JPH0983047A - Optical amplifier - Google Patents

Abstract

PROBLEM TO BE SOLVED: To widen the transmission band of an optical amplifier by connecting rare earth doped fibers, where at least one of the kind of rare earth element to be doped or the dose thereof is different, in cascade and employing the cas cade connection as an amplifying medium. SOLUTION: The (n) pieces of rare earth doped fibers (REED fiber) FA1 -FAn of (n) kinds are connected in cascade to produce an amplifying medium. Each REED fiber FAi has such characteristics Gci as the gain is highest at a wavelength λpi (i represents the i-th fiber among n fibers). More specifically, λpi and Gci are determined by selecting the dose and and/or the kind of rare earth element to be doped appropriately. A plurality of REED fibers having different gain peak characteristics are connected in cascade and employed as an amplifying medium. A pumping light source 6 generates pumping lights corresponding to (n) fibers.

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to an erbium (E
The present invention relates to an optical amplifier using an optical fiber doped with a rare earth element such as r) or neodymium (Nd).

[0002]

2. Description of the Related Art An embodiment of a conventional optical amplifier is shown in FIG.
In the figure, an optical amplifier includes a rare earth-doped fiber (hereinafter, REED fiber) 5 as an amplification medium and a pumping light source 4
And a WDM coupler 2 for injecting a pumping light source into the amplification medium. The pumping light power output from the pumping light source 4 is injected into the REED fiber 5 by the WDM coupler 2, whereby the REED fiber 5 enters the pumping state, and when the optical signal is input from the input terminal 1, the optical signal is amplified. And output from the output terminal 3. Japanese Patent Publication No. 6-24273 is an example of such an optical amplifier.

[0003]

The REED fiber has a characteristic of amplifying light of a specific wavelength band by injecting pumping light of a certain wavelength.

There is an erbium-doped fiber (EDF) as an example of the REED fiber. When this is used, an optical amplifier for the 1560 nm band having a 3 dB gain bandwidth of about 20 nm can be realized. As for the amplification bandwidth, it has a sufficient bandwidth as a repeater when it is used as a single unit, but when used in a multi-repeater system such as a submarine repeater system, the band as a system is extremely high due to the effect called auto filtering. Becomes narrower. In order to prevent this, strict accuracy is required for the optical wavelength on the transmission side, and wavelength multiplexing transmission, which is an effective means for expanding the transmission capacity, is extremely difficult.

The object of the present invention is to eliminate the above-mentioned drawbacks,
An object is to provide an optical amplifier capable of widening the transmission band.

[0006]

The optical amplifier according to the present invention comprises:
In order to solve the above-mentioned problems, a plurality of rare-earth-doped fibers each having a different wavelength that maximizes the gain of the fiber,
An excitation light source that excites the plurality of fibers is provided.

The gain characteristic of the optical amplifier using the REED fiber has wavelength dependence, and the wavelength λp at which the gain is maximum is obtained.
Varies depending on the types of rare earth elements and other elements to be doped and their amounts.

Therefore, by changing the kind or amount of the dopant, REED fibers having different λp can be realized. By using several kinds of REED fibers having different λp in cascade connection and using them in an optical amplifier, an optical amplification repeater having a wider band can be realized.

[0009]

BEST MODE FOR CARRYING OUT THE INVENTION The present invention will now be described in detail with reference to the drawings.

FIG. 1 shows an embodiment of the present invention. In Figure 1,
Conventionally, one type and one REED fiber is used as an amplification medium, whereas in this embodiment, n types and n REs are used.
The ED fibers FA1 to FAn are connected in cascade and used as an amplification medium.

Each REED fiber FAi has a gain wavelength characteristic Gci in which the gain becomes maximum at the wavelength λpi (i represents the i-th fiber of n fibers). Specifically, λpi and Gci are determined by appropriately selecting the doping amount or the type of rare earth to be doped and both. By using a plurality of REED fibers having different gain peak wavelength characteristics in cascade connection and using them as an amplifying medium, an optical amplifier having a gain wavelength characteristic GcT of a very wide band can be obtained as shown in FIG. The pumping light source 6 generates pumping light corresponding to each of these n fibers.

[0012]

As described above, by using several kinds of REED fibers having different kinds or amounts of dopants and different λp, which are cascade-connected to each other and used as an optical amplifier, a broader band optical amplification suitable for wavelength division multiplex transmission can be obtained. A repeater can be realized.

[Brief description of drawings]

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

FIG. 2 is a diagram showing a gain characteristic of the optical amplifier of the present invention.

FIG. 3 is a configuration diagram showing an example of a conventional optical amplifier.

[Explanation of symbols]

 1 Signal Input Port 2 WDM Coupler 3 Signal Output Port 4 Pumping Light Source FA Rare Earth Doped Fiber Gc Gain Wavelength Characteristic λp Gain Maximum Wavelength

Claims (4)

[Claims] 1. In an optical amplifier using a rare earth-doped fiber as an amplification medium, a plurality of types of rare earth-doped fibers differing in at least one of the type of element such as rare earth to be doped and their doping amount are used as an amplification medium. An optical amplifier characterized in that. 2. An optical amplifier comprising: a plurality of rare earth-doped fibers having different wavelengths at which the gain of the fiber is maximum, and a pumping light source for pumping the plurality of fibers. 3. The optical amplifier according to claim 1, wherein the wavelength at which the gain of the fiber is maximum is set by changing the elements such as rare earths doped in the fiber. 4. The optical amplifier according to claim 1, wherein the wavelength at which the gain of the fiber is maximum is set by varying the doping amount of an element such as rare earth doped in the fiber.