Optical waveguides – Optical fiber waveguide with cladding
Patent
1996-04-16
1997-09-09
Healy, Brian
Optical waveguides
Optical fiber waveguide with cladding
385 28, 385141, 65385, 65426, G02B 602, C03B 37023
Patent
active
056664540
DESCRIPTION:
BRIEF SUMMARY
TECHNICAL FIELD
The present invention relates to an optical fiber such as a dispersion-shifted single-mode (DSF) optical fiber or single-mode optical fiber, more particularly relates to a method of producing a core rod for optical fibers so as to obtain a DSF or single-mode optical fiber having the desired characteristics.
BACKGROUND ART
First, a description will be made of a dispersion shift single-mode optical fiber.
The usually used dispersion-shifted single-mode optical fiber (hereinafter simply referred to as a dispersion-shifted optical fiber or a DSF) having an outer diameter of 125 .mu.m has at its center a core part having a higher refractive-index than that of its circumference. When viewing the construction of this DSF from the standpoint of the distribution of the intensity of the light, the intensity of the light is the largest at the center of the DSF, and the intensity of the light becomes smaller as the light approaches the outer circumference away from the center. The change of that intensity is of a sharp bell-shaped curve. Usually, in such a case, the center portion of the DSF is called as the "mode field", and the diameter thereof is called the "mode field diameter". Note that, although the mode field diameter slightly differs according to some conditions, when the wavelength of the light which is propagated is 1.55 .mu.m, the general construction of the DSF has a mode field diameter of about 8 .mu.m.
A preform for a DSF having a construction as mentioned before is produced (manufactured) as follows. (a) First, a porous glass body of a core rod for a DSF including a core portion in which at least a metal dopant exists is synthesized by a VAD method etc (at present, frequently, part of the cladding portion is synthesized together with the core portion, and hereinafter, one including also a part of this cladding portion is referred to as a core rod for the DSF). (b) Subsequently, the porous glass body is dehydrated and sintered to form the core rod for the DSF. (c) Further, using the core rod for the DSF as a target rod, a porous glass layer having a desired thickness corresponding to the cladding layer is formed on the outer circumference thereof by an outer vapor deposition (OVD method) etc., then (d) that porous glass layer is dehydrated and formed into a glass, thereby to obtain a preform for the DSF. (e) Thereafter, that preform for the DSF is heated and drawn, thereby to obtain a DSF having a desired thickness.
In recent years, due to the advances made in various technologies, it has become possible to obtain a large size preform for a DSF. In this case, among the aforementioned manufacturing steps, the manufacturing step of forming the porous glass layer by the OVD method or the like and the manufacturing step of dehydration and glass-forming of the porous glass are often repeated to fabricate the large sized preform for a DSF.
The above conventional manufacturing method of a large size DSF is characterized in that the transmission characteristic is easily controlled. No superior manufacturing method to take the place of this has yet been found.
However, in the above manufacturing method, the manufacturing steps for making a single preform comprise at least two different manufacturing steps of the VAD method and OVD method. For this reason, a boundary surface exists between the glasses manufactured by the different steps. It is known that defects are apt to occur at the boundary surface. Also, glass has a different viscosity according to the content of impurities. Usually, the purity of the glass existing on the outer circumference of the core rod portion formed by the OVD method or the like tends to be low in comparison with the purity of the core rod portion. Also, in the core rod, the concentration of the metal dopant in the diameter direction is not constant since the distribution of refractive-index is controlled. For this reason, the viscosity of the glass of the dispersion-shifted optical fiber is not uniform.
The defects of the glass mentioned before exert the following
REFERENCES:
patent: 4217027 (1980-08-01), MacChesney et al.
patent: 4877304 (1989-10-01), Bhagavatula
patent: 5035477 (1991-07-01), Schlump
patent: 5329607 (1994-07-01), Kamikawa et al.
patent: 5361319 (1994-11-01), Antos et al.
patent: 5381503 (1995-01-01), Kanamori et al.
patent: 5446820 (1995-08-01), Ishikawa et al.
patent: 5581647 (1996-12-01), Onishi et al.
Chiba Hideaki
Kawasaki Mituhiro
Takahashi Tadashi
Terada Jun
Healy Brian
The Furukawa Electric Co. Ltd.
LandOfFree
Preform for optical fiber and method of producing optical fiber does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Preform for optical fiber and method of producing optical fiber, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Preform for optical fiber and method of producing optical fiber will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-75195