JP3215236B2 - Optical fiber amplifier - Google Patents

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 for directly amplifying signal light by injecting signal light and pump light into an optical fiber doped with a rare earth element.

2. Description of the Related Art In an optical fiber communication system currently in practical use, repeaters are inserted at regular intervals in order to compensate for attenuation of an optical signal due to loss of an optical fiber. In the repeater, the optical signal is converted into an electric signal by a photodiode, and the signal is amplified by an electronic amplifier.
The optical signal is converted into an optical signal by a semiconductor laser or the like, and is sent out again to an optical fiber transmission line.

[0003] If this optical signal can be directly amplified with low noise as it is, the optical repeater can be reduced in size and economical. Therefore, studies on optical amplifiers capable of directly amplifying optical signals are being actively conducted. Optical amplifiers to be studied are roughly classified into the following three types.

That is, (a) rare earth elements (Er, Nb, Y
b) and a combination of pumping light, (b) a semiconductor laser doped with a rare earth element, and (c) an induced Raman amplifier utilizing the nonlinear effect in the optical fiber.

[0005] Among them, the optical amplifier in which the rare-earth-doped fiber and the pumping light are combined as shown in (a) has excellent features such as no polarization dependency, low noise, and small coupling loss with the transmission line. It is expected that the transmission relay distance in an optical fiber transmission system will be dramatically increased, and that an optical signal can be distributed to a large number.

[0006]

2. Description of the Related Art FIG. 4 shows a configuration diagram of a conventional example of an optical fiber amplifier. The Er-doped fiber 2 doped with Er in the core is spliced to the connection fiber 6 by the mode conversion splice unit 4, and the connection fiber 6 and the input fiber 1 are spliced.
An optical isolator 8 is interposed between 0 and 0.

[0007] The output side of the Er-doped fiber 2 is connected to the connection fiber 14 by the mode conversion splice section 12, and a bulk type coupling having an optical isolator 34 between the connection fiber 14 and the output fiber 36. A demultiplexing module 32 is interposed.

Reference numerals 16 and 18 denote pumping laser diodes which emit pumping light having a polarization plane orthogonal to each other and having a wavelength of 1.48 μm. The fiber 20 connected to the laser diode 16 is connected to the connection fiber 24 at the splice section 22.
Is spliced.

The fiber 26 connected to the laser diode 18 is spliced to a connection fiber 30 at a splice section 28. The connection fibers 24 and 30 are connected to a bulk type multiplexing / demultiplexing module 32.

The signal light having a wavelength of, for example, 1.55 μm that has propagated through the input fiber 10 is incident on the Er-doped fiber 2 via the optical isolator 8 and the connecting fiber 6.

On the other hand, the pumping laser diode 16 or 1
The pumping light emitted from 8 is multiplexed with the signal light by the multiplexing / demultiplexing module 32, introduced into the Er-doped fiber 2 via the connecting fiber 14, and passed through the Er-doped fiber 2 in the direction opposite to the propagation direction of the signal light. Propagate.

By making the optical power of the pump light sufficiently high, the Er atoms in the Er-doped fiber 2 can be pumped to a high energy level, and the light of the same wavelength is generated by the incidence of the signal light having a wavelength of 1.55 μm. Stimulated emission causes signal light to be amplified.

The amplified signal light is supplied to the connection fiber 14,
The light is output to the output fiber 36 via the multiplexing / demultiplexing module 32. Since the mode field diameter of the Er-doped fiber 2 is reduced in order to improve the amplification characteristics, the connection loss between the connection fibers 6 and 14 (for example, a single mode fiber and a dispersion shift fiber) with the components before and after is reduced. Because it is large, a mode conversion splice technique is applied.

[0014]

By the way, the connecting fiber of each optical component needs to have a bending radius of 15 mm or more, and the fusion splice portion needs to be protected by a reinforcing tube having a length of about 5 cm. .

As a result, even if individual components of the optical fiber amplifier are reduced in size, there is a problem that the overall size of the amplifier is considerably increased. A typical size of a conventional optical fiber amplifier is, for example, about 100 mm × 190 mm.

The present invention has been made in view of such a point, and an object of the present invention is to eliminate the extra length of a connecting fiber between an Er-doped fiber and optical components before and after the Er-doped fiber. An object of the present invention is to provide an optical fiber amplifier that can be downsized.

[0017]

SUMMARY OF THE INVENTION In order to solve the above-mentioned problems, the present invention splices first and second connecting fibers to the input side and the output side of a rare earth doped fiber, respectively, and An optical fiber amplifier configured to introduce pumping light from a pumping light source into a rare earth-doped fiber via a wave module;
Inserting and fixing one of the splice portions of the connection fiber into the first ferrule, and fixing the first ferrule to the housing of the bulk-type multi / demultiplexing module;
An optical fiber amplifier characterized in that the other splice portion of the first and second connection fibers is inserted and fixed in a second ferrule, and the second ferrule is fixed to a housing of the optical isolator. .

[0018] Preferably, the one and the other splice parts are mode conversion splice parts. By employing such a mode conversion splice, it is possible to reduce connection loss.

[0019]

In the optical fiber amplifier of the present invention, the splice portions at both ends of the Er-doped fiber are fixed in the ferrules of the input and output portions of the front and rear optical components (optical isolator and bulk-type multiplexing / demultiplexing module). The extra length of the connecting fiber between the doped fiber and the optical components before and after the doped fiber can be eliminated.

As a result, as a whole optical fiber amplifier,
It is possible to reduce the size to about 1/3 of the conventional amplifier. Further, reinforcement of the splice portion can be reliably performed by fixing the splice portion in the ferrule.

[0021]

Embodiments of the present invention will be described below in detail with reference to the drawings. Referring to FIG. 1, there is shown an overall configuration diagram of a back-excitation type embodiment of the present invention. Reference numeral 42 denotes an Er-doped fiber in which erbium (Er) is doped in the core of a single mode fiber whose mode field diameter is reduced, and the signal light incident side is connected by a mode conversion splice section 46 to a single mode fiber 44 for connection. Is spliced.

The connecting fiber 44 is polished to a length of several mm, and the mode conversion splice portion 46 is inserted into the ferrule 48 and fixed with an adhesive. The collimator lens 50 is pressed into the ferrule 48, and the ferrule 48 is fixed to the housing 54 of the optical isolator 52 by laser welding or the like.

On the signal light incident side of the housing 54, an input side single mode fiber 56 and a collimator lens 6
The ferrule 58 into which 0 is inserted and fixed is fixed by laser welding or the like.

Reference numeral 62 denotes a bulk type multiplexing / demultiplexing module.
A multiplexing / demultiplexing prism unit 66 having a multiplexing / demultiplexing film 68, a polarization splitting film 70, and a total reflection film 72;
It comprises.

The signal light emission side of the Er-doped fiber 42 is spliced to a single mode fiber 76 for connection by a mode conversion splice section 78. The connection fiber 76 is polished so as to have a length of about several mm, and the mode conversion splice portion 78 is inserted into the ferrule 80 and fixed with an adhesive.

A collimating lens 81 is provided in a ferrule 80.
And the ferrule 80 is fixed to the housing 64 of the multiplexing / demultiplexing module 62 by laser welding or the like. Thus, the Er-doped fiber 42 and the connecting fiber 4
For example, the mode conversion splice technique is used to connect the Er-doped fiber 42 having a mode field diameter of 6 μm to the connection fibers 44 and 76.
(For example, when the mode field diameter is 10 μm), even if the mode field diameters are different from each other, they are connected with a low loss by the mode conversion splice.

The mode conversion splice units 46 and 78
Are fixed in the ferrules 48 and 80, respectively, so that the optical system can be configured without any problem even if the connecting fibers 44 and 76 are several mm long.

Reference numerals 82 and 90 denote laser diodes for emitting excitation light having a wavelength of 1.48 μm whose polarization planes are orthogonal to each other, and are connected to single mode fibers 84 and 92, respectively.

The ends of the fibers 84 and 92 are inserted and fixed in ferrules 86 and 94, respectively. The collimating lenses 8 from the other ends of the ferrules 86 and 94, respectively.
The ferrules 86 and 94 are fixed to the housing 64 of the multiplexing / demultiplexing module 62 by, for example, laser welding.

The output side single mode fiber 98 and the collimating lens 102 are inserted and fixed to the ferrule 100, and the ferrule 100 is fixed to the housing 64 of the multiplexing / demultiplexing module 62 by, for example, laser welding.

Hereinafter, the operation of the present embodiment configured as described above will be described. The signal light having a wavelength of 1.55 μm that has propagated through the incident fiber 56 is introduced into the Er-doped fiber 42 via the optical isolator 52 and the mode conversion splice unit 46.

The pumping laser diodes 82 and 90 are driven simultaneously to obtain sufficient pumping light power, or one of them is used as a working pumping light source and the other is used as a spare pumping light source when the working pumping light source fails. It can also be used as

Assuming that the laser diodes 82 and 90 are driven simultaneously, the excitation light from the laser diode 90 is totally reflected by the total reflection film 72 and passes through the polarization splitting film 70. On the other hand, the excitation light from the laser diode 82 is reflected by the polarization separation film 70 and is combined with the excitation light emitted from the laser diode 90.

The excitation light thus synthesized is combined with the multiplexing film 68.
And is reflected by E through the mode conversion splice portion 78.
The light is introduced into the r-doped fiber 42 and propagates in the Er-doped fiber 42 in a direction opposite to the propagation direction of the signal light.

By making the optical power of the pump light sufficiently high, the Er atoms in the Er-doped fiber 42 can be pumped to a high energy level, and the light of the same wavelength is generated by the incidence of the signal light having a wavelength of 1.55 μm. The stimulated emission causes the signal light to be amplified along the Er-doped fiber 42.

The amplified signal light is introduced into the multiplexing / demultiplexing module 62 via the mode conversion splice section 78, passes through the multiplexing film 68 and the optical isolator 74, and is introduced into the output side fiber 98.

In this embodiment, the mode conversion splice portions 46 and 78 at both ends of the Er-doped fiber 42 are fixed in the ferrules 48 and 80 of the input and output portions of the front and rear optical components (the optical isolator 52 and the multiplexing / demultiplexing module 62). So Er
The extra length of the connection fibers 44 and 76 between the doped fiber 42 and the optical components before and after the doped fiber 42 can be eliminated.

Further, the excitation laser diodes 82, 9
The ends of the fibers 84 and 92 connected to the ferrules 86 and 94 are directly inserted into and fixed in the ferrules 86 and 94, and these ferrules 86 and 94 are fixed to the multiplexing / demultiplexing module 62. The connection fiber for the light source can be omitted.

Therefore, in combination with the elimination of the extra length of the connecting fiber, the entire optical fiber amplifier can be reduced in size to about 1/3 as compared with the conventional configuration. FIG.
Referring to FIG. 1, there is shown an embodiment of the present invention of a forward-pumped optical fiber amplifier. The same components as those in the above-described embodiment are denoted by the same reference numerals, and description thereof will be omitted.

In this embodiment, the pump light propagates in the Er-doped fiber 42 in the same direction as the signal light propagates, and the signal light is amplified by stimulated emission. Also in this embodiment, the extra lengths of the connection fibers 44 and 76 can be eliminated, and the connection fiber for the excitation light source can be omitted, so that the entire optical fiber amplifier is the same as the above-described embodiment. Can be downsized.

Next, another method of fixing the mode conversion splice to the ferrule will be described with reference to FIG. FIG.
As shown in (A), the Er-doped fiber 42 and the connection single-mode fiber 76 are spliced by a mode conversion splice section 78.

Since the mode conversion splice portion 78 has a considerably large mode field diameter, the polishing portion 79 near the mode conversion splice portion 78 as shown in FIG.
The spliced fiber is polished in FIG.
As shown in (C), even if the ferrule 80 is inserted and fixed, mode conversion can be performed without a connecting fiber.

[0043]

Since the optical fiber amplifier of the present invention is constructed as described above in detail, the overall size of the optical fiber amplifier can be reduced to about 1/3 of the conventional size.

Further, the reinforcement of the splice portion and the mode conversion splice portion can be reliably performed by being fixed in the ferrule. Conventionally, it has been difficult to process the extra length of the connecting fiber, but the trouble of extra length processing is eliminated.

[Brief description of the drawings]

FIG. 1 is a block diagram of a back-excitation type embodiment of the present invention.

FIG. 2 is a configuration diagram of a forward excitation type embodiment of the present invention.

FIG. 3 is a diagram showing another method of fixing a mode conversion splice to a ferrule.

FIG. 4 is a configuration diagram of a conventional example.

[Explanation of symbols]

 42 Er-doped fiber 44, 76 Connecting fiber 46, 78 Mode conversion splice part 52, 74 Optical isolator 62 Bulk type multiplexing / demultiplexing module 68 Demultiplexing film 70 Polarization separating film 82, 90 Laser diode for excitation

Continuation of the front page (72) Inventor Shinya Inagaki 1015 Uedanaka, Nakahara-ku, Kawasaki City, Kanagawa Prefecture Inside Fujitsu Limited (56) References JP-A-4-369627 (JP, A) JP-A 5-190939 (JP, A) JP-A-5-232527 (JP, A) JP-A-3-48472 (JP, A) JP-A-3-127886 (JP, A) JP-A-4-128718 (JP, A) (58) Survey Field (Int.Cl. ⁷ , DB name) H01S 3/00-3/30 H04B 10/00 G02B 6/24 G02B 6/36 G02B 6/38 G02B 6/40 JICST file (JOIS)

Claims (5)

(57) [Claims] 1. A splicing connection of first and second connection fibers (44, 76) to an input side and an output side of a rare earth doped fiber (42), respectively, and excitation via a bulk type multiplexing / demultiplexing module (62). An optical fiber amplifier configured to introduce pumping light from a light source (82, 90) into a rare earth doped fiber (42), wherein one of the first and second connecting fibers (44, 76) is provided. Splice part (46 or 78) into first ferrule
(48 or 80) and fixed in the first ferrule (48
Or 80) is fixed to the housing (64) of the bulk-type multiplexing / demultiplexing module (62). Second ferrule (48 or
80) and fixed in the second ferrule (48 or 80)
Is fixed to a housing (54) of an optical isolator (52). 2. The splice part (46, 7) of the one and the other.
8. The optical fiber amplifier according to claim 1, wherein 8) is a mode conversion splice unit. 3. The first and second mode conversion splice portions (46, 78) are polished near the mode conversion portion, and the polished portions are inserted and fixed in the first and second ferrules (48, 80), respectively. 3. The optical fiber amplifier according to claim 2, wherein: 4. A tip of a fiber (84, 92) connected to the pumping light source (82, 90) is inserted and fixed in a third ferrule (86, 94), and the third ferrule (86, 94) is fixed. The optical fiber amplifier according to any one of claims 1 to 3, wherein the optical fiber amplifier is fixed to a housing (64) of the bulk type multiplexing / demultiplexing module (62). 5. The multiplexing / demultiplexing module (62) includes a multiplexing / demultiplexing prism unit (66) having at least a multiplexing film (68) and a total reflection film (72), and a second optical isolator (74). The optical fiber amplifier according to any one of claims 1 to 4, further comprising: