= Optical fiber coupling and bend experiment
MIT's https://ocw.mit.edu/courses/6-161-modern-optics-project-laboratory-fall-2005/862b690eb7d638cd6dd5a063942902af_lab7.pdf[Optical Waveguides and Fibers], Laboratory Exercise No. 7 (Fall 2005), describes a teaching apparatus. A cleaned, flat-ended <multimode optical fiber> receives <helium>–<neon> <laser> <light> through a microscope objective <optical lens>; a micropositioner aligns the input. The launch deliberately overfills the fibre's cone. A <beam splitter> sends a sample to a reference <photodetector> to track <laser> fluctuations. The fixed output faces a screen or a <photodetector> on a rotation stage with angular <measurement calibration>. Readings every two degrees, divided by simultaneous reference readings, give an angular profile. Repeating with an underfilled launch is a control: too few excited <normal modes> underestimate <numerical aperture>. Optional index-matching fluid removes cladding-carried <light>. Bending the fibre reveals leakage and reduced output on an <oscilloscope>. The handout supplies no measured trace or absolute detector <measurement calibration>, and this angular scan does not determine loss per kilometre.<Optical Waveguides and Fibers (MIT 6.161 laboratory exercise)>[Optical Waveguides and Fibers, MIT 6.161 Modern Optics Project Laboratory, Fall 2005, Laboratory Exercise No. 7, pp. 3 and 6–7, end-face preparation, §7.3 and Fig. 1: reference-normalized angular scan, underfill control and bend test]{ref}
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