Realization of heterodyne acquisition and tracking with diode lasers at lambda=1.55 um

摘要

We designed, realized, and tested a laboratory model of an optical intersatellite link employing InGaAs DFB semiconductor lasers operating at a wavelength of 1.55 micrometers. Heterodyne sensing was used for both the spatial acquisition and the spatial tracking processes. During the acquisition process spiral scanning of the transmitter area of uncertainty is performed. A microcomputer controls the receiver operation. For each spatial search position the local oscillator laser is swept through a predefined frequency uncertainty range until the beat signal appears at the desired intermediate frequency. A heterodyne quadrant detector was realized by using a four-sided reflecting pyramid to split the superimposed beam. During tracking, the microcomputer reads the tracking sensor output signals, calculates the required antenna correction, and feeds the appropriate signals to the beam steering unit. Thus we realized a digital tracking loop, whereas the intermediate frequency is stabilized by means of an analog control loop. The tracking sensor angular resolution, without using a telescope, is 5 micron rad. The typical tracking error measured for various system conditions amounts to less than 1/20 of the FOV, i.e., less that plus/minus 25 micron rad.