Nippon Telegraph and Telephone Corporation

Noboru Takachio

Katsumi Iwatsuki

Masamichi Fujiwara

Mitsuhiro Teshima

Hiroji Masuda

Jun-ichi Kani

Junichi Kani

Hiroo Suzuki

Shingo Kawai

Koji Akimoto

Hitoshi Obara

Kenichi Sato

Katsuhiro Araya

Yoshitada Katagiri

Osamu Ishida

Masafumi Koga

Shoko Ohteru

Fumikazu Ohira

Shinji Nagaoka

Ken-ichi Suzuki

Takuya Nakamura

Jun-Ichi Kani

An optical wavelength division multiplexing network has a multi-level structure where a plurality of optical network units (ONUs) are connected to a lowest-level network. A node apparatus connected to networks other than the lowest-level network includes (a) passive optical components to branch optical signals from a higher-level network to a lower-level network, and couple optical signals from the lower-level network to the higher-level network, and (b) optical amplifiers for the optical signals. A node apparatus connected to the lowest-level network includes (a) an optical multiplexer/de-multiplexer to de-multiplex optical signals from the higher-level network, selectively output an optical signal to each ONU, and multiplex wave-length specific optical signals from the ONUs into a multiplexed optical signal, and (b) optical amplifiers for the optical signals. The node apparatuses provide an optical communication path between the higher-level network and the lower-level (or lowest-level) network without converting the optical signals into electrical signals.

Node apparatus, optical wavelength division multiplexing network, and system switching method

A first optical fiber transmission path is used to transmit continuous-wave light for upstream signal light from the center node to each of the remote nodes, while a second optical fiber transmission path is used to transmit downstream signal light from the center node to each remote node and to transmit upstream signal light (obtained by modulating continuous-wave light) from each remote node to the center node. In this network, specific wavelength bandwidths are allocated to each remote node for the continuous-wave lights (for upstream signal lights) and the downstream signal lights, and the wavelength bandwidths for the continuous-wave lights (for upstream signal lights) and the downstream signal lights are alternately set.

Ring network using multi-wavelength generator

An optical wavelength division multiplexing network which can carry out large-capacity access service with a simple constitution is provided. In an optical network comprising a plurality of layers, a highest level network comprises a ring network having a center node and remote nodes; an intermediate level network comprises a ring centered around a node belonging to the higher level network, and a lowest level network comprises a star network centered around an access node which multiplexes traffic from a plurality of ONU, the ONU and the access node being directly joined together by optical fibers; the center node belonging to the highest level network and the ONU establish a direct communication path by using lights of different wavelengths; at nodes provided therebetween, the optical signals are not electrically processed but are amplified, branched, and routed.

Multi-wavelength light having a frequency band equal to or greater than the FSR of an AWG is demultiplexed into individual wavelength channels, and power level deviations between wavelength channels are suppressed. An optical demultiplexer includes a wavelength-group demultiplexer that demultiplexes multi-wavelength light into wavelength groups formed from wavelength channels, and channel demultiplexers that demultiplex each wavelength group into wavelength channels light. An optical multiplexer includes channel multiplexers that multiplex modulated signal light of each wavelength channel for each wavelength group, and a wavelength-group multiplexer that multiplexes, for each wavelength group, WDM signal light output from the channel multiplexers. The FSR of the wavelength-group multiplexer/demultiplexer is set to be equal to or greater than the frequency band of the multi-wavelength light. The channel multiplexer/demultiplexer is an AWG in which the FSR is approximately the full width at half maximum of the transmission characteristics of each port of the wavelength-group multiplexer/demultiplexer.

Multi-wavelength optical modulation circuit and wavelength-division multiplexed optical signal transmitter

To generate light with the degree of polarization zeroed and the spread of an optical spectrum suppressed even with temporal overlapping between optical pulses each of which is polarized orthogonally to the succeeding pulse, a polarization scrambler includes an optical pulse generator that generates optical pulses with an intensity waveform repetition period T/2 and an electrical field repetition period T in which the same intensity waveform is repeated every repetition period T/2 and in which phase is inverted every repetition period T/2, and an orthogonal polarization delay unit which receives each of the optical pulses, separates the optical pulse into two optical pulses with orthogonal states of polarization, and relatively shifts the temporal position of one of the two optical pulses from that of the other optical pulse by (2n&#x2212;1)T/4 (n is a natural number) to generate light in which each pulse is polarized orthogonally to a succeeding pulse.

Polarization scrambler and optical network using the same

To generate light with the degree of polarization zeroed and the spread of an optical spectrum suppressed even with temporal overlapping between optical pulses each of which is polarized orthogonally to the succeeding pulse, a polarization scrambler includes an optical pulse generator that generates optical pulses with an intensity waveform repetition T/2 and an electrical field repetition period T in which the same intensity waveform is repeated every repetition period T/2 and in which phase is inverted every repetition period T/2, and an orthogonal polarization delay unit which receives each of the optical pulses, separates the optical pulse into two optical pulses with orthogonal states of polarization, and relatively shifts the temporal position of one of the two optical pulses from that of the other optical pulse by (2n&#x2212;1)T/4 (n is a natural number) to generate light in which each pulse is polarized orthogonally to a succeeding pulse.

A multilevel light-intensity modulating circuit for suppressing the amplitude distortion regarding intermediate levels, caused by the conversion from a multilevel electric signal to a multilevel modulated optical signal. The circuit comprises a section for distributing an input optical carrier into n-channel optical carriers; n light-intensity modulators for modulating intensities of the optical carriers by using input two-level electric signals; a control section for producing a phase difference between the n-channel two-level modulated optical signals; a control section for assigning a different light intensity to each of the n-channel two-level modulated optical signals; and a section for combining the n-channel two-level modulated optical signals obtained via the control sections, and outputting a 2 -level modulated optical signal. The phase difference and the different light intensity are defined in advance so as to produce the 2 -level modulated optical signal.

Multilevel light-intensity modulating circuit

An optical amplifier is implemented which can reduce its size and cost by using a smaller number of components. Signal light coupled by an optical combiner with pump light fed from a pumping light source is incident on an EDF (erbium-doped fiber) to be pumped and amplified by the pump light, is emitted from the EDF to be incident on a second optical circulator and output from its second port, passes through an optical component to be fed back to the second optical circulator and launched into the EDF from the second optical circulator, passes through the EDF again in the direction opposite to the first passing direction followed by passing through the optical combiner, and is output from the third port of a first optical circulator.

Optical amplifier and optical fiber communication system using the amplifier

In the optical amplifier an optical divider based on long wavelength (or short wavelength) transmission type dielectric multi-layer filter divides input signal light according to wavelengths, and amplifying sections disposed in parallel and having different respective wavelength amplification regions respectively amplify light signals emitted from the optical divider, and an optical combiner based on long wavelength (or short wavelength) transmission type dielectric multi-layer filter combines light signals output from the respective amplifying sections. In another configuration of the optical amplifier, input signal light is divided using an optical divider based on a dielectric multi-layer filter of a long wavelength (or short wavelength) transmission type, and output signals from the divider are filtered using an optical filter connected in series to a short wavelength (or long wavelength) amplifier generating a loss in the long wavelength (or short wavelength) region of the light signals. Interference noise caused by residual reflection components in the dielectric multi-layer filter is thus suppressed, thereby increasing the bandwidth of useable wavelengths in the signal light.

Optical amplifier

By using a combination of a plurality of completely unequally spaced channel allocations, the influence of four wave mixing is mitigated even while it is incompletely unequally spaced channel allocation, and it is possible both to decrease the occupied bandwidth and increase the number of channels. A plurality of completely unequally spacing channel allocations are combined, and the number of channels changes depending on the amount of scattering of an optical fiber and the frequency that there exists zero dispersion wavelengths on a transmission path. The completely unequally spaced channel allocations of N -channels in a first wavelength region including the zero dispersion wavelength &lgr; or the mode zero dispersion wavelength &lgr; are partitioned, and then in sequence the completely unequally spaced channel allocation of N -, N -, . . . , channels is partitioned, and the wavelength interval of N channels is set by combining all or a part thereof (where N &gE;N 24  . . . >N &gE;N &gE;N ).

Wavelength allocation method, a transmission equipment and receiving equipment using this method and a wavelength division multiplex transmission system

The present invention provides a light generation method and a light source that are preferable in obtaining a single-mode light having high outputs, a small wavelength spectral bandwidth, and a low intensity noise. A white output from a white-light source and having wavelength components over a wide-band in a wavelength spectrum passes through an isolator and is then filtered by a disc-shaped optical filter. A transmitted light is input to a semiconductor optical amplifier having its polarization plane regulated by a polarization controller. An output from the amplifier passes through an isolator and is then filtered by a disc-shaped optical filter again to generate a single-mode light having a small spectral bandwidth and high outputs. Polarization control by the polarization controller corresponds to control of the polarization plane of a semiconductor laser in the semiconductor optical amplifier so as to obtain a maximum gain from the amplifier. This configuration enables a single-mode light having a small spectral bandwidth and high outputs to be easily generated at an arbitrary wavelength.

Light generation method and light source

An optical cross-connect system which can be constructed using the same kind of optical switches having a small extinction ratio and a small number of optical switch driving circuits is provided. The optical signal selector in the system comprises a first optical switching device for permitting only the wavelength-division multiplexed light beam passing through one of plural optical paths to pass, a wavelength router for demultiplexing the permitted multiplexed light beam into optical signals of different wavelengths and respectively outputting these demultiplexed signals into different output ports, this router having a routing characteristic such that the output port to which each demultiplexed signal is output is different for each input port, a second optical switching device for permitting only one of the optical signals output from plural optical paths connected to the output ports of the wavelength router to pass, and an optical combiner for combining the optical paths of the second optical switching device.

Growing community of inventors

Yokosuka, Japan

Noboru Takachio