Fujitsu Corporation

Hirofumi Araki

Taku Saito

Osamu Takeuchi

Kosuke Komaki

Katsumi Fukumitsu

Hiroshi Nishida

Makoto Shimizu

Taketo Endo

Hisao Nakashima

Nobukazu Koizumi

Yoshitaka Taki

Kanji Naito

Shoichi Murakami

Daijiro Tanaka

Yoshio Nabeyama

Satoru Miyazaki

Shuzo Matsushita

An optical transmission apparatus includes: a coherent detector configured to receive light including different polarization components from an optical transmission path, and perform coherent detection of received light including the different polarization components; an adaptive equalizer configured to adaptively equalize, by a digital filter, a complex electric signal for each of the polarization components obtained by the coherent detection, a gain value for controlling an amplitude of the complex electric signal being applied to the complex electric signal; and a polarization dependent loss monitor configured to determine a polarization dependent loss of the optical transmission path, based on a correction filter parameter obtained by correcting a filter parameter of the digital filter according to the gain value, the filter parameter being adaptively updated by an adaptive equalization of the adaptive equalizer.

Optical transmission apparatus, optical transmission system, and polarization dependent loss monitor

An optical transmission apparatus includes: an optical receiver configured to receive an optical signal; a variable optical attenuator configured to adjust a power of the optical signal to be input to the optical receiver according to a variable attenuation amount; and a controller configured to control the attenuation amount of the variable optical attenuator based on an electrical signal obtained by performing a coherent detection and a photoelectric conversion on the optical signal received by the optical receiver.

Optical transmission apparatus and method for controlling optical power

An optical transmission system includes: a transmission node to transmit wavelength-multiplexed light of a plural wavelengths arranged in a predetermined transmission band; and a reception node to receive the wavelength-multiplexed light, and to include a monitor to monitor a detection sensitivity indicating a sampling phase shift with respect to a phase of light corresponding to one among the received plural wavelengths, and a transmitter to transmit information indicating that the monitored detection sensitivity for light corresponding to a wavelength adjacent to an outer edge of the transmission band, among the plural wavelengths, has been reduced below a threshold value, to the transmission node, wherein the transmission node includes a receiver to receive information indicating a reduction in the detection sensitivity, and a controller to stop wavelength control of shifting the wavelength adjacent to the outer edge in a direction approaching the outer edge in response to reception of the information.

Optical transmission system, wavelength control method and node

An optimization unit in an optical receiver divides a symbol region out of a plurality of symbol regions into which signal points that specifies symbol information included in an optical signal are classified, into a plurality of division regions from the symbol center coordinate of the symbol region. Moreover, the optimization unit accumulates the signal points of the symbol information for every division region in the symbol region. Furthermore, based on the accumulated number of signal points for every division region, the optimization unit controls the average length of a phase estimation unit when the phase noise of the optical signal is calculated.

Optical signal processing device, optical signal processing method and recording medium

An optical transceiver converts a received optical signal to an electric signal and converts the electric signal to a digital signal, and has an adaptive equalizer to adaptively equalize the digital signal, a synchronization part to synchronize a first polarized wave and a second polarized wave contained in the adaptively equalized digital signal and having polarization axes perpendicular to each other, and a symbol offset determination part to determine an amount of symbol offset between the first polarized wave and the second polarized wave based upon symbol synchronization information of the first polarized wave and the second polarized wave supplied from the synchronization part, the symbol offset determination part being configured to repeat determination of the amount of symbol offset and restart the adaptive equalizer until the symbol offset is minimized.

Optical receiver and signal processing method for optical receiver

A method of tap coefficient correction includes: obtaining a synchronization symbol difference between a first polarization and a second polarization orthogonal to the first polarization; obtaining a delay amount of each of the first polarization and the second polarization in an adaptive equalizer; calculating, in a case where a horizontal axis represents a tap number and a vertical axis represents a tap coefficient and a tap number or a nearest tap number with which an area of a drawn figure is halved is set as a gravity center of tap coefficients, a correction reference gravity center of the tap coefficients set in the adaptive equalizer, based on the synchronization symbol difference and the delay amount; and performing a correction of shifting an entire tap coefficients in units of symbol to cause the correction reference gravity center to be closest to a tap center.

Adaptive equalizer tap coefficient correction method and optical receiver

Disclosed is a method of switching between redundant routes of a communication system in which terminal stations are connected by an uplink transmission line and a downlink transmission line that are devoid of redundancy. The method includes adopting working/protection redundancy for first and second apparatuses constituting each terminal station, detecting line failure, which has occurred on the side of the first terminal station, by the second terminal station, multiplexing additional data, which includes a line failure alarm, onto main signal sent from the second terminal station to the first terminal station (or inserting the line failure alarm in the form of overhead bytes), and causing the first terminal station to perform line switching upon detecting the alarm included in the additional data or overhead bytes.

Method of switching between redundant routes in communication system devoid of redundant transmission

Disclosed is a method and apparatus for preventing the occurrence of surge light that may be caused by an off-to-on transition of input signal light in an optical amplifier using an erbium-doped optical fiber. An input electrical signal, optical modulator output, leakage light, or light output is monitored to detect the off-to-on transition of the signal light, and the energy level of the input signal light or pumping light is gradually increased from a low level to an operating level.

Growing community of inventors

Kawasaki, Japan

Hirofumi Araki