CN111537069B - Terahertz time-domain spectrum and imaging system with distributed temperature measurement function - Google Patents
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- G01N21/3581—Investigating relative effect of material at wavelengths characteristic of specific elements or molecules, e.g. atomic absorption spectrometry using infrared light using far infrared light; using Terahertz radiation
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Abstract
The invention discloses a terahertz time-domain spectrum and imaging system with a distributed temperature measurement function, which comprises a femtosecond laser, a primary optical fiber branching device, a terahertz spectrum unit, a pulse light modulation unit, a distributed optical fiber sensor unit and a signal acquisition processing unit, wherein the primary optical fiber branching device divides femtosecond pulse laser generated by the femtosecond laser into excitation light and excitation light, the excitation light is transmitted to the terahertz spectrum unit to generate a current signal carrying sample information, the excitation light is modulated into modulated pulse light by the pulse light modulation unit, the modulated pulse light is transmitted to the distributed optical fiber sensor unit to generate an analog signal carrying temperature information, and the signal acquisition processing unit acquires and processes the current signal carrying the sample information and/or the analog signal carrying the temperature information. The femtosecond laser is successfully applied to a distributed optical fiber temperature sensing system, a complete femtosecond pulse light modulation and management scheme is provided, and the multi-system multiplexing of the femtosecond laser is realized.
Description
Technical field:
the invention belongs to the technical field of terahertz spectrum and imaging, and particularly relates to a terahertz time-domain spectrum and imaging system with a distributed temperature measurement function.
The background technology is as follows:
the full-fiber terahertz time-domain spectrum and terahertz imaging system has the advantages of low photon energy, special penetrability, fingerprint spectrum characteristics, flexibility of a full-fiber coupling structure and the like due to terahertz waves as a product with the highest commercialization degree of terahertz technology, and has wide application potential in numerous scenes such as industrial nondestructive detection, process quality control and the like. However, the measurement parameters provided by the terahertz product cannot completely meet the comprehensive monitoring of the industrial manufacturing process, so that the purpose of improving quality and enhancing efficiency is achieved, the performance of the terahertz system is affected by temperature, certain substances to be detected can show different attributes at different temperatures, the existing terahertz time-domain spectroscopy system is difficult to directly obtain the temperature parameters, and the accuracy of terahertz spectroscopy data lacking temperature correction and indexing is to be improved. In addition, the high price also often becomes a reason for restricting the application and popularization of the product.
As a new sensing technology that has been rapidly developed in recent years, a distributed optical fiber sensing technology has been grown along with the progress of optical fiber technology and optical fiber communication technology. The optical fiber sensor has obvious advantages, and the common single-mode optical fiber can stably work under various severe environments such as high temperature and high pressure, electromagnetic radiation, corrosion and the like, and has incomparable huge advantages as the sensor due to the huge information capacity of the optical fiber. Among the optical fiber sensing technologies, a distributed optical fiber temperature sensing system (DTS) is the most mature representative for commercialization, and one optical fiber with the length of 1000m can realize real-time monitoring of at least 1000 temperature points, so that the distributed optical fiber temperature sensing system has good application effects in fire safety, electric power, pipeline and production process temperature monitoring. Patent CN103207033a discloses a spectroscopic optical fiber sensing device for simultaneously measuring temperature and strain, after the incident light generated by a narrow linewidth laser passes through an isolator, the incident light is divided into two branches through the coupler, the first branch is modulated into pulse light by the pulse light generating device, and the pulse light is amplified by the erbium-doped optical fiber amplifier and then is used as pulse pumping light to be connected with a first port of the circulator, and a second port of the circulator is connected with one end of the sensing optical fiber; the second branch is subjected to frequency shift by the frequency shift device and is used as detection light after frequency shift to be connected to the other end of the sensing optical fiber, a third port of the circulator is connected with the photoelectric detector for photoelectric conversion, and finally the data acquisition card and the computer obtain the Brillouin frequency shift quantity of the sensing optical fiber; the two narrow linewidth lasers are different-wavelength narrow linewidth lasers which are not connected at the same time, and when the two narrow linewidth lasers work, the two narrow linewidth lasers are connected with the narrow linewidth laser at the first wavelength for measurement, and then connected with the narrow linewidth laser at the second wavelength for measurement.
The invention comprises the following steps:
the invention aims to overcome the defects of the prior art, and provides a comprehensive monitoring system capable of simultaneously carrying out terahertz spectrum and imaging and distributed temperature measurement, so as to overcome the defects of single measurement parameters and low cost performance of the two independent systems at present.
In order to achieve the above purpose, the terahertz time-domain spectroscopy and imaging system with the distributed temperature measurement function comprises a femtosecond laser, a primary optical fiber branching device, a terahertz spectroscopy unit, a pulse light modulation unit, a distributed optical fiber sensor unit and a signal acquisition processing unit, wherein the primary optical fiber branching device is connected with the femtosecond laser and divides femtosecond pulse laser generated by the femtosecond laser into excitation light and excitation light, an excitation light output end of the primary optical fiber branching device is connected with the terahertz spectroscopy unit, the excitation light is transmitted to the terahertz spectroscopy unit and generates a current signal carrying sample information, an excitation light output end of the primary optical fiber branching device is connected with the pulse light modulation unit, the excitation light is modulated into modulated pulse light by the pulse light modulation unit, the distributed optical fiber sensor unit is connected with the pulse light modulation unit, the modulated pulse light is transmitted to the distributed optical fiber sensor unit and generates an analog signal carrying temperature information, and the signal acquisition processing unit is respectively connected with the terahertz spectroscopy unit and the distributed optical fiber sensor unit and acquires and processes the current signal carrying the sample information and/or the analog signal carrying the temperature information. Wherein the pulse light modulation unit and the distributed optical fiber sensor unit form a distributed temperature sensing system,
Specifically, the pulse light modulation unit comprises an optical fiber isolator, a pulse stretching device and an electro-optic modulator, wherein the optical fiber isolator is connected with a first-stage optical fiber shunt excitation light output end to restrict the laser transmission direction, the pulse stretching device is connected with the optical fiber isolator to quantitatively stretch femtosecond laser pulses, the femtosecond pulses are stretched to nanosecond levels, and the electro-optic modulator is connected with the pulse stretching device and used for amplitude modulation of femtosecond pulse sequences to obtain modulated pulse light.
Specifically, the distributed optical fiber sensor unit comprises a coarse wavelength division multiplexer, a temperature sensing optical fiber and a photoelectric detector, wherein the coarse wavelength division multiplexer is connected with the photoelectric modulator, the coarse wavelength division multiplexer is connected with the photoelectric modulator through a second port, the temperature sensing optical fiber is connected with a first port of the coarse wavelength division multiplexer, the transmission of pulse light in the optical fiber is modulated, anti-Stokes light is generated, the anti-Stokes light carrying temperature information at different positions of the optical fiber returns to the coarse wavelength division multiplexer, the photoelectric detector is connected with a third port of the coarse wavelength division multiplexer, and the returned anti-Stokes light carrying temperature information at different positions of the optical fiber is subjected to photoelectric conversion under the triggering of synchronous pulse with an output modulation signal, and an analog signal is output.
The terahertz spectrum unit comprises a second-stage optical fiber branching device, an optical fiber delay line, a modulation bias voltage source, a terahertz transmitting antenna and a terahertz detecting antenna, wherein the second-stage optical fiber branching device is connected with an excitation light output end of a first-stage optical fiber branching device, excitation light is divided into pumping light and detecting light, the pumping light output end of the second-stage optical fiber branching device is connected with the terahertz transmitting antenna, the modulation bias voltage source is connected with the terahertz transmitting antenna and is used for generating bias voltage, the detection light output end of the second-stage optical fiber branching device is connected with the terahertz detecting antenna through the optical fiber delay line, the terahertz transmitting antenna generates pulse terahertz waves under the combined action of the pumping light and the modulation bias voltage source, the terahertz waves are refocused on the terahertz detecting antenna after being collimated by a free light path, meanwhile, the detecting light output by the second-stage optical fiber branching device meets on the terahertz detecting antenna after passing through the optical fiber delay line, free carriers are generated by the terahertz detecting antenna, and the free carriers migrate under the induction electric field generated by the terahertz detecting antenna, and a current signal which is in proportion to the intensity of the terahertz signal is formed.
Specifically, the signal acquisition processing unit comprises a signal acquisition and data processing unit and a PC, the signal acquisition and data processing unit is connected with the terahertz detection antenna and acquires a current signal proportional to the terahertz signal intensity, the signal acquisition and data processing unit is connected with the femtosecond laser and controls the generation of femtosecond pulse laser, the signal acquisition and data processing unit is connected with a modulation bias source and controls the generation of bias voltage, the signal acquisition and data processing unit is connected with an electro-optical modulator and sends a modulation signal to the electro-optical modulator, the signal acquisition and data processing unit is connected with the photoelectric detector and acquires an output analog signal, and the PC is connected with the signal acquisition and data processing unit and used for data processing, analysis, visual display and storage of the comprehensive system. In order to avoid the flow crossing among different systems, the signal acquisition and data processing unit comprises two paths of modulation signal output and two acquisition channels working in an asynchronous mode, wherein one path of modulation signal output is connected with the femtosecond laser and the modulation bias source, one acquisition channel is connected with the terahertz detection antenna, the other path of modulation signal output is connected with the electro-optical modulator, and the other acquisition channel is connected with the photoelectric detector.
Specifically, the photodetector is an APD detector.
Further, after passing through the primary optical fiber splitter, the optical power for the terahertz spectrum and the imaging system is generally not less than 80mw, the optical power for the optical fiber temperature sensing system is generally not more than 10mw, and the average power after passing through the electro-optical modulator is not more than 2mw.
Further, to ensure a good signal to noise level of the sensing system, the extinction ratio parameter of the electro-optic modulator is not less than 35dB.
Further, an optical fiber scrambler is placed in front of the isolator 4 to convert the linearly polarized light into natural polarized light.
Compared with the prior art, the invention has the following beneficial effects:
1. The temperature of the substance to be detected is obtained through the temperature sensing optical fiber, the terahertz spectrum and the imaging system can realize multi-dimensional imaging of the added thermodynamic diagram of the detected object, can be used as the auxiliary parameter input of the spectrum analysis of the temperature sensitive sample, provides more parameters for the sample analysis, and enables the measurement of the terahertz spectrum and the imaging system to be more accurate
2. The femtosecond laser is successfully applied to the distributed optical fiber temperature sensing system, a complete femtosecond pulse light modulation and management scheme is provided, the multi-system multiplexing of the femtosecond laser is realized, the problem that the femtosecond laser is difficult to be directly applied to the optical fiber temperature sensing system is solved, and the system has the advantages of saving resources and reducing energy consumption while realizing more abundant system functions.
3. The integration of the optical fiber integrated terahertz time-domain spectrum and the imaging system with the distributed optical fiber temperature sensing system is realized, the key resource sharing is realized, the terahertz system with multi-parameter output is formed, the more accurate measurement is realized, the requirement of comprehensive monitoring is met, and the application scene applicability is wider.
Description of the drawings:
Fig. 1 is a schematic structural diagram of a terahertz time-domain spectrum and imaging system with a distributed temperature measurement function.
The specific embodiment is as follows:
the invention will now be further illustrated by means of specific examples in connection with the accompanying drawings.
Example 1
As shown in fig. 1, the terahertz time-domain spectroscopy and imaging system with distributed temperature measurement function according to this embodiment includes a femtosecond laser 1, a primary optical fiber splitter 2, a secondary optical fiber splitter 3, an optical fiber isolator 4, a pulse widening device 5, an electro-optic modulator 6, an optical fiber delay line 7, a modulation bias source 8, a Coarse Wavelength Division Multiplexer (CWDM) 9, a terahertz transmitting antenna 10, a terahertz detecting antenna 11, a temperature sensing optical fiber 13, an APD photodetector 12, a signal acquisition and data processing unit 14, and a PC 15,
The functions of each unit are as follows:
the femtosecond laser 1 is used for generating a femtosecond pulse laser signal and is used as an excitation source of a photoconductive antenna and an excitation light source of a distributed temperature sensing system;
the primary optical fiber splitter 2 is used for splitting the output of the laser, the splitting ratio is generally set to be 1:19, wherein 5% of the splitting is used for temperature detection, and 95% of the splitting is used for terahertz signal acquisition;
the secondary optical fiber splitter 3 performs secondary light splitting on the front-stage input according to the attenuation conditions of the terahertz transmitting antenna and the detecting antenna. The beam split ratio is generally set to 3:7, wherein 30% of the beam split is used for laser input of the transmitting antenna, and 70% of the beam split is used for laser input of the detecting antenna;
The optical fiber isolator 4 is used for restraining the laser transmission direction and avoiding the damage of the device caused by the return of the echo to the laser;
the pulse stretching device 5 is used for quantitatively stretching the femtosecond laser pulse, and can adopt chirped volume Bragg grating, volume holographic diffraction grating and other devices;
The electro-optical modulator 6 is used for amplitude modulation of the femtosecond pulse sequence, pulse selection is carried out, and the repetition frequency is reduced;
the optical fiber delay line 7 is used for realizing pulse scanning by detecting the time delay of the optical path of the terahertz system;
the modulation bias source 8 provides bias voltage for a terahertz system transmitting antenna;
The Coarse Wavelength Division Multiplexer (CWDM) 9 is a 3-port device and is used for wavelength selection and optical path guidance, the Coarse Wavelength Division Multiplexer (CWDM) 9 comprises a first port, a second port and a third port, specifically, the coarse wavelength division multiplexer 9 is connected with an electro-optic modulator through the second port, a temperature sensing optical fiber is connected with the first port of the coarse wavelength division multiplexer, transmission of modulated pulse light in the optical fiber generates anti-Stokes light, the anti-Stokes light carrying temperature information at different positions of the optical fiber returns to the coarse wavelength division multiplexer through the first port, an APD photoelectric detector is connected with the third port of the coarse wavelength division multiplexer, and the returned anti-Stokes light carrying temperature information at different positions of the optical fiber is subjected to photoelectric conversion under the triggering of synchronous pulse with an output modulation signal, and an analog signal is output. Specifically, the first port is a com port, the second port is a 1550nm port and the third port is a 1451nm port;
The terahertz transmitting antenna 10 is used for generation of terahertz waves;
The terahertz detection antenna 11 is used for detecting terahertz waves;
the APD photodetector 12 is used for detection of raman scattered signals (anti-stokes light);
the temperature sensing optical fiber 13 is used as a temperature sensor for detecting the temperature sensing of an object;
The signal acquisition and data processing unit 14 is used for synchronizing signal generation, data acquisition and control, signal preprocessing and communication with an upper PC;
The PC 15 is used for data processing, analysis, visual display, storage, etc. of the integrated system.
A terahertz time-domain spectrum and imaging system with a distributed temperature measurement function has the following working principle:
The femtosecond laser emitted by the femtosecond laser 1 is divided into two beams of light after passing through the primary optical fiber splitter 2, and the splitting ratio is generally set as 1:19, wherein the output of 95% of the two-stage optical fiber splitter 3 is further split, and the split ratio is set to be 3:7. The 30% of the light is transmitted into the terahertz transmitting antenna 10 through a section of dispersion compensating optical fiber, the terahertz transmitting antenna 10 generates pulse terahertz waves under the combined action of the femtosecond excitation pulse and the bias source 8, and the terahertz waves are refocused on the terahertz detecting antenna 11 after being collimated by a free optical path. Meanwhile, 70% of light output by the second-stage optical fiber splitter passes through the optical fiber delay line 7 and then meets the terahertz detection antenna 11, free carriers are generated by the photoconductive antenna, the free carriers migrate under the induction electric field generated by the terahertz detection antenna 11 to form a current signal in direct proportion to the terahertz signal intensity, and the current signal enters the signal acquisition and data processing unit 14 to be acquired and preprocessed, and finally the current signal is sent to the PC 15 to be subjected to signal processing and visual display. The complete terahertz waveform can be obtained by changing the delay amount of the optical fiber delay line. The external scanning translation stage is combined, so that sample scanning with a certain area can be realized, and the terahertz imaging function is realized. The above is the terahertz spectrum and imaging system unit implementation principle.
The output of 5% of the first-stage optical fiber splitter enters the optical fiber isolator 4 at first to restrict the propagation direction of light, so that the damage of echoes to the laser is avoided. The output light of the optical fiber isolator 4 enters a pulse stretching device 5 (the pulse stretching device can adopt devices such as a chirped volume Bragg grating, a volume holographic diffraction grating and the like) for stretching, and femtosecond-level pulses are stretched to nanosecond level, so that the peak power of single pulse is reduced, and various nonlinear effects in the excited optical fiber are avoided. The light output by the pulse stretching device 5 further enters the electro-optical modulator 6 for amplitude modulation, the modulated signal is output by the signal acquisition and data processing unit 14, the repetition frequency is set to 10 kHz-100 kHz (determined according to the length of the temperature sensing optical fiber), and the opening time is set to 10ns. The high repetition frequency quasi-continuous pulse laser sequence (generally 100 MHz) is modulated and then becomes modulated pulse light with the repetition frequency of several kHz and the width time of 10ns. The modulated pulse light is continuously input into 1550nm port of Coarse Wavelength Division Multiplexer (CWDM) 9, the port bandwidth is set to 7nm, so as to filter the input broadband femtosecond pulse light, reduce the frequency domain width of the pulse, and further widen the pulse (still in ns order). The modulated pulse light continues to be transmitted, is output through the com port of the Coarse Wavelength Division Multiplexer (CWDM) 9 and is injected into the temperature sensing optical fiber 13, the modulated pulse light is transmitted in the temperature sensing optical fiber 13, and interacts with the temperature sensing optical fiber 13 to excite spontaneous Raman scattering, wherein the Raman scattering comprises two branches, one branch absorbs one optical phonon to generate an up-shift, namely anti-Stokes light with the wavelength of 1451nm, and the other branch releases one optical phonon to generate a down-shift, namely Stokes light with the wavelength of 1663 nm. The intensity of the anti-stokes light is sensitive to temperature, the intensity of the anti-stokes light is modulated by the temperature, the anti-stokes light carrying temperature information at different positions along the optical fiber is transmitted backwards along the optical fiber, the anti-stokes light enters a com port of a Coarse Wavelength Division Multiplexer (CWDM) 9 again, is output through a 1451nm port of the Coarse Wavelength Division Multiplexer (CWDM) 9, enters an APD photoelectric detector 12, is subjected to photoelectric conversion under the triggering of synchronous pulse (pulse signal synchronous with the signal input by the photoelectric modulator) of the output modulation signal, and the analog signal output by the APD photoelectric detector 12 enters a signal acquisition and data processing unit 14 for acquisition and preprocessing, and finally is sent to a PC (personal computer) 15 for signal processing and visual display. The above is the principle of realizing the distributed optical fiber temperature sensing system unit.
Further, after passing through the primary optical fiber splitter, the optical power for the terahertz spectrum and the imaging system is generally not less than 80mw, so that enough pulse energy on the terahertz antenna is ensured to be achieved, the optical power for the optical fiber temperature sensing system is generally not more than 10mw, and the average power after passing through the electro-optical modulator 6 is not more than 2mw, so that the nonlinear threshold of the long-distance optical fiber is avoided being exceeded, various nonlinear effects are generated, and the effective acquisition of the Raman signal is influenced.
Further, to ensure a good signal-to-noise level of the sensing system, the extinction ratio parameter of the electro-optic modulator 6 is not less than 35dB;
To further illustrate, to eliminate polarization-dependent noise of the sensing system, an optical fiber scrambler may be placed in front of the isolator 4 to convert linearly polarized light into naturally polarized light;
Further, the signal acquisition and data processing unit 14 serves as a core control unit, and includes two paths of modulated signal outputs and two acquisition channels, and is required to operate in an asynchronous mode in order to avoid flow crossover between different systems;
Further, as the distributed temperature measurement function is added, the terahertz spectrum and imaging system can realize multi-dimensional imaging of the added thermodynamic diagram of the measured object, can be used as the auxiliary parameter input of the spectrum analysis of the temperature sensitive sample, provides more parameters for the sample analysis, and enables the measurement of the terahertz spectrum and the imaging system to be more accurate.
The innovation point of the scheme system is that the integration of the optical fiber integration terahertz time-domain spectrum and the integration of the imaging system and the distributed optical fiber temperature sensing system are realized for the first time, the key resource sharing is realized, the terahertz system with multi-parameter output is formed, the more accurate measurement is facilitated, the requirement of comprehensive monitoring is met, and the system has wider application scene applicability.
The system of the scheme is innovative in that the femtosecond laser is applied to the distributed optical fiber temperature sensing system for the first time, a complete femtosecond pulse light modulation and management scheme is provided, the multi-system multiplexing of the femtosecond laser is realized, the richer system functions are realized, the resources are saved, and the energy consumption is reduced.
Claims (5)
1. The terahertz time-domain spectrum and imaging system with distributed temperature measurement function is characterized by comprising a femtosecond laser, a primary optical fiber branching device, a terahertz spectrum unit, a pulse light modulation unit, a distributed optical fiber sensor unit and a signal acquisition processing unit, wherein the primary optical fiber branching device divides femtosecond pulse laser generated by the femtosecond laser into excitation light and exciting light, the excitation light is transmitted to the terahertz spectrum unit to generate a current signal carrying sample information, the exciting light is modulated into modulated pulse light by the pulse light modulation unit, the modulated pulse light is transmitted to the distributed optical fiber sensor unit to generate an analog signal carrying temperature information, the signal acquisition processing unit is respectively connected with the terahertz spectrum unit and the distributed optical fiber sensor unit, the pulse light modulation unit comprises an optical fiber isolator, a pulse stretching device and an electro-optic modulator, the optical fiber isolator is connected with an output end of the primary optical fiber branching excitation light, the laser is restrained in a transmission direction, the pulse stretching device is connected with the optical fiber isolator, the femtosecond laser pulse is quantitatively stretched, the femtosecond pulse is stretched to the femtosecond pulse temperature sensor unit, the pulse temperature sensor unit is connected with the pulse temperature sensor unit to generate an analog signal carrying temperature information, the signal carrying sample information is acquired and processed by the signal acquisition processing unit, the pulse light modulation unit comprises a first optical fiber isolator, the pulse stretching device and the pulse stretching device is connected with an electro-optic multiplexer, the optical fiber multiplexer, the optical multiplexer is connected with an electro-optical fiber multiplexer, the optical multiplexer is connected with a coarse wavelength multiplexer, the multiplexer is connected with an optical fiber multiplexer, and a multiplexer, the multiplexer, and the multiplexer, the multiplexer is connected with a multiplexer, the photoelectric detector is connected with a third port of the coarse wavelength division multiplexer, the returned anti-Stokes light carrying the temperature information at different positions of the optical fiber is subjected to photoelectric conversion under the triggering of synchronous pulse of an output modulation signal, and analog signals are output, the terahertz spectrum unit comprises a second-stage optical fiber branching device, an optical fiber delay line, a modulation bias source, a terahertz transmitting antenna and a terahertz detecting antenna, the second-stage optical fiber branching device is connected with an excitation light output end of a first-stage optical fiber branching device, excitation light is divided into pumping light and detecting light, the pumping light output end of the second-stage optical fiber branching device is connected with the terahertz transmitting antenna, the modulation bias source is connected with the terahertz transmitting antenna and used for generating bias voltage, the terahertz transmitting antenna generates pulse terahertz waves under the combined action of the pumping light and the modulation bias source, the terahertz waves are focused on the terahertz detecting antenna after being collimated by a free optical path, the pumping light is output by the second-stage optical fiber branching device, the terahertz wave current is generated by the terahertz transmitting antenna after the terahertz wave is in direct proportion to the terahertz carrier current, the free carrier is generated by the terahertz carrier, the terahertz carrier is generated after the terahertz carrier is migrated by the terahertz transmitting antenna,
The pulse widening device adopts a chirped volume Bragg grating or a volume holographic diffraction grating.
2. The terahertz time-domain spectroscopy and imaging system with distributed temperature measurement function according to claim 1, wherein the signal acquisition and processing unit comprises a signal acquisition and data processing unit and a PC, the signal acquisition and data processing unit is connected with a terahertz detection antenna to acquire current signals proportional to the terahertz signal intensity, the signal acquisition and data processing unit is connected with a femtosecond laser to control generation of femtosecond pulse laser, the signal acquisition and data processing unit is connected with a modulation bias source to control generation of bias voltage, the signal acquisition and data processing unit is connected with an electro-optical modulator to send to the electro-optical modulator to modulate signals, the signal acquisition and data processing unit is connected with a photoelectric detector to acquire output analog signals, the PC is connected with the signal acquisition and data processing unit to perform data processing, analysis, visual display and storage of the integrated system, and to avoid flow crossover between different systems, the signal acquisition and data processing unit comprises two paths of modulating signal output and two acquisition channels operating in an asynchronous mode, one path modulating signal output is connected with the femtosecond laser and a modulation bias source, one path is connected with the photoelectric modulator, the other acquisition antenna is connected with the other acquisition channel is connected with the electro-optical modulator.
3. The terahertz time-domain spectroscopy and imaging system with distributed temperature measurement function according to claim 2, wherein the optical power for the terahertz spectroscopy and imaging system is not less than 80mw after passing through the primary optical fiber splitter, the optical power for the optical fiber temperature sensing system is not more than 10mw, and the average power after passing through the electro-optical modulator is not more than 2mw.
4. The terahertz time-domain spectroscopy and imaging system with distributed temperature measurement function of claim 3, wherein the extinction ratio parameter of the electro-optical modulator is not less than 35dB in order to ensure a good signal-to-noise level of the sensing system.
5. The terahertz time-domain spectroscopy and imaging system with distributed temperature measurement function of claim 4, wherein an optical fiber scrambler is placed in front of the isolator to convert linearly polarized light into naturally polarized light.
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