The Furukawa Electric Co., Ltd.

Tamotsu Kamiya

Youichi Akasaka

Yasuhiro Shibayama

Nobuhito Uchiyama

Ryuichi Sugizaki

Shinichi Arai

Noritsugu Enomoto

Shigeo Takagi

Sakae Katano

Noboru Sato

Optical communication link

An optical fiber having a good signal-to-noise ratio (SNR) and high Raman efficiency in an optical signal transmission system using Raman amplification, the optical fiber having a refractive index profile, including at least one annular region between a center core and a cladding layer, a Rayleigh scattering coefficient not more than 1 &mgr;m &middot;dB/km, a relative refractive index difference of the center core with respect to the cladding layer of a positive value not more than 0.9%, a relative refractive index difference of an annular region adjoining the center core with respect to the cladding layer from &minus;0.7% to &minus;0.2%, an effective area (Aeff) Aeff not more than 60 &mgr;m , and a zero dispersion wavelength outside of the range of 1400 to 1600 nm, and an optical signal transmission system using that optical fiber for part of the optical signal transmission line in a Raman amplifier or as an optical signal amplification fiber and introducing wavelength multiplexed stimulated light into the optical fiber so as to obtain an amplification effect.

Optical fiber and optical signal transmission system using this optical fiber

The present invention relates to a dispersion shifted optical fiber having zero dispersion at a wavelength band of 1.5 &mgr;m, which suppresses an increase of transmission loss and an increase of polarization mode dispersion when carrying out fiber drawing. An optical fiber according the invention is provided with the first core (refractive index n,.), the second core (refractive index n,), the first clad (refractive index n,) and second clad (refractive index n,) in this order from the center to outside, wherein the abovementioned refractive indexes are in a relationship of n,>n,>n,>n,, Ge which is at a ratio of 0.4 to 1.0% for the value of relative refractive index difference with respect to the second clad is doped on the first core, which is at a ratio of 0.1 to 0.5% for the value of relative refractive index difference with respect to the second clad is doped on the second core as in the above, and the second clad is SiO,, which has a thickness from 1 &mgr;m or more to 40 &mgr;m or less.

Dispersion shifted optical fiber

A dispersion compensating optical fiber is connected to an optical fiber having chromatic dispersion at a transmission wavelength to cancel the chromatic dispersion out, thereby making the chromatic dispersion of an entire transmission system at the transmission wavelength substantially zero or making the chromatic dispersion close to zero. The dispersion compensating optical fiber comprises a core consisting of a quartz-based glass and a cladding formed on the surface of the core and consisting of a quartz-based glass, and a coating layer formed on the surface of the cladding and consisting of a resin, and the dispersion compensating optical fiber has an outer diameter of less than 250 .mu.m. The coating layer has a thickness of 20 .mu.m or more and a two-layer structure consisting of at least two layers including an inner layer and an outer layer having a Young's modulus higher than that of the inner layer.

Dispersion compensating optical fiber

A method of fabricating an optical fiber base material which comprises the steps of sequentially accumulating glass made of doped quartz on the inner peripheral surface of a quartz tube to form glass layers, and then forming by heating means the interior of the tube in a solid state, temporarily thermally shrinking the tube when the accumulating step of the glass layers approaches the final period, then again accumulating glass on the inner periphery of the resultant glass layer and then forming the interior of the tube in a solid state. Thus, this method can reduce the center-dip without loss of the controllability of a refractive index distribution.

Method of fabricating optical fiber base material

An apparatus for fabricating an optical fiber preform having a support for rotatably holding a reaction tube, a raw material supply unit for supplying a glass raw material from one end of the reaction tube to the interior of the reaction tube and a heater for heating the reaction tube by reciprocating in the axial direction of the reaction tube which comprises a pressure measuring unit at the other end of the reaction tube, a gas pressure control chamber having a gas inlet and an exhaust port, and a blower capable of controlling the introduced gas pressure according to the measured value of the pressure memasuring unit in the gas inlet. Thus, the apparatus can accurately control the internal pressure of a reaction tube in good responsiveness.

Apparatus for fabricating optical fiber preform

A process for fabricating an optical fiber by inner-lining a quartz tube with synthetic glass having a refractive index higher than the quartz tube and collapsing it while wire-drawing it via a wire-drawing furnace, comprising the steps of inner-lining the synthetic glass in the quartz tube so that the value of the inner diameter/the outer diameter of the quartz tube is 0.85 or less, sealing one end of the quartz tube to form a sealed end, then holding the quartz tube in a wire-drawing furnace, and wire-drawing it from the sealed end while holding the internal pressure of the quartz tube in negative pressure. Thus, the process prevents moisture from the exterior from mixing and allows the wire-drawing and collapsing steps to be performed stably and reliably.

Growing community of inventors

Ichihara, Japan

Tamotsu Kamiya