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We report the growth of GaAs/AlGaAs core-shell nanowire ensembles grown on p- and n-doped GaAs substrate respectively and the fabrication of these nanowire photodetectors. The I-V characteristics and spectral response of both detectors were investigated by comparison.
The sufficient condition for Gaussian Schell-model (GSM) beam to keep the polarization properties unchanged for a space-to-ground optical communication downlink is derived analytically. The results indicate when three coherence lengths (δxx, δyy and δxy) are equal to each other, the GSM beam maintains the polarization properties on propagation
Atmospheric turbulence leads to a stochastic process of optical intensity and phase of beam. Thus, errors of departure angle detection are induced. In the paper, a new method to modify of departure angle detection is introduced to Free Space Optical Communications. Based on the phase retrieval, the new method only needs the intensity of the image on the focal plane to calculate the revising phase...
Heterodyne efficiency in free-space optical communications based on heterodyne detection is degraded by the aberrations of the optics antenna used for reception of optical beams. The evolution of heterodyne efficiency with the change of rms of primary aberrations is investigated. It is shown that heterodyne efficiency decreases gradually with increasing primary aberrations. The comparison shows that...
In this paper, the synergy of the channel coding and aperture averaging is applied to the downlink optical channel for the low earth orbit (LEO) satellite. Bit error rates (BER) of the convolutional code and low-density parity code (LDPC) are evaluated versus different diameters for the optical systems with avalanche photodiode (APD) receivers. Results indicate that when the temporal correlation time...
Optical pulse temporal spreading can restrict the capability of space optical communication. This paper provides most of the details of Monte Carlo simulation method about pulsed laser propagation in inferior atmospheric layer. Several conclusions of this work are obtained. One is that the temporal spreading of pulsed laser is strongly influenced by propagation length and aerosol concentration. Another...
Based on the complementation of advantages and disadvantages of genetic algorithms (GA) and neural network (NN), a new hybrid genetic algorithms and neural network model (GANN) is presented in this paper. In this model, the relationship model is established by error back propagation network (BP), the connection weights and thresholds of BP are optimized by GA, and then the precision of model is increased...
In this paper, we discuss feasibility of the concept that the effect of angle of arrival fluctuation can be taken as an effective simulation of satellite platform vibration in the ground test process of PAT system for a laser satellite communication system. Spectrum characteristic of satellite platform vibration is introduced, referring to the model used by the European Space Agency (ESA) in design...
The image of a beacon on the photosensitive plane of pointing sensor in a receiving terminal is usually considered as the acquisition and tracking target of optical antenna for the Free Space Optical Communications (FSOC). The receiver processes the acquired image to ascertain the position of the transmitting terminal by the relevant algorithm. The tracking veracity of the algorithm to a target position...
Wavelet model is built to depict the diversified wave-front distortion. Compared to Gaussian model, the effect on pointing error is analyzed. For it is difficult to detect the wave-front distortion to the receiver, especially for long distance, a near field center power measurement method is proposed.
We propose a novel fractional Fourier transform named M-parameter fractional Fourier transform (MPFRFT), and using this MPFRFT algorithm successfully acquire a new image encryption method. This MPFRFT is not only a fractionization of Fourier transform, but also an extension of four-item weighted fractional Fourier transform defined by Shih, and it owns four free parameters in the weight coefficients...
We first give a new fractionalization of discrete cosine and sine transforms of types I, IV, V and VIII. The fractional discrete cosine and sine transforms with four random parameters are defined, to which we refer as random fractional discrete cosine and sine transforms. A novel image encryption algorithm based on random fractional discrete cosine or sine transform and random phase encoding technique...
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