Abstract

Blazed diffraction gratings are important devices in wavelength division multiplexing optical communication systems. Echelon gratings are used to obtain higher linear dispersion and correspondingly higher resolution. We propose a transreflective blazed grating to achieve further increase in the resolving power. The proposed grating has the same structure as the reflection-type echelon grating except that the angle between the two edges of the groove (blazed angle) is 45° where the horizontal edge is transmissive while the other edge is reflective. For a horizontal illuminating light beam, the light reflected by one (reflective) edge is normally incident on the other (transmissive) edge and passes vertically through the medium of the grating. The optical path difference per step is d = H + nW, where H is the horizontal step size, W is the vertical step size, and n is the refractive index of the grating material. The proposed grating acts as a combination of reflection and transmission type echelon gratings with optical path difference per step of ~H + W or (n – 1)W larger than that of a reflection-or a transmission-type grating of the same size, respectively. Thus, the interference order and the linear dispersion are larger than those of the echelon grating, which results in a much higher channel capacity, arranged side-by-side symmetrically.

© 1991 Optical Society of America