JP2001119087A - Er-doped optical fiber amplifier - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a high gain and a wide-band width. SOLUTION: Signal lights are incident on one end of an Er-doped optical fiber(EDF) via an optical circulator 21, and excited lights are injected into the EDF 12 via an optical coupler 13 from the other end of the EDF 12, and the signal lights passed the EDF 12 are again made incident on the EDF 12 by an optical return means 21, and emitted light from the EDF 12 are extracted via the optical circulator 21.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

TECHNICAL FIELD The present invention relates to an erbium (E)
The present invention relates to an Er-doped optical fiber amplifier that amplifies by passing signal light while pumping light is injected into an optical fiber doped with r).

[0002]

2. Description of the Related Art In a conventional Er-doped optical fiber amplifier, as shown in FIG. 3, signal light (incident light) is incident on one end of an Er-doped optical fiber (EDF) 12 via an optical isolator 11 and is Er-doped. A wavelength division type optical coupler 13 is coupled to the other end of the optical fiber 12, and excitation light from an excitation laser 14 is injected into the Er-doped optical fiber 12 via the optical coupler 13. The signal light that has passed through the Er-doped optical fiber 12 and has been amplified passes through the optical coupler 13 and is output as output light via the optical isolator 15.

[0003] The crosses in the figure indicate the coupling of optical fibers. Er-doped optical fiber 12 is made of erbium ions (E
(r ³⁺ ) doped in the core of the optical fiber, and the concentration of Er is, for example, 900 ppm. The length of the Er-doped optical fiber 12 is relatively short, for example, 13 m. The excitation light (pump light) is 1465, which is the absorption wavelength of the Er-doped optical fiber 12.
nm or 980 nm and for example 10 mW
Of the degree of power.

[0004] The excitation laser 14 is provided with an optical isolator to prevent light from entering from outside. This conventional Er-doped optical fiber amplifier has an amplification band of 1530-1565 nm, that is, a bandwidth of 35
nm, which was relatively narrow. However, although a wavelength division multiplexing (WDM) transmission method is used in the optical communication method, a wideband optical amplifier is desired to increase the communication capacity.

In order to widen the amplification bandwidth of an Er-doped optical fiber amplifier, for example, as shown in FIG. 4 corresponding to FIG. It is conceivable to use a laser having such a long length and a laser having a large output of several hundred mW as the pumping laser 14. In FIG. 4, the optical coupler 13 is provided on the incident side of the Er-doped optical fiber 12 unlike FIG.

[0006]

As described above, the conventional Er-doped optical fiber amplifier has a relatively narrow amplification bandwidth. On the other hand, in order to widen the amplification bandwidth, it is necessary to remarkably increase the length of the Er-doped optical fiber and significantly increase the power of the pump light so as to sufficiently pump the long Er-doped optical fiber. There was a problem that it was large and expensive.

[0007]

According to the present invention, there is provided optical feedback means for returning signal light having passed through an Er-doped optical fiber to the Er-doped optical fiber.

[0008]

FIG. 1 shows an embodiment of the present invention.
Parts corresponding to those in FIG. 3 are denoted by the same reference numerals. As the Er-doped optical fiber (EDF) 12, a slightly longer one such as 35 m or more is used. The signal light (incident light) that has passed through the optical isolator 11 is incident on the port P1 of the optical circulator 21 and is incident on one end of the Er-doped optical fiber 12 from the port P2 of the optical circulator 21 through the optical fiber. In the case where a wavelength division optical coupler 13 is provided on the other end side of the Er-doped optical fiber 12, excitation light from the pumping laser 14 is incident on the Er-doped optical fiber 12 via the optical coupler 13. . In this example, a pump light having a wavelength of 1465 nm and a power of 10 mW is used as the excitation light. E of the optical coupler 15
Optical feedback means 22 is coupled to the side from which the signal passing through the r-doped optical fiber 12 is emitted. As shown in the drawing, the optical feedback means 22 branches one end of one optical fiber 22a into two optical fibers 22b and 22c, and connects the other ends of the branched optical fibers 22b and 22c to a coupling part 22d. The optical fiber loop reflector is configured by being coupled to each other.

The signal light that has passed through the Er-doped optical fiber 12 and reached the optical fiber 22a through the optical coupler 13 is split into optical fibers 22b and 22c.
After going around the loop composed of the optical fibers 22b and 22c, the optical fiber 22a returns to the optical fiber 22a, and is combined with each other.
Through the Er-doped optical fiber 12, pass through the Er-doped optical fiber 12, enter the port P2 of the optical circulator 21, exit from the port P3 of the optical circulator 21, and enter the optical isolator 15 And emitted as emission light.

The signal light thus input is amplified through the Er-doped optical fiber 12, then passes through the Er-doped optical fiber 12 again by the optical feedback means 22, and is further amplified and emitted. Compared with the conventional Er-doped optical fiber amplifier, when the length of the Er-doped optical fiber 12 is the same, the power of the pumping light is the same, and the parameters are the same, a larger amplification gain than the conventional one can be obtained.

In particular, by setting the parameters so that the amplification gain is saturated, a large gain and a wide amplification bandwidth can be obtained. By the way, Er
Erbium concentration is 900p as doped optical fiber 12
pm, a length of 55 m, an excitation light having a power of 10 mW and a wavelength of 1465 nm, and an ASE (Amplified Spontaneous Emission) spectrum with and without optical feedback means 22. The measurement was performed, and the results are shown in FIG. FIG. 2A is provided with the optical feedback means 22, and FIG. 2B is provided with no optical feedback means 22. Figure 2 for easy comparison
FIG. 2C shows a superposition of A and FIG. 2B. From these figures, it can be seen that the 3 dB lowering bandwidth is significantly wider than the one without the optical feedback means 22 and the characteristic of ± 1 dB change or less over the bandwidth of 40 nm or more. The reason why the gain is flat and the bandwidth is wide is considered that the gain is saturated. It has been confirmed that the power of the pumping light may be about 6 mW if the optical feedback means 22 is provided and if the same characteristics as in FIG. 2B are sufficient.

In the above description, the optical feedback means 22 is not limited to the optical fiber loop reflector. For example, an optical fiber mirror in which a reflector such as a metal foil is attached to one end surface of the optical fiber is used. The transmitted signal light may be configured to be reflected by the reflector of the optical fiber mirror and to be incident on the Er-doped optical fiber 22 again. Other optical feedback means may be used.

The optical coupler 13 may be provided on the optical circulator 21 side of the Er-doped optical fiber 12, and the excitation light may be injected into the Er-doped optical fiber 12 from the optical circulator 21. However, as shown in FIG.
When the pumping light is injected into the Er-doped optical fiber 12 from the optical feedback means 22 side, a gain with higher amplification gain, better flatness, and wider bandwidth can be obtained.

The Er concentration is not limited to 900 ppm, but is changed according to the intended gain characteristic.
The length of the r-doped optical fiber 12 and the power and wavelength of the pump light are also changed according to the desired gain characteristics. According to the present invention, the pump light having a wavelength of 1465 nm is used for 1560 to 1
It was confirmed that amplification with a 620 nm bandwidth of 60 nm was possible. The wavelength of the excitation light is set to 1480 n as in the conventional case.
The effect of the present invention can be obtained by selecting various parameters for m. Instead of the optical circulator 21, the input light and the output light can be separated by another means such as a light directional coupler.

[0015]

As described above, according to the present invention, the optical feedback means is provided, and the signal light having passed through the Er-doped optical fiber is again incident on the Er-doped optical fiber, so that a relatively short Er-doped optical fiber can be obtained. Using doped optical fiber, and
A high gain can be obtained even with a low power pumping light, and a wide amplification bandwidth can be obtained.

[Brief description of the drawings]

FIG. 1 is a diagram showing an embodiment of the present invention.

FIG. 2 is a diagram showing an experimental result of measuring an ASE spectrum of an Er-doped optical fiber amplifier.

FIG. 3 is a diagram showing a conventional Er-doped optical fiber amplifier.

FIG. 4 shows a proposed Er-doped optical fiber amplifier.

Claims (3)

[Claims] 1. An optical fiber amplifier for injecting pump light into an Er-doped optical fiber and amplifying signal light incident on the Er-doped optical fiber, wherein the signal light passing through the Er-doped optical fiber is subjected to the E-doped optical fiber.
An Er-doped optical fiber amplifier, comprising optical feedback means for returning to the r-doped optical fiber. 2. The Er-doped light according to claim 1, wherein the means for injecting the pump light into the Er-doped optical fiber is provided on the optical feedback means side of the Er-doped optical fiber. Fiber amplifier. 3. The magnitude of the power of the pumping light is equal to the E
3. The Er-doped optical fiber amplifier according to claim 1, wherein the optical amplification gain in the r-doped optical fiber is selected so as to be saturated.