Holographic encoding phase modulation method

Abstract

The application provides a holographic encoding phase modulation method, which comprises the following steps: loading a hologram in a spatial light modulator, wherein the hologram comprises a first area and a second area; modulating a laser beam with a polarization direction of 45 degrees in a first polarization direction by using the first area of the hologram to form a first modulated light beam; reflecting the first modulated light beam to the second area of the hologram and modulating the first modulated light beam in a second polarization direction by using the second area of the hologram to form a second modulated light beam; wherein the second polarization direction is perpendicular to the first polarization direction; and performing data writing on a target storage medium by using the second modulated light beam. The holographic encoding phase modulation method provided by the application can realize independent modulation of a single light beam in two orthogonal polarization directions by using a single spatial light modulator, which is beneficial to the compactness of a holographic encoding system.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of 5D optical storage technology, and in particular to a holographic encoding phase modulation method. BACKGROUND

[0002] Five-dimensional (5D) optical data storage is an advanced technology for permanently storing data in transparent materials such as fused quartz, which uses femtosecond laser writing beams to create nanograting structures in transparent materials to encode information. Five-dimensional (5D) optical data storage technology in transparent materials can provide an unlimited data storage solution for future cloud services. However, traditional phase-type liquid crystal silicon-based spatial light modulators (LCOSSLM) can only modulate phase or amplitude and cannot directly control polarization state. Currently, polarization control of holographic images output by phase-type liquid crystal silicon-based spatial light modulators (LCOSSLM) still needs to be achieved through external polarization modulators. In the prior art, two spatial light modulators are used in cooperation or a spatial light modulator is used in cooperation with other devices to adjust the phase of the light beam. However, this adjustment method is usually difficult to achieve a compact layout and has very high requirements for cost and space. SUMMARY

[0003] The holographic encoding phase modulation method provided by the present application can achieve independent modulation of a single light beam in two orthogonal polarization directions using a single spatial light modulator, which is beneficial to the compactness of the holographic encoding system.

[0004] The present application provides a holographic encoding phase modulation method, the method comprising:

[0005] loading a hologram in a spatial light modulator, wherein the hologram comprises a first region and a second region;

[0006] modulating a laser beam with a polarization direction of 45° in a first polarization direction using the first region of the hologram to form a first modulated light beam;

[0007] reflecting the first modulated light beam to the second region of the hologram and modulating the first modulated light beam in a second polarization direction using the second region of the hologram to form a second modulated light beam; wherein the second polarization direction is perpendicular to the first polarization direction;

[0008] performing data writing on a target storage medium using the second modulated light beam.

[0009] Optionally, the modulating the laser beam with the polarization direction of 45° in the first polarization direction using the first region of the hologram comprises:

[0010] emitting a laser beam along a direction parallel to the spatial light modulator using a laser;

[0011] splitting the laser beam by using a first beam splitter to form a first perpendicular beam perpendicular to the spatial light modulator and a first parallel beam parallel to the spatial light modulator;

[0012] modulating and reflecting the first perpendicular beam in a first polarization direction by using a first area of the hologram to form a first intermediate beam;

[0013] determining a portion of the first intermediate beam transmitted through the first beam splitter as a first modulated beam.

[0014] Optionally, the reflecting the first modulated beam to a second area of the hologram and modulating the first modulated beam in a second polarization direction by using the second area of the hologram to form a second modulated beam comprises:

[0015] changing a propagation direction of the first modulated beam by using a mirror group and rotating a polarization direction of the first modulated beam by 90° by using a half wave plate, so that the first modulated beam is incident to a second beam splitter in an incident direction perpendicular to the spatial light modulator;

[0016] splitting the first modulated beam by using a second beam splitter to form a second perpendicular beam perpendicular to the spatial light modulator and a second parallel beam parallel to the spatial light modulator;

[0017] modulating and reflecting the second perpendicular beam in a second polarization direction by using a second area of the hologram to form a second intermediate beam;

[0018] determining a portion of the second intermediate beam reflected by the second beam splitter as a second modulated beam.

[0019] Optionally, the method further comprises:

[0020] arranging a blocking film between the first beam splitter and the second beam splitter to block the first parallel beam from entering the second beam splitter and to block the second parallel beam from entering the first beam splitter.

[0021] Optionally, the changing the propagation direction of the first modulated beam by using a mirror group and rotating the polarization direction of the first modulated beam by 90° by using a half wave plate comprises:

[0022] rotating the polarization direction of the first modulated beam by 90° by using a half wave plate before, after or in the process of changing the propagation direction of the first modulated beam by using a mirror group.

[0023] Optionally, before modulating the laser beam with polarization direction of 45° in the first polarization direction by using the first area of the hologram, the method further comprises:

[0024] Expanding and collimating the laser beam to make the diameter of the laser beam reach a first preset size;

[0025] Filtering the laser beam after the expanding and collimating processing by using a polarizer to make the polarization direction of the laser beam be 45°.

[0026] Optionally, the using the second modulated light beam to write data on the target storage medium comprises:

[0027] Processing the second modulated light beam by using a Fourier lens to focus the second modulated light beam at the focal plane of the Fourier lens.

[0028] Optionally, the using the second modulated light beam to write data on the target storage medium comprises:

[0029] Focusing the write light beam on the storage medium by using a four-fold focal length imaging system composed of a double-convex lens to write on the write medium.

[0030] Optionally, the focusing the write light beam on the storage medium by using a four-fold focal length imaging system composed of a double-convex lens comprises:

[0031] Removing the zero-order information and the side lobe stray components of the write light beam by using a spatial filter at the focal plane of the front convex lens in the four-fold focal length imaging system.

[0032] Optionally, before loading the hologram in the spatial light modulator, the method further comprises:

[0033] Converting the target write data into the polarization state of each point of the target storage medium according to the mapping relationship between the target write data and the polarization state;

[0034] Decomposing the polarization state of each point to obtain the polarization component of each point in the first polarization direction and the second polarization direction;

[0035] Determining the first area information of the hologram according to the polarization component of each point in the first polarization direction, and determining the second area information of the hologram according to the polarization component of each point in the second polarization direction.

[0036] In the technical scheme provided by the present application, the light beam is modulated in the first polarization direction by the first area, and then the modulated light beam passes through the second area to be modulated in the second polarization direction perpendicular to the first polarization direction. On the basis of realizing the independent modulation of the light beam in the two orthogonal directions, the polarization direction of the single light beam is flexibly configured by the single spatial light modulator without the cooperation of other devices. Meanwhile, since the first area and the second area independently modulate the light beam in the two orthogonal directions, the amplitude of the light beam in the direction can be controlled by the phase modulation in each direction during the final writing. Since the polarization direction of the light beam during the final writing is determined by the amplitude components in the two orthogonal directions, the polarization direction of the light beam during the final writing can be flexibly controlled. BRIEF DESCRIPTION OF DRAWINGS

[0037] Figure 1 A flowchart of a holographic coding phase modulation method according to an embodiment of the present application;

[0038] Figure 2 A light path principle diagram of a holographic coding phase modulation method according to another embodiment of the present application. DETAILED DESCRIPTION

[0039] To make the objectives, technical schemes and advantages of the embodiments of the present application clearer, the technical schemes in the embodiments of the present application will be described clearly and completely below with reference to the drawings in the embodiments of the present application. Obviously, the described embodiments are only part of the embodiments of the present application, rather than all the embodiments of the present application. Based on the embodiments in the present application, all other embodiments obtained by those skilled in the art without creative work fall within the protection scope of the present application.

[0040] An embodiment of the present application provides a holographic coding phase modulation method, as shown in Figure 1 The method comprises the following steps.

[0041] A hologram is loaded in a spatial light modulator, wherein the hologram comprises a first area and a second area.

[0042] In some embodiments, the first area and the second area of the hologram are respectively used to modulate the components of the laser beam in two orthogonal polarization directions.

[0043] The first area of the hologram is used to modulate the laser beam with a polarization direction of 45° in the first polarization direction to form a first modulated light beam.

[0044] In some embodiments, the linearly polarized laser beam with a polarization direction of 45° has the same polarization intensity in the horizontal polarization direction and the vertical polarization direction. In an implementation, the linearly polarized laser beam with a polarization direction of 45° provides a prerequisite for subsequent independent modulation of the horizontal and vertical directions. The first polarization direction can be either the horizontal polarization direction or the vertical polarization direction. The first modulated light beam is a holographic light beam carrying modulated phase information in the first polarization direction.

[0045] The first modulated light beam is reflected to a second area of the hologram, and the second area of the hologram is used to modulate the first modulated light beam in a second polarization direction to form a second modulated light beam; wherein the second polarization direction is perpendicular to the first polarization direction.

[0046] In some embodiments, the second polarization direction is perpendicular to the first polarization direction, so that when the first polarization direction is modulated, the phase and amplitude of the second polarization direction are not affected, and similarly, when the second polarization direction is modulated, the phase and amplitude of the first polarization direction are not affected, so as to achieve independent modulation of the first polarization direction and the second polarization direction, and then form the second modulated light beam carrying the hologram information after modulation.

[0047] Data writing is performed on a target storage medium using the second modulated light beam.

[0048] In some embodiments, the first region and the second region are both modulated by holograms, so that the second modulated light beam forms a hologram in which each point is modulated to a specific polarization state, and thus, in the writing process, the voxels in the range can be written all at once with the size of the hologram as the writing range, which can effectively improve the writing efficiency. Since the present embodiment writes all the data points of different polarization states of all the points at the same time according to pages, the number of movements of the glass storage medium platform is significantly reduced, the mechanical motion delay is reduced, and thus the overall data writing rate is greatly improved. This page writing method effectively avoids the time overhead caused by point-by-point movement. At the same time, since the single light beam is modulated by two spatial light modulators in the present embodiment, there is no need to perform beam combining, and thus there is no need to consider the precision problem in the beam combining process. Based on the modulation principle of the liquid crystal spatial light modulator (LCOS-SLM), the horizontal polarization direction component, i.e., the X-direction component Ax, and the vertical polarization direction component, i.e., the Y-direction component Ay, can be accurately controlled by modulating the phase depth of the first polarization direction and the second polarization direction by using two spatial light modulators. The polarization direction of the second modulated light beam is determined by the ratio of Ax and Ay. The first polarization direction can be the X direction or the Y direction. In some embodiments, it should be understood that the polarization direction of the light beam may

[0049] In the technical scheme provided in the embodiment of the present application, the first region modulates the light beam in the first polarization direction, and then the modulated light beam passes through the second region to be modulated in the second polarization direction perpendicular to the first polarization direction. On the basis of realizing the independent modulation of the light beam in the two orthogonal directions, the polarization direction of the single light beam of the single spatial light modulator is flexibly configured without the cooperation of other devices. Meanwhile, since the first region and the second region independently modulate the light beam in the two orthogonal directions, the amplitude of the light beam in the direction can be controlled by the phase modulation in each direction during the final writing. Since the polarization direction of the light beam during the final writing is determined by the amplitude components in the two orthogonal directions, the polarization direction of the light beam during the final writing can be flexibly controlled. In the embodiment of the present application, the spatial light modulator (SLM) is used to independently load the computer-generated hologram in the two regions to realize the independent modulation of the first polarization direction and the second polarization direction. The amplitude ratio of the two regions of the hologram (CGH) can be adjusted to continuously control the linear polarization angle of 0° to 180°. The polarization freedom degree is improved compared with the scheme of the traditional half-wave plate matrix (HPM) with only four fixed polarization states. The polarization exchange and the holographic modulation are synchronously completed, the phase mismatch caused by the traditional step-by-step modulation is eliminated, and the edge definition of the output point array is improved. Meanwhile, the first region and the second region are both modulated by the hologram, and the polarization direction of each point can be freely controlled. Therefore, the single-page writing can be realized based on the full-electric dynamic refresh mechanism of the SLM refresh rate (60-100 Hz), without the need of mechanical moving parts, and the single-data-page multi-polarization-state exposure is completed in situ. The multi-polarization-state (such as 0°, 45°, 90° and 135°) point array light field is generated by dynamically updating the hologram, the sample stage does not need to be moved during the single-data-page exposure, and the writing speed is improved.

[0050] As an optional implementation manner, as shown in Figure 2 The first region of the hologram modulates the laser beam with a polarization direction of 45° in the first polarization direction includes:

[0051] A laser is used to emit a laser beam along a direction parallel to the spatial light modulator;

[0052] A first beam splitter is used to split the laser beam to form a first vertical light beam perpendicular to the spatial light modulator and a first parallel light beam parallel to the spatial light modulator;

[0053] The first region of the hologram modulates the first vertical light beam in the first polarization direction and reflects it to form a first intermediate light beam;

[0054] The portion of the first intermediate light beam transmitted by the first beam splitter is determined as a first modulated light beam.

[0055] In some embodiments, the first beam splitter needs to reflect the laser beam to the first region and transmit the first intermediate light beam after the first region is modulated and reflected, so as to avoid the first intermediate light beam returning along the path of the laser beam, thus, in the present embodiment, the first beam splitter needs to be used.

[0056] As an optional embodiment, continuing as shown in Figure 2 The second region of the hologram is used to modulate the first modulated light beam in the second polarization direction to form a second modulated light beam.

[0057] The propagation direction of the first modulated light beam is changed by using a mirror set, and the polarization direction of the first modulated light beam is rotated by 90° by using a half-wave plate, so that the first modulated light beam is incident on the second beam splitter in a direction perpendicular to the incident direction of the spatial light modulator.

[0058] The first modulated light beam is split by using the second beam splitter to form a second vertical light beam perpendicular to the spatial light modulator and a second parallel light beam parallel to the spatial light modulator.

[0059] The second region of the hologram is used to modulate the second vertical light beam in the second polarization direction and reflect it to form a second intermediate light beam.

[0060] The portion of the second intermediate light beam reflected by the second beam splitter is determined as a second modulated light beam.

[0061] In some embodiments, the second beam splitter needs to transmit the first modulated light beam to the first region and reflect the second intermediate light beam after the second region is modulated and reflected, so as to avoid the second intermediate light beam returning along the path of the first modulated light beam, thus, in the present embodiment, the second beam splitter needs to be used. The mirror set may, for example, use two mirrors arranged at an interval and having a vertical angle.

[0062] As an optional embodiment, the method further comprises:

[0063] A blocking film is arranged between the first beam splitter and the second beam splitter to block the first parallel light beam from entering the second beam splitter and block the second parallel light beam from entering the first beam splitter.

[0064] In some embodiments, the first beam splitter and the second beam splitter are arranged in parallel with the laser beams, and without the blocking film, the first parallel light beam enters the second beam splitter and the second parallel light beam enters the first beam splitter, which can easily interfere with each other. Therefore, the blocking film is arranged in the embodiment to avoid interference with each other.

[0065] As an optional implementation, the changing of the propagation direction of the first modulated light beam by the mirror group and the rotating of the polarization direction of the first modulated light beam by 90° by the half-wave plate include:

[0066] The rotating of the polarization direction of the first modulated light beam by 90° by the half-wave plate is performed before, after or during the changing of the propagation direction of the first modulated light beam by the mirror group.

[0067] In some embodiments, since simple reflection has little effect on the polarization direction of light, in the implementation, the half-wave plate can be arranged at any position after the first modulated light beam exits from the first beam splitter and before the first modulated light beam enters the second beam splitter.

[0068] As an optional implementation, before the laser beam with a polarization direction of 45° is modulated in the first polarization direction by the first area of the hologram, the method further includes:

[0069] The laser beam is expanded and collimated to have a diameter of a first preset size;

[0070] The laser beam after the expansion and collimation is filtered by a polarizer to have a polarization direction of 45°.

[0071] In some embodiments, the laser beam can use a high-coherence 633 nm single-longitudinal-mode semiconductor laser (0.3 mW, horizontal linear polarization output) as a light source, for example. The laser beam is first expanded and collimated by a double-convex lens (the focal length of the first lens is 30 mm and the focal length of the second lens is 150 mm) to a laser beam with a diameter greater than 10 mm from an original laser beam with a diameter close to 3 mm, so as to improve the space-bandwidth product and ensure the width of the modulation area of the subsequent spatial light modulator.

[0072] As an optional implementation, the writing of data on the target storage medium by the second modulated light beam includes:

[0073] The second modulated light beam is processed by a Fourier lens to be focused at the focal plane of the Fourier lens.

[0074] As an optional implementation, the writing data on the target storage medium by using the second modulated light beam comprises:

[0075] The four-fold focal length imaging system composed of the bi-convex lens focuses the writing light beam on the storage medium to write on the writing medium.

[0076] As an optional implementation, the four-fold focal length imaging system composed of the bi-convex lens focuses the writing light beam on the storage medium comprises:

[0077] The spatial filter is used in the focal plane of the front convex lens in the four-fold focal length imaging system to remove the zero-order information and the side lobe stray components of the writing light beam.

[0078] In some implementations, when the light field of the second modulated light beam enters the four-fold focal length imaging system, the zero-order and side lobe disturbance are removed by the first Fourier lens and the spatial filter, and then focused to the image plane by the second lens, thereby realizing high signal-to-noise ratio reconstruction of the vector hologram. The integrated scheme preserves the phase and polarization information.

[0079] As an optional implementation, before the hologram is loaded in the spatial light modulator, the method further comprises:

[0080] According to the mapping relationship between the target writing data and the polarization state, the target writing data is converted into the polarization state of each point of the target storage medium;

[0081] The polarization state of each point is decomposed to obtain the polarization component of each point in the first polarization direction and the second polarization direction;

[0082] According to the polarization component of each point in the first polarization direction, the first area information of the hologram is determined, and according to the polarization component of each point in the second polarization direction, the second area information of the hologram is determined.

[0083] In some embodiments, when writing data to the target storage medium, the written data usually has a mapping relationship with the polarization state, so the polarization state of each point can be determined according to the mapping relationship. After obtaining the polarization state of each point, the vector information of the polarization state can be decomposed into the first polarization direction and the second polarization direction, so as to determine the phase information of each point in the first polarization direction and the second polarization direction, and then the corresponding phase diagram is loaded through the first area and the second area, so as to realize the modulation of the light beam.

[0084] As shown in Figure 2 An exemplary optical path schematic diagram formed by the foregoing embodiments is shown, in which the Jones vector of the input 45° linearly polarized laser beam is represented as:

[0085]

[0086] The first region of the hologram loaded by the spatial light modulator (SLM) is modulated at the first level, the light beam loaded the first region encodes the target image, the first region loaded the component only responding to the first polarization direction is modulated, and the component of the second polarization direction is not modulated in phase and amplitude information; after the modulation of the first region, the vector light field of the output first modulation light beam is as follows:

[0087]

[0088] wherein, is the amplitude coefficient of the first modulation light beam in the first polarization direction, is the phase function of the first region at the position, is the imaginary unit,

[0089] When the first modulation light beam is rotated in the polarization direction by the half-wave plate, since the Jones matrix of the half-wave plate fast axis at 45° is as follows:

[0090]

[0091] wherein, θ is the included angle between the fast axis of the half-wave plate and the polarization direction of the first modulation light beam.

[0092] After the processing of the half-wave plate, the horizontal and vertical components of the light beam are exchanged, at this time, the Jones matrix of the light field of the first modulation light beam is as follows:

[0093]

[0094] The light beam is split by two reflecting mirrors and is incident to the second region of the hologram loaded by the spatial light modulator (SLM), the second region encodes the phase and amplitude of the target image to the component of the rotated second polarization direction:

[0095]

[0096] wherein, is the phase function of the second region at the position, is the imaginary unit, is the amplitude coefficient of the second modulation light beam in the second polarization direction. When the horizontal component and the vertical component are consistent in phase, the target holographic pattern image is realized. The polarization state can be determined by the amplitude ratio. By updating the contents of the first region and the second region of the hologram, the holographic pattern and the polarization state are switched synchronously within the refresh rate of the spatial light modulator (SLM).

[0097]

[0098] ​​In the foregoing embodiments, only the spatial light modulator (SLM) is used to drive the change of polarization state, and the combination of double-part holographic encoding and polarization rotation technology is used to realize the synchronous generation of holographic images and arbitrary linear polarization states, thereby breaking through the limitation of traditional spatial light modulators (SLMs) that can only modulate phase or amplitude. By using a single device to load double-computer-generated holograms (CGHs), the independent rotation of two polarization component directions is introduced to adapt to the direction of a single liquid crystal molecule, realize the sequential information encoding of two polarization components, simplify the system structure, effectively solve the inherent contradiction between the single working direction of the liquid crystal molecule and the double polarization control, and provide a new technical path for optical data storage. Through the double-part precise illumination of the spatial light modulator (SLM), the single spatial light modulator (SLM) is multiplexed as a "virtual double modulator" through the folding light path design of the combination of the non-polarizing beam splitter (NPBS) and the mirror, thereby breaking through the physical limitation of discrete devices, improving the light flux utilization rate, and effectively avoiding polarization-dependent loss; in terms of system reliability, the calibration process is greatly simplified, and only the single beam needs to be aligned at 45° with the spatial light modulator (SLM), without the need for multiple calibrations.

[0099] In some preferred embodiments, 3D printing integrated structure can be used to greatly reduce the volume of the optical path and significantly improve the system integration and portability; the polarization switching delay of the system is only limited by the refresh rate of the spatial light modulator (SLM), and the response speed is improved compared with the traditional mechanical wave plate array scheme. By updating the hologram (CGH) in real time, the microsecond-level synchronous switching of the holographic pattern and the polarization state can be realized, thereby meeting the needs of high-speed data writing scenarios. Moreover, in the entire optical path system, there is no moving part design, which improves the vibration tolerance and significantly enhances the mechanical stability.

[0100] The above merely describes specific embodiments of the present application, but the protection scope of the present application is not limited thereto, and any changes or replacements within the technical scope disclosed by the present application can be easily thought of by those skilled in the art, and should be covered within the protection scope of the present application. Therefore, the protection scope of the present application should be subject to the protection scope of the claims.

Claims

1. A holographic coding phase modulation method, characterized in that, The method includes: A hologram is loaded into a spatial light modulator, wherein the hologram includes a first region and a second region; The first region of the hologram is used to modulate a laser beam with a polarization direction of 45° in the first polarization direction to form a first modulated beam; The first modulated beam is reflected to the second region of the hologram, and the first modulated beam is modulated in the second polarization direction using the second region of the hologram to form a second modulated beam; wherein the second polarization direction is perpendicular to the first polarization direction; The second modulated beam is used to write data onto the target storage medium; The method further includes, prior to loading the hologram into the spatial light modulator: Based on the mapping relationship between the target data and the polarization state, the target data is converted into the polarization state of each bit in the target storage medium; The polarization state of each point is decomposed to obtain the polarization components of each point in the first polarization direction and the second polarization direction. Based on the polarization component of the first polarization direction at each point, the first region information of the hologram is determined, and based on the polarization component of the second polarization direction at each point, the second region information of the hologram is determined.

2. The method according to claim 1, characterized in that, The modulation of a laser beam with a polarization direction of 45° in the first polarization direction using the first region of the hologram includes: A laser beam is emitted from a laser in a direction parallel to the spatial light modulator; The laser beam is split using a first beam splitter to form a first vertical beam perpendicular to the spatial light modulator and a first parallel beam parallel to the spatial light modulator. The first vertical beam is modulated and reflected in the first polarization direction using the first region of the hologram to form a first intermediate beam; The portion of the first intermediate beam that passes through the first beam splitter is defined as the first modulated beam.

3. The method according to claim 2, characterized in that, The step of reflecting the first modulated beam to the second region of the hologram and modulating the first modulated beam in the second polarization direction using the second region of the hologram to form the second modulated beam includes: The propagation direction of the first modulated beam is changed by using a set of mirrors and the polarization direction of the first modulated beam is rotated by 90° by using a half-wave plate, so that the first modulated beam is incident on the second beam splitter in an incident direction perpendicular to the spatial light modulator. The first modulated beam is split by a second beam splitter to form a second vertical beam perpendicular to the spatial light modulator and a second parallel beam parallel to the spatial light modulator. The second vertical beam is modulated and reflected in the second polarization direction using the second region of the hologram to form a second intermediate beam; The portion of the second intermediate beam reflected by the second beam splitter is defined as the second modulated beam.

4. The method according to claim 3, characterized in that, The method further includes: A blocking membrane is provided between the first beam splitter and the second beam splitter to block the first parallel beam from entering the second beam splitter and to block the second parallel beam from entering the first beam splitter.

5. The method according to claim 3, characterized in that, The step of changing the propagation direction of the first modulated beam using a set of mirrors and rotating the polarization direction of the first modulated beam by 90° using a half-wave plate includes: Before, after, or during the process of changing the propagation direction of the first modulated beam using a set of mirrors, the polarization direction of the first modulated beam is rotated by 90° using a half-wave plate.

6. The method according to claim 1, characterized in that, Before modulating a laser beam with a polarization direction of 45° in a first polarization direction using a first region of the hologram, the method further includes: The laser beam is expanded and collimated so that the diameter of the laser beam reaches a first preset size; The laser beam, after beam expansion and collimation, is filtered using a polarizer to ensure that the polarization direction of the laser beam is 45°.

7. The method according to claim 1, characterized in that, The step of writing data onto the target storage medium using the second modulated beam includes: The second modulated beam is processed using a Fourier lens so that it is focused at the focal plane of the Fourier lens.

8. The method according to claim 7, characterized in that, The step of writing data onto the target storage medium using a second modulated beam includes: A four-fold focal length imaging system using biconvex lenses focuses the write beam onto the storage medium to write to it.

9. The method according to claim 8, characterized in that, The four-times focal length imaging system using biconvex lenses focuses the write beam onto the storage medium, including: In the four-times focal length imaging system, a spatial filter is used on the focal plane of the front convex lens to remove the zero-order information and sidelobe stray components of the written beam.

Images