OPTICAL ATTENUATION IN PLANAR WAVE-GUIDES OF UNIDIRECTIONALLY ORIENTED COPOLYESTER FILM

The in-plane optical loss was correlated with molecular orientation in a unidirectionally stretched poly(ethylene terephthalate-co-isophthal ate) copolyester film. X-ray scattering was applied to ascertain the a nisotropic and amorphous natures of the stretched film. The film was a dhered onto a silicon wafer to fabricate a planar waveguide. Multiple TE and TM propagation modes were obtained on the planar waveguide usin g a prism coupler at 632.8 nm yielding in-plane refractive indices of 1.6545 and 1.5464, parallel and transverse to the stretch direction, r espectively. For each waveguide mode, a propagation streak was generat ed and registered on photographic film. The in-plane linear attenuatio n coefficient, alpha(parallel to)={ln[I(O)/I(x(parallel to))]}/x(paral lel to), was derived from the propagation streak. The optical path of each mode was determined and used to normalize alpha(parallel to). For the TE modes, alpha(parallel to) increased with the mode number and w as highly anisotropic, i.e., alpha(parallel to) (parallel to the stret ch direction)<alpha(parallel to) (transverse to the stretch direction) . However, for the TM modes, alpha(parallel to) was found to be a cons tant smaller than those of the TE modes, and was independent of mode n umber as well as molecular orientation. The bulk ail was extrapolated to remove the surface loss contributions for the planar waveguide. Dip ole interaction between the stretched copolyester, surface irregularit ies, and the TE or TM polarization was analyzed to delineate the in-pl ane optical loss behavior. (C) 1996 American Institute of Physics.