Effect of cladding layer glass transition temperature on thermal resistance of graded-index plastic optical fibers

The effect of using high-glass transition temperature polymers as the cladding of graded-index plastic optical fibers (GI POFs) on the long-term thermal stability of the fiber attenuation was investigated. Two types of commercial poly(methyl mathacrylate) resins with different glass transition temperature values were used and the long-term thermal reliability of the GI POFs in terms of fiber attenuation was compared. The difference in the cladding glass transition temperature did not affect the original fiber attenuation, as evidenced by the nearly identical spectra. When the GI POFs were exposed to a 105°C environment, which was a temperature similar to the core glass transition temperature the attenuation of the GI POF with the lower glass transition temperature cladding increased abruptly due to light scattering at the corecladding boundary, whereas the attenuation of the other GI POF with the higher glass transition temperature cladding was stable for over 6000 h. These results suggest that the long-term stability of the fiber attenuation does not depend on the core state (glassy or rubbery) but does depend on whether the cladding glass transition temperature is high enough to maintain the original flat, smooth core-cladding boundary.