Planar waveguide laser

Abstract

The invention discloses a planar waveguide laser which comprises a planar waveguide, a pumping source, a pumping beam combining system, a pumping focusing system, a total reflective mirror and an output coupling mirror. The pumping sources are symmetrically arranged on the left side and the right side of the planar waveguide, and the pumping beam combining system and the pumping focusing system are sequentially and correspondingly arranged in the light emitting direction of the pumping source on each side. The total reflective mirror is arranged on the rear end face of the planar waveguide, and the output coupling mirror is arranged on the front end face of the planar waveguide; pump light emitted by the pumping source is combined by the pumping beam combining system and focused by the pumping focusing system, and then enters the planar waveguide from the pumping incidence window, and the pumping light is totally reflected by the area, except the pumping incidence window, of the side face of the planar waveguide, so that the pumping light is repeatedly turned back between the two side faces of the planar waveguide to pass through the core layer for many times, and the pumping light is formed. Therefore, the pump light is absorbed by the core layer, the absorption efficiency and the absorption uniformity of the pump light are improved, laser oscillation is generated under the action of a resonant cavity formed by the total reflection mirror and the output coupling mirror, and laser is output from the end face of the output coupling mirror.

Description

Technical Field

[0001] The invention relates to the technical field of solid lasers, and in particular to a planar waveguide laser. Background Art

[0002] Solid-state lasers have many remarkable characteristics. They use solid materials as gain media, have compact and strong structures, are less affected by environmental factors, and therefore have high stability. At the same time, solid-state lasers can output multiple wavelengths to meet the needs of different applications for specific wavelengths. Based on these characteristics, high-power solid-state lasers are widely used in industrial manufacturing, scientific research, and military fields. Achieving high-power laser output has always been the development goal of solid-state lasers, and thermal effects are one of the main factors limiting power increases.

[0003] To solve this problem, the structure of the gain medium has evolved from a block structure to optical fiber, disk, slab, and planar waveguide structures. Fiber lasers can obtain high average power and near-diffraction-limited laser output, but due to the small core diameter, they are easily affected by nonlinear effects such as self-phase modulation and stimulated Raman scattering, resulting in the inability to obtain high peak power output. The gain medium of the disk laser is thin and has good heat dissipation performance. At the same time, it has a large beam cross-section and is not affected by nonlinear effects. However, the single-pass gain of this structure is low and the overall device is complex. The slab laser has a large aspect ratio structure and uses a large surface cooling method to effectively reduce thermal effects and obtain higher output power. However, this structure has difficulties in thermal management under high-power operating conditions, resulting in poor output beam quality.

[0004] Lasers using planar waveguides as gain media combine the advantages of fiber lasers and slab lasers. They have the characteristics of high pumping efficiency, high output power, the ability to limit the beam mode in one-dimensional direction, and good heat dissipation. They have great application potential in the field of high-power solid-state lasers. Currently, there are two pumping methods for high-power output planar waveguide lasers, namely end pumping and side pumping. The end pumping method maximizes the pump absorption length while facilitating pump coupling. However, end pumping is not easy to form a uniform pump absorption distribution, and the high pump power density at the incident end face will bring about a serious thermal lens effect, limiting the laser output power. Side pumping has a larger pumping area, and the pump power can be increased by increasing the number of diodes, thereby achieving high-power laser output; but when side pumping, the planar waveguide has an absorption gradient in the non-waveguide direction, which limits the output power and beam quality of the laser. Summary of the invention

[0005] In view of the deficiencies in the prior art, the present invention provides a planar waveguide laser, wherein pump light enters the planar waveguide from a pump incident window, and the side surface of the planar waveguide except the pump incident window totally reflects the pump light, so that the pump light can be folded back and forth between the two side surfaces of the planar waveguide for multiple times and then fully absorbed by the core layer, thereby effectively improving the absorption efficiency and uniformity of the pump light, so as to achieve high-power, high-beam-quality laser output.

[0006] The present invention provides the following technical solutions:

[0007] A planar waveguide laser comprises a planar waveguide, a pump source, a pump beam combining system, a pump focusing system, a total reflection mirror, and an output coupling mirror;

[0008] The pump sources are symmetrically arranged on the left and right sides of the planar waveguide, and the pump beam combining system and the pump focusing system are sequentially arranged correspondingly in the light emitting direction of the pump sources on each side;

[0009] The total reflection mirror is arranged on the rear end face of the planar waveguide, and the output coupling mirror is arranged on the front end face of the planar waveguide;

[0010] The left and right sides of the planar waveguide are both provided with pump incident windows, and a core layer as a gain medium is provided in the planar waveguide, and the material of the core layer is Nd:YAG crystal;

[0011] The pump light emitted by the pump source enters the planar waveguide from the pump incident window after being combined by the pump combining system and focused by the pump focusing system. The side surface of the planar waveguide except the pump incident window totally reflects the pump light, so that the pump light is folded back and forth between the two side surfaces of the planar waveguide for multiple times to pass through the core layer for multiple times, so that the pump light is absorbed by the core layer, and then laser oscillation is generated under the action of the resonant cavity formed by the total reflection mirror and the output coupling mirror, and laser is output from the end face of the output coupling mirror.

[0012] As a further improvement of the present invention, the planar waveguide is a composite structure, comprising:

[0013] The cladding layers are arranged on the upper and lower sides of the core layer, and the material thereof is Er:YAG crystal;

[0014] The light guide layer is arranged on the left and right sides of the core layer, and its material is Er:YAG crystal;

[0015] The end cap disposed on the rear end face of the core layer is made of undoped YAG crystal;

[0016] The core layer, cladding layer, light-guiding layer and end cap are formed into an integrated structure by thermal bonding technology to manufacture the planar waveguide.

[0017] As a further improvement of the present invention, the cutting angles of the left and right side surfaces of the planar waveguide are both 60°, and the front and rear end surfaces of the planar waveguide are parallelograms.

[0018] As a further improvement of the present invention, the size of the core layer is 44mm (length) × 14mm (width) × 0.4mm (height), the thickness of the cladding on the upper and lower sides of the core layer is 0.85mm, the width of the pump incident window is 0.7mm, and the overall size of the planar waveguide is 54mm (length) × 51.4mm (width) × 2.1mm (height).

[0019] As a further improvement of the present invention, the front and rear end surfaces of the planar waveguide are coated with a 1064nm anti-reflection film, the pump incident window is coated with an 808nm anti-reflection film, and the left and right side surfaces of the planar waveguide except the pump incident window are coated with SiO 2 The upper and lower surfaces of the planar waveguide are plated with SiO 2 .

[0020] As a further improvement of the present invention, the pump source is a semiconductor bar stack, and the output mode of the pump source is continuous output.

[0021] As a further improvement of the present invention, the pump beam combining system is a three-layer step mirror, the oblique side surface of each layer of the step mirror is 45°, and the oblique side surface of each layer of the step mirror is coated with an 808nm total reflection film; the three-layer step mirror is used to spatially combine the pump light emitted by the pump source to eliminate the spatial gap of the pump light in the fast axis direction.

[0022] As a further improvement of the present invention, the pump focusing system is a cylindrical lens, which focuses the pump light combined by the pump combining system in the fast axis direction, and the focused pump light enters the core layer from the pump incident window on the side of the planar waveguide.

[0023] As a further improvement of the present invention, the total reflection mirror is a plane mirror coated with a 1064nm total reflection film layer.

[0024] As a further improvement of the present invention, the output coupling mirror is a plane mirror with a transmittance of 30% for light with a wavelength of 1064 nm.

[0025] Compared with the prior art, the present invention has the following beneficial effects:

[0026] The pump light enters the planar waveguide from the pump incident window on the side of the planar waveguide. The side of the planar waveguide except the pump incident window fully reflects the pump light, so that the pump light can be folded back and forth between the two sides of the planar waveguide for many times and then fully absorbed by the core layer, which greatly increases the absorption length of the pump light and effectively improves the absorption efficiency and uniformity of the pump light, so as to achieve high-power, high-beam-quality laser output.

[0027] In the planar waveguide structure of the present invention, the core material is Nd:YAG crystal, and the cladding material is Er:YAG crystal. By controlling the doping concentration of the cladding Er:YAG crystal so that it forms a good refractive index match with the core layer, the core size during fundamental mode output is expanded by mode competition, thereby achieving high-power laser output by expanding the fundamental mode field area while ensuring the quality of the beam.

[0028] In the planar waveguide structure of the present invention, Er:YAG crystals are used as light guide layers on both sides of the planar waveguide. The pump light enters the core layer after being fully homogenized by the light guide layer, which solves the problem of pump absorption gradient during side pumping, is conducive to improving pump absorption uniformity, and reducing waveguide thermal effect; undoped YAG is used as the end cap of the planar waveguide, which effectively reduces the end face thermal effect of the planar waveguide. At the same time, the planar waveguide is prepared by thermal bonding technology, so that the overall structure of the laser is compact and has high reliability.

[0029] The pump light is combined by a pump beam combining system to eliminate the spatial gap in the fast axis direction of the pump light, and the combined pump light is focused by a pump focusing system, which is beneficial to improving the absorption efficiency and uniformity of the pump light. BRIEF DESCRIPTION OF THE DRAWINGS

[0030] Figure 1 It is a schematic diagram of the structure of a planar waveguide laser;

[0031] Figure 2 is a three-dimensional schematic diagram of a planar waveguide structure;

[0032] Figure 3 It is a front view and a top view of the planar waveguide structure;

[0033] Figure 4 is the dimension diagram of the planar waveguide structure;

[0034] Figure 5 Schematic diagram of pump light;

[0035] Figure 6 It is a schematic diagram of the structure of the pump beam combining system;

[0036] Figure 7 is the pump light absorption distribution diagram of the core layer of the planar waveguide structure;

[0037] Figure 8 is the pump intensity absorption distribution diagram of the planar waveguide structure in the non-waveguide direction;

[0038] Fig. 9 This is the temperature distribution diagram of the gain medium of the planar waveguide laser when the pump power is 800W;

[0039] Fig.10This is the thermal stress distribution diagram of the planar waveguide laser gain medium when the pump power is 800W.

[0040] Explanation of the accompanying drawings: 1. Planar waveguide; 2. Pump source; 3. Pump beam combining system; 4. Pump focusing system; 5. Total reflection mirror; 6. Output coupling mirror. DETAILED DESCRIPTION

[0041] In order to make the purpose, technical solution and advantages of the embodiments of the present invention clearer, the technical solution in the embodiments of the present invention will be clearly and completely described below in conjunction with the drawings in the embodiments of the present invention. Obviously, the described embodiments are part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0042] The present invention is further described in detail below in conjunction with the accompanying drawings:

[0043] The planar waveguide laser comprises a planar waveguide 1, a pump source 2, a pump beam combining system 3, a pump focusing system 4, a total reflection mirror 5, and an output coupling mirror 6. The structure of the planar waveguide laser is as follows: Figure 1 shown.

[0044] The pump source 2 is symmetrically arranged on the left and right sides of the planar waveguide 1, and the pump beam combining system 3 and the pump focusing system 4 are arranged in sequence in the light output direction of the pump source 2 on each side; the total reflection mirror 5 is a plane mirror coated with a 1064nm total reflection film layer, which is arranged on the rear end face of the planar waveguide 1; the output coupling mirror 6 is a plane mirror with a transmittance of 30% for light with a wavelength of 1064nm, which is arranged on the front end face of the planar waveguide 1.

[0045] The left and right sides of the planar waveguide 1 are provided with pump incident windows, and a core layer as a gain medium is provided in the planar waveguide 1. The front and rear end surfaces of the planar waveguide 1 are coated with a 1064nm anti-reflection film, the pump incident window is coated with an 808nm anti-reflection film, and the left and right sides of the planar waveguide 1 except the pump incident window are coated with SiO 2 , the upper and lower surfaces of the planar waveguide 1 are plated with SiO 2 .

[0046] The principle of laser output of the planar waveguide laser is as follows: the pump light emitted by the pump source 2 is combined by the pump beam combining system 3 and focused by the pump focusing system 4, and then enters the planar waveguide 1 from the pump incident window. The side area of ​​the planar waveguide 1 except the pump incident window totally reflects the pump light, so that the pump light is folded back and forth between the two side surfaces of the planar waveguide 1 for many times and passes through the core layer for many times, so that the pump light is fully absorbed by the core layer, and then laser oscillation is generated under the action of the resonant cavity formed by the total reflection mirror 5 and the output coupling mirror 6, and the laser is output from the end face of the output coupling mirror 6.

[0047] The planar waveguide laser provided by the present invention can greatly increase the absorption length of the pump light, effectively improve the absorption efficiency and absorption uniformity of the pump light, and realize high-power, high-beam-quality laser output

[0048] The planar waveguide 1 is a composite structure, and the specific structure is as follows Figure 2 , Figure 3 As shown, including:

[0049] The core layer A is made of Nd:YAG crystal and is the gain medium of the waveguide.

[0050] The cladding B disposed on the upper and lower sides of the core layer is made of Er:YAG crystal and is used to form a waveguide structure;

[0051] The light guide layer B is set on the left and right sides of the core layer. Its material is Er:YAG crystal, which is used to improve the thermal effect on both sides of the waveguide and improve the uniformity of pump absorption;

[0052] The end cap C is arranged on the rear end face of the core layer, and its material is undoped YAG crystal, which is used to improve the thermal effect of the waveguide end face;

[0053] The core layer, cladding layer, light-guiding layer and end cap are formed into an integrated structure by thermal bonding technology to manufacture the planar waveguide 1, so that the overall structure of the laser is compact and has high reliability.

[0054] The dimensions of the planar waveguide 1 are designed as follows: Figure 4 As shown, the specific dimensions are:

[0055] The cutting angles θ of the left and right sides of the planar waveguide 1 are both 60°, and the front and rear end faces of the planar waveguide 1 are parallelograms; the size of the core layer is 44mm (length) × 14mm (width) × 0.4mm (height), the thickness of the cladding on the upper and lower sides of the core layer is 0.85mm, and the width of the pump incident window is 0.7mm; the overall size of the planar waveguide is 54mm (length) × 51.4mm (width) × 2.1mm (height).

[0056] By designing the crystal thickness of the waveguide cladding and light guide layer, the waveguide side cut angle, and the size of the pump incident window, it is ensured that the pump light is reflected enough times in the waveguide to increase the effective absorption length of the pump light in the Nd:YAG core layer, making the absorption distribution of the core layer relatively uniform in the width direction.

[0057] The pump source 2 is a semiconductor bar stack (3 bars × 3 rows), with a central wavelength of 808 nm, a line width of 0.3 nm, and a continuous output. The pump light emitted by the pump source 2 is as follows: Figure 5 shown.

[0058] The maximum output power of a single bar is 67W, the fast axis divergence angle is 0.46° (full angle, 95% energy), and the slow axis divergence angle is 8.5° (full angle, 95% energy). The light output area of ​​a single bar is 0.8mm (fast axis) × 10mm (slow axis), and the interval between bars in the fast axis direction is 1mm.

[0059] The pump beam combining system 3 is a three-layer step mirror, each layer of the step mirror has an oblique side angle of 45°, and each layer of the step mirror has an oblique side surface coated with an 808nm total reflection film. The structure of the pump beam combining system 3 is as follows: Figure 6 The pump light emitted by the pump source 2 is spatially combined by using a three-layer step mirror, and the width of the pump light is compressed from 4.4 mm to 2.4 mm, so as to eliminate the spatial gap of the pump light in the fast axis direction and improve the absorption efficiency and uniformity of the pump light.

[0060] The pump focusing system 4 is a cylindrical lens with a focal length of 3.9 mm. The pump focusing system 4 focuses the pump light combined by the pump combining system 3 in the fast axis direction. The focused pump light enters the core layer from the pump incident window on the side of the planar waveguide 1.

[0061] The pump light absorption distribution of the Nd:YAG planar waveguide core layer is shown in Figure 7 As shown, Figure 7 The left side shows the pump light absorption distribution of the core layer. Figure 7 The right side shows the pump light absorption distribution of the core center end face. By using the Zemax ray tracing method to simulate and analyze the pump absorption distribution of the gain medium, it can be seen that the pump absorption distribution of the core large surface and the center end face is highly uniform.

[0062] The pump intensity absorption distribution of the Nd:YAG planar waveguide in the non-waveguide direction is shown in Figure 8. The pump absorption distribution of the planar waveguide in the non-waveguide direction is simulated and analyzed by the Zemax ray tracing method, and compared with the pump absorption distribution of other planar waveguides. It can be seen that the pump absorption distribution of the planar waveguide of the present invention is significantly more uniform, and there is no pump absorption gradient.

[0063] When the pump power is 800W, the temperature distribution of the gain medium of the planar waveguide laser is as follows: Fig. 9 Comsol finite element analysis combined with Zemax ray tracing method is used to simulate the temperature distribution of the gain medium. The upper and lower surfaces of the planar waveguide are cooled by water. The water cooling temperature is 293K, which can be regarded as a constant temperature. The water cooling heat conversion coefficient is 20000W / (m 2 ·K); the front and rear ends and the left and right sides of the planar waveguide use natural convection to dissipate heat, and its heat transfer coefficient is 25W / (m 2·K). It can be seen from the simulation results that the core layer has a high uniformity of temperature distribution in both the width and length directions. The temperature distribution in the length direction of the core layer is affected by the gap in the slow axis direction of the bar array, which reduces the uniformity of the temperature distribution in the length direction of the core layer. The maximum temperature of the gain medium is 325K.

[0064] When the pump power is 800W, the thermal stress distribution of the gain medium of the planar waveguide laser is as follows: Fig. 9 As shown. By simulating the thermal stress of the planar waveguide, the maximum surface stress is 29.1MPa. The fracture stress of the YAG matrix crystal is 130MPa. The calculation results show that at 800W pump power, the thermal stress generated by the planar waveguide is less than its fracture stress, which can ensure the safety and reliability of the planar waveguide.

[0065] The core layer of the planar waveguide of the present invention adopts Nd:YAG crystal, and Er:YAG crystal is bonded on both sides of the waveguide as the light guide layer. The pump light enters the waveguide from the side incident window, enters the core layer after being fully homogenized by the light guide layer, and passes through the core layer multiple times under the reflection of the upper and lower large surfaces of the waveguide to be fully absorbed by the core layer; the area outside the side incident window of the planar waveguide fully reflects the pump light, so that the pump light can be folded back between the two sides, greatly increasing the pump absorption length of the core layer, and improving the pump absorption efficiency and absorption uniformity. A step mirror is used to combine the pump light to eliminate the spatial gap in the fast axis direction to further improve the pump absorption uniformity and absorption efficiency. Undoped YAG is used as the waveguide end cap to effectively reduce the thermal effect of the waveguide end face and improve the beam quality. The planar waveguide of the present invention is prepared by thermal bonding technology, so that the overall structure of the laser is compact and reliable, and it is easy to realize integrated and high-power engineering applications.

[0066] The above are only preferred embodiments of the present invention and are not intended to limit the present invention. For those skilled in the art, the present invention may have various modifications and variations. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention shall be included in the protection scope of the present invention.

Claims

1. A planar waveguide laser, characterized in that: It comprises a planar waveguide (1), a pump source (2), a pump beam combining system (3), a pump focusing system (4), a total reflection mirror (5), and an output coupling mirror (6); The pump source (2) is symmetrically arranged on the left and right sides of the planar waveguide (1), and the pump beam combining system (3) and the pump focusing system (4) are sequentially arranged correspondingly in the light emitting direction of the pump source (2) on each side; The total reflection mirror (5) is arranged on the rear end face of the planar waveguide (1), and the output coupling mirror (6) is arranged on the front end face of the planar waveguide (1); The left and right sides of the planar waveguide (1) are both provided with pump incident windows, and a core layer as a gain medium is provided in the planar waveguide (1), and the material of the core layer is Nd:YAG crystal; The pump light emitted by the pump source (2) enters the planar waveguide (1) from the pump incident window after being combined by the pump combining system (3) and focused by the pump focusing system (4). The side area of ​​the planar waveguide (1) other than the pump incident window totally reflects the pump light, so that the pump light is folded back and forth between the two side surfaces of the planar waveguide (1) multiple times and passes through the core layer multiple times, so that the pump light is absorbed by the core layer, and then laser oscillation is generated under the action of the resonant cavity formed by the total reflection mirror (5) and the output coupling mirror (6), and the laser is output from the end face of the output coupling mirror (6).

2. The planar waveguide laser according to claim 1, characterized in that: The planar waveguide (1) is a composite structure, comprising: The cladding layers are arranged on the upper and lower sides of the core layer, and the material thereof is Er:YAG crystal; The light guide layer is arranged on the left and right sides of the core layer, and its material is Er:YAG crystal; The end cap disposed on the rear end face of the core layer is made of undoped YAG crystal; The core layer, cladding layer, light-guiding layer and end cap are formed into an integrated structure through a thermal bonding technology to manufacture the planar waveguide (1).

3. The planar waveguide laser according to claim 1, characterized in that: The cutting angles of the left and right side surfaces of the planar waveguide (1) are both 60°, and the front and rear end surfaces of the planar waveguide (1) are parallelograms.

4. The planar waveguide laser according to claim 2, characterized in that: The dimensions of the core layer are 44 mm (length) × 14 mm (width) × 0.4 mm (height), the thickness of the cladding layers on the upper and lower sides of the core layer are both 0.85 mm, the width of the pump incident window is 0.7 mm, and the overall dimensions of the planar waveguide (1) are 54 mm (length) × 51.4 mm (width) × 2.1 mm (height).

5. The planar waveguide laser according to claim 1, characterized in that: The front and rear end surfaces of the planar waveguide (1) are both coated with a 1064nm anti-reflection film, the pump incident window is coated with an 808nm anti-reflection film, the left and right side surfaces of the planar waveguide (1) except the pump incident window are both coated with SiO2, and the upper and lower surfaces of the planar waveguide (1) are both coated with SiO2.

6. The planar waveguide laser according to claim 1, characterized in that: The pump source (2) is a semiconductor bar stack, and the output mode of the pump source (2) is continuous output.

7. The planar waveguide laser according to claim 1, characterized in that: The pump beam combining system (3) is a three-layer step mirror, the oblique side surface of each layer of the step mirror is 45 degrees, and the oblique side surface of each layer of the step mirror is coated with an 808nm total reflection film; the three-layer step mirror is used to spatially combine the pump light emitted by the pump source (2) to eliminate the spatial gap of the pump light in the fast axis direction.

8. The planar waveguide laser according to claim 1, characterized in that: The pump focusing system (4) is a cylindrical lens, and the pump focusing system (4) focuses the pump light after being beam-combined by the pump beam-combining system (3) in the fast axis direction, and the focused pump light enters the core layer from the pump incident window on the side of the planar waveguide (1).

9. The planar waveguide laser according to claim 1, characterized in that: The total reflection mirror (5) is a plane mirror coated with a 1064nm total reflection film layer.

10. The planar waveguide laser according to claim 1, characterized in that: The output coupling mirror (6) is a plane mirror with a transmittance of 30% for light with a wavelength of 1064 nm.

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