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 optical amplifier (TDFA) having a configuration which enables to reduce temperature dependence of the gain with reduced power consumption and simple control. The optical amplifier includes, in the order from an input port to an output port, an optical isolator, an optical coupler, an optical amplification fiber, an optical coupler, an optical isolator, an optical gain equalizing filter, a variable optical attenuator, an optical isolator, an optical coupler, an amplification fiber, an optical coupler, and an optical isolator. At least a core region of the optical amplification fiber is doped with Tm element, and signal light in a predetermined wavelength range is amplified by supply of pumping light. The gain equalizing fiber has a loss spectrum which shifts toward the short wavelength side as the temperature of the optical waveguide is higher, thereby equalizing the optical amplification gain of the signal light in the optical amplification fiber.

Abstract: Inputted multiplexed optical signal is separated by an optical branching section into C-band multiplexed optical signal and L-band multiplexed optical signal, and the C-band multiplexed optical signal and L-band multiplexed optical signal are optically amplified by a C-band optical amplifier and an L-band optical amplifier, respectively. The amplified optical signals are combined by an optical combiner, and thus combined optical signal is outputted therefrom. The backward ASE light generated in the L-band optical amplifier upon optical amplification is blocked by an optical filter disposed between the optical amplifier and the optical branching section, so as to be prevented from traveling backward and being inputted to and amplified by the C-band optical amplifier, whereby the deterioration of noise characteristics is restrained.

Abstract: The present invention relates to a Raman amplifier where flexibility in device design considering both of Raman amplification and dispersion compensation is high. In the Raman amplifier, the Raman amplification optical fiber included in the optical amplification section and the dispersion compensating optical fiber included in the dispersion compensation section are arranged while being optically connected to each other. Since the optical amplification section and the dispersion compensation section are provided as independent optical devices, one device can be designed without being restricted to the design conditions of the other device.

Abstract: An optical amplifier 1 is constructed using an amplification optical waveguide in which a first amplification optical fiber 10 and a second amplification optical fiber 20 are connected in series. A P/Al-codoped EDF 10 excellent in noise characteristics is applied to the upstream first amplification optical fiber 10, and an EDF 20 such as an Al-doped EDF or the like is applied to the downstream second amplification optical fiber 20. This realizes the optical amplifier 1, and the optical transmission system using it, capable of amplifying the signal light in the signal light wavelength band of not less than the wavelength of 1570 nm including the L-band wavelength band of wavelengths from 1570 to 1600 nm, with good gain characteristics and achieving the improvement in the noise characteristics.

Abstract: This invention relates to an amplification optical fiber which requires no gain equalizer and has a flat gain spectrum and high polarization extinction ratio, and the like. The amplification optical fiber has a core region included in a light propagation region through which signals having different wavelengths propagate, a cladding region around the core region, and a polarization maintaining structure for maintaining the polarized states of the signals. The amplification optical fiber is mainly comprised of silica glass, and Er and Al of 4 wt % or more are doped into at least part of the light propagation region including the core region.

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: The present invention relates to a pumping light source unit for Raman amplification and the like comprising a structure for improving the pumping light spectrum controllability so as to enable output signal light spectrum adjustment within an amplification wavelength band. The pumping light source unit comprises N (≧2) pumping light sources for outputting N channels of pumping light having respective wavelengths different from each other, a multiplexer for multiplexing the N channels of pumping light, and an output structure for supplying a Raman amplification optical fiber with the pumping light outputted from the multiplexer. In particular, at least one of the N pumping light sources includes a variable length pumping light source adapted to change the channel wavelength of pumping light outputted therefrom. This configuration makes it possible to adjust pumping light spectra, thereby improving the controllability of output signal light spectra (Raman gain spectra).

Abstract: The present invention provides a Raman amplifier and the like comprising a structure for keeping the flatness of power spectrum of Raman-amplified signal light. The Raman amplifier comprises an optical fiber for Raman-amplifying a plurality of signal channels of signal light having respective center optical frequencies different from each other; a pumping light supply section for supplying N (N being an integer of 2 or more) pumping channels of pumping light having respective center optical frequencies different from each other to the optical fiber; and a feedback section for detecting a part of the signal light Raman-amplified within the optical fiber when the pumping light is supplied thereto, and controlling the pumping light supply section such that the Raman-amplified signal light has a substantially flat power spectrum with respect to an optical frequency direction according to the result of detection.

Abstract: The present invention relates to a Raman amplifier which is hard to deteriorate signal waveforms, so that it realizes an excellent transmission quality. In this Raman amplifier, an optical waveguide for Raman-amplifying signal light when pumping light is supplied thereto has a zero-dispersion wavelength &lgr;0 shifted from a center wavelength &lgr;center (=(&lgr;S, rms+&lgr;P, rms)/2) existing between a center-of-gravity wavelength &lgr;S, rms of the signal light, which is a mean weighted with respective powers of wavelength components included in the signal light, and a center-of-gravity wavelength &lgr;P, rms of the pumping light, which is a mean weighted with respective powers of wavelength components included in the pumping light, by such a wavelength spacing that non-degenerate type four-wave mixing is effectively suppressed.

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: The present invention relates to a Raman amplification optical fiber and the like comprising a structure which can Raman-amplify signal light including a plurality of wavelength components at a high efficiency and effectively restrain signal waveforms from deteriorating due to influences of nonlinear optical phenomena, while improving the degree of freedom in the design of optical fiber transmission lines and Raman amplifiers. As characteristics at each wavelength of signal light, the Raman amplification optical fiber has a chromatic dispersion with an absolute value of 6 ps/nm/km or more but 20 ps/nm/km or less, and an effective area Aeff of 20 &mgr;m2 or less, preferably less than 15 &mgr;m2. More preferably, as a characteristic at each wavelength of signal light, the Raman amplification optical fiber has a Raman gain coefficient GR/Aeff of 0.005 (W·m)−1 or more.

Abstract: The present invention relates to an optical amplifier comprising a structure which prevents transmission quality from lowering and enables constant gain control with a higher speed and higher accuracy. In a typical embodiment of the present invention, amplified light from an EDF is once guided to an optical filter by way of an optical circulator. Of thus guided amplified light, noise light passes through the optical filter, whereas each of signal components is reflected thereby, so as to separate the noise light and signal components from each other. The noise light having passed through the optical filter is detected by a photodetector, and gain control is carried out by a gain control circuit so as to suppress fluctuations in the detected noise light power.

Abstract: An optical communication system having a structure for effectively suppressing occurrence of a nonlinear optical phenomenon in WDM transmission in the 1.58 pm wavelength band. The optical communication system is a hybrid transmission unit including a dispersion-shifted optical fiber having a zero-dispersion wavelength in the 1.55 &mgr;m wavelength band, a dispersion DDSF and a length LDSF, and a high-dispersion fiber having dispersion D1 and length L1. A signal light having the shortest wavelength and having a bit rate B in the signal light wavelength band, the hybrid transmission unit satisfies the following condition: &Dgr;&phgr;XPM·DT≦18000 (unit: (ps/nm)·(Gb/s)2) DT=(DDSF·LDSF+D1·L1)·B2 where &Dgr;&phgr;XPM is the total phase shift amount of cross-phase modulation in the signal light having the shortest wavelength under the influence of signal light having the other wavelengths, and DT is the total dispersion in the hybrid transmission unit.

Abstract: The invention relates to an amplification optical fiber that is suitable for amplification of signals in the L-band, that has the effect of suppressing normal four-wave mixing (FWM) occurring between signals, and that has the structure for effectively suppressing occurrence of non-degenerative FWM as well, and a fiber optic amplifier including the same. A fiber optic amplifier according to the present invention incorporates an amplification optical fiber having a core region doped with a rare earth element, a zero-dispersion wavelength of not more than a wavelength of pumping light, and an effective cutoff wavelength of 1.1 &mgr;m or more but not more than the wavelength of the pumping light. Not only the normal FWM but also the non-degenerative FWM is effectively suppressed by application of the amplification optical fiber.

Abstract: This invention relates to an optical amplification fiber having a structure capable of exhibiting an excellent amplification characteristics, and the like. In the optical amplification fiber, the ratio (&agr;P/&agr;S) of an unsaturated absorption peak value &agr;P in a pumping light wavelength band of 0.98 &mgr;m to an unsaturated absorption peak value as in a signal wavelength band of 1.55 &mgr;m is 0.8 or more and, more preferably, 0.9 or more.

Abstract: An optical communication system having a structure for effectively suppressing occurrence of a nonlinear optical phenomenon in WDM transmission in the 1.58 &mgr;m wavelength band. The optical communication system is a hybrid transmission unit including a dispersion-shifted optical fiber having a zero-dispersion wavelength in the 1.55 &mgr;m wavelength band, a dispersion DDSF and a length LDSF, and a high-dispersion fiber having dispersion D1 and length L1.

Abstract: This invention relates to an amplification optical fiber which requires no gain equalizer and has a flat gain spectrum and high polarization extinction ratio, and the like. The amplification optical fiber has a core region included in a light propagation region through which signals having different wavelengths propagate, a cladding region around the core region, and a polarization maintaining structure for maintaining the polarized states of the signals. The amplification optical fiber is mainly comprised of silica glass, and Er and Al of 4 wt % or more are doped into at least part of the light propagation region including the core region.

Abstract: Disclosed are an optical amplifier and an optical transmission system using the same in which not only can the dispersion of optical waveguide paths for optical amplification be easily and sufficiently compensated, but also the waveform degradation of signal light can be restrained. An optical amplifier according to one embodiment of the present invention comprises at least two erbium-doped fibers 10 and 20, having erbium doped to optically amplify signal light with the pump light, and having dispersion different from each other in sign, and being connected together in series, and two pump light sources 11 and 12 for supplying pump light to them.

Abstract: Disclosed are a gain module and an optical communication system which have gain in a broad wavelength range and are of low cost. The gain module 10 has two optical fibers 111 and 112 which differ from each other with respect to the composition of their respective optical waveguide region and which are connected in series. Because they differ from each other with respect to the quantity of their respective Stokes shift, they have gain in a different wavelength, respectively. The signal lights are introduced into the input end 10a, amplified with the gain module 10 in a wide wavelength range where an optical fiber has a Raman amplification gain, and are emitted from the output end 10b.