JP4849565B2 - Waveguide and optical module and optical amplifier using the same - Google Patents

Description

  The present invention relates to a waveguide, an optical module and an optical amplifier using the waveguide, and more particularly to a fluorophosphate glass waveguide and an optical module and an optical amplifier using the same.

  2. Description of the Related Art In recent years, with rapid development of optical fiber communication technology, transmission signal density and bit rate and bandwidth have been increased in wavelength division multiplexing (WDM) communication.

  Transmission characteristics due to the influence of nonlinear effects (four-wave mixing (FWM), cross-phase modulation (XPM), self-phase modulation (SPM), etc.) in the transmission line fiber by increasing the transmission signal density and bit rate. Deterioration is a problem. In order to solve this problem, there has been proposed a method of suppressing nonlinear phenomena by using a transmission line fiber having a large effective area (see Non-Patent Document 1). Furthermore, in recent years, the influence of nonlinear effects is emerging as a problem even in optical fiber amplifiers. In particular, the L-band erbium-doped fiber amplifier (EDFA) is a serious problem because the required length of the erbium-doped fiber (EDF), which is an amplification medium, is long and the nonlinear phenomenon is enhanced. In order to overcome this problem, a method has been proposed in which an EDF having a large effective area is used to reduce the optical power density in the amplification medium and suppress the nonlinear phenomenon (see Non-Patent Document 2).

  In addition, with regard to widening the bandwidth, the conventional amplification optical fiber using quartz glass as the host has a large amplification bandwidth (about 30 nm), and this request has not been fully met. Therefore, research on non-quartz optical fibers capable of wideband amplification is in progress. Examples thereof include fluoride glass fiber, tellurite glass fiber, bismuth glass fiber, chalcogenite glass fiber, and fluorophosphate glass fiber (see Non-Patent Documents 3 to 6).

Kazumasa Otsuki, Tomoyuki Nishio, Takahiro Yamazaki, Tomomi Onose, Kotaro Tan, “Low-Linear Optical Fiber for High-Density Wavelength Multiplex Transmission”, Hitachi Cable, January 2001, No. 20, p. 7-10 Tetsuya Haruna, Motoki Tsunoi, Masahiro Takashiro, Masato Tanaka, Shinji Ishikawa, “Ultra-low nonlinear L-band optical amplifier using large core EDF”, SEI Technical Review, March 2005, No. 166, p. 65-69 Atsushi Mori, Tadashi Sakamoto, Kenji Kobayashi, Koji Shikano, Kiyoshi Oikawa, Koichi Hoshino, Terutoshi Kanamori, Yasutake Ohishi, and Makoto Shimizu, “1.58-μm Broad-Band Erbium-Doped Tellurite Fiber Amplifier,” Journal of lightwave technology, vol. 30, no. 5, MAY 2002 Makoto Yamada, Terutoshi Kanamori, Yukio Terunuma, Kiyoshi Oikawa, Makoto Shimizu, Shoichi Sudo, and Kouichi Sagawa, “Fluoride-Based Erbium-Doped Fiber Amplifier with Inherently Flat Gain Spectrum,” IEEE Photon. Technol. Lett., Vol. 8, no. 7, JULY 1996 BO Guan, HY Tam, SY Liu, PKA Wai, and N. Sugimoto, “Ultrawide-Band La-Codoped Bi2O3-Based EDFA for L-Band DWDM Systems,” IEEE Photon. Technol. Lett., Vol. 15, no. 11, NOVEMBER 2003 Hirotaka Ono, Koichi Nakagawa, Makoto Yamada, Shoichi Sudo, "Amplification characteristics of Er3 + -doped fluorophosphate glass fiber", 1996 IEICE General Conference, p. 326

  However, the technique described in Non-Patent Document 1 is not a sufficient solution because the non-linear generation efficiency decreases when the effective cross-sectional area is increased, but the bending loss also increases. In the technique described in Non-Patent Document 2, the nonlinear generation efficiency is reduced when the effective area is increased, but the conversion efficiency of the EDFA is also reduced, which is not a sufficient solution.

  In addition, with regard to widening the bandwidth, research has been conducted on the above-mentioned optical fiber as a non-quartz optical fiber capable of wideband amplification, but silica glass fiber is important for reducing the cost and increasing the reliability of optical modules or optical amplifiers. Because the refractive index is different from that of silica glass fiber (reflective glass fiber, tellurite glass fiber, chalcogenite glass fiber, fluorophosphate glass fiber, etc.) Point, which requires high-level and difficult-to-obtain oblique fusion (fluoride glass fiber, tellurite glass fiber, bismuth glass fiber, chalcogenite glass fiber, fluorophosphate glass fiber, etc.), lower loss of 1 dB / m or less Is difficult (conventional 10 dB / m for fluorophosphate glass fiber) and has low weather resistance Fluoride glass fiber, there is a problem that chalcogenide glass fiber, etc.).

  In the above description, the optical fiber has been mentioned, but the problem is also applicable to the optical waveguide. Hereinafter, an optical transmission medium including a core and a clad made of glass, including an optical fiber and an optical waveguide, is referred to as a “waveguide”.

  The present invention has been made in view of such problems, and a first object thereof is to provide a waveguide made of non-quartz glass that solves the above problems. The second object is to provide an optical module using such a waveguide as a transmission line, and an optical amplifier using such a waveguide as an amplification medium.

  The waveguide according to the present invention is characterized by using fluorophosphate glass as the glass constituting the core and the clad, and the waveguide is excellent in low nonlinearity.

  In the optical amplifier of the present invention, a fluorophosphate glass waveguide used as an amplifying medium has low nonlinearity, broadband amplification characteristics, low reflection / low loss fusion splicing, low waveguide loss, high weather resistance, and thermal stability during waveguide fabrication. It is characterized by high performance and high efficiency.

In the first aspect of the present invention, the relationship between mol% C _P1 and C _{P2 of} phosphoric acid (P ₂ O ₅ ) contained in the core and the clad and the refractive indexes n ₁ and n ₂ in the respective cases is represented by the formula (1) And the range is clarified as shown in Equation (2).
n ₁ = α ₁ + β ₁ · C _P1 , n ₂ = α ₂ + β ₂ · C _P2 (1)
1.44 <n ₁ , n ₂ <1.46, 1.40 <α ₁ , α ₂ <1.43, 0.002 <β ₁ , β ₂ <0.0035, 3 <C _P1 , C _P2 < 20 (2)
It contains at least one fluoride raw material of AlF ₃ , CaF ₂ , SrF ₂ , MgF ₂ , BaF ₂ , PbF ₂ , ZnF ₂ , and LaF ₃ , and AlF ₃ is 10 to 45 mol%, CaF ₂ 10~60mol%, SrF ₂ is 0~30mol%, MgF ₂ is 0~30mol%, BaF ₂ is 0~30mol%, PbF ₂ is 0 to 20 mol%, ZnF ₂ 0 to 20 mol%, LaF ₃ is It is 0-10 mol%.
Here, α ₁ , α ₂ , β ₁ , and β ₂ are parameters determined by the composition of the core and the clad. The amount of phosphoric acid that can achieve the desired refractive index can be determined according to this equation. Fluorophosphate glass with a composition that satisfies the relationship between the refractive index and the amount of phosphoric acid has low reflection / low loss fusion with an optical fiber or optical waveguide made of quartz glass, low nonlinearity, low waveguide loss, high It is also characterized by simultaneously satisfying weather resistance, broadband amplification characteristics, thermal stability at the time of waveguide fabrication (crystallization temperature-glass transition temperature> 100 K), and high efficiency amplification characteristics.

In the second aspect of the present invention , the relationship between mol% C _A1 and C _{A2 of} aluminate (Al ₂ O ₃ ) contained in the core and the clad and the refractive indexes n ₁ and n ₂ in the respective formulas (3) is shown. And the range is clarified as shown in Equation (4).
n ₁ = α ₁ '+ β ₁ ' · C _A1 , n ₂ = α ₂ '+ β ₂ ' · C _A2 (3)
1.44 <n ₁ , n ₂ <1.46, 1.42 <α ₁ ′, α ₂ ′ <1.44, 0.0015 <β ₁ ′, β ₂ ′ <0.0025, ₁ <C _A1 , C _A2 <30 (4)
It contains at least one fluoride raw material of AlF ₃ , CaF ₂ , SrF ₂ , MgF ₂ , BaF ₂ , PbF ₂ , ZnF ₂ , and LaF ₃ , and AlF ₃ is 10 to 45 mol%, CaF ₂ 10~60mol%, SrF ₂ is 0~30mol%, MgF ₂ is 0~30mol%, BaF ₂ is 0~30mol%, PbF ₂ is 0 to 20 mol%, ZnF ₂ 0 to 20 mol%, LaF ₃ is It is 0-10 mol%.
Here, α ₁ ′, α ₂ ′, β ₁ ′, and β ₂ ′ are parameters determined by the composition of the core and the clad. The amount of aluminate that can achieve the desired refractive index can be determined according to this equation. In addition, fluorophosphate glass having a composition that satisfies the relationship between the refractive index and the amount of aluminate is low reflection / low loss fusion with an optical fiber or optical waveguide made of quartz glass, low nonlinearity, low waveguide loss, It is also characterized by high weather resistance, broadband amplification characteristics, thermal stability during waveguide fabrication (crystallization temperature-glass transition temperature> 100 K), and high efficiency amplification characteristics at the same time.

According to the third aspect of the present invention , the low reflection / low loss fusion, the low nonlinearity, the low waveguide loss, the high weather resistance, and the broadband amplification characteristic are satisfied by simultaneously satisfying the conditions of the first and second aspects. It is characterized by further improving the thermal stability (crystallization temperature-glass transition temperature> 100 K) and high-efficiency amplification characteristics during waveguide fabrication.

According to a fourth aspect of the present invention , there is provided the fluorophosphate glass waveguide according to any one of the first to third aspects , wherein the core contains rare earth ions.

According to a fifth aspect of the present invention , there is provided an optical fiber in which the fluorophosphate glass waveguide according to any one of the first to fourth aspects is fused with an optical fiber or an optical waveguide made of quartz glass, The acid glass waveguide is an optical fiber.

A sixth aspect of the present invention is the optical module according to the fifth aspect , characterized in that the difference between the refractive index of fluorophosphate glass and the refractive index of quartz glass of the core is 0.028 or less. .

According to a seventh aspect of the present invention, there is provided the optical module according to the fifth or sixth aspect, wherein the glass component in the fused portion is not diffused at all.

An eighth aspect of the present invention is the optical module according to any one of the fifth to seventh aspects , wherein the glass component in the fused portion is diffused in the range of 1 μm or less in the longitudinal direction of the optical fiber. Features.

A ninth aspect of the present invention is the optical module according to the fifth or sixth aspect , characterized in that the glass component of the fused portion is diffused in the range of 1 to 5 μm in the longitudinal direction of the optical fiber. To do.

A tenth aspect of the present invention is the optical module according to the fifth or sixth aspect , characterized in that the glass component of the fused portion is diffused in the range of 5 to 10 μm in the longitudinal direction of the optical fiber. To do.

An eleventh aspect of the present invention is the optical module according to any one of the fifth to tenth aspects , wherein a distance in the longitudinal direction of the optical fiber at a portion where the glass is raised by adhesion is 10 μm or less. It shall be the.

According to a twelfth aspect of the present invention , in the optical module according to any one of the fifth to tenth aspects , a distance in a longitudinal direction of the optical fiber at a portion where the glass is raised by adhesion is 10 to 100 μm. It shall be the feature.

A thirteenth aspect of the present invention is an optical amplifier using the fluorophosphate glass waveguide according to any one of the fifth to twelfth aspects as an amplification medium.

  By constructing the core and clad of the waveguide with fluorophosphate glass that satisfies the predetermined relational expression, low nonlinearity, low reflection / low loss fusion with optical fiber or optical waveguide made of quartz glass, low conductivity A waveguide capable of realizing waveguide loss, high weather resistance, broadband amplification characteristics, thermal stability at the time of waveguide fabrication (crystallization temperature-glass transition temperature> 100 K), and high efficiency amplification characteristics can be provided.

  In addition, an optical amplifier can be provided using such a waveguide as an optical module and an amplification medium using the transmission line.

Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.
FIG. 1 shows the relationship between the mol% C _P1 and C _{P2 of} phosphoric acid (P ₂ O ₅ ) contained in the core and the clad and the refractive indexes n ₁ and n ₂ , respectively, expressed by the formulas (1) and (2). It is a graph which shows. α and β are uniquely determined by the respective compositions of the core and the clad, and are premised on that additivity is established to some extent with respect to the amount of phosphoric acid added. The range indicated by oblique lines in the figure represents the range of refractive index that can be considered for the composition in which the additivity is established. Although it seems that the range of the amount of phosphoric acid is simply shown in the figure, it is only necessary to follow the formulas shown in the formulas (1) and (2). Only cut out).

  The range of α and β described in Equation (2) was determined based on whether or not fusion was possible. FIG. 2 is a graph plotting the possibility of fusion at a connection loss of 0.5 dB / point or less, where α is the X axis and β is the Y axis. ○ indicates that fusion is possible, and × indicates that fusion is not possible. As can be seen from the figure, fusion is possible in the range of 1.40 <α <1.43 and 0.002 <β <0.0035, which is the basis for the range of α and β described in Equation (2). .

  FIG. 3 is a graph plotting the phosphoric acid amount dependency of the difference (Tx−Tg) between the crystallization temperature (Tx) and the glass transition point (Tg) of the composition according to the relational expressions described in the formulas (1) and (2). is there. Here, crystallization is synonymous with devitrification. As can be seen from the figure, when the amount of phosphoric acid is larger than 6 mol%, Tx-Tg becomes 100K or more. When Tx−Tg> 100K, crystallization can be suppressed to some extent during waveguide fabrication, so it is effective to make the amount 6 mol% or more. However, crystallization occurs when the amount of phosphoric acid exceeds 20 mol%. Therefore, it is appropriate that the amount of phosphoric acid is 3 mol% or more and 20 mol% or less. This is the basis for the phosphoric acid amount range of Equation (2).

  FIG. 4 is a plot of fiber loss at 1200 nm versus phosphoric acid content. As can be seen from the figure, it is desirable that the fiber loss is 1 dB / m or less when the phosphoric acid content is 20 mol% or less, and the phosphoric acid content is 20 mol% or less.

  The ranges of α and β described in the mathematical formulas (3) and (4) were determined based on the possibility of fusion. FIG. 5 is a graph plotting the possibility of fusion at a connection loss of 0.5 dB / point or less, where α is the X axis and β is the Y axis. ○ indicates that fusion is possible, and × indicates that fusion is not possible. As can be seen from the figure, fusion is possible in the range of 1.42 <α <1.44 and 0.0015 <β <0.0025, which is the basis for the range of α and β described in Equation (4). .

  FIG. 6 is a graph plotting the aluminate amount dependency of the difference (Tx−Tg) between the crystallization temperature (Tx) and the glass transition point (Tg) of the composition according to the relational expressions described in Equations (3) and (4). It is. As can be seen from the figure, when the amount of aluminate is greater than 1 mol%, Tx-Tg is 100K or more. When Tx−Tg> 100K, crystallization can be suppressed to some extent during waveguide fabrication, so it is effective to make the amount 6 mol% or more. However, crystallization occurs when the amount of aluminate exceeds 30 mol%. Therefore, it is appropriate that the amount of aluminate is 1 mol% or more and 30 mol% or less. This is the basis for the range of aluminate content in Equation (4).

AlF ₃ is an effective component for improving the weather resistance, but the effect is small at 10 mol% or less, and when it exceeds 45 mol%, the meltability of the glass is lowered. Therefore, it is desirable to limit the composition range of AlF ₃ to 10 mol% to 45 mol%. CaF ₂ , SrF ₂ , MgF ₂ , BaF ₂ , ZnF ₂ , and PbF ₂ are effective components that can promote the addition of fluorine into the glass and suppress crystallization. Since CaF ₂ , SrF ₂ , MgF ₂ , BaF ₂ , ZnF ₂ , and PbF ₂ exceed 60, 30, 30, 30, ₂₀ , and 20 mol%, respectively, crystallization is likely to occur, so that 0 to 60, 0 to 30, 0, respectively. It is desirable to make it into the range of -30, 0-30, 0-20, 0-20 mol%. NaF, LiF, and KF are components that lower the melting temperature and reduce the viscosity. However, since weather resistance will fall when it exceeds 40 mol%, 40 mol%, and 15 mol%, respectively, it is desirable to set it as the range of 0-40, 0-40, 0-15 mol%, respectively. LaF ₃ improves chemical durability and mechanical properties when added, but if it exceeds 10 mol%, it tends to crystallize, so it is desirable that it be in the range of 0 to 10 mol%.

  FIG. 7 is a plot of fiber loss at 1200 nm versus aluminate content. As can be seen from the figure, when the amount of aluminate is 30 mol% or less, the fiber loss is 1 dB / m or less, and the amount of aluminate is preferably 30 mol% or less.

FIG. 8 is a graph plotting the amount of reflection caused by the refractive index difference (| n _S −n _P |) between the quartz fiber (refractive index: n _S ) and fluorophosphate glass (refractive index: n _P ). It can be seen that the reflection loss is 40 dB or more when the refractive index difference is 0.028 or less, and 50 dB or more when 0.009 or less. If there is a difference in refractive index of 40 dB or more, in an optical amplifier incorporating a fluorophosphate glass waveguide, laser oscillation of the amplifier due to the reflectance at the fusion point does not occur even at a gain of about 20 dB. In addition, the above values may slightly vary depending on the material and the fusing conditions.

  FIG. 9 is a diagram in which the yield of fusion splicing when the connection loss is 0.1 dB or less, 0.5 dB or less, and 1 dB or less is plotted with respect to the diffusion region at the fused portion of fluorophosphate glass and quartz glass. It is. In the fused part, the two glass components may be mixed and diffused at the time of connection to join. As the diffusion region increases, a stronger bondability is obtained and the yield increases. At the same time, however, the waveguide structure also collapses, resulting in an increase in connection loss. By setting the diffusion region in accordance with the required connection loss, it is possible to set an efficient yield. In the figure, the yield peak of 0.1 dB or less is 1 μm in the diffusion region, 5 μm in the case of 0.5 dB or less, and 10 μm in the case of 1 dB or less, but it may vary depending on the glass composition and the fusing conditions.

  FIG. 10 is a diagram in which the fusion yield is plotted with respect to the distance (melting length) in the optical fiber longitudinal direction of the portion where the glass rises at the fusion portion. As the melt length increases, stronger bondability can be obtained and the yield increases, but at the same time, the waveguide structure also collapses, resulting in an increase in connection loss. By setting the melt length according to the required connection loss, it is possible to set an efficient yield. In the figure, the yield peak of 0.1 dB or less is 1 μm in the melt length, 10 μm in the case of 0.5 dB or less, and 100 μm in the case of 1 dB or less, but may differ depending on the glass composition or the fusing conditions. Further, referring to FIG. 9, the melting region and the diffusion region do not necessarily coincide. As an extreme example, there may be a case where even if there is a molten region, bonding is performed at the interface between the silica glass fiber and the fluorophosphate glass fiber and there is no diffusion region. Further, since the melting point of a fluorophosphate glass fiber is often lower than that of a quartz glass fiber, only the fluorophosphate glass fiber is often melted or the amount of melting is increased. Also, regarding the melting temperature at the time of fusing, melting occurs at the softening temperature of each glass because two different glass compositions come into contact with each other to cause a chemical reaction and lower the activation energy of melting. .

The refractive index of the waveguide described in this specification is a value at 1.55 μm. Fluorophosphate glass is a glass formed by mixing phosphoric acid and a fluoride raw material (AlF ₃ , CaF ₂ , SrF ₂ , MgF ₂ , BaF ₂ , PbF ₂ , ZnF ₂ , NaF, LiF, KF, LaF _3, etc.). Means a substance. Further, a case where a glass state is formed by further adding an oxide such as Al ₂ O ₃ , Li ₂ O, Na ₂ O, K ₂ O, etc. is also included in the category of fluorophosphate glass.

  In addition, it can be easily applied to a fiber laser.

Example 1
FIG. 11 illustrates an optical amplifier according to the first embodiment. This is an optical fiber amplifier using a fluorophosphate glass fiber as a waveguide. In the figure, 1-1 is an amplifying fluorophosphate glass fiber, 2-1 and 2-2 are optical isolators, 3-1 and 3-2 are multiplexers that combine excitation light and signal light, 4-1, 4-2 is an excitation light source and has a bidirectional excitation configuration. Similarly, FIG. 12 shows a configuration diagram in the case of the forward excitation configuration, and FIG. 13 shows a configuration diagram in the case of the backward excitation configuration.

  FIG. 14 shows an evaluation system for the amplification characteristics of the optical fiber amplifier according to the present embodiment. In the figure, reference numerals 5-1 to 5-6 denote wavelength variable light sources, reference numeral 6 denotes a multiplexer for multiplexing the signal lights of the respective variable wavelength light sources, reference numeral 7 denotes an optical attenuator for adjusting the signal light quantity, and reference numeral 8 denotes FIGS. Reference numeral 13 denotes an optical fiber amplifier 9 or a combination thereof. Reference numeral 9 denotes an optical spectrum analyzer that detects the signal light amplified by the optical fiber amplifier 8. The signal wavelengths of the variable wavelength light sources 5-1 to 5-6 are 1560, 1570, 1580, 1590, 1600, and 1610 nm.

FIG. 15 is a gain and noise spectrum of fluorophosphate glass in accordance with the relational expressions (1) and (2). The core composition of the amplification fluorophosphate glass fiber is 10 mol% P ₂ O ₅ , ₃ mol% Al ₂ O ₃ , 40 mol% AlF ₃ , 25 mol% CaF ₂ , 7 mol% SrF ₂ , 8 mol% MgF _2. , BaF ₂ is 7 mol%. The cladding composition is ₇ mol% P ₂ O ₅ , 3 mol% Al ₂ O ₅ , 40 mol% AlF ₃ , 26 mol% CaF ₂ , 8 mol% SrF ₂ , 9 mol% MgF ₂ , and 7 mol% BaF _2. Yes, the erbium addition concentration is 5000 ppm. The fiber length is 6 m, the relative refractive index difference is 0.65%, the core refractive index is 1.45, which is almost the same as quartz, and the fiber loss is 1 dB / m (@ 1200 nm). The connection loss between the quartz glass fiber and the fluorophosphate glass fiber is 0.3 dB / point, and the reflection loss is 51 dB. The amplifier configuration uses the bidirectional excitation configuration of FIG. The excitation light source is 1.48 μmL D at 100 mW, and the input signal light power is −12 dBm / ch. As can be seen from the figure, a gain spectrum having a substantially flat gain from 1570 to 1600 nm with a peak gain of 20 dB or more is realized. Moreover, when compared with quartz glass fiber under the same conditions, the amplification band of about 6 nm has been successfully expanded.

  FIG. 16 shows the result of the fiber length dependence of the gain spectrum of the fiber loss 10 dB / m (@ 1200 nm) measured under the same conditions. The composition of this fiber is outside the scope of the present invention, resulting in high fiber loss (10 dB / m). The gain shift to the L band is barely realized with the same fiber length of 6 m as in FIG. 15, but the gain is not enough for an L band amplifier of 5 dB or less. Therefore, according to the present invention, the low loss of the fiber is realized and the L band high gain amplification is made possible for the first time. Further, the results of a comparison experiment with a conventional quartz EDF are shown.

  Table 1 shows the results of the amplification characteristics when the composition of the fluorophosphate glass constituting the core and the clad according to the present invention and the amplifier configuration are changed.

“Connection loss” and “reflection loss” represent the connection loss and reflection loss between the silica glass fiber and the fluorophosphate glass fiber. The excitation power is set so that the gain is flat within the amplification band. Both amplifiers have a high gain in the L band. Further, the reflection loss depends on the degree of matching of the refractive index as shown in FIG. Moreover, the result at the time of adding Tm ion and Pr ion instead of Er ion was written together in the 8th and 9th lines of Table 1, respectively. In the case of Tm, the signal wavelengths are 1480, 1490, 1500, 1510 nm (−12 dBm / ch), and the pumping light power is 200 mW (front) +200 mW (back) (pumping wavelength: 1410 nm). In the case of Pr, the signal wavelengths are 1280, 1290, 1300, and 1310 nm (−12 dBm / ch), and the excitation light power is 200 mW (front) +200 mW (rear) (excitation wavelength: 1047 nm).

  Next, experimental results comparing the low nonlinear quartz EDF and the four-wave mixing will be shown. FIG. 17 shows a configuration diagram of the experiment. 10-1 to 10-3 are wavelength variable light sources, 11-1 to 11-3 are polarization controllers, 12 is a multiplexer that multiplexes signal light, 13-1 and 13-2 are optical isolators, and 14 is furin. Acid EDF or low nonlinear quartz EDF used for comparison, 15-1 and 15-2 are excitation light sources, and 16 is an optical spectrum analyzer. The signal light is 1579.7 nm (0 dBm), 1580.0 nm (0 dBm), 1580.3 nm (−3 dBm). The pumping light power is 150 mW forward and 200 mW backward. The fluorophosphate glass fiber has a fiber length of 6 m and an Er concentration of 5000 ppm.

  FIG. 18 is an output spectrum of the amplifier. Two FWMs are generated on both sides of the input signal wavelength. Fluoric acid EDF achieves FWM suppression over quartz EDF. FIG. 19 is a diagram showing the dependence of FWM crosstalk on the output signal light power. FWM crosstalk refers to the ratio of adjacent signal channel to FWM power. As can be seen from the figure, an improvement in FWM crosstalk of 5.5 dB with respect to the silica glass fiber is realized.

Example 2
FIG. 20 illustrates an optical amplifier according to the second embodiment. This is an optical fiber amplifier using a fluorophosphate glass fiber as a waveguide. In the figure, reference numerals 17-1 to 17-6 denote wavelength tunable light sources, 18 denotes a multiplexer that multiplexes the signal light of each wavelength tunable light source, 19 denotes an optical attenuator that adjusts the signal light quantity, and 20 denotes a fluorophosphate glass for transmission line. A fiber 21 is an optical spectrum analyzer that detects signal light after transmission.

The core composition of the fluorophosphate glass fiber is 9 mol% P ₂ O ₅ , 2.5 mol% Al ₂ O ₃ , 39.5 mol% AlF ₃ , 25 mol% CaF ₂ , 7 mol% SrF ₂ , and MgF ₂ 8 mol%, BaF ₂ 7 mol%, PbF ₂ 0.5 mol%, ZnF ₂ 0.5 mol%, NaF ₂ 0.5 mol%, LiF ₂ 0.5 mol%, KF 0.5 mol%, LaF ₃ Is 0.5 mol%. The clad composition was 6 mol% P ₂ O ₅ , _2.5 mol% Al ₂ O ₃ , 39.5 mol% AlF ₃ , 26 mol% CaF ₂ , 8 mol% SrF ₂ , 9 mol% MgF ₂ , BaF ₂ 7 mol%, PbF ₂ 0.5 mol%, ZnF ₂ 0.5 mol%, NaF ₂ 0.5 mol%, LiF ₂ 0.5 mol%, KF 0.5 mol%, LaF ₃ 0.5 mol% It is. The fiber length is 20 km, the core refractive index is 1.45, which is almost the same as that of quartz glass, and the fiber loss is 0.5 dB / km (@ 1550 nm). The connection loss between the quartz glass fiber and the fluorophosphate glass fiber is 0.2 dB / point, the reflection loss is 50.5 dB, the melt length is 20 μm, and the diffusion region is 3 μm. The optical frequencies of the variable wavelength light source are 189740 GHz, 189840 GHz, 189940 GHz, 190140 GHz, 190240 GHz, and 190340 GHz, respectively. Each signal light power is 3 dBm / ch at the fluorophosphate glass fiber input end. The waveform after transmission is shown in FIG. The spectrum for each of the three left and right waves represents the spectrum of 6ch signal light. The center solid line spectrum represents the spectrum of light generated by the FWM. The dotted optical spectrum represents the case where a quartz glass fiber (20 km, 0.5 dB / km) is used instead of the fluorophosphate glass fiber. As can be seen from the figure, by using a fluorophosphate glass fiber, FWM suppression of 20 dB was successfully achieved for the silica glass fiber.

It is a figure which shows the relationship between the amount of phosphoric acid, and the refractive index of a fluorophosphate glass. It is a figure which shows the relationship between (alpha) and (beta) represented by Numerical formula (2). It is a figure which shows the relationship between the amount of phosphoric acid, and Tx-Tg. It is a figure which shows the relationship between the amount of phosphoric acid and fiber loss (@ 1200nm). It is a figure which shows the relationship between (alpha) and (beta) represented by Numerical formula (4). It is a figure which shows the relationship between the amount of aluminates and Tx-Tg. It is a figure which shows the relationship between the amount of aluminates and fiber loss (@ 1200nm). It is a figure which shows the relationship between the refractive index difference of an optical fiber, and reflection loss. It is a figure which shows the relationship between the spreading | diffusion area | region and the yield which each connection loss can achieve. It is a figure which shows the relationship between the fusion | melting length and the yield which each connection loss can achieve. It is a figure which shows the amplifier structure at the time of bidirectional | two-way excitation. It is a figure which shows the amplifier structure at the time of forward excitation. It is a figure which shows the amplifier structure at the time of backward excitation. It is a figure showing the evaluation system of an amplification characteristic. It is a figure which shows the gain and NF spectrum of fluorophosphate EDFA and quartz EDFA. It is a figure which shows the fiber length dependence of the gain spectrum and NF spectrum in a fluorophosphate glass fiber. It is a figure which shows the evaluation system of 4 light wave mixing. It is a figure which shows the output spectrum at the time of 4 light wave mixing generation | occurrence | production. It is a figure which shows the amplifier signal output dependence of four-wave mixing crosstalk. It is a figure which shows the evaluation system of 4 light wave mixing. It is a figure which shows the output spectrum at the time of four-wave mixing generation after transmission.

Explanation of symbols

1-1 Fluorophosphate glass fiber for amplification (equivalent to fluorophosphate glass waveguide)
8 Optical fiber amplifier (equivalent to optical amplifier)
14 EDF fluorophosphate
20 Fluorophosphate glass fiber for transmission line

Claims (13)

A fluorophosphate glass waveguide having a core and a clad made of fluorophosphate glass,
Containing at least one fluoride raw material of AlF ₃ , CaF ₂ , SrF ₂ , MgF ₂ , BaF ₂ , PbF ₂ , ZnF ₂ , and LaF ₃ ,
AlF ₃ is 10~45mol%, CaF ₂ is 10~60mol%, SrF ₂ is 0~30mol%, MgF ₂ is 0~30mol%, BaF ₂ is 0~30mol%, PbF ₂ is 0 to 20 mol%, ZnF ₂ 0~20mol% is, LaF ₃ is a 0~10mol%,
The relationship between mol% C _P1 and C _{P2 of} phosphoric acid (P ₂ O ₅ ) contained in the core and the clad and the refractive indexes n ₁ and n ₂ is n ₁ = α ₁ + β ₁ · C _P1 , n ₂ = Α ₂ + β ₂・ C _P2
And
n ₁ , n ₂ , α ₁ , α ₂ , β ₁ , β ₂ , C _P1 and C _P2 are 1.44 <n ₁ , n ₂ <1.46, 1.40 <α ₁ , α ₂ <1. 43, 0.002 <β ₁ , β ₂ <0.0035, 3 <C _P1 , C _P2 <20
A fluorophosphate glass waveguide characterized by satisfying: A fluorophosphate glass waveguide having a core and a clad made of fluorophosphate glass containing aluminate (Al ₂ O ₃ ),
Containing at least one fluoride raw material of AlF ₃ , CaF ₂ , SrF ₂ , MgF ₂ , BaF ₂ , PbF ₂ , ZnF ₂ , and LaF ₃ ,
AlF ₃ is 10~45mol%, CaF ₂ is 10~60mol%, SrF ₂ is 0~30mol%, MgF ₂ is 0~30mol%, BaF ₂ is 0~30mol%, PbF ₂ is 0 to 20 mol%, ZnF ₂ 0~20mol% is, LaF ₃ is a 0~10mol%,
The relationship between mol% C _A1 and C _{A2 of} aluminate contained in the core and the clad and the refractive indexes n ₁ and n ₂ of each is n ₁ = α ₁ ′ + β ₁ ′ · C _A1 , n ₂ = α ₂ '+ Β ₂ ' ・ C _A2
And
n ₁ , n ₂ , α ₁ ′, α ₂ ′, β ₁ ′, β ₂ ′, C _A1 and C _A2 are 1.44 <n ₁ , n ₂ <1.46, 1.42 <α ₁ ′, α ₂ ′ <1.44, 0.0015 <β ₁ ′, β ₂ ′ <0.0025, ₁ <C _A1 , C _A2 <30
A fluorophosphate glass waveguide characterized by satisfying: The relationship between mol% C _A1 and C _{A2 of} aluminate contained in the core and the clad and the refractive indexes n ₁ and n ₂ of each is n ₁ = α ₁ ′ + β ₁ ′ · C _A1 , n ₂ = α ₂ '+ Β ₂ ' ・ C _A2
And
α ₁ ′, α ₂ ′, β ₁ ′, β ₂ ′, C _A1 and C _A2 are 1.42 <α ₁ ′, α ₂ ′ <1.44, 0.0015 <β ₁ ′, β ₂ ′ < 0.0025, 1 <C _A1 , C _A2 <30
The fluorophosphate glass waveguide according to claim 1, wherein: The fluorophosphate glass waveguide according to any one of claims 1 to 3 , wherein the core contains rare earth ions. An optical module fluorophosphate glass waveguide is an optical fiber or optical waveguide and fused constituted by quartz glass according to any one of claims 1 to 4, wherein the fluorophosphate glass waveguide is an optical fiber An optical module characterized by that. 6. The optical module according to claim 5 , wherein a difference between a refractive index of fluorophosphate glass and a refractive index of quartz glass of the core is 0.028 or less. 7. The optical module according to claim 5 , wherein the glass component in the fused portion is not diffused at all. 8. The optical module according to claim 5, wherein the glass component in the fused portion is diffused in a range of 1 μm or less in the longitudinal direction of the optical fiber. 9. 7. The optical module according to claim 5, wherein the glass component of the fused portion is diffused in a range of 1 to 5 μm in the longitudinal direction of the optical fiber. 7. The optical module according to claim 5, wherein the glass component of the fused portion is diffused in a range of 5 to 10 μm in the longitudinal direction of the optical fiber. 11. The optical module according to claim 5 , wherein a distance in a longitudinal direction of the optical fiber at a portion where the glass is raised by fusing is 10 μm or less. 11. The optical module according to claim 5 , wherein a distance in a longitudinal direction of the optical fiber at a portion where the glass is raised by fusing is 10 to 100 μm. An optical amplifier in which the core of the fluorophosphate glass waveguide according to any one of claims 5 to 12 contains rare earth ions, and the fluorophosphate glass waveguide is used as an amplification medium.

Images