JPH1090547A - Light amplifier - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a high reliable light amplifier preventing a connector end surface from being damaged owing to heat caused by an excess light output by using a fiber expanding a mode field size for the output connector end surface of the high output light amplifier. SOLUTION: A connector 5 is provided on a tip of an outputting optical fiber 4 leading out an optical signal amplified and outputted by the light amplifier 3, and the inserted core of the tip part of the optical fiber 4 is exposed for optically coupling to an external lead-out path. Then, the connector 5 is formed so that the mode field size of the core is expanded in a reversely tapered shape on the end surface. When the mode field size on the output fiber end surface is made a structure expanded in such a manner, spatial optical power density on the output fiber end surface is reduced by the much that an area is expanded. Thus, even when dirt exists on this part, heat absorption is reduced. That is, the caused heat is dispersed spatially, and a temp. rise is suppressed.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a high-power optical amplifier and an optical amplifier using a rare-earth-doped fiber using glass other than silica as a host glass.

[0002]

2. Description of the Related Art In optical communication, an optical fiber cable is used as a transmission line, a laser beam is optically modulated by a transmission signal, transmitted to the optical fiber cable, and demodulated on a receiving side to receive a signal. Communication technology. In recent years, with the advancement of optical communication technology, there has been an increasing number of processes to be applied to signals as they are.

[0003] In many of the techniques for processing a signal while keeping the light as it is, many techniques use the nonlinear response of an optical fiber. However, in order to cause a nonlinear response in the optical fiber, it is necessary to input signal light or control light with high optical power. In order to obtain such high optical power, an optical fiber amplifier is usually used, and this optical fiber amplifier has a maximum of 20 dB.
m (100 mW) or more.

The output part of an optical amplifier is usually an optical connector. Then, an optical connector attached to the end of the optical fiber cable is connected here, and the optical output is guided to the optical fiber cable. By the way, when connecting the optical connectors, the exposed portion of the optical fiber at the tip of the optical connector is wiped clean with alcohol or the like so that there is no adhesion of dust or the like on the exposed portion of the optical fiber. And then connect. If there is any foreign matter such as dust, the optical fiber amplifier can be up to 20d
Since an output of Bm (100 mW) or more can be output, the attached dust is burned by light energy passing through the optical fiber cable, and there is a risk that the heat may damage the optical fiber such as cracking. Also,
If there is dirt, there is also a danger of causing light reflection and reducing transmission efficiency.

In order to avoid such a danger, the exposed portion of the optical fiber at the end of the optical connector is cleaned by wiping with alcohol or the like so that the exposed portion of the optical fiber is free from dust. And then connect.

[0006] As described above, cleaning the optical connector on both the outgoing side and the incoming side prevents thermal damage,
Although it is indispensable to reduce connection loss and light reflection, hand oil may dissolve in solvents such as alcohol used in this cleaning work. The use of a method may cause a situation in which oil in the solvent adheres to the vicinity of the core of the optical fiber after wiping dust and dirt.

When an optical connector in such a state is connected and light having a power of about 20 dBm is incident on the optical connector, oil absorbs the light and the amount of heat generated there increases. May melt the core. In such a case, the connection loss and the light reflection become extremely large in the connector portion, and the function as the connector is lost.

Usually, the type of rare earth added to an optical fiber amplifier differs depending on the amplification wavelength. Erbium is added in the 1.5 μm band, and praseodymium is added in the 1.3 μm band. The type of host glass that is well suited (provides higher performance) depends on the type of rare earth added. In erbium, silica glass is usually used as a host, whereas in praseodymium, fluoride glass is often used as a host. Also, in order to make the gain wavelength characteristics flatter even with erbium,
It has been proposed to use fluoride glass for the host.

The fiber used for transmission is 1.3 μm
Both the 1.5 μm band and the 1.5 μm band are silica fibers. However, the silica fiber and the fluoride fiber have problems such as different coefficients of thermal expansion and refractive indices, and cannot be fused and spliced, that is, cannot be directly connected.

In the case of praseodymium-doped fiber,
Because the pumping efficiency of the material is slightly inferior, the NA of the fiber
(Numerical aperture) is increased, the core diameter is reduced, the mode field diameter is reduced, and the optical power density in the core is increased to improve the pump efficiency. Such a fiber has a significantly different mode field diameter from that of a silica fiber used for normal transmission. Therefore, if the fiber is directly connected to a normal silica fiber, a large loss occurs. this is,
Not only can they cause reflections and noise, but they can sometimes cause oscillations.

In order to avoid such a problem, as shown in FIG. 8, Kanamori et al. Use a method of inserting a high NA (numerical aperture) silica fiber between a normal silica fiber and a praseodymium-doped fiber. (Refer to the document “Optronics”, 1994, no. 9, p 107).

[0012] After the fusion splicing, the spliced portion is blown with a burner to enlarge the core diameter, and the mode field diameter is gradually changed at the joint portion. Thus, light loss due to mode field mismatch is prevented.

The high NA silica fiber and the praseodymium-doped fiber are each formed on a support substrate.
After the tip is placed on the groove and polished obliquely, they are butted and connected with an adhesive. Such a method is not only very complicated and time-consuming, but also has a possibility that the adhesive may be carbonized by light energy, which is not reliable.

[0014]

As described above, in a high-output optical fiber amplifier, since the energy density of the optical output is extremely high, if dirt adheres to the end face of the output connector, heat is absorbed. There is a possibility that the end face of the output connector may be burned and handling is troublesome.

In an optical fiber amplifier in which a rare-earth-doped optical fiber using a fluoride fiber as a host glass is used as an output connector, a splice cannot be made directly with the silica fiber. It was necessary to take a complicated configuration such as core enlargement, oblique polishing, and connection using an adhesive. Accordingly, it is an object of the present invention to provide an optical amplifier that eliminates these problems.

[0016]

SUMMARY OF THE INVENTION In order to solve the above-mentioned problems, according to the present invention, the amplified light is led out by an optical fiber, and the light output led out by the optical fiber is further led to the outside. In the end face of the output connector, the core of the optical fiber is characterized in that the mode field diameter is enlarged by core enlargement or the like.

An output connector is provided to guide the optical output to the outside. An external optical fiber is connected to the output connector to derive an optical signal. However, the fiber core surface at the end face of the output connector becomes dirty with hand oil or the like. In this case, the amplified light may be absorbed to generate heat and melt. The reason for melting due to the attached hand oil or the like is that a large optical power is concentrated there. Therefore, in order to avoid this, it is only necessary to prevent the light power from concentrating enough to cause the dirt to burn.

For this purpose, the mode field diameter of the core of the optical fiber in the connector output section may be increased as shown in FIG. As the mode field diameter increases, even if the total optical power is the same, the light density of the peak is reduced in the spatial distribution, and the light is spatially dispersed. Therefore, the heat generated by the light loss is also spatially dispersed, and the resulting temperature rise is reduced, and it is difficult to reach a temperature at which the fiber end face is melted.

As a method of expanding the core, TEC (ther
mally-diffused expanded c
ore). TEC is a technique in which heat is applied to an optical fiber by a burner or the like to diffuse a dopant doped in the core for raising the refractive index to the cladding. By using this, it is possible to increase the mode field diameter while maintaining the single mode property (literature;
Yanagi et al., IEICE Technical Report OQE90-7
2 etc.).

Further, according to the present invention, in an optical fiber amplifier using a rare earth-doped fiber using glass other than silica as a host glass, an optical function disposed immediately before, immediately after, or immediately before or after the rare earth-doped fiber in a signal optical bus. An optical fiber amplifier, wherein a component is configured by micro optics, and an optical pigtail fiber on a side of the optical functional component connected to the rare earth-doped fiber is made of the same kind of host glass as the rare earth-doped fiber. I do.

Further, the N of the optical pigtail fiber is
An optical amplifier characterized in that A (numerical aperture) is substantially equal to NA of the rare earth doped fiber. Further, in an optical fiber amplifier using a rare earth-doped fiber using a glass other than silica as a host glass, an optical functional component disposed immediately before, immediately after, or immediately before or after the rare earth-doped fiber in a signal optical bus is constituted by microoptics. And an optical fiber amplifier, wherein the rare-earth-doped fiber is directly connected to the optical functional component as its pigtail fiber.
Further, in these, an optical fiber amplifier is provided, wherein the host glass is a fluoride glass.

Further, in these, the present invention provides an optical fiber amplifier characterized in that the added rare earth is praseodymium. Alternatively, there is provided an optical fiber amplifier in which the rare earth added is erbium.

In an optical fiber amplifier, optical isolators are usually arranged before and after to suppress oscillation. Optical isolators are usually made with micro-optics. The pump light enters the rare-earth-doped fiber via a wavelength multiplexer / demultiplexer. There are two types of multiplexer / demultiplexer: an optical fiber type and a micro-optic type.

The configuration of the optical fiber amplifier is usually shown in FIG.
It is as shown in FIG. This is an example of bidirectional excitation. 4
The isolator 1 enters the position indicated by the arrow A when the wavelength of the pump light is far from the wavelength of the signal light and is out of the band of the isolator. In the case of only forward pumping, the 47 multiplexer / demultiplexer and the pump light source 49 are eliminated. At this time, depending on the case, an optical filter for cutting the pump light may enter the position of the multiplexer / demultiplexer 47 or the position of the arrow B. In the case of only backward pumping, there are no 40 multiplexers / demultiplexers and 48 pump light sources. In this case, a filter for cutting the pump light is rarely provided instead, but it may be provided.

In the present invention, the pigtail fiber on the side of the rare earth-doped fiber of the isolator 41 (host glass other than silica glass) in the example of FIG.
The multiplexer / demultiplexer 47 is made of micro optics, and the pigtail fiber on the side of the rare earth-doped fiber is made of the same kind of host glass as the rare earth-doped fiber, and has an NA substantially equal to the NA (numerical aperture) of the rare earth-doped fiber. By using a fiber, the mode field diameter is almost matched. As a result, splicing becomes possible, and reflection and loss due to mode field diameter mismatch are reduced.

As a host glass other than silica, fluoride glass is often used. Splices between fluoride fibers using fluoride glass as a host glass are not as simple as splices between silica fibers using silica as a host glass, but the splices by a method such as heat fusion, that is, welding. Connection is possible.

Since the isolator and the multiplexer / demultiplexer are made of micro-optics, the fiber ends at the entrance and exit, and the inside is made of bulk optical functional parts. Also, light from the input pigtail fiber to the output pigtail fiber is coupled by a lens. Therefore,
Even if the input pigtail fiber and the output pigtail fiber have different mode field diameters, the mode field diameter can be converted by appropriately designing the magnification of the lens used.

That is, the pigtail fiber on the side of the rare earth doped fiber using a host glass other than silica uses a fiber matched to the rare earth doped fiber, and the pigtail fiber on the opposite side is a fiber matched to the fiber to be connected, such as a silica fiber. Used.

In this manner, loss and reflection due to mismatch of the mode field diameter at the splice portion are almost eliminated. Further, since there is no connecting portion by the adhesive, the performance of the adhesive does not deteriorate due to the deterioration or damage of the adhesive.

However, since the splice is somewhat difficult, when the splice is incomplete, it causes loss or reflection. In order to prevent such a situation, the splice portion may be completely eliminated. Therefore, FIG.
The rare earth-doped fiber 21 using a glass other than silica glass as a host glass as in 1 is directly connected as a pigtail fiber to an isolator 43 or a multiplexer / demultiplexer 44 made of micro optics. In this case, since there is no splice point, there is no occurrence of splice failure or reflection due to incompleteness.

[0031]

Embodiments of the present invention will be described below with reference to the drawings. (First Specific Example) A first specific example of the present invention will be described with reference to FIG. In FIG. 1, reference numeral 1 denotes an input optical connector, reference numeral 2 denotes an optical fiber for inputting the optical connector 1 at one end, and reference numeral 3 denotes light input through the optical fiber 2 for optical input. An optical amplifier 4 for amplifying and outputting a signal, 4 is an output optical fiber for deriving an optical signal amplified and output by the optical amplifier 3, 5 is an output optical fiber 4
Is a connector that is a connector for connecting the optical signal guided by the above to an external outgoing path in order to send it out to, for example, a transmission path. The connector 5 is provided at the tip of the optical fiber 4, and the tip of the optical fiber 4 in the connector 5 has a sandwiched core exposed for optical connection to an external lead-out path. Therefore, the connector 5 is a connector in which the mode field diameter of the core expands in an inverted tapered shape at the end face. The shape that expands the mode field diameter of the core in a reverse taper shape is a TEC (thermally-
This is realized by a technique such as "diffused expanded core".

As described above, the example shown in FIG. 1 is an example in which the mode field diameter at the output fiber end face of the optical amplifier 3 is gradually enlarged by a technique such as TEC. That is, the mode field diameter at the end face of the output fiber is gradually expanded in an inverse tapered shape and processed so as to become thick.

If the mode field diameter at the end face of the output fiber from which the output light of the optical amplifier 3 is derived is enlarged as in this embodiment, the spatial area at the end face of the output fiber is increased by the increased area. Optical power density decreases. Therefore, even if there is dirt in this portion, heat absorption is reduced.
That is, heat generated by light loss due to dirt or dust is spatially dispersed, and as a result, temperature rise is suppressed. Thus, it is less likely that the temperature will be high enough to melt the fiber.

In FIG. 1A, the input / output fibers 2 and 4 of the optical amplifier 3 are pigtailed.
As shown in (b), the optical amplifier 3 is usually housed in the housing 6,
In some cases, input and output are adapters. in this case,
Usually, inside the housing 6, the ends of the fibers are
The output end face of the fiber on the output side (connection side to the adapter 8) has a mode field diameter enlarged as described above.

Regardless of the example shown in FIG. 1A or the example shown in FIG. 1B, the degree of expansion of the mode field diameter is usually sufficient if it is about 1.4 to 2 times the fiber diameter. .
Of course, it may be higher, but the light density of the peak is reduced to 1/2 at 1.4 times and reduced to 1/4 at 2 times. Therefore, an appropriate value is set according to the difficulty of processing.

The method of expanding the mode field is not limited to TEC alone. TEC is the one in which the refractive index difference Δn between the core and the clad is reduced to increase the core diameter.
Even if the core diameter is reduced while maintaining Δn at a normal value, the mode field diameter increases. Such a fiber can be manufactured by drawing at a higher speed than usual so as to reduce the fiber diameter in a drawing step in a normal fiber manufacturing process.

Alternatively, a fiber having a mode field diameter similar to that of the TEC or a fiber having a small core diameter is formed so as to have such a refractive index distribution at the preform stage, and a normal fiber diameter (125 μm) is used. The fiber diameter may be the same as the diameter of the fiber. However, since a fiber having a large mode field diameter has a large bending loss, it is preferable that the mode field is expanded only in the vicinity of the connector end face, such as TEC.

When an optical amplifier having an optical connector having an enlarged mode field diameter at the output connector end face as an output connector (output connector) is used, an external transmission line connected to the output connector is used. The optical connector for connection in the optical fiber cable or the like needs to have a structure in which the mode field diameter is similarly increased. If not processed into such a shape, loss or reflection occurs due to mode field mismatch.

However, since the fiber used for a normal optical component is a silica fiber having a normal mode field diameter, it is preferable to prepare an optical code for converting the mode field diameter as shown in FIG. Of course, the outgoing end face of the pig teal fiber of the component connected to the optical amplifier may have an enlarged mode field diameter.

In the example shown in FIG. 2, the conversion cord 10 is connected to the connector 5 at the tip of the optical fiber 4. The conversion cord 10 is connected at one end to a connector 9 having a structure in which the mode field diameter at the fiber end face is gradually increased (a structure having a tapered shape), and the other end is connected to the fiber core end face. A connector 9 having a structure in which the mode field diameter is a normal diameter is connected. By this conversion code 10, one end can be connected to the connector 5 and the other end can be connected to the normal connector. Become.

As described above, the connector 9 having the structure in which the mode field diameter at the end face of the fiber is gradually increased (the structure becomes thicker in a reverse taper shape) is connected to one end, and the fiber core is connected to the other end. The use of a structure having a normal mode field diameter at the end face facilitates conversion of the mode field diameter.

When the configuration using the conversion code 10 as shown in FIG. 2 is adopted, the conversion code 10 has a normal mode field diameter at the end face of the connector 11. There is a risk that the end face of the connector 11 is melted by the high output of the optical amplifier 3. However, even if it melts, the connector 5 on the optical amplifier 3 side is unlikely to be burned due to the expansion of the mode field diameter, so there is a high possibility that it will be safe. Will be able to

In the case of the conventional device, the end face of the optical fiber on the output side of the optical amplifier is burned (because of the normal mode field diameter). In that case, the entire optical amplifier needs to be repaired, which is troublesome. Was. However, the use of the technique of the present invention reduces the risk of burning the end face of the optical fiber of the optical amplifier, thereby ensuring high security. Thus, the advantage of applying the mode field expansion connector to the optical amplifier is great.

(Second Specific Example) FIG. 3 shows a second specific example of the present invention. In this specific example, the optical functional components 12 and 16 immediately before and immediately after the rare earth-doped fiber 14 using a host glass other than silica glass (fluoride glass in FIG. 3) are manufactured by micro optics. The pigtail fibers 13 and 15 on the 14 side are made of the same kind of glass (fluoride glass in FIG. 3) as the host glass of the rare earth-doped fiber 14, and the NA
(Numerical aperture) is configured to be substantially equal to the NA of the rare-earth-doped fiber 14.

In this specific example, a heat fusion splice is performed between the pigtail fiber 13 and the rare-earth-doped fiber 14, and between the pigtail fiber 15 and the rare-earth-doped fiber 14, and the two are connected.

As described above, a rare earth-doped fiber is used as a light guide at the optical signal input / output end of the optical functional component, and the connection of the light guide between the optical functional components is performed by the rare earth-doped fiber. Since the connection between the rare-earth-doped fibers is made by a heat fusion splice, the connection can be made easily and without light loss.

(Third Specific Example) FIG. 7 shows a third specific example of the present invention. In this configuration, the rare-earth-doped fiber 14 is directly connected to the micro-optics optical functional component 12.
And 16 as its pigtail fiber.

In FIGS. 3 and 7, the outside of the functional components 12 and 16 made of micro optics may have various configurations, and therefore are not shown in the drawings. Also,
What the functional components 12 and 16 made by micro optics are is not specified here because it differs depending on the configuration.

The above is the transfer of the light output to another.
Various ways of connecting the fibers to guide the light output have been described. next,
Some examples of the configuration of the optical amplifier of the present invention will be described.

(Fourth Specific Example) <Configuration Example of Forward Pumped Optical Amplifier> FIG. 4A shows a configuration example of a forward pumped optical amplifier. In the figure, 17 and 21 are pump light sources, 18 is a multiplexer / demultiplexer, 19 and 23 are optical isolators, 20 and 23 are pigtail fibers of optical isolators 19 and 23, and 21 is a rare earth-doped fiber using a host glass other than silica. is there.

In this example, optical isolators are provided immediately before and immediately after the rare-earth-doped fiber 21, and the ends of the pigtail fibers 20 and 23 of the optical isolators 19 and 23 are connected to the rare-earth-doped fiber 21.

The pigtail fibers 20, 23 of the optical isolators 19, 23 are connected to the tip of the rare-earth-doped fiber 21. The pigtail fibers 20, 23 are made of the same kind of glass as the host glass of the rare-earth-doped fiber 21, and have an NA of less. Since they are almost equal, connection processing can be easily performed by heat fusion or the like.

The pigtail fibers 20, 23 and the rare-earth-doped fiber 21 have substantially the same NA, and are spliced by heat fusion or the like. The pump light generated from the pump light source 17 and the optical signal to be amplified are mixed and amplified by the multiplexer / demultiplexer 18, and after being amplified by the pigtail fiber 20 via the optical isolator 19, the rare-earth doped fiber 21.
However, when the wavelength of the pump light is out of the transmission band of the isolator 19, the isolator 19 has a structure arranged at the position indicated by the arrow with the symbol A.

In this case, the optical functional component immediately before the rare earth-doped fiber 21 is the multiplexer / demultiplexer 18. At this time, the pigtail fiber on the side of the rare earth-doped fiber 21 of the multiplexer / demultiplexer 18 is made of the same type of glass as the host glass of the rare earth-doped fiber 21, has a substantially equal NA, and is spliced by heat fusion with the rare earth-doped fiber. adopt.

In these configurations, the filter 24 for cutting the pump light at the output stage may not be provided. A configuration in which the rare-earth-doped fiber 21 and the pigtail fibers 20 and 23 spliced therewith are put together and replaced with the rare-earth-doped fiber 21 can be adopted. In this case, the configuration example shown in FIG. 7 is used.

<Example of Back-pumped Optical Amplifier Configuration> FIG. 4B
Is a configuration example of a backward-pumped optical amplifier. In this example, the optical functional component immediately before the rare-earth-doped fiber 21 is the isolator 19, and the optical functional component immediately after the rare-earth-doped fiber 21 is the multiplexer / demultiplexer 25. The pigtail fibers 20, 26 on the rare-earth-doped fiber side are made of the same kind of glass as the host glass of the rare-earth-doped fiber 21, have substantially the same NA, and are spliced with the rare-earth-doped fiber 21 by heat fusion or the like.

The pigtail fibers 20, 26 and the rare-earth-doped fiber 21 are put together to form the rare-earth-doped fiber 21.
If it replaces with, it will become the example of a structure shown in FIG. <Configuration Example of Bidirectionally Pumped Optical Amplifier> FIG. 4C shows a configuration example of a bidirectionally pumped optical amplifier. In this example, the optical functional component immediately before the rare-earth-doped fiber 21 is the isolator 19, and the optical functional component immediately after the rare-earth-doped fiber 21 is the multiplexer / demultiplexer 25. The pigtail fiber 20 on the rare earth doped fiber side,
26 is made of the same kind of glass as the host glass of the rare earth-doped fiber 21, has almost the same NA, and is spliced by heat fusion or the like.

When the wavelength of the pump light (pump light from the pump light source 17) excited from the front is out of the transmission band of the isolator 19, the isolator 19 is arranged at the position indicated by the arrow A. In this case, the optical functional component immediately before the rare-earth-doped fiber 21 becomes the multiplexer / demultiplexer 18, and the pigtail fibers 20 and 26 on the rare-earth-doped fiber side are made of the same type of glass as the host glass of the rare-earth-doped fiber 21. They are almost equal, and are spliced by heat fusion or the like. Pigtail fiber 2
If the 0 and 26 and the rare earth-doped fiber 21 are collectively replaced by the rare earth-doped fiber 21, the configuration example shown in FIG. 7 is obtained.

An optical amplifier is constituted by such a configuration. However, in FIG. 4, the multiplexers / demultiplexers 18 and 25 and the optical isolators 19, 22, and 27 are individually provided, but they may be integrated into one micro optics module without interposing a fiber therebetween.

FIG. 5A shows an example of the configuration of a portion of the optical amplifier in which pump light is injected from the front. Reference numeral 17 denotes a pump light source, and 28 denotes a multiplexer / demultiplexer + optical isolator. Pump light is injected into the isolator 28 from the front by the pump light source 17.

The fiber (pigtail fiber 29) at the light emitting end from the multiplexer / demultiplexer + optical isolator 28 is made of the same kind of glass as the host glass of the rare-earth-doped fiber 21, has almost the same NA, and is doped with rare-earth by heat fusion or the like. Whether it is spliced with the fiber 21 (the configuration example of the invention of FIG. 3), or is directly a rare earth doped fiber (the configuration example of the invention of FIG. 7).

FIG. 5B shows a configuration example of a part of the optical amplifier for injecting pump light from the rear. Reference numeral 17 denotes a pump light source, 30 denotes a multiplexer / demultiplexer + optical isolator, and FIG. Pump light is injected into the isolator 30 from behind by the pump light source 17.

The fiber 31 at the signal light incident end of the multiplexer / demultiplexer + optical isolator 30 is made of the same kind of glass as the host glass of the rare-earth-doped fiber 21, has almost the same NA, and is spliced with the rare-earth-doped fiber by heat fusion or the like. (Example of the configuration of the invention described with reference to FIG. 3) or directly
The fiber is a rare-earth-doped fiber (a configuration example of the invention described with reference to FIG. 7).

FIG. 5C shows a part of the configuration of the optical amplifier in the case of only forward pumping. In this optical amplifier, an optical isolator and an optical bandpass filter have a composite structure. This is an example in which the optical functional components (optical isolator and optical bandpass filter) at the output end of the optical amplifier are integrated into one module.
3 is made of the same kind of glass as the host glass of the rare-earth-doped fiber 21 and has almost the same NA and is connected to the rare-earth-doped fiber 21 by heat fusion or the like (the configuration example of the invention in FIG. 3), or directly. , Rare earth doped fiber 2
1 (example of the configuration of the invention described in FIG. 7).

FIG. 6 shows an example of the internal configuration of the isolator module when it is arranged immediately before the rare-earth-doped fiber 21. 6 (a) and 6 (b), numeral 34 is made of the same kind of glass as the host glass of the rare earth-doped fiber,
A fiber having almost the same NA or a rare earth-doped fiber, and 35 is a normal fiber.

In FIG. 6A, reference numerals 36 and 37 denote lenses, which form a two-lens system.
A bulk isolator is inserted between 6 and 37. In the case of this configuration, the mode field diameter is converted by a total of two lenses, lenses 36 and 37, the mode field diameter of the fiber 35 is “W2”, and the fiber 34 is
Is "W1", the light emitted from the fiber 35 has its mode field diameter converted by the two lenses 36 and 37, and becomes "W1 '" when it enters the fiber 34. Here, “W1 ′” and “W
1 "is approximately equal.

Of course, the mode field diameter can be converted even with a single-lens system. In this case, the configuration is as shown in FIG. 6B. The pigtail fibers 34, 35
The end face on the side of the optical isolator may be subjected to non-reflection termination by a method such as oblique polishing.

While several examples of the configuration of the optical amplifier of the present invention have been described above, configurations other than those described above can be adopted as long as the configuration of the portion shown in FIG. 3 or 7 is included. The optical amplifier is generally used for optical processing of an optical communication system or an optical signal for optical communication. The wavelength band used for optical communication is
Usually, there are two types, 1.3 μm band and 1.55 μm band.
In an optical amplifier used in the m-band, a rare-earth-doped fiber 2
The rare earth element 1 is usually praseodymium, and erbium in the 1.5 μm band.

The host glass of the rare earth-doped fiber 21 used in the present invention is a fluoride glass (ZrF
₄ , InF ₃ etc.) or chalcogenide glass.

As described above, according to the present invention, the core of the optical fiber is provided at the output connector end face for guiding the amplified light through the optical fiber and further guiding the optical output guided by the optical fiber to the outside. The mode field diameter is enlarged by enlargement or the like.

An output connector is provided to guide the optical output to the outside. An external optical fiber is connected to the output connector to derive an optical signal. However, the fiber core surface at the end face of the output connector becomes dirty with hand oil or the like. In such a case, the amplified light may be absorbed and generate heat and melt, but in order to avoid this, the mode field diameter of the core of the optical fiber in the connector output section is increased. This spread prevented the concentration of light power that caused the dirt to burn.

As described above, by increasing the mode field diameter, even if the total optical power is the same, the light density of the peak is reduced in the spatial distribution, and the light is spatially dispersed. The heat generated by the loss is also spatially dispersed, and the resulting temperature rise is reduced, making it difficult to reach a temperature that melts the fiber end face, thereby suppressing thermal damage due to contamination. .

Further, according to the present invention, in an optical fiber amplifier using a rare earth-doped fiber using glass other than silica as a host glass, an optical function disposed immediately before, immediately after, or immediately before or after the rare earth-doped fiber in the signal light bus. The component is constituted by micro optics, and the optical pigtail fiber on the side of the optical functional component connected to the rare earth doped fiber is constituted by the same kind of host glass as the rare earth doped fiber. Further, the NA (numerical aperture) of the optical pigtail fiber was made substantially equal to the NA of the rare earth-doped fiber.

In an optical amplifier using a rare earth-doped fiber using a glass other than silica as a host glass,
An optical functional component disposed immediately before, immediately after, or immediately before or after the rare-earth-doped fiber in the signal optical bus is configured by microoptics, and the rare-earth-doped fiber is directly connected to the optical functional component as its pigtail fiber. And Further, in these, the host glass was fluoride glass.

As the pigtail fiber, a host glass made of fluoride glass is used. The pigtail fiber is made of the same kind of host glass as the rare earth-doped fiber.
NA almost equal to NA (numerical aperture) of rare earth doped fiber
By making the mode field diameter substantially matched by using the above-mentioned fiber, splicing between the pigtail fiber and the rare earth-doped fiber becomes possible, and reflection and loss due to mode field diameter mismatch can be reduced. . Note that the present invention is not limited to the specific examples described above, and can be implemented in various modifications.

[0076]

As described above, according to the present invention, the end face of the connector is damaged by the heat generated by the excessive light output by using the fiber having the expanded mode field diameter for the end face of the output connector of the high output optical amplifier. Can be prevented, and a highly reliable optical amplifier can be provided.

Further, according to the present invention, in an optical amplifier using a rare earth-doped fiber using glass other than silica as a host glass, the optical functional components disposed immediately before and immediately after the rare earth-doped fiber are made of micro optics. The pigtail fiber on the rare-earth-doped fiber side is made of the same kind of glass as the host glass of the rare-earth-doped fiber, the NA is almost the same, and the spliced fiber is spliced with the rare-earth-doped fiber by heat fusion, etc. Can be easily solved. Therefore, connection with small connection loss and reflection is possible, and an optical amplifier with low noise and high gain can be obtained.

[Brief description of the drawings]

FIG. 1 is a diagram for explaining the present invention, showing an embodiment of the present invention.

FIG. 2 is a diagram for explaining the present invention, showing an application example of the present invention.

FIG. 3 is a diagram for explaining the present invention, showing an embodiment of the present invention.

FIG. 4 is a diagram for explaining the present invention, showing an embodiment of the present invention.

FIG. 5 is a diagram for explaining the present invention, and is a partial view of an embodiment of the present invention.

FIG. 6 is a diagram for explaining the present invention.

FIG. 7 is a diagram for explaining the present invention, showing an embodiment of the present invention.

FIG. 8 is a diagram showing a conventional example.

FIG. 9 is a diagram illustrating the present invention.

FIG. 10 is a configuration diagram of a general optical fiber amplifier.

FIG. 11 is a diagram showing an embodiment of the present invention.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Optical connector 2, 4, 42 ... Optical fiber 3 ... Optical amplifier 5, 9 ... Connector whose mode field diameter is enlarged at the end face 6 ... Optical amplifier housing 7 ... Signal input adapter 8 ... Signal output adapter 10 ... Conversion Code 11: Connector with normal mode field diameter 12, 16 ... Optical functional component made by micro optics 13: Pigtail fiber of optical functional component 12 made by micro optics 14 ... Rare earth doped fiber using fluoride glass as host 15 ... Pig tail fiber of 16 17, 48, 49 pump light source 18, 25, 40, 44, 47 multiplexer / demultiplexer 19, 22, 27, 38, 41, 43, 45, 46 optical isolator 20 pigtail fiber of optical isolator 19 21 Rare-earth-doped fiber using host glass other than silica 23. Optical isolation Pigtail fiber of the filter 22 ... optical bandpass filter 26 ... pigtail fiber 28 of the multiplexer / demultiplexer 25, multiplexer / demultiplexer + optical isolator 30 ... 29 ... pigtail fiber of the multiplexer / demultiplexer + optical isolator 28 31 ... multiplex / demultiplex , The pigtail fiber of the optical isolator 30 32... The optical isolator and the optical bandpass filter 33. The pigtail fiber of the optical isolator and the optical bandpass filter 32, 35, and the pigtail fibers 36, 37, and 39.

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Claims (7)

[Claims] In an optical amplifier for amplifying an optical signal and outputting the amplified signal through an optical fiber, an output connector end face connected to a tip of the optical fiber has a mode field diameter due to an enlarged core or the like in order to output the amplified light. An optical amplifier having an enlarged configuration. 2. An optical fiber amplifier using a rare earth-doped fiber using a glass other than silica as a host glass, wherein an optical functional component disposed immediately before, immediately after, or immediately before or after the rare earth-doped fiber in a signal optical bus is micro-optics. Wherein the optical pigtail fiber on the side of the optical functional component connected to the rare earth-doped fiber is made of the same kind of host glass as the rare earth-doped fiber. 3. The optical amplifier according to claim 2, wherein an NA (numerical aperture) of said optical pigtail fiber is substantially equal to an NA of said rare earth-doped fiber. 4. An optical fiber amplifier using a rare earth-doped fiber using a glass other than silica as a host glass, wherein the optical functional component disposed immediately before, immediately after, or immediately before or after the rare earth-doped fiber in the signal light path is micro-optics. Wherein the rare-earth-doped fiber is directly connected to the optical functional component as its pigtail fiber. 5. The optical amplifier according to claim 2, wherein said host glass is a fluoride glass. 6. The optical amplifier according to claim 2, wherein said rare earth-doped fiber is praseodymium. 7. The optical amplifier according to claim 2, wherein the rare-earth-doped fiber is erbium-doped rare earth.