Optical amplifying glass and optical waveguide

Details Optical amplifying glass and optical waveguide Optical amplifying glass and optical waveguide

2002-10-07

2004-11-16

Kim, Ellen E. (Department: 2874)

Optical waveguides

Having particular optical characteristic modifying chemical...

Of waveguide core

C501S037000, C501S053000, C501S900000

Reexamination Certificate

active

06819860

ABSTRACT:

The present invention relates to an optical amplifying glass which is suitable for amplification of a light with a wavelength of from 1,530 to 1,630 nm.
As an optical communication system capable of coping with diversification of communication services, a wavelength division multiplexing communication system (WDM) has, for example, been proposed to increase the transmission capacity by increasing the number of wavelength division multiplexing channels.
In e.g. WDM using a light in C band (wavelength: 1,530 to 1,560 nm) or L band (wavelength: 1,570 to 1,620 nm) as a signal light, an optical fiber amplifier is essential which amplifies such a signal light. As such an amplifier, EDFA is being developed.
EDFA is an optical fiber amplifier wherein the core of the optical fiber is an Er-doped glass. As such an optical fiber, an Er-doped SiO
2
fiber wherein the core is SiO
2
glass, or an Er-doped fluoride glass fiber wherein the core is fluoride glass, may, for example, be mentioned.
However, EDFA employing the Er-doped SiO
2
fiber has had a problem that the length of the optical fiber is typically at least 20 m, and it has to be wound into a bobbin in order to accommodate it in an EDFA container having a size of about 30 cm.
Whereas, EDFA using an Er-doped fluoride glass fiber, has had a drawback that its glass transition point is typically at most 320° C., whereby a thermal damage is likely to result if the intensity of excitation light for optical amplification increases.
In order to solve these problems, JP-A-2001-102661 discloses a resin-coated glass fiber having a length of 6 cm, whereby a gain of at least 9 dB can be obtained with respect to a signal light having a wavelength of from 1.50 &mgr;m to 1.59 &mgr;m and an intensity of 0.001 mW. Here, the length is 6 cm, whereby it is unnecessary to wind it into a bobbin. Further, the core of the above resin-coated glass fiber, is an Er-doped bismuth oxide type glass (hereinafter referred to as the conventional glass) having Er doped in a proportion of 0.6 part by mass per 100 parts by mass of a bismuth oxide type matrix glass (as represented by mol %, Bi
2
O
3
: 42.8%, B
2
O
3
: 28.5%, SiO
2
: 14.3%, Ga
2
O
3
: 7.1%, Al
2
O
3
: 7.1%, and CeO
2
: 0.2%).
The above-mentioned gain of the conventional glass is one with respect to a case where the fiber length is 6 cm, and the intensity of the signal light is 0.001 mW. It is commonly known that the gain decreases as the intensity of the signal light increases, and a gain of a desired level may not be obtained by the conventional glass with respect to a signal light having an intensity of about 0.1 mW, which is commonly used for e.g. WDM.
Further, if the conventional glass is used for amplification of a light within a wavelength region including L band, a conversion efficiency of a desired level, may not be obtained.
It is an object of the present invention to provide an optical amplifying glass and an optical waveguide, which are capable of solving the above-mentioned problems.
The present invention provides an optical amplifying glass comprising 100 parts by mass of a matrix glass and from 0.1 to 10 parts by mass of Er doped to the matrix glass, wherein the matrix glass comprises Bi
2
O
3
, at least one of B
2
O
3
and SiO
2
, at least one member selected from the group consisting of Ga
2
O
3
, WO
3
and TeO
2
, and La
2
O
3
in such a ratio that Bi
2
O
3
is from 20 to 80 mol %, B
2
O
3
+SiO
2
is from 5 to 75 mol %, Ga
2
O
3
+WO
3
+TeO
2
is from 0.1 to 35 mol %, and La
2
O
3
is from 0.01 to 15 mol %.
Further, the present invention provides an optical waveguide comprising the above optical amplifying glass as the core.
Now, the present invention will be described in detail with reference to the preferred embodiments.
The optical amplifying glass of the present invention (hereinafter referred to as the glass of the present invention) is used usually as a core of an optical waveguide having a core/cladding structure, such as a glass fiber having the same structure or a plane waveguide having the same structure. Such an optical waveguide is the waveguide of the present invention.
The optical waveguide of the present invention is suitable for amplifying a light with a wavelength of from 1,530 to 1,630 nm, particularly a light in C band in a short length. Further, it is suitable for amplifying a light in L band at a high conversion efficiency.
Such amplification is carried out by introducing an excitation light together with a light to be amplified (i.e. a signal light) into the core. As such an excitation light, a laser beam having a wavelength of from 970 to 990 nm or from 1,470 to 1,490 nm is usually employed. Usually, for amplification of a light in C band, an excitation light having a wavelength of from 970 to 990 nm is used, and for amplification of a light in L band, an excitation light having a wavelength of 1,470 to 1,490 nm is used. However, the excitation light is not limited thereto.
In a case where the optical waveguide of the present invention is used for amplification of a light in C band in a length of 8 cm or less, the gain for a light having a wavelength of from 1,530 nm to 1,560 nm and an intensity of 0.1 mW, is preferably at least 8 dB when the length of the optical waveguide is 5 cm. If the gain when the length is 5 cm, is less than 8 dB, the above problem may not be solved. Namely, when the length is 8 cm or less, no adequate gain may be obtained with respect to a signal light having an intensity of 0.1 mW. The above gain when the length is 5 cm, is more preferably at least 9 dB.
In a case where the optical waveguide of the present invention is used for amplification of a light in the wavelength region including L band, the conversion efficiency &eegr; for a light having a wavelength of 1,600 nm, is preferably at least 10%. If it is less than 10%, the desired gain may not be obtained. It is more preferably at least 15%. Here, &eegr; is represented by a percentage of the ratio of the signal light output intensity to the excitation light intensity.
It is more preferred that &eegr; is at least 10%, and the 3-dB down bandwidth for a light having an intensity of 1 mW within a wavelength region of from 1,530 to 1,620 nm, is at least 55 nm, particularly preferably at least 60 nm.
Further, it is more preferred that &eegr; is at least 10%, and the gain for a light having a wavelength of 1,620 nm and an intensity of 1 mW, is at least 10 dB, particularly preferably at least 15 dB.
It is particularly preferred that &eegr; is at least 10%, the 3-dB down bandwidth for a light having an intensity of 1 mW within a wavelength region of from 1,530 to 1,620 nm, is at least 55 nm, and the gain for a light having a wavelength of 1,620 nm and an intensity of 1 mW, is at least 10 dB.
In an optical fiber having the glass of the present invention as a core (hereinafter referred to as an optical fiber of the present invention), the core diameter and the cladding diameter are typically from 2 to 10 &mgr;m, and from 100 to 200 &mgr;m, respectively.
When the optical fiber of the present invention is used for EDFA without being wound into a bobbin, its length is preferably at most 8 cm, more preferably at most 6 cm, particularly preferably at most 5 cm.
It is preferred that the refractive index n
2
of the cladding of the optical fiber of the present invention and the refractive index n
1
of the core i.e. the glass of the present invention, will satisfy the following formula. Here, n
1
is typically from 1.8 to 2.2.
0.0005≦(
n
1
−n
2
)/
n
1
≦0.1
Further, it is preferred that the above cladding is made of a glass, and it is more preferred that such a glass consists essentially of, as represented by mol %, from 25 to 70% of Bi
2
O
3
, from 5 to 74.89% of B
2
O
3
+SiO
2
, from 0.1 to 30% of Al
2
O
3
+Ga
2
O
3
, and from 0.01 to 10% of CeO
2
.
The optical fiber of the present invention may be prepared, for example, by preparing a preform having the core glass and the cladding glass combined by a well-known extrusion method, and drawing such a preform.
The gla

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