F-P interference type liquid refractive index sensor with composite optical fiber structure

Abstract

The utility model belongs to the technical field of optical fiber sensing application, and particularly relates to an F-P (Fabry-Perot) interference type liquid refractive index sensor with a composite optical fiber structure. Comprising a conical single-mode fiber, a hollow-core fiber and a single-mode fiber. The conical single-mode fiber is composed of a large-diameter section and a small-diameter section, and the large-diameter section and the small-diameter section are in transition through a conical section. The hollow-core optical fiber is provided with a micropore, one end of the hollow-core optical fiber is provided with a taper hole with the same taper as the taper of the conical section, the length of the hollow-core optical fiber is 20 mm, the outer diameter of the hollow-core optical fiber is 125 microns, the inner diameter of the hollow-core optical fiber is 100 microns, and the exposed length d of the micropore is 5 mm; the taper hole end of the hollow-core optical fiber is welded with the tapered single-mode optical fiber inserted into the hollow-core optical fiber, the other end of the hollow-core optical fiber is welded with the single-mode optical fiber, and the length h of a cavity formed by the end of the small-diameter section and the end of the hollow-core optical fiber after welding is 40 micrometers. The sensor is based on an optical fiber technology, and has the advantages of small size, light weight, easy integration and the like. The method can be used in various applications requiring high sensitivity, high stability, miniaturization and integration.

Description

Technical Field

[0001] This utility model belongs to the field of fiber optic sensing application technology, specifically relating to a composite fiber optic structure FP interferometric liquid refractive index sensor. Background Technology

[0002] The refractive index (RI) of a liquid is an important physical parameter reflecting its nature, and its measurement has wide applications in chemistry, biology, and environmental monitoring. Existing refractive index measuring instruments, such as Abbe refractometers and handheld refractometers, while easy to operate, have limitations in accuracy, stability, and real-time performance. Fiber optic sensors, on the other hand, offer advantages such as simple fabrication, high sensitivity, resistance to electromagnetic interference, compact structure, small size, and low cost, enabling precise measurement of the liquid's refractive index. Their sensitivity is typically much higher than traditional refractive index measuring instruments, allowing the sensors to detect minute changes in refractive index. Summary of the Invention

[0003] To improve the measurement accuracy of liquid refractive index, this invention provides a FP interferometric liquid refractive index sensor with a composite fiber structure. The hollow core of the composite fiber structure allows the optical signal to interact with the external environment (such as the liquid) during transmission. Since single-mode fiber exhibits high selectivity in optical signal transmission, this composite fiber structure can capture these minute changes, thereby achieving highly sensitive measurement of the liquid refractive index.

[0004] The technical solution adopted in this utility model is as follows: a FP interferometric liquid refractive index sensor with a composite optical fiber structure. The FP interferometric liquid refractive index sensor includes a tapered single-mode fiber, a hollow-core fiber, and a single-mode fiber. The tapered single-mode fiber consists of a large-diameter section and a small-diameter section, which are transitioned by a tapered section. The hollow-core fiber has micro-holes, one end of which is a tapered hole with the same taper as the tapered section. The hollow-core fiber is 20 mm long, with an outer diameter of 125 μm and an inner diameter of 100 μm. The exposed length d of the micro-hole is 3 mm - 5 mm. The tapered end of the hollow-core fiber is fused to the tapered single-mode fiber inserted inside the hollow-core fiber, and the other end is fused to the single-mode fiber. After fusion, the cavity length h formed by the end of the small-diameter section and the end of the hollow-core fiber is 40 μm. The tapered single-mode fiber, the hollow-core fiber, and the single-mode fiber are fused together to form a composite optical fiber with a single-mode-hollow-core-single-mode structure.

[0005] Furthermore, the exposed length d of the micropores is 3 mm.

[0006] Furthermore, the exposed length d of the micropores is 4 mm.

[0007] Furthermore, the exposed length d of the micropores is 5 mm.

[0008] Furthermore, the core diameter of single-mode optical fiber is 8µm-10µm.

[0009] Furthermore, the core diameter of the single-mode fiber is 8 μm.

[0010] Furthermore, the core diameter of the single-mode fiber is 9 μm.

[0011] Furthermore, the core diameter of the single-mode fiber is 10 μm.

[0012] The beneficial effects of this invention are as follows: It provides a FP interferometric liquid refractive index sensor based on a microporous composite optical fiber structure. Compared with existing technologies, in terms of performance, because the hollow fiber is disrupted, the measured liquid directly penetrates into the fiber and interacts with the optical field. Compared with traditional evanescent field sensing, this direct interaction greatly improves the sensor's sensitivity. Structurally, this sensor, based on optical fiber technology, has advantages such as small size, light weight, and ease of integration. Therefore, this sensor can be used in various applications requiring high sensitivity, high stability, miniaturization, and integration. Attached Figure Description

[0013] Figure 1 This is a schematic diagram of the structure of a composite optical fiber structured FP interferometric liquid refractive index sensor.

[0014] Figure 2 This is a schematic diagram of the structure of a tapered single-mode optical fiber.

[0015] Figure 3 This is a schematic diagram of the structure of a hollow optical fiber.

[0016] Figure 4 This is a schematic diagram of the structure of a single-mode optical fiber.

[0017] Figure 5 This is a schematic diagram of the liquid refractive index measurement system in Example 2. Detailed Implementation Example

[0018] like Figure 1-4As shown, a composite fiber structure FP interferometric liquid refractive index sensor includes a tapered single-mode fiber 1, a hollow-core fiber 2, and a single-mode fiber 3. The tapered single-mode fiber 1 consists of a large-diameter section 11 and a small-diameter section 13, which are connected by a tapered section 12. The hollow-core fiber 2 has a micro-hole 21, one end of which is a tapered hole 22 with the same taper as the tapered section 12. The hollow-core fiber 2 is 20 mm long, with an outer diameter of 125 μm and an inner diameter of 100 μm. The exposed length d of the micro-hole 21 is 5 mm. The tapered end of the hollow-core fiber 2 is fused to the tapered single-mode fiber 1 inserted inside the hollow-core fiber 2, and its other end is fused to the single-mode fiber 3. After fusion, the cavity length h formed by the end of the small-diameter section 13 and the end of the hollow-core fiber 2 is 40 μm, which is an FP cavity. The core diameter of the single-mode fiber 3 is 9 μm. After the tapered single-mode fiber 1, hollow fiber 2 and single-mode fiber 3 are fused together, a single-mode fiber-hollow fiber-single-mode fiber FP composite fiber structure is formed.

[0019] like Figure 1 As shown, the light emitted by the supercontinuum source has an intensity of I0. It enters the optical fiber and undergoes a first reflection at reflector M1, with a reflection intensity of I1. Part of the light passes through reflector M1 and reaches reflector M2 for a second reflection, with a reflection intensity of I2. The two reflected beams couple, producing interference. Example

[0020] like Figure 5 As shown, this embodiment is a measurement system for measuring the refractive index of a liquid using a FP interferometric liquid refractive index sensor with a composite optical fiber structure. The measurement system includes an amplified spontaneous radiator 31, a spectrometer 32, and a circulator 33. The system employs a stable supercontinuum light source connected to the circulator. The spectrometer receives the optical signal output from the reflector of the optical circulator and connects the liquid refractive index sensor to the circulator. The light emitted from the light source enters the hollow optical fiber through the optical circulator. Within the hollow optical fiber, the light is reflected and interference occurs. Then, the reflected light enters the spectrometer through the optical circulator, and the refractive index of different liquids can be obtained by demodulating the information.

[0021] The sensor is connected to optical devices such as a light source and a photodetector, and then placed in the liquid to be measured. Based on changes in the light signal, the refractive index of the liquid is calculated. This sensor features high sensitivity, high miniaturization and integration, good real-time monitoring stability, and broad application prospects, overcoming the shortcomings of traditional detection technologies such as complex operation and low detection sensitivity.

[0022] This sensor employs a single-mode-hollow-single-mode fiber (SMF-HCF-SMF) structure, where the hollow fiber portion is filled with air or other low-refractive-index media. Changes in the refractive index of the surrounding environment directly affect the waveguide modes within the hollow core. Furthermore, the tapered region enhances the impact of external refractive index changes on evanescent wave propagation, thereby causing changes in the effective refractive index of the fiber modes. When the refractive index of the external medium changes, the effective refractive index of the modes within the hollow fiber alters. This change affects the distribution of propagation modes in the fiber and the interference effects between modes, thus altering the coupling relationships between modes and producing wavelength shifts. Since the interference effects of these modes manifest as wavelength shifts in the spectrum, changes in refractive index can be accurately detected by monitoring wavelength shifts on a spectrometer. This structure features high sensitivity, high accuracy, a wide measurement range, and excellent environmental adaptability, making it widely applicable for monitoring changes in the refractive index of liquids.

[0023] like Figure 1 As shown, as the cavity length increases, the optical path difference increases, and the changes in the interference fringes become more pronounced. Therefore, increasing the cavity length usually increases the refractive index sensitivity of the sensor. However, an excessively long cavity length can lead to a slower sensor response time or increased attenuation of the optical signal. Therefore, an appropriate cavity length can improve the refractive index sensitivity of the sensor.

Claims

1. A composite fiber optic structure FP interferometric liquid refractive index sensor, characterized in that: The FP interferometric liquid refractive index sensor includes a tapered single-mode fiber (1), a hollow fiber (2), and a single-mode fiber (3). The tapered single-mode fiber (1) consists of a large-diameter section (11) and a small-diameter section (13), which are connected by a tapered section (12). The hollow fiber (2) has a micro-hole (21), one end of which is a tapered hole (22) with the same taper as the tapered section (12). The hollow fiber (2) is 20 mm long, with an outer diameter of 125 μm and an inner diameter of 100 μm. The exposed length d of the micro-hole (21) is 3 mm - 5 mm. The tapered end of the hollow fiber (2) is fused with the tapered single-mode fiber (1) inserted into the hollow fiber (2), and the other end is fused with the single-mode fiber (3). After fusion, the cavity length h formed by the end of the small-diameter section (13) and the end of the hollow fiber (2) is 40 μm.

2. The FP interferometric liquid refractive index sensor with a composite fiber structure according to claim 1, characterized in that: The exposed length d of the micropore (21) is 3 mm.

3. The FP interferometric liquid refractive index sensor with a composite optical fiber structure according to claim 1, characterized in that: The exposed length d of the micropore (21) is 4 mm.

4. The FP interferometric liquid refractive index sensor with a composite optical fiber structure according to claim 1, characterized in that: The exposed length d of the micropore (21) is 5 mm.

5. The FP interferometric liquid refractive index sensor with a composite optical fiber structure according to claim 1, characterized in that: The core diameter of the single-mode optical fiber (3) is 8µm-10µm.

6. The FP interferometric liquid refractive index sensor with a composite fiber structure according to claim 5, characterized in that: The core diameter of the single-mode optical fiber (3) is 8 μm.

7. The FP interferometric liquid refractive index sensor with a composite optical fiber structure according to claim 5, characterized in that: The core diameter of the single-mode optical fiber (3) is 9 μm.

8. The FP interferometric liquid refractive index sensor with a composite fiber structure according to claim 5, characterized in that: The core diameter of the single-mode optical fiber (3) is 10 μm.

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