Serial holographic encoding phase modulation method

Abstract

The application provides a serial holographic encoding phase modulation method, which comprises the following steps: modulating a linearly polarized laser beam with a polarization direction of 45 degrees by using a first spatial light modulator in a first polarization direction to form a first modulated light beam; modulating the first modulated light beam by using a second spatial light modulator in a second polarization direction perpendicular to the first polarization direction to form a second modulated light beam; and writing data on a target storage medium by using the second modulated light beam. The serial holographic encoding phase modulation method provided by the application can control the single-beam phase information and the polarization state simultaneously, and avoids the problems existing in the spatial superposition when writing by using double-beam or multi-beam.

Description

TECHNICAL FIELD

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

[0002] In the field of 5D optical storage, there is a high-efficiency laser direct writing technology based on a single spatial light modulator (SLM) combined with a half-wave plate matrix (HPM). This method can realize multi-level coding of light intensity information and polarization state, and has been applied to the writing of glass samples. The multi-level coding of light intensity is realized by loading a computer-generated hologram (CGH) SLM, and the light beam modulated by the SLM passes through the HPM to generate a preset polarization state. The HPM is composed of a half-wave plate array and can complete the coding of the polarization state of the light beam. In the existing optical storage technology, a double-beam scheme is usually used to control the dynamic polarization, which expands the available space of the polarization angle. However, although the double-beam scheme can dynamically control the polarization state, it is extremely sensitive to the assembly precision of optical elements because the two orthogonally polarized light beams need to be precisely superimposed in space, and a slight mechanical shift or environmental disturbance will destroy the modulation effect. SUMMARY

[0003] The serial holographic encoding phase modulation method provided by the present application can simultaneously control the phase information and polarization state of a single light beam, avoiding the problems existing in the spatial superposition when using a double-beam or multi-beam for writing.

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

[0005] modulating a linearly polarized laser beam with a polarization direction of 45° on a first polarization direction by using a first spatial light modulator to form a first modulated light beam;

[0006] modulating the first modulated light beam on a second polarization direction perpendicular to the first polarization direction by using a second spatial light modulator to form a second modulated light beam;

[0007] using the second modulated light beam to write data on a target storage medium.

[0008] Optionally, modulating the first modulated light beam on the second polarization direction perpendicular to the first polarization direction by using the second spatial light modulator comprises:

[0009] rotating the first modulated light beam by using a half-wave plate to rotate the polarization direction of the first modulated light beam by 90°;

[0010] incident the rotated first modulated light beam to a four-fold focal length imaging system, and irradiating the rotated first modulated light beam to the second spatial light modulator by using the four-fold focal length imaging system.

[0011] Optionally, before the step of modulating the linearly polarized laser beam with a polarization direction of 45° by a first spatial light modulator in a first polarization direction, the method further comprises:

[0012] adjusting the polarization direction of the laser beam by a polarizer to adjust the polarization direction of the laser beam to 45°.

[0013] Optionally, before the step of adjusting the polarization direction of the laser beam by a polarizer to adjust the polarization direction of the laser beam to 45°, the method further comprises:

[0014] expanding and collimating the laser beam to increase the diameter of the laser beam to a first preset size.

[0015] Optionally, the step of modulating the linearly polarized laser beam with a polarization direction of 45° by a first spatial light modulator in a first polarization direction comprises:

[0016] determining the polarization state of each point according to the target write data;

[0017] decomposing the polarization state of each point to obtain the phase information of each point in the first polarization direction;

[0018] determining the first hologram that the first spatial light modulator needs to load according to the phase information of each point in the first polarization direction;

[0019] transmitting the laser beam to the first spatial light modulator by a first beam splitter;

[0020] modulating the laser beam in the first polarization direction by the first spatial light modulator loaded with the first hologram to form a first modulated light beam, and irradiating the first modulated light beam to the first beam splitter;

[0021] reflecting the first modulated light beam according to a first preset direction by the first beam splitter;

[0022] wherein the first beam splitter is a non-reciprocal beam splitter.

[0023] Optionally, the step of modulating the first modulated light beam by a second spatial light modulator in a second polarization direction perpendicular to the first polarization direction comprises:

[0024] determining the polarization state of each point according to the target write data;

[0025] decomposing the polarization state of each point to obtain the phase information of each point in the second polarization direction;

[0026] According to the phase information of each point in the second polarization direction, a second hologram to be loaded by the second spatial light modulator is determined;

[0027] The first modulated light beam is reflected to the second spatial light modulator by a second beam splitter;

[0028] The second modulated light beam is formed by modulating the laser beam in the second polarization direction by the second spatial light modulator loaded with the second phase pattern, and the second modulated light beam is irradiated to the second beam splitter;

[0029] The second modulated light beam is transmitted to a second preset direction by the second beam splitter;

[0030] The second beam splitter is a non-reciprocal beam splitter.

[0031] Optionally, the data writing on the target storage medium by the second modulated light beam comprises:

[0032] The second modulated light beam is processed by a Fourier lens to focus the second modulated light beam at the Fourier lens focal plane.

[0033] Optionally, after the second modulated light beam is processed by the Fourier lens, the method further comprises:

[0034] The second modulated light beam is spatially filtered to improve the light field quality of the second modulated light beam.

[0035] Optionally, the data writing on the target storage medium by the second modulated light beam comprises:

[0036] The second modulated light beam is focused on the target storage medium by a four-fold focal length imaging system composed of a double-convex lens to write the target storage medium.

[0037] Optionally, the focusing of the second modulated light beam on the target storage medium by the four-fold focal length imaging system composed of a double-convex lens comprises:

[0038] A spatial filter is arranged at the Fourier transform plane of the four-fold focal length imaging system to filter out the zero-order information and the side lobe stray components of the second modulated light beam.

[0039] In the technical scheme provided by the present application, the first spatial light modulator is used to modulate the light beam in the first polarization direction, and then the modulated light beam passes through the second spatial light modulator 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 double-beam combination is not needed, and the requirement of high-precision alignment by the double-beam combination method is avoided. Meanwhile, since the first spatial light modulator and the second spatial light modulator 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

[0040] Figure 1 A flowchart of a serial holographic encoding phase modulation method according to an embodiment of the present application;

[0041] Figure 2 A light path principle diagram of a serial holographic encoding phase modulation method according to another embodiment of the present application. DETAILED DESCRIPTION

[0042] 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 labor fall within the protection scope of the present application.

[0043] An embodiment of the present application provides a serial holographic encoding phase modulation method, as shown in Figure 1 The method comprises the following steps.

[0044] A linearly polarized laser beam with a polarization direction of 45° is modulated in a first polarization direction by a first spatial light modulator to form a first modulated light beam.

[0045] 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 embodiment, the linearly polarized laser beam with a polarization direction of 45° provides a prerequisite for subsequent independent modulation in the horizontal and vertical directions. The first polarization direction can be 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.

[0046] modulate the first modulated light beam to form a second modulated light beam;

[0047] In some embodiments, the second polarization direction is perpendicular to the first polarization direction, so that the phase and amplitude of the second polarization direction are not affected when the first polarization direction is modulated, and vice versa, so as to achieve independent modulation of the first polarization direction and the second polarization direction, and further form the second modulated light beam carrying hologram information after modulation.

[0048] The second modulated light beam is used to write data on the target storage medium.

[0049] In some embodiments, the first spatial light modulator and the second spatial light modulator can each be modulated by a hologram, so that the second modulated light beam forms a hologram in which each point is modulated to a specific polarization state. Therefore, during 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 this embodiment writes all the data points of different polarization states of all the points at the same time by page, the number of glass target storage medium platform movements is significantly reduced, the mechanical motion delay is reduced, and 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 this embodiment, there is no need for beam combining, and 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, of the outgoing light can be accurately controlled by modulating the first polarization direction and the second polarization direction by two spatial light modulators. 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

[0050] In the technical scheme provided in the embodiments of the present application, the first spatial light modulator is used to modulate the light beam in the first polarization direction, and then the modulated light beam passes through the second spatial light modulator 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 double-beam combination is not needed, and the requirement of high-precision alignment by the double-beam combination method is avoided. Meanwhile, since the first spatial light modulator and the second spatial light modulator are used to 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, and 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.

[0051] As an optional implementation, as shown in Figure 2 the step of modulating the first modulated light beam in the second polarization direction perpendicular to the first polarization direction by using the second spatial light modulator comprises:

[0052] rotating the first modulated light beam by using a half-wave plate to rotate the polarization direction of the first modulated light beam by 90°;

[0053] the step of modulating the first modulated light beam in the second polarization direction perpendicular to the first polarization direction by using the second spatial light modulator comprises:

[0054] In some embodiments, in order to facilitate the loading of the hologram by the spatial light modulator, the first modulated light beam can be rotated by 90° by using a half-wave plate and then modulated by using the second spatial light modulator.

[0055] As an optional implementation, as shown in Figure 2 the method further comprises, before the step of modulating the linearly polarized laser beam with the polarization direction of 45° in the first polarization direction by using the first spatial light modulator:

[0056] adjusting the polarization direction of the laser beam by using a polarizer to adjust the polarization direction of the laser beam to 45°.

[0057] As an optional implementation, as shown in Figure 2 the method further comprises, before the step of adjusting the polarization direction of the laser beam by using a polarizer to adjust the polarization direction of the laser beam to 45°:

[0058] expanding and collimating the laser beam to increase the diameter of the laser beam to a first preset size.

[0059] In some embodiments, the laser beam can employ a high coherence 633 nm single longitudinal mode semiconductor laser (0.3 mW, horizontal linear polarization output) as a light source, which is first expanded and collimated by a double convex lens (focal length of the first lens is 30 mm, and focal length of the second lens is 150 mm) from an original laser beam with a diameter of about 3 mm to a laser beam with a diameter of more than 10 mm, so as to improve the space-bandwidth product and ensure the modulation area width of the subsequent spatial light modulator.

[0060] As an optional implementation, the modulating the linearly polarized laser beam with a polarization direction of 45° in the first polarization direction by the first spatial light modulator comprises:

[0061] determining the polarization state of each point according to the target write data;

[0062] decomposing the polarization state of each point to obtain phase information of each point in the first polarization direction;

[0063] determining the first hologram to be loaded by the first spatial light modulator according to the phase information of each point in the first polarization direction;

[0064] transmitting the laser beam to the first spatial light modulator by the first beam splitter;

[0065] modulating the laser beam in the first polarization direction by the first spatial light modulator loaded with the first hologram to form a first modulated light beam, and irradiating the first modulated light beam to the first beam splitter;

[0066] reflecting the first modulated light beam according to a first preset direction by the first beam splitter;

[0067] wherein the first beam splitter is a non-reciprocal beam splitter.

[0068] In some embodiments, when writing data to the target storage medium, the written data usually has a mapping relationship with the polarization state, and therefore 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 load the corresponding phase pattern by the first spatial light modulator and the second spatial light modulator, so as to realize the modulation of the light beam. In some embodiments, the non-reciprocal beam splitter has different beam splitting characteristics when incident in opposite directions. For example, when incident in the forward direction, the transmission component is much larger than the reflection component, and when incident in the reverse direction, the reflection component is much larger than the transmission component.

[0069] As an optional implementation, the modulating the first modulated light beam in the second polarization direction perpendicular to the first polarization direction by the second spatial light modulator comprises:

[0070] According to the target write data, the polarization state of each point is determined;

[0071] The polarization state of each point is decomposed to obtain the phase information of each point in the second polarization direction;

[0072] According to the phase information of each point in the second polarization direction, the second hologram required to be loaded by the second spatial light modulator is determined;

[0073] The first modulated light beam is reflected to the second spatial light modulator by the second beam splitter;

[0074] The second spatial light modulator loaded with the second phase diagram is used to modulate the laser beam in the second polarization direction to form a second modulated light beam, and the second modulated light beam is irradiated to the second beam splitter;

[0075] The second modulated light beam is transmitted to the second preset direction by the second beam splitter;

[0076] The second beam splitter is a non-reciprocal beam splitter.

[0077] 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 load the corresponding phase diagram through the first spatial light modulator and the second spatial light modulator, so as to realize the modulation of the light beam. In some embodiments, the non-reciprocal beam splitter has different beam splitting characteristics when incident in opposite directions, for example, when incident in the forward direction, the transmission component is much larger than the reflection component, and when incident in the reverse direction, the reflection component is much larger than the transmission component.

[0078] As an optional implementation, continuing as shown in Figure 2 The second modulated light beam is used to write data on the target storage medium, comprising:

[0079] The second modulated light beam is processed by the Fourier lens to focus at the Fourier lens focal plane.

[0080] As an optional implementation, continuing as shown in Figure 2As shown, after the second modulated light beam is processed by the Fourier lens, the method further comprises:

[0081] spatially filtering the second modulated light beam to improve the light field quality of the second modulated light beam.

[0082] As an optional implementation, the method continues as follows: Figure 2 As shown, the data writing on the target storage medium by using the second modulated light beam comprises:

[0083] a four-fold focal length imaging system composed of a bi-convex lens is used to focus the second modulated light beam on the target storage medium to write on the target storage medium.

[0084] As an optional implementation, the focusing of the second modulated light beam on the target storage medium by using the four-fold focal length imaging system composed of a bi-convex lens comprises:

[0085] a spatial filter is arranged at the Fourier transform plane of the four-fold focal length imaging system to filter out the zero-order information and the side lobe stray components of the second modulated light beam.

[0086] In some implementations, the second modulated light beam enters the four-fold focal length imaging system, wherein: the light beam first passes through the first lens of the four-fold focal length imaging system and forms a spatial spectrum distribution at the back focal plane thereof; a spatial filter is arranged at the back focal plane (Fourier transform plane) of the first lens to filter out the zero-order information and the side lobe stray components of the light beam; the filtered spectrum is subjected to inverse Fourier transform by the second lens of the four-fold focal length imaging system and is reconstructed into a filtered light field at the back focal plane (output plane) of the second lens; this integrated scheme realizes high signal-to-noise ratio reconstruction of the vector hologram by faithfully transmitting the wavefront phase and polarization state. Experiments are conducted on the foregoing implementations to test the independent control effect in the first polarization direction and the second polarization direction, and it is found through verification that, when the first spatial light modulator loads the first hologram for phase modulation in the first polarization direction and the second spatial light modulator loads the second hologram for phase modulation in the second polarization direction, the orthogonal analyzer detects that the polarization characteristics are completely separated, that is, the analyzer only displays the modulation result of the first hologram in the first polarization direction, and the analyzer only displays the modulation result of the second hologram in the second polarization direction, proving the independent modulation capability of the two polarization components and fundamentally solving the problem of pattern and polarization coupling in the traditional double-beam scheme.

[0087] In addition, experiments were conducted on the aforementioned embodiments to test the dynamic modulation capability of the polarization direction of the second modulated light beam, and it was found that when two spatial light modulators were loaded with the same hologram, two components of a single light beam vector field could be encoded. Further observation of different linear polarization states by rotating a polarization analyzer and capturing the holographic patterns of the second modulated light beam by a CMOS sensor showed that when the two SLMs were set to a specific phase depth difference, the brightest holographic image could be observed at a certain polarization angle position, while the orthogonal position showed the darkest state. This indicates that by precisely controlling the phase depth and the target pattern related hologram, a holographic pattern with a specific linear polarization state can be generated. The experimental results also confirmed that each holographic pattern designed in the experiment had the theoretically expected polarization characteristics.

[0088] The above merely provides a specific implementation of the present application, but the protection scope of the present application is not limited thereto, and any person skilled in the art can easily think of changes or replacements within the technical scope disclosed by the present application, which should be covered by 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 method of serial holographic encoding phase modulation, characterized by, The method comprises: modulating a linearly polarized laser beam with a polarization direction of 45° on a first polarization direction by using a first spatial light modulator to form a first modulated light beam; modulating the first modulated light beam on a second polarization direction perpendicular to the first polarization direction by using a second spatial light modulator to form a second modulated light beam; performing data writing on a target storage medium by using the second modulated light beam; wherein the step of modulating the linearly polarized laser beam with a polarization direction of 45° on the first polarization direction by using the first spatial light modulator comprises: determining the polarization state of each point according to the target writing data; decomposing the polarization state of each point to obtain the phase information of each point on the first polarization direction; determining the first hologram required to be loaded by the first spatial light modulator according to the phase information of each point on the first polarization direction; transmitting the laser beam to the first spatial light modulator by using a first beam splitter; modulating the laser beam on the first polarization direction by using the first spatial light modulator loaded with the first hologram to form the first modulated light beam, and irradiating the first modulated light beam to the first beam splitter; reflecting the first modulated light beam according to a first preset direction by using the first beam splitter; wherein the first beam splitter is a non-reciprocal beam splitter; wherein the step of modulating the first modulated light beam on the second polarization direction perpendicular to the first polarization direction by using the second spatial light modulator comprises: determining the polarization state of each point according to the target writing data; decomposing the polarization state of each point to obtain the phase information of each point on the second polarization direction; determining the second hologram required to be loaded by the second spatial light modulator according to the phase information of each point on the second polarization direction; reflecting the first modulated light beam to the second spatial light modulator by using a second beam splitter; modulating the laser beam on the second polarization direction by using the second spatial light modulator loaded with the second hologram to form the second modulated light beam, and irradiating the second modulated light beam to the second beam splitter; transmitting the second modulated light beam to a second preset direction by using the second beam splitter; wherein the second beam splitter is a non-reciprocal beam splitter.

2. The method of claim 1, wherein, The step of modulating the first modulated light beam on the second polarization direction perpendicular to the first polarization direction by using the second spatial light modulator comprises: rotating the first modulated light beam by using a half-plate to rotate the polarization direction of the first modulated light beam by 90°; incident the rotated first modulated light beam to a four-fold focal length imaging system, and irradiating the rotated first modulated light beam to the second spatial light modulator by using the four-fold focal length imaging system.

3. The method of claim 1, wherein, Before the step of modulating the linearly polarized laser beam with a polarization direction of 45° on the first polarization direction by using the first spatial light modulator, the method further comprises: adjusting the polarization direction of the laser beam by using a polarizer to adjust the polarization direction of the laser beam to 45°.

4. The method of claim 3, wherein, Before the step of adjusting the polarization direction of the laser beam by using the polarizer to adjust the polarization direction of the laser beam to 45°, the method further comprises: The laser beam is expanded and collimated to increase a diameter of the laser beam to a first preset size.

5. The method of claim 1, wherein, The writing data on the target storage medium using the second modulated light beam includes: The second modulated light beam is processed using a Fourier lens to focus the second modulated light beam at a Fourier lens focal plane.

6. The method of claim 5, wherein, After the second modulated light beam is processed using the Fourier lens, the method further includes: The second modulated light beam is spatially filtered to improve an optical field quality of the second modulated light beam.

7. The method of claim 6, wherein, The writing data on the target storage medium using the second modulated light beam includes: The second modulated light beam is focused on the target storage medium using a four-fold focal length imaging system composed of a lenticular lens to write on the target storage medium.

8. The method of claim 7, wherein, The focusing of the second modulated light beam on the target storage medium using the four-fold focal length imaging system composed of the lenticular lens includes: A spatial filter is arranged at a Fourier transform plane of the four-fold focal length imaging system to filter out zero-order information and side lobe stray components of the second modulated light beam.

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