Abstract: An optical module includes a fusion splicing optical fiber and a ferrule. The fusion splicing optical fiber includes a first optical fiber including optical fiber ends and a first optical fiber core, a second optical fiber including optical fiber ends and a second optical fiber core, and a fused portion splicing the first optical fiber and the second optical fiber spliced between the optical fiber ends. The ferrule includes a first port, a second port, a third port, a first end surface arranged the first port and the second port, a second end surface arranged the third port, and a ferrule housing the fused portion and the first optical fiber ends and the second optical fiber ends.

Abstract: A polarization separating element such as a beam splitter receives a first light of a first polarization plane. The polarization separating element derives out of the first light a second light of a second polarization plane set perpendicular to the first polarization plane. A photoelectric element converts the second light into an electric signal. The intensity of the second light is in this manner detected. Since the second light is derived out of the first light, the phase of the second light is allowed to synchronize with the phase of the first light. The extinction ratio of the second light accurately reflects the extinction ratio of the first light. The detection of the intensity of the second light at the photoelectric element enables an accurate detection of the intensity of the first light.

Abstract: An optical module receives light traveling through an optical fiber in two ways. A coupler is provided in a case member and is attached to an end surface of a ferule having the optical fiber. The coupler allows light of a first wavelength to pass therethrough along a first optical axis of the optical fiber and reflects light of a second wavelength so that reflected light travels along a second optical axis perpendicular to the first optical axis. A light emitting element is provided so as to be located on one of the first and second optical axes. A light receiving element is provided so as to be located on the other one of the first and second optical axes.