JP3446998B2 - Excitation method of 1.3 μm band optical amplifier or laser oscillator - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a pumping method for an optical amplifier or laser oscillator used in 1.3 .mu.m band optical communication.

[0002]

2. Description of the Related Art A large amount of optical communication fibers having a dispersion value of 0 in the 1.3 μm band have already been laid and
Since a cheaper transceiver than the 1.55 μm band can be used,
Development of a 1.3 μm band optical amplifier or laser oscillator is expected. Therefore, amplifiers and lasers using low phonon energy glass (fluoride glass or chalcogenide glass) or fibers to which rare earths such as Nd, Pr and Dy are added have been studied. In particular, P
The low phonon glass fiber to which r is added has been sample-shipped and field-tested for practical use.

[0003]

An optical waveguide using a Pr-added halide glass, chalcogenide glass, halide oxide glass or chalcogenide glass is
It is expected as an amplification medium for 1.3 μm band optical communication. In order to efficiently couple these optical waveguides (generally fibers) with the excitation light source, it is desirable to use a semiconductor laser or solid-state laser with a fiber pigtail as the excitation light source. Generally, when Pr is excited, ¹ G ₄ which is the upper level of emission is directly excited. However, since ¹ G ₄ has an extremely small absorption coefficient and slows the relaxation of the emission lower level from ³ H ₅ to the ground level, it is difficult to form a population inversion. P
Since the wavelength that efficiently excites ¹ G ₄ of r is in the 1.02 μm band, a powerful semiconductor laser or solid-state laser light source in the 1.02 μm band is required, and research is actively conducted. However, the 1.02 μm band is the wavelength range that the semiconductor laser is not most good at, and it is difficult to manufacture a high-output semiconductor laser light source. For this reason, an excitation light source in which a large number of semiconductor lasers are combined is used, but the optical system becomes complicated and the coupling loss increases. Also, 1.
No solid-state laser that oscillates in the 02 μm band is known.
For this reason, the amplifier and the laser oscillator are expensive, the absorption efficiency of the excitation light is poor, and the lifetime of the lower emission level is long, so that the amplification efficiency is extremely low.

[0004]

[Means for Solving the Problems]
As a result of intensive studies to solve the above problem, the absorption coefficient is small.
I¹G_FourFirst of all, rather than directly exciting
From³F₂Excited by³H₆De-excited state
Further¹G_FourSecond, from the ground level ³F₃
Or³F_FourExcited by³H₆De-excited state
From the state¹G_FourThe absorption efficiency
We found that it can be increased about 10 times, and reached the present invention.
It was

That is, according to the present invention, in a 1.3 μm band optical amplifier or laser oscillator in which an optical waveguide containing Pr as a core material is used as an amplification medium, 1.7 to 1.8 μm is used as a pumping light source in the first method. And 1.8 to 2.0 μm of at least two kinds of excitation light, the second method is 1.4 to
By using at least two kinds of pumping light of 1.6 μm and 1.7 to 1.8 μm, a highly efficient 1.3 μm band optical amplifier or laser oscillator is provided.

The present invention will be described in detail below. Pr 1
Halide glass added about 00 to 10,000 ppm,
When low phonon glass such as chalcogenide glass, halide oxide glass, or chalcogenide glass is used as the core of the optical waveguide to perform optical amplification or laser oscillation in the 1.3 μm band, the optimum excitation wavelength is 1.02 μm band. It is being appreciated. This is because it coincides with the absorption center wavelength of ¹ G ₄ of Pr (see FIG. 1). In addition, Pr of 1.3
Since the emission in the μm band uses the transition of ¹ G ₄ → ³ H ₅ , it seems that the efficiency of 1.02 μm excitation is higher than that of excitation at other wavelengths (Fig. 2). However, in reality, since the relaxation of the emission lower level from ³ H ₅ to the ground level ( ³ H ₄ ) is slow, it is difficult to form population inversion, and highly efficient amplification and oscillation are very difficult. Also,
^Since the absorption coefficient of ¹ G ₄ is small, there are disadvantages such as a long medium length and strong light confinement required. Therefore,
In order to improve the absorption efficiency, a method of adding rare earths such as Yb and Nd and utilizing energy transfer from these rare earths (JP-A-4-358131) has been developed, but it is difficult to form population inversion. The problem cannot be solved. In addition, a method of quenching the emission lower level by co-adding Ce has been developed (JP-A-9-169540).
The problem of using ground level → ¹ G ₄ as the main excitation method is not solved. Combining these known methods can be a means of solving the above problems,
The decrease in glass stability due to the addition of a large number of rare earths poses a problem and is not practical.

In the present invention, as a first method, the ground level (
³ H ₄ ) → ³ F ₂ → ³ H ₆ → ¹ G _{4 As} the second method,
When excited by the procedure of ground level ( ³ H ₄ ) → ³ F ₃ or ³ F ₄ → ³ H ₆ → ¹ G ₄ , not only the effective absorption coefficient can be made very large, but also the population inversion can be easily formed. Therefore, it was found that amplification or laser oscillation can be performed with high efficiency with low pumping power. Specifically, as the excitation light, two kinds of wavelengths of 1.7 to 1.8 μm and 1.4 to 1.6 μm or two kinds of wavelengths of 1.7 to 1.8 μm and 1.8 to 2.0 μm are used. By using the combination, not only effective absorption coefficient improvement can be realized, but also population inversion formation becomes easy and amplification efficiency can be improved. The concept of excitation and emission is shown in FIG. ³ H ₄ → ¹ F ₂ or ³ H ₄ → ³ F ₃ , ³ F ₄ and ³
By using H ₆ → ¹ G ₄ as the main excitation level, a population inversion can be efficiently formed even at a relatively low output, and highly efficient amplification can be achieved. This is because the excited state absorption cross section from ³ H ₆ to ¹ G ₄ is about 10 times larger than the absorption cross section when ¹ G ₄ is directly excited from the ground state. A comparison of the absorption cross sections from each level is shown in FIG. Further, as is clear from FIG. 4, in the first excitation method, excitation of ³ H ₅ → ³ F ₄ also occurs at the same time, so the population of the emission lower level ( ³ H ₅ ) is effectively reduced, and amplification is performed. Efficiency and laser oscillation efficiency are improved.

Since the selection of the excitation wavelength depends on the Pr concentration and the material of the core, it is not possible to unconditionally specify at which wavelength the optimum combination is used. For example, in the case of Pr: ZBLAN (fluoride glass), the first method is used. 1.85 to 1.95 μm
And 1.70 to 1.77 μm, the second method is 1.45.
A combination of ˜1.60 μm and 1.70 to 1.77 μm is preferred. The optimum combination of pumping light power is Pr
Since it depends on the concentration, the material, the numerical aperture of the waveguide, etc., it cannot be specified unconditionally, but it is preferable that both the first method and the second method are adjusted to obtain the maximum gain. further,
In order to achieve higher efficiency, it is possible to combine the first method and the second method.

When the excitation method of the present invention is used, it is clear that any material capable of amplifying the 1.3 μm band in the Pr-added medium can be used. As such a material, low phonon glass is generally used,
Particularly, chalcogenide glass, halide glass, chalcogenide glass, halide oxide glass and the like are preferable. Further, as the excitation laser, a semiconductor laser,
Anything can be used, such as a dye laser, a solid state laser, or a gas laser. As a method of coupling the excitation light, it may be coupled through a fiber pigtail or the like, or may be coupled using an ordinary optical system such as a lens. The direction of excitation may be any method such as forward excitation, backward excitation, bidirectional excitation, etc., as long as the excitation can be performed efficiently. Further, the excitation light may be incident after being collected by a multiplexing element or the like, or may be incident individually. It is also effective to use a laser having a wide oscillation wavelength band in order to fully utilize the Pr absorption band to enhance the excitation efficiency. Such a laser can be realized by combining a plurality of lasers having slightly different oscillation wavelengths or by using stimulated Raman scattering.

When constructing an optical amplifier, an optical element for optical communication such as a wavelength division multiplexing element (WDM) or an optical isolator can be used if necessary. Further, it is preferable that the amplifier has a gain monitoring function or a gain equalizing function built-in or attached thereto because the reliability of the optical communication system is improved.
For monitoring the gain, any method may be used as long as it can substantially compare the incident signal light intensity and the output signal light intensity. When performing wavelength division multiplexing, it is desirable to use a method capable of detecting and monitoring each signal assigned to each wavelength. The gain equalization function may be a passive method or an active method.
As a passive gain equalization method, a configuration using an optical filter is simple. The active gain equalization method is composed of a gain monitoring function and a feedback function, and any method can be used as long as it can substantially compare the incident signal light intensity and the output signal light intensity and make the gain constant. . When performing wavelength division multiplexing communication, it is desirable to use a method capable of gain equalization for each signal assigned to each wavelength. Although it has the same function as the gain equalization, the output equalization function that keeps the output signal light intensity constant is as effective as the gain equalization function. These functions are preferably automatically adjustable, such as by a remotely programmable microprocessor.

In the case of constructing a laser oscillator, the output can be increased by connecting the optical waveguides in a ring shape or connecting a plurality of optical waveguides in series or in parallel. Also in the case of a laser oscillator, as the excitation laser, a semiconductor laser, a dye laser, a solid-state laser, a gas laser, etc.,
anything is fine. As a method of coupling the excitation light, it may be coupled through a fiber pigtail or the like, or may be coupled using an ordinary optical system such as a lens. The direction of excitation may be any method such as forward excitation, backward excitation, bidirectional excitation, etc., as long as the excitation can be performed efficiently. Further, the excitation light may be incident after being collected by a multiplexing element or the like, or may be incident individually. It is also effective to use a laser having a wide oscillation wavelength band in order to fully utilize the Pr absorption band to enhance the excitation efficiency. Such a laser can be realized by combining a plurality of lasers having slightly different oscillation wavelengths or by using stimulated Raman scattering.

As described above, the excitation wavelength is 1.7 to 1.8.
Two or more wavelengths in the μm band and the 1.8 to 2.0 μm band or 1.
By using multi-wavelength pumping of two or more wavelengths in the 7 to 1.8 μm band and the 1.4 to 1.6 μm band, an optical amplifier or laser oscillator in the 1.3 μm band, which is more efficient than ordinary 1.02 μm pumping, can be obtained. Can be provided.

[0013]

EXAMPLES The present invention will be further described below with reference to examples, but the present invention is not limited to these examples.

Example 1 Fluoride glass fiber containing 0.1 wt% of Pr was added to the core. The basic glass composition of the core and clad is shown below. Pr replaces La. The numbers are mo
1%. Core: 51ZrF ₄ -19BaF ₂ -4.5LaF ₃ -2YF ₃ -2AlF ₃ -13.5LiF-8Pb
F ₂ clad: 40HfF ₄ -10ZrF ₄ -19BaF ₂ -3LaF ₃ -2YF ₃ -4AlF ₃ -22
NaF This fiber had a relative refractive index difference of 3.3% and a cutoff wavelength of 1.0 μm.

Next, the configuration of the optical amplifier used for the measurement is shown in FIG.
Shown in. The fiber used for the measurement has a length of 2 m.
For excitation, a fiber laser having a wavelength of 1.55 μm and a fiber laser having a wavelength of 1.74 μm are combined, and the optical multiplexing / demultiplexing device 2 and a high N. A. Is connected to the fluoride fiber 4 for light amplification through the quartz fiber 5. The quartz fiber 5 and the fluoride fiber 4 were coupled by using a V-groove block, and the joint end surface was obliquely optically polished to reduce reflection loss and fixed with an optical adhesive. The signal light in the 1.3 μm band was made incident from the optical multiplexing / demultiplexing element 2, the amplified emitted light was passed through the optical isolator 6, and the small signal gain was measured by the measuring instrument 7. The input signal strength is -30 dBm. FIG. 6 shows a comparison of small signal gains when pumping 1.02 μm alone and pumping at two wavelengths simultaneously. The input power for dual wavelength excitation is
The total power of two wavelengths, 1.55μm and 1.74μ
The power ratio of m is fixed at 1: 1. 1.02 μm
It can be seen that the efficiency is more than doubled and the threshold value is lowered in the dual wavelength excitation as compared with the single excitation.

Example 2 An experiment was conducted by using the same fluoride fiber as in Example 1 and changing the excitation wavelength with the same configuration. Excitation wavelength is 1.9
μm and 1.74 μm. As a result, as in Example 1, the efficiency was more than double that of 1.02 μm excitation and the threshold value was low.

[0017]

By using the excitation method of the present invention,
A highly efficient 1.3 μm band optical amplifier or 1.3 μm band laser oscillator can be configured.

[Brief description of drawings]

FIG. 1 shows an absorption spectrum of Pr.

FIG. 2 shows a level diagram of Pr.

FIG. 3 shows a conceptual diagram of excitation and emission processes.

FIG. 4 shows a diagram of an absorption cross section from each level of Pr.

FIG. 5 is a configuration diagram of an amplifier according to the first exemplary embodiment.

FIG. 6 is a diagram showing pump power dependence of amplification factor in Example 1.

[Explanation of symbols]

1 Signal light incident part 2 Optical multiplexer / demultiplexer 3 Two types of combined fiber lasers 4 Optical amplification fiber 5 High N.V. A. Quartz fiber 6 Optical isolator 7 measuring instruments

─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Kiyotaka Miura 5253 Oki Ube, Ube City, Yamaguchi Central Glass Co., Ltd. Chemical Research Laboratory (56) Reference JP 9-129951 (JP, A) JP JP 5-29699 (JP, A) JP-A-6-21560 (JP, A) JP-A-5-58674 (JP, A) JP-A-5-21874 (JP, A) JP-A-5-90693 (JP, A) A) JP-A-7-162062 (JP, A) (58) Fields investigated (Int.Cl. ⁷ , DB name) H01S 3/00-3/30

Claims (3)

(57) [Claims] 1. A pumping method of an optical amplifier for amplifying an optical signal in a 1.3 μm band by using an optical waveguide containing Pr as a core material, and pumping at two or more kinds of wavelengths different from each other,
At least one of the excitation wavelengths is 1.7 to 1.8 μm, and at least one of the other excitation wavelengths is 1.4 to 1.6 μm.
m or 1.8 to 2.0 μm, a pumping method for a 1.3 μm band optical amplifier. 2. A method of exciting a laser oscillator that oscillates a laser beam in a 1.3 μm band by using an optical waveguide containing Pr as a core material, by exciting at two or more different wavelengths from each other, and at least the excitation wavelength. One is 1.7 to 1.8
μm, and at least one of the other excitation wavelengths is 1.4 to
A method of exciting a 1.3 μm band laser oscillator, which is 1.6 μm or 1.8 to 2.0 μm. 3. The core portion of the optical waveguide is made of halide oxide glass, halide glass, chalcogenide glass, or chalcogenide glass.
Alternatively, the method for exciting a 1.3 μm band optical amplifier or laser oscillator according to claim 2.