JP2023064231A - Laser diode bar, wavelength beam combining system, and manufacturing method of wavelength beam combining system - Google Patents

Abstract

To provide a laser diode bar containing nitride semiconductor as a constituent material having multiple emitters capable of suppressing reliability degradation during long-term use.SOLUTION: A laser diode bar 10 contains a nitride semiconductor as a constituent material. Also, the laser diode bar 10 has n emitters 21 to 2n (where n is an integer equal to or greater than 4) spaced apart from each other in the X direction. Each of the n emitters 21 to 2n laser-oscillates when a current greater than or equal to the threshold current flows. The threshold current of at least one of the emitters 21 and 2n on both ends is less than the average value of the threshold currents of the remaining emitters 22 to 2n-1 excluding the emitters 21 and 2n on both ends.SELECTED DRAWING: Figure 4

Description

The present disclosure relates to laser diode bars, wavelength beam combining systems, and methods of fabricating wavelength beam combining systems.

In recent years, expectations for laser processing have increased for various materials such as copper, gold, and resin. For example, in the automobile industry, electrification, miniaturization, high rigidity, improvement in design flexibility, and productivity improvement are required, and expectations for laser processing are high. In particular, in the copper processing of motors and batteries for electric vehicles, a blue laser light source with high light absorption efficiency (wavelength 350 to 450 nm) is required. There is a need for a laser light source with a highly focused beam quality. A so-called gallium nitride (hereinafter abbreviated as GaN)-based semiconductor laser device containing a nitride semiconductor as a main semiconductor material is known as a suitable laser light source for meeting this requirement.

On the other hand, when a high-output laser beam is continuously emitted from a GaN-based semiconductor laser device, the output of the laser beam drops significantly after a predetermined time, that is, the reliability of the GaN-based semiconductor laser device decreases. Are known. This is because the siloxane contained in the atmosphere in the vicinity of the light emitting facet of the device has 350 Irradiation with a laser beam having a wavelength of ∼450 nm accelerates the photodecomposition of siloxane, and the decomposed Si adheres to the output end face where the light intensity is the highest, resulting in a decrease in reliability due to the optical tweezers phenomenon. The latter effect is a serious problem in laser processing, and the present invention also focuses on the latter.

Therefore, several techniques have been proposed for suppressing the adhesion of siloxane decomposition products to the light emitting facet. For example, Patent Literature 1 discloses a method of hermetically sealing a GaN-based semiconductor laser element in a CAN package, heating the CAN package to 101° C. or higher, and irradiating light with a wavelength of 420 nm or shorter. In this way, contaminants containing siloxane inside the CAN package are reliably vaporized and photodecomposed, thereby preventing siloxane decomposition products from adhering to the light output end face.

Further, Patent Document 2 discloses a configuration in which a GaN-based semiconductor laser element is adhered to a submount using an adhesive, and these are hermetically sealed inside a CAN package. In addition, the adhesive has a structure in which metal particles covered with a protective film having a decomposition temperature higher than the vaporization temperature of the organic matter float in the solvent made of the organic matter at room temperature. Prior to hermetic sealing, the CAN package is baked in vacuum or in dry air with a dew point below -20°C at a temperature above the decomposition temperature of the protective film. The CAN package is then hermetically sealed without breaking vacuum or while maintaining the dew point of dry air. By doing so, the atmosphere containing siloxane is suppressed from remaining inside the CAN package, and siloxane decomposition products are prevented from adhering to the light emitting end surface.

Japanese Patent No. 5095091 Japanese Patent No. 5722553

For laser processing, it is necessary to use a plurality of GaN-based semiconductor lasers in order to obtain high-output and high-quality laser light of several kW. There is a need to. In order to increase the output power of a semiconductor laser device, a device with a so-called laser array structure (hereafter referred to as a laser diode bar), in which multiple light sources (hereafter referred to as emitters) are arranged in one dimension on a single substrate. It is common to assume that However, if the optical output obtained from a single laser diode bar is to be on the order of 100 to several hundred W, the number of emitters will be on the order of several tens to hundreds, and the size of the laser diode bar will increase. It is difficult to hermetically seal such a large-sized semiconductor laser element in a general CAN package.

The present disclosure has been made in view of this point, and an object thereof is a laser diode bar containing a nitride semiconductor as a constituent material, which is capable of suppressing deterioration in reliability during long-term use. An object of the present invention is to provide a wavelength beam combining system and a method of manufacturing the wavelength beam combining system.

To achieve the above object, a laser diode bar according to the present disclosure is a laser diode bar containing a nitride semiconductor as a constituent material, wherein the laser diode bars are spaced apart from each other in a first direction. It has (n is an integer of 4 or more) emitters, and each of the n emitters oscillates when a current equal to or greater than a threshold current flows, and at least one of the emitters at both ends is equal to or less than the average value of the threshold currents of the remaining emitters excluding the emitters at both ends.

A wavelength beam combining system according to the present disclosure includes a single or a plurality of laser modules each having the laser diode bar, and an optical coupling element for combining laser light emitted from each of the plurality of emitters included in the laser diode bar. and an external resonant mirror for reflecting the laser light coupled by the optical coupling element toward the optical coupling element, and one or more of the laser modules, the optical coupling element, and the external resonant mirror. a casing, wherein the laser diode bar is provided with a reflective layer having a predetermined reflectance on the surface opposite to the emission end surface of the laser light in the n emitters, and the external resonance mirror and An external resonance structure is formed between the reflective layer of the emitter from which the laser light is emitted, and the coupled laser light coupled by the optical coupling element is emitted to the outside of the casing.

A method for manufacturing a wavelength beam combining system according to the present disclosure includes: a first step of preparing the laser diode bar; a second step of assembling a laser module having the laser diode bar; a third step of fixing and arranging the optical coupling element and the external resonance mirror while maintaining a predetermined arrangement relationship; after the three steps, a fourth step of sealing the casing; after the four steps, a fifth step of driving the laser module to continuously emit the laser light from at least one of the emitters at both ends included in the laser diode bar for a predetermined time; In assembling the laser module, an insulating adhesive material containing siloxane is used, and in the fifth step, the laser light is emitted from at least one of the emitters at both ends while the output of the laser light is being monitored. The racer module is driven so that the laser light is not emitted from the remaining emitters while the laser light is emitted, and the predetermined time is determined according to the degree of decrease in the output of the laser light. .

According to the present disclosure, adhesion of siloxane decomposition products to the light emitting end surface can be suppressed. As a result, deterioration in reliability of the laser diode bar during long-term use due to adhesion of siloxane can be suppressed.

1 is a schematic configuration diagram of a wavelength beam combining system according to an embodiment; FIG. FIG. 4 is a schematic diagram for explaining the operation of the wavelength beam combining system; 1 is an exploded perspective view of a laser module; FIG. 1 is a perspective view of a laser diode bar; FIG. FIG. 5 is a cross-sectional view taken along line VV of FIG. 4; FIG. 4 is a diagram showing temporal changes in laser light output of a laser module configured with a single emitter during continuous oscillation. FIG. 4 is a diagram showing changes in laser light output from each emitter before and after driving a laser module mounted with a laser diode bar having 38 emitters for a predetermined period of time; FIG. 10 is a schematic view of observation of deposits on the light emitting end surface of the emitter after the laser module has been driven for a predetermined period of time. FIG. 4 is a diagram showing the relationship between stripe width and threshold current; 4 is a flow chart for explaining a method of manufacturing a wavelength beam combining system; FIG. 11 is a diagram showing the state of laser light emitted from the laser module in step S5 shown in FIG. 10; FIG. 11 is a diagram showing temporal changes in monitor output in step S5 shown in FIG. 10; FIG. 11 is a diagram showing a preferred driving range of the laser diode bar in step S5 shown in FIG. 10; It is a schematic plan view showing a dummy emitter according to a modification.

Hereinafter, embodiments of the present disclosure will be described based on the drawings. It should be noted that the following description of preferred embodiments is merely illustrative in nature and is not intended to limit the present disclosure, its applications or uses.

(embodiment)
[Configuration of Wavelength Beam Combining System]
FIG. 1 shows a schematic configuration diagram of a wavelength beam combining system according to an embodiment, and FIG. 2 shows a schematic diagram for explaining the operation of the wavelength beam combining system. In addition, in FIG. 1, a portion of the casing 160 is omitted to illustrate the internal structure.

As shown in FIG. 1, the wavelength beam combining system 100 includes a plurality of laser modules 110, a plurality of optical shaping components 120, a plurality of diffraction grating elements 130, an external resonant mirror 140, a casing 160, and an optical power monitor 150. ing.

The laser module 110 includes a laser diode bar 10 (see FIGS. 2 and 3) and emits laser light in the blue wavelength range. In the specification of the present application, the “blue wavelength range” refers to a wavelength range of 350 nm or more and 450 nm or less. Also, the laser diode bar 10 is formed with eight emitters 21 to 28 (see FIG. 4), and laser light in the blue wavelength range is emitted from each of the emitters 21 to 28 . The configuration of the laser module 110 will be described later. In the following description, the eight emitters 21 to 28 may be collectively referred to as the emitter 20 when the types and positions are not particularly limited.

The light shaping component 120 is an optical component that shapes the beam shape of the laser light emitted from the laser diode bar 10 . The laser light immediately after being emitted from the laser diode bar 10 has an elliptical cross section cut along a virtual plane perpendicular to the optical axis. During laser processing using a laser beam, the shape of the cross section is preferably close to a circle, so the laser beam is shaped using the light shaping component 120 . For example, light shaping component 120 is a collimator lens.

The diffraction grating element 130 diffracts the laser light emitted from each emitter 20 of the laser diode bar 10 and directs it toward the external resonance mirror 140 .

External resonant mirror 140 transmits a portion of the incident laser light and reflects the remaining portion toward diffraction grating element 130 . By doing so, an external resonator is formed between the external resonance mirror 140 and each of the plurality of laser modules 110 . A wavelength beam combining system will be described with reference to FIG.

A single laser diode bar 10 is used in FIG. 2 to illustrate a wavelength beam combining system. A laser beam emitted from the laser diode bar 10 is diffracted by the diffraction grating element 130 and then enters the external resonance mirror 140 . Part of the incident laser light is transmitted, while the rest is reflected toward the diffraction grating element 130 and then back to the laser diode bar 10 . Most of this reflected return light is transmitted through the light emitting end face 10a (see FIG. 4) of the laser diode bar 10 and reaches the reflecting layer formed on the rear end face 10b (see FIG. 4) on the opposite side. do. Further, the laser light is reflected by the reflective layer and emitted to the outside of the laser diode bar 10 again from the light emitting end surface 10a.

Of the laser light emitted from each emitter 20 of the laser diode bar 10, only the light having a wavelength that satisfies the diffraction conditions of the diffraction grating element 130 and is reflected by the external resonance mirror 140 (hereinafter referred to as lock wavelength) returns to the original emitter 20, an external resonator is formed between the second reflective layer 19b (see FIG. 4) formed on the rear facet 10b and the external resonator mirror 14038, and the laser diode bar Specifically, laser light is output from each of a plurality of emitters 20 from 10 .

Assuming that the lock wavelength of each emitter 20 is λ _L , the period of the diffraction grating is d, the incident angle is α, the exit angle is β, and the order is m, the lock wavelength λ _L is expressed by Equation (1).
d(sinα+sinβ)= _mλL (1)
Incidentally, it is common to set the order m of the diffraction grating to 1.

For example, in the laser diode bar 10 shown in FIG. 2, the emitters 20 are formed such that the incident angle α with respect to the incident surface of the diffraction grating element 130 changes for each emitter 20 arrangement position. In this case, the lock wavelength of the emitters 20 formed on the laser diode bar 10 changes stepwise from one end of the laser diode bar 10 to the other end.

It should be noted that each emitter 20 can perform laser oscillation by external resonance only at wavelengths where the gain wavelength intensity originally possessed by the laser diode bar is equal to or greater than a predetermined value. In other words, lock wavelengths within a predetermined range from the gain peak wavelength _λg of each emitter 20 oscillate, and lock wavelengths outside the predetermined range do not oscillate. Therefore, in the wavelength beam combining system 100 of this embodiment, the upper and lower limits of the gain peak wavelength _λg of each emitter 20 are the difference _{ΔλL_bar} between the lock wavelengths _λL of the emitters 21 and 28 at both ends of the laser diode bar 10. The optical design of the laser diode bar 10 and each emitter 20 is done to fit the range. Note that the difference Δλ _{L_bar} between the lock wavelengths λ _L of the emitters 21 and 28 on both ends varies according to the distance L 1 between the laser diode bar 10 and the diffraction grating element 130 .

The arrangement relationship between the laser diode bar 10 and the diffraction grating element 130 is defined so that the optical axes of the laser beams emitted from the respective emitters of the laser diode bar 10 overlap each other when passing through the diffraction grating element 130. there is Further, in the wavelength beam combining system 100 shown in FIG. 1, the plurality of laser modules 110 are arranged inside the casing 160 such that the laser light emitting directions are different from each other with respect to the side surface of the casing 160 . Moreover, there are a plurality of sets of components each composed of one laser module 110 and a light shaping component 120 for receiving the laser light emitted from the laser module 110 and a diffraction grating element 130 . In each of the plurality of component sets, by adjusting the internal arrangement and the arrangement relationship between the component sets, the laser light emitted from each of the plurality of emitters 20 formed in the plurality of laser modules 110 is , overlap each other at the point of incidence on the external resonance mirror 140 . By doing so, a plurality of laser beams are superimposed to generate a high-power combined laser beam.

Returning to FIG. 1, the description of the configuration of the wavelength beam combining system is continued. The casing 160 is a box-shaped component made of a light shielding material. The casing 160 accommodates the plurality of laser modules 110, the plurality of optical shaping components 120, the plurality of diffraction grating elements 130, and the external resonance mirror 140 in an internal space. After these components are accommodated, a lid (not shown) is attached to the casing 160 to seal the components inside the casing 160 .

A laser light emitting block 161 is attached to the casing 160 . The coupled laser beam transmitted through the external resonance mirror 140 passes through the light exit port 161 a of the laser beam exit block 161 and exits the casing 160 . Inside the laser light emitting block 161, a reflecting mirror (not shown) and the like are provided for changing the optical path of the combined laser light. A cooling pipe 162 for cooling the casing 160 near the external resonance mirror 140 and the laser light emitting block 161 is attached to the laser light emitting block 161 .

Also, by providing an exhaust port 160 a on the side surface of the casing 160 . Gas generated inside the casing 160 by heating or the like is discharged to the outside of the casing 160 through the exhaust port 160a.

The light output monitor 150 is arranged inside the casing 160 and in the optical path of the laser light from the laser module 110 to the diffraction grating element 130 . Note that in the example shown in FIG. 1, the optical output monitor 150 is arranged at a position corresponding to one laser module 110 . Note that the optical output monitor 150 may be arranged at a position corresponding to each of the plurality of laser modules 110 . However, it is not necessary to provide the optical output monitor 150 for every laser module 110 . Also, as discussed below, optical power monitor 150 is ultimately removed from wavelength beam combining system 100 . As such, the optical power monitor 150 may be located outside the casing 160 and in the optical path of the combined laser light.

[Configuration of laser module]
The configuration of the laser module 110 will be described using the exploded perspective view of FIG. The laser module 110 has a first electrode block 30 , a submount 40 , a laser diode bar 10 , an insulating sheet 50 and a second electrode block 70 . In the laser module 110 shown in FIG. 3 and the laser diode bar 10 shown in FIGS. 4 and 5, the direction in which the emitters 20 are arranged may be called the X direction, and the thickness direction of the laser diode bar 10 may be called the Y direction. Also, the longitudinal direction of the emitter 20 is sometimes called the Z direction. The X direction, Y direction and Z direction are substantially orthogonal to each other. Also, in the Z direction, the side from which the laser beam is emitted may be called the front or front, and the opposite side may be called the rear or rear.

The first electrode block 30 is a plate-like member made of copper or copper alloy. The first electrode block 30 is formed with a concave portion 33 that is open to the front. In addition, screw holes 31 are provided at four locations in total, two on each side in the X direction with the concave portion 33 interposed therebetween and two in the Z direction. A screw hole 32 is provided behind the concave portion 33 along the Z direction.

A submount 40 and a laser diode bar 10 are installed in the recess 33 . The submount 40 is a plate-like conductive member and is bonded to the upper surface of the recess 33 with a conductive adhesive (not shown) such as Au—Sn solder. The material of the submount 40 is composed of a composite material of diamond and metal, or a conductive semiconductor material such as SiC, and preferably has a coefficient of linear expansion close to that of a nitride semiconductor and a high Young's modulus.

The laser diode bar 10 has eight emitters 21-28 spaced apart from each other in the X direction (see FIG. 4). The laser diode bar 10 is bonded to the submount 40 with a conductive adhesive 91 (see FIG. 5) such as Au—Sn solder. In this configuration, the p-side electrode 18 (see FIG. 5) of the laser diode bar 10 is joined to the surface of the submount 40 with the conductive adhesive 91 interposed therebetween. The configuration of the laser diode bar 10 will be described later.

A plurality of bump electrodes 60 are formed on the surface of the n-side electrode 17 (see FIG. 5) of the laser diode bar 10 . The n-side electrode 17 is electrically connected to the second electrode block 70 via the bump electrode 60 . A conductive sheet such as gold foil may be provided between the bump electrode 60 and the second electrode block 70 .

The second electrode block 70 is a plate-like member made of copper or copper alloy. A total of four screw holes 71 are provided in the second electrode block 70 at positions corresponding to the screw holes 31 of the first electrode block 30 . A screw hole 72 is provided between the screw holes 71 along the X direction in this case, at a position different from the screw hole 71 .

The insulating sheet 50 is a sheet-like member made of aluminum nitride, for example. Through holes 51 are provided in the insulating sheet 50 at positions corresponding to the screw holes 31 of the first electrode block 30 and the screw holes 71 of the second electrode block 70 . In this embodiment, aluminum nitride is used as the material for the insulating sheet 50 from the viewpoint of achieving both insulation and heat dissipation, but other materials may be selected.

When assembling the laser module 110 , the submount 40 and the laser diode bar 10 are mounted after positioning in the recess 33 of the first electrode block 30 . Furthermore, an insulating adhesive 90 is placed on the surface of the first electrode block 30 . The insulating adhesive 90 contains siloxane. Since the insulating adhesive 90 is used to bond the insulating sheet 50 to the surface of the first electrode block 30 while the through holes 51 and the screw holes 31 are overlapped, the insulating adhesive 90 prevents the laser module 110 from being attached. required for configuration.

Next, the second electrode block 70 is arranged on the surface of the first electrode block 30 so that the screw holes 71 and the screw holes 31 overlap. Furthermore, with a washer 83 interposed, the bolt 80 is inserted through the screw hole 31 of the first electrode block 30, the through hole 51 of the insulating sheet 50, and the screw hole 71 of the second electrode block 70, and tightened.

By doing so, the submount 40 and the laser diode bar 10 are sandwiched and fixed between the first electrode block 30 and the second electrode block 70 . At this time, the laser diode bar 10 is electrically connected to the first electrode block 30 through the submount 40 and the conductive adhesive 91 . Also, the laser diode bar 10 is electrically connected to the second electrode block 70 via the bump electrode 60 .

By forming the bump electrodes 60 on the surface of the laser diode bar 10, the pressure applied to the laser diode bar 10 at the time of fastening can be relieved, and the laser diode bar 10 can be prevented from being damaged or degraded in reliability. Note that the insulating sheet 50 may be adhered to the back surface of the second electrode block 70 using the insulating adhesive 90 in a state in which the through holes 51 and the screw holes 71 are overlapped.

A negative wiring (not shown) drawn from an external power supply (not shown) is fastened to the screw hole 32 of the first electrode block 30 by a bolt 81, and the negative wiring and the first electrode block 30 are connected. are electrically connected. A positive wiring (not shown) drawn out from an external power source is fastened to the screw hole 72 of the second electrode block 70 with a bolt 82, and the positive wiring and the second electrode block 70 are electrically connected. be done.

With such a configuration of the laser module 110 for obtaining a high optical output, it is extremely difficult to hermetically seal the laser module 110, or to hermetically seal the laser module 110 by separating only the insulating adhesive.

[Configuration of laser diode bar]
FIG. 4 shows a perspective view of the laser diode bar, and FIG. 5 shows a cross-sectional view along line VV of FIG.

As shown in FIG. 4, the laser diode bar 10 has eight emitters 21 to 28 spaced apart from each other in the X direction. Of these, the emitters 21 and 28 located at both ends and the other emitters 22 to 27 have different widths in the X direction. Specifically, in the emitters 21 and 28 positioned at both ends, the width W2 in the X direction of the stripe portion 20a, which will be described later (hereinafter referred to as stripe width), is narrower than the stripe width W1 in the other emitters 22 to 27. It's becoming The emitters 21 and 28 at both ends and the other emitters 22 to 27 have the same length L in the Z direction (hereinafter sometimes referred to as stripe length L). The front end face of the laser diode bar 10 in the Z direction is the light emitting end face 10a. A laser beam is emitted forward in the Z direction from the light emitting end surface 10a. A first reflective layer 19a is formed on the light emitting end face 10a, and a second reflective layer 19b is formed on the rear end face 10b of the laser diode bar 10, respectively. The reflectance of the second reflective layer 19b is set to be high and the reflectance of the first reflective layer 19a is set to be low with respect to the wavelength of the laser light. Preferably, the reflectance of the second reflective layer 19b with respect to the wavelength of the laser light is 90% or more, and the reflectance of the first reflective layer 19a is preferably 1% or less. Therefore, the first reflective layer 19a and the second reflective layer 19b are formed by laminating two or three types of dielectric films having different refractive indices. However, the configurations of the first reflective layer 19a and the second reflective layer 19b are not particularly limited to this.

Further, as shown in FIG. 5, the emitter 20 is composed of a plurality of nitride semiconductor layers laminated in the Y direction. Specifically, the emitter 20 has an n-type substrate 11, an n-type clad layer 12, an active layer 13, a p-type clad layer 14, and a p-type contact layer 15 as nitride semiconductor layers. An n-side electrode 17 is formed on the back surface of the n-type substrate 11 . A p-side electrode 18 is formed on the surface of the p-type contact layer 15 .

The p-type cladding layer 14 and the p-type contact layer 15 are processed into a linear stripe shape extending in the Z direction, and these are sometimes collectively called a stripe portion 20a. An insulating layer 16 is formed to cover the surface of the stripe portion 20a and the p-type clad layer 14 except for the p-side electrode 18. As shown in FIG. By providing the insulating layer 16, the p-type cladding layer 14, which is not provided with the p-side electrode 18, is prevented from being energized to the active layer 13, and the current is confined to the active layer 13 in the X direction. there is

A current flows through the laser module 110 by applying a voltage higher than a predetermined value from the outside between the first electrode block 30 and the second electrode block 70 .

Looking at each emitter 20, a predetermined voltage or more is applied between the n-side electrode 17 and the p-side electrode 18, charges are injected into the active layer 13, and the active layer 13 begins to emit light. When a current equal to or higher than the threshold current flows through the active layer 13, laser oscillation occurs between the first reflective layer 19a and the second reflective layer 19b, and laser light is emitted forward in the Z direction from the light emitting end surface 10a. .

Due to the difference in stripe width, the threshold currents of the emitters 21 and 28 at both ends and the other emitters 22 to 27 are different. Specifically, the threshold currents of the emitters 21 and 28 at both ends are smaller than the threshold currents of the other emitters 22-27.

[Knowledge leading to the present invention]
FIG. 6 shows the time variation of the laser light output of a laser module composed of a single emitter during continuous oscillation, and FIG. 7 shows the laser module mounted with a laser diode bar having 38 emitters driven for a predetermined time. The change in laser light output from each emitter before and after switching is shown.

FIG. 8 shows a schematic view of observation of deposits on the light-emitting end surface of the emitter after the laser module has been driven for a predetermined period of time. FIG. 9 shows the relationship between stripe width and threshold current. Note that the insulating layer 16 is omitted in FIG. 8 for the sake of clarity of the drawing.

In the example shown in FIG. 6, laser diode bar 10 has a single emitter 20 . This laser diode bar 10 can be mounted in a CAN package and hermetically sealed. In the case of airtight sealing, the degree of decrease in laser light output was about 10% after continuous driving for 100 hours. On the other hand, when another laser diode bar 10 having the same light output is not hermetically sealed and exposed to the atmosphere containing a constant concentration of siloxane, the degree of decrease in laser light output after continuous driving for 100 hours is reached about 60%. As described above, this is considered to be due to the adhesion of siloxane decomposition products to the light emitting end surface 10a.

On the other hand, in the example shown in FIG. 7, the laser diode bar 10 has 38 emitters 20 . After the laser diode bar 10 was assembled into the laser module 110 shown in FIG. 3, the laser module 110 was continuously driven for a certain period of time. The laser light output from each emitter 20 was measured before and after continuous driving. As is clear from FIG. 7, the degree of decrease in laser light output was 20% or less for the emitter 20 located in the center. On the other hand, the degree of decrease in the output of the laser light emitted from the emitter 20 increased from the center toward both ends.

In response to this result, when the light emitting end face 10a of each emitter 20 was observed by SEM (Scanning Electron Microscopy), as shown in FIG. 1 to 3 and emitter No. In 36 to 38, deposits were observed on the light emitting end surface 10a. Further, by EDX analysis (Energy Dispersive X-ray Spectroscopy), it was found that the main component of the deposit was Si, which is considered to be derived from siloxane. In other words, the deposit was presumed to be a decomposed product of siloxane staying in the atmosphere.

Considering the structure of the laser module 110 shown in FIG. 3, it is presumed that the siloxane contained in the insulating adhesive material 90 is more likely to adhere to the light emitting end surfaces 10a of the emitters 20 located on both ends located in the vicinity thereof. The inventors of the present application presume that the light output of the emitters 20 at both ends is lower than that of the other emitters 20 due to this.

Therefore, in the laser diode bar 10 shown in FIG. 4, the inventor of the present application attaches siloxane decomposition products only to the light emitting end faces 10a of the emitters 21 and 28 (hereinafter sometimes referred to as dummy emitters 21 and 28) at both ends. I tried to let It has been found that by doing so, when the laser module 110 as a whole is viewed, it is possible to suppress a decrease in the laser light output during long-term use. In order to achieve this, emitters 21 and 28 having smaller threshold currents than the other emitters 22 to 27 are provided at both ends. This will be further explained.

As shown in FIG. 9, the threshold current Ith of the emitter 20 generally increases as the stripe width increases. This tendency does not change even when the stripe length L changes. Using this fact, emitters 20 having different threshold currents are simultaneously formed in one laser diode bar 10 .

For example, in the laser diode bar 10 shown in FIG. 4, the stripe width W2 of the dummy emitters 21 and 28 is set to 5 μm, and the stripe widths of the other emitters 22 to 27 (hereinafter sometimes referred to as the main emitters 22 to 27). W1 is set to 30 μm. Also, a current of 200 mA is allowed to flow through each of the emitters 21-28. As is clear also from FIG. 9, the currents flowing through the dummy emitters 21 and 28 exceed the threshold current. Therefore, the dummy emitters 21 and 28 laser-oscillate, and laser light is emitted from the light emitting end surface 10a. On the other hand, in the emitters 22 to 27, only a current smaller than the threshold current flows and does not emit light.

In this case, decomposition of siloxane progresses in the vicinity of the dummy emitters 21 and 28, and siloxane decomposition products adhere to the light emitting end surface 10a. On the other hand, in the vicinity of the emitters 22 to 27, decomposition of siloxane does not occur, and siloxane decomposition products do not adhere to the light emitting end surface 10a. By emitting the laser beam for a predetermined time or longer, the adhesion of the siloxane decomposition product derived from the insulating adhesive 90 to the dummy emitters 21 and 28 on the light emitting end surface 10a progresses, and the siloxane concentration inside the casing 160 is reduced to a predetermined level or less. descend. As a result, when a current exceeding the threshold current is applied to each of the emitters 21 to 28 of the laser diode bar 10, each of the emitters 22 to 27 oscillates and emits laser light. At this time, since the siloxane concentration is low in the vicinity of the light emitting end face 10a, adhesion of siloxane decomposition products to the light emitting end face 10a is suppressed. As a result, even if the laser light is emitted from the emitters 22 to 27 for a long time, the decrease in light output is suppressed. That is, it is possible to suppress a decrease in reliability when the laser module 110 and, in turn, the wavelength beam combining system 100 are operated for a long time.

Note that the dummy emitters 21 and 28 may not only reduce the light output but also be destroyed due to adhesion of decomposed siloxane. However, even if such a thing occurs, the dummy emitters 21 and 28 will only become a minute source of heat when energized, and will not greatly affect the operation of the laser diode bar 10 itself. In addition, although the overall output of the laser light output from the laser diode bar 10 is reduced, by setting the number ratio of the main emitters 22 to 27 and the dummy emitters 21 and 28 in anticipation of the reduction, a desired output can be achieved. light output can be obtained.

Note that both of the dummy emitters 21 and 28 do not necessarily have to oscillate, and at least one of them may oscillate. In addition, when emitting laser light from the dummy emitters 21 and 28, it is preferable that the main emitters 22 to 27 do not emit light. For this reason, it is preferable that the threshold currents of the dummy emitters 21 and 28 for emitting laser light are set to 1/2 or less of the threshold currents of the main emitters 22-27.

Also, as shown in FIG. 9, the threshold current Ith increases monotonically with respect to the stripe width. Therefore, by adjusting the stripe width, the threshold current flowing through the emitter 20 can be changed. It is preferable to ensure that the dummy emitters 21 and 28 emit laser light while the main emitters 22 to 27 do not emit light. For this reason, the stripe width of the dummy emitters 21 and 28 for emitting laser light is preferably 1/3 or less of the stripe width of the main emitters 22-27.

Note that the stripe width of each emitter 21 to 28 often fluctuates due to variations in processing. In this case, the threshold current of each emitter 21-28 also varies. Taking this into consideration, the threshold currents of the dummy emitters 21 and 28 for emitting laser light are preferably set to 1/2 or less of the average value of the threshold currents of the main emitters 22-27. The stripe width of the dummy emitters 21 and 28 for emitting laser light is preferably 1/3 or less of the average stripe width of the main emitters 22-27.

Based on the knowledge obtained above, a method for manufacturing the wavelength beam combining system 100 will be described below.

[Manufacturing method of wavelength beam combining system]
FIG. 10 shows a flow chart for explaining a method of manufacturing a wavelength beam combining system. FIG. 11 shows the state of laser light emitted from the laser module in step S5 shown in FIG. 10, and FIG. 12 shows the time change of the monitor output in step S5 shown in FIG.

A laser diode bar 10 shown in FIGS. 4 and 5 is prepared (step S1; first step). The laser diode bar 10 prepared in step S1 is incorporated to assemble the laser module 110 shown in FIG. 3 (step S2; second step). The method of assembling the laser module 110 is as described above.

Next, the plurality of laser modules 110, the plurality of diffraction grating elements 130, and the external resonance mirror 140 are fixedly arranged inside the casing 160 while maintaining a predetermined arrangement relationship (step S3; third step). A lid (not shown) is used to seal the casing 160 (step S4; fourth step).

After step S4, the laser module 110 is driven using a power supply (not shown). At this time, laser light is continuously emitted from the emitters 21 and 28 at both ends included in the laser diode bar 10 for a predetermined time. Also, the output of the emitted laser beam is monitored by the optical output monitor 150 (step S5; fifth step). The predetermined time is determined according to the degree of decrease in the monitored laser light output. More on this later.

As shown in FIG. 11, in step S5, the racer module 110 is driven so that the remaining emitters 22 to 27 from which laser light is not emitted do not emit light.

Laser oscillation is stopped based on the monitoring result of the optical output monitor 150 (step S6). Specifically, as shown in FIG. 12, when the rate of change in light output with respect to driving time becomes small, laser oscillation is stopped and the light output monitor 150 is removed. All the steps are completed as described above.

[Effects, etc.]
As described above, the laser diode bar 10 according to the present embodiment contains a nitride semiconductor as a constituent material. The laser diode bar 10 also has eight emitters 21 to 28 spaced apart from each other in the X direction (first direction). Each of the eight emitters 21 to 28 causes laser oscillation when a current equal to or greater than the threshold current flows.

The threshold current of at least one of the emitters 21 and 28 on both ends is less than half the average value of the threshold currents of the main emitters 22 to 27 excluding the emitters 21 and 28 on both ends.

Each of the eight emitters 21 to 28 has a stripe-shaped stripe portion 20a whose longitudinal direction is the Z direction (second direction) intersecting the X direction.

The stripe width of at least one of the emitters 21 and 28 on both ends, that is, the width in the X direction of the stripe portion 20a, is 1/3 of the average stripe width of the main emitters 22 to 27 excluding the emitters 21 and 28 on both ends. It is below.

When a current of a predetermined value is applied to each of the eight emitters 21-28, one or both of the emitters 21 and 28 at both ends oscillate, while the main emitters 22-27 do not oscillate.

Also, the wavelength of the laser light emitted from each of the eight emitters 21 to 28 is in the range of 350 nm or more and 450 nm or less, which is the so-called blue light wavelength range.

By setting the wavelength of the laser light emitted from the dummy emitters 21 and 28 within this range, the siloxane staying in the vicinity of the laser diode bar 10 can be reliably decomposed. Moreover, the siloxane decomposition products can be reliably adhered to the light emitting end surfaces 10a of the dummy emitters 21 and 28. FIG.

According to this embodiment, it is possible to suppress adhesion of siloxane decomposed products to the light emitting end surfaces 10a of the main emitters 22-27. As a result, it is possible to suppress deterioration in reliability when the laser module 110 and, in turn, the wavelength beam combining system 100 are operated for a long period of time.

In addition, when a predetermined current is passed through each of the eight emitters 21 to 28, one or both of the emitters 21 and 28 at both ends will oscillate, and the emitters 22 to 27 will emit light in the LED mode. may be Light emission in the LED mode means light emission in a state in which laser oscillation is not performed.

FIG. 13 shows a preferred driving range of the laser diode bar in step S5 shown in FIG. In range I shown in FIG. 13, as described above, one or both of the emitters 21 and 28 at both ends laser-oscillate, and the main emitters 22 to 27 do not laser-oscillate and do not emit light. When the laser diode bar 10 is operated within this range, siloxane decomposition products will not adhere to the light emitting end surfaces 10a of the emitters 22-27.

On the other hand, in range II shown in FIG. 13, one or both of the emitters 21 and 28 at both ends laser-oscillate, and the main emitters 22 to 27 emit light in LED mode. The light emitted in this mode and emitted from the light emitting end surface 10a is not in phase spatially and temporally. Also, the light density in LED mode is significantly lower than that of laser light. In other words, even if the operating range of the laser diode bar 10 is set to range II, siloxane decomposition does not occur in the vicinity of the light emitting end faces 10a of the emitters 22 to 27, and Si does not adhere to the end faces due to the optical tweezers effect. . Therefore, the effects described above can be obtained. In other words, it is possible to prevent siloxane decomposed products from adhering to the light emitting end faces 10a of the emitters 22-27. As a result, it is possible to suppress deterioration in reliability when the laser module 110 and, in turn, the wavelength beam combining system 100 are operated for a long period of time. When the emitters 22 to 27 are caused to emit light in the LED mode, all emitting emitters 20 stop emitting light in step S6 in FIG.

When operating the laser diode bar 10 in range I or range II, the threshold current of at least one of the emitters 21 and 28 at both ends is the average value of the threshold currents of the emitters 22 to 27 excluding the emitters 21 and 28 at both ends. The following should be done. Also, the stripe width of at least one of the emitters 21 and 28 on both ends should be set to be equal to or less than the average stripe width of the main emitters 22-27.

When the stripe length L is about 1000 μm to 2000 μm, the threshold current of at least one of the emitters 21 and 28 on both ends is preferably 130 mA or more and 150 mA or less. Also, the stripe width of at least one of the emitters 21 and 28 on both ends is preferably 5 μm or more and 10 μm or less.

In this embodiment, the laser diode bar 10 has eight emitters 21 to 28, but the number of emitters 20 is not limited to n (n is an integer of 4 or more). of emitters 21 to 2n are formed.

Further, when a predetermined current is passed through each of the n emitters 21 to 2n, one or both of the emitters 21 and 2n at both ends oscillates, and the emitters 22 to 2n-1 emit light in the LED mode. may be configured to

The wavelength beam combining system 100 according to the present embodiment combines one or a plurality of laser modules 110 each having a laser diode bar 10 and laser light emitted from a plurality of emitters 21 to 2n included in the laser diode bar 10. and a diffraction grating element 130 (optical coupling element).

The wavelength beam combining system 100 also includes an external resonant mirror 140 that reflects the laser light coupled by the diffraction grating element 130 toward the diffraction grating element 130, one or more laser modules 110, the diffraction grating element 130, and an external resonant mirror 140. and a casing 160 that houses the mirror 140 .

The laser diode bar 10 has a second reflective layer (reflective layer) having a predetermined reflectance on the rear end face 10b opposite to the laser light emitting end face (light emitting end face 10a) of the n emitters 21 to 2n. 19b is provided.

An external resonator is formed between the external resonance mirror 140 and the second reflective layer 19b of the emitter 20 from which laser light is emitted, and the coupled laser light coupled by the diffraction grating element 130 is emitted to the outside of the casing 160. .

By configuring the wavelength beam coupling system 100 in this way, it is possible to suppress adhesion of siloxane decomposition products to the light emitting end surface 10a of the emitter 20 from which laser light is emitted. As a result, deterioration in reliability can be suppressed when the wavelength beam combining system 100 is operated for a long period of time. In addition, by combining the laser beams emitted from the plurality of emitters 20, a high-power combined laser beam can be obtained.

The manufacturing method of the wavelength beam combining system 100 according to the present embodiment includes a first step of preparing the laser diode bar 10 (step S1 in FIG. 10) and a second step of assembling the laser module 110 having the laser diode bar 10 (FIG. 10 steps S2).

Further, in the method of manufacturing the wavelength beam combining system 100, the third step (FIG. 10) is to fix and arrange the laser module 110, the diffraction grating element 130, and the external resonance mirror 140 inside the casing 160 while maintaining a predetermined arrangement relationship. and a fourth step (step S4 in FIG. 10) of sealing the casing 160 after the third step. Furthermore, after the fourth step, the laser module 110 is driven to continuously emit laser light from at least one of the emitters 21 and 2n at both ends included in the laser diode bar 10 for a predetermined time in a fifth step (FIG. 10 step S5).

In the second step, an adhesive containing siloxane, that is, an insulating adhesive 90 is used to assemble the laser module 110 .

In the fifth step, laser light is emitted from at least one of the emitters 21 and 2n at both ends while the laser light output is being monitored, and laser light is not emitted from the remaining emitters 22 to 2n-1. , the racer module 110 is driven. The predetermined period is determined according to the degree of decrease in the output of laser light.

According to the present embodiment, it is possible to prevent siloxane decomposition products from adhering to the light emitting end surface 10a of the emitter 20 from which laser light is emitted. As a result, deterioration in reliability can be suppressed when the wavelength beam combining system 100 is operated for a long period of time. Note that siloxane is considered to volatilize from the insulating adhesive 90 and stay in the surrounding atmosphere.

<Modification>
FIG. 14 shows a schematic plan view of a dummy emitter according to this modification. For convenience of explanation, only the stripe portion 20a of the dummy emitters 21 and 28 is shown in simplified form.

As shown in the embodiment, by narrowing the stripe width of the dummy emitters 21 and 28 to a predetermined value or less of the stripe width of the main emitters 22 to 27, the threshold current of the dummy emitters 21 and 28 is reduced to that of the main emitters 22 to 27. It can be smaller than the threshold current.

However, if the stripe width is uniformly narrowed, the electrical resistance of the dummy emitters 21 and 28 increases when current is applied, and laser oscillation may not be possible.

Therefore, for example, as shown in FIG. 14, the width of the central portion of the stripe portion 20a in the Z direction is set to W3 (≧W1), and the stripe width is gradually narrowed toward the ends in the Z direction.

By doing so, it is possible to suppress the decrease in the area of the stripe portion 20a and, in turn, the increase in the electrical resistance during energization. Moreover, since the threshold current is mainly determined by the portion where the stripe width is narrow, it is possible to suppress an increase in the threshold current. As a result, when a current of a predetermined value is passed through each of the n emitters 21 to 2n, one or both of the emitters 21 and 2n at both ends will oscillate, and the main emitters 22 to 2n-1 will not emit light. , or to create a condition that emits light in LED mode.

Therefore, it is possible to prevent siloxane decomposition products from adhering to the light emitting end faces 10a of the emitters 22 to 2n. As a result, it is possible to suppress deterioration in reliability when the laser module 110 and, in turn, the wavelength beam combining system 100 are operated for a long period of time.

The shape of the stripe portion 20a of the dummy emitters 21 and 28 is not particularly limited to the shape shown in FIG. Also, from the viewpoint of suppressing an increase in electrical resistance and an increase in threshold current, the widths W2 and W3 shown in FIG. 14 are appropriately determined. For example, width W3 may be less than or equal to W1.

(Other embodiments)
In the embodiment, one diffraction grating element 130 is arranged for one laser module 110, but one diffraction grating element 130 may be arranged for a plurality of laser modules 110. good. Moreover, although the transmission type diffraction grating element 130 is shown, the reflection type diffraction grating element 130 may be used.

Further, an optical coupling element other than the diffraction grating element 130 may be used to couple the laser beams emitted from each of the plurality of emitters. For example, a prism could be used.

Also, as shown in FIG. 1, the casing 160 in which the laser module 110 is housed does not necessarily have to be hermetically sealed.

In the embodiment, the dummy emitters 21 and 28 are arranged one by one at both ends in the X direction, but the present invention is not particularly limited to this. A plurality of dummy emitters may be arranged at both ends in the X direction. In this case, the number of dummy emitters is the total number of emitters 20 formed on the laser diode bar 10, the total light output required for the laser diode bar 10, and the amount of siloxane generated from the insulating adhesive 90. It is appropriately set according to the amount.

Also, the dummy emitters 21 and 2n may be provided at positions other than both ends of the n emitters 21 to 2n. For example, when the insulating adhesive 90 is arranged near the central emitter 20, one or more of the central emitters 20 may be used as dummy emitters.

In the embodiment, by making the stripe width W2 of the dummy emitters 21 and 28 narrower than the stripe width W1 of the main emitters 22 to 27, a difference in threshold current is provided between the two. However, the configuration in which the threshold currents are differentiated is not particularly limited to this. For example, the electrode blocks electrically connected to the dummy emitters 21 and 28 and the electrode blocks electrically connected to the main emitters 22 to 27 are electrically separated so that they can be driven independently. good too. In this case, the dummy emitters 21, 28 and the main emitters 22-27 can have the same stripe width. However, this complicates the shape of the electrode block and requires two types of drive power sources.

The laser diode bar of the present disclosure is useful as a laser light source that emits high-power blue light and has reduced reliability.

10 laser diode bar 10a light emitting facet 10b rear facet 11 n-type substrate 12 n-type clad layer 13 active layer 14 p-type clad layer 15 p-type contact layer 16 insulating layer 17 n-side electrode 18 p-side electrode 19a first reflective layer 19b Second reflective layer (reflective layer)
20 Emitter 20a Stripe 21, 28 Dummy emitters 22-27 Main emitter 30 First electrode block 40 Submount 50 Insulating sheet 60 Bump electrode 70 Second electrode block 90 Insulating adhesive 91 Conductive adhesive 100 Wavelength beam coupling system 110 Laser module 120 Light shaping component 130 Diffraction grating element (optical coupling element)
140 External resonance mirror 150 Optical output monitor 160 Casing 161 Laser light emission block 161a Light emission port 162 Cooling pipe

Claims (10)

A laser diode bar containing a nitride semiconductor as a constituent material,
The laser diode bar has n (n is an integer equal to or greater than 4) emitters spaced apart from each other in a first direction,
Each of the n emitters laser-oscillates when a current equal to or greater than a threshold current flows,
The laser diode bar, wherein the threshold current of at least one of the emitters on both ends is equal to or less than the average value of the threshold currents of the remaining emitters excluding the emitters on both ends. 2. The threshold current of at least one of the emitters on both ends is less than or equal to 1/2 of the average value of the threshold currents of the remaining emitters excluding the emitters on both ends. laser diode bar described in . 3. The laser diode bar according to claim 1, wherein the threshold current of at least one of the emitters on both ends is 130 mA or more and 150 mA or less. A laser diode bar containing a nitride semiconductor as a constituent material,
The laser diode bar has n (n is an integer equal to or greater than 4) emitters spaced apart from each other in a first direction,
Each of the n emitters laser-oscillates when a current equal to or greater than a threshold current flows,
each of the n emitters has a stripe-shaped stripe portion whose longitudinal direction is a second direction that intersects the first direction;
The width in the first direction of the stripe portion of at least one of the emitters on both ends is equal to or less than the average width of the stripe portions in the first direction on the remaining emitters excluding the emitters on both ends. A laser diode bar characterized by: The width in the first direction of the stripe portion in at least one of the emitters on both ends is the average value of the widths in the first direction of the stripe portions in the remaining emitters excluding the emitters on both ends. 5. The laser diode bar according to claim 4, characterized in that it is 1/3 or less. 6. The laser diode bar of claim 4, wherein the width of the stripe portion in at least one of the emitters at both ends in the first direction is 5 [mu]m or more and 10 [mu]m or less. It is constructed such that when a current of a predetermined value is passed through each of the n emitters, one or both of the emitters at both ends lasing, and the remaining emitters do not oscillate. 7. The laser diode bar according to any one of items 1 to 6. 7. The laser diode bar according to any one of claims 1 to 6, wherein the wavelength of the laser light emitted from each of the n emitters is in the range of 380 nm or more and 450 nm or less. one or more laser modules each having a laser diode bar according to any one of claims 1 to 8;
an optical coupling element that couples the laser beams respectively emitted from the plurality of emitters included in the laser diode bar;
an external resonance mirror that reflects the laser light coupled by the optical coupling element toward the optical coupling element;
at least a casing housing one or more of the laser modules, the optical coupling element, and the external resonance mirror;
The laser diode bar is provided with a reflective layer having a predetermined reflectance on the surface opposite to the emission end surface of the laser light in the n emitters,
an external resonator is formed between the external resonator mirror and the reflective layer of the emitter from which the laser beam is emitted;
A wavelength beam combining system, wherein the combined laser beams combined by the optical coupling element are emitted to the outside of the casing. A method of manufacturing a wavelength beam combining system according to claim 9, comprising:
a first step of preparing the laser diode bar;
a second step of assembling the laser module with the laser diode bar;
a third step of fixing and arranging the laser module, the optical coupling element, and the external resonance mirror inside the casing while maintaining a predetermined arrangement relationship;
a fourth step of sealing the casing after the third step;
at least a fifth step, after the fourth step, of driving the laser module to continuously emit the laser light from at least one of the emitters at both ends included in the laser diode bar for a predetermined time; prepared,
In the second step, an adhesive material containing siloxane is used to assemble the laser module,
In the fifth step, while the output of the laser light is being monitored, the laser light is emitted from at least one of the emitters at both ends, and the laser light is not emitted from the remaining emitters. driving the racer module;
A method of manufacturing a wavelength beam combining system, wherein the predetermined time is determined according to the degree of decrease in output of the laser light.

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