Optical multiplexer/demultiplexer

摘要

An optical multiplexer/demultiplexer includes first and second directional coupling portions in which first and second optical waveguides are provided to transfer a light between the first and second optical waveguides. Lengths of the first and second optical waveguides have a difference (DELTAL). A product between the difference (DELTAL) and a refractive index (n) of the first and second optical waveguides approximates a product between a cross-propagation wavelength (lambd2) and a value (N') substantially equal to an integer (N), and a product between a through-propagation wavelength (lambd1) and the value (N')±0.5. Power coupling ratio differences are at least approximately 1% and at most approximately 10%. Third power coupling ratios with respect to an average wavelength of the cross-propagation wavelength (lambd2) and the through-propagation wavelength (lambd1) are at least approximately 45% and at most approximately 55%.