Research On The Influence Of Wave-front Aberrations On Intersatellite Laser Link Performance

Inter-satellite optical communication (IOC) is a new and advanced technology of satellite communication, which is an effective method to accomplish satellite communication with high speed. Presently, developed countries, such as America, Europe and Japan, have begun to study the technology of satellite optical communication. American has overcome key problems in the technology made it applicable through 50 years. There are no reports on application plans from Europe and Japan up to now.To establish the laser link which can reach tens of thousands of kilometers, laser communication terminals must have the abilities of beam control with high accuracy, acquisition with high speed, detection with high sensitivity, and tracking and communication with high precision and stability. To insure the above abilities, the requirement to beam quality is very high. Therefore, it is very necessary to study optical field distribution and beam quality.In far field, the distribution of ideal laser beam can be considered to be plane or Gaussian wave. However, due to influence of the surface error of optical elements, machining error of optical system, and space environment, laser beam transmitted by optical antenna is a beam with wave-front aberrations instead of an ideal beam. Wave-front aberrations would influence the intensity distribution of the receiver beam, and then influence beam pointing, acquisition and tracking, resulting in the decline of the stability and even breaking off of laser links. The research on the influence of wave-front aberrations on the link performance of IOC is the basic scientific problem which needs be urgently resolved. Especially, we are concerned with the following four key problems:Establishing the theoretical model for local distortions which appears in optical systems, and solving the problem that the model of Zernike polynomials can not quantitatively analyze the characteristic parameters of local distortion, such as, distortion radius, depth, and position.Establishing theoretical model on which the influence of wave-front aberrations on pointing and tracking errors can be analyzed, and analyzing the effects of the whole and local wave-front deformations on pointing and tracking errors.Establishing the theoretical model on which the influence of wave-front aberrations on antenna receiver energy can be analyzed, and resolving the problem how the whole and local wave-front deformations influence pointing and tracking errors.Establishing theoretical model on which the influence of wave-front aberrations on bit-error-rate (BER) can be analyzed for the condition that satellite flat vibrates, and resolving the problem how the whole and local wave-front deformations influence BER.To reduce the influence of wave-front, conventional method is to develop the machining precision to the best of our ability. Yet, this method will add the difficulty of the research and manufacture of satellite optical communication. By analyzing the influence of wave-front aberrations on satellite laser communication performance, we can obtained the relationship of wave-front aberrations and pointing, acquisition, tracking, and communication performance, which can form the base of optimizing the optical system and proposing effective compensated method. In the dissertation, the influence of wave-front aberrations on laser communication performance is systematically studied, which includes the following four aspects:1. Established the theoretical model for local distortions which appears in optical systems.Local wave-front deformation models, truncated elliptical Gaussian model, for single and multi-local distortions in lenses and reflectors are established, respectively. The models we have proposed define explicitly the characteristic parameters of local distortion, such as, distortion radius, depth, and position, which solves the problem that the model of Zernike polynomials can not quantitatively analyze the characteristic parameters of local distortion.2. Established the theoretical model on which the influence of wave-front aberrations on pointing and tracking errors can be analyzed, and gave the effects of the whole and local wave-front deformations on pointing and tracking errors.Based on the theory of pointing, acquisition and tracking in IOC, and considering the influence of wave-front aberration on beam far-field, aberration pointing error and aberration tracking error are defined, and the theoretical model on which the influence of wave-front aberrations on pointing and tracking errors can be analyzed are established. According to transmission-type and reflector-type antennas, respectively, and related to the theory of laser beam transmission, the effects of whole and local wave-front deformation on pointing and tracking performance are studied. We find that pointing and tracking errors varies periodically with distortion depth, and that the periodicity and the peak positions do not depend on other distortion parameters.3. The theoretical model on which the influence of wave-front aberrations on antenna receiver energy can be analyzed is obtained, and the relationship of wave-front aberrations and antenna receiver energy is given.To evaluate the influence of wave-front aberrations on antenna receiver energy, aberration energy attenuation factor is introduced. According to transmission-type and reflector-type antennas, respectively, and related to the theory of laser beam transmission, the influence of the whole and local wave-front aberrations on antenna receiver energy is studied. We find that antenna receiver energy varies periodically with distortion depth, and that the periodicity and the peak positions do not depend on other distortion parameters.4. Established theoretical model on which the influence of wave-front aberrations on bit-error-rate (BER) can be analyzed for the condition that satellite flat vibrates, and analyzed the influence of whole and local wave-front aberrations on BER.Taking OOK code as an example, the expression of BER is derived under the condition that there are wave-front aberrations in the transmitter beam and other noises are not considered. For the transmitter beam with rotational wave-front, the analytic solution of BER is given, while for the transmitter beam without rotational wave-front, the numerical solution is given by simplifying the model. According to transmission-type and reflector-type antennas, respectively, the influence of the whole and local wave-front aberrations on BER is studied. We find that antenna receiver energy varies periodically with distortion depth, and that the periodicity and the peak positions do not depend on other distortion parameters. It is found that BER changes periodically with distortion depth, and the periodicity and the peak positions do not depend on other distortion parameters.IOC is being innovated and developed quickly. As usual, the development of this technology needs new basic theory. The research work of the dissertation solved the basic theory in IOC, which are the transmission of the beam with wave-front aberrations and the influence of wave-front aberrations on lase link performance of IOC. The research can provide important theoretical evidence for the key technology, such as, pointing, acquisition, tracking and communication, and can establish the basement for optimizing communication systems. Therefore, the results of the dissertation will contribute the development of satellite optical communication.