JPH0422928A - Optical fiber amplifier - Google Patents

Abstract

PURPOSE:To make it unnecessary to adjust a polarizing face by making stimulated light incident upon plural amplifying optical fibers connected in series. CONSTITUTION:A weakened signal beam 51 made incident from the end face of an optical connector 46 is made incident upon a 1st erbium doped optical fiber 32 through a 1st isolator 48 and a 1st short wavelength interrupting optical interference filter 43. The signal beam 51 made incident upon the fiber 32 is amplified by a 1st pumping light 41 and made incident upon a 2nd erbium doped optical fiber 33 through a wavelength synthesizing prism 34. The amplified signal beam 51 is then amplified by a 2nd pumping light 42 through the fiber 33 and outputted from an optical connector 47 through a 2nd short wavelength interrupting optical interference filter 44 and a 2nd isolator 49. Since the signal beam is amplified in stages, the need for the adjusting work of the polarizing wave is eliminated.

Description

[Detailed Description of the Invention] [Field of Industrial Application] The present invention relates to an optical fiber amplifier used in long-distance optical communications, optical switching systems, etc. The present invention relates to an optical fiber amplifier that amplifies signal light by inputting high-power pumping light of a specific wavelength into a fiber.

[Conventional technology]

In optical fiber communications and optical switching systems, signal light is amplified to compensate for the reduction in optical power due to insertion loss of devices such as optical switches and optical branches and increases in transmission distance. Optical amplification devices that directly amplify signal light without converting it into an electrical signal have been attracting attention.

Conventional optical fiber amplifiers for optical fiber communications include traveling wave semiconductor laser optical amplifiers and optical fiber amplifier lids that use optical fibers doped with rare earth elements, particularly erbium ions (Er'').・Ion-doped optical fiber amplifiers (optical fiber amplifiers) have higher gain, lower coupling loss, lower crosstalk during wavelength multiplexing, and no polarization dependence than semiconductor optical amplifiers. Because it is superior in many aspects such as, it is being actively developed.

The principle of this optical fiber amplifier is to excite erbium ions with semiconductor laser light as bombing light and cause stimulated emission using signal light as a trigger.

FIG. 3 shows the configuration of a conventional optical fiber amplifier.

A wavelength combining prism 14 is connected to one end of the erbium-doped optical fiber 11, into which a bombing light 12 for exciting erbium ions and a signal light 13 are respectively incident. Between the optical connectors 1 and 6 into which the signal light 13 is input and the wavelength combining prism 14, and the optical connector 1 on the output side
7 and the erbium-doped optical fiber 14, isolators 18 and 19 and a short wavelength cutoff optical interference filter 21 are connected in consideration of high isolation of the entire optical communication system.

A weak signal light 13 of a specific wavelength manually input from the end face of the optical connector 16 is inputted to the erbium-doped optical fiber 11 via the wavelength combining prism 14 . The input signal light 13 is transmitted to the first and second laser diodes 22 and 23.
Energy is absorbed from the erbium ions excited by the bombing light 12 from the erbium ions and amplified.

Generally, to obtain an optical gain of around 20 dB, 10 QmW
The above bombing light 12 is necessary.

A laser diode can currently output a laser beam of about 100 mW, but when connected to an optical fiber, the fiber output becomes about 53 mW. Therefore, the laser beams output from the first and second laser diodes 22 and 23, which have polarization directions different from each other by 90 degrees, are combined by the polarization combiner 24 to produce a 100.degree. Bumping light 12 of mW or more is obtained.

[Problem to be solved by the invention]

In this way, with conventional optical fiber amplifiers, 100 m
In order to obtain the bombing light 12 of W or more, laser lights whose polarization directions are different by 90 degrees are combined by a polarization combiner 24. Therefore, it is necessary to connect polarization maintaining fibers 26, 27, which are special fibers, to the laser diodes 22, 23 in order to maintain the output laser light as linearly polarized light. When connecting one end of the polarization maintaining fiber 26, 27 to the semiconductor laser 22, 23, it is necessary to match the planes of polarization, and the adjustment is difficult. Furthermore, when connecting the other ends of the polarization-maintaining fibers 26 and 27 to the polarization combiner 24, it was necessary to connect the polarization planes of both fibers at 90 degrees to each other, which was difficult to adjust. .

As described above, conventional optical fiber amplifiers require adjustment of the plane of polarization, which is difficult to manufacture.

SUMMARY OF THE INVENTION An object of the present invention is to provide an optical fiber amplifier that does not require adjustment of the plane of polarization and can be easily manufactured.

[Means to solve the problem]

The invention according to claim 1 provides: (1) a plurality of amplifier optical fibers doped with rare earth metals and connected in series;
i) a plurality of excitation light output means arranged corresponding to each of the plurality of amplifier optical fibers and outputting excitation light for exciting the rare earth metal, and (iii) each of the excitation light output means output from these excitation light output means. The optical fiber amplifying device is provided with a pumping light input means for making the pumping light enter the corresponding amplifier optical fiber.

In other words, the optical fiber amplifier of the present invention connects a plurality of amplifier optical fibers doped with rare earth metals in series, and injects pumping light into each amplifier optical fiber to amplify the signal light in multiple stages. It was designed to do so.

In the optical fiber amplifier according to claim 2, the excitation light input means is disposed between the amplifier optical fibers connected in series, and transmits the signal light passing through the amplifier optical fibers and reflects the excitation light. Use a dielectric interference film filter.

In the optical fiber amplifier according to the third aspect of the present invention, erbium is used as the rare earth metal.

〔Example〕

The present invention will be described in detail below with reference to Examples.

FIG. 1 shows the configuration of an optical fiber amplifier according to an embodiment of the present invention.

The optical fiber amplifier 31 includes first and second erbium-doped optical fibers 32 and 33, and both fibers are connected at an angle of 45 degrees with respect to the synthesis film of the wavelength synthesis prism 34. . Wavelength synthesis prism 34
is constructed so that a synthetic film is sandwiched between two prisms. The synthesis film of the wavelength synthesis prism is a dielectric interference film filter with a transmission loss of 0.3 dB at a wavelength of 1.48 μm and a transmission loss attenuation of 20 dB at a wavelength of 1.53 μm. This synthetic film is designed to transmit or reflect light incident at an angle of 45 degrees depending on its wavelength.

One ends of first and second single mode fibers 36 and 37 each having a length of about 1 m are connected to the wavelength combining prism 34 so as to form an angle of 45 degrees with respect to each surface of the combining film. First and second laser diodes 38.39 are connected to the other ends of the first and second single mode fibers 36.37, respectively. The first and second laser diodes 38,39 have a wavelength of 1
゜48μm 1 optical output 100mW Fabry-Perot (Fe
A laser diode of the Bry Perot type is used. First and second laser diodes 38.3
The laser light outputted from 9 is input to the wavelength combining prism 34 as first and second pumping light 41, 42 with a fiber output of 50 mW. First pumping light 41
is reflected by the synthesis film of the wavelength synthesis prism 34 and enters the first erbium-doped optical fiber 32. The second pumping light 42 is reflected by the synthetic film of the wavelength combining prism 34 and is incident on the second erbium-doped optical fiber 33.

First and second erbium-doped optical fibers 32.3
3 are connected to first and second short wavelength cutoff optical interference filters 43 and 44 each having a short wavelength side attenuation of 20 dB. First and second isolators 48,49 each having an isolation of 50 dB are connected between the first and second short wavelength cutoff interference filters 43,44 and the optical connector 46,47.

The operation of the optical fiber amplifier device configured in this way will be described next.

Wavelength 1°53 μm incident from the end face of the optical connector 46
The weakened signal light 51 passes through the first isolator 48,
The light is input to the first erbium-doped optical fiber 32 via the first short wavelength cutoff optical interference filter 43 . Signal light 51 incident on first erbium-doped optical fiber 32
After being amplified by the first pumping light 41, the light passes through the wavelength combining prism 34 and enters the second erbium-doped optical fiber 33. The amplified signal light 51 is
Furthermore, it is amplified by the second pumping light 42 in the second erbium-doped optical fiber 33 and outputted from the optical connector 47 via the second short wavelength cutoff optical interference filter 44 and the second isolator 49 .

FIG. 2 shows the configuration of an optical fiber amplifier according to another embodiment of the present invention. Components that are the same as those in FIG. 1 are designated by the same reference numerals, and description thereof will be omitted as appropriate.

The optical fiber amplifier 61 includes first and second erbium-doped optical fibers 32.33 and first and second wavelength combining prisms 62.63. These are the first
The wavelength combining prism 62, the first erbium-doped optical fiber 32, the second wavelength combining prism 63, and the second erbium-doped optical fiber 33 are connected in this order.

The first pumping light 41 outputted from the first laser diode 38 is reflected by the first wavelength combining prism 62 by a combining film, and is connected to the first erbium-doped optical fiber 32.
is connected so that it is input to the The second wavelength combining prism 63 is connected so that the second pumping light 42 output from the second laser diode 39 is reflected by the combining film and input into the second erbium-doped optical fiber 33. There is.

Since the first pumping light 41 is reflected toward the first erbium-doped optical fiber 32, in this embodiment, the first pumping light 41
No short wavelength cutoff optical interference filter is disposed between the wavelength combining prism 62 and the first isolator 48 .

In this optical fiber amplifier 61 as well, the weakened signal light 51 is amplified by the first pumping light 41 in the first erbium-doped optical fiber 32 and then amplified by the second pumping light 41 in the second erbium-doped optical fiber 33. pumping light 4
2 and is amplified and output.

〔Effect of the invention〕

As described above, according to the present invention, the signal light is amplified in multiple stages by inputting the excitation light into each of the plurality of amplifier optical fibers connected in series, so that the output of the laser diode is There is no need to keep the light linearly polarized. Therefore, there is no need to adjust the plane of polarization, making it possible to manufacture the device easily. Moreover, not only is a polarization combiner unnecessary, but also a special polarization-maintaining fiber is not used, so an inexpensive optical fiber amplification device can be provided.

[Brief explanation of drawings]

Figures 1 and 2 are for explaining one embodiment of the present invention, of which Figure 1 is a configuration diagram of an optical fiber amplifier, and Figure 2 is another embodiment of the optical fiber amplifier. FIG. 3 is a block diagram of a conventional optical fiber amplifier. 33...Second erbium-doped optical fiber 3
4... Wavelength combining prism, 36... First single mode fiber, 37
...Second single mode fiber 38...
...first laser diode, 39...second
laser diode, 62...first wavelength synthesis prism, 63...second wavelength synthesis prism.

Claims (1)

[Claims] 1. A plurality of amplifier optical fibers doped with a rare earth metal and connected in series, and an excitation device disposed corresponding to each of the plurality of amplifier optical fibers to excite the rare earth metal. It is characterized by comprising a plurality of excitation light output means for outputting light, and excitation light input means for inputting the respective excitation light output from these excitation light output means into the corresponding optical fiber for the amplifier. Optical fiber amplifier. 2. The excitation light input means is a dielectric interference film filter placed between the amplifier optical fibers connected in series, which transmits the signal light passing through the amplifier optical fibers and reflects the excitation light. The optical fiber amplifier according to claim 1. 3. The optical fiber amplifier according to claim 1 or 2, wherein the rare earth metal is erbium.