A Photonic Crystal Fiber and a Laser Spot Homogenization Device

Abstract

The present invention provides a photonic crystal fiber and a laser spot homogenization device, belonging to the field of laser technology; it solves the problems existing in the existing laser spot homogenization methods, such as high technical difficulty, unstable structure, large optical transmission loss, etc.; the photonic crystal fiber proposed by the present invention includes a core and a cladding that wraps the core. The core is located at the geometric center of the photonic crystal fiber. There are three layers of air holes distributed in the cladding, namely outer layer air holes, middle layer air holes and inner layer air holes. Among them, both the inner layer air holes and the outer layer air holes are uniformly distributed in a circular array with the core as the center of the circle. The inner layer air holes are distributed around the core, and the outer layer air holes are distributed far from the core. The middle layer air holes include a plurality of air holes with different sizes and irregular arrangements randomly distributed between the inner layer air holes and the outer layer air holes; the present invention is applied to laser spot homogenization.

Description

Technical Field

[0001] The present invention provides a photonic crystal fiber and a laser spot homogenization device, belonging to the field of laser technology. Background Art

[0002] A semiconductor laser, also known as a laser diode, is one of the most important types of lasers in practical applications. The semiconductor laser has the advantages of small size, light weight, high photoelectric conversion efficiency, long service life, etc., and has a very broad application prospect. The currently practical semiconductor lasers are limited by their own waveguide structures, and the output beam is approximately an elliptical Gaussian beam with astigmatism, and the light intensity distribution is uneven. Especially for semiconductor laser bars and stacked array lasers, increasing the number of light-emitting units to improve the laser power will inevitably bring greater beam non-uniformity. In some application fields, such as laser welding, laser stripping, laser microfabrication, etc., the uneven distribution of the laser beam energy will cause too high local temperature, thus affecting the interaction between the laser and the substance. At the same time, the too low energy at the edge part 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] Currently, laser homogenization and shaping technologies can be mainly divided into the following categories: aspherical lens method, diffractive optical element method, microlens array method, kaleidoscope method, fiber waveguide coupling method, etc. Among them, the aspherical lens method, diffractive optical element method, and microlens array method are based on geometric optical theory, designing lenses or lens combinations for specific incident beams, and have defects such as poor adaptability, high manufacturing cost, and inability to adjust in time according to the change of the incident beam. For the shaping technology of high-power semiconductor lasers with uneven light intensity distribution and poor beam coherence, currently, mainly kaleidoscope method, fiber waveguide coupling and other shaping and homogenization methods are adopted. These methods all achieve the redistribution of the output light energy by splitting the beam and superimposing the sub-beams or making the output light energy redistribute after the beam is reflected multiple times in the waveguide. These methods have been well applied in semiconductor beam homogenization and shaping due to their simple alignment, flexible design, and low price. However, the optical loss brought by them has always been a problem that is much troubled.

[0004] However, some existing technical solutions generally have various deficiencies. For example, Patent CN201921555348.1 proposes a method of setting bending grooves with different bending radii and periods, so that the multi-mode optical fibers embedded in the bending grooves have different bending radii and periods, thereby changing the transmission mode distribution of the laser in the transmission optical fiber, and then changing the laser beam mode output from the end face of the multi-mode optical fiber to achieve spot homogenization. This method has a simple structure and a low technical level, but the required bending radius of the optical fiber is small, and when the laser power is large, it is easy for the optical fiber to be burned due to the too small bending radius. Patent CN202211715232.6 proposes a device for homogenizing laser by setting a bending section 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 bending section to vibrate, so that the photons pass through different paths again after multiple mutual superposition reflections in a short time, and more uniform output is achieved by using the coherence and superposition of the laser. This method uses a vibration device to improve the homogenization effect of the laser and overcomes the problem of too small bending radius of the optical fiber, but 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 cost, the laser energy loss in the light homogenization process of ordinary optical fibers is large. At the same time, the premise of using ordinary optical fibers to generate a very flat top energy is that the optical fiber needs to have a very small coiling diameter, usually less than 4 cm. However, such a small coiling diameter does not meet the long-term reliability requirements of the optical fiber. When the laser power is large, multiple small-radius bending and coiling of the optical fiber are likely to cause the optical fiber to burn, which has a great impact on its application.

[0006] As a new product in the 20th century, photonic crystal fiber has been widely used in the fields of optical communication, optical sensing, integrated circuits, etc. 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 fibers, but also overcomes the problems of large transmission loss and narrow single-mode wavelength range of traditional optical fibers, and also has great advantages in reducing fiber loss and achieving high nonlinearity. Therefore, replacing traditional optical fibers with photonic crystal fibers in the field of semiconductor laser beam shaping and homogenization will significantly improve the deficiencies of existing homogenization methods and bring better homogenization effects. Summary of the Invention

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

[0008] The technical solution adopted by the present invention is as follows: A photonic crystal fiber includes a core and a cladding that wraps the core. The core is located at the geometric center of the photonic crystal fiber. There are three layers of air holes distributed in the cladding, namely outer air holes, middle air holes, and inner air holes. Among them, both the inner air holes and the outer air holes are evenly distributed in a circular array with the core as the center. The inner air holes are distributed around the core, and the outer air holes are distributed far from the core. The middle air holes include a plurality of air holes with different sizes and irregular arrangements randomly distributed between the inner air holes and the outer air holes.

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

[0010] Further, the core is made of a material with a refractive index greater than that of air.

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

[0012] A laser spot homogenization device includes a coiled photonic crystal fiber and a laser. 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 fiber output port.

[0013] Further, it further includes a homogenization box, and the coiled photonic crystal fiber is fixed in the homogenization box.

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

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

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

[0017] Further, the laser adopts any one of semiconductor lasers, solid-state lasers, gas lasers, liquid lasers, fiber lasers, and free-electron lasers.

[0018] The beneficial effects of the present invention compared with the prior art are as follows:

[0019] (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.

[0020] (2) Through the air hole structure with uneven sizes and irregular arrangements inside the photonic crystal fiber, the present invention further improves the irregularity of photon propagation inside the fiber, enhances the reflection, refraction, and coherence of the laser inside the fiber, thereby improving the homogenization effect of the light spot.

[0021] (3) The design of the homogenization box not only improves the structural stability, reduces optical loss, but also enhances the crosstalk between optical fibers, further improving the spot homogenization effect.

[0022] (4) The present invention is not only applicable to semiconductor lasers, but also applicable to the spot homogenization of other types of lasers. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] The present invention will be further described below in conjunction with the accompanying drawings:

[0024] Figure 1 is a schematic structural diagram of the photonic crystal fiber of the present invention;

[0025] Figure 2 is a schematic structural diagram of the homogenization device of the present invention;

[0026] Figure 3 is a schematic structural diagram of the homogenization box of the present invention;

[0027] In the figure: 1 is a photonic crystal fiber, 2 is a semiconductor laser, 3 is a coupling interface, 4 is an optical fiber light output port, 5 is a homogenization box, 11 is a core, 12 is a cladding, and 13 is an air hole. DETAILED DESCRIPTION OF THE INVENTION

[0028] As Figures 1 to 3 shown, this embodiment provides a photonic crystal fiber 1. As Figure 1 shown, the photonic crystal fiber 1 proposed by the present invention has an asymmetric structure, including a core 11 and a cladding 12. The core 11 is disposed at the geometric center of the entire photonic crystal fiber 1, and the cladding 12 is used to coat the core 11. The core 11 is generally composed of quartz or other doped materials. The cladding 12 is distributed with air holes 13 of different sizes and non-uniform and asymmetric. Specifically, a circle of inner air holes is uniformly distributed in a circular array around the periphery of the core 11, and a circle of outer air holes is uniformly distributed in a circular array away from the periphery of the core 11. Between the inner air holes and the outer air holes, intermediate air holes of different sizes and irregular arrangements are randomly distributed, and the diameter of the outer air holes is greater than that of the inner air holes. The core 11 is made of a material with a refractive index greater than that of air.

[0029] The diameter of the photonic crystal fiber 1 of the present invention is basically 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.

[0030] 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 a common optical fiber, the photonic crystal fiber 1 can greatly increase the proportion of photons undergoing total internal reflection inside the optical fiber, thereby effectively reducing the optical loss caused by photon overflow.

[0031] Since the refractive index of the core 11 is greater than that of air, according to the total internal reflection critical angle formula sinC = n2 / n1, where C is the critical angle for total internal reflection, n1 is the refractive index of the denser core 11, and n2 is the refractive index of air. Therefore, the introduction of air holes 13 in the photonic crystal fiber 1 can further increase the refractive index difference between the inside and outside of the core 11. When the laser is coupled into the core 11, more photons will be confined inside the photonic crystal fiber 1, thereby reducing optical losses.

[0032] Based on the above-mentioned photonic crystal fiber 1, the present invention also proposes a laser spot homogenization device, which is mainly used for homogenizing the semiconductor laser 2. It includes the photonic crystal fiber 1 and the 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 output port 4. The light generated by the semiconductor laser 2 is coupled into the coiled photonic crystal fiber 1, and finally the homogenization of the spot is achieved according to the principles of light refraction, reflection and coherence.

[0033] In practical applications, the photonic crystal fiber 1 will be bent into a ring structure at a certain angle. When light travels in the bent structure, its direction will be disrupted. By utilizing the refraction, reflection and coherence of light inside the photonic crystal fiber 1, the homogenization of light can be achieved. 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 fibers, the photonic crystal fiber 1 with irregular air hole 13 arrangement proposed by the present invention can achieve a more remarkable homogenization effect at a larger coiling radius and a shorter transmission distance. During specific operation, the coiling diameter of the photonic crystal fiber 1 can be controlled within 5 - 8 cm, and the number of coiling turns can be adjusted according to the actual homogenization effect.

[0034] Such as Figure 2 and 3 As shown, during 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. The homogenization box 5 is provided with a groove. Specifically, when applied, the coiled photonic crystal fiber 1 is placed in the groove of the homogenization box 5, and an appropriate amount of transparent and elastic optical glue after curing is injected into the groove. The function of the homogenization box 5 is to fix the coiled photonic crystal fiber 1, prevent optical fiber losses caused by friction between the claddings 12 during the use of the photonic crystal fiber 1, and 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, can improve the photon utilization rate, and thus improve the spot homogenization effect. The homogenization box 5 is made of a black box and is sealed with a lid after injecting the optical glue.

[0035] The device of the present invention can also be applied to various types of lasers such as semiconductor single tubes and multi-tubes. In addition, it is also applicable to non-semiconductor lasers such as solid-state 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 a uniform energy distribution is obtained at the fiber output surface, and the homogenization effect is greatly improved compared with other homogenization methods. The presence of the air holes 13 enables most photons to be retained inside the photonic crystal fiber 1 due to total internal reflection during the transmission process, resulting in lower transmission losses. The design of the homogenization box 5 further reduces the optical loss and improves the light spot homogenization effect.

[0036] The photonic crystal fiber 1 proposed by the present invention and the laser light spot homogenization device based on the photonic crystal fiber 1, on the basis of the fiber waveguide coupling theory, uses the photonic crystal fiber 1 to replace the ordinary fiber, sets a fiber coiling structure with a large radius, and uses a homogenization box 5 that is black-sealed and filled with elastic optical glue. Compared with other methods, it not only improves the light spot homogenization effect, enhances the stability of the laser, but also reduces the energy loss during the laser transmission process, thereby improving the overall transmission efficiency of the laser.

[0037] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and are not intended to limit them. Although the present invention has been described in detail with reference to the foregoing embodiments, those of ordinary skill in the art should understand that they can still modify the technical solutions described in the foregoing embodiments, or perform equivalent replacements for some or all of the technical features. And these modifications or replacements do not make the essence of the corresponding technical solutions 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 uniformly distributed in a circular array with the fiber core as the center, the inner layer air holes are distributed around 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; The diameter of the outer layer air holes is larger than the diameter of the inner layer air holes.

2. A photonic crystal fiber according to claim 1, characterized in that: The fiber core is made of a material with a refractive index greater than that of air.

3. A photonic crystal fiber according to claim 1 or 2, characterized in that: Each of the outer layer air holes, the middle layer air holes and the inner layer air holes is circular.

4. 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 3 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.

5. The laser spot homogenization device according to claim 4, characterized in that: The invention also comprises a homogenizing box, in which the coiled photonic crystal optical fiber is fixed.

6. The laser spot homogenization device according to claim 5, 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.

7. The laser spot homogenization device according to claim 6, characterized in that: The coiled photonic crystal fiber is fixed by a transparent optical glue that becomes elastic after curing.

8. A laser spot homogenization device according to any one of claims 4 to 7, characterized in that: The coil diameter of the photonic crystal fiber is 5-8cm.

9. A laser spot homogenization device according to any one of claims 4 to 7, characterized in that: The laser may be any one of a semiconductor laser, a solid laser, a gas laser, a liquid laser, and a free electron laser.

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