A device for controlling orthogonal polarized light, an interferometer and a grating displacement measurement system

Abstract

The embodiment of the application discloses a kind of orthogonal polarized light control device, interferometer and grating displacement measurement system.Therein, by setting double-frequency laser and first Wollaston prism, wherein double-frequency laser emits first light beam and second light beam, the first light beam includes first linearly polarized light, the second light beam includes second linearly polarized light, the polarization direction of the first linearly polarized light is perpendicular to the second linearly polarized light;First Wollaston prism is used to emit the first linearly polarized light at first preset angle, and the second linearly polarized light is emitted at second preset angle, can realize two linearly polarized light of complete orthogonal.This embodiment of the application solves the problem that the existing laser is difficult to meet the requirement of the measurement system on the polarization of linearly polarized light, and can realize the incident light with high polarization linearity and orthogonality, to ensure that the polarization linearity of two light beams meets the measurement requirements.

Description

Technical Field

[0001] The present invention relates to the field of laser precision measurement technology, and in particular to an orthogonal polarization light control device, an interferometer, and a grating displacement measurement system. Background Technology

[0002] In interferometer and grating displacement measurement systems based on optical heterodyne detection methods, two incident laser beams with completely orthogonal polarization directions and a fixed frequency difference are often required. Depending on the measurement scheme, it is usually necessary to control the propagation directionality and orthogonality of the polarization states of the two beams. Incompletely orthogonal polarization incident beams will cause leakage interference from subsequent polarization beam splitters, leading to nonlinear errors in the system and a decrease in displacement measurement performance.

[0003] However, existing lasers cannot emit two highly orthogonal polarized beams, resulting in poor orthogonality between the two beams emitted by the illumination device. Furthermore, existing illumination devices cannot adjust the angle and relative position of the two emitted beams, making it difficult to meet the measurement system's requirement for polarization orthogonality. Summary of the Invention

[0004] This invention provides an orthogonal polarization light control device, an interferometer, and a grating displacement measurement system to control the propagation directionality and orthogonality of the polarization states of two beams of light, avoiding light leakage interference from subsequent polarization beam splitting elements caused by incomplete orthogonality, which leads to nonlinear errors in the system and a decrease in displacement measurement performance.

[0005] In a first aspect, embodiments of the present invention provide an orthogonal polarization light modulation device, comprising:

[0006] A dual-frequency laser is used to emit a first beam and a second beam, the first beam including a first linearly polarized light and the second beam including a second linearly polarized light, wherein the polarization directions of the first linearly polarized light and the second linearly polarized light are perpendicular.

[0007] A first Wollaston prism is used to emit the first linearly polarized light at a first preset angle and to emit the second linearly polarized light at a second preset angle.

[0008] Optionally, the first Wollaston prism includes a first birefringent right-angle prism and a second birefringent right-angle prism orthogonal to the ordinary optical axis. The inclined surfaces of the first birefringent right-angle prism and the second birefringent right-angle prism are attached to each other and are centrally symmetrical about the center point of the inclined surfaces. The first beam and the second beam are incident through the first birefringent right-angle prism and exit through the second birefringent right-angle prism.

[0009] The ordinary ray optical axis of the first birefringent right-angle prism is consistent with the polarization direction of the first linearly polarized light, and the ordinary ray optical axis of the second birefringent right-angle prism is consistent with the polarization direction of the second linearly polarized light.

[0010] Optionally, it further includes: a first polarization-maintaining fiber and a second polarization-maintaining fiber, wherein the first beam and the second beam are transmitted through the first polarization-maintaining fiber and the second polarization-maintaining fiber, respectively;

[0011] A first collimating lens and a second collimating lens, the focal points of the first collimating lens and the second collimating lens are respectively located at the output ports of the first polarization-maintaining fiber and the second polarization-maintaining fiber; the first collimating lens and the second collimating lens are respectively used to collimate the first beam and the second beam and to perpendicularly incident on the first Wollaston prism;

[0012] A first linear polarizer and a second linear polarizer are respectively located between the first collimating lens and the second collimating lens and the first Wollaston prism. The transmission axis of the first linear polarizer is consistent with the polarization direction of the first linearly polarized light, and the transmission axis of the second linearly polarized light is consistent with the polarization direction of the second linearly polarized light.

[0013] Optionally, it also includes a second Wollaston prism, which is located on the light-emitting side of the first Wollaston prism;

[0014] The second Wollaston prism includes a third birefringent right-angle prism and a fourth birefringent right-angle prism orthogonal to the ordinary light optical axis. The inclined surfaces of the third birefringent right-angle prism and the fourth birefringent right-angle prism are attached to each other and are centrally symmetrical about the center point of the inclined surfaces. The first linearly polarized light and the second linearly polarized light are incident through the third birefringent right-angle prism and exited through the fourth birefringent right-angle prism.

[0015] The ordinary ray optical axis of the third birefringent right-angle prism is consistent with the polarization direction of the second linearly polarized light, and the ordinary ray optical axis of the fourth birefringent right-angle prism is consistent with the polarization direction of the first linearly polarized light.

[0016] Optionally, the first Wollaston prism and the second Wollaston prism have the same thickness, and the third birefringent right-angle prism and the fourth birefringent right-angle prism have the same wedge angle as the first birefringent right-angle prism and the second birefringent right-angle prism.

[0017] Optionally, the first Wollaston prism and the second Wollaston prism satisfy the following relationship: d≈|D-2*L*tan(α)|;

[0018] Wherein, the distance between the first linearly polarized light and the second linearly polarized light is d, the thickness of the first Wollaston prism and the second Wollaston prism is D, the relative position offset of the first Wollaston prism and the second Wollaston prism is L, and the angle between the first preset angle and the second preset angle is 2α.

[0019] Optionally, the first Wollaston prism and the second Wollaston prism have different thicknesses, and the third birefringent right-angle prism and the fourth birefringent right-angle prism have different wedge angles than the first birefringent right-angle prism and the second birefringent right-angle prism.

[0020] Optionally, the first beam further includes a third linearly polarized light, the third linearly polarized light having the same polarization direction as the second linearly polarized light; the second beam further includes a fourth linearly polarized light, the fourth linearly polarized light having the same polarization direction as the first linearly polarized light; the third linearly polarized light is emitted at a fifth preset angle, and the fourth linearly polarized light is emitted at a sixth preset angle;

[0021] The control device further includes a first light-shielding plate and a second light-shielding plate, wherein the first light-shielding plate is located on the optical path of the third linearly polarized light and the second light-shielding plate is located on the optical path of the fourth linearly polarized light.

[0022] Optionally, it further includes a first wedge and a second wedge, the first wedge and the second wedge being located on the optical path between the first beam and the second beam incident on the first Wollaston prism, respectively;

[0023] The hypotenuses of the first wedge and the second wedge are located on the side opposite to the first Wollaston prism, and the first wedge and the second wedge are axially symmetric about the line perpendicular to the light incident surface of the first Wollaston prism.

[0024] Optionally, it also includes a coupling lens and an output optical fiber, wherein the first linearly polarized light and the second linearly polarized light are focused by the coupling lens onto the input port of the output optical fiber.

[0025] In a second aspect, embodiments of the present invention also provide an interferometer, including an orthogonal polarization light modulation device as described in any one of the first aspects.

[0026] Thirdly, embodiments of the present invention also provide a grating displacement measurement system, including an orthogonal polarization light modulation device as described in any one of the first aspects, and a displacement measurement sensor, wherein the displacement measurement sensor receives a first linearly polarized light and a second linearly polarized light output by the orthogonal polarization light modulation device.

[0027] In this embodiment, a dual-frequency laser and a first Wollaston prism are used. The dual-frequency laser emits a first beam and a second beam. The first beam includes first linearly polarized light, and the second beam includes second linearly polarized light. The polarization directions of the first and second linearly polarized light are perpendicular. The first Wollaston prism is used to emit the first linearly polarized light at a first preset angle and the second linearly polarized light at a second preset angle, thus achieving two completely orthogonal linearly polarized beams. This embodiment solves the problem that existing lasers cannot meet the measurement system's requirement for orthogonal polarization of linearly polarized light, enabling the achievement of incident light with high polarization linearity and orthogonality, ensuring that the polarization linearity of the two beams meets the measurement requirements. Attached Figure Description

[0028] Figure 1 This is a schematic diagram of the structure of an orthogonal polarization light modulation device provided in an embodiment of the present invention;

[0029] Figure 2 This is a schematic diagram illustrating the working principle of the first Wollaston prism provided in an embodiment of the present invention;

[0030] Figure 3 This is a schematic diagram of another orthogonal polarization light modulation device provided in an embodiment of the present invention;

[0031] Figure 4 This is a schematic diagram of the structure of another orthogonal polarization light modulation device provided in an embodiment of the present invention;

[0032] Figure 5 This is a schematic diagram of another orthogonal polarization light modulation device provided in an embodiment of the present invention;

[0033] Figure 6 This is a schematic diagram of the structure of another orthogonal polarization light modulation device provided in an embodiment of the present invention;

[0034] Figure 7 This is a schematic diagram illustrating the working principle of the first Wollaston prism with added wedge plates provided in an embodiment of the present invention;

[0035] Figure 8 This is a schematic diagram of the light output structure of another orthogonal polarization light control device provided in an embodiment of the present invention. Detailed Implementation

[0036] The present invention will now be described in further detail with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative of the invention and not intended to limit it. Furthermore, it should be noted that, for ease of description, the accompanying drawings show only the parts relevant to the present invention, and not all of the structures.

[0037] Figure 1This is a schematic diagram of an orthogonal polarization light modulation device provided in an embodiment of the present invention. (Refer to...) Figure 1 The orthogonal polarization light control device includes: a dual-frequency laser 10 for emitting a first beam and a second beam, the first beam including a first linearly polarized light and the second beam including a second linearly polarized light, the polarization directions of the first linearly polarized light and the second linearly polarized light being perpendicular; and a first Wollaston prism 21 for emitting the first linearly polarized light at a first preset angle and emitting the second linearly polarized light at a second preset angle.

[0038] The dual-frequency laser 10 can be selected as a laser responsible for generating two laser beams with a fixed frequency difference, namely a first beam and a second beam, with beam frequencies of f1 and f2, respectively. The 632.9nm wavelength band is commonly used, and it can be a dual-frequency laser source such as visible light or near-infrared light. In this embodiment, the frequency difference between the first beam and the second beam needs to be much smaller than the optical frequency to ensure that polarization modulation is not affected. In other embodiments, a laser with an adjustable frequency difference can also be used, and the first beam and the second beam can be adjusted by the user; this is not a limitation. Generally, the two beams emitted by the dual-frequency laser 10 are linearly polarized light with orthogonal polarization directions. However, due to the linearity problem of the emitted light from the dual-frequency laser, the first beam and the second beam not only contain linearly polarized light with orthogonal polarization directions (i.e., the first beam includes first linearly polarized light and the second beam includes second linearly polarized light), but may also contain linearly polarized light with non-orthogonal polarization directions or stray light and other unpolarized light.

[0039] In this embodiment, a first Wollaston prism 21 is set in the optical path of the first beam and the second beam emitted from the dual-frequency laser 10. This allows for selective emission of linearly polarized light from the first and second beams, ensuring that the first linearly polarized light with a specific polarization direction in the first beam exits at a first preset angle, and the second linearly polarized light with a specific polarization direction in the second beam exits at a second preset angle. It should be noted that the emission angles of the first and second linearly polarized lights are related to the refractive index, thickness, and other parameters of the Wollaston prism. Based on known Wollaston prism parameters or experimental data, the emission positions and angles of the two linearly polarized lights can be clearly determined. It is understood that, based on the scheme of this embodiment, these two beams of perfectly orthogonal linearly polarized light emitted in specific directions can be applied to systems such as interferometers and grating displacement measurements based on optical heterodyne detection methods, especially in measurement scenarios with a measurement range of 1 nm or less, to ensure the accuracy of the measurement results.

[0040] In this embodiment, a dual-frequency laser and a first Wollaston prism are used. The dual-frequency laser emits a first beam and a second beam. The first beam includes first linearly polarized light, and the second beam includes second linearly polarized light. The polarization directions of the first and second linearly polarized light are perpendicular. The first Wollaston prism is used to emit the first linearly polarized light at a first preset angle and the second linearly polarized light at a second preset angle, thus achieving two completely orthogonal linearly polarized beams. This embodiment of the invention solves the problem that existing lasers cannot meet the measurement system's requirement for orthogonal polarization of linearly polarized light, enabling the achievement of incident light with high polarization linearity and orthogonality, ensuring that the polarization linearity of the two beams meets the measurement requirements.

[0041] Further reference Figure 1 The orthogonal polarization light control device further includes: a first polarization-maintaining fiber 31 and a second polarization-maintaining fiber 32, through which the first beam and the second beam are transmitted respectively; a first collimating lens 41 and a second collimating lens 42, with the focal points of the first collimating lens 41 and the second collimating lens 42 located at the output ports of the first polarization-maintaining fiber 31 and the second polarization-maintaining fiber 32 respectively; the first collimating lens 41 and the second collimating lens 42 are used to collimate the first beam and the second beam and perpendicularly incident on the first Wollaston prism 21 respectively; a first linear polarizer 51 and a second linear polarizer 52, located between the first collimating lens 41 and the second collimating lens 42 and the first Wollaston prism 21 respectively, with the transmission axis of the first linear polarizer 51 aligned with the polarization direction of the first linearly polarized light, and the transmission axis of the second linearly polarized light 52 aligned with the polarization direction of the second linearly polarized light.

[0042] Among them, the polarization-maintaining fiber transmits linearly polarized light, and the use of polarization-maintaining fiber can ensure that the linear polarization direction remains unchanged. The collimating lens is used to ensure that the two polarized beams are perpendicularly incident on the first Wollaston prism 21, while the function of the first linear polarizer 51 and the second linear polarizer 52 is to filter out the first linearly polarized light and the second linearly polarized light in the first beam and the second beam before the first Wollaston prism 21, thereby reducing other polarized light in the first beam and the second beam.

[0043] Figure 2 This is a schematic diagram illustrating the working principle of the first Wollaston prism provided in an embodiment of the present invention. (Refer to...) Figure 2Specifically, the first Wollaston prism 21 includes a first birefringent right-angle prism 201 and a second birefringent right-angle prism 202 orthogonal to the ordinary ray optical axis. The inclined surfaces of the first birefringent right-angle prism 201 and the second birefringent right-angle prism 202 are attached to each other and are centrally symmetrical about the center point of the inclined surfaces. The first beam and the second beam are incident through the first birefringent right-angle prism 201 and exit through the second birefringent right-angle prism 202. The ordinary ray (o-ray) optical axis of the first birefringent right-angle prism 201 is consistent with the polarization direction of the first linearly polarized light, and the ordinary ray (o-ray) optical axis of the second birefringent right-angle prism 202 is consistent with the polarization direction of the second linearly polarized light.

[0044] like Figure 2As shown, after the first and second beams are incident on the first Wollaston prism 21, the two linearly polarized beams can be separated by the refraction of the mutually perpendicular polarized beams by the first Wollaston prism 21, causing the first and second linearly polarized beams to exit at approximately symmetrical angles. Specifically, the first linearly polarized beam (represented by black dots in the figure, indicating a polarization direction perpendicular to the paper) is the o-ray, and the second linearly polarized beam (represented by double arrows in the figure, indicating a polarization direction parallel to the paper) is the e-ray. When they are incident perpendicularly on the surface of the first birefringent right-angle prism 201, the first and second linearly polarized beams still propagate along their original directions, but at different speeds Vo and Ve, respectively. When the first and second linearly polarized beams are incident on the second birefringent right-angle prism 202, since the ordinary ray axis of the second birefringent right-angle prism 202 is perpendicular to the ordinary ray axis of the first birefringent right-angle prism 201, the o-ray in the first birefringent right-angle prism 201 becomes the e-ray in relation to the second birefringent right-angle prism 202, and the e-ray becomes the o-ray. Therefore, the o-ray (i.e., the first linearly polarized light) originally in the first birefringent right-angle prism 201 will be refracted at the interface of the two right-angle prisms with a relative refractive index ne / no, while the e-ray (i.e., the second linearly polarized light) originally in the first birefringent right-angle prism 201 will be refracted with a relative refractive index no / ne. Taking the two right-angle prisms as negative crystals (no>ne) as an example, the e-ray (i.e., the first linearly polarized light) in the second birefringent right-angle prism 202 propagates away from the interface normal, while the o-ray (i.e., the second linearly polarized light) in the second birefringent right-angle prism 202 propagates closer to the interface normal. Ultimately, the first and second linearly polarized lights are separated and emitted at approximately symmetrical angles, with an angle α to the normal of the emission interface, the difference being that they emit from opposite sides of the normal of the emission interface. It should be noted that the figure only shows the propagation paths of the first linearly polarized light in the first beam and the second linearly polarized light in the second beam. It can be understood that when other polarized light in the first beam is incident on the first Wollaston prism 21, it will exit in a different direction from the first linearly polarized light based on the principle of birefringence. Similarly, when other polarized light in the second beam is incident on the first Wollaston prism 21, it will also exit in a different direction from the second linearly polarized light. Therefore, by using the known exit paths of the first and second linearly polarized light, two beams of linearly polarized light with completely perpendicular polarization directions can be obtained.

[0045] Furthermore, considering that the first and second beams may also contain other polarized light, a light-shielding plate can be provided in this embodiment of the invention to block the light and prevent its influence. Specifically, refer to... Figure 1The first beam further includes a third linearly polarized light, the polarization direction of which is the same as that of the second linearly polarized light; the second beam further includes a fourth linearly polarized light, the polarization direction of which is the same as that of the first linearly polarized light; the third linearly polarized light is emitted at a fifth preset angle, and the fourth linearly polarized light is emitted at a sixth preset angle; the control device further includes a first light-shielding plate 61 and a second light-shielding plate 62, the first light-shielding plate 61 being located on the optical path of the third linearly polarized light, and the second light-shielding plate 62 being located on the optical path of the fourth linearly polarized light.

[0046] In order to ensure that the orthogonally polarized light emitted by the orthogonal polarization light control device in the embodiments of the present invention meets the application requirements in different scenarios, in an optional embodiment of the present invention, the two linearly polarized light emitted from the first Wollaston prism can also be controlled. Figure 3 This is a schematic diagram of another orthogonal polarization light modulation device provided in an embodiment of the present invention, for reference. Figure 3 Based on the above embodiments, a second Wollaston prism 22 may also be provided, located on the light-emitting side of the first Wollaston prism 21. The second Wollaston prism 22 includes a third birefringent right-angle prism 203 and a fourth birefringent right-angle prism 204 orthogonal to the ordinary ray optical axis. The inclined surfaces of the third birefringent right-angle prism 203 and the fourth birefringent right-angle prism 204 are attached to each other and are centrally symmetrical about the center point of the inclined surfaces. The first linearly polarized light and the second linearly polarized light are incident through the third birefringent right-angle prism 203 and exited through the fourth birefringent right-angle prism 204. The ordinary ray optical axis of the third birefringent right-angle prism 203 is consistent with the polarization direction of the second linearly polarized light, and the ordinary ray optical axis of the fourth birefringent right-angle prism 204 is consistent with the polarization direction of the first linearly polarized light.

[0047] Furthermore, the first Wollaston prism 21 and the second Wollaston prism 22 may have the same thickness, and the third birefringent right-angle prism 203 and the fourth birefringent right-angle prism 204 may have the same wedge angle as the first birefringent right-angle prism 201 and the second birefringent right-angle prism 202.

[0048] The second Wollaston prism 22 functions by utilizing the special refraction effect on the first and second linearly polarized light to adjust their exit angles and spacing. Based on the same working principle as the first Wollaston prism 21, and since the ordinary ray optical axis of the third birefringent right-angle prism 203 is parallel to that of the second birefringent right-angle prism 202, and the ordinary ray optical axis of the fourth birefringent right-angle prism 204 is parallel to that of the first birefringent right-angle prism 201, and the wedge angles of the two Wollaston prisms are the same, the first linearly polarized light, acting as the e-ray of the third birefringent right-angle prism 203 and the o-ray of the fourth birefringent right-angle prism 204, will refract at the interface with relative angles. Similarly, the second linearly polarized light, acting as the o-ray of the third birefringent right-angle prism 203 and the e-ray of the fourth birefringent right-angle prism 204, will be refracted at the interface with a relative refractive index ne / no. The o-ray in the fourth birefringent right-angle prism 204, i.e., the first linearly polarized light, propagates closer to the interface normal, while the e-ray in the fourth birefringent right-angle prism 204, i.e., the second linearly polarized light, propagates further away from the interface normal. The degree of approach or distance is the same as the degree of interface deflection in the first Wollaston prism 21. In other words, based on the principle of optical path reversibility, the first and second linearly polarized lights emitted from the first Wollaston prism 21, after entering the second Wollaston prism 22 respectively, will exit with the opposite refraction effect to that of the first Wollaston prism 21, ultimately causing both the first and second linearly polarized lights to exit perpendicularly to the exit surface. Therefore, by setting the second Wollaston prism 22, two completely orthogonal linearly polarized beams can be obtained, which can be applied to measurement systems that require parallel incident light.

[0049] As described above, two Wollaston prisms can achieve parallel emission of the first and second linearly polarized light. However, in some more specialized applications, it is required that polarized light with perpendicular polarization directions be combined and incident. Based on this, embodiments of the present invention also provide a design scheme for adjusting the distance between the two parallel-emitting linearly polarized light beams, i.e., a scheme for achieving position separation. Specifically, the first and second Wollaston prisms can be configured to satisfy the following relationship: d≈|D-2*L*tan(α)|; where the distance between the first and second linearly polarized light is d, the thickness of both the first and second Wollaston prisms is D, the relative position offset of the first and second Wollaston prisms is L, and the angle between the first and second preset angles is 2α.

[0050] The Wollaston separation angle 2α can be calculated from the refractive indices no and ne of the birefringent material and the wedge angle θ of the Wollaston prism, and its expression is: 2α≈2arcsin[(no-ne)tan(θ)]. Therefore, the separation angle of the two parallel beams after passing through two Wollaston prisms can be calculated from the optical path difference between the wedge angles of the two Wollaston prisms: d≈|D-2*L*tan(α)|. Figure 4 This is a schematic diagram of another orthogonal polarization light modulation device provided in an embodiment of the present invention, for reference. Figure 4 Given that the angle between the first and second preset angles is 2α, i.e., the separation angle 2α of the Wollaston prism, the distance d between the emitted first and second linearly polarized beams can be made zero by reasonably setting the thickness D of the two Wollaston prisms, the initial distance d between the first and second linearly polarized beams, and the relative position offset L between the first and second Wollaston prisms. This achieves the beam combining of two orthogonal polarized beams. It should be noted that the formula satisfied by the Wollaston prism uses an approximate equality formula, which can be understood as the formula being considered approximately equal when there is a certain numerical difference between the two sides. For example, a numerical difference within the range of 5% or even 10% can be considered approximately equal, i.e., satisfying the approximate equality formula. Of course, those skilled in the art can limit the range of the numerical difference according to actual conditions, for example, limiting it to a numerical difference range of 1% or 2% to be considered approximately equal and satisfying the approximate equality formula. This embodiment of the invention does not impose excessive limitations.

[0051] Furthermore, to avoid crosstalk between the first and second linearly polarized light caused by polarization ellipticization due to optical reflecting surfaces or beam splitting surfaces in the coaxial optical path, in practical high-precision displacement measurement schemes, embodiments of the present invention can also be configured to achieve separate incidence of the first and second linearly polarized light. Besides the aforementioned position separation scheme, an angle separation scheme can also be implemented. When using an angle separation scheme, the separation angle needs to be controlled. The separation angle is mainly determined by the wedge angles of the two Wollaston prisms. As the aforementioned principle states, when the wedge angles are the same, the outgoing light is parallel to each other. If there is a difference in the wedge angles, the separation angle is equal to the difference in the individual separation angles of the two wedge plates. Based on this, the present invention also provides an optional embodiment. Figure 5 This is a schematic diagram of another orthogonal polarization light modulation device provided in an embodiment of the present invention, for reference. Figure 5 Specifically, the thickness of the first Wollaston prism 21 and the second Wollaston prism 22 may be different, and the wedge angles of the third birefringent right-angle prism 203 and the fourth birefringent right-angle prism 204 may be different from those of the first birefringent right-angle prism 201 and the second birefringent right-angle prism 202.

[0052] Similarly, in the embodiment described above with a second Wollaston prism, a light-shielding plate can also be used to block stray light. Specifically, the first beam further includes a third linearly polarized light, the polarization direction of which is the same as that of the second linearly polarized light; the second beam further includes a fourth linearly polarized light, the polarization direction of which is the same as that of the first linearly polarized light; the third linearly polarized light exits at a fifth preset angle, and the fourth linearly polarized light exits at a sixth preset angle; the optional control device further includes a first light-shielding plate 61 and a second light-shielding plate 62, the first light-shielding plate 61 being located in the optical path of the third linearly polarized light, and the second light-shielding plate 62 being located in the optical path of the fourth linearly polarized light.

[0053] Furthermore, in order to meet the requirements of small space size and avoid crosstalk between useless stray light and orthogonally polarized light, different propagation angles can be set for stray light and orthogonally polarized light. Figure 6 This is a schematic diagram of another orthogonal polarization light modulation device provided in an embodiment of the present invention, for reference. Figure 6 The dimming device also includes a first wedge plate 71 and a second wedge plate 72, which are located on the optical path between the first beam and the second beam incident on the first Wollaston prism 21, respectively. The hypotenuses of the first wedge plate 71 and the second wedge plate 72 are located on the side away from the first Wollaston prism 21, and the first wedge plate 71 and the second wedge plate 72 are axially symmetrical about the straight line perpendicular to the light incident surface of the first Wollaston prism 21.

[0054] Figure 7 This is a schematic diagram illustrating the working principle of the first Wollaston prism with added wedge plates provided in an embodiment of the present invention. (Refer to...) Figure 7 Two unpolarized wedges with the same angle are added between the first polarizer 51, the second polarizer 52, and the first Wollaston prism 21. The first and second linearly polarized light will form opposite initial incident angles after passing through the two wedges. These two opposite initial incident angles will be split into four linearly polarized beams after passing through the first Wollaston prism 21, with different exit angles θ1, θ2, θ3, and θ4. The beams with angles θ2 and θ3 have orthogonal polarization states and symmetrical reflection angles. θ1 and θ4 have different angles from θ2 and θ3. After passing through the second Wollaston prism 22, the angles of the two orthogonal polarized beams are aligned. The stray light has different propagation angles and can be filtered out by coupling lenses or setting light-blocking plates to eliminate stray light.

[0055] In addition to providing the aforementioned light-blocking sheet for filtering stray light, this embodiment of the invention also provides an optional solution for filtering stray light. Figure 8 This is a schematic diagram of the light output structure of another orthogonal polarization light modulation device provided in an embodiment of the present invention, for reference. Figure 8In the control device of this embodiment, a coupling lens 80 and an output optical fiber 90 are also provided. The first linearly polarized light and the second linearly polarized light are focused by the coupling lens 80 onto the input port of the output optical fiber 90.

[0056] Therefore, after passing through the coupling lens 80, orthogonally polarized light and stray light with different propagation angles converge at different points. The orthogonally polarized light converges at the port of the output fiber 90. When the separation angle Δθ, the fiber core diameter d′, and the focal length f of the coupling lens are set, the stray light will not be able to couple into the interior of the output fiber 90 and will not affect the orthogonally polarized light signal.

[0057] Based on the same inventive concept, embodiments of the present invention also provide an interferometer and a grating displacement measurement system, both of which include any of the orthogonal polarization light manipulation devices provided in the embodiments of the present invention. The grating displacement measurement system may further include a displacement measurement sensor, which receives a first linearly polarized light and a second linearly polarized light output from the orthogonal polarization light manipulation device. The interferometer and grating displacement measurement system provided in the embodiments of the present invention can perform measurements based on an optical heterodyne detection method. The two incident laser beams with completely orthogonal polarization directions required can be provided by the orthogonal polarization light manipulation device provided in the embodiments of the present invention. Since the above-mentioned interferometer and grating displacement measurement system include the orthogonal polarization light manipulation device provided in the embodiments of the present invention, they possess the same or similar technical effects as the orthogonal polarization manipulation device, which will not be elaborated further here.

[0058] Note that the above description is merely a preferred embodiment of the present invention and the technical principles employed. Those skilled in the art will understand that the present invention is not limited to the specific embodiments described herein, and various obvious changes, readjustments, combinations, and substitutions can be made without departing from the scope of protection of the present invention. Therefore, although the present invention has been described in detail through the above embodiments, the present invention is not limited to the above embodiments, and may include many other equivalent embodiments without departing from the concept of the present invention, the scope of which is determined by the scope of the appended claims.

Claims

1. A device for controlling orthogonal polarization of light, characterized in that, include: A dual-frequency laser is used to emit a first beam and a second beam, wherein the first beam and the second beam have a fixed or adjustable frequency difference, the frequency difference being much smaller than the optical frequency; the first beam includes first linearly polarized light, and the second beam includes second linearly polarized light, wherein the polarization directions of the first linearly polarized light and the second linearly polarized light are perpendicular. The first Wollaston prism is used to emit the first linearly polarized light at a first preset angle and to emit the second linearly polarized light at a second preset angle. The first Wollaston prism includes a first birefringent right-angle prism and a second birefringent right-angle prism orthogonal to the ordinary optical axis. The inclined surfaces of the first birefringent right-angle prism and the second birefringent right-angle prism are attached to each other and are centrally symmetrical about the center point of the inclined surfaces. The first beam and the second beam are incident through the first birefringent right-angle prism and exit through the second birefringent right-angle prism. The ordinary ray optical axis of the first birefringent right-angle prism is consistent with the polarization direction of the first linearly polarized light, and the ordinary ray optical axis of the second birefringent right-angle prism is consistent with the polarization direction of the second linearly polarized light.

2. The orthogonal polarization light modulation device according to claim 1, characterized in that, Also includes: The first polarization-maintaining fiber and the second polarization-maintaining fiber are respectively transmitted through the first polarization-maintaining fiber and the second polarization-maintaining fiber. A first collimating lens and a second collimating lens, the focal points of the first collimating lens and the second collimating lens are respectively located at the output ports of the first polarization-maintaining fiber and the second polarization-maintaining fiber; the first collimating lens and the second collimating lens are respectively used to collimate the first beam and the second beam and to perpendicularly incident on the first Wollaston prism; A first linear polarizer and a second linear polarizer are respectively located between the first collimating lens and the second collimating lens and the first Wollaston prism. The transmission axis of the first linear polarizer is consistent with the polarization direction of the first linearly polarized light, and the transmission axis of the second linearly polarized light is consistent with the polarization direction of the second linearly polarized light.

3. The orthogonal polarization light modulation device according to claim 1, characterized in that, It also includes a second Wollaston prism, which is located on the light-emitting side of the first Wollaston prism; The second Wollaston prism includes a third birefringent right-angle prism and a fourth birefringent right-angle prism orthogonal to the ordinary light optical axis. The inclined surfaces of the third birefringent right-angle prism and the fourth birefringent right-angle prism are attached to each other and are centrally symmetrical about the center point of the inclined surfaces. The first linearly polarized light and the second linearly polarized light are incident through the third birefringent right-angle prism and exited through the fourth birefringent right-angle prism. The ordinary ray optical axis of the third birefringent right-angle prism is consistent with the polarization direction of the second linearly polarized light, and the ordinary ray optical axis of the fourth birefringent right-angle prism is consistent with the polarization direction of the first linearly polarized light.

4. The orthogonal polarization light modulation device according to claim 3, characterized in that, The first and second Wollaston prisms have the same thickness, and the third and fourth birefringent right-angle prisms have the same wedge angle as the first and second birefringent right-angle prisms.

5. The orthogonal polarization light modulation device according to claim 4, characterized in that, The first Wollaston prism and the second Wollaston prism satisfy the following relationship: d≈|D-2*L*tan(α)|; Wherein, the distance between the first linearly polarized light and the second linearly polarized light is d, the thickness of the first Wollaston prism and the second Wollaston prism is D, the relative position offset of the first Wollaston prism and the second Wollaston prism is L, and the angle between the first preset angle and the second preset angle is 2α.

6. The orthogonal polarization light modulation device according to claim 3, characterized in that, The first Wollaston prism and the second Wollaston prism have different thicknesses, and the third birefringent right-angle prism and the fourth birefringent right-angle prism have different wedge angles than the first birefringent right-angle prism and the second birefringent right-angle prism.

7. The orthogonal polarization light modulation device according to claim 1 or 3, characterized in that, The first beam further includes a third linearly polarized light, the third linearly polarized light having the same polarization direction as the second linearly polarized light; the second beam further includes a fourth linearly polarized light, the fourth linearly polarized light having the same polarization direction as the first linearly polarized light; the third linearly polarized light is emitted at a fifth preset angle, and the fourth linearly polarized light is emitted at a sixth preset angle; The control device further includes a first light-shielding plate and a second light-shielding plate, wherein the first light-shielding plate is located on the optical path of the third linearly polarized light and the second light-shielding plate is located on the optical path of the fourth linearly polarized light.

8. The orthogonal polarization light modulation device according to claim 1, characterized in that, It also includes a first wedge and a second wedge, the first wedge and the second wedge being located on the optical path between the first beam and the second beam incident on the first Wollaston prism, respectively; The hypotenuses of the first wedge and the second wedge are located on the side opposite to the first Wollaston prism, and the first wedge and the second wedge are axially symmetric about the line perpendicular to the light incident surface of the first Wollaston prism.

9. The orthogonal polarization light modulation device according to claim 1, characterized in that, It also includes a coupling lens and an output optical fiber, wherein the first linearly polarized light and the second linearly polarized light are focused by the coupling lens onto the input port of the output optical fiber.

10. An interferometer, characterized in that, Includes the orthogonal polarization light modulation device as described in any one of claims 1-9.

11. A grating displacement measurement system, characterized in that, The device includes the orthogonal polarization light control device as described in any one of claims 1-9, and further includes a displacement measurement sensor, wherein the displacement measurement sensor receives the first linearly polarized light and the second linearly polarized light output by the orthogonal polarization light control device.

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