<title>Bidirectional RF-modulated fiber optic link for intra-satellite communications</title>

Abstract

Use of optical carriers to distribute RF and microwave signals can significantly reduce the size and weight of spacecraft communication systems. Optical carriers can accommodate several RF signals per fiber while permitting noise requirements for communications systems to be met. We previously reported the development of a space-qualified fiber-optic intra-satellite link that meets the requirements on single-side-band phase noise for precision RF signals. The radar altimeter radar chirp signals distributed by these links also meet system requirements. This paper reports our progress in designing a fiber-optic link that transmits RF signals in both directions on the same fiber. Tests at 5, 15, and 80 MHz showed that, for radar altimeter system applications onboard spacecraft, the bidirectional link meets the altimeter RF section's requirements on single-side-band phase noise. However, the severe attenuation requires that the modulated signals be amplified, which may increase the noise levels in the receiver section. Further work is needed to optimize the link for phase noise performance and to address power losses.