A terahertz emission modulation integrated single-pixel imaging device and system

Abstract

The application discloses a terahertz emission and modulation integrated single-pixel imaging device and system. The device comprises a spin electronics terahertz emission layer and a spatial coding modulation structure, wherein the spatial coding structure is conformally integrated with the spin electronics terahertz emission layer on the same surface, the spatial coding pattern directly defines the radiation area and the non-radiation area of the spin electronics terahertz emission layer, so that the terahertz wave is spatially coded at the moment of generation, thereby realizing the integration of emission and modulation in the physical structure. The spatial coding pattern here contains two categories, one is directly prepared according to the coding strategy, and the other is prepared for the optimized coding structure after overcoming the reverse design of the diffraction phenomenon for the coding strategy. The application integrates the emission and modulation functions in a single device, realizes the technical effects of high integration, high energy utilization rate, clear pixel edge, high modulation depth, wide working waveband and excellent far-field imaging effect.

Description

Technical Field

[0001] This invention belongs to the field of terahertz imaging technology, specifically relating to a single-pixel imaging device and imaging method based on a spintronic terahertz emission source, which directly integrates a coding structure through micro-nano fabrication to achieve synchronous terahertz wave generation and spatial light field modulation. Background Technology

[0002] Terahertz waves, falling between microwaves and infrared, possess unique advantages such as non-ionization, high penetration, and rich spectral information, making them irreplaceable in fields such as security inspection, industrial non-destructive testing, biomedical diagnostics, and semiconductor chip testing.

[0003] Traditional terahertz single-pixel imaging technology is mainly divided into two categories: one is to first emit terahertz light and then modulate it; the other is to first modulate the pump light and then emit terahertz light.

[0004] The first category of schemes (emission-then-modulation) includes mechanical mask modulation, photonic semiconductor modulation, and electronically controlled metamaterial modulation. These schemes typically require independent modulation devices, resulting in complex optical paths. Furthermore, the secondary modulation introduces significant energy loss, reducing the intensity of the detected signal and consequently affecting the imaging signal-to-noise ratio. In addition, mechanical masks are limited to a low-frequency range due to substrate absorption; while photonic semiconductors have a wider operating band, their modulation depth is limited by carrier lifetime; and electronically controlled metamaterials are limited by the need to achieve a specific response to electromagnetic waves, and their fabrication is complex, allowing modulation only at a single frequency.

[0005] The second approach (modulating the pump light before emission) uses a spatial light modulator (such as a Digital Micromirror Device, DMD) to modulate the pump light before illuminating a spintronic terahertz emitter. While this avoids the energy loss from secondary modulation, it relies on micromirror array flipping, inherently suffers from pump light pulse wavefront distortion, and requires additional optical path correction, resulting in high system cost and complexity. Furthermore, in this approach, the pump light carrying spatially encoded information illuminating consecutive emitters produces a terahertz wave encoding pattern that blurs pixel edges, further reducing image quality.

[0006] The aforementioned existing technologies all employ a discrete structure of terahertz emission units and independent modulation units, which generally suffers from drawbacks such as complex system structure, low energy utilization, insufficient modulation depth, limited operating band, and blurred pixel edges. Furthermore, all of these technologies directly utilize the coding strategies found in single-pixel imaging. In this case, the coded pattern is affected by diffraction, leading to distortion of the coded pattern at long distances and making it difficult to reconstruct the object image. Summary of the Invention

[0007] The purpose of this invention is to address the problems existing in the prior art by providing a single-pixel imaging device and system that integrates terahertz emission and modulation. By directly fabricating the coding structure on the spintronic terahertz emission unit through micro-nano processing, spatial optical field coding modulation is simultaneously completed at the moment the emission unit generates terahertz waves under femtosecond laser pumping, achieving "emission and modulation integration" and overcoming the loss and complexity problems associated with traditional discrete structures. Furthermore, to address the diffraction effect during imaging, an anti-diffraction coding pattern, designed through reverse optimization, can be fabricated on the device surface, further improving the system's effective imaging distance and imaging quality.

[0008] To achieve the above objectives, the present invention adopts the following technical solution:

[0009] A single-pixel imaging device integrating terahertz emission modulation includes:

[0010] Spintronic terahertz emitter layer; and

[0011] Spatial coding modulation structure;

[0012] The spatial coding modulation structure is conformally integrated with the spintronic terahertz emission layer on the same surface, and the coding pattern of the spatial coding modulation structure directly defines the radiation region and non-radiation region of the spintronic terahertz emission layer, so that the terahertz wave completes spatial coding synchronously at the moment of generation, thereby realizing the integration of emission and modulation in physical structure.

[0013] The present invention also provides a single-pixel imaging system integrating terahertz emission modulation, comprising a pump light source for outputting excitation light pulses; the aforementioned integrated imaging device for converting the excitation light pulses into terahertz waves carrying spatially encoded information; a focusing optical system for focusing the terahertz waves transmitted through the target onto a detector; a single-point detector for receiving the total light intensity signal after reflection or transmission from the target; and an image reconstruction module for processing the total light intensity signal based on a compressed sensing algorithm or a total variational algorithm to reconstruct a target image.

[0014] This invention also provides a method for manufacturing the above-mentioned device, specifically including the following two technical routes, either of which can be selected for implementation according to actual process requirements:

[0015] Route 1 specifically includes the following steps: S100. Depositing nanoscale spintronic multilayer thin films on a substrate by magnetron sputtering to form a terahertz emission layer; S200. Coating the surface of the terahertz emission layer with photoresist and transferring the coded pattern of the mask to the photoresist layer using ultraviolet lithography; S300. Performing ion beam etching on the developed structure to remove the multilayer thin films in areas not protected by the photoresist, retaining the patterned emission areas, and forming an integrated device.

[0016] Route 2 specifically includes the following steps: S100'. Coating photoresist on the substrate and transferring the coded pattern of the mask to the photoresist layer using ultraviolet lithography; S200'. Depositing nanoscale spintronics multilayer films on the photoresist layer and the substrate surface not covered by photoresist using magnetron sputtering to form a terahertz emission layer; S300'. Removing the photoresist area with the multilayer film using a lift-off process, retaining the patterned emission layer on the substrate area not covered by photoresist, to form an integrated device.

[0017] By utilizing the terahertz emission modulation integrated single-pixel imaging device and system proposed in this invention, the present invention has the following beneficial effects:

[0018] (1) High integration and simplified structure: The present invention integrates the emission and modulation functions into a single device, eliminating the need for a separate spatial light modulator and its supporting optical path in the traditional scheme, greatly reducing the system size and reducing the difficulty of alignment.

[0019] (2) High energy utilization: Terahertz waves are encoded instantly upon generation, with no intermediate transmission and reflection losses. Under the same pump power, the intensity of terahertz waves that can be utilized is higher.

[0020] (3) High modulation depth and wide operating band: Since the coding structure is directly prepared on the transmitter itself, the theoretical modulation depth is close to 100%. At the same time, the spintronic emission source itself has ultra-wideband radiation characteristics and is not limited to a specific resonant frequency.

[0021] (4) Excellent far-field imaging quality: The introduction of the diffraction inverse design algorithm to pre-correct the coding pattern effectively compensates for far-field diffraction distortion, so that a clear coding pattern can still be projected at a distance, breaking through the bottleneck of traditional single-pixel imaging being limited to the near field.

[0022] (5) Easy to mass-produce: It is compatible with standard micro-nano processing technology and can realize wafer-level mass production with low cost and good consistency. Attached Figure Description

[0023] Figure 1 This is a schematic diagram of the terahertz emission modulation integrated device in Embodiment 1 of the present invention;

[0024] Figure 2 This is a schematic diagram of the terahertz emission modulation integrated single-pixel imaging system in Embodiment 2 of the present invention;

[0025] Figure 3 This is a flowchart of the coding pattern optimization based on the diffraction reverse design algorithm in Embodiment 3 of the present invention;

[0026] Figure 4 This is a process flow diagram of the device fabrication in Embodiment 4 of the present invention;

[0027] Figure 5 These are schematic diagrams showing the experimental results of imaging experiments using the devices prepared in Example 1 (5×7 pixels, 2 mm resolution);

[0028] Figure 6 This is a comparison diagram of the encoding distortion effect of whether or not the reverse design algorithm is performed in Embodiment 6 of the present invention.

[0029] The same or substantially the same elements, operations, and steps shown in the various figures may be indicated by the same reference numerals. For clarity, not every element, operation, or step is shown in every figure. Detailed Implementation

[0030] Exemplary embodiments of the present application will now be described in more detail with reference to the accompanying drawings. It should be understood that this disclosure should not be construed as limiting to the exemplary embodiments described herein, but rather that it can be implemented in various other forms, provided only for a more thorough and complete understanding of the present application. It should also be understood that the accompanying drawings are given by way of example only and are not intended to limit the precise form of the embodiments or to limit the scope of protection of the present application.

[0031] The specific embodiments of the present invention will be further described in detail below with reference to the accompanying drawings. It should be noted that these embodiments are only used to explain the present invention and do not constitute a limitation thereof.

[0032] Example 1

[0033] like Figure 1 As shown, this embodiment provides a single-pixel imaging device that integrates terahertz emission modulation.

[0034] The device includes a substrate 100, a spintronic terahertz emission layer 200, and a spatially coded modulation structure 300.

[0035] The substrate 100 is a glass substrate, which has the characteristics of high transmittance in the infrared band and low absorption in the terahertz band.

[0036] The spintronic terahertz emission layer 200 is deposited on the substrate. In this embodiment, this layer is prepared sequentially by magnetron sputtering of a 2 nm Pt layer and a 2 nm Co layer. 20 Fe 60 B 20 The layer and the 2 nm W layer constitute a ferromagnetic / nonmagnetic multilayer thin film heterostructure. Under femtosecond laser pumping, this heterostructure generates ultrawideband terahertz waves based on the inverse spin Hall effect.

[0037] The spatially encoded modulation structure 300 is not a device independent of the emission layer, but rather conformally integrated with the spintronic terahertz emission layer on the same surface. Specifically, the modulation structure is composed of the retained emission layer material or a mask structure prepared on the surface, and its encoding pattern directly defines the radiating and non-radiating regions (i.e., the retained thin film region acts as a radiating unit to emit terahertz waves, and the removed region acts as a non-radiating unit to block emission).

[0038] This conformal integrated structure enables the terahertz wave to be spatially encoded instantly upon generation, forming a terahertz structured light field carrying spatial encoding information. This eliminates the secondary modulation loss caused by traditional discrete structures from a physical perspective. Furthermore, only the radiating region can radiate terahertz waves, avoiding the pixel edge blurring problem corresponding to continuous emitters.

[0039] Example 2

[0040] like Figure 2 As shown, this embodiment provides a single-pixel imaging system based on the above-mentioned integrated device.

[0041] The system includes: a pump source 1 for emitting femtosecond laser pulses with a wavelength of 800 nm; an integrated imaging device 2, as described in Example 1, for directly generating terahertz radiation carrying spatially encoded information; a focusing optical system 3, such as an off-axis parabolic mirror, for focusing the structural terahertz wave transmitted through the target onto a single-point detector; a target 4, located in the optical path; a single-point detector 5 for collecting the total terahertz light intensity signal modulated by the target object; and an image reconstruction module 6 for processing the acquired electrical signal based on a compressed sensing algorithm or a total variational algorithm to reconstruct the target image.

[0042] By integrating the "transmission and modulation" design with the pump light source module, imaging optical path module, single-point detection module and data acquisition and reconstruction module, the generation, encoding, target illumination, signal detection and image reconstruction of terahertz waves are completed in an integrated manner, which greatly simplifies the system structure and improves modulation performance and imaging stability.

[0043] Example 3

[0044] To address the issue of resolution degradation caused by diffraction effects in far-field imaging, this embodiment proposes an encoding scheme based on a diffraction inverse design algorithm.

[0045] like Figure 3 As shown, the method includes the following steps:

[0046] S1. Set the target imaging distance Z and the target encoding pattern T.

[0047] S2. Simulate the optical field diffraction process using angular spectrum propagation theory. Initially, the optical field distribution I is obtained after the pattern M0 propagates through free space at a distance Z.

[0048] S3. Calculate the loss function. Calculate the difference between the diffraction-calculated optical field I and the target optical field T, and define the loss function L = ||I - T|| 2 .

[0049] S4. Update the mask pattern on the emitter surface using the gradient descent algorithm. Adjust the mask pattern parameters according to the gradient direction of the loss function, iterating round by round.

[0050] S5. Repeat steps S2-S4 until the loss function converges, and obtain the optimized spatial coding modulation structure pattern.

[0051] This embodiment introduces a diffraction inverse design algorithm based on angular spectrum propagation theory. The original coded pattern is pre-corrected according to the target imaging distance to compensate for far-field diffraction distortion. This can create a structure on the device surface that appears "chaotic" but can project a "clear and regular" coded pattern after propagation over a specific distance, thereby achieving high-resolution imaging at long distances.

[0052] Example 4

[0053] This embodiment proposes a method for fabricating a terahertz emission modulation integrated single-pixel imaging device, including the following steps:

[0054] S100: Substrate cleaning and deposition. Using a clean glass substrate, Pt and Co are sequentially deposited using magnetron sputtering technology. 20 Fe 60 B 20 A W-nanometer-scale multilayer thin film is formed to create a spintronic terahertz emission layer.

[0055] S200: Photoresist coating and pattern transfer. Ultraviolet photoresist is uniformly spin-coated on the surface of the emitting layer, and ultraviolet exposure and development are performed using a mask pre-designed according to the algorithm in Example 3 to form a photoresist window complementary to the target coded pattern.

[0056] S300: Ion beam etching. Using an ion beam etching process (beam energy of approximately 500-1000 eV), the photoresist in the non-coding areas and the underlying multilayer films are etched away, leaving only the protective adhesive and patterned emission layer structure in the coding areas.

[0057] S400: Photoresist removal cleaning. Removes excess photoresist to obtain the final emission-modulation integrated device.

[0058] In this embodiment, an integrated device is fabricated using magnetron sputtering combined with ultraviolet lithography and ion beam etching. Compared with traditional terahertz device assembly methods, this fabrication method has the following significant advantages:

[0059] (1) Monolithic integration, eliminating alignment errors: This method defines the coding pattern directly on the surface of the spintronic terahertz emission layer using photolithography, and removes the thin film in the non-radiative region using ion beam etching. This "subtractive manufacturing" method makes the spatially coded modulation structure and the emission layer physically inseparable monolithic whole. Compared with the existing technology of attaching independent photomasks to the surface of the emission source, this method completely eliminates the instability caused by interlayer alignment errors and mechanical fixation, ensuring the spatiotemporal synchronization of terahertz wave generation and modulation.

[0060] (2) Mature process with wafer-level manufacturing capability: The magnetron sputtering, spin coating, exposure, development and etching steps used in this embodiment are all micro-nano processing procedures that are standard in the semiconductor industry. This means that the integrated device can be mass-produced on 4-inch or 6-inch wafers, which not only greatly reduces the manufacturing cost of a single device, but also ensures extremely high consistency between different batches of devices, which is conducive to the commercialization of terahertz single-pixel imaging technology.

[0061] (3) High-resolution patterning capability: Using ultraviolet lithography, this method can easily achieve micron-level or even submicron-level feature size control. This enables us to accurately reproduce complex coded patterns (such as phase holograms or complex S-matrices) calculated based on diffraction reverse design algorithms, ensuring a high degree of consistency between theoretical design and actual device performance.

[0062] Example 5

[0063] Imaging experiments were conducted using the device (5×7 pixels, 2 mm resolution) prepared in Example 1. In the experiments, the object being tested was set as one of two slits with resolutions that were integer multiples of the device's resolution, corresponding to 2 mm (1 pixel) and 4 mm (2 pixels); and the object (slit) was placed at distances of 2 mm, 1 cm, and 3 cm, respectively. Figure 5 As shown, Figure 5 (b) ~ Figure 5(d) Direct reconstruction results at the three distances. To more intuitively demonstrate the imaging resolution, the reconstruction results at the three distances are binarized into 0 / 1 with a threshold of 0.5, as shown below. Figure 5 (f)~ Figure 5 As shown in (h).

[0064] Experimental results show that correct imaging of the test object can be achieved within a certain distance range, demonstrating the feasibility of the technical approach of directly preparing coded information on the transmitter surface for single-pixel imaging. The imaging resolution of this scheme is affected by the imaging distance; for the device with a resolution of 2 mm, a limit spatial resolution of 2 mm can still be maintained within a distance of 1 cm. When the imaging distance increases to 3 cm, the spatial resolution decreases to 4 mm.

[0065] Example 6

[0066] In fabricating the device of Example 1, to avoid distortion of the long-distance encoded pattern caused by diffraction, the fabricated pattern can be replaced with an encoded pattern optimized by the proposed reverse design algorithm. In this case, each region on the transmitter is equivalent to an independent terahertz emission source, and a clear encoded pattern can be projected at a specific distance through interference. For example... Figure 6 As shown, the simulation results of the output light field distribution are presented with or without reverse design. Figure 6 (a) shows a pre-defined, clear 8×8 pixel encoded pattern, with each pixel corresponding to a side length of 300 μm; Figure 6 (b) shows the distribution of the emitted light field at a working wavelength of 300 μm and a propagation distance of 3 mm. It can be seen that the coded pattern is completely distorted at this time, and the deformation is severe compared with the preset coded pattern. At this time, the target image cannot be reconstructed. Figure 6 (c) Shows the coded pattern to be processed on the transmitter surface after reverse engineering; Figure 6 (d) illustrates the distribution of the emitted light field after reverse engineering, at a working wavelength of 300 μm and a propagation distance of 3 mm. The projected coded pattern essentially retains the spatial structure information of the preset coded pattern, significantly improving far-field imaging capabilities and verifying the advantages of this invention in long-distance high-resolution imaging.

[0067] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some of the technical features; and these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of the present invention.

[0068] The above description is merely a specific embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any person skilled in the art can easily conceive of various variations or substitutions within the technical scope disclosed in the present invention, and these should all be included within the scope of protection of the present invention. Therefore, the scope of protection of the present invention should be determined by the scope of the claims.

Claims

1. A single-pixel imaging device integrating terahertz emission modulation, characterized in that, include: Spintronic terahertz emission layer; as well as Spatial coding modulation structure; The spatial coding modulation structure is conformally integrated with the spintronic terahertz emission layer on the same surface, and the coding pattern of the spatial coding modulation structure directly defines the radiation region and non-radiation region of the spintronic terahertz emission layer, so that the terahertz wave completes spatial coding synchronously at the moment of generation, thereby realizing the integration of emission and modulation in physical structure.

2. The device according to claim 1, characterized in that, The spintronic terahertz emission layer includes a ferromagnetic / non-magnetic multilayer thin film heterojunction, which is configured to generate terahertz radiation based on the inverse spin Hall effect under femtosecond laser pumping. The spatial coding modulation structure is a micro / nano pattern formed directly on the surface of the multilayer thin film heterojunction. The micro / nano pattern defines radiating and non-radiating regions on the device surface by selectively retaining or removing the material of the multilayer thin film heterojunction, so as to achieve spatial modulation of terahertz waves.

3. The device according to claim 2, characterized in that, The multilayer thin-film heterostructure includes a heavy metal layer, a ferromagnetic metal alloy layer and another heavy metal layer stacked sequentially. The ferromagnetic metal alloy layer is Co. 20 Fe 60 B 20 The two heavy metal layers are Pt and W, respectively.

4. The device according to claim 2, characterized in that, The micro-nano pattern is a concave-convex pattern, wherein the region where the multilayer thin film heterojunction is retained constitutes the radiating region, and the region where the multilayer thin film heterojunction is removed constitutes the non-radiating region.

5. The device according to claim 1, characterized in that, The coded pattern of the spatial coded modulation structure is a pre-corrected pattern based on the diffraction inverse design algorithm. The diffraction inverse design algorithm is configured to compensate for the light field distortion caused by far-field diffraction according to the preset imaging distance, so as to reconstruct the coded light field that matches the target pattern at the preset imaging distance.

6. The device according to claim 4, characterized in that, The diffraction inverse design algorithm is configured as follows: a light field diffraction model is established based on the angular spectrum propagation theory, and the error between the diffracted light field and the target light field is minimized through an iterative optimization algorithm, thereby obtaining the coded pattern.

7. The device according to claim 1, characterized in that, The spatial coding modulation structure is configured as a cyclic S-matrix or a Hadamard matrix and its variants. Since the terahertz wave is generated and carries spatial coding information, the theoretical modulation depth is close to 100%, depending only on the detection noise of the system.

8. A terahertz emission modulation integrated single-pixel imaging system, characterized in that, include: Pump light source, used to output excitation light pulses; The single-pixel imaging device according to any one of claims 1-7 is used to convert the excitation light pulse into a terahertz wave carrying spatial coding information; A focusing optical system is used to focus the structural terahertz wave illuminating the object onto a single-point terahertz detector for single-pixel imaging detection. A single-point terahertz detector is used to receive the total light intensity signal after reflection or transmission from a target; and The image reconstruction module is used to process the total light intensity signal based on a compressed sensing algorithm or a total variation algorithm to reconstruct the target image.

9. A method for fabricating a terahertz emission modulation integrated single-pixel imaging device, characterized in that, Includes one of the following two technical approaches: Route 1 includes the following steps: S100. A terahertz emission layer is formed by depositing nanoscale spintronics multilayer thin films on a substrate via magnetron sputtering. S200. Coat the surface of the terahertz emission layer with photoresist and use ultraviolet lithography to transfer the coded pattern of the mask to the photoresist layer, wherein the photoresist layer is used to protect the target pattern area in the subsequent etching process; S300. Ion beam etching is performed on the developed structure to remove the multilayer thin film in the areas not protected by photoresist, thereby retaining the patterned emission area and forming an integrated device; Route 2 includes the following steps: S100'. Photoresist is coated on the substrate, and the coded pattern of the mask is transferred to the photoresist layer using ultraviolet lithography, wherein the photoresist layer is used to block non-target pattern areas in the subsequent sputtering process; S200'. A terahertz emission layer is formed by depositing a nanoscale spintronics multilayer film on the photoresist layer and the substrate surface not covered by the photoresist by magnetron sputtering. S300'. A lift-off process is used to remove the photoresist area with multiple thin films, leaving the patterned emission layer in the area on the substrate that is not covered by photoresist, forming an integrated device.

10. The method according to claim 8, characterized in that, Before steps S200 and S100', the method further includes: pre-correcting the original coded pattern of the mask using a diffraction inverse design algorithm based on the target imaging distance to generate anti-diffraction pattern data.

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