| 摘要 |
A planar optical wave guide comprising : (a) a core for light transmission through it comprising a polyimide having repeating units of the formula (I).R = 0-100 mole % of compound (X) and 100-0 mole % of compound (Y) : (b) a cladding comprising a polyimide having repeating units of the formula (II). R2 = 0-100 mole % of compound (X) and 100-0 mole % of compound (Y). R1 and R3 are selected from divalent hydrocarbon radicals; where the refractive index of the core is greater than that of the cladding; and where the difference between the birefringence of the core and that of the cladding is less than the difference between the TM refractive index of the core and that of the cladding, with the proviso that the core polyimide (I) and the cladding polyimide (II) are different and at least one of them is a copolymer containing at least 1 mole % 3,3',4,4'-tetracarboxybiphenyl dianhydride moiety. Also claimed is a polyimide cladding (C) for an optical waveguide which comprises a polyimide comprising the condensation product of 2,2-bis(3,4-dicarboxyphenyl)hexafluoropropane dianhydride (6FDA), 3,3',4,4'-tetracarboxydiphenyl dianhydride (BPDA) and at least one diamine selected from the group consisting of 4,4'-bis(p-aminophenoxy)biphenyl (APBP), 2,2'-bis(4-aminophenyl)hexafluoropropane (BAAF), and 4,4'-oxydianiline, also called 4,4'-diamino-phenyl-ether (ODA). Also claimed is a method for controlling the refractive index and birefringence in an optical waveguide having (a) a polyimide core and (b) a polyimide cladding, each comprising a polyimide which is the condensation product of at least one of 6FDA and BPDA, and at least one aromatic diamine, where the core and/or cladding polyimides contain at least 1 mole % BPDA, which comprises replacing 6FDA in the polyimide, with BPDA in an amount effective to provide a change in the respective refractive indices and birefringences of the core and the cladding such that the refractive index of the core is greater than that of the cladding and the difference in birefringence between core and cladding is less than the difference between the TM refractive index (RI) of the core and the TM RI of the cladding. |
