JPH04291972A - Erbium filer for optical amplifier - Google Patents

Abstract

PURPOSE:To suppress spontaneous emission in an optical amplifier using an erbium-doped fiber. CONSTITUTION:A core 22a is doped at it center with Al. A core and part or all of a clad 22b are doped with erbium thereby to perform the purpose.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an erbium-doped fiber for optical amplifiers. In general, optical amplifiers that perform optical direct amplification, which amplifies signals only in the direct optical region without converting optical signals into electrical signals, use optical fibers doped with rare earth elements (such as erbium) and pump light. There are three types: a combination, a semiconductor laser doped with rare earth elements, and a nonlinear effect in the fiber.

Among these, rare earth-doped fiber amplifiers have excellent characteristics such as no polarization dependence, low noise, and low coupling loss with the transmission line (optical fiber), and are used in optical communication systems. This enables a dramatic increase in transmission relay distance and multiple branching of optical signals.

The present invention is an invention in the art of erbium-doped fibers in rare earth element-doped optical fiber amplifiers.

0004

2. Description of the Related Art An erbium-doped fiber will be explained as an example of a conventional rare earth-doped fiber.

FIG. 7 shows the state of the energy order of an erbium-doped fiber. In FIG. 7, an erbium-doped fiber is excited with a pump light of 1.48 μm or 0.98 μm to raise the energy level of erbium to the excited level level.

[0006] There is a natural transition from the excited energy level to the metastable energy level 4I13/2. In this state, a signal light of 1.55% is applied to the erbium element.
Stimulated emission is performed by injecting μm light,
It falls to the reference level of 4I15/2.

[0007] At this time, spontaneous emission light, which is light of a wavelength different from the stimulated emission light, is also output. This spontaneous emission light has an amplification effect on the signal light because the 1.53 to 1.57 μm light is amplified by the energy of the pump light in the Er-doped fiber in the same way as the signal light. is having a negative impact on.

Therefore, as shown in FIG. 5, the Er-doped fiber 22 has aluminum (
(hereinafter referred to as Al), and Er to the core 22.
It is formed by doping a wide range throughout a.

The light intensity distribution within the Er-doped fiber 22 is as shown in FIG. In the figure, aluminum is doped in the center of the core 22a, which reduces fluorescence at a wavelength of 1.53 μm, and Er is doped over a wide range of the entire core 22a, which reduces the pump light within the core 22a. The Er distribution below the threshold does not participate in amplification, but acts on absorption loss near a wavelength of 1.536 μm, as shown in the loss characteristics of erbium with respect to wavelength in FIG.

[0010] For this reason, the spontaneously emitted light with a wavelength of around 1.53 μm is made small within the core.

[0011]

[Problems to be Solved by the Invention] Since the present invention is amplified by the energy of light, in the technique of doping only the core with erbium, in the part below the threshold of the power distribution of the pump light, the spontaneous emission light acts as an absorber, but the suppression of spontaneous emission outside the core due to optical amplification by erbium is insufficient, and there is a problem in that it has an adverse effect on the signal light amplification effect.

The object of the present invention is to provide an erbium-doped fiber having a structure that reduces spontaneous emission.

[0013]

[Means for Solving the Problems] FIG. 1 is a diagram showing the structure of the present invention, and shows a side cross section of an optical fiber doped with erbium.

In the figure, the center of the core 22a is doped with Al. Part or all of the core portion and cladding portion are doped with Er. With this configuration, spontaneous emission light generated in the cladding portion can be suppressed.

[0015]

[Operation] The operation of the present invention will be explained using FIGS. 2 and 4. In FIG. 2, it is shown that at a level higher than the threshold of the pump light, it works for amplification.

When the value of the pump light is below the threshold value, erbium acts as a load, as shown in the characteristics of FIG. Here, as for the spontaneous emission light generated outside the core, erbium attenuates the spontaneous emission light in the 1.536 μm band, as shown in the characteristics of FIG.

Furthermore, since the core is doped with Al, the fluorescence characteristics shift to the 1.55 μm band as shown in FIG. 3, so the fluorescence near 1.536 μm decreases. For this reason, 1
．． The generation of spontaneous emission light in the 536 μm band can be reduced.

[0018]

DESCRIPTION OF THE PREFERRED EMBODIMENTS In the present invention, as shown in FIG. 1, the center of the core 22a of an optical fiber is doped with aluminum Al. The core 22a is doped with erbium in order to perform optical amplification as conventionally.

The cladding 22b is doped with erbium to suppress unnecessary spontaneously emitted light (particularly light in the 1.536 μm band). It is desirable that the amount of erbium doped into the cladding decreases toward the outside of the cladding.

That is, since the optical intensity of the pump light is high in the center of the fiber, doping with a high concentration of erbium is more effective for amplification, and since the optical intensity is low in the outer part of the fiber, it is possible to suppress spontaneous emission light. An appropriate amount of erbium doping is sufficient.

As described above, by doping the cladding region with erbium, spontaneous emission light can be suppressed.

[0022]

Effects of the Invention In an erbium-doped fiber used for an erbium-doped fiber amplifier that directly amplifies light by inputting a signal light and a pump light into an erbium-doped optical fiber, only the center of the core is doped with Al, By doping some or all of the core portion and the cladding portion with Er, spontaneous emission light can be reduced.

[Brief explanation of the drawing]

FIG. 1 is a diagram showing the configuration of the present invention.

FIG. 2 is a diagram illustrating the operation of the present invention.

FIG. 3 is a diagram showing the characteristics of an Al-doped structure.

FIG. 4 is a diagram showing the attenuation characteristics of erbium.

FIG. 5 is a diagram showing a conventional configuration.

FIG. 6 is a diagram illustrating a conventional operation.

FIG. 7 is a diagram showing the state of energy levels in optical amplification.

[Explanation of symbols]

22 Fiber 22a Core 22b Clad

Claims (1)

[Claims] Claim 1: In an erbium-doped fiber used for an erbium-doped fiber amplifier that directly amplifies light by injecting a signal light and a pump light into an erbium-doped optical fiber, aluminum is added only to the center of the core (22a). Doped, the core part and cladding part (
An erbium fiber for optical amplifiers, characterized in that part or all of 22b) is doped with erbium.