Abstract: Disclosed is a Faraday rotator capable of reducing the temperature dependence on a Faraday rotation angle, thereby enhancing the temperature characteristic, particularly, in a service environment in which the magnetization direction is variable, and an optical device using the Faraday rotator. The Faraday rotator includes a Faraday element which rotates the polarization plane of polarized light rays passing through the Faraday element when an external magnetic field is applied to the Faraday element.

Abstract: A specific polarized light component out of a light wave passed through a magneto-optic crystal (for example YIG) is extracted by a polarizer. The intensity of the light beam output from the polarizer depends on strength and direction of magnetic fields applied to the magneto-optic crystal. The magneto-optic crystal is applied with a first and a second magnetic field acting in directions different from each other and the strength of the composite magnetic field of them is set to exceed a predetermined value at all times. By varying at least one of the first and second magnetic fields, the attenuation factor in the magneto-optic crystal can be changed continuously and with good reproducibility.

Abstract: The present invention relates to a tunable optical filter having a variable wavelength characteristic of transmittance. The tunable optical filter includes first and second polarizers each having a transmission axis determining a polarization axis of transmitted polarized light, a birefringent element having an optic axis determining a phase difference given between two orthogonal components of transmitted polarized light, and a Faraday rotator for giving a variable Faraday rotation angle to transmitted polarized light. The birefringent element and the Faraday rotator are provided between the first and second polarizers.

Abstract: Disclosed herein is an optical filter usable as an optical add/drop circuit. The optical filter includes a first port, an optical filter member having a characteristic changing according to a position in a predetermined direction, a second port optically coupled to the first port by a transmitted light path concerning the optical filter member, a reflecting unit optically coupled to the first port by a reflected light path concerning the optical filter member, and a mechanism for displacing the optical filter member in the above predetermined direction. With this configuration, a variable pass band or a variable stop band can be obtained, and the characteristic is stable.

Abstract: An optical connector including first and second optical fibers which each has a slanted end face. The optical connector provides a connection state where the end face of the first optical fiber is aligned with, and in close contact with, the end face of the second optical fiber so that light travelling through the first optical fiber travels into the second optical fiber. Moreover, the optical connector provides a disconnection state where a gap exists between the end face of the first optical fiber and the end face of the second optical fiber. The end face of the first optical fiber causes light travelling through the first optical fiber to be totally reflected at the end face of the first optical fiber when in the disconnection state.

Abstract: A specific polarized light component out of a light wave passed through a magneto-optic crystal (for example YIG) is extracted by a polarizer. The intensity of the light beam output from the polarizer depends on strength and direction of magnetic fields applied to the magneto-optic crystal. The magneto-optic crystal is applied with a first and a second magnetic field acting in directions different from each other and the strength of the composite magnetic field of them is set to exceed a predetermined value at all times. By varying at least one of the first and second magnetic fields, the attenuation factor in the magneto-optic crystal can be changed continuously and with good reproducibility.

Abstract: The present invention provides an optical device making use of a magneto-optical effect. The optical device comprises: a reflector for reflecting an input beam as a reflected beam; a magneto-optical crystal provided so as to pass the input and reflected beams; a first unit for applying a magnetic field to the magneto-optical crystal; and a second unit for varying the magnetic field in accordance with a control signal. The configuration described above allows a small magneto-optical crystal to be used and, thus, a small-size and a low-cost Faraday rotator to be provided. By adding a polarizer to such a Faraday rotator, a variable optical attenuator can be obtained. In particular, by employing a wedge plate as the polarizer, a polarized-independent optical attenuator can be provided.

Abstract: An optical device having a function of an optical circulator of which forward losses are uniformly small while reverse losses are uniformly great. The optical device applicable to be used as an improved three-port optical circulator has three optical coupling units connected optically to three ports respectively, a reflecting unit for giving a polarization plane rotation of 90.degree. to an input beam, and a main polarization beam splitter having a polarized-wave separating film for optically connecting the optical coupling units and the reflecting unit through transmission and reflection. Each of the optical coupling units comprises a subsidiary polarization beam splitter and a polarization converter. The subsidiary polarization beam splitter couples the relevant port to first and second polarized beams perpendicular to each other.

Abstract: An optical device which can be used as a Faraday rotator which can provide an arbitrary Faraday rotation angle in accordance with a positional condition. The optical device includes first and second ports, magneto-optical crystal, and a unit for applying a magnetic field to the magneto-optical crystal. The first port is positioned in a first region while the second port is positioned in a second region. The first and second ports are optically coupled by a light beam. The magneto-optical crystal is provided such that the light beam may pass therethrough. The unit for applying applies a magnetic field to the magneto-optical crystal so that magnetization of the magneto-optical crystal may have a given distribution in a plane substantially perpendicular to the light beam.

Abstract: An apparatus which attenuates a light signal polarized in a first direction. The apparatus includes a polarization rotation unit and an output unit. The polarization rotation unit rotates the polarization of the light signal to produce a polarization rotated light signal having a polarization component in the first direction and a polarization component in a second direction which is substantially 90 degrees with respect to the first direction. The output unit passes, as an output signal, the polarization component in the second direction of the polarization rotated light signal and blocks the polarization component in the first direction. The polarization rotation unit includes an electromagnet and a permanent magnet which apply magnetic fields in specific directions with respect to the light path. Various yoke constructions are provided for the electromagnet and the permanent magnet.

Abstract: A wavelength division multiplexing module capable of multiplexing or demultiplexing a plurality of optical signals having close wavelengths with less crosstalk. The wavelength division multiplexing module includes a housing having a bottom wall, a first side wall, and a second side wall inclined a predetermined angle with respect to the first side wall, and a common port assembly fixed to the bottom wall of the housing so as to emit a collimated beam substantially perpendicular to the first side wall. One or more filter port assemblies are fixed to the first side wall in the condition that the pass wavelength characteristic and optical axis of each assembly have been adjusted. Similarly, one or more filter port assemblies are fixed to the second side wall in the condition that the pass wavelength characteristic and optical axis of each assembly have been adjusted. Each filter port assembly includes an optical film holder rotatable in a hole having a center axis inclined a predetermined angle .theta.

Abstract: An optical device for wavelength monitoring and wavelength control. The optical device has an optical element having a first surface and a second surface not parallel to each other. The optical element separates a light beam supplied to the first surface into a first beam reflected on the first surface, a second beam passed through the first surface, reflected on the second surface, and passed through the first surface again, and a third beam passed through the first surface and the second surface in this order. An optical filter is provided so as to transmit the first and second beams. The optical filter has wavelength characteristics different according to an incidence angle. The first and second beams passed through the optical filter are supplied to first and second photodetectors, respectively. On the basis of such a difference in wavelength characteristic, the wavelength of the light beam can be monitored according to outputs from the first and second photodetectors.

Abstract: A specific polarized light component out of a light wave passed through a magneto-optic crystal, for example, YIG is extracted by a polarizer. The intensity of the light beam output from the polarizer depends on strength and direction of magnetic fields applied to the magneto-optic crystal. The magneto-optic crystal is applied with a first and a second magnetic field acting in directions different from each other. The strength of the composite magnetic field of the first and the second magnetic fields is set to exceed a predetermined value at all times. By varying at least one of the first and second magnetic fields, the attenuation factor in the magneto-optic crystal can be changed continuously and with good reproducibility.

Abstract: An apparatus which attenuates a light signal polarized in a first direction. The apparatus includes a polarization rotation unit and an output unit. The polarization rotation unit rotates the polarization of the light signal to produce a polarization rotated light signal having a polarization component in the first direction and a polarization component in a second direction which is substantially 90 degrees with respect to the first direction. The output unit passes, as an output signal, the polarization component in the second direction of the polarization rotated light signal and blocks the polarization component in the first direction. The polarization rotation unit includes an electromagnet and a permanent magnet which apply magnetic fields in specific directions with respect to the light path. Various yoke constructions are provided for the electromagnet and the permanent magnet.

Abstract: A Faraday rotator capable of maintaining a Faraday rotation angle always constant regardless of temperature variations. The Faraday rotator includes a magneto-optic crystal provided in a light propagation path, a permanent magnet for generating a magnetic field parallel to the light propagation path, and an electromagnet for generating a magnetic field orthogonal to the light propagation path. The strength of a synthetic magnetic field by the permanent magnet and the electromagnet is set to a magnitude large enough to magnetically saturate the magneto-optic crystal. The electromagnet is driven by a drive circuit. The Faraday rotator further includes a temperature sensor provided adjacent to the Faraday rotator, and a controller incorporating data on temperature dependence of a Faraday rotation angle of the magneto-optic crystal to control the drive circuit so that the Faraday rotation angle becomes constant according to a temperature detected by the temperature sensor.

Abstract: A beam splitter formed by laminating a plurality of optical films on a glass substrate having a refractive index of 1.51.+-.0.10. The optical films are first, second, third, fourth, and fifth layers laminated in this order from the glass substrate. The first layer has a refractive index of 1.44.+-.0.10 and an optical film thickness of 0.05-0.15; the second layer has a refractive index of 1.68.+-.0.10 and an optical film thickness of 0.01-0.10; the third layer has a refractive index of 1.44.+-.0.10 and an optical film thickness of 0.50-0.60; the fourth layer has a refractive index of 2.23.+-.0.10 and an optical film thickness of 0.25-0.35; and the fifth layer has a refractive index of 1.44.+-.0.10 and an optical film thickness of 0.25-0.35. The optical film thickness means a relative value represented by n.times.d/.lambda. where n denotes a refractive index; d denotes an actual film thickness, and .lambda. denotes a wavelength deciding the center of a wavelength band.

Abstract: A Faraday rotator which includes a magnetic optical element and a magnetic field generating unit. The magnetic optical element has an optical path extending therethrough. The magnetic field generating unit is positioned so as not to obstruct the optical path, and generates a uniform magnetic field in the magnetic optical element. The magnetic field generating unit can include a first magnet unit and a second magnet unit. The first magnet unit is positioned so as not to obstruct the optical path and generates a magnetic field passing through the magnetic optical element. The second magnet unit is positioned so as not to obstruct the optical path and generates a magnetic field passing through the magnetic optical element. The magnetic field generated by the second magnet unit is perpendicular to the magnetic field generated by the first magnet unit and combines with the magnetic field generated by the first magnet unit to produce a uniform magnetic field in the magnetic optical crystal.

Abstract: An apparatus, such as an optical modulator, which includes an optical waveguide and a polarizer housing device. The optical waveguide has an input end to receive light, and the polarizer housing device is connected to the input end of the optical waveguide. The polarizer housing device includes a polarizer which polarizes light, and a lens. A propagation space is in the polarizer housing device between the polarizer and the lens. The light polarized by the polarizer travels through the propagation space to the lens and is guided by the lens to the input end of the optical waveguide. The polarizer is bonded to the polarizer housing device with an adhesive so that no excess adhesive flows into the propagation space. Therefore, it is not necessary to use an optical adhesive to bond the polarizer to the polarizer housing device.

Abstract: An apparatus, such as an optical equalizer, having variable wavelength characteristics. More specifically, the apparatus attenuates an input light, and includes a beam expander, a beam condenser and an attenuator positioned between the beam expander and the beam condenser. The beam expander converts the input light into a spectral beam propagating in a first direction and having wavelength components spatially separated in a second direction perpendicular to the first direction. The attenuator intersects the spectral beam and has a planer distribution of transmittance so that the spectral beam passes through the attenuator and is attenuated in accordance with the planer distribution of transmittance. The beam expander converts the attenuated spectral beam into an output light. The attenuator is movable in a plane which is not parallel to the first direction. For example, the attenuator can be movable in a plane which is substantially perpendicular to the first direction.

Abstract: An optical device having a collimating mechanism for converting light emitted from an excitation port into a parallel beam and outputting the parallel beam onto an optical path, an optical film provided so as to pass the parallel beam output from the collimating mechanism, and a supporting mechanism for supporting the optical film so that the optical film is rotatable about an axis inclined with respect to the optical path. The optical film is inclined with respect to a plane perpendicular to the axis. An incident angle of the parallel beam upon the optical film can be changed by rotating the optical film about the axis. Thus, the optical device having the optical film that can vary the incident angle thereupon can be provided with a simple structure.