An ultra-sensitive terahertz biochemical sensor based on asynchronous twin comb principle

Abstract

The application discloses an ultra-sensitive terahertz biochemical sensor based on an asynchronous twin comb principle and belongs to the technical field of terahertz application. The device forms four parallel transmission channels in a metal waveguide through cascading double-layer microchannels, and is used for matching the characteristic time-domain sequence of the terahertz asynchronous twin comb. The high-frequency characteristic resonance frequency of the twin comb outside the effective frequency spectrum is located by tracking the double envelope of the twin comb in the effective frequency spectrum, so that the device breaks through the limitation of the effective frequency spectrum range and realizes the out-of-spectrum sensing scheme with ultra-high sensitivity. The sensitivity of the device reaches the order of 10 11 GHz / (g / mm 2 ) in the detection of biochemical samples, the detection accuracy reaches the order of 10 ‑12 g / mm 2 , the sensitivity is improved by 4 orders of magnitude compared to the existing terahertz biochemical sensing, a breakthrough in the sensing sensitivity beyond the communication band is realized, and based on this, the device can be used for observing the photoisomerization phenomenon of azo dyes in the terahertz band. The characteristic that the device breaks through the effective frequency spectrum range to realize the out-of-spectrum high-sensitivity sensing makes it show application potential in the field of terahertz biochemical sensing.

Description

Technical Field

[0001] This invention belongs to the field of terahertz application technology, specifically relating to an ultrasensitive terahertz biochemical sensor based on the asynchronous twin comb principle. Background Technology

[0002] The terahertz (0.1–10 THz) band matches the collective vibrational and rotational energy levels of many biochemical molecules, making it crucial for revealing molecular dynamics information. Terahertz-based biochemical sensing exhibits high sensitivity, label-free operation, rapid response, and on-chip integration feasibility, and has been widely applied in material spectral enhancement, trace analysis, and specific sensing, witnessing pioneering achievements in fields such as biomedicine, environmental monitoring, and food safety. Recent research advancements have seen the widespread use of supersensors based on high-Q resonance metamaterials to enhance the interaction between terahertz waves and matter, while breakthroughs in specific detection of terahertz biochemical sensing have been achieved by combining micro / nano functional materials, biomodification, and artificial intelligence [Adv. Mater., 2411490, (2024)]. However, when facing more precise trace analysis, the sample size is often mismatched with the detection wavelength, thus limiting further improvements in detection sensitivity [PhotoniX, 5, 10 (2024)]. Furthermore, the resonant frequency generated by the supersensor depends on the fixed structure of the device, which makes it challenging to achieve broadband response and acquire richer information on frequency shift and amplitude variations.

[0003] To further enhance the interaction between terahertz waves and matter and improve sensing sensitivity, terahertz waveguide sensors have emerged as a promising approach. However, traditional waveguide sensors based on electromagnetic resonance still face the constraint of balancing broadband response and high Q, with sensitivity only on the order of hundreds of GHz / RIU [Appl. Phys. Lett., 121, 011101(2022)]. To further improve sensing sensitivity and extend the broadband response capability of sensors, it is hoped to develop waveguide-based coherent detection technology. This technology exhibits ultra-high sensitivity in the visible and infrared bands; however, due to limitations in waveguide structure and coupling mode, its research in the terahertz band is still in its early stages. In existing work, a terahertz waveguide interferometer sensor has been realized by constructing a dual-channel structure within a metal parallel plate waveguide. However, due to limitations in structural size and fabrication precision, its sensitivity is still limited to within 1 THz / RIU [Sens. Actuator A-Phys., 370, 115282(2024)]. Furthermore, by constructing a multi-channel structure within a metallic waveguide, a terahertz vernier sensor with self-reference characteristics was formed, achieving an enhanced sensitivity on the order of 10 THz / RIU [Fundamental Res., 5, 2 (2025)]. However, due to limitations in the effective spectral range and the low-frequency characteristics of terahertz, the sensitivity still lags significantly behind that of the visible and infrared bands.

[0004] Achieving breakthroughs in terahertz sensing sensitivity relies on the construction of multi-level coherent signals and the acquisition of rich spectral information, which places more stringent demands on the initial time-domain signal structure. Optical frequency combs, with their dense spectral lines, act like frequency rulers, offering significant advantages in acquiring rich spectral information. Dual-comb systems combined with heterodyne detection have demonstrated 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 optic 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 acquiring richer spectral information [Science, 384, 1356-1361(2024)]. However, these technologies still focus on characterization within the effective spectral range, and further breakthroughs in terahertz biochemical sensing sensitivity depend on a new technology capable of exceeding the system's effective spectral range and obtaining high-spectral-outside sensing capabilities.

[0005] In summary, as a key window for next-generation high-speed wireless communication and high-resolution sensing, developing ultra-high-sensitivity biochemical sensors in the terahertz band has unique advantages and significant importance. Its advantages lie in the fact that, compared to communication bands, the terahertz band reduces the requirements for sensor structure construction. Furthermore, terahertz time-domain spectroscopy facilitates the modulation of sensor time-domain signals, offering richer possibilities for the construction and analysis of complex signals. Its significance lies in two aspects: firstly, the rapid development of terahertz technology and its biochemical sensing applications urgently requires the development of high-performance terahertz sensors; analyzing terahertz coherent detection technology from a time-domain perspective will bring new vitality to terahertz biochemical sensing; secondly, existing terahertz waveguide sensors suffer from low integration, low sensitivity, and limited operating frequencies. Therefore, developing novel terahertz waveguide sensors with high integration, high sensitivity, and the ability to break through the effective spectrum range and obtain extra-spectral high-frequency sensing capabilities has significant scientific research value. Summary of the Invention

[0006] The purpose of this invention is to provide an ultrasensitive terahertz biochemical sensor based on the asynchronous twin comb principle. This addresses key technical problems in the prior art, such as the low-frequency limitations, low sensitivity, and limited operating frequency range of terahertz sensors.

[0007] To achieve the above objectives, the device and structure of the present invention include: a metal waveguide upper 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 metal waveguide lower plate (6), and a sample to be tested (7). The metal waveguide upper plate (1) and the metal waveguide lower plate (6) together form a terahertz metal waveguide. The cone coupling angle of the metal waveguide is 10°-20°, and the distance between the upper and lower metal waveguide plates should be less than 100 μm. The metal waveguide along... z The shaft transmission length is 10-20 mm, along x The axial width is 20-60 mm. The waveguide channel is isolated into four transmission regions using metal thin film one (2) and metal thin film two (3), wherein metal thin film one (2) is along... y The shaft thickness is 2.5-10 μm, along... x The shaft length is 5-60 mm, along z The shaft length is 2-5mm; the metal film II (3) along y The shaft thickness is 3-12 μm, along x The shaft length is 5-60 mm, along z The shaft length is 4-10 mm; four transmission areas form four parallel transmission channels, of which areas one and two are air, and area one is along... y The shaft length is 2.5-25 μm, along... x The shaft length is 5-60 mm, along zThe shaft length is 2-5 mm; along region two y The shaft length is 2-20 μm, along x The shaft length is 5-60 mm, along z The axis length is 4-10 mm. Region 2 is mainly used to place the sample to be tested (7); Regions 3 and 4 are polymer material 1 (4) and polymer material 2 (5) respectively. The organic polymer material used has a refractive index of 1.2-1.53 ​​in the 0.1-1 THz frequency band and an extinction coefficient of less than 0.005. The material includes, but is not limited to, polyethylene. Among them, polymer material 1 (4) is along the axis length of 4-10 mm. Region 2 is mainly used to place the sample to be tested (7); Regions 3 and 4 are polymer material 1 (4) and polymer material 2 (5) respectively. The organic polymer material used has a refractive index of 1.2-1.53 ​​in the 0.1-1 THz frequency band and an extinction coefficient of less than 0.005. The material includes, but is not limited to, polyethylene. 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 must be aligned with the metal film along (2) z The axial lengths are equal; polymer material two (5) along y The shaft thickness is 5-50 μm and must be aligned with the polymer material along (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 must be aligned with the metal film along (3) z The axis lengths are equal; in order to match the characteristic time-domain sequence required to generate terahertz asynchronous twin combs and to generate characteristic resonance frequencies outside the effective spectral range, the polymer material used in region four (5) is along... z The axis length needs to be greater than that of the polymer material used in region three (4) along z The shaft length is twice the size of the shaft length, or 10-400 μm larger or smaller.

[0008] The basic working principle of this invention is as follows: When a terahertz wave is incident on a terahertz asynchronous twin-comb sensor, it is split by two metal thin films to form four parallel transmission channels. Due to the different additional phases introduced by the materials in the four transmission channels, the transmission signals of the four channels are detected sequentially. The signal time difference between channels one and two is the same as that between channels three and four, but different from that between channels two and three. This introduces an insertion phase shift and modulates the single-comb signal. In the frequency domain, this manifests as the optical frequency comb signal being split into twin-comb signals. The asynchronous characteristic of the twin-comb is that the intensity of the twin-comb is affected by the insertion phase shift, resulting in a phenomenon where one increases while the other decreases. By tracing the intersection of the twin-comb double envelopes, the high-frequency characteristic resonance frequency of the twin-comb outside the effective spectral range can be located. This frequency represents the interference cancellation between the comb signal and the modulation signal of the insertion phase shift. When the device is used for sensing, the sample to be tested (7) is placed in region two, that is, the upper surface of the metal thin film two (3). The extraspectral characteristic resonance frequency of the terahertz asynchronous twin comb sensor will shift significantly with the change of sample amount. The mechanism of extraspectral sensing using twin comb spectroscopy can break through the limitation of the effective spectrum range of the device. Due to the influence of 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 extraspectral ultrasensitive biochemical detection sensor is as follows: The time-domain signal after passing through the device is detected by the terahertz time-domain spectroscopy (THz-TDS) system, and the time-domain information is mapped to the frequency domain information by Fourier transform of the signal. The periodic time-domain signal is modulated by the insertion phase shift, which is manifested in the frequency domain as the single comb signal splitting to generate an asynchronous twin-comb spectrum. The envelopes of the two comb signals in the twin comb are extracted respectively, and the high-frequency characteristic resonance frequency of the twin comb outside the effective frequency range is located according to the intersection of the twin comb double envelopes. The sample to be tested (7) is dropped onto the upper surface of the metal thin film II (3) in the form of an aqueous solution. After drying, it is detected. When the sample to be tested (7) causes a change in the additional phase of region II, it will change the insertion phase shift of the twin comb sensor, thereby causing a change in the twin comb double envelope and a frequency shift in the extraspectral characteristic resonance frequency. The amount of sample is sensed by detecting the magnitude of the frequency shift. The effective spectral range of the sensor is 0.1-1 THz. By utilizing the periodic characteristics of the twin comb spectrum, characteristic resonant frequency sensing information in the 1-15 THz frequency range outside the effective spectral range is obtained by tracing the twin comb double envelope.

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

[0011] 1. A characteristic time-domain sequence of a terahertz asynchronous twin comb signal is generated by matching cascaded microchannels. The waveguide channel is divided into four independent regions using a thin metal film, and four parallel transmission channels are obtained through region matching. Compared with the single-channel mode, the four-channel transmission method achieves spatial multiplexing of the signal, improves space utilization, and enables the transmitted signal to carry richer information.

[0012] 2. Drawing on the principle of optical frequency combs, the comb signal is modulated by introducing defects into the periodic time-domain signal, i.e., by inserting a phase shift. In the frequency domain, this manifests as a single comb splitting to generate asynchronous twin combs. The asynchronous nature of the twin combs allows the envelopes of the two combs to be extracted separately, which facilitates the acquisition of rich spectral information.

[0013] 3. By utilizing the periodicity of asynchronous twin-comb signals in the frequency domain, the characteristic resonant frequencies outside the effective spectral range can be located by detecting the characteristics of the twin-comb signals within the effective spectral range. This overcomes the limitation of the system's effective spectral range and obtains high-frequency sensing information, eliminating the low-frequency limitations of the terahertz band. Compared to traditional terahertz band biochemical sensors, this device possesses extraspectral sensing capabilities beyond the effective spectral range. The device's spectral detection range is 0.1-1 THz, and the characteristic resonant frequencies used to characterize sensing information are located in the extraspectral high-frequency range of 1-15 THz.

[0014] 4. When the device is used for biochemical sample detection, changes in sample quantity cause a change in the insertion phase shift in the sensor's time-domain signal, thereby modulating the frequency-domain signal of the twin comb. High-frequency sensing characterization of the device's characteristic resonant frequency outside the spectrum improves the sensor's sensitivity to 10. 3 The THz / RIU level provides a detection sensitivity of 10 for biochemical samples. 11 GHz / (g / mm 2 On the order of magnitude, with a precision of 10. -12 g / mm 2 Compared to traditional terahertz biochemical sensors, the sensitivity is increased by four orders of magnitude, achieving sensor sensitivity exceeding that of the communication band. The device's high sensitivity can be used to observe photoisomerization of azo dyes in the terahertz band, which is of great significance for developing new terahertz information storage materials. Attached Figure Description

[0015] Figure 1 This is a schematic diagram of the three-dimensional structure of a terahertz asynchronous twin comb extraspectral ultrasensitive biochemical detection sensor;

[0016] Figure 2 (a) is a terahertz asynchronous twin comb extraspectral ultrasensitive biochemical detection sensor yz (a) Planar schematic diagram and structural parameters; (b) is the device xy Plan view;

[0017] Figure 3 (a) is a schematic diagram of four regions separated by two metal films in the terahertz asynchronous twin comb extraspectral ultrasensitive biochemical detection sensor; (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 length variation of the polymer material in the terahertz asynchronous twin comb extraspectral 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 of the terahertz asynchronous twin comb extraspectral ultrasensitive biochemical detection sensor when the insertion phase shift approaches 0; (b) is the detection spectrum of the sensor when the insertion phase shift approaches 0.

[0020] Figure 6 (a) shows the detection results of the terahertz asynchronous twin-comb extraspectral ultrasensitive biochemical detection sensor for different lactose area densities within the effective spectral range; (b) shows the response of the extraspectral high-frequency characteristic resonance frequency obtained by the sensor from tracking the twin-comb double envelope to different lactose area densities; (c) shows the curve of the extraspectral characteristic resonance frequency of the sensor as a function of different lactose area densities; (d) shows the sensing frequency shift and sensitivity curve of the extraspectral characteristic resonance frequency of the sensor.

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

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

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

[0024] The structural diagram of the device is as follows Figure 1 As shown. Figure 1 In the middle, a single-channel terahertz metal waveguide is composed of an upper metal waveguide plate (1) and a lower metal waveguide plate (6), and the material is aluminum alloy. The structural parameters of the metal waveguide are as follows: Figure 2 As shown, its waveguide channel along z Axis transmission lengthl wg It is 10 mm, along x Shaft width w wg The spacing between the two plates is 40 mm. d wg The thickness is 20 μm, and the cone coupling angle is 10°. The waveguide is divided into four regions using metal thin film one (2) and metal thin film two (3), as shown below. Figure 3 As shown in (a), where the metal thin film (2) is along z Shaft length l I It is 2.5 mm, along x Shaft width w I It is 5 mm, along y Shaft thickness d mI The metal thin film is 5 μm thick, and the second (3) is along... z Shaft length l II It is 5.05 mm, along x Shaft width w II It is 5 mm, along y Shaft thickness d mII The thickness is 6 μm. The polymer used in regions three and four is polyethylene, which has a refractive index of 1.5 and an extinction coefficient of 0.002 in the 0.1-1 THz frequency range. Specifically, the polymer used in region three (4) is polyethylene along... z Shaft length l I It is 2.5 mm, along x Shaft width w I It is 5 mm, along y Shaft thickness d I The polymer material used in region four is 10 μm (5) polyethylene along the [missing information]. z Shaft length l II It is 5.05 mm, along x Shaft width w II It is 5mm, along y Shaft thickness d II It is 10 μm.

[0025] The basic working principle of the device is as follows: Figure 3As shown in (b), when a terahertz wave is incident on the device, it is split by the metal thin film and coupled into four channels for parallel transmission. Because each channel has a different additional optical path length generated by the material, they are detected sequentially in the time domain. The signal detection time difference Δ between channel one and channel two is shown in (b). t 1. Time difference Δ between signal detection in channel 3 and channel 4 t 3 can be represented as:

[0026] (1)

[0027] In the formula, n PE This indicates the refractive index of polyethylene. c The speed of light. The signal detection time difference Δ between channel two and channel three. t 2 is represented as:

[0028] (2)

[0029] This yields the time factor for the phase shift insertion of the time-domain sequence. τ for:

[0030] (3)

[0031] Assuming a single-channel transmission of terahertz waves satisfies E = E e iωt+iφ Then, before and after the insertion of phase shift modulation, there are 2 N The frequency comb strength and twin comb strength of each transmission channel satisfy the following:

[0032] (4)

[0033] (5)

[0034] In the formula, φ The phase shift is caused by the repetition time of the frequency comb time-domain signal. δ =2π τf The insertion phase shift is the phase shift of the twin comb. By comparing formulas (4) and (5), it can be seen that the modulation signal generated by the insertion phase shift of the frequency comb signal is a square cosine term. When the frequency approaches 0, both the comb signal and the modulation signal produce a maximum value. At this time, the comb signal and the modulation signal interfere constructively; when the frequency... f p Make the phase of the modulated signal greater than the phase of the comb signal. N When the frequency is an integer multiple of 2π, the comb signal and the modulation signal undergo constructive interference again, at which point the envelope repetition frequency of the twin comb spectrum is obtained. f p satisfy:

[0035] (6)

[0036] When frequency f cr The phase ratio of the modulated signal to the comb signal is satisfied. N When the frequency is an odd multiple of π, the modulation signal and the comb signal undergo destructive interference, at which point the characteristic resonance frequency of the twin-comb spectrum is obtained. f cr satisfy:

[0037] (7)

[0038] In the formula, m Positive integers represent the order of the characteristic resonance frequency. Therefore, the sensitivity of the characteristic resonance frequency is:

[0039] (8)

[0040] The device operates as follows: In the terahertz asynchronous twin-comb sensor fabricated according to the above structure, the magnitude of the insertion phase shift is determined by the relative lengths of polymer material one and polymer material two, such as... Figure 4 As shown in (a), when the length of polymer material II... l II The length of the polymer material is greater than that of the first one. l I At twice the size, a positive insertion phase shift occurs, and its spectrum is as follows: Figure 4 As shown in (b), when the twin comb frequency is less than the characteristic resonant 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 resonant frequency outside the effective frequency range is located by tracking the intersection of the twin comb double envelopes. When the length of the polymer material II is... l II The length of the polymer material is less than that of the first one. l I At twice the size of the phase, a negative insertion phase shift occurs, and its spectrum is as follows: Figure 4 As shown in (c), for twin combs with frequencies lower than the characteristic resonance frequency, the intensity of the low-frequency comb is always lower than that of the high-frequency comb. Similarly, the characteristic resonance frequency outside the twin comb spectrum can be obtained by tracing the twin comb double envelope. When the length of polymer material two approaches twice the length of polymer material one, the transmission signal of the device is acquired using a THz-TDS system, and the time-domain detection signal of the terahertz asynchronous twin comb sensor prepared according to the above parameters is as follows: Figure 5 As shown in (a), the additional optical path length caused by the material in each channel is detected sequentially. The detection time difference between channels 1 and 2 is the same as that between channels 3 and 4, which is 4.80 ps. The detection time difference between channels 2 and 3 is 4.84 ps. Thus, the insertion phase shift time factor introduced by this device is obtained. τ =0.04 ps, its spectrum is as follows Figure 5 As shown in (b), the high-frequency characteristic resonance frequency of the device near 9 THz is obtained based on the twin comb double envelope.

[0041] The sensing performance of the device will be verified by detecting the areal density of lactose. In the experiment, the lactose solution concentration was 0-5 μg / ml, with a concentration gradient of 1 μg / ml, and deionized water was used as the solvent. In a single experiment, the solution volume used was 10 μl, and the effective detection area of ​​the sensing region was approximately 25 mm². 2 The detection spectrum of lactose areal density using a terahertz asynchronous twin comb sensor is as follows: Figure 6 As shown in (a) and 6(b), the frequency range of 0-1 THz represents the detection spectrum of the sensor within its effective spectral range, and the frequency range of 1-12 THz represents the extraspectral sensing results obtained by tracking the twin comb double envelope. As the lactose areal density increases, the characteristic resonance frequency near 10 THz exhibits a blue shift, specifically as the lactose areal density decreases from 0 ng / mm². 2 Increased to 2ng / mm 2 At that time, the characteristic resonance frequency shifted from 9.826 THz to 10.639 THz, with a total frequency shift of 813 GHz. This is because the increase in sample amount led to an increase in the additional optical path in region two, which in turn extended the detection time of both channel one and channel two, causing a decrease in the insertion phase shift time factor and resulting in a shift of the characteristic resonance frequency to a higher frequency. Figure 6 (c) shows the curves of the extraspectral characteristic resonance frequencies as a function of sample quantity. The frequency positions and frequency shifts are summarized as follows: Figure 6 As shown in (d), the calculation results show that the terahertz asynchronous twin comb extraspectral sensor achieves a detection sensitivity of 398 GHz / (ng / mm²) for lactose area density. 2 The detection accuracy is 2.5 pg / mm. 2 Compared to traditional terahertz biochemical sensors, this result shows a four-order-of-magnitude improvement in sensitivity, and also achieves a breakthrough in sensing sensitivity in the terahertz band, surpassing that of communication bands. The sensor detection accuracy is calculated as follows:

[0042] (9)

[0043] In the formula, S The value represents the detection sensitivity of the device, and Δ represents the spectral resolution of the THz-TDS system. In the THz-TDS system in which this device is used, Δ is 1 GHz.

[0044] The device's high response sensitivity to the sample enables it to detect minute changes in the sample. This device was used to observe the refractive index change in azo dyes caused by photoisomerization in the terahertz band. The azo molecule selected in the experiment was ethyl orange, and the concentration of the ethyl orange solution used was 1 mg / ml. The solvent was deionized water. In the experiment, 10 μl of ethyl orange solution was dropped onto the upper surface of the second metal thin film of the terahertz asynchronous twin-comb sensor, dried, and then measured. Under 532 nm laser excitation, azo molecules undergo photoisomerization, changing from a trans structure to a cis structure. The higher the laser power density, the higher the proportion of molecular structure transformation. In the experiment, the detection spectrum of the refractive index change of azo dyes caused by changing the 532 nm laser power density is shown below. Figure 7 As shown in (a), the sensing results of locating the high-frequency characteristic resonant frequency near 10 THz outside the spectrum by tracking the twin comb double envelope within the effective spectral range are as follows: Figure 7 As shown in (b), when the laser power density increases from 0 W / cm² 2 At 0.4 W / cm 2 The gradient increased to 2.4 W / cm 2 At that time, the extraspectral characteristic resonance frequency of the terahertz twin-comb sensor shifted from 8.946 THz to 11.113 THz, with a total frequency shift of 2.167 THz. Figure 7 (c) shows the curve of the sensor's extraspectral characteristic resonance frequency as a function of 532 nm laser power density. Figure 7 (d) shows the summarized frequency shift results. The calculation results indicate that the terahertz asynchronous twin comb extraspectral sensor achieves a sensitivity of 0.91 GHz / (mW / cm²) in the response of azo molecules to laser power density. 2 This result shows an improvement in sensitivity compared to related studies in the communication band. Investigating the photoisomerization of azo molecules leading to changes in their refractive index in the terahertz band demonstrates the ultrasensitive characteristics of the terahertz asynchronous twin-comb extraspectral sensor. It also has significant implications for developing potential applications of photoresponsive materials such as azo dyes in terahertz information storage and vector holographic encryption. The terahertz asynchronous twin-comb extraspectral sensing strategy represents a major breakthrough in achieving ultra-high sensitivity terahertz biochemical sensing. Furthermore, this technology is not frequency-limited and has reference value across the entire optical band, potentially leading to future achievements in areas such as optical precision metrology, artificial intelligence photonics, and integrated sensing technology.

Claims

1. A highly sensitive terahertz twin-comb biochemical sensor based on the principle of frequency comb, characterized in that, The terahertz biochemical sensor is arranged from top to bottom as follows: upper metal waveguide plate (1), metal thin film one (2), metal thin film two (3), polymer material one (4), polymer material two (5), lower metal waveguide plate (6), and sample to be tested (7). Among them, the upper metal waveguide plate (1) and the lower metal waveguide plate (6) together form a terahertz metal waveguide. The waveguide is divided into four regions by metal thin film one (2) and metal thin film two (3), forming four parallel transmission channels. Region one and region two are air, and region three and region four are polymer material one (4) and polymer material two (5), respectively. The polymer material one (4) and polymer material two (5) that make up region three and region four 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. The material includes, but is not limited to, polyethylene. Among them, polymer material one (4) is along the... 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 must be aligned with the metal film along (2) z The axial lengths are equal; polymer material two (5) along y The shaft thickness is 5-50 μm and must be aligned with the polymer material along (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 must be aligned with the metal film along (3) z With equal axis lengths, in order to match the characteristic time-domain sequence required for generating terahertz asynchronous twin combs and to produce characteristic resonance frequencies outside the effective spectral range, the polymer material used in region four (5) along... z The axis length needs to be greater than that of the polymer material used in region three (4) along z The axial length is twice the size of 10-400 μm. When a terahertz wave is incident on the waveguide, it is split by the sensor structure and transmitted in parallel through four transmission channels. Due to the additional phase difference introduced by the polymer material into the four transmission channels within the waveguide, a pair of twin combs are generated by splitting the frequency comb by inserting a phase shift into the periodic time-domain signal. The characteristic resonance frequency outside the effective spectral range is located by tracing the intersection of the twin comb double envelopes. The mechanism of extraspectral sensing using twin comb spectroscopy can overcome the limitation of the effective spectral range of the device. The effective spectral detection range of the sensor is 0.1-1 THz. By utilizing the periodic characteristics of the twin comb spectrum, the 1-15 THz range outside the effective spectral range can be obtained by tracing the twin comb double envelopes. In the sensing information of the THz frequency range, the sample to be tested (7) is placed in region two and dropped onto the upper surface of the metal thin film (3) in the form of an aqueous solution. After drying, it is detected. Therefore, the sample to be tested is a soluble biochemical molecule, including but not limited to soluble amino acids, proteins and sugars. The terahertz biochemical sensor can be used to quantitatively detect biochemical samples. When the amount of the sample to be tested (7) in region two changes, it will change the insertion phase shift of the twin comb sensor, thereby causing changes in the twin comb double envelope and a frequency shift in the extraspectral characteristic resonance frequency. The amount of sample is detected by detecting the magnitude of the frequency shift. Based on the extraspectral high-frequency sensing characteristics of the terahertz biochemical sensor, its detection sensitivity and accuracy are significantly improved compared with the traditional sensing characterization method in the effective spectrum range. The detection sensitivity of the characteristic resonance frequency of the terahertz biochemical sensor reaches 10. 11 GHz / (g / mm 2 ) magnitude, detection accuracy of 10 -12 g / mm 2 The sensitivity of the terahertz biochemical sensor is increased by four orders of magnitude compared to traditional terahertz biochemical sensors. The ultra-high sensitivity of the terahertz biochemical sensor can be applied to observe the photoisomerization phenomenon of azo molecules in the terahertz band.

2. The ultrasensitive terahertz twin-comb biochemical sensor based on the frequency comb principle according to claim 1, characterized in that, The upper metal waveguide plate (1) and the lower metal waveguide plate (6) are made of metal, including but not limited to aluminum alloy. The cone coupling angle of the metal waveguide is 10°-20°, and the distance between the upper and lower plates is 10-100 μm. The metal waveguide extends... z The shaft transmission length is 10-20mm, extending... x The shaft width is 20-60 mm.

3. The ultrasensitive terahertz twin-comb biochemical sensor based on the frequency comb principle according to claim 1, characterized in that, Region 1 and Region 2, formed by the spectral dispersion of metal thin film 1 (2) and metal thin film 2 (3), are air; wherein Region 1 is along y The shaft length is 2.5-25 μm, along... x The axis length is 5-60 mm, and the length along the z-axis is 2-5 mm; Region 2 along y The shaft length is 2-20 μm, along x The shaft length is 5-60 mm, along z The axis length is 4-10 mm. Region 2 is mainly used to place the sample to be tested (7). To improve spectral contrast and signal-to-noise ratio, Region 1 is along the axis. y Shaft thickness less than or equal to the three-axis region y Half the shaft thickness, along region two y Shaft thickness less than or equal to the four edges of the region y Half the shaft thickness, along region two y The shaft thickness is simultaneously less than that of a region along... y Shaft thickness 1-5 μm.

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

5. The ultrasensitive terahertz twin-comb biochemical sensor based on the frequency 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, axially and perpendicular to the metallic waveguide, is characterized by the absence of group velocity dispersion and cutoff frequency; when the terahertz wave travels along... z When the waveguide is axially incident, coupling is performed using the conical region of the metal waveguide, and a terahertz time-domain spectroscopy system is applied to acquire the transmitted signal in the time domain. The characteristic of the sensor's time-domain signal is that a time defect is introduced into the time-domain signal within the equal time interval, that is, the inserted phase shift causes a time delay in the time-domain signal after the defect. Specifically, the signals of the four channels are detected sequentially according to the magnitude of the additional phase shift introduced by their materials, and the detection time difference between channels one and two is the same as that between channels three and four, while the detection time difference between channels two and three differs from that between channels one and two by 0.1-1 ps. The sensor's frequency-domain signal is affected by the inserted phase shift, and the single-comb spectrum is split to generate a twin-comb spectrum. The envelopes of the twin combs can be extracted separately, and finally, the characteristic resonance frequency of the twin combs outside the effective spectral range is located by the intersection of the twin comb double envelopes.

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