Hitachi, Ltd.

Hitachi Cable, Inc.

Masao Sumi

Toshiki P Tanaka

Seiichi Onoda

Katsuyuki Imoto

Tsuneo Suganuma

Yoshitaka Takasaki

Koji Ishida

Gyozo Toda

Shojiro Kawakami

Shigeo Nishida

A three-layer structure optical fiber comprises a first transparent dielectric core layer having a relatively high refractive index, a second transparent dielectric intermediate layer having a relatively low refractive index and a third transparent dielectric cladding layer having an intermediate refractive index wherein the parameter of the optical fiber is determined as follows: ##EQU1## where B is the bandwidth of the signal to be transmitted, z is the transmission distance, C is the velocity of light in vacuum, .eta.o is the refractive index of the core layer, q is the ratio of refractive indices between the core layer and second layer, V = normalized frequency, ##EQU2## p is the ratio of refractive index between the core layer and the third layer, and U.sub.11 =2,405.

Optical fiber

In order to expand the product between the transmission length and the transmission bandwidth of an optical fiber for use in the optical communication and to facilitate the connection between the optical fibers, the optical fiber is made of transparent materials of three concentric layers of a core whose refractive index gradually decreases in the radial direction from the center, an intermediate layer which has a uniform refractive index lower than the varying refractive index of the core, and a cladding which has a uniform refractive index substantially equal to the lowest refractive index of the core.

Optical transmission line

In order to make the transmission loss of the lowest order leaky mode over the transmission length 10dB or more, an optical fiber for optical transmission is constructed of a cladding layer whose refractive index is constant, an intermediate layer which has a constant refractive index lower than the refractive index of the cladding layer, and a core whose refractive index is continuously varied so as to be the highest at the central part and to be substantially equal to that of the cladding layer at the peripheral part, and the thickness of the intermediate layer is 0.1-1 times the radius of the core.

Apparatus for producing an optical fiber including apparatus for heating an optical fiber preform, apparatus for drawing out the optical fiber from the optical fiber preform whose fore end part has been made molten by the heating and for taking up the drawn out fiber, apparatus for causing a gas to flow along the outer peripheral surface of the molten part of the optical fiber preform, and apparatus for controlling both the flow rate of the gas and the drawing-out speed of the optical fiber according to a fluctuation in the diameter of the optical fiber. The controlling apparatus includes (i) a fiber diameter detector and a fiber diameter measuring device which detect and measure the diameter of the optical fiber drawn out, (ii) a fiber diameter controlling circuit which receives an output of the fiber diameter measuring device and a reference value for specifying a fiber diameter and which compares them so as to deliver an output for controlling the fiber diameter, (iii) a gas flow rate controller which is driven by the output for controlling the fiber diameter, and (iv) a take-up speed controller which is driven by the output for controlling the fiber diameter. With this apparatus, the optical fiber of uniform diameter can be easily produced.

Apparatus for producing optical fiber

For drawing an optical fiber from an optical fiber preform there are provided means for heating an optical fiber preform, means for pulling out an optical fiber from the optical fiber preform whose fore end part has been fused by heating, and means for causing gas to flow along the outer peripheral surface of the fused part of the optical fiber preform. By further controlling the flow rate of the gas and/or the pulling-out velocity for the optical fiber according to fluctuations in the fiber diameter of the optical fiber, an optical fiber of uniform fiber diameter is easily provided.

Growing community of inventors

Higashiyamato, Japan

Masao Sumi