An integrated optical waveguide comprising: a first optical semiconductor waveguide (1201; 1401; 1601; 1701; 1801) with a first refractive index on a semiconductor substrate; a third optical semiconductor waveguide (1203; 1403; 1603; 1703; 1803) with the first refractive index on the semiconductor substrate; and a second optical waveguide (1202; 1402; 1602; 1702; 1802) disposed on the semiconductor substrate between said first optical semiconductor waveguide (1201; 1401; 1601; 1701; 1801) and said third optical semiconductor waveguide (1203; 1403; 1603; 1703; 1803), wherein a first interface (1204; 1404; 1604; 1704; 1804) between the first optical semiconductor waveguide (1201; 1401; 1601; 1701; 1801) and the second optical waveguide is inclined such that a refraction direction of a waveguide light from the first optical semiconductor waveguide (1201; 1401; 1601; 1701; 1801) at the first interface (1204; 1404; 1604; 1704; 1804) is substantially in line with the second optical waveguide (1202; 1402; 1602; 1702; 1802); and a second interface (1205; 1405; 1605; 1705; 1805) between the second optical waveguide (1202; 1402; 1602; 1702; 1802) and the third optical semiconductor waveguide (1203; 1403; 1603; 1703; 1803) is inclined such that a refraction direction of the waveguide light from the second optical waveguide (1202; 1402; 1602; 1702; 1802) at the second interface (1205; 1405; 1605; 1705; 1805) is substantially in line with the third optical semiconductor waveguide, characterized in that the second optical waveguide is composed of a material other than semiconductor having a second refractive index with a negative refractive index temperature differential coefficient such that a temperature caused change of the total optical length of the optical waveguide is suppressed, and a direction of said first optical semiconductor waveguide (1201; 1401; 1601; 1701; 1801) is parallel to a direction of said third optical semiconductor waveguide (1203; 1403; 1603; 1703; 1803), but not in a straight line thereto, or a direction of said first optical semiconductor waveguide (1201; 1401; 1601; 1701; 1801) is perpendicular to a direction of said third optical semiconductor waveguide (1203; 1403; 1603; 1703; 1803), or said second optical waveguide (1202; 1402; 1602; 1702; 1802) has an arc shape. a first optical semiconductor waveguide (1201; 1401; 1601; 1701; 1801) with a first refractive index on a semiconductor substrate; a third optical semiconductor waveguide (1203; 1403; 1603; 1703; 1803) with the first refractive index on the semiconductor substrate; and a second optical waveguide (1202; 1402; 1602; 1702; 1802) disposed on the semiconductor substrate between said first optical semiconductor waveguide (1201; 1401; 1601; 1701; 1801) and said third optical semiconductor waveguide (1203; 1403; 1603; 1703; 1803), wherein a first interface (1204; 1404; 1604; 1704; 1804) between the first optical semiconductor waveguide (1201; 1401; 1601; 1701; 1801) and the second optical waveguide is inclined such that a refraction direction of a waveguide light from the first optical semiconductor waveguide (1201; 1401; 1601; 1701; 1801) at the first interface (1204; 1404; 1604; 1704; 1804) is substantially in line with the second optical waveguide (1202; 1402; 1602; 1702; 1802); and a second interface (1205; 1405; 1605; 1705; 1805) between the second optical waveguide (1202; 1402; 1602; 1702; 1802) and the third optical semiconductor waveguide (1203; 1403; 1603; 1703; 1803) is inclined such that a refraction direction of the waveguide light from the second optical waveguide (1202; 1402; 1602; 1702; 1802) at the second interface (1205; 1405; 1605; 1705; 1805) is substantially in line with the third optical semiconductor waveguide, the second optical waveguide is composed of a material other than semiconductor having a second refractive index with a negative refractive index temperature differential coefficient such that a temperature caused change of the total optical length of the optical waveguide is suppressed, and a direction of said first optical semiconductor waveguide (1201; 1401; 1601; 1701; 1801) is parallel to a direction of said third optical semiconductor waveguide (1203; 1403; 1603; 1703; 1803), but not in a straight line thereto, or a direction of said first optical semiconductor waveguide (1201; 1401; 1601; 1701; 1801) is perpendicular to a direction of said third optical semiconductor waveguide (1203; 1403; 1603; 1703; 1803), or said second optical waveguide (1202; 1402; 1602; 1702; 1802) has an arc shape.