2009 Vol. 30, No. 1
To improve the performance of zoom systems and achieve a good imaging quality in WFOV, and to simplify the mechanical structure for the convenience of design, process and adjustment, a design concept that combines the conventional spheric optics with the aspheric optics was introduced in the design of zoom lens. A zoom lens system with f′= 6.9mm～91.6mm and FOV= 5°～60°was designed by choosing four positions of focal length for the design calculation and ZEMAX as the optical design software. The whole system is composed of 8 lenses in 4 sets，including 3 aspheric surfaces. The results show that the zoom lens has the characteristics of high magnification and large field of view, and the use of aspheric surface makes the structure compact and the imaging quality high.
The enlargement of FOV and the relative aperture is the key measure to improve the performance of underwater photographic objective under weak illumination. The characteristics and design methods of WFOV and large relative aperture underwater photography objective under weak illumination are introduced. An underwater photographic objective under weak illumination, whose relative aperture was 1/1.4, underwater FOV was 66° and focal length was 11.8mm, was designed based on the reverse-telephoto structure with 11 optical elements. The imaging quality of this lens was evaluated. The results show that it has an excellent imaging quality, at spatial frequency of 42lp/mm, its MTF value is greater than 0.5 for 0.7ω, and it meets all the specifications and requirements of WFOV and large relative aperture for underwater photographic application.
A matched filter with great tolerance of distortion was designed by using the optimal tradeoff synthetic discriminant function to overcome the low discrimination rate in the correlation recognition of the rotating and rescaling targets. The matched filter with the bandpass feature was obtained by adjusting the contribution of output noise, average power spectral density of training sample image and training sample images′ similarity to the average value of training sample images. The simulation experiment of the correlation recognition for the target with rotation angle of 0～30° and the variation dimension range of 0～20% with a single matched filter was carried out. The designed filter resembles a band-pass filter. Simulation results demonstrate the designed filter has sharp output peaks, good discrimination and high tolerance for distortion.
Since the single LED can not meet the demand of UV-curing, a new solution in which the accumulation of UV radiative energy was implemented by two-dimensional LED array is proposed to utilize the advantages of the latest high-power UV-LED, such as high electro-optical conversion efficiency, high spectral purity and small volume. The irradiance combination of each single spot on the irradiated surface was realized by the combinated design of single LED focusing system and the integrated array system. The obtained spot has the merits of uniform irradiance distribution, reasonable size and long back operation distance. The spot irradiance adjustable in the range of 1000～1 800 mW/cm2 is achieved by controlling the current and on-off state of LED array with peripheral electronics. The size of the obtained spot is 1 cm2and the back operation distance is 10cm.
Since the external disturbance may lead that horizon image formed on IR FPA plane in a panoramic optoelectronic tracker not parallel to the image projected on the focal plane array on the reflector pitching axis, a five degrees of freedom mathematic model for the panoramic electro-optical tracking system was established. The equation for horizon incidence plane was reconstructed, which included target information regenerated in geodetic rectangular coordinates. The subsequent analytic expression for the reconstructed horizon catoptric-dioptric image in IRFPA plane was obtained. The analytical expression can be used to compensate the elevation and roll disturbances when the target is detectable and the horizon is undetectable.
Base on imaging characteristics of the adaptive optical telescopes, the number of optimum subapertures is defined and analyzed when the brightness of the image spot center is maximal and the residual wavefront error is minimal. The wavefront correction of the deformable mirror with the triangular and rectangular actuator distribution was simulated by ZEMAX. The quantity of the optimum subapertures for the 600mm adaptive optical telescope was derived based on the analysis of the two cases that the adaptive telescope has or has not a fast tilting mirror.
A new method based on the self-adjusting fuzzy-PID control is presented, which is suitable for ATP（acquisition, tracking,pointing）servo system for optical space communication. The advantages of fuzzy control and traditional PID control were combined in this method. The design method of fuzzy-PID controller is discussed. The design and simulation of the system were implemented by using the fuzzy control tool box in MATLAB. The comparison of the obtained result with that of the conventional PID controller was carried out. The simulation results show that the system is much better than the conventional PID controller, and the LOS (line-of-sight) stability of ATP system is improved.
A software correction method is proposed to reduce the tracking position error caused by the gyro temperature excursion in inertial stabilization systems with position loop. The theoretical foundation of the software correction method and the implementation process of the software correction are presented. The verification experiment for the correction method was carried out. The experiment result shows that the correction program can completely correct the excursion in the case of no vibration, and can still correct the excursion in the case of vibration, but with a code error of 1～2.
To overcome the color distortion caused by wide color gamut in projection display system based on LED, a new color gamut calibration method is presented. In the time sequence display mode, in order to move the chromaticity coordinates of the trichromatic light to the proper position, other proportional trichromatic light is also introduced as an auxiliary light while a trichromatic light is adopted. A set of XYZ LED sensors is proposed to measure and feedback the chromaticity coordinates of trichromatic LED in real time so as to avoid the difference of LED consistency and the impact of environmental temperature fluctuation and the operation duration on the major wavelength and chromaticity coordinates of LED. The real-time color gamut correction was realized and the proper display color was achieved through the programming of the calibration algorithm.
Several methods of the data interpolating and curve fitting are introduced. The interpolating operation of the illumination values at the wavelength intervals required by the spectral irradiance standard lamp was performed, in which the establishment of mathematical model, calculation of parameters and analysis of errors were involved. The satisfactory interpolating method and curve fitting model are obtained, and its relative deviations are close to the best uncertainty of the spectral irradiance standard lamp provided by National Institute of Metrology, which is 0.2%.
Adaptive optical systems require the wavefront sensors to realize realtime dynamic measurement, and the wavefront curvature sensing technology can meet such requirement. A novel wavefront curvature sensor based on the twisted diffraction grating has a greater advantage in the realization of detecting device, and its wavefront reconstruction algorithm is used for the measurement of optical surfaces. The numerical simulation of the detection signal was implemented with the theory of diffraction optics, and the numerical simulation of the wavefront reconstruction was realized with Green function algorithm under Neumann boundary conditions. The results indicate that the speed of Green function algorithm is fast, it meets the requirement of the real-time wavefront reconstruction, and the result of wavefront reconstruction for low-order Zernike polynomials is good. The analysis shows that the major source of wavefront reconstruction error is the boundary noise in the gradient of light intensity.
The beam splitter based on photonic crystal waveguides is taken as an essential component in integrated optical circuits. A linear-defect 1×4 photonic crystal splitter was designed, and its characteristics were analyzed with the time-domain finite difference method. The experiment results show that the transmission properties at output end is dependent on the wavelength of incident light and the geometric shape of the branch, and the incident wave is divided equally into four output ports. The high transmittance can be obtained at each output port by adjusting the radii of the medium in the branching region to reduce the reflection of the 1×4 splitter at the three Y-branching regions.
The data acquisition in a multi-sensors electro-optical tracker, which includes TV, FLIR, laser rangefinder and fiber gyroscope, was implemented with a digital signal processor and a multi-bus architecture. CPCI bus technique combined with dual port RAM was incorporated to realize high-speed information transmission within the system. It can provide the servo control system with reliable data for fully digitalized control, high-precision sight stabilization, fast and accurate tracking, and improve the performance of the electro-optical tracker effectively. The design scheme and operation principle of the data acquisition system are presented. The control mode and interface design of each sensor in the system are studied. The data transmission between all of the sub-systems is described briefly.
In order to enable the electro-optical tracking systems to track the “S maneuver” targets, a model with the extended Kalman filtering algorithm against the maneuvering target turn is proposed based on the motion characteristics of “S maneuver” targets to overcome the shortcomings of the previous Singer model. The precision tracking for the “S maneuver” targets in 2-D plane was realized by the Monte Carlo simulation, and the root mean square error of position is much smaller than the Singer model. It proves that this method is capable of tracking the typical “S maneuver” targets.
A digital knife-edge test system is proposed based on the traditional Foucault tester. Quantitative evaluation for the wavefront of spherical optical elements was achieved by using this test system. The system configuration, principle and testing process are described in the paper. The surface of a spherical optical element with the radius of 1000mm and the aperture of 160mm was tested with the test system. The measured RMS and P-V values of the wavefront error of the optical element under test are given. The measured results are discussed.
Distortion of optical system makes focal length of advanced fire control dynamic performance test system different at different FOVs, and influences angle-measuring precision. A focal length calibration formula based on leastsquare method was used to obtain a unified focal length for all the FOVs and the influence of the distortion was reduced. For a specific fire control dynamic performance test system, its measurement result was 2.34″ by using the method, which improved angle precision from 20 to 5 arc-second. It is proved that the modified calibration formula can improve the performance specification of fire control dynamic performance test systems.
High-precision measurement of thin-film is a precondition for the process optimization and diagnositcs in the thin-film preparation. Interferometric metrology is a widely accepted high-precison measurement technology which takes wavelength as the measurement unit. A novel measurement method of thin-film thickness based on phase-shift interferometry is presented. The precision measurement for the thickness of SiO2 thin-film sample was realized after the phase unwrapping and data processing for the obtained interferogram were implemented. The results show that this method has the advantages of noncontact and high accuracy, and the PV and RMS values of the measured thin-film thickness are 0.162μm and 0.043μm respectively.
A new method for locating target with two photoelectric theodolites is presented. The real-time calculation of the parameter accuracy was performed by the method based on the common locating formula. The weight coefficient is dynamically determined according to the accuracy variation of resolved ballistic parameters. The simulation result shows that the coordinate measurement accuracy is improved in the case of the intersection locating with two theodolites of different accuracy.
Based on a brief introduction of the basic principle of ellipsometry and some derivations, the sensitivity of ellipsometric parameters with respect to film parameters and the influence of incident angle on the ellipsometric parameters were discussed, and its simulation analysis was made. It shows that the sensitivity of ellipsometric parameter Delta to the film optical constants and film thickness is apparently higher than another ellipsometric parameter Psi, and the measurement accuracy of ellipsometric parameter Delta directly affects the fitting accuracy of film optical constants and film thickness in the ellipsometric data processing. A method is provided to improve the measurement accuracy of Delta by choosing the incident angle close to the Pseudo-Brewster Angle.
Y-waveguide is widely used in the integrated optics, and it is important to know its specifications, among which the beam-splitting ratio and insertion loss are the most critical parameters. The measurement setups and methods for the two parameters are introduced. As for the beam-splitting ratio, the output luminous power for two tail fibers of Y-waveguide was measured respectively by using two sources with wavelengths at 1300nm and 1550, and the primary factors which affected the measurement were analyzed and the uncertainty was evaluated after working out the beam-splitting ratio according to the formula. As for the insertion loss, the measurement setup was built up based on the measurement principle, and the factors which affected the measurement of the insertion loss were theoretically analyzed.
Taking the fabrication of a K9 planar part with the diameter of 27mm, accuracy requirement of N=2, ΔN=0.5, B≤Ⅱ and θ≤2′ as an example, the processing flow and key techniques of deformable super-thin planar elements controlled by thicken-optical contact method are described. The parameters in manufacturing process are analyzed and summarized, and the parameters for achieving various specifications are determined. The result proves that this method can meet the requirements of high-precision surface profile and parallelism. The production efficiency was increased and the production cost was decreased while the accuracy of such optical element was ensured. This method is suitable for the mass production.
The characteristics of Large-aperture laser glass optical processing are precise, difficult and time consuming. Quality management is necessary in large-aperture laser glass optics processing to insure the fabrication quality. The paper elaborated the quality control method in large-aperture laser glass optics processing. By implementing this quality management, the qualification rate and processing efficiency of large-size glass optical laser has been enhanced.
The flow mechanism of the photoresist on the concave sphere under centrifugal state is elaborated by the analysis of the photoresist coating process with centrifugation force. The critical factors that affect the evenness of photosensitive resist and the film forming quality, such as viscosity of photoresist solution, velocity of spin coating and time of spin coating, are investigated with experiments. The various phenomena occurred due to these factors are listed and analyzed theoretically. A mathematic model which describes the relationship between layer thickness and velocity is established by quoting the formula for the spin coating of photoresist film on the concave sphere. The effect of the fluid speed on the uniformity of the layer in the limited circular space is explained according to the principle of fluid mechanics. Accordingly，the key technology for preparing microstructure patterns on the concave spherical surface is achieved.
The optical constants of diamond-like carbon (DLC) films deposited by UBMS were measured and analyzed with a broadband ellipsometer. Based on the models established previously and the analysis on it, the model structure was analyzed and adjusted according to the film forming characteristic of the DLC film. Considering the effects of surface roughness, film surface, substrate surface and interface factors on the measured result, the surface and the DLC film was divided into two layers during modeling because of its graphitization on the surface, and their effects were approximately processed with the effective media approximation (EMA). The results indicate that the ellipsometric data MSE of DLC films deposited on the silicon substrate by UBMS was reduced from 37.39 to 4.061 by this model. The measurement accuracy was improved.
The structures and applications of three telecentric systems in the image space are described. The traditional single group telecentric structure in the image space and “negative-positive” telecentric structure in the image space were made respectively during the design of the objective lens for the fiber image-transmitting bundle. The two schemes were compared. It is found that the “negative-positive” telecentric structure in the image space meets the demands of the off-axis aberration correction and image plane illumination uniformity at its image plane, and makes the lens compact. After the optimization with the optical design software Zemax, a designed lens sample is fabricated, whose operation wavelength, focal length, FOV and relative aperture are 0.38μm-0.78μm, 1.92mm, 60° and 1∶4 respectively. The result shows that MTF value of the lens is greater than 0.8 at the spatial frequency of 46lp/mm.
Proceeding from the practical application of civil engineering, an all-grating low-cost distributed sensing system for simultaneous measurement of temperature, strain and pressure based on the optic Bragg grating (FBG) is proposed by using the multiplexing and wavelength abslute coding features of the FBG sensor. A FBG multi-parameter monitoring system for the bridge structure was designed based on continuous wave modulation frequency technology. The address of distributed FBG sensing network was realized by combining optical frequency domain reflectometry (OFDR) with wavelength division multiplexing (WDM), and the content of multiplexing was increased. The experiments show that the system can accurately monitor the internal strain of the important parts of bridges, and provide the precision data for static and dynamic load testing of bridges.
In view of the lack of effective methods for the measurement of internal force under the construction loads and the long-term monitoring in service of steel tie rods, a novel high-durable smart steel tie rod based on the fiber Bragg grating (FBG) absolute measuring technology and packaged by glass fiber reinforced plastic (GFRP) was developed. The strain detected by the FBG strain sensors has a very good linearity and repeatability under 85% tensile load of the theoretical yield load, and the measured rod force agrees well with the stretching force (relative error ≤4%). The advantages of the smart steel tie rod, such as durability, anti-corrosion, electro-magnetic resistance, low cost and absolute measurement, were verified. It can indicate the state of stress in any phase, and can be regarded as a large strain load sensor used to measure the stress of the steel tie rod or some components adjacent to it. It is suitable for monitoring the stress exerted on the steel tie rod sturctures serviced in harsh environment.
Since the error of the result is comparatively large in the linear filtering demodulation with the quasi-linear waveband of LPFG when fitting the quasilinear waveband of long period fiber grating(LPFG) only once, through fitting the quasi-linear waveband of LPFG in several sub-wavebands and controlling the temperature of the LPFG were introduced so as to cause the shift of the resonant wavelength of the LPFG to realize demodulation with different sensibility. The implementation based on DSP was given, the monitoring interface realized by MFC programming based on the dialog box of the VC++ was given, and the potential application areas were given as well.
Athermalization is to eliminate the ambient temperature effect on the performance of optical systems. A passive optical athermalization design was proposed for infrared optical systems. Proceeding from single lens, a set of equations to eliminate the thermal difference of lens group was given. The coefficients for eliminating the thermal difference and chromatism of common infrared materials were described by Cartesian coordinates. The rational combination of infrared materials was derived with the graphical method, and the normalized distribution of focal power was obtained as well. The design process of the passive optical athermalisation was elaborated by an example. The result was analyzed with an optical design software. It shows that the design result meets the requirement of eliminating the thermal difference and chromatism at the temperature range of -40℃～+60℃.
In order to observe the phenomenon of the filament temperature drop caused by the board-current, the ideal diode filament temperature was detected precisely with an infrared thermometer. Since the cathode filament temperature drop caused by the boardcurrent was neglected, it resulted in about-1.86% system relative error in the measured metal work function. The phenomenon was found through a theoretical analysis, and it was verified by an experiment.When both the filament current and board-current are lower, the variation of the filament temperature with the board-current is not measurable; when the filament current is above 0.74A, it can be clearly observed that the filament temperature is (1～2)K lower than that of zero board-current after the board-current is outputted.
The numerical computation for an end-and-side pumped DPL indicates the temperature distribution in the cross section of the crystal is nearly axis symmetric, and the more proportion the end-pumping power occupies, the more axis symmetric the temperature distribution is. The thermal effect in an end-and-side pumped DPL was approximated with an equivalent lens. The calculation method for the focal length of the thermal lens was introduced. The influence of the thermal lens effect caused by combination pump on the spot radius of the fundamental-transverse-mode oscillation beam and the diffraction loss was analyzed. The proportion variation of the end-pumping power has some influence on the focal length of the thermal lens under a given total pumping power. The influences of the thermal lens effect on the oscillation beam radius and diffraction loss can be reduced by increasing the proportion of the end-pumping power.
In order to analyze the impact of the transmission of the LRF (laser range finder) optical transmitting system on the ranging performance, the quantitative analytical formula for the transmission of the LRF optical transmitting system was obtained by using the ray tracing equation and partially polarized light theory. The dependence of the transmission of a given optical transmitting system on the polarization parameters of incident laser beam and geometric optical transmitting system is analyzed quantitatively. The results show that the influence of polarization parameters on the transmission characteristics of the transmitter optics is enhanced if incident angle increases, and the energy of laser pulse emitted by LRF changes randomly if the pulse laser emitted by the transmitter is random partiallypolarized light.
The ablation experiments on different target materials such as Al, Fe, Cu and Ti were conducted by using 2 kinds of lasers to investigate the interaction of the long-pulse high-energy laser with metal target plates. The ablation ratios of various materials under different energy densities were obtained by recording the times of laser bombardment the laser took to penetrate the target material as well as measuring the laser energy going through the hole and the area of the hole. The experiments prove that the ablation ratio of the laser beam with low energy density is much lower than that of the laser beam with high energy density, even sometimes the former can still makes a limited ablation on the plate. A long-pulse laser, whose energy density can cause the liquid mass transferred, can get a greater ablation ratio and a hole with larger cross section.
The power spectrum density (PSD) distribution of Zernike polynomials and the polynomials orthogonalized in an annulus sector area (POAS) were obtained by Fourier transformation. The peak radial spatial frequency and the halfpeak radial spatial frequency range corresponding to each item of the orthogonal polynomials were calculated. In comparison with Zernike polynomials, the orthogonal polynomials have similar PSD distribution, but higher spatial frequencies. Computer simulation indicates that each item of POAS represents only a specific frequency range. According to the spatial frequency distribution of the surface figure of a mirror with annulus sector shape, the calculation time is reduced and the fitting accuracy is guaranteed if the proper items of orthogonal polynomials are selected.
When a plane wave propagates along any direction except the direction of the optical axes in biaxial crystal, there are only two solutions which have different propagation constants and polarizations. The plane wave solutions of a biaxial crystal in principal coordinate system were derived and the spatial dispersion relation of each solution was obtained by using Lagrange multiplier method and the ellipsoid concept of refractive index of the biaxial crystal. Proceeding from the obtained solution of the plane wave, the propagation of the plane wave along the optical axis is discussed. The obtained result was applied in uniaxial crystal for verification.
Using the B3LYP method based on the density functional theory, a quasi-1D SiO2 nanochain formed by SiO2 2MR, and the Raman vibration spectra of a SiO2 nanotube composed of 3MR, 4MR, 6MR and 8MR were calculated at 6-31G(d) level. Through the analysis of Raman spectra, it is found that Raman radial breathing vibration frequency of the nanochain and nanotube moves to the opposite direction with the increase of their length, namely, the red shift and blue shift turn up. However, Raman frequencies trend to reach the different stable values with the approximation of the infinite frequency, and the vibration frequencies reduce with the diameter increase of the nanochain and nanotube. Due to the internal structure stress of nanomaterial, the frequency shift is more obvious for small size material. The further analysis of bond length and bond angle of all kinds of structures shows that the function of the structure stress causes the frequency drift according to the size of the nanomaterial.
A theoretic model is proposed based on the characteristics of radiation superposition for calculating the radiative intensity of clear atmosphere background. The model was used to calculate the spectral radiation luminance of the clear atmosphere background, and an iterative method was used to resolve the radiative transfer equation and perform the dynamic stratification of the atmosphere. The comparison between the results of the model computation and the well-known 6S software computation shows that this model and calculating method are accurate for the computation of the spectral irradiation luminance in the clear atmosphere background. And the results show that the spectral luminance of the clear atmosphere is high at short wavelength and weak at the strong absorption IR band.
With energy level and the influence of incident laser pulse width on particle absorption taken into consideration, the instantaneous relationship of the particles on each energy level was simulated with the theoretical rate equation. The dynamic solution of reverse saturable absorption was given when the laser pulse width was comparable to the lifetime of energy level, which indicated the particle distribution at the energy levels. The variation of the transmittance with the light intensity was theoretically simulated with the experiment parameters of C60 and HITCI when the cross section of the excited-state absorption was larger than that of the ground-state absorption. It indicates that the larger upper energy level absorption cross section can restrain the saturation absorption caused by intense light. The nonlinear optical limiting of the optical materials was improved.