2n+1 layer vortex wave plate achromatic component and preparation method thereof

Abstract

The application relates to the technical field of optical components, and discloses an achromatic assembly based on 2N+1 layers of vortex wave plates and a preparation method thereof, so as to improve the preparation efficiency and ensure the achromatic performance of multiple wavelengths. The assembly comprises 2N+1 layers of vortex wave plates which are aligned with central singular points and are bonded by adhesive, the retardation of each layer of vortex wave plates is the same, the fast axis directions of the N+1+M layer of vortex wave plates and the N+1-M layer of vortex wave plates are parallel, the fast axis included angle between single-direction adjacent vortex wave plates is unique in the upward direction of the middle N+1 layer and the downward direction of the middle N+1 layer, and N and M are positive integers, and N is greater than M.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of optical components, in particular to a 2N+1 layer vortex wave plate achromatic assembly and a preparation method thereof. BACKGROUND

[0002] The vortex wave plate is made of liquid crystal polymer material (LCP) with birefringence characteristics. The arrangement structure of the liquid crystal polymer can be controlled by using the micron-level laser direct writing technology, so as to convert the incident light of different polarization states into a vector polarized light beam or a vortex light beam with orbital angular momentum. Moreover, the device can convert the light intensity distribution of the standard TEM00 mode Gaussian light into the light intensity distribution of the "hollow hole type" Laguerre-Gaussian beam. Based on the above characteristics, the vortex wave plate has been successfully applied in the fields of quantum optics, optical field regulation, atmospheric optical communication, super-resolution imaging, optical tweezers, precision laser processing and the like.

[0003] The conventional vortex wave plate is usually a single-wavelength device due to the phase delay amount, and the transmittance difference of different wavelengths is large. How to solve the multi-wavelength multiplexing problem and achromatism of the vortex wave plate becomes a key problem to be solved. SUMMARY

[0004] The present application aims to disclose a 2N+1 layer vortex wave plate achromatic assembly and a preparation method thereof, so as to improve the preparation efficiency and ensure the achromatic performance of multiple wavelengths.

[0005] To achieve the above-mentioned purpose, the present application discloses a 2N+1 layer vortex wave plate achromatic assembly, comprising:

[0006] 2N+1 layer vortex wave plates aligned with the central singular point and bonded with adhesive, the retardation of each layer of vortex wave plates being the same; the fast axis direction of the N+1+M layer vortex wave plate is parallel to the fast axis direction of the N+1-M layer vortex wave plate; and the fast axis included angle between the single-direction adjacent vortex wave plates in the upward direction of the middle N+1 layer and the downward direction of the middle N+1 layer is unique; wherein N and M are positive integers, and N is greater than M.

[0007] Preferably, the present application takes the N+1 layer as the symmetry axis, and the change direction and angle size of the fast axis included angle between the adjacent two vortex wave plates are symmetrically distributed in the "> " type.

[0008] Preferably, the change region of the fast axis included angle between the single-direction adjacent vortex wave plates is in the order from large to small or from small to large.

[0009] To achieve the above-mentioned purpose, the present application further discloses a preparation process of a 2N+1 layer vortex wave plate achromatic assembly, comprising:

[0010] Obtaining a target achromatic wave band and a central wavelength;

[0011] With the fast axis direction of the N+1+Mth vortex wave plate parallel to the fast axis direction of the N+1-Mth vortex wave plate, the fast axis angle between the adjacent vortex wave plates in the upward direction of the middle N+1th vortex wave plate and the downward direction of the middle N+1th vortex wave plate is uniquely designed at least two arrangement schemes of the fast axis angle between the adjacent vortex wave plates, and then the 2N+1th vortex wave plate with the same retardation is prepared into a achromatic assembly sample with the center singularity aligned with the design scheme number by using the adhesive bonding process.

[0012] During the design, the vortex wave plate achromatic assembly to be tested is placed between the two parallel polarizers, and the transmittance under different wave bands is calculated according to the Jones matrix; during the test, the vortex wave plate achromatic assembly is placed between the two orthogonal polarizers, and the transmission image is taken by the camera, and the fringe contrast of different images is calculated.

[0013] The fast axis angle design scheme corresponding to the achromatic assembly sample meeting the achromatic requirements in terms of the fringe contrast and the transmittance of each wave band is screened out for batch production.

[0014] The present application has the following beneficial effects:

[0015] The phase retardation of each layer of vortex wave plate is the same, the overall performance of the achromatic assembly can be roughly predicted according to the angle between the adjacent vortex wave plates and the Jones matrix, then the scheme meeting the achromatic requirements can be screened out by preparing the sample and actually measuring the fringe visibility under the orthogonal polarizers for batch production, so that the preparation efficiency is improved and the achromatic performance of multiple wavelengths is ensured.

[0016] The present application will be further described in detail below with reference to the accompanying drawings. BRIEF DESCRIPTION OF DRAWINGS

[0017] The accompanying drawings, which form a part of this application, are included to provide a further understanding of the application, and are incorporated herein for explanation by reference. In the drawings:

[0018] Figure 1 is a schematic view of the achromatic assembly disclosed in the embodiment of the present application.

[0019] Figure 2 is a comparison schematic view of the transmission effect corresponding to the achromatic assembly disclosed in the embodiment of the present application and two single-wavelength vortex wave plates in each wave band.

[0020] Figures 3 to 5 is Figure 2 is a comparison schematic view of the visibility curves corresponding to the three products respectively. DETAILED DESCRIPTION

[0021] The embodiments of the present invention will be described in detail below with reference to the accompanying drawings, but the present invention can be implemented in many different ways as defined and covered by the claims.

[0022] Example 1

[0023] This embodiment discloses an achromatic component, comprising: 2N+1 layers of vortex waveplates aligned at their center and bonded together with adhesive, each layer having the same delay; the fast axis directions of the N+1+Mth and N+1-Mth vortex waveplates being parallel; and the fast axis angle between adjacent vortex waveplates in the upward direction and downward direction of the middle N+1th layer being unique in a single direction; wherein N and M are positive integers, with N being greater than M.

[0024] For example, if the achromatic component uses a composite structure of 3-layer vortex waveplates, then the fast axis direction of the first vortex waveplate is parallel to the fast axis direction of the third vortex waveplate, and the fast axis direction of the second vortex waveplate is at an angle to the fast axis directions of the first and third vortex waveplates. Similarly, if a composite structure of 5-layer vortex waveplates is used, then the fast axis direction of the first vortex waveplate is parallel to the fast axis direction of the fifth vortex waveplate, the fast axis direction of the second vortex waveplate is parallel to the fast axis direction of the fourth vortex waveplate, the fast axis direction of the third vortex waveplate is at an angle theta2 to the fast axis directions of the second and fourth vortex waveplates, and the fast axis direction of the first vortex waveplate is at an angle theta1 to the fast axis direction of the second vortex waveplate, where theta1 ≠ theta2.

[0025] In this embodiment, preferably, with the N+1th layer as the axis of symmetry, the direction and magnitude of the change in the fast axis angle between two adjacent vortex waveplates are symmetrically distributed in a ">" shape, that is, the trend of the fast axis change progresses and reverses in a symmetrical ">" shape. Furthermore, the regions of change in the fast axis angle between adjacent vortex waveplates in one direction are arranged in order from large to small or from small to large.

[0026] like Figure 1 As shown, taking a three-layer m=1 order vortex half-wave plate (A-film range) as an example, the retardation of each vortex waveplate layer is the same (e.g., λ / 2@495nm), but the fast axis angle of each layer is different. The fast axis directions of the first layer 1 and the third layer 3 are consistent, while the fast axis directions of the second layer 2 and the first layer are set at an angle (e.g., 57°). Ultimately, the retardation error of the achromatic assembly is controlled within λ / 30. The fast axis direction error of the emitted light is within 10° (theoretical 10°, actual 12°). When the three-layer vortex waveplate assembly is placed under a polarizing microscope, it can be observed that the size of the central aperture remains basically consistent across different layers (measured <50µm).

[0027] Furthermore, to increase the incident angle range (~±15°), the first and third LCP layers are oriented in opposite directions, and the second glass layer is thinner (approximately ~0.3mm).

[0028] In the bonding method of the achromatic component composed of the above three layers of vortex waveplates, the alignment of the central singularity and the 0° fast axis is involved. All three vortex waveplates have cut edges, which are aligned to the 0° position of the fast axis during processing. An online alignment device (such as a polarizing microscope) can be used to place and fix the first layer of vortex waveplate on the sample stage, then place the second layer of vortex waveplate in. Adjust the central singularity (center point on the camera) and angle (according to the cut edge) of the second layer to align with the first layer. The specific alignment process can be as follows: Based on the image under the polarizing microscope, first adjust until the extinction axis coincides, then shift the second vortex waveplate left and right until the central singularity is aligned. At this point, the first and second vortex waveplates are aligned; then place the third vortex waveplate (note the front and back: refer to...). Figure 1 The first LCP (liquid crystal polymer) plated surface is aligned with the third LCP plated surface (i.e., flipped and rotated 180°). Following the steps for the second plate, the third vortex wave plate is aligned. The second vortex wave plate is rotated by 114° (vortex wave plate rotation of 2°, fast axis azimuth angle of 1°, Φ=m*φ / 2+θ, where m is the order of the vortex wave plate, Φ is the fast axis direction at a specific position on the vortex wave plate, φ is the angle between the radial direction at the specific position and the zero-degree line, and θ is the fast axis direction at the zero-degree line). Adhesive is applied, the components are bonded, and light is used for curing. The entire assembly is then placed in a UV light box for 2 hours of curing. The bonded achromatic component is flipped over and placed in the UV light box for another 2 hours of curing. The achromatic component is then removed to obtain the finished product.

[0029] Taking a three-layer m=1 order vortex half-wave plate (A-film range) as an example, its optical axis direction satisfies Φ=m*φ / 2+θ. Each vortex half-wave plate has the same retardation (e.g., λ / 2@495nm), but the 0° fast axis alignment angle between the first and second layers is different. Figure 1 The thick lines and small arrows indicate that the fast axis angle of the vortex waveplate varies continuously within the range of 0 to 180°. The 0° fast axis angle is the same for the first and third layers. Based on the Jones matrix calculations, the fast axis directions of the second and first layers are set at an angle (e.g., 57°). Specifically, the single-layer vortex waveplate structure is as follows:

[0030] The first layer consists of an antireflective coating, a glass substrate, an alignment layer, and an LCP film.

[0031] The second layer consists of a substrate, an orientation layer, and an LCP film.

[0032] The third layer consists of an LCP membrane, an orientation layer, a substrate, and an antireflective membrane.

[0033] Example 2

[0034] Corresponding to the above-mentioned embodiments, the present embodiments disclose a preparation process of a 2N+1 layer vortex wave plate achromatic assembly, comprising the following steps:

[0035] Step S1, obtaining a target achromatic waveband and a central wavelength.

[0036] Step S2, in the fast axis direction parallel to the N+1+M layer vortex wave plate and the N+1-M layer vortex wave plate, the fast axis angle between the adjacent vortex wave plates in the upward direction of the middle N+1 layer and the downward direction of the middle N+1 layer is uniquely designed, and then 2N+1 layer vortex wave plates with the same retardation are prepared by using the adhesive bonding process to prepare the achromatic assembly samples with the same number of design schemes and the central singularity alignment.

[0037] Step S3, in the design, the vortex wave plate achromatic assembly to be tested is placed between two parallel polarizers, and the transmittance under different wavebands is calculated according to the Jones matrix; in the test, the vortex wave plate achromatic assembly is placed between two orthogonal polarizers, and the transmittance image is taken by a camera, and the fringe contrast of different images is calculated.

[0038] Step S4, screening out the fast axis angle design scheme corresponding to the achromatic assembly sample which meets the achromatic requirements of the fringe contrast and the transmittance of each waveband for batch preparation.

[0039] Therefore, for the three-layer vortex wave plate bonded achromatic assembly in the above-mentioned embodiments, the corresponding angle design idea can be decomposed as follows:

[0040] 1, input the target achromatic waveband and the central wavelength, such as 495 nm.

[0041] 2, consider that the retardation of each wavelength is consistent, such as λ / 2@495 nm.

[0042] 3, consider that the fast axis directions of the first and third wave plates are consistent, and the second wave plate forms a certain angle Theta with the first wave plate.

[0043] 4, in the design waveband, take a point every 50 nm in the radial direction to calculate the transmittance, so as to speed up the program running speed.

[0044] 5, place the wave plate group between two parallel polarizers, generally, the ideal achromatic assembly has a minimum point of light intensity transmitted through the analyzer in the achromatic range, and the variable combination which is obviously unreasonable for the transmitted light intensity is removed, so as to speed up the program running speed.

[0045] 6, store the angle Theta corresponding to the minimum transmittance. The smaller the transmittance is, the more consistent the retardation is under the wide spectrum.

[0046] 7. The formula of the Jones matrix of the vortex wave plate achromatic component is solved to obtain the curves of the retardation and the fast axis angle and the wavelength.

[0047] Figure 2 For the orthogonally polarized pictures actually measured at different wavelengths (different light beams), VR1-532 and VR1-633 are first-order single-wavelength (532 nm and 633 nm) vortex wave plates, and AVR1-VIS-A is a first-order achromatic component (i.e., the achromatic component composed of the three-layer vortex wave plates in the above embodiment 1). The visibility curves corresponding to the achromatic effects of the vortex wave plates in the respective wavelength bands are shown in FIGS. 8, 9 and 10, respectively, where the abscissa is the pixel, and the ordinate is the visibility V of the extinction axis. Figure 3 Figure 4 Figure 5

[0048] In the process of calculating the visibility, the supporting program processing includes:

[0049] The center of the circle (0-pixel) is calibrated, the gray values of all the pixel points on the same radius are processed on different pixels away from the center, and the visibility V is calculated: V = (Imax-Imin) / (Imax+Imin), where Imax and Imin are the maximum and minimum gray values, respectively. It can be obviously seen that the PV value of the visibility V of the achromatic component at different wavelengths (different colors of incident light) is relatively smaller than the PV value of the visibility V of the single-point 532 nm and 633 nm, which proves that the achromatic effect is obvious.

[0050] The principle of the embodiment can be considered as follows: the liquid crystal polymer itself is a single-wavelength device, and the refractive index of the liquid crystal polymer changes (and the change range is large) corresponding to different wavelengths. The present application uses multiple layers of LCP, sets the retardation to be the same, and then sets the included angle of the 0° fast axis to be different, to realize that the overall refractive index changes little for light of different wavelengths; that is, the retardation changes little for light of different wavelengths.

[0051] In summary, the 2N+1-layer vortex wave plate achromatic component and the preparation method thereof disclosed in the embodiments of the present application have the same phase retardation of each layer of vortex wave plate, the overall performance of the achromatic component can be roughly predicted according to the included angle between adjacent vortex wave plates and the Jones matrix, then the scheme meeting the achromatic requirement can be screened out by preparing a sample and actually measuring the fringe visibility under the orthogonally polarized piece to carry out batch production, so that the preparation efficiency is improved and the achromatic performance for multiple wavelengths is ensured.

[0052] ​​​The above merely provides the preferred embodiments of the present application, and is not used to limit the present application. For those skilled in the art, the present application can have various modifications and changes. Any modifications, equivalent replacements, improvements, etc. made within the principles and technical scope of the present application shall fall into the scope of the present application.

Claims

1. A 2N+1 layer vortex waveplate based achromatic component, characterized in that, The application relates to a center singularity alignment type 2N+1-layered vortex wave plate which is bonded by adhesion, wherein the retardation of each layer of vortex wave plates is the same; the fast axis direction of the N+1+M layer of vortex wave plates is parallel to the fast axis direction of the N+1-M layer of vortex wave plates; and the fast axis included angle between single-direction adjacent vortex wave plates in the upward direction of the middle N+1 layer and the downward direction of the middle N+1 layer is unique; wherein N and M are positive integers, and N is greater than M. The fast axis included angle between adjacent vortex wave plates is symmetrically distributed in a "> " type with the N+1 layer as a symmetric axis.

2. The 2N+1 layer vortex waveplate achromatic component of claim 1, wherein, The fast axis included angle between single-direction adjacent vortex wave plates is arranged in descending or ascending order.

3. The 2N+1 layer vortex waveplate apochromatic component of claim 2, wherein, Each layer of vortex wave plates is provided with a glass substrate, an orientation layer and an LCP film.

4. The 2N+1 layer based achromatic vortex plate assembly according to any one of claims 1 to 3, characterized in that An anti-reflection film is arranged on the top surface of the uppermost vortex wave plate and the bottom surface of the lowermost vortex wave plate.

5. The 2N+1 layer vortex waveplate apochromatic component of claim 4, wherein, The application relates to a center singularity alignment type 2N+1-layered vortex wave plate which is bonded by adhesion, wherein the retardation of each layer of vortex wave plates is the same; the fast axis direction of the N+1+M layer of vortex wave plates is parallel to the fast axis direction of the N+1-M layer of vortex wave plates; and the fast axis included angle between single-direction adjacent vortex wave plates in the upward direction of the middle N+1 layer and the downward direction of the middle N+1 layer is unique; wherein N and M are positive integers, and N is greater than M.

6. A process for the preparation of an achromatic assembly based on 2N+1 layers of vortex waveplates, characterized in that, The fast axis included angle between adjacent vortex wave plates is symmetrically distributed in a "> " type with the N+1 layer as a symmetric axis. The fast axis included angle between single-direction adjacent vortex wave plates is arranged in descending or ascending order. Each layer of vortex wave plates is provided with a glass substrate, an orientation layer and an LCP film. An anti-reflection film is arranged on the top surface of the uppermost vortex wave plate and the bottom surface of the lowermost vortex wave plate. The application relates to a center singularity alignment type 2N+1-layered vortex wave plate which is bonded by adhesion, wherein the retardation of each layer of vortex wave plates is the same; the fast axis direction of the N+1+M layer of vortex wave plates is parallel to the fast axis direction of the N+1-M layer of vortex wave plates; and the fast axis included angle between single-direction adjacent vortex wave plates in the upward direction of the middle N+1 layer and the downward direction of the middle N+1 layer is unique; wherein N and M are positive integers, and N is greater than M.

7. The process for making a 2N+1 layer vortex waveplate achromatic component based on claim 6, wherein, The fast axis included angle between adjacent vortex wave plates is symmetrically distributed in a "> " type with the N+1 layer as a symmetric axis.

8. The process for making a 2N+1 layer vortex waveplate achromatic component based on claim 7, wherein, The fast axis included angle between single-direction adjacent vortex wave plates is arranged in descending or ascending order. Each layer of vortex wave plates is provided with a glass substrate, an orientation layer and an LCP film. An anti-reflection film is arranged on the top surface of the uppermost vortex wave plate and the bottom surface of the lowermost vortex wave plate.

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