Abstract: An optical fiber amplifier comprises an amplifying optical fiber 60 for optically amplifying signal light according to pumping light incident thereon, a semiconductor light-emitting device 10 for emitting the pumping light; a light-collecting optical system 30 for collecting the pumping light; and waveguide optical fibers 20 to 22 for guiding light through core regions to the amplifying optical fiber, in which the waveguide optical fibers 20 to 22 are disposed such that a maximum width direction of the core region at an input face thereof aligns with a maximum width direction of an incident beam, and the maximum width D [&mgr;m] of the core region at the input face satisfies L ⁢   ⁢ sin ⁢   ⁢ θ NA ≤ D ≤ L where NA is the numerical aperture, L [&mgr;m] is the maximum width of a light-emitting r

Abstract: The present invention relates to an optical waveguide device having a plurality of long-period gratings, and an optical device equipped with the optical waveguide device. By providing a plurality of long-period gratings having loss wavelength characteristics different from each other, which fluctuate along with an environmental condition such as temperature or tension, within a core region of an optical waveguide device, the present invention enables the loss wavelength characteristic of the whole optical waveguide device to be regulated in response to the environmental change.

Abstract: An optical fiber is for optical amplification used for 1.58 &mgr;m band signal light amplification, at least a core region thereof being doped with Er. At least a part of the core region is made of silica glass co-doped with Ge and Al together with Er. The Er average atomic concentration in the core region is from 1500 wt-ppm to 3000 wt-ppm inclusive, and cutoff wavelength is from 0.8 &mgr;m to 1.1 &mgr;m inclusive.

Abstract: An optical fiber for optical amplification used for 1.58 &mgr;m band signal light amplification, at least a core region thereof being doped with Er has a core region at least a part thereof made of silica glass co-doped with Ge and Al together with Er, and Er average atomic concentration in the core region is from 1000 wt-ppm to 3000 wt-ppm inclusive, and cutoff wavelength is from 1.3 &mgr;m to 1.5 &mgr;m inclusive.

Abstract: The present invention relates to an OFA having a high signal gain, easily manufactured, having a high mechanical strength, having a small splice loss with respect to other optical fibers, and rarely encountering the occurrence of noise at a signal wavelength. The OFA according to the present invention has a function of amplifying signals propagating therethroug by pumping light supplied thereto, and comprises, at least, a core region, an inner cladding region provided on the periphery of the core region, an outer cladding region provided on the periphery of the inner cladding region, and one or more node coupling gratings. An element for signal amplification is added to at least the core region. The core region has a structure ensuring a core mode with respect to the signals, while the inner cladding region has a structure ensuring a multi-mode with respect to the pumping light.

Abstract: This is disclosed an optical amplifier comprising: an optical waveguide for amplifying signal light incident thereon and outputting thus amplified signal light while pumping light is being supplied; a transmission device, substantially cascaded to said optical waveguide, for transmitting therethrough the signal light with a predetermined transmission characteristic; pumping device for outputting the pumping light and supplying the pumping light to the optical waveguide; temperature detecting device for detecting a temperature of or near the optical waveguide; and control unit for controlling the transmission characteristic of the transmission device according to the temperature detected by the temperature detecting device.

Abstract: An optical fiber for optical amplification used for 1.58 &mgr;m band signal light amplification, at least a core region thereof being doped with Er, wherein at least a part of the core region is made of silica glass co-doped with Ge and Al together with Er, and an average Er atomic concentration in the core region is from 950 wt-ppm to 3000 wt-ppm inclusive.

Abstract: The present invention relates to a WDM optical communication system comprising a structure which effectively suppresses the waveform deterioration resulting from nonlinear optical phenomena of each signal in a 1.58-&mgr;m wavelength band in an optical transmission line including a dispersion-shifted optical fiber having a zero-dispersion wavelength in a 1.55-&mgr;m wavelength band. The WDM optical communication system includes a hybrid transmission unit in which a single-mode optical fiber and a dispersion-shifted optical fiber are arranged such that signals successively pass therethrough. The single-mode optical fiber has a zero-dispersion wavelength in a 1.3-&mgr;m wavelength band and an effective area ASMF at a wavelength of 1.58 &mgr;m. The dispersion-shifted optical fiber has a zero-dispersion wavelength in the 1.55-&mgr;m wavelength band and, at a wavelength of 1.58 &mgr;m, a dispersion with an absolute value of 0.

Abstract: The present invention relates to an optical I/O module and light-reflecting device comprising a structure excellent in expandability having a high degree of freedom in designing. The optical I/O module according to the present invention comprises a directional coupler having, at least, input and output ports for constituting a part of a transmission line and an intermediate port for constituting a branch; and a light-reflecting device, optically connected to the intermediate port, for transmitting therethrough a specific wavelength. This structure can realize various configurations which allow a specific wavelength to be dropped from the transmission line and to be added to the transmission line, without influencing the configuration of the transmission line.

Abstract: In the optical amplifier of the present invention, a part of signal light inputted to an input connector is branched out by an optical coupler, whereby its power is detected by a light-receiving device. According to the power of input signal light detected by the light-receiving device, the temperature of an amplification optical fiber is controlled by a temperature control section by way of a Peltier device. On the other hand, a part of the signal light outputted from an output connector is branched out by an optical coupler, whereby its power is detected by a light-receiving device. The power of pumping light supplied to the amplification optical fiber from an pumping light source 152 is controlled by an output control section 162 such that the power of output signal light detected by the light-receiving device becomes a predetermined target value.

Abstract: The present invention relates to an optical filter for flattening the gain spectrum of an optical amplification system (including at least one optical amplifier) inserted in a transmission line for transmitting a plurality of signal light components having wavelengths different from each other, and a transmission system including the optical filter. The optical filter according to the invention has a transmission spectrum with inverse characteristics to those of the gain spectrum of the optical amplification system for amplifying the plurality of signal light components.

Abstract: An amplifying optical fiber (111) whose wavelength dependency of gain is approximated by a second-order function of wavelength in which the coefficient of square term of wavelength is a negative value and an amplifying optical fiber (112) whose wavelength dependency of gain is approximated by a second-order function of wavelength in which the coefficient of square term of wavelength is a positive value are cascaded to each other. The amplifying optical fiber (112) is realized as the kind and amount of co-dopant element are appropriately selected. To these amplifying optical fibers, pumping light is supplied by way of fiber type couplers (123, 132) after the light intensities of the pumping light output from pumping light sources (121, 131) are adjusted by light intensity adjusting devices (122, 132).

Abstract: This invention relates to an optical fiber amplifier for amplifying and outputting input signal light. The optical fiber amplifier includes first to third amplification optical fibers. The first to third optical fibers are arranged such that the signal light passes through the first to third optical fibers in the order named. A first value as the (emission cross-section)/(absorption cross-section) of the first optical fiber and a third value as the (emission cross-section)/(absorption cross-section) of the third optical fiber are set to be larger than a second value as the (emission cross-section)/(absorption cross-section) of the second optical fiber. With this arrangement, low noise can be achieved in the first optical fiber, and a large output can be achieved in the third optical fiber.