CN110646956A - Shear continuously adjustable birefringent beam splitter - Google Patents

Shear continuously adjustable birefringent beam splitter Download PDF

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CN110646956A
CN110646956A CN201910929354.7A CN201910929354A CN110646956A CN 110646956 A CN110646956 A CN 110646956A CN 201910929354 A CN201910929354 A CN 201910929354A CN 110646956 A CN110646956 A CN 110646956A
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angle
prism
angle prism
rectangular
beam splitter
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CN110646956B (en
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王中阳
孔心怡
高琪
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Shanghai Advanced Research Institute of CAS
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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
    • 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
    • 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

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Abstract

The invention provides a birefringence beam splitter with continuously adjustable shearing, which comprises: the combined prism is used for splitting the 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 an inclined plane, and incident light enters from a right-angle surface of the right-angle prism P1 and is output from a 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 in the combined prism, and effectively solves the technical problem that the shearing angle is not easy to change once the structure of the conventional birefringent beam splitter is determined.

Description

Shear continuously adjustable birefringent beam splitter
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 beams of linearly polarized light with mutually vertical polarization directions, and has the advantages of wide working waveband, high damage threshold value and the like. The birefringent crystal beam splitter can be classified into an angle shearing type and a transverse shearing type according to the propagation direction of the split light, wherein the transverse shearing type beam splitter typically represents a Savart board or the like, and the angle shearing type beam splitter typically represents a Wollaston prism, a Nomarski prism or the like. For the transverse shearing beam splitter, a method of adjusting the transverse shearing amount by rotating the Savart polarizer has been proposed [ simple and small, zuohun, yao, wu epi, 2007 optical bulletin, 27643 ].
Compared with a transverse shearing type beam splitter, two linearly polarized light beams split by the angular shearing type beam splitter still have a certain transverse shearing amount after being converged by the lens group, so that the transverse shearing type beam splitter has very wide application in the optical imaging fields of microscopy, remote sensing and the like. Once the structure of the existing angle shearing type beam splitter is determined, the shearing angle is not easy to change. In order to meet different requirements, different beam splitters need to be replaced, so that the cost is increased, the system stability is reduced, and inconvenience is brought to application.
Disclosure of Invention
The invention aims to provide a birefringence beam splitter with continuously adjustable shearing, which effectively solves the technical problem that once the structure of the existing birefringence beam splitter is determined, the shearing angle is not easy to change.
The technical scheme provided by the invention is as follows:
a continuously shear tunable birefringent beam splitter, comprising:
the combined prism is used for splitting the incident light; the combined prism comprises a right-angle prism P1 and a right-angle prism P2 which have the same wedge angle, the right-angle prism P1 and the right-angle prism P2 are combined with each other through an inclined plane, and incident light enters from a right-angle surface of the right-angle prism P1 and is output from a right-angle surface of the right-angle prism P2;
and the controller adjusts the shearing angle of the linearly polarized light emitted by the combined prism in a mode of adjusting the angle of the incident light entering the right-angle prism P1 or adjusting the magnitude of the voltage applied in the combined prism.
Further, the polarization directions of the incident light are not simultaneously perpendicular or parallel to the main cross sections of the right-angle prism P1 and the right-angle prism P2.
Further, including interconnect's angle of rotation unit and the control unit in the controller, the composite prism is fixed in on the angle of rotation unit, through the control unit control the angle of rotation unit rotates to the angle that control incident light got into right angle prism P1, and then adjusts the shear angle of emergent linear polarization among the right angle prism P2.
Further, the right-angle prism P1 is made of birefringent crystal, the right-angle prism P2 is made of isotropic crystal, and the refractive index of the right-angle prism P2 is matched with the refractive index of ordinary light of the right-angle prism P1;
in the constructed xyz rectangular system satisfying the right-hand rule, the rectangular surface of the rectangular prism P1 and the rectangular prism P2 opposite to the inclined surface is located in the xy plane, the inclined surface is parallel to the y axis, and the crystal principal optical axis of the rectangular prism P1 is along the z axis direction, perpendicular to a rectangular surface of the combined prism, and the incident light of the vertically incident rectangular prism P1 propagates along the z axis.
In the technical scheme, the incident angle of incident light is controlled by the controller, so that the size of the shearing angle of the two linearly polarized light beams is flexibly adjusted, the shearing angle of the beam splitter can be continuously adjusted in a wide range from 0. 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 between the ordinary light and the extraordinary light of the birefringent crystal (the 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, a right-angle surface opposite to the inclined surface in the right-angle prism P1 and the right-angle prism P2 is positioned in an xy plane, the inclined surface is parallel to a y axis, and the main optical axis of the crystal of the right-angle prism P1 is vertical to a right-angle surface of the combined prism along the z axis direction; the principal optical axis of the crystal of the right angle prism P2 is perpendicular to its slope, and the incident light that is perpendicularly incident on the right angle prism P1 propagates along the z-axis.
In the technical scheme, the incident angle of incident light is controlled through the controller, so that the size of the shearing angle of two linearly polarized light beams is flexibly adjusted, and the change curve of the shearing angle of the beam splitter along with the incident angle is approximately linear. 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 between the ordinary light and the extraordinary light 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 between the ordinary and 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 outgoing linearly 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-optical crystal;
in the constructed xyz rectangular system satisfying the right-hand rule, the rectangular surface opposite to the inclined surface among the rectangular prism P1 and the rectangular prism P2 is located in the xy plane, the inclined surface is parallel to the y axis, and the rectangular prisms P1 and P2 are uniaxial birefringent crystals when no voltage is applied, the crystal principal axis of the rectangular prism P1 is along the x axis direction, and the crystal principal axis of the rectangular prism P2 is along the y axis direction.
In the technical scheme, the controller is used for controlling the voltage applied to the combined prism, and the refractive indexes of the right-angle prism P1 and the right-angle prism P2 (the secondary photoelectric effect of the electro-optical crystal, the specific refractive index is related to the applied voltage and the length of the electro-optical crystal in the voltage applying direction) are changed, so that the shearing angles of the two linearly polarized light beams are flexibly adjusted.
Further, a voltage is applied to the right-angled prism P1 along the x-axis and a voltage is applied to the right-angled prism P2 along the y-axis.
Further, the right-angle prism P1 and the right-angle prism P2 are made of the same electro-optical crystal;
in the constructed xyz rectangular system satisfying the right-hand rule, the rectangular surface opposite to the inclined surface among the rectangular prism P1 and the rectangular prism P2 is located in the xy plane, the inclined surface is parallel to the y axis, and the rectangular prism P1 and the rectangular prism P2 are isotropic crystals when no voltage is applied, and form uniaxial birefringent crystals after the voltage is applied.
In the technical scheme, the controller is used for controlling the voltage applied to the combined prism, so that the shearing angle of the 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-optical crystal when no voltage is applied, the length of the electro-optical crystal in the direction of the applied voltage, the electro-optical coefficient of the crystal and the like.
Further, a voltage is applied to the right-angled prism P1 along the x-axis and a voltage is applied to the right-angled prism P2 along the y-axis.
In the birefringence beam splitter with continuously adjustable shearing provided by the invention, incident light enters the beam splitter from the right-angle prism P1, and is split into two beams of orthogonal linearly polarized light 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 shearing angle of the beam splitter can be continuously adjusted, the technical problems that once the structure of the beam splitter is determined, the shearing angle is determined therewith and cannot be changed in the prior art are solved, and meanwhile the technical problems that two beams of linearly polarized light with vertical polarization directions generated by the existing transverse shearing type beam splitter are parallel, are converged at the same point after being focused by a lens group and cannot form shearing amount 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 two linearly polarized light beams 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 fields of optical imaging such as microscopy, remote sensing and the like.
Drawings
The foregoing features, technical features, advantages and implementations of which will be further described in the following detailed description of the preferred embodiments in a clearly understandable manner in conjunction with the accompanying drawings.
FIG. 1 is a schematic diagram of a birefringent beam splitter according to the present invention;
FIG. 2 is a schematic structural diagram of a combining prism according to an embodiment of the present invention;
FIG. 3 is a diagram illustrating the relationship between the shear angle Δ t and the incident angle t according to an embodiment of the present invention;
FIG. 4 is a diagram of a beam splitter testing system of the present invention;
FIG. 5 is a schematic structural diagram of a combining prism according to a second embodiment of the present invention;
FIG. 6 is a graph showing the relationship between the second shear angle Δ t and the incident angle t according to the embodiment of the present invention;
FIG. 7 is a schematic diagram of a combined prism according to a third embodiment of the present invention;
FIG. 8 is a schematic representation of the triple shear angle Δ t as a function of incident angle t in accordance with an embodiment of the present invention;
FIG. 9 is a graph showing the relationship between the four shear angles Δ t and the incident angle t according to the embodiment of the present invention.
The reference numbers 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 to be understood that the drawings in the following description are merely exemplary of the invention and that other drawings and embodiments may be devised by those skilled in the art without the use of inventive faculty.
Fig. 1 is a schematic structural diagram of a continuously adjustable shearing birefringent beam splitter according to the present invention, including: the combined prism is used for splitting the incident light; the combined prism comprises a right-angle prism P1 (shown as a reference numeral 1) and a right-angle prism P2 (shown as a reference numeral 2) with the same wedge angle, the right-angle prism P1 and the right-angle prism P2 are combined with each other through an inclined plane, and incident light enters from a right-angle surface of the right-angle prism P1 and is output from a right-angle surface of the right-angle prism P2; the controller C (reference numeral 3 in the figure) adjusts the shearing angle of the outgoing linearly polarized light of the combining prism by adjusting the angle at which the incident light enters the right-angle prism P1 or adjusting the magnitude of the applied voltage in the combining prism. It is to be noted that in this beam splitter, the polarization direction of the incident light is not simultaneously perpendicular or simultaneously parallel to the main cross sections of the right-angle prism P1 and the right-angle prism P2.
Aiming at the combined prism, an xyz right-angle system which meets the right-hand rule is constructed at will, so that right-angle surfaces opposite to inclined surfaces in the right-angle prism P1 and the right-angle prism P2 are both positioned in an xy plane, the inclined surfaces are parallel to a y axis, 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 light is transmitted along the z axis.
In the constructed xyz rectangular system satisfying the right-hand rule, the rectangular surface of the rectangular prism P1 and the rectangular prism P2 opposite to the inclined surface is located in the xy plane, the inclined surface is parallel to the y axis, and the crystal principal optical axis of the rectangular prism P1 is along the z axis direction, perpendicular to a rectangular surface of the combined prism, and the incident light of the vertically incident rectangular prism P1 propagates along the z axis.
The first embodiment is as follows:
referring to fig. 2, the beam splitter includes two right-angle prisms (a right-angle prism P1 and a right-angle prism P2) with the same wedge angle and a controller C. For this combined prism, an xyz rectangular system satisfying the right-hand rule is constructed such that the rectangular surfaces opposite to the inclined surfaces in the rectangular prism P1 (reference numeral 1 in the drawing) and the rectangular prism P2 (reference numeral 2 in the drawing) are both located in the xy plane. The slopes of the right angle prism P1 and the right angle prism P2 are parallel to the y-axis. Light that is incident upon the beam splitter at normal incidence propagates along the z-axis. In this 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 figure) includes an angle rotating unit and a control unit which are connected with each other, the combined prism is fixed on the angle rotating unit, and the control unit controls the angle rotating unit to rotate, so that the angle of the incident light entering the right-angle prism P1 is controlled, and the shearing angle of the outgoing linearly polarized light in the right-angle prism P2 is further adjusted. Specifically, the combined prism is fixed to an angle rotation unit (rotatable platform) by a mirror holder, and the rotation direction is in the xz plane. In the work, the angle rotation 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 rotation unit to rotate, so that the angle of the light incident to the combined prism is controlled. The rotation speed of the angular rotation unit, the single step precision and the like are not particularly limited and can be adjusted according to actual conditions.
In the working process, after parallel incident light enters the beam splitter from the right-angle surface of the right-angle prism P1, the parallel incident light is changed into two beams of linearly polarized light with a certain included angle and mutually vertical vibration directions, and the two beams of linearly polarized light are output after passing through the right-angle surface of the right-angle prism P2 and are changed into the linearly polarized light with a certain shear angle and mutually vertical vibration directions. In the process, the controller C flexibly adjusts the size of the shearing angle of the two linearly polarized light beams by controlling the angle of the light incident to the combined prism.
Assume that the thickness of the right angle prism P1 and the thickness of the right angle prism P2 are both d, and the wedge angle is a. The refractive index of the right-angle prism P1 to ordinary light (o light) is noRefractive index n for extraordinary rays (e-rays)e. The right angle prism P2 has a refractive index n. The beam splitting principle of the beam splitter is explained by the following:
considering that a beam of parallel light enters a right-angle surface of a right-angle prism P1 at an angle t with a z axis in an xz plane, according to the theory of polarization optics and the propagation rule of light in a uniaxial crystal, the beam of light is birefringent after entering a right-angle prism P1, is split into o light and e light in the propagation direction, enters a right-angle prism P2 through an inclined surface, and is finally output by the right-angle surface of the right-angle prism P2, and the generated shear angle is delta t, as shown in formula (1):
Δt＝|to-te|(1)
wherein to is an o light output angle, as shown in formula (2); t is teIs the e light output angle, as formula (3); n ise' is the actual refractive index of the right-angled prism of e-light in P1, as in formula (4):
Figure BDA0002217945970000061
Figure BDA0002217945970000062
from the above equation, the shear angle Δ t 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 index n of the right-angle prism P1oAnd neAnd the refractive index n of the right-angle prism P2 are independent of the thicknesses d of the right-angle prism P1 and the right-angle prism P2.
When the wedge angle a is 25 °, the refractive index no is 1.54689, and the refractive index ne is 1.55609, the shearing angle varies with the incident angle of the incident light as shown in fig. 3, where the abscissa is the incident angle/degree; the ordinate is the shear angle/rad.
A system diagram of a test splitter is shown in figure 4. In the test, the light generated by the laser passed through a polarizer (corresponding to the polarizer in the figure) to form linearly polarized light (the polarization direction of the linearly polarized light cannot be simultaneously perpendicular or simultaneously parallel to the principal cross section of the birefringent crystal). After linearly polarized light passes through the beam splitter, coordinates of ordinary light and extraordinary light on a CCD (charge coupled Device) are respectively detected through a rotary analyzer, and shearing angle information of the two beams of split light is further analyzed: and Δ t is L/d, wherein L is the distance between the ordinary light and the extraordinary light on the CCD, and d is the distance between the beam splitter and the CCD.
In the beam splitter, after two output linearly polarized light beams are focused by the lens group, a certain shearing amount can be formed in the transverse direction, and the shearing amount can be continuously adjusted in a wide range from 0.
In other embodiments, the right-angle prism P1 can be replaced by other birefringent prisms, such as LN crystals, KDP crystals, some optical glasses and polymer materials with birefringent properties, liquid crystals, etc.; the right-angle prism P2 can be replaced by other isotropic crystals, such as various optical glasses like K6 glass, ZK6 glass, organic materials, etc. The controller can be composed of a rotary platform and a motor, is controlled by a CPU chip, and can also be controlled by other modes, such as manually adjusting the rotary platform and the like.
Example 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 with the same wedge angle and a controller C. For this combined prism, an xyz rectangular system satisfying the right-hand rule is constructed such that the rectangular surfaces opposite to the inclined surfaces in the rectangular prism P1 (reference numeral 1 in the drawing) and the rectangular prism P2 (reference numeral 2 in the drawing) are both located in the xy plane, the inclined surfaces of the rectangular prism P1 and the rectangular prism P2 are parallel to the y axis, and light when incident light perpendicularly enters the beam splitter propagates along the z axis. The crystal axis of the right-angle prism P1 is along the z-axis direction, and the crystal axis of the right-angle prism P2 is perpendicular to the inclined plane.
The controller C (reference numeral 3 in the figure) includes an angle rotating unit and a control unit which are connected with each other, the combined prism is fixed on the angle rotating unit, and the control unit controls the angle rotating unit to rotate, so that the angle of the incident light entering the right-angle prism P1 is controlled, and the shearing angle of the outgoing linearly polarized light in the right-angle prism P2 is further adjusted. Specifically, the combined prism is fixed to an angle rotation unit (rotatable platform) by a mirror holder, and the rotation direction is in the xz plane. In the work, the angle rotation 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 rotation unit to rotate, so that the angle of the light incident to the combined prism is controlled. The rotation speed of the angular rotation unit, the single step precision and the like are not particularly limited and can be adjusted according to actual conditions.
In the working process, after parallel incident light enters the beam splitter from the right-angle surface of the right-angle prism P1, the parallel incident light is changed into two beams of linearly polarized light with a certain included angle and mutually vertical vibration directions, and the two beams of linearly polarized light are output after passing through the right-angle surface of the right-angle prism P2 and are changed into the linearly polarized light with a certain shear angle and mutually vertical vibration directions. In the process, the controller C flexibly adjusts the size of the shearing angle of the two linearly polarized light beams by controlling the angle of the light incident to the combined prism.
Assume that the thickness of the right angle prism P1 and the thickness of the right angle prism P2 are both d, and the wedge angle is a. The refractive index of the right-angle prism P1 and the right-angle prism P2 to the ordinary ray (o light) is noRefractive index n for extraordinary rays (e-rays)e. The beam splitting principle of the beam splitter is explained by the following:
considering that a beam of parallel light enters a right-angle surface of a right-angle prism P1 at an angle t with a z axis in an xz plane, according to the theory of polarization optics and the propagation rule of light in a uniaxial crystal, the beam of light is birefringent after entering a right-angle prism P1, is split into o light and e light in the propagation direction, enters a right-angle prism P2 through an inclined surface, and is finally output by the right-angle surface of the right-angle prism P2, and the generated shear angle is delta t, as shown in formula (5):
Δt＝|to-te| (5)
wherein, toIs the o light output angle, as shown in equation (6); t is teIs e light output angle, as formula (7); n ise' is the actual refractive index of the e-light in the right angle prism P1, as in equation (8); n ise"is the actual refractive index of e-light in the right angle prism P2, as in formula (9):
to＝t (6)
te＝arcsin{sin[arcsin(ne”·sin(arcsin(sint/ne')+a)/ne')-a]/ne”} (7)
Figure BDA0002217945970000081
Figure BDA0002217945970000082
as can be seen from the above equation, the shear angle Δ t 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 not related to the thickness d of the right-angle prism P1 and the right-angle prism P2.
When the wedge angle a is 2.5 deg., the refractive index ne2.22752, refractive index noWhen 2.39223, the shear angle varies with the incident angle of the incident light as shown in fig. 6, where the abscissa is the incident angle ti/degree; the ordinate is the shear angle/rad. The system for testing the beam splitter is the same as the first embodiment, and is not described herein.
In the beam splitter, after two output linearly polarized light beams are focused by the lens group, a certain shearing amount can be formed in the transverse direction, and the change curve of the shearing amount along with the incident angle is approximately linear.
In other embodiments, the right-angle prism P1 and the right-angle prism P2 can 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, and the like. The controller can be composed of a rotary platform and a motor, is controlled by a CPU chip, and can also be controlled by other modes, such as manually adjusting the rotary platform and the like.
Example three:
referring to fig. 7, the beam splitter includes two electro-optic birefringent right-angle prisms (right-angle prism P1 and right-angle prism P2) made of LN crystals with the same wedge angle and a controller C. For this combined prism, an xyz rectangular system satisfying the right-hand rule is arbitrarily constructed such that the rectangular surfaces opposite to the inclined surfaces in the rectangular prism P1 (reference numeral 1 in the drawing) and the rectangular prism P2 (reference numeral 2 in the drawing) are both located in the xy plane, the inclined surfaces of the rectangular prism P1 and the rectangular prism P2 are parallel to the 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 figure) includes a control unit and a power supply unit connected with each other, and the control unit controls the power supply unit to adjust the magnitude of the voltage applied to the combining prism, thereby adjusting the shear angle of the outgoing linearly 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 the LN crystal in a coating process mode, and the two ends of the electrodes are respectively connected with the anode and the cathode of an adjustable voltage-stabilized power supply (power supply unit). In operation, the control unit controls the output voltage of the adjustable voltage-stabilized power supply through USB communication.
Assume that the right angle prism P1 and the right angle prism P2 are both d thick. Ordinary refractive index n when no voltage is appliedo0Extraordinary refractive index of ne0The length of the crystal at the position of applied voltage is l, the wedge angle is a, and the relevant electro-optic coefficient of the electro-optic crystal is r13And r33. The beam splitting principle of the beam splitter is explained by the following:
considering that a beam of parallel light is vertically incident to the beam splitter along the z-axis direction from the right-angle surface of the right-angle prism P1, and then becomes two linearly polarized lights with mutually perpendicular vibration directions but not separated in space, and two linearly polarized lights exit after passing through the right-angle prism P2, and become linearly polarized lights with mutually perpendicular vibration directions and a certain shear angle. By changing the voltage U, the controller C finally generates a shear angle Δ t of the beam splitter as shown in equation (10):
Δt＝|te-to| (10)
wherein, teIs e light output angle, as in equation (11); to is the o light output angleDegree, as in formula (12); n iseThe e-light refractive index of P1 or P2 after voltage application is shown as formula (13); n isoThe refractive index of o light of P1 or P2 after voltage application is as follows:
Figure BDA0002217945970000103
Figure BDA0002217945970000104
from the above equation, the shear angle generated by 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 appliedo0And ne0Length l, associated electro-optic coefficient r of the crystal13And r33And the voltage U applied by the controller, regardless of the thickness d of the right angle prism P1 and the right angle prism P2.
When the wedge angle a is 5 degrees and the length l is 5mm, the electro-optic coefficient r13＝-8.6×10-12m/V, electro-optic coefficient r33＝30.8×10-12m/V, refractive index no02.39222, refractive index ne0The shear angle as a function of applied voltage is shown in fig. 8 at 2.22752, where the voltage U/V is plotted on the abscissa and the shear angle/rad is plotted on the ordinate. The system for testing the beam splitter is the same as the first embodiment, and is not described herein.
In the beam splitter, after two output linearly polarized light beams 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, but may be replaced by other materials, such as gold, copper, some non-metallic electrode materials, etc. The control unit can also control the output voltage of the adjustable voltage-stabilized power supply in other ways, such as RS232 and the like.
Example four:
referring to fig. 7, the beam splitter includes two electro-optic birefringent right-angle prisms (right-angle prism P1 and right-angle prism P2) made of LN crystals with the same wedge angle and a controller C. For this combined prism, an xyz rectangular system satisfying the right-hand rule is arbitrarily constructed such that the rectangular surfaces opposite to the inclined surfaces in the rectangular prism P1 (reference numeral 1 in the drawing) and the rectangular prism P2 (reference numeral 2 in the drawing) are both located in the xy plane, the inclined surfaces of the rectangular prism P1 and the rectangular prism P2 are parallel to the 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 without electricity; when a voltage is applied to the crystals of the right-angle prism P1 and the right-angle prism P2, the refractive index of the LN crystal changes, and the crystal has a birefringence effect, and the crystal optical axis coincides with the direction of the applied voltage. 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 right-angle prism P2 is along the y-axis direction, and the direction in which the voltage is applied is the crystal [001] direction.
The controller C (reference numeral 3 in the figure) includes a control unit and a power supply unit connected with each other, and the control unit controls the power supply unit to adjust the magnitude of the voltage applied to the combining prism, thereby adjusting the shear angle of the outgoing linearly 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 the LN crystal in a coating process mode, and the two ends of the electrodes are respectively connected with the anode and the cathode of an adjustable voltage-stabilized power supply (power supply unit). In operation, the control unit controls the output voltage of the adjustable voltage-stabilized power supply through USB communication.
Assuming that the thickness of the right-angle prism P1 and the thickness of the right-angle prism P2 are both d, the refractive index when no voltage is applied is no0The length of the crystal at the position of applied voltage is l, the wedge angle is a, and the relevant electro-optic coefficient of the electro-optic crystal is s11And s12. The beam splitting principle of the beam splitter is explained by the following:
consider that a parallel light beam is vertically incident on the beam splitter along the z-axis direction from the right angle surface of the right angle prism P1, and then becomes two linearly polarized light beams whose vibration directions are perpendicular to each other but are not spatially separated, and two linearly polarized light beams exit after passing through the right angle prism P2, and become linearly polarized light beams whose vibration directions are perpendicular to each other with a certain shear angle. By changing the voltage U, the controller C finally generates a shear angle Δ t of the beam splitter, as shown in equation (15):
Δt＝|te-to| (15)
wherein, teIs e light output angle, as in equation (16); t is toIs the o light output angle, as in equation (17); n iseThe e-optical refractive index of P1 or P2 after voltage application is shown as formula (18); n isoThe refractive index of o light of P1 or P2 after voltage application is as follows:
Figure BDA0002217945970000111
Figure BDA0002217945970000114
from the above equation, the shear angle generated by 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 appliedo0Length l, associated electro-optic coefficient of the crystal s11And s12And the voltage U applied by the controller, regardless of the thickness d of the right angle prism P1 and the right angle prism P2.
When the wedge angle a is 25 degrees and the length l is 5mm, the electro-optic coefficient s11＝10-14m2/V2Photoelectric coefficient s12＝-10-15m2/V2Refractive index no0When 2.2, the shear angle varies with the applied voltageAs shown in FIG. 9, the voltage U/V is plotted on the abscissa and the shear angle/rad is plotted on the ordinate. The system for testing the beam splitter is the same as the first embodiment, and is not described herein.
In the beam splitter, after two output linearly polarized light beams are focused by the lens group, a certain shearing amount can be formed in the transverse direction, and the shearing amount can be continuously adjusted in a wide range from 0.
In other embodiments, the right angle prism P1 and the right angle prism P2 may be replaced by other crystals, such as a KT crystal. The electrode material may be silver, but may be replaced by other materials, such as gold, copper, some non-metallic electrode materials, etc. The control unit can also control the output voltage of the adjustable voltage-stabilized power supply in other ways, such as RS232 and the like.
It should be noted that the above embodiments can be freely combined as necessary. The foregoing is only a preferred embodiment of the present invention, and it should be noted that, for those skilled in the art, various modifications and improvements can be made without departing from the principle of the present invention, and these modifications and improvements should also be construed as the protection scope of the present invention.

Claims (10)

1. A continuously tunable shear birefringent beam splitter, comprising:
the combined prism is used for splitting the incident light; the combined prism comprises a right-angle prism P1 and a right-angle prism P2 which have the same wedge angle, the right-angle prism P1 and the right-angle prism P2 are combined with each other through an inclined plane, and incident light enters from a right-angle surface of the right-angle prism P1 and is output from a right-angle surface of the right-angle prism P2;
and the controller adjusts the shearing angle of the linearly polarized light emitted by the combined prism in a mode of adjusting the angle of the incident light entering the right-angle prism P1 or adjusting the magnitude of the voltage applied in the combined prism.
2. A birefringent beam splitter according to claim 1, wherein the polarization directions of the incident light are not both perpendicular or parallel to the principal cross-sections of right angle prism P1 and right angle prism P2.
3. A birefringent beam splitter according to claim 1 or 2, wherein said controller comprises an angle rotation unit and a control unit connected to each other, said combining prism is fixed on said angle rotation unit, and said control unit controls said 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 shear angle of the outgoing linearly polarized light in the right-angle prism P2.
4. The birefringent beam splitter of claim 3,
the right-angle prism P1 is made of birefringent crystal, the right-angle prism P2 is made of isotropic crystal, and the refractive index of the right-angle prism P2 is matched with the refractive index of ordinary light of the right-angle prism P1;
in the constructed xyz rectangular system satisfying the right-hand rule, the rectangular surface of the rectangular prism P1 and the rectangular prism P2 opposite to the inclined surface is located in the xy plane, the inclined surface is parallel to the y axis, and the crystal principal optical axis of the rectangular prism P1 is along the z axis direction, perpendicular to a rectangular surface of the combined prism, and the incident light of the vertically incident rectangular prism P1 propagates along the z axis.
5. The birefringent beam splitter of claim 3,
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, a right-angle surface opposite to the inclined surface in the right-angle prism P1 and the right-angle prism P2 is positioned in an xy plane, the inclined surface is parallel to a y axis, and the main optical axis of the crystal of the right-angle prism P1 is vertical to a right-angle surface of the combined prism along the z axis direction; the principal optical axis of the crystal of the right-angle prism P2 is perpendicular to its inclined plane, and the incident light of the right-angle prism P1 propagates along the z-axis at normal incidence.
6. A birefringent beam splitter according to claim 1 or claim 2, wherein the controller includes 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 shear angle of the linearly polarized light exiting the right angle prism P2.
7. The birefringent beam splitter of claim 6,
the right-angle prism P1 and the right-angle prism P2 are made of the same electro-optic crystal;
in the constructed xyz rectangular system satisfying the right-hand rule, the rectangular surface opposite to the inclined surface among the rectangular prism P1 and the rectangular prism P2 is located in the xy plane, the inclined surface is parallel to the y axis, and the rectangular prisms P1 and P2 are uniaxial birefringent crystals when no voltage is applied, the crystal principal axis of the rectangular prism P1 is along the x axis direction, and the crystal principal axis of the rectangular prism P2 is along the y axis direction.
8. The birefringent beam splitter of claim 7, wherein voltage is applied to right angle prism P1 along the x-axis and voltage is applied to right angle prism P2 along the y-axis.
9. The birefringent beam splitter of claim 6,
the right-angle prism P1 and the right-angle prism P2 are made of the same electro-optic crystal;
in the constructed xyz rectangular system satisfying the right-hand rule, the rectangular surface opposite to the inclined surface among the rectangular prism P1 and the rectangular prism P2 is located in the xy plane, the inclined surface is parallel to the y axis, and the rectangular prism P1 and the rectangular prism P2 are isotropic crystals when no voltage is applied, and form uniaxial birefringent crystals after the voltage is applied.
10. The birefringent beam splitter of claim 9, wherein voltage is applied to right angle prism P1 along the x-axis and voltage is applied to right angle prism P2 along the y-axis.
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Publication number Priority date Publication date Assignee Title
JPH05323118A (en) * 1992-05-20 1993-12-07 Matsushita Electric Ind Co Ltd Polarizing device and projection type display device using same
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
US20110013244A1 (en) * 2008-02-28 2011-01-20 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

Patent Citations (5)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
JPH05323118A (en) * 1992-05-20 1993-12-07 Matsushita Electric Ind Co Ltd Polarizing device and projection type display device using same
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
US20110013244A1 (en) * 2008-02-28 2011-01-20 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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