阅读说明：本技术 激光二极管条及其制造方法、使用其的波长光束耦合系统 (Laser diode bar, method of manufacturing the same, and wavelength beam coupling system using the same ) 是由 上田章雄 大野启 于 2021-04-12 设计创作，主要内容包括：本公开提供一种激光二极管条及其制造方法、使用其的波长光束耦合系统。用于波长光束耦合系统的激光二极管条具备：氮化物半导体基板,将(0001)面作为面方位,并且具有从(0001)面向m轴或a轴的至少一个轴被赋予了大于0°的偏离角的基板面；层叠构造体,形成在所述氮化物半导体基板上,包括第1导电型包层、活性层以及第2导电型包层；多个发射极,以发射极的波导方向与所述偏离角的主轴方向垂直的方式,呈条带状地形成于所述层叠构造体。(The present disclosure provides a laser diode bar, a method of manufacturing the same, and a wavelength beam coupling system using the same. A laser diode bar for a wavelength beam coupling system is provided with: a nitride semiconductor substrate having a (0001) plane as a plane orientation and a substrate plane to which an off-angle larger than 0 ° is given from the (0001) plane to at least one of an m-axis and an a-axis; a stacked structure formed on the nitride semiconductor substrate, the stacked structure including a 1 st-type-conductive-type-clad layer, an active layer, and a 2 nd-type-conductive-type-clad layer; and a plurality of emitters formed in a stripe shape in the laminated structure so that a waveguide direction of the emitters is perpendicular to a main axis direction of the off-angle.)

1. A laser diode bar for a wavelength beam coupling system,

the laser diode bar is provided with:

a nitride semiconductor substrate having a (0001) plane as a plane orientation and a substrate plane to which an off-angle larger than 0 ° is given from the (0001) plane to at least one of an m-axis and an a-axis;

a stacked structure formed on the nitride semiconductor substrate, the stacked structure including a 1 st-type-conductive-type-clad layer, an active layer, and a 2 nd-type-conductive-type-clad layer; and

and a plurality of emitters formed in a stripe shape in the laminated structure so that a waveguide direction of the emitters is perpendicular to a main axis direction of the off-angle.

2. The laser diode bar of claim 1,

the slope of the distribution in the principal axis direction of the off-angle satisfies the following formula (1) with respect to the slope of the distribution of the locking wavelengths of the plurality of emitters,

0＜ΔD≤((Δλ_{EC_bar}+3.2)/Lt)/30 formula (1)

Wherein Δ D represents a slope of a distribution in a principal axis direction of the off-angle in units of angle/mm, Lt represents a length of the laser diode bar in a length direction in units of mm, Δ λ_{EC_bar}And the locking wavelength difference of the two end positions of the laser diode bar in the length direction is expressed in nm.

3. The laser diode bar of claim 1,

the slope of the distribution in the direction of the principal axis of the off-angle and the distribution of the locking wavelengths of the plurality of emitters satisfy the following equations (2) and (3),

0≤((Δλ_{EC_bar}-1.2)/Lt)/30 formula (2)

((Δλ_{EC_bar}-1)/Lt)/0.3≤ΔD≤((Δλ_{EC_bar}+1)/Lt)/30 formula (3)

Wherein Δ D represents a slope of a distribution in a main axis direction of the off-angle in the unit of angle/mm, and Lt representsThe length of the laser diode bar in the length direction is in mm and delta lambda_{EC_bar}And the locking wavelength difference of the two end positions of the laser diode bar in the length direction is expressed in nm.

4. The laser diode bar of claim 1,

the slope of the distribution in the direction of the principal axis of the off-angle and the distribution of the locking wavelengths of the plurality of emitters satisfy the following equations (4) and (5),

0＞((Δλ_{EC_bar}-1.2)/Lt)/30 formula (4)

0＜ΔD≤((Δλ_{EC_bar}+1.2)/Lt)/30 formula (5)

Wherein Δ D represents a slope of a distribution in a principal axis direction of the off-angle in units of angle/mm, Lt represents a length of the laser diode bar in a length direction in units of mm, Δ λ_{EC_bar}And the locking wavelength difference of the two end positions of the laser diode bar in the length direction is expressed in nm.

5. The laser diode bar of claim 1,

the slope of the distribution of the locking wavelengths of the plurality of emitters is in the same direction as the slope of the distribution of the amplified spontaneous emission ASE wavelengths of the plurality of emitters.

6. The laser diode bar according to any one of claims 1 to 5,

the length of the laser diode bar in the waveguide direction is more than 0.3mm and within 8 mm.

7. The laser diode bar according to any one of claims 1 to 5,

the length of the laser diode bar in the waveguide direction is more than 1mm and within 6 mm.

8. The laser diode bar according to any one of claims 1 to 7,

the main axis direction of the off-angle is the a-axis direction.

9. A wavelength beam coupling system includes:

the laser diode bar of any one of claims 1 to 8;

a diffraction grating configured to diffract the plurality of laser beams emitted from the plurality of emitters of the laser diode bar, respectively; and

and an external resonator mirror that reflects a part of the laser light diffracted by the diffraction grating and returns the part to the laser diode bar side, and that externally resonates between the external resonator mirror and a reflective film of the laser diode bar.

10. A method of manufacturing a laser diode bar for use in a wavelength beam coupling system,

the manufacturing method of the laser diode bar comprises the following steps:

preparing a nitride semiconductor substrate having a (0001) plane as a plane orientation and a substrate plane to which an off-angle larger than 0 ° is given from the (0001) plane to at least one of an m-axis and an a-axis;

forming a stacked structure including a 1 st-conductivity-type clad layer, an active layer, and a 2 nd-conductivity-type clad layer on the nitride semiconductor substrate;

forming a plurality of emitters arranged in a stripe shape in the laminated structure such that a major axis direction of an off-angle of the nitride semiconductor substrate is perpendicular to a waveguide direction of the emitters: and

and cutting the laser diode bar having the plurality of emitters from the nitride semiconductor substrate.

11. The method of manufacturing a laser diode bar according to claim 10,

the nitride semiconductor substrate is a GaN substrate.

12. The method of manufacturing a laser diode bar according to claim 10 or 11,

the main axis direction of the off-angle is the a-axis direction.

Technical Field

The present disclosure relates to a laser diode bar, a wavelength beam coupling system using the laser diode bar, and a method of manufacturing the laser diode bar.

Background

As a system for obtaining a laser Beam of high power by coupling a plurality of beams of different wavelengths to one point, a wavelength Beam coupling system (wbc) system is known. As a WBC system, for example, a system described in patent document 1 is known.

The WBC system has laser diode (ld) bars, optical rotator units (btus), diffraction gratings, and external resonator mirrors.

The LD bar has a plurality of emitters from each of which a light beam is emitted. The plurality of light beams emitted from the LD bar are respectively rotated by 90 degrees by the BTU. Thereby, the individual spots are prevented from interfering with each other. The light beam from the BTU enters a transmission-type or reflection-type diffraction grating, and the diffraction grating diffracts the incident light beam at a diffraction angle determined by the wavelength of the light beam and emits the light beam. The light beam emitted from the diffraction grating is incident on an external resonator mirror. The external resonator mirror is a partially transmissive mirror that reflects a portion of the incident light beam vertically in the direction of the diffraction grating. Thus, a wavelength (referred to as a lock wavelength) uniquely determined by a positional relationship of each emitter, diffraction grating, and external resonance mirror of the LD bar is fed back between the rear mirror of the LD bar and the external resonance mirror, and external resonance oscillation is performed, thereby outputting a laser beam.

The emitters of the LD bar are externally resonant-oscillated at slightly different wavelengths because of different relative positions with respect to the diffraction grating, but coupled to one point by an external resonant mirror, and thus can output a laser beam with high power.

Prior art documents

Patent document

Patent document 1: japanese patent laid-open publication No. 2015-106707

Disclosure of Invention

The present disclosure, which is the primary object of the present invention, is a laser diode bar for a wavelength beam coupling system, the laser diode bar including: a nitride semiconductor substrate having a (0001) plane as a plane orientation and a substrate plane to which an off-angle larger than 0 ° is given from the (0001) plane to at least one of an m-axis or an a-axis; a stacked structure formed on the nitride semiconductor substrate, the stacked structure including a 1 st-type-conductive-type-clad layer, an active layer, and a 2 nd-type-conductive-type-clad layer; and a plurality of emitters formed in a stripe shape in the laminated structure so that a waveguide direction of the emitters is perpendicular to a main axis direction of the off-angle.

In addition, another mode is a method for manufacturing a laser diode bar for a wavelength beam coupling system, the method including: preparing a nitride semiconductor substrate having a (0001) plane as a plane orientation and a substrate plane to which an off-angle larger than 0 ° is given from the (0001) plane to at least one of an m-axis and an a-axis; forming a stacked structure including a 1 st-conductivity-type clad layer, an active layer, and a 2 nd-conductivity-type clad layer on the nitride semiconductor substrate; forming a plurality of emitters arranged in a stripe shape in the stacked structure such that a major axis direction of an off-angle included in the nitride semiconductor substrate is perpendicular to a waveguide direction of the emitters; and a step of cutting out the laser diode bar having the plurality of emitters from the nitride semiconductor substrate.

Drawings

Fig. 1 is a schematic diagram of a wavelength beam coupling system according to an embodiment of the present disclosure.

Fig. 2 is a schematic diagram of a wavelength beam coupling system according to an embodiment of the present disclosure.

Fig. 3 is a perspective view of an LD bar according to one embodiment of the present disclosure.

Fig. 4 is a diagram showing a relationship between 1 LD bar and a diffraction grating according to one embodiment of the present disclosure.

Fig. 5 is a graph showing the locking wavelength of each emitter within the LD bar.

Fig. 6 is a graph showing a range of wavelengths in which the LD bar can oscillate.

Fig. 7 shows an example of ASE spectrum.

Fig. 8 is a graph showing the relationship between the gain peak wavelength and the lock wavelength.

Fig. 9 is a graph showing a relationship between a gain peak wavelength and a lock wavelength.

Fig. 10 is a view showing the principal axis direction of the off angle of the substrate according to one embodiment of the present disclosure.

Fig. 11 is a schematic diagram illustrating an LD bar on a wafer in a method for manufacturing an LD bar according to one embodiment of the present disclosure.

Fig. 12 is a schematic diagram illustrating an LD bar on a wafer in a method for manufacturing an LD bar according to one embodiment of the present disclosure.

Fig. 13 is a schematic diagram illustrating an LD bar on a wafer in a method for manufacturing an LD bar according to one embodiment of the present disclosure.

Fig. 14 is a schematic diagram showing an LD bar on a wafer in a conventional LD bar manufacturing method.

Fig. 15 is a schematic diagram showing an LD bar on a wafer in a conventional LD bar manufacturing method.

Fig. 16 is a schematic diagram illustrating an LD bar on a wafer in a method for manufacturing an LD bar according to one embodiment of the present disclosure.

Fig. 17 is a schematic diagram illustrating an LD bar on a wafer in a method for manufacturing an LD bar according to one embodiment of the present disclosure.

Fig. 18 is a schematic diagram illustrating an LD bar on a wafer in a method for manufacturing an LD bar according to one embodiment of the present disclosure.

Fig. 19 is a schematic diagram illustrating an LD bar on a wafer in a method for manufacturing an LD bar according to one embodiment of the present disclosure.

Fig. 20 is a schematic diagram illustrating an LD bar on a wafer in a method for manufacturing an LD bar according to one embodiment of the present disclosure.

Fig. 21 is a schematic diagram illustrating an LD bar on a wafer in a method for manufacturing an LD bar according to one embodiment of the present disclosure.

Description of the symbols

10. 10' wavelength beam coupling system

100 laser diode bar

100A laser diode bar array

101 implant region

200. 200' diffraction grating

300 external resonator mirror

400 wafer

Detailed Description

In the WBC system, if the difference between the gain peak wavelength of the LD bar (i.e., the oscillation wavelength of the LD bar due to the structure of the LD bar itself, also referred to as ASE (Amplified Spontaneous Emission) wavelength) and the lock wavelength by external resonance becomes large, there is a fear that the beam cannot oscillate. The WBC system becomes an inefficient system if only a part of the emitters among the plurality of emitters within the LD bar can be externally resonant-oscillated.

The present disclosure has been made in view of the above points, and an object thereof is to provide a laser diode bar capable of improving oscillation performance of a wavelength beam coupling system, a wavelength beam coupling system using the same, and a method for manufacturing the laser diode bar.

The present disclosure, which is the primary object of the present invention, is a laser diode bar for a wavelength beam coupling system, the laser diode bar including: a nitride semiconductor substrate having a (0001) plane as a plane orientation and a substrate plane to which an off-angle larger than 0 ° is given from the (0001) plane to at least one of an m-axis or an a-axis; a stacked structure formed on the nitride semiconductor substrate, the stacked structure including a 1 st-type-conductive-type-clad layer, an active layer, and a 2 nd-type-conductive-type-clad layer; and a plurality of emitters formed in a stripe shape in the laminated structure so that a waveguide direction of the emitters is perpendicular to a main axis direction of the off-angle.

In another aspect, a wavelength beam coupling system includes: the laser diode bar; a diffraction grating configured to diffract the plurality of laser beams emitted from the plurality of emitters of the laser diode bar, respectively; and an external resonance mirror that reflects a part of the laser light diffracted by the diffraction grating and returns the part to the laser diode bar side, and that externally resonates between the external resonance mirror and a reflection film of the laser diode bar.

In addition, another mode is a method for manufacturing a laser diode bar for a wavelength beam coupling system, the method including: preparing a nitride semiconductor substrate having a (0001) plane as a plane orientation and a substrate plane to which an off-angle larger than 0 ° is given from the (0001) plane to at least one of an m-axis and an a-axis; forming a stacked structure including a 1 st-conductivity-type clad layer, an active layer, and a 2 nd-conductivity-type clad layer on the nitride semiconductor substrate; forming a plurality of emitters arranged in a stripe shape in the stacked structure such that a major axis direction of an off-angle included in the nitride semiconductor substrate is perpendicular to a waveguide direction of the emitters; and a step of cutting out the laser diode bar having the plurality of emitters from the nitride semiconductor substrate.

According to the present disclosure, the oscillation performance of the wavelength beam coupling system can be improved.

Hereinafter, embodiments of the present disclosure will be described with reference to the drawings.

Fig. 1 is a schematic diagram of a wavelength beam coupling system 10. An actual wavelength Beam coupling (wbc) system has components other than those shown in fig. 1, but these components are omitted.

The WBC system 10 has a laser diode bar array (hereinafter also referred to as LD bar array) 100A including 1 or more LD bars 100, a diffraction grating 200, and an external resonator mirror 300. An optical system (not shown) such as a BTU may be provided between the LD bar 100 and the diffraction grating 200. The LD bar 100 constitutes a laser diode bar array 100A.

In the present embodiment, a transmission type diffraction grating is used as the diffraction grating 200, but the technique of the present disclosure can be applied to a WBC system 10 'using a reflection type diffraction grating 200' as shown in fig. 2.

In fig. 3, a perspective view of a laser diode bar (hereinafter also referred to as LD bar) 100 is shown. The LD bar 100 has a plurality of emitter implantation regions (hereinafter also referred to as emitters) 101 formed at intervals. The emitters are arranged in a row along the longitudinal direction of the LD bar 100 in a stripe shape. By supplying a voltage in parallel from a power supply unit (not shown) to all the emitters 101 in the LD bar 100, laser beams are simultaneously emitted from the laser elements corresponding to the emitters 101 in the waveguide direction (i.e., in the external resonance direction).

The emitter 101 of the LD bar 100 is formed on a stacked body of a 1 st conductivity type clad layer, an active layer, and a 2 nd conductivity type clad layer on, for example, a nitride semiconductor substrate. Further, the LD bar 100 has a P-side electrode on its upper surface and an N-side electrode (not shown in fig. 3) on its lower surface. Further, a transmissive film is provided on the entire end surface of the LD bar 100 on the side where light is emitted, and a reflective film (not shown in fig. 3) is provided on the entire end surface of the LD bar facing the transmissive film on the side where light is not emitted.

In fig. 3, a laser structure having a current injection region in a ridge stripe shape is shown, but another laser structure may be adopted. The LD bar 100 may have a buried structure, and in this case, the injection region 101 for current may be selectively formed.

In the WBC systems 10 and 10', the wavelength that satisfies the diffraction condition of the diffraction grating 200 and is vertically reflected by the external resonator mirror 300 among the light beams emitted from the emitters of the LD bar 100 is fed back to the original emitter, thereby generating external resonance and enabling laser oscillation.

The oscillation wavelength of each LD bar 100 and each emitter 101 is uniquely determined by the arrangement of the diffraction grating 200 and the LD bar 100. This wavelength is referred to as the lock wavelength.

If the difference between the gain peak wavelength of the LD bar 100 (i.e., the oscillation wavelength of the LD bar 100 due to the structure of the LD bar 100) and the locking wavelength by external resonance becomes large, the light beam is difficult to oscillate.

Here, in the diffraction grating 200, if the period of the diffraction grating is d, the incident angle is α, the output angle is β, the wavelength is λ, and the order is m, the diffraction condition of the diffraction grating 200 can be expressed by the following formula (1).

d (sin α + sin β) ═ m λ equation (1)

Here, a diffraction grating arrangement in which m is 1 is the number of times that is actually effective is selected.

Fig. 4 shows the relationship of 1 LD bar 100 to the diffraction grating 200. Fig. 5 shows an example of the locking wavelength of the WBC system 10 for each emitter 101 within 1 LD bar 100. In the example of fig. 5, 50 emitters 101 are formed in 1 LD bar 100, and the length from the 1 st emitter 101 to the 50 th emitter 101 (the length W of the LD bar 100 of fig. 4) is 10 mm.

When a diffraction grating (d is 0.333 μm) having a groove period of 3000 grooves/mm is used and light having a wavelength of 400 to 500nm is set so that the incident angle α is 45 °, when the length W of the LD bar 100 is 10mm and the distance L from the LD bar 100 to the diffraction grating is 2.6m, the difference Δ λ between the lock wavelengths between the emitters 101 at the both end positions of the LD bar 100 is set to be equal to or smaller than Δ λ_{EC_bar}(hereinafter referred to as "locking wavelength difference Δ λ of both end positions of LD bar 100_{EC_bar}") is computationally about 1.0 nm. Similarly, when the length W of the LD bar 100 is 10mm and the distance L from the LD bar 100 to the diffraction grating is 1.3m, the difference Δ λ between the lock wavelengths at the both end positions of the LD bar 100 is_{EC_bar}Is about 2.0 nm.

When the LD bar 100 is applied to the WBC system 10, the incident angle of the laser beam emitted from the emitter 101 to the diffraction grating 200 changes according to the position of the emitter 101 of the LD bar 100 in the longitudinal direction of the LD bar 100. Here, the locking wavelength of each emitter 101 in the LD bar 100 typically gradually decreases or increases along the length direction of the LD bar 100. For example, in a 10mm LD bar 100, the difference between the locking wavelength of the emitter 101 on one end side and the locking wavelength of the emitter 101 on the other end side is about 1 to 2 nm.

Fig. 6 shows a range of wavelengths at which one emitter 101 of the LD bar 100 can oscillate. The graph in fig. 6 is a gain spectrum (hereinafter also referred to as ASE spectrum) of the emitter 101, and shows the wavelength dependence of the gain of the LD bar 100. The wavelength at which the LD bar 100 can oscillate is limited to a wavelength at which the gain is a given value or more. In other words, the lock wavelength within a given range from the gain peak wavelength of the LD bar 100 oscillates, and the lock wavelength outside the given range does not oscillate. In the example of fig. 6, the lock wavelength 1 is within the range of the wavelength that can be oscillated and thus oscillates, and the lock wavelength 2 is outside the range of the wavelength that can be oscillated and thus does not oscillate.

Fig. 7 shows a typical example of the ASE spectrum of the emitter 101 of the LD bar 100. The ASE spectrum is defined as an EL spectrum (current-emission spectrum) before oscillation of the LD bar 100, and is defined as an injection current value I of 0.8 × I in the present disclosure_thTime of flight EL lightSpectra. I is_thIs the threshold current of the internal resonant oscillation of the LD bar 100. Lambda [ alpha ]_ASEIs the peak wavelength of the ASE spectrum.

A bandwidth B2W with a slice level (slice level) SL value of 0.8 or more based on the peak intensity of ASE spectrum_{ASE_bar}A bandwidth B1W of 3.2nm and SL value above 0.9_{ASE_bar}Is 1.2 nm. For achieving external resonance based laser oscillation with WBC systems 10, 10', at λ_ASE±(B2W_{ASE_bar}/2) i.e.. lambda_ASEIt is important that the locking wavelength based on external resonance is consistent in the range of ± 1.6 nm. Here, if the locking wavelength based on external resonance is located at λ_ASE±(B1W_{ASE_bar}/2) i.e.. lambda_ASEIn the range of ± 0.6nm, further high performance of the WBC systems 10 and 10' can be achieved.

Fig. 8 and 9 show the relationship between the gain peak wavelength (hereinafter also referred to as ASE wavelength) of each emitter 101 of the LD bar 100 and the lock wavelength by the WBC system 10. As described above, the lock wavelength has a slope corresponding to a change in the incident angle to the diffraction grating 200. In fig. 8 and 9, the distribution of the gain peak wavelength of each emitter 101 of the LD bar 100 has a different slope according to the difference in the manufacturing method of the LD bar 100 (described later with reference to fig. 10).

In the case where the distribution of the gain peak wavelengths in the LD bar 100 is in the same direction as the positive and negative of the slope of the lock wavelength as in the example of fig. 8, all the emitters 101 can be oscillated when the difference between the gain peak wavelength and the lock wavelength is within a predetermined range in all the emitters 101. In fig. 8, the slope of the distribution of the gain peak wavelength in the LD bar 100 is close to the slope of the distribution of the lock wavelength at each position along the longitudinal direction of the LD bar 100. Therefore, the gain peak wavelength of the emitters 101 exists in the vicinity of the lock wavelength at each position within the LD bar 100, and the output of each emitter 101 can be maximized.

In contrast, when a part of the distribution of the gain peak wavelength in the LD bar 100 is shifted from the range of the lock wavelength at the both end positions of the LD bar 100 as in the example of fig. 9, the emitter 101 which is a part outside the range cannot be oscillated.

In the example of fig. 9, the gain peak wavelengths of the emitters 101 of the LD bar 100 can be converged within the range of the lock wavelengths at the both end positions of the LD bar 100 by pulling up the distribution of the gain peak wavelengths in the LD bar 100 as a whole. However, even with this configuration, since the slope of the distribution of the gain peak wavelength in the LD bar 100 is smaller than the slope of the distribution of the lock wavelength at each position along the longitudinal direction of the LD bar 100, the emitter 101 whose output is reduced by the deviation of the gain peak wavelength from the lock wavelength is generated among the plurality of emitters 101 included in the LD bar 100.

From this point of view, the method for manufacturing the LD bar 100 according to the present disclosure realizes adjustment of the relationship between the formation direction of the emitter 101 and the main axis direction of the off angle of the nitride semiconductor substrate in order to adjust the distribution of the gain peak wavelength of each emitter 101 in the LD bar 100 as shown in fig. 8.

A method of manufacturing the LD bar 100 will be described with reference to fig. 10. In the manufacturing of the LD bar 100, first, a semiconductor laser stack structure including a light emitting layer is formed on a wafer 400 by epitaxial growth, then, a ridge bar structure is formed as an emitter 101 portion on the stacked wafer 400, and then, a P-side electrode and an N-side electrode are formed. Next, the plurality of LD bars 100 are cut out, and a high reflection coating film is formed on the rear end face and an anti-reflection coating film is formed on the front end face of the LD bar. Further, by combining the cut-out plurality of LD bars 100, a laser diode bar array 100A used by the WBC system 10 is produced.

As the wafer 400, a nitride semiconductor substrate, particularly a GaN substrate, is preferably used. When a semiconductor laser having a wavelength band of 350nm to 550nm is to be produced, a GaN substrate is preferably used as the base material wafer.

In general, a GaN substrate is inclined at a certain off-angle (about 0.3 ° to 0.7 ° greater than 0 °) with respect to a certain axis for the purpose of improving the crystal formation form of the active layer. In general, the substrate surface of the GaN substrate has a plane orientation of (0001), and the principal axis direction of the off angle (which represents the direction of inclination of the substrate surface with respect to the crystal plane having an off angle of 0 °. the same applies hereinafter) is set to the ± m-axis direction or the ± a-axis direction. In fig. 10, the principal axis direction of the off angle of the substrate surface of the wafer 400 is set to the + a axis direction.

Further, since the GaN substrate is formed by crystal growth using a different substrate having a different thermal expansion coefficient, crystal warpage is generally more likely to occur in the GaN substrate than in Si or GaAs. According to the findings of the inventors of the present application, when the GaN substrate is cut out from the bulk (ingot) by providing the off-angle in the (0001) plane of the GaN substrate due to the crystal warpage in the GaN substrate, the off-angle gradually increases along the main axis direction of the off-angle in the substrate plane of the GaN substrate as shown in fig. 10. The emission wavelength (i.e., the gain peak wavelength) of the semiconductor laser light during epitaxial growth of the InGaN layer is changed at a rate of 30nm/° depending on the change in the off-angle of the GaN substrate.

The off-angle distribution existing in the plane of the GaN substrate greatly affects the formation form of the light-emitting layer of the semiconductor laser, particularly the light emission wavelength. In general, when a semiconductor laser having a wavelength band of 350nm to 550nm is to be produced, an InGaN layer containing In is preferably used for the light-emitting layer. The In composition of the InGaN layer is affected by the off-angle distribution existing In the plane of the GaN substrate, and the In composition is small In a region with a large off-angle, and the oscillation wavelength tends to be short-wave.

That is, the emission wavelengths of the emitters 101 formed in the LD bar 100 are different from each other according to the off angle of the wafer 400 at the position where the emitter 101 is formed (see, for example, fig. 8 and 9).

Based on this finding, the inventors of the present application have conceived a technical idea of optimizing a method of manufacturing the LD bar 100 so that the LD bar 100 is formed such that the waveguide direction of the LD bar 100 is perpendicular to the major axis direction of the off angle of the substrate surface of the wafer 400.

According to this structure, the plurality of emitters 101 of the LD bar 100 can be arranged in a direction in which the off angle of the wafer 400 gradually decreases or increases, and thus the distribution of the emission wavelengths (gain peak wavelengths) of the plurality of emitters 101 can be gradually decreased or increased along the length direction of the LD bar 100. That is, with this, the distribution of the gain peak wavelength at each position in the longitudinal direction of the LD bar 100 can be inclined so as to match the slope of the distribution of the lock wavelength at each position in the longitudinal direction of the LD bar 100, and the gain peak wavelength can be made to exist in the vicinity of the lock wavelength in each emitter 101 of the LD bar 100 as shown in fig. 8. In addition, this allows all the emitters 101 of the LD bar 100 to oscillate, and further, maximizes the output of each emitter 101.

Further, according to this structure, the gain peak wavelengths can be made the same along the waveguide direction of the emitter 101. This can maximize the output of each emitter 101 of the LD bar 100.

Note that the principal axis direction of the off angle of the substrate surface of the LD bar 100 is perpendicular to the waveguide direction of the LD bar 100, and the principal axis direction of the off angle of the substrate surface may be an angle of approximately 90 ° with respect to the waveguide direction.

The results of verifying the performance of the LD bar 100 manufactured by the above-described manufacturing method will be described below.

< example 1>

In the present embodiment, the LD bar 100 is formed on a GaN substrate having a off-angle in which the main axis direction is the + a axis direction, the off-angle gradient is 0.004 °/mm, and the center off-angle is 0.46 ° as shown in fig. 10, so that the lock wavelength of each emitter 101 of the LD bar 100 is included in a range in which the gain peak wavelength of the emitter 101 of the LD bar 100 can oscillate. The LD bar 100 has a bar length of 10mm and the resonator length of 2 mm. As shown in fig. 10, since the major axis direction of the off-angle in the wafer 400 plane is the + a axis direction, the major axis direction of the off-angle exists in the longitudinal direction of the LD bar 100 cut out from the wafer 400.

Fig. 11 shows the peak wavelength λ of the ASE spectrum of each LD bar 100 according to the present embodiment_ASEThe distribution width in the longitudinal direction of the LD bar 100 (see the numerical values in each LD bar 100 in fig. 11). In the present embodiment, the locking wavelength difference Δ λ of both end positions of the LD bar 100_{EC_bar}Is 2.0 nm. LD bar 10The dimension of 0 in the longitudinal direction was 10 mm. λ for the emitter 101 of the LD stripe 100_ASELD bars 100 including the locking wavelength of the emitter 101 in the range of + -1.6 nm distribution, represented as hollow, are located at the center of each LD bar 100 and λ of the emitter 101 at both ends for the locking wavelength distribution_ASEThe LD bars 100 outside the range of ± 1.6nm distribution are represented as black.

In fig. 11, in all the LD bars (60 bars/60 bars) of the plurality of LD bars 100 formed in the wafer 400 plane, the lock wavelength distribution includes λ of the emitter 101 at the center and both ends of each LD bar 100_ASEIn the range of + -1.6 nm distribution. Therefore, the LD bar 100 manufactured using the wafer 400 can perform laser oscillation by external resonance.

Fig. 12 shows the peak wavelength λ of the ASE spectrum of each LD bar 100 formed on the wafer 400 by the present embodiment_ASEThe distribution width in the longitudinal direction of the LD bar 100 (see the numerical values in each LD bar 100 in fig. 12). In fig. 12, in the same wafer 400 as in the case of fig. 11, λ of the emitter 101 at the center and both ends of each LD bar 100 is set_ASEThe range of distribution of ± 0.6nm includes LD bars 100 of a locked wavelength distribution, indicated as hollow, λ of the emitter 101 located at the center and both ends of each LD bar 100 for the locked wavelength distribution_ASEThe LD bars 100 outside the range of ± 0.6nm distribution are represented as black. Locking wavelength difference Δ λ of both end positions of LD bar 100_{EC_bar}2.0nm and an LD stripe length of 10 mm.

In the wafer 400 plane of the present embodiment shown in fig. 12, λ of the emitter 101 having a locked wavelength distribution at the center and both ends of each LD bar 100 exists_ASELD stripes 100 outside the range of + -0.6 nm, but the LD stripes 100 of 81.7% (49 stripes/60 stripes) are hollow, i.e., λ of the emitter 101 at the center and both ends of each LD stripe 100_ASEThe range of ± 0.6nm distribution includes the LD bar 100 locking the wavelength distribution. Therefore, it is understood that the LD bar 100 capable of realizing the WBC systems 10 and 10' with higher performance can be obtained at a relatively high ratio.

In this example, the off-angle of the GaN wafer 400 is set to the + a-axis direction as the main axis direction, and there is almost no off-angle (0) in the m-axis direction, which is the waveguide direction0005 °/mm or less). Therefore, the LD bars 100 cut out from the wafer 400 shown in fig. 10 have the same peak wavelength λ of the ASE spectrum in the waveguide direction_ASE. Have the same lambda with respect to the waveguide direction by the LD bar 100_ASEThe gain of laser oscillation can be maximized. Therefore, by using such LD bar 100, the WBC systems 10 and 10' can be made more efficient and higher in output.

Fig. 13 shows the peak wavelength λ of the ASE spectrum of each LD bar 100 formed on the wafer 400 according to the present embodiment_ASEThe distribution width in the waveguide direction (refer to the numerical values in each LD bar 100 of fig. 13). In fig. 13, λ in the waveguide direction of 2mm length for the LD bar 100 in the wafer 400 plane_ASEλ of the emitter 101 distributed at the center and both ends of the LD bar 100_ASELD bars 100 in the range of ± 0.6nm are shown as empty and for LD bars 100 outside the range, are shown as black.

Referring to FIG. 13, λ in the waveguide direction within the wafer 400_ASEλ of the emitter 101 distributed at the center and both ends of the LD bar 100_ASEThere were 98% LD bands in the range of. + -. 0.6nm (59 bands/60 bands). Therefore, it is understood that λ in the waveguide direction can be obtained at a high ratio_ASEWhen the LD bar 100 is manufactured from the wafer 400, the LD bar 100 within a certain range can manufacture a high-quality LD bar 100 with a high yield.

As a product, particularly, it is preferable to use an LD bar 100 which is hollow in both fig. 12 and 13 among the LD bars 100 formed in the wafer 400. That is, it is particularly preferable that the locking wavelength distribution of the LD bar 100 is at λ_ASEPeak wavelength λ of ASE spectrum in the range of + -1.6 nm distribution and in the waveguide direction_ASEλ of the emitter 101 distributed at the center and both ends of the LD bar 100_ASEIn the range of + -0.6 nm. In addition, according to fig. 12 and 13, the LD bars 100 satisfying both conditions exist in 80% (48 bars/60 bars) in the wafer plane. Therefore, it is known that a very high-quality LD bar 100 capable of maximizing the output of the WBC system with a high yield can be obtained.

In fig. 14, LD bar according to the related art is shownIn the manufacturing method of (1), the peak wavelength λ of the ASE spectrum of each LD stripe formed on the wafer_ASEThe distribution width in the longitudinal direction of the LD bar 100 (see the numerical values in each LD bar 100 in fig. 14). In fig. 14, LD stripes were formed on a GaN substrate having a off-angle of 0.38 ° with a gradient of 0.009 °/mm in the main axis direction of the off-angle being + m-axis direction. The length of each LD stripe is 10mm, and the length of the resonator is 2 mm.

In fig. 14, λ of emitter 101 at the center and both ends of each LD bar in the wafer_ASEThe range of the distribution of ± 1.6nm includes LD bars of the locked wavelength distribution, indicated as hollow, for which λ of the emitter 101 located at the center and both ends of each LD bar_ASELD bars outside the range of the + -1.6 nm distribution, indicated as black. Locking wavelength difference Δ λ of both end positions of LD bar 100_{EC_bar}Is 2.0 nm. In the wafer plane of fig. 14, λ of the emitter 101 at the center and both ends of each LD bar_ASEThere were only 65% of LD bars in the range of ± 1.6nm distribution including the locking wavelength (39 bars/60 bars).

FIG. 15 shows the peak wavelength λ of the ASE spectrum of each LD stripe formed on the wafer in the method for manufacturing LD stripes according to the prior art, similarly to FIG. 14_ASEThe distribution width in the waveguide direction (refer to the numerical values in each LD bar 100 of fig. 15). In FIG. 15, the peak wavelength λ of the ASE spectrum in the 2mm long waveguide direction for the LD stripe in the wafer plane_ASEλ of the emitter 101 distributed at the center and both ends of each LD bar 100_ASELD bars 100 in the range of ± 0.6nm, are shown as empty, and for LD bars outside the range, are shown as black.

In the wafer of fig. 15, since the principal axis direction of the off-angle is the + m-axis direction, a wavelength distribution based on the off-angle distribution is generated in the manufactured LD bar. Therefore, a sufficient peak wavelength λ of the ASE spectrum cannot be obtained with respect to the waveguide direction_ASEIn the wafer plane of FIG. 15, λ is a peak wavelength of the ASE spectrum in the waveguide direction_ASEλ of the emitter 101 distributed at the center and both ends of the LD bar 100_ASEThe LD bars in the range of. + -. 0.6nm were only 81% (49 bars/60 bars).

According to fig. 14 and 15, the locking wavelength distribution of the LD bar 100 is at λ_ASEλ in the waveguide direction within a range of + -1.6 nm distribution_ASEλ of the emitter 101 distributed at the center and both ends of the LD bar 100_ASEThe LD bars 100 in the range of. + -. 0.6nm are only 55% (34 bars/60 bars). Therefore, in the manufacturing method according to the related art, the yield in manufacturing the high-quality LD bar 100 is reduced.

As described above, as is clear from comparison between the LD bar 100 formed by the manufacturing method according to the present embodiment and the LD bar formed by the manufacturing method according to the related art, by setting the main axis direction of the off angle of the substrate surface of the LD bar 100 to be perpendicular to the waveguide direction of the LD bar 100, a high-output LD bar 100 can be manufactured.

< example 2>

In this example, LD bar 100 was formed on a GaN wafer 400 having a slip angle of + a axis direction as a main axis direction, a slip angle gradient of 0.009 °/mm, and a center slip angle of 0.44 ° by the same method as in example 1. The LD bar 100 has a bar length of 10mm and a resonator length of 2mm, as in embodiment 1. This example is different from example 1 in that the gradient of the off-angle was set to 0.009 °/mm.

In fig. 16, λ of each LD bar 100 formed on the wafer 400 by the present embodiment is shown_ASEThe distribution width in the longitudinal direction of the LD bar 100 (see the numerical values in each LD bar 100 in fig. 16). Locking wavelength difference Δ λ of both end positions of LD bar 100_{EC_bar}Is 2.0 nm. In fig. 16, λ of the emitter 101 at the center and both ends of each LD bar 100_ASEThe range of distribution of ± 0.6nm includes LD bars 100 of a locked wavelength distribution, indicated as hollow, λ of the emitter 101 located at the center and both ends of each LD bar 100 for the locked wavelength distribution_ASEThe LD bars 100 outside the range of ± 0.6nm distribution are represented as black.

In the wafer 400 plane of the present embodiment shown in fig. 16, λ of the emitter 101 having a locked wavelength distribution at the center and both ends of each LD bar 100 exists_ASELD bars 100 outside the range of + -0.6 nm, but LD bars 100 of 73.3% (44 bars/60 bars) are hollow,that is, λ of the emitter 101 at the center and both ends of each LD bar 100_ASEThe range of ± 0.6nm distribution includes the LD bar 100 locking the wavelength distribution. Therefore, it is found that even when the off-angle gradient is set to 0.009 °/mm, the LD bar 100 of the WBC systems 10 and 10' capable of achieving higher performance at a relatively high ratio can be obtained.

In fig. 17, λ of each LD bar 100 formed on the wafer 400 by the present embodiment is shown_ASEThe distribution width in the waveguide direction (see the numerical values in each LD bar 100 of fig. 17). In fig. 17, λ in the waveguide direction of 2mm length for the LD bar 100 in the wafer 400 plane_ASEλ of the emitter 101 distributed at the center and both ends of each LD bar 100_ASELD bars in the range of ± 0.6nm, indicated as open, for LD bars 100 outside the range, indicated as black.

Referring to FIG. 17, λ in the waveguide direction within the wafer 400_ASEλ of the emitter 101 distributed at the center and both ends of the LD bar 100_ASEThere were 86.7% LD stripes 100 (52 stripes/60 stripes) in the range of 0.6 nm. Therefore, it is understood that λ in the waveguide direction can be obtained at a high ratio_ASEWhen the LD bar 100 is manufactured from the wafer 400, the LD bar 100 within a certain range can manufacture a high-quality LD bar 100 with a high yield.

In addition, the LD bar 100 indicated as hollow in both fig. 16 and 17 among the LD bars 100 formed in the wafer 400 plane, that is, the LD bar 100 satisfies that the locking wavelength distribution of the LD bar 100 is at λ_ASEλ in the range of + -1.6 nm distribution and in the waveguide direction_ASEλ of the emitter 101 distributed at the center and both ends of the LD bar 100_ASELD stripes 100 in the range of + -0.6 nm, there are 61.7% (38 stripes/60 stripes) within wafer 400. Therefore, it is known that a very high-quality LD bar 100 capable of maximizing the output of the WBC systems 10, 10' can be obtained with a high yield.

In examples 1 and 2, the principal axis direction of the slip angle of the wafer 400 forming the LD bar 100 is the + a axis direction, the slip angle gradient is 0.004 to 0.009 °/mm, and the bar length of the LD bar 100 and the resonator length are 10mm and 2mm, respectively, but the slip angle gradient can be appropriately adjusted to be used for various bar lengths of the LD bar 100.

In order to optimize the WBC systems 10 and 10', the gradient Δ D of the angle of departure in the longitudinal direction of the LD bar 100 is preferably set to be within the range of the following formula (2).

0＜ΔD≤((Δλ_{EC_bar}+3.2)/Lt)/30 formula (2)

(wherein Lt (mm) is the length of the LD bar 100. DELTA.. lamda. (mm))_{EC_bar}Is a locking wavelength difference (nm) of both end positions of the LD bar 100)

Further, for constructing a high-performance WBC system 10, 10', it is preferable to set the deviation angle gradient Δ D to be within the range of the following formula (3) with respect to the longitudinal direction of the LD bar 100.

((Δλ_{EC_bar}-1)/Lt)/0.3≤ΔD≤((Δλ_{EC_bar}+1)/Lt)/30 formula (3)

The above-described formulas (2) and (3) are preferable conditions when the following formula (4) is satisfied.

0≤((Δλ_{EC_bar}-1.2)/Lt)/30 formula (4)

In the state of the following expression (5), the WBC systems 10 and 10' may be set so that the difference in the lock wavelength between the positions of both ends of the LD bar 100 falls within the range of the following expression (6).

0＞((Δλ_{EC_bar}-1.2)/Lt)/30 formula (5)

0＜ΔD≤((Δλ_{EC_bar}+1.2)/Lt)/30 formula (6)

In addition, from the viewpoint of obtaining a high-quality LD bar 100 that can maximize the output of the WBC systems 10 and 10', the off-angle gradient Δ D preferably satisfies both the expressions (2) and (3) or both the expressions (2) and (4).

< example 3>

In this example, LD bars 100 were formed on a GaN wafer 400 having an off-angle of 0.46 ° with a gradient of 0.004 °/mm in the off-angle direction of the main axis as + a axis, by the same method as in example 1. Further, the length of the LD bar 100 was 10mm as in example 1. This embodiment is different from embodiment 1 in that the resonator length of the LD bar 100 is set to 1 mm.

Fig. 18 shows λ of each LD bar formed on the wafer 400 by the present embodiment_ASEThe distribution width in the waveguide direction (refer to the numerical values in each LD bar 100 of fig. 18). In fig. 18, λ in the waveguide direction of 2mm length for the LD bar 100 in the wafer 400 plane_ASEλ of the emitter 101 distributed at the center and both ends of each LD bar 100_ASELD bars 100 in the range of ± 0.6nm are shown as empty and for LD bars 100 outside the range, are shown as black.

As shown in fig. 18, λ in the waveguide direction with respect to the LD bar 100 having a resonator length of 1mm_ASESmall distribution, λ in the waveguiding direction in the plane of the wafer 400_ASEλ of the emitter 101 distributed at the center and both ends of the LD bar 100_ASELD bars in the range of. + -. 0.6nm were 100% (120 bars/120 bars). Therefore, it was found that λ in the waveguide direction can be obtained at a high ratio even when the resonator length is 1mm_ASEWhen the LD bar 100 is manufactured from the wafer 400, the LD bar 100 within a certain range can manufacture a high-quality LD bar 100 with a high yield.

< example 4>

In this example, LD bars 100 were formed on a GaN wafer 400 having an off-angle of 0.46 ° with a gradient of 0.004 °/mm in the off-angle direction of the main axis as + a axis, by the same method as in example 1. The length of the LD bar 100 is 10mm as in embodiment 1. This embodiment is different from embodiment 1 in that the resonator length of the LD bar 100 is set to 4 mm.

Fig. 19 shows λ of each LD bar formed on the wafer 400 by the present embodiment_ASEThe distribution width in the waveguide direction (see the numerical values in each LD bar 100 in fig. 19). In fig. 19, λ in the waveguide direction of 2mm length for the LD bar 100 in the wafer 400 plane_ASEλ of the emitter 101 distributed at the center and both ends of each LD stripe_ASELD bars in the range of ± 0.6nm, indicated as open, for LD bars outside the range, indicated as black.

As shown in fig. 19, for the LD bar 100 having a resonator length of 4mm, in the wafer 400 plane, the waveguide direction isλ of_ASEλ of the emitter 101 distributed at the center and both ends of the LD bar 100_ASEThere were also 90% LD bars in the range of + -0.6 nm (27 bars/30 bars). Therefore, it was found that λ in the waveguide direction can be obtained at a high ratio even when the resonator length is 4mm_ASEWhen the LD bar 100 is manufactured from the wafer 400, the LD bar 100 within a certain range can manufacture a high-quality LD bar 100 with a high yield.

< example 5>

In this example, LD bars 100 were formed on a GaN wafer 400 having an off-angle of 0.46 ° with a gradient of 0.004 °/mm in the off-angle direction of the main axis as + a axis by the same method as in embodiment 1. The length of the LD bar 100 was 10mm in the same manner as in example 1. This embodiment is different from embodiment 1 in that the resonator length of the LD bar 100 is set to 6 mm.

Fig. 20 shows λ of each LD bar formed on the wafer 400 by the present embodiment_ASEThe distribution width in the waveguide direction (refer to the numerical values in each LD bar 100 of fig. 20). In fig. 20, λ in the waveguide direction of 2mm length for the LD bar 100 in the wafer 400 plane_ASEλ of the emitter 101 distributed at the center and both ends of each LD bar 100_ASELD bars 100 in the range of ± 0.6nm are shown as empty and for LD bars 100 outside the range, are shown as black.

As shown in fig. 20, for the LD bar 100 having a resonator length of 6mm, λ in the waveguide direction in the wafer 400 plane_ASEλ of the emitter 101 distributed at the center and both ends of the LD bar 100_ASEThere were also 78% LD bars 100 in the range of + -0.6 nm (14 bars/18 bars). Therefore, it was found that λ in the waveguide direction can be obtained at a high ratio even when the resonator length is 6mm_ASEWhen the LD bar 100 is manufactured from the wafer 400, the LD bar 100 within a certain range can manufacture a high-quality LD bar 100 with a high yield.

< example 6>

In this example, LD bars 100 were formed on a GaN wafer 400 having an off-angle of 0.46 ° with a gradient of 0.004 °/mm in the off-angle direction of the main axis as + a axis, by the same method as in example 1. The length of the LD bar 100 was 10mm in the same manner as in example 1. This embodiment is different from embodiment 1 in that the resonator length of the LD bar 100 is set to 8 mm.

Fig. 21 shows λ of each LD bar 100 formed on the wafer 400 by the present embodiment_ASEThe distribution width (in the waveguide direction) in each LD bar 100 (see the numerical values in each LD bar 100 in fig. 21). In fig. 21, λ in the waveguide direction of 2mm length for the LD bar 100 in the wafer 400 plane_ASEλ of the emitter 101 distributed at the center and both ends of each LD stripe_ASELD bars in the range of ± 0.6nm, indicated as open, for LD bars outside the range, indicated as black.

As shown in fig. 21, for the LD bar 100 having a resonator length of 8mm, λ in the waveguide direction in the wafer 400 plane_ASEλ of the emitter 101 distributed at the center and both ends of the LD bar 100_ASEThere were also 64% LD bars in the range of + -0.6 nm (9 bars/14 bars). Therefore, it was found that λ in the waveguide direction can be obtained at a high ratio even when the resonator length is 8mm_ASEWhen the LD bar 100 is manufactured from the wafer 400, the LD bar 100 within a certain range can manufacture a high-quality LD bar 100 with a high yield.

In embodiments 1 to 6 described above, the LD bar 100 having the resonator length in the range of 1mm to 8mm is manufactured, and the laser oscillation is realized by the external resonance, thereby constructing the WBC systems 10 and 10'. Considering that a typical resonator length used in a normal internal-resonance type single LD is about 0.3mm to 1mm, it is known that laser oscillation can be achieved by external resonance when the resonator length is 0.3mm or more. In addition, according to embodiments 1 to 6, it is desirable that the resonator length is 1mm or more and 6mm or less from the viewpoint of yield.

Industrial applicability

The laser diode bar and the wavelength beam coupling system can improve the oscillation performance of the wavelength beam coupling system, and therefore can be applied to a processing system with higher power.