OPTICAL MODULATOR

PROBLEM TO BE SOLVED: To provide a highly reliable optical modulator having improved temperature drift characteristics.SOLUTION: An optical modulator includes: a substrate 1 having an electro-optic effect; two optical waveguides 3 formed in the substrate; a buffer layer 2 formed on the substrate; a traveling-wave electrode including a central conductor 4a and a ground conductor 4b disposed above the buffer layer; and a base 7 holding the substrate. A conductive film 8 is disposed over the entire back surface of the substrate. The substrate is fixed to the base through the conductive film using an adhesion layer 9. The adhesion layer is disposed at a first substrate side wall side 51 that is distant from the two optical waveguides in the cross section in a direction orthogonal to the two optical waveguides. The difference in indices of stress birefringence between the two optical waveguides caused by the difference in thermal expansion coefficients between the base and the substrate when environmental temperature changes, is decreased.