JP5299959B2 - Light beam amplification method and light beam amplification apparatus - Google Patents

Description

  The present invention relates to a light beam amplification method and a light beam amplification device that increase the output of an axially symmetric polarized beam using an optical fiber including a light emitter.

  A light beam in which the polarization distribution in the beam cross section is distributed symmetrically with respect to the optical axis is called an axially symmetric polarized beam. As typical examples, a radially polarized beam having a radial polarization distribution and an azimuth polarized beam composed only of a polarized component parallel to the azimuth direction are known.

  In particular, when a radially polarized beam is condensed perpendicularly to the object plane, all light rays become p-polarized light, so that the reflectivity of the entire beam is lower than that of linearly polarized light or non-polarized light. This means that the energy of light absorbed by the object increases, and is suitable for highly efficient laser processing (see, for example, Non-Patent Document 1).

  On the other hand, when deep drilling is performed, it is convenient that the reflection of light at the hole wall is large so that the laser beam can reach the deep part of the hole. An azimuthally polarized beam that becomes polarized light is suitable (for example, see Non-Patent Document 2).

  The output of the laser used for laser processing depends on the type and size of the material, the processing range, the speed, etc., but is about several W to several tens of kW. At present, the maximum output of the axially symmetric polarized beam that has been reported to be generated is 3 kW by a carbon dioxide laser (for example, see Non-Patent Document 3).

  However, when lenses with the same focal length are used, the spot diameter when the light beam is focused is proportional to the wavelength of the light, so carbon dioxide with a wavelength of about 10 microns is required for more precise processing. A laser such as Nd: YAG or Yb: YAG having a wavelength of about 1.06 microns is more suitable than a laser, but the output in a single transverse mode remains at 200 W (for example, see Non-Patent Document 4). .

  On the other hand, when an optical fiber including a light emitter in the core portion is used as a laser medium, the effect of heat is reduced compared to a rod-type laser medium, so that high output can be obtained with high beam quality.

However, most of the optical fibers currently reported as fiber lasers are manufactured for the purpose of propagating the lowest-order Gaussian beam as a transverse mode, and it is difficult to obtain an axially symmetric polarized beam with high output. It was. The lowest order Gaussian beam is also called a TEM ₀₀ mode or an LP ₀₁ mode. The lowest transverse mode of the axially symmetric polarized beam is also called TM ₀₁ mode, TE ₀₁ mode, and HE ₂₁ mode. Alternatively, these are collectively referred to as an LP ₁₁ mode as a mode propagating in the optical fiber. The TM ₀₁ , TE ₀₁ , and HE ₂₁ modes correspond to a radially polarized beam, an azimuth polarized beam, and a hybrid mode beam, respectively.

V. G. Niziev and A. V. Nesterov, “Influence of beam polarization on laser cuttingefficiency”, J. Phys. D: Appl. Phys. 1999, 32, p. 1455 M.Meier, V. Romano, and T. Feurer, “Materials processing with pulsed radially and azimuthally polarized laser radiation”, Appl. Phys., 2007, A 86, p.329 M. Abdou Ahmed, J. Schulz, A. Voss, O. Parriaux, J.-C. Pommier, and T. Graf, “Radially polarized 3kW beam from a CO2 laser with an intracavity resonant gratingmirror”, Opt. Lett., 2007 , 32, p. 1824 I. Moshe, S. Jackel, A. Meir, Y. Lumer, and E. Leibush, “2kW, M2 <10 radically polarized beams from aberration-compensated rod-based Nd: YAG lasers”, Opt. Lett., 2007, 32 , p.47

  Therefore, an object of the present invention is to provide a light beam amplification method and a light beam amplification apparatus that can obtain a high output by increasing the output of an axially symmetric polarized beam while maintaining the intensity distribution and the polarization distribution.

The transverse mode capable of propagating in the core is determined by the refractive index of the core and cladding of the optical fiber, the core diameter, and the wavelength of light. The present invention is not only LP ₀₁ mode is a Gaussian beam, also possible propagation modes, such as LP ₁₁ is axially symmetric polarized beam, by introducing a small axially symmetric polarization beam output to an optical fiber core which includes a light emitter, The present invention relates to a light beam amplification method and a light beam amplification apparatus capable of obtaining an axially symmetric polarized beam having an increased output from the exit of an optical fiber by exciting a light emitter with light from the outside.

According to the present invention, viewed contains a light emitter, a core diameter of greater than a single mode fiber, the core of the possible optical fiber propagate axially symmetric polarized beam, is introduced axially symmetric polarized beam from the light source, the optical fiber from the outside By concentrating light on the inner cladding and the core of the light to excite the light emitter, thereby increasing the output of the axisymmetric polarized beam propagating through the optical fiber by stimulated emission of the excited light emitter , A light beam amplification method is obtained, characterized in that the axisymmetric polarized beam having an increased output is obtained from the exit of the optical fiber . Also, look containing a light emitter, a core diameter of greater than a single mode fiber, an optical fiber capable of propagating axially symmetric polarized beam, by generating an axisymmetric polarized beam, and axially symmetric polarization beam source to be introduced into the core of the optical fiber An excitation laser for condensing light from the outside to the inner cladding and the core of the optical fiber so as to excite the light emitter, and the output of the axisymmetric polarized beam propagating through the optical fiber is excited. A light beam amplifying apparatus is obtained, which is configured to obtain the axially symmetric polarized beam which is increased by stimulated emission of the illuminant and whose output is increased from the exit of the optical fiber . According to the present invention, it is possible to obtain a light beam amplification method and apparatus characterized by increasing the output of an axisymmetric polarized beam having a small output without changing the polarization, phase, and intensity distribution.

  In addition, according to the present invention, there can be obtained a light beam amplification method and a light beam amplification device characterized in that the axially symmetric polarized beam is a continuous wave or a pulse wave.

  In addition, according to the present invention, there can be obtained a light beam amplification method and a light beam amplification device characterized in that the axially symmetric polarized beam is in a single mode or a plurality of modes.

  Further, according to the present invention, there can be obtained a light beam amplification method and a light beam amplification apparatus characterized in that the optical fiber is single or plural.

  Further, according to the present invention, the light emitter of the optical fiber is included in a core or a clad in which the axially symmetric polarized beam propagates, or both, and a light beam amplification method and a light beam amplification device Is obtained.

  According to the present invention, the light emitter of the optical fiber is included in all or part of the core through which the axially symmetric polarized beam propagates. Is obtained. In addition, according to the present invention, there is obtained a light beam amplification method and a light beam amplification device characterized in that the concentration of the illuminant of the optical fiber is high at a portion where the intensity of the axially symmetric polarized beam of the core is strong. . In addition, according to the present invention, there is obtained a light beam amplification method and a light beam amplification device, wherein the light emitters of the optical fiber are erbium ions and ytterbium ions.

  According to the present invention, it is possible to provide a light beam amplification method and a light beam amplification apparatus capable of obtaining a high output by increasing the output of an axially symmetric polarized beam while maintaining the intensity distribution and the polarization distribution. In addition, a high-power axisymmetric polarized beam effective for laser processing can be obtained. Further, since an optical fiber is used, heat dissipation is easy and a compact device can be obtained. Furthermore, high-efficiency laser processing becomes possible by selecting and amplifying polarized light suitable for the purpose.

Fig. 1 shows beam cross sections of (a) radial polarization (TM ₀₁ mode), (b) azimuth polarization (TEM ₀₁ mode), and (c) hybrid mode (HE ₂₁ mode) beams as typical axisymmetric polarization beams. The polarization distribution of is shown.

FIG. 2 is an example of a light beam amplification apparatus according to an embodiment of the present invention that increases the output of an axially symmetric polarized beam. The optical fiber 5 has a core portion doped with Yb as a light emitter. The clad portion has a double structure, and the excitation light passes through the inner clad portion and the core portion. The light from the excitation laser 1 passes through the wavelength selection mirror 2 and is collected on the inner cladding and core of the optical fiber 5 by the lens 3. The light beam from the axially symmetric polarized beam light source 4 that generates the axially symmetric polarized beam is reflected by the wavelength selection mirror 2 and focused on the core of the optical fiber 5 by the lens 3. The output of the axially symmetric polarized beam propagating through the optical fiber 5 is increased by stimulated emission of excited Yb ions. As the optical fiber 5, one that can propagate not only the LP ₀₁ mode but also the LP ₁₁ mode is selected. In general, an optical fiber having a slightly larger core diameter is used than an optical fiber that can propagate only the LP ₀₁ mode, which is called a single mode fiber.

  FIG. 3 is an example of the intensity distribution of the axially symmetric polarized beam emitted from the optical fiber 5. In this example, the incident light beam to the optical fiber 5 is a radially polarized beam shown in FIG. FIG. 3A shows the total intensity, and it can be seen that the distribution has a dark donut shape at the center. FIGS. 3B to 3D are intensity distributions after passing through the linearly polarizing plate, and the direction of the linearly polarizing plate is indicated by arrows in FIGS. 3B to 3D. At this time, the output of incident light is 114 mW, and the output of outgoing light is 172 mW. From this, it can be seen that the output of the beam emitted from the optical fiber 5 is increased while maintaining the polarization and the intensity distribution.

  Although the amplification factor is low in the example of FIG. 3, the amplification factor is increased by making the wavelength of the excitation light coincide with the absorption of the light emitter or increasing the excitation light intensity.

  Whether the incident axially symmetric polarized beam is a continuous wave or a pulse wave, the output is similarly increased.

  Even if the incident axially symmetric polarized beam is one of a radially polarized beam, an azimuthally polarized beam, or a plurality of them, the output increases similarly.

  As shown in FIG. 3, the output increases even when only one optical fiber 5 is used. However, if the amplification is continuously performed using a plurality of optical fibers, the output further increases.

  Even if the light emitter included in the optical fiber 5 is included in the clad, the output light increases. Alternatively, it may be included in both the core and the clad in which the axially symmetric polarized beam propagates.

  Even if the light emitter included in the optical fiber 5 is included in a part of the core through which the axially symmetric polarized beam propagates, the output light increases. For example, as shown in FIG. 4, if the concentration of the illuminant is increased at a portion where the intensity of the axially symmetric polarized beam in the core is strong, the excitation light can be used efficiently for amplification and the output further increases. . In addition, oscillation of other transverse modes is suppressed, and a stable axisymmetric polarized beam is amplified.

  The light emitter contained in the optical fiber 5 may be ytterbium ions or erbium ions.

The polarization distribution in the beam cross section of (a) diameter polarization beam, (b) azimuth polarization beam, and (c) hybrid mode beam which are typical as an axially symmetric polarization beam of the light beam amplification apparatus of the embodiment of the present invention is shown. It is a distribution map. It is a block diagram which shows the light beam amplifier of embodiment of this invention. The light beam amplification apparatus shown in FIG. 2 passes through a linearly polarizing plate of (a) full intensity and (b) first direction of a beam output when a radially polarized beam is incident on an optical fiber. (C) intensity distribution after passing through a linearly polarizing plate in a second direction, and (d) distribution diagram showing intensity distribution after passing through a linearly polarizing plate in a third direction. In the light beam amplifying apparatus shown in FIG. 2, (a) a cross-sectional view of the core of the optical fiber and (b) a concentration distribution of the core part when the luminous body is included in a part of the core through which the axially symmetric polarized beam propagates. It is a graph to show.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Excitation laser 2 Wavelength selection mirror 3 Lens 4 Axisymmetric polarization beam light source 5 Optical fiber

Claims (16)

Look containing a light emitter, a core diameter of greater than a single mode fiber, the core of the possible optical fiber propagate axially symmetric polarized beam, it is introduced axially symmetric polarized beam from the light source, the inner cladding and the core of the optical fiber from the outside The output of the axially symmetric polarized beam propagating through the optical fiber is increased by stimulated emission of the excited light emitter, and the output from the exit of the optical fiber is increased. A method of amplifying a light beam, characterized in that an increased axially symmetric polarized beam is obtained .
  2. The light beam amplification method according to claim 1, wherein the axially symmetric polarized beam is a continuous wave or a pulse wave.   3. The light beam amplification method according to claim 1, wherein the axially symmetric polarized beam is a single mode or a plurality of modes.   4. The light beam amplification method according to claim 1, 2, or 3, wherein the optical fiber is single or plural.   5. The light beam amplification method according to claim 1, wherein the light emitter of the optical fiber is included in a core or a clad in which the axisymmetric polarized beam propagates, or both.   6. The light beam amplification method according to claim 1, wherein the light emitter of the optical fiber is included in all or part of a core through which the axially symmetric polarized beam propagates.   The light beam amplification method according to claim 6, wherein the concentration of the light emitter of the optical fiber is high in a portion where the intensity of the axially symmetric polarized beam of the core is high.   8. The light beam amplification method according to claim 1, wherein the light emitters of the optical fiber are erbium ions and ytterbium ions. Look containing a light emitter, a core diameter of greater than a single mode fiber, an optical fiber capable of propagating axially symmetric polarized beam,
An axially symmetric polarized beam light source that generates an axially symmetric polarized beam and introduces it into the core of the optical fiber;
An excitation laser for condensing light from the outside to the inner cladding and the core of the optical fiber so as to excite the illuminant,
The output of the axially symmetric polarized beam propagating through the optical fiber is increased by stimulated emission of the excited light emitter, and the axially symmetric polarized beam having an increased output is obtained from the exit of the optical fiber . An optical beam amplification device characterized by
  The light beam amplification apparatus according to claim 9, wherein the axially symmetric polarized beam is a continuous wave or a pulse wave.   11. The light beam amplifying apparatus according to claim 9, wherein the axially symmetric polarized beam has a single mode or a plurality of modes.   12. The light beam amplifying apparatus according to claim 9, 10 or 11, wherein the optical fiber is single or plural.   13. The light beam amplifying apparatus according to claim 9, 10, 11 or 12, wherein the light emitter of the optical fiber is included in a core or a clad in which the axially symmetric polarized beam propagates, or both.   The light beam amplifying apparatus according to claim 9, 10, 11, 12, or 13, wherein the light emitter of the optical fiber is included in all or part of a core through which the axially symmetric polarized beam propagates.   15. The light beam amplifying apparatus according to claim 14, wherein the concentration of the light emitter of the optical fiber is high in a portion where the intensity of the axially symmetric polarized beam of the core is high. 16. The light beam amplifying apparatus according to claim 9, wherein the light emitters of the optical fiber are erbium ions and ytterbium ions.