Optical waveguide coupling ratios can be modified for a package by providing a substrate with a photonic circuit disposed on a first section of the substrate and a plurality of optical waveguides formed in glass disposed on a second section of the substrate, the waveguides being connected to the photonic circuit, adjacent ones of the waveguides having a fixed coupling ratio. A three-dimensional region of the glass abutting an end of one or more of the waveguides is lased to change a refractive index of the glass in each three-dimensional region, and thereby extend a length of each waveguide abutting one of the three-dimensional regions so that the coupling ratio between that waveguide and an adjacent waveguide is changed as a function of the extended length. The lasing is controlled based on feedback so that each coupling ratio changed by the lasing varies by less than a target amount.