Strain demodulation device based on double Michelson interference structures
By using a strain demodulation device based on a double Michelson interferometer structure, and employing components such as a narrow-linewidth laser and a temperature control module, noise is suppressed and interference signals are processed. This solves the problems of detection stability and resolution of the Michelson interferometer under complex working conditions, and achieves high-precision strain measurement.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Utility models(China)
- Current Assignee / Owner
- GUANGDONG UNIV OF TECH
- Filing Date
- 2025-06-23
- Publication Date
- 2026-05-01
AI Technical Summary
Existing Michelson interferometers struggle to simultaneously guarantee detection resolution and stability under complex operating conditions. They are affected by laser frequency drift, fiber length, and changes in refractive index, leading to a decrease in measurement accuracy and reliability.
A strain demodulation device based on a dual Michelson interferometer structure is adopted, including a narrow linewidth laser, a temperature control module, an optical isolator, and a signal generator. The dual Michelson interferometer structure is used to convert hardware noise and ambient temperature noise into common-mode noise for suppression. The interference signal is effectively extracted and processed by the signal conversion unit and the demodulation unit.
Simultaneously ensure detection resolution and stability under complex working conditions, reduce hardware costs and implementation difficulty, and meet the high requirements of modern precision measurement and structural monitoring.
Smart Images
Figure CN224189180U_ABST
Abstract
Description
Technical Field
[0001] This invention relates to the field of modern precision measurement technology, and in particular to a strain demodulation device based on a double Michelson interferometer structure. Background Technology
[0002] With the development of new sensing technologies and fiber optic sensors, fiber optic sensing systems based on the interferometry principle have been widely used in fields such as material property research, smart structure monitoring, and biomechanical analysis. Among them, the Michelson interferometer is widely used for the precision measurement of physical quantities such as strain, temperature, and vibration due to its simple structure, high sensitivity, and strong anti-interference ability.
[0003] In practical applications, traditional Michelson interferometers suffer from at least the following technical bottlenecks: First, the accuracy of obtaining phase information in the interference signal is limited by the frequency stability of the laser. Ordinary lasers are prone to frequency drift under the influence of ambient temperature changes, leading to unstable interference fringes and thus affecting measurement accuracy and reliability. Second, the length and refractive index of the optical fiber are also affected by temperature changes and external strain. Temperature changes cause thermal expansion and contraction of the optical fiber material, resulting in changes in the physical length of the fiber. At the same time, it also changes the refractive index of the fiber through the thermo-optic effect. External mechanical stress, such as stretching or compression, not only directly changes the length of the fiber but also changes its refractive index through the photoelastic effect, causing fluctuations in the phase of the interference signal and thus affecting the detection resolution and stability.
[0004] In summary, current technologies still lack a fiber optic interferometric strain measurement device that can simultaneously ensure detection resolution and stability under complex operating conditions. Therefore, there is an urgent need to propose a novel interferometric structure to achieve high-sensitivity and high-stability demodulation of strain signals, in order to meet the higher performance requirements of modern precision measurement and structural monitoring for sensing systems. Summary of the Invention
[0005] To address the problem that existing technologies cannot simultaneously guarantee detection resolution and stability under complex working conditions, the purpose of this invention is to provide a strain demodulation device based on a dual Michelson interferometer structure.
[0006] To achieve the above-mentioned technical effects, the technical solution of the present invention is as follows:
[0007] A strain demodulation device based on a double Michelson interferometer structure includes a laser source unit for outputting a stable optical signal, a signal detection unit, and a signal demodulation unit. The signal detection unit includes a first optical coupler, a double Michelson interferometer structure, and a signal conversion unit, wherein:
[0008] The output terminal of the laser source unit is connected to the input terminal of the first optical coupler, the output terminal of the first optical coupler is connected to the input terminal of the double Michelson interference structure, the output terminal of the double Michelson interference structure is connected to the input terminal of the signal conversion unit, and the output terminal of the signal conversion unit is connected to the input terminal of the signal demodulation unit.
[0009] Preferably, the laser source unit includes a narrow linewidth laser, a temperature control module, an optical isolator, and a signal generator;
[0010] The output of the signal generator is connected to the input of the narrow linewidth laser, the output of the narrow linewidth laser is connected to the input of the optical isolator, the output of the optical isolator is connected to the input of the first optical coupler, and the narrow linewidth laser is placed in the temperature control module.
[0011] Preferably, the dual Michelson interferometer structure includes a Michelson reference interferometer and a Michelson sensing interferometer, the output of the first optical coupler is connected to the input of the Michelson reference interferometer and the Michelson sensing interferometer respectively, and the output of the Michelson reference interferometer and the Michelson sensing interferometer are both connected to the input of the signal conversion unit.
[0012] Preferably, the Michelson reference interferometer includes a first optical circulator, a second optical coupler, a first Faraday rotator, and a second Faraday rotator.
[0013] The output of the first optical coupler is connected to the input of the first optical circulator. The output of the first optical circulator is connected to the input of the signal conversion unit and the input of the second optical coupler. The output of the second optical coupler is connected to the first Faraday rotator and the second Faraday rotator.
[0014] Preferably, the first optical circulator is a three-port optical device, with the first port of the first optical circulator connected to a first optical coupler, the second port of the first optical circulator connected to a second optical coupler, and the third port of the first optical circulator connected to the input terminal of the signal conversion unit.
[0015] Preferably, the Michelson sensing interferometer includes a second optical circulator, a third optical coupler, a third Faraday rotator, and a fourth Faraday rotator.
[0016] The output of the first optical coupler is connected to the input of the second optical circulator. The output of the second optical circulator is connected to the input of the signal conversion unit and the input of the third optical coupler. The output of the third optical coupler is connected to the third Faraday rotator and the fourth Faraday rotator.
[0017] Preferably, the second optical circulator is a three-port optical device, with the first port of the second optical circulator connected to the first optical coupler, the second port of the second optical circulator connected to the third optical coupler, and the third port of the second optical circulator connected to the input terminal of the signal conversion unit.
[0018] Preferably, the signal conversion unit includes a first photodetector and a second photodetector;
[0019] The input terminal of the first photodetector is connected to the output terminal of the Michelson sensor interferometer, the output terminal of the first photodetector is connected to the input terminal of the signal demodulation unit, the input terminal of the second photodetector is connected to the output terminal of the Michelson reference interferometer, and the output terminal of the second photodetector is connected to the input terminal of the signal demodulation unit.
[0020] Preferably, the signal demodulation unit is an industrial control computer equipped with a high-speed data acquisition card, and the output terminal of the signal conversion unit is connected to the input terminal of the industrial control computer.
[0021] Preferably, the industrial control computer communicates with both the temperature control module and the signal generator.
[0022] Compared with the prior art, the beneficial effects of the technical solution of the present invention are:
[0023] This invention proposes a strain demodulation device based on a dual Michelson interferometer structure. The device outputs laser light from a laser source unit, which is then sequentially passed through a first optical coupler, the dual Michelson interferometer structure, and a signal conversion unit before being fed into a signal demodulation unit. The dual Michelson interferometer structure converts system hardware noise and ambient temperature noise into common-mode noise for suppression. Compared to directly performing external frequency locking on the laser and measuring the ambient temperature before phase correction, the device and method provided by this invention reduce hardware costs and implementation complexity. Simultaneously, the signal conversion and demodulation unit effectively extracts and processes the interference signal, thereby ensuring both detection resolution and stability under complex operating conditions, meeting the higher performance requirements of modern precision measurement and structural monitoring for sensing systems. Attached Figure Description
[0024] Figure 1 This is a first schematic diagram of the strain demodulation device structure based on the dual Michelson interferometer structure proposed in Embodiment 1 of the present invention;
[0025] Figure 2 This is a second schematic diagram of the strain demodulation device structure based on the dual Michelson interferometer structure proposed in Embodiment 2 of the present invention;
[0026] Figure 3This diagram illustrates the third structure of the strain demodulation device based on a dual Michelson interferometer structure proposed in Embodiment 2 of the present invention.
[0027] 1. Laser source unit; 11. Narrow linewidth laser; 12. Temperature control module; 13. Optical isolator; 14. Signal generator; 2. Signal detection unit; 21. First optical coupler; 22. Double Michelson interferometer structure; 221. Michelson reference interferometer; 2211. First optical circulator; 2212. Second optical coupler; 2213. First Faraday rotator; 2214. Second Faraday rotator; 222. Michelson sensing interferometer; 2221. Second optical circulator; 2222. Third optical coupler; 2223. Third Faraday rotator; 2224. Fourth Faraday rotator; 23. Signal conversion unit; 231. First photodetector; 232. Second photodetector; 3. Signal demodulation unit; 31. Industrial control computer. Detailed Implementation
[0028] The accompanying drawings are for illustrative purposes only and should not be construed as limiting the scope of this patent.
[0029] To better illustrate this embodiment, some parts of the accompanying drawings may be omitted, enlarged, or reduced, and do not represent actual dimensions.
[0030] The technical solution of the present invention will be further described below with reference to the accompanying drawings and embodiments.
[0031] Example 1
[0032] like Figure 1 As shown, the strain demodulation device based on a double Michelson interferometer structure provided by this utility model includes a laser source unit 1 for outputting a stable optical signal, a signal detection unit 2, and a signal demodulation unit 3. The signal detection unit 2 includes a first optical coupler 21, a double Michelson interferometer structure 22, and a signal conversion unit 23, wherein:
[0033] The output terminal of the laser source unit 1 is connected to the input terminal of the first optical coupler 21, the output terminal of the first optical coupler 21 is connected to the input terminal of the double Michelson interference structure 22, the output terminal of the double Michelson interference structure 22 is connected to the input terminal of the signal conversion unit 23, and the output terminal of the signal conversion unit 23 is connected to the input terminal of the signal demodulation unit 3.
[0034] In this embodiment, the stable laser output from the laser source unit first enters the first optical coupler, is split in the first optical coupler, and is then transmitted to the double Michelson interference structure. The double Michelson interference structure converts the laser into an interference signal and outputs it to the signal conversion unit. After photoelectric conversion processing, the interference signal is finally transmitted to the signal demodulation unit for demodulation analysis to extract strain information.
[0035] Among them, the dual Michelson interferometer structure converts the system's hardware noise and ambient temperature noise into common-mode noise for suppression, and can simultaneously ensure detection resolution and stability under complex working conditions, so as to meet the higher requirements of modern precision measurement and structural monitoring for the performance of sensing systems.
[0036] Example 2
[0037] like Figure 2 As shown, the laser source unit 1 consists of a narrow linewidth laser 11, a temperature control module 12, an optical isolator 13, and a signal generator 14.
[0038] In this embodiment, the narrow linewidth laser 11 generates a laser with a changing frequency under the internal modulation of the signal generator 14, which enters the double Michelson interference structure 22 to generate an interference signal. Placing the narrow linewidth laser 11 in the temperature control module 12 can, to a certain extent, avoid frequency fluctuations caused by temperature changes of the narrow linewidth laser 11.
[0039] Specifically, the narrow linewidth laser 11 is a single-mode laser or an external cavity laser. Such lasers have relatively small frequency fluctuations, reducing phase noise caused by frequency fluctuations at the source. Driven by the periodic voltage signal generated by the signal generator 14, the narrow linewidth laser 11 periodically changes the frequency of its output laser. After emission, the laser light from the narrow linewidth laser 11 passes through an optical isolator 13 to prevent back-reflected laser light from entering the narrow linewidth laser 11 and affecting its operational stability and lifespan. The temperature control module 12 consists of a metal thermostatic bath, a semiconductor cooling chip, a temperature sensor, and a temperature feedback control circuit. Placing the narrow linewidth laser 11 within the temperature control module 12 isolates it from external temperature influences, maintaining the stability of its center wavelength. The operating temperature of the temperature control module 12 is monitored in real-time by the industrial control computer 31.
[0040] The dual Michelson interferometer structure 22 includes a Michelson reference interferometer 221 and a Michelson sensing interferometer 222. The output terminal of the first optical coupler 21 is connected to the input terminals of the Michelson reference interferometer 221 and the Michelson sensing interferometer 222, respectively. The output terminals of the Michelson reference interferometer 221 and the Michelson sensing interferometer 222 are both connected to the input terminal of the signal conversion unit 23.
[0041] In this embodiment, the Michelson reference interferometer 221 and the Michelson sensing interferometer 222 are two Michelson interferometers with essentially the same parameters. The laser light passing through the optical isolator 13 enters the first optical coupler 21, which splits the laser light into two beams in a 1:1 ratio, which then enter the Michelson reference interferometer 221 and the Michelson sensing interferometer 222 respectively.
[0042] Specifically, the first optical coupler 21 is a 1×2 3dB coupler. Ensuring that the parameters of the Michelson reference interferometer 221 and the Michelson sensing interferometer 222 are consistent can better suppress the common-mode noise of the system.
[0043] The signal conversion unit 23 includes a first photodetector 231 and a second photodetector 232.
[0044] In this embodiment, the Michelson reference interferometer 221 and the Michelson sensing interferometer 222 convert the two laser beams into two interference signals and transmit them to the first photodetector 231 and the second photodetector 232, respectively.
[0045] The signal demodulation unit 3 is an industrial control computer 31 equipped with a high-speed data acquisition card, and the output terminal of the signal conversion unit 23 is connected to the input terminal of the industrial control computer 31. The high-speed acquisition card acquires signals generated by two Michelson interferometers under the trigger of the signal generator 14. Using a high-speed acquisition card can improve the frequency resolution of the interference signal, which can be expressed as... ,in This refers to the frequency change of the output laser light from the narrow linewidth laser 11 under triangular wave modulation. The number of data acquisition points within the modulation period of the narrow linewidth laser 11 can be expressed as: In the formula The sampling rate of the data acquisition card. The frequency modulated within the narrow linewidth laser 11 is also the trigger acquisition frequency of the acquisition card.
[0046] In this embodiment, the interference signals that are respectively input into the first photodetector 231 and the second photodetector 232 are converted into interference electrical signals. The interference electrical signals are then converted from analog to digital by the industrial control computer 31 and acquired for data demodulation processing.
[0047] Example 3
[0048] like Figure 3 As shown, the Michelson reference interferometer 221 includes a first optical circulator 2211, a second optical coupler 2212, a first Faraday rotator 2213, and a second Faraday rotator 2214. The output terminal of the first optical coupler 21 is connected to the input terminal of the first optical circulator 2211, and the output terminal of the first optical circulator 2211 is connected to the input terminal of the signal conversion unit 23 and the input terminal of the second optical coupler 2212, respectively. The output terminal of the second optical coupler 2212 is connected to the first Faraday rotator 2213 and the second Faraday rotator 2214, respectively.
[0049] The output terminal of the first optical coupler 21 is connected to the input terminal of the first optical circulator 2211. The output terminal of the first optical circulator 2211 is connected to the input terminal of the signal conversion unit 23 and the input terminal of the second optical coupler 2212. The output terminal of the second optical coupler 2212 is connected to the first Faraday rotator 2213 and the second Faraday rotator 2214.
[0050] The Michelson sensing interferometer 222 includes a second optical circulator 2221, a third optical coupler 2222, a third Faraday rotator 2223, and a fourth Faraday rotator 2224;
[0051] The output of the first optical coupler 21 is connected to the input of the second optical circulator 2221. The output of the second optical circulator 2221 is connected to the input of the signal conversion unit 23 and the input of the third optical coupler 2222. The output of the third optical coupler 2222 is connected to the third Faraday rotator 2223 and the fourth Faraday rotator 2224.
[0052] In this embodiment, both the first optical circulator 2211 and the second optical circulator 2221 have three ports. The first port of the first optical circulator 2211 is connected to the first optical coupler 21, the second port of the first optical circulator 2211 is connected to the second optical coupler 2212, and the third port of the first optical circulator 2211 is connected to the input terminal of the signal conversion unit 23. The second optical circulator 2221 is a three-port optical device. The first port of the second optical circulator 2221 is connected to the first optical coupler 21, the second port of the second optical circulator 2221 is connected to the third optical coupler 2222, and the third port of the second optical circulator 2221 is connected to the input terminal of the signal conversion unit 23.
[0053] Specifically, the lasers entering the first optical circulator 2211 and the second optical circulator 2221 follow a transmission pattern of entering through the first port and exiting through the second port, and entering through the second port and exiting through the third port. The two equally divided laser beams enter the reference arm of the Michelson reference interferometer 221 and the sensing arm of the Michelson sensing interferometer 222, respectively. The reference arm of the Michelson reference interferometer 221 is connected to the first Faraday rotator 2213 and the second Faraday rotator 2214 for reflecting the laser. The reference arm of the Michelson sensing interferometer 222 is connected to the third Faraday rotator 2223 and the fourth Faraday rotator 2224 for reflecting the laser.
[0054] The reflected light from the sensing arm enters the third optical coupler 2222, where it converges and interferes before entering the second port of the second optical circulator 2221. It then exits from the third port to the second photodetector 232. Similarly, the reflected light from the reference arm enters the second optical coupler 2212, where it converges and interferes before entering the second port of the first optical circulator 2211. It then exits from the third port to the first photodetector 231. During reflection, the laser passes through a Faraday rotator twice, rotating its polarization state by 45° each time. After passing through the Faraday rotator twice, the laser reflected back to the coupler is orthogonal to the newly incident laser in the interferometer arm, with a polarization state difference of 90°, effectively suppressing polarization state fading during interference. The second optical coupler 2212 and the third optical coupler 2222 are 1×2 3dB couplers.
[0055] Obviously, the above embodiments of the present invention are merely examples for clearly illustrating the present invention, and are not intended to limit the implementation of the present invention. Those skilled in the art can make other variations or modifications based on the above description. It is neither necessary nor possible to exhaustively describe all embodiments here. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention should be included within the scope of protection of the claims of the present invention.
Claims
1. A strain demodulation device based on a dual Michelson interferometer structure, characterized in that, It includes a laser source unit (1) for outputting a stable optical signal, a signal detection unit (2) and a signal demodulation unit (3). The signal detection unit (2) includes a first optical coupler (21), a double Michelson interference structure (22) and a signal conversion unit (23). The output end of the laser source unit (1) is connected to the input end of the first optical coupler (21), the output end of the first optical coupler (21) is connected to the input end of the double Michelson interference structure (22), the output end of the double Michelson interference structure (22) is connected to the input end of the signal conversion unit (23), and the output end of the signal conversion unit (23) is connected to the input end of the signal demodulation unit (3).
2. The strain demodulation device based on a dual Michelson interferometer structure according to claim 1, characterized in that, The laser source unit (1) includes a narrow linewidth laser (11), a temperature control module (12), an optical isolator (13), and a signal generator (14). The output of the signal generator (14) is connected to the input of the narrow linewidth laser (11), the output of the narrow linewidth laser (11) is connected to the input of the optical isolator (13), the output of the optical isolator (13) is connected to the input of the first optical coupler (21), and the narrow linewidth laser (11) is controlled by the temperature control module (12).
3. The strain demodulation device based on a dual Michelson interferometer structure according to claim 1, characterized in that, The dual Michelson interferometer structure (22) includes a Michelson reference interferometer (221) and a Michelson sensing interferometer (222). The output of the first optical coupler (21) is connected to the input of the Michelson reference interferometer (221) and the Michelson sensing interferometer (222), respectively. The output of the Michelson reference interferometer (221) and the Michelson sensing interferometer (222) is connected to the input of the signal conversion unit (23), respectively.
4. The strain demodulation device based on a dual Michelson interferometer structure according to claim 3, characterized in that, The Michelson reference interferometer (221) includes a first optical circulator (2211), a second optical coupler (2212), a first Faraday rotator (2213), and a second Faraday rotator (2214). The output of the first optical coupler (21) is connected to the input of the first optical circulator (2211). The output of the first optical circulator (2211) is connected to the input of the signal conversion unit (23) and the input of the second optical coupler (2212). The output of the second optical coupler (2212) is connected to the first Faraday rotator (2213) and the second Faraday rotator (2214).
5. The strain demodulation device based on a dual Michelson interferometer structure according to claim 4, characterized in that, The first optical circulator (2211) is a three-port optical device. The first port of the first optical circulator (2211) is connected to the first optical coupler (21), the second port of the first optical circulator (2211) is connected to the second optical coupler (2212), and the third port of the first optical circulator (2211) is connected to the input terminal of the signal conversion unit (23).
6. The strain demodulation device based on a dual Michelson interferometer structure according to claim 3, characterized in that, The Michelson sensing interferometer (222) includes a second optical circulator (2221), a third optical coupler (2222), a third Faraday rotator (2223), and a fourth Faraday rotator (2224). The output of the first optical coupler (21) is connected to the input of the second optical circulator (2221). The output of the second optical circulator (2221) is connected to the input of the signal conversion unit (23) and the input of the third optical coupler (2222). The output of the third optical coupler (2222) is connected to the third Faraday rotator and the fourth Faraday rotator (2224).
7. The strain demodulation device based on a dual Michelson interferometer structure according to claim 6, characterized in that, The second optical circulator (2221) is a three-port optical device. The first port of the second optical circulator (2221) is connected to the first optical coupler (21), the second port of the second optical circulator (2221) is connected to the third optical coupler (2222), and the third port of the second optical circulator (2221) is connected to the input terminal of the signal conversion unit (23).
8. The strain demodulation device based on a dual Michelson interferometer structure according to claim 3, characterized in that, The signal conversion unit (23) includes a first photodetector (231) and a second photodetector (232); The input terminal of the first photodetector (231) is connected to the output terminal of the Michelson sensor interferometer (222), the output terminal of the first photodetector (231) is connected to the input terminal of the signal demodulation unit (3), the input terminal of the second photodetector (232) is connected to the output terminal of the Michelson reference interferometer (221), and the output terminal of the second photodetector (232) is connected to the input terminal of the signal demodulation unit (3).
9. The strain demodulation device based on a dual Michelson interferometer structure according to claim 2, characterized in that, The signal demodulation unit (3) is an industrial control computer (31) equipped with a high-speed data acquisition card, and the output end of the signal conversion unit (23) is connected to the input end of the industrial control computer (31).
10. The strain demodulation device based on a dual Michelson interferometer structure according to claim 9, characterized in that, The industrial computer (31) communicates with the temperature control module (12) and the signal generator (14) respectively.