Fluorinated ether ketone oligomers bearing a crosslinkable ethynyl group at the chain end have been investigated for low-loss polymer optical waveguide devices. These oligomers are designed to achieve low birefringence and were synthesized by the reaction of 4,4'-(hexafluoroisopropylidene)diphenol with an excess decafluorobenzophenone, followed by reaction with (phenylethynyl)phenol or ethynylphenol. The molecular weights (M(n)s) and polydispersities of the oligomers determined by GPC with polystyrene standard are in the range of 6600-8500 g/mol and 1.79-2.04, respectively. By spin coating and thermal crosslinking, the polymer solutions easily provide the good optical quality thin films. The cured films show good chemical resistance and high thermal stability up to 460 degrees C under nitrogen. At 1.55 mu m wavelength, the refractive index and birefringence of the films show in the range of 1.5104-1.5172 and 0.0078-0.0014, respectively. The propagation loss of the single-mode channel waveguide was measured to be less than 0.5 dB/cm at 1.55 mu m.