Nippon Telegraph and Telephone Corporation

Takashi Kotanigawa

Yoshiaki Yamada

Hideki Maeda

Takuya Ohara

Kei Kitamura

Kaoru Arai

Masahiro Yokota

Kengo Shintaku

Takafumi Hamano

Kohei Saito

Tsutomu Kubo

[Problem] To reduce a filter penalty caused by narrowing of an optical signal band due to optical filters having a multiplexing/demultiplexing function in an optical transmission line between transponder units. [Solution] In an optical transmission systemA, transponder unitstoandtoconnected by optical fibersin which optical filters having a multiplexing/demultiplexing function of an optical signal are interposed include a transmission unitthat transmits the optical signal obtained by modulating laser light from a laser light sourcewith an electric signal from a communication apparatus to the optical fibers, and a reception unitthat receives the optical signal from the optical fibersand converts the received optical signal into an electric signal. The reception unitincludes a BER measurement unit that measures a BER, based on a received signal, and feeds the measured BER back to a transmitting side. The transmission unitincludes a frequency shift control unit that performs frequency shift control of making a center frequency of the laser light match a center frequency of the received optical signal so that the fed back BER is minimized.

Optical transmission system and filter penalty reduction method

A fault location in an optical cable at a long distance is easily measured and detected with low-cost equipment in a configuration in which an isolator is disposed in the vicinity of an optical amplifier for improved optical transmission performance and for stabilization. An optical amplifier has a configuration in which multiplexing/demultiplexing units as first WDM filters and that multiplex/demultiplex main signal light and OTDR light and (measurement light) for submarine cable fault measurement transmitted to a submarine cable in opposite directions from a transmission device side and a reception device side, transmit the multiplexed/demultiplexed main signal light to a main path passing through an isolators and an EDF, and transmit the multiplexed/demultiplexed OTDR light to a bypass path bypassing the isolators and the EDF are included on both sides of a set of the isolators and the EDF of the submarine cable.

Optical amplifier, optical transmission system, and optical cable failure part measurement method

In the optical transport system a transport frame generator divides a transport frame accommodating plural client signals into plural transmission signals. Subcarrier transmission units convert the signals into optical signals using different optical carriers and transmit the converted optical signals. Subcarrier reception units receive the transmitted optical signals and convert the optical signals into reception signals. A transport frame termination unit combines the reception signals to restore the transport frame. A time-demultiplexing processor time-demultiplexes the restored transport frame to be separated into the client signals. A time slot control unit determines a new time slot allocation when time-multiplexing the client signals in the transport frame and stops supply of electric power to a subcarrier transmission unit and a subcarrier reception unit that transmit and receive an optical signal to which the client signals are not allocated.

Optical transport system and resource optimization method

A framer in a transmission device allocates plural optical channel time slots to a plurality of logical prioritized paths. It allocates received client signals to the allocated time slots, and transmits the client signals by a plurality of optical subcarriers that use a plurality of optical wavelengths corresponding to the plurality of time slots. The framer includes: a time slot allocation unit that, in a case where an optical wavelength corresponding to a time slot allocated to a logical path having a high transmission priority is not used, allocates at least one of the plurality of time slots to the logical path having the high transmission priority while the time slot corresponding to the unused optical wavelength is avoided, to change the time slot allocated to the logical path having the high transmission priority.

Framer and framing method

A framer in a transmission device that allocates time slots of an optical channel to a logical path, divides client signals received via the logical path to the time slots allocated to the logical path, and transmits the client signals by a plurality of optical subcarriers using optical wavelengths correlated with the time slots includes: a time slot allocating unit configured to perform a process of reducing a transmission band of the logical path when some of the optical wavelengths are unavailable and changing the time slots allocated to the logical path depending on the reduced transmission band to avoid using the time slots corresponding to the unavailable optical wavelengths.

There is provided a tray which is connected to a plurality of transmitters that multicarrier-transmit a plurality of parallel signals by optical subcarriers. The framer selects time slots to be allocated to a path to be accommodated such that the number of optical subcarriers corresponding to the time slots satisfies a predetermined condition on the basis of empty time slots which are specified by path accommodation information indicating a correspondence between paths allocated to a client signal and time slots in a signal frame and the optical subcarriers corresponding to the empty time slots indicated by time slot information indicating a correspondence between the time slots and the optical subcarriers, and sets the selected time slot in the path accommodation information. The framer sets a client signal to the time slots on the basis of the path accommodation information.

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Tokyo, Japan

Takashi Kotanigawa