JPH09252157A - Optical fiber amplifier - Google Patents

Abstract

PROBLEM TO BE SOLVED: To make the optical output levels of signals flat in multi-wavelength transmission characteristics, without increasing the number of components by superimposing the gain characteristic of a rare earth-added optical fiber amplifier for signal lights on the insertion loss characteristic of a WDM coupler for combining an exciting light with the signal lights. SOLUTION: An input signal light inputted to the front of a rare earth added fiber 61 passes through an optical fiber 2 of a WDM coupler 41 optically coupled with the back of the fiber 61 to an optical fiber 3. An optical fiber 1 of the other output port of the coupler 41 is optically connected to a semiconductor laser (LD) 5, i.e., an exciting light source, thereby inputting the exciting light from LD5 to the back of the fiber 61 through the fiber 2 from the fiber 1. Thus the insertion loss characteristics between the fibers 2 and 3 of the signal path of the coupler 41 are comlementary to result in an approximately constant wavelength characteristic of the light output.

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, and more particularly to an optical fiber amplifier suitable for use in a multi-wavelength transmission device.

[0002]

2. Description of the Related Art Recently, a method of inputting multi-wavelength signals into one transmission line to increase the capacity of transmission information is becoming widespread. Along with this, it has become more common to input a plurality of optical signals to an optical fiber amplifier and use it as a multi-wavelength amplifier. However, the conventional optical fiber amplifier is optimally designed mainly for transmitting signal light of one wavelength.

Therefore, in conventional multi-wavelength transmission,
WDM (Wavelength Divison Multipl) as shown in Fig. 3.
exing) The coupler 42 is used. This WDM coupler 4
2 is a signal light and a semiconductor laser (LD) which is an excitation light source
5 for combining the excitation light emitted from 5,
It is optimally designed so that the insertion loss between the optical fiber 2 and the optical fiber 3 in the signal light transmission line has almost no wavelength characteristic in a certain wavelength band.

The pumping light from the LD 5 optically connected to the optical fiber 1 is input from the optical fiber 1 which is the other port of the WDM coupler 42. The pumping light is input from the optical fiber 2 to the erbium-doped fiber (EDF) 62 placed immediately before the WDM coupler 42, amplifies the optical signal input from the front of the erbium-doped fiber 62, and the amplified output signal light is It is output from the optical fiber 3.

As shown in FIG. 4A, the erbium-doped fiber 62 has a wavelength characteristic of amplification (the gain is large on the long wavelength side), and therefore, the light of each wavelength is used in the application of multi-wavelength transmission. When flattening the output level, the slope of the wavelength characteristic of the erbium-doped fiber 62 was minimized.

Further, even in the case of single wavelength amplification in which the signal light wavelength range is wide, the above technique (that is, the inclination of the wavelength characteristic of the optical fiber amplifier is minimized) is used to change the optical output level in the wavelength range. Plans for flattening.

[0007]

The above prior art has the following problems.

The first problem is that the conventional optical fiber amplifier is optimally designed mainly for transmitting signal light of one wavelength. Therefore, when the conventional optical fiber amplifier is used, many That is, it becomes difficult to flatten the optical level of the optical wavelength of each signal of the wavelength.

This is because the wavelength characteristic of loss (see FIG. 4B) of each optical component forming the optical fiber amplifier is superposed, and the superposed one becomes the wavelength characteristic of the optical fiber amplifier. (See FIG. 4C).
Note that the vertical axis of the wavelength characteristics of FIG. 4 is shown on a logarithmic scale, and the wavelength characteristics of FIG. 4 (C) are the gain characteristics of the optical fiber amplifier of FIG. 4 (A) and the WDM of FIG. 4 (B). It is given by the logarithmic sum of the loss characteristics of the signal light path of the coupler.

A second problem is that in the conventional optical fiber amplifier, it is necessary to insert another optical component for flattening the wavelength characteristic into the optical transmission line, so that the number of components is large. It will be.

Therefore, the present invention has been made in view of the above circumstances, and an object thereof is to increase the optical wavelength of each signal in a multi-wavelength transmission characteristic without increasing the number of components of the optical fiber amplifier. It is to flatten the output level.

[0012]

In order to achieve the above object, the present invention provides a gain characteristic of a rare earth-doped optical fiber amplifier for amplifying signal light, and a WDM for multiplexing pump light and signal light.
Provided is an optical fiber amplifier characterized in that the wavelength characteristic of an optical output level formed by superimposing an insertion loss characteristic of a signal light path of a coupler is substantially constant.

In the present invention, the WDM coupler is
In addition to the function of combining the pumping light and the signal light, it is further adjusted so as to compensate for the wavelength characteristic of the signal light path.

[0014]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of the present invention will be described below with reference to the drawings. Referring to FIG. 1, in the embodiment of the present invention, the input signal light is erbium (Er).
³⁺ ), etc., is input from the front of the rare earth-doped fiber 61 doped with rare earth ions, passes through the rare earth-doped fiber 61, and passes through the optical fiber 2 of the WDM coupler 41 optically connected to the rear of the rare earth-doped fiber 61. And is output to the optical fiber 3 which is one of the output side ports of the WDM coupler 41. The optical fiber 1 at the other output side port of the WDM coupler 41 is a semiconductor laser (LD) that is a pumping light source.
5, the pumping light from the LD 5 passes from the optical fiber 1 to the optical fiber 2, and the rare earth-doped fiber 61
Is typed behind. The pumping light from the LD 5 amplifies the signal light input from the front side of the rare earth-doped fiber 61 and is output from the optical fiber 3.

The amplification characteristic of the rare earth-doped fiber 61 and W
The insertion loss characteristics between the optical fibers 2 and 3 which are the signal light paths of the DM coupler 41 are made complementary, and the wavelength characteristics of the optical output become substantially constant. It should be noted that the present invention is not limited to the backward pumping method shown in FIG. 1, and pumping light may be supplied to the rare earth-doped fiber 61 from the front side thereof via a coupler. Can be obtained.

[0016]

Next, an embodiment of the present invention will be described with reference to the drawings.

FIG. 1 is a diagram showing the configuration of an embodiment of the optical fiber amplifier of the present invention. In this embodiment, a fiber fusion type WDM 41 is used as the WDM coupler.

The fiber fusion-bonded WDM coupler 41 has one optical fiber on the input side and two optical fibers on the output side, and has a function of multiplexing signal light and pump light. The optical fiber 1 on the output side is connected to the LD 5 which is a light source for excitation,
The optical fiber 2 is optically connected to an erbium-doped fiber (EDF) 61 placed immediately before.

The pumping light from the optical fiber 1 passes through the optical fiber 2 and is 1.55 μm input from the front of the EDF 61.
The signal light having a wavelength in the m band is amplified, and the amplified output signal light is output from the optical fiber 3 on the output side of the fiber fusion type WDM coupler 41.

A case where the LD5 in the 1.48 μm band is used as the excitation light will be described. EDF with 1.48 μm excitation
Reference numeral 61 has a wavelength characteristic having a larger gain on the long wavelength side, as shown as the wavelength characteristic in FIG. This wavelength characteristic is expressed by the following equation (1).

G = g (λ) (1)

The wavelength characteristic of the EDF 61 having a steep slope on the long wavelength side as shown in FIG. 2A can obtain a desired slope by changing the power of the pumping light. .

On the other hand, the signal light path of the fusion-bonded WDM coupler 41, that is, the wavelength characteristic of the insertion loss between the optical fibers 2 and 3 is expressed by the following equation (2) (see FIG. 2B). . That is, the fusion-bonded WDM coupler 41 shown in FIG.
The loss characteristic is adjusted as shown in FIG.

F = f (λ) (2)

In this embodiment, the relationship of the following expression (3) is established between the above expressions (1) and (2).

G (λ) × f (λ) = constant (3)

In the present embodiment, the wavelength characteristics of the loss of the optical components constituting the optical fiber amplifier are superposed, and the wavelength characteristics of the optical output level are as shown in FIG. 2 (C). It is possible to flatten the optical output level of each signal light wavelength when performing multi-wavelength amplification by the amplifier.

[0028]

As described above, according to the present invention,
There is a remarkable effect that the optical output level of each signal light wavelength at the time of multi-wavelength amplification can be flattened.

This is because, in the present invention, the wavelength characteristic of the optical component used in the optical fiber amplifier and another optical component having a characteristic for compensating the wavelength characteristic of this optical component are combined and inserted.

Further, according to the present invention, since the WDM coupler has the wavelength characteristic for compensating for the wavelength characteristic of the rare earth-doped fiber, the characteristic can be optimized without increasing the number of the conventional optical components. Have.

[Brief description of drawings]

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

FIG. 2 is a diagram illustrating an embodiment of the present invention.

FIG. 3 is a diagram for explaining a conventional optical fiber amplifier.

FIG. 4 is a diagram for explaining a conventional optical fiber amplifier.

[Explanation of symbols]

1, 2, 3 Optical fiber 41 Fiber fusion type WDM coupler 42 WDM coupler 5 Excitation light source (LD) 61, 62 Er ³⁺ doped fiber

Claims (2)

[Claims] 1. An optical output level obtained by superposing gain characteristics of a rare earth-doped optical fiber amplifier for amplifying signal light and insertion loss characteristics of a signal light path of a WDM coupler for multiplexing pumping light and signal light. The optical fiber amplifier is characterized in that the wavelength characteristics of are substantially constant. 2. The WDM coupler, in addition to a function of combining pumping light and signal light, is further adjusted to compensate for wavelength characteristics of the signal light path.
An optical fiber amplifier as described.