Method for improving optical storage performance by superposing and rewriting Type X structure based on femtosecond laser direct writing

Abstract

The invention discloses a method for improving optical storage performance by superposing and rewriting a Type X structure based on femtosecond laser direct writing, and belongs to the technical field of optical storage, and the method comprises the steps: 1, determining a processing parameter window of the Type X structure; 2, determining a seed pulse parameter and a write-in pulse parameter; 3, random data writing and reading are carried out; according to the method, the storage points are superposed and rewritten by utilizing the erasable rewriting characteristic of the Type X, so that the limitation of optical diffraction limit can be bypassed, the storage capacity of the femtosecond laser permanent optical storage technology is improved by at least one order of magnitude, the number of pulses required by each storage point can be reduced, and the data writing speed is improved.

Description

Technical Field

[0001] The present invention belongs to the field of optical storage technology, and in particular relates to a method for superimposing and rewriting a Type X structure to improve the storage density and writing speed of a femtosecond laser permanent optical storage technology. Background Art

[0002] With the rapid development of information technology, the explosive growth of data has posed unprecedented challenges to storage technology. Femtosecond laser permanent optical storage technology based on nanogratings has shown great potential in the field of big data storage with its advantages of high density, long life, and corrosion resistance. In order to further improve the storage capacity of femtosecond laser permanent optical storage technology, researchers continue to explore the growth mechanism of nanogratings to seek solutions. For example, in 2020, Peter Kazansky's research group at the University of Southampton in the UK discovered anisotropic nanopores with higher transmittance and named them Type X. The femtosecond laser permanent optical storage technology using this structure as a storage point has little scattering of light, which is conducive to the writing and reading of multi-layer data, and greatly improves the storage density in the spatial z dimension.

[0003] However, the writing of Type X still relies on femtosecond laser micro-nano processing, and the size of the laser spot will be affected by the optical diffraction limit. Therefore, the spacing between adjacent storage points cannot be reduced indefinitely, and the storage density is difficult to continue to increase. Summary of the invention

[0004] In view of the above problems, the present invention proposes a method for improving the optical storage performance by superimposing and rewriting the Type X structure based on femtosecond laser direct writing. The present invention utilizes the erasable and rewritable characteristics of Type X to superimpose and rewrite each storage point, which can not only bypass the limitation of the optical diffraction limit and increase the storage capacity of the femtosecond laser permanent optical storage technology by at least one order of magnitude, but also reduce the number of pulses required for each storage point and improve the data writing speed.

[0005] The present invention is achieved through the following technical solutions:

[0006] The method for improving optical storage performance by superimposing and rewriting Type X structure based on femtosecond laser direct writing specifically comprises the following steps:

[0007] Step 1: Determine the processing parameter window of Type X structure;

[0008] The specific steps are as follows: using a femtosecond laser direct writing processing system, selecting lasers with different wavelengths, pulse widths and repetition frequencies, focusing the lasers on objective lenses with different numerical apertures, and obtaining multiple sets of processing parameter windows of pulse numbers and pulse energies; dividing the above processing parameter windows into Type I structure, Type X structure, Type II structure and Type III structure according to morphological characteristics and birefringence characteristics, thereby determining the processing parameter window of Type X structure;

[0009] Step 2: Determine the seed pulse parameters and write pulse parameters;

[0010] The specific steps are as follows: first, modulate the pulse energy and quantity to induce a seed structure inside the sample, i.e., the starting point of the entire row of data; then move the displacement platform to adjust the point spacing, and on the basis of the seed structure, modulate the pulse energy and quantity to induce an anisotropic Type X structure as a storage point; and so on, each storage point uses the previous storage point as a seed, and only needs to write a pulse to record the data; when modulating the seed pulse and the write pulse, it is necessary to ensure that each storage point is still a Type X structure after superposition and rewriting, and will not become a nano grating due to the increase in pulse density;

[0011] Step 3: Random data writing and reading;

[0012] The specific steps are as follows: when writing, a piece of text information is first converted into ASCII code, then converted into N-base, and N types of Type X with different orientations are used to correspond respectively, and then written directly into the fused quartz sample by femtosecond laser; when reading, the sample is measured by a birefringence microscope system, and the Type X structures with different orientations have different colors; the results can be classified by MATLAB and compared with the written data to obtain the accuracy.

[0013] Furthermore, the slow axis orientation of the Type X structure is regulated by the laser polarization direction and is always perpendicular to the laser polarization direction; the laser polarization angle takes N discrete values ​​in the range of 0-180°, wherein 1≤N≤180, corresponding to N orientations of the Type X structure; the Type X structure with different slow axis orientations is measured under a birefringence microscope to obtain different colors, representing different codes respectively.

[0014] Furthermore, in step 1, if the refractive index of the structure changes positively and the transmittance is greater than 99%, it is a Type I structure; if the structure can be detected to have birefringence and the optical transmittance is greater than 97%, it is a Type X structure; if the structure can be detected to have birefringence but the optical transmittance is less than 80%, it is a Type II structure based on nanogratings; if the structure size is 100nm-1μm, it has no birefringence and the optical transmittance is less than 70%, it is a Type III micro-explosion structure.

[0015] Furthermore, in step 1, the wavelength of the femtosecond laser center of the femtosecond laser direct writing processing system is 343-1030nm, the pulse width is 100fs-10ps, and the repetition frequency is 1kHz-40MHz; the objective lens NA is 0.16-0.65, the magnification is 10×-60×; and the single pulse ablation energy is 0.1-0.7μJ.

[0016] Furthermore, in step 2, the sample is a fused quartz glass sample with a thickness of 0.1-7 mm.

[0017] Furthermore, in step 2, the dot spacing must be smaller than the storage dot diameter to ensure partial overlap. The minimum dot spacing depends on the readout recognition accuracy and is in the range of 100-1000 nm.

[0018] Furthermore, in step 2, the displacement platform is an Aerotech three-axis air-floating displacement platform, wherein the X-axis movement range is 0-150mm, and the movement accuracy is 0-200nm; the Y-axis movement range is 0-100mm, and the movement accuracy is 0-200nm; the Z-axis movement range is 0-60mm, and the movement accuracy is 0-200nm.

[0019] Furthermore, in step 2 and step 3, the scanning speed is 0.1-300 mm / s; the point spacing of the processed data is 100-1000 nm; and the laser polarization is modulated jointly by a Glan prism, a Pockels cell and a quarter-wave plate.

[0020] Furthermore, in step three, the birefringence microscope system is an Oosight imaging system equipped with an Olybas BX53 optical microscope.

[0021] The principle of the superposition rewriting Type X structure based on femtosecond laser direct writing of the present invention for improving the optical storage performance is as follows:

[0022] Principle of high storage capacity beyond the diffraction limit: In 2007, Paul Corkum's research group in Canada discovered the erasable and rewritable characteristics of nano-gratings, that is, when subsequent laser pulses are irradiated on the nano-gratings, the slow axis orientation of the nano-gratings will deflect with the new laser polarization direction, achieving the effect of being "erased and rewritten". Experiments have shown that the Type X structure, as a precursor of the nano-grating, also has the characteristics of being erasable and rewritable, and the stretching direction of the nano-hole can be changed by changing the polarization direction of the subsequent laser.

[0023] Based on the erasable and rewritable characteristics of the Type X structure, a "write-while-erasing" mode is proposed, that is, after writing a storage point, the subsequent laser pulse erases the second half of the previous storage point while inducing a Type X with a new slow axis orientation. This process is repeated, and the storage points are arranged like tiles. In this process, it is necessary to ensure that the information of the previous storage point is retained during erasure, so the spacing cannot be reduced infinitely. However, compared with traditional femtosecond laser permanent optical storage technology, the spacing of storage points is affected by the optical diffraction limit. The spacing of storage points in the proposed "write-while-erasing" mode depends only on the writing spacing of the laser beam. This method bypasses the limitation of the optical diffraction limit and reduces the point spacing to below 500nm, thereby significantly increasing the storage capacity.

[0024] Principle of improving storage speed: The formation mechanism of Type X structure can be considered to involve two stages: in the first stage, laser irradiates the inside of fused quartz to generate isotropic nanopores; in the second stage, the laser stretches these nanopores in the direction perpendicular to the polarization to make them anisotropic. Based on this, the laser pulses in the two stages are divided into seed pulses (inducing the generation of nanopores) and write pulses (stretching nanopores). When the superposition rewriting method is used for data storage, the laser spot action area overlaps in spatial position, so the previous storage point (Type X structure) can be used as the seed of the next storage point (Type X structure), that is, the generation of the subsequent Type X structure no longer requires a seed pulse with energy exceeding the threshold of fused quartz to induce the generation of isotropic nanopores, but only requires a write pulse with slightly lower energy to stretch the existing nanopores. Therefore, the superposition rewriting method of Type X structure optimizes the number and energy of pulses required to write storage points at the same time.

[0025] In addition, using high-repetition-rate lasers for direct data writing is an important way to increase the data writing speed. However, the resulting heat accumulation will damage the structure of the storage unit and cause data loss. The proposed superposition rewriting Type X structure method modulates the laser energy and pulse number, effectively reducing the heat accumulation effect, so that the temperature of the machining center is controlled within a range that does not destroy the birefringence structure. Therefore, the superposition rewriting Type X structure method supports high-repetition-rate laser high-speed writing more than the traditional femtosecond laser direct writing method.

[0026] Compared with the prior art, the advantages of the present invention are as follows:

[0027] (1) The method of improving optical storage performance by superimposing and rewriting Type X structure based on femtosecond laser direct writing of the present invention can bypass the limitation of optical diffraction limit, reduce the storage point spacing to below 600nm, and increase the storage capacity by at least one order of magnitude;

[0028] (2) The present invention can reduce the number of pulses required for each storage point and improve the theoretical data writing speed;

[0029] (3) The present invention effectively reduces thermal effects through energy modulation and pulse number modulation, thereby supporting high repetition frequency laser processing, achieving high-speed data direct writing, and greatly improving the actual data writing speed. BRIEF DESCRIPTION OF THE DRAWINGS

[0030] In order to more clearly illustrate the specific embodiments of the present invention or the technical solutions in the prior art, the following is a brief introduction to the drawings required for the specific embodiments or the description of the prior art. In all the drawings, similar elements or parts are generally identified by similar reference numerals. In the drawings, the elements or parts are not necessarily drawn according to the actual scale.

[0031] Figure 1 It is a schematic diagram of the optical path of the femtosecond laser processing system of the present invention;

[0032] Among them, the electrically controlled attenuator modulates the energy of a single pulse; the Glan prism, Pockels cell and quarter-wave plate jointly modulate the angle of linear polarized light; after the laser spot is expanded, its diameter is expanded to fill the entrance pupil of the objective lens; finally, the laser is focused into the sample through the objective lens;

[0033] Figure 2 It is the parameter window diagram of pulse quantity and pulse energy;

[0034] The laser selected pulse width is 300fs, repetition frequency is 200kHz, and the white frame lines are all Type X structures;

[0035] Figure 3 It is a schematic diagram of the writing principle of the method for improving the optical storage performance by superimposing and rewriting the Type X structure proposed by the present invention;

[0036] After the seed structure is written at the starting point, the subsequent storage points partially overlap and overwrite the previous point;

[0037] Figure 4 The effect diagram of the method of stacking and rewriting Type X structure to improve optical storage performance proposed by the present invention: the upper diagram was taken by the birefringence measurement system, and the lower diagram was taken by SEM;

[0038] Among them, the structural morphology captured by SEM images shows that each storage point still maintains an anisotropic nanopore, namely Type X structure;

[0039] Figure 5 This is a diagram showing the random data writing and reading effects of the method for improving optical storage performance by stacking and rewriting the Type X structure proposed in the present invention. DETAILED DESCRIPTION

[0040] In order to clearly and completely describe the technical solution and its specific working process of the present invention, the specific implementation methods of the present invention are as follows in conjunction with the accompanying drawings of the specification:

[0041] Example 1

[0042] This embodiment provides a method for improving optical storage performance by overlaying and rewriting a Type X structure based on femtosecond laser direct writing, which specifically includes the following steps:

[0043] Depend on Figure 1 It can be seen that the femtosecond laser direct writing processing system used in this embodiment is specifically as follows: the laser emits 1030nm femtosecond laser which passes through a reflector, an electrically controlled attenuator in sequence, and then passes through a reflector, a Glan prism, a Pockels cell and a quarter-wave plate, and then passes through a beam expander and a reflector to focus at the objective lens.

[0044] Step 1: Determine the processing parameter window of Type X structure;

[0045] The wavelength of the femtosecond laser is selected as 1030nm, the pulse width range is 170-500fs, the repetition frequency range is 100-1000kHz, the numerical aperture range of the objective lens is 0.16-0.5, the pulse energy is 0.1-0.7μJ, and the number of pulses is 1-300; the obtained structure is classified according to the morphological characteristics and the birefringence measurement results, and the processing parameter window of the Type X structure is found: the structure refractive index change is positive and the transmittance is greater than 99%, which is the Type I structure; the structure can be detected birefringence and the optical transmittance is greater than 97%, which is the Type X structure; the structure can be detected birefringence but the optical transmittance is less than 80%, which is the Type II structure based on nanograting; the structure size is 100nm-1μm, there is no birefringence, and the optical transmittance is less than 70%, which is the TypeIII micro-explosion structure; after comparing the results, when the laser pulse width is 300fs, the repetition frequency is 200kHz, and the numerical aperture of the objective lens is 0.25, the parameter window of the number of pulses and the pulse energy is the largest, such as Figure 2 As shown, the structures within the white frame are all Type X;

[0046] Depend on Figure 2 It can be seen that there are 16 structures with the same energy and pulse number, which are divided into 4 colors; each color measured in the birefringence system corresponds to the slow axis angle of a birefringence structure;

[0047] Step 2: Determine the seed pulse parameters and write pulse parameters;

[0048] Depend on Figure 3 It can be seen that the method of improving optical storage performance by superimposing and rewriting the Type X structure proposed in the present invention requires that after a femtosecond laser writes a seed structure at the starting point, each storage point is partially superimposed and rewritten using the previous point as a seed;

[0049] First, in the parameter window obtained in step 1, the parameters for inducing the Type X structure are selected: laser wavelength 1030nm, pulse width 300fs, repetition frequency 200kHz, single pulse energy 0.29μJ, pulse number 60, objective numerical aperture 0.25, and stage scanning speed 3mm / s. The seed structure is induced inside the fused silica sample using these parameters. Then the stage moves 500nm along the x direction, the pulse number is reduced to 20, and other parameters remain unchanged. On the basis of the seed structure, anisotropic nanopores (Type X structure) are induced as storage points. By analogy, the subsequent storage points are all seeded with the previous storage point, and the writing parameters are all selected as laser wavelength 1030nm, pulse width 300fs, repetition frequency 200kHz, single pulse energy 0.29μJ, pulse number 20, objective numerical aperture 0.25, and stage scanning speed 3mm / s.

[0050] Write effect as Figure 4 As shown. From the birefringence measurement results in the above figure, it can be seen that the actual storage point size is the original point size minus the erased and rewritten part. The color information from left to right is: light blue, green, yellow, orange, red, pink, purple, dark blue, light blue, green, yellow, orange, red, pink, purple, dark blue, which corresponds to the written data one by one, that is, the stored data can be completely saved. The figure below is the SEM measurement result. The sample was polished until the structure was exposed to the surface, etched with 1% HF solution at room temperature for 10s, and then cleaned with acetone, ethanol and deionized water in sequence. The structure was then observed under SEM, and it can be seen that the storage points are uniformly randomly distributed nanopores with different orientations, indicating that each storage point is still a Type X structure.

[0051] Step 3: Random data writing and reading;

[0052] First, the excerpt from the novel "The Call of the Wild" was converted into ASCII code and then into octal. Then, the angle of the laser linear polarization light was evenly divided into 8 discrete values, namely 0°, 22.5°, 45°, 67.5°, 90°, 112.5°, 135° and 157.5°, respectively, to induce Type X structures of 90°, 112.5°, 135°, 157.5°, 0°, 22.5°, 45° and 67.5°; the eight orientations of Type X structures correspond to the codes 0-7 in octal. Then, the method of superposition rewriting Type X structure in step 2 was adopted, with a single point pulse energy of 0.29μJ, a seed pulse number of 60, a write pulse number of 20, a scanning speed of 3mm / s, an x ​​spacing of 500nm, and a y spacing of 2μm. Femtosecond laser writing was performed in Corning 7979 glass sample in contrast to the octal text.

[0053] Finally, a birefringence microscope system was used to measure and read the sample. The Type X structures with different orientations showed different colors when measured in this system. Figure 5 As shown. The storage points of light blue, green, yellow, orange, red, pink, purple and dark blue represent octal codes 0-7 respectively. In order to verify the feasibility and practicality of the method of improving optical storage performance by superimposing and rewriting Type X structure proposed in the present invention, two rows of data were randomly selected, and the color information was read through the MATLAB program to classify and count the readout results. The results show that the storage points of different color information are clearly classified, and compared with the original information, the readout accuracy can reach 100%.

[0054] In this example, the dot pitch is reduced to 500nm, which increases the storage capacity by 4-10 times compared to the 2-5μm of the existing technology. 3 -10 3 times; in addition, the number of pulses per storage point is reduced to 20, which is at least 5 times faster than the hundreds of pulses in the existing technology. At the same time, this technical method effectively reduces the thermal effect through energy modulation and pulse number modulation. Compared with the existing technology, it supports high repetition frequency laser processing and realizes high-speed data direct writing. In this example, the accuracy of the readout result can still reach 100% when compared with the written data, proving that this method is effective.

[0055] The preferred embodiments of the present invention are described in detail above in conjunction with the accompanying drawings. However, the present invention is not limited to the specific details in the above embodiments. Within the technical concept of the present invention, a variety of simple modifications can be made to the technical solution of the present invention, and these simple modifications all belong to the protection scope of the present invention.

[0056] It should also be noted that the various specific technical features described in the above specific embodiments can be combined in any suitable manner without contradiction. In order to avoid unnecessary repetition, the present invention will not further describe various possible combinations.

[0057] In addition, various embodiments of the present invention may be arbitrarily combined, and as long as they do not violate the concept of the present invention, they should also be regarded as the contents disclosed by the present invention.

Claims

1. A method for improving optical storage performance by superimposing and rewriting Type X structure based on femtosecond laser direct writing, characterized in that: The specific steps include: Step 1: Determine the processing parameter window of Type X structure; The specific steps are as follows: using a femtosecond laser direct writing processing system, selecting lasers with different wavelengths, pulse widths and repetition frequencies, focusing the lasers on objective lenses with different numerical apertures, and obtaining multiple sets of processing parameter windows of pulse numbers and pulse energies; dividing the above processing parameter windows into Type I structure, Type X structure, Type II structure and Type III structure according to morphological characteristics and birefringence characteristics, thereby determining the processing parameter window of Type X structure; Step 2: Determine the seed pulse parameters and write pulse parameters; The specific steps are as follows: first, modulate the pulse energy and quantity to induce a seed structure inside the sample, which is the starting point of the entire row of data; Then the displacement platform is moved to control the distance between the dots. Based on the seed structure, the pulse energy and number are modulated to induce an anisotropic Type X structure as a storage dot. By analogy, each storage point uses the previous storage point as a seed, and only a write pulse is needed to record the data; When modulating the seed pulse and write pulse, it is necessary to ensure that each storage point remains a Type X structure after superposition and rewriting, and does not become a nano-grating due to the increase in pulse density; Step 3: Random data writing and reading; The specific steps are as follows: when writing, a piece of text information is first converted into ASCII code, then converted into N-base, and N types of Type X with different orientations are used to correspond to each other, and then directly written into the fused silica sample by femtosecond laser; when reading, the sample is measured using a birefringence microscope system, and the Type X structures with different orientations have different colors; The results can be classified by MATLAB and compared with the written data to obtain the accuracy.

2. The method for improving optical storage performance by superimposing and rewriting Type X structure based on femtosecond laser direct writing as claimed in claim 1, characterized in that: The slow axis orientation of the Type X structure is regulated by the laser polarization direction and is always kept perpendicular to the laser polarization direction; the laser polarization angle takes N discrete values ​​in the range of 0-180°, where 1≤N≤180, corresponding to N orientations of the Type X structure; the Type X structure with different slow axis orientations is measured under a birefringence microscope to obtain different colors, representing different codes.

3. The method for improving optical storage performance by superimposing and rewriting Type X structure based on femtosecond laser direct writing as claimed in claim 1, characterized in that: In step 1, if the refractive index of the structure changes positively and the transmittance is greater than 99%, it is a Type I structure; if the structure can be detected to have birefringence and the optical transmittance is greater than 97%, it is a Type X structure; if the structure can be detected to have birefringence but the optical transmittance is less than 80%, it is a Type II structure based on nanogratings; if the structure size is 100nm-1μm, it has no birefringence and the optical transmittance is less than 70%, it is a Type III micro-explosion structure.

4. The method for improving optical storage performance by superimposing and rewriting Type X structure based on femtosecond laser direct writing as claimed in claim 1, characterized in that: In step 1, the wavelength of the femtosecond laser center of the femtosecond laser direct writing processing system is 343-1030nm, the pulse width is 100fs-10ps, and the repetition frequency is 1kHz-40MHz; the objective lens NA is selected to be 0.16-0.65, the magnification is 10×-60×; the single pulse ablation energy is 0.1-0.7μJ.

5. The method for improving optical storage performance by superimposing and rewriting Type X structure based on femtosecond laser direct writing as claimed in claim 1, characterized in that: In step 2, the sample is a fused quartz glass sample with a thickness of 0.1-7 mm.

6. The method for improving optical storage performance by superimposing and rewriting Type X structure based on femtosecond laser direct writing as claimed in claim 1, characterized in that: In step 2, the dot spacing must be smaller than the storage dot diameter to ensure partial overlap. The minimum dot spacing depends on the readout recognition accuracy and is in the range of 100-1000nm.

7. The method for improving optical storage performance by superimposing and rewriting Type X structure based on femtosecond laser direct writing as claimed in claim 1, characterized in that: In step 2, the displacement platform is an Aerotech three-axis air-floating displacement platform, wherein the X-axis movement range is 0-150mm, and the movement accuracy is 0-200nm; the Y-axis movement range is 0-100mm, and the movement accuracy is 0-200nm; the Z-axis movement range is 0-60mm, and the movement accuracy is 0-200nm.

8. The method for improving optical storage performance by superimposing and rewriting Type X structure based on femtosecond laser direct writing as claimed in claim 1, characterized in that: In step 2 and step 3, the scanning speed is 0.1-300 mm / s; the point spacing of the processed data is 100-1000 nm; and the laser polarization is modulated by Glan prism, Pockels cell and quarter wave plate.

9. The method for improving optical storage performance by superimposing and rewriting Type X structure based on femtosecond laser direct writing as claimed in claim 1, characterized in that: In step three, the birefringence microscope system is an Oosight imaging system equipped with an Olybas BX53 optical microscope.

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