Terahertz frequency comb generation verification method and system based on optical fiber microcavity optical frequency comb

Abstract

The invention provides a terahertz frequency comb generation verification method and system based on an optical fiber microcavity optical frequency comb, and the method comprises the steps: injecting a continuous wave laser into an optical fiber microcavity resonator to generate a stable Kerr optical frequency comb, enabling the Kerr optical frequency comb to work in a single soliton state or a soliton crystal state, and obtaining an optical frequency reference with low phase noise. Furthermore, spectrum selection is performed on the optical frequency comb, multiple groups of optical comb tooth pairs comprising comb teeth of different orders are actively selected, and the optical frequency difference of each group of comb tooth pairs is directly converted into an electric signal in a terahertz frequency band by utilizing a beat frequency effect of a photoelectric detector. A plurality of terahertz electric signals generated by different comb tooth pairs are integrated to form a multi-channel terahertz frequency comb. The method allows a plurality of discrete and frequency-controllable terahertz signal channels to be generated in parallel on a single optical platform through one-time optical processing and photoelectric conversion, so that multichannel terahertz frequency comb generation is realized.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of terahertz signal generation and microwave photonics, and particularly relates to a terahertz frequency comb generation verification method and system based on a fiber microcavity optical frequency comb. BACKGROUND

[0002] The terahertz band (0.1-10 THz) has important application prospects in high-speed wireless communication, high-resolution imaging, precision spectroscopy, and radar detection. However, due to the operating frequency and phase noise characteristics of electronic devices, traditional electronic methods usually rely on frequency multiplication links or high-order harmonic generation to generate terahertz signals, and the phase noise deteriorates rapidly with the multiplication order, making it difficult to meet the requirements of high frequency, low noise, and high coherence at the same time.

[0003] In recent years, terahertz signal generation methods based on optical generation of microwaves and optical-electric beat frequency have attracted widespread attention. Using a stable laser or an optical frequency comb as a frequency reference, the optical frequency stability can be transferred to the microwave and terahertz bands through photoelectric detection, thereby obtaining a low phase noise signal. However, existing schemes based on stable lasers or high-quality factor optical cavities usually rely on bulky reference cavities, precise modulation devices, and complex locking control systems, which have high system complexity and are not conducive to miniaturization and engineering applications.

[0004] Microcavity Kerr optical frequency combs are considered an ideal platform for generating terahertz signals due to their large free spectral range, wide spectral bandwidth, and on-chip integration potential. However, existing microcavity optical frequency comb-generated terahertz signals are mostly concentrated in a single frequency channel, and are limited by the fixed free spectral range of the microcavity and the bandwidth of existing terahertz detectors, making it difficult to achieve multi-channel, characterizable terahertz frequency comb output, thereby failing to fully exploit the inherent advantages of multi-tooth optical frequency combs. SUMMARY

[0005] The present application provides a terahertz frequency comb generation verification method and system based on a fiber microcavity optical frequency comb to solve the problem of difficult multi-channel, characterizable terahertz frequency comb output of terahertz signals.

[0006] In a first aspect, the present application provides a terahertz frequency comb generation verification method based on a fiber microcavity optical frequency comb, comprising: injecting continuous wave laser into a fiber microcavity resonator to generate a first fiber microcavity Kerr optical frequency comb; adjusting the parameters of the continuous wave laser to control the first fiber microcavity Kerr optical frequency comb to work in a single soliton state or a soliton crystal state; performing spectral selection on the first fiber microcavity Kerr optical frequency comb in the single soliton state or the soliton crystal state to select multiple groups of optical comb teeth pairs, wherein each group of comb teeth pairs includes optical comb teeth of different orders; The optical comb teeth are input to a photodetector to perform beat frequency, and the photodetector converts the optical frequency difference between the two comb teeth in each optical comb tooth pair into an electrical signal located in the terahertz frequency band. Based on the electrical signal, a multi-channel terahertz frequency comb is obtained. The spacing between the frequency channels in the multi-channel terahertz frequency comb is determined by the frequency spacing of the first fiber microcavity Kerr frequency comb.

[0007] Secondly, this application provides a terahertz frequency comb generation and verification system based on an optical fiber microcavity optical frequency comb, comprising: A fiber optic microcavity resonator is used to inject continuous wave laser into the fiber optic microcavity resonator to generate a first fiber optic microcavity Kerr frequency comb. The control module is used to adjust the parameters of the continuous wave laser to control the first fiber microcavity Kerr frequency comb to operate in a single soliton state or a soliton crystal state. The spectral selection module is used to perform spectral selection on the first fiber microcavity Kerr optical frequency comb in the single soliton state or soliton crystal state to select multiple sets of optical comb tooth pairs, wherein each set of comb tooth pairs includes optical comb teeth of different orders. The photoelectric detection module is used to input the optical comb pair to the photoelectric detector to perform beat frequency, and convert the optical frequency difference between two comb teeth in each optical comb pair into an electrical signal in the terahertz frequency band through the photoelectric detector; and obtain a multi-channel terahertz frequency comb based on the electrical signal, wherein the spacing between the frequency channels in the multi-channel terahertz frequency comb is determined by the frequency spacing of the first fiber microcavity Kerr optical frequency comb.

[0008] As can be seen from the above technical solutions, this application provides a method and system for generating and verifying a terahertz frequency comb based on a fiber microcavity optical frequency comb. The method includes: injecting a continuous wave laser into a fiber microcavity resonator to generate a first fiber microcavity Kerr optical frequency comb; adjusting the parameters of the continuous wave laser to control the first fiber microcavity Kerr optical frequency comb to operate in a single soliton state or a soliton crystal state; performing spectral selection on the first fiber microcavity Kerr optical frequency comb in the single soliton state or soliton crystal state to select multiple sets of optical comb tooth pairs, wherein each set of comb tooth pairs includes optical comb teeth of different orders; inputting the optical comb tooth pairs to a photodetector to perform beat frequency, and converting the optical frequency difference between two comb teeth in each set of optical comb tooth pairs into an electrical signal located in the terahertz frequency band through the photodetector; obtaining a multi-channel terahertz frequency comb based on the electrical signal, wherein the spacing between the frequency channels in the multi-channel terahertz frequency comb is determined by the frequency spacing of the first fiber microcavity Kerr optical frequency comb. The method allows multiple discrete and frequency-controllable terahertz signal channels to be generated in parallel on a single optical platform through one-time optical processing and photoelectric conversion, thereby realizing the generation of multi-channel terahertz frequency combs. BRIEF DESCRIPTION OF DRAWINGS

[0009] In order to more clearly illustrate the technical solutions of the present application, the following will briefly introduce the drawings needed to be used in the embodiments, and obviously, other drawings can also be obtained by those skilled in the art without any creative effort on the premise of not paying any creative effort.

[0010] Figure 1 A flowchart of a terahertz frequency comb generation verification method based on a fiber microcavity optical frequency comb provided by the embodiment of the present application is shown in the figure. Figure 2 A double optical frequency comb heterodyne beat frequency system diagram provided by the embodiment of the present application is shown in the figure. Figure 3 A spectrum diagram of a first optical frequency comb and a second optical frequency comb provided by the embodiment of the present application is shown in the figure. Figure 4 A low-frequency electrical signal diagram provided by the embodiment of the present application is shown in the figure. Figure 5 A phase noise result diagram of a low-frequency electrical signal provided by the embodiment of the present application is shown in the figure.

[0011] Among them, 1 is a first Kerr optical frequency comb; 2 is a second Kerr optical frequency comb; 3 is an optical waveform shaper; 4 is a fiber amplifier; 5 is a traveling wave carrier photodiode; 6 is a fiber coupler; 7 is an envelope detector; 8 is a low-noise amplifier; 9 is an analysis instrument. DETAILED DESCRIPTION

[0012] The embodiments will be described in detail below, and examples are shown in the drawings. When the following description refers to the drawings, the same numbers in different drawings represent the same or similar elements unless otherwise indicated. The embodiments described in the following embodiments do not represent all the embodiments consistent with the present application.

[0013] In the prior art, the microcavity optical frequency comb often has a FSR of hundreds of GHz, which limits the number of frequency channels that can be detected and utilized by devices in the terahertz frequency band; at the same time, the terahertz generation and characterization scheme based on electronic frequency multiplication or harmonic mixing usually relies on external reference sources and complex mixing links, which is easy to introduce additional phase noise, and the system structure is complex, the device demand is high, and it is difficult to realize high coherence verification of multi-channel terahertz signals.

[0014] The present application is to overcome the trade-off between the large free spectral range (FSR) in the existing microcavity optical frequency comb system and the limited bandwidth of the terahertz device and detection device, and to realize stable generation and effective verification of multi-channel, low-noise terahertz frequency comb under the condition of limited device bandwidth.

[0015] To solve the above problems, the present application provides a terahertz frequency comb generation verification method based on a fiber microcavity optical frequency comb. A first fiber microcavity Kerr optical frequency comb with a free spectral range of 1-50 GHz is generated based on a microcavity system of a fiber microcavity. The optical frequency comb can generate a multi-band, low-phase-noise terahertz signal C in a device-detectable frequency band in a single soliton state or a soliton crystal state. At the same time, a second soliton optical frequency comb with the same structure but a different free spectral range is used to generate a low-noise terahertz signal D in the device-detectable frequency band. The terahertz signals C and D are heterodyne frequency-mixed, and frequency down-conversion is performed by combining a coherent envelope detection method to realize the mapping of the terahertz signal to an intermediate frequency or a radio frequency signal.

[0016] The present application can effectively avoid the background noise introduced by the external reference source in the electronic harmonic mixing scheme and the additional phase noise generated in the harmonic mixing process, and significantly reduces the dependence on the number of terahertz frequency multipliers, mixers and high-bandwidth detection devices. Therefore, under the condition of limited terahertz device and detector bandwidth, the generation and verification of multi-frequency terahertz signals are realized, while low phase noise, large equivalent bandwidth and high coherence are also achieved.

[0017] In addition, by using the double optical frequency comb heterodyne detection method, the consistency and coherence of the generated multi-channel terahertz frequency comb can be further verified. The method has the advantages of simple implementation, high frequency band utilization rate, low device requirement and strong scalability, and can provide a reliable technical solution for terahertz parallel communication, multi-band spectroscopy, high-resolution coherent detection and other applications.

[0018] As shown in Figure 1 the method comprises the following steps: S100: injecting a continuous wave laser into a fiber microcavity resonator to generate a first fiber microcavity Kerr optical frequency comb.

[0019] The continuous wave laser is coupled into the fiber microcavity resonator as an energy source. The microcavity structure of the resonator enhances the interaction between light and matter. When the pump power exceeds a certain threshold and matches the resonance of the cavity, the Kerr nonlinear effect in the cavity will be significantly excited, thereby generating the first fiber microcavity Kerr optical frequency comb.

[0020] The continuous wave laser can be generated by a semiconductor laser, a fiber laser or a solid-state laser, etc. The implementation parameters include center wavelength, output power and linewidth, which need to be matched with the resonance mode of the fiber microcavity resonator.

[0021] In this embodiment, for the convenience of description, the fiber microcavity Kerr optical frequency comb is defined as a Kerr optical frequency comb, and the first fiber microcavity Kerr optical frequency comb is defined as a first Kerr optical frequency comb 1. In the subsequent steps, the second fiber microcavity Kerr optical frequency comb is defined as a second Kerr optical frequency comb 2.

[0022] The first Kerr optical frequency comb 1 is an optical frequency comb generated based on Kerr nonlinear effect in a fiber microcavity resonator. The spectrum of the optical frequency comb is composed of a series of discrete and equally spaced spectral lines arranged like comb teeth in the frequency domain. The fixed frequency interval between the comb teeth, i.e., each optical spectral line, is called the free spectral range.

[0023] The first Kerr optical frequency comb 1 includes a fiber cavity and high-reflection dielectric films arranged at both ends of the cavity to form a high-Q fiber microcavity.

[0024] The fiber microcavity resonator is a micro resonant cavity constructed based on an optical fiber. The resonator can confine light in a micro cavity, making the light repeatedly propagate and resonate in the cavity. The fiber microcavity resonator is composed of a special fiber, the inside or end face of which is processed to form high-reflection interfaces, thereby forming optical feedback. The function of the resonator is to provide an enhanced interaction environment for nonlinear optical processes.

[0025] For example, the fiber microcavity resonator can specifically be a fiber Fabry-Perot cavity, which is composed of a fiber and high-reflection films plated at both ends of the fiber. For another example, it can also be a fiber ring microcavity, which forms resonance by bending the fiber into a micro ring and making the light circulate in the ring.

[0026] In the embodiment, the fiber microcavity resonator is a fiber Fabry-Perot resonant cavity, and high-reflection dielectric films are arranged at both ends of the fiber Fabry-Perot resonant cavity. The high-reflection dielectric film is a thin film coating plated on the surface of an optical element to greatly improve the reflectivity of the optical element to light waves of a specific wavelength. The high-reflection dielectric film is specifically arranged on both end faces of the fiber Fabry-Perot resonant cavity. The function of the film is to form a high-reflection mirror necessary for optical feedback, and the reflectivity of the film directly determines the quality factor of the resonant cavity. The higher the quality factor, the longer the storage time of light in the cavity, the more significant the light intensity enhancement effect, and the more conducive to the generation of nonlinear effects. The high-reflection dielectric film is usually formed by alternately plating multiple layers of inorganic dielectric materials such as silicon dioxide and tantalum pentoxide through physical vapor deposition or chemical vapor deposition. Through film layer design, the effect of nearly total reflection to the pump laser wavelength can be achieved.

[0027] After the resonant cavity is constructed, pump light needs to be introduced into the resonant cavity. Specifically, a continuous wave laser is injected into the fiber microcavity resonator to generate the first Kerr optical frequency comb 1, including: coupling the continuous wave laser into the fiber Fabry-Perot resonant cavity; and generating the first Kerr optical frequency comb 1 through nonlinear interaction between the fiber Fabry-Perot resonant cavity and the continuous wave laser.

[0028] When a strong enough pump light is confined in a high quality factor microcavity, nonlinear effects start to dominate. The first Kerr optical frequency comb 1 is generated through the nonlinear interaction between the fiber Fabry-Perot resonator and the continuous wave laser. Specifically, the initial continuous wave laser circulates in the cavity, and its intensity becomes very high due to the enhancement effect of the cavity. The Kerr nonlinearity of the fiber material causes the phase of the light to change with the light intensity, which can first trigger a modulation instability, transferring part of the pump light energy to the sideband.

[0029] With parameter adjustment, for example, slowly scanning the frequency of the pump laser to cross a certain resonance peak of the cavity, a dynamic phase transition will be experienced, and eventually a stable state will be reached, in which the nonlinear effects in the cavity and the dispersion, loss, and other factors are balanced, thus forming a stable optical frequency comb, i.e., the first Kerr optical frequency comb 1.

[0030] Since the entire process occurs in a Fabry-Perot cavity defined by high-reflectivity films, the generated optical frequency comb has a very narrow linewidth, and the phase relationship between the comb teeth is coherent. The optical frequency comb generated based on a specific cavity structure is closely related to the parameters of the cavity, for example, its free spectral range is determined by the optical length of the cavity.

[0031] For example, in this embodiment, a piece of few-mode fiber with a length of about 5 mm is used as a nonlinear gain medium, and dielectric reflection films with a reflectivity of more than 99.95% are deposited on both ends to form a high-Q (>108) fiber microcavity. By tuning the pump laser frequency to cross the cavity resonance mode, the system can sequentially enter the continuous wave state, the modulation instability state, and the soliton state, etc. When the pump conditions are appropriate, a stable soliton state optical frequency comb is formed in the cavity, i.e., the first Kerr optical frequency comb 1.

[0032] S200: Adjusting the parameters of the continuous wave laser to control the first fiber microcavity Kerr optical frequency comb to work in a single soliton state or a soliton crystal state.

[0033] In order to make the generated optical frequency comb have excellent coherence and low phase noise characteristics, the interaction state of the laser and the microcavity needs to be controlled, and the parameters of the continuous wave laser, such as its frequency or driving current, are adjusted, which essentially changes the pump conditions to manipulate the nonlinear dynamics in the microcavity.

[0034] In some embodiments, adjusting the parameters of the continuous wave laser to control the first Kerr optical frequency comb 1 to work in a single soliton state or a soliton crystal state includes: tuning the frequency or driving current of the continuous wave laser to control the first Kerr optical frequency comb 1 to enter a soliton state working region; and stabilizing the driving current to a preset working point to control the first Kerr optical frequency comb 1 to work in a single soliton state or a soliton crystal state.

[0035] When the continuous wave laser is initially coupled into the fiber microcavity resonator and generates a broadband optical spectrum, the system can be in a modulation instability regime or a chaotic regime. At this time, the pumping condition can be scanned by slowly and continuously changing the injection current of the laser or finely adjusting the external cavity length of the laser using a piezoelectric ceramic element to change the output frequency. During the scanning process, the evolution of the optical spectrum can be observed by real-time monitoring of the output spectrum or the time-domain waveform of the microcavity. When the spectrum suddenly becomes smooth and the bandwidth significantly increases, or a stable pulse sequence is observed on the oscilloscope, it indicates that the system has entered the soliton regime operating region, and the parameter space capable of generating solitons is sought and reached.

[0036] After entering the soliton regime operating region, the system can be in one of multiple soliton states or in an unstable state. In order to stabilize the system in a specific target state, more precise adjustment is needed, and then the driving current is stabilized to a preset operating point to control the first Kerr optical frequency comb 1 to work in a single soliton state or a soliton crystal state.

[0037] The preset operating point is obtained through prior experimental verification, which corresponds to a specific driving current value of the laser. At this current, in combination with the already adjusted laser frequency, for example, locked at a certain specific detuning position of the microcavity resonance peak, the system can be stably maintained in a single soliton state or a soliton crystal state for a long time. This stabilization process ensures the long-term reliable operation of the optical frequency comb.

[0038] Through this adjustment, the system can be guided from the initial continuous wave state, through the modulation instability state, to the stable soliton state region. Controlling the first Kerr optical frequency comb 1 to work in a single soliton state or a soliton crystal state is to utilize the inherent time-domain stability and frequency-domain coherence of these states. The stable soliton state ensures that the optical frequency comb has a determined phase relationship between each comb tooth, which is the physical basis for subsequent generation of low-noise terahertz signals.

[0039] The single soliton state and the soliton crystal state are two different stable dissipative soliton states of the optical frequency comb in the nonlinear dynamics of the fiber microcavity. The single soliton state is a stable optical soliton pulse existing in the cavity and circulating, and the corresponding optical frequency comb spectrum has a smooth envelope. The soliton crystal state is a plurality of phase-locked soliton pulses arranged in a specific pattern in the cavity, and the corresponding optical frequency comb spectrum can have a complex modulation structure. Both of these states can produce low-phase-noise coherent optical frequency comb outputs. By precisely adjusting the pumping condition, the system can be stabilized in any desired state.

[0040] The free spectral range (FSR) of the soliton optical frequency comb is in the range of 1-50 GHz, and works in a single soliton state or a soliton crystal state to obtain different spectral structures and spectral line distributions, providing flexible frequency selection conditions for subsequent terahertz frequency synthesis.

[0041] For example, by fine-tuning the laser driving current, for example, 120 mA, the system is stabilized to operate in the single soliton regime. After spectral filtering, amplification and photo-detection, a microwave signal with a repetition frequency of about 20.23 GHz is obtained, and the signal-to-noise ratio is more than 90 dB. Further phase noise test shows that the microwave signal reaches -95.4 dBc / Hz, -130 dBc / Hz and -141.2 dBc / Hz at 1 kHz, 10 kHz and 100 kHz frequency offset, respectively, which represents excellent low noise characteristics.

[0042] S300: performing spectral selection on the first fiber microcavity Kerr optical frequency comb in the single soliton regime or the soliton crystal regime to select a plurality of groups of optical comb tooth pairs.

[0043] After obtaining a stable and low-noise optical frequency comb, it is necessary to extract the frequency component that can be directly converted to the terahertz band. Spectral selection is to select specific wavelength or frequency components from a wide spectrum light source. In this embodiment, the operation object is the first Kerr optical frequency comb 1 in the stable state, and the role of spectral selection is to select specific groups of optical spectral lines from the numerous comb teeth of the optical frequency comb according to the needs.

[0044] The optical device for realizing spectral selection can be an adjustable optical bandpass filter, a wavelength selection switch, a combination of an optical diffraction grating and a slit, or a programmable optical waveform shaper.

[0045] Since the inherent frequency interval of the optical frequency comb is usually in the microwave band, if only adjacent comb teeth beat frequency is used, only a microwave signal can be obtained. In order to reach the terahertz band, the frequency difference between multiple comb teeth must be used. Therefore, spectral selection selects multiple groups of optical comb tooth pairs from the optical frequency comb, and each group contains two optical comb teeth that are far apart in the frequency sequence, i.e., different orders.

[0046] The optical frequency difference between these comb tooth pairs has already fallen into the terahertz band through simple frequency subtraction.

[0047] Each group of comb tooth pairs includes optical comb teeth of different orders, and different orders mean that the two comb teeth are not adjacent in frequency, and the frequency difference between them is an integer multiple of the free spectral range. These optical comb tooth pairs are direct optical carriers for subsequent photoelectric beat frequency to generate terahertz signals.

[0048] S400: inputting the optical comb tooth pairs into a photoelectric detector to perform beat frequency, and converting the optical frequency difference between the two comb teeth in each group of the optical comb tooth pairs into an electrical signal in the terahertz band through the photoelectric detector.

[0049] The optical comb pair is still an optical signal itself, and needs to be converted into an electrical signal that can be processed and utilized by an electronic system. The optical comb pair is input into a photodetector to perform frequency mixing to complete the photoelectric conversion. The photodetector is an optoelectronic device that converts an optical signal into an electrical signal. When light is incident on the light-sensitive surface of the photodetector, the internal photoelectric effect of the photodetector will generate a photocurrent related to the optical power.

[0050] In this embodiment, the photodetector performs frequency mixing detection on the incident multiple groups of optical comb pairs. When multiple groups of optical comb pairs are incident on the photodetector at the same time, due to the square-law detection characteristic, the output electrical signal will contain the beat frequency signals between the frequency components of the optical signals. The photodetector used for this purpose needs to have sufficient bandwidth to respond to the terahertz frequency beat signals. For example, a traveling-wave carrier photodiode 5.

[0051] When two optical combs containing a specific frequency difference are incident on the light-sensitive surface of the photodetector at the same time, the interference beat frequency effect of the light intensity will be responded by the photodetector. Due to the square-law detection characteristic of the photodetector, an oscillation component will be contained in the output photocurrent of the photodetector, and the frequency of the oscillation component is exactly equal to the difference between the optical frequencies of the two incident light beams.

[0052] The photodetector converts the optical frequency difference between the two combs in each group of optical comb pairs into an electrical signal in the terahertz frequency band. This process uses the photoelectric effect to achieve coherent down-conversion from optical frequency to radio frequency or terahertz frequency, and the conversion process itself does not introduce significant additional phase noise.

[0053] S500: Based on the electrical signal, a multi-channel terahertz frequency comb is obtained, and the interval between the frequency channels in the multi-channel terahertz frequency comb is determined by the frequency interval of the first fiber microcavity Kerr optical frequency comb.

[0054] Since each group of comb pairs generates an independent terahertz frequency electrical signal, and multiple groups of such comb pairs are selected in the spectral selection step, multiple parallel terahertz frequency channels are obtained. The positions of these channels on the frequency axis are determined by the selected comb pairs, and the interval between the frequency channels in the multi-channel terahertz frequency comb is determined by the frequency interval of the first Kerr optical frequency comb 1. This is because the frequency difference of any pair of combs is an integer multiple of the basic frequency interval, and therefore the minimum distinguishable interval between the generated terahertz frequency channels is also an integer multiple of the basic frequency interval, thereby ensuring the regularity and predictability of the output frequency comb.

[0055] The obtained multi-channel terahertz frequency comb is a signal set composed of a plurality of terahertz band electrical signals of different frequencies, which are discretely distributed in the frequency domain to form a comb-like structure. Each independent frequency component in the multi-channel terahertz frequency comb is referred to as a frequency channel.

[0056] For example, the free spectral range of the first Kerr optical frequency comb 1 is 20 GHz. Through spectral selection, the nth comb tooth and the n+5th comb tooth can be selected to form a pair, and the nth comb tooth and the n+8th comb tooth can be selected to form another pair. After the two pairs of comb teeth are input into the photodetector for frequency mixing, an electrical signal with a frequency of 100 GHz and an electrical signal with a frequency of 160 GHz are generated, which together constitute a terahertz frequency comb with two channels.

[0057] It can be understood that if the number of comb teeth of the optical frequency comb is sufficient and the bandwidth of the photodetector allows, more terahertz frequency combs with more channels can be generated by selecting more comb tooth pairs with different intervals.

[0058] The method solves the problem that the microcavity optical frequency comb cannot fully play its multi-tooth advantage to generate multi-channel terahertz signals in the prior art. The existing scheme is limited by device bandwidth or limited by ideas, and only generates a single or a few terahertz frequency points by using an optical frequency comb. The present application fully utilizes the inherent characteristics of the optical frequency comb, such as wide spectrum and numerous comb teeth, by combining spectral selection of multiple high-order comb tooth pairs and direct conversion of photoelectric frequency mixing. This allows multiple discrete and frequency-controllable terahertz signal channels to be generated in parallel on a single optical platform through one-time optical processing and photoelectric conversion, thereby realizing a breakthrough from a single channel to a multi-channel terahertz frequency comb.

[0059] At the same time, since the terahertz signal is a direct product of coherent optical comb teeth, noise accumulation caused by traditional electronic frequency multiplication links can be avoided, so that the generated multi-channel terahertz frequency comb can simultaneously maintain high coherence and low phase noise characteristics in each channel.

[0060] To verify the coherence and noise performance of the terahertz frequency comb, the present embodiment further constructs a double optical frequency comb heterodyne frequency mixing system. As shown in Figure 2 Two sets of FFPR optical frequency comb modules with the same structure but slightly different repetition frequencies are arranged in the system, and the repetition frequencies thereof are about 20.293 GHz (the first Kerr optical frequency comb 1) and 19.959 GHz (the second Kerr optical frequency comb 2), respectively.

[0061] In some embodiments, the method further includes: providing a second Kerr optical frequency comb 2; generating a reference terahertz signal based on the second Kerr optical frequency comb 2; and performing heterodyne beat frequency analysis between the optical signal generated based on the first Kerr optical frequency comb 1 and the reference terahertz signal to obtain an intermediate frequency beat frequency signal or a radio frequency beat frequency signal.

[0062] The second Kerr optical frequency comb 2 is another independent optical frequency comb source. Its generation method is similar to that of the first Kerr optical frequency comb 1, also based on fiber microcavity resonators and continuous-wave laser pumping. The function of the second Kerr optical frequency comb 2 is not to directly generate the final output multi-channel terahertz frequency comb, but rather to serve as an independent, highly coherent reference signal source. Its existence makes it possible to compare and characterize the terahertz signal generated by the first Kerr optical frequency comb 1.

[0063] In terms of system implementation, the second Kerr optical frequency comb 2 can be configured in an optical fiber microcavity module that is physically separate from but structurally similar to the first Kerr optical frequency comb 1.

[0064] The second Kerr optical frequency comb 2 is a reference source with an independent, known frequency scale. The physical implementation of the second Kerr optical frequency comb 2 can be completely symmetrical with the first Kerr optical frequency comb 1, using the same fiber microcavity and pump laser, but by designing or adjusting it to have a slightly different cavity length, thereby obtaining different free spectral ranges.

[0065] After obtaining the second Kerr optical frequency comb 2, a reference signal for comparison needs to be derived from it. Similar to generating a terahertz signal from the first Kerr optical frequency comb 1, a pair of specific high-order comb teeth are selected by spectral selection of the second Kerr optical frequency comb 2 and then sent to a separate photodetector for beat frequency, thereby generating a single-frequency terahertz electrical signal with a known and stable frequency, i.e., the reference terahertz signal, which serves as the frequency reference for the verification process.

[0066] like Figure 3 As shown in the figure, (a) is the first Kerr optical frequency comb 1, which has a large mode spacing corresponding to the free spectral range of the optical frequency comb. (b) is the second Kerr optical frequency comb 2, which has a very small free spectral range and serves as a high-precision reference ruler.

[0067] In some embodiments, the optical waveform shaper 3 performs optical spectral selection and waveform shaping on the first Kerr optical frequency comb 1 and the second Kerr optical frequency comb 2, respectively. The shaper selects the optical signals corresponding to the comb tooth pairs that constitute the multi-channel terahertz comb from the first Kerr optical frequency comb 1, and selects the optical signals corresponding to the comb tooth pair used to generate the reference terahertz signal from the second Kerr optical frequency comb 2.

[0068] The two shaped optical signals are amplified in optical power by optical fiber amplifiers 4 to improve the signal strength. Then, the amplified two optical signals are combined by an optical coupler 6 to be transmitted together. Finally, the combined optical signal is input to a traveling wave carrier photodiode 5 (UTC-PD) for photoelectric beat frequency conversion. Inside the photoelectric diode, complex heterodyne effects occur between all optical comb teeth from the two optical frequency combs. Among them, each tooth of the first Kerr optical frequency comb 1 produces a terahertz frequency component, which will produce a reference terahertz frequency component from the second Kerr optical frequency comb 2 to generate a beat signal with lower frequency, i.e. an initial beat electric signal.

[0069] The frequency of the initial beat electric signal may still be high or contain complex components, which needs to be further processed for measurement. In some embodiments, the method further comprises coherent envelope detection of the intermediate frequency beat signal or the radio frequency beat signal, specifically inputting the initial beat electric signal to an envelope detector 7 for envelope detection to obtain a down-converted signal, and the envelope detector 7 extracts the amplitude envelope of the initial beat electric signal, and the fluctuation frequency of the envelope corresponds to the beat signal which has been reduced to the intermediate frequency or radio frequency band.

[0070] To improve the signal strength, the generated signal is further amplified by a low noise amplifier 8 and down-converted to the intermediate frequency or radio frequency band by envelope detection, which is convenient for electronic system detection and analysis. Then, the down-converted signal is input to the low noise amplifier 8 for amplification to output the intermediate frequency beat signal or the radio frequency beat signal. Thus, the signal originally belonging to the terahertz band in each channel is mapped and converted into an independent low frequency electric signal which can be transmitted and measured by a conventional cable.

[0071] After obtaining the low frequency electric signal which is convenient for processing, accurate characterization can be performed. Based on the low frequency electric signal, verification of the multi-channel terahertz frequency comb is performed. This includes performing spectral analysis on the low frequency electric signal by a spectrum analyzer, which can simultaneously display the beat signal peaks corresponding to multiple channels, measure the signal-to-noise ratio and line width of each peak, and the line width directly reflects the frequency stability of the corresponding terahertz channel.

[0072] At the same time, the same low frequency electric signal is tested for phase noise by an analysis instrument 9, such as a phase noise analyzer, to obtain the phase noise power spectrum density at different frequency offsets. This phase noise characteristic is equivalent to the phase noise characteristic of the original terahertz signal. Finally, based on the comprehensive analysis of the signal-to-noise ratio, line width and phase noise spectrum density measured for all channels, it can be verified whether different frequency channels in the multi-channel terahertz frequency comb have good and consistent coherence and low noise performance.

[0073] In a specific experiment, the first Kerr optical frequency comb 1 is configured as a multi- FSR spaced soliton crystal state for generating a low-noise reference terahertz signal; the second Kerr optical frequency comb 2 is operated in a single soliton state, whose repetition rate determines the minimum frequency spacing of the generated terahertz frequency comb. By selecting different spectral line combinations in the optical domain, multiple discrete terahertz frequency components can be simultaneously generated within a limited terahertz detection bandwidth. The reference terahertz signal generated by the first Kerr optical frequency comb 1 and the multi-channel terahertz signal generated by the second Kerr optical frequency comb 2 are mixed and envelope-detected to obtain multiple corresponding intermediate frequency beat signals in the radio frequency band.

[0074] The optical signal generated based on the first Kerr optical frequency comb 1 is mixed with the reference terahertz signal to obtain an intermediate frequency beat signal or a radio frequency beat signal. It should be understood that the operation object here is essentially the optical signals of the two optical frequency combs.

[0075] In some embodiments, the method further comprises: coherently envelope detecting the intermediate frequency beat signal or the radio frequency beat signal to extract the amplitude envelope of the beat signal; by extracting the amplitude envelope, down-converting the frequency information in the beat signal to a target detection frequency band to obtain a low-frequency electrical signal; based on the low-frequency electrical signal, performing verification on the multi-channel terahertz frequency comb.

[0076] Wherein, the coherent envelope detection is for demodulation of the amplitude modulation signal, and the low-frequency information modulated on the high-frequency carrier signal is recovered without loss. In this embodiment, the carrier is the intermediate frequency or radio frequency beat signal, and the information modulated on it is a parameter related to the characteristics of the original terahertz signal. The coherent envelope detection is performed to strip the information from the carrier and convert it into a more basic low-frequency waveform for accurate quantitative analysis.

[0077] In order to avoid directly sampling and spectrum analyzing the terahertz high-frequency carrier, the envelope detector 7 can extract the amplitude envelope of the mixed signal, thereby down-converting the beat information originally in the terahertz frequency band to the radio frequency or intermediate frequency range, i.e. the target detection frequency band, to obtain a low-frequency electrical signal.

[0078] The low-frequency electrical signal is one or more sinusoidal waves or narrowband signals, each corresponding to a frequency channel in the multi-channel terahertz comb. Due to its low and stable frequency, its accurate center frequency and extremely narrow -3 decibel bandwidth (line width) can be directly measured by a high-resolution spectrum analyzer to evaluate the frequency stability, and the electrical signal is amplified and detected by a low-noise amplifier 8.

[0079] As Figure 4As shown in the figure, (a)-(e) are high-resolution scans performed near five different center frequency points to finely observe the signal in each channel. Sharp peaks protrude from the substrate by more than 20 dB, demonstrating an extremely high signal-to-noise ratio.

[0080] Using the above method, the frequency differences between each frequency component in the terahertz frequency comb and the reference signal are mapped one by one to low-frequency beat signals that can be directly measured by a conventional electronic spectrum analyzer. In the experiment, multiple intermediate-frequency beat components were successfully observed, with frequencies within the coverage range of the electronic spectrum analyzer. Each beat signal exhibited high signal-to-noise ratio and narrow linewidth characteristics, and no significant broadening was observed at a 100 Hz resolution bandwidth, indicating that the multi-channel terahertz frequency comb maintained good coherence.

[0081] like Figure 5 As shown, further phase noise tests revealed that the intermediate frequency signals corresponding to different terahertz channels have almost identical phase noise levels within the frequency offset range of 1 kHz to 1 MHz, proving that through soliton state modulation and heterodyne verification, the flexible generation of multi-channel terahertz frequency combs can be achieved without sacrificing noise performance.

[0082] As can be seen from the above embodiments, the method proposed in this application can realize the generation and verification of multi-channel, low-noise, and high-coherence terahertz frequency combs under the condition of limited bandwidth of existing terahertz devices, avoid the noise accumulation problem introduced by traditional electronic frequency doubling links in the high-frequency band, and significantly reduce the system's dependence on high-bandwidth terahertz devices. It has the advantages of compact structure, high stability, and suitability for integrated packaging.

[0083] In some embodiments, the multi-channel terahertz frequency comb generated by the method is applied to at least one of a multi-carrier terahertz communication system, a coherent terahertz radar system, a broadband terahertz spectral analysis system, or a frequency metrology system.

[0084] In the application scenario of multi-carrier terahertz communication system, the multi-channel terahertz frequency comb is directly used as the signal source of the transmitter. Each independent frequency channel in the frequency comb, i.e. each terahertz electrical signal, can be regarded as an independent communication carrier. The baseband processing unit of the communication system performs serial-to-parallel conversion on the user data stream to be transmitted, and divides the user data stream into multiple parallel sub-data streams corresponding to the number of frequency comb channels. Each sub-data stream is modulated onto a corresponding terahertz frequency channel by a modulator (such as amplitude shift keying, phase shift keying or quadrature amplitude modulation). All modulated channels are combined by a power combining network and radiated out through a terahertz antenna. At the receiving end, after the receiving antenna captures the signal, a local oscillator frequency comb that matches the frequency comb structure of the transmitting end is used for coherent demodulation, so that all sub-data streams are recovered in parallel, and the original data is obtained through parallel-to-serial conversion. In this process, the multi-channel terahertz frequency comb provides multiple carriers that are naturally synchronized and have accurate frequency intervals, eliminating the need for multiple independent oscillators and complex phase-locked loops in traditional schemes.

[0085] In the application scenario of coherent terahertz radar system, the multi-channel terahertz frequency comb is used as the transmitting signal source of the radar. The radar transmitter directly amplifies and radiates the frequency comb signal. When this multi-frequency signal illuminates the target, different frequency components will experience different phase delays and Doppler shifts, but maintain strict coherence with each other. After the reflected echo is captured by the receiver, it is mixed with a part of the transmitted signal (reference signal) for coherent mixing. Since the transmitted signal is a frequency comb structure, a series of corresponding intermediate frequency signals will be generated after mixing. By simultaneously analyzing the phase and frequency changes of these intermediate frequency signals, the signal processor can simultaneously obtain the response of the target at multiple discrete frequency points. This processing method is equivalent to simultaneously transmitting multiple coherent pulses or linear frequency modulated signals, which can synthesize a wider equivalent bandwidth, thereby greatly improving the range resolution and facilitating feature extraction and identification of complex targets.

[0086] In the application scenario of wideband terahertz spectrum analysis system, the multi-channel terahertz frequency comb is used as the illumination light source of the system. The frequency comb signal is directly illuminated onto the sample to be measured. Since the frequency comb itself contains multiple discrete terahertz spectral lines with known frequencies, it is equivalent to simultaneously using multiple monochromatic lights to perform parallel detection on the sample. The light signal transmitted through or reflected by the sample is received by a terahertz detector. By measuring the light intensity attenuation or phase change of each frequency channel, the optical parameters of the sample at these discrete frequency points can be immediately obtained. By increasing the number of channels of the frequency comb or adjusting its basic frequency interval, an absorption or reflection spectrum covering a certain frequency range with a certain resolution can be flexibly constructed. This method can avoid the slow process of mechanical scanning delay line in traditional time-domain spectrum technology, and also avoid the low power and poor signal-to-noise ratio problems when using a wide-spectrum thermal light source.

[0087] In the application scenario of frequency metrology system, the multi-channel terahertz frequency comb serves as a bridge connecting the microwave frequency standard and the terahertz band. First, the repetition frequency (i.e. comb tooth interval) of the first Kerr optical frequency comb 1 generating the frequency comb is locked to a microwave frequency standard, such as a hydrogen clock or a cesium clock, through a phase-locked loop or other technology. At this time, each tooth of the optical frequency comb has an absolute frequency accuracy traced back to the microwave standard. Further, the frequency of each terahertz frequency channel generated by photodetector beating is the frequency difference between two locked teeth of the optical frequency comb, and therefore also has the same absolute frequency accuracy and stability. In this way, the multi-channel terahertz frequency comb generates a series of terahertz standard signals with known frequencies and extremely high stability. These signals can be directly used to calibrate the frequency response of other terahertz sources or detectors, or through further heterodyne measurement, to provide accurate frequency calibration for unknown terahertz signals.

[0088] It should be noted that the method of the present application is applicable to any system that needs to simultaneously utilize multiple discrete, coherent and low-noise terahertz frequency channels. Such systems rely on the parallel signal processing, high-precision frequency operation or wideband spectrum analysis capabilities of the terahertz band, including but not limited to specific application fields such as high-speed communication, precision detection, material analysis and metrology.

[0089] Based on the above-mentioned verification method for generating a terahertz frequency comb based on an optical fiber microcavity optical frequency comb, some embodiments of the present application also provide a verification system for generating a terahertz frequency comb based on an optical fiber microcavity optical frequency comb, comprising: an optical fiber microcavity resonator for injecting continuous wave laser into the optical fiber microcavity resonator to generate a first optical fiber microcavity Kerr optical frequency comb; a control module for adjusting the parameters of the continuous wave laser to control the first optical fiber microcavity Kerr optical frequency comb to work in a single soliton state or a soliton crystal state; a spectrum selection module for performing spectrum selection on the first optical fiber microcavity Kerr optical frequency comb in the single soliton state or the soliton crystal state to select a plurality of groups of optical comb tooth pairs, wherein each group of comb tooth pairs includes optical comb teeth of different orders; a photoelectric detection module for inputting the optical comb tooth pairs into a photoelectric detector to perform beating, converting the optical frequency difference between two teeth in each group of optical comb tooth pairs into an electrical signal in the terahertz band through the photoelectric detector, and obtaining a multi-channel terahertz frequency comb based on the electrical signal, wherein the interval between the frequency channels in the multi-channel terahertz frequency comb is determined by the frequency interval of the first optical fiber microcavity Kerr optical frequency comb.

[0090] From the above scheme, the application can realize the simultaneous generation of multi-channel terahertz frequency comb on a single fiber microcavity optical frequency comb platform, break through the limitation that only a single or a few terahertz frequency points can be obtained in the prior art, and significantly increase the number of available frequency channels in the terahertz frequency band. At the same time, without relying on complex external phase locking or high-speed feedback control circuit, high coherence and narrow linewidth output can be maintained in the terahertz frequency band, effectively reducing the system complexity and noise level. By introducing the verification method of heterodyne frequency and coherent envelope detection, under the condition of limited electrical and terahertz device bandwidth, the synchronization down-conversion and accurate characterization of multiple terahertz frequency channels are realized, which can solve the problem that the multi-channel terahertz frequency comb is difficult to verify in the prior art.

[0091] The second Kerr optical frequency comb is only introduced as a reference and verification unit and does not participate in the actual generation process of the terahertz frequency comb, so that reliable verification of the coherence, frequency consistency and noise performance of the multi-channel terahertz frequency comb is realized without increasing the complexity of the system. The application has a wide applicable range of free spectral range of the optical frequency comb (1 GHz-50 GHz), good parameter scalability and device compatibility, is suitable for different terahertz frequency bands and various application scenarios, and has high engineering implementation value.

[0092] In summary, the scheme provided by the application has a compact structure and clear implementation path, is easy to package and system integrate, and provides an expandable, low-noise and verifiable terahertz frequency comb solution for multi-carrier terahertz communication, coherent terahertz radar and high-precision frequency measurement applications.

[0093] The similar parts between the embodiments provided by the application can be referred to each other, the specific embodiments provided above are only a few examples under the general concept of the application, and do not limit the protection scope of the application. For those skilled in the art, any other embodiments extended according to the application scheme without creative labor are within the protection scope of the application.

Claims

1. A method for generating and verifying terahertz frequency combs based on fiber microcavity optical frequency combs, characterized in that, include: A continuous wave laser is injected into a fiber microcavity resonator to generate a first fiber microcavity Kerr frequency comb. Adjust the parameters of the continuous wave laser to control the first fiber microcavity Kerr frequency comb to operate in a single soliton state or a soliton crystal state; Spectral selection is performed on the first fiber microcavity Kerr frequency comb in the single soliton state or soliton crystal state to select multiple sets of optical comb tooth pairs, wherein each set of comb tooth pairs includes optical comb teeth of different orders; The optical comb teeth are input to a photodetector to perform beat frequency, and the photodetector converts the optical frequency difference between the two comb teeth in each optical comb tooth pair into an electrical signal located in the terahertz frequency band. Based on the electrical signal, a multi-channel terahertz frequency comb is obtained. The spacing between the frequency channels in the multi-channel terahertz frequency comb is determined by the frequency spacing of the first fiber microcavity Kerr frequency comb.

2. The method for generating and verifying a terahertz frequency comb based on a fiber microcavity optical frequency comb according to claim 1, characterized in that, The step of injecting continuous-wave laser into the fiber microcavity resonator to generate a first fiber microcavity Kerr frequency comb includes: The fiber optic microcavity resonator is provided, wherein the fiber optic microcavity resonator is a fiber optic Fabry-Perot resonator, and high-reflectivity dielectric films are disposed on both end faces of the fiber optic Fabry-Perot resonator; The continuous wave laser is coupled into the fiber Fabry-Perot resonant cavity; The first fiber microcavity Kerr frequency comb is generated through the nonlinear interaction between the fiber Fabry-Perot resonator and the continuous wave laser.

3. The method for generating and verifying a terahertz frequency comb based on a fiber microcavity optical frequency comb according to claim 1, characterized in that, Adjusting the parameters of the continuous wave laser to control the first fiber microcavity Kerr frequency comb to operate in a single soliton state or a soliton crystal state includes: The frequency or driving current of the continuous wave laser is tuned to control the first fiber microcavity Kerr frequency comb to enter the soliton state working region; The driving current is stabilized to a preset operating point to control the first fiber microcavity Kerr frequency comb to operate in a single soliton state or a soliton crystal state.

4. The method for generating and verifying a terahertz frequency comb based on a fiber microcavity optical frequency comb according to claim 1, characterized in that, The method further includes: A second fiber microcavity Kerr frequency comb is provided, wherein the free spectral range of the second fiber microcavity Kerr frequency comb is different from the frequency spacing of the first fiber microcavity Kerr frequency comb; A reference terahertz signal is generated based on the second fiber microcavity Kerr frequency comb. The optical signal generated based on the first fiber microcavity Kerr optical frequency comb is heterodyne-beat frequencyed with the reference terahertz signal to obtain an intermediate frequency beat frequency signal or a radio frequency beat frequency signal.

5. The method for generating and verifying a terahertz frequency comb based on a fiber microcavity optical frequency comb according to claim 4, characterized in that, The method further includes: Coherent envelope detection is performed on the intermediate frequency beat frequency signal or the radio frequency beat frequency signal to extract the amplitude envelope of the beat frequency signal; By extracting the amplitude envelope, the frequency information in the beat frequency signal is down-converted to the target detection frequency band to obtain a low-frequency electrical signal; The multi-channel terahertz frequency comb is verified based on the low-frequency electrical signal.

6. The method for generating and verifying a terahertz frequency comb based on a fiber microcavity optical frequency comb according to claim 5, characterized in that, The verification of the multi-channel terahertz frequency comb based on the low-frequency electrical signal includes: The low-frequency electrical signal is analyzed using a spectrum analyzer to obtain the signal-to-noise ratio and linewidth. The phase noise of the low-frequency electrical signal was tested using a phase noise analyzer to obtain the phase noise power spectral density at different frequency offsets. Based on the signal-to-noise ratio, linewidth spectrum, and phase noise power spectral density at different frequency offsets, the coherence and noise performance of different frequency channels in the multi-channel terahertz frequency comb are verified to obtain consistent verification results.

7. The method for generating and verifying a terahertz frequency comb based on a fiber microcavity optical frequency comb according to claim 4, characterized in that, The step of heterodyne beating the optical signal generated based on the first fiber microcavity Kerr frequency comb with the reference terahertz signal to obtain an intermediate frequency beating signal or a radio frequency beating signal includes: The first fiber microcavity Kerr optical frequency comb is subjected to optical spectral selection and waveform shaping by an optical waveform shaper to obtain a first shaped optical signal; and the second fiber microcavity Kerr optical frequency comb is subjected to optical spectral selection and waveform shaping by an optical waveform shaper to obtain a second shaped optical signal. The first shaped optical signal is amplified by an optical fiber amplifier to obtain a first amplified signal; and the second shaped optical signal is amplified by an optical fiber amplifier to obtain a second amplified signal. The first amplified signal and the second amplified signal are combined using an optical fiber coupler to obtain a combined optical signal; The combined optical signal is input to a traveling wave carrier photodiode for photoelectric beat frequency conversion to generate an initial beat frequency electrical signal; Based on the initial beat frequency electrical signal, an intermediate frequency beat frequency signal or a radio frequency beat frequency signal is generated.

8. The method for generating and verifying a terahertz frequency comb based on a fiber microcavity optical frequency comb according to claim 7, characterized in that, The step of generating an intermediate frequency (IF) beat frequency signal or a radio frequency (RF) beat frequency signal based on the initial beat frequency electrical signal includes: The initial beat frequency electrical signal is input to the envelope detector for envelope detection to obtain the down-converted signal. The down-converted signal is input to a low-noise amplifier for amplification to output an intermediate frequency beat frequency signal or a radio frequency beat frequency signal.

9. The method for generating and verifying a terahertz frequency comb based on a fiber microcavity optical frequency comb according to claim 1, characterized in that, The multi-channel terahertz frequency comb generated by the method can be applied to at least one of a multi-carrier terahertz communication system, a coherent terahertz radar system, a broadband terahertz spectral analysis system, or a frequency metrology system.

10. A terahertz frequency comb generation and verification system based on fiber microcavity optical frequency comb, characterized in that, include: A fiber optic microcavity resonator is used to inject continuous wave laser into the fiber optic microcavity resonator to generate a first fiber optic microcavity Kerr frequency comb. The control module is used to adjust the parameters of the continuous wave laser to control the first fiber microcavity Kerr frequency comb to operate in a single soliton state or a soliton crystal state. The spectral selection module is used to perform spectral selection on the first fiber microcavity Kerr optical frequency comb in the single soliton state or soliton crystal state to select multiple sets of optical comb tooth pairs, wherein each set of comb tooth pairs includes optical comb teeth of different orders. The photoelectric detection module is used to input the optical comb pair to the photoelectric detector to perform beat frequency, and convert the optical frequency difference between two comb teeth in each optical comb pair into an electrical signal in the terahertz frequency band through the photoelectric detector; and obtain a multi-channel terahertz frequency comb based on the electrical signal, wherein the spacing between the frequency channels in the multi-channel terahertz frequency comb is determined by the frequency spacing of the first fiber microcavity Kerr optical frequency comb.

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