JP2001305479A - Optical coupling method for backward excitation and optical coupler for backward excitation using the method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To solve many conventional problems that at least a polarized wave combiner, a WDM coupler and excessive optical fibers are necessary in order to input exciting light for posterior excitation in an erbium doped fiber(EDF), an optical coupler is large and expensive, and a loss is large and so on. SOLUTION: The above problems are solved by making a WDM coupler function, a polarized wave synthesis function, an isolator function, and further an isolator function for protection of an excitation light source together by one isolator element. Specifically, a single mode fiber(SMF) collimator is arranged at the input side of an isolator element, the SMF collimator and a polarization maintaining fiber(PMF) collimator are arranged at the output side of the isolator element, then exciting light is inputted from the PMF collimator.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a backward pumping optical coupling method such as a pumping light source coupling pumping module constituting an optical fiber amplifier, and a backward pumping optical coupler using the method.

In the following description, an optical coupler for backward pumping will be mainly described as an example, and the optical coupling method of the present invention will be described through the description.

[0003]

2. Description of the Related Art An erbium-doped fiber amplifier, which is one of the optical fiber amplifiers, is used.
ber Amplifier (hereinafter, also referred to as EDFA) has been widely used in the field of optical fiber communication systems.

FIG. 5 shows a typical example of a conventional backward-pumped EDFA, which is one of the configurations of the EDFA. As is well known, an EDFA has an input signal port 403, an output signal port 404, and an excitation light input port 505 as shown in FIG. 5, and an input signal light having a wavelength of, for example, 1.55 μm incident from the input signal port 403. Is EDF
It is amplified at A and reaches the output signal port 404. In this case, in order for the optical amplification action to be performed, pumping light having a different wavelength (for example, a wavelength of 1.48 μm) is used.
From the pump light input port 505, WDM (Waveleng)
th Divis-on Multiplexer)
It must be coupled to an erbium-doped fiber (hereinafter also referred to as EDF) 402 via a coupler 501.

[0005] An optical path inside the EDFA shown in FIG. 5 will be described below. First, the signal light having a wavelength of, for example, 1.55 μm that has entered the input signal port 403 travels in the signal light propagation direction indicated by the arrow 1123 and is input-side optical isolator (hereinafter, the optical isolator is also simply referred to as an isolator).
The EDF 402 passes through a module (hereinafter, an optical isolator module is also referred to as an isolator module. The isolator module includes an isolator element with a fiber collimator on the input side of the isolator element and a fiber collimator on the output side of the isolator element) 401. Reach

On the other hand, separately from the pump light input port 50,
Excitation light incident from 5 (for example, wavelength 1.48 μm)
Is transmitted through the WDM coupler 501 in the pumping light propagation direction indicated by arrows 1134 and 1135.
To join. At this time, it goes without saying that the traveling directions of the input signal light and the pump light entering the EDF 402 are opposite directions inside the EDF 402.

That is, by injecting a large output pump light from behind the EDF 402, a weak input signal light is
It is amplified inside the DF. The signal light amplified in this way travels in the direction of arrow 1124, passes through the WDM coupler 501 from the common port 506, travels in the direction of arrow 1125, that is, travels to the output port 507, and sets the output-side isolator module 508 to After passing, it reaches output signal port 404.

In general, to increase the output signal from the EDFA, it is necessary to increase the pump light output. In order to achieve this object, the EDFA having the configuration shown in FIG. 5 has two excitation light sources (here, semiconductor laser light sources 405 and 40).
6), and linearly polarized light emitted from these light sources is respectively polarized in a polarization maintaining fiber (Polarisati-o).
n Maintaining Fiber, PM
F) 502 and 503, and further combines the respective linearly polarized lights emitted from these PMFs in a polarization combiner 504, and inputs the combined output to an excitation input port 505 of the WDM coupler 501. ing.

The polarization combiner 504 combines optical powers corresponding to the sum of two linearly polarized input optical powers, thereby generating a high-power pumping light source and supplying it to the pumping light input port 505. EDFA with high output.

As described above, in the conventional optical coupling method for backward pumping, at least the polarization combiner 504 and the WDM coupler 50 are required to allow the light from the backward pumping light source to enter the EDF.
No. 1 had to be used, and an extra optical fiber had to be used for that. Therefore, these polarization combiners, W, are included in the backward-pumping optical coupler using the conventional method.
It was necessary to incorporate DM couplers and the optical fibers required for them.

[0011]

As described above, according to the conventional method, at least a polarization combiner, a WDM coupler, and an extra optical fiber are required to input the pump light for backward pumping to the EDF. Therefore, not only is there a major drawback that the optical coupler for backward pumping becomes large and the product cost increases, but also there is a major drawback in that the insertion loss increases in terms of optical characteristics. These issues will be described below.

(1) Large and expensive optical couplers The increase in size and the increase in product cost due to the implementation of the polarization combiner and the WDM coupler can be understood without any particular description. However, in addition to this, connecting each of these parts with an optical fiber requires an optical fiber of a predetermined length, which requires a considerable amount of mounting space for the operation of the optical fiber, and reduces the connection cost of the optical fiber. This is in addition to the mounting cost of each optical component.

In general, a semiconductor laser light source used as a backward pumping light source uses an isolator (not shown) in each semiconductor laser module for the purpose of stabilizing the pumping light source. The reason why the isolator is used in this portion is to absorb light from the EDF side toward the laser diode element.

[0014] This contributes to an increase in the cost of the EDFA.

Therefore, it is difficult to reduce the size of the conventional optical coupler for backward pumping, and it is difficult to reduce the product price.

(2) Increasing Insertion Loss The WDM coupler, the polarization combiner, and the isolator module each have an inherent insertion loss. In each of these, a lens coupling system for forming optical coupling between optical fibers is mounted inside, and coupling loss of the lens coupling itself occurs, and therefore, coupling loss of each lens coupling system increases insertion loss. I have.

However, when these components are optically coupled to each other, the total insertion loss after the optical coupling is not only the cumulative loss of the insertion loss of these individual functional components, but also the loss associated with the optical fiber connection that couples them. Is added. These insertion losses hinder the increase in the output of the EDFA.

In a conventional WDM coupler, a wavelength separating element is generally mounted inside, and light of different wavelengths is combined and separated. The characteristics of the WDM coupler depend on the characteristics of the wavelength separation element itself, and the imperfections of the characteristics have been a factor of deteriorating the signal transmission characteristics of the EDFA.

It is desirable that the insertion loss characteristics be flat with respect to the signal light wavelength.

(3) Conventional Attempt to Solve the Problem Another example of the conventional backward-pumped EDFA is shown in FIG.
There is a configuration using an optical circulator as shown in FIG.

In FIG. 7, the excitation light from the semiconductor laser light source 701 (the excitation light wavelength is, for example, 1.48 μm).
m) shows the single mode fiber 702 with the arrow 1137.
After entering the pumping light input port 505 of the optical circulator 703, the light exits from the common port 506 and proceeds in the direction of arrow 1138 to reach the EDF 402.

On the other hand, the light enters from the input signal port 403 and travels in the direction of arrow 1126, and the signal light (for example, the wavelength of 1.55 μm) amplified inside the EDF 402 changes to the direction of arrow 11.
After traveling in the direction of 27 and entering the common port 506 of the optical circulator 703, proceeding in the direction of arrow 1128 and exiting from the exit port 507, it is guided to the output signal port 404 via the output side isolator module 508. In this case, it goes without saying that the signal light wavelength and the pump light wavelength are close to each other, and both wavelength bands are within the operating range of the optical circulator.

However, this configuration also requires an externally provided polarization combiner for increasing the output, and the above problem cannot be avoided.

The present invention solves all of the above-mentioned problems, and provides the above-mentioned two kinds of module functions required for the backward pumping section of the high-output EDFA, the functions of the output-side isolator module, and further stabilizes the pumping light source. To provide a new optical coupling method for backward pumping that can realize a total of four functions of isolator functions for a single module using only one isolator element, and an optical coupler for backward pumping using the method. And

[0025]

SUMMARY OF THE INVENTION The present invention provides a WDM coupler function, a polarization combining function, an isolator function, and a pump light source protection which are necessary functions in a backward pumping section of a backward pumping type EDFA aiming at a large output characteristic. The isolator function is used together with one isolator element.

As means for achieving this, a particularly significant feature of the present invention is not only the isolator function inherent to the isolator element but also the polarization synthesis using a birefringent optical crystal inherent in the isolator element. Another object of the present invention is to perform the function and to simultaneously use the WDM function using the non-reciprocal characteristics of the optical isolator element.

More specifically, in the backward pumping optical coupling method of the present invention and the backward pumping optical coupler using the method, an SMF collimator is arranged on the input side of the isolator element, and the SMF collimator and the polarization side are arranged on the output side. Wave holding fiber (hereinafter, P
This is characterized in that a collimator (also referred to as MF) is arranged, and excitation light is input from the PMF collimator.

As an example of a backward pumping optical coupler method and a backward pumping optical coupler using the same, which are highly effective according to the present invention,
One SMF collimator is arranged at the input side of the isolator element, and one SMF collimator is arranged at the output side of the isolator element.
While arranging the collimator, the two PMF collimators are arranged together with the optical path changing prism described later,
Each of the collimators on the input side and the output side of the isolator element is arranged so as to satisfy a coupling condition described later.

Further, as another example of the optical coupler for backward excitation of the present invention and the optical coupler for backward excitation using the same,
It is characterized by using an optical path turning prism to reduce the size of the device and to enable all input / output ports to be arranged on the same side of the housing case.

[0030]

Embodiments of the present invention will be described below with reference to the drawings. It should be noted that the drawings used in the description schematically show the dimensions, shapes, arrangement relations, and the like of the components so that these inventions can be understood, and therefore, the dimensions of each part in each drawing are not necessarily the actual ones. It may not be similar. In addition, in each of the drawings, the same components are denoted by the same reference numerals, and redundant description may be omitted.

Before showing the structure of the backward pumping optical coupler using the backward pumping optical coupling method of the present invention, the structure and operating principle of the isolator element itself, which is one of the components of the backward pumping optical coupler, will be described. Will be described with reference to FIG.

FIG. 6 is a diagram for explaining the configuration of a general isolator module 600. The basic configuration of this type of isolator element 611 is described in the document “12th Euro.
pean Conference on Optica
l Communication Sept. 22/2
5 1986 ", the Faraday rotator 6 positioned at the coaxial center of the cylindrical permanent magnet 610.
It is composed of wedge-shaped birefringent optical crystals 607 and 608 having different crystal optical axis directions before and after 09 (non-reciprocal garnet).

Before and after the isolator element 611, a lens 603 and a single mode fiber (Single Mo
de Fiber (hereinafter, also referred to as SMF) 601 single mode fiber collimator (hereinafter, SMF)
602), lens 606 and SMF
The isolator module 600 is configured by arranging the SMF collimator 604 including the reference numeral 605.

In the isolator module 600, the light traveling rightward in FIG. 6 from the SMF collimator 602 is split into two light beams inside the isolator element 611 and emitted from the isolator element 611. At this time, the two light beams are emitted from the isolator element 611 in such a manner that the optical axes of the two light beams are parallel to each other and close to each other. Due to the characteristics of the collimator, when the two light beams are parallel to each other and are close to each other, the SMF collimator 604 can receive any of the light beams.

Thus, the light from the SMF collimator 602 is directly coupled to the SMF collimator 604 with low loss.

On the other hand, conversely, the SMF collimator 60
Consider a case where light is incident from 4 to the left in FIG. At this time, due to the non-reciprocal effect of the isolator element 611,
Unlike the above case, the two split light beams are separated into linearly polarized light beams orthogonal to each other, but the optical axes of the light beams are emitted to the left side of the isolator element 611 without being parallel to each other. I do. Due to the characteristics of the collimator,
Light with a different optical axis direction of the light beam cannot be coupled to the SMF collimator 602, and thus the SMF collimator 6
02 and the SMF collimator 604, no optical coupling system can be formed.

This means that, in FIG. 6, light traveling in the right direction has optical coupling, but light traveling in the left direction has no optical coupling. That is, it indicates that the function as the isolator module is achieved.

In the present invention, instead of using only the above-described isolator characteristics as it is, emphasis is placed on actively utilizing the following secondary effects.

That is, in the present invention, (1) the reverse direction of the isolator (the SMF collimator 6
04 (toward the SMF collimator 602) during operation, the light beams are split into two light beams having non-parallel light beam optical axes. At this time, these two light beams have their polarization planes orthogonal to each other. Take advantage of what you do.

(2) Next, the light beams having the above two linearly polarized lights are respectively converted into SMFs from opposite directions of the isolator.
A means is provided for coupling to the collimator 602.

(3) Further, this type of isolator utilizes the fact that the wavelength characteristics of insertion loss are wide. Specifically, when amplifying an optical signal having a wavelength of 1.5 μm in an EDFA, pump light having a wavelength of 1.48 μm is required. Fortunately, these wavelength bands are close to each other. ,
This wavelength band is in the low insertion loss region of the isolator.

From the viewpoint described above, a backward pumping optical coupling method and a backward pumping optical coupler of the present invention will be described.

FIG. 1A is a block diagram showing a first embodiment of the present invention, in which a group of collimators is opposed to each other with an isolator element 109 interposed therebetween.

As described above, the collimator is formed by the fiber and the lens, and has a function of converting light propagating in the fiber into a parallel beam. Here, two types of collimators are used. One of them is a collimator that does not limit the polarization direction of the propagation light.
The fiber used for this is a regular SMF, SM
Applied to F collimators 101 and 103.

On the other hand, another type is a collimator for limiting the polarization direction of propagating light, which is a polarization maintaining fiber collimator (Polarization Mai).
nt-aining fiber collimator,
(Also referred to as PMF collimator) 105 and 108.

The two PMF collimators 105 and 108 are disposed adjacent to both sides of the SMF collimator 103, and are optically coupled to the isolator element 109 via optical path changing prisms 110 and 111, respectively.

The arrow 1131 from the PMF collimator 105
The excitation light traveling in the direction indicated by the arrow has a polarization direction perpendicular to the paper surface indicated by the reference numeral 114, enters the isolator 109 at a deflection angle θ1 as shown in FIG.
The excitation light traveling in the direction indicated by arrow 1132 from FIG.
5 has a vertical polarization direction in the plane of the paper, and a deflection angle θ
The light enters the isolator 109 at 2 and is coupled to the SMF collimator 101, respectively. Note that the deflection angles θ1 and θ2 may be equal, and are approximately 2 to 4 degrees.

Next, the operation principle of this module will be described.

In FIG. 1A, first, an SMF collimator 101 including an SMF 102 and a lens 116 is moved rightward in FIG.
9 is assumed to correspond to the forward direction of the isolator element 109 (the direction indicated by the arrow 1121).

The incident light having an arbitrary polarization plane is split into two light beams in the isolator element 109, and when the light exits from the isolator element 109, these two light beams are separated.
The two light beams have optical axes parallel to each other, and
Split into two adjacent light beams. The two adjacent lights travel in the direction indicated by the arrow 1122, and due to the nature of the collimator, any of the light is converted into the SMF collimator 103 (ie, the SMF 10) including the lens 118 and the SMF 104.
4) Coupling with low loss.

Conversely, light emitted from the SMF collimator 103 in the left direction is split into two lights having optical axes of light beams that are not parallel to each other inside the isolator element 109 and having linear polarization planes orthogonal to each other. . In this way, light having optical axes of light beams that are not parallel to each other cannot be coupled to the same collimator, that is, the SMF collimator 101 in principle.

The operation of the above-described isolator is well known in the art, and details thereof are described in the literature as an isolator (12th European Conference).
on Optical Communication
n Sept. 22/251986).

In order to obtain a polarization combining function without using a conventional polarization combiner, which is one of the objects of the present invention, each linearly polarized light propagating in the opposite direction inside the isolator element is required. In any case, it is necessary to efficiently couple to the same SMF.

In order to realize this, the backward propagating light is not emitted from the SMF collimator 103 as the backward propagating light but inside the isolator element 109 at an angle corresponding to the deflection angle generated at the time of the backward propagating. This is made possible by making the light incident from the opposite direction of the isolator element 109. However, at this time, it goes without saying that the plane of polarization of light traveling from the right side to the left side in the isolator element 109 must be linearly polarized light having an appropriate polarization rotation angle.

What is important here is that the isolator element 1
09 from the opposite direction at an appropriate deflection angle (the angles indicated by θ1 and θ2 in FIG. 1 (A)) (not the polarization rotation angle), and only one light can be coupled to the SMF collimator 101. But the fact that there are two.

That is, the PM composed of the polarization maintaining fiber
Light emitted from the F collimators 105 and 108 in the directions indicated by arrows 1131 and 1132 respectively has their polarization planes orthogonal to each other, and the incident deflection angles θ1 and θ to the isolator element 109 of each collimator.
Only when the two are properly arranged, after propagating the isolator element 109 in the backward direction in the direction indicated by the arrow 1133, any of the SMF collimators 101, ie, the SMF
102.

In the example shown in FIG. 1A, the direction of linear polarization emitted from the PMF collimator 105 is perpendicular to the plane of the drawing.
Also, the case where the linear polarization direction emitted from the PMF collimator 108 is parallel to the paper surface is illustrated as one example.

Here, since the incident deflection angles θ1 and θ2 of these two linearly polarized lights to the isolator element 109 are generally small (about 2 degrees), the collimators disposed adjacent to each other, ie, the PMF collimator 105 and the SMF Each interval between the collimator 103 and the PMF collimator 108 and the SMF collimator 103 tends to be small. The optical path changing prisms 110 and 111 are used to increase the distance.

In the example shown in FIG.
The collimators are arranged such that the polarization direction of the light emitted from the collimator 105 is perpendicular to the paper surface (illustrated by a black circle) and the polarization direction of the light emitted from the PMF collimator 108 is parallel to the paper surface (illustrated by a line). Have been.

As described above, the linearly polarized light from each of the polarization maintaining fibers (PMFs) 106 and 107 is
Coupling to the same SMF 102. In other words, this means that the polarization combining function is achieved in this part.

Next, the characteristics of the optical coupler for backward excitation of the present invention will be described.

First, the SMF collimator 101 sends the SMF
EDFA is applied to the signal light going to the collimator 103.
The light in the 1.5 μm band, which is the optical amplification wavelength band, is coupled with low loss, and conversely, the light traveling from the SMF collimator 103 to the SMF collimator 101 has a large loss in the same wavelength band.

This characteristic is the isolator characteristic itself, and acts as an indispensable condition for giving the amplifying effect of the EDFA.

On the other hand, the linearly polarized light having a wavelength of 1.48 μm emitted from the PMF collimator 105 is converted into SM light as excitation light.
The light reaches the F collimator 101. Since this wavelength is in a wavelength region where the loss of the isolator element 109 is low, the pump light can be coupled to the SMF collimator 101 with low loss.

Similarly, the linearly polarized light having a wavelength of 1.48 μm emitted from the PMF collimator 108 is also used for the SMF collimator 1.
01 can be combined.

Further, in the optical coupler for backward excitation, the light from the SMF collimator 101 is coupled to the SMF collimator 103 as described above, but cannot be coupled to the PMF collimator 105 or the PMF collimator 108. This means that the light from the SMF collimator 101 is
This means that light directed to a semiconductor laser which is an excitation light source connected to the other ends of the PMF collimator 105 and the PMF collimator 108 is blocked.

FIG. 1B is a specific mounting configuration diagram of the first embodiment of the present invention. Each collimator 101, 103, 1
05 and 108 are directly fixed to a housing case (hereinafter, also simply referred to as a case) 1116 by YAG welding or the like. In the light passage portion of each collimator, through holes 1117, 1118, 1119, and 1120 are provided, respectively.

FIG. 2 shows a second embodiment of the present invention.
(A) is a diagram for explaining the configuration and function.

In the basic configuration shown in FIG. 2A, the difference from the first embodiment is that an optical path turning prism 201 is used. The SMF collimator 10 is separated from the isolator element 109 by the optical path turning prism 201.
3 and PMF collimators 105 and 1
FIG. 2 shows an optical path from the optical path 08 to the isolator element 109.
By inverting as shown in (A), all collimators can be arranged on the same side of the isolator element 109 and on the same side of the case 202 as shown in FIG.

The actual mounting form is shown in FIG.
Numerals 3 to 206 denote through-holes, and each of the collimators 101, 10
3, 105 and 108 are formed in the case 20 by YAG welding or the like.
It is fixed to 2.

The operation is basically the same as that described with reference to FIG. 1 in the first embodiment.

FIG. 3 shows a third embodiment of the present invention. FIG.
As shown in (A), the optical path turning prisms 301 and 302 separate the SMF from the isolator element 109.
By reversing the optical path toward the collimator 103 and the optical path from the PMF collimators 105 and 108 to the isolator element 109, the overall dimensions can be reduced.

FIG. 3B is an actual mounting configuration diagram.
Reference numerals 301 and 302 denote optical path turning prisms, 303 denotes a case, and 304 to 307 denote through holes. Case 303
Are provided with through holes 304 to 307 in the light passage portion of each collimator. Each collimator 101, 103, 10
5, 108 is case 3 by YAG welding or screwing.
03.

The operation is basically the same as that described with reference to FIG. 1 in the first embodiment.

FIG. 4 is a diagram showing an example of an application form to a high-output EDFA using the optical coupler for backward pumping according to the present invention.

In FIG. 4, the portions of the input side isolator module 401 and the EDF 402 are the same as those of the conventional EDFA shown in FIG. 5, but the backward pumping section includes a backward pumping optical coupler (indicated by a dotted line). (Enclosed part) 412 is applied.

In this configuration, the signal light in the 1.5 μm wavelength band to be amplified passes through the input side isolator module 401 from the input signal port 403 and then enters the EDF 4.
Reach 02.

On the other hand, pumping light having linearly polarized light having a wavelength of 1.48 μm incident from the semiconductor laser light source 405 through the pumping light input port 407 passes through the PMF 410 and becomes
The MF collimator 105 reversely moves the isolator element 109 in the form of a linearly polarized light beam (from the right to the left in FIG. 4, that is, in the direction shown by the arrow 1133), and
It couples to the collimator 101 and excites the EDF 402.

Similarly, a wavelength of 1.4 entered from another semiconductor laser light source 406 via an excitation light input port 408.
The excitation light in the 8 μm band also undergoes a similar process,
Excite 2.

In this state, the input signal port 403
1.5 μm band signal light incident from the EDF 402 is amplified to a large output inside the EDF 402, input to the common port 409,
The light travels from the MF collimator 101 in the direction indicated by the arrow 1121 and is output from the SMF collimator 103 to the output port 404 via the isolator element 109.

As described above, it can be seen that the backward-pumping optical coupler of the present invention functions as a basic component of a high-output EDFA.

[0082]

When the optical coupler for backward pumping is applied to an EDFA, its advantages are as follows as compared with a conventional EDFA.

(1) Four functions can be operated by using one isolator element.

That is, according to the optical coupling method of the present invention,
One isolator element has an isolator function for signal light, a polarization combining function for pump light, a WDM function for pump light (couples pump light to EDF, and also couples signal light to SMF collimator 103 and outputs to output signal port 404. Function), and a function of blocking light going to the excitation light source.
Compared with the configuration A, the number of components is extremely reduced, and the reliability of quality is increased.

(2) A low-cost backward excitation module can be provided.

A module having the above four functions can be realized by one isolator element. Therefore, the present module is much cheaper than the conventional sum of the individual module costs. Further, there is no need to connect (fusion-splicing) the individual modules to each other with an optical fiber as in the related art, so that there is no cost involved in the work.

(3) It is compact.

Since the individual modules are not connected by the optical fiber unlike the conventional backward pumping module, there is no space for mounting the fiber at that portion.

Further, as shown in the second embodiment, when all four ports are mounted in the same direction of the case, all the spaces for processing the extra fiber length can be made common, and the size can be further reduced. Can be achieved. Therefore, the module size can be reduced.

(4) Optical coupling loss is small.

When individual modules are connected by an optical fiber as in the prior art, the total insertion loss exceeds at least their cumulative loss. In addition, connection loss between the fibers occurs.

However, in the backward pumping optical coupling method of the present invention and the backward pumping optical coupler using the method, only the isolator element is inserted between one facing collimator beam. Therefore, not only the fiber connection loss but also the cumulative loss does not occur. Therefore, optical coupling loss is small.

(5) The wavelength loss characteristics of the signal light are flat.

Conventionally, when the pump light and the signal light are multiplexed and demultiplexed on a common fiber, a wavelength separation element (for example, a dielectric thin film) having a multiplexing / demultiplexing function has been used.
As is well known, the wavelength separation element has a sharp wavelength and loss characteristic at the boundary between the wavelengths of the pump light and the signal light.
The wavelength loss characteristics of the pump light wavelength band and the signal light wavelength band are hardly flat.

In an optical fiber communication system, this flatness is an important characteristic in signal transmission characteristics.

However, since the optical coupler for backward pumping of the present invention does not include such a wavelength separation element, flatness can be obtained in both wavelength bands, and therefore, deterioration of signal transmission characteristics due to this is not caused. .

Although the details of the present invention have been mainly described with reference to the optical coupler for backward pumping of the present invention, the optical coupling method for backward pumping of the present invention is mainly described in FIGS. This is the same as the optical coupling method used in the backward pumping optical coupler described above, and the effect of the present invention is also the same.

[Brief description of the drawings]

FIGS. 1A and 1B are diagrams for explaining a first embodiment of an optical coupler for backward excitation according to the present invention, in which FIG. 1A shows a basic configuration, and FIG.
FIG. 3 is a diagram showing a mounting configuration.

FIGS. 2A and 2B are diagrams for explaining a second embodiment of the optical coupler for backward excitation according to the present invention, wherein FIG. 2A is a diagram showing a basic configuration, and FIG.
FIG. 3 is a diagram showing a mounting configuration.

3A and 3B are diagrams illustrating a third embodiment of the optical coupler for backward excitation according to the present invention, wherein FIG. 3A is a diagram illustrating a basic configuration, and FIG.
FIG. 3 is a diagram showing a mounting configuration.

FIG. 4 shows a high-power EDFA using a backward-pumping optical coupler according to the present invention.
Is a diagram for explaining an example applied to

FIG. 5 is a diagram illustrating a first example of a configuration of a conventional EDFA.

FIG. 6 is a diagram illustrating a configuration of a conventional isolator module.

FIG. 7 is a diagram showing a second example of the configuration of a conventional EDFA.

[Explanation of symbols]

101, 103, 602, 604: SMF collimator 102, 104, 601, 605, 702: SMF 105, 108: PMF collimator 106, 107, 410, 411, 502, 503: P
MF (Polarization maintaining fiber) 109, 611: Isolator element 110, 111: Optical path changing prism 1121, 1122, 1123, 1124, 1125
1126, 1127, 1128: Arrows indicating signal light propagation directions 1131, 1132, 1133, 1134, 1135
1137, 1138: Arrow indicating the direction of propagation of the excitation light 114: Polarization direction (perpendicular to the paper) 115: Polarization direction (parallel to the paper) 1116, 202, 303: Cases 116 to 120, 603, 606: Lens 1117 ~ 1120,203 ~ 206,304 ~ 30
7: Through-holes 201, 301, 302: Optical path turning prism 401: Input side isolator module 402: EDF 403: Input signal port 404: Output signal port 405, 406: Semiconductor laser light source 407, 408, 505: Excitation light input port 409 , 506: common port 412: backward pump module 501 of the present invention 501: WDM 504: polarization combiner 505: pump light input port 506: common port 507: output port 508: output side isolator module 600: isolator module 607, 608: Birefringent optical crystal 609: Faraday rotator 610: permanent magnet 701: semiconductor laser light source 703: optical circulator

Claims (18)

[Claims] 1. When light having an arbitrary polarization plane is made to enter in the forward direction, the emitted light is separated into two light beams having optical axes parallel to each other and adjacent to each other. An optical isolator (hereinafter, also referred to as an isolator) having a function of splitting the emitted light into two lights having linear polarization planes orthogonal to each other and having optical axes non-parallel to each other when the light having the Element) and an input side of the isolator element (hereinafter, an incident side of light when light is made to enter in the forward direction is referred to as an input side of the isolator element, and a side from which the incident light exits the isolator element is referred to as an isolator. A single-mode fiber collimator (hereinafter, also referred to as an SMF collimator) is disposed on the output side of the isolator element. An optical coupler for backward pumping, comprising an iva collimator. 2. An optical coupler for backward pumping according to claim 1, wherein said S is disposed on an input side of said isolator element.
An MF collimator (hereinafter, also referred to as an input-side SMF collimator) and an SM disposed on an output side of the isolator element.
An F collimator (hereinafter also referred to as an output-side SMF collimator) is disposed so that optical coupling is formed with the isolator element interposed therebetween, and the polarization maintaining fiber collimator and the input-side SMF collimator are arranged in the isolator. An optical coupler for backward excitation, wherein the optical coupling is arranged so as to face each other with an element interposed therebetween. 3. An optical coupler for backward excitation according to claim 1, wherein an optical path changing prism is arranged on an output side of said isolator element. 4. The optical coupler for backward pumping according to claim 3, wherein the input side SMF collimator is one, the output side SMF collimator is one, the optical path changing prism is one, and the polarization is one. There is one wave holding fiber collimator, and the polarization holding fiber collimator is disposed so as to face the input side SMF collimator via the optical path changing prism and the isolator element so that optical coupling is formed. An optical coupler for backward pumping, comprising: 5. The optical coupler for backward pumping according to claim 3, wherein the input side SMF collimator is one, the output side SMF collimator is one, the optical path changing prism is two, and the polarization is two. An optical coupler for backward pumping, comprising two wave holding fiber collimators. 6. The optical coupler for backward pumping according to claim 5, wherein a polarization maintaining fiber collimator is arranged adjacent to both sides of the output-side SMF collimator, and the output-side SMF collimator replaces the isolator element. The input side SMF collimator and the input side SMF collimator are disposed so that optical coupling is formed opposite to the input side SMF collimator, and each of the polarization maintaining fiber collimators is connected to the input side SMF collimator via the optical path changing prism and the isolator element. And an optical coupler for backward pumping, wherein the optical coupler is arranged so as to oppose each other. 7. The backward-pumping optical coupler according to claim 5, wherein the two optical path changing prisms have a gap between the vertices of the prisms, and the gap between the prisms is the input side of the isolator element and the gap between the prism apexes. An optical coupler for backward pumping, wherein a pair of single-mode fiber collimators facing the output side is disposed so as to have substantially the same diameter as a light beam diameter formed by the pair. 8. The optical coupler for backward pumping according to claim 1, further comprising an optical path turning prism between the output side SMF collimator and the isolator element for returning an optical path in a plane. An optical coupler for backward pumping, wherein all four collimators are arranged on the same side surface of the case by disposing and inverting the optical path of that part. 9. The optical coupler for backward pumping according to claim 1, wherein two optical paths are folded between the output side SMF collimator and the isolator element for planarly folding an optical path. The prisms are arranged so that their light passing surfaces face each other, and by moving the optical path in that part in parallel, the input side SMF collimator and the other three collimators are arranged on the opposing side surfaces of the case. Optical coupler for backward excitation. 10. When light having an arbitrary plane of polarization is made to enter in the forward direction, the emitted light is split into two light beams having optical axes parallel to each other and adjacent to each other. An optical isolator (hereinafter, also referred to as an isolator) having a function of splitting the emitted light into two lights having linear polarization planes orthogonal to each other and having optical axes non-parallel to each other when the light having the Element) and an input side of the isolator element (hereinafter, an incident side of light when light is made to enter in the forward direction is referred to as an input side of the isolator element, and a side from which the incident light exits the isolator element is referred to as an isolator. Single-mode fiber collimator (hereinafter also referred to as SMF collimator)
Wherein an SMF collimator and a polarization maintaining fiber collimator are arranged on the output side of the isolator element to perform optical coupling. 11. An optical coupling method for backward excitation according to claim 10, wherein an SMF collimator (hereinafter also referred to as an input-side SMF collimator) disposed on an input side of the isolator element and an output side of the isolator element. The SMF collimator (hereinafter, also referred to as an output side SMF collimator) is disposed so that optical coupling is formed with the isolator element interposed therebetween, and the polarization maintaining fiber collimator and the input side SMF collimator are disposed. An optical coupling method for backward excitation, wherein the optical coupling is arranged so as to be opposed to each other with the isolator element interposed therebetween. 12. The optical coupling method for backward excitation according to claim 10, wherein an optical path changing prism is disposed on an output side of the isolator element. 13. The optical coupling method for backward pumping according to claim 12, wherein the input side SMF collimator is one,
The output side SMF collimator is one, the optical path changing prism is one, and the polarization maintaining fiber collimator is one.
The polarization maintaining fiber collimator is disposed so as to be optically coupled to the input side SMF collimator via the optical path changing prism and the isolator element. Optical coupling method for excitation. 14. The optical coupling method for backward excitation according to claim 12, wherein the input side SMF collimator is one,
The output side SMF collimator is one, the optical path changing prism is two, and the polarization maintaining fiber collimator is two.
An optical coupling method for backward excitation. 15. The optical coupling method for backward pumping according to claim 14, wherein both sides of the output side SMF collimator are:
Each of the polarization maintaining fiber collimators is disposed adjacent to each other, and the output-side SMF collimator is disposed so that the optical coupling is formed opposite to the input-side SMF collimator with the isolator element interposed therebetween. The wave coupling fiber collimator is disposed so as to oppose the input side SMF collimator via the optical path changing prism and the isolator element so as to form optical coupling, respectively. . 16. The optical coupling method for backward excitation according to claim 14, wherein the two optical path changing prisms have a gap between the vertices of the prisms, and the gap between the prism apexes and the input side of the isolator element. An optical coupling method for backward excitation, wherein a pair of single-mode fiber collimators facing the output side are arranged so as to have substantially the same diameter as a light beam diameter formed by the pair. 17. The optical coupling method for backward pumping according to claim 10, further comprising: an optical path turning prism between the output side SMF collimator and the isolator element for returning an optical path in a plane. An optical coupling method for backward excitation, wherein all four collimators are arranged on the same side surface of a case by arranging and inverting an optical path of the portion. 18. The optical coupling method for backward pumping according to claim 10, wherein two optical paths are folded between the output side SMF collimator and the isolator element for planarly folding an optical path. The prisms are arranged so that their light passing surfaces face each other, and by moving the optical path in that part in parallel, the input side SMF collimator and the other three collimators are arranged on the opposing side surfaces of the case. Optical coupling method for backward excitation.