Aerospace: science and technology including aeronautics (atmospheric transportation) and space (transportation outside of atmosphere or interplanetary).
Optical fiber is generally used for point to point link. One side is connected to a laser and the other side to a lens or a collimator adapted to free space transmission.
Examples: Atomic clock PHARAO, MTG, SWARM.
The technical constraints besides optical system definition comes from the necessity to cope with vibration, acceleration and outgassing on a mixed fiber and free space system.
Typically a fiber optic bundle designed to transmit the light between the focal point of a space telescope and a spectrometer. (see documentation on Astronomy / Telescope)
Examples: BepiColombo PHEBUS, R&T II.
Technical constraints are numerous. They include the problematic of ground telescopes, reliability, focal ration degradation as low as possible, percentage of broken fibers<1%, plus all constraints of space conditions, weight, low outgassing, radiation resistance, temperature range, acceleration, vibrations.