GLAS is a satellite laser altimeter designed to measure ice-sheet topography and cloud and atmospheric properties. The onboard Nd:YAG laser emits 1064nm and (frequency doubled) 532nm light, which is reflected from the Earth and atmosphere and collected by a telescope. A small portion of the light emitted toward the Earth is picked off by a free space to fiber optic coupling system and routed around the instrument by connectorized fiber optic cables. There is also a 2 km fiber optic delay line to provide for onboard timing calibration, a fiber optic pigtailed diode laser onboard test source and a fiber optic connectorized LED onboard test source. The stability of the signals through the fiber optic system must be maintained to 10% in amplitude and 20ps in timing for certain critical signal paths. It has been challenging to meet these requirements with the spacecraft resources available. Components from many commercial vendors have been used to satisfy these requirements. The system design, components selected and testing performed will be discussed in this paper.