new liquid level measuring system with the advanced fiberoptic sensing technology based on the traditional floater level meter is developed. It measures the liquid level of an oil tank by using the principle of force balance, captures and transmits optical signals by means of the fiberoptic sensors, implements optical signal modulation with the selfmade light code disc. Moreover, It was tested in a chemical plant. The testing results indicate that the measurement error is ≤±6 mm，relative error is ＜2% when its measuring range is 0～ 1 000 mm. It is proved that every specification of the system meets the demands of its users and its performance is reliable.
Scientific error analysis for the test data is critical to improve the RD product evaluation quality of the test range. Using testing data not verified by distribution law for accuracy analysis will mislead the evaluation and final conclusion. With the help of new data processing technique and drawing software (such as Excel, Matlab, Origin and so on), a lot of test data were studied, it is concluded the partial sample data and the whole sample data conform with normal distribution after they are separated into some parts. Kolmogorov and Pearson x2 methods are introduced to function as a unified norm for verifying the distribution of large amount of data obtained from target detection in the test range. This norm can greatly increase the credibility of the test. If the confidence level is reasonably selected, the number of flights can be decreased to 10%～50%. The method has the potential to be used in almost all the system and device testing.
Polarizationdependent loss(PDL) of optical components is one of the key problems that must be solved to develop the fiber communication． A novel high precision automatic test system for polarizationdependent loss is introduced in this paper. A coupler and optical power meter are employed in the system to realize the measurement of the polarizationdependent loss with a single connection，which can eliminate the effect of system power stability on the test result. In the same system，the measurement for the polarizationdependent loss can be carried out with several methods. With the delay compensation technology of polarization controller, high precision polarizationdependent loss test could be made in all the wave band． Since the wavelength range of the system is 1200～1600 nm, the measurement range of the polarizationdependent loss is 0～5dB and the measurement uncertainty is up to 0.005 dB+PDL×4％, the system can meet the measuring requirement for polarizationdependent loss of every optical component.