2009 Vol. 30, No. 6
Night vision pilotage systems (NVPS) are used to assist helicopter pilots to realize taking off, landing and hedgehopping at night by providing the highdefinition and largearea images. Based on the engineering application requirements and the state of art of the NVPS, the design methods of the NVPS are studied by analyzing and calculating some important issues, such as the design of adaptability to environment, the selection of photoelectric sensors and the design of control systems. The analysis and calculation results confirm the feasibility of the design, and the design shows that it is suitable when it applied in the engineering.
The optical characteristics of several space targets with simple shape and the satellite models are studied according to simulation measurement of spatial targets distinct in shape and material. The result indicates that the location of light source, target and detector plays a decisive function in detecting the optical characteristic of the spatial targets. As for the spherical and cylindric targets, the phase angle of the light source and detector is the main factor to effect the reception of light radiation, as for the three-dimensional targets, the detecting effect is relative to incident and observing angles, and as for the earth synchronous satellites, the optical characteristic is influenced mainly by the observing area and the angle included between the solar panel and earth. This research is significant for deducing the attitude of space targets from observed results.
The mathematic model of the relationship between the misalignment and aberration in the process of computer -aided alignment is presented. The misalignment state of three-mirror-anastigmat system was simulated with Zemax, and the alignment data was obtained. The corresponding relationship between the misalignment error and elementary aberration is analyzed, and the misalignment characteristic of three-mirror-anastigmat system is summarized. The alignment scheme is determined by the above analysis. In order to verify the alignment scheme, the three-mirroranastigmat system was aligned according to the value which was calculated in accordance with the alignment scheme. The result demonstrates that the alignment scheme is feasible and guidable to the alignment of three-mirror-anastigmat systems.
Experimental and theoretical investigations on the vibration spectrum of Cyclotrimethylene-trinitramine（RDX）-in the region of 0.2～2.5 terahertz are presented. The refractive index and absorption coefficient of an explosive sample were measured by terahertz time-domain spectroscopy. The theoretical simulation according to density functional theory (DFT) is in agreement with the experimental data. The obtained results indicate that the single chemical compound explosive RDX has a characteristic absorption peak, and the single chemical compound explosive can be tested and identified with THz-TDS technology.
A new kind of polarization-independent and temperature-insensitive electro-optical modulator is presented by the aid of the relationship between the electro-optical coefficients of LiNbO3 crystal. The modulator is comprised of two pieces of LiNbO3 crystals, and a pair of collimators. The light propagation in the modulator is studied with the wave coupling theory of linear electro-optic effect. It demonstrates that the modulated output intensity doesnt depend on the polarization of incident light. Furthermore, it shows that the disturbance of the output intensity is less than 1.5% as the temperature variation is -20℃～60℃, and dI0/dT is better than 0.0002, which means that the modulator has a wonderful thermal stability.
In combination with the advantages and disadvantages of ordinary double-reflection and three-reflection, one special two-mirror optical system with three reflections is designed and the method for calculating the parameters of its initial structure is given. This initial system composed by two mirrors is a focal system, and the rays are focused after reflecting twice on primary mirror and once on second mirror. The defects of this initial system are analyzed and some steps are taken, which are beneficial to compensate the defects and obtain the better image quality. Two systems were designed with the method. The focal length of them is 5000mm, the F/# of them is 5 and the field angles are 0.4and 1respectively. The result of evaluation demonstrates that the image quality of the systems is near diffraction limit and the systems are of high resolution, long focal length and small volume.
For a panoramic optoelectronic detecting system to compensate three disturbances to track offshore targets by azimuth and pitching axes, based on a five dimensional analytical expression for a image line projected on focal plane, a compensation algorithm for azimuth intercept of panoramic image rotation stabilizing sea-sky line, which takes target point and image rotation centerline as the compensation intercept, is derived. The absolute value of the compensation angle is obtained by extracting the arc tangent function for the ratio of the compensation intercept and system focal length. The coordinators of the target image point and image rotation center point is converted into the coordinator of azimuth rotation. The algebraic difference sign for the abscissa of the two points is taken as the sign criterion of the compensation dosage. The algorithm allows the target image point to approach to the image rotation centerline in the case of the nonlinear large-angle image rotation, and always approach to the original point on the focal plane in combination with the compensation algorithm of the vectorial angle for the pitching mechanism. The simulation of the mathematical model shows that a single compensation can reduce the residual by a factor of 1%. The reasonableness of the compensation algorithm for azimuth intercept was proved by an actual condition test.
A large-aperture camera lens working in the wide spectral range is designed, whose main optical parameters are shown as follows: f= 200mm, D= 160mm, 2=18, =400～950nm. The double Gauss objective is complicated by adding the quantity of lens, dividing a thick lens into some lenses and choosing glasses with similar dispersive characteristic, and the imaging quality is improved by minishing the clear aperture of the lens to eliminate partial marginal beam. The MTF of the finallydesigned system is higher than 0.55 at the spatial frequency of 30lp/mm. All sorts of the aberrations are corrected well, and the image quality is uniform in all the fields. The parameters obtained for the system meet the requirement of the large aperture camera lens working in the wide spectral range.
The propagation of multiple incoherent beams in biased two-photon non-photovoltaic photorefractive crystal is investigated under steady-state conditions. It shows that the two-photon incoherently-coupled bright-dark hybrid screening soliton families exist in the biased two-photon non-photovoltaic photorefractive crystals, and that the soliton families are formed by the mutually incoherent beams which have same polarization and wavelength. Moreover, two-photon photorefractive crystals, whose optical axis direction is same to the direction of the external field, can support bright-dark soliton families in which the peak intensity of the bright component is slightly larger than that of the dark component. When the direction of the applied electric field is reversed to that of the optical axis, the two-photon photorefractive crystals can support the bright-dark soliton families in which the peak intensity of the bright component is slightly lower than that of dark component.
A mobile phone lens assembly composed of 4 plastic aspheric lenses and an IR filter was designed by use of ZEMAX (optical engineering software). Considering the production and cost，the plastic lens E48R was chosen．The 1/3.2 in (7.94mm) 5 mega-pixel CMOS made by Aptina is taken as the image sensor of the lens assembly，whose pixel size is 1.75m and the limiting resolution is 285lp/mm. The F-number and FOV of the camera are 2.85 and 60 respectively. The results show that the lens has excellent imaging quality, the MTF value is more than 0.3 within 0.7 FOV at the Nyquist frequency, the MTF value of FOV are more than 0.5 at the 1/2 Nyquist frequency, wavefront mean square error is less than 0.1, and the distortion is less than 1％.
A mathematic model for dual-wedge prism system is proposed to analyze the refractive property of light. By use of the theories of geometric optics and scalar diffraction, it is found that the dual-wedge prism can be simplified as a single-wedge prism whose angle between two refractive planes and main optical plane are changed with the rotary angle between two wedges. When these two wedges rotate in the different angle speed and opposite direction, the refractive light from this system is in two dimensions. Besides, taking the dual-wedge system as a diffractive screen, a theoretical analysis is made on the diffraction light field distribution of the beam which passes through the rotary dual-wedge system. Under the condition of Fraunhofer diffraction, the variation law of diffraction light spots with the rotary angle was obtained. This research may give a developing direction for the 2-D controllable scan.
According to the second-order moments intensity formula of the beam propagating in the gain or loss media, an analytical expression for M2-factor of partially coherent flat-top beams propagating in the media is derived, and Gaussian-Schell model beams propagation in gain or loss media, which is taken as a particular case, is integrated into a common expression. The research result shows that the M2-factor of partially coherent flat-top beams propagating in the gain or loss media is relative to the propagation distance, the coherent length, the order of the beams and the character of media. The propagation characteristic of the beams propagating in the gain or loss media provides a theoretical basis for the application and control of the beam propagation.
The testing system for creeping movement attitude of soldiers was designed for overcoming the low efficiency and strong subjectivity existing in the training appraisal with the traditional method. The real-time detection for the creeping movement attitude of soldiers can be implemented by the testing system based on infrared and single-chip computer technologies. The parallel multiplexing signal processing circuit and beam path adjustment setup were designed to direct at the characteristic of great IR interference in the open air, which improved the anti-interference ability and acceptance range of the system. The synchronous simulation of sound in battlefield enhances the efficiency of training. The training effect evaluation provided by this system can meet the requirement of the training.
Matlab software and Burch coding method are used to achieve the fast generation of the Fresnel hologram and Fourier transform hologram. The experimental principle, methods and procedures are discussed particularly. Combining computer-generated hologram (CGH) with digital holography, the digital reconstruction of hologram was realized. The computer simulation of the whole holographic recording and reconstruction process was achieved. Matlab is proved to be more convenient and flexible in comparison with the traditional algorithm languages and drawing methods, and takes several measures to improve the reconstruction quality. The influence of zero-order and conjugate images is eliminated and clear digital reconstruction images are obtained.
The stray light which is generated by the residual multi-reflection on the surfaces in optical system easily forms ghost images near the image plane and they influence the acuity and contrast gradient of images, decrease the resolution of lens, and disturb the target discrimination. It is difficult to be simulated and analyzed due to the excessive surfaces, complex structure and locomotory parts in zoom lens. All the transmission planes taken as the partial reflection and partial transmission planes were simulated with ASAP（advanced system analysis program）and the stray rays on dangerous surfaces which easily generate the ghost images in zoom lens were analyzed. Based on it, the zoom lens was optimized and the quality of image was improved by changing the curvature and refractive index of the second reflection planes.
A novel 3D model analysis of circular feature is addressed in this paper for machine vision. We use an efficient method for fitting ellipses to data points by minimizing the algebraic distance subject to a constraint, which a conic should be an ellipse, and solve the ellipse parameters with Lagrange multiplier method. After analyzing the perspective model of circular feature, the 3D position and orientation of a circular feature with known radius is obtained using closed form solution. A set of identical circles are detected with the model analysis. Experimental results show that our method is efficient and accurate.
In order to measure optical components of large aperture in fine grinding process, the relationship of the contrast of interference fringes and the surface roughness was described by rigorous mathematical analysis based on the electromagnetic scattering theory. The mathematical derivation was verified with experimental data at different roughness. 280# rough sphere with aperture =1130mm, curvature radius R=3600mm, was measured by using the infrared interferometer. When a large aperture rough sphere was measured, the alignment method of infrared interferometer was introduced. The result shows that the rough sphere has obvious spherical aberration. The PV value of the rough sphere is 0.526 (=10.6m), and the RMS value is 0.117 (=10.6m).
A new method for measuring targets 3D pose angle from mono-view in shooting ranges was presented in order to improve the measurement capability of 3D pose by live recording systems，which could get targets 3D pose precisely and quickly by utilizing the proportions of feature pointscoordinates. The model of imaging system and the definition of coordinates were introduced. The collinear equation was transformed including the scale of feature points on target, and the 3D pose angle of target was obtained by solving the nonlinear equations. The feasibility and errors of the algorithm were analyzed. Experiment results indicate that the algorithm is accurate and robust.
Twyman-Green interference plays an important role in high-precision optical measurement. Anomalous interference pattern often appears in TwymanGreen Interferometer when CCD is used as an image sensor, which prevents scientific researchers from recording and testing real pattern accurately. Therefore, the principle of optical Moir and the spacing structure of CCD are used to analyze the anomalous interference pattern, which is proven to be Moir pattern theore tically. Based on the optical field distribution calculation, numerical simulation is used to recover the anomalous pattern to further verify the theory. Moir fringe hinders the observation of interference fringes and should be decreased or even eliminated by using a proper CCD or changing the CCD detector sampling algorithm.
Temperature dependence of reflectivity of 45# steel at the wavelength of 1.319m was measured by using an integrating sphere system. The change of the reflectivity was explained by analyzing the surface energy spectrum of steel plates, which was heated. Reflectivity didnt change remarkably in the range of room temperature to 325℃, and it decreased from 0.64 at 325℃ to 0.15 at 395℃. As the temperature kept on increasing, the reflectivity didnt change obviously. In the cooling process, reflectivity held as a nearly constant value, which was the same as the value at the highest temperature. The change of reflectivity is mainly due to the oxidation of surface. As the temperature rises, oxidation reaction becomes severe and the atom percentage of oxygen in the surface increases, so the reflectivity decreases.
In order to determine the reliability of each sensor and how to fuse the data measured by sensors, a multi-sensor data fusion method based on fuzzy theory is proposed and its measurement application is studied. Firstly, the sensors consistency is obtained from the admissible function and the measurement error data are deleted. Then the measurement data are fuzzied. Finally, the fusion result could be produced on the basis of fuzzy similarity degree. The method is computationally simple and can objectively reflect the reliability and consistency between these sensors. A measurement example proves that the method is feasible, it can give higher priority to stable and reliable sensor, and it is simple and efficient for real-time measurement.
The modern interferometry measurment features high precision and non-contact, which makes it widely used. As an essential part of the measruement, apre-processing of interferogram was proposed, and it included edge identification based on mathematical morphology, regional extension based on 2D fast fourier transformation (FFT), as well as unwrapped and wrapped phase based on non-weighted least square method for discrete cosine transform (DCT). At last, surface distribution was obtained. The image aquisition of the SiO2 film and the preprocessing of interferogram was performed.The result indicates that it is consistent with the result measured by Zygo interferometer.
The principle of gas detection with spectrum absorption is explained and the typical gas in coal mine is given. A goaf spontaneous combustion prediction system with multiple parameters is introduced in detail. The system uses a distributed feedback diode laser as light source, which is driven by a low frequency sawtooth wave overlapped with a high-frequency sinusoidal signal. Signal extraction is achieved with a lock-in amplifier. The method to determine spontaneous combustion of coal mine goaf is explained according to the theory of static distribution of three zones. The system uses fiber to detect gas and transmit signal, which makes the real time detection accurate, stable and reliable due to absence of electricity.
The analysis of random walk coefficient is very important to the overall performance evaluation of fiber optic gyro (FOG). Two methods were introduced to analyze FOG random walk noise, Allan variance and modified Allan variance. Static data were used to calculate the noise contents in fiber optic gyroscope (FOG)s output with these two methods, and the results were compared. The final results show that modified Allan variance can distinguish all types of noise easily with increased computation time and the computation accuracy of the various FOG random walk noise coefficients can be improved.
In order to real-time get optical power signal transmitted in optical fiber，a new high-speed acquisition system is designed.Based on LabVIEW virtual instrument programming language and USB technique, the system combines an optical receiver with an USB DAQ card USB-M6251 of NI Company．It overcomes the disadvantages of the traditional system, such as low sampling rate，single channel display，insufficient man machine interface function and poor portability, and realizes the real-time acquisition，display and storage of optical-power signal in dual channels with sampling parameter controllable.Experiments prove that the optical power signal acquisition system is reliable and practical，and it provides a good man machine interface. It can be used to monitor the optical power signal in various optical fiber communication systems.
The compensation method for MEMS gyro random drift error is discussed. Based on the fundamental theories of wavelet analysis for signal de-noising, an improved wavelet threshold de-noising method incorporating the polynomial interpolation function is presented for compensating the MEMS gyro output noise. The measurement data of MEMS gyro is analyzed, and the result proves that the proposed method performs well for MEMS signal de-noising.
Dynamic bandwidth allocation of the uplink is a hot technique in EPON system. By analyzing the merits and weaknesses of the existing algorithms, a novel dynamic bandwidth allocation algorithm is proposed, which supports differentiating service levels and guarantees the quality of the service. The new algorithm determines the polling cycle, allocates the requested bandwidth to high-priority services, and allocates bandwidth to middle and low priority sevices by weight. It also takes the reallocation of the excess bandwidth into account. Simulation results show that this scheme can meet the bandwidth need of high priority service while taking low priority service into account. The algorithm makes the distribution of system bandwidth more rational and improves the efficiency of up-link bandwidth and the quality of service.
A refractive infrared zoom optical system working in (8～12)m is designed, based on long-wave uncooled thermal IR focal plane arrays (160 pixel120 pixel) detector. The system has characteristics of large relative aperture, F#=1.2, high zoom ratio and high imaging quality. Two common infrared materials of Ge and KCl are used in this optical system. The off axis aberration and higher order aberration of the system are corrected by introducing an aspheric surface into the system, and the zoom ratio is rapidly improved by solving the compensated curves at the middle-focus length. The modulation transfer function (MTF) is above 0.55 within the whole focal range at the spatial frequency of 17lp/mm and approaches the diffraction limit. The energy concentration ratio is greater than 72% within the sensing element of the detector whose receiving radius is 17.5m. The above mentioned parameters show that the optical system has good imaging quality.
The double-channel digital IR radiometer was developed for eliminating the disadvantages of the IR radiance testing system being used in testing some military infrared products. The double channels simultaneously test the IR radiance and connect the data when the ignition test of an IR radiation product is carried out. Six contrast experiments between the double-channel digital IR radiometer and IR radiance testing system were performed at 25℃ and -15℃. The result indicates that the error of the two systems are all less than 5％, and the difference of the two channels of the double-channel digital IR radiometer is also less than 5％. But 1905A testing system missed out twice and the radiator did not omit anything. The principle, design of key components, calibration and application are discussed in this paper.
The regular granule heavy sampling algorithm is proposed for solving the deterioration of the granules in the infrared imaging denoising process. The granule cloud is obtained by the algorithm based on the granule resampling which can eliminate the phenomena of the granule diversity vanishing and granule want, the granules with great weight value observed at the next moment are marked to make the granule weight value more stable by adding some auxiliary granules, and then an infrared imaging denoising model of a moving object is established. The experimental result indicates that the method makes the effect of the infrared imaging denoising much better, and the imaging definition above 95%.
A new alignment system based on the two-beam focus is proposed for the exact installation and alignment of the inertial confinement laser-fusion diagnostic instrument. The alignment theory and system configuration is also discussed. The same structure as Lister microscope is selected for the optical pointing system, whose objective image distance is 180mm, magnification is 10 and NA is 0.25. The two-dimensional adjustable and threedimensional adjusting mechanism which moves along axis of optical pointer is adopted in the design of mechanical structure. The space cone angle of the whole system is 28, which is less than the limitation of 30. It is found that the optical pointer error is 25m by analyzing the error of the system, which can attain the design specification. The instrument can be manipulated easily and so that can be widely used in ICF.
In order to achieve high reliability, narrow pulse width and high peak power laser output, an all-solid-state electrooptical Q-switched green laser with diode side pump was designed with the side-pumped and electrooptical Q-switched technology. The stable laser output of LD side-pumped Nd: YAG pulse green laser with extra-cavity frequency-doubled KTP was achieved by the simple and compact flat-flat cavity design. When the pump current is 120A and repetition rate is 600Hz, the highest pulse green output average power of 3.62W, the conversion efficiency (from 1064 nm to 532 nm) of 15.3%, the pulse width of 21ns, peak power of 300 kW, and single pulse energy of 6.01mJ were achieved. Experimental results show that the stability of laser output is high, pulse width is relatively narrow, and peak power is high.
A novel range-gated gain-control photomultiplier tube (PMT) detector system was designed in order to detect the backscattering signal under water dynamically in real time. The gating of PMT was realized with the method of adding the applied gating and gain-control nano-second pulse, and by changing the electric potential difference between the cathode and the first dynode. The gain control of PMT was complemented by the aid of adding the high voltage pulse to the last dynode of PMT to change the electric potential difference between the last dynode and front dynode. The experiment result shows that, when the gating and gain-control pulses come, the anode outputs the relevant pulse signal whose pulse-wide is 40 ns. It proves that this method can realize the gating and gain-control of PMT.
In view of Doppler wind lidar has found widespread applications in aerospace, aviation, space-based remote sensing and atmospheric observation, several typical coherent Doppler wind lidars with different bands are introduced in combination with the principle of coherent detection. Some key techniques such as laser transmitter/receiver, space scanning and data processing are analyzed. In addition, the wide prospects of application are expected. The results indicate that we are still lagging behind developed countries in the field of coherent Doppler wind lidar to a great extent though some achievements have been made.
The design principle of the laser receiver with wide FOV for the laser command guidance and laser-beam riding guidance is introduced. A mathematic model of receiving light field is presented. The formula for the viewing angle of the detecting optical system was derived according to the diffraction light field of the oblique incidence parallel light. Taking a detecting optical system with the collecting objective for example, the design characteristic that the receiving optical system needs not only an extra large relative aperture but also an unvignetting receiving performance is discussed on the premise of meeting the requirement of 1064nm WFOV laser receiver. A narrow band interference filter was adopted to realize the noise reduction. A design example of a low noise amplifier suitable to the high-repetition-rate (200kHz) is given. The design principle of the low noise amplification circuit is introduced. The tested results of receiving FOV angle, dynamic range and receiving sensitivity of the laser receiver with wide FOV are provided.
The laser multispectral detection is an important development direction of laser technology, belongs to active detection technology, and exhibits higher precision than the former passive detection. Aiming at the demand of laser-based multispectral detection for multicolor laser source, a method using spectral beam combining technique in an external cavity to obtain the multispectral laser is proposed. The experimental results of spectral beam combination for two fiber lasers taking large-mode-area Er3+/Yb3+ co-doped double-cladding fiber as the gain medium in an external cavity are reported. Tunable dual-spectrum lasers with 29.3nm and 11.52nm 3dB linewidth were obtained. Experimental results and theoretical analysis show that spectral beam combination in an external cavity is a feasible approach for obtaining the multispectral laser sources.