CN110646956B - Shearing continuously adjustable double refraction beam splitter - Google Patents
Shearing continuously adjustable double refraction beam splitter Download PDFInfo
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- CN110646956B CN110646956B CN201910929354.7A CN201910929354A CN110646956B CN 110646956 B CN110646956 B CN 110646956B CN 201910929354 A CN201910929354 A CN 201910929354A CN 110646956 B CN110646956 B CN 110646956B
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- G—PHYSICS
- G02—OPTICS
- G02F—OPTICAL DEVICES OR ARRANGEMENTS FOR THE CONTROL OF LIGHT BY MODIFICATION OF THE OPTICAL PROPERTIES OF THE MEDIA OF THE ELEMENTS INVOLVED THEREIN; NON-LINEAR OPTICS; FREQUENCY-CHANGING OF LIGHT; OPTICAL LOGIC ELEMENTS; OPTICAL ANALOGUE/DIGITAL CONVERTERS
- G02F1/00—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics
- G02F1/01—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics for the control of the intensity, phase, polarisation or colour
- G02F1/03—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics for the control of the intensity, phase, polarisation or colour based on ceramics or electro-optical crystals, e.g. exhibiting Pockels effect or Kerr effect
- G02F1/0305—Constructional arrangements
- G02F1/0311—Structural association of optical elements, e.g. lenses, polarizers, phase plates, with the crystal
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- G—PHYSICS
- G02—OPTICS
- G02F—OPTICAL DEVICES OR ARRANGEMENTS FOR THE CONTROL OF LIGHT BY MODIFICATION OF THE OPTICAL PROPERTIES OF THE MEDIA OF THE ELEMENTS INVOLVED THEREIN; NON-LINEAR OPTICS; FREQUENCY-CHANGING OF LIGHT; OPTICAL LOGIC ELEMENTS; OPTICAL ANALOGUE/DIGITAL CONVERTERS
- G02F1/00—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics
- G02F1/01—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics for the control of the intensity, phase, polarisation or colour
- G02F1/0136—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics for the control of the intensity, phase, polarisation or colour for the control of polarisation, e.g. state of polarisation [SOP] control, polarisation scrambling, TE-TM mode conversion or separation
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- G—PHYSICS
- G02—OPTICS
- G02F—OPTICAL DEVICES OR ARRANGEMENTS FOR THE CONTROL OF LIGHT BY MODIFICATION OF THE OPTICAL PROPERTIES OF THE MEDIA OF THE ELEMENTS INVOLVED THEREIN; NON-LINEAR OPTICS; FREQUENCY-CHANGING OF LIGHT; OPTICAL LOGIC ELEMENTS; OPTICAL ANALOGUE/DIGITAL CONVERTERS
- G02F1/00—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics
- G02F1/01—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics for the control of the intensity, phase, polarisation or colour
- G02F1/03—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics for the control of the intensity, phase, polarisation or colour based on ceramics or electro-optical crystals, e.g. exhibiting Pockels effect or Kerr effect
- G02F1/0338—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics for the control of the intensity, phase, polarisation or colour based on ceramics or electro-optical crystals, e.g. exhibiting Pockels effect or Kerr effect structurally associated with a photoconductive layer or having photo-refractive properties
Abstract
The invention provides a birefringent beam splitter with continuously adjustable shear, comprising: the combined prism is used for splitting incident light; the combined prism comprises a right-angle prism P1 and a right-angle prism P2 with the same wedge angle, the right-angle prism P1 and the right-angle prism P2 are combined with each other through inclined surfaces, and incident light enters from the right-angle surface of the right-angle prism P1 and is output from the right-angle surface of the right-angle prism P2; the controller adjusts the shearing angle of the linearly polarized light emitted by the combined prism by adjusting the angle of the incident light entering the right-angle prism P1 or adjusting the voltage applied by the combined prism, so that the technical problem that the shearing angle is not easy to change once the existing birefringent beam splitter structure is determined is effectively solved.
Description
Technical Field
The invention relates to the technical field of crystal optical devices, in particular to a beam splitter.
Background
The birefringent crystal polarization beam splitter can divide incident light into two linearly polarized light beams with mutually perpendicular polarization directions, and has the advantages of wide working band, high damage threshold and the like. The birefringent crystal beam splitter can be classified into an angular shearing type and a lateral shearing type according to the propagation direction of light after beam splitting, wherein typical examples of the lateral shearing type beam splitter are Savart plates and the like, and typical examples of the angular shearing type beam splitter are Wollaston prisms, nomarski prisms and the like. For the transverse shearing beam splitter, a method of adjusting the transverse shearing amount by rotating a Savart polarizer has been proposed [ Jian Xiaohua, zhang Chunmin, sun Yao, wu Lei, 2007 optical journal, 27643].
Compared with a transverse shearing type beam splitter, the two linearly polarized lights split by the angle shearing type beam splitter still have a certain transverse shearing amount after being converged by the lens group, so that the angle shearing type beam splitter has very wide application in the optical imaging fields such as microscopy, remote sensing and the like. The structure of existing angle shear beam splitters, once determined, does not allow the shear angle to be easily changed. In order to meet different requirements, different beam splitters need to be replaced, so that the cost is increased, the stability of the system is reduced, and inconvenience is brought to application.
Disclosure of Invention
The invention aims to provide a birefringent beam splitter with continuously adjustable shearing, which effectively solves the technical problem that once the structure of the existing birefringent beam splitter is determined, the shearing angle is not easy to change.
The technical scheme provided by the invention is as follows:
a shear-continuously adjustable birefringent beam splitter comprising:
the combined prism is used for splitting incident light; the combined prism comprises a right-angle prism P1 and a right-angle prism P2 with the same wedge angle, the right-angle prism P1 and the right-angle prism P2 are combined with each other through inclined surfaces, and incident light enters from the right-angle surface of the right-angle prism P1 and is output from the right-angle surface of the right-angle prism P2;
and the controller is used for adjusting the shearing angle of the linearly polarized light emitted by the combined prism by adjusting the angle of the incident light entering the right-angle prism P1 or adjusting the magnitude of the applied voltage in the combined prism.
Further, the polarization direction of the incident light is not perpendicular to or parallel to the main sections of the right angle prism P1 and the right angle prism P2.
Further, the controller includes an angle rotation unit and a control unit that are connected to each other, the combined prism is fixed on the angle rotation unit, and the control unit controls the angle rotation unit to rotate, so as to control the angle of the incident light entering the right angle prism P1, and further adjust the shearing angle of the emergent linear polarized light in the right angle prism P2.
Further, the right-angle prism P1 is made of a birefringent crystal, the right-angle prism P2 is made of an isotropic crystal, and the refractive index of the right-angle prism P2 is matched with the ordinary refractive index of the right-angle prism P1;
in the constructed xyz right angle system meeting the right hand rule, right angle surfaces of the right angle prism P1 and the right angle prism P2, which are opposite to the inclined surfaces, are positioned in an xy plane, the inclined surfaces are parallel to a y axis, the main optical axis of crystals of the right angle prism P1 is along the direction of the z axis, the right angle surfaces of the combined prism are vertical, and incident light of the vertical incidence right angle prism P1 propagates along the z axis.
In the technical scheme, the controller is used for controlling the incident angle of incident light, so that the shearing angle of two linearly polarized light beams can be flexibly adjusted, and the shearing angle of the beam splitter can be continuously adjusted from 0 within a wide range. In addition, the adjustable precision of the shearing angle of the beam splitter can be improved by designing the wedge angle of the prism and the refractive index difference of ordinary rays and extraordinary rays of the birefringent crystal (right-angle prism P1).
Further, the right angle prism P1 and the right angle prism P2 are made of the same birefringent crystal;
in the constructed xyz right-angle system meeting the right-hand rule, right-angle surfaces, opposite to the inclined surfaces, of the right-angle prism P1 and the right-angle prism P2 are positioned in an xy plane, the inclined surfaces are parallel to a y axis, and a crystal main optical axis of the right-angle prism P1 is vertical to a right-angle surface of the combined prism along the direction of the z axis; the principal optical axis of the crystal of the right angle prism P2 is perpendicular to the inclined plane thereof, and the incident light of the perpendicular incidence right angle prism P1 propagates along the z-axis.
In the technical scheme, the controller is used for controlling the incident angle of incident light, so that the shearing angle of two linearly polarized light beams is flexibly adjusted, and the shearing angle of the beam splitter is approximately linear along with the change curve of the incident angle. In addition, the adjustable precision of the shearing angle of the beam splitter can be improved by designing the prism wedge angle and the refractive index difference of the ordinary rays and the extraordinary rays of the birefringent crystal (the right-angle prism P1 and the right-angle prism P2). The minimum shear angle is adjusted even by designing the prism wedge angle or selecting the refractive index difference of the extraordinary rays of the birefringent crystal.
Further, the controller comprises a control unit and a power supply unit which are connected with each other, and the control unit controls the power supply unit to adjust the voltage applied to the combined prism, so that the shearing angle of the emergent linear polarized light in the right-angle prism P2 is adjusted.
Further, the right angle prism P1 and the right angle prism P2 are made of the same electro-optic crystal;
in the constructed xyz right angle system meeting the right hand rule, right angle surfaces, opposite to the inclined surfaces, of the right angle prism P1 and the right angle prism P2 are positioned in an xy plane, the inclined surfaces are parallel to a y axis, the right angle prism P1 and the right angle prism P2 are uniaxial birefringent crystals when no voltage is applied, a crystal main optical axis of the right angle prism P1 is along an x axis direction, and a crystal main optical axis of the right angle prism P2 is along a y axis direction.
In the technical scheme, the refractive indexes of the right-angle prism P1 and the right-angle prism P2 (the secondary photoelectric effect of the electro-optic crystal, the specific refractive index is related to the applied voltage and the length of the electro-optic crystal in the direction of the applied voltage) are changed by controlling the voltage applied to the combined prism through the controller, so that the shearing angle of two linearly polarized light beams is flexibly adjusted.
Further, a voltage is applied to the right angle prism P1 along the x-axis and a voltage is applied to the right angle prism P2 along the y-axis.
Further, the right angle prism P1 and the right angle prism P2 are made of the same electro-optic crystal;
in the constructed xyz right angle system meeting the right hand rule, right angle surfaces, opposite to the inclined surfaces, of the right angle prism P1 and the right angle prism P2 are positioned in an xy plane, the inclined surfaces are parallel to a y axis, and the right angle prism P1 and the right angle prism P2 are isotropic crystals when no voltage is applied, and the uniaxial birefringent crystals are formed after the voltage is applied.
In the technical scheme, the voltage applied to the combined prism is controlled by the controller, so that the shearing angle of two linearly polarized light beams can be flexibly adjusted from 0. In addition, the adjustable precision of the shearing angle of the beam splitter can be improved by designing the wedge angle of the prism, the refractive index of the electro-optic crystal when no voltage is applied, the length of the electro-optic crystal in the direction of the applied voltage, the electro-optic coefficient of the crystal and the like.
Further, a voltage is applied to the right angle prism P1 along the x-axis and a voltage is applied to the right angle prism P2 along the y-axis.
In the birefringent beam splitter with continuously adjustable shearing, incident light enters the beam splitter from the right-angle prism P1, and is split into two orthogonal linearly polarized light beams with a certain shearing angle after passing through the right-angle prism P1 and the right-angle prism P2. The structure is simple and compact, the continuous adjustable shearing angle of the beam splitter can be realized, the technical problems that once the structure of the beam splitter is determined, the shearing angle is determined and cannot be changed in the prior art are solved, and meanwhile, the technical problems that two linearly polarized lights with vertical polarization directions generated by the traditional transverse shearing beam splitter are parallel, are focused by a lens group and are converged at the same point and cannot form shearing quantity are solved. The beam splitter can meet the requirement of multiple tasks, effectively reduce the cost and improve the stability and reliability of the system. In addition, after the two linearly polarized lights split by the beam splitter are converged by the lens group, a certain transverse shearing amount still exists, and the beam splitter has very wide application in the optical imaging fields such as microscopy, remote sensing and the like.
Drawings
The above features, technical features, advantages and implementation thereof will be further described in the following detailed description of the preferred embodiments with reference to the accompanying drawings in a clearly understandable manner.
FIG. 1 is a schematic diagram of a birefringent beam splitter according to the present invention;
FIG. 2 is a schematic view showing a structure of a combined prism according to an embodiment of the present invention;
FIG. 3 is a graph showing the relationship between the shearing angle Deltat and the incident angle t in the first embodiment of the present invention;
FIG. 4 is a diagram of a beam splitter test system of the present invention;
FIG. 5 is a schematic view of a combined prism according to a second embodiment of the present invention;
FIG. 6 is a graph showing the relationship between the second shearing angle Deltat and the incident angle t according to the embodiment of the present invention;
FIG. 7 is a schematic view of a combined prism in a third embodiment of the present invention;
FIG. 8 is a graph showing the relationship between the three shearing angles Deltat and the incident angle t according to the embodiment of the present invention;
fig. 9 is a graph showing the relationship between the fourth shearing angle Δt and the incident angle t according to the embodiment of the present invention.
Reference numerals illustrate:
1-right angle prism P1, 2-right angle prism P2, 3-controller.
DETAILED DESCRIPTION OF EMBODIMENT (S) OF INVENTION
In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, specific embodiments of the present invention will be described below with reference to the accompanying drawings. It is evident that the drawings in the following description are only some embodiments of the present invention, from which other drawings and other embodiments can be obtained by those skilled in the art without inventive effort.
FIG. 1 is a schematic view of a continuously shear-adjustable birefringent beam splitter according to the present invention, including: the combined prism is used for splitting incident light; the combined prism comprises a right-angle prism P1 (reference numeral 1 in the figure) and a right-angle prism P2 (reference numeral 2 in the figure), wherein the wedge angles of the right-angle prism P1 and the right-angle prism P2 are the same, the right-angle prism P1 and the right-angle prism P2 are combined with each other through inclined surfaces, and incident light enters from the right-angle surface of the right-angle prism P1 and is output from the right-angle surface of the right-angle prism P2; the controller C (reference numeral 3 in the drawing) adjusts the shearing angle of the linearly polarized light exiting the combination prism by adjusting the angle at which the incident light enters the right angle prism P1 or by adjusting the magnitude of the voltage applied to the combination prism. Note that in this beam splitter, the polarization direction of incident light is not simultaneously perpendicular or simultaneously parallel to the main sections of the right angle prism P1 and the right angle prism P2.
For the combined prism, an xyz right angle system which meets the right hand rule at will is constructed, so that right angle surfaces of the right angle prism P1 and the right angle prism P2, which are opposite to the inclined surface, are both positioned in the xy plane, the inclined surface is parallel to the y axis, incident light enters from the right angle surface of the right angle prism P1, is output from the right angle surface of the right angle prism P2, and light propagates along the z axis.
In the constructed xyz right angle system meeting the right hand rule, right angle surfaces of the right angle prism P1 and the right angle prism P2, which are opposite to the inclined surfaces, are positioned in an xy plane, the inclined surfaces are parallel to a y axis, the main optical axis of crystals of the right angle prism P1 is along the direction of the z axis, the right angle surfaces of the combined prism are vertical, and incident light of the vertical incidence right angle prism P1 propagates along the z axis.
Embodiment one:
referring to fig. 2, the beam splitter includes two right angle prisms (right angle prism P1 and right angle prism P2) with the same wedge angle and a controller C. For the combined prism, an xyz rectangular system which satisfies the right-hand rule arbitrarily is constructed so that the right-angle faces of the rectangular prism P1 (reference numeral 1 in the drawing) and the rectangular prism P2 (reference numeral 2 in the drawing) which are opposite to the inclined faces are both located in the xy plane. The inclined surfaces of the right angle prism P1 and the right angle prism P2 are parallel to the y-axis. Light from incident light normally incident on the beam splitter propagates along the z-axis. In the beam splitter, the right angle prism P1 is a prism made of quartz crystal, and the crystal optical axis is along the z-axis direction; the right angle prism P2 is a prism made of isotropic optical glass, and its refractive index matches the ordinary refractive index of the right angle prism P1.
The controller C (reference numeral 3 in the drawing) includes an angle rotation unit and a control unit connected to each other, the combined prism is fixed on the angle rotation unit, and the control unit controls the angle rotation unit to rotate, so as to control the angle of the incident light entering the right angle prism P1, and further adjust the shearing angle of the outgoing linearly polarized light in the right angle prism P2. Specifically, the combined prism is fixed on an angle rotation unit (rotatable platform) by a lens frame, and the rotation direction is in an xz plane. In operation, the angle rotating unit is controlled by a motor, communication is carried out in a mode of converting USB into CAN bus, and the CPU chip automatically controls and outputs pulse signals to drive the angle rotating unit to rotate, so that the angle of the light incident combination prism is controlled. The rotation speed, single-step precision, etc. of the angular rotation unit are not particularly limited, and may be adjusted according to actual conditions.
In the working process, after entering the beam splitter from the right angle surface of the right angle prism P1, the parallel incident light is changed into two linearly polarized lights with a certain included angle and mutually perpendicular vibration directions, and the two linearly polarized lights are output after passing through the right angle surface of the right angle prism P2 and are changed into linearly polarized lights with a certain shearing angle and mutually perpendicular vibration directions. In the process, the controller C flexibly adjusts the shearing angle of the two linearly polarized lights by controlling the angle of the light incident on the combined prism.
Let the thicknesses of the right angle prism P1 and the right angle prism P2 be d, and the wedge angle be a. The refractive index of the right-angle prism P1 to the ordinary light (o light) is n o Refractive index n for extraordinary ray (e ray) e . The refractive index of the right angle prism P2 is n. The beam splitting principle of the beam splitter is described by the following:
considering that a beam of parallel light enters a right angle surface of a right angle prism P1 in an xz plane at an angle t with a z axis, according to the theory of polarization optics and the propagation rule of light in a single-axis crystal, the beam of light enters the right angle prism P1 to generate double refraction, is divided into o light and e light in the propagation direction, enters a right angle prism P2 through an inclined plane, and is finally output by the right angle surface of the right angle prism P2, wherein the generated shearing angle is deltat, as shown in formula (1):
Δt＝|to-t e |(1)
wherein to is the o light output angle, as in formula (2); t is t e E is the light output angle, as in formula (3); n is n e ' is the actual refractive index of the right angle prism of e light in P1, as in formula (4):
from the above, the shearing angle Δt generated by the beam splitter is equal to the wedge angle a of the right angle prism P1 and the right angle prism P2, the angle t of the incident light, and the refractive index n of the right angle prism P1 o And n e And the refractive index n of the right angle prism P2, and is independent of the thicknesses d of the right angle prisms P1 and P2.
When the wedge angle a=25°, the refractive index no=n= 1.54689, and the refractive index ne= 1.55609, the shear angle varies with the incident angle of the incident light as shown in fig. 3, wherein the abscissa is the incident angle/degree; the ordinate is shear angle/rad.
A system diagram of the beam splitter is tested as shown in fig. 4. In the test, after light generated by the laser passes through the polarizer (corresponding to the polarizing plate in the figure), linearly polarized light is formed (the polarization direction of the linearly polarized light cannot be perpendicular to or parallel to the birefringent crystal main section at the same time). After passing through the beam splitter, the linearly polarized light is respectively detected by a rotary analyzer to obtain the coordinates of ordinary light and extraordinary light on a CCD (Charge Coupled Device, charge coupled device image sensor), and the shearing angle information of the two beams of light after beam splitting is further analyzed: Δt=l/d, where L is the distance of the ordinary and extraordinary rays on the CCD and d is the distance of the beam splitter from the CCD.
In the beam splitter, the two output linearly polarized lights can still form a certain shearing amount in the transverse direction after being focused by the lens group, and the shearing amount can be continuously adjustable in a wider range from 0.
In other embodiments, the right angle prism P1 may be replaced by other birefringent prisms, such as LN crystals, KDP crystals, some optical glass and polymer materials with birefringent properties, liquid crystals, etc.; the right angle prism P2 may be replaced by other isotropic crystals, such as various optical glasses such as K6 glass and ZK6 glass, organic materials, etc. The controller may be composed of a rotary platform and a motor, controlled by a CPU chip, or may be otherwise, for example, manually adjusted.
Embodiment two:
referring to fig. 5, the beam splitter includes two birefringent right angle prisms (right angle prism P1 and right angle prism P2) made of LN crystals and having the same wedge angle, and a controller C. For the combined prism, an xyz right angle system which meets the right hand rule at will is constructed, so that right angle surfaces of a right angle prism P1 (reference numeral 1 in the drawing) and a right angle prism P2 (reference numeral 2 in the drawing) which are opposite to the inclined surfaces are positioned in an xy plane, the inclined surfaces of the right angle prism P1 and the right angle prism P2 are parallel to a y axis, and light when incident light perpendicularly enters the beam splitter propagates along the z axis. The crystal optical axis of the right-angle prism P1 is along the z-axis direction, and the crystal optical axis of the right-angle prism P2 is perpendicular to the inclined plane thereof.
The controller C (reference numeral 3 in the drawing) includes an angle rotation unit and a control unit connected to each other, the combined prism is fixed on the angle rotation unit, and the control unit controls the angle rotation unit to rotate, so as to control the angle of the incident light entering the right angle prism P1, and further adjust the shearing angle of the outgoing linearly polarized light in the right angle prism P2. Specifically, the combined prism is fixed on an angle rotation unit (rotatable platform) by a lens frame, and the rotation direction is in an xz plane. In operation, the angle rotating unit is controlled by a motor, communication is carried out in a mode of converting USB into CAN bus, and the CPU chip automatically controls and outputs pulse signals to drive the angle rotating unit to rotate, so that the angle of the light incident combination prism is controlled. The rotation speed, single-step precision, etc. of the angular rotation unit are not particularly limited, and may be adjusted according to actual conditions.
In the working process, after entering the beam splitter from the right angle surface of the right angle prism P1, the parallel incident light is changed into two linearly polarized lights with a certain included angle and mutually perpendicular vibration directions, and the two linearly polarized lights are output after passing through the right angle surface of the right angle prism P2 and are changed into linearly polarized lights with a certain shearing angle and mutually perpendicular vibration directions. In the process, the controller C flexibly adjusts the shearing angle of the two linearly polarized lights by controlling the angle of the light incident on the combined prism.
Let the thicknesses of the right angle prism P1 and the right angle prism P2 be d, and the wedge angle be a. The refractive index of the right angle prism P1 and the right angle prism P2 to ordinary light (o light) is n o Refractive index n for extraordinary ray (e ray) e . The beam splitting principle of the beam splitter is described by the following:
considering that a beam of parallel light enters a right-angle surface of a right-angle prism P1 in an xz plane at an angle t with a z axis, according to the theory of polarization optics and the propagation rule of light in a single-axis crystal, the beam of light enters the right-angle prism P1 and is subjected to double refraction, is divided into o light and e light in the propagation direction, enters a right-angle prism P2 through an inclined plane, and is finally output by the right-angle surface of the right-angle prism P2, and the generated shearing angle is deltat, as shown in formula (5):
Δt＝|t o -t e | (5)
wherein t is o An o light output angle as in formula (6); t is t e E is the light output angle, as in formula (7); n is n e ' is the actual refractive index of e light in the right angle prism P1, as in formula (8); n is n e "is the actual refractive index of e light in the right angle prism P2, as in formula (9):
t o ＝t (6)
t e ＝arcsin{sin[arcsin(n e ”·sin(arcsin(sint/n e ')+a)/n e ')-a]/n e ”} (7)
as can be seen from the above, the shearing angle Δt generated by the beam splitter is related to the wedge angle a of the right angle prism P1 and the right angle prism P2, the angle t of the incident light, and the refractive indices no and ne of the right angle prism P1, and is independent of the thicknesses d of the right angle prism P1 and the right angle prism P2.
When wedge angle a=2.5°, refractive index n e Refractive index n= 2.22752 o When= 2.39223, the shear angle varies with the incident angle of the incident light as shown in fig. 6, wherein the abscissa is the incident angle ti/degree; the ordinate is shear angle/rad. The system for testing the beam splitter is the same as that of the first embodiment, and will not be described here.
In the beam splitter, after the two output linearly polarized lights are focused by the lens group, a certain shearing amount can be formed in the transverse direction, and the shearing amount is approximately linear along with the change curve of the incident angle.
In other embodiments, the right angle prism P1 and the right angle prism P2 may be replaced by other birefringent prisms, such as quartz crystal, LN crystal, KDP crystal, some optical glass and polymer materials with birefringent properties, liquid crystal, etc. The controller may be composed of a rotary platform and a motor, controlled by a CPU chip, or may be otherwise, for example, manually adjusted.
Embodiment III:
referring to fig. 7, the beam splitter includes two electro-optical birefringent rectangular prisms (rectangular prism P1 and rectangular prism P2) made of LN crystals and having the same wedge angle, and a controller C. For the combined prism, an xyz right angle system which meets the right hand rule at will is constructed, so that right angle surfaces of a right angle prism P1 (reference numeral 1 in the drawing) and a right angle prism P2 (reference numeral 2 in the drawing) which are opposite to the inclined surfaces are positioned in an xy plane, the inclined surfaces of the right angle prism P1 and the right angle prism P2 are parallel to a y axis, and the light propagation direction when incident light perpendicularly enters the beam splitter is along the z axis. The main optical axis of the right angle prism P1 is along the x axis, the main optical axis of the right angle prism P2 is along the y axis, and the controller applies electricity to the right angle prism P1 and the right angle prism P2 along the x axis and the y axis respectively.
The controller C (reference numeral 3 in the drawing) includes a control unit and a power supply unit connected to each other, and the control unit controls the power supply unit to adjust the magnitude of the voltage applied to the combination prism, thereby adjusting the shearing angle of the outgoing linear polarized light in the right angle prism P2. Specifically, before working, silver electrodes are coated on a voltage input surface and a voltage output surface of an LN crystal in a film coating process mode, and the two ends of the electrodes are respectively connected with the positive electrode and the negative electrode of an adjustable voltage stabilizing power supply (a power supply unit). In operation, the control unit controls the output voltage of the adjustable stabilized power supply through USB communication.
Let the thicknesses of the right angle prism P1 and the right angle prism P2 be d. Refractive index of ordinary ray when no voltage is applied is n o0 Refractive index of extraordinary ray n e0 The length of the crystal at the applied voltage is l, the wedge angle is a, and the relative electro-optic coefficient of the electro-optic crystal is r 13 And r 33 . The beam splitting principle of the beam splitter is described by the following:
considering that one beam of parallel light vertically enters the beam splitter along the z-axis direction from the right-angle surface of the right-angle prism P1, the beam splitter is changed into two beams of linearly polarized light with mutually perpendicular vibration directions but not separated in space, and the two beams of linearly polarized light are emitted after passing through the right-angle prism P2 and become linearly polarized light with mutually perpendicular vibration directions with a certain shearing angle. The controller C generates a final beam splitter shear angle Δt by varying the voltage U as in equation (10):
Δt＝|t e -t o | (10)
wherein t is e E is the light output angle, as in formula (11); to is the o light output angle, as in formula (12); n is n e The refractive index of e light of P1 or P2 after voltage application is shown as formula (13); n is n o For the o-refractive index of P1 or P2 after voltage application, as in formula (14):
from the above, the shearing angle of the beam splitter is equal to the wedge angle a of the right angle prism P1 and the right angle prism P2, and the refractive index n when no voltage is applied o0 And n e0 Length l, correlation electro-optic coefficient r of crystal 13 And r 33 And the voltage U applied by the controller, is independent of the thickness d of the right angle prism P1 and the right angle prism P2.
When the wedge angle a=5°, the length l=5 mm, the electro-optic coefficient r 13 ＝-8.6×10 -12 m/V, electro-optic coefficient r 33 ＝30.8×10 -12 m/V, refractive index n o0 Refractive index n= 2.39222 e0 When= 2.22752, the change of the shearing angle with the applied voltage is shown in fig. 8, wherein the abscissa is the voltage U/V and the ordinate is the shearing angle/rad. The system for testing the beam splitter is the same as that of the first embodiment, and will not be described here.
In the beam splitter, after the output two linearly polarized lights are focused by the lens group, a certain shearing amount can be formed in the transverse direction, and the shearing amount is linear along with the change curve of the applied voltage.
In other examples, the right angle prism P1 and the right angle prism P2 may be replaced by other crystals, such as LT crystals, liquid crystals, and the like. The electrode material may be silver or may be replaced by other materials such as gold, copper, some non-metallic electrode materials, etc. The control unit may also control the output voltage of the adjustable regulated power supply in other ways, such as RS232, etc.
Embodiment four:
referring to fig. 7, the beam splitter includes two electro-optical birefringent rectangular prisms (rectangular prism P1 and rectangular prism P2) made of LN crystals and having the same wedge angle, and a controller C. For the combined prism, an xyz right angle system which meets the right hand rule at will is constructed, so that right angle surfaces of a right angle prism P1 (reference numeral 1 in the drawing) and a right angle prism P2 (reference numeral 2 in the drawing) which are opposite to the inclined surfaces are positioned in an xy plane, the inclined surfaces of the right angle prism P1 and the right angle prism P2 are parallel to a y axis, and the light propagation direction when incident light perpendicularly enters the beam splitter is along the z axis. The right angle prism P1 and the right angle prism P2 crystals are isotropic crystals under the condition of no power; after voltages are applied to the crystals of the right-angle prism P1 and the right-angle prism P2, the refractive index of the LN crystal changes, the birefringent effect is achieved, and the optical axis of the crystal is consistent with the direction of the applied voltages. Specifically, the crystal [001] direction of the right angle prism P1 is along the x-axis direction, and the applied voltage direction is along the crystal [001] direction; the crystal [001] direction of the rectangular prism P2 is along the y-axis direction, and the direction of the applied voltage is the crystal [001] direction.
The controller C (reference numeral 3 in the drawing) includes a control unit and a power supply unit connected to each other, and the control unit controls the power supply unit to adjust the magnitude of the voltage applied to the combination prism, thereby adjusting the shearing angle of the outgoing linear polarized light in the right angle prism P2. Specifically, before working, silver electrodes are coated on a voltage input surface and a voltage output surface of an LN crystal in a film coating process mode, and the two ends of the electrodes are respectively connected with the positive electrode and the negative electrode of an adjustable voltage stabilizing power supply (a power supply unit). In operation, the control unit controls the output voltage of the adjustable stabilized power supply through USB communication.
Assuming that the thicknesses of the right angle prism P1 and the right angle prism P2 are d, the refractive index when no voltage is applied is n o0 The length of the crystal at the applied voltage is l, the wedge angle is a, and the relative electro-optic coefficient of the electro-optic crystal is s 11 Sum s 12 . The beam splitting principle of the beam splitter is described by the following:
considering that one beam of parallel light vertically enters the beam splitter along the z-axis direction from the right-angle surface of the right-angle prism P1, the beam splitter is changed into two beams of linearly polarized light with mutually perpendicular vibration directions but not separated in space, and the two beams of linearly polarized light are emitted after passing through the right-angle prism P2 and are changed into linearly polarized light with mutually perpendicular vibration directions with a certain shearing angle. The controller C generates a final beam splitter shear angle Δt by varying the voltage U as in equation (15):
Δt＝|t e -t o | (15)
wherein t is e E is the light output angle, as in formula (16); t is t o An o light output angle as in formula (17); n is n e The refractive index of e light of P1 or P2 after voltage application is shown as formula (18); n is n o For the o-refractive index of P1 or P2 after voltage application, as in formula (19):
from the above, the shearing angle of the beam splitter is equal to the wedge angle a of the right angle prism P1 and the right angle prism P2, and the refractive index n when no voltage is applied o0 Length l, relative electro-optic coefficient s of the crystal 11 Sum s 12 And the voltage U applied by the controller, is independent of the thickness d of the right angle prism P1 and the right angle prism P2.
When the wedge angle a=25°, the length l=5 mm, the electro-optic coefficient s 11 ＝10 -14 m 2 /V 2 Electro-optic coefficient s 12 ＝-10 -15 m 2 /V 2 Refractive index n o0 When=2.2, the change of the shearing angle with the applied voltage is shown in fig. 9, where the abscissa is the voltage U/V and the ordinate is the shearing angle/rad. The system for testing the beam splitter is the same as that of the first embodiment, and will not be described here.
In the beam splitter, the two output linearly polarized lights are focused by the lens group, and a certain shearing amount can be formed in the transverse direction, and the shearing amount can be continuously adjustable in a wide range from 0.
In other embodiments, right angle prism P1 and right angle prism P2 may be replaced by other crystals, such as KT crystals. The electrode material may be silver or may be replaced by other materials such as gold, copper, some non-metallic electrode materials, etc. The control unit may also control the output voltage of the adjustable regulated power supply in other ways, such as RS232, etc.
It should be noted that the above embodiments can be freely combined as needed. The foregoing is merely illustrative of the preferred embodiments of this invention, and it will be appreciated by those skilled in the art that variations and modifications may be made without departing from the principles of the invention, and such variations and modifications are to be regarded as being within the scope of the invention.
Claims (9)
1. A shear-continuously adjustable birefringent beam splitter, comprising:
the combined prism is used for splitting incident light; the combined prism comprises a right-angle prism P1 and a right-angle prism P2 with the same wedge angle, the right-angle prism P1 and the right-angle prism P2 are combined with each other through inclined surfaces, and incident light enters from the right-angle surface of the right-angle prism P1 and is output from the right-angle surface of the right-angle prism P2;
the controller is used for adjusting the shearing angle of linearly polarized light emitted by the combined prism in a mode of adjusting the angle of incident light entering the right-angle prism P1 or adjusting the applied voltage in the combined prism;
the controller comprises an angle rotating unit and a control unit which are connected with each other, the combined prism is fixed on the angle rotating unit, the angle rotating unit is controlled to rotate through the control unit, so that the angle of incident light entering the right-angle prism P1 is controlled, and the shearing angle of emergent linear polarized light in the right-angle prism P2 is adjusted.
2. The birefringent beam splitter as claimed in claim 1 wherein the polarization direction of the incident light is not simultaneously perpendicular or simultaneously parallel to the principal cross-sections of the right angle prism P1 and the right angle prism P2.
3. The birefringent beam splitter as claimed in claim 1, wherein,
the right-angle prism P1 is made of birefringent crystals, the right-angle prism P2 is made of isotropic crystals, and the refractive index of the right-angle prism P2 is matched with the ordinary refractive index of the right-angle prism P1;
in the constructed xyz right angle system meeting the right hand rule, right angle surfaces of the right angle prism P1 and the right angle prism P2, which are opposite to the inclined surfaces, are positioned in an xy plane, the inclined surfaces are parallel to a y axis, the main optical axis of crystals of the right angle prism P1 is along the direction of the z axis, the right angle surfaces of the combined prism are vertical, and incident light of the vertical incidence right angle prism P1 propagates along the z axis.
4. The birefringent beam splitter as claimed in claim 1, wherein,
the right-angle prism P1 and the right-angle prism P2 are made of the same birefringent crystal;
in the constructed xyz right-angle system meeting the right-hand rule, right-angle surfaces, opposite to the inclined surfaces, of the right-angle prism P1 and the right-angle prism P2 are positioned in an xy plane, the inclined surfaces are parallel to a y axis, and a crystal main optical axis of the right-angle prism P1 is vertical to a right-angle surface of the combined prism along the direction of the z axis; the principal optical axis of the crystal of the right-angle prism P2 is perpendicular to the inclined plane thereof, and the incident light of the right-angle prism P1 propagates along the z-axis at the time of normal incidence.
5. The birefringent beam splitter as claimed in claim 1 or 2, wherein the controller comprises a control unit and a power supply unit connected to each other, the control unit controlling the power supply unit to adjust the magnitude of the voltage applied to the combining prism, thereby adjusting the shearing angle of the outgoing linearly polarized light in the right angle prism P2.
6. The birefringent beam splitter as claimed in claim 5, wherein,
the right-angle prism P1 and the right-angle prism P2 are made of the same electro-optic crystal;
in the constructed xyz right angle system meeting the right hand rule, right angle surfaces, opposite to the inclined surfaces, of the right angle prism P1 and the right angle prism P2 are positioned in an xy plane, the inclined surfaces are parallel to a y axis, the right angle prism P1 and the right angle prism P2 are uniaxial birefringent crystals when no voltage is applied, a crystal main optical axis of the right angle prism P1 is along an x axis direction, and a crystal main optical axis of the right angle prism P2 is along a y axis direction.
7. The birefringent beam splitter as claimed in claim 6 wherein a voltage is applied to the right angle prism P1 along the x-axis and a voltage is applied to the right angle prism P2 along the y-axis.
8. The birefringent beam splitter as claimed in claim 5, wherein,
the right-angle prism P1 and the right-angle prism P2 are made of the same electro-optic crystal;
in the constructed xyz right angle system meeting the right hand rule, right angle surfaces, opposite to the inclined surfaces, of the right angle prism P1 and the right angle prism P2 are positioned in an xy plane, the inclined surfaces are parallel to a y axis, and the right angle prism P1 and the right angle prism P2 are isotropic crystals when no voltage is applied, and the uniaxial birefringent crystals are formed after the voltage is applied.
9. The birefringent beam splitter as claimed in claim 8 wherein a voltage is applied to the right angle prism P1 along the x-axis and a voltage is applied to the right angle prism P2 along the y-axis.
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| JPH05323118A (en) * | 1992-05-20 | 1993-12-07 | Matsushita Electric Ind Co Ltd | Polarizing device and projection type display device using same |
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| CN2175425Y (en) * | 1993-10-21 | 1994-08-24 | 南开大学 | Adjustable angle of skew prism |
| JPH07128408A (en) * | 1993-11-04 | 1995-05-19 | Nec Corp | Eo probe |
| DE102008000438A1 (en) * | 2008-02-28 | 2009-09-10 | Seereal Technologies S.A. | Controllable deflection device |
| CN103592774A (en) * | 2013-10-17 | 2014-02-19 | 中国科学院上海光学精密机械研究所 | Wollaston prism for generating one beam of linearly polarized light |
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