2006 Vol. 27, No. 3
Light weapon sights are widely equipped in the armed forces of different nations because they could improve the attack accuracy and lethality for the weapons. This paper briefly reviews the operation principles and features of mechanical sight, optical sight, electrooptical sight and integrated sight. The status of mechanical sight, traditional optical sight, lowlightlevel night vision sight, new electrooptical sight and integrated sight equipped in different nations worldwide is given. The development status and parameters of various typical electrooptical sights as well as simple day and night firecontrol systems are described. It is pointed out that mechanical sight and optical sight are still necessary for future light weapons. However, electrooptical sight shall prevail in equipment procurement, and light weapon sight equipped in the future shall be the integrated electrooptical sight.
Addressing codes frequently used in optical codedivision multipleaddress (OCDMA) systems are introduced. They are typically one dimensional timespreading code, twodimensional code and three dimensional code. The means and variances of crosscorrelation for these codes were analyzed. Based on the fundamental principle of optical correlation receivers used in incoherent OCDMA systems, with different addressing codes taken into account, the bit error probability (BEP) of the system was studied. The dependence of optimum decision threshold on the basic parameters of addressing codes and the number of simultaneous users was obtained. Finally, numerical simulations are carried out, and the results show that system BEP performance is optimized when appropriate decision threshold is taken.
Distortion in optical lenses for wide field of view application, which reduces image quality, has to be corrected. A new correction method is proposed in this paper, and the distortion correction formula is deduced based on the definition of distortion coefficient. It’s easy to correct the distortion with this method when the lens’s distortion data is known. A distortion model is presented for the lens with unknown distortion data, through which the distortion data can be calculated. A conclusion for controlling distortion can be obtained by controlling a certain parameter in the distortion model. The practical use of the distortion correction method presented in this paper proved that the model could meet the requirement of distortion correction of lenses in most cases.
Optical parallelism errors caused by the angle errors of pentagonal prism,which is generated in manufacture process, are analyzed, and the formulae for determining incidence ray and adjusting prism are derived. The dependence of the output plane wavefront of pentagonal prism on the angle errors of pentagonal prism and kinematical errors caused by guide rail is established according to the prism rotation theorem. The wavefront error of scanning beam turning caused by the angle errors of pentagonal prism and the kinematical errors of guide rail was analyzed with computer simulation. This study is useful to pentagonal prism manufacture process and adjustment, and helpful to correct wavefront error of scanning beam turning during wavefront measurement of large aperture telescope.
In the fluorescence analysis of pesticides, the fluorescence intensity corresponding to the maximum peak is always chosen as the research subject. In order to obtain the fluorescence intensity of the measured pesticide more accurately and further improve the detection accuracy of the pesticide residues in food, the wavelet transformation is adopted to conduct the denoising process for the measured fluorescence spectrum of the pesticide. In view of the disadvantages of the softthreshold and the hardthreshold methods, a new threshold method, i.e. softandhardthreshold tradeoff method is introduced. The denoised fluorescence spectrum via the wavelet transformation using this threshold method is compared to the denoised spectrum via the analog lowpass filter. The result shows that the denoising spectrum via the wavelet transformation keeps more information for the original signal. Thus the detection accuracy of the system will be improved with the aid of this method.
Based on the paraxial imaging formula, the differential conditions of thermal compensation for optical systems with the object planes at random distance are derived in the cases of single lens, touched multilens system and separated multilens system. It is assumed that the object distance and the incident height of each lens do not change with temperature. The relationship between the normalized temperature variation of image distance and the optothermal expansion coefficient of each lens is established with the derived conditions, which is very useful in the design of mechanical and servo systems for an athermalized optical system. The conditions obtained for single lens and touched multilens system are coincided with the regular conditions of thermal compensation when the object plane is at infinity, i.e., the optothermal expansion coefficient of the optical system is equal to the housing expansion coefficient.
The paper introduces a method for the optical design software package OCAD to link and exchange data with other frequently used optical design softwares developed both in China and other countries, such as CodeⅤby ORA and Zemax by Focus Software in US,as well as Oslo, LENSVIEW, ASAP,TRACEPRO and domestic software SOD88. In addition to the basic functions of the optical design software, the OCAD optical design software package could call the abovementioned design softwares on its function interface, implement links and data exchange between different softwares. It can also link and interact with frequently used word processing programs or operational chart programs, such as Word and Excel. By combining available functions and characteristics in the existing softwares, what we need to do is just to develop a professional software aiming at our specific requirement. Based on Chinese standards (GB), industry standards and enterprise standards, the optical design software package OCAD is developed.
The design of the cam curves of the zoom system is critical to keep the precise, smooth and balance movement of the optical system. The article analyzes the characteristics of equal space design (ESD) and equal angle step design (EASD), the former means the motion of zoom group is linear to turning angle of cam and the cam curves are expanded as a beeline, the latter means the focus is linear to turning angle of cam. A solution to overcome the shortcomings of these design methods is proposed, which combines the merits on their adaptable zoom segments. At last, a kind of cam assistant design software OZSAD (optical zoom system assistant design software) V1.2 is introduced, which can conveniently and quickly meet all three kinds of design requirements. It is proved that the pressure angle of cam curve, the total expanded angle and the points of cam curve could be effectively reduced. Therefore, the design precision could be reached.
The infrared double halfwave filter was traditionally implemented with sixteen λ/4 layers and a low refractive index material as its interval according to the design introduced in Applications Optical Coating written by Mr. Tang Jinfa, Zheng Quan. However, the film prepared by such design tends to crack easily.To solve this problem, a new design for infrared double halfwave filter is presented. A high refractive index material was taken as interval and twelve λ/4 layers was used. Compared to the previous design, it is more economic and timesaving. Detailed technology on how to design and fabricate infrared double halfwave filter is given, and process parameters such as base pressure of chamber, control of temperature and the rate of deposition are described. In the course of deposition, ion source was employed to process substrate and to assist ZnS and Ge evaporation. A satisfactory result was achieved with such design.
The paper reviews the ion barrier adopted in 3rd generation image intensifier, which has dual effects on the GaAs photocathode, protecting it from being damaged by ion feedback, at the same time degrading the quantum efficiency. The origin of pernicious gases and the formation mechanism of ion feedback are explored, then some restraint techniques are introduced, including the latest developed GaAs image intensifiers with a highperformance MCP as its feature, which made the film significantly thinner or even removed due to the large reduction of pernicious gases. The latest bulk conductive MCP and Si MCP with excellent advantage on restraining ion feedback are exhibited. The development of longlife filmless GaAs image intensifier remains a great challenge. Further progress in MCP is needed to restrain ion feedback, and the GaAs photocathode’s resistance to ionized and native gases still needs enhancing.
Eight kinds of typical coal samples were chosen for studying the influence of coal characteristics on laserinduced plasmas. Element analysis and industry analysis were carried out for every sample. Experimental study on the interaction between laser and different coal samples was completed, and factors affecting laser plasma were analyzed, such as coal moisture and coal dust. The experiment result indicates that the coal samples with different coalification degrees have different plasma timeresolved spectral characteristics, all of them tend to rise at the beginning of plasma formation (＜1μs), then with the decay of plasmas emission, they tend to decrease in about 1μs, while secondary ionization occurs in highly coalificated coals after 2μs. The plasma temperature differs from one kind to another, the higher the coalification degree is, the higher the plasma temperature will be.
The selfstarting modelocked mechanism of nonlinear polarization rotation and the characteristics of the pulses were theoretically investigated with various parameters taken into account, such as gain, loss, group velocity dispersion, self phase modulation and fast absorber. A fiber ring laser with a small segment of highly Er3+doped fiber as gain medium, which is pumped by 980nm LD laser and modelocked by using the nonlinear polarization rotation technique, is successfully demonstrated for the generation of femtosecond pulses. When the laser was pumped at 23mW, stable modelocked pulses centered at 1552nm with 7.6nm bandwidth and an average output power of 0.43mW was successfully obtained at the repetition rate of 14.6MHz. The threshold power of the selfstarting modelocked pumping is about 11.5mW. The highorder stable modelocked pulses were also observed experimentally. Compared to the fiber lasers with the similar structures reported previously, the laser presented here has the advantages of very low selfstarting pumping threshold, high pulseenergy, small spectral sideband and better stability.
The operation principle and circuit structure of halfbridge zerocurrent quasiresonant CO2 laser switching power supply are presented and analyzed, and its mathematical model is established. The mathematical model was simulated with MATLAB program and verified by the experiment. It could be used as a reliable reference for system parameter design of the halfbridge zerocurrent quasiresonant CO2 laser switching power supply.
A novel aluminum plate based fiber Bragg grating (FBG) sensor is proposed to detect temperature and flowvelocity. Fiber Bragg grating (FBG) was sealed on an aluminum plate by a hightemperatureresistant glue, then placed in a thermostat for solidification so as to retain the stability of FBG. The temperature and flowvelocity sensing characteristics of the encapsulated FBG sensor were theoretically and experimentally studied. Encapsulated FBG sensor was placed in a digital thermostat to detect its temperature characteristics. In the temperature range of -20℃～100℃, the experiment result indicates that the temperature sensing sensitivity coefficient of encapsulated FBG sensor is 0.0392nm/℃ and is 3.5 times as much as that of bare FBG. The temperature response curve of the encapsulated FBG sensor keeps very good linearity and repetition. In the flowvelocity experiment, the reflection peakwavelength of the encapsulated FBG sensor moved 0.13nm when the flowvelocity changed from 0 to 20m/s with constant water temperature at 14.5℃. So it is feasible to use the encapsulated FBG sensor to detect the flowvelocity. The result proves that the aluminum plate encapsulated FBG sensor can detect temperature and flowvelocity. The encapsulated FBG sensor is easy to make, cost effective and practical.
According to the nonlinear Schro¨dinger equation on picosecond pulse transmission in optical fiber，the pulse compression at 1553 nm in dispersioncompensation fiber and dispersionshifted fiber were studied with numerical method. Three different dispersion values were simulated and compared. The chirp curves of the pulse before and after dispersioncompensation fiber are given. As a result, the optical pulse from gainswitched distributedfeedback laser diode can be compressed from 45.00 ps to 7.39 ps by dispersioncompensation fibers, and the larger the fiber dispersion value is, the shorter the fiber is needed to achieve the same compression effect. The pulse was further compressed using dispersionshifted fiber from 7.39 ps to 1.23 ps with fiber dispersion value of 6.0 ps/(nm·km). The results indicate that optical pulse can be compressed very efficiently with dispersioncompensation fiber and dispersionshifted fiber in the two consecutive modes.
he fiber Bragg gratings (FBG) have found wide applications in the field of communication and sensing. Temperature, strain and other physical parameters can be measured by detecting the shift of the central wavelength in FBGs, but cross sensitivity of FBG to temperature and strain needs to be solved. The principle and advantage of FBG sensors are investigated briefly, reference grating method and Erbiumdoped fiber amplifying method to separate the temperature effect are given. A method to demodulate the shift of the central wavelength in FBGs by using the main mode and the side mode of a tilted fiber grating is introduced. With this method, the effect of temperature on strain detection is discriminated successfully.
In recent years, there is increasing interest in photorefractive polymer due to its good optical processing capability. Compared to photorefractive crystal, it has the advantages of large nonlinear optical coefficient, quick response, low cost and great compositional flexibility, thus there is a potential for photorefractive polymer to become the materials for preparing photonic integrated device in the future. The applications of photorefractive polymer in pattern recognition, holographic storage and optical coherence tomography(OCT) are summarized. At last, it is pointed out that there is band gap in photorefractive polymer.
In order to explain atom photolithography’s role in nanometrology and standard transfer, nanometrology and its status are briefly introduced, the principle of atom photolithography and its features in nanometrology are presented. The mechanism for atom photolithography was analyzed with an experimental setup of Cr atom photolithography. The experimental results indicate that nanometer level stripe could be obtained to provide more precise means for nanometrology and standard transfer. Finally, two kinds of atom photolithography technology, depositatom and dummyslit atom photolithography are elaborated, and their differences are pointed out. The technology mentioned in this paper can be used as a reference for atom photolithography under different conditions.
The working principle of a doubleblackbody measurement unit for parameters of infrared cameras is introduced. The unit employs doubleblackbody and a set of reflective infrared targets as thermoemitting sources, which makes it easy to control the temperature and temperature difference, therefore measurement reproducibility is guaranteed. The apparatus can be used for the periodic calibration of collimated irradiation of temperature difference, and to measure the parameters of infrared cameras in controllable and steadily way. A mathematic model for testing and evaluating signal transform function (SiTF) of infrared cameras was established, all the factors affecting the apparatus constant were listed in this model. Experiments were conducted to observe the effect of apparatus constants on SiTF measurement. The experiments show that the apparatus constants greatly affect SiTF measurement, temporal NETD measurement, spatial NETD measurement and 3D noise.
Thinfilm thickness is one of the most important parameters for holographic plate. Thinfilm thicknesses of two types of holographic plates were measured by Michelson interferometer which took the white light as its incident source. By analyzing the errors of the results, the relation of the measurement errors to thinfilm thickness and refractive index, and the applicable range of this method were studied. The result shows that with the increasing of film thickness, when it is from 8μm to 41μm, the absolute errors are ≤2μm with little fluctuations, but the relative errors decrease from 14.1% to 2.2%. The value of refractive indexes contributes to error propagation, and it is inversely proportional to absolute errors. In order to guarantee the validity of results, the thicknesses of films should be≥ 40μm when the refractive indexes are about 1.5. There are some advantages,such as a large measuring range, fewer experiment instruments and accurate result, when Michelson interferometer is used to measure some thicker thin films.
The optical constants of thin film are decisive factors for its optical properties. A simplified numeric algorithm expression for solving transcendental equation of optical constants was obtained by analyzing the test principle of ellipsometer. A Microsoft Windows based calculating program for optical constants of thin films with “Solve Block” module of MathCAD by ellipsometer was developed. It can be used to calculate refractive index and thickness of thin films with little absorption or even no absorption as its feature. The results of practical operation indicate that this method has the advantages of better accuracy, high precision, high speed, and universal usage. It can be used in online test with ellipsometer during the process of film preparation.