Abstract: Provided are an optical amplifier, for amplifying a light signal; first and second light dividers, optically connected to an output terminal of the optical amplifier; and first and second light receivers, for receiving light divided by these light dividers. A variable wavelength filter is located between the first optical coupler and the second optical couler. In addition, provided are a filter driver, for sweeping a center wavelength that passes through the variable wavelength filter; a counter circuit, for counting output peaks of the second light receiver; and an output controller, for controlling an output of the optical amplifier so as to maintain a constant output by the first light receiver. The output controller employs a voltage output by the count circuit as a reference voltage for controlling changes in the light output power of the optical amplifier that are in consonance with the value held by the counter, i.e., in consonance with the number of signal light wavelengths.

Abstract: In an optical coupler comprising a first optical fiber (1) and a second optical fiber (2), first and second outgoing fiber ends of the first and second optical fibers are optically coupled along a predetermined length. First and second incidence fiber ends of the first and second incidence fibers are supplied with first and second lights, respectively. A primary condensing lens (10) is supplied with first and output lights from the first and second optical fibers and condenses the first and second output lights to produce a first condensing light. An optical isolator (8) has an incidence isolator end and an outgoing isolator end. The optical isolator is supplied with the first condensing light from the primary condensing lens through the incidence isolator end to output the first condensing light from the outgoing isolator end. The optical isolator prevents output of an unwanted light at the incidence isolator end.