Nippon Telegraph and Telephone Corporation

Hitoshi Obara

Katsumi Iwatsuki

Noboru Takachio

Hiroshi Abe

Kazuo Aida

Mitsuhiro Teshima

Shingo Kawai

Yoshitada Katagiri

Ken-Ichi Suzuki

Masafumi Koga

Fumikazu Ohira

Shinji Nagaoka

Yoshiaki Tachikawa

Ken'ichi Sato

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

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.

A disk shaped tunable optical filter is formed by a transparent substrate in a disk shape, and a filter layer formed on a top surface of the substrate, having such a filter characteristic that a transmission central wavelength varies along a circumferential direction as a monotonic function of a viewing angle. This disk shaped tunable optical filter can be advatageously utilized in realizing a wavelength discrimination apparatus, a reference wavelength light generation apparatus, an optical packet generation apparatus, and a tunable optical filter module, which are also disclosed.

Disk shaped tunable optical filter

A multiwavelength simultaneous monitoring circuit capable of precise discrimination of wavelengths of a WDM (Wavelength Division Multiplexed) signal including multiplexed wavelength waves, and suitable for optical integrated circuits having large resistance to vibration. It includes a reference optical source, an AWG (Arrayed-waveguide grating) having periodic center transmission wavelength (or crossover wavelengths) corresponding to the wavelength spacing between multiplexed waves of the WDM signal, a first wavelength error detector for generating a wavelength error signal of an RF signal (reference optical signal) with respect to a zero-cross wavelength on the basis of a ratio between the levels of the RF signal outputted from two output waveguides of the AWG, a control circuit for locking the zero-cross wavelength to the wavelength of the RF signal in response to the wavelength error signal, and a second wavelength error detector for generating wavelength error signals of the multiplexed waves of the WDM signal by detecting signal levels of respective wavelength signals of the WDM signal outputted from each pair of output ports of the AWG.

Multiwavelength simultaneous monitoring circuit employing

Growing community of inventors

Yokohama, Japan

Hitoshi Obara