A trigger signal generation device and acquisition system for terahertz pulse acquisition

Abstract

The present invention relates to a trigger signal generating device and an acquisition system for terahertz pulse acquisition. The trigger signal generating device of the present invention uses a single-cavity dual optical comb light source to generate coherent pulsed light (the coherent pulsed light is used to generate terahertz pulses), and extracts the trigger signal for terahertz pulse acquisition by means of beat frequency and detection based on an optical beat frequency element and an envelope extraction unit, that is, a trigger signal with the same frequency as the terahertz pulse is generated, so as to perform real-time acquisition of terahertz pulse signals, thereby solving the problems of complex light source structure, strict trigger signal phase matching requirements, data acquisition redundancy, etc. in the process of terahertz pulse generation and acquisition.

Description

Technical Field

[0001] The present invention relates to the technical field of terahertz pulse generation and detection, and particularly to a trigger signal generation device and an acquisition system for terahertz pulse acquisition. Background Art

[0002] Terahertz waves refer to electromagnetic waves with frequencies in the range of 0.1 THz to 10 THz, corresponding to wavelengths between 0.03 mm and 3 mm. They coincide with millimeter waves in the long wavelength band and infrared light in the short wavelength band. Due to their location in the transition region from electronics to photonics, they have rich physical characteristics, such as no ionizing radiation, strong penetrability, and spectral fingerprint characteristics, and are thus widely used in application fields such as terahertz spectroscopy, terahertz imaging, and terahertz communication.

[0003] Generally, a terahertz time-domain spectroscopy system (THz-TDS) is a terahertz system based on mechanical delay scanning. It needs to use an electric displacement stage to sample the sample point by point at equal intervals, but the single scan time is long, the stability of the scanning device is poor, and the acquisition efficiency is low. In recent years, researchers have proposed using two independent optical frequency comb light sources for terahertz pulse generation. However, the coherence of the two independent optical frequency combs needs to rely on a complex electronic feedback control device to eliminate the randomness of the output frequencies of the two single-cavity dual optical comb light sources to achieve the coherence purpose, which greatly increases the complexity and cost of the system.

[0004] In addition, whether it is based on mechanical delay scanning or the application of two independent laser light sources to terahertz pulse generation and detection, the trigger signal of the terahertz pulse mostly uses two beams of light to beat frequencies in a nonlinear crystal (such as BBO). This requires fine adjustment of parameters such as the intensity, polarization, and distance of the two beams of light, and strictly meets the phase matching conditions of the two beams of light to generate a terahertz pulse acquisition trigger signal. Moreover, due to the low duty cycle of the terahertz signal within a single period, using this method, it is impossible to locate and synchronously acquire the terahertz pulse signal, and tens of thousands of averaging times are required to improve the signal-to-noise ratio, resulting in too long acquisition time. Summary of the Invention

[0005] In view of this, the present invention provides a trigger signal generation device and an acquisition system for terahertz pulse acquisition to overcome problems such as complex light source structure, strict phase matching requirements for trigger signals, and redundant data acquisition in the process of terahertz pulse generation and acquisition in the prior art.

[0006] To achieve the above object, the present invention provides the following solutions:

[0007] A trigger signal generating device for terahertz pulse acquisition, the trigger signal generating device comprising: a single-cavity dual optical comb light source, an optical beat frequency element, and an envelope extraction unit connected in sequence;

[0008] The single-cavity dual optical comb light source is used to generate two coherent pulse lights with different repetition frequencies; the two coherent pulse lights with different repetition frequencies are pulse lights for generating terahertz pulses;

[0009] The optical beat frequency element is used to perform beat frequency on the two coherent pulse lights with different repetition frequencies to obtain a beat frequency signal;

[0010] The envelope extraction unit is used to detect the beat frequency signal to generate a trigger signal; the frequency of the trigger signal is the repetition frequency difference between the two coherent pulse lights.

[0011] Optionally, the single-cavity dual optical comb light source includes: a pump source, a wavelength division multiplexer, an erbium-doped fiber, an isolator, a first optical coupler, a polarization controller, a polarization-maintaining fiber, a carbon nanotube saturable absorber, and a single-mode fiber;

[0012] The pump source is connected to an input end of the wavelength division multiplexer, an output end of the wavelength division multiplexer is connected to one end of the erbium-doped fiber, and the light source provided by the pump source is coupled into the erbium-doped fiber through the wavelength division multiplexer;

[0013] The isolator is embedded in the erbium-doped fiber, the light source generates laser in the erbium-doped fiber, and the isolator is used to make the laser transmit unidirectionally in the erbium-doped fiber;

[0014] The other end of the erbium-doped fiber is connected to an input end of the polarization controller, an output end of the polarization controller is connected to one end of the polarization-maintaining fiber, and the polarization controller is used to change the twisting state of the erbium-doped fiber;

[0015] The other end of the polarization-maintaining fiber is connected to an input end of the carbon nanotube saturable absorber, and an output end of the nanotube saturable absorber is connected to the other input end of the wavelength division multiplexer through the single-mode fiber;

[0016] An input end and an output end of the first optical coupler are connected in the erbium-doped fiber, and the other output end of the first optical coupler is connected to the optical beat frequency element.

[0017] Optionally, the optical beat frequency element includes one or more of an optical intensity modulator, an optical phase modulator, a second optical coupler, a non-phasic crystal, and a non-linear fiber.

[0018] Optionally, the envelope extraction unit includes one or more of a diode envelope detector, a synchronous detector, and an integrated circuit demodulation.

[0019] Optionally, the trigger signal generating device further includes a trigger signal amplification module;

[0020] The trigger signal amplification module is connected to the envelope extraction unit, and the trigger signal amplification module is configured to amplify the trigger signal output by the envelope extraction unit.

[0021] Optionally, the trigger signal amplification module is a voltage amplifier, and the bandwidth of the voltage amplifier is 40 MHz.

[0022] A single-cavity dual-optical comb light source in the above-mentioned trigger signal generating device for terahertz pulse acquisition.

[0023] A terahertz pulse acquisition system, the acquisition system includes the above-mentioned trigger signal generating device, and the acquisition system further includes a beam splitter, an asynchronous sampling terahertz pulse generating unit, and a data acquisition unit;

[0024] The beam splitter is arranged between the single-cavity dual-optical comb light source and the optical beat frequency element in the trigger signal generating device. The input end of the beam splitter is connected to the single-cavity dual-optical comb light source. The second signal output end and the third signal output end of the beam splitter are respectively connected to the two input ends of the optical beat frequency element; the first signal output end and the fourth signal output end of the beam splitter are respectively connected to the transmitting photoconductive antenna and the receiving photoconductive antenna in the asynchronous sampling terahertz pulse generating unit; the first signal output end and the second signal output end are used to output two sub-pulse lights divided from the first pulse light, and the third signal output end and the fourth signal output end are used to output two sub-pulse lights divided from the second pulse light. The first pulse light and the second pulse light are two coherent pulse lights with different repetition frequencies;

[0025] The output end of the asynchronous sampling terahertz pulse generating unit is connected to the input end of the data acquisition unit;

[0026] The output end of the trigger signal generating device is connected to the trigger control end of the data acquisition unit.

[0027] Optionally, the asynchronous sampling terahertz pulse generating unit includes a transmitting photoconductive antenna, and a first collimating and focusing lens, a second collimating and focusing lens, and a receiving photoconductive antenna are sequentially arranged along the transmitting direction of the transmitting photoconductive antenna;

[0028] The sample to be measured is arranged between the first collimating and focusing lens and the second collimating and focusing lens.

[0029] According to the specific embodiments provided by the present invention, the present invention discloses the following technical effects:

[0030] The present invention discloses a trigger signal generation device and an acquisition system for terahertz pulse acquisition. The trigger signal generation device of the present invention uses a single-cavity dual optical comb light source to generate coherent pulsed light (the coherent pulsed light is used to generate terahertz pulses), and extracts the trigger signal for terahertz pulse acquisition by means of beat frequency and detection based on an optical beat frequency element and an envelope extraction unit, that is, a trigger signal with the same frequency as the terahertz pulse is generated, so as to perform real-time acquisition of terahertz pulse signals, thus solving the problems of complex light source structure, strict trigger signal phase matching requirements, data acquisition redundancy, etc. in the process of terahertz pulse generation and acquisition.

[0031] The single-cavity dual optical comb light source of the present invention utilizes that within the same optical resonator (i.e., the single-cavity dual optical comb light source, and the light source is also called the optical resonator), two beams of light share the same physical path, can reuse the pulse transmission mechanism, are subject to the same external interference and internal noise, and by adjusting the intracavity dispersion, polarization state and nonlinear effect, the generation of two beams of coherent optical frequency combs within a single optical resonator is realized without the aid of a complex electronic feedback control device. BRIEF DESCRIPTION OF THE DRAWINGS

[0032] In order to more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the following will briefly introduce the drawings required to be used in the embodiments. Obviously, the drawings in the following description are only some embodiments of the present invention, and for those of ordinary skill in the art, other drawings can be obtained according to these drawings without creative efforts.

[0033] Figure 1 It is a schematic structural diagram of a terahertz pulse acquisition system provided by an embodiment of the present invention;

[0034] Figure 2 It is a schematic structural diagram of a single-cavity dual optical comb light source provided by an embodiment of the present invention;

[0035] Figure 3 It is a mode-locking spectrogram of a single-cavity dual optical comb light source based on polarization multiplexing provided by an embodiment of the present invention;

[0036] Figure 4 It is a mode-locking frequency spectrum diagram of a single-cavity dual optical comb light source based on polarization multiplexing provided by an embodiment of the present invention;

[0037] Figure 5 It is a schematic diagram of a beat frequency signal provided by an embodiment of the present invention;

[0038] Figure 6 It is a schematic diagram of a trigger signal provided by an embodiment of the present invention;

[0039] Figure 7 provided by an embodiment of the present invention Figure 6 The partial enlarged view of the trigger signal in Specific embodiments

[0040] The following will clearly and completely describe the technical solutions in the embodiments of the present invention with reference to the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all the embodiments. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention without creative efforts shall fall within the protection scope of the present invention.

[0041] The purpose of the present invention is to provide a trigger signal generation device and an acquisition system for terahertz pulse acquisition, so as to overcome the problems existing in the prior art, such as complex light source structure, strict trigger signal phase matching requirements, and redundant data acquisition, during the generation and acquisition of terahertz pulses.

[0042] To make the above objects, features, and advantages of the present invention more obvious and understandable, the present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments.

[0043] Embodiment 1

[0044] Embodiment 1 of the present invention provides a trigger signal generation device for terahertz pulse acquisition. As Figure 1 shown, the trigger signal generation device includes: a single-cavity dual-comb light source 1, an optical beat frequency element 2, and an envelope extraction unit 3 connected in sequence; the single-cavity dual-comb light source 1 is used to generate two coherent pulse lights with different repetition frequencies, and the two coherent pulse lights with different repetition frequencies are pulse lights for generating terahertz pulses; the optical beat frequency element 2 is used to perform beat frequency on the two coherent pulse lights with different repetition frequencies to obtain a beat frequency signal; the envelope extraction unit 3 is used to detect the beat frequency signal to generate a trigger signal; the frequency of the trigger signal is the repetition frequency difference between the two coherent pulse lights.

[0045] Among them, the single-cavity dual-optical-comb light source 1 is composed of a single optical resonator, which can simultaneously generate two beams of coherent pulsed light with different repetition frequencies. The two beams of pulsed light are transmitted in the optical resonator, passing through the same optical devices and optical paths, forming a dual-optical-frequency comb with different repetition frequencies. The two beams of coherent light generated by a single optical resonator are each divided into two paths. In one path, the two beams of coherence generate a beat frequency in the optical device. After photoelectric conversion, the envelope extraction unit extracts the envelope of the beat frequency signal, amplifies the power, and uses it as a trigger signal. In the other path, the two beams of coherent light respectively excite the photoconductive antenna at the receiving end to generate terahertz waves. The signal acquisition and processing unit synchronously triggers the real-time acquisition of terahertz pulses through the trigger signal, and finally obtains the terahertz pulse signal. Based on the above principle, the single-cavity dual-optical-comb light source 1 only includes a single optical resonator. In a single optical resonator, two sets of pulses are generated in the same optical resonator by adopting pulse multiplexing transmission mechanisms such as wavelength multiplexing, polarization multiplexing, direction multiplexing, and cavity space multiplexing. By regulating the intracavity dispersion, nonlinear effect, or mode-locking mechanism, the transmission time or phase of the pulses is made different, and finally a dual-optical comb with slightly different repetition frequencies is realized in a single optical resonator.

[0046] The single-cavity dual-optical-comb light source 1 includes: a pump source 2-1, a wavelength division multiplexer 2-2, an erbium-doped fiber 2-3, an isolator 2-4, a first optical coupler 2-5, a polarization controller 2-6, a polarization-maintaining fiber 2-7, a carbon nanotube saturable absorber 2-8, and a single-mode fiber 2-9; the pump source 2-1 is connected to an input end of the wavelength division multiplexer 2-2, the output end of the wavelength division multiplexer 2-2 is connected to one end of the erbium-doped fiber 2-3, and the light source provided by the pump source 2-1 is coupled into the erbium-doped fiber 2-3 through the wavelength division multiplexer 2-2; the isolator 2-4 is embedded in the erbium-doped fiber 2-3, the light source generates laser light in the erbium-doped fiber 2-3, and the isolator 2-4 is used to make the laser light transmit unidirectionally in the erbium-doped fiber 2-3; the other end of the erbium-doped fiber 2-3 is connected to the input end of the polarization controller 2-6, the output end of the polarization controller 2-6 is connected to one end of the polarization-maintaining fiber 2-7, and the polarization controller 2-6 is used to change the twisting state of the erbium-doped fiber 2-3; the other end of the polarization-maintaining fiber 2-7 is connected to the input end of the carbon nanotube saturable absorber 2-8, and the output end of the nanotube saturable absorber 2-8 is connected to the other input end of the wavelength division multiplexer 2-2 through the single-mode fiber 2-9; the input end and one output end of the first optical coupler 2-5 are connected in the erbium-doped fiber 2-3, and the other output end of the first optical coupler 2-5 is connected to the optical beat frequency element 2.

[0047] Two coherent pulsed lights generated by the single - cavity dual - optical - comb light source 1 are used as the pump light and the probe light respectively to excite the corresponding terahertz photoconductive antenna to generate a dual - terahertz comb. The frequency difference of the dual - terahertz comb is related to the repetition - frequency difference of the two coherent pulsed excitation lights. Two terahertz combs with slightly different repetition - frequency differences scan and sample each other evenly and finely. Due to the fixed difference in the repetition frequencies, an accumulated time - domain interval difference will appear in the pulse sequence in the time domain until they coincide. This process realizes the conversion from the photon domain to the microwave domain.

[0048] The two optical combs in the coherent dual - optical - comb first (two coherent pulsed lights) are adjusted into linearly polarized lights through the polarization controller 2 - 6, so that the two lights vibrate in the same direction in the same propagation direction. According to the principle of vibration superposition, two coherent lights with slightly different repetition frequencies, the same propagation speed, and collinear propagation can form a beat - frequency signal in the optical beat - frequency element. The outer edge of the amplitude of the beat - frequency signal, that is, the envelope, forms a signal with strong - weak changes with a certain period. The envelope extraction unit 3 is used to detect and extract the modulation process of the beat - frequency signal to form a synchronous trigger signal for dual - optical - comb terahertz pulse acquisition. The frequency of the trigger signal is consistent with the repetition - frequency difference of the two lights.

[0049] Exemplarily, the two coherent pulsed lights need to be pre - processed by the polarization controller 2 - 6 to become linearly polarized lights, so that the two pulses vibrate in the same direction. The outer edge of the amplitude of the beat - frequency signal, that is, the envelope, is formed in the corresponding optical beat - frequency element, and a coherent strong - weak change signal is generated within the period. The optical beat - frequency element 2 includes one or more of an optical intensity modulator, an optical phase modulator, a second optical coupler, a non - phase - matching crystal, and a nonlinear optical fiber.

[0050] Exemplarily, the envelope extraction unit 4 is used to detect the periodic strong - weak change signal formed by the two coherent pulsed lights in the corresponding optical beat - frequency element to obtain a trigger signal synchronous with the terahertz acquisition pulse. The frequency of the trigger signal is related to the repetition - frequency difference of the dual - optical - comb. The envelope extraction unit 4 includes one or more of a diode envelope detector, a synchronous detector, and an integrated - circuit demodulator.

[0051] Exemplarily, in order to meet the requirement of the data acquisition unit for the rising - edge trigger amplitude of the trigger signal, a voltage amplifier with a maximum gain of 40 dB and a bandwidth of 40 MHz is designed as the trigger - signal amplification module 4 to amplify the trigger signal output by the envelope extraction unit 3.

[0052] Optionally, the trigger - signal amplification module is a voltage amplifier, and the bandwidth of the voltage amplifier is 40 MHz.

[0053] Embodiment 2

[0054] Embodiment 2 of the present invention provides a single-cavity dual-optical comb light source. The specific structure of the single-cavity dual-optical comb light source is the same as that in Embodiment 1 and will not be described in detail here.

[0055] Embodiment 3

[0056] Embodiment 3 of the present invention provides a terahertz pulse acquisition system. As Figure 1 shown, the acquisition system includes the above-mentioned trigger signal generation device. The acquisition system further includes a beam splitter 5, an asynchronous sampling terahertz pulse generation unit, and a data acquisition unit;

[0057] The beam splitter 5 is arranged between the single-cavity dual-optical comb light source 1 and the optical beat frequency element 2 in the trigger signal generation device. The input end of the beam splitter 5 is connected to the single-cavity dual-optical comb light source 1. The second signal output end OP2 and the third signal output end OP3 of the beam splitter 5 are respectively connected to the two input ends of the optical beat frequency element 2. The first signal output end OP1 and the fourth signal output end OP4 of the beam splitter 5 are respectively connected to the transmitting photoconductive antenna Tx and the receiving photoconductive antenna Rx in the asynchronous sampling terahertz pulse generation unit. The first signal output end OP1 and the second signal output end OP2 are used to output two sub-pulse lights divided from the first pulse light. The third signal output end OP3 and the fourth signal output end OP4 are used to output two sub-pulse lights divided from the second pulse light. The first pulse light and the second pulse light are two coherent pulse lights with different repetition frequencies.

[0058] The output end of the asynchronous sampling terahertz pulse generation unit is connected to the input end of the data acquisition unit. The output end of the trigger signal generation device is connected to the trigger control end of the data acquisition unit.

[0059] Exemplarily, the asynchronous sampling terahertz pulse generation unit includes a transmitting photoconductive antenna Tx, and a first collimating and focusing lens 6, a second collimating and focusing lens 7, and a receiving photoconductive antenna Rx arranged in sequence along the transmitting direction of the transmitting photoconductive antenna. The sample to be measured 8 is arranged between the first collimating and focusing lens 6 and the second collimating and focusing lens 7.

[0060] In a specific embodiment, the single-cavity dual-optical comb light source 1 only includes one optical resonator. By utilizing the different physical dimension resources of the fiber-related waveguide and the propagation characteristic differences of the pulses on different physical dimension resources, coherent asynchronous pulses with a weak repetition frequency difference are realized in one optical resonator. As Figure 2As shown in the figure, in the single-cavity dual-optical-comb light source 1 based on polarization multiplexing, the 980 nm DC pump source serves as the pump source 2-1 to provide the light source. The light source is coupled and injected into the erbium-doped fiber 2-3 through the wavelength division multiplexer 2-2. The erbium-doped fiber 2-3 serves as the gain medium. When light is incident on the erbium-doped fiber 2-3, photons are emitted due to stimulated emission, and a laser with a wavelength of 1550 nm is generated in the single-cavity dual-optical-comb light source 1. The optical isolator 2-4 ensures the unidirectional transmission of the laser in the optical resonator, reduces the additional noise of the reflected light, and improves the optical wave propagation efficiency. By adjusting the polarization controller 2-6, the fiber twist state is changed, and the polarization state of the light in the optical resonator is changed. The single-walled carbon nanotube saturable absorber 2-8 has unique electrical and optical properties and can play a role in the passive mode-locking process. By introducing the polarization-maintaining fiber 2-7, the two groups of pulses can be transmitted in two approximately orthogonal polarization states. The optical coupler divides the generated laser into two parts, 60% of the laser continues to be transmitted in the optical resonator of the single-cavity dual-optical-comb light source 1, and 40% is output at the output end. Since the two groups of pulses are multiplexed and mode-locked along two orthogonal polarization states in the optical resonator, and the group velocity differences of the two polarization states are different, the repetition frequencies of the mode-locked pulses in the two polarization states finally achieved are different. The spectra of the two polarization states measured by the spectrometer are as Figure 3 shown. The spectra measured by the photodetector and the spectrum analyzer are as Figure 4 shown. It can be seen that the central wavelength of the mode-locked spectrum of the two coherent pulse lights is 1560.5 nm, and the repetition frequency f 1 is 74.527276 MHz, and the repetition frequency f 2 is 74.526930 MHz, and the difference between the two repetition frequencies is about 346 Hz.

[0061] In the above specific embodiment, the two groups of mode-locked pulses output by the single-cavity dual-optical-comb light source 1 pass through the polarization controller 2-6 and the beam splitting device 5. By adjusting the polarization controller 2-6, the polarization state is changed, and the two groups of pulses are separated according to the two orthogonal polarization propagation directions. After separation, they pass through the beam splitting device 5. The pulse with the repetition frequency of f 1 is divided into two paths, OP1 and OP2, and the pulse with the repetition frequency of f 2 is divided into two paths, OP3 and OP4. The two groups of pulses with different repetition frequencies, OP2 and OP3, enter the optical beat frequency element 2 for beat frequency. Here, the optical beat frequency element 2 is selected as the optical coupler (i.e., the second optical coupler). The two groups of pulses with different repetition frequencies, OP1 and OP2, are respectively input to the photoconductive antennas for transmitting and receiving terahertz (the transmitting photoconductive antenna Tx and the receiving photoconductive antenna Rx) to generate terahertz pulses.

[0062] Two coherent lights with different repetition frequencies enter a 2×2 optical coupler (i.e., the type of the second optical coupler is a 2×2 optical coupler) for beat frequency. Let the wave equations of the two lasers be respectively:

[0063] E1 = E R1 cos 2πf 1 t

[0064] E 2 = E R2 cos 2πf 2 t

[0065] E R1 and E R2 are the amplitudes of two coherent light beams respectively; f 1 and f 2 are the repetition frequencies of two coherent light beams respectively; t is time. According to the trigonometric function formula, the beat-frequency light after coupling of two coherent light beams can be expressed as

[0066] E = E 1 + E 2

[0067] It can be derived that:

[0068]

[0069] where E R is the amplitude of the beat-frequency signal.

[0070] Two coherent light beams beat-frequency in a 2×2 optical coupler and enter a balanced photodetector (BPD). At the front end of the balanced photodetector, two capacitors, two photodiodes with matched responsivity, and a low-noise transimpedance amplifier (TIA) are adopted. The two beat-frequency signals enter the balanced photodetector to eliminate its common-mode noise. While achieving a good common-mode rejection ratio, the tiny change of the effective signal can be extracted from the interference signal. Two cycles of coherent light beat-frequency detected by the balanced photodetector are as Figure 5 shown, and the frequency of the beat-frequency signal is 346 Hz. Figure 6 is the enlarged diagram of a single coherent light beat-frequency signal. After the coherent light beat-frequency signal is photoelectrically converted, it is input to the envelope extraction unit 3. The envelope extraction unit 3 adopts a synchronous detection circuit based on the ADL5511 chip. The input bandwidth of the synchronous detection circuit is 0 - 6 GHz, and the envelope bandwidth is 130 MHz, meeting the bandwidth requirements for envelope extraction of the coherent optical comb beat-frequency. By using this method, without considering the problem of phase matching of two laser beams, a trigger signal synchronized with the terahertz pulse signal to be measured can be obtained. After being amplified by a voltage amplifier, the finally amplified trigger signal obtained through a digital oscilloscope is as Figure 7 shown.

[0071] In the above specific embodiments, the sub-pulse lights with slightly different repetition frequencies output from the first signal output end OP1 and the fourth signal output end OP4 of the beam splitter device 5 of the single-cavity dual optical comb light source 1 respectively irradiate the transmitting photoconductive antenna Tx and the receiving photoconductive antenna Rx. The terahertz pulse generated at the transmitting end of the transmitting photoconductive antenna Tx is collimated by the first collimating and focusing lens 6. The terahertz beam propagates after collecting information from the sample to be measured and is focused on the receiving photoconductive antenna by the second collimating and focusing lens 7. Based on the asynchronous sampling principle, the system does not require an external mechanical delay line device. By using the time difference accumulation method between the THz sampling pulse and the pump pulse, signal points on different cycles can be collected to realize the reconstruction of the sampling signal. The superior repetition frequency difference stability and the ultra-high repetition frequency ensure extremely high accuracy and resolution.

[0072] In the above specific embodiments, the width of the dual optical comb pulse light for irradiating the photoconductive antenna is about 120 fs and the power is about 20 mW. The gain bandwidth f of the preset current amplifier gb is 10 MHz. The data acquisition unit uses a NI data acquisition board card with a maximum sampling rate of 100 MHz / s. According to the repetition frequency of the single-cavity dual optical comb light source 1 being about f r of 74.527 MHz and the repetition frequency difference Δf = 346 Hz, the amplification time magnification factor (TMF) corresponding to the down-conversion of the terahertz signal after asynchronous sampling and the measurable range (MR) of the THz spectroscopy measurement system can be calculated.

[0073]

[0074] MR = TMF * f gb

[0075] It can be calculated that: TMF ≈ 2.153960×10 5 , MR ≈ 2.15 THz. That is, the terahertz asynchronous optical sampling range in this experimental device is 2.15 THz. According to the principle of generating terahertz pulses by asynchronous sampling of dual optical combs, the repetition frequency of the terahertz pulses generated by this method is Δf, which is the same as the frequency of the trigger signal.

[0076] The trigger signal and the terahertz pulse signal with the same frequency are input into the data acquisition unit. The data acquisition unit synchronously collects the terahertz pulse signal carrying sample information according to the coherent optical envelope trigger signal, accurately detects the position of the terahertz pulse signal, and collects the amplitude, phase, frequency or their change amounts of the terahertz pulse signal. In some cases, the sample information can also be analyzed and processed. The specific analysis and processing process needs to be set according to the measurement requirements and will not be elaborated here.

[0077] Example 4

[0078] Embodiment 4 of the present invention provides a method for collecting terahertz pulses, including the following steps:

[0079] Step 1, a single-cavity dual-frequency comb light source 1 generates two coherent pulsed lights with slightly different repetition frequencies;

[0080] Step 2, input the two coherent lights generated by the single-cavity dual-frequency comb light source 1 into an optical beat frequency element 2 to generate a beat frequency signal with a frequency approximately equal to the repetition frequencies of the two lights and a varying amplitude. Subsequently, input the beat frequency signal into an envelope extraction unit 3 for detection to generate a trigger signal with a frequency equal to the difference between the repetition frequencies of the two lights.

[0081] Step 3, simultaneously excite a photoconductive antenna (a transmitting photoconductive antenna Tx and a receiving photoconductive antenna Rx) with the two coherent lights generated by the single-cavity dual-frequency comb light source 1, and generate a terahertz pulse signal with a frequency equal to the difference between the repetition frequencies of the two lights through asynchronous sampling of two sets of terahertz pulses.

[0082] Step 4, a data acquisition unit performs real-time synchronous trigger acquisition on the terahertz pulse signal according to the amplitude and frequency of the trigger signal to obtain the amplitude, phase, or their variation of the terahertz pulse.

[0083] According to the specific embodiments provided by the present invention, the following technical effects are disclosed:

[0084] The present invention discloses a trigger signal generation device and an acquisition system for terahertz pulse acquisition. The trigger signal generation device of the present invention uses a single-cavity dual-frequency comb light source to generate coherent pulsed light (the coherent pulsed light is used to generate terahertz pulses), and extracts the trigger signal for terahertz pulse acquisition by means of beat frequency and detection based on an optical beat frequency element and an envelope extraction unit, that is, generates a trigger signal with the same frequency as the terahertz pulse, so as to perform real-time acquisition of the terahertz pulse signal, thereby solving the problems of complex light source structure, strict phase matching requirements for trigger signals, and redundant data acquisition in the process of terahertz pulse generation and acquisition.

[0085] The single-cavity dual-frequency comb light source of the present invention utilizes two lights sharing the same physical path in the same optical resonator cavity, can reuse the pulse transmission mechanism, withstand the same external interference and internal noise, and realizes the generation of two coherent optical frequency combs in a single optical resonator cavity by adjusting the intracavity dispersion, polarization state, and nonlinear effect, without the need to rely on a complex electronic feedback control device.

[0086] In the present specification, each embodiment is described in a progressive manner, and the key point of each embodiment is to illustrate the differences from other embodiments. The same or similar parts among the embodiments can be referred to each other.

[0087] In this text, specific examples are used to elaborate on the principles and implementation manners of the present invention. The description of the above embodiments is only used to help understand the method and its core idea of the present invention; at the same time, for those of ordinary skill in the art, according to the idea of the present invention, there will be changes in the specific implementation manners and application scopes. In summary, the content of this specification should not be construed as a limitation on the present invention.

Claims

1. A trigger signal generation device for terahertz pulse acquisition, characterized in that, the trigger signal generation device includes: a single-cavity dual optical comb light source, an optical beat frequency element, and an envelope extraction unit connected in sequence; the single-cavity dual optical comb light source is used to generate two coherent pulsed lights with different repetition frequencies, and the two coherent pulsed lights with different repetition frequencies are pulsed lights for generating terahertz pulses; the single-cavity dual optical comb light source includes: a pump source, a wavelength division multiplexer, an erbium-doped fiber, an isolator, a first optical coupler, a polarization controller, a polarization-maintaining fiber, a carbon nanotube saturable absorber, and a single-mode fiber; the pump source is connected to one input end of the wavelength division multiplexer, the output end of the wavelength division multiplexer is connected to one end of the erbium-doped fiber, and the light source provided by the pump source is coupled into the erbium-doped fiber through the wavelength division multiplexer; the isolator is embedded in the erbium-doped fiber, the light source generates laser in the erbium-doped fiber, and the isolator is used to make the laser transmit unidirectionally in the erbium-doped fiber; the other end of the erbium-doped fiber is connected to the input end of the polarization controller, the output end of the polarization controller is connected to one end of the polarization-maintaining fiber, and the polarization controller is used to change the twisting state of the erbium-doped fiber; the other end of the polarization-maintaining fiber is connected to the input end of the carbon nanotube saturable absorber, and the output end of the nanotube saturable absorber is connected to the other input end of the wavelength division multiplexer through the single-mode fiber; the input end and one output end of the first optical coupler are connected in the erbium-doped fiber, and the other output end of the first optical coupler is connected to the optical beat frequency element; the optical beat frequency element is used to perform beat frequency on two coherent pulsed lights with different repetition frequencies to obtain a beat frequency signal; the envelope extraction unit is used to detect the beat frequency signal to generate a trigger signal; the frequency of the trigger signal is the repetition frequency difference between the two coherent pulsed lights; the envelope extraction unit performs detection processing on the periodically strong and weak change signals formed by the two coherent pulsed lights in the corresponding optical beat frequency element to obtain a trigger signal synchronized with the terahertz acquisition pulse, and the trigger signal frequency is related to the double optical comb repetition frequency difference; the envelope extraction unit includes one or more of a diode envelope detector, a synchronous detector, and an integrated circuit demodulator.

2. The trigger signal generation device for terahertz pulse acquisition according to claim 1, characterized in that, the optical beat frequency element includes one or more of an optical intensity modulator, an optical phase modulator, a second optical coupler, a non-phasic crystal, and a non-linear fiber.

3. The trigger signal generation device for terahertz pulse acquisition according to claim 1, characterized in that, the trigger signal generation device further includes a trigger signal amplification module; the trigger signal amplification module is connected to the envelope extraction unit, and the trigger signal amplification module is used to amplify the trigger signal output by the envelope extraction unit.

4. The trigger signal generation device for terahertz pulse acquisition according to claim 3, characterized in that, the trigger signal amplification module is a voltage amplifier, and the bandwidth of the voltage amplifier is 40 MHz.

5. A single-cavity dual-optical comb light source in the trigger signal generation device for terahertz pulse acquisition according to any one of claims 1-4.

6. A terahertz pulse acquisition system, characterized in that the acquisition system includes the trigger signal generation device according to any one of claims 1-4, and the acquisition system further includes a beam splitter, an asynchronous sampling terahertz pulse generation unit, and a data acquisition unit; the beam splitter is arranged between the single-cavity dual-optical comb light source and the optical beat frequency element in the trigger signal generation device, the input end of the beam splitter is connected to the single-cavity dual-optical comb light source, and the second signal output end and the third signal output end of the beam splitter are respectively connected to the two input ends of the optical beat frequency element; the first signal output end and the fourth signal output end of the beam splitter are respectively connected to the transmitting photoconductive antenna and the receiving photoconductive antenna in the asynchronous sampling terahertz pulse generation unit; the first signal output end and the second signal output end are used to output two sub-pulse lights divided from the first pulse light, and the third signal output end and the fourth signal output end are used to output two sub-pulse lights divided from the second pulse light, and the first pulse light and the second pulse light are two coherent pulse lights with different repetition frequencies; the output end of the asynchronous sampling terahertz pulse generation unit is connected to the input end of the data acquisition unit; the output end of the trigger signal generation device is connected to the trigger control end of the data acquisition unit.

7. The terahertz pulse acquisition system according to claim 6, characterized in that the asynchronous sampling terahertz pulse generation unit includes a transmitting photoconductive antenna, and a first collimating and focusing lens, a second collimating and focusing lens, and a receiving photoconductive antenna are sequentially arranged along the transmitting direction of the transmitting photoconductive antenna; the sample to be measured is arranged between the first collimating and focusing lens and the second collimating and focusing lens.

Images