JPH04322228A - Optical fiber amplifier - Google Patents

Abstract

PURPOSE:To excite an optical fiber with sufficient excitation density and to level the excitation state of the core part of a multi-mode fiber while using a coherent light source as to the optical fiber amplifier which uses a rare-earth doped multi-mode optical fiber. CONSTITUTION:Excitation light beams from plural light sources 1a, 1b, and 1c are multiplexed by an optical multiplexer 5 and supplied to the multi-mode optical fiber 7 whose core is doped with rare earth to excite this multi-mode optical fiber. Consequently, the number of excited modes increases statistically to enable multi-mode operation.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical fiber amplifier in which an optical fiber whose core is doped with a rare earth element is excited by a suitable light source to obtain an inversion level, thereby amplifying light.

0002

[Background Art] In recent years, optical amplifiers using optical fibers doped with rare elements, especially erbium (Er), have made remarkable progress (for example, Nakazawa, "Optical amplification using Er-doped optical fibers and its applications", Physics, Vol. 59, No. 9 (1990), P1175-1192, Horiguchi, "Optical Fiber Amplifier", Optics, Vol. 19, No. 5 (1990)
), see pages 276-282, etc.).

Research and development of these Er-doped fiber amplifiers has been carried out mainly with long-distance optical communications in mind, and therefore optical amplification of single-mode optical fiber systems has become a central issue.

However, optical amplification is difficult to achieve, for example, in an optical LAN (
local area network) and optical CATV (
community antennaelevisi
It is also promising for applications such as compensating for distribution losses in on) systems. Multimode optical fibers, which are easy to handle, are suitable for such short-distance optical communication networks.

[0005]

Problems to be Solved by the Invention When considering the realization of a multimode optical fiber amplifier for optical LAN, the following problems arise.

1) Multimode optical fiber naturally has many modes, for example, a core diameter of 60 μm, N
In a graded index fiber with A (numerical aperture) = 0.2, the number of possible modes is as high as 500 (for example, Noda, "Optical fiber transmission", Institute of Electronics and Communication Engineers (IEICE)).
1978), p. 42. ). To obtain equal gain for any mode, the interior of the core must be uniformly excited. In other words, each mode must be uniformly irradiated with excitation light. However, since laser light has coherence, when a laser light source is used as an excitation light source, it is difficult to uniformly irradiate each mode with excitation light.

2) The multimode fiber has a core diameter of 5
Compared to a single mode fiber, which has a large diameter of 0 to 60 μm and a core diameter of about 10 μm, it is necessary to irradiate several tens of times as much excitation light to obtain the same excitation density.

The present invention was devised to solve the above-mentioned problems, and an object of the present invention is to make it possible to pump a multimode optical fiber with sufficient pumping density. Further, the present invention uses a coherent light source and
The purpose is to equalize the excited state of the core of a multimode fiber.

[0009]

[Means for Solving the Problems] The optical fiber amplifier of the present invention combines a multimode optical fiber whose core is doped with rare earth and pumping light from a plurality of light sources and supplies the combined pump light to the multimode optical fiber. and a light combining means for exciting the multimode optical fiber.

0010

[Operation] By combining excitation light from a plurality of light sources, the excitation density increases and the multimode fiber is sufficiently excited. Also, even when using a laser as a light source,
By combining excitation light from a plurality of light sources, the coherence of each excitation light is reduced. This results in
The number of modes excited in the rare earth doped fiber is statistically increased, allowing multimode operation.

[0011]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, features of the present invention will be specifically explained based on embodiments with reference to the drawings.

FIG. 1 shows a schematic configuration of an embodiment of the optical fiber amplifier of the present invention. Multiple independent light sources 1a, 1b
, 1c via the respective input optical fibers 2a, 2b, 2c, and the input signal light supplied from the signal input end 3 via the input optical fiber 4, are multiplexed by a multiplexer 5. , pumps the rare earth doped fiber 7 through the optical isolator 6. The multiplexer 5, as shown in FIG.
It is constructed by forming an optical waveguide 5b on a glass or polycarbonate substrate 5a by ion selection or selective polymerization.

The signal light amplified by the excitation of the rare earth doped fiber 7 passes through a narrow band filter 8 and reaches an output end 9, where an output signal light is obtained.

Each of the light sources 1a, 1b, and 1c has the same configuration. Taking the light source 1a as an example, as shown in FIG. 3, for example, as shown in FIG. 12 and irradiates the core portion 13 of the multimode input optical fiber 2a. Note that 14 is a cladding portion of the input optical fiber 2a.

As mentioned above, a plurality of light sources 1a, 1b, 1c
The number of excited modes is statistically increased by combining the light from the light source and exciting the rare earth-doped fiber 7. That is, since the phases of the lights from the plurality of light sources 1a, 1b, and 1c become different from each other, the number of excited modes increases. Furthermore, the amount of excitation light also increases compared to the case of a single light source. That is, by combining light from a plurality of individually coherent light sources to form an excitation light source, the overall coherence is reduced, and at the same time, the amount of light is increased.

Next, another configuration example of a light source used in an optical fiber amplifier is shown in FIG. The example shown in FIG. 4 differs from the light source shown in FIG. 3 in that a laser diode array 15 is used as each light source 1a, 1b, 1c. As shown in FIG.
A light emitting element formed on one chip at intervals of 10 μm is used as a light source. In order to prevent the laser diodes from being phase-synchronized, for example, each diode may be placed in an optical waveguide with a relatively high confinement effect.

[0017] As a result, the three input optical fibers 2a,
Three laser light sources are arranged for each of 2b and 2c. Therefore, by combining the lights from a total of nine independent laser light sources, it is possible to further reduce the coherence of the excitation light and increase the amount of light.

If the number of multiplexed waves in the multiplexer 5 is further increased, the coherence can be further reduced and the amount of light can be increased. Increasing the number of arrays is limited by the fact that the core diameter of the optical fiber is 50 to 60 μmm, so it is difficult to increase the number of arrays any further with current manufacturing technology. However, as manufacturing technology improves,
If the distance between laser diodes can be made sufficiently shorter than 10 μm, it is possible to further increase the number of arrays.

[0019]

[Effects of the Invention] As described above, in the present invention, since the light from multiple light sources is combined to excite the multimode rare earth doped fiber, a coherent light source such as a laser is used as the single light source. Even in this case, the light is excited with reduced coherence. Therefore, the number of excited modes increases, and the excitation of the core can be leveled. Furthermore, since the light is combined, the amount of pumping light increases, and a large-diameter multimode optical fiber can be pumped with sufficient pumping density.

[Brief explanation of drawings]

FIG. 1 is an optical wiring diagram showing the overall configuration of an optical fiber amplifier of the present invention.

2 is a schematic plan view showing a configuration example of an optical multiplexer used in the optical fiber amplifier shown in FIG. 1. FIG.

3 is an enlarged view of a main part showing an example of the configuration of a light source used in the optical fiber amplifier shown in FIG. 1. FIG.

4 is an enlarged view of main parts showing another example of the configuration of a light source used in the optical fiber amplifier shown in FIG. 1. FIG.

[Explanation of symbols]

1a, 1b, 1c light source, 2a, 2b, 2c input optical fiber, 3 signal input end, 4 input optical fiber, 5 multiplexer, 5a substrate, 5b waveguide, 6
Optical isolator, 7 Rare earth doped fiber, 8
Narrowband filter, 9 Output end, 10 Semiconductor laser diode, 11 Pumping light, 12 Lens, 1
3 core part, 14 clad part, 15 laser diode array, 15a, 15b, 15c laser diode

Claims (1)

[Claims] 1. A multimode optical fiber having a core doped with a rare earth element, and a light synthesizing means for combining excitation light from a plurality of light sources and supplying the combined excitation light to the multimode optical fiber to excite the multimode optical fiber. fiber optic amplifier.