2006 Vol. 27, No. 6
Compound seeker technology is a new technical solution to realize precise guidance, which has higher precision and countercountermeasure performance than singlemode seeker. Compound imaging guidance technology is capable of capturing sufficient target information such as target shape, basic structure, etc, suppressing the background interference and recognizing the target reliably, so it is an important development direction for compound seeker technology. The features of visual TV/IR imaging compound homing guidance technique are analyzed, and the status quo of the compound seekers is introduced. Some key techniques and principles are described. Finally, a design example of visual TV/IR imaging compound homing guidance is provided and its developing trend is forecasted.
The critical design for the control system of shipborne electrooptical equipment is how to isolate external disturbance and reduce the dynamic lag error. Several kinds of gyroscope inertial stabilization technology are described and their comparison is made. The investigation indicates that gyroscope feedback loop with higher measurement bandwidth can effectively enhance the system′s disturbance isolation capability, and the formula for calculating system disturbance isolation capability is derived. The principle of computer auxiliary tracking technology is elaborated. The application of gyroscope stabilizationbased computer auxiliary tracking in shipborne electrooptical system is described. The experimental data are given to prove the validity and effectiveness of this integrated control technology.
Successive approximation method is adopted in the design, manufacture, and test of freeform optics. This approach requires repeated trialanderror processes before a satisfactory result is achieved. Such repetitions are not only expensive, but also time consuming, and it becomes a bottleneck in the overall process flow. The virtual technology is an effective and fast way to solve this problem. An investigation into a virtual manufacturing and testing procedure (VMTP) for freeform optics is presented in this paper. The essential concepts about VMTP for optics ultraprecision machining（UPM） are put forward, including the construction of a VMTP model, the prototype structure of an optical system, and the virtual testing and sensitivity analysis of the imaging quality. The investigation indicates that this approach can accelerate the RD process, reduce the cost, enhance the manufacturability and improve the product quality.
Lineofsight stabilization is a key specification for stabilized sighting system. With manual tracking as research subject, the model of stabilization servo control system was established based on the concept of two gimbals, four axes design. Based on the helicopter scenario, the mathematical models were also built for disturbances such as linear disturbance, angle disturbance, friction and elastic torque. Matlab software was used to simulate the manual tracking mode of the airborne stabilized sighting system under various disturbance torques. A suitable controller was designed. The model is verified in real system and could be used in servo control design.
In order to ensure the proper operation of optical instrument in harsh environment, detailed engineering analyses are frequently needed. Traditional analysis, integrated analysis and unified analysis for optomechanical systems were investigated. Their operation principles, processes, as well as their advantages and disadvantages are described. Some issues on thermalelastic analysis and the fitting of Zernike polynomial in integrated analysis are addressed. The problems need to be considered in unified analysis are summarized. Based on the tradeoff investigation of the three methods, the development trend of the optomechanical analysis methods is forecasted. It is concluded that integrated analysis is the most frequently used opto-mechanical analysis method in the long run.
The operation principle and configuration of electrical interfacebased freespace optical communication system are introduced in the paper. The antenna efficiency and collimated divergence angle of optical antenna are measured, antenna efficiency is about 35% and the collimated divergence angle is about 1.3mrad. The optical power of communication link is calculated. The result shows that the design meets the demand of 2km optical communication. The system consists of three parts: laser transmitting and receiving subsystems, optical antenna subsystem and media communication subsystem. Double transmitting and double receiving optical antenna is adopted to overcome atmospheric turbulence. The communication between computer and internet (or between computers) was implemented. The communication rate is 10Mbps/100Mbps and self adaptive, operational distance is 500m.
Measurement error from the photoelectric theodolite is the main error in the ballistic trajectory measurement. In order to measure ballistic trajectory accurately, the measurement precision of the photoelectric theodolite should be investigated. The measurement accuracy of the photoelectric theodolite is decided based on measurement requirement of the ballistic trajectory. Two simple equations were derived mathematically, one expression for positioning error of the ballistic trajectory, angle error of the photoelectric theodolite, ranging error, target slant range and height when one instrument is used, another expression for positioning error of the ballistic trajectory, angel error of the photoelectric theodolite, target slant range and intersection angle when two symmetrical intersection instruments are used. The two equations provide a theoretical base for designing precision of the photoelectric theodolite.
A blind restoration algorithm for turbulencedegraded image based on the steepest descent method is proposed. An objective function based on frequency spectrums of the object image and the pointspread function (PSF) is set up in the frequency domain, which is minimized by the steepest descent method in an iterative manner. FFT and IFFT are used to transfer the object image and the PSF between frequency domain and time domain, and the constraints of the frequency domain and space domain are introduced in each iteration to modify them, so as to obtain the expected image restoration effect, the proposed algorithm robustness and better immunity to noise. A series of restoration experiments for infrared object turbulencedegraded images are performed to test the proposed algorithm in the microcomputer, and the experimental results show that the proposed algorithm is robust and immune to noise.
To correct the distortion of scanned book image, a polynomial is proposed to describe the relation between g(zi) and zi, where g(zi) is the grayscale of a pixel and ziis the distance from the pixel′s corresponding point to the scanner′s operation plane. With an image of a twisted plane object whose distortion parameters are known, zican be calculated and the polynomial can be established by the leastsquare method using the actual grayscale gi of every pixel. The experiment indicates, accuracy of the polynomial is good enough when q=4, and every coefficient is computed for later use. For distorted image of plane object twisted at will, distortion parameters are calculated automatically as follows, distortion parameters are estimated by using grayscale of pixels located at the book margin, and the estimation of zi is calculated, and zi is used in the established polynomial to calculate g(zi); the optimal distortion parameters are found by adjusting the parameters until every calculated g(zi) is close to gi. In the experiment, good image correction results are achieved with the parameters obtained by this method. The maximum error is reduced from 41 percent to 6.9 percent. Thus, image correction can be done automatically without manual operation.
Algorithm of projection reconstruction from fewer views is a puzzle in the field of image reconstruction, genetic algorithm is one of these algorithms applied in this field, but there are some disadvantages in it. In order to overcome these disadvantages existing in optimization process, such as premature convergence, simulated annealing was introduced into genetic algorithm and a new algorithm was created. By selecting test function, an optimized model for incomplete projection image reconstruction was built based on this algorithm. The computer simulation results indicate that this new algorithm could achieve accurate image reconstruction with data obtained from evenly distributed 12 projection angles of 15°.
A flame length measurement method is introduced in this paper. The image is obtained by color matrix CCD and is extracted based on brightness according to the relationship between radiant intensity and the brightness of the flame. The algorithms to determine the flame boundary and compute the flame length are designed based on the extracted image. Finally, the test experiment is evaluated with the candle in the laboratory. The brightness image is extracted and filtered by Matlab. The actual flame length is obtained in Visual C#. The method is more convenient and simpler than traditional manual measurement.
A new method of aspheric lens design is introduced. The aspheric lens was designed according to the contribution of the quadric constant and aspheric coefficient in aspheric equation to aberration of optical system, and the design process of aspheric lens was analyzed. The aspheric collimation lens with a focal length of 50 mm was designed for the fiber coupled semiconductor laser with the numerical aperture NA=0.37 and the fibercore diameter Φ=600μm. The evaluation results show that the image quality almost reaches the diffraction limit, wavefront aberration of the collimation optical system is less than 0.3λ. The experiment results indicate that the aspheric collimation system can maximize the laser efficiency and improve the beam collimation. The validity of the design is proved.
As a camera lens for intraoral camera system, GRIN (gradient refractive index lens) lens has many merits such as light weight, simple structure, small volume and big focal depth. A heat treatment method is put forward to improve the quality of GRIN lens. The boundary conditions are modified to control the refractive index profile in heat diffusion. GRIN lens can be used to achieve the image for oral cavity and the images are transformed to electrical signals by CCD, then electrical signals are converted into digital signals, stored in computer and displayed on monitor.
As a compact electron multiplier of high gain, microchannel plate (MCP) is widely used in particle and photon detection systems. MCP is intrinsically very fast detector. The pulse transmission time through the intense electric field is of order 10-10 second. The transmission process of the channel electron can be investigated by analytical method and Monte Carlo simulation respectively, but the dispersion of transmission time can not be explained with both methods. A statistical method is introduced to investigate the distribution characteristic of the crossing time during the transmission. The distribution function of the crossing time dispersion degree is obtained, i.e. the relationship between dispersion time and second multiplication times. The dispersion degree is dependent on the collision times.
Since Mie model and Debyeseries expansion model can not accurately explain the back scattering phenomenon of large dimensional bubbles in seawater when the size of the bubbles reaches micron order of magnitude and their calculation speeds are slow, a geometricalphysical optical model is put forward. The numerical calculation method of the scattering property for the large spherical bubbles, based on geometricalphysical optical model, is described. In comparison with Debye model, the calculation result of the geometricalphysical optical model agrees with Debye model basically. The calculation process of the method is independent of size parameters, and it is more stable and faster than the traditional methods based on LorenzMie theory or Debyeseries expansion. Some calculation results for the angular distributions of the scattering intensity are also given.
Light scattering measurement technology based on the classical Mie theory is widely used in the measurement of particle diameter and particle density measurement. The characteristics of light scattering from spherical particles in aerosol are analyzed with a numerical calculation method based on the classical Mie theory and discretedipole approximation (DDA) theory respectively. A numerical calculation method for intensity function and polarization ratio of the collimated incident beam scattered by small particles is given. The 3D graph for variation of the intensity function and polarization ratio with the relative physical parameters was obtained for the research of small particle scattering. The calculation results show that the results obtained by two methods based on DDA theory or classical Mie theory differ slightly when dimension parameter x＜4, and the results differ greatly along with the increase of dimension parameters. In comparison with the classical Mie theory, the DDA theory has greater potential in application since it may solve particle scattering problem for different shapes of particles.
In order to properly evaluate the performance and efficacy of night vision systems and save the test resource, a new method, in which a software of VC++CreatorVega is taken as a tool for performance evaluation of LLL night vision system, is put forward based on the threshold detection theory and the scene simulation technology of LLL night vision systems. The experiments on a LLL night vision system with Gen III intensifier were carried out under the specific circumstances. The viewing distance was estimated and simulated by the software. The comparison between theoretical data and the experimental data was made. The result proves that the performance evaluation software is effective and the system design is feasible.
To reduce the noise and increase the electron gain of microchannel plate (MCP) is one of the best solutions to improve the signaltonoise ratio, FOV definition and brightness gain for image intensifiers. The high performance MCP was fabricated by adopting the clad glass which has high and stable secondary emission coefficient, the core glass which matches the thermal physical property of the clad glass, but its etch rate is 4 orders greater than that of clad glass, and the border glass which matches the clad glass and core glass in the whole manufacture process. The MCP fabricated with this optimized technique shows better performance, its dark current density is less than 5×10-13A/cm2，its fixed pattern noise and scintillating noise are significantly reduced. After it is scrubbed by electrons of 40μAh, its electron gain（800V）is greater than 500 in vacuum system. The experiment results indicate it meets the expectation.
To detect the wind speed in upper atmosphere at 250km over low and middle latitude area, a scanning FabryPerot interferometer was used to collect the interference images of the nightglow radiation spectral line of OI630 nm at the altitude of 250 km. By analyzing and processing the images, Gaussian function was adopted to match the intensity distribution of interference fringes to get the exact position of intensity center, and to derive Doppler shifts of the spectral line. Then the two vectors of wind in the directions of latitude and longitude were deduced, the effect of the drift vector of the space of FabryPerot etalons on wind velocity was derived by theoretical derivation, and the deduced wind velocity was amended. The result shows that during the measurement period, the longitude wind is towards south, estimated to be 4～67m/s, the latitude wind towards east, estimated to be 20～100m/s, and the error of wind velocity is about 6m/s.
A new method of precise star back scanning for reducing the influence of atmosphere refraction on the measurement accuracy of optoelectronic instrument is presented. Atmosphere refraction changes with the variation of atmosphere density, temperature and pressure. The atmosphere refraction calculation based on theoretical standard atmosphere differs from that of the real situation. Accurate star library is used to guide the instrument to back scan the stars close to the observed target in realtime, and the correction factor for correcting the atmosphere refraction could be achieved from fitting back scattering data. The factors influencing correct precision are analyzed, such as shafting and encoder. Field experiments in low elevation under symmetrical changed atmosphere turbulence show that the correction precision can reach 1 arc second.
The visual inspection technique based on the automated vision has many advantages, such as noncontact, high speed, accurate and online etc. It is widely used in the online examination of the industrial product. CCD camera is the key part in the Automated Visual Inspection. The accuracy of the examination is based on the CCD′s parameter. So the calibration of CCD is critical for the process. In order to resolve the problems caused by traditional calibration methods, a new method is introduced to calibrate the tubing thread measurement system. The new griddedparallel line calibration method adopts CCD subpixel technique. Theoretical analysis and experimental results show this method has the advantages of high accuracy, easy operation and good repeatability.
The femtosecond soliton pulse transmission system NLSE was derived from the Maxwell electromagnetic theory, with highstep dispersion, highstep nonlinear, selfphase modulation, crossphase modulation, selfsteepening, Raman scattering in pulse and PMD taken into account. Then the equation was calculated with Fourier transform method, the influence of PMD on the transmission of the femtosecond soliton was analyzed. The result indicates that the transmission system can hardly be affected by PMD if Dp≤0.1ps/km1/2; but the system property is deteriorated quickly with the increase of Dp. If Dp=0.3ps/km1/2, the transmission distance is decreased by more than 3 times. If the highorder effect of the optical fiber is considered, the system taking femtosecond soliton as its carrier can not realize highspeed and longdistance transmission.
The fiber Bragg grating has a wide application in the field of communication and sensing. According to the special structure of the tilted fiber Bragg grating, the effect of the tilted angle θ on reflection spectrum of tilted fiber Bragg grating was studied by using the couplemode theory and transfer matrix. The simulation result shows that the center wavelength of reflection spectrum moves to the longwavelength side, and the bandwidth and the reflectivity decreases with the increase of θ. The experimental result coincides with the simulation result. This conclusion is of great aid to the fabrication and application of the tilted fiber Bragg grating.
The peak value of reflection spectrum can be measured and used as characteristic value for the central wavelength by sampling the reflection spectrum of FBG. With this method, a great deal of data need to be collected and processed, and the demodulation speed of the system is decreased. A simple but effective method is put forward to solve the problem. The analysis on FBG reflection spectrum indicates that the FBG reflection spectrum is very symmetrical. Based on this characteristic, the method to average the double edge of a wavelength is proposed for demodulating the central wavelength of FBG. The experiment proved that the demodulation system using this technique can process the reflection signal of FBG easily and obtain the central wavelength of FBG accurately. With this technique, the speed of demodulation for FBG sensing signal was improved.
Combination of programmed chirp and dispersion profiles produced a quasisoliton nonlinear pulse with a stable structure. With the nonlinear effects taken into account, the concept of quasisoliton is introduced and the comparison between the quasisoliton solution and the soliton solution is made. Compared with soliton, quasi optical soliton has more advantages, such as reduced interaction, smaller peak power and pulse width adjustable by modulating fiber parameters. Quasisoliton transmission has great potential in next generation of communication system.
The benign and adverse temperature condition in open air is simulated in the temperature and humidity alternated test chamber. The transmission performances of optical fibers are monitored and measured by OTDR and CD300. The testing samples are made with the identical material and process, but in different batches, and testing temperature is from -60℃ to 140℃. The experiments indicate that the transmission performances of optical fibers fluctuate with temperatures in - 60℃ to 140℃. The temperature induced attenuation of fibers is less than or equal to 0.05dB/km at 1310nm and 1550nm. The dispersion coefficient of optical fibers decreases with the temperature increase at 1550nm. The PMD of optical fibers increase when the temperature increases. On the basis of temperature cycling test, taking communication standards as criteria and using “3σ” principle of the quality control, fiber transmission performance adaptability to communication system in temperature changing environment is discussed. It is concluded that the attenuation, chromatic dispersion and PMD of G.652 optical fiber could meet the requirement of high speed communication system for less than 10Gbit/s from -60℃ to 140℃, but the PMD does not meet the requirements of high speedcommunication system for higher than 10Gbit/s. If the PMD is required to meet the requirements of hyperspeed systems, proper measures must be taken to minimize it during fiber drawing process.
In order to generate an ideal output shape, the on-line filtering technology was introduced into fiber Mach-Zehnder interleaver. The sharp edge filtered output of approximating wideband was realized by adding interference orders，adjusting the interference length of the two pairs of interference arms and coupling ratio of the coupler. The coupling ratio should be corrected to improve the output characteristics. By comparison with Fourier function of trapezoid filter, the key parameters of Mach-Zehnder interleaver were worked out. The properties of output and the temp-stability are optimized. A sample component with the channel interval of 50 GHz was made. When its output is -0.5dB, the band width is more than 0.185nm and the interval between the consecutive channels is over 30dB. The theoretical results are consistent with the experimental results and they meet the requirement of DWDM system.