Coupling interactions between the low loss‐modes of dielectric waveguides and the high‐loss modes supported by semiconductor waveguide claddings are of prime importance in the design and fabrication of integrated optical photodetectors and polarizers. It is desirable to maximize energy transfer from dielectric waveguides to semiconductor claddings in order to achieve optimal operation of detectors and polarizers. We have experimentally verified that the intermodal coupling of light from a low‐loss dielectric guiding region to a highly absorbing semiconductor cladding region is periodic as a function of cladding thickness. Results were obtained by theinsitumonitoring of output intensity during the growth and etching of hydrogenated amorphous silicon on polarization‐preserving, D‐shaped, optical fiber. Strong correlation exists between theoretical and experimental results for both TE and TM polarizations. Theinsitu, intensity monitoring technique allows for precise control of attenuation characteristics in clad‐waveguide devices allowing for optimum performance of clad‐waveguide polarizers and detectors.