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: An optical communication apparatus performs wavelength division multiplexing with respect to signals of a plurality of signal transmission bands. The apparatus includes a first optical unit which effects distributed Raman amplification and has a characteristic that compensates for dispersion of a transmission path to which the optical communication apparatus is connected, with respect to at least one of the signal transmission bands.

Abstract: An optical network ensures substantially same received optical powers even if optional optical paths are connected between node apparatuses in a ringed optical network, and to provide a node apparatus for use in the network. The optical ring network system includes a plurality of node apparatuses each sending out wavelength division multiplexed optical signals; an optical transmission line connecting the plurality of node apparatuses in a ring; and at least one optical amplifier disposed on the optical transmission line, wherein the sending power of optical signals to be inserted at each of the plurality of node apparatuses is set such that the received levels of the optical signals sent out from the plurality of node apparatuses and received at the input of the optical amplifier become equal.

Abstract: In a method of measuring an optical signal-to-noise ratio according to the present invention, a partial optical signal-to-noise ratio is defined, the partial optical signal-to-noise ratio is calculated from a predetermined physical quantity, the sum of inverse numbers of the partial optical signal-to-noise ratios is calculated, and further an inverse number of the sum is calculated to acquire an optical signal-to-noise ratio. The present invention makes it possible to measure optical SNR without directly measuring ASE in the optical signal. The present invention provides a measuring apparatus, a measuring circuit, a pre-emphasis method, an optical communication system, and a controlling apparatus each utilizing this method.

Abstract: The present invention aims to provide a WDM optical communication system that can arrange efficiently optical signals of a plurality of bit rates at different wavelength spacing.

Abstract: The present invention relates to an optical communication apparatus for detecting the intensity of light in an optical modulator or the intensity of a modulation signal and for controlling the operating point of the optical modulator based on the result of detection. In the optical communication apparatus having such a configuration, the operating point of the optical modulator can be kept stable even when the input light or the modulation signal is temporarily non-existent in the optical communication apparatus.

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: It is an object of the present invention to provide a variable wavelength light source apparatus capable of changing continuously wavelengths of a plurality of oscillation light over a wideband and an optical amplifier using the same.

Abstract: A wavelength-selectable laser with a resonance region formed by two reflecting surfaces include a gain medium generating a laser beam, a first filter, and a second filter. The first filter has a first controllable transmission region and transmits a first predetermined wavelength region of the laser beam generated in the gain medium, the first predetermined wavelength region matching the first controllable transmission region. The second filter has a plurality of periodically arranged second transmission regions and transmits a second predetermined wavelength region of the laser beam transmitted by the first filter, the second predetermined wavelength region matching one of the second transmission regions.

Abstract: A light branching/inserting apparatus which can easily control light signal wavelengths, and which can branch, insert or transmit light signals having an optional wavelength and optional multiplexed number, by using a wavelength selection filter utilizing acousto-optic effects.

Abstract: The present invention aims at providing a control method and a control apparatus for controlling the operation setting of an optical device with high accuracy, so as to reliably obtain characteristics according to a desired relationship to be set corresponding to a signal light, immediately after the control start.

Abstract: In an OADM system, an OADM device includes an AOTF. The AOTF can select an optional wavelength by changing the frequency of an RF signal to be applied. An optical signal having a specified wavelength can be dropped from a wavelength-multiplexed optical signal input from an input terminal, or a wavelength-multiplexed optical signal input from an add port can be multiplexed with a through optical signal. However, considering the increase in coherent cross talk, the AOTF should be exclusively used for dropping in an actual device configuration. Otherwise, a drop optical signal is branched by an optical coupler with the wavelength selected by a tributary station. Thus, the wavelength selected by the tributary station can be extracted by the AOTF from the through optical signal.

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: M wavelength separating sections receive multiplexed optical signals each having N kinds of wavelengths different. Each of the multiplexed optical signals are separated into N optical signals. M relays conduct optical reproduction and relay to convert each of the N optical signals into electric signals and then produce optical signals modulated with desired optical wavelengths. A refill section mutually refills M sets of the reproduced and relayed optical signals. A focusing section focuses the M sets of optical signals refilled in the refill section. A light source supplies input lights having desired wavelengths, which lights are modulated in the relays. The light source includes N light sources outputting N kinds of optical wavelengths. A multiplexer/brancher multiplexes the lights from the N light sources to produce a multiplexed light and branches the multiplexed light into M×N distributed lights. M wavelength filters distribuitively receive N distributed lights of the M×N distributed lights.

Abstract: A light branching/inserting apparatus which can easily control light signal wavelengths, and which can branch, insert or transmit light signals having an optional wavelength and optional multiplexed number, by using a wavelength selection filter utilizing acousto-optic effects.

Abstract: In a wavelength-division multiplexing transmission technique, a loss difference compensator for compensating a loss difference of an optical signal at each wavelength generated in a wavelength-division-multiplexed optical signal due to a wavelength-dependent transmission loss characteristic of an optical transmission line is disposed to the optical transmission line for transmitting the wavelength-division-multiplexed optical signal having a wide wavelength band in which optical signals at a plurality of wavelengths are wavelength-division-multiplexed to compensate the loss difference of the optical signal at each wavelength generated in the wavelength-division-multiplexed optical signal due to the wavelength-dependent transmission loss characteristic of the optical transmission line and a dispersion compensator, thereby transmitting the wavelength-division-multiplexed optical signal in a wide wavelength band for a long distance.

Abstract: In an OADM system, an OADM device includes an AOTF. The AOTF can select an optional wavelength by changing the frequency of an RF signal to be applied. An optical signal having a specified wavelength can be dropped from a wavelength-multiplexed optical signal input from an input terminal, or a wavelength-multiplexed optical signal input from an add port can be multiplexed with a through optical signal. However, considering the increase in coherent cross talk, the AOTF should be exclusively used for dropping in an actual device configuration. Otherwise, a drop optical signal is branched by an optical coupler with the wavelength selected by a tributary station. Thus, the wavelength selected by the tributary station can be extracted by the AOTF from the through optical signal.

Abstract: Disclosed herein is an optical node device applicable to an optical network including a closed loop provided by an optical fiber. This optical node device includes a tunable wavelength selecting element adapted to input WDM signal light obtained by wavelength division multiplexing a plurality of optical signals having different wavelengths, the tunable wavelength selecting element having a function of dropping at least one optical signal from the WDM signal light and a function of adding at least one optical signal to at least one unassigned wavelength channel of the WDM signal light; and a wavelength selecting filter optically connected to the tunable wavelength selecting element for removing noise present in any bands other than a signal band of each optical signal passing through the tunable wavelength selecting element.

Abstract: An optical transmission system in which a wavelength-division-multplexed (WDM) optical signal including a plurality of optical signals having different wavelengths is demultiplexed into first optical signals and second optical signals. The second optical signals have wavelengths longer than wavelengths of the first optical signals. A first dispersion compensator compensates dispersion of the first optical signals. A second dispersion compensator compensates dispersion of the second optical signals. The dispersion compensated first and second optical signals are then multiplexed together.

Abstract: An optical amplifier for amplifying light in a longer wavelength band. The optical amplifier includes first and second optical fibers doped with a rare earth element and optically connected so that a signal light travels through the first optical fiber and then through the second optical fiber. Excitation light causes the signal light to be amplified in both the first and second optical fibers. Spontaneous emission lights are generated in the first optical fiber. An oscillation generator causes the spontaneous emission lights to oscillate in the first optical fiber, to thereby generate laser oscillation. Light generated by the laser oscillation is supplied to the second optical fiber as excitation light in the second optical fiber. The oscillation generator can be formed by fiber gratings along the first optical fiber and which reflect spontaneous emission light at a predetermined wavelength, thereby causing spontaneous emission lights to oscillate between the fiber gratings in the first optical fiber.