Terahertz modulator based on VCSEL array and imaging system thereof

Abstract

The utility model discloses a terahertz modulator based on a vertical cavity surface emitting laser (VCSEL) array and an imaging system thereof. According to the modulator, a VCSEL array arranged in a matrix mode is adopted, and modulation of terahertz waves is achieved by directly irradiating output light of the array to a semiconductor modulation material. The system adopts an optical coupling structure to couple a space coding light field of the VCSEL array with terahertz waves, and the modulated terahertz waves are received through a single-point detector. According to the technical scheme, the problems of energy loss and speed limitation in the prior art are solved, the modulation efficiency and the system integration degree are improved, and the method has important application value in the fields of industrial nondestructive testing, biomedical imaging and the like.

Description

TECHNICAL FIELD

[0001] The utility model belongs to the field of terahertz imaging technology, concretely relates to a kind of terahertz modulator based on vertical cavity surface emitting laser array and its application system, mainly for the terahertz single-pixel imaging in the field such as industrial nondestructive testing, biomedical imaging. BACKGROUND

[0002] Terahertz imaging technology is an important application link in terahertz technology, and has important application prospect in industrial quality inspection, security and protection, biomedical and other fields. Due to the low yield, high price and poor performance of commercial terahertz area array detector, the development of terahertz imaging technology is limited.

[0003] To solve the above problems, terahertz single-pixel imaging technology has attracted widespread attention from scientific research and industry due to its low cost, high scalability and wide spectrum. The basic principle of this technology is to use a terahertz single-point detector combined with spatial coding and decoding technology to realize two-dimensional image reconstruction of the target object. Spatial coding and decoding technology is the core technology, which realizes two-dimensional modulation of terahertz light field on the one hand, and two-dimensional reconstruction of the target object on the other hand, involving the design of devices and algorithms.

[0004] Unlike visible light and infrared waveband, there are almost no commercial products for terahertz waveband spatial modulator. In recent years, the development of metasurface technology has provided a new solution for terahertz spatial modulation. For example, Watts et al. designed an 8x8 terahertz dynamic metamaterial absorber, which combined with compressed sensing algorithm to realize the imaging speed of seconds; Jin Biao et al. designed a liquid crystal metasurface terahertz modulator, which combined with adaptive compressed sensing algorithm to realize 8x8 terahertz imaging. However, although the metasurface terahertz modulator has good terahertz modulation efficiency, its imaging resolution is low due to the low design yield, and it cannot realize spectral imaging. These problems seriously restrict the promotion of metasurface terahertz modulation technology in practical application.

[0005] To overcome the limitations of metasurface technology, researchers have turned to photo-induced semiconductor terahertz modulation technology. This method uses photo-induced carriers to modulate terahertz waves, which not only realizes wide-spectrum terahertz modulation, but also significantly improves the imaging resolution. In specific implementation, researchers generally use a scheme of Digital Micromirror Device (DMD) combined with laser illumination. For example, She et al. proposed to use laser to irradiate DMD, and project the code in DMD to semiconductor silicon wafer through lens to realize two-dimensional modulation of terahertz light field. This scheme combined with compressed sensing algorithm realizes 32x32 terahertz imaging, and further combined with Hadamard and Fourier single-pixel imaging algorithm, the imaging time is shortened to 10% of the original.

[0006] However, the DMD and laser coding semiconductor-based scheme still has two main problems: first, when illuminating the DMD with a laser, the laser energy is severely lost due to diffraction effects, and the optical field energy is closely related to the terahertz modulation depth, and this energy loss will directly lead to insufficient terahertz wave modulation and reduce the imaging quality; second, the highest refresh speed of the DMD is only 20-30 kHz, which does not match the response speed of the semiconductor itself, limiting the modulation speed of the terahertz optical field, and thus fast imaging cannot be achieved.

[0007] In summary, the existing terahertz single-pixel imaging technology still faces many challenges: the metasurface technology has a simple structure, but has low resolution and cannot achieve spectral imaging; the photo-induced semiconductor technology can achieve wide-spectrum modulation and relatively high resolution, but has the problems of low energy utilization efficiency and limited modulation speed. These technical bottlenecks seriously restrict the practical application of terahertz imaging technology, and a new type of terahertz modulation technology is urgently needed to overcome the above defects. Practical new type

[0008] In view of the problems existing in the prior art, the present application provides a terahertz modulator based on a vertical cavity surface emitting laser (VCSEL) array and an application system thereof. The application adopts a technical solution of directly outputting a VCSEL array acting on a semiconductor modulation material, avoiding the energy loss problem in the traditional DMD reflection scheme; at the same time, through the design of a special driving circuit and control system, high-speed matrix scanning is realized, breaking through the limitation of the refresh speed of the DMD. Specifically, the present application provides the following technical solutions:

[0009] A terahertz modulator based on a vertical cavity surface emitting laser (VCSEL) array, the modulator comprising a VCSEL array arranged in a matrix, a driving circuit for controlling the VCSEL array, and a semiconductor modulation material arranged on the light output path of the VCSEL array. The driving circuit generates a spatially coded optical field by controlling the switching of the VCSEL array, and the optical field irradiates the semiconductor modulation material to modulate the terahertz wave. This direct action scheme avoids the energy loss caused by the traditional DMD reflection, and also lays the foundation for high-speed modulation.

[0010] Preferably, the VCSEL array adopts a common anode structure, and the anodes of all VCSELs are connected to the same power supply end, and the cathodes are independently led out to form a plurality of control ends. This structure design not only simplifies the power supply wiring, but also improves the consistency of the power supply, effectively reducing the power consumption of the system.

[0011] In some embodiments, the driving circuit of the VCSEL array adopts a complementary structure, including a plurality of P-type metal oxide semiconductor tubes and a plurality of N-type metal oxide semiconductor tubes, wherein the drains of the P-type tubes are connected with the rows of the VCSEL array respectively, and the drains of the N-type tubes are connected with the columns respectively. This complementary driving scheme not only reduces the static power consumption, but also realizes a faster switching speed.

[0012] Further, the VCSEL array is directly fixed on the printed circuit board and electrically connected with the driving circuit. This directly fixed structure design improves the integration of the system, improves the heat dissipation performance, and makes the system more compact and reliable.

[0013] The utility model also provides a kind of terahertz imaging system, including above-mentioned terahertz modulator, terahertz emitter, optical coupling piece and terahertz detector. Wherein, optical coupling piece is arranged between terahertz emitter and semiconductor modulation material, for guiding terahertz wave and VCSEL array emitted spatially encoded light field to semiconductor modulation material;Terahertz detector is used to receive modulated and pass through the terahertz wave of measured object, and the received terahertz wave is converted into electrical signal.This system composition realizes the efficient coupling of optical path, ensures the imaging quality.

[0014] A kind of terahertz imaging system, comprising:

[0015] The above-mentioned terahertz modulator is used to generate spatially encoded light field and modulate terahertz wave;

[0016] Terahertz emitter is used to generate and emit terahertz wave as detection light source;

[0017] Optical coupling piece is arranged between the terahertz emitter and the semiconductor modulation material, for guiding the terahertz wave emitted by the terahertz emitter and the spatially encoded light field emitted by the vertical cavity surface emitting laser array to the semiconductor modulation material;

[0018] Terahertz detector is used to receive modulated and pass through the terahertz wave of measured object, and the received terahertz wave is converted into electrical signal;

[0019] Wherein, the spatially encoded light field emitted by the vertical cavity surface emitting laser array is irradiated onto the semiconductor modulation material after passing through the optical coupling piece, and the terahertz wave emitted by the terahertz emitter sequentially passes through the semiconductor modulation material and measured object after passing through the optical coupling piece, and finally is received by the terahertz detector.

[0020] Preferably, the optical coupling of the system adopts indium tin oxide glass arranged in an inclined manner, for reflecting the spatially encoded light field and transmitting the terahertz wave, or reflecting the terahertz wave and transmitting the spatially encoded light field. This design greatly improves the light energy utilization efficiency of the system.

[0021] In some embodiments, the system further comprises a projection lens arranged between the VCSEL array and the optical coupling, for shaping and projecting the spatially encoded light field onto the optical coupling. This optical design improves the accuracy of spatial encoding.

[0022] The system is preferably configured with a field programmable gate array (FPGA) controller electrically connected to the driving circuit of the VCSEL array, for outputting matrix scanning control signals to realize row and column driving of the VCSEL array, thereby improving the control accuracy and response speed of the system.

[0023] Further, the system further comprises a memory for storing a preset spatial encoding pattern and an encoding controller for controlling the VCSEL array according to the preset spatial encoding pattern. This configuration enables the system to flexibly implement various encoding strategies.

[0024] In other embodiments, the system is equipped with a data acquisition card electrically connected to the terahertz detector for acquiring electrical signals and a processor for processing the acquired electrical signals and reconstructing target images, realizing efficient signal acquisition and processing.

[0025] The utility model discloses a through the innovative scheme of VCSEL array direct action on semiconductor material, realized many technical improvements and breakthroughs. Compared with the prior art, the following technical effects are mainly embodied:

[0026] Firstly, in terms of energy utilization efficiency, the utility model avoids the diffraction loss problem in the traditional DMD reflection scheme. Since the light of the VCSEL array is directly irradiated onto the semiconductor material, there is no need for intermediate links such as reflection and imaging, greatly reducing the loss of optical energy. This efficient energy utilization directly improves the modulation depth of the terahertz wave, thereby significantly improving the imaging quality.

[0027] Secondly, in terms of modulation speed, the utility model breaks through the 20-30kHz refresh speed limit of DMD. By designing a complementary driving circuit structure and cooperating with a matrix scanning control strategy, the system can fully utilize the high-speed characteristics of the VCSEL device, realizing faster modulation speed. This speed improvement not only speeds up the time of single imaging, but also creates conditions for realizing real-time imaging.

[0028] In terms of integration and reliability, the utility model discloses a direct mount process is used to fix the VCSEL array on the printed circuit board, and wiring is simplified through the common anode structure. This design not only improves the integration of the system, makes the overall structure more compact, but also improves the heat dissipation performance, improves the working stability and reliability of the system.

[0029] In terms of optical path design, the utility model discloses the high -efficient coupling of spatial coding light field and terahertz wave through the special design optical coupling structure. Compared with the super surface technology, this scheme not only improves the spatial resolution, but also maintains good spectral characteristics, and can realize the terahertz modulation of wide frequency band.

[0030] In terms of control precision, the utility model discloses the spatial coding method based on time sequence decomposition, and the complex Hadamard coding is converted into simple row and column control signals, which not only guarantees the integrity of the coding, but also simplifies the control implementation. This control strategy significantly improves the working stability and repeatability of the system.

[0031] Finally, in terms of system cost, the VCSEL array used in the utility model has a good industrialization basis, and the simplified system structure significantly reduces the overall cost. This high cost-effective solution creates favorable conditions for the practical application and promotion of terahertz imaging technology.

[0032] In summary, the utility model not only solves the key problems in the prior art, but also realizes overall improvement in multiple technical indicators, showing good application prospects. The realization of these technical effects provides a new idea and scheme for the development of terahertz imaging technology. BRIEF DESCRIPTION OF DRAWINGS

[0033] Figure 1 is the principle diagram of the VCSEL array of the utility model;

[0034] Figure 2 is the principle diagram of the driving circuit of the utility model;

[0035] Figure 3 is the PCB layout of the utility model, wherein: Figure 3 (a) is the PCB board of the VCSEL array; Figure 3 (b) is the PCB processing diagram of the driving board;

[0036] Figure 4 is the overall structure schematic diagram of the terahertz single-pixel imaging system of the utility model;

[0037] Figure 5 is the flow chart of the terahertz single-pixel imaging method of the utility model;

[0038] Figure 6It is the timing decomposition drawing of the Hadamard mask of the utility model;

[0039] Figure 7 It is the FPGA timing diagram based on the Hadamard mask of the utility model. DETAILED DESCRIPTION

[0040] The technical solutions of the patent will be further explained in detail in combination with specific embodiments. It should be pointed out that the following detailed explanations are exemplary and aim to provide further explanation of the utility model. However, it is known to those skilled in the art that the technical solutions are still applicable to multiple application scenarios. Unless otherwise specified, all technical and scientific terms used in this paper have the same meaning as generally understood by those skilled in the art to which the utility model belongs.

[0041] Embodiment one: terahertz modulator based on VCSEL array

[0042] The embodiment provides a novel terahertz modulator, and the core innovation is to use a vertical cavity surface emitting laser (VCSEL) array as a modulation light source, and to realize efficient modulation of terahertz waves by directly irradiating the output light of the VCSEL array onto a semiconductor modulation material. This direct action scheme not only avoids the energy loss problem in the traditional scheme, but also lays the foundation for realizing high-speed modulation. The specific implementation mode of the modulator will be described in detail below.

[0043] The structural design of the VCSEL array is the key to realizing efficient terahertz modulation, and its arrangement mode and control interface directly affect the modulation performance and control flexibility of the system. Figure 1 It is the principle diagram of the VCSEL array of the utility model, which shows the overall layout structure, distribution of row and column interfaces and internal connection mode of the array. As shown in Figure 1 The embodiment adopts a large-scale array structure of 32x32, with a total of 1024 VCSEL units. These units are arranged in a matrix, which not only ensures sufficient degrees of freedom of spatial coding, but also facilitates efficient control. From Figure 1 It can be clearly seen that the entire array adopts a common anode structure design, that is, the anodes of all VCSEL units are connected to the same power supply end. Specifically, these anodes are controlled through Figure 1 The 32 row interfaces labeled "32+" to "1+" on the right; while the cathode of each VCSEL is controlled individually through the 32 column interfaces labeled "32-" to "1-" at the bottom. This row-column control structure greatly simplifies the wiring complexity, and also provides convenience for subsequent matrix scanning control.

[0044] In order to ensure that the VCSEL array can work stably and efficiently, the parameters of the VCSEL unit are optimized in this embodiment. In terms of electrical characteristics, the forward voltage of a single VCSEL is 2V. The selection of this voltage value ensures that the device can be reliably turned on, and does not cause excessive power consumption. The threshold current is set to 1.3mA, which ensures that the VCSEL can stably emit laser, while maintaining the power consumption within a reasonable range. The reverse voltage is also set to 2V, which provides sufficient safety margin for the device. In particular, the selection of these parameters allows the device to work stably in a wide temperature range of-30℃ to 80℃, which is very important for practical applications.

[0045] In terms of optical characteristics, the wavelength selection and optical power design of the VCSEL array are directly related to the effect of terahertz modulation. Each VCSEL unit emits 850nm near-infrared laser. The selection of this wavelength takes into account the photoelectric characteristics of semiconductor materials, which can effectively excite carriers for modulation. The optical power of a single VCSEL is set to 5mW, which is determined after precise calculation. This power level can ensure sufficient excitation of semiconductor materials, and will not cause excessive heat effect. The half divergence angle of the device is controlled at 10°. This moderate divergence characteristic ensures the uniformity of the light spot, while avoiding excessive diffusion of energy, which is beneficial to improve the energy utilization efficiency of the system.

[0046] In order to realize accurate control of large-scale VCSEL array, the design of the driving circuit is very important. Figure 2 is the principle diagram of the driving circuit of the utility model, which shows the complete driving circuit structure, including the PMOS driving module in the upper half and the NMOS driving module in the lower half, and the corresponding resistance configuration network. The figure clearly shows the specific connection mode of each driving unit, and the corresponding relationship between the control signal and the device. As shown in Figure 2 The driving circuit adopts a complementary structure design. The upper half uses P-type metal oxide semiconductor tube (PMOS), model SI2301CDS-T1-GE3, responsible for row driving; the lower half uses N-type metal oxide semiconductor tube (NMOS), model AO3400A, responsible for column driving. This complementary structure makes PMOS as a high-end switch, which can provide high-level output close to the power voltage, ensuring that the VCSEL obtains sufficient driving voltage; while NMOS as a low-end switch, has excellent conduction characteristics, and can provide stable and reliable ground path.

[0047] In the specific implementation of the driving circuit, the bias network of each MOS tube is optimized. From Figure 2As can be clearly seen, the gate of each MOS transistor is connected to two resistors of different resistance values simultaneously: a 51kΩ bias resistor and a 1kΩ pull-up / pull-down resistor. The dual-resistor configuration serves multiple purposes: the large 51kΩ resistor provides a stable bias condition, prevents the gate from floating, and effectively suppresses the leakage current; the small 1kΩ resistor provides a fast charge / discharge path during switching, significantly improving the dynamic response characteristics of the circuit. The synergistic effect of the two resistors not only improves the reliability of the drive circuit, but also enhances the anti-interference ability of the system.

[0048] In terms of hardware implementation, the utility model adopts a special printed circuit board (PCB) design. Figure 3 A complete PCB layout scheme is shown, in which Figure 3 (a) is the PCB design for the VCSEL array, Figure 3 (b) is the PCB design for the drive board. These two figures fully present the circuit layout, the position distribution of key devices, and the wiring scheme of signal lines. First, let's look at Figure 3 (a) the VCSEL array PCB board shown in the figure, which adopts a standard size of 8cm x 8cm, and a 62mm x 62mm VCSEL light-emitting area is arranged in the central region, and each VCSEL unit occupies an area of 2mm x 2mm. The setting of these size parameters not only ensures sufficient spatial resolution, but also takes into account the feasibility of the processing technology. It is particularly important to note that the PCB board leads out the P16 interface on the lower edge and the right edge respectively, and adopts a radial wiring method. This layout not only ensures signal integrity, but also facilitates subsequent assembly and maintenance.

[0049] Figure 3 (b) the drive board adopts a highly symmetrical layout design, reflecting the comprehensive consideration of signal integrity and electromagnetic compatibility. The drive board is provided with 2 P16 interfaces on the left and right sides, respectively, corresponding to the interfaces on the VCSEL array board. It is particularly noteworthy that the central region of the drive board is arranged with 64 independent pin arrays, which are specially used for connecting with the general IO port of the FPGA. The layout of the pin array is optimized, which not only shortens the signal transmission path, but also provides a good ground reference plane, effectively reducing signal interference.

[0050] In the aspect of packaging process, the utility model discloses advanced chip direct bonding (COB) technology. This technology breaks through the limitation of traditional packaging mode, through directly bonding VCSEL chip on specially designed PCB substrate, then realizing electrical interconnection by wire bonding technology, finally carrying out overall packaging protection. The adoption of COB technology brings many technical advantages: first, because of the independent packaging link is saved, the integration of the system is significantly improved, so that the whole modulator module is more compact;Second, the direct contact of chip and PCB provides a shorter heat conduction path, forms an efficient heat dissipation channel, effectively improves the thermal performance of the device;Third, the shortening of the electrical connection distance significantly reduces the influence of parasitic effect, improves the electrical performance of the system;Finally, this packaging mode also has better mechanical stability, improves the overall reliability of the system.

[0051] In actual work process, the control process of the modulator embodies the high integration and cooperation of system design. First, FPGA will output control signals through 64 general IO ports on the driving board according to the pre-set encoding scheme. These signals are converted into accurate row and column control levels through carefully designed driving circuit. Through the ordered combination of row and column control signals, the system can realize accurate control of any position unit in the VCSEL array. Especially worth mentioning is that, thanks to the adoption of efficient driving circuit design and matrix control strategy, the modulation speed of the modulator has far exceeded the limitation of 20-30kHz of traditional DMD scheme, which provides the possibility for high-speed terahertz imaging. More importantly, since the light of VCSEL can directly act on the semiconductor modulation material, the energy loss caused by multiple reflections in the DMD scheme is completely avoided, greatly improving the energy utilization efficiency of the system.

[0052] Overall, the modulator of the embodiment has unexpected technical effects in multiple technical indicators through the above design. In terms of modulation efficiency, the scheme of directly using VCSEL array matrix fundamentally solves the energy loss problem in the traditional scheme, providing deeper modulation depth;In terms of modulation speed, the new driving scheme breaks through the speed bottleneck of DMD, creating conditions for real-time imaging applications;In terms of system reliability, COB packaging technology and optimized heat dissipation design ensure that the system can run stably under various working conditions;In terms of integration, the compactness and modularity of the overall design greatly improve the practicability of the system. The comprehensive embodiment of these technical advantages makes the modulator particularly suitable for high-demand terahertz imaging occasions.

[0053] Embodiment two: terahertz single-pixel imaging system

[0054] The embodiment provides a single-pixel imaging system based on the foregoing terahertz modulator. Figure 4 It is the whole structure schematic diagram of the terahertz single-pixel imaging system, and the figure completely shows the light path arrangement, the spatial position relation of various function modules and the signal transmission path of the system.

[0055] In the overall light path design, the system adopts an optical coupling scheme to realize the effective combination of spatially encoded light field and terahertz wave.

[0056] In the embodiment, the inclination angle of the ITO glass is optimized to ensure the effective coupling of the two light beams.

[0057] In order to improve the accuracy of spatial coding, the embodiment sets a projection lens between the VCSEL array and the optical coupling element.

[0058] In terms of control system, the embodiment designs a complete control and data acquisition processing scheme. The core is the FPGA-based controller, which is responsible for generating accurate control signals according to the preset encoding sequence. These signals are converted into row and column control levels of the VCSEL array through a special driving circuit, realizing high-speed modulation of the spatial light field. At the same time, the system is equipped with a high-performance data acquisition card for acquiring the electrical signals output by the terahertz detector. These signals are processed in real time by the processor, and finally the image of the target object is reconstructed.

[0059] After the terahertz wave passes through the modulation and the object to be measured, it is focused by the second lens and received by the terahertz detector. The embodiment uses a high-sensitivity single-point detector, which not only reduces the cost of the system, but also avoids various technical limitations of the area array detector in the terahertz wave band.

[0060] Each component of the entire system has undergone precise spatial layout and optical path matching design. For example, the position and angle of the optical elements are strictly calculated to ensure the collimation and coupling effect of the optical path; the arrangement of the control unit and the data acquisition module takes into account the timing requirements of signal transmission, minimizing interference and delay.

[0061] At the same time, the system also has good scalability, mainly reflected in the following aspects: First, the flexibility of semiconductor modulation material selection. The system can select different semiconductor materials according to actual needs, for example, using a silicon wafer can adapt to the imaging needs of 0.5-2THz frequency band, using a gallium arsenide wafer can expand to a higher frequency range, and using a germanium wafer can obtain higher modulation efficiency. The selection of different materials provides the possibility for the optimization of the system in different application scenarios. Second, the adjustability of the optical system parameters. By adjusting the focal length of the projection lens, the imaging size of the VCSEL array on the semiconductor surface can be changed, thereby affecting the resolution of spatial modulation; by adjusting the parameters of the collimating and focusing lenses, the working distance and field of view of the system can be changed, for example, using a large-aperture lens can obtain a larger field of view, and using a long-focus lens can realize long-distance imaging. Third, in terms of control strategy, the system also has diversified adjustment space. For example, different scanning strategies can be selected according to the imaging speed requirements, local scanning mode can be used when high-speed imaging is required, and complete encoding sequence can be used when high-quality imaging is pursued; appropriate encoding scheme can also be selected according to the characteristics of the object to be measured, for example, compressed sensing algorithm can be used for sparse targets to improve imaging efficiency, and special encoding sequence can be used for applications requiring spectral information to realize spectral resolution.

[0062] It should be noted that the above specific implementation manners are only preferred technical solutions. Based on the understanding of the technical concept of the present application, those skilled in the art can make appropriate adjustments to the system structure according to actual needs. For example, different specifications of optical elements can be selected according to actual application, or other types of optical coupling schemes can be used, as long as the technical effects of the present application can be achieved, which should belong to the protection scope of the present application.

[0063] Embodiment three: terahertz single-pixel imaging method

[0064] In order to further facilitate the understanding of the working principle of the terahertz single-pixel imaging system, the preferred imaging method is further described.

[0065] The embodiment provides an imaging method based on the foregoing terahertz single-pixel imaging system, and mainly illustrates how to realize efficient terahertz imaging through two-dimensional spatial coding controlled by FPGA. The method projects the coding mask on the semiconductor (the semiconductor can be a silicon wafer, a germanium wafer or a gallium arsenide wafer) through the projection lens, realizes the two-dimensional light field control of the terahertz wave. By changing the distribution P of the spatial mask, the coding intensity I at this time is collected by the acquisition card, the target image Y is reconstructed, Y=PI. This method not only avoids the energy loss problem in the traditional scheme, but also realizes efficient modulation of the terahertz wave.

[0066] Figure 5 It is a flowchart of the terahertz single-pixel imaging method of the present application, which completely shows the whole process from spatial coding generation to image reconstruction, including the generation of Hadamard coding, mask conversion, time sequence decomposition, VCSEL array control, signal acquisition and image reconstruction and the logical relationship between them. The organic combination of these steps ensures the efficient implementation of the whole imaging process.

[0067] In the present application, the mask image is preferably set as a Hadamard mask, which is selected based on the orthogonality and completeness characteristics of Hadamard transform. The Hadamard mask P(x,y) can be obtained by inverse Hadamard transform of the impulse function:

[0068]

[0069] Wherein, x, y are Cartesian coordinates, u, v are frequency domain coordinates, H-1 is inverse Hadamard transform, and δ(u,v) is an impulse function: when u=u0, v=v0, δ(u,v)=1; otherwise, δ(u,v)=0. This mathematical expression ensures the completeness and orthogonality of the coding.

[0070]

[0071] In actual implementation, since the Hadamard mask is composed of -1 and 1, and the VCSEL array can only represent two states of laser on and off, the Hadamard mask needs to be processed differentially. First, a Hadamard mask P(x, y) is generated, wherein -1 is set to 0, and then another mask is obtained by using [1-P(x, y)]. Through this conversion, the binary Hadamard code can be adapted to the physical characteristics of the VCSEL array. Then the Hadamard spectrum can be obtained by difference:

[0072] H(u, v) = D + -D -

[0073] Wherein, the signal D + and D- represent the intensity values obtained by projecting the mask P(x, y) and the mask [1-P(x, y)], respectively, and the reconstructed target image R = H -1 (H(u, v)). This differential processing method not only ensures the integrity of the code, but also improves the signal-to-noise ratio.

[0074] Figure 6 It is a timing diagram of the Hadamard mask of the utility model, which details how to decompose a 3x3 Hadamard mask into four timing masks. The -1 and +1 Hadamard mask is decomposed into two masks composed of only 0 and 1, and each mask can be decomposed into two timing masks, that is, one Hadamard mask is decomposed into four timing, and each timing mask will correspond to three row signals and three column signals. This timing decomposition strategy fully considers the row and column scanning characteristics of the VCSEL array, and realizes the effective conversion of spatial coding to hardware control.

[0075] Figure 7 It shows the FPGA timing diagram based on the Hadamard mask, which specifically explains the timing control of the general IO of the FPGA for the 3x3 Hadamard mask. Three row signals (P1-P3) and three column signals (N1-N3) are used, when the row signal is 101 and the column signal is 011, the VCSEL displays Figure 6 ① in the middle; and when the row signal is 010 and the column signal is 101, it corresponds to display Figure 6 ② in the middle; when the row signal and the column signal are 101 and 101 respectively, it corresponds to display Figure 6 ③ in the middle; and finally, when the row signal and the column signal are 010 and 010 respectively, the VCSEL array displays the distribution of Figure 6 ④ in the middle. This timing control scheme not only ensures the accurate presentation of the coded pattern, but also improves the working efficiency of the system.

[0076] In the aspect of signal acquisition and processing, the method adopts a complete differential processing strategy. The masks of ①, ②, ③ and ④ are projected respectively to obtain terahertz encoding signals d1, d2, d3 and d4, then H(3, 3) = (d1+d2)-(d3-d4), and other frequency components of H(u, v) can be traversed in the same way, so as to obtain the Hadamard spectrum of the target image, and the target image is reconstructed by using the inverse Hadamard transform. This processing method effectively suppresses system noise and improves the quality of image reconstruction.

[0077] In practical applications, for targets with strong spatial sparsity, the imaging speed can be improved by reducing the sampling frequency in combination with the theory of compressed sensing; for dynamic scenes, an adaptive scanning strategy can be designed to realize rapid tracking; and for specific application requirements, specific performance indicators can be improved by optimizing the encoding sequence. The implementation of these optimization strategies benefits from the flexibility of the method framework.

[0078] It should be noted that the above specific implementation manners are only exemplary descriptions, and those skilled in the art can make various changes on the basis of the scheme of the utility model. For example, the resolution of the Hadamard mask can be adjusted according to actual requirements, different encoding sorting methods can be used, or other types of encoding sequences can be designed. As long as these changes do not deviate from the technical idea of the utility model, they should belong to the protection scope of the utility model.

[0079] In summary, the utility model provides a terahertz modulator based on a vertical cavity surface emitting laser (VCSEL) array and an application system and method thereof, forming a complete technical solution. From hardware to method, from device to system, innovative design and optimization are carried out at each level.

[0080] At the modulator level, the utility model adopts a scheme in which the VCSEL array directly acts on the semiconductor material, breaking through the limitation of the traditional DMD reflection scheme. Through the design of a common anode structure and a complementary driving circuit, efficient control of the VCSEL array is realized. In particular, the use of chip direct mounting technology and reasonable heat dissipation design significantly improves the integration and reliability of the system. This innovative design not only fundamentally solves the problem of energy loss, but also realizes a modulation speed higher than that of the DMD scheme.

[0081] At the system level, the utility model realizes efficient coupling of spatially encoded light field and terahertz waves through ingenious optical path design. Indium tin oxide glass is used as an optical coupling element, which not only ensures efficient use of optical energy, but also simplifies the system structure. The modular design and standardized interface of the system not only provide good scalability, but also facilitate practical application and maintenance.

[0082] At the method level, the utility model develops complete space coding and image reconstruction scheme. Through the design of Hadamard coding and time sequence decomposition, the theoretical coding scheme is successfully converted into the hardware control strategy which can be realized. The accurate control based on FPGA and differential signal processing not only ensure the accurate realization of coding, but also improve the signal noise ratio, finally realize the high quality image reconstruction.

[0083] Through the organic combination of these technical innovations, the utility model has achieved significant technical effects in multiple aspects: first, the comprehensive improvement of performance. Compared with the prior art, the utility model not only improves the modulation efficiency, but also realizes faster modulation speed, while maintaining good signal quality. Second, the high integration of the system. The use of advanced technologies such as direct mounting makes the system more compact and reliable. Third, the flexibility of application. The modular design and scalable control scheme of the system make it adapt to various actual application requirements. Finally, the optimization of cost. Through reasonable technical route selection and design optimization, the performance is improved while the system cost is controlled.

[0084] The realization of these technical effects provides new possibilities for the practical application of terahertz imaging technology, especially suitable for industrial nondestructive testing, biomedical imaging and other application scenarios with high requirements for imaging efficiency and quality.

[0085] The above only describes some embodiments of the utility model. For those skilled in the art, without departing from the creative concept of the utility model, a number of modifications and improvements can be made, which all belong to the protection scope of the utility model.

Claims

1. A VCSEL array based terahertz modulator comprising a semiconductor modulating material, characterized in that, The terahertz modulator further comprises: a vertical cavity surface emitting laser array arranged in a matrix, comprising a plurality of vertical cavity surface emitting lasers; a driving circuit electrically connected to the vertical cavity surface emitting laser array, configured to control the switching of each vertical cavity surface emitting laser in the vertical cavity surface emitting laser array; the semiconductor modulation material is arranged on the light emitting path of the vertical cavity surface emitting laser array; wherein the driving circuit generates a spatially encoded light field by controlling the switching of the vertical cavity surface emitting laser array, and the spatially encoded light field irradiates the semiconductor modulation material to modulate the terahertz wave.

2. The terahertz modulator of claim 1, wherein, The vertical cavity surface emitting laser array is of a common anode structure, and the anodes of all the vertical cavity surface emitting lasers in the vertical cavity surface emitting laser array are connected to the same power supply end, and the cathodes are independently led out to form a plurality of control ends.

3. The terahertz modulator of claim 2, wherein, The driving circuit comprises: a plurality of P-type metal oxide semiconductor tubes and a plurality of N-type metal oxide semiconductor tubes, the drains of the P-type metal oxide semiconductor tubes are respectively connected to the same power supply end, and the drains of the N-type metal oxide semiconductor tubes are respectively connected to the plurality of control ends.

4. The terahertz modulator of claim 1, wherein, The vertical cavity surface emitting laser array is directly fixed on a printed circuit board and electrically connected to the driving circuit.

5. A terahertz modulator imaging system, characterized by, It comprises: the terahertz modulator according to any one of claims 1-4, which is used to generate a spatially encoded light field and modulate a terahertz wave; a terahertz emitter, which is used to generate and emit a terahertz wave as a probe light source; an optical coupling element arranged between the terahertz emitter and the semiconductor modulation material, which is used to guide the terahertz wave emitted by the terahertz emitter and the spatially encoded light field emitted by the vertical cavity surface emitting laser array to the semiconductor modulation material; a terahertz detector, which is used to receive the modulated terahertz wave that has passed through an object to be detected and convert the received terahertz wave into an electrical signal; wherein the spatially encoded light field emitted by the vertical cavity surface emitting laser array irradiates the semiconductor modulation material after passing through the optical coupling element, and the terahertz wave emitted by the terahertz emitter passes through the semiconductor modulation material and the object to be detected in sequence after passing through the optical coupling element, and is finally received by the terahertz detector.

6. The terahertz modulator imaging system of claim 5, wherein, The optical coupling element is an indium tin oxide glass arranged obliquely, which is used to reflect the spatially encoded light field and transmit the terahertz wave, or to reflect the terahertz wave and transmit the spatially encoded light field.

7. The terahertz modulator imaging system of claim 5, wherein, It further comprises: a projection lens arranged between the vertical cavity surface emitting laser array and the optical coupling element, which is used to shape and project the spatially encoded light field onto the optical coupling element.

8. The terahertz modulator imaging system of claim 5, wherein, It further comprises: a field programmable gate array controller electrically connected to the driving circuit of the vertical cavity surface emitting laser array, which is used to output a matrix scanning control signal to realize the row and column driving of the vertical cavity surface emitting laser array.

9. The terahertz modulator imaging system of claim 5, wherein, It further comprises: a memory for storing a preset spatially encoded pattern; and a terahertz modulator according to any one of claims 1-4, which is used to generate a spatially encoded light field and modulate a terahertz wave; A coding controller is electrically connected with the memory and the driving circuit of the vertical cavity surface emitting laser array, and is used for controlling the vertical cavity surface emitting laser array according to the preset spatial coding pattern.

10. The terahertz modulator imaging system of any of claims 5-9, wherein, Further comprising: A data acquisition card is electrically connected with the terahertz detector, and is used for acquiring the electrical signal output by the terahertz detector; And a processor is electrically connected with the data acquisition card, and is used for processing the electrical signal acquired by the data acquisition card and reconstructing a target image.

Images