JPH0473718A - Optical amplifier - Google Patents

Abstract

PURPOSE:To perform optical amplification at a bank with wavelength 1.5-1.7mum by making excitation light at a band less than wavelength 0.70mum which enables Tm<3+> light emission to be performed at the band with wavelength 1.5-2.7mum incident on an optical fiber. CONSTITUTION:A laser beam source 12 outputs the excitation light at the band with wavelength less than 70mum. The excitation light is made incident on a coupler 13 via the optical fiber 19a, and furthermore, is made incident on the optical fiber 10 via the optical fiber 18b. Since Tm<3+> as an activator material is added on the core of the optical fiber 10, Tm<3+> excited by the excitation light can emit light at the band with wavelength 1.5-1.7mum. Signal light at the band with wavelength 1.5-1.7mum outputted from a signal source 11 is made incident on the coupler 13 via the optical fiber 18a The signal light made incident on the coupler 13 is coupled with the excitation light from the beam source 12, and is made incident on the optical fiber 10. The signal light made incident on the optical fiber 10 generates simulated emission light at the band with wavelength 1.5-1.7 by inducing pumped Tm<3+>. The excitation light is cut with a filter 16, and only amplified signal light is made incident on a light spectrum analyzer 15.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to an optical amplification device used in a wavelength band of 1.5 to 1.7 μm.

[Conventional technology]

Efforts are being made to fabricate optical amplification devices such as fiber amplifiers, fiber sensors, and fiber lasers using optical core innos doped with rare earth elements for applications in the field of optical communications in the wavelength band of 1.5 to 1.7 μm. Core ino doped with rare earth elements (especially erbium ion (
There have been many reports on optical cores having a core made of quartz glass doped with E r 3"), and optical amplifiers using such optical fibers have a
It is known that optical amplification gain can be obtained in the 3-1.56 μm band.

[Problem to be solved by the invention]

However, optical amplifiers made of optical fibers doped with Er3+ were not able to adequately support the wavelength range of 1.5 to 1.7 μm, which is covered by laser diodes (LDs) used as signal light sources. . Also, wavelength 1.
For the purpose of using it as a fault detection system for maintenance of optical communication systems such as 55 μm band, for example, an optical amplification device with a wavelength of 1.65 band on the longer wavelength side may be required. Optical amplification devices made of doped optical fibers have not always been able to adequately support this 1.65 μm band.

Therefore, in view of the above-mentioned circumstances, the present invention provides wavelengths of 1.5 to 1.
The present invention aims to provide an optical amplification device having sufficient optical amplification gain in the , 7 μm band.

[Means to solve the problem]

In order to achieve the above object, an optical amplifying device according to the present invention includes an optical transmission line, a pumping light source, and an optical means. Here, the optical transmission line contains thulium ions (T
It is composed of optically functional glass doped with 1.5 μm to 1.7 μm of wavelength band. Further, the excitation light source generates excitation light having a wavelength of 0.70 μm or less. Further, the optical means causes excitation light from the excitation light source to enter the optical transmission path.

[Effect]

In the optical amplification device according to the present invention, Tm3+, which is an active substance, is excited by excitation light with a wavelength of 0.70 μm or less introduced into the optical transmission line, and efficient light emission in the 47yj/H system is achieved. enable. This will be explained more specifically by taking into consideration the energy level of Tm3+. When the wavelength of the excitation light is below the 0.70 μm band, the excitation light excites electrons at the ground level 3H6 and transitions to the energy level 3F2 or a higher energy level. Such excitation and subsequent relaxation results in a degree
Between H4 and level H4, or between level 3F and level
When a population inversion is formed between H5 and H5, the wavelength is 1.5 to 1.
, it becomes possible to emit light in the 7 μm band. At this time, when a signal light with a wavelength band of 1.5 to 1.7 μm is incident on the excited Tm3+, Tm3+ is guided by this signal light, and the wavelength],
Generates light in the 5-1.7 μm band. As a result, wavelength 1.
Optical amplification in the 5-1.7 μm band becomes possible.

〔Example〕

Embodiments of the optical amplification device of the present invention will be described below.

FIG. 1 shows a fiber amplifier which is an optical amplification device for a wavelength band of 1.5 to 1.7 μm.

As the signal light source 11, a laser diode is used. One end of an optical fiber 18a is optically connected to the output side of the signal light source 11.
The other end is connected to the input side of coupler 13. Also,
A dye laser or an Ar laser is used as the laser light source 12, which is an excitation light source. Laser light Iti,
One end of an optical fiber 19a is optically connected to the output side of the coupler 12, and the other end of the optical fiber 19a is connected to the input side of the coupler 13.

The output side of the coupler 13 has two optical fibers 18b, 1
9b is extended, the end of one optical fiber 19b is immersed in matching oil 17 for preventing return light, and the end of the other optical fiber 18b is connected to the tip fiber 1 which is an optical transmission path.
It is connected to one end of o via a connector or the like. An optical spectrum analyzer 15 is provided on the output side of the other end of this optical fiber 10, and a filter 1 is provided between them.
6 is interposed.

Here, the coupler 13 is produced by fusion drawing of two optical fibers 18 and 19, and this coupler 13 and the optical fibers 18a-, 18bs]9a51
9b constitutes an optical means for optically coupling the signal light and the excitation light.

The optical fiber 10 is a 3M fiber with a length of 2 m and includes a core made of quartz glass doped with Tm3+.

The operation of the fiber amplifier shown in FIG. 1 will be briefly explained below.

The laser light source 12 outputs excitation light having a wavelength of 0.70 μm or less. This excitation light enters the coupler 13 via the optical fiber 1.9a and further enters the optical fiber 10 via the optical fiber 18b.

Since the core of the optical fiber 1o into which the excitation light enters is doped with Tm''+ as an active substance, the Tm3+ excited to a predetermined state by this excitation light has a wavelength of 1.5~
It becomes possible to emit light in the 1.7 μm band.

Signal light having a wavelength of 1.5 to 1.7 μm outputted from the signal light source 11 enters the coupler 13 via the optical fiber 18a. The signal light incident on the coupler 13 is transmitted to the laser light source 1
It is combined with the excitation light from 2 and enters the optical fiber 10. The signal light incident on the optical fiber 10 induces the pumped Tm''+ to produce stimulated emission light in the wavelength range of 1.5 to 1.7 μm.

Pumping light and amplified signal light are output from the output side of the optical fiber 10 , but among these, the pumping light is cut by the filter 16 . For this reason,
Only the amplified signal light enters the optical spectrum analyzer 15, and the gain of optical amplification by the Tm''+ doped optical fiber can be determined as l'lF+.

The principle of increasing the gain of the fiber amplifier shown in FIG. 1 will be briefly explained using FIG. 3.

Figure 3 shows Tm added to a glass sample such as quartz glass.
FIG. 3 is a diagram showing an example of a 3+ energy level.

Electrons at the ground level H6 of Tm are excited by the excitation 3+3 light of 0.70 μm or less introduced into the optical fiber. For example, when the wavelength of the excitation light is about 0.68 μm, the electrons that were at the ground level T m "" (7) are once excited to the energy level F2, emit phonons, and then move to the level H4 or Transition to level 3F. Through this process, population inversion is formed between level 3H and level 3F, or between level F and level F
An anti-light distribution is formed between 5 and 5. As a result, the level H
The electrons present at level 4 will transition to level F4 with light emission, and the electrons present at level 3F will transition to level F5 with light emission. That is, two sets of radiative transitions enable light emission of a four-level system with a peak wavelength in the 1.5-1.7 μm band. As a result, wavelength 1.
Not only does effective stimulated emission in the 5-1.7 μm band become possible, but it also makes it possible to amplify light with wavelengths corresponding to either of the two sets of radiative transitions depending on the purpose, making it possible to achieve a wider band. Optical amplification becomes possible.

Note that when the excitation light has a shorter wavelength, for example, when the wavelength of the excitation light is about 0.47 μm, the electrons that were at the ground level of Tm''+ are excited to the energy level 3G, and they generate phonons, etc. After releasing energy, it transitions to level H or level F3.After that, it is the same as in the case of excitation light with a wavelength of 0.68 μm, and it is a four-level system with a peak wavelength of 1.5 to 1.7 μm. It becomes possible to emit light.

The optical amplification gain of the fiber amplifier shown in FIG. 1 was measured under three conditions in which the wavelength of the pumping light was changed.

Under the first condition, the wavelength of the incident excitation light from the laser light source 12 was 0.79 μm, and the output thereof was 30 mW. In addition, the wavelength of the input signal light from the signal light source 11 is set to 1.65μ.
m, and its output was set to 1 μW. From the API determination results obtained by the optical spectrum analyzer 5, it was found that the optical amplification gain of the fiber amplifier of the example was about 0.8 dB.

Under the second condition, the wavelength of the incident excitation light from the laser light source 12 was changed to 0.68 μm, and the output was set to 30 mW. As a result, the amplification gain was 4 dB.

In the third condition, the wavelength of the incident excitation light from the laser light source 12 was changed to 0.47 μm, and the output was set to 30 mW. As a result, the amplification gain was 4.5 dB.

As is clear from the above results, the wavelength of the excitation light was set to about 0.
By setting it to 70 μm or less, the wavelength], 65 μm
It can be seen that the amplification gain at the end of the band increases.

Similar to FIG. 3, FIG. 4 shows an example of the energy level of Tm3+ added to a glass sample such as quartz glass. For reference, the phenomenon in which the optical amplification gain decreases when the wavelength of pumping light is 0.79 μm will be explained based on this figure.

According to experiments, Tm3+ has a wavelength of 0.78 to 0.80 μm.
It is known that there is a large absorption in the wavelength band, but for example, as in the above case (condition 1), the wavelength is 0.79μ.
Even if pumping light of m is used, sufficient gain cannot be obtained for signal light in the wavelength band of 1.5 to 1.7 μm. This phenomenon can be considered as follows. In other words, Tm3+ is excited by the excitation light introduced into the optical fiber, and its ground level 3
Electrons in H directly transition to level 3H.

Generally, in such a level-based light emission, if a population inversion is formed between the level 3H and the level 3F, pumping to the level 3H becomes difficult.

As a result, effective stimulated emission in the wavelength band of 1.5 to 1.7 μm cannot be expected.

For reference, FIG. 2 shows the structure of the fiber O using the fiber amplifier of FIG. 1.

Optical fiber 0 includes a core made of quartz doped with Tm and a cladding made of quartz doped with fluorine (F). Its core diameter is 6 μm and its outer diameter is 125 μm. Further, the relative refractive index difference Δ between the core and the cladding is about 0.7%.

Below, a brief explanation will be given regarding the production of the optical fiber shown in FIG.

First, Tm
Quartz glass to which 3+ is added as an oxide is melted and formed into a rod shape to form a glass rod for the core. The concentration of thulium ion, which is an active substance added to this quartz glass, is 300 ppm by weight.

Next, fluorine-doped quartz glass is melted and formed into a clad vibe. Clad Vibe does not contain thulium ions. These core lots and clad pipes are formed into a preform by a lot-in-tube method. This preform is set in a known drawing device and drawn into a final fiber. As a result, a 3M fiber with a core diameter of 6 μm and an outer diameter of 125 μm is obtained. This 3M fiber was cut into a sample with a length of 2 m for measurement, and was used as the optical fiber 10 used in the fiber amplifier shown in FIG.

Although silica glass was used as the matrix glass for the core in the optical fiber of this example, the composition of the matrix glass is not limited to this. For example, silicate glass, phosphate glass, fluoride glass, etc. may be used.

By changing the composition of the matrix glass in this way,
It is also possible to adjust the wavelength of light emission or stimulated emission within the wavelength range of 1.5 to 1.7 μm.

Further, the optical transmission line of the present invention is not limited to the above-mentioned optical fiber. For example, the Tm3+ doped glass may be formed into a planar waveguide or the like. However, it is preferable to form the optical fiber in order to obtain a long optical transmission path.

By taking advantage of low optical loss, Tm3+ can be achieved at a low threshold.
This is because it is possible to cause population inversion.

The optical fiber used as the optical transmission line of the optical amplification device according to the present invention can also be applied to devices such as a fiber laser, for example.

Specifically, the fiber laser is configured to include the above-mentioned optical fiber, an excitation light source, optical means, and an optical resonator. Here, the excitation light source generates excitation light having a wavelength of 0° to 70 μm or less. The optical means also allows excitation light to enter the optical fiber from the excitation light source. Further, the optical resonator feeds back emitted light in the wavelength band of 1.5 to 1.7 μm from within the optical fiber to the optical fiber.

According to the above-described fiber laser, Tm3+ is excited by excitation light having a wavelength of 0.70 μm or less that is introduced into the fiber by optical means.

A part of this excited T rn 3+ is composed of emitted light in the wavelength band of 1.5 to 1.7 μm from within the end fiber and light in the wavelength band of 1.5 to 1.7 μm that is fed back into the optical fiber. , and generates emitted light in the wavelength band of 1.5 to 1.7 μm. By repeating this, wavelength 1
, laser emission in the 5-1.7 μm band becomes possible.

Examples of fiber lasers will be described below.

The specific configuration is similar to a known Er-doped fiber laser (“Er-doped fiber J, Oplu
s E, January 1990, pp.

See 112-118, etc. ). However, in the case of this example, the optical fiber of the above example doped with Tm"+ is used as the end fiber. Also, as the excitation light source, the wavelength 0,
A laser diode generating 68 μm excitation light is used.

The excitation destination of the wavelength 0.68 μm from the laser diode is
It is introduced into the optical fiber shown in the above embodiments by suitable optical means, such as a lens. Tm3+ within the optical fiber is excited to a predetermined state, and light emission in the wavelength band of 1.5 to 1.7 μm becomes possible. Here, since the output end of the fiber is finished with a mirror finish, this output end and the end face of the laser diode constitute a resonator. As a result, when the output of the excitation light exceeds a predetermined value, laser oscillation occurs at any wavelength in the 1.5-1.7 μm wavelength band.

Note that the resonator may be of a type that uses a dielectric mirror or the like.

〔Effect of the invention〕

As explained above, according to the optical amplification device according to the present invention, wavelengths of 1.5 to 1.7. The presence of excitation light with a wavelength of 0.70 μm or less, which enables T m "" emission in the czm band, enables optical amplification in the wavelength band of 1.5 to 1.7 μm.

Fig. 2 is a diagram showing the structure of the optical fiber used in the fiber amplifier of Fig. 1, and Fig. 3 is a diagram for explaining T m ``0'') pumping by pumping light in the 0.70 μm band or below. , Figure 4 shows Tm3+ due to excitation light in the wavelength band of 0.78 μm.
FIG. 2 is a diagram for explaining excitation.

10... Optical fiber serving as an optical transmission line; 12... Laser light source serving as an excitation light source; 13.18.19... Optical means.

Claims (1)

[Scope of Claims] An optical transmission line comprising optically functional glass doped with Tm^3^+ as an active substance and propagating signal light in the wavelength band of 1.5 to 1.7 μm; An optical amplification device comprising: a pumping light source that generates pumping light in the 70 μm band or less; and an optical means for making the pumping light from the pumping light source enter the optical transmission path.