Preparation method of variable grating constant circular grating and variable grating constant circular grating

Abstract

The invention relates to the technical field of optical materials and optical devices, and provides a preparation method of a variable-grating constant circular grating and the variable-grating constant circular grating, and the preparation method comprises the steps: enabling a pulse laser beam to enter from the front surface of a transparent optical medium, to penetrate through the transparent optical medium, and to be focused on the rear surface of the transparent optical medium; forming a plasma area on the rear surface of the transparent optical medium, wherein the plasma area reflects part of the pulse laser beam; the reflected pulse laser beam is divergently propagated in the transparent optical medium, returns to the front surface of the transparent optical medium and induces the front surface material of the transparent optical medium to generate local phase change damage; by regulating and controlling the wavelength, the energy and the relative position of the focus of the pulse laser beam, a non-equidistant concentric annular damage structure is formed on the front surface of the transparent optical medium, and the variable grating constant circular grating is obtained. The problems that in a traditional method for preparing the variable-grating-constant circular grating, the machining precision is insufficient, and the control difficulty is large are solved.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of optical materials and optical devices, in particular to a preparation method of a variable grating constant circular grating and the variable grating constant circular grating. BACKGROUND

[0002] At present, the traditional grating preparation methods such as mechanical etching, photolithography and electron beam exposure have the problems of high processing cost, long cycle and great technical difficulty, especially when manufacturing micro-nano non-equidistant structure, the precision is seriously limited. Although the existing laser-induced processing technology can realize high-precision microstructure processing, it is mainly limited to manufacturing equidistant gratings such as fiber gratings and diffraction gratings, and it is difficult to efficiently generate non-equidistant concentric circular grating structures on transparent media such as fused quartz. SUMMARY

[0003] The present application aims to at least solve the problem that the traditional process cannot efficiently prepare the gradually changing period grating in the related art.

[0004] In order to solve the above technical problems, the present application is realized as follows: In a first aspect, the present application provides a preparation method of a variable grating constant circular grating, comprising: incidenting a pulse laser beam from a front surface of a transparent optical medium, penetrating the transparent optical medium and focusing on a rear surface of the transparent optical medium; forming a plasma region on the rear surface of the transparent optical medium, the plasma region reflecting part of the pulse laser beam; the reflected pulse laser beam propagates inside the transparent optical medium and returns to the front surface of the transparent optical medium, and induces local phase change damage of the material of the front surface of the transparent optical medium; by adjusting the wavelength, energy and relative position of the focusing focal point of the pulse laser beam, a non-equidistant concentric circular ring damage structure is formed on the front surface of the transparent optical medium, and a variable grating constant circular grating is obtained; wherein the distance between the concentric circular rings of the damage structure increases from the inner ring to the outer ring, the ring distance in the range from the center to 20% of the maximum radius is 0.5-1um, and the ring distance in the range from 80% to 100% of the maximum radius is 2-5um.

[0005] The application provides a preparation method of a variable grating constant circular grating, which comprises the following steps: a pulse laser beam is incident from a front surface of a transparent optical medium and accurately focused on a rear surface, a light filament channel not connected to the front surface is formed by using a laser self-focusing effect, a high-density plasma region is generated by ionization at the rear surface, and the plasma in the plasma region forces the laser to reflect from the edge of the light filament channel, and self-phase modulation divergence is caused due to the density difference between the light filament channel and the transparent optical medium, the divergence angle is 5-30°, and a concentric circular ring damage structure with an inner ring spacing of 0.5-1 mu m and an outer ring spacing of 2-5 mu m is spontaneously formed at the front surface of the transparent optical medium. By adjusting the laser pulse energy, wavelength, relative position of the focal point and the scanning path, the problem that a traditional process cannot efficiently prepare a gradually changing period grating is solved.

[0006] In a second aspect, the application provides a variable grating constant circular grating prepared by the preparation method in the above-mentioned scheme, and the variable grating constant circular grating has a non-equidistant concentric circular ring structure induced by a pulse laser beam at the front surface of the transparent optical medium, the depth of the concentric circular ring structure is different, and the ring spacing of the concentric circular ring structure increases in a gradient along the radial direction.

[0007] The variable grating constant circular grating provided by the application is prepared by the preparation method of the above-mentioned technical scheme, so it has all the beneficial effects of the preparation method of the variable grating constant circular grating, which will not be repeated here.

[0008] Additional aspects and advantages of the application will become apparent in the light of the following description and the accompanying drawings. BRIEF DESCRIPTION OF DRAWINGS

[0009] The above and / or additional aspects and advantages of the application will become apparent and be readily understood by considering the following detailed description, from which the above-mentioned aspects and advantages will become apparent and be readily understood, in which: Figure 1 One of the flowcharts of the preparation method of the variable grating constant circular grating according to an embodiment of the application; Figure 2 The second flowchart of the preparation method of the variable grating constant circular grating according to an embodiment of the application; Figure 3 The third flowchart of the preparation method of the variable grating constant circular grating according to an embodiment of the application; Figure 4 The principle diagram of the preparation method of the variable grating constant circular grating according to an embodiment of the application; Figure 5 The physical diagram of the variable grating constant circular grating prepared by the preparation method of the variable grating constant circular grating according to an embodiment of the application.

[0010] In the above-mentioned embodiments of the application, the following are used: Figure 4The correspondence between the reference signs and the component names is as follows: 100 transparent optical medium, 110 front surface of the transparent optical medium, 120 back surface of the transparent optical medium, 130 plasma, 140 pulsed laser beam, 150 non-equidistant concentric circular ring-like damage structure, 160 reflected self-phase modulated light beam. DETAILED DESCRIPTION

[0011] In order to enable a clearer understanding of the above-mentioned objects, features and advantages of the present application, the present application will be further described below with reference to the drawings and specific embodiments. It should be noted that the embodiments of the present application and the features in the embodiments can be combined with each other without conflict.

[0012] In the following description, a large number of specific details are set forth in order to facilitate a thorough understanding of the present application, however, the present application can also be implemented in other manners different from those described herein, and therefore, the protection scope of the present application is not limited by the specific embodiments disclosed below.

[0013] The preparation method and the variable grating constant circular grating according to some embodiments of the present application will be described below with reference to the accompanying drawings. Figures 1 to 5 The preparation method and the variable grating constant circular grating according to some embodiments of the present application will be described below with reference to the accompanying drawings.

[0014] As shown in Figures 1 to 5 , Figure 1 is one of the flowcharts of the preparation method of the variable grating constant circular grating according to an embodiment of the present application; Figure 2 is the second flowchart of the preparation method of the variable grating constant circular grating according to an embodiment of the present application; Figure 3 is the third flowchart of the preparation method of the variable grating constant circular grating according to an embodiment of the present application; Figure 4 is the schematic diagram of the preparation method of the variable grating constant circular grating according to an embodiment of the present application; Figure 5 is the actual diagram of the variable grating constant circular grating prepared by the preparation method of the variable grating constant circular grating according to an embodiment of the present application.

[0015] According to a first aspect of the present application, as Figure 1As shown, one embodiment of the application provides a method for preparing a variable-grating-constant circular grating, which comprises: incidenting a pulsed laser beam from a front surface of a transparent optical medium, penetrating the transparent optical medium and focusing on a rear surface of the transparent optical medium; forming a plasma region on the rear surface of the transparent optical medium, the plasma region reflecting part of the pulsed laser beam; the reflected pulsed laser beam diverges and propagates inside the transparent optical medium and returns to the front surface of the transparent optical medium, and induces local phase change damage of the material of the front surface of the transparent optical medium; by adjusting the wavelength, energy and relative position of the focus of the pulsed laser beam, a non-equidistant concentric circular ring damage structure is formed on the front surface of the transparent optical medium, and a variable-grating-constant circular grating is obtained; wherein the interval between the concentric circular rings of the damage structure increases from the inner ring to the outer ring, the ring interval in the range from the center to 20% of the maximum radius is 0.5 μm to 1 μm, and the ring interval in the range from 80% to 100% of the maximum radius is 2 μm to 5 μm.

[0016] The application provides a method for preparing a variable-grating-constant circular grating, which comprises: incidenting a pulsed laser beam from a front surface of a transparent optical medium, penetrating the transparent optical medium and focusing on a rear surface of the transparent optical medium; forming a plasma region on the rear surface of the transparent optical medium, the plasma region reflecting part of the pulsed laser beam; the reflected pulsed laser beam diverges and propagates inside the transparent optical medium and returns to the front surface of the transparent optical medium, and induces local phase change damage of the material of the front surface of the transparent optical medium; by adjusting the wavelength, energy and relative position of the focus of the pulsed laser beam, a non-equidistant concentric circular ring damage structure is formed on the front surface of the transparent optical medium, and a variable-grating-constant circular grating is obtained; wherein the interval between the concentric circular rings of the damage structure increases from the inner ring to the outer ring, the ring interval in the range from the center to 20% of the maximum radius is 0.5 μm to 1 μm, and the ring interval in the range from 80% to 100% of the maximum radius is 2 μm to 5 μm. By adjusting the laser pulse energy, wavelength, focus relative position and scanning path, the problem of inefficient preparation of the traditional process of the gradually changing period grating is solved.

[0017] Specifically, gratings, as important optical elements, have been widely used in many fields such as optical communication, spectral analysis, lasers, laser display, etc. The traditional manufacturing methods of gratings mainly include mechanical etching, photolithography and electron beam exposure, etc. These methods can produce gratings with periodic structures, but usually have problems such as high processing cost, long processing cycle, high technical difficulty, etc., especially when processing micro-nano structures, the processing precision and efficiency of the traditional methods are often limited.

[0018] In recent years, laser processing technology has become a new method for manufacturing optical elements as a non-contact processing technology due to its high precision and high flexibility. In particular, laser-induced processing technology has been widely used in the microstructure processing of different materials, and can form micro-nano structures of different shapes and sizes on the surface of the material. However, existing laser-induced processing is mostly used for manufacturing equidistant structures, such as fiber gratings, diffraction gratings, etc., and less for manufacturing non-equidistant damage structures, especially on transparent optical materials. In addition, in some applications, the introduction of variable grating constant circular damage structures can often improve the performance of the grating, such as having a significant effect on beam control, optical transmission, optical filtering, etc. The existing technology does not fully utilize the potential of this periodic variable grating constant circular grating structure. For transparent optical materials, the traditional laser processing method has problems such as uneven damage depth, inaccurate processing temperature control, and difficult control of the damage area, which makes it difficult to ensure the performance and stability of the material during processing.

[0019] To solve the problems of the prior art, the present application provides a new laser-induced transparent optical material periodic circular non-equidistant damage structure grating to overcome the defects in the prior art. By introducing a non-equidistant damage structure, the performance of the grating can be improved, such as improving the transmission characteristics of the light beam, improving the stability and durability of the grating, and enabling efficient processing on transparent optical materials.

[0020] As shown in Figure 1 The present application provides a preparation method of a variable grating constant circular grating, and the steps of the preparation method of the variable grating constant circular grating are as follows: S202, a pulsed laser beam is incident from the front surface of the transparent optical medium, penetrates the transparent optical medium and is focused on the back surface of the transparent optical medium; S204, an plasma region is formed on the back surface of the transparent optical medium, and the plasma region reflects part of the pulsed laser beam; S206, the reflected pulsed laser beam propagates inside the transparent optical medium and returns to the front surface of the transparent optical medium, and induces local phase change damage of the material on the front surface of the transparent optical medium; S208, by adjusting the wavelength, energy and focal point relative position of the pulsed laser beam, a non-equidistant concentric circular ring damage structure is formed on the front surface of the transparent optical medium, and a variable grating constant circular grating is obtained.

[0021] The distance between the concentric circular rings of the damage structure increases from the inner ring to the outer ring, and the ring distance in the range from the center to 20% of the maximum radius is 0.5 μm to 1 μm, and the ring distance in the range from 80% to 100% of the maximum radius is 2 μm to 5 μm.

[0022] Specifically, asFigure 4 as shown, Figure 4 is a schematic diagram of a method for preparing a variable-grating-constant circular grating, wherein, Figure 4 The transparent optical medium 100 includes a front surface 110 of the transparent optical medium and a back surface 120 of the transparent optical medium, the gray translucent cuboid represents the transparent optical medium 100, for example, a fused quartz sample, the black arrow represents the incident pulsed laser beam 140, the pulsed laser beam 140 passes through the front surface 110 of the transparent optical medium and is focused on the back surface 120 of the transparent optical medium. The black sphere represents the plasma 130 formed at the back surface 120 of the transparent optical medium, and the gray arrow represents the laser beam reflected by the high-density plasma.

[0023] The principle of the method for preparing a variable-grating-constant circular grating is as follows: during the formation of the damage structure, the incident pulsed laser beam 140 generates a self-focusing effect when it propagates inside the transparent optical medium 100, forming a filament channel that extends to the back surface 120 of the transparent optical medium, inducing ionization and generating plasma 130 at the back surface 120 of the transparent optical medium. Since the filament structure is not directly connected to the front surface 110 of the transparent optical medium, the pulsed laser beam 140 is reflected from the edge of the filament channel after self-focusing transmission. Due to the difference in density between the filament structure and the fused quartz, the reflected self-phase modulation beam 160 will diverge when it propagates out of the filament structure, inducing the formation of a non-equidistant concentric circular ring damage structure 150 on the front surface 110 of the transparent optical medium. Among them, the outer ring is sparse and the inner ring is dense, that is, the spacing between the concentric circular rings of the damage structure increases from the inner ring to the outer ring, and the ring spacing in the range of 0% to 20% of the maximum radius is 0.5-1 pm, and the ring spacing in the range of 80% to 100% of the maximum radius is 2-5 pm. As shown in Figure 5 as shown, Figure 5 When a nanosecond pulsed laser beam, a picosecond pulsed laser beam or a femtosecond pulsed laser beam is focused on the back surface of the transparent optical medium, a non-equidistant concentric circular ring damage structure, i.e. a variable-grating-constant circular grating structure, is formed on the front surface of the transparent optical medium. As shown in FIG. 5, A is the damage pit morphology of the back surface of the transparent optical medium, and B is the non-equidistant concentric circular ring on the front surface of the transparent optical medium.

[0024] The present application provides a novel method for preparing a variable-grating-constant circular grating, which can effectively control the morphology of laser-induced damage structure and ensure the controllability, uniformity and depth of the damage region, thereby providing technical support for the preparation of variable-grating-constant gratings. The laser-induced transparent optical material variable-grating-constant circular grating and its preparation method provided by the present application can solve the problems of insufficient processing precision and difficulty in control of the periodic structure in the prior art, and provide a new solution for efficient and low-cost grating manufacturing technology, while providing more high-performance optical elements for related optical application fields.

[0025] In some embodiments, optionally, the pulsed laser beam is a nanosecond pulsed laser beam, a picosecond pulsed laser beam, or a femtosecond pulsed laser beam.

[0026] Specifically, by setting the pulsed laser beam as a nanosecond pulsed laser beam, a picosecond pulsed laser beam, or a femtosecond pulsed laser beam, it can be ensured that the pulsed laser beam breaks through the breakdown threshold of the transparent optical medium, and a high-reflection plasma is stably generated at the back surface of the transparent optical medium; moreover, the depth of the heat-affected zone is precisely controlled in the range of 0.5 μm to 5 μm, avoiding damage to the structure penetrating through the transparent medium, and ensuring the formation of an independent concentric ring structure on the front surface of the transparent optical medium, and realizing the adaptive inter-ring spacing gradient distribution under single-point laser action.

[0027] In specific applications, for example, for nanosecond pulses, the pulse width can be specifically set to 1 ns, 10 ns, 20 ns, 40 ns, 60 ns, 80 ns, and 100 ns, and the pulse energy can be specifically set to 10 mJ, 20 mJ, 30 mJ, 50 mJ, 80 mJ, and 100 mJ, which can be selected according to actual use, and will not be listed here.

[0028] In some embodiments, optionally, the wavelength of the pulsed laser beam includes an infrared wavelength, a visible wavelength, or an ultraviolet wavelength.

[0029] Specifically, by setting the wavelength of the pulsed laser beam as a short wavelength, the high photon energy characteristics of the ultraviolet band can be fully utilized to directly dissociate the transparent optical medium, and a high-density plasma is efficiently induced at the back surface of the transparent optical medium; moreover, the nonlinear absorption effect of the pulsed laser in the transparent optical medium promotes the stable extension of the self-focusing optical filament channel to the focal point region of the back surface, avoiding early damage to the front surface; at the same time, the short-wavelength diffraction limit advantage is exerted, and the minimum damage point diameter is controlled in the range of 0.8 μm to 1.5 μm, ensuring the formation of a gradual grating structure with an inner-outer ring spacing of 0.5 μm to 5 μm on the front surface of the transparent optical medium.

[0030] In specific applications, the wavelength of the nanosecond pulsed laser beam can be specifically set to 193 nm, 213 nm, 266 nm, 355 nm, etc., which can be selected according to actual use. The wavelengths of other pulse width laser beams will not be listed here.

[0031] In some embodiments, optionally, the single-point diameter of the concentric ring-shaped damage structure is controlled in the range of 1 μm to 10 μm, and the depth is controlled in the range of 0.5 μm to 5 μm.

[0032] Specifically, by controlling the diameter of a single point in the concentric ring-shaped damage structure to 1 μm to 10 μm and the depth to 0.5 μm to 5 μm, the diffraction efficiency of the grating can be significantly enhanced, the volume of the heat-affected zone at a single point can be limited, thermal fusion of adjacent damage structures can be avoided, and the independence and periodicity of the concentric rings can be guaranteed. Through depth gradient control and coordinated ring spacing gradient distribution, the inner spacing of the concentric rings is made denser and the outer spacing is made sparser, which spontaneously forms a phase difference accumulation effect of beam wavefront modulation under the action of a single point laser.

[0033] In some embodiments, optionally, a plasma region is formed on the rear surface of the transparent optical medium, specifically including: when a pulsed laser beam propagates inside the transparent optical medium, it generates a self-focusing effect to form a filament channel, the filament channel extends to the rear surface of the transparent optical medium, ionization is induced at the rear surface of the transparent optical medium and plasma is generated, thus forming a plasma region.

[0034] Specifically, the laser energy is highly localized and transmitted to a precise position on the rear surface through the optical filament channel formed by the self-focusing effect, inducing the generation of high-density plasma without physical connection with the front surface. After some of the pulsed laser is reflected back to the front surface, a radially decreasing energy gradient distribution is formed, thereby autonomously generating a concentric ring structure with a dense inner ring and a sparse outer ring in a single laser action, realizing the control of the gradient grating constant without the need for a complex scanning path.

[0035] In some embodiments, optionally, a non-equidistant concentric ring-shaped damage structure is formed on the front surface of the transparent optical medium, specifically including: plasma forcing a pulsed laser beam to reflect from the edge of the optical filament channel to the front surface of the transparent optical medium; in the case of a density difference between the optical filament channel and the transparent optical medium, the reflected pulsed laser beam undergoes self-phase modulation and diverges at a preset angle; after the diverging beam reaches the front surface of the transparent optical medium, a concentric ring-shaped damage structure with radial energy gradient distribution is formed, wherein the preset angle is 5°~30°.

[0036] Specifically, the confinement of the laser by the plasma forces the beam to be reflected directionally from the edge of the optical filament channel. Combined with the density difference between the optical filament channel and the substrate medium, a self-phase modulation effect is triggered, causing the reflected beam to naturally form a spatial divergence. When this diverging beam propagates to the front surface, it automatically generates a radial energy gradient distribution with a strong center and weak edges. Thus, under the action of a single-point laser, a self-organized concentric ring structure with high-density damage in the inner ring and low-density damage in the outer ring is simultaneously induced, achieving one-step precise shaping of the gradient grating constant.

[0037] like Figure 2 As shown, the specific steps for fabricating a circular grating with variable grating constant are as follows: S302, the pulsed laser beam is incident from the front surface of the transparent optical medium, penetrates the transparent optical medium and is focused on the rear surface of the transparent optical medium; S304, the pulsed laser beam generates a self-focusing effect when transmitting inside the transparent optical medium, forms a filament channel, the filament channel extends to the rear surface of the transparent optical medium, induces ionization at the rear surface of the transparent optical medium and generates a plasma, forms a plasma region, and the plasma region reflects part of the pulsed laser beam; S306, the reflected pulsed laser beam diverges and propagates inside the transparent optical medium, and returns to the front surface of the transparent optical medium, and induces local phase change damage of the material of the front surface of the transparent optical medium; S308, by adjusting the laser parameters of the pulsed laser beam, the plasma forces the pulsed laser beam to reflect from the edge of the filament channel to the front surface of the transparent optical medium; in the case that there is a density difference between the filament channel and the transparent optical medium, the reflected pulsed laser beam is self-phase modulated to diverge at a preset angle, and after the divergent light beam reaches the front surface of the transparent optical medium, a concentric circular ring damage structure with radial gradient distribution of energy is formed, and a variable grating constant circular grating is obtained.

[0038] In specific applications, the preset angle can be specifically set to 5°, 10°, 15°, 20° and 30°, and can be specifically selected according to actual use, which will not be listed here.

[0039] In some embodiments, optionally, as shown in Figure 4 The transparent optical medium is fused quartz or calcium oxide, and the thickness of the transparent optical medium is 0.1mm~10mm.

[0040] Specifically, by selecting fused quartz as the transparent optical medium and controlling the thickness in the range of 0.1mm~10mm, both the laser self-focusing effect can fully develop to form a stable filament channel extending to the rear surface, and the laser beam diverging from the rear surface plasma region can maintain sufficient energy gradient distribution when reaching the front surface; at the same time, the high optical uniformity of fused quartz avoids random scattering of the light beam during transmission, ensuring the edge sharpness of the concentric circular ring structure and the spatial consistency of the gradual grating constant. The thickness of the transparent optical medium is H, and the thickness H is preferably 2mm.

[0041] In specific applications, the thickness of the transparent optical medium fused quartz can be specifically set to 1mm, 2mm, 3mm, 5mm or 10mm, and can be specifically selected according to actual use, which will not be listed here.

[0042] In some embodiments, after forming the non-equidistant concentric circular ring damage structure on the front surface of the transparent optical medium, the preparation method of the variable grating constant circular grating further comprises: using a grinding device to grind the surface of the transparent optical medium with an abrasive having a particle size of 5-10 μm at a pressure of 0.5-2 N / cm2 to remove the molten residue generated by laser processing; polishing the surface of the transparent optical medium with an abrasive having a particle size of 1-2 μm at a pressure of 0.1-0.5 N / cm2 to eliminate cracks and reduce the surface roughness of the transparent optical medium; detecting the integrity of the front surface concentric ring structure by an optical microscope to ensure that the grinding process only removes the rear surface defects while retaining the front surface grating structure.

[0043] Specifically, through the step-by-step grinding and polishing process, the molten residue and micro-crack layer generated on the rear surface due to the high temperature of the plasma are accurately peeled off, and at the same time, the inherent physical isolation characteristics of the front surface concentric circular ring structure and the substrate medium are utilized to ensure that the grinding stress is completely limited to the rear surface area; in combination with real-time monitoring by an optical microscope, the front surface micro-nano ring grating structure is completely retained while the rear processing defects are completely removed, thereby achieving the dual goals of “rear surface purification” and “front surface fidelity”.

[0044] Specifically, as shown in FIG. 1, the specific preparation method of the variable grating constant circular grating comprises the following steps: Figure 3 S402, the pulsed laser beam is incident from the front surface of the transparent optical medium, penetrates the transparent optical medium and is focused on the rear surface of the transparent optical medium; S404, an plasma region is formed on the rear surface of the transparent optical medium, and the plasma region reflects part of the pulsed laser beam; S406, the reflected pulsed laser beam diverges and propagates inside the transparent optical medium and returns to the front surface of the transparent optical medium, and induces local phase change damage of the material of the front surface of the transparent optical medium; S408, a non-equidistant concentric circular ring damage structure is formed on the front surface of the transparent optical medium by adjusting the wavelength, energy and focal point relative position of the pulsed laser beam; S410, the rear surface of the transparent optical medium that has been damaged is ground away to obtain a variable grating constant circular grating.

[0045] By adjusting the wavelength, energy and focal point relative position of the pulsed laser beam, the ring spacing and ring width can be adjusted, thereby adjusting the circular grating constant.

[0046] ​In some embodiments, optionally, the preparation method of the variable-constant circular grating further comprises: collecting a front surface topography image of the transparent optical medium by an optical stereomicroscope, dynamically adjusting the pulse wavelength, pulse energy and pulse focal point relative position of the pulsed laser beam; and feeding back and controlling the scanning speed of the pulsed laser beam according to the diffraction efficiency detected by the spectrum analyzer.

[0047] Specifically, the forming state of the front surface concentric ring is captured in real time by the optical stereomicroscope, the pulse energy is dynamically adjusted according to the integrity and gradient distribution characteristics of the ring structure, so as to ensure that the plasma generation condition is always in the optimal interval; the diffraction efficiency change is monitored synchronously based on the spectrum analyzer, the matching degree of the ring spacing gradient and the design target is deduced reversely, and the scanning speed is adjusted adaptively to maintain the consistency of the variable-constant gradient of the whole area.

[0048] According to a second aspect of the present application, a variable-constant circular grating prepared by the preparation method in the above embodiments is also provided, the front surface of the transparent optical medium has a non-equal-interval concentric ring structure induced by a pulsed laser beam, the depth of the concentric ring structure is different, and the ring spacing of the concentric ring structure increases in a gradient along the radial direction.

[0049] Specifically, the variable-constant circular grating provided by the present application is prepared by the preparation method of the above embodiments, and therefore has all the beneficial effects of the preparation method of the variable-constant circular grating, which will not be described here again.

[0050] The present application provides a new type of variable-constant circular grating and a preparation method thereof formed on the surface of a laser-induced transparent optical medium, such as fused quartz. The core is that a laser beam with a pulse width of, for example, nanoseconds is focused on the back surface of the transparent optical medium, fused quartz, to induce a unique non-equal-interval concentric ring circular grating structure, i.e., a micro-nano optical structure, on the front surface of the material. By precisely controlling the laser pulse width, pulse energy, laser beam focal point position and other parameters, a plurality of periodic circular damage points are induced on the surface of the fused quartz. The single damage structure presents a non-equal-interval concentric ring shape, in which the outer ring is sparse and the inner ring is dense. The diameter and depth of each circular damage point and the concentric circle can be finely adjusted according to the design requirements of the grating, so as to realize a specific optical function.

[0051] Due to the existing optical structure preparation technology, the common grating or microstructure is often processed by directly laser processing or etching the front surface, although certain effects have been achieved, but there are certain limitations in precision, structural stability and preparation efficiency. The traditional process needs multiple operations, and can only form fixed form structures on the material surface, which is difficult to control and optimize the micro-optical performance. The key innovation of the present application is the unique non-equal-interval concentric ring grating structure, and the morphology, size and distribution of these microstructures can be accurately controlled according to the parameters of the laser such as wavelength, energy, focusing mode, etc., so as to realize specific optical functions.

[0052] The grating structure of the present application is based on the non-interval concentric ring circular damage structure formed on the surface of the laser-induced transparent optical material. By scanning the transparent optical material with a laser beam of a certain pulse width, the parameters such as laser pulse energy, scanning speed, laser beam focal point position are controlled, and a plurality of circular damage points are induced on the surface of the transparent optical material. The single damage structure presents a non-equal-interval concentric ring shape, in which the outer ring is sparse and the inner part is dense, and the diameter and depth of each damage point can be finely controlled according to the grating design requirements. For example, in the grating design for diffraction of specific wavelength light, the damage point diameter can be controlled in 1-10 μm, and the depth can be flexibly adjusted between 0.5-5 μm. The grating action area can be set with different damage structures according to actual needs, and by combining the design of damage point distribution, shape and size, the diffraction, interference and other optical effects of specific wavelength light can be realized. For example, in the field of optical communication, high-efficiency separation and transmission of different communication wavelengths can be realized by optimizing the damage structure. Through laser focusing on the back surface, complex and fine front surface optical structures can be quickly generated.

[0053] The method for fabricating a circular grating with variable grating constant presented in this application significantly improves fabrication efficiency compared to the complex etching or photolithography processes of traditional techniques. The specific fabrication steps are as follows: First, prepare the fused silica substrate. Select high-purity fused silica material with excellent optical properties as the substrate. Clean its surface using ultrasonic cleaning and chemical reagent wiping to remove dust, oil, and other contaminants, ensuring a clean surface and providing a good foundation for subsequent laser processing. Second, adjust the laser equipment parameters. Precisely adjust parameters such as laser pulse width, beam power, pulse frequency, and focal position. For example, set the nanosecond laser pulse width to 1 nanosecond to 100 nanoseconds and adjust the beam power between 1 watt and 10 watts to generate a controllable thermal effect on the fused silica surface, achieving localized melting of the material. Third, laser scanning forms the damage structure. Scan the fused silica surface with the adjusted laser beam according to a pre-designed scanning path. During the scanning process, the laser energy causes localized instantaneous melting of the material, followed by cooling and solidification to form a circular damage structure. By rationally planning the scanning path, a non-periodic distribution of damage points within the grating region is achieved. The fourth step involves adjusting parameters to control the grating function. Based on the grating design requirements, the scanning parameters of the laser beam, including scanning speed, pulse energy, and laser wavelength, are adjusted in real time to precisely control the distribution, diameter, and depth of damage points, thereby achieving the desired grating function. Finally, surface grinding and structural optimization are performed. High-precision grinding equipment is used, with step-by-step processing from coarse grinding (particle size 5μm~10μm) to fine grinding (particle size 1μm~2μm). The focus is on removing defects, cracks, or molten residue generated during laser processing, leaving only concentric ring structures on the transparent medium to fabricate a circular grating with a variable grating constant. During the fabrication process, optical microscopes and spectrometers can be used to monitor the formed damage structure in real time, and parameters are optimized based on the monitoring results. Finally, real-time monitoring ensures accuracy. Throughout the entire fabrication process, a real-time monitoring system is established. High-resolution microscopes are used to observe changes in the morphology of the fused silica surface, and spectrometers are used to detect the optical performance of the grating. Problems encountered during processing are identified and resolved promptly, ensuring the accuracy and stability of the grating structure.

[0054] By precisely controlling laser parameters, non-periodic circular damage structures can be efficiently and accurately formed on the surface of transparent media. Compared with traditional fabrication methods, the processing accuracy can be significantly improved, and the processing speed is fast, greatly shortening the production cycle and meeting the high performance requirements of gratings in modern optics. The laser technology used in this application eliminates the need for complex photolithography masks, reducing mask manufacturing costs and process complexity. At the same time, equipment costs and raw material consumption are also significantly reduced, resulting in lower production costs compared to traditional methods, making it suitable for large-scale production.

[0055] In the description of this application, the term "multiple" refers to two or more. Unless otherwise expressly defined, the terms "upper," "lower," etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings, and are only for the convenience of describing this application and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation, and therefore should not be construed as a limitation of this application. The terms "connection," "installation," "fixing," etc., should be interpreted broadly. For example, "connection" can be a fixed connection, a detachable connection, or an integral connection; it can be a direct connection or an indirect connection through an intermediate medium. For those skilled in the art, the specific meaning of the above terms in this application can be understood according to the specific circumstances.

[0056] In the description of this specification, the terms "one embodiment," "some embodiments," "specific embodiment," etc., refer to a specific feature, structure, material, or characteristic described in connection with that embodiment or example, which is included in at least one embodiment or example of this application. In this specification, the illustrative expressions of the above terms do not necessarily refer to the same embodiment or example. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in one or more embodiments or examples.

[0057] The above are merely preferred embodiments of this application and are not intended to limit this application. Various modifications and variations can be made to this application by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of this application should be included within the protection scope of this application.

Claims

1. A method for fabricating a circular grating with variable grating constant, characterized in that, include: A pulsed laser beam is incident from the front surface of a transparent optical medium, penetrates the transparent optical medium, and is focused on the rear surface of the transparent optical medium; A plasma region is formed on the rear surface of the transparent optical medium, and the plasma region reflects a portion of the pulsed laser beam; The reflected pulsed laser beam diverges and propagates inside the transparent optical medium, then returns to the front surface of the transparent optical medium, inducing local phase transition damage to the front surface material of the transparent optical medium. By adjusting the wavelength, energy, and focal relative position of the pulsed laser beam, a non-equidistant concentric ring-shaped damage structure is formed on the front surface of the transparent optical medium, resulting in a variable grating constant circular grating. The spacing between the concentric rings of the damaged structure increases gradually from the inner ring to the outer ring. The spacing between the rings is 0.5μm to 1μm within the range from the center to 20% of the maximum radius, and the spacing between the rings is 2μm to 5μm within the range from 80% to 100% of the maximum radius.

2. The method for fabricating a circular grating with variable grating constant according to claim 1, characterized in that, The pulsed laser beam is a nanosecond pulsed laser beam, a picosecond pulsed laser beam, or a femtosecond pulsed laser beam.

3. The method for fabricating a circular grating with variable grating constant according to claim 1, characterized in that, The wavelength of the pulsed laser beam includes infrared wavelength, visible wavelength, or ultraviolet wavelength.

4. The method for fabricating a circular grating with variable grating constant according to claim 1, characterized in that, The diameter of a single point in the concentric annular damage structure is controlled between 1 μm and 10 μm, and the depth is controlled between 0.5 μm and 5 μm.

5. The method for fabricating a circular grating with variable grating constant according to claim 1, characterized in that, The formation of a plasma region on the rear surface of the transparent optical medium specifically includes: The pulsed laser beam generates a self-focusing effect when propagating inside the transparent optical medium, forming an optical filament channel. The optical filament channel extends to the rear surface of the transparent optical medium, inducing ionization and generating plasma at the rear surface of the transparent optical medium, thus forming the plasma region.

6. The method for fabricating a circular grating with variable grating constant according to claim 5, characterized in that, The formation of non-equidistant concentric ring-shaped damage structures on the front surface of the transparent optical medium specifically includes: The plasma forces a portion of the pulsed laser beam to be reflected back to the front surface of the transparent optical medium; When there is a density difference between the optical filament channel and the transparent optical medium, the reflected pulsed laser beam undergoes self-phase modulation and diverges at a preset angle. After the diverging beam reaches the front surface of the transparent optical medium, it forms a concentric ring-shaped damage structure with radial energy gradient distribution, wherein the preset angle is 5°~30°.

7. The method for fabricating a circular grating with variable grating constant according to claim 1, characterized in that, The thickness of the transparent optical medium is 0.1 mm to 10 mm.

8. The method for fabricating a circular grating with variable grating constant according to claim 1, characterized in that, After forming a non-equidistant concentric annular damage structure on the front surface of the transparent optical medium, the method for fabricating the variable grating constant circular grating further includes: The surface of the transparent optical medium is ground using a grinding device with a particle size of 5μm to 10μm and a pressure of 0.5 N / cm² to 2 N / cm² to remove molten residues generated during laser processing. The surface of the transparent optical medium is polished using abrasive with a particle size of 1μm to 2μm and a pressure of 0.1 N / cm² to 0.5 N / cm² to eliminate cracks and reduce the surface roughness of the transparent optical medium. The integrity of the concentric ring structure on the front surface is inspected using an optical stereomicroscope to ensure that the grinding process removes only the damaged rear surface while preserving the grating structure on the front surface.

9. The method for fabricating a circular grating with variable grating constant according to claim 1, characterized in that, The method for fabricating the variable grating constant circular grating further includes: The morphology image of the front surface of the transparent optical medium is acquired using the optical stereo microscope, and the pulse wavelength, pulse energy, and relative position of the pulse focus of the pulsed laser beam are dynamically adjusted. The scanning speed of the pulsed laser beam is controlled based on the diffraction efficiency detected by the spectrometer.

10. A circular grating with variable grating constant, characterized in that, Prepared by the preparation method according to any one of claims 1 to 9, the front surface of the transparent optical medium has a non-equidistant concentric ring structure induced by the pulsed laser beam, the inter-ring depths of the concentric ring structure are different, and the inter-ring spacing of the concentric ring structure increases in a gradient along the radial direction.

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