Nippon Telegraph and Telephone Corporation

Fujikura Limited

Osaka Prefecture University Public Corporation

Shimane University

Kyouzou Tsujikawa

Shoichiro Matsuo

Katsuhiro Takenaga

Makoto Yamada

Hiroji Masuda

Kentaro Ichii

Hirotaka Ono

Takashi Matsui

Shoji Tanigawa

Taiji Sakamoto

Shigeru Tomita

A plurality of coresis disposed around the center axis of a first claddingin a state in which an inter-core distance &#x39b; of cores adjacent to each other is equal, a refractive index nof the coreis provided higher than a refractive index nof the first cladding, and the refractive index nof the first claddingis provided higher than a refractive index nof a second cladding. Moreover, 5.8&#x2266;&#x39b;/MFD(2&#x3bb;c/(&#x3bb;c+&#x3bb;op))&#x2266;8 is satisfied, where the inter-core distance is defined as &#x39b;, a mode field diameter of the core is defined as MFD, a cutoff wavelength is defined as &#x3bb;c, and a wavelength of communication light incident on the coreis defined as &#x3bb;op.

Amplifying optical fiber and optical amplifier

The first claddinghas a two-layer structure formed of a solid inner layerA passed through the center axis of the first claddingand an outer layerB enclosing the inner layerA and the plurality of coreswith no gap. A refractive index nof the coreis provided higher than refractive indexes nand nof the inner layerA and the outer layerB, the refractive indexes nA and nB of the inner layerA and the outer layerB are provided higher than a refractive index nof the second cladding, and the refractive index nof the inner layerA is provided lower than the refractive index nof the outer layerB.

Each of a first clad region () and a second clad region () has holes () which have identical diameters and are periodically formed so that the first clad region () and the second clad region () each have an effective refractive index lower than a refractive index of a core region (), the effective refractive index of the first clad region () being lower than that of the second clad region ().

Optical fiber having holes

Growing community of inventors

Tsukuba, Japan

Kyouzou Tsujikawa