Development of the Apache Point Observatory Galactic Evolution Experiment (APOGEE) near-infrared spectrograph
has motivated thorough investigation into the properties and performance of optical fibers. The fiber selected for
APOGEE is a step index, multi-mode fiber, developed by PolyMicro, with a 120μm low OH, fused silica core, 25μm
cladding, and 10μm buffer. The instrument design includes a 40 meter fiber run, connecting the spectrograph to the
2.5m Sloan Digital Sky Survey (SDSS) telescope, and an additional 2.5 meter fiber segment located within the
instrument dewar, a vacuum-sealed, cryogenic environment. This light path is convoluted and includes many transitions
and connections where the beam is susceptible irrevocable loss. To optimize the spectrograph performance it is
necessary to minimize the losses incurred in the fiber system, especially those resulting in focal ratio degradation (FRD).
The focus of this research has been to identify potential sources of loss and where applicable, select material components
to minimize this effect. There is little previous documented work concerning the performance of optical fibers within
this wavelength band (1.5-1.7μm). Consequently, the following includes comprehensive explanations of the APOGEE
fiber system components, our experimental design and optical test bed set-up, beam alignment procedures, fiber
terminating and polishing techniques, and results from our examination of FRD as correlated with source wavelength,
fiber length and termination, and environmental conditions.