JPH11312833A - Optical waveguide and optical direct amplifier - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an optical waveguide which allows incidence of high power excitation light and an optical direct amplifier using the optical waveguide. SOLUTION: An optical waveguide 20 comprises a core part 2 where rate earth element is added, a clad part 21 of density lower than the core part 2, and a clad part 22 of density lower than the clad part 21, while and end surface of the clad part 21 is cut to form a cut surface 23. A condenser 31 causes the light emitted from an excitation light source 30 to converge, which is made incident on the cut surface 23 as excitation light 32, and the incident light is allowed to propagate in the clad part 21 to excite the rare earth element of the core part 2. A condenser 33 condenses a pulse light 6 generated by a signal light source 5, which is made incident on the end surface of the core part 2 as a signal light 34. The incident signal light 34 is optically amplified by the core part 2 to provide output light 10.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical waveguide for amplifying laser light emitted from a semiconductor laser and an optical direct amplifier using the optical waveguide, and particularly to an application requiring high power such as material processing. It relates to a suitable optical waveguide and an optical direct amplifier.

[0002]

2. Description of the Related Art FIG. 7 is a perspective view showing an example of the structure of an optical waveguide according to the prior art. The optical waveguide 1 shown in FIG. 1 is an optical fiber that functions as an optical amplification medium, and only one end of the optical fiber is shown in FIG. In the optical waveguide 1, reference numeral 2 denotes a core formed in an elongated rod shape. The core 2 is doped with a rare earth element 3 so that the optical waveguide 1 functions as an optical amplification medium. Reference numeral 4 denotes a cylindrical cladding portion formed so as to surround the outer periphery of the core portion 2, and the density of the cladding portion 4 is
It is lower than the density.

On the other hand, FIG. 8 shows an optical waveguide 1 in the direction of the arrow in FIG.
FIG. 8 is a sectional view taken along the line CC. In FIG. 8, the same components as those shown in FIG. 7 are denoted by the same reference numerals, and illustration of the rare earth element 3 is omitted. Then, the light given to the end face of the optical waveguide 1 enters, for example, from the left end of the core 2, propagates through the core 2, and is finally output from the right end of the core 2.

FIG. 9 is a block diagram showing an example of the configuration of an optical direct amplifier using the optical waveguide 1 shown in FIGS. 7 and 8, and the same parts as those shown in FIG. In addition, the illustration of the rare earth element 3 is omitted as in FIG. In FIG. 9, reference numeral 5 denotes a pulse light 6 as shown.
Is a signal light source for generating excitation light, and reference numeral 7 is an excitation light source for generating excitation light. Each of the signal light source 5 and the excitation light source 7 is constituted by a semiconductor laser. Then, the optical multiplexer 8 causes the light (reference numeral 9 in the figure) obtained by multiplexing the signal light generated by the signal light source 5 and the excitation light generated by the excitation light source 7 to enter the core unit 2.

According to such a configuration, by transmitting the excitation light to the core portion 2, the rare earth element 3 in the core portion 2 becomes excited by absorbing the excitation light. In this state, when the signal light generated by the signal light source 5 is made to enter the left end of the core unit 2 from the optical multiplexer 8, the signal light is optically amplified in the process of propagating through the core unit 2, and the optically amplified output The light 10 is emitted from the right end of the core 2. As shown in FIG. 9, the waveform 11 of the output light 10 is larger than the level of the pulse light 6 due to optical amplification.

[0006]

By the way, generally,
The core 2 has a very small diameter of about 5 to 10 microns. Therefore, such a small diameter core portion 2
There is a problem that it is actually very difficult to combine the signal light and the pump light into the light and to make it incident. In addition, considering the use as an optical direct amplifier, if the usage is to amplify a small signal, it is not necessary to increase the power of the pump light so much because the output power is not so required. However, for example, when an optical direct amplifier is used for material processing, high power is required as output light, so that it is necessary to increase the power of pumping light to increase the output power.

Here, as a high-power semiconductor laser used for the pumping light source 7, one having a structure in which a plurality of emitters are arranged in a line can be considered. However, it is extremely difficult to collect the excitation light emitted from the semiconductor laser having such a structure and make it incident on the small-diameter core portion 2.
There is also a problem that it is difficult to combine the pump light and the signal light having such a large power. As described above, the high-power pumping light cannot enter the core portion 2 of the optical waveguide 1 only by using the conventional technology. Therefore, due to such restrictions, the peak power of the output light of the optical direct amplifier cannot be increased beyond a certain level. The present invention has been made in view of the above points, and an object of the present invention is to provide an optical waveguide to which a high-power pump light can be made incident and an optical direct amplifier using the optical waveguide.

[0008]

In order to solve the above-mentioned problems, the present invention is directed to an optical waveguide having a core to which a rare earth element is added, wherein the optical waveguide surrounds the core.
Excitation light for exciting the rare earth element is incident on a cut surface formed by cutting an end portion obliquely to the longitudinal direction of the core, a first clad having a density lower than the density of the core, A second cladding surrounding the first cladding and having a density lower than the density of the first cladding. According to a second aspect of the present invention, in the first aspect, a plurality of the cut surfaces are formed in the first clad.

According to a third aspect of the present invention, there is provided an optical waveguide according to the first or second aspect, signal light input means for converging a signal light to enter the core, and the number of the cut surfaces. And an excitation light generating means for condensing the generated excitation light and making it incident on the cut surface. According to a fourth aspect of the present invention, in the third aspect of the present invention, the excitation light generating means is disposed to face the excitation light source for generating the excitation light and the cut surface, and the excitation light source is generated. And a condensing means for condensing the excited excitation light and making it incident on the cut surface. According to a fifth aspect of the present invention, in the fourth aspect of the invention, the excitation light source is a laser diode configured by arranging a plurality of emitters.

[0010]

Embodiments of the present invention will be described below with reference to the drawings. [First Embodiment] FIG. 1 is a perspective view showing the structure of an optical waveguide according to the present embodiment. In the drawing, the same components as those shown in FIG. 7 are denoted by the same reference numerals. FIG. 2 shows AA when the optical waveguide 20 is viewed in the direction of the arrow in FIG.
FIG. 9 is a sectional view, in which the same components as those shown in FIG. 1 are denoted by the same reference numerals, and illustration of the rare earth element 3 is omitted as in FIG.

As shown in FIGS. 1 and 2, the optical waveguide 20 in the present embodiment has a double clad structure.
That is, the clad portion 21 as the first clad is formed so as to surround the outer periphery of the core portion 2, and the outer periphery of the clad portion 21 is formed so as to be surrounded by the clad portion 22 as the second clad. ing. Here, the density of the clad portion 21 is lower than the density of the core portion 2,
The density of the clad portion 22 is lower than the density of the clad portion 21.

Further, in the optical waveguide 20 of the present embodiment, when viewed in the sectional view shown in FIG.
The upper portion of the clad portion 22 sandwiching the core portion 2 is cut obliquely to the longitudinal direction of the core portion 2.
Thus, the cut surface 23 is formed in the clad portion 21 and the cut surface 24 is formed in the clad portion 22. As will be described later, the cut surface 23 is for allowing the excitation light to enter, and the beam diameter of the incident excitation light is allowed to be as large as the area of the cut surface 23. On the other hand, since it is not necessary to make excitation light incident on the cut surface 24, the cut surface 24 does not necessarily need to be cut obliquely, and its shape is appropriately adjusted in consideration of the ease of processing when forming the cut surface. The angle of the cut surface 23 is not necessarily required to be approximately 45 ° as shown in the figure, and may be appropriately determined so that the excitation light can be incident.

FIG. 3 is a block diagram showing the configuration of an optical direct amplifier using the optical waveguide 20 shown in FIGS. 1 and 2, and shows the same components as those shown in FIG. 1 or FIG. Are given the same reference numerals. In the present embodiment, it is assumed that a high-output pump light source is used. Therefore, as shown in FIG. 3, the pump light source 30 is configured by a laser diode in which three emitters are arranged. In addition, the concentrator 31 is provided on the cut surface 23 of the clad portion 21.
The light emitted from the excitation light source 30 is condensed, and the collected light is made to enter the cladding portion 21 from the cut surface 23 as excitation light 32.

As described above, since the beam diameter of the excitation light 32 is allowed up to the area of the cut surface 23, in this embodiment, the excitation light is transmitted to the cut surface 23 without being condensed by the light collector 31. There is no particular problem even if it is made incident. on the other hand,
The configuration for causing the signal light to enter the optical waveguide 20 is basically the same as that in FIG. That is, the concentrator 33 is disposed so as to face the end face of the core unit 2, the signal light generated by the signal light source 5 is condensed by the concentrator 33, and the condensed light is converted into a signal light 34 by the core. It is incident on the part 2.

The operation of the optical direct amplifier having the above configuration is as follows. First, the condenser 31 condenses the light generated by the excitation light source 30 and obtains the excitation light 3
2 is made to enter the cladding 21 from the cut surface 23. The incident light passes through the core portion 2 from the cladding portion 21 and excites the rare earth element 3 (not shown) in the core portion 2 at that time. Thereafter, the light further travels through the clad part 21 and is reflected at the boundary between the clad part 21 and the clad part 22, and then propagates through the clad part 21, the core part 2, and the clad part 21, and sandwiches the core part 2. The light is reflected on a boundary surface facing the boundary surface. Thereafter, the series of operations just described is repeated, and the light incident from the cut surface 23 propagates while reflecting in the clad portion 21 while exciting the rare earth element 3 in the core portion 2. Go on.

In this state, when the pulse light 6 is generated from the signal light source 5, the condenser 33 condenses the pulse light 6 emitted from the signal light source 5, and this is incident on the end face of the core 2 as a signal light 34. Let it. This incident light propagates through the core portion 2, is optically amplified in the process, and becomes the signal light 3 as the output light 10.
The pulse light obtained by optically amplifying No. 4 is obtained. At this time, since the power of the pump light 32 is higher than that in the case shown in FIG. 9, the amplification degree of the optical waveguide 20 is higher than that of the optical waveguide 1 shown in FIG. Is also higher than the level of waveform 11 in FIG.

[Second Embodiment] FIG. 4 is a perspective view showing the structure of an optical waveguide according to this embodiment. In the figure, the same components as those shown in FIG. 1 are denoted by the same reference numerals. . FIG. 5 is a sectional view taken along the line BB when the optical waveguide 40 is viewed in the direction of the arrow in FIG. 4, and the same parts as those shown in FIG. The illustration of the rare earth element 3 is omitted.

As can be seen from FIGS. 4 and 5, in this embodiment, two oblique cut surfaces are provided with respect to the clad portion. That is, in the cross-sectional view shown in FIG. 5, a cut surface 23 and a cut surface 24 are provided for the upper portion sandwiching the core portion 2 as in the first embodiment, while the lower portion sandwiching the core portion 2 is provided. Has a cut surface 41 formed in the clad portion 21 and a cut surface 42 formed in the clad portion 22. In addition, it is the same as the case of the cut surface 24 that the cut surface 42 does not necessarily need to be inclined.

FIG. 6 is a block diagram showing a configuration of an optical direct amplifier using the optical waveguide 40 shown in FIGS. 4 and 5, and the same parts as those shown in FIGS. Are attached. In the present embodiment, the optical waveguide 40
Is provided with two cut surfaces, so that it has an excitation light source 43 having the same configuration as the excitation light source 30 and a light collector having the same configuration as the light collector 31 arranged opposite to the cut surface 41. 44. As a result, the condenser 44 condenses the light emitted by the excitation light source 43, and makes the incident light 45 enter the cladding portion 21 from the cut surface 41.

The operation of the optical direct amplifier having the above configuration is the first.
This is the same as in the embodiment. That is, the light collector 3
1 and 44 condense the light generated by the excitation light sources 30 and 43, respectively, and cause the obtained excitation lights 32 and 45 to enter the cladding 21 from the cut surfaces 23 and 41, respectively. As a result, similarly to the first embodiment, each incident light propagates while being reflected in the cladding portion 21, and each time light passes through the core portion 2, the rare earth element 3 (not shown) in the core portion 2. ) Will be excited. In this state, the pulse light 6 generated by the signal light source 5 is condensed by the condenser 33 and the signal light 34 is made incident on the core unit 2. As a result, the signal light 34 is optically amplified when passing through the core section 2, and a higher level waveform 46 than the waveform 35 shown in FIG. 3 is obtained as the output light 10 from the optical waveguide 40.

In this embodiment, the number of cut surfaces is two. However, it is needless to say that the number of cut surfaces is not limited to two. If the number of cut surfaces is too large, the area of the cut surface when the excitation light is made incident on the cladding portion 21 will be too small. May be provided.

[0022]

As described above, according to the first aspect of the present invention, the core to which the rare earth element is added is surrounded, and the end is cut obliquely with respect to the longitudinal direction of the core. A first clad having a density lower than that of the core and having a first cladding surrounding the first cladding and having a lower density than the first cladding is provided. As a result, the excitation light incident from the cut surface excites the rare earth element in the core when propagating while reflecting off the first cladding, and in this state, the signal light is incident from the end face of the core. If it functions as an optical amplification medium. In this way, it is sufficient to make the excitation light incident on the cut surface having an area much larger than the diameter of the core, and it becomes extremely easy to make the excitation light enter the optical waveguide as compared with the related art.

According to the second aspect of the present invention, a plurality of cut surfaces are formed on the first clad. Thus, by injecting the pumping light from each of the plurality of cut surfaces, the degree of amplification of the signal light incident on the end face of the core can be further increased, and higher output light can be obtained. According to the third to fifth aspects of the present invention, in addition to providing the optical waveguide according to the first or second aspect and signal light input means for condensing the signal light and making it incident on the core, the generated excitation light is condensed. The number of excitation light generating means to be incident on the cut surface is provided by the number corresponding to the number of cut surfaces. This makes it possible to use a high-output pump light source as the pump light source in the pump light generating means, so that the power of the pump light can be increased, which is suitable for applications requiring high power such as material processing. An optical direct amplifier can be realized.

[Brief description of the drawings]

FIG. 1 is a perspective view showing a structure of an optical waveguide according to a first embodiment of the present invention.

FIG. 2 is a sectional view of the optical waveguide shown in FIG.

FIG. 3 is a block diagram showing a configuration of an optical direct amplifier using the optical waveguide shown in FIGS. 1 and 2;

FIG. 4 is a perspective view illustrating a structure of an optical waveguide according to a second embodiment of the present invention.

5 is a sectional view of the optical waveguide shown in FIG.

6 is a block diagram showing a configuration of an optical direct amplifier using the optical waveguide shown in FIGS. 4 and 5. FIG.

FIG. 7 is a perspective view showing a structure of an optical waveguide according to a conventional technique.

8 is a cross-sectional view of the optical waveguide shown in FIG.

FIG. 9 is a block diagram showing a configuration of an optical direct amplifier using the optical waveguide shown in FIGS. 7 and 8.

[Explanation of symbols]

2 core part, 3 rare earth element, 5 signal light source, 6 pulse light, 10 output light, 20, 40 optical waveguide, 21 and 22
2 ... clad part, 23, 24, 41, 42 ... cut surface, 3
0, 43 ... excitation light source, 31, 33, 44 ... condenser, 3
2,45 ... excitation light, 34 ... signal light

Claims (5)

[Claims] 1. An optical waveguide having a core to which a rare earth element is added, wherein the rare earth element is cut into a cut surface formed by surrounding the core and cutting an end thereof obliquely with respect to a longitudinal direction of the core. A first cladding, to which excitation light to be excited is incident and having a lower density than the core; and a second cladding surrounding the first cladding and having a lower density than the first cladding. An optical waveguide, comprising: 2. The optical waveguide according to claim 1, wherein a plurality of the cut surfaces are formed in the first clad. 3. The optical waveguide according to claim 1, wherein the signal light is condensed and the signal light is inputted to the core. An optical direct amplifier, comprising: excitation light generating means for condensing the excitation light and making it incident on the cut surface. 4. An excitation light generating means, comprising: an excitation light source that generates the excitation light; and an excitation light source that is disposed to face the cut surface, condenses the excitation light generated by the excitation light source, and cuts the excitation light. 4. An optical direct amplifier according to claim 3, further comprising a condensing means for causing the light to enter the optical amplifier. 5. The optical direct amplifier according to claim 4, wherein the pumping light source is a laser diode configured by arranging a plurality of emitters.