To relax the accuracy with respect to a deviation with respect to an optical axis or an angular deviation, and thus to reduce costs.
An optical waveguide is included that performs propagation only in a reference mode at a first wavelength. Communication is performed using light of a second wavelength that enables the optical waveguide to perform propagation in at least a first order mode in addition to the reference mode. When light entering the optical waveguide deviates with respect to an optical axis or deviates angularly, propagation is performed in at least the first order mode in addition to the reference mode, the first order mode being generated due to the deviation with respect to the optical axis or the angular deviation. This results in a reduction in a loss of coupling of optical power. This makes it possible to relax the accuracy with respect to a deviation with respect to an optical axis or an angular deviation, and thus to reduce costs.