CN102289080B - Method and device for generating radial polarization beam - Google Patents

Abstract

The invention discloses a method and a device for generating radially polarized light beams. In this method, firstly, the collimated light beam is polarized and split into parallel and vertical linearly polarized lights with a light intensity ratio of 1:1, which are respectively turned into circularly polarized lights with opposite handedness, and the starting points are respectively carried out for right-handed and left-handed circularly polarized lights. The same 0-2π vortex phase encoding and the reverse 0-2π vortex phase encoding, after the phase-encoded two beams of light are turned by the optical path, the beams are combined to obtain a radially polarized beam. The device includes: a laser, a polarization beam splitter, a first λ/4 wave plate, a second λ/4 wave plate, a 0-2π vortex phase plate, a reverse 0-2π vortex phase plate, an optical path deflection device and a light beam A beam combining device, wherein the phase starting lines of the 0-2π vortex phase plate and the opposite 0-2π vortex phase plate coincide. The method of the invention is easy to realize, the structure of the device is simple, easy to adjust, and the manufacturing cost is low; the device has good stability and does not need other special optical elements.

Description

A method and device for generating radially polarized light beams

technical field

The invention belongs to the field of applied optics, and specifically relates to a method and device for generating radially polarized light beams, which are mainly used in the fields of optical information storage, photolithography, super-resolution microscopy and the like.

Background technique

As a vector characteristic of light waves, polarization has attracted more and more attention in recent years, and it can be widely used in polarization difference imaging, super-resolution focusing, laser lithography and other fields. During the research, it was found that the polarization state of the beam not only includes the traditional linearly polarized light, circularly polarized light and elliptically polarized light, but also includes radial polarized light (radial polarization beam) and tangentially polarized light (azimuthally polarized beam), etc. Cylindrical polarized beams. Due to the symmetrical distribution of polarization state and light intensity of cylindrically polarized beams, it has been widely studied. The Chinese invention patent application with publication number CN101465512A discloses a laser that produces cylindrically symmetric polarized light. Radial polarized light or tangentially polarized light is realized by designing a special asymmetric cavity structure. However, due to the need to change the existing laser Resonant cavity, so the production cost is high. The Chinese Utility Model Patent No. ZL 200820165973.0 discloses a device for converting linearly polarized light into radially polarized light beams, but the adjustment is cumbersome and requires high adjustment accuracy.

Contents of the invention

The invention provides a method and device for generating radially polarized light beams, which are simple to adjust and low in cost.

A method of producing a radially polarized beam comprising the steps of:

(1) The collimated light beam emitted by the laser is split by a polarization beam splitter to obtain parallel linearly polarized light and vertically linearly polarized light with a light intensity ratio of 1:1;

(2) Make the parallel linearly polarized light become right-handed circularly polarized light after passing through the first λ/4 wave plate and the vertical linearly polarized light become left-handed circularly polarized light after passing through the second λ/4 wave plate ;

Alternatively, the parallel linearly polarized light becomes left-handed circularly polarized light after passing through the first λ/4 wave plate and the vertically linearly polarized light becomes right-handed circularly polarized light after passing through the second λ/4 wave plate;

(3) Perform 0-2π vortex phase encoding on the right-handed circularly polarized light, and reverse 0-2π vortex phase encoding on the left-handed circularly polarized light, and the reverse 0-2π vortex phase encoding The starting point of the phase encoding is the same as the starting point of the 0-2π vortex phase encoding. The two beams of light after the phase encoding are turned by the optical path and then incident on the same beam combining device for beam coherent combining. The beam combining The beam emitted by the beam device is a radially polarized beam.

In step (2), the parallel linearly polarized light becomes right-handed circularly polarized light after passing through the first λ/4 wave plate and the vertical linearly polarized light becomes left-handed after passing through the second λ/4 wave plate Circularly polarized light can be realized by setting the positions of the first λ/4 wave plate and the second λ/4 wave plate, that is, the fast axis of the first λ/4 wave plate is set at the position of the parallel linearly polarized light Where the polarization direction rotates counterclockwise by 45°, the fast axis of the second λ/4 wave plate is set at the position where the polarization direction of the vertically linearly polarized light rotates clockwise by 45°.

Similarly, the parallel linearly polarized light becomes left-handed circularly polarized light after passing through the first λ/4 wave plate and the vertical linearly polarized light becomes right-handed circularly polarized light after passing through the second λ/4 wave plate, It can also be realized by setting the positions of the first λ/4 wave plate and the second λ/4 wave plate, that is, the fast axis of the first λ/4 wave plate is set in the direction of polarization of the parallel linearly polarized light along the At the position where the clockwise rotation is 45°, the fast axis of the second λ/4 wave plate is set at the position where the polarization direction of the vertical linearly polarized light is rotated counterclockwise by 45°.

In step (3), the two phase-encoded light beams are incident on the same beam combining device after the optical path is turned for coherent beam combining to obtain radially polarized light beams. The setting of the light path refraction is based on the fact that the two beams of light can be incident on the same beam combining device. The following will take the radially polarized beam emitted by the beam combining device to be parallel or perpendicular to the collimated beam emitted by the laser as an example to illustrate its implementation:

To make the radially polarized beam emitted by the beam combining device parallel to the collimated beam emitted by the laser, the following two implementation methods can be adopted respectively:

(a) When the right-handed circularly polarized light and the left-handed circularly polarized light in step (2) are respectively converted from the parallel linearly polarized light and the vertically linearly polarized light: performing 0 on the right-handed circularly polarized light ～2π vortex phase encoding, and then incident on the beam combining device; reverse 0～2π vortex phase encoding for the left-handed circularly polarized light, and then pass through the optical path turning device to perform optical path turning, and then incident on the said On the beam combining device, the coherent beams emitted by the beam combining device are radially polarized beams.

(b) When the right-handed circularly polarized light and the left-handed circularly polarized light in step (2) are respectively converted from the vertical linearly polarized light and the parallel linearly polarized light: reverse the left-handed circularly polarized light After the 0-2π vortex phase encoding, it is incident on the beam combining device; the 0-2π vortex phase encoding is performed on the right-handed circularly polarized light, and then the optical path is turned by the optical path turning device, and then it is incident on the said On the beam combining device, the coherent beams emitted by the beam combining device are radially polarized beams.

Similarly, making the radially polarized beam emitted by the beam combining device perpendicular to the collimated beam emitted by the laser can also be realized in two ways. That is: in (a), the right-handed circularly polarized light encoded by the 0-2π vortex phase is refracted and then incident on the beam combining device, while the left-handed circularly polarized light encoded by the reverse 0-2π vortex phase The light is directly incident on the beam combiner. In (b), the optical path of the left-handed circularly polarized light encoded by the reverse 0-2π vortex phase is refracted and then incident on the beam combining device, while the right-handed circularly polarized light encoded by the 0-2π vortex phase is incident to the beam combiner.

The above-mentioned method for producing a radially polarized light beam may also adopt the following scheme, that is, comprising the following steps:

(1) The collimated light beam emitted by the laser is split by a polarization beam splitter to obtain parallel linearly polarized light and vertically linearly polarized light with a light intensity ratio of 1:1;

(2') Perform 0-2π vortex phase encoding on the parallel linearly polarized light, perform reverse 0-2π vortex phase encoding on the vertical linearly polarized light, and the reverse 0-2π vortex phase encoding The starting point of the phase encoding is the same as the starting point of the 0-2π vortex phase encoding, and the two beams of light after the phase encoding are turned by the optical path and then incident on the same beam combining device for coherent beam combining;

(3') The light beam emitted by the beam combining device is converted into a radially polarized light beam by the λ/4 wave plate, and the fast axis of the λ/4 wave plate is set at the parallel linearly polarized light Position where the polarization direction is rotated 45° counterclockwise.

The principle of the light path refraction in step (2') is similar to that in the aforementioned step (3).

Step (3') The principle of converting the light beam emitted by the beam combining device into a radially polarized light beam after passing through the λ/4 wave plate is:

The parallel linearly polarized light encoded in the 0-2π vortex phase in the output beam of the beam combining device is converted into right-handed circularly polarized light by a λ/4 wave plate, and the output beam of the beam combining device is reversed 0～2π vortex phase-encoded vertical linearly polarized light is converted into left-handed circularly polarized light by a λ/4 wave plate, and two beams of right-handed circularly polarized light and left-handed circularly polarized light are coherently combined to obtain a radially polarized beam.

A device for implementing the method for generating a radially polarized light beam, comprising:

a laser for emitting a collimated beam;

A polarizing beam splitter for splitting the collimated beam into parallel linearly polarized light and vertically linearly polarized light with a light intensity ratio of 1:1;

The first λ/4 wave plate and the second λ/4 wave plate are used to convert the parallel linearly polarized light and vertical linearly polarized light into right-handed circularly polarized light and left-handed circularly polarized light respectively. At this time, the first The fast axis of the λ/4 wave plate is set at the position where the polarization direction of the parallel linearly polarized light is rotated counterclockwise by 45°, and the fast axis of the second λ/4 wave plate is set at the polarization direction of the vertical linearly polarized light The direction rotates clockwise by 45°; or it is used to convert the parallel linearly polarized light and vertical linearly polarized light into left-handed circularly polarized light and right-handed circularly polarized light respectively. At this time, the first λ/4 wave plate The fast axis of the second λ/4 wave plate is set at the position where the polarization direction of the parallel linearly polarized light rotates clockwise by 45°, and the fast axis of the second λ/4 wave plate is set at the position where the polarization direction of the vertical linearly polarized light rotates counterclockwise 45° position;

A 0-2π vortex phase plate, used for encoding the right-handed circularly polarized light with a 0-2π vortex phase;

The reverse 0-2π vortex phase plate is used for reverse 0-2π vortex phase encoding on the left-handed circularly polarized light; The phase initial lines of the 0～2π vortex phase plate overlap;

The optical path turning device is used for turning the optical path of the left-handed circularly polarized light encoded by the reverse 0-2π vortex phase or the right-handed circularly polarized light encoded by the 0-2π vortex phase;

And a beam combining device, which is used for beam coherent combining of the two beams of light after the phase encoding and optical path turning.

The above-mentioned device for realizing the method for generating a radially polarized beam may also be the following scheme, that is, including:

a laser for emitting a collimated beam;

A polarizing beam splitter for splitting the collimated beam into parallel linearly polarized light and vertically linearly polarized light with a light intensity ratio of 1:1;

A 0-2π vortex phase plate, used for encoding the parallel linearly polarized light with a 0-2π vortex phase;

The reverse 0-2π vortex phase plate is used for reverse 0-2π vortex phase encoding to the vertical linearly polarized light; the phase start line of the reverse 0-2π vortex phase plate is aligned The phase initial lines of the 0～2π vortex phase plate overlap;

The optical path turning device is used for turning the optical path of the vertical linearly polarized light encoded by the reverse 0-2π vortex phase or the parallel linearly polarized light encoded by the 0-2π vortex phase;

A beam combining device, used for beam coherent combining of the two beams of light after the phase encoding and optical path turning;

and a λ/4 wave plate, used to convert the parallel linearly polarized light encoded in the 0-2π vortex phase into right-handed circularly polarized light in the outgoing beam of the beam combining device, and the outgoing beam of the beam combining device The vertical linearly polarized light encoded by the reverse 0-2π vortex phase is converted into left-handed circularly polarized light, and the two beams of right-handed circularly polarized light and left-handed circularly polarized light are coherently combined to obtain a radially polarized beam. The λ/4 The fast axis of the wave plate is set at a position where the polarization direction of the parallel linearly polarized light rotates counterclockwise by 45°.

Described optical path turning device is a high-precision flat reflector, the root mean square value (RMS) of its surface shape accuracy is 0.011λ, and the PV value (representing the difference between the highest point and the lowest point of the surface) is 0.071λ; It is necessary to place multiple plane mirrors, preferably metal film mirrors.

Principle of the present invention is as follows:

For radially polarized light, in the beam cross-section perpendicular to the optical axis, its polarization is expressed as where θ is the azimuth coordinate in the polar coordinate system. At any moment, in the cross-section of the beam, the polarization direction at any point is determined, all along the radial direction of the point. For left-handed circularly polarized light or right-handed circularly polarized light, within one cycle of beam propagation, the wavefront of the entire light wave undergoes a phase change at the same time, and the phase change increases from 0 to 2π. For left-handed circularly polarized light or right-handed circularly polarized light, within a time period, at any moment, the light beam is linearly polarized light, and as time increases, the polarization direction of the electric field changes along the radial direction. For left-handed circularly polarized light or right-handed circularly polarized light, for an observer facing the propagation of the beam, the direction in which the end of the light vector changes is left-handed or right-handed. Therefore, using the calculation rule of the Jones matrix, after performing phase delay e ^-iθ on the left-handed circularly polarized light and e ^iθ on the right-handed circularly polarized light, after combining the beams, it is found that the polarization state of the combined beams satisfies the path The polarization distribution of a polarized beam.

Compared with the prior art, the present invention has the following beneficial technical effects:

(1) Directly using circularly polarized light to realize radially polarized beams, the principle is simple and easy to implement;

(2) The structure is simple, easy to adjust, and the manufacturing cost is low;

(3) The device has good stability and does not require other special optical components.

Description of drawings

Fig. 1 is a schematic structural view of the first embodiment of the device of the present invention.

Fig. 2 is a schematic structural view of a second embodiment of the device of the present invention.

3 is a schematic diagram of the relationship between the fast axis direction of the λ/4 wave plate and the polarization directions of vertically linearly polarized light (s light) and parallel linearly polarized light (p light) in the second embodiment of the device of the present invention.

Fig. 4 is a schematic diagram of the polarization of right-handed circularly polarized light within a period of time.

Fig. 5 is a schematic diagram of 0-2π phase encoding.

Fig. 6 is a schematic diagram of reverse 0-2π phase encoding.

Fig. 7 is a schematic diagram of polarization of radially polarized light.

Detailed ways

The present invention will be described in detail below in conjunction with the embodiments and accompanying drawings, but the present invention is not limited thereto.

Example 1

As shown in Figure 1, a device for generating radially polarized light includes: a laser 1, a polarization beam splitter 2, a first λ/4 wave plate 3, a second λ/4 wave plate 4, and a 0-2π vortex phase Plate 5 , reverse 0-2π vortex phase plate 6 , first high-precision plane mirror 7 , second high-precision plane mirror 8 and depolarization beam splitter 9 .

The method of producing radially polarized light with the device shown in 1 is as follows:

(1) After the collimated beam emitted by the laser 1 is split by the polarization beam splitter 2, the transmitted beam is parallel linearly polarized light, and the reflected beam is vertically linearly polarized light. The ratio of the light intensity of the transmitted beam to the reflected beam is 1:1.

(2) Parallel linearly polarized light is converted into right-handed circularly polarized light after passing through the first λ/4 wave plate 3, wherein the fast axis of the first λ/4 wave plate 3 is set so that the polarization direction of the parallel linearly polarized light rotates counterclockwise The position of 45°; the schematic diagram of the polarization of right-handed circularly polarized light in one cycle time is shown in Figure 4. In the beam cross section perpendicular to the optical axis, the polarization direction of right-handed circularly polarized light can be represented by the following unit matrix:

$\left[\begin{array}{c}{\mathrm{<span\; class="notranslate">\; p</span>}}_{\mathrm{<span\; class="notranslate">\; x</span>}}\\ {\mathrm{<span\; class="notranslate">\; p</span>}}_{\mathrm{<span\; class="notranslate">\; the\; y</span>}}\end{array}\right]<span\; class="notranslate">\; =</span>\left[\begin{array}{c}\mathrm{<span\; class="notranslate">\; 1</span>}\\ <span\; class="notranslate">\; -</span>\mathrm{<span\; class="notranslate">\; i</span>}\end{array}\right]<span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; i</span>}<span\; class="notranslate">\; )</span>$

Wherein, Px, Py, and i are the polarization component in the X-axis direction, the polarization component in the Y-axis direction, and the imaginary number unit, respectively.

The vertically linearly polarized light is converted into left-handed circularly polarized light after passing through the second λ/4 wave plate 4, wherein the fast axis of the second λ/4 wave plate is set so that the polarization direction of the vertically linearly polarized light rotates 45° clockwise position; in the beam cross section perpendicular to the optical axis, the identity matrix of the polarization direction of left-handed circularly polarized light is expressed as:

$\left[\begin{array}{c}{\mathrm{<span\; class="notranslate">\; p</span>}}_{\mathrm{<span\; class="notranslate">\; x</span>}}\\ {\mathrm{<span\; class="notranslate">\; p</span>}}_{\mathrm{<span\; class="notranslate">\; the\; y</span>}}\end{array}\right]<span\; class="notranslate">\; =</span>\left[\begin{array}{c}\mathrm{<span\; class="notranslate">\; 1</span>}\\ \mathrm{<span\; class="notranslate">\; i</span>}\end{array}\right]<span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; i</span>}<span\; class="notranslate">\; )</span>$

(3) The right-handed circularly polarized light passes through the 0-2π vortex phase plate 5 for 0-2π vortex phase encoding. The 0～2π vortex phase plate 5 has a phase starting line, which is a straight line along the radial direction. By placing the 0～2π vortex phase plate 5 at an appropriate position, the phase starting line and any The radii coincide to achieve phase delay. In this embodiment, the phase starting line L1 of the 0-2π vortex phase plate 5 shown in FIG. 5 is along the positive direction of the x-axis as an example for illustration.

The vortex direction of the 0-2π vortex phase plate 5 (that is, the phase encoding direction) is opposite to that of right-handed circularly polarized light, and its phase encoding effect can be expressed by the following formula:

和

分别为入射光(右旋圆偏振光)和经过0～2π涡旋位相板5进行0～2π涡旋位相编码后的出射光的电场矢量。i为虚数单位，θ为坐标轴原点到位相编码点的连线与X轴正方向所成的角度。in,

and

are the electric field vectors of the incident light (right-handed circularly polarized light) and the outgoing light after passing through the 0-2π vortex phase plate 5 and performing 0-2π vortex phase encoding, respectively. i is the imaginary unit, θ is the angle formed by the line connecting the origin of the coordinate axis to the phase code point and the positive direction of the X axis.

After the right-handed circularly polarized light passes through the 0-2π vortex phase plate 5 for 0-2π vortex phase encoding, the electric field vector of the beam is expressed as:

${\mathrm{<span\; class="notranslate">\; e</span>}}^{\mathrm{<span\; class="notranslate">\; i\&theta;</span>}}\left[\begin{array}{c}\mathrm{<span\; class="notranslate">\; 1</span>}\\ <span\; class="notranslate">\; -</span>\mathrm{<span\; class="notranslate">\; i</span>}\end{array}\right]<span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; iv</span>}<span\; class="notranslate">\; )</span>$

The right-handed circularly polarized light after 0-2π vortex phase encoding is directly incident on the depolarization beam splitter 9 .

The left-handed circularly polarized light passes through the reverse 0-2π vortex phase plate 6 for reverse 0-2π vortex phase encoding. The reverse 0～2π vortex phase plate 6 has a phase initial line, which is a straight line along the radial direction. By placing the reverse 0～2π vortex phase plate 6 at an appropriate position, the phase initial line is aligned with the entrance pupil Any radius within the spot coincides to achieve phase delay.

Corresponding to the phase start line L1 of the 0-2π vortex phase plate 5 in Fig. 5 along the positive direction of the x-axis, the phase start line L2 of the reverse 0-2π vortex phase plate 6 in this embodiment is also along the The positive direction of the x-axis is shown in Figure 6. At this time, the starting point of the reverse 0-2π vortex phase encoding is the same as the starting point of the 0-2π vortex phase encoding.

The direction of the vortex (that is, the phase encoding direction) of the reversed 0-2π vortex phase plate 6 is opposite to that of left-handed circularly polarized light, and its phase encoding effect can be expressed by the following formula:

和

分别为入射光(左旋圆偏振光)和经过反向0～2π涡旋位相板6进行反向0～2π涡旋位相编码后的出射光的电场矢量。in,

and

are the electric field vectors of the incident light (left-handed circularly polarized light) and the outgoing light after undergoing reverse 0-2π vortex phase encoding through the reverse 0-2π vortex phase plate 6 , respectively.

After the left-handed circular polarization undergoes reverse 0-2π vortex phase encoding by the reverse 0-2π vortex phase plate 6, the electric field vector of the beam is expressed as:

${\mathrm{<span\; class="notranslate">\; e</span>}}^{<span\; class="notranslate">\; -</span>\mathrm{<span\; class="notranslate">\; i\&theta;</span>}}\left[\begin{array}{c}\mathrm{<span\; class="notranslate">\; 1</span>}\\ \mathrm{<span\; class="notranslate">\; i</span>}\end{array}\right]<span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; vi</span>}<span\; class="notranslate">\; )</span>$

The left-handed circularly polarized light encoded with the reversed 0-2π vortex phase passes through the first high-precision plane mirror 7 and the second high-precision plane mirror 8 for light path deflection, and then enters the depolarization beam splitter 9 . The depolarizing beam splitter 9 performs coherent beam combining on the incident two beams.

The beams emitted from the depolarizing beam splitter 9 are combined coaxial collimated beams, and the polarization state of the combined beams can be expressed as:

${\mathrm{<span\; class="notranslate">\; e</span>}}^{\mathrm{<span\; class="notranslate">\; i\&theta;</span>}}\left[\begin{array}{c}\mathrm{<span\; class="notranslate">\; 1</span>}\\ <span\; class="notranslate">\; -</span>\mathrm{<span\; class="notranslate">\; i</span>}\end{array}\right]<span\; class="notranslate">\; +</span>{\mathrm{<span\; class="notranslate">\; e</span>}}^{<span\; class="notranslate">\; -</span>\mathrm{<span\; class="notranslate">\; i\&theta;</span>}}\left[\begin{array}{c}\mathrm{<span\; class="notranslate">\; 1</span>}\\ \mathrm{<span\; class="notranslate">\; i</span>}\end{array}\right]<span\; class="notranslate">\; =</span>\left[\begin{array}{c}\mathrm{<span\; class="notranslate">\; cos</span>}\mathrm{<span\; class="notranslate">\; \&theta;</span>}\\ \mathrm{<span\; class="notranslate">\; sin</span>}\mathrm{<span\; class="notranslate">\; \&theta;</span>}\end{array}\right]<span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; viii</span>}<span\; class="notranslate">\; )</span>$

The expression of the polarization state of the combined beam is just the polarization expression of the radially polarized light, thus realizing the direct conversion of the beam into the radially polarized light. The schematic diagram of the polarization of radially polarized light is shown in FIG. 7 .

In this embodiment, the first high-precision plane mirror 7 and the second high-precision plane mirror 8 are both metal film mirrors, the root mean square value of their surface shape accuracy is 0.011λ, and the PV value is 0.071λ.

Example 2:

As shown in Figure 2, a device for generating radially polarized light beams includes: a laser 1, a polarization beam splitter 2, a 0-2π vortex phase plate 5, a reverse 0-2π vortex phase plate 6, and a first high-precision A plane mirror 7, a second high-precision plane mirror 8, a depolarizing beam splitter 9 and a third λ/4 wave plate 10.

The difference from Embodiment 1 is that in this embodiment, the parallel linearly polarized light and the vertical linearly polarized light are respectively phase encoded, and the parallel linearly polarized light and the vertically linearly polarized light after phase encoding are combined through the depolarization beam splitter 9 After being coaxially collimated beams, they are converted into phase-encoded right-handed circularly polarized light and left-handed circularly polarized light respectively through the third λ/4 wave plate 10, and the combined beams are radially polarized light beams. The specific process of producing radially polarized light with the device shown in 2 is as follows:

(1) After the collimated beam emitted by the laser 1 is split by the polarization beam splitter 2, the transmitted beam is parallel linearly polarized light, and the reflected beam is vertically linearly polarized light. The ratio of the light intensity of the transmitted beam to the reflected beam is 1:1.

(2') Parallel linearly polarized light passes through the 0-2π vortex phase plate 5 for 0-2π vortex phase encoding. The 0～2π vortex phase plate 5 has a phase starting line, which is a straight line along the radial direction. By placing the 0～2π vortex phase plate 5 at an appropriate position, the phase starting line and any The radii coincide to achieve phase delay. In this embodiment, the phase start line L1 of the 0-2π vortex phase plate 5 shown in FIG. 5 is taken as an example along the positive direction of the x-axis for illustration, and its phase encoding function can be expressed by the following formula:

和分别为入射光(平行线偏振光)和经过0～2π涡旋位相板5进行0～2π涡旋位相编码后的出射光的电场矢量。i为虚数单位，θ为坐标轴原点到位相编码点的连线与X轴正方向所成的角度。in,

and are the electric field vectors of the incident light (parallel linearly polarized light) and the outgoing light after undergoing 0-2π vortex phase encoding through the 0-2π vortex phase plate 5 , respectively. i is the imaginary unit, θ is the angle formed by the line connecting the origin of the coordinate axis to the phase code point and the positive direction of the X axis.

The parallel linearly polarized light after 0-2π vortex phase encoding is directly incident on the depolarization beam splitter 9 .

The vertical linearly polarized light passes through the reversed 0-2π vortex phase plate 6 for reverse 0-2π vortex phase encoding. The reverse 0～2π vortex phase plate 6 has a phase initial line, which is a straight line along the radial direction. By placing the reverse 0～2π vortex phase plate 6 at an appropriate position, its phase initial line is aligned with the entrance pupil Any radius within the spot coincides to achieve phase delay.

Corresponding to the phase start line L1 of the 0-2π vortex phase plate 5 in Fig. 5 along the positive direction of the x-axis, the phase start line L2 of the reverse 0-2π vortex phase plate 6 in this embodiment is also along the The positive direction of the x-axis, as shown in Figure 6, at this time, the starting point of the reverse 0～2π vortex phase encoding is the same as the starting point of the 0～2π vortex phase encoding, and the phase encoding of the reverse 0～2π vortex phase plate 6 The effect can be expressed by the following formula:

和

分别为入射光(垂直线偏振光)和经过反向0～2π涡旋位相板6进行反向0～2π涡旋位相编码后的出射光的电场矢量。in,

and

are the electric field vectors of the incident light (vertical linearly polarized light) and the outgoing light after undergoing reverse 0-2π vortex phase encoding through the reverse 0-2π vortex phase plate 6, respectively.

The vertically linearly polarized light encoded with the reversed 0-2π vortex phase passes through the first high-precision plane mirror 7 and the second high-precision plane mirror 8 for light path deflection, and then enters the depolarization beam splitter 9 . The depolarizing beam splitter 9 performs coherent beam combining on the incident two beams.

(3') The beam emitted from the depolarizing beam splitter 9 is a coaxial collimated beam. The coaxially collimated phase-coded parallel linearly polarized light and vertical linearly polarized light pass through the third λ/4 wave plate 10, and the fast axis of the third λ/4 wave plate 10 is set so that the polarization direction of the parallel linearly polarized light is along the opposite direction. The position where the clockwise rotates 45° (that is, the position where the polarization direction of the vertical linearly polarized light is rotated 45° clockwise), as shown in Figure 3, converts the beam-combined phase-encoded right-handed circularly polarized light and left-handed circularly polarized light polarized light.

The beam polarization state after combining the right-handed circularly polarized light encoded by 0-2π vortex phase and the left-handed circularly polarized light encoded by reverse 0-2π vortex phase is expressed as:

${\mathrm{<span\; class="notranslate">\; e</span>}}^{\mathrm{<span\; class="notranslate">\; i\&theta;</span>}}\left[\begin{array}{c}\mathrm{<span\; class="notranslate">\; 1</span>}\\ <span\; class="notranslate">\; -</span>\mathrm{<span\; class="notranslate">\; i</span>}\end{array}\right]<span\; class="notranslate">\; +</span>{\mathrm{<span\; class="notranslate">\; e</span>}}^{<span\; class="notranslate">\; -</span>\mathrm{<span\; class="notranslate">\; i\&theta;</span>}}\left[\begin{array}{c}\mathrm{<span\; class="notranslate">\; 1</span>}\\ \mathrm{<span\; class="notranslate">\; i</span>}\end{array}\right]<span\; class="notranslate">\; =</span>\left[\begin{array}{c}\mathrm{<span\; class="notranslate">\; cos</span>}\mathrm{<span\; class="notranslate">\; \&theta;</span>}\\ \mathrm{<span\; class="notranslate">\; sin</span>}\mathrm{<span\; class="notranslate">\; \&theta;</span>}\end{array}\right]<span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; viii</span>}<span\; class="notranslate">\; )</span>$

That is radially polarized light. The schematic diagram of the polarization of radially polarized light is shown in FIG. 7 .

Claims (8)

1. A method of producing a radially polarized beam of light, comprising the steps of:

(1) collimated light beams emitted by a laser are split by a polarization beam splitter to obtain parallel polarized light and vertical polarized light with the light intensity ratio of 1: 1;

(2) the parallel line polarized light is changed into right-handed circularly polarized light after passing through a first lambda/4 wave plate and the vertical line polarized light is changed into left-handed circularly polarized light after passing through a second lambda/4 wave plate; or the parallel line polarized light is changed into left-handed circularly polarized light after passing through a first lambda/4 wave plate and the vertical line polarized light is changed into right-handed circularly polarized light after passing through a second lambda/4 wave plate;

(3) carrying out 0-2 pi vortex phase encoding on the dextrorotation circularly polarized light through a 0-2 pi vortex phase plate, wherein the 0-2 pi vortex phase plate is provided with a phase initial line which is a straight line along the radius direction of the phase initial line and is superposed with any radius in an entrance pupil spot; carrying out reverse 0-2 pi vortex phase encoding on the left-handed circularly polarized light through a reverse 0-2 pi vortex phase plate, wherein the reverse 0-2 pi vortex phase plate is provided with a phase starting line which is a straight line along the radius direction of the reverse 0-2 pi vortex phase plate, and the phase starting line is superposed with any radius in an entrance pupil spot; the starting point of the reverse 0-2 pi vortex phase code is the same as the starting point of the 0-2 pi vortex phase code, two beams of light after the phase code are deflected by a light path and then enter the same light beam combiner to be combined in a coherent manner, and the light beam emitted by the light beam combiner is a radial polarized light beam.

2. A method of producing a radially polarized beam of light, comprising the steps of:

(1) collimated light beams emitted by a laser are split by a polarization beam splitter to obtain parallel polarized light and vertical polarized light with the light intensity ratio of 1: 1;

(2') carrying out 0-2 pi vortex phase coding on the parallel linear polarized light, and carrying out reverse 0-2 pi vortex phase coding on the vertical linear polarized light, wherein the starting line of the reverse 0-2 pi vortex phase coding is overlapped with the starting line of the 0-2 pi vortex phase coding, the starting lines of the two vortex phase codes are respectively straight lines along the radius direction of the vortex phase plate, and meanwhile, the starting lines of the two vortex phase codes are overlapped with any radius in the entrance pupil spot; the starting point of the reverse 0-2 pi vortex phase code is the same as the starting point of the 0-2 pi vortex phase code, and two beams of light after the phase code are deflected by a light path and then are incident on the same light beam combining device for light beam coherent combining;

(3') the light beam emitted by the light beam combining device is converted into a radial polarized light beam after passing through a lambda/4 wave plate, and the fast axis of the lambda/4 wave plate is arranged at the position where the polarization direction of the parallel linearly polarized light rotates 45 degrees along the counterclockwise direction.

3. An apparatus for implementing the method of claim 1 for producing a radially polarized beam of light, comprising:

a laser for emitting a collimated beam;

the polarization beam splitter is used for splitting the collimated light beam into parallel line polarized light and vertical line polarized light with the light intensity ratio of 1: 1;

the first lambda/4 wave plate and the second lambda/4 wave plate are used for converting the parallel line polarized light and the vertical line polarized light into right-handed circularly polarized light and left-handed circularly polarized light respectively, at the moment, the fast axis of the first lambda/4 wave plate is arranged at the position where the polarization direction of the parallel line polarized light rotates 45 degrees along the counterclockwise direction, and the fast axis of the second lambda/4 wave plate is arranged at the position where the polarization direction of the vertical line polarized light rotates 45 degrees along the clockwise direction; or the fast axis of the first lambda/4 wave plate is arranged at the position where the polarization direction of the parallel linear polarized light rotates by 45 degrees clockwise, and the fast axis of the second lambda/4 wave plate is arranged at the position where the polarization direction of the vertical linear polarized light rotates by 45 degrees anticlockwise;

the 0-2 pi vortex phase plate is used for carrying out 0-2 pi vortex phase coding on the dextrorotation circularly polarized light, and the 0-2 pi vortex phase plate is provided with a phase starting line which is a straight line along the radius direction of the phase starting line and is superposed with any radius in the pupil entrance light spot;

the reverse 0-2 pi vortex phase plate is used for performing reverse 0-2 pi vortex phase encoding on the left-handed circularly polarized light, the reverse 0-2 pi vortex phase plate is provided with a phase starting line which is a straight line along the radius direction of the reverse 0-2 pi vortex phase plate, the phase starting line is superposed with any radius in the entrance pupil spot, and the phase starting line of the reverse 0-2 pi vortex phase plate is superposed with the phase starting line of the 0-2 pi vortex phase plate; the light path turning device is used for turning the light path of the left-handed circularly polarized light coded by the reverse 0-2 pi vortex phase or the right-handed circularly polarized light coded by the 0-2 pi vortex phase;

and the beam combining device is used for carrying out beam coherent combining on the two beams of light after the phase coding and the light path turning.

4. The apparatus of claim 3, wherein said optical path turning device is one or more high-precision plane mirrors having a surface profile precision with a root mean square value of 0.011 λ and a PV value of 0.071 λ.

5. The apparatus of claim 4 wherein said high precision planar mirror is a metal film mirror.

6. An apparatus for implementing the method of claim 2 for producing a radially polarized beam of light, comprising:

a laser for emitting a collimated beam;

the polarization beam splitter is used for splitting the collimated light beam into parallel line polarized light and vertical line polarized light with the light intensity ratio of 1: 1;

the 0-2 pi vortex phase plate is used for carrying out 0-2 pi vortex phase encoding on the parallel linearly polarized light, and the 0-2 pi vortex phase plate is provided with a phase starting line which is a straight line along the radius direction of the phase starting line and is superposed with any radius in the pupil entrance light spot;

the reverse 0-2 pi vortex phase plate is used for performing reverse 0-2 pi vortex phase encoding on the vertical linear polarized light, the reverse 0-2 pi vortex phase plate is provided with a phase starting line which is a straight line along the radius direction of the reverse 0-2 pi vortex phase plate, the phase starting line is superposed with any radius in an entrance pupil spot, and the phase starting line of the reverse 0-2 pi vortex phase plate is superposed with the phase starting line of the 0-2 pi vortex phase plate;

the light path turning device is used for turning the light path of the vertical linear polarized light coded by the reverse 0-2 pi vortex phase or the parallel linear polarized light coded by the 0-2 pi vortex phase;

the beam combining device is used for carrying out beam coherent combining on the two beams of light after the phase coding and the light path turning;

and the lambda/4 wave plate is used for converting parallel linear polarized light encoded by a 0-2 pi vortex phase in the emergent light beam of the light beam combining device into right-handed circularly polarized light, converting vertical linear polarized light encoded by a reverse 0-2 pi vortex phase in the emergent light beam of the light beam combining device into left-handed circularly polarized light, coherently combining the right-handed circularly polarized light and the left-handed circularly polarized light to obtain a radial polarized light beam, and the fast axis of the lambda/4 wave plate is arranged at a position where the polarization direction of the parallel linear polarized light rotates 45 degrees along the counterclockwise direction.

7. The apparatus of claim 6, wherein said optical path turning device is one or more high-precision plane mirrors having a surface profile precision with a root mean square value of 0.011 λ and a PV value of 0.071 λ.

8. The apparatus of claim 7 wherein said high precision planar mirror is a metal film mirror.

Images