Abstract: A single or multilayer optical interference filter and method of forming filter by ion implantation. One or more layers of nitrogen ions are implanted into a single crystal silicon with the crystal at a temperature of from about 600.degree. C. to about 1000.degree. C. The implanted ions create a buried layer(s) of silicon nitride (Si.sub.3 N.sub.4) whose refractive index is substantially different from that of silicon (Si) such that appreciable multiple reflection of incident light occurs between the buried layer(s) and the front surface. The resulting interference maxima and minima in transmitted or reflected light which occur at well-defined positions in wavelength may be controlled both in amplitude and wavelength position. The ions may be implanted in layers at different depths to produce a "thin film" interference filter.