CN103792605A - Forked liquid crystal grating preparation method and application of forked liquid crystal grating in vortex beam - Google Patents
Forked liquid crystal grating preparation method and application of forked liquid crystal grating in vortex beam Download PDFInfo
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Abstract
A forked liquid crystal grating is characterized in that liquid crystal orientation of adjacent liquid crystal areas of the forked liquid crystal grating is controlled differently such that the following three types of forked liquid crystal gratings can be formed, namely a TN/PA-type forked liquid crystal grating, an orthogonal PA-type liquid crystal grating and an orthogonal HAN-type liquid crystal grating; 90-degree twisted phase microcells of liquid crystal and parallel-oriented microcells of and the liquid crystal are alternately arranged so as to form the TN/PA-type forked liquid crystal grating; uniformly parallel microcells of the liquid crystal of which optical axes are in the same region and microcells in an adjacent region which are orthogonal to each other are alternately arranged to form the orthogonal PA-type liquid crystal grating. According to the preparation of the forked liquid crystal grating, a photoalignment method is adopted to control liquid crystal micro orientation so as to control the director distribution of the liquid crystal. Since a digital micro-mirror device (DMD)-based micro projection-type lithography system is realized, a digital control device outputs liquid crystal forked gritting pattern signals to control the reflected light of each pixel of a digital micro-mirror device (DMD), such that the imaging of a liquid crystal forked grating pattern can be realized; and after being narrowed through a micro objective, light beams are projected to photoalignment material agent conductive glass through a polarizing film.
Description
Technical field
The present invention relates to micro-lithography system, liquid crystal aligning control, electric light is adjustable technical fields such as prepared by components and parts, be specifically related to a kind of can electricity regulating and the preparation of the liquid crystal fork like grating that light rewrites and in the application generating in light vortex based on liquid crystal light control, friction orientation and numerical control micro mirror battle array DMD etching system.
Background technology
In recent years, because vortex beams is in the application of the aspects such as optics trapping, manipulation fine particle, super-resolution optical microscope and uranology, people more and more pay close attention to the research of vortex beams.The method that produces vortex beams is a lot, can produce with angle phase factor Ψ by the method such as resonator cavity and pumping mode, spiral phase plate and computing holography of laser instrument
1=exp (im θ) light vortex, wherein m is topological charge number, θ is the position angle in the cylindrical coordinate system of z axle take direction of beam propagation.The wherein method of computing holography, is used by increasing researcher because its method is simple.It calculates the pattern that produces fork like grating by computer, concrete grammar is: because incident light is Gaussian beam, its phase factor is Ψ
2=exp (ikx), k is space wave vector, so can be by computer target beam Ψ
1with incident beam Ψ
2the interference figure of this two-beam calculates, and just can obtain producing the template of vortex beams, is the pattern of fork like grating.In current research method, or pattern exposure is flushed on transparent film, or transfers in spatial light modulator, but the former complex steps can not be adjusted by electricity; The latter's cost is higher, and resolution is low.Also have people computing holography and the combination of polymer mixed type liquid crystal phase, by spatial light modulator pattern exposure to above-mentioned liquid crystal, under photochemical reaction, realize patterning.But its diffraction efficiency of fork like grating that this method produces is lower, and incident light is had to polarization dependence.
The present invention proposes the orientation control based on liquid crystal, and the fork like grating of preparing by the micro-projection lithography system of DMD of designed, designed has overcome the defect of above-mentioned technology completely.The present invention can change the size of pattern magnitude and fork like grating by the object lens multiple changing in DMD system, thereby can realize the preparation of high-resolution fork like grating.The sample volume of preparing is little, simple in structure, and cost is low, and stability and repeatability all meet real requirement, provides a kind of brand-new convenient simple method for producing vortex beams.
Summary of the invention
The present invention seeks to: propose a kind of preparation of liquid crystal fork like grating and the application in generation light vortex thereof, the fork like grating that preparation simply can electricly be adjusted and light rewrites is realized generation, control and the reconstruct of vortex beams.
Technical scheme of the present invention: liquid crystal fork like grating, in liquid crystal grating, the liquid crystal aligning in adjacent lcd region has different control: the one, TN/PA type, the parallel-oriented microcell of 90 of liquid crystal ° of distortion phase microcells and liquid crystal alternately forms fork like grating; The 2nd, orthogonal PA type, by the optical axis direction of liquid crystal be in the same area even parallel microcell and adjacent area each other orthogonal film micro area alternately form fork like grating; The 3rd, orthogonal HAN type, alternately forms fork like grating by liquid crystal side microcell direction of orientation and mutually orthogonal hybrid orientation microcell.Wherein two and three align incident laser and present polarization without dependency characteristic.
Utilize photo orientated method control liquid crystal microcell orientation, and then the director distribution of control liquid crystal is prepared fork like grating; Graphically liquid crystal microcell is exposed and is orientated by a set of micro-projection lithography system based on numerical control micro mirror battle array DMD and realize, the micro-projection lithography system based on numerical control micro mirror battle array DMD is made up of light source, beam path alignment device, numerical control micro mirror battle array DMD, beam splitter prism, object lens, CCD, polaroid, minute adjustment objective table etc.Ultraviolet after beam path alignment device or blue beam are through the light beam of beam splitter prism beam splitting, uniform irradiation to DMD surface, and the each pixel reflects light of fork like grating figure signal control DMD of numerical control device output liquid crystal microcell is realized the imaging of fork like grating figure; After described light beam is miniature by microcobjective, is projected to through polaroid the surface being placed on objective table and scribbles on light control orientation material agent electro-conductive glass sheet, control exposure dose and complete exposure; The direction of orientation of light control orientation material is determined by induced orientation polarisation of light, is convenient to the accurate control of direction of orientation; Press on electro-conductive glass sheet fork like grating figure to the exposure of liquid crystal microcell after to liquid crystal aligning; The direction of orientation of light control orientation material is that induced orientation polarisation of light determines by exposure.Light control orientation material has erasable characteristic, and orientation is determined by the polarization direction of exposing for the last time, is beneficial to the reconstruct of pattern and the rewriting of vortex beams.Liquid crystal material used can be nematic liquid crystal, dual-frequency liquid crystal or ferroelectric liquid crystals.
Light source ultraviolet or blue beam that especially high pressure mercury arc lamp etc. forms.
Thick will coupling with liquid crystal property and alignment mode of liquid crystal cell, makes the difference of the phase shift of adjacent area to e light and o light be greater than π, and box is thick to be controlled by choosing introns or mylar, to obtain optimized switch ratio, diffraction efficiency and response speed.
Liquid crystal cell is that plate electrode drives up and down, realizes the control of diffraction efficiency by applying the adjusting of electric field, thereby control vortex beams switch state.
With laser illumination liquid crystal fork like grating generation diffraction spot pattern, the non-zero order of diffraction presents vortex beams, and its orbital angular momentum m=nl is the product of the order of diffraction time n and fork like grating topological charge l, and unit is
as shown in Figure 5.
Fork-shaped liquid crystal grating of the present invention can be converted to vortex beams by common gauss laser beam, and due to the erasable property of electro-optical characteristic and the light control orientation material of liquid crystal, and the vortex light of generation can electric-controlled switch and carried out the real-time change of orbital angular momentum; The vortex beams producing is in the application in quantum communication, quantum calculation, particle capture, light tweezer, light motor, astronomical sight field.
Beneficial effect of the present invention: disclose a kind of technology based on the adjustable erasable fork like grating of photo orientated technology control liquid crystal microcell orientation preparation, this fork-shaped liquid crystal grating can be converted to vortex beams by common laser (Gaussian beam), and the vortex light producing possess can electric-controlled switch and change in real time the characteristic of orbital angular momentum.Such device has simple in structure, light energy conversion efficiency is high, can power up adjusting, low-voltage, low energy consumption, can change in real time orbital angular momentum, polarization is without dependence, the features such as multi-wavelength is suitable for, technology implementation cost is low, efficiency is high, be suitable for batch production, and the repeatability of device and stability all meet real requirement.Have a wide range of applications in scientific research technical fields such as quantum communication, quantum calculation, particle capture, light tweezer, light motor, astronomical sights.
(1) utilize DMD system to expose, saved mask manufacture cost, total digitalization operation, flexible.Owing to being projection exposure, the figure deformation of having avoided beam broadening to cause, has improved resolution greatly;
(2) adopt SD1 as light control orientation material, the light of having realized pattern is erasable;
(3) due to the optimal design of liquid crystal cell structure, device architecture is simple, and light energy conversion efficiency is high, and the sample polarization of preparing is without dependence, insensitive to lambda1-wavelength, and high on-off ratio can be realized in electric tune;
(4) service band wide ranges, low-voltage, low energy consumption, preparation scheme simple and effective, cheapness, small and exquisite portable, can be mass, the fork like grating stable performance realizing with liquid crystal, reproducible, indices meets the real requirement in the fields such as quantum communication, quantum calculation, particle capture, light tweezer.
(5) by prepare simply can electricity be adjusted and light rewrites fork like grating realize generation, control and the reconstruct of vortex beams.Open up technology of preparing easy, small and exquisite, cheap, efficient, stable, erasable, that can be mass, realize the preparation without relying on, to the insensitive vortex beams maker of incident wavelength of high-diffraction efficiency, polarization, meet its application needs in fields such as quantum communication, quantum calculation, particle capture, light tweezer, light motor, astronomical sights.
Accompanying drawing explanation
Fig. 1 DMD projection lithography system schematic;
The detection light path schematic diagram of Fig. 2 vortex beams diffraction spot;
Fig. 3 difference is done the fork like grating micrograph of different structure under box mode.(a), (b) be TN/PA type, is (c) orthogonal HAN type, is (d) orthogonal PA type, engineer's scale length is 100 μ m.
The vortex beams diffraction pattern schematic diagram that Fig. 4 receives with blank screen;
The orthogonal HAN type m=1 fork like grating of Fig. 5 (a)-(d) adds the variation of zero level and first-order diffraction spot under electric control; (e) be the fork like grating micrograph of the m=2 after erasable; (f) be the positive first-order diffraction hot spot of (e);
Fig. 6 is the diffraction efficiency curve from the lower orthogonal HAN type m=1 fork like grating of polarization state (b) of different incident lights in different incident wavelengths (a).
Embodiment
Further illustrate the inventive method and application below by embodiment, rather than limit the present invention with these embodiment.Shown in Fig. 1, the liquid crystal cell (sample) 7 of UV light source 1, beam splitter prism 2, DMD3, CCD4, polaroid 5, microcobjective 6, preparation.Be prepared by Fig. 1 system, be specially the photo orientated film of spin coating on ITO electro-conductive glass, be prepared into box and carry out graph exposure by microlithography technology and give fork like grating pattern, the molecules align direction of constraint oriented material, and then the orientation of control liquid crystal, form fork-shaped liquid crystal grating.
This grating of Ear Mucosa Treated by He Ne Laser Irradiation can produce whirlpool light beam by diffraction, and change applies voltage and can regulate and then realize dynamic switch to vortex light intensity.By the light of orientation texture being wiped and figuration again, can generate in real time the vortex beams with different orbital angular momentum values.
1. according to the difference of alignment mode, the type of alignment of liquid crystal cell is as above-mentioned, and the early-stage preparations of liquid crystal cell processed can be divided into three kinds, and preparation method is as follows:
TN/PA type:
(e) clean glass sheet, spin coating light control orientation material SD1, annealing in process forms homogeneous film;
(f) two sheet glass sheets are obtained and carry out initial orientation along glass sheet long side direction with line polarisation uniform exposure;
(g) incident polarization half-twist, carries out fork like grating graph exposure to a slice wherein by DMD micro-lithography system;
(h) on a slice glass sheet, spray space powder or place mylar therein, then two sheet glass sheets being composed to box.
Orthogonal PA type:
First two steps are the same with TN/PA type, and the 3rd step first composes box by two sheet glass sheets, and then incident polarization half-twist carries out fork like grating figuration to liquid crystal cell exposure by DMD system.
Orthogonal HAN type:
(a) clean glass sheet, a slice spin coating SD1, a slice spin coating vertical-tropism agent PI, annealing in process forms homogeneous film;
(b) glass sheet of spin coating SD1 is carried out, as TN/PA type (b)-(c) identical operation of step, the glass sheet of spin coating PI being carried out to friction orientation, frictional direction and edge are all 45 ° of angles.
(c) on a slice glass sheet, spray space powder or place mylar therein, then two sheet glass sheets being composed to box.
2. according to the thick parameter of box of box type processed and drive pattern design optimization liquid crystal cell, choose the introns of appropriate particle diameter, realize the optimum balance between switching rate and diffraction efficiency;
3. ready-made liquid crystal cell is placed on hot platform, more than the cleaning point of liquid crystal, pours into liquid crystal.At polarized light microscopy Microscopic observation, obtain the fork like grating pattern of different orientation structure, as shown in Figure 3.Wherein (a), (b) are TN/PA type, are (c) orthogonal HAN type, are (d) orthogonal PA type.
4. the parts such as LASER Light Source, fork like grating sample, CCD are adjusted, opened light source, with blank screen reception, can see that the diffraction spot of vortex beams distributes, as shown in Figure 4.Can further clearly observe the diffraction pattern of vortex beams with CCD.Liquid crystal cell is powered up, and diffraction efficiency is with change in voltage, thereby realized the control of vortex beams switch state.
5. receive the light intensity of first-order diffraction spot with photo-detector, test it with powering up big or small variation, obtain diffraction efficiency.
6. change the wavelength of incident light source, can obtain its diffraction efficiency curve under different-waveband.
7. change the polarization state of incident light, test its diffraction efficiency under different polarization states incident light irradiates.
8. it is carried out to light and rewrite fork like grating pattern, and survey its electro-optical characteristic.
Embodiment 1:
The present embodiment is the detection that realizes patterning and the vortex beams diffraction pattern of fork like grating on TN type liquid crystal cell.
Numerical control micro mirror battle array etching system consists of: 405 ± 10nm blue-ray LED light source, by beam splitter prism (size 25mm × 25mm), uniform irradiation is a pixel to DMD(1024 × 768, each pixel 13.68 μ m, optimum matching ultraviolet and blue wave band), computing machine is transported to DMD signal input part by CAD software (formation numerical control device) by image control signal; Figure is through microcobjective (lens opening 50mm, focal length 150mm, numerical aperture 0.3, operating distance 34mm, depth of focus 3 μ m, 10 times of enlargement ratios) miniature, before sample stage, sub-wavelength metal wire grid polarizer (diameter 50mm, extinction ratio is greater than 2000:1) is placed at 5cm place; Focusing on monitor component is beam splitter prism, the CCD image device (selecting industrial UV, visible light near infrared imaging CCD) in real-time monitoring system and is connected with terminal by USB; Objective table accurate displacement adjuster bar stroke is 25mm, precision 1 μ m.
Select the ito glass sheet of 14mm × 20mm size, carry out ultrasonic cleaning 30 minutes with acetone or alcohol, and then with twice ultrasonic cleaning of pure water 10 minutes.In 120 ℃ of baking ovens, dry after 40 minutes, carry out UVO and clean 30 minutes to increase wellability and adhesiveness.By azo light oriented material SD1, be spin-coated on glass sheet, spin coating parameter is: low speed spin coating 5 seconds, 800 revs/min of rotating speeds, high speed spin coating 40 seconds, 3000 revs/min of rotating speeds.After spin coating, be placed on hot platform and dry 10 minutes with 100 ℃.
With blue light 405nm LED see through polaroid vertical exposure (5J/cm
2), on two, obtain uniform initial orientation.Then, a slice glass sheet is wherein placed on the focal plane of DMD etching system.Select to need the fork like grating figure of exposure, outputed to DMD surface with computer, and the polarization direction of polaroid is adjusted to vertical with former exposure directions, exposure (5J/cm again
2).The direction of orientation in the region of re-expose will with all the other regions perpendicular.
On a slice glass sheet, evenly spraying diameter is the space powder of 6 μ m therein, then two sheet glass sheets is made to liquid crystal cell, pours into liquid crystal E7 more than cleaning point.Naturally cool to after room temperature, liquid crystal molecule is reorientation, the two identical regions of sheet glass sheet oriented layer direction, and liquid crystal molecule is parallel-oriented (PA orientation); The orthogonal region of oriented layer direction, liquid crystal molecule will be 90 ° of twisted nematics to (TN orientation).Under the observation of vertical polarization sheet, TN region is bright state, and PA region is dark state, thereby realizes the patterning of fork like grating, as shown in Fig. 3 (a), (b).
The Ear Mucosa Treated by He Ne Laser Irradiation liquid crystal cell fork like grating area of the pattern that is 671nm with wavelength, receives diffraction spot with blank screen, obtains vortex beams diffraction spot and distributes, as shown in Figure 4.
Embodiment 2:
The present embodiment is the patterning of realizing fork like grating on orthogonal PA type liquid crystal cell.
Step of exposure is identical with embodiment 1 above, different, first two sheet glass sheets of initial exposure is composed to box, then takes and in DMD system, carry out re-expose fork like grating pattern.The direction of re-expose is vertical with initial exposure direction.The method of doing box and filling liquid crystal is identical with embodiment 1.Under the method, in liquid crystal cell, re-expose region is all parallel PA orientation with re-expose region liquid crystal molecule not, but that both are orientated is mutually orthogonal.The advantage of arranging of this kind of liquid crystal molecule is, the diffraction spot of its generation and diffraction efficiency thereof to incident light polarization without dependence.Be embodied on its micro-image, for re-expose has area of the pattern and do not have area of the pattern color basically identical, as shown in Fig. 3 (d).
Embodiment 3:
The present embodiment is the diffraction efficiency under incident light and the different wave length of different polarization states that realizes the patterning of fork like grating on orthogonal HAN type liquid crystal cell and survey its vortex beams diffraction spot.Change exposing patterns, can realize the erasable characteristic of vortex beams.
Identical to making in the exposure-processed of wherein a slice glass sheet of liquid crystal cell and embodiment 1, to carry out friction orientation processing to another sheet.First the cleaning to glass sheet is identical with embodiment 1, then spin coating PI vertical-tropism agent.It should be noted that before PI vertical-tropism agent uses and need within 3～4 hours, from refrigerator, to take out in advance, after it returns to room temperature, can open and use.Spin coating parameter is low speed spin coating 6 seconds, 300 revs/min of rotating speeds, high speed spin coating 20 seconds, 2000 revs/min of rotating speeds.After spin coating, be placed in baking oven first with 80 ℃ of preliminary dryings 10 minutes, then oven temperature be adjusted to 250 ℃ and dry 1 hour.After having solidified, turn off baking oven, it is cooled to after room temperature naturally, take out glass sheet.Can't quenching, prevent excessive temperature differentials, make glass sheet cracked.Then to glass sheet friction orientation, the right-angle side of frictional direction and glass sheet is angle at 45 ° all, conveniently liquid crystal cell is powered up to rear liquid crystal molecule and arranges towards this direction.Finally make box and fill with liquid crystal, identical in method and embodiment 1.Under the method, a side of spin coating SD1, liquid crystal molecule is arranged along glass sheet surface, but the region of re-expose pattern and do not have the orientation of region liquid crystal molecule of pattern orthogonal; A side of spin coating PI, liquid crystal molecule is along arranging perpendicular to glass sheet surface.In whole liquid crystal cell, the arrangement of liquid crystal molecule is parallel to glass sheet by a side and changes gradually opposite side into perpendicular to glass sheet.The advantage of arranging of this kind of liquid crystal molecule is, the diffraction spot of its generation and diffraction efficiency thereof to incident light polarization without dependence.Be embodied on its micro-image, for re-expose has area of the pattern and do not have area of the pattern color basically identical, as shown in Fig. 3 (c).Be embodied in its diffraction efficiency, for, the incident light that it is carried out to different polarization states irradiates, and can obtain basically identical diffraction efficiency curve, as shown in Fig. 6 (b).And the diffraction efficiency of the vortex beams first-order diffraction spot recording under this method is higher, can reach 37% left and right.Change respectively incident light wavelength to 532nm and 632.8nm, also all can obtain diffraction efficiency up to 37% diffraction efficiency curve, as shown in Fig. 6 (a).This means, we can realize 74% gross energy and focus on the vortex beams of first-order diffraction spot.Sample is exposed again, can obtain inverted m=2 fork like grating structure (Fig. 5 (e)), survey its positive first-order diffraction spot with CCD, can obtain the vortex beams that topological charge number is m=-2 (Fig. 5 (f)).This has shown, if carry out the operation of light tweezer with our sample, we can change angular velocity of rotation and the direction of the particulate that is hunted down simultaneously.
Embodiment 4:
The present embodiment, for to introduce dual-frequency liquid crystal in orthogonal HAN type liquid crystal cell, is realized the quick response of vortex beams switch state.
In order to realize the quick response of liquid crystal fork like grating, in HAN type liquid crystal cell, pour into HEF951800-100 dual-frequency liquid crystal; By the optimization to the thick parameter of box, the box of choosing 5 μ m is thick.Can obtain by test, under 15V/80kHz, the ON state response time is 300 μ s; Under 15V/1kHz, the OFF state response time is 570 μ s.Wherein, the ON state response time is defined as vortex beams by 10% the strongest brightness to 90% required time of the strongest brightness, and the OFF state response time, vice versa.By thick to box in optimization material, realize well the quick response of the sub-millisecond of vortex beams switch state.
Claims (9)
1. liquid crystal fork like grating, is characterized in that the liquid crystal aligning in adjacent lcd region in liquid crystal grating has different control: the one, TN/PA type, and the parallel-oriented microcell of 90 of liquid crystal ° of distortion phase microcells and liquid crystal alternately forms fork like grating; The 2nd, orthogonal PA type, by the optical axis direction of liquid crystal be in the same area even parallel microcell and adjacent area each other orthogonal film micro area alternately form fork like grating; The 3rd, orthogonal HAN type, alternately forms fork like grating by liquid crystal side microcell direction of orientation and mutually orthogonal hybrid orientation microcell.
2. the preparation method of liquid crystal fork like grating, it is characterized in that utilizing photo orientated method control liquid crystal microcell orientation, and then the director distribution of control liquid crystal is prepared liquid crystal fork like grating;
Fork like grating graph exposure and liquid crystal aligning: realized by a set of micro-projection lithography system based on numerical control micro mirror battle array DMD, the micro-projection lithography system based on numerical control micro mirror battle array DMD is made up of light source, beam path alignment device, numerical control micro mirror battle array DMD, beam splitter prism, object lens, CCD, polaroid, minute adjustment objective table; Ultraviolet after beam path alignment device or blue beam are through the light beam of beam splitter prism beam splitting, uniform irradiation to DMD surface, and the each pixel reflects light of numerical control device output liquid crystal fork like grating figure signal control DMD is realized the imaging of the liquid crystal fork like grating figure of liquid crystal microcell; After described light beam is miniature by microcobjective, is projected to through polaroid the surface being placed on objective table and scribbles on light control orientation material agent electro-conductive glass sheet, control exposure dose and complete exposure; The direction of orientation of light control orientation material is determined by induced orientation polarisation of light, is convenient to the accurate control of direction of orientation; Press on electro-conductive glass sheet fork like grating figure to the exposure of liquid crystal microcell after to liquid crystal aligning; The direction of orientation of light control orientation material is that induced orientation polarisation of light determines by exposure; Light control orientation material has erasable characteristic, and orientation is determined by the polarization direction of exposing for the last time, is beneficial to the reconstruct of pattern and the rewriting of vortex beams.
3. the preparation method of liquid crystal fork like grating according to claim 2, is characterized in that liquid crystal material used can be nematic liquid crystal, dual-frequency liquid crystal or ferroelectric liquid crystals.
4. the preparation method of liquid crystal fork like grating according to claim 2, it is characterized in that thick will coupling with liquid crystal property and alignment mode of liquid crystal cell makes the difference of the phase shift of adjacent area to e light and o light be greater than π, box is thick to be controlled by choosing introns or mylar, to obtain optimized switch ratio, diffraction efficiency and response speed; Liquid crystal cell is that plate electrode drives up and down, realizes the control of diffraction efficiency by applying the adjusting of electric field, thereby controls vortex beams switch state.
5. the preparation method of liquid crystal fork like grating according to claim 2, is characterized in that step is as follows,
1) prepare TN/PA type liquid crystal fork like grating:
(a) clean glass sheet, spin coating light control orientation material SD1 on glass sheet, annealing in process forms homogeneous film;
(b) two sheet glass sheets are obtained and carry out initial orientation along glass sheet long side direction with line polarisation uniform exposure;
(c) incident polarization half-twist, carries out liquid crystal fork like grating graph exposure to a slice wherein by DMD micro-lithography system;
(d) on a slice glass sheet, spray space powder or place mylar therein, then two sheet glass sheets being composed to box.
2) prepare orthogonal PA type liquid crystal fork like grating:
(a) and (b) first two steps are the same with TN/PA type; (c) first two sheet glass sheets are composed to box, then incident polarization half-twist, carries out liquid crystal fork like grating figuration to liquid crystal cell exposure by DMD system;
3) prepare orthogonal HAN type liquid crystal fork like grating:
(a) clean glass sheet, a slice spin coating SD1, a slice spin coating vertical-tropism agent PI, annealing in process forms homogeneous film;
(b) glass sheet of spin coating SD1 is carried out as TN/PA type 1) in (b)-(c) identical operation of step, the glass sheet of spin coating PI is carried out to friction orientation, frictional direction and edge are all 45 ° of angles;
(c) on a slice glass sheet, spray space powder or place mylar therein, then two sheet glass sheets being composed to box.
6. the preparation method of liquid crystal fork like grating according to claim 2, it is characterized in that numerical control micro mirror battle array etching system consists of: 405 ± 10nm blue-ray LED light source, by beam splitter prism (size 25mm × 25mm), uniform irradiation is a pixel to DMD(1024 × 768, each pixel 13.68 μ m, optimum matching ultraviolet and blue wave band), computing machine is transported to DMD signal input part by CAD software (formation numerical control device) by image control signal; Figure is through microcobjective (lens opening 50mm, focal length 150mm, numerical aperture 0.3, operating distance 34mm, depth of focus 3 μ m, 10 times of enlargement ratios) miniature, before sample stage, sub-wavelength metal wire grid polarizer (diameter 50mm, extinction ratio is greater than 2000:1) is placed at 5cm place; Focusing on monitor component is beam splitter prism, the CCD image device (selecting industrial UV, visible light near infrared imaging CCD) in real-time monitoring system and is connected with terminal by USB; Objective table accurate displacement adjuster bar stroke is 25mm, precision 1 μ m.
7. the preparation method of liquid crystal fork like grating according to claim 2, is characterized in that selecting ito glass sheet, carries out ultrasonic cleaning 30 minutes with acetone or alcohol, and then with twice ultrasonic cleaning of pure water 10 minutes.In 120 ℃ of baking ovens, dry after 40 minutes, carry out UVO and clean 30 minutes to increase wellability and adhesiveness; By azo light oriented material SD1, be spin-coated on glass sheet, spin coating parameter is: low speed spin coating 5 seconds, 800 revs/min of rotating speeds, high speed spin coating 40 seconds, 3000 revs/min of rotating speeds; After spin coating, be placed on hot platform and dry 10 minutes with 100 ℃.
8. the preparation method of liquid crystal fork like grating according to claim 2, is characterized in that seeing through polaroid vertical exposure (5J/cm with blue light 405nm LED
2), on two, obtain uniform initial orientation; Then, a slice glass sheet is wherein placed on the focal plane of DMD etching system.Select to need the fork like grating figure of exposure, outputed to DMD surface with computer, and the polarization direction of polaroid is adjusted to vertical with former exposure directions, exposure (5J/cm again
2).The direction of orientation in the region of re-expose will with all the other regions perpendicular.
9. the application in generation vortex beams according to the described fork-shaped liquid crystal grating of one of claim 2-8, this fork-shaped liquid crystal grating can be converted to vortex beams by common gauss laser beam, and the vortex light of generation can electric-controlled switch and carried out the real-time change of orbital angular momentum; The vortex beams producing is in quantum communication, quantum calculation, particle capture, light tweezer, light motor, the application of astronomical sight field.
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