PURPOSE: To attain effective coupling in a wide temperature range by using fiber carriers having the same anisotropic thermal expansion coefficient as that of an integrated optic device along a known optical axis in the case of joining an obliquely cut optical fiber with the device.

CONSTITUTION: The integrated optic device 12 consisting of lithium niobate is joined with the surface 18 of a substrate 14 having the same anisotropic thermal expansion coefficient. An waveguide of the device 12 is arranged on 'Y-propagation' parallel with an Y axis. Fiber carriers 34, 36, 38 have the same thermal expansion coefficient as that of the device 12 along the same axis as the device 12 and arranged similarly to 'Y-propagation'. In the state, optical fibers 40, 42, 44 are obliquely cut off and joined with grooves formed on the carriers 34, 36, 38 by adhesives so that the end faces of the cut fibers 40, 42, 44 are aligned to the same surfaces as the auxiliary faces 46, 48, 50 of the carriers 34, 36, 38. The inclined end faces are fitted to the fitting faces 22, 24 of the device 12 so as to be matched with the ports of the waveguide. Consequently effective coupling can be attained in a wide temperature range.