Optical device

摘要

The invention provides a small optical device with which incident light can be demultiplexed. The optical device includes a demultiplexing portion 4 (first optical member) separating TE waves and TM waves of incident light of a wavelength lambd and an optical fiber 1 (optical input portion) inputting incident light into the demultiplexing portion 4. The demultiplexing portion 4 has a periodically changing refractive index. The angle defined by the first reciprocal lattice vector alpha1 and the second reciprocal lattice vector alpha2 of the demultiplexing portion 4 at the wavelength lambd is not greater than 90°. In the direction of the first reciprocal lattice vector alpha1 the wave number of the TE wave is larger than the wave number of the TM wave. In the direction of the second reciprocal lattice vector alpha2 the wave number of the TE wave is smaller than the wave number of the TM wave. The optical fiber 1 inputs the incident light in a direction that is parallel to a plane including the first reciprocal lattice vector alpha1 and the second reciprocal lattice vector alpha2.