CN117148601B - Device and laser processing method for generating linearly polarized light with different azimuth angles - Google Patents

Abstract

The invention discloses a device for generating linearly polarized light with different azimuth angles and a laser processing method. The device includes: a laser, a half-wave plate, an electro-optical modulator, a reflection system and a quarter-wave plate; The one-wave plate is used to adjust the light into linearly polarized light whose polarization direction is at an angle of 45 degrees with the horizontal plane; the electro-optical modulator is used to adjust the linearly polarized light output by the half-wave plate so that its own emitted light The polarization state always falls on a meridian of the Poincaré sphere, thus outputting the Poincaré meridian polarized light; the reflection system is used to reflect the Poincaré meridian polarized light to the quarter wave plate; quarter wave The film is used to adjust the reflected light so that the polarization state of its own emitted light always falls on the equator of the Poincaré sphere, thereby outputting linearly polarized light with different azimuth angles. The invention solves the problem in the existing linearly polarized light generating device that the reflection mirror causes the change of polarization state and affects the laser processing effect.

Description

Device and laser processing method for generating linearly polarized light with different azimuth angles

Technical field

The present invention relates to the technical field of laser processing, and specifically, to a device for generating linearly polarized light with different azimuth angles and a laser processing method.

Background technique

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 polarization. Existing linearly polarized light generating devices often include a reflection system. Since the mirrors 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 the same), unless The polarization azimuth angle of the incident light must be parallel or perpendicular to the reflective surface. Otherwise, the reflector will cause a change in polarization state. This will affect the fidelity of stored data and the efficiency of polarization control for optical storage technology and optical device processing that require precise polarization angles. problems such as decline. Therefore, there is an urgent need to solve the problem that the reflection mirror in the existing linearly polarized light generating device causes the change of polarization state and affects the laser processing effect.

Contents of the invention

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 invention proposes a device and a laser processing method for generating linearly polarized light with different azimuth angles.

In order to achieve the above object, the present invention provides a device for generating linearly polarized light with different azimuth angles. The device includes: a laser, a half-wave plate, an electro-optical modulator, a reflection system and a quarter-wave plate;

The laser is used to generate laser light;

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

The voltage of the electro-optical modulator scans 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 own emitted light always falls within the Ponca A meridian of the Ley sphere, from which the Poincaré meridian polarized light is output;

The reflection system is used to reflect the Poincaré meridian polarized light and incident the reflected light onto the quarter-wave plate;

The quarter-wave plate is used to adjust the reflected light so that the polarization state of its own emitted light always falls on the equator of the Poincaré sphere, thereby outputting linearly polarized light with different azimuth angles.

The beneficial effects of the present invention are:

The invention uses an electro-optical modulator to generate Poincaré meridian polarized light whose polarization state always falls on a meridian of the Poincaré sphere. This Poincaré meridian polarized light can absorb the phase difference error caused by the mirror in the reflection system and avoid It eliminates the change of polarization state caused by the reflector and solves 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.

Description of drawings

In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings needed to be used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings in the following description are: For some embodiments of the present invention, those of ordinary skill in the art can also obtain other drawings based on these drawings without exerting creative efforts. In the attached picture:

Figure 1 is a schematic diagram of the optical path of a device for generating linearly polarized light with different azimuth angles according to the present invention;

Figure 2 is a schematic diagram of the adjustment of the meridian polarization of the Poincaré sphere;

Figure 3 is a schematic diagram of the adjustment of the equatorial polarization of the Poincaré sphere;

Figure 4 shows the birefringence microscopy image of the optical storage unit before and after optimization;

Figure 5 is a line chart of the birefringence delay of the optical storage unit before and after optimization;

Figure 6 shows the distribution of polarization states with different ellipticities on the Poincaré sphere before and after optimization;

Figure 7 shows birefringence microscopy images of nanogratings processed using different ellipticities.

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

Detailed ways

In order to enable those skilled in the art to better understand the solutions of the present invention, the technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments are only These are some embodiments of the present invention, rather than all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative efforts should fall within the scope of protection of the present invention.

It should be noted that, as long as there is no conflict, the embodiments and features in the embodiments of the present invention can be combined with each other. The present invention will be described in detail below with reference to the accompanying drawings and embodiments.

Thanks to the high-precision three-dimensional direct writing technology of femtosecond laser, the sub-wavelength grating structure with birefringence effect induced by femtosecond laser on the surface or inside the material - nanograting, has attracted widespread attention in the fields of data storage, polarization control metamaterials and other fields. and applications. Especially in the era of rapid data growth, five-dimensional optical storage technology based on femtosecond laser-induced nanogratings offers an alternative to traditional big data storage solutions such as optical disks and tapes with its advantages of high storage density, long life, and resistance to extreme environments. Solution; Under the general trend of miniaturization and integration of optical systems, the technology of micro-nano polarization optical devices based on nanogratings has also attracted much attention.

The processing quality of nanogratings is closely related to the laser used for processing, especially the polarization parameter. However, when building an actual system, especially when passing through a reflection system composed of multiple mirrors, the mirrors often have a phase difference between s-polarization and p-polarization (and the reflectivity of s-polarization and p-polarization can be basically the same) , unless the polarization azimuth angle of the incident light is parallel or perpendicular to the reflective surface, the mirror will cause a change in the polarization state, which will affect the fidelity and polarization of the stored data for optical storage technology and optical device processing that require precise polarization angles. Problems such as reduced regulatory efficiency.

Therefore, there is an urgent need to solve the polarization maintenance problem in polarization reflection systems with different azimuth angles.

In view of the shortcomings of the existing technology, the present invention provides a device for generating linearly polarized light with different azimuth angles based on electro-optical modulation. The present invention uses electro-optical modulation to solve the problem of polarization transmission and polarization maintenance. The main principle is to modulate the incident light through the electro-optical modulator into a linear polarization-circular polarization array (the polarization state is on a meridian of the Poincaré sphere). After passing through the meridian containing s, p The reflection system with polarization phase difference is then adjusted to linear polarization through a wave plate (the polarization state is on the equator of the Poincaré sphere), thereby achieving the purpose of maintaining polarization (preserving ellipticity); solving the problem of the reflection transmission process of polarization states in various directions. It solves the problem of losing the original ellipticity in the process, improves polarization-related laser processing accuracy, and solves problems such as data distortion and reduced control accuracy caused by the degradation of processing laser polarization in optical storage and polarization device processing.

Figure 1 is a schematic optical path diagram of a device for generating linearly polarized light with different azimuth angles according to the present invention. As shown in Figure 1, in some embodiments of the present invention, the device for generating linearly polarized light with different azimuth angles includes: a laser, Half wave plate HWP, electro-optical modulator P, reflection system M and quarter wave plate QWP.

The laser is used to generate laser light;

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

The voltage of the electro-optical modulator scans 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 own emitted light always falls within the Ponca A meridian of the Ley sphere, from which the Poincaré meridian polarized light is output;

The reflection system is used to reflect the Poincaré meridian polarized light and incident the reflected light onto the quarter-wave plate;

The quarter-wave plate is used to adjust the reflected light so that the polarization state of its own emitted light always falls on the equator of the Poincaré sphere, thereby outputting linearly polarized light with different azimuth angles.

In the present invention, the polarization state always falls on the equator of the Poincaré sphere, which means that the emitted light is linearly polarized light and the ellipticity is 0.

The invention uses an electro-optical modulator to generate Poincaré meridian polarized light whose polarization state always falls on a meridian of the Poincaré sphere. This Poincaré meridian polarized light can absorb the phase difference error caused by the mirror in the reflection system and avoid It eliminates the change of polarization state caused by the reflector and solves 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.

In order to achieve the effects described in the present invention, the present invention has clear requirements for the polarization state passing through the half-wave plate, the electro-optical modulator and the quarter-wave plate, and all of them are indispensable. The laser output by the laser is generally horizontal or vertical linearly polarized light. The polarization direction of the linearly polarized light can be adjusted by using a half-wave plate. After passing through the half-wave plate, the linearly polarized light must be 45 degrees, otherwise the subsequent The operation will fail to generate a Poincaré meridian polarization that meets the conditions.

It should be noted that the Poincaré meridian polarized light output by the electro-optical modulator of the present invention is light whose polarization state always falls on a meridian of the Poincaré sphere, where a meridian here specifically refers to the meridian on the S2-S3 plane. A meridian, only this meridian can absorb the phase difference. The meridian on the S2-S3 plane specifically refers to the meridian located on the plane formed by the coordinate axis S2 and the coordinate axis S3 of the Poincaré sphere.

In a specific embodiment of the present invention, 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 own emitted light always falls on the Poincaré sphere located by The Poincaré meridian polarized light is output on the meridian on the plane formed by the coordinate axis S2 and the coordinate axis S3.

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

In the present invention, the voltage of the electro-optical modulator scans within a preset range, whereby the electro-optical modulator outputs Poincaré meridian polarized light. The Poincaré meridian polarized light enters the quarter-wave plate through the reflection system and is adjusted to obtain linearly polarized light with different azimuth angles.

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

In some embodiments of the present invention, the reflecting system includes at least one reflecting mirror.

In some embodiments of the present invention, the electro-optical modulator is also used to adjust the azimuth angle of the linearly polarized light output by the quarter-wave plate. Specifically, the electro-optical modulator adjusts the azimuth angle of the linearly polarized light output by the quarter-wave plate by adjusting the voltage.

As shown in Figure 2, in some embodiments of the present invention, the device for generating linearly polarized light at different azimuth angles of the present invention also includes: a first polarization state measuring instrument; the first polarization state measuring instrument is used to measure The polarization state of the emitted light from the electro-optical modulator.

The electro-optical 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 emitted light always falls on a meridian of the Poincaré sphere. .

Specifically, the present invention scans the voltage of the electro-optic modulator within a preset range, rotates the roll angle of the electro-optic modulator, and observes the first polarization state measuring instrument placed behind the electro-optic modulator until the intensity of the light emitted from the electro-optic modulator. The polarization state always falls on a meridian of the Poincaré sphere, that is, Poincaré meridian polarized light is obtained.

As shown in Figure 3, in some embodiments of the present invention, the device for generating linearly polarized light at different azimuth angles of the present invention also includes: a second polarization state measuring instrument; the second polarization state measuring instrument is used to measure The polarization state of the light emitted from 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 emitted light always falls on the equator of the Poincaré sphere. .

Specifically, the present invention 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 light emitted from the quarter-wave plate always falls within the Pangaea On the equator of the Raid sphere, linearly polarized light with different azimuth angles is obtained.

In some embodiments of the present invention, the half-wave plate is also used to adjust the ellipticity of the emitted light from the quarter-wave plate.

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

In some embodiments of the present invention, the present invention 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 needs. processing needs.

Specifically, the present invention rotates the angle of the half-wave plate HWP so that the polarization state of the outgoing light of the quarter-wave plate always falls on a latitude line of the Poincaré sphere, so that the quarter-wave plate Outputs polarized light at different azimuth angles with consistent ellipticity.

In the present invention, the polarization state always falling on a meridian of the Poincaré sphere refers to all polarization states in which the Stokes vectors S1 and S2 are always proportional and the sum of the squares is unit 1.

In the present invention, the polarization state always falling on the equator of the Poincaré 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 unit 1.

The Stokes vectors S1 and S2 jointly represent the azimuth angle of the polarization state; the Stokes vector S3 represents the ellipticity of the polarization state. The Stokes vectors S1, S2, and S3 jointly determine the three coordinates of x, y, and z. The position of the polarization state on the Poincaré sphere.

In some embodiments of the present invention, the voltage of the electro-optic modulator scans within a preset range, and the preset range is greater than 0 and less than or equal to a half-wave voltage, that is, the voltage scan range of the electro-optic modulator is ( 0, half-wave voltage].

As shown in Figure 1, in some embodiments of the present invention, the device of the present invention for generating linearly polarized light with different azimuth angles also includes: a 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 multiple of the beam expander is The value range is greater than or equal to 1 and less than or equal to 3.

As shown in Figure 1, in a specific embodiment of the present invention, when the device for generating linearly polarized light with different azimuth angles of the present invention is used, first, the femtosecond laser emitted from the laser passes through the beam expander E successively, and the light spot is It is expanded by 2 times, and then the original polarization angle is adjusted through the half-wave plate HWP, and then passes through the electro-optical modulator P, through the reflection system M and the quarter-wave plate QWP, and then is focused by the objective lens OL before being incident on the displacement The target position of the sample on the stage; the illumination light source LED is fixed on the frame of the reflection system M, so that the white light emitted by the illumination light source LED is incident into the objective lens OL and focused on the surface of the glass sample to illuminate the sample; the illumination light passes through the reflection system M Then focus the image into the charge-coupled device CCD, and connect the charge-coupled device CCD to the computer PC; adjust the overall optical path and level the sample stage.

Another aspect of the present invention also provides a laser processing method for an optical storage unit. The laser processing method of the optical storage unit of the present invention specifically uses the linearly polarized light output from the device for generating linearly polarized light with different azimuth angles described in any of the above embodiments to perform laser processing on the optical storage unit.

When the present invention performs laser processing on the optical storage unit, the linearly polarized light with different azimuth angles output by the quarter-wave plate is focused inside the quartz glass through the objective lens for processing, and is processed through different laser parameters. Through the birefringence microscope, Characterize it with a scanning electron microscope to find the generation condition interval of sub-wavelength gratings. When storing data, encode it by changing the laser power and azimuth angle of the processing laser. Among them, the laser power of the processing laser is adjusted by the laser. , the azimuth angle of the processing laser can be quickly set using an electro-optical modulator, and the multi-photon absorption effect of femtosecond laser in hard materials can be used to achieve processing in the three dimensions of X, Y and Z, that is, five-dimensional optical data storage.

Another aspect of the present invention also provides a laser processing method for a polarization device control unit. The laser processing method of the polarization device control unit of the present invention specifically uses the light output from the device for generating linearly polarized light with different azimuth angles described in any of the above embodiments to perform laser processing on the polarization device control unit.

When the present invention performs laser processing on the polarization device control unit, the linearly polarized light with different azimuth angles output by the quarter-wave plate is focused inside the quartz glass through the objective lens for processing, and is processed through different laser parameters. Through birefringence, Microscope and scanning electron microscope are used for characterization to find the generation condition interval of sub-wavelength grating, and then the required ellipticity value is selected by rotating a half-wave plate, and the voltage of the electro-optical modulator is used to generate the polarized laser with the required azimuth angle. Processing of polarization device control unit.

Figure 4 shows the birefringence microscopy image of the optical storage unit before and after optimization. Each column in Figure 4 shows the birefringence microscopy image of the data storage unit written with polarization at different azimuth angles. The optimized image can be seen from Figure 4 The birefringence delay (brightness) is more uniform and stable, which proves that the quality of the written memory unit (nano grating) has been improved. Since the delay is an important basis for the readout of stored data, this technology improves the fidelity of data readout. promote.

Figure 5 is a line graph of the birefringence retardation of the optical storage unit before and after optimization. From the line graph of Figure 5 showing the retardation of the polarization state at different azimuth angles and the nanograting processed, it can be seen that the birefringence retardation after optimization More uniform and stable, which proves that the quality of the written memory cells (nanogratings) has been improved, which in turn leads to improved data fidelity.

Figure 6 shows the distribution of various ellipticity polarization states on the Poincaré sphere before and after optimization. As shown in Figure 6, the present invention can generate elliptically polarized light with different ellipticities by rotating a half-wave plate, and in Different polarization azimuth angles can maintain uniform ellipticity (the dotted line in Figure 6 represents the movement trajectory of the polarization state on the Poincaré sphere controlled by the electro-optical modulator before optimization; the solid line represents the movement trajectory after optimization. Parallel to The trajectories in the equatorial plane all have the same ellipticity). Therefore, the present invention can achieve polarization with uniform ellipticity at different azimuth angles and promote research on elliptical polarization-induced nanograting formation.

Figure 7 is a birefringence microscopy image of nanogratings processed using different ellipticities. It can be seen from Figure 7 that the birefringence retardation (brightness) of nanogratings processed by elliptical polarization at multiple azimuthal angles under different ellipticity parameters All are relatively uniform and stable.

It can be seen from the above embodiments that compared with the prior art, the advantages of the present invention are as follows:

1. This invention modulates Poincaré meridian polarized light through electro-optical modulation, absorbs the phase difference error caused by the mirror, avoids the use of high-cost mirror custom coatings and other complex compensation mechanisms, and effectively solves the problem of femtosecond laser in optical storage. The problem of polarization degradation during reflection transmission in the processing system enables high-fidelity storage of data;

2. Compared with traditional polarization modulation technology, this invention can output elliptical polarization with consistent ellipticity and any azimuth angle for polarization-related processing;

3. By combining high-speed electro-optical modulation technology, the present invention 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.

The above descriptions are only preferred embodiments of the present invention and are not intended to limit the present invention. For those skilled in the art, the present invention may have various modifications and changes. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present invention shall be included in the protection scope of the present invention.

Claims (10)

1. An apparatus for generating linearly polarized light of different azimuth angles, comprising: a laser, a half-wave plate, an electro-optic modulator, a reflection system, and a quarter-wave plate;

the laser is used for generating laser rays;

the half wave plate is used for adjusting the laser light into linearly polarized light with a polarization direction and a horizontal plane forming an included angle of 45 degrees;

the voltage of the electro-optical modulator scans in a preset range, and the electro-optical modulator is used for adjusting linearly polarized light output by the half wave plate to enable the polarization state of emergent light of the electro-optical modulator to fall on one meridian of the poincare sphere all the time, so that poincare linearly polarized light is output;

the reflection system is used for reflecting the Poincare linearly polarized light and making the reflected light incident to the quarter wave plate;

the quarter wave plate is used for adjusting the reflected light to enable the polarization state of the emergent light to fall on the equator of the poincare sphere all the time, and therefore linearly polarized light with different azimuth angles is output.

2. The apparatus for generating linearly polarized light of different azimuth angles according to claim 1, further comprising: a first polarization state measurement instrument;

the first polarization state measuring instrument is used for measuring the polarization state of emergent light of the electro-optical modulator;

the electro-optical modulator is specifically configured to rotate a roll angle of the electro-optical modulator according to the polarization state measured by the first polarization state measuring instrument until the polarization state of the emergent light of the electro-optical modulator is always falling on one meridian of the poincare sphere.

3. The apparatus for generating linearly polarized light of different azimuth angles according to claim 1, further comprising: a second polarization state measuring instrument;

the second polarization state measuring instrument is used for measuring the polarization state of the emergent light of the quarter wave plate;

the quarter wave plate is specifically configured to rotate the wave plate according to the polarization state measured by the second polarization state measuring instrument until the polarization state of the emergent light of the quarter wave plate is always falling on the equator of the poincare sphere.

4. The apparatus for generating linearly polarized light of different azimuth angles according to claim 1, wherein said electro-optical modulator is further configured to adjust the azimuth angle of the linearly polarized light outputted from said quarter wave plate.

5. The apparatus for generating linearly polarized light of different azimuth angles according to claim 1, wherein said half wave plate is further used for adjusting ellipticity of outgoing light of said quarter wave plate.

6. The device for generating linearly polarized light of different azimuth angles according to claim 1, wherein the polarization state always falls on one meridian of poincare sphere means that stokes vectors S1 and S2 are always proportional and the sum of squares is all polarization states of unit 1; the polarization state always falling on the equator of the poincare sphere means that the stokes vector S3 is always zero, and the sum of squares of the stokes vectors S1 and S2 is all polarization states of unit 1; wherein stokes vectors S1 and S2 together represent the azimuth angle of the polarization state; stokes vector S3 represents the ellipticity of the polarization state, and stokes vectors S1, S2, S3 together determine the position of the polarization state on the poincare sphere as x, y, z three coordinates.

7. The apparatus for generating linearly polarized light of different azimuth angles according to claim 1, wherein the preset range is more than 0 and less than or equal to half-wave voltage.

8. The apparatus for generating linearly polarized light of different azimuth angles according to claim 1, further comprising: a beam expander;

the beam expander is used for expanding the laser beam generated by the laser, then the expanded laser beam is incident to the half wave plate, and the range of the beam expansion multiple of the beam expander is more than or equal to 1 and less than or equal to 3.

9. A laser processing method of an optical memory cell, characterized in that the optical memory cell is laser processed by using the linearly polarized light outputted from the device for generating linearly polarized light of different azimuth angles according to any one of claims 1 to 8.

10. A laser processing method of a polarization device controlling unit, characterized in that the polarization device controlling unit is laser processed by using the light outputted from the apparatus for generating linear polarized light of different azimuth angles according to any one of claims 1 to 8.