Photonic crystal fiber and laser light spot homogenizing device

Abstract

The invention provides a photonic crystal fiber and a laser light spot homogenizing device, and belongs to the technical field of laser. The problems that an existing laser light spot homogenizing method is large in technical difficulty, unstable in structure, large in light transmission loss and the like are solved. The photonic crystal fiber comprises a fiber core and a wrapping layer wrapping the fiber core, the fiber core is located in the geometric center of the photonic crystal fiber, three layers of air holes are distributed in the wrapping layer and include outer layer air holes, middle air holes and inner layer air holes, and the inner layer air holes and the outer layer air holes are evenly distributed in a circular array mode with the fiber core as the circle center. The inner-layer air holes are distributed in the periphery of the fiber core, the outer-layer air holes are distributed away from the fiber core, and the middle air holes comprise a plurality of air holes which are randomly distributed between the inner-layer air holes and the outer-layer air holes, are different in size and are irregularly arranged; the method is applied to laser light spot homogenization.

Description

Technical Field

[0001] The invention provides a photonic crystal optical fiber and a laser spot homogenizing device, belonging to the technical field of lasers. Background Art

[0002] Semiconductor lasers, also known as laser diodes, are the most important type of lasers in practical applications. Semiconductor lasers have the advantages of small size, light weight, high photoelectric conversion efficiency, and long service life, and have very broad application prospects. The current practical semiconductor lasers are limited by their own waveguide structure, and the output beam is approximately an elliptical Gaussian beam with astigmatism, and the light intensity distribution is uneven, especially for semiconductor bar and stacked array lasers. Relying on increasing the number of light-emitting units to increase the laser power will inevitably bring greater beam unevenness. In some application fields, such as laser welding, laser peeling, laser micro-machining, etc., the uneven distribution of laser beam energy will cause local temperature to be too high, thereby affecting the interaction between laser and matter. At the same time, the low energy at the edge greatly reduces the energy utilization rate. Therefore, it is necessary to shape the uneven beam into a flat-top beam with uniform energy distribution to improve the laser application effect.

[0003] At present, laser homogenization and shaping technology can be mainly divided into the following categories: aspheric lens method, diffractive optical element method, microlens array method, kaleidoscope method, fiber waveguide coupling method, etc. Among them, the aspheric lens method, diffractive optical element method, and microlens array method are based on the theory of geometric optics. They design lenses or lens combinations for specific incident light beams, and have the defects of poor adaptability, high production cost, and inability to adjust in time according to the changes of the incident light beam. For high-power semiconductor laser shaping technology with uneven light intensity distribution and poor beam coherence, the kaleidoscope method, fiber waveguide coupling and other shaping and homogenization methods are currently mainly used. These methods are all through the division of the beam and the superposition of sub-beams to achieve the redistribution of the output light energy or to make the light beam redistribute the output light energy after multiple reflections in the waveguide. These methods are currently well applied in semiconductor beam homogenization and shaping due to their simple installation, flexible design, and low price. However, the optical loss they bring has always been a problem that has been troubled.

[0004] However, some existing technical solutions also generally have various shortcomings. For example, patent CN201921555348.1 proposes a method of setting curved grooves with different bending radii and periods to make the bending radius and period of the multimode optical fiber embedded in the curved groove different, thereby changing the distribution of the laser transmission mode in the transmission optical fiber, and then changing the laser beam mode output from the end face of the multimode optical fiber to achieve spot homogenization. This method has a simple structure and a low technical level, but the required optical fiber bending radius is small. When the laser power is large, it is easy for the optical fiber to burn due to the small bending radius. Patent CN202211715232.6 proposes a device for homogenizing the laser by setting a curved segment to increase the propagation path of the laser and using the coherence of the laser in the optical fiber. In addition, a vibration device is set to drive the vibration of the curved segment, so that the photons pass through different paths again in a short time after multiple mutual superposition reflections, and the coherence and superposition of the laser are used to achieve a more uniform output. This method uses a vibration device to improve the homogenization effect of the laser and overcomes the problem of the optical fiber radius being too small to bend. However, the introduction of the vibration device has a great impact on the overall light output stability of the laser.

[0005] Although the traditional method of using fiber coupling to achieve semiconductor laser spot homogenization has a simple structure and low price, the laser energy loss of ordinary optical fibers in the homogenization process is relatively large. At the same time, the premise of using ordinary optical fibers to produce very flat top energy is that the optical fiber needs to have a very small winding diameter, usually less than 4 cm, but such a small winding diameter does not meet the long-term reliability requirements of the optical fiber. When the laser power is large, the multiple small-radius bending and winding of the optical fiber can easily cause the optical fiber to burn, which has a great impact on its application.

[0006] As a new product of the 20th century, photonic crystal fiber has been widely used in optical communications, optical sensing, integrated circuits and other fields due to its unique and excellent optical properties. Compared with the traditional fiber waveguide coupling homogenization method, photonic crystal fiber not only has all the advantages of traditional optical fiber, but also overcomes the problems of large transmission loss and narrow single-mode wavelength range of traditional optical fiber. It also has great advantages in reducing fiber loss and achieving high nonlinearity. Therefore, the use of photonic crystal fiber instead of traditional optical fiber in the field of semiconductor laser beam shaping and homogenization will significantly improve the shortcomings of existing homogenization methods and bring better homogenization effects. Summary of the invention

[0007] In order to solve the problems of high technical difficulty, unstable structure, large light transmission loss and the like in the existing laser spot homogenization method, the present invention proposes a photonic crystal fiber and a laser spot homogenization device.

[0008] The technical solution adopted by the present invention is: a photonic crystal optical fiber, comprising a core and a cladding covering the core, wherein the core is located at the geometric center of the photonic crystal optical fiber, and three layers of air holes are distributed in the cladding, namely, an outer layer of air holes, a middle layer of air holes and an inner layer of air holes, wherein the inner layer of air holes and the outer layer of air holes are uniformly distributed in a circular array with the core as the center, the inner layer of air holes are distributed on the periphery of the core, the outer layer of air holes are distributed away from the core, and the middle air holes include a plurality of air holes of different sizes and irregular arrangement randomly distributed between the inner layer of air holes and the outer layer of air holes.

[0009] Furthermore, the diameter of the outer layer air holes is greater than the diameter of the inner layer air holes.

[0010] Furthermore, the fiber core is made of a material having a refractive index greater than that of air.

[0011] Furthermore, each of the outer layer air holes, the middle layer air holes and the inner layer air holes is circular.

[0012] A laser spot homogenizing device comprises a coiled photonic crystal fiber and a laser, wherein one end of the coiled photonic crystal fiber is connected to a coupling interface of the laser, and the other end of the coiled photonic crystal fiber is connected to a fiber light output port.

[0013] Furthermore, it also includes a homogenization box, in which the coiled photonic crystal optical fiber is fixed.

[0014] Furthermore, a groove is provided in the homogenizing box, and the coiled photonic crystal optical fiber is placed in the groove of the homogenizing box.

[0015] Furthermore, the coiled photonic crystal fiber is fixed by an optical glue which is transparent and elastic after curing.

[0016] Furthermore, the coiling diameter of the photonic crystal fiber is 5-8 cm.

[0017] Furthermore, the laser is any one of a semiconductor laser, a solid laser, a gas laser, a liquid laser, a fiber laser, and a free electron laser.

[0018] The beneficial effects of the present invention compared with the prior art are as follows: (1) Compared with the traditional fiber homogenization method, the present invention reduces the loss of laser during fiber transmission, thereby improving the overall optical conversion efficiency of the laser.

[0019] (2) The present invention further improves the irregularity of photon propagation in the optical fiber through the uneven size and irregular arrangement of air holes in the optical fiber, enhances the reflection, refraction and coherence of lasers in the optical fiber, and thus improves the homogenization effect of the light spot.

[0020] (3) The design of the homogenization box not only improves the stability of the structure and reduces optical loss, but also enhances the crosstalk between optical fibers, further improving the light spot homogenization effect.

[0021] (4) The present invention is not only applicable to semiconductor lasers, but also to the spot homogenization of other types of lasers. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] The present invention will be further described below in conjunction with the accompanying drawings: Figure 1 It is a schematic diagram of the structure of the photonic crystal fiber of the present invention; Figure 2 It is a structural schematic diagram of the homogenization device of the present invention; Figure 3 It is a structural schematic diagram of the homogenization box of the present invention; In the figure: 1 is a photonic crystal fiber, 2 is a semiconductor laser, 3 is a coupling interface, 4 is a fiber light output port, 5 is a homogenization box, 11 is a fiber core, 12 is a cladding, and 13 is an air hole. DETAILED DESCRIPTION

[0023] like Figures 1 to 3 As shown, this embodiment provides a photonic crystal fiber 1, such as Figure 1 As shown, the photonic crystal fiber 1 proposed in the present invention is an asymmetric structure, including a core 11 and a cladding 12, wherein the core 11 is arranged at the geometric center of the entire photonic crystal fiber 1, and the cladding 12 is used to cover the core 11. The core 11 is generally composed of quartz or other materials doped. Air holes 13 of different sizes and non-uniform and asymmetric are distributed in the cladding 12. Specifically, a circle of inner air holes are evenly distributed in a circular array on the periphery of the core 11, and a circle of outer air holes are evenly distributed in a circular array on the periphery away from the core 11. Intermediate air holes of different sizes and irregular arrangement are randomly distributed between the inner air holes and the outer air holes, and the diameter of the outer air holes is larger than the diameter of the inner air holes. The core 11 is made of a material with a refractive index greater than the refractive index of air.

[0024] The diameter of the photonic crystal optical fiber 1 of the present invention is substantially the same as that of a common optical fiber, the diameter of the core 11 is 9 um, and the diameter of the cladding 12 is 125 um.

[0025] Due to the addition of the air holes 13, the cladding 12 has a smaller equivalent refractive index than the core 11. According to the total internal reflection condition, compared with ordinary optical fibers, the photonic crystal fiber 1 can greatly increase the proportion of total reflected photons inside the optical fiber, thereby effectively reducing the optical loss caused by photon overflow.

[0026] Since the refractive index of the core 11 is greater than that of air, according to the formula of the critical angle of total internal reflection sinC=n2 / n1, where C is the critical angle of total internal reflection, n1 is the refractive index of the core 11 with a higher density, and n2 is the refractive index of air, the introduction of the air hole 13 in the photonic crystal fiber 1 can further increase the difference in refractive index between the inside and outside of the core 11. When the laser is coupled into the core 11, more photons will be trapped inside the photonic crystal fiber 1, thereby reducing optical loss.

[0027] Based on the above-mentioned photonic crystal fiber 1, the present invention also proposes a laser spot homogenization device, which is mainly used for homogenization of a semiconductor laser 2, including a photonic crystal fiber 1 and a semiconductor laser 2. One end of the photonic crystal fiber 1 is connected to the semiconductor laser 2 through a coupling interface 3, and the other end of the photonic crystal fiber 1 is connected to a fiber light output port 4. The light generated by the semiconductor laser 2 is coupled into the coiled photonic crystal fiber 1, and the homogenization of the light spot is finally achieved according to the refraction, reflection and coherence principles of light.

[0028] In practical applications, the photonic crystal fiber 1 will be bent into a ring structure at a certain angle. The direction of light will be disrupted when it is transmitted in the curved structure. The light can be homogenized by utilizing the refraction, reflection and coherence of light inside the photonic crystal fiber 1. The arrangement of the irregular air holes 13 will further increase the irregularity of light transmission inside the photonic crystal fiber 1, thereby further improving the light homogenization effect. Compared with traditional optical fibers, the photonic crystal fiber 1 with irregular air holes 13 arranged in the present invention can achieve a more significant homogenization effect at a larger coiling radius and a shorter transmission distance. In specific operations, the coiling diameter of the photonic crystal fiber 1 can be controlled at 5-8 cm, and the number of coiling turns can be adjusted according to the actual homogenization effect.

[0029] like Figure 2 and 3 As shown, in actual use, the photonic crystal fiber 1 needs to be coiled and fixed in the homogenization box 5 to ensure the stability of the semiconductor laser 2 during operation. A groove is provided in the homogenization box 5. In specific applications, the coiled photonic crystal fiber 1 is placed in the groove of the homogenization box 5, and an appropriate amount of transparent optical glue that is elastic after curing is injected into the groove. The function of the homogenization box 5 is to fix the coiled photonic crystal fiber 1 to prevent the photonic crystal fiber 1 from being lost due to friction between the claddings 12 during use. At the same time, fixing the coiled photonic crystal fiber 1 can further improve the stability during laser transmission. The use of optical glue increases the crosstalk between the photonic crystal fibers 1, which can improve the utilization rate of photons and thus improve the light spot homogenization effect. The homogenization box 5 uses a black box and is sealed with a lid after injecting the optical glue.

[0030] The device of the present invention can also be applied to various types of semiconductor single-tube and multi-tube lasers. In addition, it is also applicable to non-semiconductor lasers such as solid lasers, gas lasers, liquid lasers, and fiber lasers. The light coupled into the photonic crystal fiber 1 is reflected multiple times, and a light spot with uniform energy distribution is obtained on the fiber output surface, and the homogenization effect is greatly improved compared with other homogenization methods. The presence of the air hole 13 allows most of the photons to be retained inside the photonic crystal fiber 1 due to total internal reflection during the transmission process, and the transmission loss is lower. The design of the homogenization box 5 further reduces the optical loss and improves the light spot homogenization effect.

[0031] The photonic crystal fiber 1 and the laser spot homogenization device based on the photonic crystal fiber 1 proposed in the present invention are based on the fiber waveguide coupling theory, use the photonic crystal fiber 1 to replace the ordinary optical fiber, and set up a fiber winding structure with a large radius, and use a homogenization box 5 that is sealed in black and filled with elastic optical glue. Compared with other methods, not only the spot homogenization effect is improved, the stability of the laser is improved, but also the energy loss of the laser during the transmission process is reduced, thereby improving the overall transmission efficiency of the laser.

[0032] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit it. Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the aforementioned embodiments, or replace some or all of the technical features therein with equivalents. However, these modifications or replacements do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A photonic crystal optical fiber, comprising a core and a cladding covering the core, characterized in that: The fiber core is located at the geometric center of the photonic crystal fiber, and three layers of air holes are distributed in the cladding, namely, outer layer air holes, middle layer air holes and inner layer air holes, wherein the inner layer air holes and the outer layer air holes are evenly distributed in a circular array with the fiber core as the center, the inner layer air holes are distributed on the periphery of the fiber core, the outer layer air holes are distributed away from the fiber core, and the middle air holes include a plurality of air holes of different sizes and irregular arrangement randomly distributed between the inner layer air holes and the outer layer air holes.

2. A photonic crystal fiber according to claim 1, characterized in that: The diameter of the outer layer air holes is larger than the diameter of the inner layer air holes.

3. A photonic crystal fiber according to claim 2, characterized in that: The fiber core is made of a material with a refractive index greater than that of air.

4. A photonic crystal fiber according to any one of claims 1 to 3, characterized in that: Each of the outer layer air holes, the middle layer air holes and the inner layer air holes is circular.

5. A laser spot homogenization device, characterized in that: The invention comprises a coiled photonic crystal fiber as claimed in any one of claims 1 to 4 and a laser, wherein one end of the coiled photonic crystal fiber is connected to the coupling interface of the laser, and the other end of the coiled photonic crystal fiber is connected to the optical fiber light output port.

6. The laser spot homogenization device according to claim 5, characterized in that: The invention also comprises a homogenizing box, in which the coiled photonic crystal optical fiber is fixed.

7. The laser spot homogenization device according to claim 6, characterized in that: A groove is arranged in the homogenizing box, and the coiled photonic crystal optical fiber is placed in the groove of the homogenizing box.

8. The laser spot homogenization device according to claim 7, characterized in that: The coiled photonic crystal fiber is fixed by a transparent optical glue that becomes elastic after curing.

9. A laser spot homogenization device according to any one of claims 5 to 8, characterized in that: The coil diameter of the photonic crystal fiber is 5-8cm.

10. A laser spot homogenization device according to any one of claims 5 to 8, characterized in that: The laser may be any one of a semiconductor laser, a solid laser, a gas laser, a liquid laser, a fiber laser, and a free electron laser.

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