Optical coupler and an optical amplifier and its manufacturing method using the same

In an optical amplifier wherein pumping laser light and signal laser light are multiplexed and supplied as input to a fiber doped with a rare earth element, by decreasing the number of connected sections, loss due to the connection to the rare earth-doped fiber is decreased. A pair of fibers, each consisting of an undoped optical fiber (1a, 1b) fusion spliced to a rare earth-doped fiber (4a, 4b), are arranged in parallel and heated and fused with each other to form a fused jointed portion (3) which is stretched in the vicinity of the connection point (2), thereby forming the optical coupler.