Hitachi, Ltd.

Yasushi Sawada

Hideaki Tsushima

Shigeki Kitajima

Yasuhiro Shiraki

Yoshifumi Katayama

Eiichi Maruyama

Tomoyoshi Mishima

Takao Kuroda

Makoto Morioka

Yoshimasa Murayama

Yukio Nakano

Yasushi Takahashi

Akihiko Takase

Masahiro Takatori

Kiichi Ueyanagi

Shinji Sakano

Yoshitaka Takasaki

Ken Yamaguchi

Toshiyuki Usagawa

Tatsuo Kanetake

Naoya Kobayashi

Masahiro Koya

Yoshiaki Takemura

Yoshiaki Ikoma

A medium-scale IP telecommunications network is configured in a low-cost optical network with good reliability and expandability. A physical configuration example has a center node-and eight local nodes-through-connected in one OADM ring--. The logical configuration is a star configuration with the central node-at its origin with all traffic passing through the center node-. The local nodes-through-are connected to the central node-by wavelength-unit optical channels or optical paths &#x3bb;through &#x3bb;. Channels are added as required. Initially, for example, the center node-and the local node-are connected by &#x3bb;, but &#x3bb;can added when the need arises. Since the logical star network is limited to approximately two add/drop optical channels at local nodes, costs are reduced by using inexpensive filters (e.g., dielectric interference film filters or fiber Bragg reflectors) that are capable of extracting only the specific wavelength of the optical channel. High reliability is provided through the use of optical switches for correction of fiber transmission path failures.

Optical network

An optical transmission apparatus, an optical repeater using the optical transmission apparatus, and an optical cross-connect equipment for controlling switches depending on supervisory information, comprising: a doped fiber for amplifying an optical signal of wavelength &#x3bf;d; a wavelength multiplexer for outputting a pumping light to the doped fiber; a wavelength multiplexer for multiplexing an amplified optical signal and a supervisory optical signal to as to output it to an optical fiber at downstream side; a pumping and supervisory light source; an optical coupler for distributing the light from the light source at a ratio of N:1 to the wavelength multiplexers; and a driver for controlling the light source by adding the supervisory information and a direct current signal.

Optical transmission apparatus and optical systems

An optical transmission apparatus, an optical repeater using the optical transmission apparatus, and an optical cross-connect equipment for controlling switches depending on supervisory information, comprising: a doped fiber for amplifying an optical signal of wavelength Od; a wavelength multiplexer for outputting a pumping light to the doped fiber; a wavelength multiplexer for multiplexing an amplified optical signal and a supervisory optical signal to as to output it to an optical fiber at downstream side; a pumping and supervisory light source; an optical coupler for distributing the light from the light source at a ratio of N:1 to the wavelength multiplexers; and a driver for controlling the light source by adding the supervisory information and a direct current signal.

An optical transmission apparatus, an optical repeater using the optical transmission apparatus, and an optical cross-connect equipment for controlling switches depending on supervisory information, comprising: a doped fiber for amplifying an optical signal of wavelength &lgr;d; a wavelength multiplexer for outputting a pumping light to the doped fiber; a wavelength multiplexer for multiplexing an amplified optical signal and a supervisory optical signal to as to output it to an optical fiber at downstream side; a pumping and supervisory light source; an optical coupler for distributing the light from the light source at a ratio of N:1 to the wavelength multiplexers; and a driver for controlling the light source by adding the supervisory information and a direct current signal.

A method for restoration from a fault in a communication network formed by interconnecting a plurality of nodes including at least one set of node equipment each including a line terminal equipment and an optical cross-connect equipment, via a plurality of transmission lines using optical fibers. According to this method for restoration from a fault, if a line terminal equipment of at least one set of node equipment has detected a fault in an optical fiber under communication, it gives a command functioning as trigger for optical fiber change-over to an optical cross-connect equipment included in the node equipment. Upon receiving this command functioning as the trigger, the optical cross-connect equipment exchanges change-over control information indicating optical switch setting situation between it and an optical cross-connect equipment included in another node equipment, and forms a restoration route.

Fault restoration control method and it's apparatus in a communication network

A communication network system includes a communication line, a plurality of communication stations each having a node coupled to the communication line and a network controller coupled to the stations for controlling routing for communication messages between nodes. In one embodiment, the messages are sent from plural terminals connected with each node along with communication performance prerequisites. The communication performance prerequisites for a communication message are discriminated in the node which receives the message. Traffic in various routes between the nodes is continually measured in the communication stations and the measuring results are stored in a database storage unit. Future traffic in the various routes is predicted on the basis of the information on the continually measured traffic by the use of a predetermined algorithm and stored in the storage unit for use in determination of routes for communication messages on the basis of the result of the communication performance prerequisites discrimination and predetermined criteria with respect to the updated information on the predicted traffic in the storage unit.

Communication network system and method of controlling a communication

There is disclosed a semiconductor device comprising at least first and second semiconductor layers positioned to form a hetero-junction therebetween, such a hetero-junction being adapted to form a channel, means for controlling carriers, and source and drain areas on opposite edges of the channel, wherein the first and second semiconductor layers formed between the source and drain regions have an area containing only 10.sup.16 cm.sup.-3 or less of an impurity; the first semiconductor layer has a wider forbidden band than that of the second semiconductor layer; and further including at least one semiconductor layer having a higher activation efficiency of impurities than that of the first semiconductor layer, with such at least one semiconductor layer being located on the side of the first semiconductor layer not in contact with the second semiconductor layer. A multi-quantum well structure may be used as the higher impurity activation efficiency semiconductor layer. The electrical resistance in the semiconductor area constituting the source and drain regions can be lowered by utilizing such a higher impurity activation efficiency semiconductor layer.

Heterojunction FET with doubly-doped channel

A semiconductor member has a structure wherein a first semiconductor layer is held between second and third semiconductor layers which have forbidden band widths greater than a forbidden band width of the first semiconductor layer, and wherein only the second semiconductor layer which is formed on a side of the first semiconductor layer close to a substrate is doped with impurities. The semiconductor member constructs the depletion type with the first and second semiconductor layers, and the enhancement type with the first and third semiconductor layers. A semiconductor device can be properly formed in the enhancement or depletion type by selectively connecting the semiconductor layers.

Semiconductor member and semiconductor device employing the same

In a semiconductor device having at least a first semiconductor layer and a second semiconductor layer which are arranged so as to form a heterojunction, an edge of a conduction band of the first semiconductor layer being positioned lower in energy than an edge of a conduction band of the second semiconductor layer in the vicinity of the heterojunction, at least one pair of electrodes which are electronically connected with the first semiconductor layer, and means to control carriers induced in the vicinity of the heterojunction; a semiconductor device characterized in that a low impurity concentration region is comprised in at least the part of the first semiconductor layer between the pair of electrodes, that a region adjoining each of the pair of electrodes is a high impurity concentration region, and that at least one layer containing an impurity which has a conductivity type identical or opposite to that of an impurity contained in the aforementioned regions is comprised in the first semiconductor layer.

Growing community of inventors

Yokohama, Japan

Yasushi Sawada