Patent Grant
7551348
This application claims the benefit of Korean Patent Application No. 10-2005-0058651, filed on Jun. 30, 2005, in the Korean Intellectual Property Office, the disclosure of which is incorporated herein in its entirety by reference.
1. Field of the Invention
The present invention relates to a tellurite glass composite and an optical waveguide and an optical amplifier using the same.
2. Description of the Related Art
In general, optical amplifiers, for example optical fiber amplifiers, have been developed focusing on C band, i.e., wavelength between 1530 nm and 1565 nm based on an erbium-doped fiber amplifier (EDFA). However, studies on Raman optical fiber amplifiers useable in various bands have been briskly made as the ultrahigh, large capacity optical communication system highly demands broad useable optical communication bands through the optical fiber. In particular, the Raman optical fiber amplifiers have been extensively investigated as a key player of the broad-band optical communications employing wavelength multiplexing optical communication systems with the recent development of high power semiconductor laser diodes and silica optical fibers having improved Raman gain coefficients.
However, normal silica optical fiber-based Raman optical fiber amplifiers have low gain coefficients and require at least several kilometers (Km) of fiber. Thus, high power pumping sources are required. Also, signal-to-noise ratios (SNRs) of optical fiber amplifiers are low due to a near distance of about 100 nm between a pumping source wavelength and a signal wavelength.
Thus, tellurite glass optical fiber-based Raman optical fiber amplifiers have been suggested. A tellurite glass generates two Raman scattering peaks respectively existing at a wave number of about 450 cm−1 and 700 cm−1. The Raman scattering peak of 700 cm−1 is 170 nm distant from the pumping source. Thus, when the tellurite glass uses multi-wavelength pumping, the tellurite glass is more advantageous to amplify a wide band and improve an SNR than silica glass.
Also, the tellurite glass has a high non-linearity and thus has a high Raman gain coefficient which is about 16 times higher than that of the silica glass. Thus, the tellurite glass can amplify signals through an optical fiber having a relatively short length. As a result, an optical fiber amplifier of about 160 nm reaching from S band to L band has been realized using a tellurite optical fiber of about 250 m and four or more pumping sources.
However, since Raman scattering has a full-width at half maximum (FWHM) of less than about 200 cm− centered at 700 cm−1, an existing tellurite glass optical fiber-based Raman amplifier has its drawbacks requiring a plurality of pumping sources for wide-band operation.
The present invention provides a tellurite glass composite increasing a FWHM of Raman scattering so as to realize a wideband Raman amplifier or a laser using a small number of excitation sources.
The present invention also provides an optical waveguide using the tellurite glass composite as a core layer.
The present invention also provides a wideband optical amplifier using an optical fiber or an optical waveguide using the tellurite glass composite as a core layer or a gain medium.
According to an aspect of the present invention, there is provided a tellurite glass composite including an entire composite including 25 (mol %)≦TeO2≦90 (mol %), 1 (mol %)≦T1O3≦55 (mol %) or 1 (mol %)≦T2O3≦40 (mol %), 0 (mol %)≦ZnO≦35 (mol %), 0(mol %)≦M2O≦35 (mol %), and 0 (mol %)≦Bi2O3≦20 (mol %). Here, T1 may include a transition metal Mo, T2 may include a transition metal W, M2O may include Li2O, Na2O, or two or more of Li2O, Na2O, K2O, Rb2O, and Cs2O including metals having +1 valence electrons, and amounts of M2O and ZnO may not simultaneously be “0.”
The tellurite glass composite may be used as a core layer of an optical fiber or an optical waveguide.
The tellurite glass composite may be used as a core layer of an optical fiber or an optical waveguide so as to constitute the optical fiber or the optical waveguide. Also, an optical amplifier or a laser using an optical fiber or an optical waveguide formed of the tellurite glass composite as a gain medium may be constituted. The optical amplifier or the laser may use pump sources having one or two or more wavelengths between 1150 nm and 1500 nm.
The tellurite glass composite may include a molybdenum oxide or a tungsten oxide to increase a FWHM of Raman scattering to about 300 cm−1 or more centered at about 700˜800 cm−1 so as to perform wideband amplification using a small number of light sources.
The above and other features and advantages of the present invention will become more apparent by describing in detail exemplary embodiments thereof with reference to the attached drawings in which:
The present invention will now be described more fully with reference to the accompanying drawings, in which exemplary embodiments of the invention are shown. The invention may, however, be embodied in many different forms and should not be construed as being limited to the embodiments set forth herein; rather, these embodiments are provided so that this disclosure will be thorough and complete, and will fully convey the concept of the invention to those skilled in the art. In the drawings, the thicknesses of layers and regions are exaggerated for clarity.
A tellurite glass composite will now be described. The tellurite glass composite includes TeO2, ZnO, Na2O (or Li2O), and a plurality of oxide-doped composites. The tellurite glass composite may be formed of a two-component composite such as TeO2—ZnO and TeO2—PbO but is mainly formed of a multi-component composite. TeO2 exists as various structures such as TeO4, TeO3, and TeO3+δ inside the tellurite glass composite and forms a network of the tellurite glass composite, and ZnO and Na2O (or Li2O) exist as modifiers changing structures inside of the tellurite glass composite or as charge compensators inside the tellurite glass composite.
As previously described, the tellurite glass composite shows two wide and strong Raman scattering peaks. In other words, the tellurite glass composite includes a peak of about 450 cm−1 corresponding to the Te—O—Te bending vibration mode and a peak of about 700 cm−1 which can be assigned to the vibration mode from network forming structural units such as TeO4, TeO3 and TeO3+δ. A FWHM of the peak of about 700 cm−1 is about 200 cm−1 in normal tellurite glasses and an additional Raman scattering peak is required to increase the FWHM.
Thus, the present inventors added a transition metal oxide, for example a molybdenum oxide (MoO3) and a tungsten oxide (WO3), to a general tellurite glass composite to increase the FWHM. Transition metal oxides such as the molybdenum and tungsten oxides have structures with strong Raman scatterings at about 900 cm−1. Thus, the FWHM could be increased if the transition metal oxides are incorporated. Also, composites of the transition metal oxides may be adjusted to obtain a flattened Raman scattering spectrum from which a flattened signal gain could be expected.
Based on this, the present inventors have invented a tellurite glass composite optimal to flatten a Raman scattering peak of 700 cm−1 through various experiments.
A tellurite glass composite according to an embodiment of the present invention includes an entire composite including 25 (mol %)≦TeO2≦90 (mol %), 1 (mol %)≦MoO3≦55 (mol %), 0 (mol %)≦ZnO≦35 (mol %), 0 (mol %)≦M2O≦35 (mol %), and 0 (mol %)≦Bi2O3≦20 (mol %). M2O is Li2O or Na2O and includes two or more of metal oxides including metals having valence electrons of +1 such as Li2O, Na2O, K2O, Rb2O, or Cs2O. For example, M2O may include both of Li2O and Na2O to satisfy the composite range. Dosages of the M2O and ZnO must not be “0” at the same time.
One or two or more of MoO3, WO3, Ta2O5, PbO, Nb2O3 and Al2O3 may be added as a first additive to the entire composite constituting the tellurite glass composite by amount of between 0 mol % and 20 mol %. Also, a composite of oxides or fluorides except WO3, Ta2O5, PbO, Nb2O3, and Al2O3 may be added as a second additive to the entire composite by an amount between 0 mol % and 40 mol %, the rare-earth oxides or the rare-earth fluorides being not suggested to constitute the tellurite glass composite.
In other words, a composite of an oxide excluding Te, Mo, W, Zn, M, or Bi constituting the tellurite glass composite, an oxide excluding Ta, Pb, Nb, or Al, and fluorides may be added as the second additive to the entire composite by the amount between 0 mol % and 40 mol %, the oxides and the fluorides excluding rare-earth oxides and rare-earth fluorides. The fluorides are metal fluorides including metals constituting the tellurite glass composite.
One or two or more of rare-earth oxides including Pr2O3, Nd2O3, Sm2O3, Eu2O3, Tb2O3, Dy2O3, Ho2O3, Er2O3, Tm2O3, or Yb2O3 or fluorides including PrF3, NdF3, SmF3, EuF3, TbF3, DyF3, HoF3, ErF3, TmF3, and YbF3 may be added as a third additive to the entire composite constituting the tellurite glass composite by an amount between 0 mol % and 5 mol %. All of the first, second, and third additives may be added or only one of the first, second, and third additives may be added.
According to another embodiment of the present invention, a tellurite glass composite according to another embodiment of the present invention includes an entire composite including 25 (mol %)≦TeO2≦90 (mol %), 1 (mol %)≦WO3≦40 (mol %), 0 (mol %)≦ZnO≦35 (mol %), 0 (mol %)≦M2O≦35 (mol %), and 0 (mol %)≦Bi2O3≦20 (mol %). M2O is Li2O or Na2O or includes two or more metal oxides of metal oxides including metals having valence electrons of +1 such as Li2O, Na2O, K2O, Rb2O, or Cs2O. For example, M2O may include all of Li2O and Na2O to satisfy the composite range. Dosages of M2O and ZnO must not be “0” at the same time.
One or two or more of MoO3, Ta2O5, PbO, Nb2O3 and Al2O3 may be added as a first additive to an entire composite constituting the tellurite glass composite by an amount between 0 mol % and 20 mol %. Also, a composite of oxides or fluorides except MoO3, Ta2O5, PbO, Nb2O3, and Al2O3 may be added as a second additive to the entire composite by an amount between 0 mol % and 40 mol %, the rare-earth oxides or the rare-earth fluorides being not suggested to constitute the tellurite glass composite.
In other words, a composite of an oxide excluding Te, W, Mo, Zn, M, or Bi constituting the tellurite glass composite, an oxide excluding Ta, Pb, Nb, or Al, and fluorides may be added as the second additive to the entire composite by the amount between 0 mol % and 40 mol %, the oxides and the fluorides excluding rare-earth oxides and rare-earth fluorides. The fluorides are metal fluorides including metals constituting the tellurite glass composite.
One or two or more of rare-earth oxides including Pr2O3, Nd2O3, Sm2O3, Eu2O3, Tb2O3, Dy2O3, Ho2O3, Er2O3, Tm2O3, or Yb2O3, or fluorides including PrF3, NdF3, SmF3, EuF3, TbF3, DyF3, HoF3, ErF3, TmF3, and YbF3 may be added as a third additive to the entire composite constituting the tellurite glass composite by an amount between 0 mol % and 5 mol %. All of the first, second, and third additives may be added or only one of the first, second, and third additives may be added.
A Raman scattering spectrum of a tellurite glass composite including a molybdenum oxide and a tungsten oxide will now be described. A tellurite glass composite adopted in the present invention representatively uses a composite of the above-described composites of the present invention that will be described later.
In detail, the tellurite glass composite shown in
As shown in
As shown in
A Raman scattering peak of about 700 cm31 1 generated by TeO4, TeO3, and combinations of TeO4 and TeO3 gradually moves to about 800 cm−1. This movement shows due to a gradual change of TeO4 inside the tellurite glass composite into TeO3 or TeO3+δ due to the addition of the molybdenum oxide.
In detail, the telluriate glass composite shown in
As shown in
In detail,
As shown in
The above-described tellurite glass composite of the present invention may be used as a core layer of an optical fiber or an optical waveguide. In other words, if the tellurite glass composite of the present invention is used as a core layer, the tellurite glass composite may have Raman gain coefficient 16 times higher than that of the general silica glass composite and thus may be used as a core layer of an optical fiber or waveguide having a relatively short length.
In particular, as previously described, a FWHM of a Raman scattering peak of 700 cm−1 can be increased in an optical fiber or waveguide using the tellurite glass composite of the present invention. Thus, a wideband optical amplifier or laser can be realized using a small number of excitation sources. Hereinafter, an optical amplifier using the tellurite glass composite of the present invention as a core layer of an optical fiber will now be described representatively.
In detail, an optical fiber 23 formed of the tellurite glass composite of the present invention is used as a gain medium and first and second excitation sources (first and second pump sources) 25 and 27 are used so as to realize an optical amplifier. Wavelengths of the first and second excitation sources 25 and 27 may be selected within a range between 1150 nm and 1500 nm to properly amplify a communication band.
However, as shown in
In more detail, signal light goes into the optical fiber 23 including a core layer 23a formed of the tellurite glass composite of the present invention and a clad layer 23b enclosing the core layer 23a. Here, the signal light passes through an optical isolator 21 to the optical fiber 23 for unidirectional operation.
The signal light is coupled through a WDM (wavelength division multiplexing) coupler 22 to the optical fiber 23, amplified inside the optical fiber 23 by the first excitation source (the first pump source) 25 having the wavelength of 1342 nm and the second excitation source (the second pump source) 27 having the wavelength of 1407 nm, and goes out as output light. As previously described, the tellurite glass composite may generate a strong peak at a distance of about 900 cm−1 (at a wavelength of 200 nm) from wavelengths of an excitation light source. Thus, a gain flattening filter 29 may be installed in front of an output node to attenuate a signal in this wavelength so as to obtain a flattened gain.
The Raman optical amplifier shown in
The optical amplifier using the optical fiber 23 has been described with reference to
In detail, as shown in
In detail, the laser includes an optical fiber 31 including a core layer 31a using the tellurite glass composite of the present invention and a clad layer 31b, excitation sources 33 and 35, an WDM coupler 37, a total reflection fiber bragg grating optical fiber element 39, and an output coupling fiber bragg grating optical fiber element 41. Wavelengths of the excitation sources 33 and 35 may be selected within a range between 1150 nm and 1500 nm so as to be properly amplified. The core layer 31a of the optical fiber 31 emits spontaneous Raman scattering by the excitation sources 33 and 35. The spontaneous Raman scattering is amplified between the total reflection fiber bragg grating optical fiber element 39 and the output coupling fiber bragg grating optical fiber element 41 constituting a resonator 43 so as to emit laser light 45 through the output coupling fiber bragg grating optical fiber element 41.
As described above, a tellurite glass composite of the present invention can include a transition metal oxide such as a molybdenum oxide or a tungsten oxide. A FWHM of a Raman scattering peak can be increased from about 200 cm−1 to about 300 cm−1 centered on about 700˜800 cm−1. Thus, the tellurite glass composite can be used in an optical fiber or waveguide used for an optical amplifier having a short length and a wide amplification band.
In addition, the optical amplifier or a laser using the tellurite glass composite of the present invention can obtain wideband optical amplification or laser oscillation using a small number of excitation sources due to the increase in the FWHM of the Raman scattering peak.
While the present invention has been particularly shown and described with reference to exemplary embodiments thereof, it will be understood by those of ordinary skill in the art that various changes in form and details may be made therein without departing from the spirit and scope of the present invention as defined by the following claims.
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