Patent ID: 8693827

Claim:
A three-wavelength optical multiplexer, comprising: three waveguides including a first waveguide capable of performing single-mode transmission, a second waveguide capable of performing single-mode transmission, and a third waveguide capable of performing single-mode transmission, which are arranged parallel to one another in this order, as observed from a cross sectional direction orthogonal to a fiber axis direction, wherein the first waveguide, the second waveguide, and the third waveguide are single-mode optical fibers, and these three waveguides are collectively fused and drawn, the first waveguide and the third waveguide are not in contact with each other, but are in contact with the second waveguide, of the three waveguides, the first waveguide has parameters which are the same as parameters of the second waveguide, and the third waveguide have parameters which are different from the parameters of the first waveguide and the parameters of the second waveguide, where a relation among wavelengths of light injected into the three waveguides is λ 1 <λ 2 <λ 3 , light injected into the first waveguide has the wavelength of λ 1 , light injected into the second waveguide has the wavelength of λ 2 , light injected into the third waveguide has the wavelength of λ 3 , and multiplexed light of light having these wavelengths λ 1 , λ 2 , and λ 3 is emitted from the first waveguide, and one of the parameters is a secondary-mode cutoff wavelength, and a secondary-mode cutoff wavelength C 1 of the first single-mode optical fiber and the second single-mode optical fiber, a secondary-mode cutoff wavelength C 2 of the third single-mode optical fiber, and a wavelength λ 3 of light injected into the third single-mode optical fiber have a relation of C 1 <C 2 <λ 3 .