JPH0450140A - Optical fiber for amplification - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION <Industrial Application Field> The present invention relates to an amplification optical fiber used as an optical amplification element such as an optical amplifier or a laser.

<Prior Art> In optical fiber communication systems currently in practical use, repeating optical amplifiers are installed at predetermined distances to compensate for optical signal attenuation due to optical fiber loss. In this optical amplifier, an optical signal is converted into an electrical signal by a photodiode, etc., the signal is amplified by an electronic amplifier, and then converted into an optical signal by a semiconductor laser (LD), etc., and sent out again to an optical fiber transmission line. ing.

However, in an optical amplifier with such a configuration, it is necessary to convert the optical signal back into an electrical signal and then convert it back into an optical signal, so there is a lot of connection loss with the optical fiber, and the overall size of the device increases. There are some drawbacks such as:

Therefore, in recent years, optical amplifiers that utilize the stimulated emission effect have been considered. As shown in FIG. 3, this optical amplifier includes an amplification optical fiber a doped solely with one rare earth element, and a pumping light source such as a semiconductor laser for pumping the amplification optical fiber a. The signal light transmitted through the transmission optical fiber and the excitation light from the excitation light source are mixed by a multiplexer C, and these lights are transferred to the amplification optical fiber a.
incident on . Then, the rare earth element ions doped in the amplification optical fiber a are excited to a high energy level by the excitation light, and the power of the signal light is gradually amplified by stimulated emission. In addition, d is the connection part of optical fiber a,
f is a filter for passing signal light and cutting off excitation light.

By using this optical amplifier, optical signals can be amplified as they are, resulting in low noise, good coupling with transmission optical fibers and low connection loss, and the equipment can be made smaller and less expensive. It has advantages such as:

Incidentally, optical fibers for optical transmission are required to have excellent characteristics such as transmission loss, coefficient of thermal expansion, mechanical strength, and durability, and quartz-based fibers are preferred as those that meet these requirements. It is. It is known that this silica-based optical fiber has low transmission loss in the 1.55 μm wavelength band. Therefore, when using signal light in this wavelength band, the amplification optical fiber a should also be adjusted accordingly. It is necessary to select and dope a rare earth element with good amplification characteristics. An example of a rare earth element that has such amplification characteristics is Er (erbium). Therefore, in the conventional technology, the core of a silica-based optical fiber or the outer periphery of the core is solely doped with Er to be used as an amplification optical fiber. One thing has been proposed.

<Problems to be Solved by the Invention> In order to increase the amplification factor of the amplification optical fiber, it is considered that - for boat fishing, it is better to increase the amount of rare earth element topes. For this reason, in the conventional technology, even when doping Er, the amount of Er to be doped is increased as much as possible (for example, I
(approximately 000 ppm) was added.

However, the inventors of the present invention have studied in detail the relationship between the amount of Er doped and the amplification factor, and have found that simply increasing the amount of Er doped causes the amplification factor to decrease. That is, even if the amount of Er doped is increased unilaterally, the gain does not increase in accordance with the increased amount.

This is because when excessively doped with Er, Er ions aggregate microscopically in the silica-based optical fiber, resulting in a shortened fluorescence lifetime and so-called concentration quenching, which no longer contributes to increasing the amplification factor. it is conceivable that.

<Means for Solving the Problems> On the other hand, the present inventors have discovered that when the amount of Er doped is conversely made smaller than the value conventionally thought, agglomeration of Er can be avoided.

The present invention has been made in view of the above circumstances, and is intended to avoid concentration quenching and obtain high gain in amplification optical fibers used as optical amplification elements such as optical amplifiers and lasers. It is something to do.

Therefore, in the amplification optical fiber according to the present invention, the amount of Er doped inside the core or the outer peripheral edge of the core is 120
It is characterized by being set to less than ppm.

<Function> In the amplification optical fiber having the above configuration, when the Er doping amount is set to a relatively small amount, microscopic aggregation of Er ions is reduced and uniformly dispersed. Moreover, the absorption efficiency of excitation light can also be improved. Therefore, a decrease in the amplification factor is avoided.

<Embodiment> As shown in FIG. 1, the amplification optical fiber 1 of the embodiment according to the first invention has a quartz glass core 2 having a circular cross section and a quartz glass core 2 having a smaller refractive index than the core 2. A glass cladding 3 is formed, and furthermore, the inside of the core 2 or the outer peripheral edge of the core 2 is doped with both Er and Ge.

The amount of Er doped is set within a range of 120 ppm or less in order to prevent microscopic aggregation in the optical fiber as much as possible.

In this way, microscopic aggregation of Er ions is reduced and the Er ions are uniformly dispersed.

In order to confirm the effect of each amplification optical fiber according to the present invention, the amplification factors of these amplification optical fibers were investigated and the results are shown in FIG. In addition, in this experiment, Er doping amount x optical fiber length was 100100opp, 2000opp
The tendency was investigated when three conditions were set: ppm-m and 500 oppm-m, and the Er doping amount was varied from about 1 ppm to about 1000 ppm. The measurement conditions were to set the power of the 1.48 μm excitation light to approximately 30 μm.
mw, the wavelength of the signal light to be amplified was 1.548 μx, and its power was -30 dBm, and the amplification factors of Er-doped optical fibers of various compositions were plotted against the amount of Er doping. Note that the amount of Ge added in this example is 3 to 15% by weight.

As is clear from this result, the peak of the amplification factor is near the Er doping amount of 100 ppm, and in practical terms
±20 ppm is considered suitable.

However, even if the concentration is 80 ppm or less, the same effect can be obtained if the length is increased. In any case, it is understood that in order to obtain a high amplification factor, the concentration of Er should be 120 ppm or less.

The amplification optical fiber 1 of this embodiment is manufactured by applying a chemical vapor deposition method (CMCVD method) or a VAD method or a tenth-stuffing method.

In addition, in the above embodiment, the case where the core is doped with Ge which increases the refractive index is explained, but conversely, the technology of the present application may be applied when the cladding is doped with F which lowers the refractive index. Of course. In short, any optical fiber with a refractive index difference between the core and cladding can be applied.

<Effects of the Invention> According to the present invention, in an amplification optical fiber used as an optical amplification element such as an optical amplifier or a laser, Er is doped inside the core or the outer periphery of the core, and the Er doping Since the amount was set to t 20 ppm or less, Er
The microscopic aggregation of ions is reduced and the ions are uniformly dispersed.
In addition, a high amplification factor can be obtained.

[Brief explanation of the drawing]

1 and 2 show examples of the present invention, FIG. 1 is a cross-sectional view of an Er-doped optical fiber, and FIG. 2 shows the measurement results of the amplification factor of the amplification optical fiber according to the present invention. FIG. FIG. 3 is a block diagram of the optical amplifier. 1... Optical fiber for amplification, 2... Core, 3... Club.

Claims (1)

[Claims] (1) An amplification optical fiber in which a silica-based glass cladding having a refractive index smaller than that of the core is formed around a silica-based glass core, and the inside of the core or the outer peripheral edge of the core is doped with Er, An amplification optical fiber characterized in that the amount of Er doped is set to 120 ppm or less.