JPH043482A - Fiber laser medium and optical amplifier using the same - Google Patents

Abstract

PURPOSE:To obtain the light of a 1.3mum band with high efficiency, and to enable connection with a fiber for infrared light for optical communication in low coupling loss by using the fluoride glass fiber simultaneously containing specific quantities of Nb and Eu in a core section. CONSTITUTION:The composition of a fiber laser medium is composed of ZrF4=50-58mol%, BaF2=33-36mol%, LaF3=3-6mol% and AlF3=2-5mol%, and both NbF3 and EuF3 are brought to 1mol% or less The core diameter of the fluoride fiber is set at 5.5-7.5mum, a clad diameter at 125mum and a cutoff wavelength at 0.78-0.80. Excitation light 4 input to a synthesizer 6 through an optical fiber 5 is brought to approximately 95% of intensity, where a laser medium 1 begins to oscillate, laser beams 2 as an optical signal are input to the synthesizer 6 through an optical fiber 3, and an optical signal amplified is taken out of the laser medium 1 coupled with the output end of the synthesizer.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) 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) In recent years, there has been remarkable progress in optical communication systems using optical fibers. Optical communication systems have advantages over other communication systems, such as longer relay distances, no need for electromagnetic induction noise countermeasures, and the ability to propagate high-density information over long distances. The system is being replaced.

In the development of optical fibers used in such optical communications, in order to reduce optical transmission loss, we need to develop materials for the core and gland of optical fibers, as well as optical elements such as light emitting elements, light receiving elements, and optical amplifiers. is being actively promoted. In particular, the recent dramatic expansion of transmission distance through the use of Er-doped fiber optical amplifiers has greatly contributed to the development of optical trace systems. The Er-doped fiber optical amplifier is an in-line type amplifier that has no polarization dependence, high gain, low noise, almost no gain change due to temperature fluctuation, and no coupling loss with the optical fiber. is small, etc.
It has many advantages. Among the 1.3 μm band and 1.55 μm band used in today's optical communication systems, 1.
It also has the disadvantage of being limited to use as an amplifier in the 55μ band. This is because the light emission unique to the doped element is used, and Er does not emit light at 1.3 μ-. On the other hand, in the 1.3μ-band optical fiber amplifier,
It has been considered to utilize the allowable luminescence transition of 1.3 μm of Nd, and quartz glass, phosphate glass, poronic acid glass, and fluoride glass doped with Nd have also been made. However, the probability of absorption to further excite electrons in an excited state (called excitation absorption) is greater than the probability of laser transition, so in silica glass, the total <1.
Amplification in the 3 μm band cannot be expected. Among other glasses, fluoride glass has the smallest effect of excitation absorption, 1.3
Although amplification in the μm band could be obtained, the efficiency was very low. Therefore, there is a need for a fiber laser medium that can efficiently emit light using fluoride glass, and for an optical amplifier using the same.

(Problems to be Solved by the Invention) The present invention provides that the oscillation wavelength of the laser beam is in the 1.3 μm band,
Moreover, it is an object of the present invention to provide a fiber laser medium having an optical fiber shape that can be connected to an infrared light fiber for optical communication with low coupling loss, and an optical amplifier using the same.

(Means for Solving the Problems) As a solution to the above-mentioned problems, the inventors of the present invention have conducted extensive studies and research, and have determined that Nd is replaced by Nd'' and E
When a fluoride glass fiber containing u as Eu'' is used as a laser medium, it can oscillate and propagate with high efficiency through optical fibers such as silica glass fibers used in current 1.3 μ optical communication systems. It has been found that it can be easily connected to an optical fiber and can be used as an optical amplifier.In other words, according to the present invention, the core part is composed of Nd and E.
It is possible to provide a fluoride glass fiber laser medium which contains u at the same time and is characterized by obtaining oscillation light of an infrared wavelength.

In addition, the present inventors have discovered that by co-doping Eu'',
Energy transfer occurs from the '113/2 level of Nd'' to the 7F level of Eu'', which is at the same energy level, and the life of the 'l1ff/□ level of Nd'° becomes shorter. As a result, it was found that the 4F37□→'III/□ transition probability, which is involved in 1.3μ■ oscillation, is greater than the excitation absorption. This makes it possible to obtain light in the 1.3 μm band with high efficiency.

(Example) Examples of the present invention will be described in detail below with reference to the drawings, but the present invention is not limited thereto.

FIG. 1 shows the configuration of an embodiment of the optical amplifier of the present invention.

The illustrated device includes an optical fiber 3 for transmitting laser light 2 as an optical signal, an optical fiber 5 for transmitting excitation light 4 for exciting a laser medium 1, and a coupling between these optical fibers 3 and 5. The fiber laser medium 1 of the present invention is in contact with the end of the multiplexer 6. In the embodiment of the present invention, the multiplexer 6 has a diameter of 0.8 μm.
/1.3 μm wavelength division multiplexing type optical coupler is suitable. The laser beam 2, which is an optical signal, has the same wavelength as the laser beam oscillated by the fiber laser medium 1 of the present invention. Further, the excitation light 4 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, the pumping light 4 is input to the multiplexer 6 through the optical fiber 5, and the output of the pumping light 4 is increased so that the laser medium 1 oscillates. do. The excitation light 4 is set at approximately 95% of the intensity (threshold) at which the laser medium 1 starts to oscillate, and the laser light 2 as an optical signal is input to the multiplexer 6 through the optical fiber 3. Due to the wavelength dependence of the multiplexer (combiner 1) 6, the laser beam 2, which is an optical signal, is emitted to the output end to which the laser medium 1 is connected. Through such operations, the laser medium 1
The amplified optical signal can be extracted from.

In the present invention, in which Eu'' is contained in Nd3°, Nd
Since the fluorescence intensity in the 1.3 μm band is higher than that when the fiber laser medium is only doped, a large gain can be obtained.The reason for this is that the Nd and Eu contained in the fiber laser medium are
Each exists in the form of Nd" and Eu3+ in the fiber, and in order to promote the transition between the electronic excitation levels of the four-level system of Nd", the same level of Eu" is added from the laser final level of Nd". This is because infrared laser oscillation is efficiently realized by utilizing the energy transfer to the energy level of . That is, as shown in FIG. 2, the electrons in Nd'' are excited to a high energy state by a light source with an appropriate wavelength (energy) (in the present invention, a high-output semiconductor laser with a wavelength of about 0.79 μm is preferable). 1 from the ground state by a non-radiative process due to energy relaxation accompanied by lattice vibrations.
1500 cm-' Relaxes to the laser starting level ('F3/□) which is in a high energy state. In the present invention, which is designed to be applied to a 1.3 μm band optical communication system, from the starting level,
Laser oscillation is performed based on 1.3 μ#l stimulated radiation to the laser final level ('113/Z) in an energy state approximately 4000 cm-' higher than the ground state. However, the starting level is the same and the final level is 1 from 'l1ff/2.
Since the stimulated emission cross section of the transition to 'I11/□ (emission wavelength 1.06 μm) in the low state of 500-2000C11-' is larger, the competing oscillation of 1 and 3 μ- was not performed efficiently.

As a result of intensive studies on the above-mentioned problems, the inventors of the present invention discovered that by co-doping Eu'', the '11
Energy transfer occurs from the 3/□ level to the 'F3 and ?F4 levels of Eu'', which are at similar energy levels, and the lifetime of the 'I+3/□ level of Nd'' becomes shorter, resulting in 4, which is involved in oscillation at 1.3 μm rather than excitation absorption.
It was found that the transition probability of F, 7□→'113/□ increases. This makes it possible to obtain light in the 1.3 μI band with high efficiency.

In the present invention, ZrF is used as the fiber laser medium.
An optical fiber whose main component is a 4-BaF2-LaF:+-AlF3-based fluoride glass material is used. When the material of the optical fiber is mainly composed of a material such as quartz glass, even if it contains Nd'' or Eu'', excitation absorption becomes more dominant than laser transition, which is not preferable.

As a preferable composition of the fiber laser medium according to the present invention, the above-mentioned ZrF4-BaF4=LaF3A is added to the fiber.
When the main component is j2F3 type fluoride glass,
ZrFn=50~58 mof%, BaFz=33~
36mol%, LaF3=3-6IIlo1%, AIF
3=2~5IIlo! %, NdF:+ and Eu
F3 is both 1 mof% or less. Furthermore, the core diameter of this fluoride fiber is 5.5 to 7.5 μm, the cladding diameter is 125 μm, and the cutoff wavelength is 0.78 to 0.
．． Single mode fiber, such as 80μ-, is preferred.

As a fiber laser oscillation method using the infrared fiber laser medium of the present invention, the fiber laser medium is cut into a predetermined length such that the laser oscillation wavelength λ satisfies L'=(λ/2)n, Ag, Au, Aj2, etc. are evaporated on both cross sections so that the reflectance is about 90%, and the amount of evaporation on one side is controlled to form a half mirror, thereby forming a laser output section. Such a fiber can be fixed and irradiated with excitation light in the length direction to cause laser oscillation.

A high-power AI GaAs semiconductor laser or the like is used as the excitation light.

The fiber laser medium described above can be used as an optical amplifier. When used as an optical amplifier, the intensity of the pumping light to be irradiated should be set to 95 to 95, which is the threshold value for laser oscillation.
It is sufficient to set the ratio to about 98% and input an optical signal having the same wavelength as the oscillation wavelength of the laser medium into the laser medium. On this occasion,
Since the optical signal passes through the laser medium in which population inversion occurs, accompanied by stimulated emission, a laser beam having the same wavelength and phase as the optical signal is generated. Therefore, an amplified signal can be extracted from the laser medium.

(Effects of the Invention) As explained above, the fiber laser medium of the present invention is a light emitting element for optical fibers that has oscillation wavelength characteristics that reduce transmission loss of optical fibers, and can be easily connected to optical fibers. .

Furthermore, the fiber laser medium of the present invention can be used as an optical amplifier by connecting at a relay point of optical fibers in a 1.3 μm band optical communication system, so it will be useful as a future optical fiber system. .

[Brief explanation of drawings]

FIG. 1 is a schematic diagram showing the configuration of an embodiment of the optical amplifier of the present invention, and FIG. 2 is a diagram showing Nd"+ and Eu" in the LaF3 crystal.
FIG. ■... Laser medium 2... Optical signal (laser light) 3... Optical fiber 4... Excitation light 5...
...Optical fiber 6...Multiplexer (coupler)
Fig. 2 Shoulder LaFs Eu”: LaFJ

Claims (1)

[Claims] 1. In a fluoride glass fiber laser medium whose core portion contains both Nd (neodymium) and Eu (eurobium) and is capable of obtaining oscillation light of an infrared wavelength,
The composition of the fiber laser medium is ZrF_4=50-58
mol%, BaF_2=33-36 mol%, LaF_
3=3 to 6 mol%, AlF_3=2 to 5 mol%, both NdF_3 and EuF_3 are 1 mol% or less, and the core diameter of this fluoride fiber is 5.5 to 7.
5 μm, a cladding diameter of 125 μm, and a cutoff wavelength of about 0.8 μm. 2. A means for propagating an optical signal, a means for propagating pumping light, an optical multiplexer connected to the means for propagating the optical signal and pumping light, and an optical amplification effect on the output part of the optical multiplexer. In an optical amplifier configured by connecting optical fibers having
A semiconductor laser having a wavelength of 0.78 to 0.80 μm is used as excitation light, and the optical fiber is an optical amplification medium that efficiently amplifies light with an infrared wavelength, and the composition of this optical fiber is according to claim 1. An optical amplifier characterized in that the composition is the same as that of a fiber laser medium.