A rear-projection photodetection yarn clearing apparatus includes a light emitting diode and a detector arranged behind a to-be-detected yarn, and further includes a reflector arranged in front of the to-be-detected yarn. A front end face of the light emitting diode is flush with a photosurface of the detector, a light filter for capturing light rays having a waveband from 330 nm to 470 nm is also arranged in front of the light emitting diode and the detector, and a light-reflecting surface of the reflector is in parallel with the photosurface of the detector. The light emitting diode includes an ultraviolet light emitting diode, and the detector includes an ultraviolet enhanced silicon photodiode. The ultraviolet enhanced silicon photodiode is made from a high-resistivity N-type (111) silicon wafer having a resistivity of 3,000 .Math.cm and a field oxide thickness of 1,000 nm.

The present invention relates to a fiber production system (1) and production method which enables heat treatment applied during fiber production to be performed as applying laser on the fiber. The objective of the present invention is to provide a fiber production system (1) and production method which enables to perform momentary heat treatment on the filament (F) via laser beam (L) and which eliminates defected points in the filament structure by heating fast and drawing in fiber production.