JP2002014256A - Laser beam coupling module - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a laser beam having a sufficiently high power density with a simply structured laser beam coupling module. SOLUTION: One optical waveguide 10 is provided, a plurality of laser light sources 21, 22, 23, 24 are arranged along the light guiding direction of this optical waveguide 10. The laser beams L1, L2, L3, L4 emitted from these laser light sources, 21, 22, 23, 24 are each made incident on the light guiding part 11 of the optical waveguide 10 from the lateral side in the light guiding direction, and are multiplexed in the optical waveguide 10.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a laser light coupling module which multiplexes laser lights emitted from a plurality of laser light sources coaxially to obtain one laser light having a higher power density. .

[0002]

2. Description of the Related Art Conventionally, so-called laser ablation for irradiating a processing material with a high-energy laser beam to ablate the irradiated portion has been put to practical use. Recently, in addition to general marking, welding, cutting, cladding, etc., this laser ablation is used for recording on printing plates, surface processing using high-energy light, surface processing using surface shock waves, etc. Has been widely applied in the field of In this laser ablation, higher intensity laser light is required in order to increase processing accuracy and shorten processing time.

[0003] As one of the techniques for obtaining a laser beam of higher intensity, a technique of combining laser beams emitted from a plurality of laser light sources into one is conventionally known. More specifically, the laser beam multiplexing technique includes (1) a method in which two laser beams are polarized and multiplexed using a polarizing beam splitter or the like (for example, “Laser Research”, January 2000, Nos. 34 to 39). Page Nobuyuki Abe “Refer to“ Material Processing Using High-Power High-Power-Density Semiconductor Lasers ”), (2) a method in which a plurality of laser light sources are respectively coupled to optical fibers and the optical fibers are bundled (eg, GJDixon“ Fibers turn free- space b
eams intoguided waves ”Laser Focus World Nov.199
7, (3) using a folding optical system (for example, James R Leger “Geometrical Transformatio”)
n of Linear Diode-Laser Arrays for Longitudinal Pu
mping of Solid-State Lasers ”IEEE, JQE, Vol.128, No.
4,1992, pp1088-1100), (4) An optical coupling device in which one end of a plurality of optical waveguides is used as a light entrance, and the other ends of those optical waveguides are combined into a single light exit. Those used (for example, see JP-A-2000-19362) are widely known.

[0004]

However, the technique (1) has a problem that it is difficult to sufficiently increase the power density of the laser light because only two kinds of light in the vertical and horizontal polarization directions can be combined. Is recognized.

[0005] The technique (2) employs a structure in which a plurality of optical fibers are bundled, so that in this case also, it is difficult to sufficiently increase the power density of the laser light. .

In the technique (3), since a bulk optical system is used, it is necessary to precisely lay out expensive optical parts, and there is a problem that the cost of the apparatus is inevitably extremely high.

The techniques (3) and (2) are:
Since a plurality of laser beams are not multiplexed coaxially with each other, there is a problem that a high power density of the laser beam cannot be expected from this point.

On the other hand, in the technique (4), if the relationship of (optical waveguide width after multiplexing) = (optical waveguide width before multiplexing) × (number of multiplexing) is not strictly satisfied, optical There is a problem that a large loss occurs and the function as a multiplexing device cannot be obtained.

Since the techniques (1) to (4) have the above-described problems, the power density of the laser light obtained by combining these techniques is at most 1 MW / cm ^2.
It is only about degree.

The present invention has been made in view of the above circumstances, and an object of the present invention is to provide a laser light coupling module capable of obtaining laser light having a sufficiently high power density with a simple configuration.

[0011]

According to the laser light coupling module of the present invention, laser light is sequentially incident on one optical waveguide from the side, and the laser light is multiplexed in the one optical waveguide. Is to be made to
Specifically, one optical waveguide and a plurality of optical waveguides arranged along the waveguide direction of the optical waveguide, each of which is configured to make laser light incident on the waveguide portion of the optical waveguide from the side in the waveguide direction. And a laser light source.

The above optical waveguide may be, for example, a multi-mode optical waveguide. In this case, the laser light emitted from each of the plurality of laser light sources may be different from each other in a different waveguide mode in the optical waveguide. Combined. To do so, the angle of incidence of the laser light emitted from each laser light source on the optical waveguide may be made to coincide with the propagation angle of each waveguide mode.

In such a case, the difference between the incident angles of the laser beams respectively emitted from the two laser light sources that make the laser light incident on the optical waveguide at mutually adjacent incident angles among the plurality of laser light sources is as follows: It is desirable that the angle is set to be larger than the spread angle of the laser light.

The optical waveguide may be a vertical / horizontal single mode optical waveguide. In this case, it is desirable to use a vertical / horizontal single mode light source as a plurality of laser light sources. In that case, it is desirable that an optical isolator that cuts light returning from the optical waveguide to the laser light source be provided between each of the plurality of laser light sources and the optical waveguide.

Further, in the laser light coupling module of the present invention, when an optical waveguide having a clad outside the waveguide is applied, an opening for passing the laser light emitted from the laser light source is formed in the clad. Is preferably formed.

The waveguide portion of the optical waveguide is made of SiO ₂
Alternatively, it is desirable that Al ₂ O ₃ be the main material.

On the other hand, of the laser light sources applied to the laser light coupling module of the present invention, typical semiconductor laser devices include InGaN-based (oscillation wavelength: 360 to 500 nm) and ZnSSe-based (oscillation wavelength:
410-540 nm), InGaAlP-based (oscillation wavelength:
600-730 nm), AlGaAs-based (oscillation wavelength: 7
50-870 nm), InGaAsP-based (oscillation wavelength: 7
00 to 1200 nm, 1300 to 1900 nm), In
GaAs system (oscillation wavelength: 950 to 1200 nm, 130
0-1900 nm), InGaSb-based (oscillation wavelength: 1.
(8 to 3.0 μm) having a semiconductor laser structure using each material.

The laser light source in the laser light coupling module of the present invention is not limited to the semiconductor laser device described above, but may be a solid-state laser light source or an SHG (second laser light source) which is a combination of a solid-state laser light source and a light wavelength conversion element. A laser or the like can be applied. As a typical solid state laser light source, it may be mentioned solid laser lamp or the semiconductor laser pumping using a solid-state laser medium such as YAG crystal or YVO _4.

[0019]

The laser light coupling module according to the present invention has the following features.
Since laser light is successively incident on the waveguide from a plurality of laser light sources arranged along the waveguide direction of one optical waveguide, and the laser light is multiplexed in the optical waveguide, multiplexing of the laser light is performed. Therefore, as compared with a conventional laser light coupling module using an optical waveguide or an optical fiber having a special structure, or a special bulk optical system, the overall structure can be relatively simple.

Further, in the laser light coupling module of the present invention, as described above, since the laser light sources are arranged along the waveguide direction of the optical waveguide, it is easy to arrange a large number of laser light sources. Therefore, it is possible to obtain a laser beam having a sufficiently high power density.

In the laser light coupling module of the present invention, in particular, a multi-mode optical waveguide is used as the optical waveguide, and the laser light emitted from each of the plurality of laser light sources is coupled to a different waveguide mode in the optical waveguide. In the case where the laser beams are coupled to each other, it is possible to suppress a loss due to interference between laser beams emitted from each of the plurality of laser light sources, which is advantageous in realizing a high power density.

In the laser light coupling module of the present invention, a vertical / horizontal single mode optical waveguide is used as an optical waveguide, and the vertical / horizontal single mode optical waveguide is connected to each vertical / horizontal mode optical waveguide.
Even in the case where an optical isolator that cuts light returning from the optical waveguide to the laser light source is disposed between the horizontal single mode laser light source and the laser light emitted from each of the plurality of laser light sources, interference occurs. Loss can be suppressed, which is advantageous in realizing high power density.

[0023]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 shows a laser light coupling module according to a first embodiment of the present invention. As shown, the laser light coupling module includes one multi-mode optical waveguide 10 and the multi-mode optical waveguide 10.
For example, four multi-mode semiconductor lasers 21, 22, 23, and 24 are provided along the waveguide direction, that is, along the horizontal direction in the drawing, and correspond to each of the multi-mode semiconductor lasers 21, 22, 23, and 24. Four incident optical systems 30, 40, provided
It consists of 50 and 60.

The multimode optical waveguide 10 has a waveguide portion 11 formed by cutting and polishing a sapphire (Al ₂ O ₃ ) having a refractive index n = 1.67, which is a dielectric, into a channel having a cross section of 50 μm × 50 μm. And a cladding layer 12 made of SiO ₂ having a refractive index of n = 1.48 formed so as to cover the four side surfaces of the waveguide 11. In FIG. 1, the waveguide direction in the multimode optical waveguide 10 is defined as a Z direction, and two directions parallel to the side surfaces of the waveguide 11 and orthogonal to the Z direction are defined as an X direction and a Y direction, respectively.

The clad layer 12 is provided with an opening at a portion to be a light incident portion, and each of the openings is provided with a band-pass filter 32 constituting a part of the incident optical systems 30, 40, 50 and 60. , 42, 52 and 62 are formed. These bandpass filters 32, 42, 52 and 62 will be described later in detail.

The one end face of the waveguide 11 has a reflectivity of 9
A high reflection coat 13 having a reflectance of 5% or more is formed, and a low reflection coat 14 having a reflectance of 1% or less is formed on the other end surface serving as a light emitting surface.

The incident optical system 30 provided corresponding to the multi-mode semiconductor laser 21 has a collimating lens 31 for parallelizing the diverging laser light L1 emitted from the multi-mode semiconductor laser 21 and the collimating lens 31 described above. Band-pass filter 32 formed in the opening of clad layer 12
And a condenser lens 33 for condensing the laser light L1 reflected on the upper side surface of the waveguide section 11, and a mirror 34 for reflecting the condensed laser light L1.

An incident optical system 40 provided corresponding to the multimode semiconductor laser 22 is a collimating lens similar to the collimating lens 31, band-pass filter 32, condenser lens 33 and mirror 34 in the incident optical system 30.
41, bandpass filter 42, condenser lens 43 and mirror
Consists of 44.

An incident optical system 50 provided corresponding to the multi-mode semiconductor laser 23 has a collimating lens similar to the collimating lens 31, band-pass filter 32, condenser lens 33 and mirror 34 in the incident optical system 30. 51, a band-pass filter 52, a condenser lens 53 and a mirror 54.

Further, the incident optical system 60 provided corresponding to the multimode semiconductor laser 24 is also provided with the incident optical system 30.
, A collimating lens 31, a bandpass filter 32,
It is composed of a collimator lens 61, a band-pass filter 62, a condenser lens 63, and a mirror 64 similar to the condenser lens 33 and the mirror 34, respectively.

As an example of the multi-mode semiconductor laser 21, the size of the light emitting portion is 0.8 to 2 μm × 50 μm.
A laser having an oscillation wavelength of 809 ± 2 nm and an output of 1 W is used. The divergence angle of the laser light L1 emitted from the multimode semiconductor laser 21 after being made parallel by the collimator lens 31 is 25 mrad (milliradian) in full width at half maximum in both the thickness direction of the active layer and the direction perpendicular thereto. ), That is, 1.5 ° (± 0.75 °) or less. Other multimode semiconductor lasers 22, 23
And 24 are similar.

Hereinafter, in the plane shown in FIG.
Consider the propagation mode in the plane. FIG. 2 shows the relationship between the propagation mode order and the propagation angle in the multimode optical waveguide 10. Multimode optical waveguide 10
N-th mode in the propagation angle of the guided light as _{θ N, sinθ N = λ (} N + 1) / nd [However lambda is the wavelength of the laser beam L1, n is the refractive index of the waveguide 11, d is the waveguide Part 11
Thickness).

Here, as described above, the incident angle of the laser beam L1 has a full width at half maximum of θ _N ± 0.75 ° (that is, the spread is 1.5 °), but the actual spread angle is 2 °. ° Expands to near. The propagation angle difference between adjacent modes in the multimode optical waveguide 10 is 0.55 to
Since it is 0.75 °, it is considered that four modes exist between 2.2 ° (= 0.55 ° × 4) even at the lowest 0.55 °. That is, the angle of incidence (θ _N ± 0.
At 75 °), the laser light L1 incident on the multimode optical waveguide 10 can be coupled to at most N-1, N, N + 1, N + 2th four modes.

In the multimode optical waveguide 10 of the present embodiment,
There are 46 propagation modes allowed in the ZX plane. As is well known, this is determined by the total reflection condition defined by the refractive indexes of the waveguide 11 and the cladding layer 12, and the above-mentioned propagation angle condition. However, since it is necessary to avoid coupling a plurality of modes of one semiconductor laser in the multimode optical waveguide 10, the maximum number of available modes is 11 (∵46 / 4 = 11.5). .

[0035] In view of the above, the multi-mode semiconductor laser 21 laser beam L1 emitted from, by setting the incident angle theta to that multimode optical waveguide 10 in theta _N,
The laser light L1 is coupled with only the N-th mode. The laser beam L1 reflected on the upper side surface of the waveguide 11
Also reflected by the mirror 34 enters the multi-mode optical waveguide 10 at the same angle of incidence theta _N.

The laser beams L2, L3, and L4 emitted from the other multimode semiconductor lasers 22, 23, and 24, respectively, are similarly coupled to only one waveguide mode. That is, for the laser beam L2, the incident angle θ is θ
Is set to _{N + 5} is coupled only N + 5 th mode, the laser beam L3 is bound only set to N + 10-th mode the incident angle theta in theta _{N + 10,} the incident angle theta for the laser beam L4 in theta _{N + 15} Set N
Combine only with the + 15th mode.

[0037] In order to do so, a bandpass filter 32 that transmits laser light L1 under the optical path length determined from the incident angle theta _N in the thickness and refractive index, as well as the laser beam L1, good laser beam L1 It has the property of transmitting light. As an example, the band-pass filter 32 having such characteristics includes SiO ₂ (refractive index = 1.48), TiO 2
₂ (refractive index = 2.4) quarter-wave films are L,
When H is written, from the waveguide 11 side to the air side (H
L) ² HH (HL) ² L (HL) ² HH (HL) ²
It can be formed by a layer structure arranged side by side. Note that (HL) ² means that the layer arranged with HL is repeated twice.

Similarly, the band-pass filter 42 for transmitting the laser beam L2 has a characteristic of transmitting the laser beam L2 well under an optical path length determined by its thickness and refractive index and the incident angle θ _{N + 5} of the laser beam L2. The band-pass filter 52 that transmits the laser light L3 has a thickness and a refractive index, and an incident angle θ _{N +} of the laser light L3.
_The band-pass filter 62 has a characteristic of transmitting the laser beam L3 well under an optical path length determined from _10, and the band-pass filter 62 transmitting the laser beam L4 is determined by its thickness and refractive index and the incident angle θ _{N + 15 of the} laser beam L4. The laser light L4 has a characteristic of being transmitted well under the optical path length.

According to the above configuration, four laser beams L
1, L2, L3, and L4 are coaxially multiplexed in the multimode optical waveguide 10, and one multiplexed laser beam L having a higher power density is supplied from the end face of the optical waveguide on which the low reflection coat 14 is formed. It can be emitted.

As described above, in the multimode optical waveguide 10 of the present embodiment, up to 11 propagation modes and external light can be coupled in the ZX plane. In the multi-mode optical waveguide 10, the waveguide 11 has the same size in the X and Y directions, so that a maximum of 11 propagation modes and external light can be coupled in the ZY plane. Therefore, as a whole, 11 × 11 = 121 propagation modes and external light can be coupled.

Specifically, assuming that the output of one multi-mode semiconductor laser is 1 W, 50 μm ×
A combined laser beam L having an output of 121 W is obtained from the waveguide section 11 having a cross-sectional shape of 50 μm. At this time, the power density of the combined beam reaches 4.84 MW / cm ² .

The number of propagation modes allowed in the multi-mode optical waveguide 10 is further increased by selectively using a material having a larger refractive index difference between the material of the waveguide portion 11 and the material of the cladding layer 12. Can be increased. For example, if the cladding layer is air, the number of propagation modes allowed in the ZX plane is 82. Therefore, a total of 441 (＝ 82/4 = 21, 21 × 21 = 441) propagation modes can be coupled with external light. At this time, if the output of one semiconductor laser is 1 W,
The power density of the combined laser light reaches 17.6 MW / cm ² .

Further, by combining the laser light coupling module according to the present invention with a conventional technique such as polarization multiplexing, 1 GW / cm ² which is the optical damage level of the optical waveguide.
It is also possible to obtain a multiplexed laser beam having a power density of the order.

Next, a second embodiment of the present invention will be described with reference to FIG. As shown in the figure, this laser light coupling module is disposed along one vertical / horizontal single mode optical waveguide 70 and along the waveguide direction of this vertical / horizontal single mode optical waveguide 70, that is, along the horizontal direction in the drawing. As an example, three vertical and horizontal single mode semiconductor lasers 81 and 82 and
83, and three incident optical systems 91, 92, and 93 provided corresponding to the vertical and horizontal single mode semiconductor lasers 81, 82, and 83, respectively.

The vertical / horizontal single mode optical waveguide 70 is
Sapphire having a refractive index n = 1.67 (Al ₂
O ₃ ) is cut and polished into a channel having a cross-sectional shape of 2 μm × 2 μm and has a waveguide portion 71 and a refractive index n = 1.48 formed to cover four side surfaces of the waveguide portion 71. SiO
₂ and a cladding layer 72 made of _two .

The cladding layer 72 is provided with an opening at a portion serving as a light incident portion, and the opening is provided with a band-pass filter 90 constituting a part of each of the incident optical systems 91, 92 and 93. Is formed.

The one end face of the waveguide section 71 has a reflectance of 9%.
A high reflection coat 13 having a reflectance of 5% or more is formed, and a low reflection coat 14 having a reflectance of 1% or less is formed on the other end surface serving as a light emitting surface.

An incident optical system 91 provided corresponding to the vertical / horizontal single mode semiconductor laser 81 is a collimator for collimating the divergent laser light L11 emitted from the vertical / horizontal single mode semiconductor laser 81. A lens 94, a band-pass filter 90 formed at the opening of the cladding layer 72, and a laser beam L 11 reflected by the upper surface of the waveguide 71.
Lens 95 for condensing light, and the condensed laser light L
An optical isolator interposed between a mirror 96 for reflecting light 11 and a collimator lens 94 and a bandpass filter 90
97.

The incident optical system 92 provided corresponding to the vertical / horizontal single mode semiconductor laser 82 and the incident optical system 93 provided corresponding to the vertical / horizontal single mode semiconductor laser 83 also have the above-mentioned incident optical system 91. The configuration is the same as described above.

The vertical / horizontal single mode semiconductor laser 81 is
The laser light L11 emitted therefrom is arranged in a direction to be coupled with the zero-order mode in the vertical / horizontal single mode optical waveguide 70. That is, in this example, the propagation angle θ ₀ of the 0-order mode guided light is 14.01 °, and the laser beam L11 is incident on the vertical / horizontal single mode optical waveguide 70 at an incident angle equal to this angle θ _0. Has been.

Another vertical / horizontal single mode semiconductor laser 82
Similarly, each of the laser beams L emitted from them
12 and L13 are incident on the vertical / horizontal single-mode optical waveguide 70 at an incident angle θ ₀ = 14.01 °, and are arranged in such a direction as to couple with the zero-order mode.

In the configuration of this embodiment, a plurality of vertical
Since each of the lateral single mode semiconductor lasers 81, 82 and 83 is coupled to only one mode in the vertical and horizontal single mode optical waveguide 70, the combined laser light having an output exceeding the maximum allowable internal power of each of the semiconductor lasers 81, 82 and 83 is used. May return to each of the semiconductor lasers 81, 82 and 83. In such a case, the vertical / horizontal single mode semiconductor lasers 81, 82 and 83 may be destroyed. To prevent this destruction, if the output of each semiconductor laser 81, 82 and 83 exceeds the maximum allowable internal power. The wave laser light L cannot be expected.

In order to avoid this inconvenience, in this embodiment, the above-mentioned optical isolator 97 is provided to prevent the light from returning from the optical waveguide 70 side to each of the vertical and horizontal single mode semiconductor lasers 81, 82 and 83. Preventing. Thus, also in the present embodiment, a plurality of laser beams L11, L12 and L13 are coaxially multiplexed in the vertical / horizontal single mode optical waveguide 70, and from the optical waveguide end face where the low reflection coat 14 is formed,
One combined laser beam L having a high power density can be emitted.

Specifically, for example, when a vertical / horizontal single mode semiconductor laser having an oscillation wavelength of 809 nm and an output of 50 mW is used, and this semiconductor laser is coupled to 20 elements in the same configuration as above, the vertical / horizontal single mode optical waveguide is used. The combined laser light L of 1 W can be emitted from the wave path 70. In this case, the power density of the combined laser light L is 6.25.
Reaches MW / cm ² .

In the laser light coupling module of the present invention, the number of laser light sources to be coupled is not limited to the number described above. Further, the laser light source is not limited to the semiconductor laser used in the above embodiment, but may be the solid-state laser or the SHG laser described above.

Further, the multi-mode optical waveguide and the single-mode optical waveguide used for the multiplexing are not limited to those used in the above-mentioned embodiments, but may be appropriately selected from known ones.

[Brief description of the drawings]

FIG. 1 is a schematic side view showing a laser light coupling module according to a first embodiment of the present invention.

FIG. 2 is a graph showing a relationship between a mode order and a propagation angle of guided light in a multi-mode optical waveguide used in the laser light coupling module of FIG.

FIG. 3 is a schematic side view showing a laser light coupling module according to a second embodiment of the present invention.

[Explanation of symbols]

10 Multimode optical waveguide 11 Waveguide section 12 Cladding layer 13 High reflection coat 14 Low reflection coat 21, 22, 23, 24 Multimode semiconductor laser 30, 40, 50, 60 Incident optical system 31, 41, 51, 61 Collimating lens 32, 42, 52, 62 Bandpass filter 33, 43, 53, 63 Condenser lens 34, 44, 54, 64 Mirror 70 Vertical / horizontal single-mode optical waveguide 71 Waveguide section 72 Cladding layer 81, 82, 83 Vertical / Lateral single mode semiconductor laser 90 Band pass filter 91, 92, 93 Incident optical system 94 Collimating lens 95 Condensing lens 96 Mirror 97 Optical isolator L1, L2, L3, L4, L11, L12, L13 Laser beam before combining L Waved laser light

Claims (7)

[Claims] 1. A plurality of optical waveguides, each of which is arranged along a waveguide direction of the optical waveguide, and in which a laser beam is incident on a waveguide portion of the optical waveguide from a side in the waveguide direction. A laser light coupling module comprising a laser light source. 2. The optical waveguide according to claim 1, wherein the optical waveguide is a multi-mode optical waveguide, and laser light emitted from each of the plurality of laser light sources is coupled to a different waveguide mode in the optical waveguide. The laser light coupling module according to claim 1. 3. A difference between incident angles of laser beams respectively emitted from two laser light sources that cause the laser light to enter the optical waveguide at mutually adjacent incident angles among the plurality of laser light sources. 3. The laser light coupling module according to claim 2, wherein the divergence angle is larger than the divergence angle. 4. The laser light coupling module according to claim 1, wherein the optical waveguide is a vertical / horizontal single mode optical waveguide, and the plurality of laser light sources are vertical / horizontal single mode light sources, respectively. 5. An optical isolator for cutting light returning from each of said plurality of laser light sources to said laser light source is provided between said plurality of laser light sources and said optical waveguide. Laser light coupling module. 6. The optical waveguide according to claim 1, wherein the optical waveguide includes a cladding outside the waveguide, and the cladding is formed with an opening through which the laser light emitted from the laser light source passes. The laser light coupling module according to any one of claims 1 to 5, wherein 7. The laser light coupling module according to claim 1, wherein the waveguide of the optical waveguide is made of SiO ₂ or Al ₂ O ₃ as a main material.