Study on planar concave diffraction grating with Bragg reflector facets

Abstract

Based on the fact that Bragg reflection grating(BRG) is a special one-dimensional photonic crystal, we propose to apply the one-dimensional photonic crystal band gap theory to the design of Bragg reflection grating and then to make an analysis of its optical performance. According to the above band gap theory, FDTD solution is used to build the elliptical Bragg etched diffraction grating (EDG) based on the Rowland circle. We have studied the spectral characteristics for both TE and TM modes and the angle dispersion due to the variation of the incident angle, at the same time, the optical performances in the air dielectric type Bragg grating and the Al metallic line type Bragg grating are also made to compare with each other. It turns out that by choosing appropriate parameters the diffraction efficiency can be got more than 95% within the scope of 1.465-1.615 μm in both TE and TM modes, and the air dielectric type Bragg grating structure behaves better in the uniformity throughout the whole channel than in the Al metallic line type Bragg grating structure. When the incident angle varies from 30° to 60°, the angle dispersion in TM mode is larger than that in TE mode. This is the foundation of a new type of EDG wavelength division multiplexer with advantages of small size and high diffraction efficiency. It may have the potential to promote the development of high diffraction efficiency dense wavelength division multiplexer in the future.