Optical grating polarizer and optimization method and manufacturing method thereof

Abstract

The application discloses a grating polarizer and an optimization method and a preparation method thereof. The grating polarizer comprises a substrate 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 substrate layer. The metal film layer, the first dielectric film layer and the second dielectric film layer form a multilayer grating structure. The embodiment of the application 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] This invention relates to the field of optical device technology, and in particular to a grating polarizer and its optimization and fabrication methods. Background Technology

[0002] The study of the polarization of light in the sky can be traced back to 1809, when the French natural philosopher Arago first discovered and studied it. Later, more detailed research was conducted. Sky polarization patterns can be used as indicators of atmospheric turbidity and as navigation compasses. Understanding these optical properties has always been one of the most interesting and important problems in atmospheric optics. The polarization patterns of the sky convey rich information about the sun's position. When natural sunlight enters the Earth's atmosphere, it is scattered by air molecules. The scattered skylight is partially polarized, meaning it is a complex of natural light and linearly polarized components. In a clear sky, the polarization pattern is very regular. If the sky is partially covered by clouds, its polarization pattern becomes quite complex because the polarization of skylight rays is interfered with by the clouds. Many theoretical and experimental studies have been conducted on skylight polarization patterns to utilize skylight polarization for high navigation accuracy or to study atmospheric conditions for meteorological services.

[0003] Measuring the intensity of PL (Polarized Light) light requires polarizing optical devices, specifically polarizers. The optical performance of the polarizer directly affects the measurement accuracy, and thus the accuracy of attitude angle extraction. Therefore, the design and fabrication of polarizers are crucial for this technology. Existing grating polarizers suffer from insufficient extinction ratio and light transmission efficiency. Summary of the Invention

[0004] In view of this, in order to solve one of the above problems, the purpose of this invention is to provide a grating polarizer and its optimization and preparation methods, which can improve the extinction ratio and light transmission efficiency.

[0005] On one hand, embodiments of the present invention provide a grating polarizer, which sequentially includes 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 greater than or equal to the refractive index of the photoresist layer, and the refractive index of the second dielectric film layer is greater than the refractive index of the substrate layer. 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 an elemental metal or a metal alloy.

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

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

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

[0010] On the other hand, embodiments of the present invention provide an optimization method for a grating polarizer, comprising:

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

[0012] Simulations were used to determine the grating polarizer that best performs for the first and second influencing factors.

[0013] Optionally, the simulation determines the grating polarizer with the best effect corresponding to the first influencing factor and the second influencing factor, including:

[0014] The first influencing factor is determined, the second influencing factor is changed, and the local optimal grating polarizer is determined by simulation.

[0015] The first and second influencing factors are changed, and the locally optimal grating polarizer is updated according to the simulation results until the simulation is completed. The locally optimal grating polarizer is then 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, second, and third weights, and test transmittance, extinction ratio, and total energy loss;

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

[0019] On the other hand, embodiments of the present invention provide a method for preparing a grating polarizer, comprising:

[0020] Provides nanoimprint templates and substrate layers;

[0021] A photoresist layer is prepared on the substrate layer, and the pattern of the nanoimprint template is transferred onto 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 includes:

[0024] A mask layer is fabricated in the gaps of the grating structure;

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

[0026] The implementation of this invention provides the following beneficial effects: In this embodiment, the grating polarizer 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 greater than or equal to the refractive index of the photoresist layer, and the refractive index of the second dielectric film layer is greater than the refractive index of the substrate layer. The metal film layer, the first dielectric film layer, and the second dielectric film layer form a multilayer grating structure. By using this multilayer metal grating structure, the extinction ratio and light transmission efficiency are effectively improved, and absorption loss is reduced, thereby improving navigation accuracy. Furthermore, by changing the first and second influencing factors of the grating polarizer, the optimal grating polarizer is determined, the parameters of the grating polarizer are optimized, and the optical performance of the grating polarizer is improved. Simultaneously, the grating polarizer is fabricated using nanoimprint technology, reducing fabrication costs. Attached Figure Description

[0027] Figure 1 This is a schematic diagram of the structure of a grating polarizer provided in an embodiment of the present invention;

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

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

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

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

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

[0033] Figure 7 This is a schematic flowchart of the steps of an optimization method for a grating polarizer provided in an embodiment of the present invention;

[0034] Figure 8 This is a schematic diagram of the steps for optimizing and verifying a grating polarizer according to an embodiment of the present invention;

[0035] Figure 9 This is a schematic flowchart of a method for preparing a grating polarizer according to an embodiment of the present invention;

[0036] Figure 10 This is a schematic flowchart of another method for preparing a grating polarizer provided in an embodiment of the present invention;

[0037] Figure 11 This is a schematic flowchart of another method for preparing a grating polarizer provided in an embodiment of the present invention;

[0038] Figure 12 This is a test optical path diagram of a grating polarizer provided in an embodiment of the present invention. Detailed Implementation

[0039] The present invention will now be described in further detail with reference to the accompanying drawings and specific embodiments. The step numbers in the following embodiments are only for ease of explanation and do not limit the order of the steps. The execution order of each step in the embodiments can be adapted according to the understanding of those skilled in the art.

[0040] This invention provides a grating polarizer, which sequentially includes 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 greater than or equal to the refractive index of the photoresist layer, and the refractive index of the second dielectric film layer is greater than the refractive index of the substrate layer. The metal film layer, the first dielectric film layer, and the second dielectric film layer form a multilayer grating structure.

[0041] See Figure 1 , Figure 1 A grating polarizer provided in this embodiment of the 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 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 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 Figure 2 , Figure 2 In another grating polarizer provided in this embodiment of the 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. 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. 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 Figure 3 , Figure 3In another grating polarizer provided in this embodiment of the 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. The photoresist layer M2 retains a portion of the photoresist in the gaps of the grating structure. 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 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.

[0044] Alternatively, the material of the metal film may include an elemental metal or a metal alloy.

[0045] Specifically, elemental metals include, but are not limited to, gold, silver, aluminum, or copper, while metal alloys include, but are not limited to, metal alloys of gold, silver, aluminum, or copper.

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

[0047] Optionally, the refractive index of the second dielectric film is determined based on 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 slightly greater than 1.5.

[0049] Optionally, the thickness of the first dielectric film layer is determined based on 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 some photoresist, the thickness of the first dielectric film is approximately equal to the average thickness of the photoresist layer, or the thickness of the first dielectric film is slightly less than the average thickness of the photoresist layer. When the gaps in the grating structure do not retain photoresist, the thickness of the first dielectric film is equal to that of the photoresist layer.

[0051] It should be noted that photoresist materials with low refractive index, such as PMMA, can be selected.

[0052] See 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 the middle, h 2-t and h 2-b These 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 the relationship is: 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 chosen. Figure 4-6 In this context, h1 can be selected from a range of several hundred nanometers to tens of micrometers. When h1 is large, n5 is chosen to be much greater than 1.5; when h1 is small, n5 is chosen to be slightly greater than 1.5.

[0053] See Figure 7 This invention provides an optimization method for a grating polarizer, comprising:

[0054] S110. Determine the first and second influencing factors of the grating polarizer; the first influencing factor includes any one or more of the material composition, structural composition or waveband, and the second influencing factor includes the structural parameters of the grating polarizer.

[0055] S120. Simulation determines the grating polarizer with the best effect corresponding to the first and second influencing factors.

[0056] It should be noted that the optical wave calculation algorithm used in the simulation of this invention is the Fourier Mode Method (FMM, also called the Rigorous Coupled Wave Analysis (RCWA)). The structure of the grating polarizer includes... Figure 1-3 The structure of the grating polarizer is available in wavelengths including blue light and near-infrared. The structural parameters of the grating polarizer include, but are not limited to, eight parameters such as the grating structure period, groove depth, aspect ratio, and thickness of each layer.

[0057] Specifically, first, the first and second influencing factors of the grating polarizer are determined. Then, the first and second influencing factors are changed in turn, and the corresponding effects are determined by simulation. Finally, the grating polarizer with the best effect is determined based on the results of multiple simulations.

[0058] Optionally, simulations determine the grating polarizer that best performs for the first and second influencing factors, including:

[0059] S121. Determine the first influencing factor, change the second influencing factor, and use simulation to determine the local optimal grating polarizer;

[0060] S122. Change the first and second influencing factors, update the locally optimal grating polarizer according to the simulation results, until the simulation is completed, and take the locally optimal grating polarizer as the grating polarizer with the best effect.

[0061] Specifically, first, the specific value of the first influencing factor is determined, the second influencing factor is changed, and the local optimal grating polarizer corresponding to the second influencing factor corresponding to a certain first influencing factor is determined by simulation. Then, the specific value of the first influencing factor is changed, and the second influencing factor is changed at the same time. The local optimal grating polarizer corresponding to the second influencing factor corresponding to other first influencing factors is determined by simulation. At the same time, the grating polarizer with better effect is updated to the local optimal grating polarizer, until all first influencing factors and second influencing factors are simulated. The local optimal grating polarizer is then taken as the best grating polarizer.

[0062] Alternatively, the effect of the grating polarizer is determined by the following method:

[0063] S123. Determine the first weight, second weight, and third weight, and test transmittance, extinction ratio, and total energy loss;

[0064] S124. Determine the effect of the grating polarizer based on the first weight and test transmittance, the second weight and extinction ratio, and the third weight and total energy loss.

[0065] It should be noted that the specific values ​​of the first, second, and third weights are determined based on the actual application, and this embodiment does not impose specific limitations. The principle of optimizing the indicators is that the higher the transmittance, the higher the extinction ratio, and the lower the total energy loss, the higher the indicator value. The first and second weights are positive values, and the third weight is a negative value.

[0066] The sum of 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 values ​​is determined to have the best effect.

[0067] See Figure 8 In one specific embodiment, a set of material compositions, structural compositions, or wavebands is determined from the first influencing factor. Each time, one of the eight parameters in the second factor is changed, and this parameter is optimized using simulation software. Finally, the eight optimal parameters are combined to obtain a locally optimal solution, which is taken as the optimization result. Then, the material groups are changed to the second and third groups, and the optimization is completed sequentially. The best of the three optimization results is selected as the final optimized result for the structure. Then, the structural composition is changed to another, and the cyclical optimization process continues. Finally, the best of the three structures is determined as the final selected structure for that waveband. For the optimization of other wavebands, the above process is repeated by changing the waveband. In this way, the optimal structure for each waveband can be obtained, allowing for processing and testing.

[0068] It should be noted that during optimization, the values ​​of all surface parameters (especially w1 and w2) should be combined with the actual processing level. If the calculated optimal value is too small or too large and cannot be processed, then the value needs to be discarded and the parameters should be readjusted to a better value that can be processed.

[0069] This invention provides a method for fabricating a grating polarizer, comprising:

[0070] S210 provides a nanoimprint template and a substrate layer;

[0071] S220. A photoresist layer is prepared on the substrate layer, and the pattern of the nanoimprint template is transferred onto the photoresist layer to form a grating structure.

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

[0073] It should be noted that the nanoimprint template is determined based on the grating structure of the grating polarizer, and the photoresist layer can be prepared using methods such as spin coating. The pattern of the nanoimprint template is transferred onto the photoresist layer using imprinting technology to form the grating structure. The metal film, the first dielectric film, and the second dielectric film are then prepared using methods such as evaporation or magnetron sputtering.

[0074] Optionally, the preparation method further includes:

[0075] A mask layer is fabricated in the gaps of the grating structure;

[0076] After preparation, remove the mask layer.

[0077] Specifically, before fabricating the metal film layer, the first dielectric film layer, and the second dielectric film layer on the photoresist layer, a mask layer is fabricated in the gaps of the grating structure; after fabricating 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 in the gaps of the grating structure are also removed.

[0078] See Figure 9-11 The process flow diagrams for the three structures are shown. Figure 9 In the middle: Step (1), P1, use thermal nanoimprinting to transfer the pattern to the IPS polymer layer N1 using a high-temperature Ni template; Step (2), demold to obtain the IPS nanoimprint template; Step (3), prepare a glass substrate; Step (4), spin-coat a layer of photoresist P2 on the glass substrate; Step (5), use ultraviolet nanoimprinting to transfer the pattern of the IPS mold to the photoresist layer; Step (6), cover the gaps in the grating structure with a mask, evaporate (P4) the metal film, the first dielectric film and the second dielectric film to form a multilayer metal grating structure; Step (7), remove the mask. Figure 10 The process shown is the same as Figure 9 The structure is basically the same, except that the photoresist layer obtained in step (5) does not contain a complete bottom film layer; this structure is fabricated using a deep IPS template, while Figure 9 The structure in step (5) is prepared using an IPS template with a small groove depth. Figure 11 and Figure 9 The process is basically the same, except that there is no need to add or remove a mask. After evaporating the metal film, the first dielectric film and the second dielectric film on the structure in step (5), the final sample can be obtained.

[0079] It should be noted that the mask is fabricated as follows: Periodically distributed elongated holes are cut into a relatively rigid rectangular material. The length of these holes is equal to the total width of the entire grating sample, and the width is slightly greater than w1. The width of one periodic structure of the mask is equal to w2. The total length and width of the mask are both greater than the total length and width of the entire grating sample. This mask is then aligned and fitted onto the grating to be processed, exposing each spine of the grating.

[0080] After the grating sample is prepared, the optical path needs to be set up for testing. Figure 12 The optical path diagram of the polarizer being measured is shown. The transmittance of the prepared polarizer was measured using a Fourier transform spectrometer. Before the measurement began, the sample to be tested was not placed in the sample. Light perpendicular to the sample surface was incident on a reference polarizer (extinction ratio > 20 dB). This polarizer converted the light emitted from the light source into linearly polarized light and directly incident it on the detector. At this time, the light intensity was recorded as 1. The grating to be tested was installed behind the aperture. First, it was ensured that the grating lines of the grating to be tested were perpendicular to the polarization direction of the incident light (i.e., the transmission axis of the polarizer was parallel to the polarization direction of the incident light). Then, the sample was rotated to observe the changes in light intensity on the detector. The angles of rotation of the polarizer corresponding to the maximum and minimum light intensities were recorded. Parameters such as TM transmittance, extinction ratio, and energy loss could then be calculated.

[0081] After the high-performance gratings for each band have passed testing, they are arranged according to the azimuth angle requirements of the measurement channel transmission axis in the subsequent attitude angle algorithm to obtain a composite band polarization array. Installing this array into a custom camera allows for the acquisition of PL intensity maps for attitude angle algorithm research. This composite band array can also be used to study the relationship between the optimal detection band and climatic conditions.

[0082] The implementation of this invention provides the following beneficial effects: In this embodiment, the grating polarizer 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 greater than or equal to the refractive index of the photoresist layer, and the refractive index of the second dielectric film layer is greater than the refractive index of the substrate layer. The metal film layer, the first dielectric film layer, and the second dielectric film layer form a multilayer grating structure. By using this multilayer metal grating structure, the extinction ratio and light transmission efficiency are effectively improved, and absorption loss is reduced, thereby improving navigation accuracy. Furthermore, by changing the first and second influencing factors of the grating polarizer, the optimal grating polarizer is determined, the parameters of the grating polarizer are optimized, and the optical performance of the grating polarizer is improved. Simultaneously, the grating polarizer is fabricated using nanoimprint technology, reducing fabrication costs.

[0083] The above is a detailed description of the preferred embodiments of the present invention. However, the present invention is not limited to the embodiments described. Those skilled in the art can make various equivalent modifications or substitutions without departing from the spirit of the present invention. All such equivalent modifications or substitutions are included within the scope defined by the claims of this application.

Claims

1. A grating polarizer, characterized in that, The structure comprises, in sequence, 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 greater than or equal to that of the photoresist layer, and the refractive index of the second dielectric film layer is greater than that of the substrate layer. The metal film layer, the first dielectric film layer, and the second dielectric film layer form a multilayer grating structure. A portion of the photoresist is retained in the gaps of the grating structure. The thickness of the first dielectric film layer is determined based on the average thickness of the photoresist layer. The formula for calculating the average thickness of the photoresist layer is as follows: h avg =( w 1 / w 2) h 2-t +(( w 2- w 1) / w 2) h 2-b in, h avg This indicates the average thickness of the photoresist layer. w 1 represents the width of the grating. w 2 represents the period of the grating. h 2-t This indicates the total thickness of the photoresist layer. h 2-b This indicates the height of the photoresist retained in the gaps of the grating structure.

2. The grating polarizer according to claim 1, characterized in that, The material of the metal film layer includes elemental metals or metal alloys.

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

5.

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

5. An optimization method for a grating polarizer, characterized in that, Applied to the grating polarizer according to any one of claims 1-4, comprising: Determine the first and second influencing factors of the grating polarizer; the first influencing factor includes any one or more of the material composition, structural composition, or waveband, and the second influencing factor includes the structural parameters of the grating polarizer; Simulations determine the optimal grating polarizer for the first and second influencing factors; the simulations include far-field data simulations and near-field data simulations. The simulation determines the grating polarizer with the best effect corresponding to the first and second influencing factors, including: The first influencing factor is determined, the second influencing factor is changed, and the local optimal grating polarizer is determined by simulation. The first and second influencing factors are changed, and the locally optimal grating polarizer is updated according to the simulation results until the simulation is completed. The locally optimal grating polarizer is then used as the grating polarizer with the best effect.

6. The optimization method according to claim 5, characterized in that, The effect of the grating polarizer is determined by the following method: Determine the first, second, and third weights, and test transmittance, extinction ratio, and total energy loss; The effectiveness of the grating polarizer is determined based on the first weight and test transmittance, the second weight and extinction ratio, and the third weight and total energy loss.

7. A method for preparing a grating polarizer, characterized in that, Applied to the grating polarizer according to any one of claims 1-4, comprising: Provides nanoimprint templates and substrate layers; A photoresist layer is prepared on the substrate layer, and the pattern of the nanoimprint template is transferred onto 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.

8. The preparation method according to claim 7, characterized in that, The preparation method further includes: A mask layer is fabricated in the gaps of the grating structure; After preparation, the mask layer is removed.

Images