Although there is an urgent demand, it is still a tremendous challenge to use the coherent optical communication technology to the satellite-to-ground data transmission system especially at large zenith angle due to the influence of atmospheric turbulence. Adaptive optics (AO) is a considerable scheme to solve the problem. In this paper, we integrate the adaptive optics (AO) to the coherent laser communications and the performances of mixing efficiency as well as bit-error-rate (BER) at different zenith angles are studied. The analytical results show that the increasing of zenith angle can severely decrease the performances of the coherent detection, and increase the BER to higher than 10, which is unacceptable. The simulative results of coherent detection with AO compensation indicate that the larger mixing efficiency and lower BER can be performed by the coherent receiver with a high-mode AO compensation. The experiment of correcting the atmospheric turbulence wavefront distortion using a 249-element AO system at large zenith angles is carried out. The result demonstrates that the AO system has a significant improvement on satellite-to-ground coherent optical communication system at large zenith angle. It also indicates that the 249-element AO system can only meet the needs of coherent communication systems at zenith angle smaller than 65̊ for the 1.8m telescope under weak and moderate turbulence.
The energy efficiency of MIMO transmissions in wireless sensor networks is analyzed considering the trade-off between diversity and multiplexing gains. Various MIMOs are studied with noncooperative, half-cooperative or cooperative realizations. Energies consumed in transmission, processing circuitry and cooperation are obtained, which show that the optimal energy efficiency requires both the diversity and the multiplexing gains be exploited.
All-optically controlled nanoparticle manipulating units based on optical waveguide intersections are designed and their performance on nanoparticle trapping, redirecting, sorting and binding force measurement are theoretically analyzed. Our calculation shows that these simple units have trapping abilities comparable with most near field trapping tools and are capable of realizing multiple sorting and analyzing functions.
The vortex beams carried Orbital Angular Momentum (OAM) have recently generated considerable interest due to their potential used in communication systems to increase transmission capacity and spectral efficiency. In this paper, the distorted wavefront detection based on Shack–Hartmann wavefront sensor (HWS) for the vortex beams is investigated. The detection slope of the helical phase sub-spot pattern is used as the calibrated slope zero point, and then the distortion phase of the vortex beam is detected by the HWS. Simulation and experimental results demonstrate that this method can detect the distortion phase of vortex beam with high precision and high frame rate, which is expected to accelerate the application of optical communication systems with vortex beams.
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