JPH06302921A - Optical amplifier - Google Patents

Abstract

PURPOSE:To make distortionless analog transmission possible by a method wherein wavelength dependency in the wavelength region of optical signals to be transmitted is made flat, by combining and connecting in series two or more kinds of optical fiber amplifiers containing different amplification medium, so as to cancel the wavelength dependencies. CONSTITUTION:Optical fiber amplifier 1a, 1b are constituted of erbium-doped optical fibers, have different host glass compositions, and are different in wavelength dependency of the gain. At the wavelength of 1.55mum, the amplifier 1a has wavelength dependency of 0.03db/m/nm, and the amplifier 1b has wavelength dependency of 0.01db/m/nm. When the optical fiber amplifiers 1a and 1b are connected in series under the condition that the fiber length ratio is 1:3, the flat characteristics at a wavelength of 1.55mum can be obtained. Fusion-bonding is desirable for the connection of the optical fiber amplifiers 1a and 1b. An optical isolator 2 restrains oscillation due to excited light from a excited light source 3, return light, etc.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical amplifying device using an optical fiber amplifier doped with a rare earth element ion exhibiting an optical amplifying effect by photoexcitation, and is mainly used for amplifying an optical signal in optical communication. It is what is done.

[0002]

2. Description of the Related Art An optical fiber amplifier doped with rare earth element ions is convenient because it can amplify optical power without optical-electrical conversion and is an essential device for future optical communication. In particular, an erbium-doped fiber amplifier using, for example, erbium as an amplifying medium has a gain in the 1.55 μm band used for optical communication, and is therefore being actively researched.

Since the gain of an optical fiber amplifier depends on absorption and emission cross sections, which are parameters peculiar to the amplification medium,
The gain of the optical fiber amplifier also has a wavelength dependence according to the wavelength dependence of the absorption and emission cross sections.

[0004]

In analog communication, there is a problem that an amplified optical signal is distorted by the above wavelength dependence of gain and chirping of a light source. Since the distortion of the optical signal depends on the wavelength dependence of the small signal gain, the problem of distortion remains even if the optical amplifier is saturated.

An object of the present invention is to realize an optical amplifier device in which the wavelength dependence of gain is eliminated.

[0006]

As a result of repeated studies to solve the above problems, the present inventors have found that in order to eliminate the wavelength distortion at the time of analog signal amplification in the optical fiber amplifier, the wavelength λ of the optical signal is eliminated. Wavelength dependence of gain G at ₀ dG / dλ
I knew that I should set 0 to 0. The present invention was developed based on this finding.

That is, the optical amplifying device of the present invention is an optical amplifying device using an optical fiber amplifier, in which two or more kinds of optical fiber amplifiers 1a, 1b ...
Are connected in series so that the wavelength-dependent characteristics of these optical fiber amplifiers 1a, 1b, ... Are cancelled.

[0008]

In the optical amplifying apparatus of the present invention, two or more kinds of optical fiber amplifiers 1a, 1b ... Containing different amplifying media are used so that the wavelength dependence characteristics of these optical fiber amplifiers 1a, 1b. Since it is connected in series by combining
By combining two or more kinds of optical fiber amplifiers 1a, 1b ... With different signs of dG / d.lamda. at an appropriate ratio (length ratio), the optical fiber amplifiers 1a, 1b. dG / dλ = 0 at the wavelength λ ₀
Therefore, the wavelength distortion at the time of analog signal amplification in the optical fiber amplifier can be eliminated.

[0009]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The optical amplifying device of the present invention will be described in detail based on the embodiment of FIG. Optical fiber amplifiers 1a and 1b of FIG.
Are both erbium-doped fibers, but since both have different host glass compositions, the wavelength dependence of gain is different. The respective gains at the time of strong excitation are shown in FIG.
It shows in (b). At the wavelength of 1.55 μm, the optical fiber amplifier 1a is 0.03 dB / m / n as shown in FIG.
m, the optical fiber amplifier 1b is as shown in FIG.
The wavelength dependence of the gain is 0.01 dB / m / nm. Therefore, by connecting the lengths of both the optical fiber amplifiers 1a and 1b at a ratio of 1: 3, it is possible to provide a flat characteristic at 1.55 μm. FIG. 2C shows a gain characteristic when the optical fiber amplifier 1a is connected to 10 m and the optical fiber amplifier 1b is connected to 30 m and strongly pumped.

The optical fiber amplifiers 1a and 1b are preferably connected by fusion. The wavelength dependency of the fiber length and the gain is not limited to the above example, and the wavelength dependency of the gain may be eliminated as a whole.

Reference numeral 2 in FIG. 1 is an optical isolator for suppressing oscillation due to pumping light, return light, etc. from the pumping light source 3, and 4 is a fusion type optical coupler provided on the output side of the optical fiber amplifier 1b. The fusion type optical coupler 4 is for making the light from the excitation light source enter the erbium-doped fiber.

The above description also applies when used with saturated output. That is, when the small signal gain has wavelength dependency, the saturation output wavelength dependency is apparently flat, but the amplified signal is distorted, so that the present invention needs to be applied.

[0013]

According to the optical amplifying device of the present invention, the wavelength dependence of the transmitted optical signal in the wavelength region becomes flat, the wavelength dependence of the gain is eliminated, and analog transmission without distortion can be performed.

[Brief description of drawings]

FIG. 1 is an explanatory diagram showing an embodiment of an optical amplifier of the present invention.

2A is an explanatory diagram showing an example of wavelength dependency of gain of an optical fiber amplifier, FIG. 2B is an explanatory diagram showing wavelength dependency of a fused optical coupler of an optical amplification device of the present invention, FIG. 4) is an explanatory diagram of wavelength dependence of total gain of the optical amplifying device of the present invention.

[Explanation of Codes] 1a, 1b ... Optical fiber amplifier

Claims (1)

[Claims] 1. An optical amplifying device using an optical fiber amplifier, wherein two or more kinds of optical fiber amplifiers 1a, 1b ... Containing different amplification media are wavelength dependent of these optical fiber amplifiers 1a, 1b. An optical amplifying device characterized by being connected in series so as to cancel out the characteristics.