Ultra-sensitive terahertz biochemical sensor based on asynchronous twin comb principle

Abstract

The invention discloses an ultra-sensitive terahertz biochemical sensor based on an asynchronous twin comb principle, and belongs to the technical field of terahertz application. According to the device, four parallel transmission channels are formed in a metal waveguide through a cascade double-layer micro-channel, and are used for matching a characteristic time domain sequence of a terahertz asynchronous twin comb. The high-frequency characteristic resonance frequency outside the frequency spectrum is positioned by tracking the double envelopes of the twin comb in the effective frequency spectrum range, so that the device breaks through the limitation of the effective frequency spectrum range, and an out-spectrum sensing scheme with ultrahigh sensitivity is realized. The sensitivity of the device in biochemical sample detection reaches 1011 GHz / (g / mm < 2 >) magnitude, the detection precision reaches 10-12 g / mm < 2 > magnitude, the sensitivity is improved by 4 orders of magnitude compared with the existing terahertz biochemical sensing sensitivity, the breakthrough exceeding the sensing sensitivity of a communication band is realized, and based on this, the device can be used for observing the photoisomerization phenomenon of azo dyes in the terahertz frequency band. The device breaks through the characteristic of out-of-spectrum high-sensitivity sensing in an effective spectral range, so that the device has application potential in the field of terahertz biochemical sensing.

Description

Technical Field

[0001] The present invention belongs to the technical field of terahertz applications, and particularly relates to a highly sensitive terahertz biochemical sensor based on the asynchronous twin comb principle. Background Art

[0002] The terahertz (0.1 - 10 THz) band matches the collective vibrational and rotational energy levels of many biochemical molecules, which is of great significance for revealing molecular dynamics information. Terahertz-based biochemical sensing exhibits high sensitivity, label-free, fast response, and feasibility of on-chip integration, and is widely used in substance spectral enhancement, trace analysis, and specific sensing. The fields of biomedicine, environmental monitoring, food safety, etc. have jointly witnessed its pioneering achievements. In recent research progress, hypersensors based on high-Q resonance metamaterial technology have been widely used to enhance the interaction between terahertz waves and substances. At the same time, breakthroughs in the specific detection of terahertz biochemical sensing have been achieved by combining means such as micro-nano functional materials, biological modification, and artificial intelligence [Adv. Mater., 2411490, (2024)]. However, when facing more precise trace analysis, the size of the sample to be measured is usually mismatched with the detection wavelength, thus limiting the further improvement of detection sensitivity [PhotoniX, 5, 10(2024)]. In addition, the resonance frequency generated by the hypersensor depends on the fixed structure of the device, making it challenging to achieve broadband response and obtain more abundant frequency shift and amplitude change information.

[0003] To further enhance the interaction between terahertz waves and matter and improve the sensing sensitivity, terahertz waveguide sensors have become a promising solution. However, traditional waveguide sensors based on electromagnetic resonance still face the restrictive relationship between broadband response and high Q, and their sensitivity is only on the order of hundreds of GHz / RIU [Appl. Phys. Lett., 121, 011101(2022)]. To further improve the sensing sensitivity and expand the broadband response ability of the sensor, it is expected to develop waveguide-based coherent detection technology, which exhibits ultra-high sensitivity characteristics in the visible and infrared bands. However, limited by the waveguide structure and coupling mode, its research in the terahertz band is still in its infancy. In previous work, a terahertz waveguide interferometer sensor was realized by constructing a dual-channel structure in a metal parallel-plate waveguide. Limited by the structural size and fabrication accuracy, its sensitivity is still limited within 1 THz / RIU [Sens. Actuator A-Phys., 370, 115282(2024)]. Further, by constructing a multi-channel structure in a metal waveguide, a terahertz vernier sensor with self-reference characteristics was formed, and the enhanced sensitivity reached the order of 10 THz / RIU [Fundamental Res., 5, 2 (2025)]. However, limited by the effective spectral range and the low-frequency characteristics of terahertz waves, there is still a large gap between the sensitivity and that in the visible and infrared bands.

[0004] Achieving a breakthrough in terahertz sensing sensitivity depends on the construction of multi-stage coherent signals and the acquisition of rich spectral information, which poses more stringent requirements on the initial time-domain signal structure. Optical frequency combs have dense spectral lines, and their role is like a frequency ruler, which has important advantages in obtaining rich spectral information. The dual-comb system combined with heterodyne detection shows advantages in detection speed, resolution, sensitivity, and dynamic range in typical applications such as high-resolution absorption spectroscopy, laser-based optical detection and ranging, distributed fiber sensing, and trace detection of biochemical samples [Nat. Commun., 15, 4990(2024)]. In recent years, the emergence of topological frequency combs has further revealed new applications of strongly driven nested comb systems in multi-region high-resolution analysis, providing a new perspective for obtaining richer spectral information [Science, 384, 1356-1361(2024)]. However, these technologies still focus on the characterization within the effective spectral range. Further breaking through the terahertz biochemical sensing sensitivity depends on a new technology that can break through the system's effective spectral range and obtain high-frequency spectral out-of-band sensing capabilities.

[0005] In summary, as a key window for next-generation high-speed wireless communication and high-resolution sensing, developing biochemical sensors with ultra-high sensitivity in the terahertz band has unique advantages and great significance. Its advantages lie in that compared with the communication band, the terahertz band reduces the requirements for sensor structure construction. In addition, terahertz time-domain spectroscopy technology facilitates the modulation of the sensor time-domain signal and provides richer possibilities for the construction and analysis of complex signals. Its significance lies in that on the one hand, the rapid development of terahertz technology and its biochemical sensing applications urgently require the development of high-performance terahertz sensors. Analyzing terahertz coherent detection technology from the time-domain perspective will bring new vitality to terahertz biochemical sensing. On the other hand, existing terahertz waveguide sensors have problems such as low integration, low sensitivity, and limited operating frequency. Therefore, developing a new type of terahertz waveguide sensor with high integration, high sensitivity, capable of breaking through the effective spectral range and obtaining out-of-band high-frequency sensing capabilities has important scientific research value. Summary of the Invention

[0006] The purpose of the present invention is to provide an ultrasensitive terahertz biochemical sensor based on the asynchronous twin-comb principle, solving key technical problems such as the low-frequency limitation, low sensitivity, and limited operating frequency range of terahertz sensors in the background technology.

[0007] To achieve the above purpose, the devices and structures of the present invention include: an upper metal waveguide plate (1), a first metal thin film (2), a second metal thin film (3), a first polymer material (4), a second polymer material (5), a lower metal waveguide plate (6), and a sample to be measured (7). Among them, the upper metal waveguide plate (1) and the lower metal waveguide plate (6) together form a terahertz metal waveguide. The taper region coupling angle of the metal waveguide is 10° - 20°. The distance between the upper and lower plates of the metal waveguide should be less than 100 μm. The axial transmission length of the metal waveguide is 10 - 20 mm, and the width along the z axis is 20 - 60 mm. The waveguide channel is isolated into four transmission regions by the first metal thin film (2) and the second metal thin film (3). The thickness of the first metal thin film (2) along the x axis is 2.5 - 10 μm, the length along the y axis is 5 - 60 mm, and the length along the x axis is 2 - 5 mm. The thickness of the second metal thin film (3) along the z axis is 3 - 12 μm, the length along the y axis is 5 - 60 mm, and the length along the x axis is 4 - 10 mm. The four transmission regions form four parallel transmission channels. Among them, regions one and two are air. Region one has an axial length of 2.5 - 25 μm along the z axis, an axial length of 5 - 60 mm along the y axis, and an axial length of 5 - 60 mm along the x axis, and an axial length of 5 - 60 mm along the zThe shaft length is 2 - 5 mm; Region two is along y The shaft length is 2 - 20 μm, along x The shaft length is 5 - 60 mm, along z The shaft length is 4 - 10 mm. Region two is mainly used for placing the sample to be measured (7); Region three and region four are respectively the first polymer material (4) and the second polymer material (5). The refractive index of the organic polymer material used is 1.2 - 1.53 in the 0.1 - 1 THz frequency band, and the extinction coefficient is less than 0.005. This material includes but is not limited to polyethylene. Among them, the first polymer material (4) is along y The shaft thickness is 5 - 50 μm, along x The shaft length is 5 - 60 mm, along z The shaft length is 2 - 5 mm and needs to be along with the first metal film (2) z The shaft length is equal; The second polymer material (5) is along y The shaft thickness is 5 - 50 μm and needs to be along with the first polymer material (4) y The shaft thickness is the same, along x The shaft length is 5 - 60 mm, along z The shaft length is 4 - 10 mm and needs to be along with the second metal film (3) z The shaft length is equal; To match and generate the characteristic time-domain sequence required for terahertz asynchronous twin comb and generate characteristic resonance frequencies outside the effective frequency spectrum range, the shaft length of the second polymer material (5) used in region four is along z The shaft length needs to be 10 - 400 μm larger or smaller than twice the shaft length of the first polymer material (4) used in region three z

[0008] ​The basic working principle of the present invention is as follows: When a terahertz wave is incident on the terahertz asynchronous twin-comb sensor, it will be split by two metal thin films and form four parallel transmission channels. Due to the different additional phases introduced by the material in the four transmission channels, the transmission signals of the four channels are detected successively. The signal time difference between Channel 1 and Channel 2 is the same as that between Channel 3 and Channel 4, but different from the signal time difference between Channel 2 and Channel 3. Thus, an inserted phase shift is introduced and the single-comb signal is modulated. In the frequency domain, it is manifested as the splitting of the optical frequency comb signal into twin-comb signals. The asynchronous characteristic of the twin-comb is manifested as the intensity of the twin-comb changing in an ebb and flow manner under the influence of the inserted phase shift. By tracking the intersection points of the twin-comb double envelopes, the high-frequency characteristic resonance frequency outside the effective spectral range of the twin-comb can be located. This frequency characterizes the interference cancellation between the comb signal and the modulation signal of the inserted phase shift. When the device is applied to sensing, the sample to be measured (7) is placed in Region 2, that is, on the upper surface of the second metal thin film (3). The off-spectrum characteristic resonance frequency of the terahertz asynchronous twin-comb sensor will have a significant frequency shift with the change of the sample quantity. Using the mechanism of off-spectrum sensing with the twin-comb spectrum can break through the limitation of the effective spectral range of the device. Affected by the high-frequency characteristics, the detection sensitivity and accuracy of the sensor will be significantly improved.

[0009] The working method of the terahertz asynchronous twin-comb off-spectrum ultrasensitive biochemical detection sensor is as follows: Use a terahertz time-domain spectroscopy (THz-TDS) system to detect the time-domain signal after passing through the device, and perform a Fourier transform on this signal to map the time-domain information into frequency-domain information. The periodic time-domain signal is modulated by the inserted phase shift, which is manifested as the splitting of the single-comb signal into an asynchronous twin-comb spectrum in the frequency domain. Extract the envelopes of the two comb signals in the twin-comb respectively, and locate the high-frequency characteristic resonance frequency outside the effective spectral range of the twin-comb according to the intersection points of the twin-comb double envelopes. The sample to be measured (7) is dropped in the form of an aqueous solution on the upper surface of the second metal thin film (3), and after drying, it is detected. When the sample to be measured (7) causes a change in the additional phase in Region 2, it will change the inserted phase shift of the twin-comb sensor, thereby causing a change in the twin-comb double envelope and a frequency shift of the off-spectrum characteristic resonance frequency. The sensing detection of the sample quantity is realized by detecting the magnitude of the frequency shift. The effective spectral range for the spectral detection of the sensor is 0.1 - 1 THz, and the characteristic resonance frequency sensing information in the 1 - 15 THz frequency range outside the effective spectral range is obtained by tracking the twin-comb double envelopes using the periodic characteristics of the twin-comb spectrum.

[0010] The beneficial effects and advantages of the present invention are:

[0011] 1. Generate the characteristic time-domain sequence of terahertz asynchronous twin-comb signals through the form matching of cascaded microchannels. Use a metal thin film to divide the waveguide channel into four independent regions, and obtain four parallel transmission channels through regional matching. Compared with the single-channel mode, the four-channel transmission method realizes the spatial division multiplexing of signals, improves the space utilization rate, and enables the transmitted signals to carry richer information.

[0012] 2. Drawing on the principle of optical frequency combs, modulate the comb signal by introducing defects, that is, inserting phase shifts, into the periodic time-domain signal. In the frequency domain, it is manifested as the splitting of a single comb to generate asynchronous twin-combs. The asynchronous characteristics of the twin-combs enable the envelopes of the two combs to be extracted separately, facilitating the acquisition of rich spectral information.

[0013] 3. Utilize the periodicity of the asynchronous twin-comb signal in the frequency domain. The characteristic resonance frequency outside the effective spectral range can be located by detecting the characteristics of the twin-comb signal within the effective spectral range, thereby breaking through the limitation of the system's effective spectral range and obtaining high-frequency sensing information, eliminating the low-frequency limitations of the terahertz band. Compared with traditional terahertz-band biochemical sensors, this device has the ability of extra-spectral sensing outside the effective spectral range. The spectral detection range of the device is 0.1 - 1 THz, and the characteristic resonance frequency for characterizing sensing information is in the extra-spectral high-frequency range of 1 - 15 THz.

[0014] 4. When the device is used for biochemical sample detection, the change in the sample volume will cause a change in the inserted phase shift in the time-domain signal of the sensor, thereby modulating the frequency-domain signal of the twin-combs. The high-frequency sensing characterization of the device's characteristic resonance frequency outside the spectrum improves the sensor sensitivity to the order of 10 3 THz / RIU, and the detection sensitivity to biochemical samples reaches 10 11 GHz / (g / mm 2 ) order of magnitude, and the accuracy reaches 10 -12 g / mm 2 order of magnitude. Compared with traditional terahertz biochemical sensors, the sensitivity is increased by four orders of magnitude, and the sensor sensitivity beyond the communication band is achieved. The high-sensitivity characteristics of the device can be used to observe the photoinduced isomerization phenomenon of azo dyes in the terahertz band, which is of great significance for the development of new materials for terahertz information storage. Description of the Drawings

[0015] Figure 1 It is a three-dimensional structural schematic diagram of a terahertz asynchronous twin-comb extra-spectral ultrasensitive biochemical detection sensor;

[0016] Figure 2 (a) is the planar schematic diagram and structural parameters of a terahertz asynchronous twin-comb extra-spectral ultrasensitive biochemical detection sensor yz ; (b) is the planar schematic diagram of the device xy ;

[0017] Figure 3 (a) is a schematic diagram of a four - region structure of a terahertz asynchronous dual - comb spectroscopy - based ultrasensitive biochemical detection sensor separated by two metal films; (b) is a schematic diagram of four parallel transmission channels composed of the four regions.

[0018] Figure 4 (a) is a schematic diagram of the change in the length of the polymer material two of the terahertz asynchronous dual - comb spectroscopy - based ultrasensitive biochemical detection sensor; (b) is the detection spectrum when the sensor generates a positive insertion phase shift; (c) is the detection spectrum when the sensor generates a negative insertion phase shift.

[0019] Figure 5 (a) is the time - domain signal when the insertion phase shift of the terahertz asynchronous dual - comb spectroscopy - based ultrasensitive biochemical detection sensor approaches 0; (b) is the detection spectrum when the insertion phase shift of the sensor approaches 0.

[0020] Figure 6 (a) is the detection result of the terahertz asynchronous dual - comb spectroscopy - based ultrasensitive biochemical detection sensor for different lactose area densities within the effective spectral range; (b) is the response of the out - of - band high - frequency characteristic resonance frequency obtained by the sensor tracking the dual - comb double - envelope to different lactose area densities; (c) is the curve of the out - of - band characteristic resonance frequency of the sensor varying with different lactose area densities; (d) is the curve of the out - of - band characteristic resonance frequency sensing frequency shift amount and sensitivity of the sensor.

[0021] Figure 7 (a) is the spectral result of the terahertz asynchronous dual - comb spectroscopy - based ultrasensitive biochemical detection sensor detecting the response of ethyl orange to different 532 nm laser power densities within the effective spectral range; (b) is the response of the out - of - band high - frequency characteristic resonance frequency obtained by the sensor tracking the dual - comb double - envelope to different laser power densities; (c) is the curve of the out - of - band characteristic resonance frequency of the sensor varying with different laser power densities; (d) is the curve of the out - of - band characteristic resonance frequency sensing frequency shift amount and sensitivity of the sensor.

[0022] In the figure: metal waveguide upper plate (1), metal film one (2), metal film two (3), polymer material one (4), polymer material two (5), metal waveguide lower plate (6), sample to be measured (7). Detailed implementation mode

[0023] The working principle and method of the present invention will be illustrated by the following examples:

[0024] The schematic diagram of the device structure is as Figure 1 shown. Figure 1 In it, a single - channel terahertz metal waveguide is jointly composed of a metal waveguide upper plate (1) and a metal waveguide lower plate (6), and the material is aluminum alloy. The structural parameters of the metal waveguide are as Figure 2 shown, and its waveguide channel transmits along the z axis with a transmission lengthl wg is 10 mm, along the x axis width w wg is 40 mm, the distance between the two plates d wg is 20 μm, and the coupling angle of the conical region is 10°. The waveguide is divided into four regions by the metal thin film I (2) and the metal thin film II (3) as shown in Figure 3 (a), where the metal thin film I (2) along the z axis length l I is 2.5 mm, along the x axis width w I is 5 mm, along the y axis thickness d mI is 5 μm, and the metal thin film II (3) along the z axis length l II is 5.05 mm, along the x axis width w II is 5 mm, along the y axis thickness d mII is 6 μm. The polymer materials used in Region III and Region IV are polyethylene, and in the frequency range of 0.1 - 1 THz, its refractive index is 1.5 and the extinction coefficient is 0.002. Among them, the polymer material (4) polyethylene used in Region III along the z axis length l I is 2.5 mm, along the x axis width w I is 5 mm, along the y axis thickness d I is 10 μm, and the polymer material (5) polyethylene used in Region IV along the z axis length l II is 5.05 mm, along the x axis width w II is 5mm, along the y axis thickness d II is 10 μm.

[0025] The basic working principle of the device is as follows: As shown in Figure 3As shown in (b), when terahertz waves are incident on the device, they will be split by the metal film and coupled to four channels for parallel transmission. Since the additional optical paths generated by the materials in each channel are different, they are detected successively in the time domain. The signal detection time difference Δ t 1 between Channel 1 and Channel 2 and the signal detection time difference Δ t 3 between Channel 3 and Channel 4 can both be expressed as:

[0026] ,(1)

[0027] In the formula, n PE represents the refractive index of polyethylene, c is the speed of light. The signal detection time difference Δ t 2 between Channel 2 and Channel 3 is expressed as:

[0028] ,(2)

[0029] Thus, the time factor τ of the inserted phase shift of this time domain sequence is:

[0030] .(3)

[0031] Assume that the single-channel transmission of terahertz waves satisfies E = E e iωt+iφ . Then, before and after the inserted phase shift modulation, the frequency comb intensity and the twin comb intensity with 2 N transmission channels respectively satisfy:

[0032] ,(4)

[0033] ,(5)

[0034] In the formula, φ is the phase shift caused by the repetition time of the frequency comb time domain signal, δ =2π τf is the inserted phase shift of the twin comb. By comparing formula (4) and formula (5), it can be seen that the modulation signal generated by the inserted phase shift on the frequency comb signal is a squared cosine term. When the frequency approaches 0, both the comb signal and the modulation signal generate maximum values, and at this time, the comb signal and the modulation signal interfere constructively; when the frequency f p makes the phase of the modulation signal larger than N times the phase of the comb signal by an integer multiple of 2π, the comb signal and the modulation signal interfere constructively again. At this time, the envelope repetition frequency f p of the twin comb spectrum satisfies:

[0035] .(6)

[0036] When the frequency f cr satisfies that the phase of the modulation signal is an odd multiple of π greater than that of the comb signal phase, the modulation signal and the comb signal interfere destructively, and at this time, the characteristic resonance frequency of the twin-comb spectrum is obtained N satisfies: f cr wherein,

[0037] ,(7)

[0038] In the formula, m is a positive integer representing the order of the characteristic resonance frequency. Thus, the sensitivity of the characteristic resonance frequency is:

[0039] .(8)

[0040] The working method of the device is as follows: The terahertz asynchronous twin-comb sensor prepared according to the above structure, the magnitude of the inserted phase shift is determined by the relative lengths of the polymer material one and the polymer material two. As shown in Figure 4 (a), when the length of the polymer material two l II is greater than twice the length of the polymer material one l I , a positive inserted phase shift is generated, and its spectrum is as shown in Figure 4 (b). When the twin-comb frequency is less than the characteristic resonance frequency, the intensity of the low-frequency comb in a pair of twin-combs is always higher than that of the high-frequency comb. The characteristic resonance frequency outside the effective spectral range of the sensor is located by tracking the intersection of the twin-comb double envelopes; when the length of the polymer material two l II is less than twice the length of the polymer material one l I , a negative inserted phase shift is generated, and its spectrum is as shown in Figure 4 (c). At this time, for the twin-comb with a frequency less than the characteristic resonance frequency, the intensity of its low-frequency comb is always less than that of the high-frequency comb. Similarly, the characteristic resonance frequency outside the twin-comb spectrum can be obtained by tracking the twin-comb double envelope; when the length of the polymer material two approaches twice the length of the polymer material one, the THz-TDS system is used to collect the transmission signal of the device, and the time-domain detection signal of the terahertz asynchronous twin-comb sensor prepared according to the above parameters is as shown in Figure 5 (a). The additional optical paths caused by the materials in each channel are detected in turn. The detection time difference between channel one and channel two is the same as that between channel three and channel four, both being 4.80 ps, and the detection time difference between channel two and channel three is 4.84 ps. Thus, the inserted phase shift time factor τ introduced by the device is obtained as = 0.04 ps, and its spectrum is as shown inFigure 5 As shown in (b), the high-frequency characteristic resonance frequency of the device near 9 THz is obtained according to the twin-comb double envelope at this time.

[0041] The sensing performance of the device will be verified by detecting the lactose areal density. In the experiment, the concentration of the lactose solution is 0 - 5 μg / ml, the configured concentration gradient is 1 μg / ml, and the solvent is deionized water. In a single experiment, the usage amount of the solution is 10 μl, and the effective detection area of the sensing region is about 25 mm 2 . The detection spectrum of the lactose areal density by the terahertz asynchronous twin-comb sensor is as shown in Figure 6 (a) and 6(b). In the figure, the frequency range of 0 - 1 THz is the detection spectrum of the sensor within the effective spectral range, and the frequency range of 1 - 12 THz is the out-of-spectrum sensing result obtained by tracking the twin-comb double envelope. As the lactose areal density increases, the characteristic resonance frequency near 10 THz shows a blue shift. Specifically, when the lactose areal density increases from 0 ng / mm 2 to 2 ng / mm 2 , the characteristic resonance frequency shifts from 9.826 THz to 10.639 THz, and the total frequency shift is 813 GHz. This is because the increase in the sample amount leads to an increase in the additional optical path in Region 2, thereby simultaneously extending the detection times of both Channel 1 and Channel 2, causing the inserted phase shift time factor to decrease, resulting in the characteristic resonance frequency shifting towards higher frequencies. Figure 6 (c) is the curve of the out-of-spectrum characteristic resonance frequency versus the sample amount, and the summary of its frequency position and frequency shift amount is as shown in Figure 6 (d). The calculation results show that the detection sensitivity of the terahertz asynchronous twin-comb out-of-spectrum sensor for the lactose areal density reaches 398 GHz / (ng / mm 2 ), and the detection accuracy is 2.5 pg / mm 2 . Compared with traditional terahertz biochemical sensors, the sensitivity of this result is increased by 4 orders of magnitude, and a breakthrough in sensing sensitivity beyond the communication band is achieved in the terahertz band. The calculation method of the sensor detection accuracy is as follows:

[0042] ,(9)

[0043] In the formula, S represents the detection sensitivity of the device, and Δ represents the spectral resolution of the THz-TDS system. In the THz-TDS system applied to this device, Δ is 1 GHz.

[0044] The high response sensitivity of the device to the sample to be measured enables it to detect tiny changes in the sample. This device is used to observe the refractive index changes caused by the photoisomerization of azo dyes in the terahertz band. The azo molecule selected in the experiment is ethyl orange. The concentration of the ethyl orange solution used is 1 mg / ml, and the solvent is deionized water. In the experiment, 10 μl of the ethyl orange solution is dropped onto the upper surface of the metal film II of the terahertz asynchronous twin comb sensor, and after drying, the measurement is carried out. Under the excitation of a 532 nm laser, the azo molecule will undergo photoisomerization, changing from the trans structure to the cis structure, and the higher the laser power density, the higher the proportion of the molecular structure transformation. In the experiment, the detection spectrum of the refractive index change of the azo dye by changing the 532 nm laser power density is as Figure 7 (a) shows. By tracking the twin comb double envelope within the effective frequency spectrum, the high-frequency characteristic resonance frequency sensing results near 10 THz outside the spectrum are located as Figure 7 (b) shows. When the laser power density increases from 0 W / cm 2 to 2.4 W / cm 2 at a gradient of 0.4 W / cm 2 , the off-spectrum characteristic resonance frequency of the terahertz twin comb sensor shifts from 8.946 THz to 11.113 THz, and the total frequency shift is 2.167 THz. Figure 7 (c) is the curve of the off-spectrum characteristic resonance frequency of the sensor changing with the 532 nm laser power density. Figure 7 (d) is the summary result of the frequency shift. The calculation results show that the sensitivity of the terahertz asynchronous twin comb off-spectrum sensor reaches 0.91 GHz / (mW / cm 2 ), and this result also shows an improvement compared with the sensitivity of related studies in the communication band. Exploring the refractive index changes of azo molecules in the terahertz band caused by photoisomerization demonstrates the ultrasensitive characteristics of the terahertz asynchronous twin comb off-spectrum sensor. At the same time, it is of great significance for developing the potential applications of photo-responsive materials such as azo dyes in the fields of terahertz information storage, vector holographic encryption, etc. The terahertz asynchronous twin comb off-spectrum sensing strategy is a major breakthrough in realizing ultra-high-sensitivity terahertz biochemical sensing. At the same time, this technology is not limited by frequency and has reference value for the entire optical frequency band. It may achieve achievements in the future in the fields of optical precision metrology, artificial intelligence photonics, and communication-sensing integration technology applications.

Claims

1. An ultra-sensitive terahertz biochemical sensor based on the asynchronous twin-comb principle, characterized in that: The device is arranged from top to bottom in sequence as a metal waveguide upper plate (1), a metal film one (2), a metal film two (3), a polymer material one (4), a polymer material two (5), a metal waveguide lower plate (6), and a sample to be tested (7); wherein the metal upper plate (1) and the metal lower plate (6) together form a terahertz metal waveguide, and the waveguide is divided into four regions by using the metal film one (2) and the metal film two (3), and four parallel transmission channels are formed, wherein the region one and the region two are air, and the region three and the region four are the polymer material one (4) and the polymer material two (5), respectively; When a terahertz wave is incident on the waveguide, it will be split by the sensor structure and transmitted in parallel in four transmission channels. Since the four transmission channels in the waveguide have different additional phases introduced by the polymer material, the frequency comb is split into a pair of twin combs by inserting a phase shift in the periodic time domain signal, and the characteristic resonance frequency outside the effective spectrum range is located by tracking the intersection of the twin comb double envelope. When the amount of the sample (7) to be measured in region two changes, it will cause a change in the twin comb insertion phase shift, thereby causing a significant change in the twin comb double envelope and the characteristic resonance frequency outside the spectrum, thereby achieving ultra-high sensitivity detection of biochemical samples.

2. The ultra-sensitive terahertz biochemical sensor based on the asynchronous twin-comb principle according to claim 1, characterized in that: The material of the metal waveguide upper plate (1) and the metal waveguide lower plate (6) should be metal, including but not limited to aluminum alloy. The taper coupling angle of the metal waveguide is 10°-20°. The distance between the upper and lower plates should be 10-100 μm. The metal waveguide extension z The shaft transmission length is 10-20 mm, x The shaft width is 20-60 mm.

3. The ultra-sensitive terahertz biochemical sensor based on the asynchronous twin-comb principle according to claim 1, characterized in that: The area 1 and area 2 formed by the light splitting of the metal film 1 (2) and the metal film 2 (3) are air; y The axis length is 2.5-25 μm, along x The shaft length is 5-60 mm, along z The axis length is 2-5 mm; the area along y The axis length is 2-20 μm, along x The shaft length is 5-60 mm, along z The axis length is 4-10 mm. Area 2 is mainly used to place the sample to be tested (7). To improve the spectral contrast and signal-to-noise ratio, area 1 is y The shaft thickness should be less than or equal to the area three edges y Half the thickness of the shaft, area along y The shaft thickness should be less than or equal to the area around the y Half the thickness of the shaft, area along y The shaft thickness should also be smaller than the area along the y Shaft thickness 1-5 μm.

4. The ultra-sensitive terahertz biochemical sensor based on the asynchronous twin-comb principle according to claim 1, characterized in that: The material of the metal film 1 (2) and the metal film 2 (3) should be metal, including but not limited to copper; y The thickness of the axis is 2.5-10 μm. x The shaft length is 5-60 mm, along z The axis length is 2-5 mm; the metal film is y The thickness of the axis is 3-12 μm. x The shaft length is 5-60 mm, along z The axis length is 4-10 mm; the metal film 1 (2) and the metal film 2 (3) are mainly used for the guided mode splitting in the metal waveguide. In order to improve the spectral contrast and signal-to-noise ratio, the metal film 2 (3) is y The thickness of the shaft should be greater than one (2) y Shaft thickness 1-5 μm.

5. The ultra-sensitive terahertz biochemical sensor based on the asynchronous twin-comb principle according to claim 1, characterized in that: The polymer material 1 (4) and the polymer material 2 (5) constituting the region 3 and the region 4 have a refractive index of 1.2-1.53 ​​in the 0.05-1 THz frequency band and an extinction coefficient of less than 0.005, and the material includes but is not limited to polyethylene; wherein the polymer material 1 (4) is y The thickness of the axis is 5-50 μm. x The shaft length is 5-60 mm, along z The shaft length is 2-5 mm and must be along the metal film (2) z The axes are of equal length; the polymer material is two (5) along y The thickness of the shaft is 5-50 μm and must be along the same (4) side as the polymer material. y The thickness of the shaft is the same, along x The shaft length is 5-60 mm, along z The axis length is 4-10 mm and needs to be along the metal film (3) z The lengths of the axes are equal. In order to match the characteristic time domain sequence required to generate the terahertz asynchronous twin comb and generate characteristic resonance frequencies outside the effective spectrum range, the polymer material used in region 4 is 2 (5) along z The axis length should be longer than the polymer material used in area 3 (4) along z 10-400 μm larger or smaller than twice the axis length.

6. The ultra-sensitive terahertz biochemical sensor based on the asynchronous twin-comb principle according to claim 1, characterized in that: The incident terahertz wave is a transverse magnetic mode, and its electric field vector is along y The lowest-order transverse magnetic mode is characterized by no group velocity dispersion and cutoff frequency. z When the axial incident waveguide is used, the conical region of the metal waveguide is used for coupling, and the terahertz time-domain spectroscopy system is used to collect the transmission signal in the time domain. The characteristic of the sensor time domain signal is that a time defect is introduced into the time domain signal with equal time interval, that is, the insertion of the phase shift causes the time domain signal after the defect to have a time delay. Specifically, the signals of the four channels are detected in sequence according to the size of the additional phase shift introduced by their materials, and the detection time difference between channel one and channel two is the same as the detection time difference between channel three and channel four, and the detection time difference between channel two and channel three is 0.01-1 ps different from the detection time difference between channel one and channel two. The sensor frequency domain signal is affected by the inserted phase shift, and the single comb spectrum is split to generate a twin comb spectrum. The respective envelopes of the twin combs can be extracted respectively, and finally the characteristic resonance frequency of the twin comb outside the effective spectral range is located through the intersection of the double envelopes of the twin combs.

7. An ultra-sensitive terahertz biochemical sensor based on the asynchronous twin-comb principle according to claims 1-6, characterized in that: The mechanism of using twin-comb spectroscopy for extra-spectral sensing can break through the limitation of the effective spectrum range of the device. The effective spectrum range of the sensor's spectrum detection is 0.1-1 THz. The periodic characteristics of the twin-comb spectrum are used to track the twin-comb double envelope to obtain sensing information in the frequency range of 1-15 THz outside the effective spectrum range. In the sensing detection, the sample to be tested (7) is placed in the second region and dripped on the upper surface of the metal film second (3) in the form of an aqueous solution. After drying, the detection is performed. Therefore, the sample to be tested is a soluble biochemical molecule, including but not limited to soluble amino acids, proteins and sugars. The device can be used for quantitative detection of biochemical samples. When the sample to be tested causes a change in the additional phase of the second region, the insertion phase shift of the twin-comb sensor will be changed, thereby causing the twin-comb double envelope to change and the extra-spectral characteristic resonance frequency to shift. The sensing detection of the sample amount is achieved by detecting the magnitude of the frequency shift. Based on the extra-spectral high-frequency sensing characteristics of the device, its detection sensitivity and accuracy are significantly improved compared with the traditional sensing characterization method within the effective spectrum range. The characteristic resonance frequency detection sensitivity of the device reaches 10 11 GHz / (g / mm 2 ) level, and the detection accuracy is 10 -12 g / mm 2 The sensitivity of the device is increased by 4 orders of magnitude compared with traditional terahertz biochemical sensors. The ultra-high sensitivity of the device can be used to observe the photoisomerization phenomenon of azo molecules in the terahertz band.

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