Patent ID: 8040933

Claim:
A diffraction grating device comprising: a substrate; a first end facet and a second end facet opposite to the first end facet; a diffraction grating structure providing a chirped grating whose pitch monotonically changes from the first end facet to the second end facet along a predetermined axis direction; a core layer that is optically coupled with the diffraction grating structure with a coupling coefficient; and a perturbing layer changing the coupling coefficient between the diffraction grating structure and the core layer, wherein the diffraction grating device is arranged in a plurality of grating portions including a portion of the diffraction grating structure and a portion of the core layer, the grating portions including a first portion and a second portion, the perturbing layer is disposed at the first portion or the second portion, the grating portions are periodically arranged with a constant period in the predetermined axis direction, and the first portion and the second portion are arranged alternately in the predetermined axis direction.