CN201985432U - Off-axis spectrum beam combination device for a laser diode array - Google Patents

Abstract

The utility model relates to an off-axis spectrum beam combining device of a laser diode array, which comprises a laser diode array and a fast-axis collimating mirror; There is a second lens and a high reflective mirror, and the high reflective mirror forms an off-axis off-axis feedback cavity with the second lens, the first lens and the rear end surface of the diode array; An output coupling mirror is arranged between the first lens, and a spectral beam structure is formed between the output coupling mirror, the diffraction grating and the first lens; the light emitted upward by the laser diode array is compressed by the first lens and the second lens to reach a high Reflective mirrors, those parallel to the high reflective mirrors are found to be reflected to the fast axis collimating mirror, the light emitted by the laser diode array is directed to the diffraction grating through the lower part of the first lens, and after being diffracted by the diffraction grating, it passes through the output coupling mirror, and part of the light is along the The original path is fed back to the active area of the diode array, and part of it is output as laser. The utility model has a simple and compact structure, can improve the beam quality of the two-dimensional laser diode array, and is safe and reliable.

Description

Off-axis Spectral Beaming Device of Laser Diode Array

technical field

The utility model relates to a spectrum beam combining device, in particular to an off-axis spectrum beam combining device of a laser diode array.

Background technique

High-power laser diode arrays have the advantages of high efficiency, compact structure, and long service life, so they have been widely used in many fields, such as industry, military, and medical fields (Opt. Express 12, 609). However, the beam quality in the direction of the slow axis of the diode array is relatively poor, about 1000 times the diffraction limit (Opt. Lett. 21, 375-377). This restricts the application of high-power laser diode arrays in many fields, such as pumping solid-state or fiber lasers. Spectral beam combining technology (Opt. Lett. 30, 2104-2106; Appl.Phys.B 83 225-228) is also a very effective method to improve the beam quality of diode arrays; its core idea is to sacrifice the width of the spectrum to Improve beam quality. Another method to improve the beam quality of the diode array is the off-axis external cavity feedback technology (Opt. Lett. 29, 361-363), which uses a strip plane mirror as the feedback element, and optimizes the optimum beam quality by changing the inclination angle of the strip plane mirror. Optimum feedback angle, so as to obtain laser output with good beam quality. At present, the off-axis spectral beam assembly device is mainly used to improve the beam quality of the one-dimensional laser array, but the output laser power of the one-dimensional laser diode array is relatively low, which limits the application in actual production.

Contents of the invention

The purpose of the utility model is to overcome the deficiencies in the prior art, and provide an off-axis spectrum beam combining device of a laser diode array, which has a simple and compact structure, can improve the beam quality of a two-dimensional laser diode array, and is safe and reliable.

According to the technical solution provided by the utility model, the off-axis spectral beam combining device of the laser diode array includes a laser diode array and a fast axis collimating mirror located in the fast axis direction of the laser diode array; the feature is: the fast The axis collimating mirror is corresponding to the other side that is connected with the laser diode array to be provided with the first lens, and the back upper part of described first lens is provided with the second lens and high reflection mirror successively, and described high reflection mirror and second lens and The first lens and the rear end surface of the laser diode array form an off-axis external feedback cavity; a diffraction grating is arranged at the rear and lower part of the first lens, and an output coupling mirror is arranged between the diffraction grating and the first lens, and the output coupling mirror and the diffraction grating and the first lens to form a spectral beam structure; the light emitted upward by the laser diode array is compressed by the first lens and the second lens for the divergence angle, and then fed back to the active area of the laser diode array through the high-reflection mirror. The light emitted from the bottom is directed to the diffraction grating through the lower part of the first lens, and after being diffracted and selected by the diffraction grating, part of the light is fed back to the active area of the laser diode array along the original path through the output coupling mirror, and part of it is used as output laser light.

The laser diode array includes a one-dimensional laser diode array or a two-dimensional laser diode array formed by at least two one-dimensional laser diode arrays.

The one-dimensional laser diode array includes 19 or 49 LD light emitting units.

The fast-axis collimating mirror is a cylindrical mirror with a focal length less than 1mm.

A spatial filter for mode selection is provided between the first lens and the second lens.

The diffraction grating is a blazed grating.

Both the first lens and the second lens are cylindrical lenses; the focal length of the second lens is 2 to 8 times that of the first lens.

The high reflection mirror is a plane reflection mirror coated with an antireflection film; the reflectivity of the high reflection mirror is greater than 99%.

The output coupling mirror is a partially transmissive plane mirror.

The utility model has the advantages that the fast-axis collimating mirror is located in the fast-axis direction of the laser diode array, and the rear end faces of the first lens, the second lens, the high reflection mirror and the diode array form an off-axis external feedback cavity, which can improve the laser diode array. The beam quality of each light-emitting unit in the interior, the spectral beam structure formed between the first lens, the diffraction grating and the output coupling mirror can improve the output beam quality of the laser diode array, the structure is simple, the application range of the laser diode array is improved, and it is safe and reliable .

Description of drawings

Fig. 1 is the structural representation of the utility model.

Fig. 2 is a structural schematic diagram of the laser diode array of the present invention.

FIG. 3 is a top view of FIG. 2 .

Detailed ways

Below in conjunction with specific accompanying drawing and embodiment the utility model is further described.

As shown in Figures 1 to 3: the utility model includes a laser diode array 1, a fast axis collimating mirror 2, a first lens 3, a second lens 4, a high reflection mirror 5, a diffraction grating 6, an output coupling mirror 7, a space Filter 8 , two-dimensional laser diode array 9 and one-dimensional laser diode array 10 .

As shown in Figure 1: fast-axis collimating mirror 2 is installed on the fast-axis direction of described laser diode array 1, and described fast-axis collimating mirror 2 is a cylindrical mirror with a focal length less than 1mm; 2 pairs of fast-axis collimating mirrors The light emitted in the direction of the fast axis of the laser diode array 1 is collimated; wherein, the direction of the x-axis in the figure is the direction of the slow axis, and the direction of the y-axis is the direction of the fast axis. The fast-axis collimating mirror 2 can collimate the fast-axis direction to the diffraction limit, and the divergence angle is about 1 degree. A schematic structural view of the laser diode array 1, as shown in Figure 2 and Figure 3; the laser diode array 1 can be a one-dimensional laser diode array 10, or a two-dimensional laser diode array 9 composed of at least two one-dimensional laser diode arrays 9 . Each one-dimensional laser diode array 10 is composed of 19 or 49 independent laser photodiode units, and 19 or 49 independent diodes are arranged along the x-axis direction to form a one-dimensional array; multiple one-dimensional laser diode arrays 10 are arranged along the y axis A two-dimensional laser diode array 9 is formed in the axial direction.

The fast-axis collimating mirror 2 is fixed on the output end of the laser diode array 1, the fast-axis collimating mirror is provided with a first lens 3 behind it, and a second lens 4 is provided above the first lens 3. A beam expander system is formed between the first lens 3 and the second lens 4 , which can compress the divergence angle of the light emitted upward by the laser diode array 1 . The second lens 4 corresponds to the other side that is connected with the first lens 3 and is provided with a high reflection mirror 5, and the high reflection mirror 5 is a plane mirror coated with an anti-reflection film, and the reflectivity of the high reflection mirror 5 is higher than 99%. %; The high reflective mirror 5 feeds back the light emitted by the laser diode array 1 upward along a specific angle to the active area of each light-emitting unit in the laser diode array 1 along the original path. Both the first lens 3 and the second lens 4 are cylindrical lenses, and the focal length of the second lens 4 is 2-8 times of the focal length of the first lens 3 . A spatial filter 8 is provided between the first lens 3 and the second lens 4, and the spatial filter 8 is a hole or a slit whose size and position can be adjusted, and is used for further mode selection of the output laser mode of the laser diode array 1 .

The first lens 3 is provided with a diffraction grating 6 below the back, and the diffraction grating 6 is a blazed grating; an output coupling mirror 7 is arranged between the diffraction grating 6 and the first lens 3, and the output coupling mirror 7 is a partially transmissive plane mirror; The output laser will be output from the output coupling mirror 7 .

表示发光单元在慢轴方向上的宽度，

表示波数。The rear upper branch of the first lens 3 utilizes the reflection of the high reflection mirror 5 as a feedback, and the high reflection mirror 5 and the rear end face of the laser diode array 1 form a resonant cavity, i.e. an external cavity; the high reflection mirror 5 is not on the optical axis , thus forming an off-axis feedback cavity. For each light-emitting unit in the laser diode array 1, under free-running conditions, there are generally dozens of side modes oscillating in the slow axis direction (y direction) of the diode, so the beam quality is poor. The far-field distribution of each mode is a double lobe structure, and the lateral spatial modes of different orders have different spatial radiation angles. Equation (1) represents the spatial radiation angle of the mth order mode, where,

Indicates the width of the light-emitting unit in the direction of the slow axis,

Indicates the wave number.

                                     （1）

(1)

Because the spatial modes of different orders have different radiation angles, a lobe of a certain spatial mode can be selected by adjusting the inclination angle of the high reflection mirror 5, and fed back to the active area of each light-emitting unit of the laser diode array 1 Inside, make it continue to oscillate and amplify, and the other lobe is used for laser output. According to the theory of mode competition, the oscillation of the feedback mode is strengthened, and other modes are effectively suppressed, so that the number of spatial modes of the output laser is greatly reduced, and the quality of the output beam will be improved. Since the upper branch of the first lens 3 uses the high reflection mirror 5 as a common feedback mirror, the direction of the spatial radiation angle fed back by each light-emitting unit to the back mode is basically the same, so that the directionality of the output laser light of all light-emitting units becomes Relatively good, with a big improvement in beam quality.

The rear lower branch of the first lens 3 is a spectral beam structure, which includes the first lens 3 , the diffraction grating 6 and the output coupling mirror 7 . The output coupling mirror 7 is a partially transmissive plane mirror. The laser diode array 1 and the diffraction grating 6 are respectively placed on the front focal plane and the back focal plane of the first lens 3, and the first lens 3 is used as a transformation lens. The output laser light from the light-emitting units in different positions of the laser diode array 1 passes through the first lens 3 and hits the diffraction grating 6 at different incident angles. After being diffracted by the diffraction grating 6, it hits the output coupling mirror 7. Since the output coupling mirror 7 is Partially transmitted plane mirror, so the part of the diffracted light parallel to the normal of the output coupling mirror 7 will return along the original path. The incident angles of the laser light output by different light-emitting units in the laser diode array 1 incident on the diffraction grating 6 are different. To make the diffracted light parallel to the normal line of the output coupling mirror 7, that is, the direction of the diffracted light is the same, then along the normal line of the output coupling mirror 7 The wavelength of the light diffracted by the direction is different, so the feedback wavelength of each light-emitting unit is different. Since the output coupling mirror 7 serves as the common feedback of part of the laser light, the laser light from the laser diode array 1 all propagates coaxially after passing through the output coupling mirror 7 . In this way, the direction of the laser light output by all units is similar to the beam quality of the laser output by a single light-emitting unit; therefore, the beam quality has been greatly improved.

As shown in FIGS. 1 to 3 , the light emitted by the laser diode array 1 first passes through a fast-axis collimating mirror 2 to collimate the fast-axis direction. The laser diode 1 is divided into upper and lower branches by the first lens 3 in the direction of the slow axis, and the light from the upper branch passes through the beam expander system formed by the first lens 3 and the second lens 4 and hits the high reflection mirror 5 superior. By adjusting the inclination angle of the high reflection mirror 5, one lobe of a certain spatial mode is selected, and it is fed back to the laser diode array 1 to make it continue to oscillate and magnify, and the other lobe passes through the lower branch of the first lens 3 for spectrum bundle.

For the lower branch, the output laser light from the light-emitting units in different positions of the laser diode array 1 passes through a lens 3 and hits the diffraction grating 6 at different incident angles. After diffracted by the grating, it hits the output coupling mirror 7, and the diffracted light and Most of the normal parallel light from the output coupling mirror 7 returns along the original path for feedback, and the other part of the light passes through the output coupling mirror 7 for laser output. The output coupling mirror 7 is used as a common feedback mirror, so the laser output from all light-emitting units propagates coaxially after passing through the output coupling mirror 7, and the laser beam output from all units is similar to the beam quality of the laser output from a single light-emitting unit, which improves the beam quality.

The utility model combines the principle of off-axis feedback external cavity and the principle of spectral beam combination to improve the output beam quality of the laser diode array 1; the utility model can not only effectively improve the beam quality of the one-dimensional laser diode array 10 (Laser diode bar), Moreover, it can also improve the beam quality of the two-dimensional laser diode stack 9 (Laser diode stack). The spectral beam combining technology can improve the output beam quality of the laser diode array to be equivalent to the beam quality of a single light-emitting unit, and the off-axis feedback external cavity device can improve the beam quality of each light-emitting unit, so the combination of these two methods will further improve Beam quality of laser diode arrays.

Claims (9)

1. An off-axis spectral beam combining device of a laser diode array, comprising a laser diode array (1) and a fast-axis collimating mirror (2) located in the fast-axis direction of the laser diode array (1); it is characterized in that: The fast-axis collimating mirror (2) is provided with a first lens (3) corresponding to the other side connected to the laser diode array (1), and a second lens is sequentially provided behind and above the first lens (3) (4) and a high reflection mirror (5), the high reflection mirror (5) forms an off-axis off-axis feedback cavity with the second lens (4), the first lens (3) and the rear end surface of the laser diode array; the first lens ( 3) A diffraction grating (6) is provided at the rear and lower part, and an output coupling mirror (7) is provided between the diffraction grating (6) and the first lens (3), and the output coupling mirror (7) and the diffraction grating (6) ) and the first lens (3) to form a spectral beam structure; the light emitted upward by the laser diode array (1) is compressed by the first lens (3) and the second lens (4) on the divergence angle, and then passes through the high reflection mirror ( 5) Feedback to the active area of the laser diode array (1), the light emitted downward passes through the lower part of the first lens (3) to the diffraction grating (6), and after being diffracted and selected by the diffraction grating (6) Part of the light passing through the output coupling mirror (7) is fed back to the active area of the laser diode array (1) along the original path, and part of it is used as output laser light. 2. The off-axis spectral beam combining device of laser diode array according to claim 1, characterized in that: the laser diode array (1) comprises a one-dimensional laser diode array or is formed by at least two one-dimensional laser diode arrays Two-dimensional laser diode array. 3 . The off-axis spectral beam combining device of laser diode array according to claim 2 , wherein the one-dimensional laser diode array includes 19 or 49 LD light emitting units. 4 . 4. The off-axis spectral beam combining device of a laser diode array according to claim 1, characterized in that: the fast-axis collimating mirror (2) is a cylindrical mirror with a focal length less than 1 mm. 5. The off-axis spectral beam combining device of laser diode array according to claim 1, characterized in that: a spatial filter for mode selection is provided between the first lens (3) and the second lens (4) ( 8). 6. The off-axis spectral beam combining device of laser diode array according to claim 1, characterized in that: the diffraction grating (6) is a blazed grating. 7. The off-axis spectral beam combining device of laser diode array according to claim 1, characterized in that: the first lens (3) and the second lens (4) are both cylindrical mirrors; the second lens The focal length of (4) is 2 to 8 times that of the first lens (3). 8. The off-axis spectral beam combining device of laser diode array according to claim 1, characterized in that: the high reflection mirror (5) is a plane reflection mirror coated with an antireflection film; the high reflection mirror (5 ) reflectivity greater than 99%. 9. The off-axis spectral beam combining device of laser diode array according to claim 1, characterized in that: the output coupling mirror (7) is a partially transmissive plane mirror.

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