The fabrication process of waveguide grating couplers with parallelogramic tooth profiles is described, using a novel reactive‐ion etching (RIE) geometry to generate oblique anisotropic etching. The blazing effect of nonresonant parallelogramic grating couplers is demonstrated experimentally, with nearly 90% radiation directionality measured. The radiation factors of the grating couplers are also measured, and comparisons with simulated results show that the measured value is lower than that predicted theoretically. This is attributed to the deviation of the grating tooth profile from the ideal parallelogramic shape. © 1996 Society of Photo−Optical Instrumentation Engineers.