Output optical system of fiber laser

Abstract

The invention discloses an output optical system of an optical fiber laser, and relates to the technical field of laser, the output optical system of the optical fiber laser comprises an optical fiber, a first plane mirror, a collimating lens group and a focusing lens group which are sequentially arranged along the direction of an optical axis, the first plane mirror is obliquely arranged relative to the optical axis, the inclination angle is A, and the inclination angle is B; the numerical aperture of the light outlet of the optical fiber is NA, and sinA is larger than or equal to 1 / 2NA. According to the technical scheme provided by the invention, the inclined first plane mirror is arranged, so that the laser in the optical fiber is reflected by the first plane mirror and then does not enter the light outlet of the optical fiber again, thereby preventing high-power return light from damaging a laser amplifier, a resonant cavity and other optical devices, by limiting the relationship between the inclination angle and the numerical aperture, the inclination angle is matched with the numerical aperture, so that the reflected light can be ensured not to enter the optical fiber when facing light outlets with different numerical apertures, and the applicability of the system is improved.

Description

Technical Field

[0001] The invention relates to the field of laser technology, and in particular to an output optical system of a fiber laser. Background Art

[0002] Fiber lasers are light emitted by semiconductor pump tubes. The light is absorbed by the gain fiber doped with rare earth elements, and then amplified by FBG (Fiber Bragg Grating) fiber grating oscillation. After multi-stage amplification and multi-way coupling, the laser beam is output through the output end cap QBH (Quasi-Brewster Angle High-power Fiber Coupler Output Cap) through the energy transmission fiber. Compared with traditional solid lasers, fiber lasers have the advantages of good laser beam quality, high coherence, high brightness, high conversion efficiency, small size, and long life. They are widely used in material processing, such as marking, drilling, welding, cutting, cleaning, coating, as well as optical communication, spectral imaging, and medical fields. In recent years, with the development of semiconductor pumping technology, the improvement of large mode area double-clad fiber manufacturing technology, and the development of fiber beam combining technology, the output power of fiber lasers is developing at an astonishing speed. It is precisely because of the continuous improvement of the output power and peak power of fiber lasers that various needs in modern high-tech material processing are met.

[0003] However, one of the problems currently faced by fiber lasers in processing materials is that when processing highly reflective materials, such as highly reflective metal materials such as gold, silver, and copper, the laser output by the fiber laser will act on the surface of the material and then be reflected by the material and enter the laser light path again. When this reflected light reaches the oscillation end of the laser, it will be gradually amplified, eventually causing irreversible damage to the fiber laser optical system and burning of the optical devices.

[0004] The current solution to this problem in the fiber laser industry is to direct the laser output head at a certain angle to the material working surface when processing the material, so that most of the reflected laser light will be transmitted along the angle direction and cannot enter the laser light path. However, the disadvantage of this method is that some of the reflected light still returns to the laser light path, causing damage to the laser. Summary of the invention

[0005] In view of the shortcomings of the prior art, the main purpose of the present invention is to propose an output optical system for a fiber laser, aiming to solve the problem that during the current use of the laser, reflected light returns to the laser optical path, causing damage to the laser.

[0006] To achieve the above-mentioned purpose, the present invention proposes an output optical system of a fiber laser, comprising an optical fiber, a first plane mirror, a collimating lens group and a focusing lens group arranged in sequence along the optical axis, wherein the first plane mirror is tilted relative to the optical axis, and the tilt angle is A, and the numerical aperture of the light outlet of the optical fiber is NA, satisfying sinA≥1 / 2NA.

[0007] In one embodiment, the collimating lens group includes a first lens with positive optical power, a second lens with negative optical power, and a third lens with positive optical power, which are sequentially arranged along the optical axis.

[0008] In one embodiment, the first lens is a biconvex lens;

[0009] The second lens is a concave-convex lens, and the side surface of the second lens facing the first lens is a concave surface;

[0010] The third lens is a meniscus lens, and the side surface of the third lens facing the first lens is a convex surface.

[0011] In one embodiment, the focusing lens group includes a fourth lens with positive optical power and a fifth lens with positive optical power which are sequentially arranged along the optical axis.

[0012] In one embodiment, the fourth lens is a biconvex lens;

[0013] The fifth lens is a meniscus lens, and the side surface of the fifth lens facing the fourth lens is a concave surface.

[0014] In one embodiment, the output optical system of the fiber laser further includes a second plane mirror disposed between the fourth lens and the fifth lens, wherein the second plane mirror is tilted relative to the optical axis to correct the aberration caused by the first plane mirror.

[0015] In one embodiment, the first plane mirror, the second plane mirror, the collimating lens group and the focusing lens group are all made of fused quartz.

[0016] In one embodiment, the tilt angle A and the numerical aperture NA also satisfy NA≥sinA.

[0017] In one embodiment, the output optical system of the fiber laser further includes a photoelectric detection device, and a filter hole is provided on the photoelectric detection device for receiving part of the reflected light of the first plane mirror.

[0018] In one embodiment, the output optical system of the fiber laser further includes an electrically connected monitoring device and an alarm device, wherein the monitoring device is electrically connected to the photoelectric detection device and is used to monitor the power of the reflected light, and the alarm device is used to alarm an abnormal condition detected by the monitoring device.

[0019] An optical fiber, a first plane mirror, a collimating lens group, and a focusing lens group are sequentially arranged along the optical axis, wherein the first plane mirror is tilted relative to the optical axis, the tilt angle is A, the numerical aperture of the light outlet of the optical fiber is NA, and sinA≥1 / 2NA is satisfied

[0020] The technical solution of the present invention, by setting the collimating lens group and the focusing lens group, makes the laser light in the divergent form in the optical fiber gradually collimated and focused to form an output light beam that can converge at one point. Furthermore, by setting the inclined first plane mirror, the laser light in the optical fiber will not be re-injected into the light outlet of the optical fiber after being reflected by the first plane mirror, thereby avoiding the damage of the laser amplifier, the resonant cavity and other optical devices caused by the high-power return light. Among them, by limiting the relationship between the tilt angle and the numerical aperture, the tilt angle is matched with the numerical aperture, so that when facing the light outlets with different numerical apertures, it can be ensured that the reflected light is not injected into the optical fiber, thereby improving the applicability of the system. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on the structures shown in these drawings without paying creative work.

[0022] Figure 1 A schematic structural diagram of an embodiment of an output optical system of a fiber laser provided by the present invention;

[0023] Figure 2 for Figure 1 Light path diagram of the output optical system of the fiber laser;

[0024] Figure 3 for Figure 1 Flow chart of the photoelectric detection device.

[0025] Description of Figure Numbers:

[0026] 1000. Output optical system of fiber laser; 1. optical fiber; 2. first plane mirror; 3. collimating lens group; 31. first lens; 32. second lens; 33. third lens; 4. focusing lens group; 41. fourth lens; 42. fifth lens; 5. second plane mirror; 6. photoelectric detection device; 61. filter hole; 7. monitoring device; 8. alarm device.

[0027] The realization of the purpose, functional features and advantages of the present invention will be further explained in conjunction with embodiments and with reference to the accompanying drawings. DETAILED DESCRIPTION

[0028] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only 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.

[0029] It should be noted that if the embodiments of the present invention involve directional indications (such as up, down, left, right, front, back, etc.), the directional indications are only used to explain the relative position relationship, movement status, etc. between the components in a certain specific posture. If the specific posture changes, the directional indication will also change accordingly.

[0030] In addition, if there are descriptions involving "first", "second", etc. in the embodiments of the present invention, the descriptions of "first", "second", etc. are only used for descriptive purposes and cannot be understood as indicating or implying their relative importance or implicitly indicating the number of technical features indicated. Therefore, the features limited to "first" and "second" may explicitly or implicitly include at least one of the features. In addition, if "and / or" or "and / or" appears in the full text, its meaning includes three parallel solutions. Taking "A and / or B" as an example, it includes solution A, solution B, or solutions that satisfy both A and B. In addition, the technical solutions between the various embodiments can be combined with each other, but it must be based on the ability of ordinary technicians in this field to implement. When the combination of technical solutions is contradictory or cannot be implemented, it should be deemed that such combination of technical solutions does not exist and is not within the scope of protection required by the present invention.

[0031] One of the problems currently faced by fiber lasers in processing materials is that when processing highly reflective materials, such as highly reflective metal materials such as gold, silver, and copper, the laser output by the fiber laser will act on the surface of the material and then be reflected by the material and enter the laser light path again. When this reflected light reaches the oscillation end of the laser, it will be gradually amplified, eventually causing irreversible damage to the fiber laser optical system and burning of the optical devices.

[0032] In response to the above problems, the existing solution is to direct the laser output head to the material working surface at a certain angle when processing the material, so that most of the reflected laser will be transmitted along the angle direction and cannot enter the laser light path. However, the defects of this method are: first, it reduces the power of the output laser acting on the processed material to a certain extent, making the processing effect worse; second, since the transmission of the laser is reversible, part of the reflected light will also return to the laser light path and be amplified, causing damage to the laser.

[0033] The main purpose of the present invention is to provide an output optical system of a fiber laser, aiming to solve the problem that during the use of the laser, reflected light returns to the laser optical path, causing damage to the laser.

[0034] To achieve the above purpose, please refer to Figure 1 and Figure 2 The present invention proposes an output optical system 1000 of a fiber laser, comprising an optical fiber 1, a first plane mirror 2, a collimating lens group 3 and a focusing lens group 4 arranged in sequence along the optical axis, wherein the first plane mirror 2 is tilted relative to the optical axis, and the tilt angle is A, and the numerical aperture of the light outlet of the optical fiber 1 is NA, satisfying sinA≥1 / 2NA.

[0035] The technical solution of the present invention, by providing the collimating lens group 3 and the focusing lens group 4, the laser light in the divergent form in the optical fiber 1 is gradually collimated and focused to form an output light beam that can converge at one point. Furthermore, by providing the inclined first plane mirror 2, the laser light in the optical fiber 1 will not be re-injected into the light outlet of the optical fiber 1 after being reflected by the first plane mirror 2, thereby avoiding damage to the laser amplifier, the resonant cavity and other optical devices caused by high-power return light. Among them, by limiting the relationship between the tilt angle and the numerical aperture, the tilt angle is matched with the numerical aperture, so that when facing light outlets with different numerical apertures, it can be ensured that the reflected light is not injected into the optical fiber 1, thereby improving the applicability of the system.

[0036] Furthermore, the tilt angle A and the numerical aperture NA also satisfy NA≥sinA. Considering the magnitude of the aberration introduced by the first plane mirror 2, the greater the tilt, the greater the aberration, which affects the propagation of the light beam, and the complexity of the subsequent correction of the tilted light beam, by limiting the size of the tilt angle according to the numerical aperture, the aberration value is controlled within a reasonable range, thereby ensuring the laser output quality of the optical system.

[0037] In a specific embodiment provided by the present invention, please refer to Figure 2, the collimating lens group 3 includes a first lens 31 with positive focal power, a second lens 32 with negative focal power, and a third lens 33 with positive focal power, which are arranged in sequence along the optical axis. Among them, the first lens 31 is a biconvex lens, the second lens 32 is a concave-convex lens, and its side facing the first lens 31 is a concave surface, and the third lens 33 is a concave-convex lens, and its side facing the first lens 31 is a convex surface. The focusing lens group 4 includes a fourth lens 41 with positive focal power and a fifth lens 42 with positive focal power, which are arranged in sequence along the optical axis. Among them, the fourth lens 41 is a biconvex lens; the fifth lens 42 is a concave-convex lens, and its side facing the fourth lens 41 is a concave surface. With such a configuration, the system not only realizes the collimation and focusing of the laser, but also can correct the aberration of the optical system, thereby improving the laser output quality of the device. It is worth mentioning that the exit angle of the light focused by the fourth lens 41 and the fifth lens 42 is opposite to the incident angle of the light at the light outlet of the optical fiber 1, and the angles are similar in size within the range of ±5°, so that the convergence point can be better designed according to the incident angle of the laser.

[0038] Furthermore, the output optical system 1000 of the fiber laser further includes a second plane mirror 5 disposed between the fourth lens 41 and the fifth lens 42, and the second plane mirror 5 is tilted relative to the optical axis to correct the aberration caused by the first plane mirror 2. It should be noted that the tilt angle of the second plane mirror 5 is further optimized based on the coma introduced by the tilt setting of the front optical system, especially the first plane mirror 2.

[0039] It should be noted that the basic parameter table of the output optical system 1000 of the fiber laser in one embodiment provided by the present invention is shown in Table 1, wherein the units of thickness and focal length are both millimeters (mm).

[0040]

[0041] Please refer to Figure 1 and Figure 3 In one embodiment of the present invention, the output optical system 1000 of the fiber laser further includes a photoelectric detection device 6, and a filter hole 61 is provided on the photoelectric detection device 6 for receiving part of the reflected light of the first plane mirror 2. With such a configuration, the photoelectric detection device 6 can obtain the power of the reflected light in real time, and by monitoring the reflected light, it can indirectly determine whether the light output of the optical fiber 1 is normal, and at the same time, it can also detect whether the inclination angle of the first plane mirror 2 is reasonable.

[0042] In one embodiment, the output optical system 1000 of the fiber laser further includes an electrically connected monitoring device 7 and an alarm device 8, wherein the monitoring device 7 is electrically connected to the photoelectric detection device 6 and is used to monitor the power of the reflected light, and the alarm device 8 is used to alarm an abnormal condition detected by the monitoring device 7. With such a configuration, when the optical fiber 1 emits light abnormally, the alarm device 8 can issue an alarm in time to avoid damage to components caused by a long-term failure, thereby improving the safety of the system.

[0043] In this embodiment, the numerical aperture NA of the optical fiber 1 in the output optical system 1000 of the optical fiber laser is 0.2, the inclination angle A of the first plane mirror 2 is 10°, the diameter of the filter hole 61 is 1mm, the target surface of the photoelectric detection device 6 is 2.5mm, the filter hole 61 is 5mm away from the target surface, and the target surface is flush with the light outlet of the optical fiber 1. In the main optical path, the spot diameter of the light beam is within the diffraction limit, the energy concentration is higher than 90%, and the wavefront difference RMS is less than 1 / 10λ. It can be seen that in the entire field of view of the optical system, the deviation between the actual wavefront and the ideal wavefront is very small, indicating that the optical system in this embodiment has extremely high laser output quality.

[0044] Furthermore, the materials of the first plane mirror 2, the second plane mirror 5, the collimating lens group 3 and the focusing lens group 4 are all set to fused quartz. It is worth mentioning that fused quartz is an amorphous silicon dioxide formed by rapid cooling of natural quartz after melting at high temperature. It has excellent thermal shock resistance, can remain stable over a large temperature range, and is not easily broken due to rapid temperature changes. Compared with other glass materials, fused quartz has a lower thermal expansion coefficient, which means that its size changes little when heated or cooled, greatly improving the power damage threshold of optical components.

[0045] The above description is only an exemplary embodiment of the present invention, and does not limit the patent scope of the present invention. All equivalent structural changes made by using the contents of the present invention specification and drawings under the technical concept of the present invention, or directly / indirectly applied in other related technical fields are included in the patent protection scope of the present invention.

Claims

1. An output optical system of a fiber laser, characterized in that: It includes an optical fiber, a first plane mirror, a collimating lens group and a focusing lens group arranged in sequence along the optical axis, wherein the first plane mirror is tilted relative to the optical axis, the tilt angle is A, the numerical aperture of the light outlet of the optical fiber is NA, and sinA≥1 / 2NA is satisfied.

2. The output optical system of the fiber laser according to claim 1, characterized in that: The collimating lens group includes a first lens with positive optical power, a second lens with negative optical power, and a third lens with positive optical power, which are sequentially arranged along the optical axis.

3. The output optical system of the fiber laser according to claim 2, characterized in that: The first lens is a biconvex lens; The second lens is a concave-convex lens, and the side surface of the second lens facing the first lens is a concave surface; The third lens is a meniscus lens, and the side surface of the third lens facing the first lens is a convex surface.

4. The output optical system of the fiber laser according to claim 2, characterized in that: The focusing lens group includes a fourth lens with positive optical power and a fifth lens with positive optical power which are sequentially arranged along the optical axis.

5. The output optical system of the fiber laser according to claim 4, characterized in that: The fourth lens is a biconvex lens; The fifth lens is a meniscus lens, and the side surface of the fifth lens facing the fourth lens is a concave surface.

6. The output optical system of the fiber laser according to claim 4, characterized in that: The output optical system of the fiber laser further includes a second plane mirror disposed between the fourth lens and the fifth lens, wherein the second plane mirror is tilted relative to the optical axis to correct the aberration caused by the first plane mirror.

7. The output optical system of the fiber laser according to claim 6, characterized in that: The materials of the first plane mirror, the second plane mirror, the collimating lens group and the focusing lens group all include fused quartz.

8. The output optical system of the fiber laser according to claim 1, characterized in that: The tilt angle A and the numerical aperture NA also satisfy: NA≥sinA.

9. The output optical system of the fiber laser according to claim 1, characterized in that: The output optical system of the fiber laser also includes a photoelectric detection device, and a filter hole is provided on the photoelectric detection device for receiving part of the reflected light emitted by the first plane mirror.

10. The output optical system of the fiber laser according to claim 9, characterized in that: The output optical system of the fiber laser also includes an electrically connected monitoring device and an alarm device. The monitoring device is electrically connected to the photoelectric detection device and is used to monitor the power of the reflected light. The alarm device is used to alarm for abnormal conditions detected by the monitoring device.

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