Optical fiber and optical component including the same

Details Optical fiber and optical component including the same Optical fiber and optical component including the same

2001-08-29

2003-07-22

Sanghavi, Hemang (Department: 2874)

Optical waveguides

Optical fiber waveguide with cladding

Utilizing multiple core or cladding

C385S142000, C385S144000, C385S037000

Reexamination Certificate

active

06597849

ABSTRACT:

BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an optical fiber comprising a structure which can yield a favorable characteristic when formed with a grating whose refractive index changes along an advancing direction of light, and an optical component such as an optical fiber coupler constituted by the optical fiber.
2. Related Background Art
An optical fiber coupler is an optical component in which respective predetermined parts (optical coupling portions) of a plurality of optical fibers are optically coupled, and has functions of multiplexing, demultiplexing, and branching out light, for example. For instance, each of Satoda, et al., “Add-Drop Multiplexer Using Optical Fiber Grating Coupler,” Advance Proceedings of the 2000 IEICE Spring Conference, Lecture No. C-3-65 (literature 1); Igarashi, et al., “Fabrication of Fused Optical Fiber Grating Coupler,” Advance Proceedings of the 1999 Fall JSAP Conference, Lecture No. 2p-ZF-8 (literature 2); and Igarashi, et al., “Improvement of Fused Optical Fiber Grating Coupler,” Advance Proceedings of the 2000 Spring JSAP Conference, Lecture No. 30a-ZG-18 (literature 3) discloses an optical component (optical fiber grating coupler) having an optical coupling part formed with a grating whose refractive index changes periodically.
FIG. 1
is a view showing the configuration of an optical fiber grating coupler as an optical component. The optical fiber grating coupler
1
shown in this drawing comprises a first optical fiber
11
and a second optical fiber
12
which are optically coupled to each other at a predetermined part (optical coupling portion)
13
. The optical coupling portion
13
is provided with a Bragg grating whose refractive index changes along a signal direction of light. The optical fiber grating coupler
1
is manufactured by the steps of preparing the first and second optical fibers
11
,
12
each having a core region doped with GeO
2
; arranging the first and second optical fibers
11
,
12
closely in contact with each other in parallel and fusing their predetermined parts together while extending them, so as to form the optical coupling portion
13
; and irradiating the optical coupling portion
13
with ultraviolet light by a phase grating method or two-beam interference method so as to form a grating.
In the optical fiber grating coupler
1
, light entering from a first end
11
a
of the first optical fiber
11
reaches the optical coupling portion
13
. Here, if light having a wavelength satisfying the Bragg condition of the grating in the optical coupling portion
13
reaches the optical coupling portion
13
, the light is reflected by the optical coupling portion
13
, so as to be emitted from a first end
12
a
of the second optical fiber
12
. If light having a wavelength not satisfying the Bragg condition of the optical coupling portion
13
reaches the optical coupling portion
13
from the first end
11
a
of the first optical fiber
11
, then the light having reached the optical coupling portion
13
is transmitted through the optical coupling portion
13
, so as to be emitted from a second end
12
b
of the second optical fiber
12
. In this case, the optical fiber grating coupler
1
functions as a demultiplexer by which the light entering from the first end
11
a
of the first optical fiber
11
is emitted to one of the first end
12
a
and second end
12
b
of the second optical fiber
12
depending on its wavelength.
In the optical fiber grating coupler
1
, light entering from the first end
11
a
of the first optical fiber
11
reaches the optical coupling portion
13
. Here, if light having a wavelength not satisfying the Bragg condition of the grating provided in the optical coupling portion
13
reaches the optical coupling portion
13
, then the light having reached the optical coupling portion
13
is transmitted through the optical coupling portion
13
, so as to be emitted from the second end
12
b
of the second optical fiber
12
. On the other hand, light entering from a second end
11
b
of the first optical fiber
11
also reaches the optical coupling portion
13
. Here, if light having a wavelength not satisfying the Bragg condition of the grating provided in the optical coupling portion
13
reaches the optical coupling portion
13
, then the light is reflected by the optical coupling portion
13
, so as to be emitted from the second end
12
b
of the second optical fiber
12
. In this case, the optical fiber grating coupler
1
functions as a multiplexer by which the light entering from the first end
11
a
of the first optical fiber
11
(light having a wavelength not satisfying the Bragg condition) and the light entering from the second end
11
b
of the first optical fiber
11
(light having a wavelength satisfying the Bragg condition) are multiplexed, and thus multiplexed light is emitted from the second end
12
b
of the second optical fiber
12
.
Since the optical fiber grating coupler
1
has the respective functions of the demultiplexer and multiplexer, it also functions as an optical ADM (add-drop multiplexer). An optical component (optical fiber coupler) whose optical coupling portion
13
is not provided with a grating functions as a demultiplexer by which light entering from the first end
11
a
of the first optical fiber
11
is branched out so that one of thus branched light components is emitted from the second end
11
b
of the first optical fiber
11
whereas the other of the branched light components is emitted from the second end
12
b
of the second optical fiber
12
.
SUMMARY OF THE INVENTION
The inventors studied the conventional techniques mentioned above and, as a result, have found problems as follows. The grating provided at the optical coupling portion
13
in the optical fiber grating coupler
1
acting as the optical component is required to function so as to reflect light having a wavelength satisfying the Bragg condition at a high reflectivity and transmit light having a wavelength not satisfying the Bragg condition at a high transmissivity. Therefore, as suggested in F. Bakhti, et al., “Optical add/drop multiplexer based on UV-written Bragg grating in a fused 100% coupler,” Electronics Letters, Vol. 33, No. 9, pp. 803-804 (1997) (literature 4), and the above-mentioned literatures 2 and 3, for example, adding GeO
2
not only to the respective core regions of the first and second optical fibers
11
,
12
but also throughout their cladding regions so as to form a grating not only in the core region but also throughout the cladding region in the optical coupling portion
13
has been under consideration.
However, the inventors have found that the following problems occur if GeO
2
is contained not only in the core region of each optical fiber but also throughout the cladding region thereof. Namely, strength extremely decreases in an optical fiber in which the whole cladding region including the core region is doped with GeO
2
. When making the optical fiber grating coupler
1
such as the one mentioned above by using this optical fiber, GeO
2
is likely to evaporate and diffuse upon the fusion for forming the optical coupling portion
13
, thereby generating bubbles in the optical fibers. As a consequence, there has been a problem that the fusion becomes difficult or the fusing strength weakens.
In order to overcome the above-mentioned problems according to the inventors' findings, it is an object of the present invention to provide an optical fiber having a sufficient strength, in which not only a core region but also a cladding region is doped with GeO
2
; and an optical component including the same and having excellent optical coupling characteristics, which is easy to manufacture.
The present invention provides an optical fiber, mainly composed of silica glass, having an outer diameter D; the optical fiber comprising, at least, a core region extending along a predetermined axis, a first cladding region disposed at an outer periphery of the core region, and a second cladding region disposed at an outer perip

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