Method for manufacturing variable-raster constant circular grating and variable-raster constant circular grating

Abstract

The application 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. The preparation method comprises the following steps: a pulse laser beam is incident from a front surface of a transparent optical medium, penetrates the transparent optical medium and is focused on a 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 part of the pulse laser beam; the reflected pulse laser beam diverges and propagates inside the transparent optical medium, 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 focal point relative position of the pulse laser beam, a non-equal-interval concentric circular ring damage structure is formed on the front surface of the transparent optical medium, and the variable-grating-constant circular grating is obtained. The problems of insufficient machining precision and great control difficulty in the traditional preparation method of the variable-grating-constant circular grating 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 implemented as follows:

[0005] 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.

[0006] 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.

[0007] 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.

[0008] 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 described here.

[0009] Additional aspects and advantages of the application will become apparent in the light of the following description and the practices of the application. BRIEF DESCRIPTION OF DRAWINGS

[0010] 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 aspects and advantages of the application will be readily understood, in connection with the accompanying drawings.

[0011] Figure 1 One of the flowcharts of the preparation method of the variable grating constant circular grating according to an embodiment of the application;

[0012] Figure 2 The second flowchart of the preparation method of the variable grating constant circular grating according to an embodiment of the application;

[0013] Figure 3 The third flowchart of the preparation method of the variable grating constant circular grating according to an embodiment of the application;

[0014] Figure 4 The principle diagram of the preparation method of the variable grating constant circular grating according to an embodiment of the application;

[0015] Figure 5Figure 1 is a photograph of a variable grating constant circular grating prepared by a preparation method of a variable grating constant circular grating according to an embodiment of the present application.

[0016] wherein, Figure 4 The correspondence between the reference signs and the component names in the drawings is as follows:

[0017] 100 transparent optical medium, 110 front surface of the transparent optical medium, 120 back surface of the transparent optical medium, 130 plasmon, 140 pulsed laser beam, 150 non-equidistant concentric circular ring-like damage structure, 160 reflected self-phase modulation beam. DETAILED DESCRIPTION

[0018] In order to enable a more complete understanding of the above-mentioned objects, features and advantages of the present application, the present application will be described in further detail below with reference to the accompanying 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, if possible.

[0019] In the following description, a large number of specific details are set forth in order to facilitate a thorough understanding of the present application, but the present application can also be implemented in other ways different from those described herein, and therefore the scope of protection of the present application is not limited by the specific embodiments disclosed below.

[0020] The preparation method of a variable grating constant circular grating 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 of a variable grating constant circular grating 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.

[0021] As Figures 1 to 5 shown, Figure 1 Figure 1 is a photograph of a variable grating constant circular grating prepared by a preparation method of a variable grating constant circular grating according to an embodiment of the present application. Figure 2 Figure 1 is a photograph of a variable grating constant circular grating prepared by a preparation method of a variable grating constant circular grating according to an embodiment of the present application. Figure 3 Figure 1 is a photograph of a variable grating constant circular grating prepared by a preparation method of a variable grating constant circular grating according to an embodiment of the present application. Figure 4 Figure 1 is a photograph of a variable grating constant circular grating prepared by a preparation method of a variable grating constant circular grating according to an embodiment of the present application. Figure 5 Figure 1 is a photograph of a variable grating constant circular grating prepared by a preparation method of a variable grating constant circular grating according to an embodiment of the present application.

[0022] 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.

[0023] 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 non-connected front surface optical filament channel by using the laser self-focusing effect, inducing ionization to generate a high-density plasma region on the rear surface, and forcing the laser to reflect from the edge of the optical filament channel by the plasma in the plasma region; due to the density difference between the optical filament channel and the transparent optical medium, self-phase modulation divergence is induced, the divergence angle is 5° to 30°, and a concentric circular ring damage structure with inner dense and outer sparse is spontaneously formed on the front surface of the transparent optical medium, wherein the inner ring interval is 0.5 μm to 1 μm, and the outer ring interval is 2 μm to 5 μm. By adjusting the laser pulse energy, wavelength, focus relative position and scanning path, the problem of being unable to efficiently prepare a gradually changing period grating by traditional process is solved.

[0024] Specifically, gratings are important optical elements and 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 traditional methods are often limited.

[0025] In addition, in recent years, laser processing technology as a non-contact processing technology has become a new method for manufacturing optical elements 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 damage area control, which makes it difficult to ensure the performance and stability of the material during processing.

[0026] 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.

[0027] 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:

[0028] S202, 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 back surface of the transparent optical medium;

[0029] S204, forming a plasma region on the back surface of the transparent optical medium, the plasma region reflecting part of the pulsed laser beam;

[0030] 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;

[0031] 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.

[0032] The interval between the concentric rings of the damage structure increases from the inner ring to the outer ring, the interval between the rings in the range of 0-20% of the maximum radius is 0.5-1 pm, and the interval between the rings in the range of 80-100% of the maximum radius is 2-5 pm.

[0033] Specifically, as shown in Figure 4 , Figure 4 is a schematic diagram of the preparation method of the 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, and the black arrow represents the incident pulsed laser beam 140, which 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.

[0034] The principle of the preparation method of the 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 transmitting 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 propagating out of the filament structure, inducing the formation of a non-equidistant concentric ring damage structure 150 on the front surface 110 of the transparent optical medium. Wherein, the outer ring is sparse and the inner ring is dense, that is, the interval between the concentric rings of the damage structure increases from the inner ring to the outer ring, the interval between the rings in the range of 0-20% of the maximum radius is 0.5-1 pm, and the interval between the rings in the range of 80-100% of the maximum radius is 2-5 pm. As shown in Figure 5 , 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 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 ring of the front surface of the transparent optical medium.

[0035] The application provides a preparation method of a novel variable grating constant circular grating, which can effectively control laser-induced damage structure morphology and ensure controllability, uniformity and depth of the damage area, thereby providing technical support for preparation of the variable grating constant grating. The laser-induced transparent optical material variable grating constant circular grating and the preparation method thereof can solve the problems of insufficient processing precision of the periodic structure and great control difficulty in the prior art, provide a new solution for efficient and low-cost grating manufacturing technology, and provide an optical element with higher performance for related optical application fields.

[0036] 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.

[0037] 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 stably generates a high-reflection plasma at the rear surface of the transparent optical medium; moreover, the depth of the heat-affected zone is accurately controlled in the range of 0.5 μm to 5 μm, the damage structure is prevented from penetrating the transparent medium, the independent concentric ring structure is formed on the front surface of the transparent optical medium, and the self-adaptive ring spacing gradient distribution under single-point laser action is realized.

[0038] 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.

[0039] In some embodiments, optionally, the wavelength of the pulsed laser beam includes an infrared wavelength, a visible wavelength or an ultraviolet wavelength.

[0040] 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 rear 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 area of the rear surface, avoiding the damage of the front surface in advance; at the same time, the short-wavelength diffraction limit advantage is exerted, the minimum damage point diameter is controlled in the range of 0.8 μm to 1.5 μm, and the gradual grating structure with the inner and outer ring spacing in the range of 0.5 μm to 5 μm is formed on the front surface of the transparent optical medium.

[0041] 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., and can be selected according to actual use.

[0042] In some embodiments, optionally, the single-point diameter of the concentric circular ring damage structure is controlled to be 1 μm to 10 μm, and the depth is controlled to be 0.5 μm to 5 μm.

[0043] Specifically, by controlling the single-point diameter of the concentric circular ring damage structure to be 1 μm to 10 μm and the depth to be 0.5 μm to 5 μm, the diffraction efficiency of the grating can be significantly enhanced, the single-point heat affected zone volume can be limited, the adjacent damage structure thermal fusion can be avoided, and the independence and periodicity of the concentric circular ring can be ensured; through depth gradient control, the inter-ring spacing gradient distribution is coordinated, the inner density and the outer sparsity are realized, and the phase difference accumulation effect of beam wavefront modulation is spontaneously formed under the action of a single laser.

[0044] In some embodiments, optionally, the plasmonic region is formed on the rear surface of the transparent optical medium, specifically including: the self-focusing effect is generated when the pulsed laser beam is transmitted inside the transparent optical medium, the optical filament channel is formed, the optical filament channel extends to the rear surface of the transparent optical medium, ionization is induced and the plasmonic region is generated at the rear surface of the transparent optical medium, and the plasmonic region is formed.

[0045] Specifically, the optical filament channel formed by the self-focusing effect transmits the laser energy to the precise position of the rear surface in a highly localized manner, induces the generation of high-density plasma under the premise of avoiding physical connection with the front surface, and after part of the pulsed laser is reflected and returned to the front surface, a radial decreasing energy gradient distribution is formed, thereby spontaneously generating the concentric circular ring structure with inner ring density and outer ring sparsity in a single laser action, and realizing the gradient grating constant control without complex scanning path.

[0046] In some embodiments, optionally, a non-equal-interval concentric circular ring damage structure is formed on the front surface of the transparent optical medium, specifically including: the plasmonic region forces the 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 that there is a density difference between the optical filament channel and the transparent optical medium, the reflected pulsed laser beam is self-phase modulated, diverges at a preset angle, and after the divergent beam reaches the front surface of the transparent optical medium, the concentric circular ring damage structure with radial energy gradient distribution is formed, wherein the preset angle is 5° to 30°.

[0047] Specifically, the confinement of the plasma to the laser forces the beam to be reflected from the edge of the filament channel, combined with the density difference between the filament channel and the base medium, triggering the self-phase modulation effect, making the reflected beam naturally form a spatial divergence; the divergent beam automatically generates a radial energy gradient distribution with a strong center and a weak edge when propagating to the front surface, thereby synchronously inducing a self-organizing concentric ring structure of inner ring high-density damage and outer ring low-density damage under single-point laser action, and realizing one-step precise shaping of the gradually changing grating constant.

[0048] As shown in Figure 2 , the preparation method of the variable grating constant circular grating is as follows:

[0049] 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;

[0050] S304, the pulsed laser beam generates a self-focusing effect when transmitting inside the transparent optical medium, forming 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, forming a plasma region, the plasma region reflects part of the pulsed laser beam;

[0051] 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;

[0052] 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 of 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 the divergent beam forms an energy radial gradient distribution after reaching the front surface of the transparent optical medium, obtaining a variable grating constant circular grating.

[0053] In specific applications, the preset angle can be specifically set to 5°, 10°, 15°, 20° and 30°, which can be selected according to actual use, and will not be listed here.

[0054] In some embodiments, optionally, as shown in Figure 4 , the transparent optical medium is fused quartz or calcium oxide, etc., and the thickness of the transparent optical medium is 0.1mm ~10mm.

[0055] Specifically, by selecting fused quartz as the transparent optical medium and controlling the thickness in the range of 0.1 mm to 10 mm, the laser self-focusing effect can fully develop to form a stable optical fiber channel extending to the back surface, and the laser beam returned from the back 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 ring structure and the spatial consistency of the gradient grating constant. The thickness of the transparent optical medium is H, and the thickness H is preferably 2 mm.

[0056] In specific applications, the thickness of the transparent optical medium fused quartz can be specifically set to 1 mm, 2 mm, 3 mm, 5 mm or 10 mm, which can be specifically selected according to actual use, and will not be listed here.

[0057] In some embodiments, after forming the non-equidistant concentric ring damage structure on the front surface of the transparent optical medium, the method for preparing 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 μm to 10 μm at a pressure of 0.5 N / cm2 to 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 μm to 2 μm at 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; detecting the integrity of the front surface concentric ring structure by an optical microscope to ensure that the grinding process only removes the defects on the back surface while retaining the front surface grating structure.

[0058] Specifically, by using the step-by-step grinding and polishing process, the molten residue and micro-crack layer generated on the back surface due to the high temperature of the plasma are accurately peeled off, and the inherent physical isolation characteristics of the front surface concentric ring structure and the substrate medium are utilized to ensure that the grinding stress is completely limited to the back surface region; combined with real-time monitoring by an optical microscope, the front surface micro-nano ring grating structure is completely retained while the defects on the back surface are completely removed, finally achieving the dual goals of "back surface purification" and "front surface fidelity".

[0059] Specifically, as shown in Figure 3 the preparation method of the variable grating constant circular grating comprises the following steps:

[0060] 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 back surface of the transparent optical medium;

[0061] S404, forming a plasma region on the back surface of the transparent optical medium, the plasma region reflecting part of the pulsed laser beam;

[0062] S406, the reflected pulse 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 front surface material of the transparent optical medium;

[0063] S408, by adjusting the wavelength, energy and focal point relative position of the pulse laser beam, a non-equidistant concentric circular ring damage structure is formed on the front surface of the transparent optical medium.

[0064] S410, grinding away the damaged rear surface of the transparent optical medium to obtain a variable grating constant circular grating.

[0065] Wherein, by adjusting the wavelength, energy and focal point relative position of the pulse laser beam, the ring spacing and ring width can be adjusted, so as to adjust the circular grating constant.

[0066] In some embodiments, optionally, the preparation method of the variable grating constant circular grating further comprises: collecting the front surface topography image of the transparent optical medium according to the optical stereomicroscope, dynamically adjusting the pulse wavelength, pulse energy and pulse focal point relative position of the pulse laser beam; according to the diffraction efficiency detected by the spectrum analyzer, feedback and control the scanning speed of the pulse laser beam.

[0067] Specifically, by real-time capturing the forming state of the front surface concentric circular ring through the optical stereomicroscope, dynamically feedback adjusting the pulse energy according to the integrity and gradient distribution characteristics of the ring structure, and ensuring that the plasma generation condition is always in the optimal interval; synchronously based on the diffraction efficiency change monitored by the spectrum analyzer, inversely deduce the matching degree of the ring spacing gradient and the design target, and adaptively adjust the scanning speed to maintain the consistency of the gradual change of the grating constant in the whole area.

[0068] According to the second aspect of the present application, a variable grating constant circular grating prepared by the preparation method of the above-mentioned embodiments is also proposed, the front surface of the transparent optical medium has a non-equidistant concentric circular ring structure induced by the pulse laser beam, the ring spacing of the concentric circular ring structure is different, and the ring spacing of the concentric circular ring structure increases along the radial direction.

[0069] Specifically, the variable grating constant circular grating provided by the present application is prepared by the preparation method of the above-mentioned embodiments, so it has all the beneficial effects of the preparation method of the variable grating constant circular grating, which will not be repeated here.

[0070] The application provides a laser-induced transparent optical medium, such as fused quartz, a novel variable grating constant circular grating formed on a surface and a preparation method thereof. The core is that a laser beam with a pulse width of, for example, nanoseconds is focused on the rear surface of the transparent optical medium fused quartz to induce a unique non-equidistant concentric ring circular grating structure, that is, a micro-nano optical structure, on the front surface of the material. By precisely controlling parameters such as the pulse width, pulse energy and laser beam focus position of the laser, a plurality of periodic and repeatable circular damage points are induced on the surface of the fused quartz. The single damage structure presents a non-equidistant 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 non-equidistant concentric rings can be finely adjusted according to the design requirements of the grating, so as to realize specific optical functions.

[0071] In the existing optical structure preparation technology, common gratings or microstructures are usually processed or etched on the front surface by laser, although certain effects are achieved, there are certain limitations in precision, structure stability and preparation efficiency. The traditional process needs multiple operations and can only form fixed structures on the surface of the material, and it is difficult to control and optimize the micro-optical performance. The key innovation of the application is the unique non-equidistant concentric ring grating structure, and the shape, size and distribution of the microstructure 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.

[0072] The grating structure of the application is based on the non-equidistant 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 with a certain pulse width, the pulse energy, scanning speed, laser beam focus position and other parameters are controlled to induce a plurality of circular damage points on the surface of the transparent optical material. The single damage structure presents a non-equidistant concentric ring shape, in which the outer ring is sparse and the inner ring is dense, and the diameter and depth of each damage point can be finely controlled according to the design requirements of the grating. For example, in the grating design for diffraction of specific wavelength light, the damage point diameter can be controlled to be 1-10 μm, and the depth can be flexibly adjusted to be 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, the damage structure can be optimized to realize efficient separation and transmission of different communication wavelengths. By focusing the laser on the rear surface, complex and fine front surface optical structures can be quickly generated.

[0073] Compared with the complex etching or lithography process in the traditional technology, the preparation method of the variable grating constant circular grating of the application greatly improves the preparation efficiency. The specific preparation steps are as follows: first, the first step is to prepare the fused quartz substrate. Select high-purity and excellent optical performance fused quartz material as the substrate, and clean the surface by ultrasonic cleaning, chemical reagent wiping and other methods to remove dust, oil stains and other pollutants, and ensure the surface cleanliness to provide a good foundation for subsequent laser processing. The second step is to adjust the laser equipment parameters. The laser pulse width, beam power, pulse frequency, focal point position and other parameters of the laser equipment are accurately adjusted. For example, the nanosecond laser pulse width is set to 1 nanosecond~100 nanoseconds, and the beam power is adjusted between 1 watt~10 watts, so that the laser beam produces controllable thermal effect on the surface of the fused quartz to realize the local melting of the material. The third step is to form a damage structure by laser scanning. The laser beam with adjusted parameters is scanned on the surface of the fused quartz according to the pre-designed scanning path. In the scanning process, the laser energy makes the material locally melt instantaneously, and then cools and solidifies to form a circular damage structure. By reasonably planning the scanning path, the non-periodic distribution of the damage points in the grating area is realized. The fourth step is to adjust the parameters to control the grating function. According to the design requirements of the grating, the scanning parameters of the laser beam are adjusted in real time, including scanning speed, pulse energy, laser wavelength, etc., to accurately control the distribution, diameter and depth of the damage points, so as to realize the required grating function. Finally, the rear surface is ground and the structure is optimized. High-precision grinding equipment is used for step-by-step processing from coarse grinding (particle size 5μ ~10μm) to fine grinding (particle size 1μm~2μm), focusing on removing defects, cracks or melting residues generated during the laser processing process, and only leaving the concentric ring structure on the transparent medium, that is, the variable grating constant circular grating can be prepared. During the preparation process, optical microscope, spectrometer and other equipment can be used to monitor the damage structure formed in real time, and the parameters are optimized according to the monitoring results. Finally, real-time monitoring ensures accuracy. During the whole preparation process, a real-time monitoring system is established, the surface morphology change of the fused quartz is observed by high-resolution microscope, the optical performance of the grating is detected by spectrometer, and the problems occurring in the processing process are found and solved in time to ensure the accuracy and stability of the grating structure.

[0074] By accurately adjusting the laser parameters, non-periodic circular damage structures can be efficiently and accurately formed on the surface of the transparent medium. Compared with the traditional preparation method, the processing accuracy can be greatly improved, and the processing speed is fast, which greatly shortens the production cycle and meets the high requirements of modern optical field on the performance of the grating. The laser technology used in the application does not need complex photolithography mask, which reduces the mask manufacturing cost and process complexity. At the same time, the equipment cost and raw material consumption are also significantly reduced, the production cost is lower than that of the traditional method, and it is suitable for large-scale production.

[0075] In the description of the application, the term "a plurality" means two or more, unless otherwise expressly specified. The terms "upper", "lower", and the like, indicate the orientation or position relationship based on the orientation or position relationship shown in the drawings, and are only used to facilitate the description of the application and simplify the description, and do not indicate or imply that the device or element referred to must have a particular orientation, be constructed and operated in a particular orientation, and therefore cannot be understood as a limitation on the application. The terms "connection", "installation", "fixation" and the like should be understood broadly, for example, "connection" can be fixed connection, or detachable connection, or integral connection; can be directly connected, or indirectly connected through an intermediate medium. For those skilled in the art, the specific meaning of the above terms in the application can be understood according to the specific circumstances.

[0076] In the description of the application, the terms "one embodiment", "some embodiments", "a specific embodiment" and the like are intended to mean that the specific features, structures, materials or characteristics described in connection with the embodiment or example are included in at least one embodiment or example of the application. In the present application, the illustrative description of the above terms does not necessarily refer to the same embodiment or example. Moreover, the specific features, structures, materials or characteristics described can be combined in any one or more embodiments or examples in a suitable manner.

[0077] The above is only the preferred embodiment of the application and is not intended to limit the application. For those skilled in the art, the application can have various modifications and changes. Any modification, equivalent replacement, improvement, etc. within the spirit and principles of the application shall be included in the protection scope of the application.

Claims

1. A method for producing a variable-raster constant-circular grating, characterized by, Comprising: incident a pulsed laser beam from a front surface of a transparent optical medium, penetrate the transparent optical medium and focus on a back surface of the transparent optical medium; forming a plasma region on the back surface of the transparent optical medium, the plasma region reflects 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 front surface material of the transparent optical medium; forming a non-equidistant concentric circular ring damage structure on the front surface of the transparent optical medium by adjusting the wavelength, energy and relative position of the focus of the pulsed laser beam, and obtaining a variable grating constant circular grating; 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 0.5μm~1μm, and the ring distance in the range from 80% to 100% of the maximum radius is 2μm~5μm.

2. The preparation method of the variable grating constant circular grating according to claim 1, wherein the pulsed laser beam is a nanosecond pulsed laser beam, a picosecond pulsed laser beam or a femtosecond pulsed laser beam.

3. The preparation method of the variable grating constant circular grating according to claim 1, wherein the wavelength of the pulsed laser beam includes infrared light wavelength, visible light wavelength or ultraviolet light wavelength.

4. The preparation method of the variable grating constant circular grating according to claim 1, wherein the diameter of a single point of the concentric circular ring damage structure is controlled to be 1μm~10μm, and the depth is controlled to be 0.5μm~5μm. The forming of the plasma region on the back surface of the transparent optical medium specifically comprises: When the pulsed laser beam transmits inside the transparent optical medium, a self-focusing effect is generated to form a light filament channel, the light filament channel extends to the back surface of the transparent optical medium, ionization is induced at the back surface of the transparent optical medium, and a plasma is generated to form the plasma region. The forming of the non-equidistant concentric circular ring damage structure on the front surface of the transparent optical medium specifically comprises:

5. The method of claim 1, wherein the variable-raster constant- circular-raster optical grating is prepared by using a variable-raster constant-circular-raster optical grating mask. The plasma forces part of the pulsed laser beam to reflect back to the front surface of the transparent optical medium; In the case that there is a density difference between the light filament channel and the transparent optical medium, the reflected pulsed laser beam is self-phase modulated to diverge at a preset angle, and the divergent beam forms a concentric circular ring damage structure with a radial energy gradient distribution after reaching the front surface of the transparent optical medium, wherein the preset angle is 5°~30°.

6. The method of claim 5, wherein the variable-raster constant- circular-raster optical grating is prepared by using a variable-raster constant-circular-raster optical grating mask. The thickness of the transparent optical medium is 0.1mm ~10mm. 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 abrasive particles of 5μm~10μm at a pressure of 0.5N / cm2~2N / cm2 to remove the molten residues generated by laser processing; 7. The method of claim 1, wherein the variable-raster constant- circular-raster optical grating is prepared by using a variable-raster constant-circular-raster optical grating mask. ​ 8. The method of claim 1, wherein the variable-raster constant- circular-raster optical grating is prepared by using a laser beam having a wavelength of 1064 nm. ​ ​ The surface of the transparent optical medium is polished, cracks are eliminated and the surface roughness of the transparent optical medium is reduced by using abrasive grains with a particle size of 1 μm-2 μm and a pressure of 0.1 N / cm2-0.5 N / cm2. The integrity of the concentric ring structure on the front surface is detected by an optical stereomicroscope, so that the grinding process only removes the damaged back surface and retains the front surface grating structure.

9. The method of claim 8, wherein the variable-raster constant- circular-raster optical grating is prepared by using a variable-raster constant- circular-raster optical grating mask. The preparation method of the variable grating constant circular grating further comprises: According to the front surface topography image of the transparent optical medium collected by the optical stereomicroscope, the pulse wavelength, pulse energy and pulse focal point relative position of the pulsed laser beam are dynamically adjusted. According to the diffraction efficiency detected by the spectrum analyzer, the scanning speed of the pulsed laser beam is fed back and controlled.

10. A variable-echelette circular grating, characterized by, The transparent optical medium is prepared by the preparation method in any one of claims 1-9, the front surface of the transparent optical medium has a non-equidistant concentric circular ring structure induced by the pulsed laser beam, the depth of the concentric circular ring structure is different, and the ring spacing of the concentric circular ring structure increases in the radial direction.

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