To provide a CWDM (coarse wavelength division multiplex) filter capable of preventing light leak and noise, which is applied to a CWDM apparatus.
The CWDM filter comprises a substrate; a first portion; a second portion; and a first coupling layer formed between the first and second portions. The first portion has at least two first stacking structure, each of the first stacking structures having a Fabry-Perot cavity and a first coupling layer which are stacked over each other in turn from the substrate. The second potion comprises at least two second stacking structures, each of the second staking structures having a (HnLH) structure and a second spacer layer which are stacked over each other in turn from the substrate, wherein n represents a positive integer equal to or greater than 2, L represents a low refractive index layer with a thickness of λ0/4, H represents a high refractive index layer with a thickness of λ0/4, and λ0 is the center wavelength of the noise.
Takashi Watanabe
Yasuhiko Murayama
Shinya Mitsuhiro