Patent ID: 6490089
Filing Date: 2002-12-03
Classification: G02B

Abstract:
A diffraction grating for diffracting an optical signal of wavelength &lgr; in an interference order m=2, the diffraction grating comprising:a substrate; and an arrangement of reflective faces oriented at respective blaze angles &thgr;b spaced along a surface of the substrate with an average separation d, each reflective face being supported by a support wall, wherein the blaze angles &thgr;b define blaze wavelengths &lgr;b=(2d/m) sin &thgr;b that differ from &lgr; by more than 3%, and wherein each reflective face has an extent such that its orthogonal projection on the substrate is less than the average separation d, whereby a trench having a trench width s is defined between each support wall and the reflective face subsequent to that support wall within the arrangement and a groove depth t is defined by the altitude of the support wall with respect to the surface of the substrate, wherein the wavelength &lgr; is within the range 1500-1600 nm, and the reflective faces are uniformly spaced at a grating density 1/d between 350 and 550 faces/mm.