BLAZED BINARY SUBWAVELENGTH GRATINGS WITH EFFICIENCIES LARGER THAN THOSE OF CONVENTIONAL ECHELETTE GRATINGS

We introduce a new structural cutoff beyond which subwavelength gratin gs cease to behave as homogeneous media and discuss its effects on the proper selection of the sampling periods of subwavelength diffractive elements. According to this analysis, a 3 lambda-period blazed binary grating composed of square pillars is designed for He-Ne operation an d is fabricated by etching of a TiO2 layer deposited upon a glass subs trate. Its first-order measured diffraction efficiency is 12% larger t han the theoretical efficiency of an ideal blazed echelette grating in glass with the same period. (C) 1998 Optical Society of America.