Sub-micron thickness waveplate based on niobium oxychloride and its preparation and measurement method

Abstract

This invention discloses a submicron-thickness waveplate based on niobium oxychloride and its polarization modulation measurement method, belonging to the field of polarization optics. The waveplate preparation method includes: cleaning and drying a silicon wafer; mechanically peeling off a bulk NbOCl2 sample using adhesive tape to form a thin NbOCl2 sample on the blue tape; attaching PDMS to the NbOCl2 sample area on the blue tape, then peeling it off to allow the NbOCl2 sample to adhere to the PDMS; attaching the PDMS with the NbOCl2 sample to the surface of the silicon wafer and heating it; and finally removing the PDMS to obtain the NbOCl2 waveplate on the silicon wafer. The obtained waveplate is subjected to polarization response testing and control analysis using a polarization modulation device, which can systematically obtain its modulation characteristics and phase delay behavior for different incident polarization directions. This invention's preparation method is simple to operate, has high device compatibility, good optical stability and scalability, and can be widely used in multifunctional photonic devices, photoelectric detection, polarization imaging, and on-chip integrated optical paths.

Description

Technical Field

[0001] This invention belongs to the field of polarization optics, specifically relating to submicron-thickness waveplates based on niobium oxychloride and their preparation and measurement methods. Background Technology

[0002] A waveplate is an optical element that uses a specific birefringence effect to introduce phase delay and achieve optical polarization state control. It has been widely used in various optical systems, such as quantum optics and polarization sensing. With the rapid development of on-chip integrated optoelectronic chips, miniaturization of waveplates is crucial. However, miniaturization of traditional commercial waveplates faces two main bottlenecks: First, some waveplate materials, such as quartz and calcite, have low intrinsic birefringence, requiring a light-matter interaction length of at least sub-millimeter thickness to meet specific phase delay requirements. Second, traditional waveplates achieve thickness reduction through polishing, but the polishing process typically increases the surface roughness of the waveplate, leading to scattering losses and affecting phase delay, making it difficult to achieve accuracy of less than one-tenth of a wavefront.

[0003] Therefore, there is an urgent need to develop a novel waveplate to meet the requirements of miniaturized and high-quality polarization control. Developing waveplates based on artificially designed metamaterial structures is a feasible solution, as it can generate different phase delays for light waves along two orthogonal polarization directions by designing specific micro / nano structures (such as periodic metal or dielectric structures) at the subwavelength scale. However, metamaterial waveplates typically require fabrication techniques such as electron beam lithography and nanoimprinting, which are complex and costly. Against this backdrop, layered van der Waals materials have attracted considerable attention due to their atomically flat van der Waals interfaces and significant differences in in-plane and out-of-plane bonding properties. Typical two-dimensional materials such as hexagonal boron nitride and transition metal dichalcogenides exhibit significant out-of-plane birefringence. However, because the incident light needs to be incident perpendicular to the optical axis, this out-of-plane anisotropy is difficult to apply practically to polarization optics for ultrathin two-dimensional materials. Summary of the Invention

[0004] To address the shortcomings of existing technologies, the present invention aims to provide a submicron-level thickness waveplate based on niobium-oxychloride and its polarization modulation measurement method, thereby solving the problems in the prior art.

[0005] The objective of this invention can be achieved through the following technical solutions: The method for preparing submicron-thickness waveplates based on niobium oxychloride includes the following steps: Clean and dry the silicon wafers for later use; Mechanical peeling of the NbOCl2 block was performed using adhesive tape, resulting in a thin NbOCl2 sample on the blue adhesive tape. Apply PDMS to the NbOCl2 thin-layer sample area on the blue tape, then peel it off to allow the NbOCl2 thin-layer sample to adhere to the PDMS. PDMS with a thin NbOCl2 sample attached was attached to the surface of the silicon wafer and then heated; After removing the PDMS, an NbOCl2 waveplate is obtained on the silicon wafer.

[0006] Furthermore, a silicon dioxide thin film with a thickness of 285 nm is grown on the surface of the silicon wafer.

[0007] Furthermore, the silicon wafer cleaning and drying process involves sequentially ultrasonic treatment with acetone, isopropanol, and deionized water, followed by drying with a nitrogen gun.

[0008] Furthermore, the tape is blue tape.

[0009] Furthermore, the heating temperature is 70°C and the heating time is 10 minutes.

[0010] A niobium oxychloride wave plate is prepared using the above-described preparation method.

[0011] A polarization modulation measurement device includes a white light source. One side of the white light source, along the incident light path, includes, in sequence: a polarizer, a first beam splitter, an objective lens, and a rotating platform for mounting the niobium-oxygen-chlorine wave plate. The polarization modulation measurement device also includes, along the light reflection path: an analyzer, a second beam splitter, a spectrometer, and a camera. White light emitted from a white light source is polarized by a polarizer to become linearly polarized light. After being reflected by the first beam splitter, it passes through the objective lens and is incident on the waveplate of the rotating platform. After being reflected by the waveplate, it passes through the objective lens to the analyzer, and is then sent by the second beam splitter to the camera and spectrometer respectively. The spectrometer acquires the spectrum. By adjusting the angles of the rotating platform and the analyzer, the modulation response of the niobium-oxygen-chlorine waveplate to light under different incident polarization directions is obtained, and its polarization-dependent spectral characteristics are obtained.

[0012] The above-described polarization modulation test method for niobium-oxygen-chlorine waveplates, using the aforementioned polarization modulation measurement device, includes the following steps: S1, turn on the white light source, camera, and spectrometer; S2, apply carbon adhesive to the center of the rotating platform; S3, attach the niobium-oxygen-chlorine corrugated sheet to the carbon adhesive, and gently press the edges and corners of the substrate to prevent the niobium-oxygen-chlorine corrugated sheet from tilting; S4, locate the waveplate to be tested through real-time imaging with the camera, and align the aperture with the waveplate area; S5, adjust the polarization direction of the polarizer to 0°; S6, keep the rotation angle of the rotating platform unchanged, the analyzer starts from 0° and performs a spectral measurement every 15°. When it rotates to 180°, the first set of measurements is completed. S7. Rotate the rotating platform by 15°, fix the rotating platform, and reposition it under the optical microscope to the position of the niobium-oxygen-chlorine wave plate. The analyzer starts from 0° and performs a spectral measurement every 15°. When it is rotated to 180°, the second set of measurements is completed. S8. Repeat step S7. Perform the same operation once every 15° rotation of the platform until the platform is rotated to 360°, at which point the measurement is complete.

[0013] The above-mentioned niobium-oxygen-chlorine waveplates are used in photoelectric detection and polarization imaging.

[0014] A polarization-sensitive optical sensing system, equipped with the aforementioned niobium-oxygen-chlorine waveplate.

[0015] The beneficial effects of this invention are: 1. This invention proposes a method for preparing ultrathin waveplates using two-dimensional van der Waals material niobium oxychloride. By utilizing the strong in-plane birefringence and weak interlayer electron coupling characteristics of niobium oxychloride, the required phase delay can be met at a size of hundreds of nanometers, thereby breaking through the size limit of traditional waveplates. This method is convenient to operate, has low manufacturing cost, and is highly compatible with current silicon-based processes, thus having strong practicality.

[0016] 2. This invention utilizes a polarization modulation measurement method to obtain the polarization modulation information of a waveplate. Furthermore, the complete modulation of the waveplate to different polarization states is analyzed, and the specific values ​​of ellipticity and phase delay are extracted. The intuitive and complete polarization modulation information obtained through this measurement method is beneficial for the rapid selection and further application of waveplates. Attached Figure Description

[0017] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, for those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0018] Figure 1 This is a schematic diagram of the polarization modulation device structure of the present invention; Figure 2 This is a schematic diagram of the polarization control of the niobium-oxygen-chlorine waveplate of the present invention; Figure 3 This is a diagram showing the polarization modulation results of the 269 nm thick NbOCl2 of the present invention at a wavelength of 614 nm; Figure 4 This is a diagram showing the polarization modulation results of the empty silicon wafer of the present invention; Figure 5 This is a graph showing the dependence of the ellipticity of the present invention on the number of sample layers and wavelength. Figure 6 This is a diagram showing the polarization modulation results of 282 nm thick NbOCl2 at a wavelength of 605 nm according to the present invention; Figure 7 This is a diagram showing the polarization modulation result of the quarter-wave plate fitted by the theory of this invention; Figure 8 This is a normalized light intensity result diagram corresponding to each analyzer angle when the crystal axis of the 282 nm thick NbOCl2 sample is at a wavelength of 605 nm and the angle between the crystal axis and the polarizer is 45°. Figure 9 This is a comparison diagram of the delay tolerance between the niobium oxychloride waveplate of this invention and some commercial waveplates.

[0019] In the diagram: 1-White light source, 2-Polarizer, 3-First beam splitter, 4-Objective lens, 5-Rotating platform, 6-Analyzer, 7-Second beam splitter, 8-Camera, 9-Spectrometer. Detailed Implementation

[0020] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0021] Example 1 The method for preparing submicron-thickness waveplates based on niobium oxychloride includes the following steps: S1. A silicon wafer with a silicon dioxide layer thickness of 285 nm (i.e., a silicon dioxide thin film with a thickness of 285 nm grown on the surface of the silicon wafer) is ultrasonically treated with acetone, isopropanol and deionized water respectively, and then dried with a nitrogen gun. S2, use blue tape to mechanically peel off the NbOCl2 block. By repeatedly tearing, the NbOCl2 block is dissociated until a thin NbOCl2 sample with a semi-transparent contrast appears on the blue tape. S3, attach PDMS (polydimethylsiloxane) to the NbOCl2 thin film sample area on the blue tape, and then slowly peel it off to allow the NbOCl2 thin film sample to adhere to the PDMS; S4, attach the PDMS sample with the NbOCl2 thin layer to the silicon wafer surface and heat it at 70°C for 10 minutes using a hot plate; S5, PDMS is removed to obtain an NbOCl2 waveplate on the silicon wafer.

[0022] Then, waveplates with uniform thickness and appropriate size were found under an optical microscope, and the thickness was initially screened by contrast under an optical microscope. Then, the thickness of the sample was further characterized by atomic force microscopy.

[0023] Example 2 This embodiment proposes a polarization modulation measurement method, which includes using, for example... Figure 1 The polarization modulation measurement device shown performs corresponding measurements on the sample; in this embodiment, the structure of the polarization modulation device and the measurement process are described.

[0024] like Figure 1 As shown, the polarization modulation measurement device includes a white light source 1. One side of the white light source 1, along the incident light path, includes: a polarizer 2, a first beam splitter 3, an objective lens 4, and a rotating platform 5 for mounting the waveplate. The polarization modulation measurement device also includes: an analyzer 6, a second beam splitter 7, a spectrometer 9, and a camera 8 along the light reflection path. The white light emitted by the white light source 1 is linearly polarized by the polarizer 2. After being reflected by the first beam splitter 3, it passes through the objective lens 4 and is incident on the waveplate of the rotating platform 5. After being reflected by the waveplate, it passes through the objective lens 4 and reaches the analyzer 6. Then, it is sent by the second beam splitter 7 to the camera 8 and the spectrometer 9 respectively. The spectrometer 9 acquires the spectrum, the camera 8 is used to image and align the sample surface, and the analyzer 6 is used to analyze the polarization state of the light emitted after being reflected from the sample. By adjusting the angles of the rotating platform 5 and the analyzer 6, the modulation response of the waveplate to light under different incident polarization directions can be obtained, thereby obtaining its polarization-dependent spectral characteristics.

[0025] Specifically, the process of measuring the waveplate prepared in Example 1 using this measuring device includes the following steps: S1, turn on the white light source 1, camera 8 and spectrometer 9; S2, apply carbon adhesive to the center of the rotating platform 5; S3, attach the waveplate to the carbon adhesive and gently press the edges of the substrate to prevent the waveplate from tilting; S4, use camera 8 to image in real time to find the waveplate to be tested, and use the aperture to align the waveplate area; S5, adjust the polarization direction of polarizer 2 to 0°, that is, the direction perpendicular to the optical platform; S6, keep the rotation angle of the rotating platform 5 unchanged, and start the analyzer 6 from 0°, perform a spectral measurement every 15°, and complete the first set of measurements when it rotates to 180°; S7. Rotate the rotating platform 5 by 15°, fix the rotating platform, and reposition it to the sample position under the optical microscope. The analyzer starts from 0° and performs a spectral measurement every 15°. When it is rotated to 180°, the second set of measurements is completed. S8. Repeat the above steps. Perform the same operation once every 15° rotation of the rotating platform 5 until the rotating platform 5 reaches 360°, at which point the measurement is complete.

[0026] like Figure 2 As shown, after the light wave interacts with the niobium-oxygen-chlorine waveplate, it will produce different phase delays along two orthogonal polarization directions.

[0027] Example 3 In this embodiment, based on the measurement data from Embodiment 2, a two-dimensional mapping distribution diagram is plotted with the angles of the rotating platform 5 and the analyzer 6 as independent variables and light intensity as the dependent variable, as shown below. Figure 3 As shown, polarization control data, including but not limited to those obtained after measuring a specific angle, can be obtained from this mapping diagram. Figure 3 This reflects the polarization modulation results of a 269 nm thick NbOCl2 waveplate at a wavelength of 614 nm; the polarization modulation results of an empty silicon wafer are as follows: Figure 4 As shown, the polarization modulation mapping map under the empty silicon wafer is used as a substrate background reference; contrast Figure 3 and Figure 4 It can be seen that in the polarization modulation test on an empty silicon substrate, when the analyzer 6 is fixed at a specific angle, rotating the substrate angle does not significantly affect the emitted light intensity, indicating that the substrate does not have a significant impact on the modulation result. However, in the polarization modulation test on an NbOCl2 waveplate, for linearly polarized light incident in any polarization direction, the emitted light intensity exhibits varying degrees of fluctuation as the angle of the analyzer 6 changes, corresponding to different emitted polarization states. This verifies that the NbOCl2 waveplate, due to its birefringence characteristics, can significantly change the polarization state of light and possesses the ability to modulate polarization.

[0028] Example 4 In this embodiment, the light intensity values ​​corresponding to each analyzer angle 6 when the niobium-oxygen-chlorine waveplate crystal axis is at an angle of 45° to polarizer 2 are extracted from the measurement data of embodiment 2. A dependency graph is plotted using Origin software, and the ellipticity is calculated using the ratio of the minimum to the maximum value. e ); The dependence of ellipticity on the number of sample layers and wavelength is as follows: Figure 5 As shown, it can be seen that for niobium-oxygen-chlorine waveplates with similar thicknesses, the overall spectral shape of their ellipticity spectra is basically the same, and the peaks are correspondingly shifted to a certain extent, indicating that the polarization modulation of the niobium-oxygen-chlorine waveplate can be adjusted to a certain extent according to its thickness.

[0029] The polarization modulation results of the 282 nm thick NbOCl2 waveplate at a wavelength of 605 nm are as follows: Figure 6As shown, it can be seen that when the angle of the NbOCl2 waveplate is fixed and the analyzer 6 is rotated one revolution, the intensity of the emitted light exhibits a uniform sinusoidal change. Furthermore, it can be seen that at a specific angle (i.e., when the angle with the crystal axis of the NbOCl2 waveplate is 45°), the intensity of the emitted light remains basically unchanged as the angle of the analyzer 6 changes. This indicates that the incident linearly polarized light is converted into circularly polarized light, which is also one of the main characteristics of a quarter-wave plate.

[0030] The polarization modulation results of the quarter-wave plate theoretically fitted by this invention are as follows: Figure 7 As shown, the waveplate results above are highly consistent with the theoretical results.

[0031] Figure 8 This diagram shows the normalized light intensity at each analyzer angle when the crystal axis of the 282 nm thick NbOCl2 sample is at a wavelength of 605 nm and the angle between the crystal axis and the polarizer is 45°. It can be further seen that for a 269 nm thick niobium oxychloride waveplate (wavelength: 614 nm), when its crystal axis is at a 45° angle with the linear polarization direction of the incident light, circularly polarized outgoing light is effectively obtained through interaction with the waveplate.

[0032] In this embodiment, the phase delay of the niobium-oxygen-chlorine quarter-wave plate selected by ellipticity and polarization modulation mapping is explained; to find a niobium-oxygen-chlorine based quarter-wave plate, the following steps are performed: Step 1: Based on the data obtained from the measurement steps in Example 2, extract the light intensity values ​​at the same wavelength, and plot a two-dimensional mapping distribution diagram with the rotation platform and analyzer angle as independent variables and light intensity as dependent variable. This allows for analysis of the sample's modulation of different polarized light.

[0033] Step 2: Extract the light intensity value corresponding to each analyzer angle when the crystal axis of the niobium oxychloride sample is at a 45° angle to polarizer 2 from the data measured in Example 2. Plot the dependency graph using Origin software, and calculate the ellipticity using the ratio of the minimum to the maximum value. e ).

[0034] Step 3: From the ellipticity-wavelength dependence spectrum, find the wavelength positions with peak values ​​greater than 0.9, plot the corresponding two-dimensional mapping distribution, compare it with the theoretical results of a quarter-wave plate, and calculate the phase delay and its deviation.

[0035] The theoretical result of the quarter-wave plate described in step 3 corresponds to the following formula: in, I QWPThe theoretical light intensity value obtained by polarization modulation measurement of a quarter-wave plate. For the angle of the rotating platform, The polarization angle of the analyzer.

[0036] The phase delay is obtained by fitting the following formula: in, e For ellipticity, I b and I c The polarizer orientation is respectively aligned with the sample crystal axis b shaft and c The light intensity value corresponding to when the axes are aligned. This represents the phase delay.

[0037] Example 5 In this embodiment, the niobium oxychloride waveplate prepared in Example 1 was compared with commercial waveplates (Thorlabs WPQSM05-514 (514 nm), WPQSM05-588 (588 nm), WPQ05ME-633 (633 nm) and Edmund Optics #49-221 (670 nm)). The testing process is as follows: The test was conducted according to Example 2. Based on Example 4, the ellipticity was obtained and fitted to obtain the specific value of the phase delay. The delay tolerance was obtained by subtracting the theoretical value of the quarter-wave plate (π / 2≈1.5708). The test was conducted using an optical microscope (Olympus BX51 model) connected to an Ocean Optics Flame miniature spectrometer.

[0038] Test results are as follows Figure 9 As shown, Figure 9 This is a comparison diagram of the phase delay deviation between the niobium-oxygen-chlorine waveplate prepared in Example 1 and a commercial waveplate. The diagram shows that, compared to the commercial waveplate, the niobium-oxygen-chlorine waveplate of this invention maintains a delay tolerance comparable to that of traditional commercial waveplates while achieving a significantly thinner thickness (error bars represent the magnitude of the delay tolerance). Specific values ​​are shown in Table 1. Table 1. Comparison of performance parameters between niobium-oxygen-chlorine waveplates and some commercially available waveplates. In the description of this specification, references to terms such as "an embodiment," "example," "specific example," etc., indicate that a specific feature, structure, material, or characteristic described in connection with that embodiment or example is included in at least one embodiment or example of the invention. In this specification, illustrative expressions of the above terms do not necessarily refer to the same embodiment or example. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in one or more embodiments or examples.

[0039] The foregoing has shown and described the basic principles, main features, and advantages of the present invention. Those skilled in the art should understand that the present invention is not limited to the above embodiments. The embodiments and descriptions in the specification are merely illustrative of the principles of the invention. Various changes and modifications can be made to the invention without departing from its spirit and scope, and all such changes and modifications fall within the scope of the claimed invention.

Claims

1. A method for preparing submicron-thickness waveplates based on niobium oxychloride, characterized in that, Includes the following steps: Clean and dry the silicon wafers for later use; Mechanical peeling of the NbOCl2 block was performed using adhesive tape, resulting in a thin NbOCl2 sample on the blue adhesive tape. Apply PDMS to the NbOCl2 thin-layer sample area on the blue tape, then peel it off to allow the NbOCl2 thin-layer sample to adhere to the PDMS. PDMS with a thin NbOCl2 sample attached was attached to the surface of the silicon wafer and then heated; After removing the PDMS, an NbOCl2 waveplate is obtained on the silicon wafer.

2. The method for preparing submicron-thickness waveplates based on niobium oxychloride according to claim 1, characterized in that, A silicon dioxide thin film with a thickness of 285 nm was grown on the surface of the silicon wafer.

3. The method for preparing submicron-thickness waveplates based on niobium oxychloride according to claim 1, characterized in that, The process of cleaning and drying the silicon wafer is as follows: ultrasonic treatment is performed sequentially with acetone, isopropanol, and deionized water, followed by drying with a nitrogen gun.

4. The method for preparing submicron-thickness waveplates based on niobium oxychloride according to claim 1, characterized in that, The tape is blue tape.

5. The method for preparing submicron-thickness waveplates based on niobium oxychloride according to claim 1, characterized in that, The heating temperature is 70℃ and the heating time is 10 minutes.

6. A niobium-oxygen-chlorine waveplate, characterized in that, It is prepared by the preparation method according to any one of claims 1-5.

7. A polarization modulation measurement device, characterized in that, include: The white light source (1) includes, along the incident light path direction, a polarizer (2), a first beam splitter (3), an objective lens (4), and a rotating platform (5) for mounting the niobium-oxygen-chlorine wave plate as described in claim 6; the polarization modulation measurement device also includes, along the light reflection path, an analyzer (6), a second beam splitter (7), a spectrometer (9), and a camera (8). The white light emitted by the white light source (1) is linearly polarized by the polarizer (2), and after being reflected by the first beam splitter (3), it is incident on the waveplate of the rotating platform (5) through the objective lens (4). After being reflected by the waveplate, it reaches the analyzer (6) through the objective lens (4), and is then sent to the camera (8) and the spectrometer (9) by the second beam splitter (7). The spectrometer (9) acquires the spectrum. By adjusting the angle of the rotating platform (5) and the analyzer (6), the modulation response of the niobium oxychloride waveplate to light under different incident polarization directions is obtained, and its polarization-dependent spectral characteristics are obtained.

8. The polarization modulation test method for the niobium-oxygen-chlorine wave plate according to claim 6, using the polarization modulation measurement device according to claim 7, is characterized in that, Includes the following steps: S1, turn on the white light source (1), camera (8) and spectrometer (9); S2, apply carbon adhesive to the center of the rotating platform (5); S3, attach the niobium-oxygen-chlorine corrugated sheet to the carbon adhesive, and gently press the edges and corners of the substrate to prevent the niobium-oxygen-chlorine corrugated sheet from tilting; S4, the waveplate to be tested is found by real-time imaging through the camera (8), and the aperture is used to align the waveplate area; S5, adjust the polarization direction of the polarizer (2) to 0°; S6, keep the rotation angle of the rotating platform (5) unchanged, and start the analyzer (6) from 0°, perform a spectral measurement every 15°, and complete the first set of measurements when it reaches 180°; S7, rotate the rotating platform (5) by 15°, fix the rotating platform (5), and reposition it to the position of the niobium oxygen chloride wave plate under the optical microscope. The analyzer starts from 0° and performs a spectral measurement every 15°. When it is rotated to 180°, the second set of measurements is completed. S8. Repeat step S7. Rotate the platform (5) 15° and perform the same operation once, until the platform (5) reaches 360°, and the measurement is completed.

9. The application of the niobium-oxygen-chlorine waveplate according to claim 6 in photoelectric detection and polarization imaging.

10. A polarization-sensitive optical sensing system, characterized in that, It is equipped with the niobium oxychloride wave plate as described in claim 6.

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