Device for generating linearly polarized light having different azimuth angles, and laser beam machining method

Abstract

A device for generating linearly polarized light having different azimuth angles, and a laser beam machining method. The device comprises: a laser, a half wave plate, an electro-optical modulator, a reflection system and a quarter wave plate, wherein the quarter wave plate is used for adjusting light to linearly polarized light of which the polarization direction has an included angle of 45 degrees relative to a horizontal plane; the electro-optical modulator is used for adjusting the linearly polarized light output by the half wave plate, such that a polarization state of emergent light of the electro-optical modulator always lies on a meridian of a Poincaré sphere, thereby outputting Poincaré meridian polarized light; the reflection system is used for reflecting the Poincaré meridian polarized light to the quarter wave plate; and the quarter wave plate is used for adjusting the reflected light, such that the polarization state of emergent light of the quarter wave plate always lies on the equator of the Poincaré sphere, thereby outputting the linearly polarized light having different azimuth angles. The problem that the laser beam machining effects are affected by change in polarization state caused by reflectors in existing linearly polarized light generating devices is solved.

Description

Device for generating linearly polarized light of different azimuth angles and laser processing method Technical Field

[0001] The present application relates to the field of laser processing technology, and in particular to a device for generating linearly polarized light of different azimuth angles and a laser processing method. Background Art

[0002] At present, linearly polarized light is widely used in the field of laser processing technology. The quality of laser processing is closely related to the laser used for processing, especially the parameter of polarization. Existing linearly polarized light generating devices often include a reflection system. Since the reflectors in the reflection system often have a phase difference between s-polarization and p-polarization (and the reflectivity of s-polarization and p-polarization can be basically consistent), unless the polarization azimuth of the incident light is parallel or perpendicular to the reflecting surface, the reflectors will cause a change in the polarization state. This will cause problems such as decreased fidelity of stored data and decreased polarization control efficiency for optical storage technologies and optical device processing that require precise polarization angles. Therefore, there is an urgent need to solve the problem of the reflectors in existing linearly polarized light generating devices causing changes in the polarization state, which affects the laser processing effect.

[0003] Summary of the Invention

[0004] In order to solve the problem that the change of polarization state caused by the reflector in the existing linearly polarized light generating device affects the laser processing effect, the present application proposes a device for generating linearly polarized light with different azimuth angles and a laser processing method.

[0005] In order to achieve the above object, the present application provides a device for generating linearly polarized light of different azimuth angles, the device comprising: a laser, a half-wave plate, an electro-optical modulator, a reflection system, and a quarter-wave plate;

[0006] The laser is used to generate laser light;

[0007] The half-wave plate is used to adjust the laser light into linearly polarized light with a polarization direction forming an angle of 45 degrees with the horizontal plane;

[0008] The voltage of the electro-optical modulator is scanned within a preset range, and the electro-optical modulator is used to adjust the linearly polarized light output by the half-wave plate so that the polarization state of its output light always falls on a longitude line of the Poincare sphere, thereby outputting Poincare meridian polarized light;

[0009] The reflection system is used to reflect the Poincare meridian polarized light and make the reflected light incident on the quarter-wave plate;

[0010] The quarter wave plate is used to adjust the reflected light so that the polarization state of its outgoing light always falls on the equator of the Poincare sphere, thereby outputting linearly polarized light of different azimuth angles.

[0011] The beneficial effects of this application are:

[0012] The present application uses an electro-optical modulator to generate Poincare meridian polarized light whose polarization state always falls on a meridian of the Poincare sphere. The Poincare meridian polarized light can absorb the phase difference error caused by the reflector in the reflection system, avoiding the change of polarization state caused by the reflector, and solving the problem that the change of polarization state caused by the reflector in the existing linear polarized light generating device affects the laser processing effect. BRIEF DESCRIPTION OF THE DRAWINGS

[0013] In order to more clearly illustrate the embodiments of the present application or the technical solutions in the prior art, the following briefly introduces the drawings required for the embodiments or the description of the prior art. Obviously, the drawings described below are only some embodiments of the present application. For those skilled in the art, other drawings can be obtained based on these drawings without creative work. In the drawings:

[0014] FIG1 is a schematic diagram of the optical path of a device for generating linearly polarized light of different azimuth angles according to the present invention;

[0015] FIG2 is a schematic diagram of adjusting the meridian polarization of the Poincare sphere;

[0016] FIG3 is a schematic diagram of adjusting the equatorial polarization of the Poincare sphere;

[0017] FIG4 is a birefringence microscopic image of the optical storage unit before and after optimization;

[0018] FIG5 is a line graph showing the birefringence delay of the optical storage unit before and after optimization;

[0019] Figure 6 shows the distribution of polarization states with different ellipticities on the Poincare sphere before and after optimization;

[0020] Figure 7 shows birefringence microscopic images of nanogratings fabricated with different ellipticities.

[0021] In the accompanying drawings: E is a beam expander, HWP is a half wave plate, P is an electro-optical modulator, M is a reflection system, QWP is a quarter wave plate, OL is an objective lens, and CCD is a charge coupled device (i.e., a camera). DETAILED DESCRIPTION

[0022] The following will be combined with the drawings in the embodiments of this application to clearly and completely describe the technical solutions in the embodiments of this application. Obviously, the embodiments described are only part of the embodiments of this application, not all of the embodiments. Based on the embodiments in this application, all other embodiments obtained by ordinary technicians in this field without making creative efforts are within the scope of protection of this application.

[0023] It should be noted that, in the absence of conflict, the embodiments and features of the embodiments in this application can be combined with each other. The present application will be described in detail below with reference to the accompanying drawings and in combination with the embodiments.

[0024] Thanks to femtosecond laser high-precision three-dimensional direct writing technology, nanogratings—subwavelength grating structures with birefringence induced by femtosecond lasers on or within materials—are attracting widespread attention and application in fields such as data storage and polarization-controlled metamaterials. In an era of rapidly growing data, five-dimensional optical storage technology based on femtosecond laser-induced nanogratings offers advantages such as high storage density, long lifespan, and resistance to extreme environments, offering an alternative to traditional big data storage solutions like optical discs and magnetic tapes. In line with the trend toward miniaturization and integration of optical systems, the technology of micro- and nano-polarization optical devices based on nanogratings is also attracting significant attention.

[0025] The processing quality of nanogratings is closely related to the laser used for processing, especially the polarization parameter. However, when setting up a practical system, especially when passing through a reflective system composed of multiple mirrors, because the mirrors often have a phase difference between s-polarization and p-polarization (while the reflectivity of s-polarization and p-polarization can be basically the same), unless the polarization angle of the incident light is parallel or perpendicular to the reflecting surface, the mirrors will cause the polarization state to change. This will cause problems such as reduced storage data fidelity and polarization control efficiency for optical storage technologies and optical device processing that require precise polarization angles.

[0026] Therefore, it is urgent to solve the polarization-maintaining problem in polarization-state reflection systems with different azimuth angles.

[0027] In response to the shortcomings of the existing technology, the present application provides a device for generating linearly polarized light of different azimuth angles based on electro-optical modulation. The present application adopts electro-optical modulation to solve the problem of polarization-maintaining transmission. The main principle is to modulate the incident light into a linear polarization-circular polarization array (the polarization state is on a meridian of the Poincare sphere) through an electro-optical modulator, and then adjust it to linear polarization (the polarization state is on the equator of the Poincare sphere) after passing through a reflection system containing s and p polarization phase differences, thereby achieving the purpose of polarization maintenance (ellipticity maintenance); solving the problem that the polarization states in various directions lose their original ellipticity during the reflection transmission process, improving the polarization-related laser processing accuracy, and solving the problems of data distortion and reduced control accuracy caused by the degradation of processing laser polarization in optical storage and polarization device processing.

[0028] Figure 1 is a schematic diagram of the optical path of the device for generating linearly polarized light of different azimuth angles of the present application. As shown in Figure 1, in some embodiments of the present application, the device for generating linearly polarized light of different azimuth angles of the present application includes: a laser, a half-wave plate HWP, an electro-optical modulator P, a reflection system M and a quarter-wave plate QWP.

[0029] The laser is used to generate laser light;

[0030] The half-wave plate is used to adjust the laser light into linearly polarized light with a polarization direction forming an angle of 45 degrees with the horizontal plane;

[0031] The voltage of the electro-optical modulator is scanned within a preset range, and the electro-optical modulator is used to adjust the linearly polarized light output by the half-wave plate so that the polarization state of its output light always falls on a longitude line of the Poincare sphere, thereby outputting Poincare meridian polarized light;

[0032] The reflection system is used to reflect the Poincare meridian polarized light and make the reflected light incident on the quarter-wave plate;

[0033] The quarter wave plate is used to adjust the reflected light so that the polarization state of its outgoing light always falls on the equator of the Poincare sphere, thereby outputting linearly polarized light of different azimuth angles.

[0034] In this application, the polarization state always falls on the equator of the Poincare sphere, which means that the outgoing light is linearly polarized light and the ellipticity is 0.

[0035] The present application uses an electro-optical modulator to generate Poincare meridian polarized light whose polarization state always falls on a meridian of the Poincare sphere. The Poincare meridian polarized light can absorb the phase difference error caused by the reflector in the reflection system, avoiding the change of polarization state caused by the reflector, and solving the problem that the change of polarization state caused by the reflector in the existing linear polarized light generating device affects the laser processing effect.

[0036] To achieve the effects described in this application, this application has clear requirements for the polarization state after passing through the half-wave plate, electro-optic modulator, and quarter-wave plate, and none of them can be missing. The laser output is generally horizontally or vertically linearly polarized light. The half-wave plate can be used to adjust the polarization direction of linearly polarized light. After passing through the half-wave plate, the linear polarization must be 45 degrees, otherwise subsequent operations will not generate the required Poincare meridian polarization.

[0037] It should be noted that the Poincare meridian polarized light output by the electro-optical modulator of the present application is light whose polarization state always falls on a meridian of the Poincare sphere. The meridian here specifically refers to the meridian on the S2-S3 plane, and only this meridian can absorb phase difference. The meridian on the S2-S3 plane specifically refers to the meridian located in the plane formed by the coordinate axes S2 and S3 of the Poincare sphere.

[0038] In some embodiments of the present application, the electro-optic modulator is used to adjust the linearly polarized light output by the half-wave plate so that the polarization state of its own output light always falls on the longitude of the Poincare sphere located on the plane formed by the coordinate axis S2 and the coordinate axis S3, thereby outputting Poincare longitudinal polarized light.

[0039] The Poincare meridian polarized light of the present application can absorb the phase difference error caused by the reflector. The principle is that the dynamic polarization state generated by the electro-optical modulator appears as a circle on the Poincare sphere, and the circle has infinite-order rotational symmetry. The operation of the reflector on the polarization state is reflected on the Poincare sphere as the rotation of the circle. Under a specific rotation axis, a circle can be rotated and still coincide with itself, thereby absorbing the error.

[0040] In the present application, the voltage of the electro-optical modulator is scanned within a preset range, thereby outputting Poincare linearly polarized light. The Poincare linearly polarized light passes through a reflection system and enters the quarter-wave plate for adjustment to obtain linearly polarized light of different azimuth angles.

[0041] In some embodiments of the present application, the laser light generated by the laser is linearly polarized light with an uncertain azimuth angle.

[0042] In some embodiments of the present application, the reflection system includes at least one reflector.

[0043] In some embodiments of the present application, the electro-optic modulator is further configured to adjust the azimuth angle of the linearly polarized light output by the quarter-wave plate. Specifically, the electro-optic modulator adjusts the azimuth angle of the linearly polarized light output by the quarter-wave plate by adjusting a voltage.

[0044] As shown in FIG2 , in some embodiments of the present application, the device for generating linearly polarized light of different azimuth angles of the present application further includes: a first polarization state measuring instrument; the first polarization state measuring instrument is used to measure the polarization state of the output light of the electro-optical modulator.

[0045] The electro-optical modulator is specifically configured to rotate its own roll angle according to the polarization state measured by the first polarization state measuring instrument until the polarization state of its outgoing light always falls on a meridian of the Poincare sphere.

[0046] Specifically, the present application scans the voltage of the electro-optical modulator within a preset range, rotates the roll angle of the electro-optical modulator, and observes a first polarization state measuring instrument placed behind the electro-optical modulator until the polarization state of the light emitted by the electro-optical modulator always falls on a longitude of the Poincare sphere, thereby obtaining Poincare meridian polarized light.

[0047] As shown in FIG3 , in some embodiments of the present application, the device for generating linearly polarized light of different azimuth angles of the present application further includes: a second polarization state measuring instrument; the second polarization state measuring instrument is used to measure the polarization state of the output light of the quarter-wave plate.

[0048] The quarter wave plate is specifically used to rotate the wave plate according to the polarization state measured by the second polarization state measuring instrument until the polarization state of its own output light always falls on the equator of the Poincare sphere.

[0049] Specifically, the present application rotates the quarter-wave plate and observes the second polarization state measuring instrument placed behind the quarter-wave plate until the polarization state of the output light of the quarter-wave plate always falls on the equator of the Poincare sphere, thereby obtaining linearly polarized light of different azimuth angles.

[0050] In some embodiments of the present application, the half-wave plate is further used to adjust the ellipticity of the output light of the quarter-wave plate.

[0051] In this application, ellipticity refers to the ratio of the major axis to the minor axis in the polarization ellipse. Furthermore, the adjustment range of the ellipticity in this application is greater than or equal to 0 and less than positive infinity, that is, [0, +∞).

[0052] In some embodiments of the present application, the present application can rotate the angle of the half wave plate HWP so that the quarter wave plate outputs polarized light with different azimuth angles and consistent ellipticity to meet different processing requirements.

[0053] Specifically, the present application rotates the angle of the half-wave plate HWP so that the polarization state of the output light of the quarter-wave plate always falls on a latitude line of the Poincare sphere, so that the quarter-wave plate outputs polarized light with different azimuth angles and consistent ellipticity.

[0054] In the present application, the polarization state always falling on a meridian of the Poincare sphere refers to all polarization states in which the Stokes vectors S1 and S2 are always proportional and the sum of their squares is unity.

[0055] In the present application, the polarization state always falling on the equator of the Poincare sphere refers to all polarization states in which the Stokes vector S3 is always zero and the sum of the squares of the Stokes vectors S1 and S2 is unity.

[0056] The Stokes vectors S1 and S2 together represent the azimuth of the polarization state; the Stokes vector S3 represents the ellipticity of the polarization state. The Stokes vectors S1, S2, and S3, as the x, y, and z coordinates, together determine the position of the polarization state on the Poincare sphere.

[0057] In some embodiments of the present application, the voltage of the electro-optical modulator is scanned within a preset range, and the preset range is greater than 0 and less than or equal to the half-wave voltage, that is, the voltage scanning range of the electro-optical modulator is (0, half-wave voltage].

[0058] As shown in FIG1 , in some embodiments of the present application, the device for generating linearly polarized light of different azimuth angles of the present application further includes: a beam expander;

[0059] The beam expander is used to expand the laser light generated by the laser, and then the expanded laser light is incident on the half-wave plate. The beam expansion factor of the beam expander ranges from greater than or equal to 1 to less than or equal to 3.

[0060] As shown in Figure 1, in some embodiments of the present application, when the device for generating linearly polarized light of different azimuth angles of the present application is used, first, the femtosecond laser emitted by the laser passes through the beam expander E to expand the light spot by 2 times, and then passes through the half wave plate HWP to adjust the original polarization angle, and then passes through the electro-optic modulator P, through the reflection system M and the quarter wave plate QWP, and then through the objective lens OL to be focused and incident on the target position of the sample on the translation stage; the illumination light source LED is fixed on the mirror frame of the reflection system M, so that the white light emitted by the illumination light source LED is incident on the objective lens OL, focused on the surface of the glass sample to illuminate the sample; the illumination light passes through the reflection system M and is focused and imaged into the charge coupled device CCD, and the charge coupled device CCD is connected to the computer PC; the overall optical path is adjusted and the sample stage is leveled.

[0061] Another aspect of the present application provides a laser processing method for an optical storage unit. The laser processing method for an optical storage unit of the present application specifically utilizes the linearly polarized light output by the device for generating linearly polarized light of different azimuth angles described in any of the above embodiments to laser process the optical storage unit.

[0062] When performing laser processing on an optical storage unit, the present application focuses linearly polarized light of different azimuth angles output by a quarter-wave plate into the interior of quartz glass through an objective lens for processing. The processing is performed using different laser parameters and characterized using a birefringence microscope and a scanning electron microscope to find the generation condition range of the subwavelength grating. When performing data storage, encoding is performed by changing the laser power and azimuth angle of the processing laser. The laser power of the processing laser is adjusted by a laser, and the azimuth angle of the processing laser can be quickly set using an electro-optical modulator. The multi-photon absorption effect of a femtosecond laser in a hard material is used to achieve processing in three dimensions: X, Y, and Z, i.e., five-dimensional optical data storage.

[0063] Another aspect of the present application provides a method for laser processing a polarization device control unit. The method utilizes light output from the device for generating linearly polarized light of different azimuth angles described in any of the above embodiments to laser process the polarization device control unit.

[0064] When laser processing the polarization device control unit, the present application focuses the linearly polarized light of different azimuth angles output by the quarter-wave plate through an objective lens inside the quartz glass for processing. The processing is performed using different laser parameters and characterized using a birefringence microscope and a scanning electron microscope to find the generation condition range of the subwavelength grating. Subsequently, the required ellipticity value is selected by rotating the half-wave plate, and the voltage of the electro-optical modulator is used to generate the polarized laser of the required azimuth angle to process the polarization device control unit.

[0065] Figure 4 shows the birefringence microscopic images of the optical storage unit before and after optimization. Each column in Figure 4 shows the birefringence microscopic images of the data storage unit with polarization written at different azimuth angles. It can be seen from Figure 4 that the birefringence delay (brightness) of the optimized image is more uniform and stable, which proves that the quality of the written storage unit (nanograting) has been improved. Since the delay is an important basis for reading the stored data, this technology improves the fidelity of data reading.

[0066] Figure 5 is a line graph of the birefringence delay of the optical storage unit before and after optimization. From the line graph of the polarization states at different azimuth angles and the delay of the processed nanograting in Figure 5, it can be seen that the birefringence delay after optimization is more uniform and stable, which proves that the quality of the written storage unit (nanograting) has been improved, thereby improving the data fidelity.

[0067] Figure 6 shows the distribution of isotropic polarization states of different ellipticities on the Poincare sphere before and after optimization. As shown in Figure 6, the present application can generate elliptically polarized light of different ellipticities by rotating the half-wave plate, and can maintain uniform ellipticity at different polarization azimuths (the dotted line in Figure 6 represents the motion trajectory of the polarization state on the Poincare sphere before optimization, controlled by the electro-optic modulator; the solid line represents the motion trajectory after optimization. The trajectories parallel to the equatorial plane all have the same ellipticity). Therefore, the present application can achieve polarization with uniform ellipticity at different azimuths, promoting research on elliptical polarization-induced nanograting formation.

[0068] FIG7 is a birefringence microscopic image of nanogratings processed with different ellipticities. As can be seen from FIG7 , the birefringence retardation (brightness) of the nanogratings processed with elliptical polarization at multiple azimuth angles using different ellipticity parameters is relatively uniform and stable.

[0069] It can be seen from the above embodiments that, compared with the prior art, the advantages of this application are as follows:

[0070] 1. This application uses electro-optical modulation to generate Poincare meridian polarized light, absorbing the phase difference error caused by the reflector, avoiding the use of high-cost custom reflector coatings and other complex compensation mechanisms. This effectively solves the polarization degradation problem of femtosecond lasers during reflection transmission in optical storage and processing systems, and achieves high-fidelity data storage.

[0071] 2. Compared with traditional polarization modulation technology, this application can output elliptical polarization with consistent ellipticity and arbitrary azimuth angle for polarization-dependent processing;

[0072] 3. By combining high-speed electro-optical modulation technology, this application can achieve high-speed changing polarization output with consistent ellipticity, providing technical support for high-quality and high-speed optical storage technology, and can be applied to polarization-related communications, imaging and other fields.

[0073] The above description is merely a preferred embodiment of the present application and is not intended to limit the present application. Various modifications and variations are possible for those skilled in the art. Any modifications, equivalent substitutions, or improvements made within the spirit and principles of the present application shall be included within the scope of protection of the present application.

Claims

1. A device for generating linearly polarized light of different azimuth angles, characterized in that: include: Lasers, half-wave plates, electro-optic modulators, reflective systems, and quarter-wave plates; The laser is used to generate laser light; The half wave plate is used to adjust the laser light into linear polarized light whose polarization direction is at an angle of 45 degrees to the horizontal plane; The voltage of the electro-optic modulator is scanned within a preset range, and the electro-optic modulator is used to adjust the linearly polarized light output by the half-wave plate so that the polarization state of its output light always falls on a meridian of the Poincare sphere, thereby outputting Poincare meridian polarized light; The reflection system is used to reflect the Poincare meridian polarized light and make the reflected light incident on the quarter wave plate; The quarter wave plate is used to adjust the reflected light so that the polarization state of its outgoing light always falls on the equator of the Poincare sphere, thereby outputting linear polarized light of different azimuth angles.

2. The device for generating linearly polarized light of different azimuth angles according to claim 1, characterized in that: Also includes: The first polarization state measuring instrument; The first polarization state measuring instrument is used to measure the polarization state of the output light of the electro-optic modulator; The electro-optic modulator is specifically used to rotate its own roll angle according to the polarization state measured by the first polarization state measuring instrument until the polarization state of its own output light always falls on a meridian of the Poincare sphere.

3. The device for generating linearly polarized light of different azimuth angles according to claim 1, characterized in that: Also includes: A second polarization state measuring instrument; The second polarization state measuring instrument is used to measure the polarization state of the output light of the quarter wave plate; The quarter wave plate is specifically used to rotate the wave plate according to the polarization state measured by the second polarization state measuring instrument until the polarization state of its own output light always falls on the equator of the Poincare sphere.

4. The device for generating linearly polarized light of different azimuth angles according to claim 1, characterized in that: The electro-optic modulator is also used to adjust the azimuth angle of the linearly polarized light output by the quarter-wave plate.

5. The device for generating linearly polarized light of different azimuth angles according to claim 1, characterized in that: The half wave plate is also used to adjust the ellipticity of the output light of the quarter wave plate.

6. The device for generating linearly polarized light of different azimuth angles according to claim 1, characterized in that: The polarization state always falls on a meridian of the Poincare sphere, which refers to all polarization states in which the Stokes vectors S1 and S2 are always proportional and the sum of the squares is unity; the polarization state always falls on the equator of the Poincare sphere, which refers to all polarization states in which the Stokes vector S3 is always zero and the sum of the squares of the Stokes vectors S1 and S2 is unity; wherein the Stokes vectors S1 and S2 jointly represent the azimuth of the polarization state; the Stokes vector S3 represents the ellipticity of the polarization state, and the Stokes vectors S1, S2, and S3 as the x, y, and z coordinates jointly determine the position of the polarization state on the Poincare sphere.

7. The device for generating linearly polarized light of different azimuth angles according to claim 1, characterized in that: The preset range is greater than 0 and less than or equal to the half-wave voltage.

8. The device for generating linearly polarized light of different azimuth angles according to claim 1, characterized in that: Also includes: Beam expander; The beam expander is used to expand the laser light generated by the laser, and then the expanded laser light is incident on the half wave plate. The beam expansion factor of the beam expander ranges from greater than or equal to 1 to less than or equal to 3.

9. A laser processing method for an optical storage unit, characterized in that: The optical storage unit is laser processed using the linearly polarized light output by the device for generating linearly polarized light of different azimuth angles as claimed in any one of claims 1 to 8.

10. A laser processing method for a polarization device control unit, characterized in that: The polarization device control unit is laser processed using the light output by the device for generating linearly polarized light of different azimuth angles as described in any one of claims 1 to 8.

Images