A linear fluorinated bis-phenol-A novolac resin
(LFAR) for optical waveguide was synthesized based on
4,4
-(hexafluoro-isopropylidene)diphenol, epoxy chloropropane
and formaldehyde. Negative fluorinated photoresist
(FP) was made by composing the LFAR, diphenyl iodonium
salt and solvent. The film, which was made by spincoating
FP, had good UV light lithograph sensitivity, large
hardness and high glass transition temperature (Tg > 170°C,
after crosslinking). Low-loss optical waveguides with very
smooth top surface were fabricated from the resulting FP
by direct UV exposure and chemical development. For
waveguides without upper cladding, the propagation loss of
the channel waveguides was measured to be 0.21 dB/cm at
1550 nm.