Abstract: A repeating apparatus disposed at an end point of each divisional repeating interval of a light transmission line performs a first dispersion compensation step, an optical add/drop multiplexing step and a second dispersion compensation step to perform repeating transmission. The ratio of an over compensation amount at the second dispersion compensation step to the sum of dispersion compensation amounts at the first and second dispersion compensation steps is set so as to gradually vary together with the transmission distance from the terminal apparatus for transmission at which the repeating apparatus is disposed on the light transmission line so that degradation of wavelengths to be received by the terminal apparatus for reception is suppressed while dispersion compensation is performed with a high degree of accuracy at each optical add/drop multiplexing point on the transmission line.

Abstract: An optical fiber transmission line including first, second and third optical fibers connected together so that light travels through the transmission line from the first optical fiber, then through the second optical fiber and then through the third optical fiber. The first, second and third optical fibers have first, second and third characteristic values, respectively. The second characteristic value is larger than the first characteristic value and the third characteristic value. The characteristic value of a respective optical fiber being a nonlinear refractive index of the optical fiber divided by an effective cross section of the optical fiber. Pump light is supplied to the transmission line so that Raman amplification occurs in the transmission line as an optical signal travels through the transmission line.

Abstract: The present invention relates to a method for gain equalization, for example. First, an optical transmission line including an optical amplifier having a gain changing nonlinearly with wavelength is provided (step (a)). Secondly, gain equalization of the optical transmission line is performed so as to obtain a gain changing substantially linearly with wavelength (step (b)). Finally, gain equalization of the optical transmission line is performed so as to obtain a gain remaining substantially unchanged with wavelength (step (c)). According to this method, gain equalization of the optical transmission line is performed so as to obtain a gain changing substantially linearly with wavelength. Accordingly, variations in equalization error due to changes in system condition can be easily suppressed.

Abstract: The degree of polarization of an optical signal is measured by a polarimeter and used for providing a feedback signal to adjust adaptive optics of a polarization mode dispersion compensator. The polarization properties of the polarimeter are determined with high accuracy to match the polarimeter through calibration and used to produce the feedback signal.

Abstract: The present invention aims at providing an optical transmission system for improving transmission characteristics, taking account of the nonlinear optical effect to be caused not only in an optical fiber transmission path wherein the distributed Raman amplification is performed but also in an amplifying medium wherein the discrete Raman amplification is performed, within an optical transmission device.

Abstract: An optical fiber transmission line including first, second and third optical fibers connected together so that light travels through the transmission line from the first optical fiber, then through the second optical fiber and then through the third optical fiber. The first, second and third optical fibers have first, second and third characteristic values, respectively. The second characteristic value is larger than the first characteristic value and the third characteristic value. The characteristic value of a respective optical fiber being a nonlinear refractive index of the optical fiber divided by an effective cross section of the optical fiber. Pump light is supplied to the transmission line so that Raman amplification occurs in the transmission line as an optical signal travels through the transmission line.

Abstract: The invention aims to provide a monitoring method that can measure an optical SNR in an ultra high speed optical transmission system with high accuracy, and an optical transmission system using the same. To this end, in the optical transmission system to which the monitoring method of the present invention is applied, the degree of polarization of an optical signal transmitted from an optical transmission apparatus to an optical receiving apparatus via an optical transmission path is measured by a DOP measuring device, and an optical SNR of the optical signal is determined by an optical SNR calculation circuit based on a measured value of the degree of polarization.

Abstract: An optical filter including first and second polarizers, a Faraday rotator and a birefringent element operating together to filter light with a changeable optical transmittance versus wavelength characteristic curve. The curve has specific characteristics.

Abstract: The invention aims to provide an optical transmission system that specifies such a transmission condition so as to obtain high spectrum efficiency and a large transmission distance-capacity product at the same time, and uses low cost and small sized optical senders and optical receivers, to realize a high density wavelength multiplexing optical transmission. For this purpose, a WDM optical transmission system of the invention has a system structure that specifies by calculation the spectrum efficiency at which transmission distance-capacity product becomes a maximum value based on the determination of the type of signal light modulation and the assumption of an equation model expressing transmission characteristics of an optical multiplexer and an optical demultiplexer, and optimizes a bit rate and frequency spacing of signal light output from each optical sender, and the transmission characteristics of the optical multiplexer and the optical demultiplexer, so as to approach the spectrum efficiency.

Abstract: The present invention relates to a method for gain equalization, for example. First, an optical transmission line including an optical amplifier having a gain changing nonlinearly with wavelength is provided (step (a)). Secondly, gain equalization of the optical transmission line is performed so as to obtain a gain changing substantially linearly with wavelength (step (b)). Finally, gain equalization of the optical transmission line is performed so as to obtain a gain remaining substantially unchanged with wavelength (step (c)). According to this method, gain equalization of the optical transmission line is performed so as to obtain a gain changing substantially linearly with wavelength. Accordingly, variations in equalization error due to changes in system condition can be easily suppressed.

Abstract: There is provided in an optical amplifier device used for a system in which a power transfer takes place from comparatively short wavelength signal to a comparatively long wavelength signal. The device includes an amplifier stage coupled to an optical transmission medium, a monitor monitoring a status of a first band; and a pump light source unit supplying at least one first pump light to the optical transmission medium on the basis of the status of the first band monitored, so that the above at least one first pump light supplies additional power to longer wavelength channels related to the status of the first band.

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 invention provides a remote control device of an acousto-optic tunable filter, which comprises an acousto-optic tunable filter interpolated in an optical transmission line, capable of controlling an output state of an input light signal by being supplied with a surface acoustic wave control signal through a control port; a surface acoustic wave control signal source to generate the surface acoustic wave control signal, which is provided at a remote place from the acousto-optic tunable filter; and a control unit that receives an information of the surface acoustic wave control signal from the surface acoustic wave control signal source through remote transmission means, and supplies the surface acoustic wave control signal to the control port of the acousto-optic tunable filter.

Abstract: In order to compensate for chromatic dispersion ad dispersion slope over an entire wavelength band of the optical signal, the wavelength band is split into a plurality of bands, and chromatic dispersion compensation is made to make chromatic dispersion in a central wavelength of each of the bands zero.

Abstract: The present invention relates to a method for gain equalization, for example. First, an optical transmission line including an optical amplifier having a gain changing nonlinearly with wavelength is provided (step (a)). Secondly, gain equalization of the optical transmission line is performed so as to obtain a gain changing substantially linearly with wavelength (step (b)). Finally, gain equalization of the optical transmission line is performed so as to obtain a gain remaining substantially unchanged with wavelength (step (c)). According to this method, gain equalization of the optical transmission line is performed so as to obtain a gain changing substantially linearly with wavelength. Accordingly, variations in equalization error due to changes in system condition can be easily suppressed.

Abstract: A distributed optical amplifier comprises an optical amplifying medium for distributed optical amplification, light supplying means for supplying a pump light to said optical amplifying medium, a pump light detecting part for detecting optical power of said pump light, adjusting means for adjusting an incident power of the light amplified with said optical amplifying medium, and control means for adjusting incident optical power of said light according to an output of said pump light detecting means. Because of this, the present invention can be controlled with a simplified structure of an optical power of an pump light, and an optical power of light to be amplified. A distributed optical amplifier as such can, for example, be applied in optical transmission systems.

Abstract: In a WDM transmission system employing a plurality of short wavelength bands having great attenuation due to optical fiber transmission, an optical repeater is constructed of a first multiplexing section and a second multiplexing section. The first multiplexing section is used for wavelength-multiplexing both the excitation light from a first Raman excitation light source, which distributively amplifies an S+ band included in light propagating through an optical fiber, and the light propagating through the optical fiber. The second multiplexing section is used for wavelength-multiplexing both the excitation light from a second Raman excitation light source, which distributively amplifies an S+ band included in light propagating through an optical fiber, and the light propagating through the optical fiber. The first and second multiplexing sections are provided between the optical fibers disposed between end offices. Thus an equal and satisfactory optical SN ratio even at any band are obtained.

Abstract: The present invention relates to a method for gain equalization, for example. First, an optical transmission line including an optical amplifier having a gain changing nonlinearly with wavelength is provided (step (a)). Secondly, gain equalization of the optical transmission line is performed so as to obtain a gain changing substantially linearly with wavelength (step (b)). Finally, gain equalization of the optical transmission line is performed so as to obtain a gain remaining substantially unchanged with wavelength (step (c)). According to this method, gain equalization of the optical transmission line is performed so as to obtain a gain remaining substantially unchanged with wavelength after the step (b) of performing gain equalization so as to obtain a gain changing substantially linearly with wavelength. Accordingly, variations in equalization error due to changes in system condition can be easily suppressed.

Abstract: The present invention aims at providing an optical transmission system for improving transmission characteristics, taking account of the nonlinear optical effect to be caused not only in an optical fiber transmission path wherein the distributed Raman amplification is performed but also in an amplifying medium wherein the discrete Raman amplification is performed, within an optical transmission device.

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.