Laser active suppressing jamming is one of the most effective technologies to cope with optoelectronic imaging system. Multiple horizontal crosstalk lines have been observed with the increase of incident laser power on the optoelectric detector, when we carried out the test of supercontinuum laser jamming optoelectronic imaging system. When the laser incident power reached 5mW, there was a longitudinal crosstalk line passing through the center of the main laser spot in the output image. The width of the longitudinal crosstalk line increased with the increase of incident power and it gradually covered the main spot. Multiple horizontal crosstalk lines faintly appeared in the output image when the incident power increased to 200mW. We continued to increase the incident power to reach 500mW and the multiple horizontal crosstalk lines cover the entire output image. We analyzed the generation mechanism of multiple crosstalk lines based on the working principle of photodetectors and have found that the photo-generated charges sharply increased during the integration time of the detector when the power of incident laser is very high. Overflow charges exceeding full well capacity quickly filled the entire column of vertical transfer CCD, secondly overflowed to the horizontal transfer CCD, and lastly filled the entire row of horizontal transfer CCD. The research results can provide the theoretical reference and data support for the research on laser active suppressing interference technology
Infrared imaging systems have many advantages, such as full-time employment, good concealment, high resolution, strong anti-interference ability, so they have become the military and civilian focus so far. In this paper, we explored to construct the evaluation system about detection performance of infrared imaging systems based on infrared physics theory and the action mechanism between infrared radiation and detector. First of all, infrared detection mechanism of point target has been investigated under long distance condition. We derived the solving formula of detection range and proposed the method of calculating the mutual position of target and detection system to reduce false alarm rate. Secondly, we constructed the evaluation system on detection performance of area target, and mainly combined the area distribution of target imaging on the photodetector, signal to noise ratio of target, the contrast between target and background. The detection range of area target was the minimum value of the three factors. The simulation results indicated that the constructed evaluation system of point target and area target can fully evaluate detection performance of infrared imaging systems.
High power laser transmission in optical system is a key link for laser coping with electro-optical imaging system. When laser goes through the entrance pupil of optical system, diffraction effect inevitably comes into being due to the limitation of the entrance pupil. The energy distribution on the photodetector caused by diffraction effect can have a serious impact on the target detection and recognition. The correction method of diffraction effect among the different optical systems has been proposed based on Fraunhofer diffraction theory in this paper. The simulations results have indicated that diffraction effect simulated by the oscillation envelope approximation have a good agreement with the results simulated by Bessel function on energy distribution profile and changing trend. The difference is the lack of fine modulation of sidelobes, but the modulation is lower than the sidelobes by 3 orders of magnitude. The agreement has proved that the correction method is practicable, which can effectively solve the effect estimation among the different types and F number of optical systems.
Laser active suppressing jamming is one of the most effective technologies to cope with electro-optical imaging system. In order to obtain the exact assessment of laser jamming effect, we must acquire the laser jamming effect image. We proposed two methods for simulation implementation of laser jamming effect image in this paper, which were respectively based on theoretical model and measured data. First of all, the implementation flows of two methods were introduced. Secondly, we successively finished the simulation of laser jamming effect image according to the two flows. By comparing with the measured image, the significant correlation can be obtained with the method based on measured data, regardless of whether the jamming laser energy was high or low. The significant correlation can be achieved with the method based on theoretical model when the jamming laser energy was low. The research results can provide the technical reference for carrying out laser jamming experiment.
Vector mode properties in a 3×1 conventional photonic lantern (CPL) are theoretically investigated. Analytical solutions of vector modes in fiber cores at the weak tapering region of a 3×1 CPL are derived based on coupled mode theory and linear combination method. While at the strong tapering region of a 3×1 CPL where core modes cut off, vector modes in cladding can be derived by ignoring the impact of original fiber cores. These analytical solutions are verified by numerical calculations by a fully vectorial finite element mode solver. Further investigation shows that although there is no linear polarization selection mechanism in the tapering region of a CPL, linear polarization (LP) modes are still suitable for CPLs only if fiber modes finally evolve into LP modes in the output fiber. This conclusion can be very useful for simplifying the mode analysis of CPLs.
Square array CCD detector is widely used in image acquisition, photoelectric measurement and other fields. However, its inherent dynamic range is affected by noise and saturation crosstalk effect, which can not meet the application requirements of laser jamming effect measrement. In this paper, an image date fusion method based on linear compensation and orthogonal compensation is proposed. By controlling the jamming laser power, collecting multi-frame laser jamming effect images, and making full use of the effective measurement information in the image for compensation, the target laser energy distribution data with lager dynamic range can be obtained. In the experiment, the laser energy distribution on the target surface diffracted by circular aperture and rectangular aperture is inversed respectively, and the dynamic range is expanded by 40dB.
Irradiating experiments with a 532nm laser were conducted to investigate the effect of integration time on crosstalk line intensity for IT-CCD. Crosstalk lines were observed in all the experimental images with different integration times when laser power was high enough. Crosstalk line gray value was calculated by eliminating the impact of background light and main spot. Calculation results show that crosstalk line intensity is independence of integration time while proportional to laser power. According to the working principle of IT-CCD image sensor, the formation mechanism of crosstalk line is the quantitative overflow of stored charges from photodiode to vertical CCD in the process of vertical transfer. According to the working principle of electric shutter, the reason of the independence of integration time on crosstalk line intensity is that the period of shutter pulse is an invariant. This research enriches the knowledge of crosstalk effects for IT-CCD, and provides important support for deep searching the mechanism of laser jamming on CCD.
The beam quality factor (M2 parameter) of output laser in a three-core and seven-core conventional photonic lantern excited by incoherent sources is analyzed based on analytical and numerical method. Theoretical results show that the limitation of output laser beam quality is M2=1.75 for a three-core photonic lantern and M2=2.70 for a seven-core photonic lantern. Both the mode evolution process and beam quality factors of these two kinds of photonic lanterns are verified by numerical calculations. It is shown that good beam quality of the theoretical limitations can be realized only if the adiabatic conditions are satisfied very well. These results are very meaningful for practical application of high brightness incoherent beam combining based on conventional photonic lanterns.
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