To mitigate the accuracy of misalignment to reduce costs, and to suppress an inter-mode propagation delay difference to enable high-quality transmission of signals. An optical waveguide is configured to propagate only a fundamental mode at a first wavelength and propagate at least a first-order mode as well as the fundamental mode at a second wavelength. The optical waveguide is configured such that a refractive index distribution of a core and a cladding is controlled so that the inter-mode propagation delay difference is within a predetermined threshold, for example, the inter-mode propagation delay difference is zero, when communication is performed using light of the second wavelength. For example, the first wavelength is in a 1310-nm band and the second wavelength is in an 850-nm band.