Role of Ampliied Spontaneous Emission in Optical Free-space Communication Links with Optical Ampliication { Impact on Isolation and Data Transmissionn Utilization for Pointing, Acquisition, and Tracking

We investigate the role of ampli ed spontaneous emission (ASE) produced by an optical booster ampli er at the transmitter of free-space optical communication links. In a communication terminal with a single telescope for both transmission and reception, this ASE power has to be taken into account in connection with transmit-to-receive channel isolation, especially since it partly occupies the same state of polarization and the same frequency band as the receive signal. We show that the booster ASE intercepted by the receiver can represent a non-negligible source of background radiation: In a typical optical intersatellite link scenario, the ASE power spectral density generated by the booster ampli er at the transmitter and coupled to the receiver will be on the order of 10 W=Hz, which equals the background radiation of the sun. Exploiting these ndings for pointing, acquisition, and tracking (PAT) purposes, we describe a patent-pending PAT system doing without beacon lasers and without the need for diverting a part of the data signal for PAT. Utilizing the transmit booster ASE over a bandwidth of e.g. 20nm at the receiver, a total power of about 46dBm is available for PAT purposes without extra power consumption at the transmitter and without the need for beacon laser alignment.