Patent Application
20190341745
The present invention relates to a laser apparatus used for laser processing, laser welding, laser marking, and the like.
There is known a laser apparatus that couples beams emitted from a plurality of laser diodes (LD) to one fiber core to obtain a high output from a fiber.
Patent Document 1 (JP2005-114977A) describes a light power composing optical system capable of efficiently coupling light from a plurality of light sources to one light receiver to obtain a high output. According to this light power composing optical system, the magnification of the lens system can be reduced by making a luminous flux in the vertical direction and a luminous flux in the horizontal direction have equivalent magnitude by using an anamorphic optical element, and therefore the condensation diameter can be reduced. Therefore, the coupling efficiency to the light receiver can be improved, and thus a high-power laser beam can be obtained.
A beam emitted from a laser diode can be regarded as a Gaussian beam, and the product of a beam waist diameter w0 and a beam divergence angle θ0 is constant. Using a factor M2 (M square) representing the beam quality, the relationship of these is expressed by Formula (1) using a wavelength λ.
M
2=(Πw0·θ0)/λ (1)
The light emitting surface of the laser diode is a rectangle which is narrow in a lamination direction of the laser diode chip, that is, in a fast axis direction, and is wide in the lateral direction, that is, in a slow axis direction. It is known that the emitted beam has, as a result of diffraction, an elliptical shape spread in the fast axis direction. Assuming that the beam waist diameter is w0f, the beam divergence angle is θ0f, and the beam factor is M2f in the fast axis direction, and that the beam waist diameter is w0s, the beam divergence angle is θ0s, and the beam factor is M2s in the slow axis direction, this shape is represented by relationships of w0s>w0f, θ0f>θ0s, and M2f<M2s.
In a high-power laser diode, since the area of a light emitting surface of the laser diode chip represented by (2×w0f)×(2×w0s) is large. Therefore, the value of M2 is worse than that of a laser diode of a transverse single mode, one can see that the beam quality is worse.
In addition, if a beam is incident on a core at an incident angle equal to or larger than the fiber NA (numerical aperture), total reflection does not occur between the core and the cladding, and the beam leaks to a resin layer and a protective layer covering the cladding and the surroundings thereof. Further, if a beam having a beam diameter equal to or larger than the core diameter of the fiber is incident on the core, the beam also leaks into the cladding. On the other hand, in order to reduce the size of the optical system after emission from the fiber and to reduce the diameter at the time of beam convergence after emission from the fiber, a fiber with a small NA and a small core diameter is required.
Therefore, when coupling a beam to a fiber having a small NA and a small core diameter, the beam is collected near the fiber axis (optical axis) by using a mirror, a prism, or the like, and the collimated beam is incident on a coupling lens in a direction perpendicular to the fiber axis. In this manner, a beam can be efficiently coupled to a fiber having a small NA and a small core diameter.
For example, beams emitted from a plurality of laser diodes can be coupled to a small core, for example, a fiber with a small NA of Φ 25, 50, or 100 um, and thus a beam of a high luminance and a high power can be obtained.
However, a high-power laser diode has poorer beam quality than a laser diode with a low-power (single mode, etc.) light emitting surface, so that it is difficult to efficiently couple beams emitted from a plurality of laser diodes to a small core.
Further, in the case where the anamorphic optical element described in Patent Literature 1 is used, the cost of the optical element and the number of assembling and adjusting steps are increased. In the case of obtaining a high-luminance and high-power beam from a fiber of a small core, the proportion of energy loss in an incident portion of the fiber is large due to a loss, and therefore there is a tendency that the beam quality is degraded further by degradation of reliability caused by heating of the incident portion of the fiber or cladding leaked light.
The present invention provides a high-luminance and high-power laser apparatus capable of coupling beams to a smaller fiber core and improving beam quality.
In order to solve the problem described above, a laser apparatus according to the present invention is a laser apparatus for coupling a plurality of beams to a single fiber, the laser apparatus including a plurality of laser diodes that emit the plurality of beams, a plurality of optical elements provided in correspondence with the plurality of laser diodes to make the plurality of beams emitted from the plurality of laser diodes parallel, a plurality of selective transmission elements that are provided in correspondence with the plurality of optical elements and that selectively transmit the beams emitted from the plurality of laser diodes or beams excluding an outer periphery portion of the beams emitted from the plurality of optical elements, one or more light traveling direction control members that control light traveling directions of the plurality of beams having passed through the plurality of optical elements and the plurality of selective transmission elements so as to move the plurality of beams to the vicinity of an optical axis of the fiber, and a light converging unit that converges the plurality of beams emitted from the one or more light traveling direction control members to the fiber.
In addition, the present invention is a laser apparatus for coupling a plurality of beams to a single fiber, the laser apparatus including a plurality of laser diodes that emit the plurality of beams, a plurality of optical elements provided in correspondence with the plurality of laser diodes to make the plurality of beams emitted from the plurality of laser diodes parallel, one or more first light traveling direction control members that control light traveling directions of the plurality of beams emitted from the plurality of optical elements, a plurality of selective transmission elements that selectively transmit beams excluding an outer periphery portion of the beams emitted from the one or more first light traveling direction control members, one or more second light traveling direction control members that control light traveling directions of the plurality of beams emitted from the plurality of selective transmission elements so as to move the plurality of beams to the vicinity of an optical axis of the fiber, and a light converging unit that converges the plurality of beams emitted from the one or more second light traveling direction control members to the fiber.
According to the present invention, the plurality of selective transmission elements block a high M2 component contained in an outer periphery portion of beams emitted from the laser diodes and selectively transmit only a low M2 component included in beams excluding the outer periphery portion of the beams. Although the high M2 component is a heat loss, by extracting only the low M2 component, it is possible to reduce the spot diameter and the incident angle when converging a plurality of beams. Therefore, it is possible to couple the beams to a fiber core smaller than a conventional fiber core.
Accordingly, by narrowing the distance between the one or more light traveling direction control members constituted by mirrors, prisms, or the like, that is, by narrowing the interval between the beams, the number of beams projected onto a coupling lens (light converging unit) arranged before a fiber can be increased, and thus a larger number of beams can be coupled to the fiber core.
By removing the high M2 component, a loss occurs in the power of each laser diode, but a beam filling factor that can be coupled to one fiber (the sum of sectional areas of beams on the coupling lens/an effective area contributing to fiber coupling on the coupling lens) increases, so that a high output can be achieved in total. In addition, increasing the beam filling factor means that the beams can be collected to the vicinity of the optical axis of the coupling lens, and the fiber incident NA can be reduced. That is, it is possible to use a low NA fiber capable of obtaining a beam with a higher luminance. Since the component which becomes cladding leakage is removed in an early stage, the fiber output beam quality is improved.
In addition, it becomes possible to reduce the diameter of the laser diode output beam, and thus it is possible to miniaturize optical members such as lenses, mirrors, prisms, wavelength plates, and the like to be used in later stages.
Hereinafter, a laser apparatus according to an embodiment of the present invention will be described in detail with reference to drawings.
First, a basic configuration of the laser apparatus of the present invention will be described.
The laser apparatus includes a plurality of laser diodes 10, a plurality of collimating lenses 11 (corresponding to optical elements of the present invention) provided in correspondence with the plurality of laser diodes 10, a plurality of units 12 provided in correspondence with the plurality of laser diodes 10 and formed by fixing the laser diodes 10 and the collimating lenses 11 for the respective laser diodes 10, a coupling lens 15 (corresponding to a light converging unit of the present invention) for converging beams emitted from the laser diodes 10 to a fiber 16, and a holder 20 that accommodates the plurality of units 12 and the coupling lens 15.
As illustrated in
As illustrated in
Next, a diaphragm member serving as a characteristic element of the present invention will be described.
The diaphragm member 21a illustrated in
Further, a substance having a predetermined absorption coefficient to the wavelength of the beams emitted from the laser diodes 10 may be formed on the surfaces of the diaphragm members 21a to 21c. For example, by subjecting the surfaces of the diaphragm members 21a to 21c to black alumite treatment, it is possible to reduce reflected beams to efficiently absorb unnecessary beams. Instead of subjecting the surfaces of the diaphragm members 21a to 21c to black alumite treatment, a dielectric thin film may be applied.
Further, as examples of sections of the diaphragm members 21a to 21c, a diaphragm member 21d having a quadrangular hole portion 22d illustrated in
The diaphragm member 21A illustrated in
Further, the diaphragm member 21B illustrated in
In addition, the distance between the diaphragm members 21-1 to 21-3 and the radiator plate 23 may change due to a positional shift between the LD holders 10-1 and the collimating lens holders 11-1. In this case, by inserting a heat transfer material between the diaphragm members 21-1 to 21-3 and the radiator plate 23, heat can be efficiently dissipated by the heat transfer material.
The conventional laser apparatus illustrated in
As illustrated in
A plurality of laser diodes 10, a plurality of collimating lenses 11, a plurality of diaphragm members 21, prisms 31a and 31b that control light traveling directions of a plurality of beams having passed through the plurality of collimating lenses 11 so as to move the plurality of beams onto the optical axis of a fiber 16, and a coupling lens 15 for converging the plurality of beams emitted from the prisms 31a and 31b to the fiber 16 are provided.
Next, description will be given by exemplifying that the beam filling factor is improved by using the diaphragm member 21. It is assumed that the intensity distribution of a beam emitted from a laser diode is a perfect Gaussian distribution. Assuming a point where the intensity of the Gaussian beam takes the maximum value Io, an intensity I(r) at a point distant from the central axis by a distance r on a plane perpendicular to the beam traveling direction is expressed by the following formula (2).
I(r)=I0 exp(−2r2/w02) (2)
At this time, the power of the beam passing through the diaphragm member 21 is 99.97%, 98.89%, 94.39%, 86.47%, and 72.2%, respectively. It can be seen that when the diameter of the diaphragm member 21 is reduced, the power of the beam transmitted through the diaphragm member 21 is reduced.
Here, among the beams incident on the coupling lens 15, letting D be a diameter on the lens effective for fiber core coupling, a case where a plurality of beams are coupled to the core 17 of the fiber 16 as illustrated in
In the above example, although an example of using the diaphragm member 21 in both the fast axis direction and the slow axis direction has been described, it is also possible to use a diaphragm member having an arbitrary size in the fast axis direction or slow axis direction in accordance with the core diameter and the core shape of the fiber to be used.
As described above, according to the laser apparatus of the first embodiment, the plurality of diaphragm members 21 block a high M2 component contained in an outer periphery portion of beams emitted from the laser diodes and selectively transmit only a low M2 component included in beams excluding the outer periphery portion of the beams. Although the high M2 component is a heat loss, by extracting only the low M2 component, it is possible to reduce the spot diameter and the incident angle when converging a plurality of beams. Therefore, it is possible to couple the beams to a fiber core smaller than a conventional fiber core.
Accordingly, by narrowing the distance between the prisms 31a and 31b, that is, by narrowing the interval between the beams, the number of beams projected onto the coupling lens 15 arranged before the fiber 16 can be increased, and thus a larger number of beams can be coupled to the core 17 of the fiber 16.
By removing the high M2 component, a loss occurs in the power of each laser diode 10, but a beam filling factor that can be coupled to one fiber 16 (the sum of sectional areas of beams on the coupling lens/an effective area contributing to fiber coupling on the coupling lens) increases, so that a high output can be achieved in total. In addition, increasing the beam filling factor means that the beams can be collected to the vicinity of the optical axis of the coupling lens, and the fiber incident NA can be reduced. That is, it is possible to use a low NA fiber of a higher luminance. Since the component which becomes cladding leakage is removed in an early stage, damage to the fiber 16 is reduced, and the fiber output beam quality is improved.
In addition, it becomes possible to reduce the diameter of the laser diode output beam, and thus it is possible to miniaturize optical members such as lenses, mirrors, prisms, wavelength plates, and the like to be used in later stages.
The spectral linewidth of a laser diode 10 of a transverse multimode is wider than that of a laser diode 10 of a transverse single mode. In applications requiring a high intensity and a narrow spectral line width such as a light source for fluorescence excitation, it is necessary to improve the spectral line width. Therefore, a laser apparatus according to a second embodiment of the present invention is characterized in that the spectral line width is improved by using a diffraction grating-incorporating diaphragm.
As illustrated in
That is, the diffraction grating-incorporating diaphragm member 21d corresponds to a reflection-type diffraction grating of the present invention, and returns, to a light emitting surface of a laser diode 10, a part of a beam BM10 emitted from a laser diode 10 to a surface facing the laser diode 10, and a beam BM11 is obtained by a hole portion 32a.
As illustrated in
According to the above configuration, an external resonator is formed between the laser diode 10 and the diffraction grating-incorporating diaphragm member 21d and 33. A component having a low M2 value passes through the diffraction grating-incorporating diaphragm members 21d and 33, and a component having a high M2 value is returned to the light emitting surface of the laser diode 10. Therefore, it is possible to realize both of reducing the linewidth of and stabilizing the wavelength of the laser wavelength, and increasing the output.
The condensing lens 34 condenses a beam collimated by the collimating lens 11 to a hole PH formed in the pinhole 35. The pinhole 35 removes the high M2 component at the hole PH, and thus extracts and outputs only the low M2 component to the collimating lens 36. The collimating lens 36 collimates the beam of only the low M2 component extracted by the pinhole 35.
In this manner, the same effect as that of the laser apparatus according to the first embodiment can be achieved also by the laser apparatus including the pinhole according to the third embodiment.
Regarding the plurality of laser diodes 10a to 10c, three laser diodes are arranged in the vertical direction as illustrated in
According to such a configuration, beams emitted from the laser diodes 10a to 10c become collimated beams by the collimating lenses 11a to 11c arranged at focal positions. The collimated beams are reflected by the cylindrical concave mirrors 37a and 37b, and the high M2 component in the vertical direction or the horizontal direction is removed by the pinholes 38a and 38b arranged at the focal positions of the cylindrical concave mirrors 37a and 37b.
The beams that have passed through the pinholes 38a and 38b become collimated beams again by the cylindrical concave mirrors 39a and 39b and travel in the optical axis direction (axis perpendicular to the fiber 16). The position of each collimated beam can be shifted toward the center of the optical axis of the coupling lens 40, so that it is possible to reduce the fiber NA while reducing the influence of aberration in the coupling lens 40. In addition, since the number of beams that can be incident on the coupling lens 40 increases, the output can be increased.
Also, depending on the positions and shapes of the cylindrical concave mirrors 37a, 37b, 39a, and 39b, the shapes of the collimated beams after reflection by the cylindrical concave mirrors 37a, 37b, 39a, and 39b can be freely controlled.
The beams of the nine laser diodes 10 become nine circular collimated beams CBM1 as a result of the nine collimating lenses 11. The sizes of the circles of the collimated beams CBM1 indicate an initial M2 value.
Next, as indicated by vertical arrows, when the pinholes 38 are applied to the horizontal direction of the first column (1, 1), (2, 1), and (3, 1) and the third column (1, 3), (2, 3), and (3, 3) of the plurality of laser diodes, the collimated beams CBM1 of the first column (1, 1), (2, 1), and (3, 1) and the third column (1, 3), (2, 3), and (3, 3) are reduced in the horizontal direction, and thus beams CBM2 are obtained. Therefore, the high M2 component in the horizontal direction is removed.
Next, as indicated by horizontal arrows, when the pinholes 38 are applied to the vertical direction of the first row (1, 1), (1, 2), and (1, 3) and the third row (3, 1), (3, 2), and (3, 3) of the plurality of laser diodes, the collimated beams CBM2 of the first row (1, 1), (1, 2), and (1, 3) and the third row (3, 1), (3, 2), and (3, 3) are reduced in the vertical direction, and thus beams CBM3 are obtained. Therefore, the high M2 component in the vertical direction is removed.
As described above, for the beams emitted from the nine laser diodes 10, the high M2 component of beams at positions affected by the aberration of the coupling lens is removed depending on the positional relationship with the optical axis, the diameters of the collimated beams are reduced, and thus the filling factor of the beams can be improved.
To be noted, regarding the laser diode at the center of the matrix (2, 2), the high M2 component has not passed through a pinhole or a slit and thus remains. However, since the central laser diode is arranged on the optical axis, the central laser diode is the least likely to be affected by the aberration of the coupling lens, and therefore the high M2 component being included is not a big problem.
Similarly, for the beams CBM3 in (1, 2), (2, 1), (2, 3), and (3, 2) of the matrix, the high M2 component has not been removed for one axis, but the effect thereof is small as compared with the laser diode of the four corners (1, 2, (1, 3), (3, 1), and (3, 3) of the matrix.
To be noted, if necessary, in order to remove the high M2 component, the pinhole 35 and the collimating lens 36 described in the third embodiment may be added behind the coupling lens 40.
The present invention is applicable to a fine laser processing machine used for soldering, bonding wire connection, substrate welding of electronic parts, minute spot annealing, and the like.
This application relates to, and claims priority from, Ser. No.: PCT/JP2016/077228 filed Sep. 15, 2016, the entire contents of which are incorporated herein by reference.
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/JP2016/077228 | 9/15/2016 | WO | 00 |
