2008 Vol. 29, No. 2
Scanning electron microscope (SEM), Rutherford backscattering (RBS), atomic force microscope (AFM), energy dispersive spectrometer (EDS), photometer and microchannel plate (MCP) tester were used to investigate the effect of acidetched time on electron gain, bulk resistance, noise current density, electron image brightness of MCP from the surface composition, morphology and structure of cladding glasses. The results show that the electrical performances of MCP is dependent on acid etching time. The electron gain and image brightness reach their maximum after the acid etching of 120min. The bulk resistance reduces to a certain value and then keeps constant with the increase of the acid-etched time. The noise current density, however, increases with the etching time.
The spectral matching coefficients between two kinds of BV-EMCCDs and dark green paint, rough concrete, green vegetation under clear starlight and full moon were calculated and compared, according to the expression of spectral matching coefficient. The matching coefficients for EMCCD with red-AR and the reflective radiation spectra of these objects are 0.4555, 0.4298 and 0.3685 under clear starlight, and 0.7290, 0.7194 and 0.6294 under full-moon, respectively. For EMCCD with blue-AR, the matching coefficients are 0.4233, 0.3910 and 0.3180, as well as 0.7832, 0.7448 and 0.5816 respectively. These values can be used to estimate the field performance and optimize the design of night vision systems.
Residual fixed pattern noise (RFPN) is becoming a major limitation for system recognition capability due to the continuous decrease of temporal NETD in thermal imager. Based on the analysis of non-uniformity mechanism in thermal imager, a method to achieve scene averaged irradiance in scanning thermal imager is introduced and the scene averaged irradiance is used as a reference to implement dynamic correction. The achieved system RFPN is less than 15mK in the scene dynamic range of (0～50)℃. The prototype was field tested in various environmental conditions. It was proved that such design enables thermal imager performance immune to the temperature change of thermal imager as well as the change of scene irradiance.
As an important part of the air-to-air missile, IR optical system will experience various complex dynamical situations. A complete analysis to the deformation, stress, and resonance of IR optical system was made with the finite element method to validate whether the optical system meets the image quality and mechanical stiff requirements, and the distinct deformation area was determined. The key structures of the optical system were analyzed in detail, and the approach to optimize the structure of the system was proposed.
The fiber hydrophone utilizes the interferential optical signal to detect. The effect of the stimulated Brillouin scattering (SBS) occurs with the increase of the optical power, which makes noise, limits the incident light power and affects the detecting signal seriously. For suppressing the SBS to improve the characteristic of fiber hydrophones, research, based on the Michelson fiber hydrophone, was done, and the methods of increasing the threshold, especially the method of using the optical isolator were investigated according to the threshold equation. The time-space distribution of incident light, Stokes light and sound wave in the fiber is analyzed with FDTD. The time-space distribution of each wave in the fiber can be obtained so long as the initial condition and fiber parameters are given. The research on suppressing this effecting can offer a new way to produce the tunable coherent light, and it can be an effective method to study the characteristic of different scatterings in fiber system.
The high quality x-ray sources, especially for the microfocal x-ray source with high-brightness are crucial components for modern x-ray imaging techniques. They are widely used in applications such as non-destructive diagnostics, lifescience, material science, and biomedicine. The methods to make the microfocal x-ray source and its applications are briefly introduced. Various focusing x-ray optical elements related to microfocal x-ray, including Kirkpatrick-Baez mirror, multilayer mirror, Fresnel zone plate, Bragg-Fnesnel zone plate, polycapillary x-ray lens, multilayer blazed grating, compound refractive x-ray lens, are introduced. The potential applications for the microfocal x-ray source in mircometer and nanometer test and analysis are discussed.
A new approach to calibrate camera parameters by image pair is presented. With this method, the parameters of a camera is calculated by using the invariance of lines under the projective transformation, different from previous methods which estimate the fundamental matrix by the image characteristics. Two parallel lines on each of the image pair were extracted. The focus and the extrinsic parameters were solved according to the projective invariance of parallel lines with the center of the image taken as initialization of the principal point. Based on the polar constraint, the nonlinear optimization was employed to compute the precise parameters of the camera. The algorithm needs less information of the scene and accurate self-calibration is easily realized. The recovery of 3D scene structure can be accomplished with the new algorithm. Experimental results on the synthetic and real images demonstrate the feasibility of this algorithm.
To overcome the atmospheric attenuation effect, the non-line-of-sight scattering atmospheric optical communication system usually adopt an optical antenna to enhance the signal collection ability and increase its communication distance. Some conventional optical antennas like hemispherical lens, compound parabolic concentrator (CPC), Cassegrain telescope were analyzed with the software of ZEMAX. The results show that the field of view (FOV) of hemispherical lens and CPC are wider and its gain is higher compared with other optical antennas. The variation of the photons′ energy intensity distribution with the communication distance was calculated with Monte Carlo method, with CPC and hemispherical lens as the optical antennas. The result shows that the light collection capacity of CPC optical antenna is better than hemispherical lens optical antenna, and CPC is the more suitable optical antenna for non-line-of-sight scattering atmospheric optical communication.
A high-stable control system based on the MCU of MSP430 for semiconductor laser is introduced to realize stable, reliable and accurate power output. According to the working principle of semiconductor laser, the controlled constant current source, temperature control system, light power feedback system and protection circuit was designed. It has real-time control, display and reset functions, and provides protection to the laser power. The light power feedback was used to achieve the light power stability. The thermoelectric cooler driven by high-accurate PWM amplifier was employed to control temperature. The light power stability is better than 0.25%.
To study the influence of background on detection, a 3-D noise model and a measurement system were established. The temporal noise and spatial noise of CCD camera were measured and analyzed at different illuminances. The block diagram of the test system and some test results are given. The dominant noise which influences the output quality of CCD image was found, the dependence of temporal noise and spatial noise on illuminance was obtained. Measurement results indicate that the spatial noise and temporal noise increase with the increase of illuminance on the active area of CCD camera. It is consistent with the performance of CCD cameras.
Based on the normative fractional Fourier transform and the concept of the optical transfer function, using the linear system theory, the mathematic expressions of fractional transfer function in Fresnel diffraction system and Fraunhofer diffraction system are given respectively. It is proved that the fractional Fourier transform has the cascade feature, and the optical transfer function is the special case of fractional transfer function. The result can be used to support the application of fractional Fourier transform in information processing and image quality assessment.
In order to improve the laser transmitting power of laser detection system, assuming exit laser is a fundamental mode Gaussian beam, the effect of the obscuration ratio of Cassegrain telescope and the waist radius of the incident light beam on the light power transmission was analyzed based on the transformation and transmission characteristics of Gaussian beam passing through the optical system. The numerical calculation indicates that the optical power transmission of the system decreases with the increase of the obscuration ratio and the waist radius of the incident light beam. The best match between the obscuration ratio and the spot size of the transmitting aperture was given. The effect of the defocusing error (installation error) of 0.2mm on the spot size of emergent beam was discussed.
An underwater low-light-level imaging system for anti-terrorism operation is introduced, and its key techniques are addressed. According to the optical characteristics of ocean water and low-light-level imaging environment, a dedicated underwater lens was designed, which can correct the aberration and overcome the influence of water medium. The finite element analysis was made for the sealed cabin of its detectors to ensure its reliability and make the mechanic design simple. The system was successfully demonstrated in Qingdao sailing boat game. The test results show that the system works reliably under the water pressure of 300 meters, its imaging quality is high and it can provide time critical warning for dangerous item.
A new method to align the optical axis of parabolic mirrors is introduced. The position of the mirror was adjusted to align its optical axis with the slewing axis by utilizing the movement of the image points of two parallel beams (one beam parallel to the slewing axis and another beam oblique to slewing axis with φ angle) reflected by the parabolic mirror, when the parabolic mirror is rotating on the mechanical axis. The theoretical analysis shows that the tilted error of the method is less than 1′and the deviation error is less than 5μm. This method can be used to the detection and optical adjustment of parabolic mirrors.
The miniaturization of spectrometer is helpful to increase its application. An optical layout was designed for a miniature CCD spectrometer for visible light. The proper optical fiber, plane directional optical grating and concave reflector were chosen and integrated together based on the theoretical computation for the optical layout of the spectrometer. The entrance light was dispersed and directly projected onto the active area of a CCD by focusing reflection and beam splitting. The optical layout was greatly simplified and the size of the spectrometer was reduced. Compared with other products, it is more accurate.
A new method to calculate the effect of temperature on refractive index is presented. A continuous temperature field was created in lens by fitting discrete node temperatures obtained from the finite element thermal analysis. Based on the temperature and input data of ray tracing points, the relative refractive index and its gradient information were calculated and returned to CODE V by the selfmade subroutine in ray tracing process, which made the simulation more accurate. Parameters such as wavelength, atmospheric pressure, temperature coefficient of the refractive index were inputted as variables to make the calculation of the relative refractive index more flexible. At last, the analysis of the calculation error was performed, and feasibility of the way was confirmed.
The influence of the thermal effect of the active medium on the laser oscillating modes distribution of end-pumped solid-state lasers is theoretically analyzed. With the fiber coupled diode lasers which end-pump the Nd∶YAG laser, the influence of the thermal effect on laser oscillating modes was studied. It proves that TEM00 mode volume becomes larger when the pumping power increases，and TEM00 mode becomes dominant in the mode competition. As the pumping beam departures from the geometry cavity axis, the light spot center of TEM00 mode moves to the axis of the pumping beam and the quantity of the beam wandering becomes linear with that of the pumping beam axis. The results of the experiment agree with the theory.TEM00 mode output in which the ellipticity is 0.98 and M2 is 1.01 was obtained.
An Internet based remote monitor and control system was developed for a highpower solid-state laser-processing systems. It incorporated a new web frame for the products. The newly designed system features high efficiency, accuracy and real-time performance. An advanced software architecture was adopted in the design. The operation status and parameters of the laser-processing system can be remotely monitored, the current data and history data of the laser-processing system can be inquired, some of the data can be modified if authorized. Questions could be answered via on line communication.
Based on the analyses of induction heating temperature model and laser induction hybrid cladding energy function, the dilution expression was derived, which quantitatively reflect the relationship between dilution and hybrid cladding process parameters. The expression was proved by the laser induction hybrid cladding experiments. The results show that the dilution increases with the increase of laser power, while the dilution decreases with the increase of powder feeding rate and scanning speed. The dilution increases significantly with the increase of induction energy, when the other processing parameters are not changed. The dilution model is helpful to control the dilution in laser induction hybrid cladding. It can be used for optimizing the process parameters and quality control of cladding coatings.
Based on the generalized Huygens-Fresnel diffraction integral, taking Gaussian beam as a laser beam model, the propagation formula is deduced. When the laser beam passes through the misaligned beam spread collimation optical system. The influence of the optical element misalignment on the output beam transmitting properties was analysed and the numerical simulation was carried out based on the analysis. The result shows that the output beam becomes an off axis Gaussian beam and the beam quality becomes worse if the misalignment is greater when Gaussian beam is passing through the misaligned beam spread collimation system. With the same misalignment, long-focus optical elements have greater influence on the output beam. The adjustment of the long-focus optical elements is more important in the beam spread collimation optical systems.
Frequency modulation tunable diode laser absorption spectroscopy (FM-TDLAS) is a high-sensitivity trace gas detection technique. In order to improve the signal to noise ratio（SNR）of a methane gas detection system, and to enhance detection sensitivity, a high-frequency phase-sensitive detector with Double Balanced Mixer (DBM) as the core and a modulation circuit were designed to detect the small signals in strong noise. Based on the design and analysis of the high-frequency phase-sensitive detector and the modulation circuit of the system, the performance testing for the overall circuit in the FM-TDLAS system was carried out in the experiment, in which the near-infrared absorption spectrum of CH4 gas around 1653nm was utilized. The experiment shows that the first harmonic and second harmonic signals with high SNR are obtained, and the detection sensitivity reaches 10 ×10-6.
A novel measurement method and a full-automatic measurement facility for optical angular deviation of airplane windscreens are presented. Compared with the existing automatic measurement method, this method has clear physical meaning, well defined measurement position and it could achieve more accurate result. The target is a pin-hole instead of a cross or a “L”. A tungsten halogen lamp and a projecting lens are used to generate the collimated light. A CCD detector is used as light spot position sensor to measure the changes of the spot position at the rear focal plane of the imaging lens, and the optical angular deviation can be derived. The measurement facility is traceable to the national angle primary standard with standard optical angular deviation samples. The analysis shows that the measurement uncertainty of the system reaches 7.3″(k=2).
Since the lifesaving signal detonator is an essential marine lifesaving appliance in the merchant ships, its quality is critical to personal safety. Based on the illuminance inversesquare law, incorporated with photoelectric technology and computer-aided technology, a test system was set up. The test for the signal light intensity was investigated. The detected signal data was directly input to the computer and displayed on the screen through the test software. The easy and fast test of the light intensity of the lifesaving signal detonator was realized. The experiment proves that this system is robust and reliable, and meets the demand of the on-line test in the production process of the lifesaving signal detonators.
Michelson interferometer experiment for extended lights was performed. When the extended light was incident upon the Michelson interferometer, and the transparent optical layers were added into each interferential arm, the dislocation phenomena of the peak of the time and space coherent envelop for exit light was observed under two conditions. It is proved that the optical wave coherent characteristic in the interference field can be destroyed by adding optical layers in the different interferential arm, which results in lead or lag for the time and the spatial coherence. Based on this effect, the measurement of the thickness and refractive index of optical elements can be implemented experimentally with two incident beams. The relevant calculation formulas are given.
An edge detection method of moving plate objects was designed by means of the image gathering function of a linear array CCD. The hardware structure was effectively simplified with a parallel beam projector as an illuminating source, an AVR single-chip computer to drive the CCD and to dispose the detected results. The measurement circuit and the binarization principle of CCD output signals are introduced. The design plan of the hardware and software are also provided. The experiment shows that the measuring accuracy of this instrument is better than 0.03mm，and the response time is fewer than 0.2ms.
The mathematic model for distortion is discussed. The distortion measurement with a precision goniometer and a bench comparator is introduced. The pixel distance equivalent of the CCD detector was calculated by the magnification method. The centroid of point target was derived by the centroid method. The pixel distance between the centroid and the origin on the image plane was multiplied by the pixel distance equivalent to achieve accurate distance. The absolute distortion was acquired by tangent function. The equation was worked out to calculate the coefficient. The results of the calculation and data processing indicate that the fitting effect of the distortion mathematic model is satisfactory in medium field of view.
Based on the center-surround mechanism of biological vision, a method which uses an improved LoG (Laplacian of Gaussian) operator to detect light blobs is proposed. First of all, the imaging model of light blob targets was established. The properties of LoG operators and their response to image were analyzed and a normalized LoG operator was proposed. The normalized LoG operators can be used to detect light blobs according to theoretical deduction. Simulation and test show that the proposed operator is effective in detecting size-known and size-unknown blobs in an image. The proposed operator can also be used to track single target and rigid-body in image sequence if combined with Kalman filter or particle filter. This method is proven to be robust and effective.
A key technology used in the processing of crystal window elements is illustrated by a germanium window element, whose diameter is 20mm and parallellism is 10″. Such a high-quality optical element is difficult to process because the element diameter is small, the parallellism requirement is high and the material is single crystal. Regardless of the conventional idea that crystal element can not be cemented, an‘optical cement’method was used and a set of control measures for high-precision crystal elements processing was summarized. With the method and the control measures, the crystal window element with high quality was made. It was proved that the method can be used in mass production.
SiO2-TiO2 planar optical waveguides were prepared with the sol-gel method. The thermal properties of SiO2/TiO2 sol-gel were analyzed with differential scanning calorimeter (DSC) and thermo gravimetric analysis (TGA). The morphologies of planar waveguides were characterized by SEM and AFM. The propagation loss of the planar optical waveguide at 1550nm was measured. The experimental results demonstrate that the gel thin film with the drying processing at 200℃ in 30min presents the porous structure, and for the unsymmetrical planar waveguide, there is a light flux cut-off thickness for a core layer. When the thickness of SiO2-TiO2 core layer is 0.5 μm, the cladding thickness should be at least 6 μm to prevent 155 0 nm light from propagating into the substrate of monocrystalline silicon. At present, the minimum propagation loss of the planar optical waveguides at 155 0 nm is 0.34 dB/cm.
For testing large aperture telescope with a segmented primary mirror, a low-coherence-spectrum interferometric detection system based on the Michelson interferometer principle was put forward to detect the phase error between the “sub-mirrors”, and subsequently correcting the misaligned segments to achieve the mirror coplanar. The phase error between the segments was extracted from the interferograms mismatching. The physical structure of the interferometric detection system with the low-coherence-spectrum was presented, and the detection principle of the interferometric detection system was explained. The interferometric fringe contrast and SNR were analyzed for the interferometric detection system. The feasibility of detecting the phase error with the low-coherence-spectrum interferometric detection system was demonstrated .
The expressions of single-photon acquisition probability in free-space quantum key distribution were deduced based on TEM10 mode Laguerre-Gaussian beams. The single-photon acquisition was analyzed for the laser link between a ground station and a satellite in a low earth orbit. The results show that single-photon can be acquired by the receiver in the satellite with maximum probability if highly attenuated laser pulses based on TEM10 mode Laguerre-Gaussian beams are used as single-photon sources and a bright precursor reference pulse is used to set a short time window for the single-photon acquisition. Unlike the fundamental-mode Gaussian beam, the TEM10 mode Laguerre-Gaussian beam does not cause the single-photon acquisition probability losses due to the movement of satellites.
The transmittance curves of the photopolymer which sensitized by different dual-dyes were fitted based on the basic photochemical reaction process of the photopolymer and its theoretical function model, and the parameters in the theoretical model of the photochemical reaction were obtained. A new method to realize the curve fitting by MATLAB and obtain the photomechanical parameters in the photopolymer, based on the theoretical model and experimental data, was analyzed. The analysis shows that the R-Square of fitting statistics for three photopolymers are 0.9687,0.9958 and 0.9902 respectively when the exposure wavelength is 633nm and the exposure intensity is 65mW/cm2. It means that the fitting method is successful.
Mach-Zehnder waveguide is an important part in integrated optics. The transverse distribution of refractive index of polymeric ridge waveguide was calculated with the effective index method (EIM) and 3-D propagation was converted into 2-D propagation according to the structural characteristics of the polymeric ridge waveguide. Based on paraaxial scalar equation, using CrankNicholson scheme, the basic calculation scheme of Taylor series expansion method was obtained and optimized. By simulating the TM mode of a real Mach-Zehnder waveguide, the influence of various parameters on the loss was analyzed. The results show that this method is accurate, stable and easy to program.
The propagation characteristics of second-order solitons were acquired by solving the nonlinear Schrodinger (NLS) equation with the method of step Fourier transform. The second-order solitons are compressed and their amplitude oscillates during the propagation. Periodic collision does not take place during propagation process of two second-order solitons. Two secondorder solitons will periodically yield a smaller soliton when their time-interval is small enough. It is concluded that the propagation characteristics of secondorder soliton are different from those of one-order soliton.