JPH0422927A - Optical fiber amplifier - Google Patents

Abstract

PURPOSE:To obtain a highly efficient optical fiber amplifier by providing two 0.98mum band reflecting filters on both the end parts of an optical fiber into which Yb and Er are doped so that the interval between two filters becomes the resonator length of 0.98mum light. CONSTITUTION:The 0.98mum band reflecting filters 14, 16 are respectively inserted into the upstream side end part of a Yb doped optical fiber 10 and the downstream side end part of an Er doped optical fiber 12 and the distance between both filters 14, 16 is set up to the resonator length of 0.98mum light. Since the 0.98mum band reflecting filters 14, 16 are provided on both end parts of the optical fibers 10, 12 and the interval between the filters 14, 16 is set up to the resonator length of 0.98mum light, laser oscillation at 0.98mum can be attained. Thus, the highly efficient optical fiber amplifier can be obtained.

Description

[Detailed Description of the Invention] Summary Regarding an optical fiber amplifier, the purpose of the present invention is to provide an optical fiber amplifier that can efficiently contribute the energy of pumping light to the excitation of <Er. Pumping light with a wavelength of 0°8 μm or more and 0.98 μm or less is incident to excite yb, and the light emitted from yb is absorbed by Er to excite Er, and the signal light in the 1°55 μm band is converted to the light. In an optical fiber amplifier that directly amplifies signal light by inputting it into a fiber, 0.98 μm band reflection filters are provided at both ends of the optical fiber so that the interval between them is the resonator length for light of 0.98 μm; It is configured to oscillate a laser in the 98 μm band.

INDUSTRIAL APPLICATION FIELD The present invention relates to an optical fiber amplifier that directly amplifies signal light by inputting signal light and pumping light (pumping light) into a rare earth-doped optical fiber doped with a rare earth element.

In optical fiber communication systems currently in practical use, repeaters are inserted at fixed distances to compensate for optical signal attenuation due to optical fiber loss. The repeater is configured to convert an optical signal into an electrical signal using a photodiode, amplify the signal using an electronic amplifier, convert it into an optical signal using a semiconductor laser, etc., and send it out again to the optical fiber transmission line. If this optical signal can be directly amplified as an optical signal with low noise, the optical repeater can be made smaller and more economical.

Therefore, research into optical amplifiers that can directly amplify optical signals is actively underway, and the optical amplifiers that are the subject of research can be roughly divided into: ■ Rare earth elements (Er).

There are three types: - A combination of an optical fiber doped with Nd, Yb, etc.) and pumping light, - A semiconductor laser doped with rare earth elements, - A stimulated Raman amplifier and a stimulated Brillouin amplifier that utilize the nonlinear effect in the optical fiber. .

Among these, the optical amplifier that combines rare earth doped optical fiber and pumping light has excellent characteristics such as no polarization dependence, low noise, and low coupling loss with the transmission line, and is used for optical fiber transmission. It is expected that this technology will dramatically increase the transmission relay distance in the system and enable the distribution of optical signals to a large number of users.

BACKGROUND OF THE INVENTION FIG. 4 shows the principle of optical amplification using a rare earth doped optical fiber. 2 is an optical fiber composed of a core 4 and a cladding 6, and the core 4 is doped with erbium (,Er). When pumping light (excitation light) is incident on such an Er-doped optical fiber 2, Er atoms are excited to a high energy level. When a signal light having an energy equal to the energy excited by the Er atoms in the optical fiber 2 excited to a high energy unit enters, the Er atoms rapidly transition to the ground level and guide the light. The power of the signal light gradually increases along the optical fiber, and the signal light is amplified.

As the pumping light for the Er-doped optical fiber amplifier,
Conventionally, the wavelength was 1.48μ because it was easily available.
m semiconductor lasers were used. However, wavelength 1.
Since the 48 μm light is close to the transmitted signal light in the 1.55 μm wavelength band, the amplification factor cannot be set too high.

Therefore, focusing on the fact that absorption in Er-doped optical fiber occurs in the 0.98 μm band in addition to the 1°55 μm band, research is being conducted to amplify signal light in the 1.55 μm band using pumping light of this wavelength. . However, 0.98
Because there is no suitable light source that oscillates laser light in the μm band,
Using a semiconductor laser that oscillates a 0.83 μm laser beam as a bombing light source, 1.55
Optical fiber amplifiers that amplify signal light in the μm band have been proposed.

That is, a Yb-doped optical fiber doped with ytterbium (Yb) and an Er-doped optical fiber doped with erbium (Er) are spliced together, or an optical fiber whose core is doped with Yb and Er is used. Then, Yb is excited with a laser beam having a wavelength of 0.83 μm, and the fluorescence is absorbed by Er to bring Er into an excited state. When signal light with a wavelength of 1.55 μm is input into an optical fiber in which Er atoms are excited, light of the same wavelength is stimulated to be emitted, and the signal light can be directly amplified.

The invention tries to solve 8! However, in the conventional method, the fluorescence generated by exciting Yb with a 0.83 μm laser beam is absorbed by Er to excite Er, but the fluorescence generated by exciting Yb is not only in the 0.98 μm band but also in other regions. Therefore, there was a problem in that the energy of the pumping light that excites Yb was not effectively utilized because the light with wavelengths that are not absorbed by Er was wasted.

The present invention has been made in view of these points, and an object of the present invention is to provide an optical fiber amplifier that can efficiently contribute the energy of pumping light to excitation of <Er.

Means for Solving the Problems In order to solve the above-mentioned problems, the present invention provides Yb and Er
Optical fiber doped with wavelength 0.8 μm or more 0.98
Pumping light of μm or less is incident to excite yb, and the y
By making Er absorb the light emitted from b, Er
In an optical fiber amplifier that directly amplifies a signal light by exciting a 1.55 μm band signal light into the optical fiber, the distance between both ends of the optical fiber is 0.
0°98 so that the cavity length for light of 98 μm
A feature is that a μm band reflection filter is provided to cause laser oscillation in the 0.98 μm band.

Function: A gap of 0.0 mm is placed between both ends of the optical fiber doped with Yb and Er so that the cavity length for light is 0.98 μm.
By providing the 98 μm band reflection filter, most of the energy of the pumping light that excites Yb can be converted into the 0.98 μm band by laser oscillation, and this light can efficiently excite Er.

Embodiments Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.

FIG. 1 is an overall configuration diagram of an embodiment of the present invention. A Yb-doped optical fiber 10 in which Yb is doped in the core and an Er-doped optical fiber 12 in which Er is doped in the core are denoted by reference numeral 13.
Connected by splicing. 0°98 μm band reflection filters 14 and 16 are inserted into the upstream end of the Yb-doped optical fiber 10 and the downstream end of the Er-doped optical fiber 12, respectively, and the distance between the filters is 0.98 μm.
The resonator length is set for light of 98 μm. 18
is an input side optical fiber, into which an optical isolator 26 is inserted. 20 is pumping light # (excitation light source) composed of a semiconductor laser (LD), and has a wavelength of 0.83μ.
m pumping light (excitation light) is emitted. The signal light having a wavelength of 1.55 μm and having been transmitted through the input optical fiber 18 and the pumping light having a wavelength of 0.83 μm from the pumping light source 20 are multiplexed by a multiplexer/demultiplexer 22 . An output side optical fiber 24 is connected to the Er-doped optical fiber 12, and an optical isolator 28 is connected to this output side optical fiber 24.
is inserted.

Thus, pumping light with a wavelength of 0.83 μm is input from the pumping light source 20 via the multiplexer/demultiplexer 22 into the spliced Yb-doped optical fiber 10 and Er-doped optical fiber 12 .

As shown in the energy level diagram of FIG. 2, when 0.83 μm pumping light is incident on the Yb-doped optical fiber 10, Yb atoms are excited to the 0.83 μm energy level; Since the position is unstable, the wavelength is 0.
It generates fluorescence containing 98 μm and transitions to a lower energy level. Of this fluorescence, light in the wavelength band of 0.98 μm is 0.98 μm.
The laser beam is amplified by a laser resonator composed of 98 μm band reflection filters 14 and 16 to cause laser oscillation, and is input into the Er-doped optical fiber 12. This laser beam is Er
It is absorbed by the atom and excites the Er atom to the 0.98 μm energy level, but since this energy level is unstable, it immediately transitions to the 1.55 μm energy level, and the Er atom at this level increases. This results in population inversion between the ground level and the ground level.

In such a state, the optical isolator 26, the multiplexer/demultiplexer 22, the filter 14, and the Yb-doped optical fiber 10 are installed.
into the Er-doped optical fiber 12 via a wavelength of 1.55μ
When the m-band signal light is input, this signal light is gradually amplified along the Er-doped optical fiber 12 and passed through the filter 16.
and the output side optical fiber 24 via the optical isolator 28
It is emitted to

As described above, in this embodiment, since the bombing light with a wavelength of 0.83 μm emitted from the bombing light source 20 can be efficiently converted into light with a wavelength of 0.98 μm by laser oscillation, the bombing light emitted from the bombing light source 20 Wavelength 0.
Efficient use of the energy of the 83 μm pumping light can be achieved.

FIG. 3 shows an overall configuration diagram of another embodiment of the present invention. In this embodiment, a doped optical fiber 30 in which the core of the optical fiber is doped with Yb and Er is used, and both ends of the doped optical fiber 30 have a distance between them with a wavelength of 0.98 μm.
The resonator length for the light is set to 0,98
μm band reflection filters 14 and 16 are inserted. The other configuration of this embodiment is the same as that of the embodiment shown in FIG. 1, so the explanation thereof will be omitted.

Effects of the Invention As described in detail above, the present invention uses laser oscillation to generate most of the energy of the pumping light that excites Yb by 0.98μ.
It is possible to obtain an efficient optical fiber amplifier that can convert to m-band and contribute to excitation of Er.

[Brief explanation of the drawing]

Figure 1 is an overall configuration diagram of an embodiment of the present invention, Figure 2 is an energy level diagram, Figure 3 is a configuration diagram of another embodiment of the invention, and Figure 4 is the principle of optical amplification using a rare earth doped optical fiber. FIG. 0...Yb-doped optical fiber, 2...Er-doped optical fiber, 4.16...0.98 μm band reflection filter, 0...
Bumping light source, 2... multiplexer/demultiplexer.

Claims (1)

[Claims] 1. Optical fiber doped with Yb and Er (10, 12,
30) to excite Yb by injecting pumping light with a wavelength of 0.8 μm or more and 0.98 μm or less, and excite Er by causing Er to absorb the light emitted from Yb.
5 μm band signal light is connected to the optical fiber (10, 12, 30)
In an optical fiber amplifier that directly amplifies signal light by making it incident on the optical fiber, there is a resonator at both ends of the optical fiber (10, 12, 30) with a gap of 0.98 μm, which corresponds to the resonator length for light.
．． A 98 μm band reflection filter (14, 16) is provided, and a 98 μm band reflection filter (14, 16) is provided.
An optical fiber amplifier characterized in that it oscillates a laser in the 98 μm band. 2. The optical fibers (10, 12, 30) are constructed by splicing and connecting a Yb-doped fiber (10) doped with Yb and an Er-doped fiber (12) doped with Er, and connect the Yb-doped fiber (10) upstream. An optical fiber amplifier characterized in that it is arranged on the side so that pumping light and signal light are incident thereon.