Hitachi, Ltd.

Hitachi Communication Technologies, Ltd.

Kenro Sekine

Shinya Sasaki

Nobuhiko Kikuchi

Shinji Nishimura

Toshiki Sugawara

Junya Kosaka

Yukio Hayashi

Yasunobu Matsuoka

Hidehiro Toyoda

Masato Shishikura

Tadashi Matsuoka

Yoshiyuki Niwa

Shuuji Furumoto

Ken'ichi Tanaka

Nobuaki Tajimi

An embodiment of the invention is an optical node configured to transmit/receive a wavelength-division-multiplexed signal. An optical monitoring unit monitors power levels of the wavelength-division-multiplexed signal on a wavelength-by-wavelength basis to acquire wavelength-by-wavelength power level values of the optical signals. A comparison arithmetic unit performs a comparison between each of the acquired wavelength-by-wavelength power level values of the optical signals, and a predetermined upper limit value and a predetermined lower limit value. A target value calculation unit determines target values of power levels at wavelengths whose acquired power level values exceed the upper limit value to be values between a center value and the upper limit value, and determines target values of power levels at wavelengths whose acquired power level values fall below the lower limit value to be values between the center value and the lower limit value.

Optical transport system and optical node

In a quaternary phase modulator including two phase modulators disposed in parallel and a phase adjuster that adjusts a phase difference when the outputs of the two phase modulators are combined, there are provided a second light source that introduces light propagated in a backward direction, a first controller that controls the bias of the two phase modulators so that the intensity of the backward light is a minimum on the input side of the quaternary phase modulator, and a second controller that controls the bias of the phase adjuster so that a result monitored by a photodiode having a bandwidth not exceeding the bit rate on the output side of the quaternary phase modulator is a minimum, the first controller being implemented after the second controller is implemented.

Quaternary phase modulator

A data transmission system comprising a transmitter and a receiver. The transmitter comprises a phase encoder for partitioning consecutive bit data to be input in data in units of X bits; and converting a 2value indicated by the data of X bits in unique association with an (N/2&#x2212;1)value of a Y symbol, and for confining use of signal points, from among the signal points of N-ary phase, only to a signal point P(at a phase angle 0) and N/2&#x2212;2 signal points P(+2) (where 1&#x2266;n&#x3c;N/2&#x2212;2). The receiver comprises a phase decoder for notifying an error detection when a signal point other than a signal point that are permitted to be used is received, and performing an error correction by changing the signal point to a signal point which has a smaller hamming distance.

Data transmission system and transmission code generating method for the same

To provide an optical transceiver module comprising an optical prism for optical communications which has mounting portions, a light emitting portion, light receiving portions, a substrate and a sub-mount that are used as the basis of the optical transceiver module, whose configuration is compact with reduced components which are accurately mounted. A sub-mount is provided on the substrate. The composite optical prism is formed with an optical lens provided with mounting supports and a wavelength division film in an integrated fashion. By using marks on the sub-mount for alignment, the composite optical prism can be mounted accurately on the sub-mount. In addition, the light receiving portions and the light emitting portion can be mounted accurately by using marks for alignment provided on the substrate and the sub-mount.

Optical prism and optical transceiver module for optical communications

A problem to be solved in an optical communication system for carrying out bidirectional transmission between communication nodes by wavelength-division-multiplexed optical signals is that a plurality of optical add-drop multiplexers installed in the communication nodes are required for each transmission direction, and therefore, the communication cost is increased. An optical circulator or an optical coupler is arranged at an input/output port of the optical add-drop multiplexer and the wavelength-division-multiplexed optical signals are assembled for each transmission direction, whereby optical signals transmitted bidirectionally can be handled by one optical add-drop multiplexer.

Optical add-drop multiplexer

Part of an inputted optical add signalis reflected by a mirror, and is thereby inputted into an optical wavelength multiplexerin the reverse direction so that the optical add signal is returned to paths-through-corresponding to wavelengths &#x3bb;through &#x3bb;. If the returned optical add signal is an optical add signal having a correct wavelength, the optical signal enters its corresponding backward direction optical detector-. Accordingly, it is possible to check whether or not a wavelength of the optical add signal is correct.

Optical wavelength add-drop multiplexer

A low-cost configuration of, and at the same time to control the variable dispersion compensator at a high speed in a variable dispersion compensator for compensating the wavelength dependent accumulated dispersion resulting from the wavelength dependency of the transmission fiber and fixed dispersion compensator in a long-distance high-speed WDM transmission system. In order to achieve the object mentioned above, the wavelength dependent representative characteristic of the transmission fibers-. . . n, and the wavelength dependent representative characteristic of the DCFs-. . . n are recorded and maintained in advance in the dispersion control circuit-. . . n of the variable dispersion compensator, and based on the input of dispersion amount at the representative length of the transmission fiber and the fiber length, the dispersion amount at the representative wavelength of the DCF, the accumulated dispersion amount is computed from the wavelength dependent representative characteristic recorded and maintained in advance, and the dispersion amount of the variable dispersion compensatoris determined by taking this as the reference.

Wavelength division multiplex (WDM) transmission system

An optical transmission apparatus includes a demultiplexer for separating wavelength-division multiplexing light received from a first optical transmission line into signals of different wavelengths to transmit the signals to an outside and a multiplexer for multiplexing signals of different wavelengths received from the outside to transmit multiplexed signals to a second optical transmission line. An input check unit is provided for monitoring a power level of a signal separated by the demultiplexer and for providing an output indicative thereof. An output adjuster is provided for intercepting a signal from the outside so as to inhibit receipt of the signal from the outside by the multiplexer depending on the output of the input check unit.

Optical transmission equipment preventing malfunction in recovery from fault

A variable dispersion slope compensator with a high-accuracy and a low-cost structure for compensating the dispersion slope compensation error accompanying variations in the zero-dispersion wavelength in transmission fibers in long-distance, high-speed WDM (wavelength division multiplexing) transmission systems. When the value by which the optical fiber dispersion slope (ps/nm/nm/km) is divided by the dispersion coefficient (ps/nm/km) is defined as the relative dispersion slope RDS (/nm), then the variable dispersion slope compensator includes a first dispersion compensation fiber group including at least two dispersion compensation fibers with a common relative dispersion slope; and a second dispersion compensation fiber group including at least two dispersion compensation fibers with a common relative dispersion slope different from the relative dispersion slope of the first group; and a patch cable group or an optical switching group for making an optional connection combination between the first and second dispersion compensation fiber groups.

Dispersion compensator, optical transmission system and optical transmission method

An optical access network system having a function of correcting upstream signal waveform distortions occurring in the PON section, wherein a central office side apparatus comprises a main controller to notify each subscriber connection apparatus of a transmission grant period, an equalizer of a tap gain adaptive control type to correct waveform distortions of signals received from the subscriber connection apparatuses, an equalizer controller, and a parameter table for storing, for each subscriber connection apparatus, the initial values of tap gains to be set for the equalizer. The main controller issues a switchover request for switching the equalization characteristic to the equalizer controller each time notifying a subscriber connection apparatus of a transmission grant period, and the equalizer controller retrieves the initial values of the tap gains for the subscriber connection apparatus from the parameter table in response to the switchover request, and sets these values to the equalizer.

Optical access network system

In the variable gain compensating apparatus, input power of optical amplifiers employed in respective optical repeaters is monitored, and the monitored input power is transferred to a down-stream side by using supervisor (SV) light. In a repeater equipped with a variable gain tilt compensator, input power monitor information of the optical amplifiers employed in the respective repeaters provided on the upper stream side is acquired from a supervisor signal. While utilizing a linear relationship established between a gain tilt of an optical amplifier and input power of the optical amplifier, the acquired input power monitor information is compared with a reference power value so as to calculate gain tilt amounts of the respective optical amplifiers. Then, the optimum gain tilt compensation amount of the variable gain tilt compensator is determined based upon the calculated gain tilt amounts.

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Fuchu, Japan

Kenro Sekine