JP3277494B2 - Amplifying optical fiber and optical fiber amplifier for 1.3 μm band using the same - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an amplifying optical fiber used in an optical communication system and the like, and a 1.3 .mu.m optical fiber using the same.
The present invention relates to an optical fiber amplifier for a band.

[0002]

2. Description of the ^Related Art In recent years, researches on an optical fiber amplifier using a stimulated emission of a transition in a 4f shell by doping a core of an optical fiber with rare earth ions, particularly Er ³⁺ ions, have been vigorously conducted. Is being applied to optical communication systems. Rare-earth doped optical fiber amplifiers have high gain and polarization-independent gain characteristics, and have low noise figure and broadband wavelength characteristics, making them extremely attractive for applications in optical communication systems.

On the other hand, the 1.3 μm band where the chromatic dispersion of a silica-based optical fiber becomes zero is an important wavelength band in optical communication along with the 1.5 μm band, and an optical fiber amplifier operating in the 1.3 μm band is used. Research has been carried out using silica-based optical fibers or fluoride-based optical fibers doped with Nd ³⁺ ions. However, at 1.31 μm, both of the above fibers are used for optical communication, and the Nd ³⁺ ion Excited State Ab
Because of high absorption (excitation state absorption), for example, WJ
Miniscalco, LJAndrews, BAThompson, RSQuinby,
LJBVacha and MGDrexhage, “Electron Lett.” (V
ol. 24, 1988, P. 28), or Y. Miyajima, T. Komukai, Y.
Sugawa and Y.Katsuyama, “Technical Digest Optical
Fiber Communication Conference '90 San Francisco ”
(1990, PD16), amplification was not confirmed.

Under such circumstances, realization of an optical fiber amplifier having an amplifying action at 1.31 μm is strongly desired. One of the candidates is Y. Ohishi, T. Kanamori, TK
itagawa, S. Takahashi, E. Snitzer and GHSigel “Tec
hnical Digest Optical Fiber Communication Conferenc
e '91 in San Diego "(1991, PD2) , ZrF 4
An optical fiber amplifier using an optical fiber doped with Pr ³⁺ using a system fluoride glass as a host material has been proposed. The optical fiber amplifier is obtained by utilizing the ¹ G ₄ → ³ H ₅ transition of the induced emission of Pr ³⁺ ions as can be seen from the energy diagram of Pr ³⁺ ions shown in FIG.

[0005]

However, the optical fiber amplifier has a disadvantage that the energy difference between the ¹ G ₄ level and the ³ F ₄ level is as small as about 3000 cm ⁻¹ . That is, since the phonon energy of the ZrF ₄ -based fluoride glass as the host material is 500 cm ⁻¹ , phonon relaxation is likely to occur from the ¹ G ₄ level to the ³ F ₄ level, and ZrF 4
In ₄ based fluoride glass in becomes what quantum efficiency of transition of ¹ G ₄ → ³ H ₅ is as low as 3%. Therefore, there is a problem that a high pump light power of 180 mW (pump wavelength 1.02 μm) is required to obtain a gain of 5 dB, for example.

[0006] In view of the above-mentioned conventional problems, the present invention relates to 1.3.
It is an object of the present invention to provide an amplification optical fiber that operates efficiently in the μm band and a 1.3 μm band optical fiber amplifier using the same.

[0007]

In order to achieve the above object, according to the present invention, as a first aspect, a material having a phonon energy of less than 500 cm ^-1 is used as a host material, and Pr ³⁺ is doped as an active ion. The fabricated optical fiber for amplification, and as claim 2, a claim using any one of As-S-based, Ge-S-based, Ge-PS-based or As-Ge-S-based chalcogenide glass as a host material The optical fiber for amplification according to claim 1, and as claim 3, E together with Pr ³⁺ as active ions.
The optical fiber for amplification according to claim 2, which is co-doped with u3 ⁺ .
In a fourth aspect, ZnF ₂ -I is used as a host material.
nF ₃ —PbF ₂ —LaF ₃ or ZnF ₂ —InF ₃
-PbF ₂ -GaF ₃ amplifying optical fiber according to claim 1, wherein using -laf ₃ based fluoride glass and as claimed in claim 5, together with Pr ³⁺ as an active ion Eu
Claim 3 proposes an optical fiber for amplification according to claim 4, which is co-doped with ^3+, and as claim 6, an optical fiber for amplification according to any one of claims 1 to 5, a pump light source for generating pump light, and a signal. An optical fiber amplifier for a 1.3 μm band including an optical coupler for multiplexing light and pump light and entering the optical fiber for amplification is proposed.

[0008]

According to the first aspect of the present invention, since a material having a phonon energy of less than 500 cm ^-1 is used as the host material, phonon relaxation of Pr ^{3+ from} the ¹ G ₄ level to the ³ F ₄ level hardly occurs. This improves the amplification efficiency at 1.31 μm. According to the second aspect, As-
S-based, Ge-S-based, Ge-PS-based or As-Ge-S
Since any of the chalcogenide glasses of the system having a phonon energy of 350 cm ^-1 was used as the host material, phonon relaxation of Pr ^{3+ from} the ¹ G ₄ level to the ³ F ₄ level hardly occurred. The amplification efficiency is improved. According to the third aspect, since Eu ³⁺ is co-doped together with Pr ³⁺ as active ions, the phonon relaxation of Pr ^{3+ from} the ³ H ₅ level to the ³ H ₄ level is accelerated. The amplification efficiency is further improved. According to claim 4,
ZnF ₂ —InF ₃ —PbF ₂ —LaF ₃ or ZnF
_Since a material having a phonon energy of about 400 cm ⁻¹ , which is a fluoride glass based on _2- InF ₃ —PbF ₂ —GaF ₃ —LaF _3, was used as a host material, Pr ^{3+ was changed from} a ¹ G ₄ level to a ³ F ₄ level. Phonon relaxation is unlikely to occur, which improves the amplification efficiency at 1.31 μm. According to claim 5, Pr ^{3+ is used} as active ions.
In addition, co-doping with Eu ³⁺ accelerates the phonon relaxation of Pr ^{3+ from} the ³ H ₅ level to the ³ H ₄ level, thereby further improving the amplification efficiency at 1.31 μm. According to the sixth aspect, since the amplification optical fiber having high amplification efficiency at 1.31 μm is used, a required gain can be obtained with low excitation light power, and a small excitation light source such as a semiconductor laser is used. be able to.

[0009]

Embodiment 1 As a host material of an amplification optical fiber, As
-S-based chalcogenide glass was used. At this time, the composition of the core glass was As ₄₀ S ₆₀ (atomic%), and the composition of the clad glass was As ₃₈ S ₆₂ (atomic%). The phonon energy of these glasses is 350 cm ^-1 .

Further, PrCl _{3 is} used as a raw material reagent for Pr ^3+.
Was used. PrCl ₃ is contained in the As ₄₀ S ₆₀ core glass.
Was added so that the Pr ³⁺ concentration was 500 ppm (weight concentration).

A single mode fiber was manufactured by the double crucible method using the core glass and the clad glass described above. Here, the core diameter was 4.6 μm, the refractive index difference between the core and the clad was 0.2%, and the cutoff wavelength was 1.0 μm.

FIG. 1 shows an embodiment of a 1.3 μm band optical fiber amplifier using an optical fiber for amplification according to the present invention, and how the amplification characteristics are measured. In the figure, 1 is an excitation light source, 2 is a lens, 3 is an optical coupler, 4 is a signal source, 5 is an amplification optical fiber, 6 is a fiber pigtail, and 7 is an optical spectrum analyzer.

The excitation light source 1 is, for example, a titanium sapphire laser excited by an argon laser, and its oscillation (excitation) wavelength is 1.02 μm. The optical coupler 3 is, for example, a WDM type optical fiber coupler, and the excitation light from the excitation light source 1 is incident on one fiber on the input side via the lens 2. The signal source 4 has, for example, an oscillation wavelength of 1.3.
The emitted light, that is, the signal light, is a 1 μm semiconductor laser and is incident on the other fiber on the input side of the optical coupler 3. The amplification optical fiber 5 is obtained by cutting the single-mode fiber manufactured as described above into a length of 8 m, and coating both sides of the single-mode fiber with anti-reflection coating. One end is connected to the fiber on the output side of the optical coupler 3. The other end is connected to an optical spectrum analyzer 7 via a fiber pigtail 6.

In the above construction, the excitation light source 1, the lens 2, the optical coupler 3, and the amplifying optical fiber 5 provide 1.3 μm.
An m-band optical fiber amplifier is configured (however, lens 2
Is for coupling the excitation light source 1 and the optical coupler 3 without loss, and is not always necessary. ).

As a result of measuring the amplification characteristics of the light by the above configuration, it was found that the pumping power was 1.3 m at 1.31 μm with the excitation light power of 50 mW.
A gain of dB was obtained, and it was confirmed that the excitation light power could be reduced to one third or less as compared with the case where ZrF ₄ -based fluoride glass was used.

As a host material, a Ge—S system, G
Even when an amplifying optical fiber made of e-PS-based or As-Ge-S-based chalcogenide glass and doped with 500 ppm of Pr ³⁺ is used,
It was confirmed that the excitation light power can be reduced to one third or less as compared with the case where ZrF ₄ -based fluoride glass is used.

In the above description, PrCl ₃ is used as a raw material reagent for Pr ³⁺ , but halides such as PrBr ₃ and PrI ₃ and sulfides Pr ₂ S ₃ can also be used.

[0018]

Example 2 The same As-S-based chalcogenide glass as in Example 1 was used as a host material of an amplification optical fiber. Further, in the same As ₄₀ S ₆₀ core glass as in Example 1, not only Pr ³⁺ but also EuCl ₃ was used as a raw material reagent.
Wt% Eu ³⁺ ions were co-doped. Further, a single mode fiber was produced in the same manner as in Example 1.

The single mode fiber manufactured in this manner was used as an amplification optical fiber in a 1.3 μm
As a result of configuring an optical fiber amplifier for a band and measuring the optical amplification characteristics, a pump light power of 40 mW (wavelength 1.02 μm) was obtained.
As a result, a gain of 5 dB was obtained at 1.31 μm, and it was confirmed that the pumping efficiency was improved as compared with the case of Example 1.

This is based on the following reasons. That is, Pr
^When Eu ³⁺ is co-doped together with ³⁺ , energy transfer occurs from the ³ H ₅ level of Pr ³⁺ to the ⁷ F ₃ level of Eu ³⁺ as shown in FIG. 3, and is indicated by an arrow 8 in the Eu ³⁺ ion. Relaxation by such phonon emission occurs. In materials with low phonon energy, such as chalcogenide glass, relaxation due to phonon emission hardly occurs,
The ³ H ₅ level of Pr ³⁺ has a long lifetime approaching 0.1 second. And concentration of ions gain 1.3μm-band optical fiber amplifier that is pumped to ¹ G ₄ level,
³ H ₅ in order that depends on the difference between the concentration of ions in level, the density difference becomes large, the gain also increases the faster the relaxation from ³ H ₅ level to ³ H ₄ level. Codoped of Eu ³⁺ from ³ H ₅ level Pr ^{3+ 3} H
Effective for quickening to ₄ levels, 1.3μ
The gain of the m-band optical fiber amplifier can be improved.

[0021]

Embodiment 3 Zn as a host material for an amplification optical fiber
With F ₂ -InF ₃ -PbF ₂ -LaF ₃ based fluoride glass. At this time, the composition of the core glass was ZnF ₂ (1
_{9) -InF 3 (30) -PbF} 2 (45) -LaF 3
(6) (mol%), the composition of the clad glass is ZnF
_{2 (21) -InF 3 (30} ) -PbF 2 (43) -L
aF ₃ (6) (mol%). The phonon energy of these glasses is about 400 cm ^-1 .

The core glass was doped with Pr ³⁺ to a concentration of 500 ppm in the same manner as in Example 1, and a single mode fiber was manufactured in the same manner as in Example 1. Here, the core diameter is 4 μm, and the cutoff wavelength is 0.5
It was 3 μm.

The single mode fiber manufactured in this manner was used as an amplification optical fiber in the same 1.3 μm as in FIG.
The optical fiber amplifier for the band was constructed and the amplification characteristics of the light were measured. As a result, the pump light power of 50 mW (wavelength 1.02 μm) was obtained.
It was confirmed that a gain of 5 dB was obtained at 1.31 μm.

In the same manner as in Example 2, not only Pr ³⁺ but also 1% by weight of Eu ³⁺ was co-doped to produce a single mode fiber, and an optical fiber amplifier for 1.3 μm band using the same. As a result, the gain of 5 dB was obtained at 40 mW, and it was confirmed that the excitation efficiency was improved as compared with the case where only Pr ³⁺ was doped.

As a host material, ZnF ₂ —InF
₃ -PbF with ₂ -GaF ₃ -LaF ₃ based fluoride glass, this was doped with Pr ³⁺ or Pr ³⁺ and Eu ³⁺
It was confirmed that the gain was improved even when the amplification optical fiber produced by co-doping was used, as compared with the case where ZrF ₄ -based fluoride glass was used.

[0026]

Embodiment 4 Al is used as a host material for an amplification optical fiber.
_{F 3 -ZrF 4 -YF 3 -MgF 2} -CaF 2 -SrF
Using ₂ -BaF ₂ -PbF ₂ -NaF type fluoride glass. At this time, the composition of the core glass was AlF ₃ (30.2)
−ZrF ₄ (10.2) −YF ₃ (8.3) −MgF ₂ (3.5
) -CaF ₂ (18.0) -SrF ₂ (11.7) -BaF ₂
(9.3) -PbF ₂ (5.0) -NaF (3.8) (mol%), the composition of the clad glass was AlF ₃ (30.2) -Zr
F ₄ (10.2) -YF ₃ (8.3) -MgF ₂ (3.5) -C
aF ₂ (19.2) -SrF ₂ (12.4) -BaF ₂ (9.9)
-PbF ₂ (2.5) was -NaF (3.8) (mol%).

Further, the core glass was doped with Pr ³⁺ to a concentration of 500 ppm in the same manner as in Example 1, and a single mode fiber was manufactured in the same manner as in Example 1. Here, the core diameter is 4.2 μm, and the cutoff wavelength is 1
μm.

The single mode fiber manufactured in this manner was used as an amplification optical fiber in the same 1.3 μm as in FIG.
As a result of configuring an optical fiber amplifier for a band and measuring the optical amplification characteristics, a pump light power of 100 mW (wavelength 1.02 μm) was obtained.
m), it was confirmed that a gain of 5 dB was obtained at 1.31 μm.

The refractive index n _D of the core glass having the above composition is 1.45.
8, which is the same as quartz glass, so that when this optical fiber is connected to a silica-based fiber, the loss due to reflection between the end faces can be extremely reduced.
An optical fiber amplifier for the 3 μm band can be easily configured.

Further, AlF ₃ —YF _{3 is} used as a host material.
_{-MgF 2 -CaF 2 -SrF 2 -BaF 2} -PbF 2
System or _{AlF 3 -HfF 4 -YF 3 -MgF 2} -CaF
Even when an amplification optical fiber made of _2- SrF ₂ -BaF ₂ -PbF ₂ -NaF-based fluoride glass is used, the refractive index can be matched with that of a silica-based fiber, making it effective as an amplification optical fiber. It is.

[0031]

As described above, according to the first aspect of the present invention, since a material having a phonon energy of less than 500 cm ^-1 is used as the host material, the level of Pr ³⁺ changes from the ¹ G ₄ level to the ³ F ₄ level. Phonon relaxation hardly occurs, which can improve the amplification efficiency at 1.31 μm.

According to a second aspect of the present invention, As-
S-based, Ge-S-based, Ge-PS-based or As-Ge-S
Since any of the chalcogenide glasses of the system having a phonon energy of 350 cm ^-1 was used as the host material, phonon relaxation of Pr ^{3+ from} the ¹ G ₄ level to the ³ F ₄ level hardly occurred. Amplification efficiency can be improved.

According to the third aspect of the present invention, since Eu ³⁺ is co-doped with Pr ³⁺ as active ions, the phonon relaxation of Pr ^{3+ from} the ³ H ₅ level to the ³ H ₄ level is accelerated. Thereby, the amplification efficiency at 1.31 μm can be further improved.

According to the fourth aspect of the present invention, ZnF
₂ -InF ₃ -PbF ₂ -LaF ₃ system or ZnF ₂ -I
Since nF ₃ -PbF ₂ -GaF ₃ -LaF ₃ -based fluoride glass having a phonon energy of about 400 cm ⁻¹ was used as the host material, Pr ³⁺ was reduced from the ¹ G ₄ level to ³ %.
Phonon relaxation to the F ₄ level is unlikely to occur, thereby improving the amplification efficiency at 1.31 μm.

According to the fifth aspect of the present invention, since Eu ³⁺ is co-doped with Pr ³⁺ as active ions, phonon relaxation of Pr ^{3+ from} the ³ H ₅ level to the ³ H ₄ level is accelerated, Thereby, the amplification efficiency at 1.31 μm can be further improved.

Further, according to claim 6 of the present invention, 1.3.
Since an amplification optical fiber with high amplification efficiency at 1 μm is used, required gain can be obtained with low pumping light power, and a small pumping light source such as a semiconductor laser can be used. There is an advantage that it becomes possible.

[Brief description of the drawings]

FIG. 1 shows 1.3 μm using the amplification optical fiber of the present invention.
FIG. 1 is a configuration diagram showing an embodiment of an m-band optical fiber amplifier and how the amplification characteristics are measured.

Fig. 2 Energy diagram of Pr ³⁺

FIG. 3 is an energy diagram of Pr ³⁺ and Eu ³⁺

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Pump light source, 2 ... Lens, 3 ... Optical coupler, 4 ... Signal source, 5 ... Optical fiber for amplification, 6 ... Fiber pigtail,
7 ... Optical spectrum analyzer.

──────────────────────────────────────────────────続 き Continuation of the front page (51) Int.Cl. ⁷ Identification symbol FI G02F 1/35 501 G02F 1/35 501 (56) References JP-A-4-3482 (JP, A) JP-A-4-265251 JP-A-2-275726 (JP, A) JP-A-4-89635 (JP, A) JP-A-63-184386 (JP, A) Electron. Lett. , April 11, 1991, Vol. 27 No. 8, p. 626-628 Chem. Phys. Lett. , June 7, 1985, Vol. 117 Num. 2, p. 108-114 Electron. Lett. , April 11, 1991, Vol. 27 No. 8, p. 628-629 IEEE. J. Quantum. Electron. Lett. , Vol. 24 No. 6, p. 1118-1123 (58) Fields investigated (Int. Cl. ⁷ , DB name) H01S 3/00-3/30 C03C 3/32 C03C 13/04 G02B 6/00 G02F 1/35 501 JICST file (JOIS)

Claims (8)

(57) [Claims] 1. A phonon energy is used as a host material.
As-S system, Ge-S system, Ge- smaller than 500 cm ^-1
An amplifying optical fiber using a chalcogenide glass of either PS or As-Ge-S and doped with Pr ³⁺ as active ions. Wherein amplifying optical fiber according to claim 1, characterized in that codoped with Eu ³⁺ with Pr ³⁺ as an active ion. 3. A phonon energy is used as a host material.
ZnF ₂ —InF ₃ —PbF ₂ − smaller than 500 cm ⁻¹
LaF ₃ system or ZnF ₂ -InF ₃ -PbF ₂ -GaF
Amplifying optical fiber it <br/> characterized by using a ₃ -laf ₃ based fluoride glass. 4. The amplifying optical fiber according to claim 3, characterized in that codoped with Eu ³⁺ with Pr ³⁺ as an active ion. 5. A amplifying optical fiber according to any one of claims 1 to 4, a pumping light source for generating excitation light, an optical coupler which multiplexes the signal light and the excitation light incident on the amplifying optical fiber 1.3 μm characterized by having
Optical fiber amplifier for band. 6. An amplification optical fiber, an excitation light source, and a signal
Combining the light and the pump light generated by the pump light source to increase the
Optical fiber having an optical coupler for entering the optical fiber for width.
In the optical amplifier, the pump light source is a semiconductor laser, and the amplification optical fiber is a phonon laser as a host material.
Using a material with an energy of 350 cm ^-1 to 400 cm ^-1
Both are made by doping Pr ³⁺ as active ions.
1.3μm optical fiber amplifier characterized by being manufactured
vessel. 7. A phonon energy as a host material.
Using chalcogenide glass smaller than 500 cm ^-1
Both are made by doping Pr ³⁺ as active ions.
An amplification optical fiber characterized by being manufactured. 8. A phonon energy as a host material.
Use a material smaller than 500 cm ^-1
Work and co-doped with Eu ³⁺ with Pr ³⁺ as Buion
An amplification optical fiber characterized by being manufactured.