Low−loss single−mode optical waveguides (∼4×1.5 &mgr;m), optical directional couplers, and grating couplers were made by the photolocking process in a new high−resolution system using naphthalenethiol as the dopant. Index changes of up to 1.3% and optical losses typically 0.3 dB/cm were achieved (at &lgr;=633 nm). The directional couplers had coupling lengths as short as 150 &mgr;m, with virtually complete transfer of the guided energy from one guide to another. Grating couplers were written in which the bulk index of the guiding film is spatially modulated with periods as short as 0.28 &mgr;m, giving coupling strengths of up to 15 dB/cm.