Grating polaroid and optimization method and preparation method thereof

Abstract

The invention discloses a grating polaroid and an optimization method and a preparation method thereof.The grating polaroid sequentially comprises a substrate layer, a photoresist layer, a metal film layer, a first dielectric film layer and a second dielectric film layer, the refractive index of the first dielectric film layer is larger than or equal to that of the photoresist layer, and the refractive index of the second dielectric film layer is larger than that of the photoresist layer; the refractive index of the second dielectric film layer is greater than that of the substrate layer, and the metal film layer, the first dielectric film layer and the second dielectric film layer form a multi-layer grating structure. The embodiment of the invention can improve the extinction ratio and the light transmission efficiency, and can be widely applied to the technical field of optical devices.

Description

Technical Field

[0001] The present invention relates to the technical field of optical devices, and in particular to a grating polarizer and an optimization method and a preparation method thereof. Background Art

[0002] The study of the polarization of light in the sky dates back to 1809, when the French natural philosopher Arago first discovered and studied it. Later, it was studied in more detail. The sky polarization pattern can be used both as an indicator of atmospheric turbidity and as a navigation compass. The understanding of these optical properties has always been one of the most interesting and important problems in atmospheric optics. The polarization pattern of the sky conveys rich information about the position of the sun. When natural sunlight enters the Earth's atmosphere, it is scattered by air molecules. The scattered sky light is partially polarized, which means that it is a composite of natural light and linearly polarized components. In a clear sky, the polarization pattern is very regular. If the sky is partially covered with clouds, its polarization pattern is quite complex, because the polarization of the sky light is disturbed by the clouds. Many theoretical and experimental studies of the sky light polarization pattern have been carried out in order to use the sky light polarization to achieve high navigation accuracy or to study atmospheric conditions for the purpose of meteorological services.

[0003] The measurement of PL (Polarized Light) intensity must rely on polarization optical devices, that is, polarizers. The optical performance of polarizers directly affects the measurement accuracy, thereby affecting the accuracy of attitude angle extraction. Therefore, the design and preparation of polarizers are very important for this technology. Existing grating polarizers have problems with low extinction ratio and light transmission efficiency. Summary of the invention

[0004] In view of this, in order to solve one of the above problems, an object of an embodiment of the present invention is to provide a grating polarizer and an optimization method and a preparation method thereof, which can improve the extinction ratio and light transmission efficiency.

[0005] On the one hand, an embodiment of the present invention provides a grating polarizer, which includes a base layer, a photoresist layer, a metal film layer, a first dielectric film layer and a second dielectric film layer in sequence, wherein the refractive index of the first dielectric film layer is greater than or equal to the refractive index of the photoresist layer, the refractive index of the second dielectric film layer is greater than the refractive index of the base layer, and the metal film layer, the first dielectric film layer and the second dielectric film layer form a multilayer grating structure.

[0006] Optionally, the material of the metal film layer includes a metal element or a metal alloy.

[0007] Optionally, the refractive index of the second dielectric film layer is greater than 1.5.

[0008] Optionally, the refractive index of the second dielectric film layer is determined according to the thickness of the substrate layer.

[0009] Optionally, the thickness of the first dielectric film layer is determined according to the average thickness of the photoresist layer.

[0010] On the other hand, an embodiment of the present invention provides a method for optimizing a grating polarizer, comprising:

[0011] Determine a first influencing factor and a second influencing factor of the grating polarizer; the first influencing factor includes any one or more of material composition, structural composition or waveband, and the second influencing factor includes a structural parameter of the grating polarizer;

[0012] The simulation determines the grating polarizer with the best corresponding effects of the first influencing factor and the second influencing factor.

[0013] Optionally, the simulation to determine the grating polarizer with the best corresponding effects of the first influencing factor and the second influencing factor includes:

[0014] Determine the first influencing factor, change the second influencing factor, and determine the local optimal grating polarizer by simulation;

[0015] The first influencing factor and the second influencing factor are changed, and the local optimal grating polarizer is updated according to the simulation result until the simulation is completed, and the local optimal grating polarizer is used as the grating polarizer with the best effect.

[0016] Optionally, the effect of the grating polarizer is determined by the following method:

[0017] Determine the first weight, the second weight and the third weight, and test the transmittance, the extinction ratio and the total energy loss;

[0018] The effect of the grating polarizer is determined according to the first weight and the test transmittance, the second weight and the extinction ratio, and the third weight and the total energy loss.

[0019] On the other hand, an embodiment of the present invention provides a method for preparing a grating polarizer, comprising:

[0020] providing a nanoimprint template and a substrate layer;

[0021] Preparing a photoresist layer on the base layer, and transferring the pattern of the nanoimprint template to the photoresist layer to form a grating structure;

[0022] A metal film layer, a first dielectric film layer and a second dielectric film layer are sequentially prepared on the photoresist layer.

[0023] Optionally, the preparation method further comprises:

[0024] preparing a mask layer in the gaps of the grating structure;

[0025] After the preparation is completed, the mask layer is removed.

[0026] The implementation of the embodiment of the present invention includes the following beneficial effects: In the embodiment, the grating polarizer includes a base layer, a photoresist layer, a metal film layer, a first dielectric film layer and a second dielectric film layer in sequence, the refractive index of the first dielectric film layer is greater than or equal to the refractive index of the photoresist layer, the refractive index of the second dielectric film layer is greater than the refractive index of the base layer, the metal film layer, the first dielectric film layer and the second dielectric film layer form a multilayer grating structure, and by using the multilayer metal grating structure, the extinction ratio and light transmission efficiency are effectively improved, the absorption loss is reduced, and the navigation accuracy is improved. In addition, by changing the first influencing factor and the second influencing factor of the grating polarizer, the grating polarizer with the best effect is determined, the parameters of the grating polarizer are optimized, and the optical performance of the grating polarizer is improved. At the same time, the grating polarizer is prepared by nanoimprinting technology to reduce the preparation cost. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] Figure 1 is a schematic structural diagram of a grating polarizer provided by an embodiment of the present invention;

[0028] Figure 2 is a schematic structural diagram of another grating polarizer provided by an embodiment of the present invention;

[0029] Figure 3 is a schematic structural diagram of another grating polarizer provided by an embodiment of the present invention;

[0030] Figure 4 is a schematic diagram of parameters of a grating polarizer provided by an embodiment of the present invention;

[0031] Figure 5 is a schematic diagram of parameters of another grating polarizer provided by an embodiment of the present invention;

[0032] Figure 6 is a schematic diagram of parameters of another grating polarizer provided by an embodiment of the present invention;

[0033] Figure 7 It is a schematic diagram of the steps of a method for optimizing a grating polarizer provided by an embodiment of the present invention;

[0034] Figure 8 It is a schematic flow chart of the steps of optimizing and verifying a grating polarizer provided by an embodiment of the present invention;

[0035] Fig. 9 It is a schematic flow chart of the steps of a method for preparing a grating polarizer provided by an embodiment of the present invention;

[0036] Fig.10 It is a schematic flow chart of the steps of another method for preparing a grating polarizer provided by an embodiment of the present invention;

[0037] Fig.11 It is a schematic flow chart of the steps of another method for preparing a grating polarizer provided by an embodiment of the present invention;

[0038] Fig.12 The present invention provides a test light path diagram of a grating polarizer. DETAILED DESCRIPTION

[0039] The present invention is further described in detail below in conjunction with the accompanying drawings and specific embodiments. The step numbers in the following embodiments are only provided for the convenience of explanation and description, and the order between the steps is not limited in any way. The execution order of each step in the embodiment can be adaptively adjusted according to the understanding of those skilled in the art.

[0040] An embodiment of the present invention provides a grating polarizer, which includes a base layer, a photoresist layer, a metal film layer, a first dielectric film layer and a second dielectric film layer in sequence, the refractive index of the first dielectric film layer is greater than or equal to the refractive index of the photoresist layer, the refractive index of the second dielectric film layer is greater than the refractive index of the base layer, and the metal film layer, the first dielectric film layer and the second dielectric film layer form a multilayer grating structure.

[0041] See also Figure 1 , Figure 1 A grating polarizer is provided in an embodiment of the present invention, wherein M1 represents a substrate layer, M2 represents a photoresist layer, M3 represents a metal film layer, M4 represents a first dielectric film layer, and M5 represents a second dielectric film layer, wherein the photoresist layer M2 retains a portion of the photoresist in the gap of the grating structure, the refractive index n2 of the photoresist layer M2 is less than the refractive index n1 of the substrate layer M1, the refractive index n4 of the first dielectric film layer M4 is greater than the refractive index n2 of the photoresist layer M2, and the refractive index n5 of the second dielectric film layer M5 is greater than the refractive index n1 of the substrate layer M1.

[0042] See also Figure 2 , Figure 2 Another grating polarizer provided in an embodiment of the present invention, M1 represents a substrate layer, M2 represents a photoresist layer, M3 represents a metal film layer, M4 represents a first dielectric film layer, and M5 represents a second dielectric film layer, wherein the photoresist layer M2 does not retain photoresist in the gaps of the grating structure, the refractive index n2 of the photoresist layer M2 is less than the refractive index n1 of the substrate layer M1, the refractive index n4 of the first dielectric film layer M4 is equal to the refractive index n2 of the photoresist layer M2, and the refractive index n5 of the second dielectric film layer M5 is greater than the refractive index n1 of the substrate layer M1.

[0043] See also Figure 3 , Figure 3Another grating polarizer provided in an embodiment of the present invention, M1 represents a base layer, M2 represents a photoresist layer, M3 represents a metal film layer, M4 represents a first dielectric film layer, and M5 represents a second dielectric film layer, wherein the photoresist layer M2 retains part of the photoresist in the gaps of the grating structure, and the metal film layer M3, the first dielectric film layer M4 and the second dielectric film layer M5 are also retained in the gaps of the grating structure, the refractive index n2 of the photoresist layer M2 is less than the refractive index n1 of the base layer M1, the refractive index n4 of the first dielectric film layer M4 is greater than the refractive index n2 of the photoresist layer M2, and the refractive index n5 of the second dielectric film layer M5 is greater than the refractive index n1 of the base layer M1.

[0044] Optionally, the material of the metal film layer includes a metal element or a metal alloy.

[0045] Specifically, the metal element includes but is not limited to gold, silver, aluminum or copper, and the metal alloy includes but is not limited to gold, silver, aluminum or copper.

[0046] Optionally, the refractive index of the second dielectric film layer is greater than 1.5.

[0047] Optionally, the refractive index of the second dielectric film layer is determined according to the thickness of the substrate layer.

[0048] Specifically, the second dielectric film layer can be selected from various optical thin film materials with a refractive index greater than 1.5. When the thickness of the substrate layer is large, the refractive index n5 of the second dielectric film layer is much greater than 1.5; when the thickness of the substrate layer is small, the refractive index n5 of the second dielectric film layer is much greater than 1.5.

[0049] Optionally, the thickness of the first dielectric film layer is determined according to the average thickness of the photoresist layer.

[0050] Specifically, the first dielectric film can be selected from various optical thin film materials with a refractive index greater than or equal to that of the photoresist layer. When the gaps in the grating structure retain part of the photoresist, the thickness of the first dielectric film layer is approximately equal to the average thickness of the photoresist layer, or the thickness of the first dielectric film layer is slightly less than the average thickness of the photoresist layer. When the gaps in the grating structure do not retain the photoresist, the thickness of the first dielectric film layer is equal to the photoresist layer.

[0051] It should be noted that the photoresist may be a photoresist material with a low refractive index such as PMMA.

[0052] See also Figure 4-6 , w1 / w2 is the duty cycle of the grating structure and w2 is the period of the grating. Figure 4 and Figure 6 In, h 2-t and h 2-b are the total height of the photoresist layer and the height of the bottom layer respectively. The average thickness of the photoresist layer is denoted as h avg ,h avg=(w1 / w2)h 2-t +((w2-w1) / w2)h 2-b , then we have the relationship: h4≈h avg Or h4 is slightly smaller than h avg .exist Figure 5 In order to ensure near perfect symmetry, n4=n2 and h4=h2 are selected. Figure 4-6 In the example, h1 can be selected to be in the range of several hundred nanometers to more than ten micrometers. When h1 is large, n5 is selected to be much larger than 1.5; when h1 is small, n5 is selected to be slightly larger than 1.5.

[0053] See also Figure 7 , an embodiment of the present invention provides a method for optimizing a grating polarizer, comprising:

[0054] S110, determining a first influencing factor and a second influencing factor of the grating polarizer; the first influencing factor includes any one or more of material composition, structural composition or wavelength band, and the second influencing factor includes a structural parameter of the grating polarizer;

[0055] S120, determining by simulation the grating polarizer having the best corresponding effects of the first influencing factor and the second influencing factor.

[0056] It should be noted that the light wave solution algorithm used in the simulation of the embodiment of the present invention is the Fourier modal method (FMM, also called rigorous coupled wave analysis (RCWA)). The structure of the grating polarizer includes Figure 1-3 The structure includes a blue light band or a near infrared band. The structural parameters of the grating polarizer include but are not limited to 8 parameters such as the period of the grating structure, the groove depth, the duty ratio, and the thickness of each layer.

[0057] Specifically, first, the first influencing factor and the second influencing factor of the grating polarizer are determined, then, the first influencing factor and the second influencing factor are changed in turn, and the corresponding effects are determined by simulation, and finally, the grating polarizer with the best effect is determined according to multiple simulation results.

[0058] Optionally, simulating and determining the grating polarizer with the best corresponding effects of the first influencing factor and the second influencing factor includes:

[0059] S121, determining a first influencing factor, changing a second influencing factor, and determining a local optimal grating polarizer by simulation;

[0060] S122, changing the first influencing factor and the second influencing factor, and updating the local optimal grating polarizer according to the simulation result until the simulation is completed, and using the local optimal grating polarizer as the grating polarizer with the best effect.

[0061] Specifically, first, determine the specific value of the first influencing factor, change the second influencing factor, and simulate to determine the local optimal grating polarizer corresponding to the second influencing factor corresponding to a certain first influencing factor. Then, change the specific value of the first influencing factor and change the second influencing factor at the same time, and simulate to determine the local optimal grating polarizer corresponding to the second influencing factor corresponding to other first influencing factors. At the same time, update the local optimal grating polarizer with a better effect, until all the first influencing factors and the second influencing factors are simulated, and use the local optimal grating polarizer as the grating polarizer with the best effect.

[0062] Optionally, the effect of the grating polarizer is determined by:

[0063] S123, determining a first weight, a second weight, and a third weight, and testing transmittance, extinction ratio, and total energy loss;

[0064] S124, determining the effect of the grating polarizer according to the first weight and the test transmittance, the second weight and the extinction ratio, and the third weight and the total energy loss.

[0065] It should be noted that the specific values ​​of the first weight, the second weight and the third weight are determined according to the actual application, and this embodiment does not impose any specific restrictions. The principle of optimizing the index is that the greater the transmittance, the greater the extinction ratio, and the smaller the total energy loss, the greater the value of the index. The first weight and the second weight are positive values, and the third weight is a negative value.

[0066] The sum of the values ​​is calculated based on the first weight and the test transmittance, the second weight and the extinction ratio, and the third weight and the total energy loss. The grating polarizer with the largest sum of the values ​​is determined to have the best effect.

[0067] See also Figure 8 In a specific embodiment, a group of material compositions, structural compositions or bands in the first influencing factor is determined, and one of the eight parameters in the second factor is changed each time, and the parameter is optimized using simulation software. Finally, the eight optimal parameters are combined to obtain a local optimal solution as the optimization result. Then, the material groups are changed to the second and third groups respectively, and the optimization is completed in turn, and the best one of the three optimization results is selected as the final optimization result of the structure. Then, the structural composition is changed to another one, and the cyclic optimization process is continued. Finally, the better one of the three structures is determined as the final selected structure of the band. For the optimization of other bands, the band is changed and the above process is repeated. In this way, the optimal structure of each band can be obtained, so as to carry out processing and testing.

[0068] It should be noted that when optimizing, attention should be paid to the size of all surface parameters (especially w1 and w2) in combination with the actual process processing level. If the calculated optimal value is too small or too large and cannot be processed, it is necessary to discard the value and readjust this / these parameters to a better value that can be processed.

[0069] An embodiment of the present invention provides a method for preparing a grating polarizer, comprising:

[0070] S210, providing a nanoimprint template and a base layer;

[0071] S220, preparing a photoresist layer on the base layer, and transferring the pattern of the nanoimprint template to the photoresist layer to form a grating structure;

[0072] S230, sequentially preparing a metal film layer, a first dielectric film layer, and a second dielectric film layer on the photoresist layer.

[0073] It should be noted that the nanoimprint template is determined according to the grating structure of the grating polarizer, and the photoresist layer can be prepared by spin coating or the like. The pattern of the nanoimprint template is transferred to the photoresist layer by imprinting technology to form a grating structure. The metal film layer, the first dielectric film layer and the second dielectric film layer are prepared by evaporation or magnetron sputtering or the like.

[0074] Optionally, the preparation method further comprises:

[0075] preparing a mask layer in the gaps of the grating structure;

[0076] After the preparation is completed, the mask layer is removed.

[0077] Specifically, before preparing the metal film layer, the first dielectric film layer and the second dielectric film layer on the photoresist layer, a mask layer is prepared in the gaps of the grating structure; after preparing the metal film layer, the first dielectric film layer and the second dielectric film layer on the photoresist layer, the mask layer is removed, and the metal film layer, the first dielectric film layer and the second dielectric film layer on the gaps of the grating structure are removed at the same time.

[0078] See also Figure 9-11 , showing the processing flow chart of three structures. Fig. 9 In the method, the invention relates to a method for preparing a nanostructured film of an IPS polymer layer. The method comprises the following steps: (1) using thermal nanoimprinting to transfer the pattern to the IPS polymer layer N1 using a high-temperature Ni template; (2) demolding to obtain an IPS nanoimprinting template; (3) preparing a glass substrate; (4) spin coating a layer of photoresist P2 on the glass substrate; (5) transferring the pattern of the IPS mold to the photoresist layer using ultraviolet nanoimprinting; (6) covering the gaps in the grating structure with a mask and evaporating (P4) a metal film, a first dielectric film and a second dielectric film to form a multilayer metal grating structure; and (7) removing the mask. Fig.10 The process shown is Fig. 9 The structure is basically the same, except that the photoresist layer obtained in step (5) does not contain a complete bottom film layer; the structure is prepared using an IPS template with a large groove depth, and Fig. 9 The structure in step (5) is prepared using an IPS template with a small groove depth. Fig.11 and Fig. 9 The process is basically the same as that of step (5), except that there is no need to add or remove the mask. The final sample can be obtained by directly evaporating the metal film, the first dielectric film and the second dielectric film on the structure in step (5).

[0079] It should be noted that the preparation method of the mask is as follows: On a relatively hard rectangular material, hollow out long strips of holes that are periodically distributed. The length of these holes is equal to the overall width of the entire grating sample, and the width is slightly larger than w1. The width of a periodic structure of the mask is equal to w2. The length of the entire mask is greater than the overall length of the entire grating sample, and the width of the entire mask is greater than the overall width of the entire grating sample. Align this mask and put it on the grating to be processed to expose each spine of the grating.

[0080] After the grating sample is prepared, it is necessary to build an optical path for testing. Fig.12 The optical path diagram of the measured polarizer is shown. The transmittance of the prepared polarizer is measured using a Fourier transform spectrometer. Before the measurement begins, the sample to be tested is not placed first. The light perpendicular to the sample surface is incident on the reference polarizer (extinction ratio>20dB). The polarizer converts the light emitted by the light source into linear polarized light and directly incidents on the detector. At this time, the light intensity is recorded as 1. The grating to be tested is installed behind the light bar. First, ensure that the direction of the grating line of the test is perpendicular to the polarization direction of the incident light (that is, the transmission axis of the polarizer is parallel to the polarization direction of the incident light). Then rotate the sample to observe the changing light intensity on the detector, and record the angle of rotation of the polarizer corresponding to the maximum light intensity and the minimum light intensity. Parameters such as TM transmittance, extinction ratio and energy loss can be calculated.

[0081] After the high-performance gratings of each band have passed the test, they are arranged according to the requirements of the attitude angle algorithm for the azimuth angle of the transmission axis of the measurement channel to obtain a composite band polarization array. Installing the array into a customized camera, the PL intensity map can be collected for the study of the attitude angle algorithm. The composite band array can also be used to study the relationship between the optimal detection band and climate conditions.

[0082] The implementation of the embodiment of the present invention includes the following beneficial effects: In the embodiment, the grating polarizer includes a base layer, a photoresist layer, a metal film layer, a first dielectric film layer and a second dielectric film layer in sequence, the refractive index of the first dielectric film layer is greater than or equal to the refractive index of the photoresist layer, the refractive index of the second dielectric film layer is greater than the refractive index of the base layer, the metal film layer, the first dielectric film layer and the second dielectric film layer form a multilayer grating structure, and by using the multilayer metal grating structure, the extinction ratio and light transmission efficiency are effectively improved, the absorption loss is reduced, and the navigation accuracy is improved. In addition, by changing the first influencing factor and the second influencing factor of the grating polarizer, the grating polarizer with the best effect is determined, the parameters of the grating polarizer are optimized, and the optical performance of the grating polarizer is improved. At the same time, the grating polarizer is prepared by nanoimprinting technology to reduce the preparation cost.

[0083] The above is a specific description of the preferred implementation of the present invention, but the invention is not limited to the embodiments. Those skilled in the art may make various equivalent modifications or substitutions without violating the spirit of the present invention. These equivalent modifications or substitutions are all included in the scope defined by the claims of this application.

Claims

1. A grating polarizer, characterized in that: The invention comprises a base layer, a photoresist layer, a metal film layer, a first dielectric film layer and a second dielectric film layer in sequence, wherein the refractive index of the first dielectric film layer is greater than or equal to the refractive index of the photoresist layer, the refractive index of the second dielectric film layer is greater than the refractive index of the base layer, and the metal film layer, the first dielectric film layer and the second dielectric film layer form a multilayer grating structure.

2. The grating polarizer according to claim 1, characterized in that: The material of the metal film layer includes a single metal or a metal alloy.

3. The grating polarizer according to claim 1, characterized in that: The refractive index of the second dielectric film layer is greater than 1.

5.

4. The grating polarizer according to claim 1, characterized in that: The refractive index of the second dielectric film layer is determined according to the thickness of the substrate layer.

5. The grating polarizer according to claim 1, characterized in that: The thickness of the first dielectric film layer is determined according to the average thickness of the photoresist layer.

6. A method for optimizing a grating polarizer, characterized in that: include: Determine a first influencing factor and a second influencing factor of the grating polarizer; the first influencing factor includes any one or more of material composition, structural composition or waveband, and the second influencing factor includes a structural parameter of the grating polarizer; The simulation determines the grating polarizer with the best corresponding effects of the first influencing factor and the second influencing factor.

7. The optimization method according to claim 6, characterized in that: The simulation determines the grating polarizer with the best corresponding effects of the first influencing factor and the second influencing factor, including: Determine the first influencing factor, change the second influencing factor, and determine the local optimal grating polarizer by simulation; The first influencing factor and the second influencing factor are changed, and the local optimal grating polarizer is updated according to the simulation result until the simulation is completed, and the local optimal grating polarizer is used as the grating polarizer with the best effect.

8. The optimization method according to claim 6, characterized in that: The effect of the grating polarizer was determined by the following method: Determine the first weight, the second weight and the third weight, and test the transmittance, the extinction ratio and the total energy loss; The effect of the grating polarizer is determined according to the first weight and the test transmittance, the second weight and the extinction ratio, and the third weight and the total energy loss.

9. A method for preparing a grating polarizer, characterized in that: include: providing a nanoimprint template and a substrate layer; Preparing a photoresist layer on the base layer, and transferring the pattern of the nanoimprint template to the photoresist layer to form a grating structure; A metal film layer, a first dielectric film layer and a second dielectric film layer are sequentially prepared on the photoresist layer.

10. The preparation method according to claim 9, characterized in that: The preparation method further comprises: preparing a mask layer in the gaps of the grating structure; After the preparation is completed, the mask layer is removed.

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