JPH05136490A - Optical fiber amplifier - Google Patents

Abstract

PURPOSE:To obtain a wave synthesizing and dividing means excellent in separated wavelength precision by causing an optical circulator having first to third photoelectric input-output terminals to amplify outgoing signal light into an output signal, and supplying excitation light received from the third photoelectric input-output terminals to an optical fiber from the first photoelectric input-output terminals. CONSTITUTION:Input signal light 6a is supplied to an erbium ion-doped optical fiber 1 from an input-side optical fiber 9 through an optical isolator 4. Excitation light generated by an excitation light source 3 which excites erbium ions is supplied to the port-3 of an optical circulator 2, and transmitted to the erbium ion-doped optical fiber 1 from the port-1. The excitation light is supplied to the optical fiber 1 from a direction opposite to the incident direction of the signal light. Besides the signal light amplified in the optical fiber 1 is supplied to the port-1 of the optical circulator 1, and transmitted to the output optical fiber 10 from the port-2.

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 using an optical fiber used for optical communication as an amplification medium.

[0002]

2. Description of the Related Art When constructing an optical communication system, it is necessary to amplify an optical signal weakened in a transmission cable. In order to meet this demand, in recent years, an optical fiber amplifier which directly amplifies an optical signal as it is without converting the optical signal into an electric signal has been put into practical use.

The structure of the optical fiber amplifier will be described below. Here, in order to make the description more specific, referring to FIG. 2, a fiber in which erbium (Er) ions, which are one of rare earth ions, are added to the amplification medium is used.
A so-called erbium ion-doped optical fiber amplifier will be described as an example.

The conventional optical fiber amplifier 102 is composed of an erbium ion-doped optical fiber 1, a multiplexer / demultiplexer 2 ', a pumping light source 3, and first and second optical isolators 4 and 5. ..

The multiplexer / demultiplexer 2'is for wavelength-synthesizing and separating the signal light having a wavelength of 1.55 μm and the pumping light 7 having a wavelength of 1.48 μm. A wavelength separation film 8 is built in the multiplexer / demultiplexer 2 '. The wavelength separation film 8 has a wavelength of 1.4
It has a function of reflecting light of 8 μm and transmitting light of wavelength 1.55 μm.

The first optical isolator 4 is used to prevent the pumping light from adversely affecting the front stage of the input side optical fiber 9. The second optical isolator 5 is used to prevent oscillation due to reflected return light from the output side optical fiber 10.

The optical fiber amplifier having such a structure is described in "Optics", 1 of the Japan Optical Society (Japan Society of Applied Physics).
It is described in detail in "Optical Fiber Amplifier" described on pages 276 to 282 of Vol. 19, No. 5, issued May 990.

[0008]

In the conventional optical fiber amplifier shown in FIG. 2, the wavelength separation film 8 is used for combining and separating the signal light and the pump light. The wavelength separation film 8 is
It has a drawback that it is necessary to have extremely special characteristics that the reflectance ratios differ by 20 dB or more at two wavelengths extremely close to each other, 1.48 μm and 1.55 μm. Further, the wavelength separation film 8 has a drawback that the separation wavelength is sensitive to the film thickness and the refractive index of the substance, and it is difficult to manufacture it with high precision.

It is also conceivable to use a multiplexer / demultiplexer using a diffraction grating instead of the wavelength separation film 8. The multiplexer / demultiplexer having such a configuration is effective in improving the separation wavelength accuracy, but has the drawback that the diffraction grating is expensive and the size of the multiplexer / demultiplexer using the diffraction grating becomes large. ing.

Therefore, it is an object of the present invention to provide an optical fiber amplifier including a multiplexing / demultiplexing means with good accuracy of the separated wavelength.

Another object of the present invention is to provide an optical fiber amplifier including an inexpensive multiplexing / demultiplexing means.

Still another object of the present invention is to provide an optical fiber amplifier including a compact multiplexing / demultiplexing means.

[0013]

An optical fiber amplifier of the present invention is an optical fiber amplifier for amplifying an input signal light and outputting an output signal light, wherein the input signal light is received as an incident signal light, and the incident signal light is received. An optical fiber having an amplifying function of amplifying the signal light and outputting the amplified signal light as outgoing signal light,
A pumping light source for generating pumping light; and a multiplexer / demultiplexer connected to the exit end of the optical fiber and supplying the pumping light to the optical fiber and extracting the exiting signal light as the output signal light. In the optical fiber amplifier, the multiplexing / demultiplexing means is an optical circulator having at least first to third optical input / output terminals (ports), and the optical circulator receives from the first optical input / output terminals. The emitted signal light is output from the second optical input / output terminal as the output signal light, and the excitation light received from the third optical input / output terminal is output from the first optical input / output terminal to the optical fiber. The optical fiber is connected to the output end of the optical fiber so as to be supplied.

In the above optical fiber amplifier, it is preferable that an optical isolator for supplying the input signal light as the incident signal light to the optical fiber is connected to the incident end of the optical fiber.

[0015]

Embodiments of the present invention will now be described in detail with reference to the drawings.

Referring to FIG. 1, an optical fiber amplifier 101 according to an embodiment of the present invention includes an optical circulator 2 instead of the multiplexing / demultiplexing device 2'as a multiplexing / demultiplexing means, and does not have an optical isolator 5. The optical fiber amplifier 102 has the same configuration as that of the conventional optical fiber amplifier 102 shown in FIG. Therefore, the same components as those shown in FIG. 2 are designated by the same reference numerals, and the description thereof will be omitted.

The optical circulator 2 has three ports, port 1, port 2 and port 3. In the optical circulator 2, the first path from port 1 to port 2,
Light circulates in three paths, that is, a second path of port 2 → port 3 and a third path of port 3 → port 1. The output end of the erbium ion-doped optical fiber 1 is connected to the port 1 of the optical circulator 2. The incident end of the output side optical fiber 10 is connected to the port 2 of the optical circulator 2. An excitation light source 3 is connected to the port 3 of the optical circulator 2.

Next, the operation of the optical fiber amplifier 101 of the present invention will be described with reference to FIG.

The input signal light 6a having a wavelength of 1.55 μm is supplied from the input side optical fiber 7 to the erbium ion-doped optical fiber 1 through the optical isolator 4. The excitation light source 3 for exciting the erbium ion has a wavelength of 1.48 μm.
Generate excitation light. The excitation light is supplied to the port 3 of the optical circulator 2 and is sent from the port 1 to the erbium ion-doped optical fiber 1. Therefore, the excitation light is supplied to the erbium ion-doped optical fiber 1 from the direction opposite to the incident direction of the signal light.

The signal light amplified in the erbium ion-doped optical fiber 1 is supplied to the port 1 of the optical circulator 2 and sent from the port 2 to the output side optical fiber 10. Here, the reflected return light from the output side optical fiber 10 escapes from the port 2 of the optical circulator 2 to the port 3, so that oscillation can be prevented.

Assume the following: That is, the excitation light emitted from the excitation light source 3 is +20 dBm. The passage loss of the optical circulator 2 is 2 dB. The passage loss of the optical isolator 4 is 1 dB. The conversion efficiency of the erbium ion-doped optical fiber 1 is 80%. in this case,
The wavelength of 1.55 μm input to the optical fiber amplifier 101,
The input signal light 6a having an intensity of −20 dBm is amplified by the optical fiber amplifier 101 to have an intensity of +15 dBm, and the output signal light 6a is amplified.
It is output as b.

In the above embodiments, the erbium ion-doped optical fiber 1 used in the 1.5 μm band is used in the optical fiber amplifier, but instead, the praseodymium (Pr) ion used in the 1.3 μm band is used. A doped optical fiber or a neodymium (Nd) ion-doped optical fiber may be used.

[0023]

As described above, the optical fiber amplifier of the present invention has an effect that a special wavelength separation film and an expensive diffraction grating are not required by using the optical circulator as the multiplexing / demultiplexing means. .. Further, since an optical isolator for preventing oscillation is unnecessary, there is also an advantage that the configuration is simple.

[Brief description of drawings]

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

FIG. 2 is a block diagram showing a conventional optical fiber amplifier.

[Explanation of symbols]

 1 Erbium ion-doped optical fiber 2 Optical circulator 3 Pumping light source 4, 5 Optical isolator 6a Input signal light 6b Output signal light 7 Pumping light 9 Input side optical fiber 10 Output side optical fiber

Claims (2)

[Claims] 1. An optical fiber amplifier for amplifying input signal light and outputting output signal light, wherein the input signal light is received as incident signal light, and the incident signal light is amplified and emitted as signal light. An optical fiber having an amplifying action for outputting as signal light, a pumping light source for generating pumping light, and an output end of the optical fiber are connected to supply the pumping light to the optical fiber and output the output signal light. An optical fiber amplifier having a multiplexing / demultiplexing means for extracting as signal light, wherein the multiplexing / demultiplexing means is an optical circulator having at least first to third optical input / output terminals, and the optical circulator comprises: The outgoing signal light received from the first optical input / output terminal is output from the second optical input / output terminal as the output signal light, and the excitation light received from the third optical input / output terminal is the first optical input / output terminal. Light in and out To supply to the optical fiber from the terminal, an optical fiber amplifier, characterized in that connected to the exit end of the optical fiber. 2. The optical fiber amplifier according to claim 1, wherein an optical isolator for supplying the input signal light as the incident signal light to the optical fiber is connected to an incident end of the optical fiber.