Wavelength multiplexer and optical unit

A wavelength multiplexer including at least:

• first, second and third optical waveguides;
• a fourth optical waveguide capable of propagating light in a multi-mode;
• and
• an optical filter disposed perpendicularly to a traveling direction of light in said fourth optical waveguide;
• said first optical waveguide being connected to a first end face of said fourth optical waveguide,
• said second and third optical waveguides being connected to predetermined individual positions of a second end face opposed to the first end face of said fourth optical waveguide, and
• said fourth optical waveguide being an optical waveguide wherein when standardized shapes of light intensity distributions on two planes spaced a predetermined distance from the first and second end faces of the fourth optical waveguide are superimposed one on the other, said shapes are in axial symmetry or approximately axial symmetry with respect to a central axis extending in the light traveling direction of the fourth optical waveguide.

A wavelength multiplexer wherein:

• a first optical waveguide is connected to a first end face of a fourth optical waveguide capable propagating light in a multi-mode;
• second and third optical waveguides are connected to a second end face opposed to said first end face of said fourth optical waveguide at a predetermined spacing from each other in their connections to said second end face;
• an optical filter is installed in said fourth optical waveguide;
• and
• an incident plane of said optical filter is parallel or approximately parallel to the wave front of light in each of said first, second and third optical waveguides at the connected position of each of the optical waveguides connected to said fourth optical waveguide.