An optical waveguide element includes a core and a cladding that is made of SiO2. When ng_i_TE is a group refractive index of a TE0 polarized wave in the i-th waveguide counted from a light incidence plane of the core and ng_i_TM is a group refractive index of a TM0 polarized wave in the i-th waveguide, the length L—i[m] of the i-th waveguide satisfies a predetermined relation.
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