In this paper, we give the far-field diffraction theory for calculating the divergence by using the superposition of Gaussian beams instead of the aperture function and obtain the explicit express for calculating the beam divergence. We analyze in detail the influence of the diffraction adding defocus aberrations upon the transmitter's divergence and get the simulated result. These researches are useful to system design and give us some suggestions of avoiding the influence of the aberrations and the diffractions on the transmitter.
In the field of intersatellite communication, laser beam transmitted from the optical terminal is required to be highly collimated with diffraction-limit divergence. Then, the maximal wavefront aberration at the edge of exit pupil is about 0.3λ. In order to measure the diffraction-limit wavefront, we present a whole-field double-shearing interferometer based on double-shearing theory. In this paper, firstly, the principle and configuration of the interferometer is introduced. Then the theory of double shearing is discussed. At the same time, we extend the applications of the interferometer. Lastly, we present the simulations of interference fringes with different primary aberrations and give the experimental results for the measurement of diffraction-limit wavefront.
In this paper, a subsystem of coupling semiconductor laser diode to the single-mode fiber and producing the diffraction-limited beam is described in detail, and beam wavefront is measured by a double shearing-interferometer experimentally. As a result, the divergence of the collimated beam is only 65.84μrad, which indicates that the transmitted beam achieves the diffraction-limited, and this optical subsystem is coincident very well with our design.
Because PAT (pointing-acquisition-tracking) parameters and integrated technical specifications of laser communication terminals for inter-satellite link must be pre-verified and assessed thoroughly on a ground-based test-bed before launched into the space, it is necessary to develop a system as a primary part of the test bed to simulate the relative trajectory between the satellites. In this paper, an original high-precision satellite relative-trajectory simulating servosystem is introduced in detail as well as its structures and characteristics. The system is used to simulate the motion of relative-trajectory between satellites in different orbits. The principle of the system is to import the data of two satellites’ orbits into a computer-based control system in advance. After processed and analyzed, the data is transformed into the angular displacement of the servomotor which drives the gimbal directly. The angular displacement of the two axes of the gimbal can simulate precisely the relative-trajectory, namely elevation angle and azimuth angle of the two satellites in communication. A laser communication terminal mounted on the gimbal then performs the PAT mechanisms to evaluate the system’s capacity.
The support schemes and thermoelastic deformation of 460-mm diameter interferometer mirrors are studied by means of finite element method. The surface deformation and stress distribution in a variety of support schemes are analyzed. By comparison, the band support with 180°wrap angle and a dentiform rubber-lined strip is accepted to be the optimum. In the optimal support scheme, the thermoelastic deformation analyses for mirrors are carried out at specified thermal gradients (axial, radial, circumferential temperature differences). The contours of surface deformation and the transmitted wavefront distortion are presented respectively. According to the results, it is clear that the influence of thermal effects is much greater than the ones of mechanical forces. Lastly, some suggestions are given to eliminate the effects of thermal turbulence.