Abstract: A first optical system (11) has a first beam splitter (211). The first beam splitter (211) splits light arriving through a first optical path (P1) into two light beams, and outputs one light beam to a second optical path (P2) and the other light beam to a third optical path (P3). A second optical system (21) outputs the light output from the first beam splitter (221) to the second optical path (P2) and arriving at the second optical system (21) upon giving the light an intensity change with wavelength dependence and a phase change, and has a second beam splitter (221), first reflecting mirror (223), and second reflecting mirror (222). This makes it possible to provide an optical filter (200) which can realize a characteristic excellent in isolation with a very simple arrangement.

Abstract: In a polarized wave interleaver 100, signal light of a first wavelength band ?1 of polarized light component in a first orientation, which enters an input port 111, proceeds to a first path P1 through a first polarized wave separation element 131. Even after passing through a wavelength filter 140, the polarized light component in the first orientation is maintained as it is. And the light proceeds to a third path P3 through a second polarized wave separation element 132, and is output from a first output port 121. Signal light of a second wavelength band ?2 of polarized light component in a second orientation, which enters the input port 111, proceeds to a second path P2 through the first polarized wave separation element 131, and is converted to the polarized light component in the first orientation by the wavelength filter 140. And the light proceeds to a fourth path P4 through the second polarized wave separation element 132, and is output from a second output port 122.

Abstract: An interleaver is provided with an optical system configured to split light having traveled from a first port to a half mirror, into two beams and direct the beams toward first and second reflectors, respectively. Light reflected by the first reflector and arrived at the half mirror is split into two beams and directed toward second and third ports, respectively. Light reflected by the second reflector and arrived at the half mirror is split into two beams directed toward the second and third ports, respectively. An etalon filter configured to cause a loss on either one of light incident thereto from the first port and the beams directed toward the second port and toward the third port.

Abstract: A first optical system (11) has a first beam splitter (211). The first beam splitter (211) splits light arriving through a first optical path (P1) into two light beams, and outputs one light beam to a second optical path (P2) and the other light beam to a third optical path (P3). A second optical system (21) outputs the light output from the first beam splitter (221) to the second optical path (P2) and arriving at the second optical system (21) upon giving the light an intensity change with wavelength dependence and a phase change, and has a second beam splitter (221), first reflecting mirror (223), and second reflecting mirror (222). This makes it possible to provide an optical filter (200) which can realize a characteristic excellent in isolation with a very simple arrangement.

Abstract: The light which is input from an optical fiber to a first port is output to an optical path. The light which is input from the optical path to a half mirror is branched into two, and is output to the optical paths. The light which is output to the optical path reaches to and is reflected from a first reflecting mirror, and returns to the half mirror by an optical path. The light which is input to the half mirror by the optical path is branched into two, and is output to the optical paths. The light which is output to the optical path reaches to and is reflected from a second reflecting mirror, and returns to the half mirror by an optical path. The light which is input to the half mirror by the optical path is branched into two, and is output to the optical paths. The light which is output to the optical path is output from a second port to an optical fiber, and the light which is output to the optical path is output from a third port to an optical fiber.

Abstract: Light entering a first port is incident to an etalon filter, suffers a loss according to a loss characteristic of the etalon filter, and is fed into a first optical path. The light incident through the first optical path to a half mirror is split into two beams and the beams are fed into a second optical path and a third optical path. The beam fed into the second optical path travels forward and backward between the half mirror and a first reflector to return to the half mirror. The beam incident to the half mirror is split into two beams and the beams are fed into a fourth optical path and a fifth optical path. The beam fed into the third optical path travels forward and backward between the half mirror and a second reflector to return to the half mirror. The beam incident to the half mirror is split into two beams and the beams are fed into the fourth optical path and the fifth optical path.

Abstract: The light which is input from an optical fiber to a first port is output to an optical path. The light which is input from the optical path to a half mirror is branched into two, and is output to the optical paths. The light which is output to the optical path reaches to and is reflected from a first reflecting mirror, and returns to the half mirror by an optical path. The light which is input to the half mirror by the optical path is branched into two, and is output to the optical paths. The light which is output to the optical path reaches to and is reflected from a second reflecting mirror, and returns to the half mirror by an optical path. The light which is input to the half mirror by the optical path is branched into two, and is output to the optical paths. The light which is output to the optical path is output from a second port to an optical fiber, and the light which is output to the optical path is output from a third port to an optical fiber.

Abstract: The invention relates to a temperature-compensated optical communication interference device. In this device, an optical divider divides light entering an input port into two light beams. An optical coupler superposes these beams and feeds the superposed light to an output port. First and second optical paths are provided between the divider and the coupler. First and second optical components are placed on the first and second optical paths, respectively. The divider, coupler, and optical components are placed on a substrate. The substrate has members with coefficients of linear expansion having different signs. Temperature dependence of an optical path length difference between the first and second paths is reduced due to the difference between the signs of the coefficients.