JP2756510B2 - Broadband fiber laser medium and optical amplifier using the same - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a fiber laser medium used as an optical fiber type light emitting element and an optical amplifier using the same.

(Prior art and problems) Unlike other communication systems, an optical communication system has many advantages such as a long relay distance, no need for electromagnetic induction measures, and high-speed transmission of high-density information. Therefore, its position as a communication system is being established. In recent years, the development of core and cladding materials for optical fibers themselves, and the development of optical devices such as light-emitting and light-receiving devices and optical amplifiers have been actively pursued, with the aim of achieving higher performance and longer distances and higher capacity in optical communication systems. Have been.

In an optical fiber communication system currently in practical use, repeaters are inserted at regular intervals to compensate for optical signal attenuation due to optical fiber loss. After the signal is amplified by an electronic amplifier, the signal is converted into an optical signal by a semiconductor laser or the like, and sent out again to an optical fiber transmission line. Therefore, an Er-doped quartz fiber amplifier that amplifies optical signals without converting them into electrical signals has been developed. An Er-doped quartz fiber amplifier is a type in which when signal light enters Er atoms in an optical fiber pumped to a high energy level by pumping light, stimulated emission occurs and the power of the signal light gradually increases along the optical fiber. is there. This amplifier has a low gain of 1.535 μm having a sharply high gain, but has a peak of the gain at 1.552 μm, which has a rather wide band. The amplification band defined by the wavelength width of 3dB reduction of the peak gain is 1.535μm, 1.
3 nm to 5 nm and 10 nm respectively at 552 μm, and WDM (W
ave Division Multiplexing)
The problem is that the amplification band is narrow. Therefore, it is necessary to develop an optical amplifier exhibiting high amplification characteristics over a wide amplification band, and its realization has been demanded.

Furthermore, in an Er-doped quartz fiber optical amplifier, clustering occurs when Er is doped at a high concentration, and the amplification characteristics deteriorate. Therefore, in the Er-doped silica fiber optical amplifier, the Er concentration in the medium is suppressed to about several tens of ppm, and a large gain is obtained by setting the length of the fiber as the medium to several tens of meters. However, if the length of the fiber is several tens of meters, it is difficult to make the fiber compact in practical use. Considering the case where the fiber is inserted into a repeater or the like, it is desirable that the fiber be as small as possible. Therefore, it is necessary to develop an optical amplifier that has a wide amplification band, a large gain, and is made compact with a short medium length.
There is a demand for its realization.

(Object of the Invention) An object of the present invention is to provide a laser light having an oscillation wavelength of 1.5 to 1.6 μm.
Another object of the present invention is to provide a fiber laser medium having an optical fiber shape and a compact broadband optical amplifier using the same.

(Structure of the Invention) The present inventors have proposed Er to solve the above problem.
It has been found that when a fluoride glass fiber containing Er ³⁺ as a laser medium is used as a laser medium, light can be oscillated in a wide wavelength range, and can be easily connected to an optical fiber and used as a broadband optical amplifier.

In addition, the inventors found that since the Er solubility limit of the fluoride glass fiber was larger than that of the quartz glass fiber, clustering was suppressed, and as a result, a short and compact optical amplifier could be realized.

That is, according to the present invention, there is provided a fluoride glass fiber laser medium characterized in that the core portion contains Er ³⁺ and oscillating light having an infrared wavelength is obtained.

Further, according to the present invention, an optical amplifier comprising a means for propagating an optical signal, a means for propagating pump light, an optical multiplexer connected to the means for propagating the optical signal and pump light, and an optical fiber serving as an amplification medium. The core of the optical fiber is Er ³⁺
And amplifying light of an infrared wavelength.

In the present invention, Er contained in the fiber laser medium exists in the form of Er ^{3+ in} the fiber, and the object is to cause infrared laser oscillation based on the transition between the electronically excited states of the three-level system of Er ^3+. Is what you do. The Er ³⁺ concentration is preferably 1 mol% or less. If the amount exceeds 1 mol%, the characteristics of the fiber medium deteriorate.

In the present invention, as the fiber laser medium, for example, an optical fiber mainly containing a material such as fluoride glass such as ZrF ₄ —BaF ₂ —LaF ₃ —AlF ₃ is used.

If as the fiber laser medium according to the present invention using as a main component the ZrF ₄ -BaF ₂ -LaF ₃ -AlF ₃ based fluoride glass fiber are preferably ZrF ₄ = 50~58mol
%, BaF ₂ = 33 to 36 mol%, LaF ₃ = _{3 to} 6 mol%, AlF ₃ = 2
55 mol% and ErF ₃ = 10000 ppm (1 mol%) or less. If the composition is out of this range, excellent properties may not be obtained.

In addition, when the same glass material is used as a fiber, the fiber shape has a core diameter and a cladding diameter of 5.5 to 11 μm and 125 μm, respectively.
m is good. If the ratio is outside the above range, the characteristics as a fiber medium may be deteriorated.

Further, a fiber having a cutoff wavelength of 1.45 μm is preferable.

As a method of oscillating a fiber laser using the infrared fiber laser medium of the present invention, the fiber laser medium is cut into a predetermined length L such that the laser oscillation wavelength λ satisfies L = (λ / 2) n. Au, Ag, Al, and the like are vapor-deposited so that the reflectivity is about 90% on the cross section, and the amount of both of them is controlled to form a half mirror to constitute a laser output unit. The fiber can be fixed and irradiated with excitation light from the axial direction of the fiber via a half mirror to cause laser oscillation. GaInAsP with emission band at 1.48μm as excitation light
High power semiconductor laser or In with emission band at 0.98μm
A GaAs high power semiconductor laser is used.

Further, the fiber laser medium described above can be used as an optical amplifier. In order to use the optical amplifier as an optical amplifier, it is sufficient to irradiate an excitation light and to input an optical signal having the same wavelength as the oscillation wavelength of the laser medium into the laser medium.

At this time, since the optical signal passes through the laser medium having the population inversion with a stimulated emission phenomenon, light having the same wavelength as the optical signal is generated. Therefore, an amplified signal can be extracted from the laser medium. At this time, the point that the fluoride glass material is doped with Er as a laser medium is different from the conventional optical amplifier in which quartz glass is doped with Er.
Fluoride glass material has more physical properties than quartz glass,
A large amount of Er atoms can be dissolved in the solid solution, and therefore, the Er concentration per unit length can be made higher than that of quartz glass. This is a problem with quartz glass fibers
The problem that the fiber must be used for a long time because the Er concentration cannot be increased can be solved. In other words, it is expected to be smaller than the Er-doped quartz fiber optical amplifier.

Further, fluoride glass is a multi-component glass, and the effect of the crystal field received from the base material on the doped Er atoms is complicated, so that the energy levels of the Er atoms are spread.
As a result, the emission spectrum can be broadened and the amplification band can be made wider than in the case of Er-doped quartz glass. Therefore, the amplified signal can be extracted from the amplification medium over a wide band.

Example 1 ZrF ₄ = 57 mol%, BaF ₂ = 34 mol%, LaF ₃ = 5 mol%, AlF ₃
= A 4 mol% and ErF ₃ = 1000 ppm fiber laser medium was cut to have a length of about 1m of the same glass material. When the fiber is formed, the core and clad diameters are 6.5 μm and 125 μm, respectively. The relative refractive index difference between the core and the clad is 0.5%, and the cutoff wavelength is 1.45 μm.
m.

The fiber laser medium was cut so that a cut surface perpendicular to the long axis of the fiber was obtained when cutting. At least 90% reflectance of Au, Ag, or Al on both end surfaces
Thus, a resonator required for laser oscillation was manufactured by controlling the amount of deposition on one side to form a half mirror and the other on a total reflection mirror.

FIG. 1 shows the configuration of a laser device using the fiber laser medium of the present invention obtained in this way. An oscillation wavelength of 1.48 μm is provided as an excitation light source 2 at one end of a fiber laser medium 1.
A high-power semiconductor laser of GaInAsP or InGaAs having an oscillation wavelength of 0.98 μm is provided. At this time, the semiconductor laser is arranged so that the laser oscillation intensity becomes maximum.

Irradiation from the semiconductor laser 2 as described above excites Er ³⁺ in the fiber laser medium 1 and emits light in a transition accompanied by radiation. The cavity length,
That is, only the relationship determined by the interval between the half mirror and the total reflection mirror and only the satisfying wavelength are selectively amplified, laser oscillated, and laser output through the half mirror.

Second Embodiment Next, an optical amplifier using the fiber laser medium of the present invention obtained in the first embodiment will be described.

FIG. 2 is a schematic diagram showing a specific example of the optical amplifier of the present invention.

The illustrated device includes an optical fiber 5 for transmitting a laser beam (optical signal) 6 as an optical signal, a semiconductor laser 2 for an excitation light source for exciting a laser medium 1, an optical fiber 4 for transmitting an excitation light, and their light. A multiplexer 3 for coupling the fibers 4 and 5
And the fiber laser medium 1 of the present invention in contact with the end of the multiplexer 3. The laser beam 6 as an optical signal is a laser beam having the same wavelength as the laser beam oscillated by the fiber laser medium 1 of the present invention. The excitation light 2 is a light source for exciting the fluoride glass laser medium 1 of the present invention.

In order to amplify an optical signal using such an optical amplifier, first, a laser beam 2 is input to a multiplexer 3 through an optical fiber 4, and an output of the laser beam 2 is generated so that the laser medium 1 has a population inversion. To increase. The intensity of the laser medium 1 is set to be inverted distribution, and the optical signal is transmitted through the optical fiber 5 to the multiplexer 3.
To enter. By such an operation, an amplified optical signal can be extracted from the end of the laser medium 1. At this time, the gain characteristics using the optical amplifier for each signal wavelength are shown in FIG.

In FIG. And two types of 36 mW (symbol a) and 55 mW (symbol b), Shows the results of a total of three measurements of 55 mW (symbol c).

1.5 μm to 1.6 μm
If the amplification band in the μm band is defined by the wavelength interval between the gain values of 1.530 μm at 3 dB reduction, it is about 10 nm, but in this embodiment, it is noted that both are as wide as about 40 nm. ing.

(Effect of the Invention) As described above, the fiber laser medium of the present invention is a light emitting element for an optical fiber, and can be easily connected to an optical fiber.

The fiber laser medium of the present invention is very useful because it can be used as an optical amplifier by being connected at a relay point of an optical fiber.

Furthermore, the optical fiber type amplifier according to the present invention has a wider bandwidth than the conventional Er-doped silica fiber optical amplifier, and is very useful as an optical amplifier inserted into, for example, a WDM system.

Further, the fiber laser medium of the present invention is a fluoride glass material different from a quartz glass material, so that the Er atom concentration can be increased, and thus the medium length can be shortened, so that a small and compact optical amplifier can be manufactured.

[Brief description of the drawings]

FIG. 1 is a specific example of a laser device using the laser medium of the present invention, FIG. 2 is a schematic diagram of an example of an optical amplifier of the present invention, and FIG. 3 is an optical amplification characteristic of the optical amplifier of the present invention. It is. 1 ... fiber laser medium, 2 ... semiconductor laser (excitation light), 3 ... multiplexer, 4, 5 ... optical fiber, 6 ... laser light.

Claims (2)

(57) [Claims] (1) ZrF ₄ is 50 to 58 mol%, BaF ₂ is 33 to 36 mol%,
In a fiber laser medium having a core portion of fluoride glass in which LaF ₃ has a composition ratio of ₃ to 6 mol% and a cladding portion of fluoride glass provided around the core portion, the core portion contains Er ^3+. A broadband fiber laser medium characterized by obtaining oscillation light in the 1.5 to 1.6 μm band. 2. The fiber laser medium according to claim 1, wherein said fiber laser medium is an optical multiplexer and an amplifying medium for connecting means for transmitting an optical signal and means for transmitting pumping light to means for transmitting said optical signal and pumping light. And an optical amplifier comprising a fluoride fiber, wherein the fluoride optical fiber has a core portion containing Er ³⁺ and obtains oscillation light in a 1.5 to 1.6 μm band. .