Light path structure for improving fineness of interference fringes of Fabry-Perot sensor

Abstract

The invention provides an optical path structure for improving the fineness of interference fringes of a Fabry-Perot sensor, which belongs to the technical field of optical fiber sensing and comprises a laser, a 2 * 1 optical fiber combiner, an optical fiber circulator, the Fabry-Perot sensor, a 1 * 2 optical fiber splitter, a photoelectric detector and an erbium-doped optical fiber amplifier. The laser generates a stable light source, and an optical signal enters the Fabry-Perot sensor through the 2 * 1 optical fiber combiner and the optical fiber circulator to generate interference fringes. Then, the 1 * 2 optical fiber beam splitter divides the optical signal into two parts, one part is transmitted to a photoelectric detector for signal detection, and the other part enters an erbium-doped optical fiber amplifier for amplification and is circulated back to the system through a feedback optical path. The optical path structure realizes multi-beam interference by introducing an optical path design of signal amplification and multiple feedback, the fineness of interference fringes is remarkably improved, and the sensitivity of the Fabry-Perot sensor in displacement and phase detection is further improved.

Description

Technical Field

[0001] The invention belongs to the technical field of optical fiber sensing, and in particular relates to an optical path structure for improving the fineness of interference fringes of a Fabry-Perot sensor. Background Art

[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 interfered by environmental noise, and the propagation characteristics of the signal are affected by the detection medium; electromagnetic wave detection is susceptible to external electromagnetic interference, which may lead to misjudgment; and conventional optical detection equipment has limitations in sensitivity and resolution, making it difficult to accurately capture weak signals in complex environments.

[0003] Optical fiber sensors are widely used in the fields of online monitoring of high-voltage power equipment, hydroacoustic detection, vibration detection, etc., due to their significant advantages such as anti-electromagnetic interference, high sensitivity, small size, and light weight. Among them, optical fiber sensors based on the Fabry-Perot (FP) interferometer principle are particularly eye-catching. Fabry-Perot interferometer optical fiber sensors form an interference effect through multiple reflections of light in the cavity, and can achieve high-precision detection of weak changes in the external environment (such as sound waves, pressure, vibration, or temperature).

[0004] The present invention aims to solve the shortcomings of the existing Fabry-Perot fiber optic sensor in terms of the fineness of the interference fringes, especially the poor resolution and signal contrast performance of the traditional sensor due to the wide fringes and signal loss problems. In the existing technology, the fineness of the interference fringes is low, which limits the sensor's detection ability and accuracy for weak signals, especially in complex application scenarios (such as partial discharge detection of power systems, underwater acoustic wave detection and structural vibration monitoring, etc.). Summary of the invention

[0005] In order to solve the above technical problems, the present invention adopts the following technical solutions:

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

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

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

[0009] The present invention 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), an optical fiber circulator, and a Fabry-Perot (FP) sensor. By introducing a laser light source with continuously adjustable characteristics, the present invention 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 invention enhances the optical signal through an erbium-doped fiber amplifier (EDFA), and through a 2×1 optical fiber combiner and a 1×2 optical fiber splitter to construct a circulating optical path design, which improves the utilization rate of the optical signal and the interference light intensity, 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. This improvement enables the sensor to capture partial discharge signals more accurately in complex electromagnetic environments, greatly enhancing the ability to monitor and diagnose the operating status of high-voltage power equipment, providing reliable technical support for real-time monitoring of transformer partial discharge and safe operation of power grids, and enhancing its performance in applications such as underwater acoustic wave and structural vibration detection, demonstrating broad application prospects. BRIEF DESCRIPTION OF THE DRAWINGS

[0010] Figure 1 The optical path structure for improving the fineness of interference fringes of a Fabry-Perot sensor of the present invention comprises: 1-laser, 2-2×1 optical fiber combiner, 3-optical fiber circulator, 4-Fabry-Perot sensor, 5-1×2 optical fiber beam splitter, 6-erbium-doped optical fiber amplifier, and 7-photoelectric detector;

[0011] Figure 2 is an interference curve according to an embodiment of the present invention. DETAILED DESCRIPTION

[0012] In order to make the purpose, technical solutions and advantages of the present invention more clearly understood, the present invention is further described in detail below in conjunction with the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not intended to limit the present invention. In addition, the technical features involved in the various embodiments of the present invention described below can be combined with each other as long as they do not conflict with each other.

[0013] The present invention provides an optical path structure for improving the fineness of interference fringes of a Fabry-Perot sensor. The structure mainly comprises a laser 1, a 2×1 optical fiber combiner 2, an optical fiber circulator 3, a Fabry-Perot sensor 4, a 1×2 optical fiber splitter 5, an erbium-doped optical fiber amplifier 6 and a photodetector 7.

[0014] The laser light emitted by the laser 1 is input from an input port of the 2×1 fiber combiner 2, and is transmitted to the first port of the fiber circulator 3 after passing through the 2×1 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 Fabry-Perot sensor 4 is connected to the second port, and the light is reflected back to the optical fiber from the sensitive diaphragm of the Fabry-Perot sensor 4, 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 1×2 fiber splitter 5. The splitting ratio of the 1×2 fiber splitter 5 is P: (1-P), wherein the light with a ratio of P is detected by the photodetector 7, and the light with a ratio of (1-P) is amplified K times by the erbium-doped fiber amplifier 6 and then transmitted back to the other input port of the 2×1 fiber combiner 2. The light emitted by the laser is synthesized with this part of the light source amplified K times and continues to enter the next optical path cycle.

[0015] The laser 1 is the core light source of the optical path system, providing a wavelength-tunable and stable output light. As the signal 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, thereby ensuring the adaptability and accuracy of the system in various complex environments.

[0016] The 2×1 fiber combiner 2 is used to combine the optical signal output by the laser 1 with the light source amplified by the erbium-doped fiber amplifier 2 (EDFA) and transmit it to the fiber circulator 3. This component realizes the efficient synthesis of multi-path optical signals and ensures the 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 optical fiber circulator 3 is an asymmetric transmission device having three transmission ports, namely, a first port, a second port and a third port. The optical signal can only be transmitted in a specified direction, i.e., from Port 1 to Port 2, and then from Port 2 to Port 3, and reverse transmission is prohibited. The main function of the device is to guide the unidirectional flow of the optical signal, avoiding interference caused by reflection or signal aliasing, thereby improving the stability and directionality of signal transmission.

[0018] The Fabry-Perot sensor 4 is composed of a Fabry-Perot cavity (Fabry-Perot cavity) composed of an optical fiber end face and a sensitive membrane, and the pigtail of the Fabry-Perot sensor 4 is connected to the second port of the optical fiber circulator 3. The Fabry-Perot sensor 4 uses multiple reflections of light in the cavity to form an interference signal to perform high-precision detection of external environmental changes (such as pressure, temperature or vibration). With its high sensitivity and miniaturized design, the Fabry-Perot sensor is particularly suitable for the detection of weak signals in complex electromagnetic environments.

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

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

[0021] The erbium-doped fiber amplifier 6 amplifies the optical signal in the splitting path from the 1×2 optical fiber beam splitter 5 to compensate for the power loss of the optical signal during transmission. It provides high-gain amplification of the optical signal, ensures that the intensity of the optical signal meets the requirements of multiple cycles, and further enhances the fineness of the interference fringes and the system sensitivity.

[0022] The optical signal amplified by the erbium-doped fiber amplifier is reintroduced into the 2×1 fiber combiner 1 and circulated into the optical path structure. This design improves the intensity and fringe fineness of the interference signal through multiple optical path cycles, thereby 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 and optimizes the overall performance of the system.

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

[0024] according to Figure 1 , explaining the working process of the feedback optical path structure: In this embodiment, it is assumed that the original light intensity input by the laser 1 is After the Fabry-Perot cavity interference of the Fabry-Perot sensor 4, the expression of the interference light intensity is: , the unit of interference light intensity is W, where is the reflectivity of the acoustic sensitive diaphragm of the Fabry-Perot sensor 4 (the value is between 0 and 1), is the angle corresponding to the relative phase difference between the light waves. The expression of the interference light intensity after the optical path cycle is: , is the number of times the light passes through the feedback loop.

[0025] (0) Without considering the cycle, that is, 0 cycles, the light emitted by laser 1 passes through 2×1 fiber combiner 2, fiber circulator 3, Fabry-Perot sensor 4, 1×2 fiber splitter 5 and directly reaches photodetector 7. The light signal detected is ; is the intensity of the optical signal without circulation, in W, As a ratio, the splitting ratio of the fiber beam splitter is , is the expression of interference light intensity.

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

[0027] (2) The signal detected by the photodetector after the second optical cycle is ;

[0028] (3) After the third optical cycle, the signal detected by the photodetector is , and so on, the signal detected by the photodetector 7 after the nth cycle is Because the optical path cycle can be considered infinite, in order to obtain stable interference fringes, the following conditions should be met:

[0029] ;

[0030] in is the amplification factor of the erbium-doped fiber amplifier, then Approaching 0, we have:

[0031] ;

[0032] The following is a specific example to illustrate the calculation process. Input the light intensity , reflectivity , splitting ratio , magnification , number of cycles , then:

[0033] ;

[0034] ;

[0035] According to the above steps, we can calculate Figure 2 Interference curve. Fringe fineness is an important parameter that describes the sharpness of interference fringes and the resolution of the system. It is defined as the ratio of the free spectral range (FSR) to the full width at half maximum (FWHM). . In the case of the same free spectrum, The full width at half maximum (FWHM) is less than The full width at half maximum (FWHM), so the interference curve The fringe fineness is smaller than the interference curve The fineness of the stripes.

[0036] Interference curve Sensitivity Smaller than the interference curve Sensitivity ,in, is the phase change, Interference curve The intensity change, Interference curve The reason for the increased sensitivity is that the slope of the interference fringe curve is positively correlated with the fringe fineness. When the fineness is high, the change in input parameters can more significantly cause the change in fringe position, thereby improving sensitivity.

Claims

1. An optical path structure for improving the fineness of interference fringes of a Fabry-Perot sensor, characterized in that: include: Laser (1), 2×1 fiber combiner (2), fiber circulator (3), Fabry-Perot sensor (4), 1×2 fiber beam splitter (5), erbium-doped fiber amplifier (6) and photodetector (7); The laser (1) is used to emit laser light. The laser (1) is connected to an input port of a 2×1 optical fiber combiner (2). The output port of the 2×1 optical fiber combiner (2) is connected to a first port of an optical fiber circulator (3). The second port of the optical fiber circulator (3) is connected to a Fabry-Perot sensor (4). The third port of the optical fiber circulator (3) is connected to an input end of a 1×2 optical fiber splitter (5). Two output ends of the 1×2 optical fiber splitter (5) are respectively connected to an erbium-doped optical fiber amplifier (6) and a photodetector (7). The erbium-doped optical fiber amplifier (6) is connected to another input port of the 2×1 optical fiber combiner (2).

2. The optical path structure for improving the fineness of interference fringes of a Fabry-Perot sensor according to claim 1, characterized in that: The optical fiber circulator (3) has three transmission ports, namely a first port, a second port and a third port. The optical signal can only be transmitted from the first port to the second port and then from the second port to the third port, and cannot be transmitted in the reverse direction.

3. The optical path structure for improving the fineness of interference fringes of a Fabry-Perot sensor according to claim 2, characterized in that: Laser light emitted by the laser (1) is input from an input port of the 2×1 optical fiber combiner (2), and is transmitted to a first port of the optical fiber circulator (3) after passing through the 2×1 optical fiber combiner (2). The light is transmitted from the first port of the optical fiber circulator (3) to a second port of the optical fiber circulator (3), and a Fabry-Perot sensor (4) is connected to the second port of the optical fiber circulator (3).

4. The optical path structure for improving the fineness of interference fringes of a Fabry-Perot sensor according to claim 3, characterized in that: Light is reflected from the sensitive diaphragm of the Fabry-Perot sensor (4) back to the optical fiber, and then transmitted from the second port to the third port of the optical fiber circulator (3), and then transmitted from the third port to the 1×2 optical fiber beam splitter (5), and the third port of the optical fiber circulator (3) is connected to the input end of the 1×2 optical fiber beam splitter (5).

5. The optical path structure for improving the fineness of interference fringes of a Fabry-Perot sensor according to claim 4, characterized in that: The 1×2 optical fiber beam splitter (5) splits 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 optical fiber amplifier (6).

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

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

8. The optical path structure for improving the fineness of interference fringes of a Fabry-Perot sensor according to claim 1, characterized in that: The Fabry-Perot sensor (4) is composed of a pigtail fiber and a probe, wherein the probe is composed of a Fabry-Perot cavity, the Fabry-Perot cavity is composed of an optical fiber end face and a sensitive membrane, and the pigtail fiber is connected to the second port of the optical fiber circulator (3).

9. The optical path structure for improving the fineness of interference fringes of a Fabry-Perot sensor according to claim 1, characterized in that: The 1×2 optical fiber beam splitter (5) is configured as a passive optical device, and is used to distribute an input optical signal from one port to two output ports, and the two output ports split the optical signal according to a specific splitting ratio.

10. The optical path structure for improving the fineness of interference fringes of a Fabry-Perot sensor according to claim 9, characterized in that: The 1×2 optical fiber beam splitter (5) has a splitting ratio of P:(1-P), wherein light with a ratio of P is detected by a photodetector (7) through one of the output ports, and light with a ratio of (1-P) enters an erbium-doped optical fiber amplifier (6) through another output port.

11. The optical path structure for improving the fineness of interference fringes of a Fabry-Perot sensor according to claim 1, characterized in that: The photoelectric detector (7) is used to detect an optical signal that matches the optical waveband output by the laser (1).

12. The optical path structure for improving the fineness of interference fringes of a Fabry-Perot sensor according to claim 10, characterized in that: The erbium-doped fiber amplifier (6) is used to amplify the light with a ratio of (1-P) by K times and transmit it back to another input port of the 2×1 fiber combiner (2); the laser light emitted by the laser and the light amplified by K times are combined by the 2×1 fiber combiner (2) and 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 in that: The original light intensity of the laser (1) input is , after the interference of the Fabry-Perot cavity of the Fabry-Perot sensor (4), the interference light intensity is , where the interference light intensity unit is W, is the reflectivity of the acoustic sensitive membrane of the Fabry-Perot sensor (4), and its value is between 0 and 1. is the angle corresponding to the relative phase difference between 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 light emitted by the laser (1) passes through the 2×1 fiber combiner (2), the fiber circulator (3), the Fabry-Perot sensor (4), and the 1×2 fiber splitter (5) and directly reaches the photodetector (7). The light signal detected by the photodetector (7) is ; is the intensity of the optical signal without circulation, in W, As a ratio, the splitting ratio of the fiber beam splitter is , is the expression of interference light intensity; The signal detected by the photodetector (7) after the first optical cycle is ; After the second optical cycle, the signal detected by the photodetector (7) is ; After the third optical cycle, the signal detected by the photodetector (7) is ; After the nth cycle, the signal detected by the photodetector (7) is ;in, is the number of times the light passes through the feedback loop; When the optical path is considered to be infinitely cycled, in order to obtain stable interference fringes, the following conditions should be met: ;in, is the amplification factor of the erbium-doped fiber amplifier (6), then Approaching 0, After infinite cycles, the signal detected by the photodetector (7) is: .

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