JP2687680B2 - Optical fiber amplifier - Google Patents

Description

The present invention relates to an optical fiber amplifier used in long-distance optical communication, an optical switching system, and the like, and more specifically, to an optical fiber doped with a rare earth metal (Dope). The present invention relates to an optical fiber amplifier that amplifies signal light by injecting high power pumping light having a specific wavelength into a fiber.

[Conventional technology]

In optical fiber communication and optical switching systems, signal light is amplified in order to compensate for reduction in optical power due to insertion loss of devices such as optical switches and optical branches and increase in transmission distance. Then, attention is paid to an optical amplifying device that directly amplifies the signal light without exchanging it with an electric signal.

As an optical fiber amplifier for conventional optical fiber communication, there are a traveling waveform semiconductor laser light amplifier and an optical fiber amplifier using an optical fiber doped with a rare earth element, especially erbium ion (Er ³⁺ ). Compared to semiconductor optical amplifiers, erbium ion-doped optical fiber amplifiers (optical fiber amplifiers) have higher gain, lower coupling loss, lower crosstalk during wavelength multiplexing, and moreover polarization dependence. Since it is excellent in many respects, such as lacking, it is being actively developed.

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

FIG. 2 shows the configuration of a conventional optical fiber amplifier.

To one end of the erbium-doped optical fiber 11, a wavelength synthesizing prism 14 for connecting pumping light 12 for exciting erbium ions and signal light 13 is connected.
Optical connector 16 to which signal light 13 is input and wavelength combining prism
14 and between the optical connector 17 on the output side and the erbium-doped optical fiber 14 in consideration of high isolation of the entire optical communication system, the isolators 18 and 19 and the short wavelength cutoff optical interference filter 21. Are connected.

The weak signal light 13 having a specific wavelength input from the end face of the optical connector 16 is incident on the erbium-doped optical fiber 11 via the wavelength combining prism 14. The incident signal light 13 is
Energy is absorbed and amplified from the erbium ions excited by the pumping light 12 from the first and second laser diodes 22, 23.

Generally, to obtain an optical gain of around 20 dB, 100 mW or more of pumping light 12 is required. Currently, it is possible to output a laser beam of about 100 mW from a laser diode, but if it is connected to an optical fiber, the fiber output will be
It will be about 50mW. Therefore, the laser lights output from the first and second laser diodes 22 and 23, which are different in polarization directions by 90 degrees, are combined by the polarization combiner 24 to obtain pumping light 12 of 100 mW or more.

[Problems to be solved by the invention]

Thus, with the conventional optical fiber amplifier, 100 mW
In order to obtain the above pumping light 12, the polarization directions of the
The polarization combiner 24 combines laser beams different by 90 degrees. For this reason, it is necessary to connect polarization maintaining fibers 26 and 27, which are special fibers, to the laser diodes 22 and 23 in order to maintain the output laser light as linearly polarized light. When connecting one ends of the polarization-maintaining fibers 26 and 27 to the semiconductor lasers 22 and 23, it is necessary to match the polarization planes, and the adjustment is difficult. Also, when the other ends of the polarization-maintaining fibers 26 and 27 are connected to the polarization combiner 24, it is necessary to connect them so that the polarization planes of both fibers are 90 degrees with each other, and the adjustment is difficult .

As described above, the conventional optical fiber amplifier requires the work of adjusting the plane of polarization, and its manufacture is difficult.

Therefore, an object of the present invention is to provide an optical fiber amplification device which does not require polarization plane adjustment and can be easily manufactured.

[Means for solving the problem]

In the invention described in the oscillator 1, both (a) a wavelength synthesizing prism configured to sandwich a dielectric interference film filter between two prisms and (b) a dielectric synthesizing film filter of the wavelength synthesizing prism are both 45 First and second pumping light output means for outputting pumping light for exciting the rare-earth metal in a direction forming 45 degrees with respect to the dielectric interference film filter, the pumping light outputting means being arranged so as to sandwich it at positions that form a degree. (C) A first amplifier optical fiber that optically amplifies the signal light by injecting the excitation light output from the first excitation light output means and reflected by the dielectric interference film filter from the rear side, and (d). Second
And a second amplifier optical fiber for optically amplifying the signal light which is output from the pumping light output means and reflected by the dielectric interference film filter and which is incident from the front and transmitted through the constituent films. Prepare for.

That is, in the invention of claim 1, the first and second amplifier optical fibers doped with a rare earth metal are connected in series so as to be sandwiched between wavelength synthesizing prisms, and excitation light is incident on these amplifier optical fibers. The signal light is amplified in two stages. The wavelength synthesizing prism is configured such that a dielectric interference film filter is sandwiched between two prisms, and uses a dielectric interference film filter that transmits signal light and reflects excitation light.

In the optical fiber amplifying device according to the second aspect, erbium is used as the rare earth metal.

〔Example〕

 Hereinafter, the present invention will be described in detail 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, both of which are connected to the synthetic film of the wavelength synthesizing prism 34 at an angle of 45 degrees. . The wavelength synthesizing prism 34 is configured such that the synthesizing film is sandwiched by two prisms. The synthetic film of the wavelength synthesizing prism has a transmission loss of 0.3d at a wavelength of 1.48 μm.
B, a dielectric interference film filter with a transmission loss attenuation of 20 dB at a wavelength of 1.53 μm. This synthetic film transmits or reflects light incident at an angle of 45 degrees depending on its wavelength.

The wavelength synthesizing prism 34 has first and second lengths of about 1 m so as to form an angle of 45 degrees with respect to each surface of the synthesizing film.
One ends of the single mode fibers 36 and 37 are connected respectively. First and second single mode fibers
First and second laser diodes 38 and 39 are connected to the other ends of 36 and 37, respectively. The first and second laser diodes 38, 39 have a wavelength of 1.48 μm and an optical output of 100 mW
A Fabry-Perot type laser diode is used. First and second laser diodes
The laser beams output from 38 and 39 are incident on the wavelength synthesizing prism 34 as the first and second pumping beams 41 and 42 with a fiber output of 50 mW. The first pumping light 41 is reflected by the synthetic film of the wavelength synthesizing prism 34 and is incident on the first erbium-doped optical fiber 32. Second pumping light
42 is reflected by the synthetic film of the wavelength synthesizing prism 34 and is incident on the second erbium-doped optical fiber 33.

First and second erbium-doped optical fibers 32, 33
The other ends of the first and second short wavelength cutoff optical interference filters 43 and 44 each having a short-wave side attenuation amount of 20 dB are connected. First and second short wavelength cutoff interference filters 43, 44
And the optical connectors 46 and 47 are connected to first and second isolators 48 and 49 having an isolation of 50 dB, respectively.

Next, the operation of the optical fiber amplifier configured as described above will be described.

The weakened signal light 51 having a wavelength of 1.53 μm incident from the end face of the optical connector 46 is incident on the first erbium-doped optical fiber 32 through the first isolator 48 and the first short wavelength cutoff optical interference filter 43. To be done. The signal light 51 incident on the first erbium-doped optical fiber 32 is amplified by the first pumping light 41, then passes through the wavelength combining prism 34, and is incident on the second erbium-doped optical fiber 33. The amplified signal light 51 is further amplified by the second erbium-doped optical fiber 33 into the second pumping light 42, and the second short wavelength cutoff optical interference filter 44 and the second isolator.
It is output from the optical connector 47 via 49.

〔The invention's effect〕

As described above, according to the present invention, the first and second amplifier optical fibers are arranged with the wavelength synthesizing prism in between, and the pumping light is incident on these amplifier optical fibers to generate the signal light.
Since the configuration is such that amplification is performed in stages, there is no need to maintain the linearly polarized light output from the laser diode. Therefore, the work of adjusting the polarization plane is unnecessary, and the optical fiber amplifier can be easily manufactured. In addition, a polarization combiner is not required and a special polarization-preserving facsimile is not used, so that an inexpensive optical fiber amplifier can be realized.

Moreover, since the first and second amplifier optical fibers and the first and second pumping light output means can be connected using one wavelength combining prism, there is an effect that the configuration of the optical fiber amplifier is simplified. .

[Brief description of the drawings]

FIG. 1 is a block diagram of an optical fiber amplifier according to an embodiment of the present invention, and FIG. 2 is a block diagram of a conventional optical fiber amplifier. 33 …… Second erbium-doped optical fiber, 34 …… Wavelength combining prism, 36 …… First single-mode fiber,
37 ... second single-mode fiber, 38 ... first laser diode, 39 ... second laser diode, 62 ...
… First wavelength synthesizing prism, 63 …… Second wavelength synthesizing prism.

Claims (2)

(57) [Claims] 1. A wavelength synthesizing prism configured such that a dielectric interference film filter is sandwiched between two prisms, and a wavelength synthesizing prism of this wavelength synthesizing prism is arranged at a position that forms 45 degrees with respect to the dielectric interference film filter. First and second pumping light output means, which are arranged so as to sandwich the rare earth metal and output pumping light for exciting the rare earth metal in directions of 45 degrees with respect to the dielectric interference film filter, respectively, and the first pumping light output. A first amplifier optical fiber that optically amplifies the signal light by injecting the pumping light that is output by the means and reflected by the dielectric interference film filter from the rear side; and is output by the second pumping light output means. Secondly, the pumping light reflected by the dielectric interference film filter is incident from the front and the signal light transmitted through the constituent film is amplified.
And an optical fiber for an amplifier. 2. The optical fiber amplifier according to claim 1, wherein the rare earth metal is erbium.