Optical loss and refractive indices of fluorinated polyimides and copolyimides are studied for application to optoelectronic components. These polyimides and copolyimides are prepared from 2,2-bis(3,4-dicarboxyphenyl)hexafluoropropane dianhydride (6FDA), pyromellitic dianhydride (PMDA), and 2,2’bis(trifluoromethyl)-4,4’-diaminobiphenyl (TFDB). The polyimide 6FDA/TFDB prepared from GFDA and TFDB cured at 350 degrees C has an optical loss of 0.7 dB/cm at 0.63 mu m, and this is the lowest of all polyimides cured at high temperature. Direct measurement of the optical loss of a polyimide at 1.3 mu m was achieved for the first time by using a 6FDA/TFDB block with unequal length, width, and thickness. The optical loss was also low, 0.3 dB/cm. 6FDA/TFDB, PMDA/TFDB, and their copolyimides cured on a silicon substrate at 350 degrees C have two different refractive indices, an in-plane refractive index (n(TE)) and an out-of-plane refractive index (n(TM)). The n(TE) of the copolyimide at 1.3 mu m can be controlled between 1.523 (6FDA/TFDB) and 1.614 (PMDA/TFDB) by changing the 6FDA/TFDB content. It decreases monotonically with increasing 6FDA/ TFDB content. The n(TM), on the other hand, can be controlled between 1.514 (6FDA/TFDB) and 1.521 (copolyimides with 60 mol % 6FDA/TFDB), but it has a maximum value at a 6FDA/TFDB content of 60 mol %. These polyimides and copolyimides prepared on a silicon substrate have birefringences between 0.008 (6FDA/TFDB) and 0.123 (PMDA/TFDB). Low optical loss and precise refractive index control are very important characteristics for optoelectronic components, especially at the telecommunication wavelength of 1.3 mu m.