New insights into dopant design for graded-index plastic optical fibers for transmission at 850 nm

• Aromatic chlorinated dopants for GI POFs for transmission at 850 nm were prepared.
• Optical properties of doped poly(pentafluorostyrene) were examined.
• Doped poly(pentafluorostyrene) showed no absorption losses at 850 nm.
• Doped poly(pentafluorostyrene) also satisfied numerical aperture requirement.
• Thermal stability of poly(pentafluorostyrene) was not affected by the dopants.

To develop graded-index plastic optical fibers (GI POFs) which can be utilized for transmissions at 850 nm, not only do molecular vibrational absorptions of the base polymeric materials need to be considered, but also the dopants used. In this study, chlorinated aromatic dopants were synthesized and their effects on the optical and thermal properties of poly(pentafluorostyrene), which has the low-loss window at 850 nm, were studied. The polymers doped with chlorinated dopants showed no absorption peak and retained the broad windows around the source wavelength. Furthermore, they showed higher glass transition temperatures when compared at similar refractive indices than the polymer doped with diphenyl sulfide, which is the most common dopant for acrylates and styrenes-based GI POFs. However, as the chlorine content per dopant molecule increased, the compatibility with the base material became worse and the doped polymer exhibited a higher attenuation due to an increment of light scattering.

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