JP2021118307A - Laser diode bar and wavelength beam coupling system - Google Patents

Abstract

To provide a laser diode bar and a wavelength beam coupling system capable of contributing to the efficiency of a wavelength beam coupling system by improving the oscillation performance of the wavelength beam coupling system.SOLUTION: A disclosed laser diode bar 100 has injection regions 101 of n (n≥2) emitters formed at intervals from each other. When the array direction of the injection region 101 is the X coordinate, the center position of the array direction is the origin of the X coordinate, the X coordinate of each injection region 101 is Xi (i=1 to n), and the area of each injection region 101 is Si (i=1 to n), the injection region 101 is formed so as to satisfy the following inequality.SELECTED DRAWING: Figure 9

Description

The present disclosure relates to laser diode bars used in wavelength beam coupling systems.

A wavelength beam combining system (WBC (Wavelength Beam Combining) system) is known as a system for obtaining a high-power laser beam by combining a plurality of beams having different wavelengths at one point. The WBC system is described in, for example, Patent Document 1 and the like.

The WBC system includes a laser diode bar (LD (Laser Diode) bar), a beam twister unit (BTU (Beam Twister Lens Unit)), a diffraction grating, an external resonance mirror, and the like.

The LD bar emits beams from a plurality of emitters. The plurality of beams emitted from the LD bar are individually rotated by 90 degrees by the BTU. This makes it possible to prevent the individual spots from interfering with each other. The beam emitted from the BTU is incident on a transmission type or reflection type diffraction grating. The diffraction grating diffracts the incident beam at a diffraction angle determined by its wavelength and emits it. The beam emitted from the diffraction grating is incident on the external resonant mirror. The external resonant mirror is a partially transmissive mirror that reflects part of the incident beam perpendicular to the direction of the diffraction grating. As a result, only the wavelength (called the lock wavelength) uniquely determined by the positional relationship between the individual emitters of the LD bar, the diffraction grating, and the external resonance mirror is fed back between the rear mirror and the external resonance mirror of the LD bar. A laser beam is output by external resonance oscillation.

Japanese Unexamined Patent Publication No. 2015-106707

By the way, in the WBC system, if the difference between the gain peak wavelength of the LD bar (that is, the oscillation wavelength of the LD bar due to the configuration of the LD bar itself) and the lock wavelength due to external resonance becomes large, the beam cannot oscillate. Conventionally, in a WBC system using a plurality of LD bars, each LD bar is designed and manufactured so as to optimize the gain peak wavelength of each LD bar according to the arrangement position of each LD bar.

However, the gain peak wavelength in one LD bar has not been sufficiently studied, and as a result, there is a possibility that external resonance oscillation can be performed only in a part of the plurality of emitters in the LD bar. In this case, the WBC system becomes an inefficient system.

The present disclosure has been made in consideration of the above points, and provides a laser diode bar and a wavelength beam coupling system that can improve the oscillation performance of the wavelength beam coupling system and contribute to the efficiency of the wavelength beam coupling system.

One aspect of the laser diode bar of the present disclosure is:
A laser diode bar used in wavelength beam coupling systems.
The laser diode bar has injection regions of n (n ≧ 2) emitters formed at intervals from each other.
The arrangement direction of the injection region is the X coordinate, the center position in the arrangement direction is the origin of the X coordinate, the X coordinate of each injection region is Xi (i = 1 to n), and the area of each injection region is Si ( When i = 1 to n), the injection region is formed so as to satisfy the following equation.

One aspect of the wavelength beam coupling system of the present disclosure is:
It is a wavelength beam coupling system that combines multiple beams with different wavelengths at one point.
With the laser diode bar
A diffraction grating that diffracts a plurality of beams emitted from the laser diode bar, and
An external resonance mirror that feeds back a part of the beam diffracted by the diffraction grating to the laser diode bar to cause external resonance.
To be equipped.

According to the present disclosure, it is possible to improve the oscillation performance of the wavelength beam coupling system and contribute to the efficiency of the wavelength beam coupling system.

Schematic diagram of WBC system Schematic diagram of WBC system (in the case of reflective diffraction grating) Perspective view showing the configuration of one LD bar The figure which shows the relationship between one LD bar and a diffraction grating The figure which showed the example of the lock length of the WBC system for each emitter in one LD bar. The figure which shows the range of the wavelength that the LD bar can oscillate. The figure which showed the relationship between the gain peak wavelength of each emitter of an LD bar and the lock wavelength by a WBC system. The figure which showed the relationship between the gain peak wavelength of each emitter of an LD bar and the lock wavelength by a WBC system. It is a figure which shows the schematic structure of the LD bar used for the explanation of embodiment, FIG. 9A is a plan view, and FIG. 9B is a cross-sectional view. The figure which shows the relationship between the positive direction of the X coordinate of FIG. 9 and the angle of incidence on the diffraction grating of the WBC system. It is a figure which shows the schematic structure of the LD bar used for the explanation of embodiment, FIG. 11A is a plan view, and FIG. 11B is a cross-sectional view. 12A-12E are diagrams provided for explaining the electrode width in the embodiment. Diagram showing an example of a data plot for performing a simulation Diagram showing simulation results The figure which showed the distribution example of an ideal electrode width The figure which shows the injection region by another embodiment

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

<1> Background to the present invention First, before explaining the embodiment of the present invention, the background to the present invention will be described.

FIG. 1 is a schematic view of the WBC system 10. Of course, the actual WBC system has components other than those shown in FIG. 1, but they are omitted.

The WBC system 10 has a plurality of LD bars 100, a transmission type diffraction grating 200, and an external resonance mirror 300. Actually, an optical system such as BTU (not shown) is provided between the LD bar 100 and the diffraction grating 200.

Although the transmission type diffraction grating 200 is used in the present embodiment, the technique of the present disclosure can also be applied to the WBC system 10'using the reflection type diffraction grating 200'as shown in FIG. ..

FIG. 3 shows the configuration of one LD bar 100. The LD bar 100 has injection regions (which may be referred to as electrodes) 101 of n (n ≧ 2) emitters formed at intervals from each other. The injection regions 101 are arranged in stripes along the longitudinal direction of the LD bar 100. By supplying a voltage in parallel to all the injection regions 101 in the LD bar 100 from a power supply unit (not shown), a laser beam is simultaneously emitted from the laser element corresponding to each injection region 101 in the external resonance direction.

It will be described back to FIG. The WBC system 10 has the following features.

-Of the beams emitted from the LD bar 100, only the wavelengths that satisfy the diffraction conditions of the diffraction grating 200 and are reflected by the external resonance mirror 300 can be oscillated by the external resonance.

The oscillation wavelength of each LD bar 100 and each emitter corresponding to the injection region 101 is uniquely determined by the arrangement of the diffraction grating 200 and the LD bar 100.

-If the difference between the gain peak wavelength of the LD bar 100 (that is, the oscillation wavelength of the LD bar 100 due to the configuration of the LD bar 100 itself) and the lock wavelength due to external resonance becomes large, the beam cannot oscillate.

Here, in the diffraction grating 200, assuming that the period of the diffraction grating is d, the incident angle is α, the emission 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 equation. ..

Here, it is common to select a diffraction grating arrangement in which the actually effective order is only m = 1.

In the conventional WBC system, in order to satisfy this diffraction condition, as shown in FIG. 1, the LD bar 100 generates a beam having a longer wavelength as the LD bar 100 having a smaller incident angle α on the diffraction grating 200. Designed and manufactured to do.

The same applies to the emitters arranged in one LD bar 100. That is, as shown in FIG. 3, one LD bar 100 should be designed and manufactured so that an emitter having a smaller incident angle α on the diffraction grating 200 generates a beam having a longer wavelength.

That is, even within one LD bar, the angle of incidence α of the beam emitted from each emitter in the LD bar on the diffraction grating 200 changes minutely. Therefore, in order to sufficiently satisfy the external resonance condition, the LD bar is required. The gain peak wavelengths should be slightly different for the plurality of emitters within 100.

FIG. 4 is a diagram showing the relationship between one LD bar 100 and the diffraction grating 200. FIG. 5 is a diagram showing an example of the lock wavelength of the WBC system 10 for each emitter in one LD bar 100. In the example of the figure, 50 emitters are formed in one LD bar 100, and the length from the first emitter to the 50th emitter (length W of the LD bar 100 in FIG. 4) is 10 [mm]. This is an example.

In calculation, when the length W of the LD bar 100 is 10 [mm] and the distance L from the LD bar 100 to the diffraction grating is 2.6 [m], the difference in the lock wavelengths of the emitters at both ends of the LD bar 100 is Δλ _{EC_bar.} Is about 1.0 [nm]. Further, in calculation, when the length W of the LD bar 100 is 10 [mm] and the distance L from the LD bar 100 to the diffraction grating is 1.3 [m], the difference between the lock wavelengths of the emitters at both ends of the LD bar 100. Δλ _{EC_bar} is about 2.0 [nm].

FIG. 6 is a diagram showing a range of wavelengths at which the LD bar 100 can oscillate. The curve in the figure shows the gain of the LD bar 100. The LD bar 100 can oscillate only at wavelengths whose gain is equal to or higher than a predetermined value. In other words, the lock wavelength within a predetermined range from the gain peak wavelength of the LD bar 100 oscillates, and the lock wavelength outside the predetermined range does not oscillate. In the example of the figure, the lock wavelength 1 oscillates because it is within the oscillating wavelength range, but the lock wavelength 2 does not oscillate because it is outside the oscillating wavelength range.

7 and 8 show the relationship between the gain peak wavelength of each emitter of the LD bar 100 and the lock wavelength of the WBC system 10. As described above, the lock wavelength has a slope corresponding to a change in the angle of incidence on the diffraction grating 200.

As in the example of FIG. 7, when the distribution of the gain peak wavelength of the emitter in the LD bar 100 is in the same direction as the positive and negative of the slope of the lock wavelength, the difference between the gain peak wavelength and the lock wavelength is different in all the emitters. Since it is within a predetermined range, all emitters can be oscillated.

On the other hand, as in the example of FIG. 8, when the distribution of the gain peak wavelength of the emitter in the LD bar 100 is in a direction different from the positive / negative of the slope of the lock wavelength, the gain peak wavelength is used in some emitters. Since the difference from the lock wavelength is out of the predetermined range, some emitters cannot be oscillated.

Incidentally, conventionally, the gain peak wavelengths of the emitters are almost the same in the same LD bar. Therefore, in a graph such as FIG. 7 and FIG. 8, it is represented as a straight line having a slope of 0. Therefore, in relation to the tilted lock wavelength, oscillation may not occur at the emitter near the end.

The inventor of the present invention has reached the present disclosure based on such consideration.

One feature of the present disclosure is the temperature distribution in the LD bar so that the distribution of the gain peak wavelength of the emitter in the LD bar is inclined so as to correspond to the inclination of the lock wavelength in the LD bar generated in the WBC system. It is to have. More specifically, the gain peak of the emitter in the LD bar is controlled by controlling the temperature of the emitter in the LD bar by utilizing the fact that the wavelength of the emitted beam becomes longer as the temperature of the emitter is higher. The wavelength distribution is tilted.

<2> Embodiment FIG. 9 is a diagram showing a schematic configuration of the LD bar 100 used for the description of the embodiment, FIG. 9A is a plan view of the LD bar 100, and FIG. 9B is A- of the LD bar 100. A'Cross section.

As shown in the figure, the arrangement direction of the injection region 101 of the emitter is the X-axis direction (X coordinate). Further, the center position in the array direction is set as the origin of the X coordinate. The center position may be simply the center position of the length of the LD bar 100 in the longitudinal direction (arrangement direction of the injection regions 101), or may be a position where the same number of injection regions 101 exist on both sides. Further, the center position may be the center position of the injection regions 101 at both ends.

Further, in the present embodiment, the intervals of the injection regions 101 in the arrangement direction are equal intervals.

The injection region 101 of the LD bar 100 of the present embodiment has the X coordinates of each injection region (1 to n) 101 (for example, the center position in the array direction of each injection region 101) as Xi, and each injection region (1 to n). When the area of is Si, it is formed so as to satisfy the following equation.

By doing so, the injection region 101 of the LD bar 100 of the present embodiment has an area biased in the positive direction from the center position. Here, as described above, since the voltage is supplied in parallel to all the injection regions 101 in the LD bar 100 from the power supply unit (not shown), the current supplied to the emitter is proportional to the area of the injection region 101. The size is decided, and the temperature is also decided. Therefore, under the condition of the equation (3), the temperature of the emitter is higher in the positive direction than in the central position than in the negative direction, and a beam having a long wavelength is emitted.

Here, as shown in FIG. 10, the positive direction of the X coordinate in FIG. 9 is the angle between the incident direction from each emitter of the LD bar 100 to the diffraction grating 200 and the exit direction from the diffraction grating 200 (< 180 °) corresponds to the decreasing direction

Thus, according to the present embodiment, by forming the injection region 101 that satisfies the condition of the equation (3), the distribution of the gain peak wavelength of the emitter in the LD bar 100 can be distributed as in the example of FIG. , The slope of the lock wavelength and the positive and negative directions can be the same. As a result, the difference between the gain peak wavelength and the lock wavelength of all the emitters can be kept within a predetermined range, so that all the emitters can be oscillated.

The above-described embodiments are merely examples of embodiment of the present invention, and the technical scope of the present invention should not be construed in a limited manner by these. That is, the present invention can be implemented in various forms without departing from its gist or its main features.

As shown in FIG. 11, if the lengths D of the plurality of injection regions 101 are the same, the equation (3) is equivalent to the following equation when the width of each injection region (1 to n) is Wi. ..

Therefore, if the injection region 101 that satisfies the condition of the equation (4) is formed, the same effect as that of the above-described embodiment can be obtained.

Further, even when the injection region 101 is formed as illustrated in FIG. 12, the same effect as that of the above-described embodiment can be obtained. The positive direction of the emitter position in FIGS. 12A-12E is the angle (<180 °) between the incident direction from each emitter of the LD bar 100 to the diffraction grating 200 and the exit direction from the diffraction grating 200 as described above. ) Is decreasing. .. Further, the electrode corresponds to the injection region 101, and thus the electrode width corresponds to the width (stripe width) Wi of the injection region 101.

FIG. 12A is an example in which the electrode width of the emitter is linearly increased in the direction in which the angle of incidence on the diffraction grating 200 decreases. 12B and 12C are examples in which the electrode width is gradually increased. FIG. 12D is an example in which the electrode width is linearly increased and then constant near the end. FIG. 12E shows an example in which the degree of increase in the electrode width is increased near the end portion.

FIG. 13 is an example of a data plot for performing a simulation. The point of "Ref" in the figure is an example in which the electrode width is constant as in the conventional case. In FIG. 13, the points corresponding to FIGS. 12A, 12C, 12D, and 12E are also plotted.

FIG. 14 shows the simulation results. The emitter temperature of the conventional configuration "Ref" is almost constant at all emitter positions, only the temperature of the emitters in the vicinity of both ends where heat dissipation is large is lowered.

On the other hand, the emitter temperature of the configurations of FIGS. 12C and 12E tends to increase as the emitter No. increases (that is, the emitter at a position where the angle of incidence α on the diffraction grating 200 decreases). As a result, the distribution of the gain peak wavelength of the emitter in the LD bar 100 can be set so that the positive and negative slopes of the lock wavelength and the positive and negative slopes are in the same direction.

FIG. 15 is a diagram showing a fairly ideal distribution example of the electrode width, which is the same as the plot of the legend (FIG. 12E) in FIG. As shown in the figure, the electrode width tends to increase monotonically toward the emitter at the position where the angle (<180 °) formed by the incident direction to the diffraction grating 200 and the exit direction 200 decreases, and the end of the LD bar 100. It is preferable that the electrode width of the nearby emitter increases monotonically toward the end. By making the electrode width of the emitter near the end of the LD bar 100 monotonically increasing toward the end, it is possible to suppress a decrease in temperature near the end of the LD bar 100, which has a large heat dissipation. Become.

In other words, the area of the injection region 101 is monotonous in the direction corresponding to the direction in which the angle (<180 °) formed by the incident direction to the diffraction grating 200 and the exit direction decreases in the arrangement direction of the injection region 101. It is preferable that the area of the injection region monotonically increases toward the ends at both ends of the injection region 101 in the arrangement direction.

In a preferred embodiment of the present embodiment, as shown in the legend of FIG. 14 (FIG. 12E), the operating wavelength of the laser element (emitter) corresponding to each injection region 101 is the injection region in the positive direction of the X coordinate (FIG. 9). It increases almost monotonously from end to end in the arrangement direction of 101.

As shown in FIG. 16, instead of changing the width of the injection region (electrode) 101, the length of the injection region (electrode) 101 may be changed. The "positive direction" in FIG. 16 corresponds to the "positive direction" in FIG.

In the present embodiment, the case where the intervals of the injection regions 101 in the arrangement direction are equal intervals has been described, but the intervals may not be equal.

However, since a multi-emitter compatible optical element called BTU is generally used in the WBC system, the manufacturing accuracy of the lens may not be established unless the intervals between the injection regions 101 are equal. Considering this, it can be said that it is preferable to change the injection area at equal intervals when the injection area is used by incorporating it into the WBC system.

By providing a dummy resistor at at least one end of the LD bar 100 in the arrangement direction (X-axis direction), a temperature drop near the end of the LD bar 100 may be suppressed.

In all the embodiments so far, the WBC system 10 using the transmission type diffraction grating 200 as shown in FIG. 1 has been described, but the WBC using the reflection type diffraction grating 200'as shown in FIG. 2 has been described. Since the same relationship holds in the case of the system 10', it is possible to improve the performance of the WBC system 10'using the reflection type diffraction grating 200'by using the same LD bar.

The laser diode bar of the present invention is suitable for wavelength beam coupling systems.

10, 10'wavelength beam coupling system (WBC system)
100 laser diode bar (LD bar)
101 Injection area 200, 200'diffraction grating 300 External resonant mirror

Claims (7)

A laser diode bar used in wavelength beam coupling systems.
The laser diode bar has injection regions of n (n ≧ 2) emitters formed at intervals from each other.
The arrangement direction of the injection region is the X coordinate, the center position in the arrangement direction is the origin of the X coordinate, the X coordinate of each injection region is Xi (i = 1 to n), and the area of each injection region is Si ( When i = 1 to n), the injection region is formed so as to satisfy the following equation.

Laser diode bar. The positive direction of the X coordinate corresponds to the direction in which the angle (<180 °) formed by the incident direction from each emitter of the laser diode bar to the diffraction grating and the exit direction from the diffraction grating decreases.
The laser diode bar according to claim 1. The operating wavelength of the laser element corresponding to each injection region monotonically increases from end to end in the array direction in the positive direction of the X coordinate.
The laser diode bar according to claim 1 or 2. At both ends in the arrangement direction, the area of the injection region monotonously increases toward the ends.
The laser diode bar according to any one of claims 1 to 3. The spacing between the injection regions in the alignment direction is equal.
The laser diode bar according to any one of claims 1 to 4. A dummy resistor is provided at at least one end in the arrangement direction.
The laser diode bar according to any one of claims 1 to 5. The laser diode bar according to any one of claims 1 to 6.
A diffraction grating that diffracts a plurality of beams emitted from the laser diode bar, and
An external resonance mirror that feeds back a part of the beam diffracted by the diffraction grating to the laser diode bar to cause external resonance.
A wavelength beam coupling system that combines multiple beams with different wavelengths into a single point.

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