Title: Tm3+-doped silicate glass and the use thereof
Abstract: The present invention is a thulium doped silicate glass having an excellent fluorescent emission in the 1.4 μm band, and the usage thereof. The silicate glass of this invention includes: 65˜95 mol % SiO2; 0.5˜30 mol % bivalent metal oxide consisting of one or more material selected from ZnO, BaO, SrO and PbO; and 1˜15 mol % of SnO2 or TiO2, wherein 3˜30 mol % oxygen of the glass composition are replaced with fluorine, and 0.01˜1 mol % of thulium ions are doped, and the fluorescence lifetime of the 3H4 level of the Tm3+ is more than 50 μs. The silicate glass can be easily formed into a waveguide, such as optical fiber, and it has an excellent ability to splice with the optical fiber for transmission. They have excellent chemical durability and the characteristic of 1.4 μm band fluorescent emission by suppressing the non-radiative transition through multi-phonon relaxation. Thus they have long fluorescence lifetime of the 3H4 of Tm3+.
Patent Number: 6,916,753 Issued on 07/12/2005 to Cho, et al.
| Inventors:
|
Cho; Doo Hee (Daejon, KR);
Choi; Yong Gyu (Daejon, KR);
Seo; Hong Seok (Daejon, KR);
Park; Bong Je (Busan, KR)
|
| Assignee:
|
Electronics and Telecommunications Research Institute (Daejon, KR)
|
| Appl. No.:
|
331353 |
| Filed:
|
December 31, 2002 |
Foreign Application Priority Data
| May 06, 2002[KR] | 10-2002-0024689 |
| Current U.S. Class: |
501/57; 501/64; 501/54; 501/72; 252/301.4F; 252/301.4H; 428/426; 428/427; 428/428; 385/142; 385/144 |
| Intern'l Class: |
C03C 004/12; C03C003/11.2 |
| Field of Search: |
501/57,64,54,72
252/301.4,301.4
428/426,427,429
385/142,144
|
References Cited [Referenced By]
U.S. Patent Documents
Other References
Brian Cole, et al.; "S-band amplification in a thulium doped silicate fiber";
OFC 2001; pp. TuQ3-1-3.
Mira Naftaly, et al.; "Tm3+-doped tellurite glass for a broadband
amplifier at 1.47 μm"; Applied Optics; vol. 39, No. 27; Sep. 20, 2000; pp. 4979-4984.
T. Komukai, et al.; "1.47 μm Band Tm3+Doped Fluoride Fibre Amplifier
Using a 1.064 μm Upconversion Pumping Scheme"; Electronics Letters; Jan.
7, 1993; vol. 29, No. 1; pp. 110-112.
|
Primary Examiner: Koslow; C. Melissa
Attorney, Agent or Firm: Mayer, Brown, Rowe & Maw LLP
Claims
1. A thulium doped silicate glass, comprising:
65˜95 mol % SiO
2;
0.5˜30 mol % bivalent metal oxide consisting of one or more material selected
from ZnO, BaO, SrO and PbO; and
1˜15 mol % of SnO
2 or TiO
2,
wherein 3˜30 mol % oxygen of the glass composition are replaced with fluorine,
and 0.01˜1 mol % of thulium ions are doped, and the fluorescence lifetime
of the
3H
4 level of the Tm
3+ is more than 50 μs.
2. The glass as recited in claim 1, further comprising: 0.5˜5 mol % alkali
metal oxide consisting of one or more material selected from K
2O, Rb
2O
and Cs
2O.
3. The glass as recited in claim 1, further comprising: 1˜15 mol % trivalent
metal oxide consisting of one or more material selected from In
2O3 and Sb
2O
3.
4. The glass as recited in claim 1, further comprising: 0.5˜5 mol % alkali
metal oxide consisting of one or more material selected from K
2O, Rb
2O
and Cs
2O; and 1˜15 mol % trivalent metal oxide consisting of one
or more material selected from In
2O
3 and Sb
2O
3.
5. An optical fiber, comprising: a core having the same composition recited in
claim 1 and a cladding having a lower refractive index than the core.
6. The optical fiber as recited in claim 5, wherein the core further comprises:
0.5˜5 mol % alkali metal oxide consisting of one or more material selected
from K
2O, Rb
2O and Cs
2O.
7. The optical fiber as recited in claim 5, wherein the core further comprises:
1˜15 mol % trivalent metal oxide consisting of one or more material selected
from In
2O
3 and Sb
2O
3.
8. The optical fiber as recited in claim 5, wherein the core further comprises:
0.5˜5 mol % alkali metal oxide consisting of one or more material selected
from K
2O, Rb
2O and Cs
2O; and 1˜15 mol %
trivalent metal oxide consisting of one or more material selected from In
2O
3
and Sb
2O
3.
Description
FIELD OF THE INVENTION
The present invention relates to a Tm
3+-doped silicate glass and the
usage thereof: and, more particularly, to a Tm
3+-doped silicate glass
having an excellent fluorescent emission in the S-band, and the usage of the Tm
3+-doped
silicate glass.
DESCRIPTION OF RELATED ART
Since a wavelength division multiplexing (WDM) optical communication system
was developed, the wavelength bandwidth of the optical communication has been stimulated
to be expanded. At present C-band (1530˜1570 nm) is widely used, and an L-band
(1570˜1610 μm) is used in WDM optical communications gradually. However,
the two bands account for less than a quarter of the low-loss transmission window
of a silicate optical fiber.
Recently an efficient optical amplifier of another band has been developed
and the transmission wavelength bandwidth has been extended remarkably. A thulium
doped fiber amplifier (TDFA) that can be used in the so-called S-band (1450˜1530nm)
was developed. Since the TDFA using the transition of Tm
3+:
3H
4→
3F
4
was realized by Komukai et al., which is disclosed in an article entitled "1.47
μm band Tm
3+ doped fluoride fiber amplifier using a 1.064 μm
upconversion pumping scheme,
Electronics Letters Vol. 29 No. 1, in January,
1993, the wavelength bandwidth of the TDFA was extended and the optical gain was
raised by using various kinds of pump light sources. However, a TDFA uses Tm
3+-doped
fluoride glass fiber as a gain medium, thus its poor long-term stability and difficulties
in fiber fabrication are pointed as problems.
The
3H
4→
3F
4 transition of
Tm
3+ ion is usually used for the active transition of the S-band. The
energy levels of the thulium ions are consist of
3H
6,
3F
4,
3H
5,
3H
4,
3F
3 and
1G
4. Since there is
3H
5 between
3H
4
and
3F
4 and the energy gap between the
3H
4
and
3H
5 is about 4000 cm
-;1, the
3H
4→
3F
4
transition is near non-radiative transition through multi-phonon relaxation
in the high phonon energy glass such as a silicate glass. So, the fluorescence
lifetime of the
3H
4 level is very short and the fluorescent
emission is very weak. Accordingly, the silicate glass could not be used as a fiber
amplifier or a fiber laser medium. The fluorescence of the thulium ion doped in
a silica glass medium is reported to be less than 20 μs. For this reason,
it has been thought so far that a material having low phonon energy, such as fluoride
glass, tellurite glass and heavy metal oxide glass, should be used as a matrix
glass for the conventional TDFA in order to use the 1.4 μm band fluorescence
of the Tm
3+ ions.
However, it is hard to manufacture the special glasses into an optical waveguide,
e.g., an optical fiber, compared to a silicate glass. They have poor chemical durability
and waterproofness. Accordingly, there are many problems in applying the special
glasses to optical communication devices.
The silicate glass based on quartz glass used for the fiber amplifiers or fiber
lasers can be easily fabricated into optical fibers, and it has excellent chemical
stability, durability and optical transmittance. So, high long-term reliability
is expected when the silicate glass is used as an optical device in optical communications.
If the non-radiative transition through the multi-phonon relaxation due to high
phonon energy of the glass matrix is suppressed, the fluorescence lifetime of the
3H
4 level can be extended.
In 2001, a research group of Corning and Naval Res. Lab have fabricated a Tm
3+-doped
silicate fiber and manufactured an S-band fiber amplifier. They, however, failed
to obtain sufficient optical gain with a modest pumping power due to short fluorescence
lifetime of the
3H
4 level.
U.S. Pat. No. 5,251,062, issued on Oct. 5, 1993, by Elisa Snitzer, Eva M. Vogel
and Jau-Sheng Wang, discloses a tellurite glass applicable to a solid laser oscillator
an optical amplifier. The patent discloses glasses having composition of TeO
2
58˜84 mol %, Na
2O 0˜24 mol %, and ZnO 10˜30 mol %.
The glass composition of U.S. Pat. No. 5,251,062 is favorable to the fabrication
of optical fiber, and it is easy to make the refractive index difference between
core and cladding. The glass having a composition with Tm
3+ ions is
good to obtain fluorescent emission in the 1.4 μm band. However, the glass
having the composition with Tm
3+ ions does not have long-term durability
and it can be hardly fabricated into an optical waveguide such as optical fiber
compared to a silicate glass.
U.S. Pat. No. 5,366,937, issued on Nov. 22, 1994, by H. Schneider et al., describes
thulium-doped glass fabricated into optical fiber. As a glass matrix, heavy metal
fluoride glasses are predominantly used, and terbium (Tb), holmium (Ho), europium
(Eu) and praseodymium (Pr) are doped selectively to obtain the fluorescence in
the 1.4 μm band more efficiently. However, it has a problem in chemical durability
and the fabrication of optical fiber, because heavy metal fluoride glasses are
used as glass matrix.
U.S. Pat. No. 5,067,134, issued on Nov. 19, 1991, by E. W. J. L. Oomen discloses
an optical fiber laser using the fiber made of thulium-doped heavy metal fluoride
glass. The wavelength of the laser is around 450 nm . Since the laser medium uses
a heavy metal fluoride glass, the fluorescence lifetime of the
3H
4
level is long, however, it has problems in chemical durability and the fabrication
of optical fiber.
SUMMARY OF THE INVENTION
It is, therefore, an object of the present invention to provide a thulium-doped
silicate glass that can be used for a fiber amplifier or a fiber laser of the 1.45˜1.52
μm band by solving its problem of short fluorescence lifetime of the
3H
4 level.
It is another object of the present invention to provide a thulium-doped silicate
glass, which has high waterproofness and chemical durability and is not crystallized
or phase separated during the optical fiber fabrication process at a high temperature.
The present invention relates to a thulium-doped silicate glass that can be used
for a fiber amplifier or a fiber laser in the S-band (1450˜1530 nm), more
particularly, to a silicate glass having 0.01˜1 mol % Tm
3+ ions
as active ions, and the usage of the thulium-doped silicate glass.
In accordance with an aspect of the present invention, there is provided a thulium-doped
silicate glass, including: 65˜95 mol % SiO
2; 0.5˜30 mol
% bivalent metal oxide consisting of one or more material selected from ZnO, BaO,
SrO and PbO; and 1˜15 mol % of SnO
2 or TiO
2, wherein
3˜30 mol % oxygen of the glass composition are replaced with fluorine, and
0.01˜1 mol % of thulium ions are doped, and the fluorescence lifetime of
the
3H
4 level of the Tm
3+ is more than 50 μs.
The thulium-doped silicate glass further includes: 0.5˜5 mol % alkali metal
oxide consisting of one or more material selected from K
2O, Rb
2O
and Cs
2O; and 1˜15 mol % trivalent metal oxide consisting of one
or more material selected from In
2O
3 and Sb
2O
3.
In accordance with another aspect of the present invention, there is provided
a thulium-doped silicate glass as described above, wherein the silicate glass is
used for a laser oscillator, optical fiber laser, optical fiber amplifier, or planar
waveguide optical amplifier.
In accordance with another aspect of the present invention, there is provided
an optical fiber, including: a core having the glass composition described above
and a cladding having a lower refractive index than the core.
DETAILED DESCRIPTION OF THE INVENTION
Other objects and aspects of the invention will become apparent from the following
description of the embodiments with reference to the accompanying drawings, which
is set forth hereinafter.
SiO
2 used in the silicate glass of the present invention
is a basic element of a glass network former. The SiO
2 has high chemical
durability, optical transmission. However, as described before, due to its high
phonon energy (1100 cm
-;1), when it forms a glass matrix alone, the
fluorescent emission in the 1.4 μm band by the
3H
4→
3F
4
transition of Tm
3+ ions is degraded remarkably, and the doping
amount of rare earth ions is limited to very low level.
To solve these problems, SnO
2 or TiO
2 added in the composition
of a glass is suggested in the present invention. The SnO
2 or TiO
2
which is a material having a characteristic between the glass network former
and modifier reduces the phonon energy of the glass and raises the refractive index
of the glass. The above effects can be confirmed when SnO
2 or TiO
2
is added more than 1 mol %. If SnO
2 or TiO
2 is added
more than 15 mol %, the silicate glass becomes phase-separated. Accordingly, it
should not be added too much.
Also, one or more bivalent metal oxides selected from a group consisting of
ZnO, SrO, BaO and PbO is a glass network modifier. It reduces the melting point
of the glass, makes the doping of rare-earth ions easier, and raises the refractive
index of the glass. The phonon energy of the glass is reduced by selecting the
modifying ion with heavy atomic weight. When the amount of the modifying ions is
too small, the desired effects do not appear. If they are added too much, the glass
structure becomes weak and the chemical durability is lowered remarkably. The amount
of the additive amount to the glass structure is 0.5˜30 mol %.
One or more alkali metal oxide selected from a group consisting of K
2O,
Rb
2O and Cs
2O could be added to the glass matrix to lower
the melting point of the glass and ease the addition of rare earth ions. They are
not essential elements to achieve the object of the present invention. However,
when they are added, the lifetime extending effects are enhanced. If the alkali
oxide is added too much, it lowers the melting point of the glass excessively and
reduces the fluorescent lifetime of the
3H
4 level. Therefore,
it is desirable to add the alkali metal oxide less than 5 mol %.
Trivalent metal oxides, such as In
2O
3 or Sb
2O
3
have a characteristic between the glass network former and the modifiers.
They lower the phonon energy of the glass, raise the refractive index of the glass,
and make the doping rare earth ions easier. Thus the lifetime extending effects
are enhanced when they are added in a small amount. Like TiO
2 and SnO
2,
In
2O
3 and Sb
2O
3 may cause phase separation
when they are added to the silicate glass too much. Therefore, it is desirable
to add the trivalent metal oxide no more than 10 mol %.
In accordance with the present invention, 3 to 30 mol % of oxygen is replaced
with fluorine in the silicate glass. This lowers the phonon energy of glass matrix
and raises the fluorescence lifetime of the
3H
4 level of
Tm
3+ ions. Here, the fluorine substitution may be accomplished by substitution
of metal fluorides for parts of the metal oxides in the melting and quenching method,
or by mixing fluorine gas in a deposition method such as MCVD method. When the
amount of the substituted fluorine is less than 3 mol %, the effect of enhancing
the fluorescence lifetime is not remarkable. If the amount of substituted fluorine
is more than 30 mol %, the glass structure becomes too weak, thus dropping the
chemical durability considerably.
The Tm
3+ ion of an active ion generating fluorescence in the 1.4 μm
band is doped into the matrix glass of the present invention. In order to generate
1.4 μm fluorescence, at least 0.01 mol % of Tm
3+ should be doped
in the form of an oxide. However, when it is added too much, the Tm
3+
ions are agglomerated each other, so the fluorescence lifetime is largely reduced.
Therefore, it is desirable to add the Tm
3+ ion no more than 1 mol %.
When a certain transition of a rare earth ion is used for an optical amplifier
or a laser, the upper levels of the ion should have long fluorescence lifetime
and large emission cross-section of the transition. Then the high efficiency of
the laser or the optical amplifier can be attained. The Tm
3+:
3H
4→
3F
4
transition having a center wavelength of approximately 1470 nm can be applied to
an optical amplifier in the 1450˜1520 nm band. Generally, the fluorescence
lifetime of the
3H
4 level of Tm
3+ ion doped into
the silica glass is less than 20 μs, and the fluorescence lifetime of the
3H
4 level of Tm
3+ ion is approximately 30 μs
in the soda-lime silicate glass. This is very small compared to that of the
3H
4
level of Tm
3+ ion doped into the fluoride glass commonly used
for the TDFA. The lifetime of the
3H
4 level of Tm
3+
ion doped into the fluoride glass is about 1 ms. So, generally silicate glass is
not proper for the medium glass of the TDFA.
However, the glass having a composition of 70SiO
2-5TiO
2-2Sb
2O
3-10ZnF
2-10PbF
2-3KF
and doped with 0.2 mol % Tm
2O
3, which is an example of the
glasses fabricated in accordance with the present invention, represents 180 μs
of the fluorescence lifetime of the
3H
4 level. This is long
enough to be used as a medium glass of the TDFA. The fluorescence lifetime could
be extended because the cations of heavy atomic weights and fluorine ions are preferentially
coordinated around the Tm
3+ ions to reduce the phonon energy affecting
the fluorescence lifetime directly. This reduces the non-radiative transition rate.
The intrinsic lifetime is considered to increase by doping of the heavy metal oxides
and fluorine because the local crystal field around the Tm
3+ ions is reduced.
In accordance with the present invention, glasses can be fabricated in two methods:
a melting and quenching method and a vapor deposition method. In the melting and
quenching method, highly pure powders of oxide, carbohydrate and fluoride materials
are mixed in solid phase, melted at a high temperature at higher than 1500 C. The
melt is cooled down gradually and annealed, then formed into a bulk glass. The
bulk glass fabricated as the above method is formed into a cylindrical glass using
a core drilling, and then it is formed into a preform including core and cladding
by a rod-in-tube method.
In the vapor deposition method like a modified chemical vapor deposition (MCVD)
or vapor phase axial deposition (VAD) method, a porous glass preform is formed
of such materials as SiO
2, TiO
2, SnO
2 and F that
can be deposited easily. Then, the porous glass preform is dipped in a solution
containing Tm
3+ ion and the rest materials, and is sintered at a high
temperature to be vitreous preform.
A thulium doped optical fiber can be obtained by heating the cylindrical preform
at the end in the optical fiber drawing apparatus and drawing the softened glass
at a high speed to form the fiber.
Hereinafter, an embodiment of the present invention, Tm
3+-doped
silicate glass will be described more in detail. The following embodiments are
mere examples for describing the present invention, and any description in the
embodiment of the present invention should not be construed to define or limit
the scope of the invention.
Embodiments 1-2
Glass samples having a composition with 0.2 w % of Tm
2O
3
shown in table 1 are prepared by the following method. Powder materials having
99.9% purities are weighed and mixed, then melted in the air at 1500 C for one
hour and cooled down rapidly, and then annealed at 600 C for 30 minutes to form
bulk glasses.
The glass samples are cut and polished. Then, the fluorescence lifetime of the
3H
4 of Tm
3+ ion is measured at 1470 nm by using
a 795 nm Ti: sapphire laser, band pass filters, a chopper wheel, an InSb detector
and a digital oscilloscope. The results are shown in the table 1.
Comparative Embodiments 1-2
To compare the glasses of the present invention with the conventional soda-lime
silicate glasses, they are formed in the same method as the embodiments 1-2. The
soda-lime silicate glass compositions are shown in the table 1. Then, the fluorescence
lifetime of the
3H
4 of Tm
3+ is measured in the
same method described in the embodiments 1-2. The result is shown in the table 1.
| TABLE 1 |
| Composition of glass samples and fluorescence lifetimes |
| of the embodiments 1-2 and comparative embodiments 1-2 |
| |
|
Fluorescence |
| |
|
Lifetime of |
| |
Composition of Glass Sample |
Tm3+:3H4. |
| |
| Comp. Embodiment 1 |
70SiO2 15NaO½ 15CaO |
33 μs |
| Comp. Embodiment 2 |
70SiO2 15KO½ 15ZnO |
35 μs |
| Embodiment 1 |
70SiO2 5SnO2 15BaO 10PbO |
47 μs |
| Embodiment 2 |
70SiO2 5SnO2 15PbO 5ZnO |
75 μs |
| |
15ZnF2 |
The result of the table 1 shows that the fluorescence lifetimes of the
3H
4
level of the glasses of the present invention are increased remarkably compared
to the conventional soda-lime silicate glass. Also, it shows that the fluorine
substitution enhances the fluorescence lifetime of the
3H
4 level.
Embodiments 3-6
Glass samples having compositions shown in a table 2 with 0.2 w % of Tm
2O
3
are prepared by the following method. Powder materials having 99.9% purities are
weighed and mixed, then melted in the air at 1500 C for one hour and cooled down
rapidly, and then annealed at 600 C for 30 minutes to form bulk glasses.
The glass samples are cut and polished. Then, the fluorescence lifetime of the
3H
4 of Tm
3+ ion is measured at 1470 nm by using
a 795 nm Ti: sapphire laser, band pass filters, a chopper wheel, an InSb detector
and a digital oscilloscope. The results are shown in the table 2.
| TABLE 2 |
| Tm3+:3H4 fluorescence lifetime of Tm2O3-doped fluore |
| substitution silicate glass |
| |
|
Fluorescence |
| |
Composition of |
Lifetime of |
| |
Glass Sample |
Tm3+:3H4. |
| |
| Embodiment 3 |
70SiO2 5TiO2 2Sb2O3 10ZnO 10PbO |
56 μs |
| |
3KO½ |
| Embodiment 4 |
70SiO2 15TiO2 2Sb2O3 10ZnO 10PbO |
99 μs |
| |
3KF |
| Embodiment 5 |
70SiO2 5TiO2 2Sb2O3 10ZnF2 10PbO |
170 μs |
| |
3KF |
| Embodiment 6 |
70SiO2 5TiO2 2Sb2O3 10ZnF2 10PbF2 |
180 μs |
| |
3KF |
The result of the table 2 shows that the more the amount of fluore substitution
can extended the fluorescence lifetime of the
3H
4 level.
Therefore, it shows that the glass having the composition of the present invention
has excellent spectral properties as a medium glass of the TDFA.
When the glass of the present invention is used as a medium glass of the TDFA
or a fiber laser, the fabrication process is controlled easily compared to the
fluoride and tellurite glass. Moreover, it has excellent chemical durability and
the longer fluorescence lifetime of the
3H
4 level compared
to the conventional silicate glass. Therefore, the glass composition of the present
invention can realize a highly efficient TDFA or fiber laser.
The glasses of the present invention are silicate glasses of new compositions
to be used for a medium glass of a TDFA or fiber laser. They are the silicate glass
that can be formed into a waveguide, such as an optical fiber, easily compared
to the conventional Tm
3+-doped fluoride glasses, tellurite glasses and
heavy metal oxide glasses. They have an excellent ability to splice with the optical
fiber for transmission. They have excellent chemical durability and the characteristic
of 1.4 μm band fluorescent emission by suppressing the non-radiative transition
through multi-phonon relaxation. Thus they have long fluorescence lifetime of the
3H
4 of Tm
3+.
While the present invention has been described with respect to certain preferred
embodiments, it will be apparent to those skilled in the art that various changes
and modifications may be made without departing from the scope of the invention
as defined in the following claims.
*
