Optical path structure for improving interference fringe fineness of fabry-perot sensor

Abstract

The application provides an optical path structure for improving the fineness of interference fringes of a Fabry-Perot sensor, and belongs to the technical field of fiber-optic sensing, comprising a laser, a 2x1 fiber combiner, a fiber circulator, a Fabry-Perot sensor, a 1x2 fiber splitter, a photodetector and an erbium-doped fiber amplifier. The laser generates a stable light source, and the optical signal enters the Fabry-Perot sensor through the 2x1 fiber combiner and the fiber circulator to generate interference fringes. Then, the 1x2 fiber splitter divides the optical signal into two parts: one part is transmitted to the photodetector for signal detection, and the other part enters the erbium-doped fiber amplifier for amplification and is circulated back to the system through a feedback optical path. The optical path structure realizes multi-beam interference through the introduction of signal amplification and multiple feedback optical path design, significantly improves the fineness of the interference fringes, and further improves the sensitivity of the Fabry-Perot sensor in displacement and phase detection.

Description

TECHNICAL FIELD

[0001] The present application belongs to the technical field of optical fiber sensing, and particularly relates to an optical path structure for improving the interference fringe fineness of a Fabry-Perot sensor. BACKGROUND

[0002] Traditional signal detection methods mainly include ultrasonic detection, electromagnetic wave detection and optical detection, etc. These methods face many challenges in practical applications. For example, ultrasonic detection is easily disturbed by environmental noise, and the propagation characteristics of the signal are affected by the detection medium; electromagnetic wave detection is easily disturbed by external electromagnetic interference, which may lead to misjudgment; and conventional optical detection equipment has limitations in sensitivity and resolution, making it difficult to meet the precise capture of weak signals in complex environments.

[0003] Optical fiber sensors have been widely used in online monitoring of high-voltage power equipment, underwater sound detection, vibration detection and other fields due to their advantages of anti-electromagnetic interference, high sensitivity, small size and light weight. Among them, optical fiber sensors based on the Fabry-Perot (F-P) interference principle are particularly attractive. Fabry-Perot interferometric fiber sensors can achieve high-precision detection of external environmental changes (such as sound waves, pressure, vibration or temperature) through multiple reflections of light in the cavity to form an interference effect.

[0004] The present application aims to solve the problem of the Fabry-Perot optical fiber sensor in the interference fringe fineness in the prior art. Due to the wide fringe and signal loss problems of traditional sensors, the resolution and signal contrast performance of the sensor are poor. In the prior art, the fineness of the interference fringe is low, which limits the detection ability and accuracy of the sensor for weak signals, especially in complex application scenarios such as partial discharge detection of power systems, underwater sound wave detection and structural vibration monitoring. SUMMARY

[0005] To solve the above technical problems, the present application adopts the following technical solution:

[0006] An optical path structure for improving the interference fringe fineness of a Fabry-Perot sensor, comprising: a laser, a 2x1 optical fiber combiner, an optical fiber circulator, a Fabry-Perot sensor, a 1x2 optical fiber splitter, an erbium-doped fiber amplifier and a photodetector.

[0007] The laser is used to emit laser light, the laser is connected to one input port of the 2x1 optical fiber combiner, the output port of the 2x1 optical fiber combiner is connected to the first port of the optical fiber circulator, the second port of the optical fiber circulator is connected to the Fabry-Perot sensor, the third port of the optical fiber circulator is connected to the input end of the 1x2 optical fiber splitter, the two output ends of the 1x2 optical fiber splitter are respectively connected to the erbium-doped fiber amplifier and the photodetector, and the erbium-doped fiber amplifier is connected to the other input port of the 2x1 optical fiber combiner.

[0008] The beneficial effects of the present application are as follows:

[0009] The present application significantly improves the fineness of interference fringes and the overall sensitivity of the system by optimizing the optical path structure, combining a continuously tunable wavelength laser, an erbium-doped fiber amplifier (EDFA), a fiber circulator, and a Fabry-Perot (F-P) sensor. By introducing a laser light source with continuous tunable characteristics, the present application not only achieves high-stability optical signal output, but also optimizes the interference conditions of the optical signal, thereby improving the detection resolution and sensitivity of the system to weak signals. At the same time, the present application enhances the optical signal through an erbium-doped fiber amplifier (EDFA) and improves the utilization rate of the optical signal and the intensity of the interference light through a 2x1 fiber combiner and a 1x2 fiber splitter, making the interference fringes clearer. This design effectively solves the problems of wide fringes and signal loss in traditional sensors, thereby significantly improving the resolution, sensitivity, and signal contrast of the system. The improvement enables the sensor to more accurately capture partial discharge signals in complex electromagnetic environments, greatly enhancing the ability to monitor and diagnose the operating state of high-voltage power equipment, providing reliable technical support for real-time monitoring of transformer partial discharge and safe operation of the power grid, and enhancing its performance in underwater acoustic wave and structure vibration detection applications, showing broad application prospects. BRIEF DESCRIPTION OF DRAWINGS

[0010] Figure 1 The present application provides an optical path structure for improving the fineness of Fabry-Perot sensor interference fringes, wherein 1-laser, 2-2x1 fiber combiner, 3-fiber circulator, 4-Fabry-Perot sensor, 5-1x2 fiber splitter, 6-erbium-doped fiber amplifier, 7-optoelectronic detector.

[0011] Figure 2 The present application provides an optical path structure for improving the fineness of Fabry-Perot sensor interference fringes, wherein 1-laser, 2-2x1 fiber combiner, 3-fiber circulator, 4-Fabry-Perot sensor, 5-1x2 fiber splitter, 6-erbium-doped fiber amplifier, 7-optoelectronic detector. DETAILED DESCRIPTION

[0012] In order to make the purpose, technical scheme and advantages of the present application more clear, the present application is further described in detail below in combination with the drawings and examples. It should be understood that the specific examples described herein are only used to explain the present application and do not limit the present application. In addition, the technical features involved in each embodiment of the present application described below can be combined with each other as long as they do not conflict with each other.

[0013] The present application provides an optical path structure for improving the fineness of Fabry-Perot sensor interference fringes, wherein 1-laser, 2-2x1 fiber combiner, 3-fiber circulator, 4-Fabry-Perot sensor, 5-1x2 fiber splitter, 6-erbium-doped fiber amplifier, 7-optoelectronic detector.

[0014] The laser 1 emits laser light from one input port of the 2x1 fiber combiner 2, which is transmitted to the first port of the fiber circulator 3 after passing through the 2x1 fiber combiner 2. The light is transmitted from the first port of the fiber circulator 3 to the second port of the fiber circulator 3. The F-P sensor 4 is connected to the second port. The light is reflected from the sensitive diaphragm of the F-P sensor 4 back to the fiber and then transmitted from the second port to the third port of the fiber circulator 3. The third port is connected to the input end of the 1x2 fiber splitter 5. The splitting ratio of the 1x2 fiber splitter 5 is P:(1-P), where the light with a proportion of P is detected by the photodetector 7, and the light with a proportion of (1-P) is amplified K times by the erbium-doped fiber amplifier 6 and then transmitted to the other input port of the 2x1 fiber combiner 2. The combined light of the laser and the amplified light is then transmitted to the next optical path.

[0015] The laser 1 is the core light source of the optical path system, providing wavelength-tunable and stable output light. As the starting point of the entire system, the stability and wavelength tunability of the laser directly affect the measurement accuracy and sensitivity of the system. By adjusting the wavelength, the laser can adapt to different application requirements, ensuring the adaptability and accuracy of the system in various complex environments.

[0016] The 2x1 fiber combiner 2 is used to combine the light signal output by the laser 1 with the light source amplified by the erbium-doped fiber amplifier 2 (EDFA) and then transmit it to the fiber circulator 3. This component realizes efficient synthesis of multiple optical signals, ensuring stable transmission of optical signals. In multiple optical path cycles, it also effectively improves the utilization rate of optical signals. Its compact design and low loss characteristics ensure the reliability of system performance.

[0017] The fiber circulator 3 is an asymmetric transmission device with three transmission ports: first port, second port, and third port. Optical signals can only be transmitted in a specified direction, i.e., from Port1 to Port2 and then from Port2 to Port3, and reverse transmission is prohibited. The main function of this device is to guide the unidirectional flow of optical signals, avoiding interference caused by reflection or signal aliasing, thereby improving the stability and directionality of signal transmission.

[0018] The F-P sensor 4 is composed of a Fabry-Perot cavity composed of an optical fiber end face and a sensitive diaphragm. The tail fiber of the F-P sensor 4 is connected to the second port of the fiber circulator 3. The F-P sensor 4 uses the multiple reflections of light within the cavity to form an interference signal, allowing for high-precision detection of external environmental changes such as pressure, temperature, or vibration. The F-P sensor is particularly suitable for detecting weak signals in complex electromagnetic environments due to its high sensitivity and small size.

[0019] The 1x2 optical fiber beam splitter 5 is a passive optical device that distributes the input optical signal from one port (1x) to two output ports (2x) and can split the light in a specific ratio (e.g. 30:70 or 10:90). The two light signals after splitting are transmitted to the photodetector 7 and the erbium-doped fiber amplifier 6 respectively. The flexible splitting ratio setting ensures the satisfaction of the light intensity requirements of each optical path, while maximizing the utilization efficiency of the optical signal.

[0020] The photodetector 7 is responsible for detecting the optical signal matching the output wavelength band of the laser 1, converting it into an electrical signal, and recording the intensity changes of the interference fringes. As the output end of the signal, its high sensitivity and wide band response capability ensure accurate detection of weak optical signals, providing a reliable foundation for subsequent data processing and analysis.

[0021] The erbium-doped fiber amplifier 6 amplifies the optical signal in the light splitting path from the 1x2 optical fiber beam splitter 5, compensating for the power loss of the optical signal during transmission. It provides high gain amplification of the optical signal, ensuring that the optical signal intensity meets the requirements of multiple cycles, further enhancing the fineness of the interference fringes and the system sensitivity.

[0022] The amplified optical signal after the erbium-doped fiber amplifier is reintroduced into the 2x1 optical fiber combiner 1 and enters the optical path structure in a cycle. This design improves the intensity of the interference signal and the fineness of the fringes through multiple optical path cycles, enhancing the system's ability to detect weak signals. At the same time, this cyclic structure also improves the utilization efficiency of the optical signal, optimizing the overall performance of the system.

[0023] Figure 1 The present application is a fiber-optic structure for improving the fineness of the interference fringes of a Fabry-Perot sensor. As shown in Figure 1As shown, the optical path structure is mainly composed of the following key parts: a laser 1, which provides a wavelength-stable and tunable optical signal. The light emitted by the laser 1 first passes through a 2×1 optical fiber combiner 2, and after being combined with the amplified optical signal from the subsequent optical path cycle, it is transmitted to the first port of the optical fiber circulator 3. In the optical fiber circulator 3, the optical signal is transmitted unidirectionally along the specified direction from the first port to the second port and enters the F-P sensor 4 connected to the second port. The F-P sensor 4 forms an interference signal through multiple reflections of the sensitive diaphragm for detecting environmental changes, and then the interference signal returns to the second port of the optical fiber circulator 3 and is transmitted to the third port through the second port. The interference signal from the third port of the optical fiber circulator enters the 1×2 optical fiber splitter 5, which distributes the optical signal according to the splitting ratio P:(1-P). Among them, the optical signal with a proportion of P is transmitted to the photodetector 7 to convert the interference fringe signal into an electrical signal for subsequent analysis; and the optical signal with a proportion of (1-P) enters the erbium-doped fiber amplifier 6, which is amplified by K times and returns to the 2×1 optical fiber combiner 2. In the optical fiber combiner 2, the original optical signal from the laser 1 and the amplified optical signal are combined again and enter the optical fiber circulator to form an optical path cycle.

[0024] According to Figure 1 , the working process of the feedback optical path structure is described: this embodiment assumes that the original light intensity input by the laser 1 is , after the F-P cavity interference of the F-P sensor 4, the interference light intensity expression is , the unit of the interference light intensity is W, wherein is the reflectivity of the sound-sensitive diaphragm of the F-P sensor 4 (the value is between 0 and 1), is the angle corresponding to the relative phase difference between the light waves. After the optical path cycle, the interference light intensity expression is , is the number of times the light passes through the feedback cycle.

[0025] (0) Without considering the cycle, i.e. 0 cycles, the light signal detected by the photodetector 7 after the light emitted by the laser 1 passes through the 2×1 optical fiber combiner 2, the optical fiber circulator 3, the F-P sensor 4 and the 1×2 optical fiber splitter 5 is ; is the light signal intensity without cycle, the unit is W, is the proportion, and the splitting ratio of the optical fiber splitter is , is the interference light intensity expression.

[0026] (1) Considering one optical path cycle, the signal detected by the photodetector 7 is ;

[0027] (2) After the second optical path cycle, the signal detected by the photodetector is ;

[0028] (3) The signal detected by the photoelectric detector after the third light path cycle is , and so on. The signal detected by the photoelectric detector 7 after the nth cycle is . Because the light path cycle can be regarded as infinite times, in order to obtain stable interference fringes, the following should be met:

[0029] ;

[0030] wherein is the amplification of the doped fiber amplifier, and then tends to 0, and has

[0031] ;

[0032] The calculation process is described below with specific examples. The input light intensity is , the reflectivity is , the splitting ratio is , the amplification is , and the cycle number is , and then

[0033] ;

[0034] ;

[0035] The interference curve of Figure 2 is obtained according to the above steps. The fringe fineness is an important parameter for describing the sharpness of the interference fringes and the resolution capability of the system, and is defined as the ratio of the free spectral range (FSR) to the full width at half maximum (FWHM), . Under the condition of the same free spectral range, the full width at half maximum (FWHM) of is less than that of , so the fringe fineness of the interference curve is less than that of the interference curve

[0036] The sensitivity of the interference curve is less than that of the interference curve , wherein is the phase change amount, is the intensity change amount of the interference curve , and is the intensity change amount of the interference curve is the intensity change amount of the interference curve ​The sensitivity of the intensity variation of the interference fringes is increased because the slope of the interference fringes is positively correlated with the fineness of the fringes. When the fineness of the fringes is high, the change of the input parameter can more significantly cause the change of the position of the fringes, thereby improving the sensitivity.

Claims

1. A light path structure for improving the fineness of interference fringes of a Fabry-Perot sensor, characterized by comprising: The application relates to a fiber-optic interferometer system. The laser (1) is used for emitting laser light, the laser (1) is connected with one input port of a 2*1 fiber-optic combiner (2), the output port of the 2*1 fiber-optic combiner (2) is connected with a first port of a fiber-optic circulator (3), a second port of the fiber-optic circulator (3) is connected with a F-P sensor (4), a third port of the fiber-optic circulator (3) is connected with the input end of a 1*2 fiber-optic splitter (5), two output ends of the 1*2 fiber-optic splitter (5) are respectively connected with an erbium-doped fiber amplifier (6) and a photoelectric detector (7), and the erbium-doped fiber amplifier (6) is connected with the other input port of the 2*1 fiber-optic combiner (2). The erbium-doped fiber amplifier (6) and the 2*1 fiber-optic combiner (2) form a feedback light path, which is used for cyclically amplifying interference signals generated by the F-P sensor (4) so as to improve the stripe fineness and the system sensitivity. The fiber-optic circulator (3) has three transmission ports, i.e., a first port, a second port and a third port, and the light signal transmission direction can only be from the first port to the second port and then from the second port to the third port, and cannot be reversely transmitted.

2. The optical path structure for improving the fineness of interference fringes of a Fabry-Perot sensor according to claim 1, characterized by, The laser light emitted by the laser (1) is input from one input port of the 2*1 fiber-optic combiner (2), is transmitted to the first port of the fiber-optic circulator (3) after passing through the 2*1 fiber-optic combiner (2), is transmitted from the first port of the fiber-optic circulator (3) to the second port of the fiber-optic circulator (3), and is connected with the F-P sensor (4).

3. The optical path structure for improving the fineness of interference fringes of a Fabry-Perot sensor according to claim 2, characterized by, The light is reflected from the sensitive diaphragm of the F-P sensor (4) to the fiber, is transmitted from the second port to the third port of the fiber-optic circulator (3), and is transmitted from the third port to the 1*2 fiber-optic splitter (5).

4. The optical path structure for improving the fineness of interference fringes of a Fabry-Perot sensor according to claim 3, characterized by, The 1*2 fiber-optic splitter (5) divides the light into two paths, one path of light enters the photoelectric detector (7) to be detected, and the other path of light enters the erbium-doped fiber amplifier (6).

5. The optical path structure for improving the fineness of interference fringes of a Fabry-Perot sensor according to claim 4, characterized by, The laser (1) provides a wavelength-tunable and stable output light source for the system.

6. The optical path structure for improving the fineness of interference fringes of a Fabry-Perot sensor according to claim 1, characterized by, The 2*1 fiber-optic combiner (2) combines the laser light output by the laser (1) and the light source amplified by the erbium-doped fiber amplifier (6).

7. The optical path structure for improving the fineness of interference fringes of a Fabry-Perot sensor according to claim 1, characterized by, The F-P sensor (4) is composed of a tail fiber and a probe, the probe is composed of a F-P cavity, the F-P cavity is composed of a fiber end face and a sensitive diaphragm, and the tail fiber is connected with the second port of the fiber-optic circulator (3).

8. The optical path structure for improving the fineness of interference fringes of a Fabry-Perot sensor according to claim 1, characterized by, The 1*2 fiber-optic splitter (5) is a passive optical device, which is used for distributing the input light signal from one port to two output ports, and the two output ports distribute the light according to a specific splitting ratio.

9. The optical path structure for improving the fineness of interference fringes of a Fabry-Perot sensor according to claim 1, characterized by, The splitting ratio of the 1*2 fiber-optic splitter (5) is P:(1-P), wherein the light with the ratio P is detected by the photoelectric detector (7) through one output port, and the light with the ratio (1-P) enters the erbium-doped fiber amplifier (6) through the other output port.

10. The optical path structure for improving the fineness of interference fringes of a Fabry-Perot sensor according to claim 9, wherein ​ 11. The optical path structure for improving the fineness of interference fringes of a Fabry-Perot sensor according to claim 1, characterized by, The photoelectric detector (7) is used for detecting the optical signal matched with the output light wave band of the laser (1).

12. The optical path structure for improving the fineness of interference fringes of a Fabry-Perot sensor according to claim 10, wherein The erbium-doped fiber amplifier (6) is used for amplifying the light with the proportion of (1-P) by K times and then transmitting the amplified light back to another input port of the 2×1 optical fiber combiner (2); the laser emitted by the laser and the light amplified by K times are combined by the 2×1 optical fiber combiner (2) and then enter the next optical path cycle.

13. The optical path structure for improving the fineness of interference fringes of a Fabry-Perot sensor according to any one of claims 1 to 12, characterized by, The original light intensity inputted by the laser (1) is After the interference of the F-P cavity of the F-P sensor (4), the interference light intensity is , wherein the unit of the interference light intensity is W, is the reflectivity of the sound-sensitive diaphragm of the F-P sensor (4), and the value is between 0 and 1, is the angle corresponding to the relative phase difference between the light waves.

14. The optical path structure for improving the fineness of interference fringes of a Fabry-Perot sensor according to any one of claims 1 to 12, characterized in that, 0 cycles, the laser (1) emits light through 2x1 fiber combiner (2), fiber ring (3), Fabry-Perot sensor (4), 1x2 fiber beam splitter (5) directly to photodetector (7), photodetector (7) detected light signal is ; The light signal intensity without circulating is W, The proportion is the splitting ratio of the fiber beam splitter , The interference light intensity expression is The signal detected by the photoelectric detector (7) after the first light path cycle is ; The signal detected by the photoelectric detector (7) after the second light path circulation is ; After the third light path cycle, the signal detected by the photoelectric detector (7) is ; The signal detected by the photodetector (7) after the nth feedback cycle is ; wherein is the number of feedback cycles through which the light passes. When the optical path cycle is considered to be infinite times, in order to obtain stable interference fringes, the following condition should be met: ; wherein is the amplification factor of the doped fiber amplifier (6), then approaches 0, After infinite number of cycles the signal detected by the photodetector (7) is: .

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