Wide-Field-of-Regard Pointing, Acquisition and Tracking-System for small Laser Communication Terminals

Abstract

Pointing, Acquisition and Tracking (PAT)-systems are one of the central parts of a Laser Communication Terminal. In Laser Communication Terminals a staggered PAT-system consisting of Coarse Pointing Assembly (CPA) and Fine Pointing Assembly (FPA) is common. The CPA provides a Wide-Field-of-Regard (FoR) and the FPA a precise and fast alignment of the beam to the communication partner. The disadvantage is the mechanical complexity. This paper presents the development challenges of a Wide-Field-of-Regard PAT-system for small Laser Communication Terminals by combining and miniaturizing the functionality of the CPA and FPA to a single actuator.

To get a small and lightweight Wide-Field-of-Regard PAT-system, the number of moving parts has to be minimized. Therefore, the system consists of an optical setup that provides a large Field-of-View (FoV) and one single mirror actuator for beam steering – thus, CPA and FPA can be combined in just one moving component. The actuator is controlled by a Digital Signal Processor (DSP). The tracking sensor is a 4-Quadrants-Detector (4QD). During the acquisition mode, the actuator moves in a predefined scan pattern until a signal can be detected on the 4QD. Consequently, the system changes to tracking mode.

Our design approach succeeded in a FoR of more than 45° without a traditional CPA. The scan time for the complete FoR is less than 1 second. The block diagram and measurements taken with the prototype in the laboratory will be presented in this paper.