  When gravitational waves travel from their source to an observer, they
interact with matter structures along their path, causing distinct deformations
in their waveforms. In this study we introduce a novel theoretical framework
for wave optics effects in gravitational lensing, addressing the limitations of
existing approaches. We achieve this by incorporating the proper time
technique, typically used in field theory studies, into gravitational lensing.
This approach allows us to extend the standard formalism beyond the eikonal and
paraxial approximations, which are traditionally assumed, and to account for
polarization effects, which are typically neglected in the literature. We
demonstrate that our method provides a robust generalization of conventional
approaches, including them as special cases. Our findings enhance our
understanding of gravitational wave propagation, which is crucial for
accurately interpreting gravitational wave observations and extracting unbiased
information about the lenses from the gravitational wave waveforms.
