| Astrophysics (Index) | About |
The term fiber positioner can refer to a mechanical instrument that positions optical fibers (long strands of glass which can carry light) for use in a multi-object spectrograph, placing it so that light from the image of a particular object on the focal plane is carried to a spot along the line in a spectrograph where the light is split by wavelength, i.e., the spectrograph's slit (or its line corresponding to such a slit). Thus, objects spread out over the image at the focal plane are lined up in a row so that spectrograph can spread their spectrums, resulting in a bunch of spectrums laid out in parallel, which a CCD or similar sensor can record.
The task of positioning the fibers has been carried out by hand, which is time-consuming, requires very precise work, and spectrographs now exist that can observe hundreds of objects simultaneously, demanding a lot of such work for each such observation, making mechanical positioners a natural development, given current technology. The APOGEE spectrograph used by the Sloan Digital Sky Survey originally depended upon staff to position fibers, using pre-created aluminum plates with carefully positioned holes (plug plates, which were created using automated hole positioning). The spectrograph's fiber positioning has since been automated. Some other robotic fiber positioners:
Naturally the term fiber positioner could also refer to a person tasked with the positioning (like the word computer, which earlier referred to a person who calculates, by hand or with a calculator). Outside outside astronomy, fiber positioner can refer to devices that line up optical fibers end-to-end, such as for communication.