JPH06169122A - Optical fiber amplifier - Google Patents

Abstract

(57) [Summary] [Purpose] Elubum Doped Fiber (ED
Provided is an optical fiber amplifying device in which the generation of distortion due to the wavelength dependence of the gain of F) is minimized. [Configuration] ED for amplifying signal light by input of pumping light
In an optical fiber amplifier including F2, 5 and light sources 8, 9 for generating pumping light, a plurality of EDFs 2, 5 are
The signal lights are arranged in series so as to sequentially pass through the respective EDFs 2 and 5. The wavelength dependence of the gain of the EDF has its characteristics shifted depending on the intensity of the signal light or the intensity of the pumping light. Therefore, the intensity of the signal light input to the EDFs arranged in series is
Since the latter EDF becomes stronger, the wavelength dependence of the gain of the previous EDF 2 and the wavelength dependence of the gain of the latter EDF 5 cancel each other out, and distortion based on the wavelength dependence is suppressed.

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 used for optical communication or the like, and more particularly to suppressing distortion generated when signal light is accompanied by wavelength fluctuation.

[0002]

2. Description of the Related Art A conventional optical fiber amplifying apparatus, as shown in FIG. 7, transmits a signal light by inputting first and second optical isolators 1 and 4 for passing an optical signal only in one direction and pumping light. Amplifying Elubum Doped Fiber (E
DF) 2 and a high-power laser (LD) that is a light source of excitation light
8 and the excitation light input from point E through EDF2
And a wavelength synthesizing coupler (WDM) 3 for outputting the output light of the EDF 2 to the point D, and connecting them with an optical fiber.

In this device, the optical signal input from the point A passes through the optical isolator 1 and is input to the EDF 2. On the other hand, the pumping light output from the high power laser 8 is input to the EDF 2 through the wavelength combining coupler 3. The EDF 2, which has an amplification characteristic by the input of the pumping light, amplifies the signal light and outputs it through the wavelength combining coupler 3 and the optical isolator 4. The optical isolators 1 and 4 prevent the optical fiber amplifier from oscillating due to reflection from the outside.

As described above, the conventional optical fiber amplifier can amplify the input signal light and output it.

[0005]

However, in the conventional optical fiber amplifier, as shown in FIG. 6D, when the wavelength of the input signal light changes with time, the output optical signal is changed. There is a problem that distortion occurs. This is shown in FIG.
As shown in (a), this is because the EDF gain has wavelength dependence. When the input signal light is accompanied by wavelength fluctuation (FIG. 6C), the EDF gain at each time is As a result, the output signal of the EDF is distorted (FIG. 6B).

SUMMARY OF THE INVENTION The present invention is intended to solve such a conventional problem, and an object of the present invention is to provide an optical fiber amplifying device in which the generation of distortion due to the wavelength dependence of the gain of EDF is minimized.

[0007]

Therefore, according to the present invention, an elubeam that amplifies signal light by inputting pump light is used.
In an optical fiber amplifier including a doped fiber (EDF) and a light source that generates pumping light, a plurality of EDFs are arranged in series so that signal light sequentially passes through each EDF.

Further, the intensities of pumping light input to a plurality of EDFs are set so that the wavelength dependences of the EDF gains cancel each other out.

Further, branching means for branching the pumping light generated by the light source is provided, and the pumping light branched by the branching means is input to a plurality of EDFs.

[0010]

The wavelength dependence of the gain of the EDF shifts its characteristics depending on the intensity of the signal light or the intensity of the pump light. Therefore, since the intensity of the signal light input to the EDFs arranged in series becomes stronger as the latter EDF, the wavelength dependence of the gain of the previous EDF and the wavelength dependence of the gain of the latter EDF cancel each other out, Distortion due to wavelength dependence is suppressed.

Further, the wavelength dependence of the gain of the above EDF,
By adjusting the intensity of the pumping light input to each EDF so that the wavelength dependence of the gain of the subsequent EDF cancels each other, distortion based on the wavelength dependence can be suppressed.

Further, the intensity of the pumping light input to each EDF can be easily adjusted by changing the branching ratio of the branching means.

[0013]

【Example】

(First Embodiment) As shown in FIG. 1, the optical fiber amplifier according to the first embodiment of the present invention has two EDFs 2, 5
, Two wavelength synthesizing couplers 3 and 6, two high-power lasers 8 and 9 for outputting pumping light, and an optical isolator 1 arranged before and after and in the middle of the device for limiting the light passage direction to one direction, 4 and 7 are provided.

In this device, the optical signal input from the point A passes through the optical isolator 1 and is input to the EDF 2. On the other hand, the pumping light output from the high-power laser 8 enters the wavelength combining coupler 3 from the point E, exits from the point C, and enters the EDF 2. The EDF 2 having an amplification characteristic by the input of the pumping light amplifies and outputs the signal light, and this signal light passes from the point C of the wavelength combining coupler 3 to the point D and passes through the optical isolator 4. , Input to EDF5.

The signal light input to the EDF 5 is the EDF.
Since the signal light is amplified by 2, it has a higher intensity than the signal light input to the EDF 2. Like the EDF 2, the EDF 5 amplifies the input signal light by the excitation light of the high-power laser 9, and the amplified signal light is output through the wavelength combining coupler 6 and the optical isolator 7.

Looking at the relationship between the wavelength dependence of the gain of the EDF and the intensity of the signal light, as shown in FIG. 3, as the strength of the signal light increases, the wavelength dependence of the gain of the EDF becomes It tends to shift to the long wavelength side.

Therefore, when the gain of the EDF 2 has the wavelength dependence of the solid line in FIG. 5, the wavelength dependence of the gain of the EDF 5 that amplifies the signal light having high intensity shows the characteristic of the dotted line in FIG. . As a result, there is a region where the wavelength dependences of the gains of EDF2 and EDF5 cancel each other, and ED
The occurrence of distortion due to the wavelength dependence of F gain is reduced.

As described above, by setting the intensities of the signal lights input to the two EDFs so that the wavelength dependences of the gains of the two EDFs cancel each other out, the distortion caused by the wavelength fluctuations of the signal lights in the optical fiber amplifying apparatus is eliminated. Occurrence can be suppressed.

The wavelength dependence of EDF gain is shown in FIG.
As shown in, the wavelength dependence of the EDF gain shifts to the long wavelength side as the pump light intensity changes and the pump light intensity decreases.

Therefore, the output intensity of the high power lasers 8 and 9 is changed to set the wavelength dependence of the gain of the EDF 2 to the characteristic shown by the solid line in FIG. 5, while the wavelength dependence of the gain of the EDF 5 is set in the same FIG. By setting to the characteristic of the dotted line, the wavelength dependence of both gains is canceled and the generation of distortion due to the wavelength dependence of EDF gain is suppressed.

Further, by performing the adjustment of the pumping light intensity together with the adjustment of the intensity of the signal light input to the EDF, the distortion can be suppressed more effectively.

(Second Embodiment) In the optical fiber amplifier of the second embodiment, as shown in FIG. 2, the pump light generated by the high-power laser 8 is split into two by an optical coupler 10, and a wavelength synthesizing coupler is used. Fill in 3 and 6. The other structure is the same as that of the apparatus of the first embodiment (FIG. 1).

In this device, the intensity of the excitation light input to the EDF 2 and the EDF 5 can be adjusted by changing the branching ratio of the optical coupler 10. Therefore, EDF
The pumping light intensity can be easily adjusted to cancel the wavelength dependence of the gain.

In the first and second embodiments, the case where two EDFs are provided in the optical fiber amplifying device has been described. However, two or more EDFs are installed so that the wavelength dependence of the gain of the EDF is canceled out. It is also possible to set to.

[0025]

As is apparent from the above description, the optical fiber amplifier of the present invention can suppress the occurrence of distortion caused by the wavelength dependence of gain.

[Brief description of drawings]

FIG. 1 is a block diagram showing the configuration of an optical fiber amplifier according to a first embodiment of the present invention,

FIG. 2 is a block diagram showing a configuration of an optical fiber amplifier according to a second embodiment of the present invention,

FIG. 3 is a graph showing the relationship between the wavelength dependence of EDF gain and the intensity of signal light,

FIG. 4 is a graph showing the relationship between wavelength dependence of EDF gain and pump light intensity;

FIG. 5 is a graph showing wavelength dependence of EDF gain in the amplification device of the present invention,

FIG. 6 is a graph showing wavelength dependence in a conventional optical fiber amplifier,

FIG. 7 is a block diagram showing a configuration of a conventional optical fiber amplifier.

[Explanation of symbols]

 1, 4, 7 Optical isolator 2, 5 Elubum-doped fiber (EDF) 3, 6 Wavelength combining coupler (WDM) 8, 9 High-power laser 10 Optical coupler

Claims (3)

[Claims] 1. An optical fiber amplifier comprising an elubeam-doped fiber that amplifies signal light by inputting pumping light, and a light source that generates the pumping light. An optical fiber amplifying device, which is arranged in series so that signal light sequentially passes through each elubeam-doped fiber. 2. The intensity of the pumping light input to the plurality of elubumu-doped fibers is set so that the wavelength dependences of the gains in the elubum-doped fibers cancel each other out. 1. The optical fiber amplifier according to 1. 3. A branching means for branching the pumping light generated by the light source is provided, and the pumping light branched by the branching means is input to the plurality of elubeam-doped fibers. 2. The optical fiber amplifying device according to item 2.