An optoelectronic feedback structure is introduced to a distributed Bragg reflector mode-locked laser diode (DBR-MLLD) to improve its phase noise performance. Optical pulses with a repetition rate of 40 GHz, a pulse width of 5.2 ps, and a center wavelength tuning range of 4.3 nm are demonstrated. The phase noise of the hybrid mode-locked DBR-MLLD has been reduced by 44 dB to a level of -97 dBc/Hz at a 10 kHz frequency offset from the carrier frequency comparing to the passive mode-locked state.
Mobile, all-fiber Doppler wind lidar based on a real-time motion wind retrieval algorithm method is demonstrated. The mobile wind lidar can negate the influences of attitude, velocity, and other factors on the Doppler frequency and is capable of obtaining more accurate real-time mid- to low-altitude wind field information over a large space. In the moving platform test, the measurement error of the wind speed is 0.33 m / s, and the measurement error of the wind direction is 5.32 deg.
In the past few decades, environmental pollution problems have become more and more serious because of development of modern industry and science technology. The real-time detection and identification of atmospheric pollutants, has aroused widespread concern. Differential Absorption Lidar (DIAL) technology has become a common method for atmospheric remote sensing pollution measurement. 9~11-m-band lasers have small scattering cross sections for the air pollution cloud particles, so the laser output energy is required to reach the Joule level. The system engineering is difficult to realize detection of air pollution clouds with technology. The developed remote sensing pollution detection system is used to detect the types, concentration, orientation and distance information of common industrial chemical pollution. It is mainly divided into two parts: DIAL channel and Front Range Detecting Lidar (FRDL) channel. This paper mainly discusses remote sensing of air pollution clouds using FRDL. The working principle of FRDL is to use the Doppler effect of aerosol on the laser backward Mie scattering to realize the measurement of the aerosol cloud. In July 2017, the verification test was completed at a certain place in the north of China. The simulated pollutant spraying device and sampler were set at 400m in front of the 5km target. The measured results are in agreement with the actual situation.
This paper uses the BP neural network and grey algorithm to forecast and study radar wind field. In order to reduce the residual error in the wind field prediction which uses BP neural network and grey algorithm, calculating the minimum value of residual error function, adopting the residuals of the gray algorithm trained by BP neural network, using the trained network model to forecast the residual sequence, using the predicted residual error sequence to modify the forecast sequence of the grey algorithm. The test data show that using the grey algorithm modified by BP neural network can effectively reduce the residual value and improve the prediction precision.
The communication ways nowadays has highly developed, but because of its using limitation, the application is
restricted, especially under the emergency situations. Using infrared laser non line of sight atmosphere scattering can
solve the difficult problem effectively, and achieve the function of “minimizing communication support”. The article try
to study the 1.06μm laser atmosphere scattering communication, first, we introduce the laser scattering communication
technique and principle, and then describe the system composition and work route. In the way of building the laser
atmosphere scattering communication system math model, the article analyze the relations between the laser receiving
rate and the following elements: laser beam emission angle, receiving field vision, detector sensitivity, emission
inclination angle, receiver inclination, atmosphere attenuation, laser launch rate, and communication distance. Based on the simulations, the field experiment showed, that the 1.06μm infrared laser signals transmission has the probability to achieve the long distance atmosphere scattering communication under certain atmosphere conditions.
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