Compositionally inhomogeneous dielectric layers are realized by plasma-enhanced chemical vapor deposition (PECVD) growth of silicon oxynitride (SiON) layers. The gases used for growing inhomogeneous SiON layers are silane (SiH4), nitrogen (N-2) and nitrous oxide (N2O). The flow rates of SiH4 and N-2 are kept constant and real-time control of the N2O flow rate is achieved using a Techware PAL-68000 process controller. Linearly graded and superlattice-like SION layers with refractive indices varying from 1.46 to 2.05 are designed and fabricated. The compositional profile is analyzed by Auger electron spectroscopy sputter profiling. A ten-period rugate filter is designed and fabricated. Possible applications of inhomogeneous dielectric layers grown by PECVD include various kinds of optical filters and planar optical waveguides.