JP2007300015A - Optical unit - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an optical unit capable of highly efficiently making a beam shape isotropic. <P>SOLUTION: A semiconductor laser device 10, a longitudinal direction collimation lens 20, a transverse direction collimation lens 30, a feedback element 40, and an optical fiber 60 are arranged in the optical axis direction in this order. The feedback element 40 is equipped with an external resonator 41 provided at a part of each region at which a light can arrive from a light emitting spot 17 of the semiconductor laser device 10. Consequently, a divergence angle θs in the transverse direction of the light output from the light emitting spot 17 becomes small as compared with a divergence angle θo in the transverse direction, at the time of providing some external resonator 41 or other in all regions at which the light output from the light emitting spot 17 can arrive. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to an optical device that is suitably used for applications requiring high output.

  Currently, high-power semiconductor laser elements of about several tens of watts have been put into practical use as light sources for exciting solid-state lasers and for processing and welding materials with relatively low melting points, such as plastics. It is used. Recently, a bar laser (Bar Laser) in which this high-power semiconductor laser device is arranged in one dimension and a stack laser (Stack Laser) in which the bar laser is multi-staged in the direction perpendicular to the device arrangement direction have appeared. In this way, by increasing the number of light emitting spots, a high output of about several kW is realized.

  A high-power semiconductor laser element generally has a broad area type chip structure. As a broad area type semiconductor laser element, for example, as shown in FIG. 7, a semiconductor multilayer structure 111 composed of an n-type semiconductor layer, an active layer, and a p-type semiconductor layer having a plurality of ridges on the surface of a substrate 110. And a p-side electrode 112, and an n-side electrode 113 on the back surface of the substrate 110. In the semiconductor laser device having such a configuration, the single light emission spot 114 formed on the end face corresponding to each ridge is not usually isotropic, but is perpendicular to the semiconductor stacking direction (lateral It has a flat shape extending in the direction). Here, when viewed macroscopically, the plurality of light-emitting spots 114 are equivalent to one light-emitting spot (pseudo-light-emitting spot 115) having a very wide lateral width. It can be said that it has a beam shape with a light emission width Ws and a divergence angle θs in the direction.

  When the light output from such a flat light emission spot 115 is image-converted using a normal optical system, an image having an aspect ratio equal to the aspect ratio of the light emission spot 115 is formed. That is, when a normal optical system is used, the beam shape after conversion depends on the shape of the light emission spot 115 and is not isotropic. Therefore, various measures for making the beam shape obtained by converting the light output from the flat light emission spot 115 isotropic have been proposed.

  For example, in Patent Document 1, the light of the semiconductor laser element is reflected twice using a step-like mirror having a reflective surface oblique to the optical axis, thereby rotating the flat direction of the image by 90 °. A technique for making the beam shape isotropic is disclosed.

JP-A-8-271832

  However, when two reflections are used in this way, a light loss due to reflection always occurs, so that the beam shape cannot be made isotropic with high efficiency.

  The present invention has been made in view of such problems, and an object of the present invention is to provide an optical apparatus capable of making a beam shape isotropic with high efficiency.

  The optical device of the present invention includes a semiconductor laser element and one or more external resonators. The semiconductor laser element has one or a plurality of light emission spots on at least one end face side. The external resonator is provided in a part of each region where the light output from each light emitting spot can reach.

  In the optical device according to the present invention, an external resonator is provided in a part of each region where the light output from each light emitting spot can reach. Therefore, a current is injected into the semiconductor laser element so that light is emitted from each light emitting spot. When output, a part of the light incident on the portion where the external resonator is provided is fed back to each light emitting spot and amplified. As a result, the light output from each light emitting spot is output only to the portion where the external resonator is provided without causing optical loss.

  According to the optical device of the present invention, since the external resonator is provided in a part of each region where the light output from each light emission spot can reach, the light output from each light emission spot is light loss. Without being generated, the signal is output only to the portion where the external resonator is provided. At this time, the divergence angle of the light output from each light emission spot is smaller than that when the external resonator is provided in all regions where the light output from each light emission spot can reach. Thereby, even when the light emission spot of the semiconductor laser element has a flat shape, the beam shape can be made isotropic with high efficiency.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.

  FIG. 1 illustrates a cross-sectional configuration of a light emitting device according to an embodiment of the present invention. This light emitting device is configured by arranging a semiconductor laser element 10, a longitudinal collimating lens 20, a lateral collimating lens 30, a feedback element 40, a condenser lens 50, and an optical fiber 60 in this order in the optical axis direction. FIG. 2 is a perspective view of the semiconductor laser device 10 of FIG. The semiconductor laser device 10 in FIG. 1 represents a cross-sectional configuration of the semiconductor laser device 10 in FIG. FIG. 1 and FIG. 2 are schematic representations, and are different from actual dimensions and shapes.

  This light emitting device has a beam shape of light output from an array type semiconductor laser device 10 in which light emitting spots 16 (described later) on an end face are arranged in a row in a direction (lateral direction) perpendicular to a semiconductor stacking direction. The light is corrected by the vertical collimating lens 20, the horizontal collimating lens 30 and the feedback element 40, and the corrected light is coupled to the optical fiber 60 by the condenser lens 50.

  The semiconductor laser element 10 is obtained by growing a semiconductor multilayer structure 12 on one surface side of a substrate 11, and the semiconductor multilayer structure 12 includes, in order from the substrate 11 side, a first conductivity type semiconductor layer (not shown), an active layer. Layer 13 and a second conductivity type semiconductor layer (not shown) are included. A plurality of ridges 14 are formed at predetermined intervals from each other on the second conductive type semiconductor layer. The width of the bottom of the ridge 14 is typically several tens of μm to 500 μm, and the semiconductor multilayer structure 12 has a broad area type chip structure.

  Further, by driving the semiconductor laser element 10, a light emitting region 15 is formed in a portion corresponding to the bottom of each ridge 14 in the active layer 13, and in each light emitting region 14 on one end face of the semiconductor laser element 10. A light emission spot 16 is formed in the corresponding part. That is, the light emitting spots 16 are arranged in a row in the lateral direction at a predetermined interval on the end face. Further, each light emitting spot 16 does not have an isotropic shape because the semiconductor laminated structure 12 has a broad area type chip structure as described above, and has a flat shape extending in the lateral direction. It becomes. Further, when viewed macroscopically, the plurality of light emission spots 16 having such a flat shape are equivalent to one light emission spot (pseudo light emission spot 17) having an extremely wide lateral width, and therefore, the semiconductor laser element 10 It can be said that the light output from has a beam shape with a light emission width Ws and a divergence angle θs in the lateral direction.

  The semiconductor laser device 10 also has a p-side electrode 18 from the surface of each ridge 14 to the surface of the peripheral portion thereof, and the n-side is formed on the portion of the back surface of the substrate 11 facing the p-side electrode 15. An electrode 19 is provided.

  The longitudinal collimating lens 20 is, for example, a lens having a convex shape in a direction (longitudinal direction) parallel to the stacking direction of the semiconductor, and suppresses the divergence of the longitudinal beam to convert the longitudinal component of the beam into parallel light. It is like that. On the other hand, the lateral collimating lens 30 is, for example, a lens having a convex shape in the lateral direction, and suppresses the divergence of the beam in the lateral direction and converts the lateral component of the beam into parallel light. Therefore, by combining the vertical collimating lens 20 and the horizontal collimating lens 30, the light of the semiconductor laser element 10 is converted into parallel light.

  The feedback element 40 has an external resonator 41 corresponding to each light emitting spot 16. When each external resonator 41 is provided with any external resonator in all regions where the light output from each light-emitting spot 16 can reach, the light output from each light-emitting spot 16 is converted into the longitudinal collimating lens 20 and It is provided in a part of the individual area that can be reached via the lateral collimating lens 30. Note that the meaning of the “part” will be described in the operation of the light emitting device.

The external resonator 41 is composed of, for example, an optical element having a grating structure whose refractive index changes periodically in the optical axis direction. An example of such an optical element is VBG (Volume Brrag Grating). The VBG is configured by alternately arranging layers having thicknesses of λ / 4 (λ: oscillation wavelength) made of materials having different refractive indexes. It is formed by irradiating ultraviolet light or the like at intervals of λ / 4. Here, examples of the material whose refractive index changes by light irradiation include SiO ₂ , Al ₂ O _{3, and} Na ₂ O containing Ag, Ce, and the like. In addition, as a method of irradiating the material with ultraviolet light or the like at equal intervals, for example, two laser beams are irradiated and the intensity of the light is periodically generated by interference of the laser beams, or a mask having a diffraction grating is irradiated with a laser. Examples of the method include irradiating light and periodically creating intensity of light by a diffraction effect, or simply irradiating laser light with a spot.

  The condensing lens 50 is composed of, for example, one spherical lens or a plurality of cylindrical lenses, and the focal length of the condensing lens 50 is imaged on a core portion 61 (described later) of the optical fiber 60. Has been chosen.

  The optical fiber 60 has a core portion 61 at the center portion and a clad portion 62 at the outer peripheral portion of the core portion 61. The core portion 61 has a role as a core wire for propagating the laser light image-converted by the longitudinal collimating lens 20, the lateral collimating lens 30, the feedback element 40 and the condenser lens 50. The clad 62 has a role as an outer skin for confining the laser light propagating in the core 61 in the core 61.

  Next, functions and effects of the light emitting device having such a configuration will be described. In FIG. 1, only the light output from the central portion of each light emitting spot 16 is extracted from the light output from each light emitting spot 16, and the light is extracted from the vertical collimating lens 20 and the horizontal collimating lens 30. FIG. 6 schematically shows a state in which the feedback element 40 and the condenser lens 50 are directed. The broken line in FIG. 1 represents the light beam at the initial stage of injecting current into the semiconductor laser element 10, and the alternate long and short dash line in FIG. It represents the luminous flux at.

  When a current is injected into the semiconductor laser element 10, the current is confined by each ridge 14, and then a current is injected into the light emitting region 15 of the active layer 13, thereby causing light emission due to recombination of electrons and holes. Of this light, the light output from each light emitting spot 16 to the external resonator 41 side enters a wider area than the portion where each external resonator 41 is provided (see the broken line in FIG. 1). Of these, only the light incident on the portion where each external resonator 41 is provided is fed back to each light emitting spot 16. In addition, of the light generated in the light emitting region 15, the light directed to the side opposite to the external resonator 41 is reflected by the rear end face of the semiconductor laser element 10. In this way, laser oscillation is generated by repeating reflection by the pair of reflecting mirrors including the rear end face of the semiconductor laser element 10 and the external resonator 41. At this time, each light emitting spot 16 is connected to the external resonator 41 side. The light output to is gradually converged on the portion where each external resonator 41 is provided, and the converged light passes through the condenser lens 50 and is coupled to the optical fiber 60 (see the one-dot chain line in FIG. 1). .

  That is, “the external resonator 41 is provided in a part” means that the light output from each light emitting spot 16 to the external resonator 41 side in the initial stage of injecting a current into the semiconductor laser element 10. Is synonymous with the fact that the entrance window 41A of each external resonator 41 is provided in a part of the region where the light enters the feedback element 40.

  Accordingly, in the present embodiment, the light output from each light emitting spot 16 is output from each external resonator 41 as shown by the one-dot chain line in FIG. 1 without causing optical loss in the feedback element 40. be able to.

  Next, when each light emitting spot 16 is macroscopically regarded as one pseudo light emitting spot 17, the beam quality of light output from the pseudo light emitting spot 17 and the light output from the pseudo light emitting spot 17 are converted into a longitudinal collimating lens. 20, the beam quality after image conversion by the lateral collimating lens 30, the external resonator 41 and the condenser lens 50 will be described.

The beam shape of light output from a semiconductor laser element is generally evaluated using an index of beam quality represented by the product of the light emission width and divergence angle of a single light emission spot. In the broad area type semiconductor laser device, since the light emission spot is flat in the horizontal direction, as shown in the following formula, the light emission width and the divergence angle of the light emission spot are set in the horizontal and vertical directions. It is common to think separately.
Ws × θs = (λ / π) × Ms ² (1)
Wf × θf = (λ / π) × Mf ² (2)
λ: oscillation wavelength Ws: horizontal emission width, θs: horizontal divergence angle Wf: vertical emission width, θf: vertical divergence angle

Ms ² and Mf ² (M square) on the right side of the equations (1) and (2) are used as an index of the beam quality. When evaluating the overall beam quality of the semiconductor laser element, the product (M ² ) of Ms ² and Mf ² is used as shown in the following equation.
M ² = Ms ² × Mf ² (3)

Here, it can be said that the smaller the M ² , the easier it is to focus on a minute spot, so that the beam quality is good. When the value is 1, it can be said that the beam quality is the best. On the other hand, it can be said that the higher the M ² , the worse the beam quality because it is difficult to focus on a minute spot. Also, when only one of Ms ² and Mf ² is small and the other is extremely large, it can be said that the beam quality is poor because it is difficult to focus on an isotropically small spot. M square is a storage amount in image conversion by a normal optical lens or the like, and may increase due to lens aberration or the like, but cannot be reduced.

By the way, since the semiconductor laser element 10 is designed so that the vertical Mf ² is 1 like a general semiconductor laser element, the beam quality in the vertical direction is very good. However, Ms ² in the horizontal direction is significantly worse than Mf ^{2 in} the vertical direction, as in the case of a general semiconductor laser element, since the pseudo light-emitting spot 17 has a flat shape in the horizontal direction. Therefore, as described above, it is difficult to condense the light from the semiconductor laser element 10 into a minute spot even if the image is converted using a normal optical system.

Therefore, conventionally, as disclosed in Patent Document 1, the light of the semiconductor laser element is reflected twice by using a step-like mirror having a reflecting surface oblique to the optical axis, whereby the image It is conceivable to rotate the flat direction by 90 ° to make the Ms ² in the horizontal direction and the Mf ^{2 in} the vertical direction isotropic. However, if isotropic in this way, the vertical Mf ² , which was originally good in beam quality, in particular, the vertical divergence angle θf is deteriorated. For example, as shown in FIG. When the semiconductor laser elements 10 are stacked in the vertical direction, the Mf ^{2 in} the vertical direction of the macroscopic pseudo-light-emitting spot 27 is extremely deteriorated, and the number stacked in the vertical direction is not increased unless the core diameter of the optical fiber is increased. Will be greatly limited. Further, M ² after using the step-like mirror is surely worse than M ² when it is not used, so that it is difficult to focus on a minute spot. For this reason, even if the number of stacks in the vertical direction is increased, the brightness does not increase as expected, and it is not suitable for applications requiring extremely high output.

On the other hand, in the present embodiment, each external resonator 41 is provided in a part of each region where the light output from each light emitting spot 16 can reach, and the light output from each light emitting spot 16 is transmitted to each external resonator. Since the light is output only to the portion provided with 41, the divergence angle θs in the lateral direction of the light output from the pseudo light emission spot 17 is all the light that the light output from the pseudo light emission spot 17 can reach. This is smaller than the divergence angle θo in the lateral direction when some external resonator is provided in the region (see FIG. 1). That is, without changing the values of the light emission width Ws, the light emission width Wf in the vertical direction, and the divergence angle θf in the vertical direction, the divergence angle θs independently of these values. And M ² can be set to 1.

Thereby, even if the pseudo light emission spot 17 of the semiconductor laser element 10 has a flat shape, Ms ² in the horizontal direction and Mf ^{2 in} the vertical direction can be reduced while reducing M ² (beam quality). Can be made isotropic. Therefore, in this embodiment, the beam shape can be made isotropic with high efficiency, and further, it can be focused on a minute spot. As a result, the diameter of the core portion 61 of the optical fiber 60 can be made smaller than the conventional diameter.

As shown in FIG. 3, when the bar-shaped semiconductor laser elements 10 are stacked in the vertical direction, the vertical divergence angle θf of the macroscopic pseudo-light-emitting spot 27 is determined by the bar-shaped semiconductor laser element 10. Since it is exactly the same as that in one case, Mf ^{2 in} the vertical direction of the light emission spot 27 is only slightly increased according to the number of stacks in the vertical direction, and can be condensed into a minute spot. Thereby, when the diameter of the core part 61 is made equal to the conventional diameter, the number of bar-shaped semiconductor laser elements 10 that can be stacked in the vertical direction can be greatly increased as compared with the conventional one. Further, since the light can be focused on a minute spot, the luminance can be increased in accordance with the number of stacks in the vertical direction, which is suitable for applications requiring extremely high output.

  While the present invention has been described with reference to the embodiment, the present invention is not limited to the above embodiment, and various modifications can be made.

  For example, in the above embodiment, the feedback element 40 is arranged on the optical path between the semiconductor laser element 10 and the optical fiber 60. However, as shown in FIG. You may make it arrange | position on the optical path of the side. However, in this case, contrary to the above embodiment, the reflectance of the end face on the back side of the semiconductor laser element 10 is lowered. Further, it is preferable to arrange the vertical collimating lens 20 and the horizontal collimating lens 30 on the optical path between the back surface side of the semiconductor laser element 1 and the feedback element 40.

In the above embodiment, a plurality of external resonators 41 are arranged at a predetermined interval inside the feedback element 40. For example, as shown in FIG. The feedback elements 70 may be formed by arranging the resonators 72 at a predetermined interval. In this case, the external resonator 72 can be constituted by a metal film made of, for example, Au or Al, or a dielectric multilayer film made of Ta ₂ O ₅ , TiO _2, or SiO ₂ . The structure can be simplified as compared with the feedback element 40.

  This feedback element 70 can be manufactured, for example, as shown in FIGS. First, after applying a photoresist R1 on the support portion 71, a lithography process is performed to form a mask R2 having an opening on a region where the external resonator 72 is to be formed. Subsequently, after the material 72A used for the external resonator 72 is formed over the entire surface, the external resonator 72 is formed on the support portion 71 by performing lift-off. In this way, the feedback element 70 can be manufactured.

It is a section lineblock diagram of an optical device concerning one embodiment of the present invention. FIG. 2 is a perspective view of the semiconductor laser device of FIG. 1. It is the top view seen from the end surface direction when the semiconductor laser element of FIG. 1 is stacked in the vertical direction. It is a section lineblock diagram of an optical device concerning one modification. It is a cross-sectional block diagram of the optical apparatus which concerns on another modification. FIG. 6 is a cross-sectional configuration diagram for explaining a manufacturing process of the feedback element of FIG. 5. It is a perspective view of the semiconductor laser element in the conventional optical apparatus.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 10 ... Semiconductor laser element, 11 ... Substrate, 12 ... Semiconductor laminated structure, 13 ... Active layer, 14 ... Ridge, 15 ... Light emitting region, 16 ... Light emitting spot, 17, 27 ... Pseudo light emitting spot, 18 ... P side electrode, 19 ... n-side electrode, 20 ... longitudinal collimating lens, 30 ... lateral collimating lens, 40, 70 ... feedback element, 41, 72 ... external resonator, 41A ... entrance window, 50 ... condensing lens, 60 ... optical fiber , 61 ... core part, 62 ... clad part, 71 ... support part, θo, θs ... divergence angle, Ws ... emission width.

Claims (9)

A semiconductor laser device having at least one light emitting spot on at least one end face side;
An optical device comprising: one or a plurality of external resonators provided in a part of an individual region where light output from each light emitting spot can reach. The optical device according to claim 1, wherein the external resonator is made of a metal film or a dielectric multilayer film. The optical device according to claim 1, wherein the external resonator has a grating structure whose refractive index changes periodically. The optical apparatus according to claim 1, wherein the external resonator is provided on an optical path on a side of emitting the light of the semiconductor laser element to the outside. The optical apparatus according to claim 1, wherein the external resonator is provided on an optical path opposite to a side that emits light of the semiconductor laser element to the outside. On the optical path between the semiconductor laser element and the external resonator, a vertical collimating element that collimates vertical light out of the light output from each light emitting spot, and output from each light emitting spot The optical device according to claim 1, further comprising: a horizontal collimating element that collimates the light in the horizontal direction among the light to be emitted. The semiconductor laser element has a plurality of light emission spots,
The optical device according to claim 1, wherein the plurality of light emission spots are arranged in parallel in a horizontal direction. The optical device according to claim 7, wherein the plurality of light emission spots are arranged in parallel in the vertical direction. The optical apparatus according to claim 1, further comprising an optical fiber at an end on an optical path on a side of emitting light of the semiconductor laser element to the outside.

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