JP2005109185A - Laser beam amplification fiber device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To solve the follow problems: a laser beam to be amplified propagating a core is decreased due to displacement of the laser beam to be amplified and the core at a fiber incident end in a fiber laser, and as a result, a sufficient amplification output can not be obtained at a fiber exit end, and for a double clad fiber, as the beam leaking from the core propagates a first clad and is emitted from a fiber exit end, it is difficult to identify the component propagating the core. <P>SOLUTION: A position adjustment means arranged at either of a polarized-surface-preservation laser beam amplification fiber 1 having the double clad structure and receiving an excitation laser beam, or at an optical system which introduces to the laser beam amplification fiber 1 the laser beam to be amplified from the laser beam source 110 to be amplified to be optically amplified by the laser beam amplification fiber 1, adjusts a positional relationship between the incident end of the laser beam to be amplified at the core of the laser beam amplification fiber and the optical system at the laser beam source 110 side to be amplified. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a laser light amplifying fiber device.

Various laser light amplifying fibers have been proposed (see, for example, Patent Document 1).
A laser light amplifying fiber device using a laser light amplifying fiber, for example, as shown in a schematic configuration diagram in FIG. 8, the laser light from the excitation laser light source 102 is transmitted to the laser light amplifying fiber 1 as a transmission light. A low-power signal light that is condensed and introduced from the laser light source 110 to be amplified through the optical system 122 through the optical system 121 through the optical system 121 and is amplified through the optical system 122. Condensed light is introduced into the end 111 of the optical amplification fiber 1.

The optical system 121 on the excitation laser light source side includes lenses 104a and 104b, and a wavelength selective mirror 105a disposed therebetween.
The optical system 122 on the amplified laser light source 110 side includes lenses 104a and 104b, a wavelength selective mirror 105b disposed therebetween, and a return mirror 107.

  Further, a lens 104c, an optical isolator 109, and an optical rotator 108 are provided between the laser light source 102 to be amplified and the wavelength selective mirror of the optical system 106, and the laser to be amplified from the laser light source 102 to be amplified is provided. The light, for example, signal light is reflected by the wavelength selective mirror 105b of the optical system 122 by the mirror 106a through the collimator lens 104c, the optical isolator 109, and the optical rotator 108, and is reflected by the lens 104e. 111 is introduced into the laser light amplifying fiber 1.

  As shown in the schematic cross-sectional view of FIG. 2, the laser light amplifying fiber 1 is covered with a first cladding 12 on the outer periphery of the core 11, a second cladding 13 on the outer periphery, and a jacket 15 on the outer periphery via a buffer 14. Made up.

The laser light introduced from the pumping laser light source 102 into the optical system 121 through the transfer optical fiber 103 is transmitted through the wavelength selective mirror 105 a, condensed by the lens 104 b, and introduced into the first cladding of the laser light amplifying fiber 1. Then, the rare earth added to the core 11 of the laser beam amplifying fiber 1 is excited.
The excess laser light that is not absorbed while the excitation laser light passes from the end portion 112 to the end portion 111 of the amplification fiber 1 is reflected by the return mirror 107 of the optical system 122 and is again reflected in the laser light amplification fiber 1. To effectively contribute to excitation.

On the other hand, the amplified laser light from the low-power amplified laser light source 110 is condensed by the optical system 122 and introduced into the core 11 from the end 111 of the laser light amplification fiber 1 as described above. At this time, the wavelength of the amplified laser light is matched with the wavelength of the rare earth stimulated emission light added to the core 11 of the laser light amplifying fiber 1.
Then, in the process in which the laser light to be amplified propagates through the laser light amplifying fiber 1, the excitation laser light in the first cladding 12 is absorbed by the rare earth added to the core 11 and stimulated emission to the core 11. Induces light.
On the other hand, the laser to be amplified propagating through the core 11 is gradually increased in intensity while picking up the stimulated emission light, that is, amplified. The amplified laser light is emitted from the end 112 of the laser light amplifying fiber 1.
Since the amplified output light is reflected by the wavelength selective mirror 105a and the mirror 106b through the lens 104b, the amplified output light is derived as output light without going to the excitation laser light source 102.

In general, when a long laser beam amplifying fiber 1 uses a high-power excitation laser, the amount of absorption in the core 11 increases, and a larger amplification, that is, a large-power laser beam can be obtained.
As a specific example of the laser light amplifying fiber, a laser light amplifying fiber in which rare earth neodymium ions (Nd ³⁺ ) are added to the core is used, and a semiconductor laser light having a wavelength of about 800 nm is used as the excitation laser light. When an Nd: YAG laser beam of 1064 nm is used as the amplified laser beam, an amplified laser output of 1064 nm can be obtained.
The configuration example of a general fiber laser has been described above. However, the pumping light from the pumping laser light source 102 may be injected from the end 111 of the laser light amplifying fiber 1 based on this principle. Further, a method of injecting from both ends 111 and 112 of the laser light amplification fiber 1 using two excitation laser light sources is also used.
The fiber shown in FIG. 2 and its structure are called double clad fibers. As described above, rare earth is added to the core 11 having a high refractive index, and the laser to be amplified is injected, propagated, and amplified. In general, the cross-sectional shape of the core 11 is a circle, but an elliptical shape or the like is adopted to preserve the polarization plane. The diameter of the core 11 is generally 10 microns or less when propagating in a single mode. Further, as described above, an excitation laser is injected into the first cladding 12. The second cladding 13 has a lower refractive index than the first cladding 12, and the excitation laser propagates in the first cladding. In the process of propagating, the excitation laser also enters the core 11, and the invading light is absorbed by the rare earth added to the core.
The diameter of the first cladding is 2 to 10 times the diameter of the core and is selected according to the application. The outer side of the second cladding is a buffer 14 and a jacket 15, and materials other than optical materials are generally used for the purpose of maintaining mechanical strength.
In this fiber laser, when the beam spot of the laser to be amplified collected by the lens 104e on the fiber end 111 side and the core 11 are displaced, the laser beam to be amplified propagating through the core 11 is reduced. A sufficient amplified output cannot be obtained from the unit 112. Therefore, accurately injecting the laser to be amplified into the core 11 of the laser light amplifying fiber 1 is important for the characteristics of the fiber laser.
International Publication No. 02-03513

In a fiber laser, if the position of the laser beam to be amplified and the core is displaced at the fiber entrance end, the laser beam to be amplified propagating through the core decreases, and as a result, a sufficient amplified output cannot be obtained from the fiber exit end. If the light propagating through the core is maximized, the misalignment is eliminated. However, in the case of a double clad fiber, the light leaking from the core also propagates through the first clad and emerges from the fiber exit end. It was difficult to distinguish.
Further, since the lens and the fiber incident end in the amplified laser side optical system are fixed, it is difficult to correct the positional deviation due to a change with time.

  A laser light amplifying fiber device according to the present invention has a double clad structure having a first cladding layer and a second cladding layer on the outer periphery of a core, and a polarization-maintaining laser light amplifying fiber into which pumping laser light is introduced, An amplified laser light source that is optically amplified by the laser light amplifying fiber, an optical system on the amplified laser light source side that makes the amplified laser light from the amplified laser light source incident on the core of the laser light amplifying fiber, and a position Adjusting means, and this position adjusting means adjusts the positional relationship between the incident end of the amplified laser light of the core of the laser light amplifying fiber and the optical system on the amplified laser light source side from the amplified laser light source. The most important feature is to have a position adjusting mechanism.

  The laser light amplifying fiber device according to the present invention is provided with a means for detecting the output of the amplified laser light on the exit end side of the light amplifying laser light of the polarization plane preserving laser light amplifying fiber. The position adjustment mechanism may be controlled to adjust the incident position of the laser light to be amplified to the laser light amplification fiber laser.

  In the laser beam amplifying fiber device according to the present invention, a means for detecting the output of the amplified laser beam is provided on the light-amplified laser beam output end side of the polarization-maintaining laser beam amplification fiber, and the output of the amplified laser beam is detected. The means detects a polarization beam splitter disposed on the output end side of the optical amplification laser beam of the polarization plane preserving laser beam amplification fiber, and first and second output lights separated by the polarization beam splitter. The position adjustment mechanism can be adjusted using a difference between detection outputs from the light detection means as a control signal.

According to the laser light amplifying fiber device of the present invention, since the laser beam to be amplified is accurately injected, desired amplified light can be obtained.
In addition, since it is possible to correct misalignment due to changes over time as well as at the time of manufacturing the apparatus, a long-term reliable fiber laser can be realized. It can bring about an effect.

An embodiment of the apparatus of the present invention will be described with reference to FIG.
In this embodiment, the present invention is applied to the fiber device described in FIG. 8, but the present invention is not limited to this embodiment.

  In this embodiment, as described above, the laser light amplification fiber 1, the excitation laser light source 102, the transmission optical fiber 103, the optical system 121, the amplified laser light source 110, that is, the amplified signal laser light, for example, A light source and an optical system 122;

The optical system 121 on the excitation laser light source side includes lenses 104a and 104b, and a wavelength selective mirror 105a disposed therebetween.
The optical system 122 on the amplified laser light source 110 side includes lenses 104e and 104d, a wavelength selective mirror 105b disposed therebetween, and a return mirror 107.

  A lens 104c, an optical isolator 109, an optical rotator 108, and a mirror 106a are disposed between the laser light source 102 to be amplified and the wavelength selective mirror 105b of the optical system 122.

  In this embodiment, the polarization beam splitter 131 and the polarization beam splitter 131 branch off the optical path that is selected and branched by the wavelength selective mirror 105a of the optical system 121 on the excitation laser light source 102 side. For example, the first and second light detection units 132 and 133 that are arranged in the two optical paths, for example, using photodiodes, and the difference between detection outputs from the first and second light detection units 132 and 133 are detected. An arithmetic circuit 134 is provided.

On the other hand, the relative positions of the optical system 122 and the end 111, particularly the optical axes of both, are relatively small between the end 111 of the laser light amplifying fiber 1 on the amplified laser light source 110 side and the optical system 122. A movable part 135 to be adjusted is provided.
For example, as shown in FIG. 4, the movable portion 135 includes a fiber holder 21 that holds the end 111 of the laser light amplifying fiber 1 on the above-described amplified laser light source 110 side. For example, it is supported by the intermediate base 23 via a piezo element (PLZT element), that is, an electrostrictive element 22. The intermediate base 23 is supported by the fixed base 30 via, for example, a piezo element, that is, an electrostrictive element 24, which can be moved in the Y direction orthogonal to the X direction. be able to.

  In the example shown in FIG. 4, the end portion 111 of the fiber 1 is configured to be movable. However, the lens 104 e can be made movable by adopting the same configuration as shown in the schematic configuration in FIG. 5. . That is, in this case, the holder 26 that holds the lens 104e is supported by the intermediate base 28 via, for example, the piezo element 27 that can be moved in the X direction. The intermediate base 28 is supported by the fixed base 30 via, for example, a piezo element, that is, an electrostrictive element 29, which can be moved in the Y direction orthogonal to the X direction. be able to.

  In these configurations, the fiber 1 or the lens 104e can be moved and adjusted to X and Y by applying a control voltage to the piezoelectric element. However, this movement adjustment mechanism is not limited to the case where an electrostrictive element is used, and may be an electromagnetic actuator configuration, for example.

Next, the operation of this configuration will be described.
In this case, laser light from the excitation laser light source 102 passes through the transmission optical fiber 103 to the laser light amplification fiber 1 and passes through the lens 104a, the wavelength selective mirror 105a, and the lens 104b of the optical system 121. Condensed light is introduced into the first cladding 12 at the end 112 of the fiber 1.
On the other hand, for example, low-power signal light to be amplified is introduced from the laser light source 110 to be amplified into the wavelength selective mirror 105b of the optical system 122 by the mirror 106a through the lens 104c, the optical isolator 109, and the optical rotator 108. Accordingly, the wavelength is selected, reflected, condensed by the lens 104e, and condensed and introduced into the end 111 of the laser light amplifying fiber 1.

In this manner, the excitation laser light from the excitation laser light source 102 is introduced into the first cladding 12 of the optical amplification fiber 1, thereby exciting the rare earth added to the core 11.
The excess laser light that is not absorbed while the excitation laser light passes from the end portion 112 to the end portion 111 of the amplification fiber 1 is reflected by the return mirror 107 of the optical system 122 and is again reflected in the laser light amplification fiber 1. To effectively contribute to excitation.

On the other hand, the amplified laser light from the low-power amplified laser light source 110 is condensed by the optical system 122 and introduced into the core 11 from the end 111 of the laser light amplification fiber 1 as described above. At this time, the wavelength of the amplified laser light is matched with the wavelength of the rare earth stimulated emission light added to the core 11 of the laser light amplifying fiber 1.
Then, in the process in which the laser light to be amplified propagates through the laser light amplifying fiber 1, the excitation laser light in the first cladding 12 is absorbed by the rare earth added to the core 11 and stimulated emission to the core 11. Induces light.

The laser beam to be amplified that has been propagated through the core 11 and amplified is emitted from the end 112 of the laser beam amplification fiber 1.
The amplified output light 108 is set as described above so that the amplified output light is reflected by the wavelength selective mirror 105a and the mirror 106b through the lens 104b, and is introduced into the polarization beam splitter 131.

Now, when the excitation laser beam is not introduced into the fiber 1 and the polarization plane direction of the fiber 1 is made to coincide with the S polarization direction of the polarization beam splitter 131, the beam of the amplified laser beam at the end 111 of the fiber 1. Due to the positional deviation between the spot and the core 11 of the fiber 1, the outputs of the light detection elements 132 and 133 change.
That is, when the beam spot of the laser beam to be amplified and the core 11 of the fiber 1 coincide with each other, for example, as indicated by the solid curve 19 in FIG. The output of the other second photodetector 133 indicated by is minimized.
The reason for this change is that when the beam spot of the laser beam to be amplified is displaced from the position of the core 11 of the fiber 1, the polarization plane is preserved in the core 11 and the light propagating through the fiber 1 is reduced. The light leaking from the core 11 propagates in the first cladding 12 without preserving the polarization plane, that is, as randomly polarized light, which is led out from the end 112 of the fiber 1 and travels toward the polarization beam splitter 131. Therefore, since this is transmitted and introduced into the second photodetector 133, this output becomes large.
In the example described above, the polarization plane direction is matched with the S-polarized light of the polarization beam splitter 131, but when matched with the P-polarized light, the behavior of both the photodetectors 132 and 133 is as described above. The reverse is true.

Next, an example of the algorithm of the position control mechanism based on the characteristics of the photodetectors 132 and 133 with respect to the positional deviation will be described with reference to FIG.
In this example, when the laser to be amplified and the core 11 of the fiber 1 coincide, the difference between P1 and P2 is obtained by utilizing the fact that the output P1 of the photodetector 132 is maximum and the output of the photodetector 133 is minimum. This is a case where the movable portion 135 is controlled so that DP, that is, the output of the arithmetic circuit 134 of FIG.
That is, the fiber end or lens 104e that can move independently in the X and Y directions is slightly moved to repeatedly evaluate the change in DP, and the fiber or optical system is positioned at the position where the DP is maximized in the X and Y directions. Set the position of. A so-called open loop control method is used.

  The algorithm shown in FIG. 7 is an indicator that controls the movable part so that the output of the photodetector 133 is minimized when the position of the laser 11 to be amplified matches the position of the core 11 of the light 1. The fiber end or lens 104e, which is independently movable in the X and Y directions, is slightly moved to repeatedly evaluate the change in the output P2, and the fiber end or the lens 104e is positioned to minimize the output P2 in the X and Y directions. Set the position. Similarly, an open loop control method is used. When this method is used, the photodetector 132 is not necessary.

After adjusting the position of the laser to be amplified and the core 11 of the optical amplifying fiber 1 by the method described above, the excitation laser light is introduced into the fiber 1 and the above-described amplification operation is performed.
Further, even during the laser operation in which the excitation laser beam is introduced into the fiber 1, the amplified laser beam has a polarization plane that coincides with the polarization plane of the laser to be amplified propagating through the core. Thus, the optimum position shows the minimum value. That is, if the algorithm shown in FIG. 7 is used, it becomes possible to control the relative position between the laser to be amplified and the core 11 of the fiber 1 while using the laser operation.

  According to this configuration, it is possible to accurately inject the beam of the laser to be amplified.

It is a schematic block diagram of an example of the laser beam amplification fiber apparatus by this invention. 1 is a schematic cross-sectional view showing a structure of an example of a laser beam amplification fiber constituting a laser beam amplification fiber device according to the present invention. It is the schematic which shows an example of the means of light detection in an example of the laser beam amplification fiber apparatus by this invention. It is a schematic block diagram of an example of a movable part in the laser beam amplification fiber apparatus by this invention. It is a schematic block diagram of another example of a movable part in the laser beam amplification fiber apparatus by this invention. It is a schematic diagram of an example of the position adjustment mechanism in an example of the laser beam amplification fiber apparatus by this invention. It is a schematic diagram of another example of the position adjustment mechanism in an example of the laser beam amplification fiber apparatus by this invention. It is a schematic block diagram of the conventional laser beam amplification fiber apparatus.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 1 ... Laser beam amplifying fiber, 11 ... Core, 12 ... 1st clad, 13 ... 2nd clad, 14 ... Buffer, 15 ... Jacket, 19 ... Photodetector , 20 ... photodetector, 21 ... fiber holder, 22 ... piezo element, 23 ... intermediate base, 24 ... piezo element, 25 ... base, 26 ... holder, 27 ... Piezo element, 28 ... Intermediate base, 29 ... Piezo element, 30 ... Base, 102 ... Laser light source for excitation, 103 ... Optical fiber for transmission, 104a ... Lens, 104b ... lens, 104c ... lens, 104d ... lens, 104e ... lens, 105a ... wavelength selective mirror, 105b ... wavelength selective mirror, 106a ... mirror, 106b ··mirror, 07 ... Return mirror, 108 ... Optical rotator, 109 ... Optical isolator, 110 ... Amplified laser light source, 111 ... End, 112 ... End, 121 ... Optical system , 122 ... optical system, 131 ... polarization beam splitter, 132 ... first photodetector, 133 ... second photodetector, 134 ... arithmetic circuit, 135 ... movable , 201... Laser light amplifying fiber device

Claims (3)

A polarization-preserving laser light amplifying fiber having a double clad structure having a first clad layer and a second clad layer on the outer periphery of the core, into which pumping laser light is introduced;
An amplified laser beam source that is amplified by the laser beam amplification fiber;
An optical system on the amplified laser beam generation source side that makes the amplified laser beam from the amplified laser beam generation source incident on the core of the laser beam amplification fiber;
Position adjusting means,
The position adjusting means adjusts a positional relationship between an incident end of the amplified laser light of the core of the laser light amplifying fiber and an optical system on the amplified laser light generation source side from the generation unit of the amplified laser light. A laser light amplifying fiber device having a position adjusting mechanism. The polarization plane preserving laser light amplifying fiber is provided with a means for detecting the output of the amplified laser light on the emission end side of the optically amplified laser light,
2. The laser according to claim 1, wherein the position adjustment mechanism is controlled by the detection output to adjust an incident position of the laser light to be amplified to the laser light amplifying fiber laser. 3. Optical amplification fiber device. The polarization plane preserving laser light amplifying fiber is provided with a means for detecting the output of the amplified laser light on the emission end side of the optically amplified laser light,
A means for detecting the output of the amplified laser beam, a polarization beam splitter disposed on the output end side of the optically amplified laser beam of the polarization-maintaining laser beam amplification fiber;
First and second light detection means for detecting first and second output lights separated by the polarization beam splitter;
2. The laser light amplifying fiber device according to claim 1, wherein the position adjustment mechanism performs position adjustment using a difference in detection output from the light detection means as a control signal.

Images