Liying Tan

Log-amplitude variance for a Gaussian-beam wave propagating through non-Kolmogorov turbulence

In the past decades, both the increasing experimental evidences and some results of theoretical investigation on non-Kolmogorov turbulence have been reported. This has prompted the study of optical propagation in non-Kolmogorov atmospheric turbulence. In this paper, using a non-Kolmogorov power spectrum which owns a generalized power law instead of standard Kolmogorov power law value 11/3 and a generalized amplitude factor instead of constant value 0.033, the log-amplitude variances for a Gaussian-beam wave are derived in the weak-fluctuation regime for a horizontal path. The analytic expressions are obtained and then used to analyze the effect of spectral power-law variations on the log-amplitude fluctuations of Gaussian-beam wave.

Influence of beam wander on bit-error rate in a ground-to-satellite laser uplink communication system

Based on weak fluctuation theory and the beam-wander model, the bit-error rate of a ground-to-satellite laser uplink communication system is analyzed, in comparison with the condition in which beam wander is not taken into account. Considering the combined effect of scintillation and beam wander, optimum divergence angle and transmitter beam radius for a communication system are researched. Numerical results show that both of them increase with the increment of total link margin and transmitted wavelength. This work can benefit the ground-to-satellite laser uplink communication system design.

On Bandlimited Signals Associated With Linear Canonical Transform

We first show that the bandlimited signals associated with linear canonical transform (LCT) form a reproducing kernel Hilbert space. An orthogonal basis for the class of bandlimited signals associated with LCT is then proposed by use of the reproducing kernel, with respect to which the coordinates of signal are actually values taken by the signal at certain instants of time. Finally, a nonuniform sampling theorem for bandlimited signals associated with LCT is presented.

Experimental investigation of radiation effect on erbium-ytterbium co-doped fiber amplifier for space optical communication in low-dose radiation environment

High power erbium-ytterbium co-doped fiber amplifier (EYDFA) has been radiated to the dose of 50 krad at the dose rate of 40 rad/s. Some key parameters have been measured to investigate the radiation effect on the EYDFA for space optical communication. Considering the dose of 50 krad is big enough to the most of low-dose radiation environment, these experimental results will be a good reference for the low-dose inter-satellite optical communication designers.

Measurement of optical intensity fluctuation over an 11.8 km turbulent path

An 11.8km optical link is established to examine the intensity fluctuation of the laser beam transmission through atmosphere turbulence. Probability density function, fade statistic, and high-frequency spectrum are researched based on the analysis of the experimental data collected in each season of a year, including both weak and strong fluctuation cases. Finally, the daily variation curve of scintillation index is given, compared with the variation of refractive-index structure parameter C(n) (2), which is calculated from the experimental data of angle of arrival. This work provides the experimental results that are helpful to the atmospheric propagation research and the free-space optical communication system design.

Temporal-frequency spectra for optical wave propagating through non-Kolmogorov turbulence

Nowadays it has been accepted that the Kolmogorov model is not the only possible turbulent one in the atmosphere, which has been confirmed by the increasing experimental evidences and some results of theoretical investigation. This has prompted the scientist community to study optical propagation in non-Kolmogorov atmospheric turbulence. In this paper, using a non-Kolmogorov power spectrum which has a more general power law instead of standard Kolmogorov power law value 11/3 and a more general amplitude factor instead of constant value 0.033, the temporal power spectra of the presentative amplitude and phase effects, irradiance and angle of arrival fluctuations, have been derived for horizontal link in weak turbulence. And then the influence of spectral power-law variations on the temporal power spectrum has been analyzed. It is anticipated that this work is helpful to the investigations of atmospheric turbulence and optical wave propagation in the atmospheric turbulence.

Reconstruction of Bandlimited Signals in Linear Canonical Transform Domain From Finite Nonuniformly Spaced Samples

We investigate the reconstruction of bandlimited signals in the linear canonical transform (LCT) domain from a finite set of nonuniformly spaced samples. Based on the reproducing property of the reproducing kernel belonging to the class of bandlimited signals in LCT domain, we derive an interpolating formula with minimum mean-squared error that interpolates the finite set of nonuniformly spaced samples, and show that it is identical to the minimum energy bandlimited in LCT domain interpolator. Singular value decomposition is also used to set up a reconstruction algorithm which guarantees that the reconstruction result also achieves the minimum energy reconstruction.

Deficiencies of the cryptography based on multiple-parameter fractional Fourier transform

Methods of image encryption based on fractional Fourier transform have an incipient flaw in security. We show that the schemes have the deficiency that one group of encryption keys has many groups of keys to decrypt the encrypted image correctly for several reasons. In some schemes, many factors result in the deficiencies, such as the encryption scheme based on multiple-parameter fractional Fourier transform [Opt. Lett.33, 581 (2008)]. A modified method is proposed to avoid all the deficiencies. Security and reliability are greatly improved without increasing the complexity of the encryption process.

Generalized Prolate Spheroidal Wave Functions Associated With Linear Canonical Transform

Time-limited and (a, b, c, d)-band-limited signals are of great interest not only in theory but also in real applications. In this paper, we use the sampling theorem associated with linear canonical transform to investigate an operator whose effect on a signal is to produce its first time-limited then (b, b, c, d)-band-limited version. First, the eigenvalue problem for the operator is shown to be equivalent to a discrete eigenvalue problem for an infinite matrix. Then the eigenfunctions of the operator, which are referred to as generalized prolate spheroidal wave functions (GPSWFs), are shown to be first, orthogonal over finite as well as infinite intervals, and second, complete over L2(-L, L) and the class of (a, b, c, d)-band-limited signals. A simple method based on sampling theorem for computing GPSWFs is presented and the definite parity of GPSWFs is also given. Finally, based on the dual orthogonality and completeness of GPSWFs, several applications of GPSWFs to the representation of time-limited and (a, b, c, d)-band-limited signals are presented.

Pointing and tracking errors due to localized distortion induced by a transmission-type antenna in intersatellite laser communications

A truncated ellipse Gaussian model to express localized distortion is developed to a transmission-type optical antenna, based on which the effects of localized deformation on pointing and tracking errors are researched. It is shown that localized distortion has the greatest influence on pointing and tracking errors when distortion deepness h approximately 0.8 lambda, which does not depend on other distortion parameters. To reduce the impact of localized deformation on pointing and tracking errors, the machining precision of the objective lens of the transmission-type antenna should be much better than 0.8 lambda. The requirement of the machining precision for lenses is lower than that for mirrors. The maxima of pointing and tracking errors due to the localized distortion with different radii are given. We hope the results can be used in the design of intersatellite optical communication systems.