Nippon Telegraph and Telephone Corporation

Ntt Electronics Corporation

Shunji Kimura

Tomoaki Yoshida

Hirotaka Nakamura

Shin Kaneko

Shinya Tamaki

Koji Kitahara

Hiroshi Takada

Kazutaka Hara

Masahiro Endo

Kota Asaka

Hiroshi Takahashi

Takayuki Mizuno

Tsutomu Kitoh

Hiroaki Katsurai

Mikitaka Itoh

Masatoshi Tobayashi

Shinsuke Nakano

Masafumi Nogawa

Yoshikazu Urabe

Katsuhisa Taguchi

Shigehiro Kurita

An amplifier applied to TIA is provided to suppress the noise caused by a current source. An amplifier constituting a transimpedance amplifier includes an inductor element inserted between a current source connected to an input terminal of an amplification stage and a power source voltage line. The current source includes a first transistor in which a base terminal is connected to a current control bias and a collector terminal is connected to the input terminal. The inductor element is inserted between the emitter terminal of the first transistor and the power source voltage line.

Amplifier

An OLT configures combinations of wavelength pairs used for upstream and downstream signals, in a wavelength multiplexing optical communication system which performs single-core bidirectional transmission of a plurality of upstream and downstream signals, in such a way that the maximum value of the chromatic dispersion delay amount calculated from each wavelength pair is less than the maximum value of the chromatic dispersion delay amounts calculated when the combinations of wavelength pairs used for upstream and downstream signals are both allocated from the short wave side.

Station-side device and wavelength control method

In a case where a wavelength to be assigned to a subscriber-side device, to which a downstream wavelength has been assigned, is to be changed from the currently used (Source) downstream wavelength to a different changeover target (Target) downstream wavelength, a downstream wavelength changeover instruction message that indicates the change target wavelength is generated. In a case where a wavelength to be assigned to the subscriber-side device, to which an upstream wavelength has been assigned, is to be changed from the currently used (Source) upstream wavelength to a different changeover target (Target) upstream wavelength, an upstream wavelength changeover instruction message that indicates the change target wavelength is generated. The downstream wavelength changeover instruction message and the upstream wavelength changeover instruction message are respectively independently generated, and only the wavelength for which the wavelength changeover instruction message was generated is changed.

Station-side device and wavelength changeover method

An optical communication system of the present invention switches a communication wavelength from a current communication wavelength to a auxiliary communication wavelength when an abnormality occurs in a communication wavelength between a station-side device and any one of a plurality of subscriber devices. Further, this optical communication system switches a communication wavelength used for communication between the subscriber device and the station-side device that perform communication using the auxiliary communication wavelength from the auxiliary communication wavelength back to the current communication wavelength when communication is recovered from an abnormality in the current communication wavelength.

Optical communication system, station-side device, subscriber device, and optical communication method

A transmission start time correction method of a WDM/TDM-PON system includes: a completion instruction procedure in which a station-side subscriber accommodation apparatus issues an instruction using a downstream signal for instructing a subscriber apparatus to perform wavelength switching, the downstream signal including a transmission start time of an upstream signal indicating completion of the wavelength switching of the subscriber apparatus, the upstream signal being transmitted by the subscriber apparatus after the wavelength switching; an instruction completion transmission procedure in which the subscriber apparatus transmits the upstream signal indicating the completion of the wavelength switching at a wavelength after switching at the instructed transmission start time after the wavelength switching is completed in accordance with the instruction; and a transmission start time correction procedure in which the station-side subscriber accommodation apparatus measures a reception time of the upstream signal indicating the completion of the wavelength switching received after the wavelength switching and sets a time obtained by adding a time twice a time difference between a reception time of the upstream signal indicating the completion of the wavelength switching assumed before the wavelength switching and a reception time of the upstream signal indicating the completion of the wavelength switching received after the wavelength switching to the transmission start time of the upstream signal before the wavelength switching as a new transmission start time.

WDM/TDM-PON system and transmission start time correction method thereof

A wavelength and bandwidth allocation method which includes in order a wavelength determination step Sof determining a plurality of wavelengths of an uplink signal from each ONU to OLT to guarantee a guaranteed bandwidth corresponding to a subscription service class of each ONU and a reference bandwidth distribution step Sof distributing, as reference bandwidths, all bandwidths of the plurality of wavelengths determined in the wavelength determination step Sto each ONU according to the subscription service class of each ONU and making the reference bandwidths of ONUs whose subscription service classes are the same be the same.

Wavelength and bandwidth allocation method

In an optical communication abnormality-recovery system and method, when an abnormality occurs in transmission and reception of one wavelength of an optical line terminal of a PON system, an optical network unit that is performing communication at a certain wavelength switches the wavelength for performing the communication to another backup wavelength that is instructed in advance. The optical line terminal also performs switching so that the communication is performed using the same backup wavelength as in the optical network unit.

Optical communication system and optical communication abnormality-recovery method

A protection method wherein an ONU switches a reception wavelength to a backup wavelength so as to be logically connected to a backup OSU designated in advance for each ONU when the ONU detects a failure in an OSU to which the ONU is originally assigned, while the ONU keeps on holding its own connection information with the OLT. In the OLT, a backup OSU for the ONU which is originally assigned to the failed OSU is notified of the information on the ONU when the OLT detects a failure in an OSU. In this way, the ONUs which are originally assigned to the failed OSU resumes communication in a short period.

Protection method and optical communication system

A discovery method, an optical communication method, and an optical communication system which can reduce an error of RTTs when an identifier is fixed after an allocated wavelength has been changed in wavelength-tunable WDM/TDM-PON and can prevent lowering of the bandwidth utilization efficiency. A table, in which a correspondence between child nodes and fixed identifiers as well as the RTTs of a frame with each of the identifiers in all combinations of allocated wavelengths are recorded, is created through a discovery process.

Discovery method, optical communication method, and optical communication system

A wavelength and bandwidth allocation method which includes in order: a wavelength allocation step of allocating each wavelength of an uplink signal to each ONU so that the sum of target bandwidths each allocated as a target to each of the ONUs to which each wavelength of the uplink signal is allocated does not exceed a bandwidth allocated to each wavelength of the uplink signal; and a bandwidth allocation step of allocating a bandwidth to each of the ONUs based on any one of a plurality of requested bandwidths accepted from each of the ONUs in each wavelength of the uplink signal so that the bandwidth actually allocated to each of the ONUs converges to the target bandwidth allocated as a target to each of the ONUs.

An OLT controller makes each optical transceiver transmit a search signal at a prescribed time so that the search signals reach all ONU connection ends of an optical transmission path. In the case where an ONU connected to the ONU connection end of the optical transmission path is unregistered, when the ONU controller receives the search signal, the ONU controller tunes a wavelength of an optical transmitter of the ONU to a wavelength corresponding to the search signal and makes the optical transmitter transmit a response signal to an OLT.

Bandwidth allocation device and bandwidth allocation method

An arrayed waveguide grating provided with a first slab waveguide formed on a substrate; a second slab waveguide formed on the substrate; a first input/output waveguide connected to the first slab waveguide; a second input/output waveguide connected to the second slab waveguide; two or more channel waveguide groups connecting the first and second slab waveguides, each of the channel waveguide groups formed of an aggregate of a plurality of channel waveguides having path lengths sequentially becoming longer by a predetermined path length difference; and an optical filter arranged in at least one of the first and second slab waveguides.

Arrayed waveguide grating, optical module provided with said arrayed waveguide grating, and optical communications system

In the present invention, unlike a conventional circuit, discrimination is not made by integrating a logical code that includes '0' and '1' to some extent and produced from a random code, but repetition of an identical pattern of a well-known preamble signal added to a head portion of a signal is discriminated when a bit-rate of the signal is changed. More specifically, the repetition of the identical pattern is converted into a consecutive identical signal to generate the consecutive identical signal (having a length of tens bits to thousands bits). Although the consecutive identical signal is longer than a same-code continuation length included in the signal, and is shorter than a time constant necessary to the conventional circuit by about one to three digits. Therefore, an integration time can be shortened to the same degree as the generated consecutive identical signal length, and the bit-rate can be discriminated at high speed within a preamble signal receiving time.

Bit-rate discrimination method and its apparatus

A modulation method according to the invention is applied to a modulation device in which a light source is driven by a differential signal while a modulation circuit and the light source are capacitively coupled. In the modulation method of the invention, when an average potential fluctuates at an input terminal of the light source, a potential fluctuation is externally provided using a control circuit such that a normal phase side and a reverse phase side become equal to each other in a time constant of the fluctuation in average potential, and transient states of the average potentials at the normal phase side and reverse phase side are equalized and cancel each other as in-phase components of a signal input to the light source, which allows an optical signal to be normally transmitted from the light source. The optical signal can normally be transmitted from the light source even before the average potentials at a normal phase input terminal and a reverse phase input terminal of the light source are stabilized.

Modulation method, modulation program, recording medium, modulation device, and optical transmitter

A bit-rate automatic control circuit for feedback controlling the gain and bandwidth of a preamplifier in dependence on the bit-rate of a signal is disclosed. The circuit includes a bit-rate discrimination circuit configured to discriminate the bit rate of the signal, and an alarm circuit configured to determine whether the value of received power of the signal is less than the minimum acceptable value of the preamplifier or not. If said alarm circuit determines that the value of received power of the signal is less than the minimum acceptable value of the preamplifier, the bit-rate automatic control circuit determines, irrespective of the discrimination of said bit-rate discrimination circuit, that the bit-rate of the signal is low, and feedback controls the preamplifier based on the determination. According to the above arrangements, if a determination is made that the reception level of the input signal is lower than the minimum acceptable value of received power, the preamplifier can be switched from a state for receiving a high bit-rate signal to a state for receiving a low bit-rate signal.

Growing community of inventors

Atsugi, Japan

Shunji Kimura