A side-polished fiber/overlay waveguide architecture and process for non-invasively implementing an optical amplifier are provided for an optical communications system. A "channel" overlay waveguide is employed to constrain for amplification optical energy evanescently coupled to the overlay waveguide from the side-polished optical fiber. The overlay waveguide exhibits a non-linear response of second order, and non-linear frequency conversion is employed to down-convert a high-power, short-wavelength pump signal into the waveguide to amplify the optical energy coupled thereto. The channel overlay waveguide is dimensioned to allow for phase matching between highest order modes of the optical signal within the side-polished fiber optic and the pump signal provided to the channel overlay waveguide. A low-index matching layer is disposed between the channel overlay waveguide and the side-polished fiber optic to facilitate phase matching of the propagation modes. Amplification of optical energy in the channel overlay waveguide is established within a single beat length of evanescent removal to evanescent return of the optical energy to the side-polished fiber optic.