JP2006062916A - Optical functional waveguide material and optical amplification medium, optical amplifier, laser device, and light source - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an optical high functional waveguide material with high function and versatility and having excellent thermal stability important in the optical fiber production in addition to an aptitude as host glass with which the cross-section of induced emission of the 1.5 μm band of Er gets more flatness and particularly effective to, for example, a light amplifier with broadband and low noise characteristics, a laser device and a light source. <P>SOLUTION: The material glass for an optical fiber or an optical waveguide has a composition comprising 0<Ta<SB>2</SB>O<SB>5</SB>≤12 (mol%), 0<(BaO+SrO)≤20 (mol%), 80≤TeO<SB>2</SB>≤97 (mol%), or has compositions comprising 6<Ta<SB>2</SB>O<SB>5</SB>≤12 (mol%), 0<(BaO+SrO)≤20 (mol%), and 80≤TeO<SB>2</SB>≤97 (mol%) and 0<Al<SB>2</SB>O<SB>3</SB>≤4 (mol%). <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to an optical functional waveguide material which is a material glass for an optical fiber or an optical waveguide, and an optical amplifying medium, an optical amplifier, and a light source using the material, and particularly operates in a wavelength range of 1.5 μm to 1.7 μm. The present invention is effective for use in a wide-band optical amplifying medium that can be used, an optical amplifier having a wide-band and low-noise characteristic using the optical amplifying medium, a laser device, and a light source.

  In an optical communication system, in order to expand transmission capacity and improve functions, optical signals of a plurality of wavelengths are combined and transmitted in one optical fiber, or conversely, a plurality of optical signals propagated through one optical fiber. Research and development of a wavelength division multiplexing (WDM) technique that demultiplexes an optical signal having a wavelength of 1 for each wavelength is currently underway. In this transmission method, it is necessary to transmit a plurality of optical signals having different wavelengths through a single optical fiber, and to relay and amplify the optical signal in the same manner as in the past according to the transmission distance. Therefore, in order to increase the optical signal wavelength and increase the transmission capacity, an optical amplifier having a wide amplification wavelength band is required.

  Further, the wavelength of a system for maintaining and monitoring an optical communication system is considered to be a wavelength between 1.61 μm and 1.66 μm, and development of a light source and an optical amplifier for the maintenance and monitoring system is desired. ing.

  In recent years, for the purpose of application to the optical communication field, an optical fiber amplifier using an optical fiber with a rare earth element added to the core as an optical amplification medium, for example, an Er (Erbium) doped optical fiber amplifier (EDFA) is used. Research and development are progressing, and application to optical communication systems is actively promoted. This EDFA operates in the 1.5 μm band where the loss of silica-based optical fiber is minimized, and has excellent features such as high gain of 30 dB or more, low noise, wide gain band, gain independent of polarization, and high saturation output. It is known to have

  One of the performances required when the EDFA is applied to WDM transmission is that the amplification band is wide as described above. So far, a fluoride EDFA using fluoride glass as a host of an Er-doped optical fiber amplifier has been developed as an EDFA having a wide amplification band.

  When tellurite EDFA is used, 1.53 μm to 1.3 μm wider than the wavelength amplification band from 1.53 μm to 1.56 μm wider than the conventional quartz-based EDFA and fluoride-based EDFA amplification band. Collective amplification in a wavelength band up to 61 μm is possible. Therefore, it attracts attention as an EDFA for future ultra-high capacity WDM systems.

  By the way, the performance required for an EDFA for a WDM system is (1) wide bandwidth of amplification and (2) flatness of amplification. First, the broadband property of amplification will be described.

When this Er-doped tellurite optical fiber is used as an amplifying medium, the amplification band is widened because the ⁴ I _13/3 level and ⁴ I _15/2 level of Er causing 1.5 μm band optical amplification in tellurite glass. This is because the stimulated emission cross section of the level becomes larger than in other glasses, and in particular, in the long wavelength region of 1.6 μm band, it takes about twice as much value as in other glasses. Therefore, in the tellurite EDFA, it is easy to obtain a large gain in a long wavelength region as compared with other EDFAs.

Incidentally, the amplification degree in a short wavelength range is determined by the difference between the occupancy of ⁴ I _15/2 level position of Er ground levels and ⁴ I _13/3 level position of occupancy. That is, if the ⁴ I _15/2 level is not occupied at all, the gain can be obtained up to a short wavelength such as 1.50 μm.

However, increasing the fiber length in order to obtain a high gain in the long wavelength region (for example, around 1.60 μm) increases the occupation ratio of the entire ⁴ I _15/2 level fiber, _resulting in a gain in the short wavelength region. Cannot be obtained, and the noise figure (NF: Noise Figure) near 1.54 μm also increases. Therefore, even if it is a tellurite optical fiber, the amplification band which can be covered with one optical fiber will be limited. Actually, the operating wavelength range of low NF and high gain obtained by using one tellurite optical fiber is about 60 nm from 1.55 μm to 1.61 μm.

  Next, the flatness of amplification, which is the second property required as an EDFA for a WDM system, will be described.

  The performance required for an EDFA for a WDM system is (1) wide bandwidth of amplification and (2) flatness of amplification. While tellurite EDFA is excellent in amplification broadband, amplification flatness is inferior. For example, the gain deviation at a gain peak wavelength of 1.56 μm and 1.60 μm is 15 dB or more. Therefore, in order to flatten the gain, it is necessary to apply a gain equalizer such as a fiber Bragg grating to the EDFA. However, if the gain deviation is too large, it is difficult to design a gain equalizer for flattening, or gain equalization cannot be achieved without using a plurality of gain equalizers. is there. In fact, in the case of the tellurite EDFA, since the gain deviation is 15 dB or more, the gain deviation applied to the WDM system is not realized even if the gain equalizer is used.

  In order to change the shape of the original amplified spectrum of the EDFA, it is necessary to change the shape of the stimulated emission cross section spectrum.

  In the case of tellurite EDFA, a fiber host having a large stimulated emission cross section in the vicinity of the 1.6 μm band may be used to flatten the gain spectrum and facilitate gain equalization. This is because in that case, the gain deviation between the wavelength band from 1.53 μm to 1.56 μm and the 1.6 μm band can be reduced.

Conventional fiber hosts for tellurite EDFA include TeO ₂ —ZnO—Na ₂ O—Bi ₂ O ₃ glass (Patent Document 1), TeO ₂ —ZnO—Li ₂ O—Bi ₂ O ₃ (Patent Document 2), etc. Glass is used. In these glass systems, the gain deviation is 15 dB or more.

Here, the development status up to now will be briefly described.
In Patent Documents 3 to 6 and Patent Document 7, Cooley et al. Show that laser oscillation is possible with tellurite glass doped with rare earth elements. However, Cooley et al. Have not yet made fiber, and does not mention adjustment of the optical refractive index (specific refractive index) necessary for fiberization and thermal stability of glass.

On the other hand, in Patent Document 8, Snitzer et al., When tellurite glass is used, expands the amplification band of EDFA, and further, fiber formation is indispensable for optical amplification. The composition range of tellurite glass that can be converted into a glass is specifically disclosed. The glass is a ternary system composed of TeO ₂ , R ₂ O and QO (R is a monovalent metal other than Li and Q is a divalent metal). Li as a monovalent metal is excluded because of a decrease in thermal stability.

  In Patent Document 6, Snitzer et al. Compared the fluorescence spectra of erbium ions in the tellurite glass and quartz glass, and the tellurite glass has a wider spectrum width. This indicates that EDFA can be amplified in a wide band, and that addition of praseodymium, neodymium, etc. is possible. By adding these optically active substances, optical amplification can be achieved with an optical fiber using the ternary tellurite glass. It is possible. However, Patent Document 6 has no specific description such as gain, pumping wavelength, and signal wavelength indicating that optical amplification has actually been performed. That is, Patent Document 6 merely shows the composition range of ternary tellurite glass that can be made into a fiber, and only shows that an optically active rare earth element can be added.

  Furthermore, Snitzer et al. Show the thermal and optical characteristics of various tellurite glasses containing compositions other than those described in Patent Document 8 in Non-Patent Document 1. However, there is no specific description about optical amplification and laser oscillation here.

  Furthermore, Snitzer et al. Reported for the first time on laser oscillation using a single mode fiber of neodymium-doped tellurite glass in Non-Patent Document 2 issued immediately after Non-Patent Document 1.

The single mode fiber has a core of 76.9% TeO ₂ -6.0% Na ₂ O-15.5% ZnO-1.5% Bi ₂ O ₃ -0.1% Nd ₂ O ₃ and a cladding of It has a composition represented by 75% TeO ₂ -5.0% Na ₂ O ₂ -20.0% ZnO, and oscillates at 1061 nm with 818 nm excitation. Although the loss of the fiber is not described in Non-Patent Document ₂ , the core composition Nd ₂ O ₃ -77% TeO ₂ -6.0% Na ₂ O-15.5% ZnO- is not described in Non-Patent Document 1. Loss of 1.5% Bi ₂ O ₃ and 75% TeO ₂ -5.0% Na ₂ O ₂ -20.0% ZnO fiber (estimated to be the same as described in Non-Patent Document 2) Is 1500 dB / km at 1.55 μm and 3000 dB / km at the excitation light wavelength (0.98 μm) (see FIG. 7. This figure shows Er ³⁺ in tellurite glass described later. ⁴ I _13/2 → ⁴ I _15/2 is obtained by comparing the fluorescence and Er ³⁺ fluoride glass the ⁴ I _13/2 → ⁴ I _15/2 emission) of.

The core composition of the fiber is different from the ternary Patent Document 8 in that it applied the Bi ₂ O _3, the description about the thermal stability of the glass composition applied is Bi ₂ O ₃ in the ternary Neither in non-patent document 2 nor in non-patent document 1 or patent document 8.

  However, the above-mentioned fluoride EDFA has an amplification band of about 30 nm, and this alone is still insufficient to expand the band of the fiber amplifier for expanding the band of WDM.

On the other hand, as described so far, tellurite glass has a wide fluorescence spectrum, and thus it has been shown that the amplification band may be expanded if it is a host of EDFA. It is also shown that a ternary system composed of TeO ₂ , R ₂ O and QO (R is a monovalent metal other than Li and Q is a divalent metal) can be made into a fiber, and neodymium based on the above composition. A laser oscillation of 1061 nm was realized with the doped single mode fiber.

The following are issues for realizing the Tellurite EDFA.
For that purpose, first, the difference between the target EDFA and the Nd (neodymium) -doped fiber laser realized so far, that is, the difference between 1.5 μm emission of Er in glass and 1.06 μm emission of Nd is shown. There is a need.

  The former optical transition is schematically shown in FIG. That is, in order to obtain the intended stimulated emission from level 2 to level 1, it is excited from level 1 to level 3 (a level higher in energy than level 2), and from level 3 to level 2 An inversion distribution between levels 1 and 2 is formed by the relaxation to. This is called a three-level system. On the other hand, as shown in FIG. 18, when the final level of stimulated emission is not the ground level but level 1, which is the upper level of the ground level, this is called a 4-level system. Compared with the four-level system, the three-level system is less likely to form an inverted distribution because the final level of stimulated emission is in the ground state. Therefore, in the three-level EDFA, it is necessary to increase the excitation light intensity and to reduce the loss and the high Δn (Δn: relative refractive index difference between the core and the clad) of the fiber itself. The increase in Δn is for efficient excitation.

  Here, it is simply shown that if the loss of the fiber is large, the amplification band cannot be expanded even if optical amplification can be performed.

  FIG. 19 shows a schematic diagram of the wavelength dependence of gain for quartz-based EDFA and tellurite EDFA. As shown in this figure, the tellurite EDFA can be expected to have a wider optical amplification than the quartz EDFA. However, the glass other than the quartz glass has a larger loss in the communication wavelength band than the quartz glass. Therefore, this loss substantially reduces the gain in the optical fiber amplifier.

  As schematically shown in FIG. 20, when the loss is small, the amplification band of the tellurite glass is close to the above, but when the loss increases, the amplification band decreases.

  By the way, in recent WDM transmission, in order to increase the transmission capacity, the transmission rate per channel is increased. For this purpose, it is necessary to optimize the wavelength dispersion characteristics of the Er-doped optical fiber itself that constitutes a part of the transmission line. However, attention has been paid to the wavelength dispersion of the Er-doped optical fiber itself. Was not paid.

  In the case of tellurite glass, the wavelength at which the material dispersion value becomes zero is located in a wavelength band longer than 2 μm, and the wavelength dispersion value of a high NA (Numerical Aperture) fiber used for EDFA is usually 1.55 μm band. , And takes a value of −100 ps / km / nm or less. For this reason, even when the fiber is used as short as about 10 m, the chromatic dispersion value of the fiber is a large value of −1 ps / nm or less.

  Therefore, in order to use the tellurite EDFA for long-distance high-speed WDM transmission, it is necessary to make the chromatic dispersion value as close to zero as possible. However, as described above, since the material dispersion value of tellurite glass becomes zero in the wavelength region of 2 μm or more, in the tellurite glass fiber, the structural parameters of the fiber as in the case of quartz fiber should be optimized. As a result, it is impossible to take the method of bringing the chromatic dispersion value in the 1.55 μm band close to zero.

The tellurite optical fiber can also be used as a Pr (praseodymium) host for 1.3 μm band amplification. However, as described above, the tellurite optical fiber has a large chromatic dispersion value as an absolute value in the 1.3 μm band. Therefore, when a high-speed optical signal is amplified using a tellurite optical fiber, distortion of the pulse wavelength is induced, so that it is difficult to use the optical communication system without correcting the chromatic dispersion value.
1997 Patent Application No. 30430 1997 Patent Application No. 226890 US Pat. No. 3,836,868 US Pat. No. 3,836,869 US Pat. No. 3,836,870 US Pat. No. 3,836,871 U.S. Pat. No. 3,883,357 US Pat. No. 5,251,062 JS Wang et.al, Optical Materials, 3 (1994), pp.187-203 JS Wang et.al, Optics Letters, 19 (1994), pp.1448-1449

Accordingly, the object of the present invention is a material glass for an optical fiber or an optical waveguide, and particularly excellent in suitability as a fiber host (host glass) in which the stimulated emission cross section of Er 1.5 μm band becomes flatter. The object is to provide an optical functional waveguide material. At the same time, an object of the present invention is to provide an EDFA having a flattened gain by using this material as an optical amplification medium. Another object of the present invention is to provide an EDFA that operates with a low noise in a wider band by expanding the operating wavelength band of the conventional EDFA. It is another object of the present invention to provide an optical fiber or an optical waveguide to which an optically active rare earth element is added and a function that cannot be realized by a conventional glass material, for example, a function like a broadband EDFA can be realized. In addition, a broadband optical amplification medium that can operate in the wavelength range of 1.5 μm to 1.7 μm using the above optical functional waveguide material, an optical amplifier having a broadband and low noise characteristics using this optical amplification medium, and a laser Another object is to provide an apparatus and a light source.
Other problems and features of the present invention will become apparent from the description of the present specification and the accompanying drawings.

  As means for solving the above problems, the present invention provides the following means as an optical functional waveguide material as described below, an optical amplification medium, an optical amplifier, a laser device, and a light source using the optical functional waveguide material.

(1): A material glass for an optical fiber or an optical waveguide,
0 <Ta ₂ O ₅ ≦ 12 (mol%),
0 <(BaO + SrO) ≦ 20 (mol%), and 80 ≦ TeO ₂ ≦ 97 (mol%)
An optical functional waveguide material having a composition comprising:

(2): In (1), the amount of Ta ₂ O ₅ added to the optical functional waveguide material is
6 ≦ Ta ₂ O ₅ ≦ 12 (mol%)
The optical functional waveguide material according to claim 1, wherein the optical functional waveguide material is in the range of

(3): A material glass for an optical fiber or an optical waveguide,
0 <Ta ₂ O ₅ ≦ 12 (mol%),
0 <(BaO + SrO) ≦ 20 (mol%), and 80 ≦ TeO ₂ ≦ 94 (mol%)
An optical functional waveguide material having a composition comprising:

(4): Material glass for optical fiber or optical waveguide,
6 ≦ Ta ₂ O ₅ ≦ 12 (mol%),
4 ≦ (BaO + SrO) ≦ 12 (mol%), and 80 ≦ TeO ₂ ≦ 88 (mol%)
An optical functional waveguide material having a composition comprising:

(5): In any one of (1) to (4), a material glass for an optical fiber or an optical waveguide having at least Er added to the core, wherein Al ₂ O ₃ is added to the material glass. An optical functional waveguide material.

(6): Material glass for optical fiber or optical waveguide,
0 <Ta ₂ O ₅ ≦ 12 (mol%),
0 <(BaO + SrO) ≦ 20 (mol%), and 80 ≦ TeO ₂ ≦ 97 (mol%),
0 <Al ₂ O ₃ ≦ 4 (mol%)
An optical functional waveguide material having a composition comprising:

  (7): An optical amplifying medium comprising an optical fiber or an optical waveguide having a core glass and a clad glass, wherein the optical functional waveguide material is any one of (1) to (6). Optical amplifying medium.

  (8): In (7), Er or Er and ytterbium (Yb) are added to at least one of the optical functional waveguide material of the core glass or the optical functional waveguide material of the clad glass. A characteristic optical amplification medium.

  (9): In (7) or (8), at least one of the optical functional waveguide material of the core glass or the optical functional waveguide material of the clad glass is selected from the group consisting of boron, phosphorus, and a hydroxyl group. An optical amplifying medium comprising at least one selected from the group consisting of:

  (10): In any one of (7) to (9), at least one of the optical functional waveguide material of the core glass or the optical functional waveguide material of the clad glass is Ce, Pr, Nd, Sm, Tb. , Gd, Eu, Dy, Ho, Tm, and an element selected from the group consisting of Yb are added.

(11): In any one of (7) to (10), an optical amplifying medium composed of an optical fiber or an optical waveguide made of material glass with at least Er added to the core, wherein the composition of the material glass is Al ₂ O An optical amplification medium characterized by being an optical functional waveguide material to which ₃ is added.

  (12) The optical amplification medium according to any one of (7) to (11), wherein the cutoff wavelength is 0.4 μm to 2.5 μm.

  (13): A laser apparatus having an optical resonator and a pumping light source, wherein at least one of the optical amplification media included in the optical resonator is the optical amplification medium according to any one of (7) to (12). A laser device characterized by comprising:

  (14): A laser device in which a plurality of optical amplifying media made of optical fibers having at least Er added to the core are arranged in series, wherein at least one of the optical amplifying media is any one of (7) to (12) A laser device comprising the optical amplifying medium described in 1.

  (15) A laser device having an optical amplification medium and an excitation light source, wherein the optical amplification medium is composed of the optical amplification medium according to any one of (7) to (12).

  (16): An optical amplifier comprising an optical amplification medium and input means for inputting excitation light and signal light for exciting the optical amplification medium to the amplification medium, wherein the optical amplification medium comprises (7) to An optical amplifier comprising the optical amplification medium according to any one of (12).

  (17): An optical amplifier in which a plurality of optical amplifying media made of optical fibers having at least Er added to the core are arranged in series, wherein at least one of the optical amplifying media is any of (7) to (12) above An optical amplifier comprising the optical amplification medium according to claim 1.

  (18): An optical amplifier using an optical functional waveguide material as an amplification medium, wherein the optical amplification medium is at least one place before and after the optical amplification medium according to any one of (7) to (12). An optical amplifier comprising a dispersion medium that compensates for dispersion by chromatic dispersion values of different signs.

  (19): The optical amplifier according to (18), wherein the optical amplification medium is an optical waveguide made of an optical functional waveguide material to which a rare earth element and / or a transition metal element is added.

  (20): The optical amplifier according to (18) or (19), wherein the dispersion medium is an optical fiber or a fiber Bragg grating.

(21): An optical amplifier in which a plurality of optical amplifying units including an optical fiber doped with Er as an amplification medium are arranged in series,
An optical fiber made of the optical functional waveguide material according to any one of (1) to (6) is used as an optical fiber material for at least one of the second and subsequent stages of the plurality of optical amplification units. The optical amplifying unit upstream of the optical amplifying unit made of the functional waveguide material optical fiber uses an Er-doped optical fiber whose Er addition concentration and fiber length product are smaller than those of the optical functional waveguide material optical fiber. An optical amplifier.

  (22): In (21), as the material for the amplification medium, together with the optical functional waveguide material optical fiber, a fluoride optical fiber, a quartz optical fiber, a fluorophosphate optical fiber, a phosphate optical fiber, or a chalcogenide optical fiber. An optical amplifier characterized by being used.

  (23): In (21) or (22), an optical fiber material other than the optical functional waveguide material optical fiber is added to at least one optical amplifying unit in front of the optical amplifying unit made of the optical functional waveguide material optical fiber. An optical amplifier characterized in that is used.

  (24): In any one of (21) to (23), the Er addition concentration and the optical fiber length product of at least one optical fiber arranged in the front stage of the optical amplifying unit made of the optical functional waveguide material optical fiber are An optical amplifier characterized in that the optical functional waveguide material is smaller than that of an optical fiber.

(25): An optical amplifier using the optical fiber added with Er as an amplification medium in any one of (21) to (24),
At least two optical functional waveguide material optical fibers having different Er doping concentrations and optical fiber length products are arranged in series, and in the arrangement, an optical fiber having a small optical fiber length is an optical fiber having a large optical fiber length product. An optical amplifier comprising at least one array structure arranged in the preceding stage.

  (26): An optical functional waveguide material obtained by adding Er to the optical functional waveguide material according to any one of (1) to (6), or an optical waveguide according to any one of (7) to (12) A light source using the optical amplification medium described.

  (27): An optical amplifier characterized in that an optical waveguide formed of a glass material obtained by adding Er to the optical functional waveguide material according to any one of (1) to (6) is used as an optical amplification medium. .

  (28): In (27), at least one of the optical waveguide or the optical fiber includes an optical coupler disposed at an end thereof, and a reflector is provided at at least one terminal of the optical coupler. Optical amplifier.

  (29): The light source according to (28), wherein the reflector is made of a dielectric multilayer filter or a fiber Bragg grating.

  30. The optical amplifier according to claim 27, wherein the reflector is made of a dielectric multilayer filter or a fiber Bragg grating in (27) or (28).

By the above means, an optical functional waveguide material excellent in suitability as a fiber host, which is a material glass for an optical fiber or an optical waveguide, in particular, a stimulated emission cross section of Er 1.5 μm band is flatter is provided. be able to. At the same time, an EDFA with a flattened gain can be provided by using this material as an optical amplification medium.
Further, the operating wavelength band of the conventional EDFA can be expanded to provide an EDFA that operates with a low noise in a wider band region. Further, by adding an optically active rare earth element, it is possible to provide an optical fiber or an optical waveguide that can exhibit a function that cannot be realized by a conventional glass material, for example, a function such as a broadband EDFA.
In addition, a broadband optical amplification medium that can operate in the wavelength range of 1.5 μm to 1.7 μm using the above optical functional waveguide material, an optical amplifier having a broadband and low noise characteristics using this optical amplification medium, and a laser An apparatus and even a light source can be provided.

  Operations / effects other than those described above will be apparent from the description of the present specification and the accompanying drawings.

First, a glass material having a TeO ₂ —Ba 0 —SrO—Ta ₂ O ₂ composition according to the present invention will be described. In the embodiment of the present invention, the tellurite-based glass material can be classified into the following three forms (first to third compositions) according to the composition state. Each composition (A to C) has a unique effect and / or suitable use.

That is, in the first form (A), as shown in the composition region A in FIG.
0 <Ta ₂ O ₅ ≦ 12 (mol%),
0 <(BaO + SrO) ≦ 20 (mol%), and 80 ≦ TeO ₂ ≦ 97 (mol%)
It has a composition consisting of

In the second form (B), as shown in the composition region B in FIG.
0 <Ta ₂ O ₅ ≦ 12 (mol%),
0 <(BaO + SrO) ≦ 20 (mol%), and 80 ≦ TeO ₂ ≦ 94 (mol%)
It has a composition consisting of

In the third form (C), as shown in the composition region C in FIG.
6 ≦ Ta ₂ O ₅ ≦ 12 (mol%),
4 ≦ (BaO + SrO) ≦ 12 (mol%), and 80 ≦ TeO ₂ ≦ 88 (mol%)
It has a composition consisting of

In each composition (A to C), (BaO + SrO) represents the total ratio (mol%) of Ba and Sr. Further, in the first and second compositions, Ta ₂ O ₅ and (BaO + SrO) each contain a significant non-zero addition amount as a component.

The thermal stability of glass against fiberization can be evaluated by DSC (differential scanning calorimetry) measurement. A glass having a large Tx-Tg value ΔT (Tx: crystallization temperature, Tg: glass transition temperature) is a more stable glass. That is, when producing a single mode fiber or photonic crystal fiber, the glass base material is heated to a temperature of Tg or more twice in the drawing process and drawing process of the base material or glass tube, so that Tx is close to Tg. If so, crystal nuclei grow one after another and the scattering loss of the fiber increases. On the other hand, if the value ΔT of Tx−Tg is large, a low-loss fiber can be manufactured.
In particular, the glass in the composition regions B and C has a Tx-Tg value ΔT of 100 ° C. or more, and is suitable for use in producing a low-loss fiber. On the other hand, even if glass having a composition deviating from the above compositions (A to C) is used for both the core and the clad, it is difficult to produce a low-loss fiber. Of these compositions (A to C), especially the addition of Ta ₂ O ₅ has a great effect on the stability of the glass.

  FIG. 4 shows the result of measuring the ΔT (ΔT = Tx−Tg) of the glass, which is the optical functional waveguide material of the present invention, by the DSC. The measurement was performed by crushing a part of the glass, filling 30 mg of bulk glass into a silver gold-plated sealed container, and heating at a rate of 10 ° C./min in an argon gas atmosphere.

In the figure, graph lines (a) to (c) correspond to the following component ratios (a) to (c), respectively.
(A): BaO: SrO: Ta ₂ O ₅ = 1: 1: 2
(B): BaO: SrO: Ta ₂ O ₅ = 1: 1: 4
(C): BaO: SrO: Ta ₂ O ₅ = 1: 1: 1
As is clear from the figure, the value ΔT of Tx−Tg is as high as 237 ° C. when Ta ₂ O ₅ = 10 mol%.

Addition of Ta ₂ O ₅ also has an important effect from the viewpoint of controlling the refractive index. FIG. 5 shows the Ta ₂ O ₅ addition dependency of the optical refractive index n (specific refractive index at a wavelength of 632.8 nm) of TeO ₂ glass. In the figure, the graph lines (a) to (c) and the component ratios (a) to (c) correspond to the same as described above. As shown in the figure, when the component ratio and Ta ₂ O ₅ addition amount are changed from 2 mol% to 12 mol%, the refractive index n is between 2.115 and 2.17 in proportion to the addition amount. Can be made.

By utilizing this characteristic and changing the amount of Ta ₂ O ₅ added, the core-clad refractive index difference (relative refractive index difference between the core and the clad) is as small as about 0.2% to about 2.5%. It is possible to easily design a fiber up to a large one.

  In the optical amplifying medium according to the present invention, Er (erbium) or Er and Yb (ytterbium) are added to at least one of the tellurite glass of the core glass or the clad glass forming the optical fiber or the optical waveguide. It is characterized by.

The laser apparatus according to the present invention is a laser device having an optical amplification medium and an excitation light source, an optical fiber using the tellurite glass doped with Er as the optical amplifying medium, ⁴ I _13/2 level of Er The main feature is the use of a stimulated emission transition from the position to the ⁴ I _15/2 level.

FIG. 6 is an energy level diagram of Er ³⁺ . In this figure, it is shown that light is emitted by the transition from the upper level ⁴ I _13/2 to the ground level ⁴ I _15/2 .

Further, as shown in FIG. _{^{7, Er 4 I 13/2 → 4}} I 15/2 emission of ^3+, other glass in fluoride glass in, for example, than the quartz glass in a wide range of ⁴ I _13/2 → It is known to have a ⁴ I _15/2 emission band. However, as can be seen from FIG. 7, the emission intensity decreases on the wavelength longer side than 1.6 μm. Even if Er is in the fluoride glass, optical amplification and laser oscillation at a long wavelength of 1.6 μm or more are less likely to occur.

However, when Er is added to tellurite glass, it receives a stronger electric field than other glasses, and as a result, it is in the level due to the Stark effect received by the ⁴ I _13/2 and ⁴ I _15/2 levels. And the emission emission cross section is increased even in a longer wavelength region, and as shown in FIG. 7, fluorescence exists even at a longer wavelength of 1.65 μm or more.

  Therefore, if a tellurite fiber having at least Er added to the core is used as an optical amplifying medium, optical amplification and laser devices from 1.5 μm to 1.7 μm, which could not be realized with an Er-added silica fiber or Er-added fluoride fiber, are possible. It becomes possible.

When tellurite glass contains at least one of boron, phosphorus and hydroxyl groups, the gain coefficient and the noise figure are improved even when the ⁴ I _11/2 level is excited by 0.98 μm light. That, B-O, P-O , vibration energy of the O-H, respectively about 1400 cm ^-1, 1200 cm ^-1, is 3700 cm ^-1, phonon energy of tellurite glass containing no these 600～700Cm ^-1 Therefore, it becomes more than double. For this reason, when light of wavelength around 0.98 μm is directly excited to cause the ⁴ I _11/2 level of Er to be directly excited and light amplification of 1.5 μm due to the ⁴ I _13/2 → ⁴ I _15/2 transition, It becomes easy to receive relaxation due to emission of _electrons , and the excitation efficiency of the ⁴ I _13/2 level is unlikely to decrease (FIG. 6). In addition, ⁴ I _11/2 and it is likely to occur relaxation from level to ⁴ I _13/2 level, than to direct excitation of the ⁴ I _13/2 level in the light in the vicinity of 1.48μm, ⁴ I _{15 /} advantage _who excites the ⁴ I _13/2 level After exciting level is, ⁴ I _13/2 level position and ⁴ I _15/2 easily obtained inversion between levels, thus excellent noise characteristics There is.

  Embodiments of an optical amplifying medium according to the present invention and a broadband optical amplifier and a laser apparatus using the optical amplifying medium according to the present invention will be described below in detail with reference to the drawings.

[Example 1]
The composition after melting is (1) TeO ₂ (85 mol%)-(BaO + SrO) (15 mol%),
₍₂₎ TeO 2 (80 mol%) - (BaO + SrO) (10 _{mol%) - Ta 2 O 5 (} 10 mol%),
So that the component raw materials of each composition (1) and (2) are respectively prepared, 20 g of each of the mixed raw materials of each composition (1) and (2) is filled in a crucible, It was melted at 800 ° C. for 2 hours. Then, it casted on the plate pre-heated at 200 degreeC, and obtained glass was annealed at 250 degreeC for 4 hours. A portion of this glass was crushed, and two types of samples, a bulk glass of 30 mg each and a powder of 30 mg powdered in an agate mortar, were each filled in a silver gold-plated sealed container, and the heating rate was 10 in an argon gas atmosphere. DSC measurement was performed at ° C / min.
The value ΔT of Tx−Tg was 20 ° C. or less for the glass of (1) where Ta ₂ O ₅ = 0, and 237 ° C. for the glass of (2) where Ta ₂ O ₅ = 10 mol%. In particular, in the composition in the range of C, the thermal stability was improved to ΔT = 200 ° C. or more.

  Although it has been stated that a low-loss fiber can be produced by using glass with Tx−Tg ≧ 100 ° C. based on DSC measurement values, glass in this range is high by using three-level optical transition. A loss of 0.1 dB / m or less required for efficient optical amplification can be realized.

[Example 2]
As the core glass and the clad glass, those having the composition region shown in B (FIG. 2) or C (FIG. 3) are used. These compositions were melted in an oxygen atmosphere using a platinum crucible or a gold crucible, and a preform was produced by a suction molding (suction casting) method. Similarly, a jacket tube was produced by the rotational molding (rotational casting) method using the glass composition of A (FIG. 1). As a result of fiber drawing using these preforms and jacket tubes, the minimum loss is 0.1 dB / m or less, the cutoff wavelength is 0.5 μm to 2.5 μm, and the core-cladding refractive index difference is 0.2% to 2. A 5% tellurite fiber could be made.

  Moreover, 10% by weight or less of rare earth such as Er, Pr, Yb, Nd, Ce, Sm, Tm, Eu, Tb, Ho, or Dy could be added to the core or clad glass (Preform and jacket tube production). (See Non-Patent Document 6 for the law).

[Example 3]
Similarly to Example 2, a tellurite fiber having a glass composition in the B and C regions was prepared. As a result, a tellurite fiber having a minimum loss of 0.1 dB / m or less, a cutoff wavelength of 0.5 μm to 2.5 μm, and a core-clad refractive index difference of 0.2% to 2.5% can be manufactured. did it.
Further, 10 wt% or less of rare earth such as Er, Pr, Yb, Nd, Ce, Sm, Tm, Eu, Tb, Ho or Dy could be added to the core glass or the clad glass.

[Example 4]
TeO ₂ (88 mol%)-(BaO + SrO) (4 mol%)-Ta ₂ O ₅ (8 mol%) glass added with 1000 ppm of Er as a core material, TeO ₂ (82 mol%)-( An optical fiber having a cutoff wavelength of 1.3 μm and a core-cladding refractive index difference of 1.7% is formed by using a glass having a composition of BaO + SrO) (12 mol%)-Ta ₂ O ₅ (6 mol%) as a clad material. This was used as an optical amplification medium. Using this optical amplification medium, an optical amplifier having a wavelength band of 1.5 μm to 1.7 μm was produced, and an amplification experiment was performed. An excitation wavelength of 0.98 μm was selected, and a DFB (Distributed FeedBack) laser was used as a signal light source in the 1.5 μm to 1.7 μm band.

  FIG. 8 is a diagram showing a schematic configuration of the optical amplifier of the present embodiment. The signal light source 101 and the excitation light source 102 are connected to one end of an amplification optical fiber 104 via an optical coupler 103, and an optical isolator 105 is connected to the other end of the amplification optical fiber 104. Each component is connected by an optical fiber 106 (reference numerals 106a to 106d).

  By an amplification experiment using the optical amplifier having such a configuration, an amplification gain could be obtained at a wavelength between 1.5 μm and 1.7 μm.

  Further, a ring laser in which the tunable narrow band-pass filter shown in FIG. 9 was inserted was configured using the same optical amplification medium. In this ring laser, instead of the signal light source 101 in FIG. 8, the output side of the optical isolator 105 is connected to the optical coupler 103 to form a ring-shaped optical resonator, and a narrow band is formed in the middle of the ring-shaped optical resonator. A band-pass filter 107 is inserted. Then, the transmission region of the narrow band-pass filter 7 was varied between 1.5 μm and 1.7 μm, and light was incident from the excitation light source 102 to perform a laser oscillation experiment. As a result, it was possible to confirm laser oscillation in the wavelength band from the output end 108. Each component is connected by an optical fiber 106 (reference numerals 106a to 106e).

In the above embodiment, 0.98 μm is used as the excitation wavelength and the ⁴ I _11/2 level is excited. However, the ⁴ I _13/2 level may be directly excited using the wavelength of the 1.48 μm band. Needless to say. In addition, a level having a higher energy than the ⁴ I _11/2 level may be excited with light having a wavelength shorter than 0.98 _μm .

[Example 5]
An optical amplification experiment in the 1.5 μm band was performed using the optical amplifier shown in FIG. The excitation wavelength was 0.98 μm. As a result, amplification was possible with a noise figure of 7 dB or less in a wavelength region of 1.53 μm or more.

[Example 6]
An optical fiber similar to that in Example 3 was produced except that Er and Yb co-doped glass were used as the core, and an optical amplification medium was obtained.
Using this optical amplification medium, an optical amplification experiment and a laser oscillation experiment were performed with the configurations of Example 4 and Example 5. As the excitation wavelength, 1.029 μm (Yb-doped YAG laser), 1.047 μm (Nd-doped YLF laser), 1.053 μm (Nd-doped YAG laser), 1.064 (Nd-doped YAG laser), or the like was used. Thus, when Yb is co-added with Er, by utilizing the energy transfer from Yb to Er, laser oscillation between 1.5 μm and 1.7 μm and 1 It was possible to confirm broadband optical amplification in the .5 μm band.

In the above Examples 1 to 6, an example in which attention is paid to the composition of the optical fiber is shown, but the present invention is not limited to this. For _{example, Cs 2 O, Rb 2 O} , K 2 O, Li 2 O, CaO, MgO, BeO, La 2 O 3, Y 2 O 3, Sc 2 O 3, ThO 2, HfO 2, ZrO 2, TiO 2 , Wo ₃ , Tl ₂ O, CdO, PbO, In ₂ O ₃ , Ga ₂ O _3, etc., and glass containing TeO ₂ (see: Glass Handbook (Eighth Edition)) Edited by Sakuo Sakuo et al., Asakura Shoten, published in 1950). Further, Er or Er and Yb may be added not only to the core but also to the cladding.

  Furthermore, the optical amplifier is not limited to the above-described configuration as long as it has the optical amplification medium of the present invention, an excitation light source for exciting the optical amplification medium, and signal light input and output means.

  Further, the laser device is particularly limited as long as the optical amplifying medium of the present invention is inserted in the middle of an optical resonator composed of an optical fiber and further has a pumping light source for exciting the optical amplifying medium. It is not a thing.

[Example 7]
Amplification characteristics in the 1.5 μm band were measured using a fiber 4 m in which Er 1000 ppm was added to the core as an amplification fiber. The core glass composition TeO ₂ (88 mol%) - (BaO + SrO) (4 mol%) - Ta ₂ O ₅ and (8 mol%) was added P ₂ O ₅ 5 wt% thereto. The clad glass composition was TeO ₂ (82 mol%)-(BaO + SrO) (12 mol%)-Ta ₂ O ₅ (6 mol%).
The core-clad refractive index difference was 2.5%, and the cutoff wavelength was 0.96 μm.

When a small signal gain in the 1.5 μm band was measured using 0.98 μm light (the light source is a semiconductor laser) as a pumping light, the gain efficiency increased by a factor of 5 and reached 2 dB / mW compared to the case where phosphorus was not added. did. Further, when the gain spectrum in the saturation region was measured with the input signal level set at -10 dBm, the gain became flat with a width of 90 nm from 1530 nm to 1620 nm (excitation intensity was 200 mW). The noise figure was 7 dB when phosphorus was not added, but decreased to 4 dB by adding phosphorus. Thus, the addition of phosphorus as the core glass significantly improved the gain coefficient and noise figure.
Further, even when B ₂ O ₃ was added in place of P ₂ O ₅ , improvement in gain coefficient and noise figure could be confirmed.

[Example 8]
When a glass having a composition of TeO ₂ (88 mol%)-(BaO + SrO) (4 mol%)-Ta ₂ O ₅ (8 mol%) is used as a core glass, OH groups are added at 5000 ppm and Er is added at 1000 ppm. It was confirmed that it increased by a factor of 3 compared to when no OH group was added.
The degree of increase in gain coefficient is lower than that when phosphorus is added because the signal energy of the OH group has a large value of 3700 cm ⁻¹ , and the ⁴ I _13/2 level that is the starting level of amplification is also slightly This is because it is relaxed by polyphonic emission.

  FIG. 10 shows an example of a laser apparatus according to the present invention. In the figure, reference numerals 111 and 111 'are pumping semiconductor lasers (wavelength: 1480 nm), 112 and 112' are optical couplers for coupling signal light and pumping light, 113 and 115 are optical fibers for amplification, and 114 is an optical isolator. Respectively. The signal light enters from the port A and then exits from the port B.

A ZrF4 fluoride fiber doped with 1000 ppm of Er as the reference fiber 113 (Patent Document 6) is used, and TeO ₂ —BaO—SrO—Ta ₂ O ₅ doped with 1000 ppm of Er is used as the amplification fiber 115. A tellurite fiber was used.

  The difference in refractive index between the core and the clad of each fiber was 2.5%, the cutoff wavelength was 1.35 μm, and the fiber lengths were 10 m and 7 m, respectively. The gain spectrum in the 1.5 μm band was measured with the output light intensity of the pumping semiconductor lasers of reference numerals 111 and 111 ′ being 150 mW. The obtained gain spectrum is shown in FIG.

  According to the gain spectrum shown in FIG. 11, the curve indicating the change in the value of the signal gain is flat with an 80 nm width from the signal wavelength 1530 nm to 1610 nm. That is, it can be seen that the signal gain in such a wavelength band is maintained at a value in the vicinity of 30 dB. Therefore, the gain tilt can be kept small in such a wavelength band. When the Er-doped fluoride fiber is used, the wavelength width at which the gain becomes flat is 30 nm from 1530 nm to 1560 nm, and thus the wavelength width at which the gain becomes flat has spread more than twice. In addition, in the case of Er-doped silica fiber, the flat wavelength width is at most 10 nm, which means that it has spread eight times compared to this.

  In this embodiment, an Er-doped ZrF4 fluoride fiber is used in the former stage and an Er-doped tellurite fiber is used in the latter stage, but this may be reversed. The fluoride fiber may be an InF3 fluoride fiber. Further, an Er-doped oxide multicomponent glass fiber may be added to the amplification fiber. In short, it is important to use an Er-doped tellurite fiber as one of the amplification optical fibers.

  Further, the composition of the tellurite fiber is not limited to that used in this embodiment.

  It goes without saying that any one of forward pumping, backward pumping, and bidirectional pumping may be used as a pumping method for the amplification optical fiber.

[Example 9]
FIG. 12 shows a schematic configuration of another embodiment of the laser apparatus according to the present invention. In this embodiment, amplification fibers 113 and 115 using the first embodiment are connected in series via a tunable bandpass filter 117 (bandwidth 3 nm), and the transmittance at 1480 nm is 99%, 1500 nm to 1630 nm. A mirror 116 having a reflectance of 100% is provided. The other end was provided with a mirror 118 having a transmittance of 1500% to 1630 nm at 20% to perform laser oscillation. As a result, it was found that laser oscillation could be confirmed in a wide range of signal wavelengths from 1500 nm to 1630 nm, and that it could be used as a broadband tunable laser that can be used at 1.5 μm.

  As described above, by using the optical amplifying medium of the present invention, it is possible to construct an optical amplifier and a laser apparatus from 1.5 μm to 1.7 μm, which has been impossible with an optical fiber amplifier until now. High performance of the maintenance / monitoring system used in the .55 μm band optical communication system can be achieved, and stable operation of the optical communication system becomes possible.

  In addition, if a characteristic with a wide amplification wavelength range is used, an extremely short optical pulse such as femtosecond can be efficiently amplified, which is effective as an optical amplifier used in a wavelength division multiplexing optical transmission system.

[Example 10]
In this example, the operation of the superluminescent laser was performed using the optical fiber (tellurite fiber) used in Example 4. A 1.48 μm laser diode was used as an excitation light source, and was incident on one end of the optical fiber. The other end of the fiber was obliquely cut at an angle of 10 ° to suppress Fresnel reflection at the fiber end face. When the emission spectrum from the other end was measured, a broad emission spectrum from 1.46 μm to 1.64 μm was observed, and it was found that it could be used as a broadband superluminescent laser device.

[Example 11]
In the configuration of the optical amplifier shown in FIG. 8, a filter for equalizing gain (chirped fiber Bragg grating, programmable filter, Fabry-Perot etalon type filter, Mach-Zehnder type filter, etc.) is provided after the optical isolator. The optical amplification characteristics were measured after insertion. When light with a signal intensity of −30 dBm is incident and excited at 1.48 μm (200 mW), a peak of gain is observed from 1530 to 1580 nm unless a filter is inserted, but the loss is adjusted by inserting a filter. Was able to negate the peak of gain. It was confirmed that the WDM signal in the wavelength range from 1530 nm to 1610 nm can be operated with a gain deviation of 0.2 dB or less.

[Example 12]
The glass having the composition of the region A (FIG. 1) is used as a core and a clad, and Ce, Pr, Gd, Nd, Eu, Sm, Tb, Tm, Dy, Ho, Yb or Er is added to the core. It was operated as a waveguide laser and a waveguide type optical amplifier. As a result, in the 0.3 μm, 1.3 μm, 0.31 μm, 1.07 μm, 0.61 μm, 0.59 μm, 0.54 μm, 1.48 μm, 3.0 μm, 1.49 μm, 1 μm, and 1.55 μm bands Broadband laser oscillation and broadband optical amplification were confirmed.

[Example 13]
TeO ₂ (88 mol%) - (BaO + SrO) (4 _{mol%) - Ta 2 O 5 (} 8 mol%) as a core material with Er in the glass composition was added _{2000ppm, TeO 2 (82%)} - (BaO + SrO) (12 mol%) - Ta by ₂ O ₅ (6 mol%) to the glass composition and the cladding material to form a cut-off wavelength 1.1 .mu.m, the core-clad refractive index difference of 1.7% of the optical fiber, This was used as an amplification medium. The fiber loss at 1.3 μm was 40 dB / km. An optical amplifier was constructed using 4 m (fiber length) of this optical fiber, and an amplification experiment was conducted. The excitation wavelength used was bidirectional excitation with 0.98 μm at the front and 1.48 μm at the rear. As the signal light source, a wavelength tunable laser of 1.5 μm to 1.7 μm band was used. As a result of the amplification experiment, a small signal gain of 5 dB or more was obtained in the 110 nm band of 1500 to 1630 nm. At this time, the noise figure at a wavelength of 1530 nm or more was 5 dB or less.

[Example 14]
An optical amplifier was configured using 15 m of the same optical fiber as in Example 13, and an amplification experiment was performed. The excitation wavelength was 1.48 μm bidirectional excitation for both front and rear. As the signal light source, a wavelength tunable laser of 1.5 μm to 1.7 μm band was used. As a result of the amplification experiment, a small signal gain of 35 dB or more was obtained particularly in the 50 nm band of 1580 to 1630 nm. At this time, the noise figure was 5 dB.

[Example 15]
A laser was constructed using 15 m of the same optical fiber as in Example 13. The cavity was constructed using a total reflection mirror and a fiber Bragg grating with 3% reflectivity at 1625 nm. The excitation wavelength was 1.48 μm bidirectional excitation for both front and rear. When the incident excitation intensity was 300 mW, a high output of 150 mW was obtained at 1625 nm, which could not be obtained with a quartz fiber or a fluoride fiber.

[Example 16]
TeO ₂ (97 mol%)-(BaO + SrO) (1 mol%)-Ta ₂ O ₅ (2 mol%) 3 wt% of Er is added to the glass to form a core material, TeO ₂ (82 mol%)-(BaO + SrO) (12 mol%)-Ta ₂ O ₅ (6 mol%) glass is used as a clad material to form a fiber having a cutoff wavelength of 1.4 μm and a core-clad refractive index difference of 2.5%, and this is used as an amplification medium. . A small optical amplifier was constructed using 3 cm of this optical fiber, and an amplification experiment was conducted.

  The excitation wavelength was 1.48 μm forward excitation. As the signal light source, a wavelength tunable laser of 1.5 μm to 1.7 μm band was used. As a result of the amplification experiment, a small signal gain of 20 dB or more was obtained in the 80 nm band of 1530 to 1610 nm. At this time, the noise figure was 7 dB or less.

[Example 17]
TeO ₂ —BaO—SrO—Ta ₂ O ₅ quaternary glass was prepared by changing other compositions, and thermal characteristics were measured by DSC for each composition. As a result, a stable glass having a Tx-Tg of 150 ° C. or higher was obtained in the B composition region (FIG. 2). In the composition region of C (FIG. 3), a more stable glass having a Tx-Tg of 170 ° C. or higher was obtained. If an optical fiber is manufactured using such a thermally stable glass, not only the fiber loss is low, but also a fiber with a high yield can be produced in large quantities, and the price can be reduced. .

Therefore, by using a glass having a composition of TeO ₂ — (BaO + SrO) —Ta ₂ O ₅ selected from the above B region and adding 2000 ppm of Er to the core, the cutoff wavelength is 1.1 μm, and the core-clad refractive index difference. A 1.5% optical fiber was formed and used as an amplification medium. The fiber loss at 1.2 μm was 20 dB / km. An optical amplifier was constructed using 3 m of this fiber, and an amplification experiment was conducted.

  The excitation wavelength used was bidirectional excitation with 0.98 μm at the front and 1.48 μm at the rear. As the signal light source, a wavelength tunable laser of 1.5 μm to 1.7 μm band was used. As a result of the amplification experiment, a small signal gain of 20 dB or more was obtained in the 80 nm band of 1530 to 1610 nm. At this time, the noise figure was 5 dB or less.

[Example 18]
An optical amplifier was configured using 15 m of the optical fiber of Example 17, and an amplification experiment was performed. The excitation wavelength was 1.48 μm bidirectional excitation for both front and rear. As the signal light source, a wavelength tunable laser of 1.5 μm to 1.7 μm band was used. As a result of the amplification experiment, a small signal gain of 20 dB or more was obtained particularly in the 50 nm band of 1580 to 1630 nm. At this time, the noise figure was 5 dB or less.

[Example 19]
A laser was constructed using 15 m of the optical fiber of Example 17. The cavity was constructed using a total reflection mirror and a fiber Bragg grating with 3% reflectivity at 1625 nm. The excitation wavelength was 1.48 μm bidirectional excitation for both front and rear. When the incident excitation intensity was 300 mW, a high output of 150 mW was obtained at 1625 nm, which could not be obtained with a quartz fiber or a fluoride fiber.

The tellurite glass used in the above Examples 1 to 19 is characterized by containing Ta ₂ O ₅ , but such tellurite glass has high thermal stability and low loss when formed into a fiber. Further, by controlling the refractive index and making a fiber with a high Δn, it is possible to expand the amplification band of the EDFA using a low-efficiency three-level system.

Conventionally known tellurite glass that can be made into fiber includes tellurite glass such as Sintzer et al. (Patent Document 8) and Patent Document 9 described in the prior art. _There is no description of the utility of ₂ O _{5 on} the refractive index and glass stability. Optical functional waveguide material of the present invention as described above, the tellurite glass containing _{Ta 2 O 5, Ta 2 O} 5 -BaO-SrO-TeO 2 specifically obtained optical functions in a specific region of the composition This is clearly different from those disclosed in Patent Documents 8 and 9.
If attention is paid only to the composition of Ta ₂ O ₅ —BaO—SrO—TeO _2, the ferroelectric glass ceramic described in Non-Patent Document 3 has that composition. However, the ferroelectric glass ceramic is completely different from the optical functional waveguide material of the present invention in its composition region and function.

As described so far, the ternary tellurite glass described in Patent Document 8 is more thermally stable than the quaternary (Ta ₂ O ₅ — (BaO + SrO) —TeO ₂ ) tellurite glass of the present invention. Therefore, the loss at 1.55 μm can be reduced only to 1500 dB / km. On the other hand, as a result of examining various compositions for the purpose of reducing loss in the present invention, the quaternary system (Ta ₂ O ₅ — (BaO + SrO) —TeO ₂ ) containing Ta ₂ O ₅ can reduce loss. It was found to be specifically effective. Furthermore, since the quaternary glass can be easily controlled in refractive index, an optical fiber having a high refractive index difference Δn can be produced. Only when it has the characteristics of low loss, a high-efficiency tellurite EDFA has been realized.
In the ternary tellurite glass of Patent Document 8, it is difficult to realize an EDFA by using an inefficient three-level system. In this regard, not only in the specification of Patent Document 8 but also in Non-Patent Documents 1 and 2 filed thereafter, there is no specific description regarding the realization of EDFA.

  More specifically, in Patent Document 8, Snitzer et al. Described that a laser can be realized even in bulk glass, whereas optical amplification requires a fiber structure having a core and a clad. The composition range of ternary tellurite glass was shown as a certain tellurite glass. Therefore, although the purpose is to realize optical amplification, the conventional literature (Patent Literature 1 and Non-Patent Literatures 1 and 2) only describes a fiber laser using neodymium in Non-Patent Literature 2. In the field of optical amplification, neodymium was initially promising for application to amplification in the 1.3 μm band, but as described in Non-Patent Document 1, it is in the 1.3 μm band for absorption of excited states. Application to amplification has proved difficult.

The tellurite glass containing Ta ₂ O ₅ is also described in Non-Patent Document 1 and Patent Document 9, but is not described regarding thermal stability and loss. What is described in these documents is a completely different composition or composition region from the quaternary system of the present invention.

Non-Patent Documents 1 and 2 describe a quaternary tellurite glass having a core composition of 77% TeO ₂ -6.0% Na ₂ O-15.5% ZnO-1.5% Ta ₂ O ₅ , In particular, Non-Patent Document 1 describes even the loss, but the loss is a high value of 1500 dB / km in the 1.55 μm band, and moreover, a description about the thermal stability improvement by adding Ta ₂ O ₅ and the thermal stability There is no mention of any improvement. Non-Patent Document 3, as described above, has a report on Ta ₂ O ₅ —BaO—SrO—TeO ₂ glass ceramic, but there is no description about the glass thermal stability region. It is not about.

As described in detail in the above examples and the like, in the present invention, as a result of various investigations on the composition of the tellurite glass with the aim of reducing the loss of the tellurite glass, the quaternary tellurite glass containing Ta ₂ O ₅ is effective. It was clarified that. Although this has already been described in the examples, the thermal stability has been dramatically improved by the addition of Ta ₂ O ₅ in particular, and the loss of the tellurite glass fiber has been successfully reduced. Further, as a secondary effect, the refractive index difference Δn of the fiber can be freely controlled by adjusting the amount of Ta ₂ O ₅ added to the core and the cladding, so that a high Δn fiber can be produced. In the EDFA using the system, the amplification band was successfully expanded.

Next, the glass composition that makes the gain spectrum of the tellurite EDFA flatter will be examined. In the following examples, the main feature is to add Al as a host to tellurite glass or fiber. If adding Al to the SiO ₂ based glass, it eliminates the indentations between 1.53μm and 1.56μm of stimulated emission cross-section of Er added to SiO ₂ glass, flat toward 1.56μm from 1.54μm It is known that a good gain can be obtained (Non-Patent Document 4).

  However, this is an effect of adding Al to the silica-based fiber, and the effect is not clear for the tellurite-based fiber. Here, as shown in the following examples, the present inventors eliminated dents in the stimulated emission cross sections of 1.53 μm and 1.56 μm and added 1.6 μm band by adding Al to the tellurite glass. It has been found that the stimulated emission cross-sectional area can be changed (increased), and as a result, the gain deviation between the 1.55 μm band and the 1.6 μm band can be reduced.

[Example 20]
FIG. 13 shows TeO ₂ (88 mol%)-(BaO + SrO) (4 mol%)-Ta ₂ O ₅ (8 mol%) glass, and TeO ₂ (84 mol%)-(BaO + SrO) (4 mol%)- ta ₂ O ₅ (8 _{mol%) - Al 2 O 3 (} 4 mol%) respectively of 1.5μm emission spectra of Er in the glass. Apparent so from the figure, the intensity at 1.6μm vicinity of the emission spectrum of the glass containing Al ₂ O ₃ is stronger than the one not containing Al ₂ O _3, also a 1.53μm and 1.56μm The depth of the valley between them is also shallow.

Using this Al ₂ O ₃ -containing glass (TeO ₂ — (BaO + SrO) —Ta ₂ O ₅ glass) as a core composition, an Er-doped tellurite fiber (cutoff wavelength: 1.3 μm, Er concentration: 4000 ppm, length: 0) .9 m) and excitation (200 mW) at 1.48 μm, the gain deviation between 1.56 μm and 1.69 μm could be reduced to 10 dB or less.

When this fiber was used as an amplification medium and an EDFA using a fiber Bragg grating was configured as a gain equalizer, an EDFA having a gain deviation of 1 dB or less from 1.53 μm to 1.60 μm could be realized. . In the case of using a fiber not containing Al ₂ O ₃ , the gain deviation between 1.53 μm and 1.60 μm is 15 dB or more, and even if gain correction is performed using a gain equalizer, the gain deviation is 1 dB over a bandwidth of 70 nm. It was difficult to make it below. This became possible only when the glass containing Al ₂ O ₃ of this example was used as a fiber host.

An Er-added tellurite fiber (cut-off wavelength: 1.3 μm, Er concentration: 4000 ppm, length: 0.9 m) is produced using this Al ₂ O ₃ -containing glass as a core composition, and excited at 1.48 μm (200 mW) As a result, the gain deviation between 1.56 μm and 1.60 μm could be reduced to 10 dB or less.

When this fiber was used as an amplifying medium and a Mach-Zehnder type filter (loss medium) was used as a gain equalizer, an EDFA having a gain deviation of 1 dB or less from 1.53 μm to 1.60 μm could be realized. . When a fiber not containing Al ₂ O ₃ is used, the gain deviation between 1.56 μm and 1.60 μm is 15 dB or more, and even if gain correction is performed using a gain equalizer, the gain deviation is 1 dB over a bandwidth of 70 nm. It was difficult to make it below.

Further, when an amplification spectrum was measured using a fiber with Er addition concentration of 1000 ppm and a length of 2 m, the gain between 1.53 μm and 1.56 μm seen in the fiber not containing Al ₂ O ₃ was measured. There was no fluctuation, and a gain with good uniformity was obtained from 1.53 μm to 1.56 μm, which proved advantageous for WDM transmission applications in the same wavelength region.

The effect of improving the gain characteristics by the addition of Al ₂ O ₃ is that the specific composition region of TeO ₂ — (BaO + SrO) —Ta ₂ O ₅ (80 ≦ TeO ₂ ≦ 97, 0 <(BaO + SrO) ≦ 20, 0 <Ta ₂ ). O ₅ ≦ 12, unit mol%). It was confirmed that the fiber can be stably formed in this unique region.

In the above examples, the concentration of Al ₂ O ₃ was 4 mol%, but the concentration is not limited to this. If the concentration is higher than 0 mol%, the effect of adding Al ₂ O ₃ could be confirmed. .

  In the following Examples 21 to 26, in view of the characteristics of the tellurite optical fiber as described above, a tellurite EDFA having a low wavelength dispersion characteristic that improves the wavelength dispersion characteristic of the conventional tellurite EDFA will be described.

  In the following embodiments, in an optical amplifier using tellurite glass as an amplification medium, dispersion is compensated by a wavelength dispersion value having a sign different from that of the tellurite EDFA in front or behind the tellurite EDFA which is an amplification medium. The main feature is to adopt a structure in which a dispersing medium is inserted. Examples of media for controlling chromatic dispersion include optical fibers and fiber Bragg gratings.

  The conventional tellurite EDFA does not have a medium that compensates for the chromatic dispersion of the tellurite EDFA. Therefore, the chromatic dispersion in the optical amplifier increases, and as a result, when a high-speed optical signal is amplified, the error rate increases and the communication quality increases. This causes the problem of deterioration. On the other hand, by adopting the structure of the following embodiment, the chromatic dispersion value in the amplifier can be lowered, and even when a high-speed optical signal is amplified, the error rate does not increase and high communication quality is maintained. be able to.

[Example 21]
FIG. 14 shows a configuration example of an optical amplifier according to the present invention. In the optical amplifier shown in the figure, an optical signal enters from the left side and exits to the right side. The incident signal light passes through the optical isolator 201 a and is then combined with the excitation light from the excitation light source 202 by the optical coupler 203. The signal light combined with the pumping light passes through the dispersion medium 204, enters the amplification optical fiber 205, and is amplified. The signal light amplified by the optical fiber 205 passes through the optical isolator 201b and is output.

  In the optical amplifier of this example, a semiconductor laser having a signal wavelength of 1.55 μm and an oscillation wavelength of 1.48 μm was used as the excitation light source 202. As the amplification optical fiber 205, the Er concentration in the core was 200 ppm, the cutoff wavelength was 1.3 μm, the core-cladding refractive index difference (Δn) was 1.4%, and the fiber length was 10 m. A tellurite optical fiber was used. The chromatic dispersion value of this optical fiber 205 at 1.55 μm was −1.3 ps / nm. Further, as the dispersion medium 204, a 1.3 μm zero-dispersion silica single mode optical fiber (so-called standard single mode optical fiber) having a chromatic dispersion value of 1.5 ps at 17 ps / km / nm was used. The length of this single mode optical fiber was 76 m.

  In this configuration, the chromatic dispersion of the dispersion medium 204 and the amplification optical fiber 205 as a whole was measured and found to be 0.1 ps / nm or less.

  When such a light amplifier was used to amplify a 40 Gbit / s high-speed optical signal at a wavelength of 1.55 μm, no distortion of the pulse wavelength due to chromatic dispersion was observed. Therefore, it has been found that the optical amplifier having this configuration can be used as a booster amplifier, a relay amplifier, a preamplifier or the like in a high-speed optical communication system without significantly degrading the communication quality. On the other hand, for comparison, when a high-speed pulse of 40 Gbit / s was amplified at a wavelength of 1.55 μm without inserting the dispersion medium 204, distortion of the pulse waveform was observed, and the high-speed optical communication system was used. It turned out to be difficult to apply.

  In the present embodiment, the dispersion medium 204 is installed between the optical coupler 203 and the amplification Er-doped tellurite optical fiber 205, but the installation location is not limited to this. For example, it may be the front stage of the optical isolator 201a, between the optical isolator 201a and the optical coupler 203, between the amplification optical fiber 205 and the optical isolator 201b, or after the optical isolator 201b.

  In this embodiment, a standard single mode optical fiber is used as the dispersion medium 204. However, the present invention is not limited to this, and the wavelength dispersion of the tellurite optical fiber 205 is different from (or opposite to) the wavelength dispersion. Any optical fiber having a value can be used.

  Further, the dispersion medium 204 is not limited to an optical fiber but may be a chirped fiber grating (Non-patent Document 5) or the like.

  In the above description, the dispersion medium 204 is inserted into one of the front and rear of the amplification optical fiber 205, but the installation configuration of the dispersion medium 204 is not limited to this. That is, when an optical fiber is used as the dispersion medium 204, the optical fiber may be divided and placed at appropriate positions before and after the amplification optical fiber 205. Moreover, you may install the optical fiber which has a several different characteristic in an appropriate position. Further, a plurality of optical fibers and chirped fiber gratings may be used in combination.

[Example 22]
In the present embodiment, as the amplification optical fiber 205 in FIG. 14, Pr (praseodymium) is added at 500 ppm in the core, the cutoff wavelength is 1.0 μm, Δn is 1.4%, and the fiber length is 15 m. The tellurite optical fiber was used. Further, as the excitation light source 2, an Nd (neodymium) -added YLF laser was used. Further, a chirped fiber grating was used as the dispersion medium 4.
At this time, the chromatic dispersion at 1.31 μm of the tellurite optical fiber was −3.15 ps / nm. Therefore, the chromatic dispersion value of the chirped fiber grating was set to 3.15 ps / nm. A high-speed optical signal having a wavelength of 1.31 μm was amplified by the amplifier having such a configuration.

[Example 23]
In this example, an optical fiber constituted by using the above TeO ₂ —BaO—SrO—Ta ₂ O ₅ glass as a base material and adding Er, Pr, Tm or Nd to the core was used as the amplification optical fiber 205. . As the dispersion medium 204, a quartz optical fiber or a chirped fiber grating was used. With such a configuration, when the high-speed optical pulse is amplified without compensating for the chromatic dispersion at each amplification wavelength, the distortion of the optical pulse waveform that has occurred without the dispersion medium 204 can be suppressed, and the high-speed optical pulse can be suppressed. It was confirmed that it can be used in an optical communication system.
In addition, even when an optical fiber made of TeO ₂ —BaO—SrO—Ta ₂ O ₅ —Al ₂ O ₃ glass was used as the amplification optical fiber 5, the above effect could be confirmed.

[Example 24]
This example is a tellurite single-mode optical fiber (cut-off wavelength 1.3 μm, Δn 1.4%, long length), which is formed by using the glass system in Example 23 as a base material and without adding rare earth elements or transition metal elements. 1 km) was used for Raman amplification. The excitation wavelength was 1.48 μm, and 1.5 μm band optical amplification was performed.
At this time, the chromatic dispersion at the signal wavelength of the tellurite single-mode optical fiber was −130 ps / nm. A standard quartz single mode optical fiber was used as the dispersion medium 204.

  The dispersion medium 204 was placed in the subsequent stage of the tellurite single-mode optical fiber (amplifying optical fiber) 205 to perform optical amplification. When this standard quartz single mode optical fiber 205 for amplification is used with a length of 7.6 km, the waveform distortion of the 1.5 μm band optical pulse (due to the chromatic dispersion of the tellurite single mode optical fiber) can be suppressed. did it.

Further, it has been found that a wider Raman amplification band can be obtained than when the conventional tellurite glass described in Patent Document 9, for example, is used. This is because, as shown in FIG. 15, the inclusion of Ta ₂ O ₅ broadens the Raman scattering spectrum than the conventional one.

[Example 25]
In this example, an amplification optical fiber 205 configured by adding Cr, Ni, or Ti to the core of the tellurite optical fiber having the composition used in Example 23 was used, and the 1.5 μm band and 1.5 μm band were used. Band and 1 μm band optical amplification were performed, respectively. When a standard quartz single-mode optical fiber was connected as a dispersion medium 204 to the subsequent stage of the amplification optical fiber 205 and high-speed optical pulses were amplified, optical amplification could be performed without waveform distortion of the optical pulses.

  In the above embodiments, the case where the optical waveguide in the present invention is an optical fiber has been described. However, the optical waveguide in the present invention includes not only an optical fiber but also a planar optical waveguide. In the present invention, even when the optical waveguide is a planar optical waveguide, the same effects of the present invention as confirmed in the above embodiments can be realized.

  Hereinafter, an example in which the optical waveguide is a planar optical waveguide will be described.

[Example 26]
In this example, a planar optical waveguide having TeO ₂ —BaO—SrO—Ta ₂ O ₅ glass as a base material and Er added to the core is used instead of the optical fiber 205 in FIG. did. The dispersion of the optical waveguide was corrected using an optical fiber or a fiber Bragg grating as the dispersion medium 204. As a result, it was possible to amplify the light in the 1.5 μm band so as to reduce the distortion of the pulse waveform as compared with the case where the dispersion medium 204 was not used.
Even when Pr, Tm, Nd, Ni, Ti, and Cr were used as dopants added to the optical waveguide, it was possible to amplify the light with small distortion of the pulse waveform.

  As described above, in an optical amplifier using a tellurite optical fiber as an amplification medium, by adopting the optical amplifier structure of the above embodiments 21 to 26, an optical pulse waveform due to wavelength dispersion possessed by the tellurite fiber itself that is an amplification medium. Generation of strain can be suppressed.

  The following Examples 27 to 31 are intended to expand the amplification band of the conventional tellurite EDFA to the shorter wavelength side than 1.53 μm and to the longer wavelength side from 1.56 μm.

In order to achieve this, in the following examples, an Er-doped tellurite optical fiber is used as at least one optical fiber connected, and the Er-doped tellurite optical fiber has a shorter length (or Er concentration and An amplifying medium is formed by connecting an Er-doped tellurite optical fiber having a small fiber length product or an Er-doped optical fiber hosted from a different material. As the different materials, fluoride glass (Er-added ZrF4 fluoride glass or InF3 fluoride glass), quartz glass, fluorophosphate glass, phosphate glass, and chalcogenite glass can be used.
By adopting such an amplifier structure, it is possible to realize an EDFA that can operate with low noise in a wider wavelength range than a conventional tellurite EDFA.

[Example 27]
FIG. 16 is a diagram showing a configuration example of an optical amplifier according to the present invention. In the figure, 201a, 201b and 201c are optical isolators, 202a and 202b are optical couplers for introducing pumping light, 203a and 203b are pumping light sources, and 205 and 206 are optical fibers for amplification.

In this example, an Al (aluminum) -added silica optical fiber (length: 25 m, cutoff wavelength: 1.2 μm, concentration fiber length product: 2500 m · ppm) with an Er concentration of 100 ppm was used as the amplification optical fiber 205. A semiconductor laser having an oscillation wavelength of 1.48 μm was used as the excitation light source 203a. Further, as the amplification optical fiber 206, a glass of TeO ₂ —BaO—SrO—Ta ₂ O _{5 in which} the B and C composition regions are used as a base material, an Er addition concentration of 500 ppm, and a cutoff wavelength of 1.3 μm (concentration fiber) A tellurite optical fiber having a long product of 6000 m · ppm) and a length of 12 m was used. A semiconductor laser having an oscillation wavelength of 1.48 μm was used as the excitation light source 203b.

When the excitation light quantity of the light source 203a was 70 mW and the excitation light quantity of the light source 203b was 150 mW, a gain of 20 dB or more and a noise figure of 5 dB or less could be confirmed in the 85 nm band from a wavelength of 1.525 μm to 1.610 μm. .
Such an EDFA that operates in a wide band with low noise has not been realized with a conventional configuration.
When the amplification optical fiber 206 is not used, the noise figure is higher than 5 dB at a wavelength shorter than 1.54 μm, 10 dB or more at 1.525 μm, and the gain of 20 dB or more starts from 1.53 μm. It was obtained only in the 80 nm band of 1.61 μm.

  In this embodiment, the low noise band is extended to a short wavelength, and as a result, the operating wavelength band of the EDFA is expanded because an amplification optical fiber having a small Er-concentration fiber long product is disposed in the front stage of the tellurite optical fiber. This is because the amplification of the tellurite optical fiber is caused after the wavelength of 1.525 μm to 1.54 μm is amplified with low noise.

Next, a modification of the present embodiment will be described.
As an amplification optical fiber 205, an Al (aluminum) -doped silica optical fiber having an Er concentration of 1000 ppm (length 12 m, cutoff wavelength 1.2 μm, concentration fiber length product 12,000 m · ppm, this product is an erbium-doped tellurite fiber Larger than that).
When the excitation light amount of the light source 203a was 70 mW and the excitation light amount of the light source 203b was 150 mW, a gain of 20 dB or more and a noise figure of 5 dB or less could be confirmed in a 75 mm band from a wavelength of 1.535 μm to 1.610 μm. .
Such an EDFA that operates in a wide band with low noise has not been realized with a conventional configuration.

[Example 28]
In this embodiment, a ZrF4 fluoride optical fiber (cutoff wavelength 1.2 μm, Er concentration fiber length product 3500 m · ppm) having an Er concentration of 100 ppm fiber length of 3.5 m is used as the amplification optical fiber 205, and the excitation light source 203 is used. A semiconductor laser having an oscillation wavelength of 1.48 μm was used. Further, as the amplification optical fiber 206, the glass of the B, C composition region of the TeO ₂ —BaO—SrO—Ta ₂ O ₅ is used as a base material, the Er addition concentration is 500 ppm, the length is 12 m, and the cutoff wavelength is A tellurite optical fiber of 1.3 μm (Er concentration fiber length product 6000 m · ppm) was used. Further, a semiconductor laser having an oscillation wavelength of 1.48 μm was used as the excitation light source 203b.

  When the excitation light quantity of the light source 203a was 70 mW and the excitation light quantity of the light source 203b was 150 mW, a gain of 20 dB or more and a noise figure of 5 dB or less could be confirmed in the 85 nm band from a wavelength of 1.525 μm to 1.610 μm. . When the amplification optical fiber 206 is not used, the noise figure is higher than 5 dB at a wavelength shorter than 1.54 μm, 10 dB or more at 1.525 μm, and the gain of 20 dB or more starts from 1.53 μm. It was obtained only in the 80 nm band of 1.61 μm.

[Example 29]
In this example, both the amplification optical fibers 205 and 206 are made of the glass of the B, C composition region of the TeO ₂ —BaO—SrO—Ta ₂ O ₅ , the Er addition concentration is 500 ppm, and the cutoff wavelength is A tellurite optical fiber having a thickness of 1.3 μm was used. The amplification optical fiber 205 has a fiber length of 3 m, and the amplification optical fiber 206 has a fiber length of 12 m. A semiconductor laser with an oscillation wavelength of 0.98 μm was used as the excitation light source 203a, and a semiconductor laser with an oscillation wavelength of 1.48 μm was used as the light source 203b.

  When the excitation light quantity of the light source 203 was 100 mW and the excitation light quantity of the light source 203b was 150 mW, a gain of 20 dB or more and a noise figure of 5 dB or less could be confirmed in a 85 nm band from a wavelength of 1.525 μm to 1.610 μm. . When the amplification optical fiber 206 is not used, the noise figure is higher than 5 dB at a wavelength shorter than 1.54 μm, 10 dB or more at 1.525 μm, and the gain of 20 dB or more starts from 1.53 μm. It was obtained only in the 80 nm band of 1.61 μm.

  In the above embodiments, the amplification optical fibers 205 and 206 are all forward pumped and backward pumped, respectively. However, the pumping method is not particularly limited to these, and any pumping method including bidirectional pumping can be used. May be.

[Example 30]
In this embodiment, the amplification optical fiber 205 is the same as in Examples 27 to 29, and TeO ₂ —BaO—SrO—Ta ₂ O ₅ —Al ₂ O ₃ glass is used as the amplification optical fiber 206. An Er-doped tellurite optical fiber (Er concentration: 500 ppm, length: 14 m) was used. Also in this case, by using the amplification optical fiber 4, it was possible to confirm the expansion of the amplification band with lower noise than when not using it.

[Example 31]
In this example, a fluorophosphate optical fiber, a phosphate optical fiber, and a chalcogenite optical fiber doped with Er were used as the amplification optical fiber 205. When the Er concentration fiber length product of the amplification optical fiber 205 is smaller than the tellurite optical fiber of the amplification optical fiber 206, it was confirmed that the amplification band of the low noise was expanded. That is, the material of the amplification optical fiber 205 is not a big problem in order to achieve the effects of the present invention, and the Er concentration fiber length product is an important parameter.

  In the above Examples 40 to 44, two optical fibers having different Er addition concentration fiber length products are used as amplification media, but three or more may be used. At this time, the optical fiber having the smallest Er-doped optical fiber length product may be in any position other than the rearmost stage, but preferably the frontmost stage.

As mentioned above, although this invention was demonstrated based on the typical Example, this invention can have various aspects other than having mentioned above.
JP-A-11-236240 J.Mater.Res., Vol.17., No5, May 2002, @ 2002 Materials Research Society, pp.12081212 Erbium-Doped Fiber Amplifiers, by Emmanuel Desurvire (by Emmanuel Desavier), publisher John Wiley & Sons, 1994 KOHill CLEO / PACIFIC RIM SHORT COURSE '97 “Photosensitivity and Bragg Gratings in Optical Waveguide” Kanamori et al., Proceeding of 9th International Symposium on Non Oxide Glasses, P.74, 1994

  As described above, according to the present invention, the tellurite glass for light amplification is provided as a fiber host in which the stimulated emission cross section of Er 1.5 μm band becomes flatter, and this glass is used as the light amplification medium. It is possible to provide a tellurite EDFA with a flattened gain. In addition, the operating wavelength band of the conventional tellurite EDFA can be expanded to provide a tellurite EDFA that operates with a low noise in a wider band region. Furthermore, it becomes possible to provide a tellurite fiber that can exhibit a function that cannot be realized by conventional glass such as a broadband EDFA by adding an optically active rare earth element.

  In addition, a broadband optical amplification medium that can operate in the wavelength region of 1.5 μm to 1.7 μm using the tellurite glass, an optical amplifier having a broadband and low noise characteristic using the optical amplification medium, a laser device, It is also possible to provide a light source. Furthermore, a general-purpose and practical connection technology that connects non-silica optical fibers and silica optical fibers, or non-silica optical fibers with different core refractive indexes, reliably and with low loss and low reflection. It becomes possible to provide. Therefore, when the characteristics of the optical amplification medium, the optical amplifier and the laser device using the optical amplification medium, and the wideband characteristic of the Er-doped tellurite optical fiber amplifier are combined, the performance enhancement of the wavelength multiplexing optical transmission system and the optical CATV system is achieved. As a result, there is an advantage that it can greatly contribute to the advancement and economy of services using these systems.

  Further, if it is used in a wavelength division multiplexing optical transmission system as a broadband amplifier, it can be expected that the transmission capacity will be remarkably increased, thereby contributing to the cost reduction of information communication. In addition, if the optical CATV system is used with the characteristic that the gain tilt is small, it is possible to distribute and relay high-quality video by wavelength multiplexing, which has been difficult in the past, and the cost reduction of the optical CATV is achieved. There is a big merit that you can. Furthermore, if it is applied as a laser device, it can contribute to cost reduction of various wavelength division multiplexing optical transmission systems and high performance of optical measurement.

  Furthermore, the optical communication system can be applied not as a rare earth-doped optical fiber amplifier but as an amplification medium for a broadband Raman amplifier.

It is a coordinate diagram which shows the 1st composition area | region A of the glass which is the optical functional waveguide material of this invention. It is a coordinate diagram which shows the 2nd composition area | region B of the glass which is the optical functional waveguide material of this invention. It is a coordinate diagram which shows the 3rd composition area | region C of the glass which is an optical functional waveguide material of this invention. It is a graph which shows the difference value (DELTA) T of the crystallization temperature of glass which is an optical functional waveguide material of this invention, and a transition temperature according to a composition. The Ta ₂ O ₅ added weight dependence of the refractive index n of the glass is an optical functional waveguide material of the present invention is a graph showing. It is an energy level diagram of Er ³⁺ . It is a diagram representing the ⁴ I _13/2 → ⁴ I _15/2 emission spectra of Er in the tellurite glass. It is a figure which shows typically the example of 1 structure of the optical amplifier based on this invention. It is a block diagram which shows an example of the laser apparatus based on this invention. It is a block diagram which shows another example of the laser apparatus based on this invention. It is a figure showing the gain spectrum obtained with the laser apparatus based on this invention. It is a block diagram which shows the other example of the laser apparatus based on this invention. _{TeO 2 -BaO-SrO-Ta 2} O 5 glass, and _{TeO 2 -BaO-SrO-Ta 2} O 5 -Al 2 O 3 to 1.5μm emission spectra of Er in the glass is a diagram illustrating, respectively. It is a figure which shows one structural example of the optical amplifier which used the optical fiber based on this invention as an amplification medium. It is a figure which shows the Raman scattering spectrum of the glass based on this invention, and the conventional glass. It is a figure which shows another structural example of the optical amplifier which used the optical fiber based on this invention as an amplification medium. It is an energy level diagram of the three-level system (Er ³⁺ around 1.54 μm) (where N1 ≠ 0 in the three-level system). It is an energy level diagram (N1 = 0 in the 4-level system) of a 4-level system (Nd ³⁺ near 1.06 μm). It is a schematic diagram which shows the wavelength dependence of the gain of quartz type EDFA and tellurite EDFA. It is explanatory drawing which shows the difference state of the amplification band by the magnitude of loss.

Explanation of symbols

111,111 'pumping semiconductor laser
112, 112 'optical coupler
113 Optical fiber for amplification
114 optical isolator
115 Amplifying optical fiber
116 mirror
117 filter
118 mirror
201 optical isolator
202 Excitation light source
203 Optical coupler
204 Dispersion medium 205 Optical fiber for amplification
206 Optical fiber for amplification

Claims (30)

A material glass for optical fiber or optical waveguide,
0 <Ta ₂ O ₅ ≦ 12 (mol%),
0 <(BaO + SrO) ≦ 20 (mol%), and 80 ≦ TeO ₂ ≦ 97 (mol%)
An optical functional waveguide material having a composition comprising: The amount of Ta ₂ O ₅ added to the optical functional waveguide material is
6 ≦ Ta ₂ O ₅ ≦ 12 (mol%)
The optical functional waveguide material according to claim 1, wherein the optical functional waveguide material is in the range of A material glass for optical fiber or optical waveguide,
0 <Ta ₂ O ₅ ≦ 12 (mol%),
0 <(BaO + SrO) ≦ 20 (mol%), and 80 ≦ TeO ₂ ≦ 94 (mol%)
An optical functional waveguide material having a composition comprising: A material glass for optical fiber or optical waveguide,
6 ≦ Ta ₂ O ₅ ≦ 12 (mol%),
4 ≦ (BaO + SrO) ≦ 12 (mol%), and 80 ≦ TeO ₂ ≦ 88 (mol%)
An optical functional waveguide material having a composition comprising: A material glass for optical fiber or an optical waveguide was added Er (erbium) in at least the core, in any one of claims 1 to 4, characterized by having a composition obtained by adding Al ₂ O ₃ to the material glass The optical functional waveguide material described. A material glass for optical fiber or optical waveguide,
0 <Ta ₂ O ₅ ≦ 12 (mol%),
0 <(BaO + SrO) ≦ 20 (mol%), and 80 ≦ TeO ₂ ≦ 97 (mol%),
0 <Al ₂ O ₃ ≦ 4 (mol%)
An optical functional waveguide material having a composition comprising:   An optical amplifying medium comprising an optical fiber or an optical waveguide having a core glass and a clad glass, wherein the optical amplifying medium is made of the optical functional waveguide material according to claim 1.   The optical functional waveguide material of the core glass or the optical functional waveguide material of the cladding glass is doped with Er or Er and ytterbium (Yb). Light amplification medium.   The optical functional waveguide material of the core glass or the optical functional waveguide material of the cladding glass contains at least one selected from the group consisting of boron, phosphorus, and a hydroxyl group. The optical amplification medium according to 7 or 8.   At least one of the optical functional waveguide material of the core glass or the optical functional waveguide material of the clad glass is a group consisting of Ce, Pr, Nd, Sm, Tb, Gd, Eu, Dy, Ho, Tm, and Yb. The optical amplification medium according to claim 7, wherein an element selected from the group consisting of: An optical amplifying medium comprising an optical fiber or optical waveguide made of material glass with at least Er added to the core, wherein the composition of the material glass is an optical functional waveguide material added with Al ₂ O _3. Item 10. The optical amplification medium according to Item 9.   The optical amplification medium according to any one of claims 7 to 11, wherein a cutoff wavelength is 0.4 µm to 2.5 µm.   A laser apparatus having an optical resonator and a pumping light source, wherein at least one of the optical amplification media provided in the optical resonator is composed of the optical amplification medium according to any one of claims 7 to 12. Laser device.   13. A laser apparatus in which a plurality of optical amplifying media made of optical fibers having at least Er added to a core are arranged in series, wherein at least one of the optical amplifying media is the optical amplifying medium according to claim 7. A laser apparatus comprising:   A laser apparatus having an optical amplification medium and an excitation light source, wherein the optical amplification medium is composed of the optical amplification medium according to claim 7.   An optical amplifier comprising: an optical amplifying medium; and input means for inputting excitation light and signal light for exciting the optical amplifying medium to the amplifying medium, wherein the optical amplifying medium is any one of claims 7 to 12. An optical amplifier comprising the optical amplifying medium described in 1.   An optical amplifier in which a plurality of optical amplifying media made of an optical fiber having at least Er added to a core are arranged in series, wherein at least one of the optical amplifying media is the optical amplifying medium according to any one of claims 7 to 12. An optical amplifier comprising:   13. An optical amplifier using an optical functional waveguide material as an amplification medium, wherein at least one position before and after the optical amplification medium according to claim 7 is a wavelength dispersion value having a sign different from that of the optical amplification medium. An optical amplifier characterized in that a dispersion medium for compensating dispersion is provided.   19. The optical amplifier according to claim 18, wherein the optical amplification medium is an optical waveguide made of an optical functional waveguide material to which a rare earth element and / or a transition metal element is added.   The optical amplifier according to claim 18 or 19, wherein the dispersion medium is an optical fiber or a fiber Bragg grating. An optical amplifier in which a plurality of optical amplification units including an optical fiber to which Er is added as an amplification medium are arranged in series,
An optical fiber made of the optical functional waveguide material according to any one of claims 1 to 6 is used as an optical fiber material for at least one of the second and subsequent stages of the plurality of optical amplification units. The optical amplifying unit upstream of the optical amplifying unit made of a waveguide material optical fiber uses an Er-doped optical fiber having an Er addition concentration and a fiber length product smaller than those of the optical functional waveguide material optical fiber. Optical amplifier.   The optical functional waveguide material optical fiber is a fluoride optical fiber, a silica-based optical fiber, a fluorophosphate optical fiber, a phosphate optical fiber, or a chalcogenide optical fiber as a material of the amplification medium. 21. The optical amplifier according to item 21.   The optical fiber material other than the optical functional waveguide material optical fiber is used for at least one optical amplifying unit preceding the optical amplifying unit made of the optical functional waveguide material optical fiber. Or the optical amplifier of 22.   The Er addition concentration and the optical fiber length product of at least one optical fiber disposed in the front stage of the optical amplifying unit made of the optical functional waveguide material optical fiber are smaller than that of the optical functional waveguide material optical fiber. An optical amplifier according to any one of claims 21 to 23. An optical amplifier using an optical fiber doped with Er as an amplification medium,
At least two optical functional waveguide material optical fibers having different Er doping concentrations and optical fiber length products are arranged in series, and in the arrangement, an optical fiber having a small optical fiber length is an optical fiber having a large optical fiber length product. The optical amplifier according to any one of claims 14 to 24, comprising at least one array structure arranged in the preceding stage.   The optical functional waveguide material obtained by adding Er to the optical functional waveguide material according to any one of claims 1 to 6, or an optical waveguide using the optical amplification medium according to any one of claims 7 to 12. A light source characterized by that.   An optical amplifier comprising an optical waveguide formed of a glass material obtained by adding Er to the optical functional waveguide material according to any one of claims 1 to 6.   28. The optical amplifier according to claim 27, wherein at least one of the optical waveguide or the optical fiber includes an optical coupler disposed at an end thereof, and a reflector is provided at at least one terminal of the optical coupler.   The light source according to claim 28, wherein the reflector comprises a dielectric multilayer filter or a fiber Bragg grating. 29. The optical amplifier according to claim 27 or 28, wherein the reflector comprises a dielectric multilayer filter or a fiber Bragg grating.

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