Research On The Key Technology Of ATP For Optical Wireless Communication

Acquisition tracking and pointing (ATP) as the key technology is becoming more and moreprominent. The position sensitive detector (PSD) is used to keep the ATP system provide highaccuracy and alignment of the communication target to adjust the beam. By the analysis, to improvethe accuracy of PSD detector it is necessary to overcome the problem of background lightinterference.In this thesis, the author has a depth discussion on the approach to eliminate background lightinterference of PSD detector. After the analysis of the working principle of PSD and the relationshipbetween the signal light and background light, the author gives two methods.The first method to eliminate background light interference is based on SPPs. By designing anoptical filter based on the principle of Kretschmann structure and simulating on finite defferencetime domain (FDTD) and Numerical Analysis. The simulation results show the visible light’sElectromagnetic field strength is between104-103A/m, even the largest value is less than101A/m after the optical filter. However the light at wavelength of850nm coupling efficiency isapproximately85%and the Extinction ratio is almost25dB. The result verified the optical filterdesigned based on the theory of SPPs can effectively eliminate PSD detector background lightinterference.The second method is based on BP Neural Networks. By designing a Neural Networksincluding two input layers one hidden layer and two output layers; it is trained in Improved BPAlgorithm (L-M Algorithm). The simulation result shows network output relative tolerance is lowerthan0.03%and the network has a good generalization ability. After the neural networkcompensation PSD detector overcomes the interference of background light, the detection accuracyand reliability are improved.The method to eliminate background light interference is based on SPPs is a new idea to makefilter, while the method based on BP Neural Networks is not influenced by the different types ofbackground light, which has some practical value.