<title>Design of a 2.5-Gbps optical transmitter for the International Space Station</title>

A high data rate laser transmitter assembly (LTA) has been designed as the source for an optical free-space communication link between the International Space Station and the 1-meter Optical Communication Telescope Laboratory (OCTL) to be built at the Table Mountain Facility (TMF, Wrightwood, CA). the transmitter design concept uses a fiber-based master oscillator power amplifier (MOPA) configuration with an average output power of 200 mW at a 1550 nm transmit wavelength. This transmitter source is also designed to provide a signal at 980 nm to the silicon-based focal plane array for the point-ahead beam control function. This novel integration of a 980 nm boresight signal allows the use of silicon based imagers for the acquisition/tracking and point- ahead functions, yet permits the transmit signal to be at any wavelength outside the silicon sensitivity. The LTA, a sub- system of the Flight Terminal, has been designed to have a selectable data rate from 155 - 2500 Mbps in discrete steps. It also incorporates a 2.5 Gbps pseudo-random bit sequence (PRBS) generator for complete link testing and diagnostics. The design emphasizes using commercial off the shelf components (COTS).