Engineering terahertz time-domain spectroscopy system for biaxial optical fiber transmission

Abstract

The invention discloses an engineering terahertz time-domain spectroscopy system for biaxial optical fiber transmission. The engineering terahertz time-domain spectroscopy system comprises a terahertz host, a transmission cable, a terahertz detection module, a detection sample and a robot, the terahertz detection module is fixed at the tail end of a robot manipulator, and the terahertz host is connected with the terahertz detection module through a transmission cable 2; pump light and probe light which are mutually perpendicular in polarization direction and output by a terahertz host are incident into a terahertz detection module through a transmission cable and are excited to generate terahertz time-domain pulses, the terahertz time-domain pulses penetrate through a detection sample, carry phase information of the detection sample and then are reflected into the terahertz detection module to generate induction current, and the terahertz time-domain pulses are transmitted to the terahertz detection module through a transmission cable. And the terahertz host carries out detection path simulation on the detection sample, adjusts the detection posture of the robot and carries out scanning according to a planned path, so that in-situ terahertz detection of the detection sample is completed. The method can be flexibly applied to various engineering field detection environments.

Description

Technical Field

[0001] The present invention relates to a terahertz time-domain spectroscopy system, in particular to an engineering terahertz time-domain spectroscopy system of dual-axis optical fiber transmission used on-site for terahertz nondestructive testing. Background Art

[0002] Terahertz time-domain spectroscopy has very important application prospects in many fields such as biomedicine, material science, quality inspection, safety inspection and non-destructive testing. In the field of non-destructive testing, terahertz time-domain spectroscopy is widely used in industries such as aerospace, automobiles and ships, biopharmaceuticals and cultural relics protection, especially in the non-destructive testing of coatings, composite materials and artworks, and can successfully characterize the defects of the test samples such as delamination, cracks, inclusions, debonding and pores.

[0003] In actual engineering applications, typical terahertz time-domain nondestructive testing systems often face problems such as a wide variety of test samples, large differences in the thickness of the test samples, diverse test scenarios, and different test distance requirements. Especially in the in-situ detection of samples on the engineering site, automated robots are usually used in conjunction with terahertz time-domain spectroscopy systems. The posture changes of different joints of the robot will generate external stress on the optical fiber in the terahertz transmission cable. The external stress changes to the uniaxial polarization-maintaining optical fiber during the detection process are different, which will directly affect the polarization characteristics and birefringence characteristics of the optical fiber, causing the signal-to-noise ratio of the terahertz signal to decrease, affecting the stability and reliability of the terahertz detection signal. Summary of the invention

[0004] In order to reduce the influence of external stress on the quality of polarization-maintaining optical fiber transmission beam, the present invention provides an engineering terahertz time-domain spectroscopy system with dual-axis optical fiber transmission, which can be flexibly applied to a variety of engineering site detection environments.

[0005] The purpose of the present invention is achieved through the following technical solutions, in conjunction with the accompanying drawings:

[0006] An engineering terahertz time-domain spectroscopy system for dual-axis optical fiber transmission comprises a terahertz host 1, a transmission cable 2, a terahertz detection module 3, a detection sample 4 and a robot 5; the terahertz detection module 3 is fixed to the end of the manipulator of the robot 5, and the terahertz host 1 and the terahertz detection module 3 are connected through the transmission cable 2; the pump light and the detection light with mutually perpendicular polarization directions output by the terahertz host 1 are incident into the terahertz detection module 3 through the transmission cable 2 and stimulate to generate a terahertz time-domain pulse, the terahertz time-domain pulse passes through the detection sample 4, carries the phase information of the detection sample, is reflected into the terahertz detection module 3 to generate an induced current, and is transmitted back to the terahertz host 1 through the transmission cable 2, the terahertz host 1 performs detection path simulation on the detection sample 4, adjusts the detection posture of the robot 5 and scans according to the planned path, and completes the in-situ terahertz detection of the detection sample 4.

[0007] Furthermore, the terahertz host 1 includes a linearly polarized femtosecond laser 11, an adaptive dispersion compensation module 12, a polarization-maintaining fiber splitter 13, a polarization-maintaining fiber circulator 14, a scanning delay line module 15, a polarization-maintaining fiber combiner 16, a digital acquisition module 17, and a host computer processor 18; the femtosecond laser pulse emitted by the linearly polarized femtosecond laser 11 is pre-compensated for pulse width by the adaptive dispersion compensation module 12, and then divided into a pump light and a detection light with mutually perpendicular polarization directions by the polarization-maintaining fiber splitter 13; the detection light is directly transmitted to the polarization-maintaining fiber combiner 16; The pump light is incident into the scanning delay line module 15 through the polarization-maintaining fiber circulator 14, and the optical path difference between the detection light and the pump light is changed by the scanning delay line module 15 and transmitted back to the polarization-maintaining fiber circulator 14, and then transmitted to the polarization-maintaining fiber combiner 16 by the polarization-maintaining fiber circulator 14; the polarization-maintaining fiber combiner 16 mixes the pump light and the detection light together and outputs them to the transmission cable 2; the terahertz instantaneous signal transmitted back by the terahertz detection module 3 through the transmission cable 2 is collected by the digital acquisition module 17, and the collected signal is processed and displayed by the host computer processor 18.

[0008] Furthermore, the scanning delay line module 15 includes a displacement stage and a reflector; the movement of the displacement stage causes the optical path difference to change, and the moving position of the displacement stage is collected by the digital acquisition module 17; the pump light is incident into the scanning delay line module 15 through the polarization-maintaining fiber circulator 14, and is reflected back to the polarization-maintaining fiber circulator 14 by the reflector.

[0009] Furthermore, the adaptive dispersion compensation module 12 is used to pre-compensate for pulse width broadening caused by the transmission of pump light and detection light in the terahertz host 1, transmission cable 2 and terahertz detection module 3; the adaptive dispersion compensation module 12 compensates for the optical fiber length of 5m to 40m.

[0010] Furthermore, the transmission cable 2 is composed of an electric cable and a dual-axis polarization-maintaining optical fiber; the electric cable provides voltage to the terahertz detection module 3 and transmits terahertz instantaneous signals; the fast and slow axes of the dual-axis polarization-maintaining optical fiber work simultaneously, and are used to simultaneously transmit pump light and detection light with mutually perpendicular polarization directions.

[0011] Furthermore, the biaxial polarization-maintaining optical fiber is a panda-type polarization-maintaining optical fiber, wherein the transmission direction of the fast axis 22 is perpendicular to the direction of the panda eye 21 , and the transmission direction of the slow axis 23 is parallel to the direction of the panda eye 21 .

[0012] Furthermore, the terahertz detection module 3 includes a polarization-maintaining fiber beam splitter 31, a photoconductive transmitting antenna 32, a bias voltage module 33, a photoconductive detection antenna 34, a micro-current amplification module 35, a terahertz beam splitter 36 and a terahertz lens 37; the polarization-maintaining fiber beam splitter 31 injects the pump light and the detection light with mutually perpendicular polarization directions in the transmission cable 2 into the photoconductive transmitting antenna 32 and the photoconductive detection antenna 34 respectively, and the photoconductive transmitting antenna 32 generates a terahertz time domain signal under the action of the bias voltage module 33. The terahertz time domain pulse is split by the terahertz beam splitter 36, and the transmitted terahertz time domain pulse is focused by the terahertz lens 37 and incident on the detection sample 4. After the terahertz time domain pulse passes through the detection sample 4 carrying the sample information, it is reflected by the terahertz beam splitter 36 again through the terahertz lens 37 to the photoconductive detection antenna 34; under the simultaneous action of the terahertz time domain pulse and the detection light, the photoconductive detection antenna 34 generates an induced current, which is amplified by the micro-current amplification module 35 and then transmitted back to the terahertz host 1 through the transmission cable 2.

[0013] Furthermore, the detection sample 4 is a sample that can be penetrated by terahertz signals.

[0014] The present invention has the following beneficial effects:

[0015] Compared with the existing conventional systems, the present invention provides an engineering terahertz time-domain spectroscopy system with dual-axis optical fiber transmission, which is mainly aimed at the in-situ detection of samples on engineering sites. The dual-axis polarization-maintaining optical fiber with fast and slow axes working simultaneously is used to replace the separate pump light and detection light optical fibers in the conventional system, thereby simplifying the terahertz transmission cable and reducing the influence of uneven optical fiber stress caused by the change of robot automation posture during the detection process on the quality of terahertz detection signals. By modularly separating the terahertz host, transmission cable and terahertz detection system of the terahertz system, it is beneficial to the integration and replacement of the transmission cable and the terahertz detection module, and can meet the needs of various detection scenarios such as detection of samples of different thicknesses. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] Figure 1 A schematic diagram of an engineering terahertz time-domain spectroscopy system for dual-axis optical fiber transmission according to an embodiment of the present invention;

[0017] Figure 2 This is a schematic diagram of the composition principle of the terahertz host described in an embodiment of the present invention;

[0018] Figure 3 Schematic diagram of the fast and slow axes of the dual-axis polarization-maintaining optical fiber described in an embodiment of the present invention;

[0019] Figure 4 This is a schematic diagram of the composition principle of the terahertz detection module described in an embodiment of the present invention;

[0020] In the figure:

[0021] 1-Terahertz host; 2-transmission cable; 3-Terahertz detection module; 4-detection sample; 5-robot;

[0022] 11- linearly polarized femtosecond laser; 12- adaptive dispersion compensation module; 13- polarization-maintaining fiber beam splitter; 14- polarization-maintaining fiber circulator; 15- scanning delay line module; 16- polarization-maintaining fiber combiner; 17- digital acquisition module; 18- host computer processor;

[0023] 21-panda eye; 22-fast axis; 23-slow axis;

[0024] 31-Polarization-maintaining fiber beam splitter; 32-Photoconductive transmitting antenna; 33-Bias voltage module; 34-Photoconductive detecting antenna; 35-Microcurrent amplification module; 36-Terahertz beam splitter; 37-Terahertz lens. DETAILED DESCRIPTION

[0025] The technical solution of the present invention is further described in detail below in conjunction with the accompanying drawings and specific implementation methods.

[0026] like Figure 1 As shown, this embodiment is an engineering terahertz time-domain spectroscopy system with dual-axis optical fiber transmission, comprising five parts: a terahertz host 1, a transmission cable 2, a terahertz detection module 3, a detection sample 4 and a robot 5; the terahertz detection module 3 is fixed to the end of the robot 5 manipulator by a tooling, the terahertz host 1 and the terahertz detection module 3 are connected by a transmission cable 2, and the transmission cable 2 is fixed along the arm of the robot 5. The terahertz host 1 outputs linearly polarized pump light and detection light with mutually perpendicular polarization directions, which are incident into the terahertz detection module 3 through the transmission cable 2 and stimulate the generation of terahertz time-domain pulses. The terahertz time-domain pulses pass through the detection sample 4, carry the phase information of the detection sample, and are reflected into the terahertz detection module 3 to generate an induced current (the magnitude of the induced current is proportional to the amplitude of the terahertz time-domain pulse signal and is in phase with the terahertz time-domain pulse signal). The induced current is sent to the terahertz host 1 through the transmission cable 2 and displayed by the host computer processor in the terahertz host module 1. The terahertz host 1 performs detection path simulation on the detection sample 4, adjusts the robot 5 to a suitable detection posture, and scans according to the planned path to complete the in-situ terahertz detection of the detection sample 4.

[0027] Furthermore, if Figure 2As shown, the terahertz host 1 is composed of a linearly polarized femtosecond laser 11, an adaptive dispersion compensation module 12, a polarization-maintaining fiber splitter 13, a polarization-maintaining fiber circulator 14, a scanning delay line module 15, a polarization-maintaining fiber combiner 16, a digital acquisition module 17 and a host computer processor 18. After the femtosecond laser pulse emitted by the linearly polarized femtosecond laser 11 is pre-compensated for pulse width by the adaptive dispersion compensation module 12, it is divided into pump light and detection light with mutually perpendicular polarization directions by the polarization-maintaining fiber splitter 13; the detection light is directly transmitted to the polarization-maintaining fiber combiner 16; the pump light is incident on the scanning delay line module 15 through the polarization-maintaining fiber circulator 14, and the optical path difference between the detection light and the pump light is changed by the scanning delay line module 15 and is transmitted back to the polarization-maintaining fiber circulator 14, and then transmitted to the polarization-maintaining fiber combiner 16 by the polarization-maintaining fiber circulator 14; finally, the pump light and the detection light are mixed together by the polarization-maintaining fiber combiner 16 and output to the transmission cable 2; the terahertz instantaneous signal transmitted back by the terahertz detection module 3 through the transmission cable 2 is collected by the digital acquisition module 17, and finally the collected signal is processed by the host computer processor 18 such as feature recognition and extraction and displayed.

[0028] Furthermore, the scanning delay line module 15 includes a displacement stage and a reflector; the movement of the displacement stage causes the optical path difference to change, and the moving position of the displacement stage is collected by the digital acquisition module 17; the pump light is incident into the scanning delay line module 15 through the polarization-maintaining fiber circulator 14, and is reflected back to the polarization-maintaining fiber circulator 14 by the reflector.

[0029] Furthermore, the adaptive dispersion compensation module 12 is used to pre-compensate for the pulse width broadening caused by the pump light and the detection light being transmitted in the terahertz host 1, the transmission cable 2 and the terahertz detection module 3. The pulse width will be broadened when it is transmitted in the optical fiber terahertz host 1, the transmission cable 2 and the terahertz detection module 3, and the adaptive dispersion compensation module is used to pre-compensate for the pulse width broadening so that the pump light and the detection light meet the pulse width requirements when they reach the photoconductive antenna.

[0030] Preferably, the adaptive dispersion compensation module 12 compensates for an optical fiber length of 5 m to 40 m.

[0031] Furthermore, the transmission cable 2 consists of two parts: an electric cable and a dual-axis polarization-maintaining optical fiber; the electric cable is responsible for providing voltage to the terahertz detection module 3 and transmitting terahertz instantaneous signals; the fast and slow axes of the dual-axis polarization-maintaining optical fiber work simultaneously, and are used to simultaneously transmit pump light and detection light with mutually perpendicular polarization directions.

[0032] like Figure 3As shown, preferably, the biaxial polarization-maintaining optical fiber is a panda-type polarization-maintaining optical fiber, and the fast and slow axes of the biaxial polarization-maintaining optical fiber work simultaneously, wherein the transmission direction of the fast axis 22 is perpendicular to the direction of the panda eye 21, and the transmission direction of the slow axis 23 is parallel to the direction of the panda eye 21; the fast and slow axes are used to simultaneously transmit pump light and detection light whose polarization directions are perpendicular to each other.

[0033] Preferably, the transmission cable 2 is connected to the terahertz host 1 and the terahertz detection module 3 only by a cable port and an optical fiber port, and can be replaced with different lengths according to different detection scenarios.

[0034] Furthermore, if Figure 4 As shown, the terahertz detection module 3 is composed of a polarization-maintaining fiber beam splitter 31 , a photoconductive transmitting antenna 32 , a bias voltage module 33 , a photoconductive detection antenna 34 , a micro-current amplification module 35 , a terahertz beam splitter 36 and a terahertz lens 37 . Among them, the polarization-maintaining fiber beam splitter 31 respectively injects the pump light and the detection light with mutually perpendicular polarization directions in the transmission cable 2 into the photoconductive transmitting antenna 32 and the photoconductive detecting antenna 34, and the photoconductive transmitting antenna 32 generates a terahertz time-domain pulse under the action of the bias voltage module 33. The terahertz time-domain pulse is split by the terahertz beam splitter 36, and the transmitted terahertz time-domain pulse is focused by the terahertz lens 37 and then incident on the detection sample 4. After the terahertz time-domain pulse passes through the detection sample 4 and carries the sample information, it is reflected by the terahertz beam splitter 36 again through the terahertz lens 37 to the photoconductive detecting antenna 34; under the simultaneous action of the terahertz time-domain pulse and the detection light, the photoconductive detecting antenna 34 generates an induced current, which is amplified by the micro-current amplification module 35 and then transmitted back to the terahertz host 1 through the transmission cable 2.

[0035] The detection sample 4 is a sample that can be penetrated by terahertz signals, and can be a single dielectric material or a multi-layer composite material.

Claims

1. An engineering terahertz time-domain spectroscopy system with dual-axis optical fiber transmission, characterized in that: The invention comprises a terahertz host (1), a transmission cable (2), a terahertz detection module (3), a detection sample (4) and a robot (5); the terahertz detection module (3) is fixed at the end of a manipulator of the robot (5), and the terahertz host (1) and the terahertz detection module (3) are connected via the transmission cable (2); the pump light and the detection light with mutually perpendicular polarization directions output by the terahertz host (1) are incident into the terahertz detection module (3) via the transmission cable (2) and stimulate the generation of terahertz time-domain pulses; the terahertz time-domain pulses pass through the detection sample (4), carry the phase information of the detection sample, and are reflected into the terahertz detection module (3) to generate an induced current, which is then transmitted back to the terahertz host (1) via the transmission cable (2); the terahertz host (1) performs detection path simulation on the detection sample (4), adjusts the detection posture of the robot (5) and scans according to the planned path, thereby completing in-situ terahertz detection of the detection sample (4).

2. The engineering terahertz time-domain spectroscopy system with dual-axis optical fiber transmission according to claim 1, characterized in that: The terahertz host (1) comprises a linearly polarized femtosecond laser (11), an adaptive dispersion compensation module (12), a polarization-maintaining fiber beam splitter (13), a polarization-maintaining fiber circulator (14), a scanning delay line module (15), a polarization-maintaining fiber beam combiner (16), a digital acquisition module (17) and a host computer processor (18); after the femtosecond laser pulse emitted by the linearly polarized femtosecond laser (11) is pre-compensated for pulse width by the adaptive dispersion compensation module (12), it is divided into a pump light and a detection light with mutually perpendicular polarization directions by the polarization-maintaining fiber beam splitter (13); the detection light is directly transmitted to the polarization-maintaining fiber beam combiner (16); the pump light The pump light is incident on a scanning delay line module (15) via a polarization-maintaining optical fiber circulator (14), and the optical path difference between the detection light and the pump light is changed by the scanning delay line module (15) and transmitted back to the polarization-maintaining optical fiber circulator (14), and then transmitted from the polarization-maintaining optical fiber circulator (14) to a polarization-maintaining optical fiber combiner (16); the polarization-maintaining optical fiber combiner (16) mixes the pump light and the detection light and outputs them to a transmission cable (2); a terahertz instantaneous signal transmitted back from the terahertz detection module (3) via the transmission cable (2) is collected by a digital collection module (17), and the collected signal is processed and displayed by a host computer processor (18).

3. The engineering terahertz time-domain spectroscopy system with dual-axis optical fiber transmission according to claim 2, characterized in that: The scanning delay line module (15) comprises a displacement stage and a reflector; the displacement stage moves so that the optical path difference changes, and the moving position of the displacement stage is collected by the digital collection module (17); the pump light is incident into the scanning delay line module (15) via a polarization-maintaining optical fiber circulator (14), and is reflected back into the polarization-maintaining optical fiber circulator (14) by the reflector.

4. The engineering terahertz time-domain spectroscopy system with dual-axis optical fiber transmission according to claim 2, characterized in that: The adaptive dispersion compensation module (12) is used to pre-compensate for pulse width broadening caused by the transmission of pump light and detection light in a terahertz host (1), a transmission cable (2) and a terahertz detection module (3); the adaptive dispersion compensation module (12) compensates for an optical fiber length of 5 m to 40 m.

5. The engineering terahertz time-domain spectroscopy system with dual-axis optical fiber transmission according to claim 1, characterized in that: The transmission cable (2) is composed of an electric cable and a dual-axis polarization-maintaining optical fiber; the electric cable provides voltage for the terahertz detection module (3) and transmits a terahertz instantaneous signal; the fast and slow axes of the dual-axis polarization-maintaining optical fiber work simultaneously, and are used to simultaneously transmit pump light and detection light whose polarization directions are perpendicular to each other.

6. The engineering terahertz time-domain spectroscopy system with dual-axis optical fiber transmission as claimed in claim 2, characterized in that: The dual-axis polarization-maintaining optical fiber is a panda-type polarization-maintaining optical fiber, wherein the transmission direction of the fast axis (22) is perpendicular to the direction of the panda eye (21), and the transmission direction of the slow axis (23) is parallel to the direction of the panda eye (21).

7. The engineering terahertz time-domain spectroscopy system with dual-axis optical fiber transmission according to claim 1, characterized in that: The terahertz detection module (3) comprises a polarization-maintaining optical fiber beam splitter (31), a photoconductive transmitting antenna (32), a bias voltage module (33), a photoconductive detection antenna (34), a microcurrent amplification module (35), a terahertz beam splitter (36) and a terahertz lens (37); the polarization-maintaining optical fiber beam splitter (31) injects the pump light and the detection light in the transmission cable (2) whose polarization directions are perpendicular to each other into the photoconductive transmitting antenna (32) and the photoconductive detection antenna (34), respectively, and the photoconductive transmitting antenna (32) generates a terahertz time domain signal under the action of the bias voltage module (33). The terahertz time domain pulse is split by a terahertz beam splitter (36), the transmitted terahertz time domain pulse is focused by a terahertz lens (37) and then incident on a detection sample (4), the terahertz time domain pulse passes through the detection sample (4) carrying sample information, and then is reflected by the terahertz beam splitter (36) again through the terahertz lens (37) to a photoconductive detection antenna (34); under the simultaneous action of the terahertz time domain pulse and the detection light, the photoconductive detection antenna (34) generates an induced current, which is amplified by a micro-current amplification module (35) and then transmitted back to the terahertz host (1) through a transmission cable (2).

8. The engineering terahertz time-domain spectroscopy system with dual-axis optical fiber transmission according to claim 1, characterized in that: The detection sample (4) is a sample that can be penetrated by a terahertz signal.

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