Nippon Telegraph and Telephone Corporation

Ntt Electronics Corporation

Yoshiki Yamauchi

Tadao Ishibashi

Akimasa Kaneko

Yoshihisa Sakai

Kouichi Fujisaki

Takashi Asaoka

A part of a wavelength division multiplexed optical signal output from a multiplexing area is extracted as a check signal, and then the extracted signal is guided to a multiplexing area. A reentered check signal is detected at a facet located opposite a facet from which the check signal has been reentered, and the state of the detected check signal is determined. Furthermore at need, on the basis of the result of the determination, a control signal is output that controls operations of a plurality of optical signals input to the multiplexing area.

Optical multiplexing circuit and optical multiplexer

A heterojunction bipolar transistor includes an emitter layer of a first conductivity type, a base layer of a second conductivity type adjacent to the emitter layer, a collector buffer layer of the first conductivity type, and a collector layer arranged between the collector buffer layer and the base layer. The collector layer includes a first collector layer formed at the side of the base layer and a second collector layer arranged at the side of the collector buffer layer. The first collector layer is a semiconductor layer having an impurity concentration lower than that of the base layer. The second collector layer is a semiconductor layer of the second conductivity type having an impurity concentration higher than that of the first collector layer.

Heterojunction bipolar transistor

Growing community of inventors

Hiratsuka, Japan

Yoshiki Yamauchi