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.
In this experiment, the visible array CMOS image sensor irradiated by 532 nm pulse laser was carried out. The experimental results revealed that, with the increase of the incident power density, regular lightspot arrays appear around the main laser spot. When the laser energy density continued to increase, the phenomenon of asymmetric crosstalk appears in the image. It is analyzed that, the reason for the formation of spot array of CMOS image sensor is that after the laser was reflected by the CMOS photosensitive surface, it was reflected back to the CMOS photosensitive surface by the window glass and imaged on the photosensitive surface again. By analyzing the characteristic parameters of crosstalk line, it was considered that the crosstalk of CMOS image was the result of superposition of optical crosstalk and charge crosstalk.
The CMOS Image Sensor (CIS) is photoelectricity image device which focused the photosensitive array, amplifier, A/D transfer, storage, DSP, computer interface circuit on the same silicon substrate[1]. It has low power consumption, high integration,low cost etc. With large scale integrated circuit technology progress, the noise suppression level of CIS is enhanced unceasingly, and its image quality is getting better and better. It has been in the security monitoring, biometrice, detection and imaging and even military reconnaissance and other field is widely used. CIS is easily disturbed and damaged while it is irradiated by laser. It is of great significance to study the effect of laser irradiation on optoelectronic countermeasure and device for the laser strengthening resistance is of great significance. There are some researchers have studied the laser induced disturbed and damaged of CIS. They focused on the saturation, supersaturated effects, and they observed different effects as for unsaturation, saturation, supersaturated, allsaturated and pixel flip etc. This paper research 1064nm laser interference effect in a typical before type CMOS, and observring the saturated crosstalk and half the crosstalk line. This paper extracted from cmos devices working principle and signal detection methods such as the Angle of the formation mechanism of the crosstalk line phenomenon are analyzed.
We report an experiment of incoherent beam combining based on a 7×1 all-fiber signal combiner with output power up to 6.08 kW. Properties of transmission efficiency and beam quality are analyzed by beam propagation method. Based on the calculative results, a 7×1 all-fiber signal combiner is fabricated. The handle power capacity is tested with average transmission efficiency of 98.9% and beam quality of M2≈10.
KEYWORDS: Amplifiers, Signal attenuation, Single mode fibers, Signal processing, Fabrication, Refractive index, Multimode fibers, High power fiber amplifiers, Fiber lasers, Polymers
A high-efficiency pump-signal combiner for high power fiber amplifiers based on thermally expanded core (TEC)
technique is reported in this paper. TEC technique is used to fabricate mode-field adapter which allows optimization of
signal fibers in a monolithic (6+1) ×1 fiber combiner. The combiner is fabricated by connecting a tapered fiber bundle
(TFB) to a passive 25/250 (NA=0.06/0.46) double-clad fiber (DCF). By this method, the coupling efficiency of SMF-28
signal fiber at 1064nm improves from 54% to 92.7%. The average pump coupling efficiencies of six 105/125 (NA=0.15)
fibers are measured to be 96.7% at 976nm. Furthermore, the average signal transmission efficiency is around 93.3%. The
fabricated fiber combiner is spliced to an Yb-doped DCF for use as an all-fiber amplifier. The slope efficiency is
measured to be 71.6%.
KEYWORDS: Single mode fibers, Cladding, Multimode fibers, Capillaries, Fabrication, Laser systems engineering, Fiber lasers, High power fiber lasers, High power lasers, Polarization
We study the mode evolution properties in a 3 x 1 adiabatic tapered single-mode fiber combiner (ATSMFC) in theory. The fabrication of the combiner for single mode fibers based on adiabatic tapered fused bundle (TFB) technique with the assistant of low index glass capillary is introduced. The whole taper region can be seen as three phase: single-mode fibers, multi-core fiber and multi-mode fiber. Supermodes of three-core fiber with scalar mode results are derived based on coupling mode theory. The analysis is verified with numerical examples by fully vectorial finite element mode solver (Cosmol Multiphysics). Simulation results show that the three input core modes in single-mode fibers gradually evolve into three supermodes in three-core fiber and then evolve into three low-order modes in the multi-core fiber. Effective indices for different modes are calculated which can depict the evolution process vividly. The results may be useful for practical high power fiber laser systems.
Pumping coupler technology is one of the critical technologies for high power laser and amplifier. Side-pumping
technology can couple pumping beam into inner cladding of the double-clad fiber through the side of the fiber.
Compared to the end-pumping technology by tapered fused bundle (TFB), it has many superiorities. That the signal fiber was not disconnected guarantees high transmission efficiency, providing the possibility of transmitting a high power signal. Additionally, the pump light is coupled into the double-cladding fiber all along the coupler’s body (~5-10 cm long), which reduces the thermal effects caused by leakage of pumping light, resulting in high pump power handling capabilities. For the realization of reliable, rugged and efficient high power fiber amplifiers and fiber laser systems, a novel kind of fused side-pumping coupler based on twisting is developed. The complete simulations were carried out for the process of side-pumping. From detailed information about simulations, we found that the pump efficiencies, one of the vital parameters of pumping coupler, have a significant influence with coupling length, the numerical aperture (NA) and taper ratio of pump fiber. However, the diversification of the parameters drops the high transmission efficiency barely. Optimized the parameters in the simulations, the pump and signal coupling efficiencies are 97.3% and 99.4%, respectively. Based on theoretical analysis, the side-pumping coupler was demonstrated at the pump and signal coupling efficiencies are 91.2% and 98.4%, respectively. This fiber coupler can be implemented in almost any fiber laser or amplifier architecture.
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