An optical planar wavelength selective filter is formed on a printed circuit substrate. Low optical loss polymers are used to make a layered structure that contains waveguides and free travel zones. A diffraction grating is strategically placed on the printed circuit substrate so that light from one waveguide is diffracted by the grating to exit the free travel zone and pass through the other waveguides. The low optical loss polymer is a reaction product of the hydrolysis and polycondensation reaction of organically functionalized alkoxysilanes. With a proper grating, the apparatus can be used as an optical triplexer at frequencies of 1310, 1490, and 1550 nanometers.