High-sensitivity micro-nanofiber multi-parameter sensor based on vernier effect

Abstract

The invention discloses a cascade micro-nano optical fiber multi-parameter sensor based on a vernier effect, and belongs to the technical field of optical fiber sensing. The method is used for improving the sensitivity of the micro-nano optical fiber multi-parameter sensor, and multi-parameter distinguishing analysis and simultaneous sensibilization of a micro-nano optical fiber interferometer working near a dispersion turning point can be realized by utilizing the vernier effect. The multi-parameter sensing sensitivity of the cascaded micro-nano optical fiber sensor can be improved by several times to dozens of times that of a single micro-nano optical fiber interferometer. As the sensor is more sensitive, the sensor has huge potential in some application occasions, such as the fields of trace gas sensing and the like.

Description

Technical Field

[0001] The present invention relates to the technical field of fiber optic sensing, and more specifically, to a high-sensitivity micro-nano fiber multi-parameter sensor based on the Vernier effect. Background Art

[0002] Micro-nano fibers have a much larger evanescent field than conventional fibers. Therefore, micro-nano fiber sensors have the advantages of high sensitivity, small size, low cost, and strong anti-electromagnetic interference ability, and are widely used in many fields such as industrial production, environmental monitoring, and biomedicine. Research shows that when the waist diameter of the micro-nano fiber makes the effective refractive index difference between two modes transmitted therein reach the dispersion turning point, the sensitivity of the sensor will tend to infinity. In 2018, Wang Jing et al. prepared a tapered micro-nano fiber sensor with ultra-high sensitivity. Experiments showed that the refractive index sensitivity of the sensor was about 1.26×10 5 nm / RIU (Wang J, et al, Ultrasensitive optical sensing in aqueous solution based on microfiber modal interferometer. Optics Express, 2018). Although the tapered micro-nano fiber working near the dispersion turning point has high sensitivity, in some application scenarios, such as trace gas detection, it is still necessary to further improve the sensitivity of the fiber optic sensor. The Vernier effect is considered an effective method to improve the sensitivity or resolution of fiber optic sensors. The measurement principle of the Vernier effect is very similar to that of a Vernier caliper, which can amplify the small phase differences in fiber optic sensors, thereby improving the sensitivity of the sensors.

[0003] However, the Vernier effect fiber optic sensors reported in the current literature all achieve the sensitivity enhancement of single-parameter sensing. The phase difference in the tapered micro-nano fiber sensor is sensitive to various factors such as temperature, stress, and the refractive index of the external environment. Therefore, it is necessary to achieve the discrimination and analysis of multiple parameters. The present invention designs a fiber optic sensor that combines the Vernier effect and the dispersion turning point effect of tapered micro-nano fibers, which can simultaneously achieve the Vernier effect sensitivity enhancement of multi-parameter sensing. After literature retrieval, no identical public report to the present invention was found. Summary of the Invention

[0004] In order to solve the problems of the prior art, the purpose of the present invention is to overcome the deficiencies of the existing technology and propose a cascaded micro-nano fiber multi-parameter sensor based on the Vernier effect; the sensor realizes the separation and analysis of multi-parameter sensing and the simultaneous Vernier effect sensitivity enhancement by cascading two tapered micro-nano fiber interferometers working near the dispersion turning point and having similar free spectral ranges.

[0005] To achieve the above object of the invention-creation, the present invention adopts the following technical solutions:

[0006] A cascaded micro-nano fiber multi-parameter sensor based on the Vernier effect, characterized in that the sensing device includes a broadband light source, an input fiber, a tapered micro-nano fiber modal interferometer for sensing, a tapered micro-nano fiber modal interferometer for reference, an output fiber and a spectrometer;

[0007] The laser with a continuous wavelength emitted by the broadband light source is transmitted to the tapered micro-nano fiber modal interferometer for sensing and the tapered micro-nano fiber modal interferometer for reference after passing through the input fiber; the light output from the cascaded micro-nano fiber interferometer is transmitted to the spectrometer through the output fiber to obtain an interference spectral envelope with the Vernier effect.

[0008] The micro-nano fiber interferometers for sensing and reference can be in series or in parallel;

[0009] The laser with a continuous wavelength emitted by the broadband light source is transmitted to the tapered micro-nano fiber modal interferometer for sensing and the tapered micro-nano fiber modal interferometer for reference after passing through the input fiber coupler; the light output from the cascaded micro-nano fiber interferometer is transmitted to the spectrometer through the output fiber coupler to obtain an interference spectral envelope with the Vernier effect.

[0010] The waist diameters of the micro-nano fiber interferometer for sensing and the micro-nano fiber interferometer for reference should satisfy that the sensor operates near the dispersion turning point:

[0011]

[0012] where Δn eff12 is the effective refractive index difference between two modes HE 11 and HE 12 in the interferometer, and λ is the wavelength of the incident light. At this time, the free spectral range FSR of the fiber interferometer = λ 2 / Δn eff12 L w The relationship with the wavelength is non-linear, and L w is the waist length of the micro-nano fiber.

[0013] The waist lengths of the micro-nano fiber interferometer for sensing and the micro-nano fiber interferometer for reference should meet the requirements of the Vernier effect:

[0014] FSR s ≈FSR R

[0015] where FSR s and FSR R are the free spectral ranges of the micro-nano fiber interferometer for sensing and the micro-nano fiber interferometer for reference respectively, and the free spectral range of the output spectral envelope of the cascaded micro-nano fiber sensor is:

[0016]

[0017] For the micro-nano fiber optic interferometer for sensing, the free spectral range of the cascaded micro-nano fiber optic sensor is amplified by M times: M = FSR R / (FSR R -FSR S )

[0018] Since the relationship between the FSR of the tapered micro-nano fiber optic interferometer and the wavelength is non-linear, M is also a function of the wavelength M(λ), and the sensitivity S of the characteristic wavelength of the envelope of the cascaded micro-nano fiber optic sensor E is:

[0019] S E = M(λ)·S S

[0020] where S S is the sensitivity of the micro-nano fiber optic interferometer for sensing. Select the characteristic wavelength λ k of the spectral envelope of the cascaded micro-nano fiber optic sensor, and its sensitivity amplification factor is M k , and the analytical equation of the multi-parameter sensor is:

[0021]

[0022] where S i (λ j ) represents the sensitivity of the micro-nano fiber optic interferometer for sensing to the i-th parameter to be measured at λ j . Therefore, the sensor designed by the present invention can realize the separation analysis and simultaneous sensitivity enhancement of multiple parameters to be measured.

[0023] Compared with the prior art, the present invention has the following obvious outstanding substantial features and remarkable advantages:

[0024] 1. The present invention uses a tapered micro-nano fiber optic interferometer operating near the dispersion turning point as a sensor, which has high sensitivity itself; at the same time, there is an obvious non-linearity between the sensitivity of the sensor and the wavelength;

[0025] 2. The present invention cascades two tapered micro-nano fiber optic interferometers operating near the dispersion turning point, and its output spectral envelope can realize vernier effect sensitivity enhancement; at the same time, different characteristic wavelengths of the output spectral envelope have different sensitivity amplification factors, and the separation analysis and simultaneous sensitivity enhancement of multi-parameter sensing can be realized;

[0026] 3. By cascading the sensing and reference micro-nano fiber interferometers in series or parallel forms, the "main scale" and "sub-scale" structures required for the Vernier effect are formed. And both interferometers operate near the dispersion turning point, and their free spectral range (FSR) has a non-linear relationship with the wavelength, which greatly improves the sensitivity, realizes the separation and analysis of multiple parameters such as temperature, stress, and refractive index, and solves the problem of multi-parameter cross-sensitivity in the prior art. Description of the Drawings

[0027] Figure 1 is a schematic diagram of a series micro-nano fiber multi-parameter sensor based on the Vernier effect according to a preferred embodiment of the present invention;

[0028] Figure 2 is a schematic diagram of a parallel micro-nano fiber multi-parameter sensor based on the Vernier effect according to a preferred embodiment of the present invention;

[0029] Figure 3 is the output spectrum of the cascaded micro-nano fiber multi-parameter sensor according to a preferred embodiment of the present invention, where a is the output spectrum of the reference micro-nano fiber interferometer and b is the output spectrum of the sensing micro-nano fiber interferometer;

[0030] Figure 4 is the response of the cascaded micro-nano fiber multi-parameter sensor to seawater salinity before and after cascading according to a preferred embodiment of the present invention, where a is the salinity response of a single micro-nano fiber sensor and b is the salinity response of the cascaded micro-nano fiber sensor;

[0031] Figure 5 is the response of the cascaded micro-nano fiber multi-parameter sensor to seawater temperature before and after cascading according to a preferred embodiment of the present invention, where a is the temperature response of a single micro-nano fiber sensor and b is the temperature response of the cascaded micro-nano fiber sensor; Detailed Embodiments

[0032] The following describes the specific embodiments of the present invention with reference to the drawings, so that those skilled in the art can better understand the present invention. It should be particularly noted that in the following description, when the detailed description of known functions and designs may dilute the main content of the present invention, these descriptions will be omitted here.

[0033] Embodiment 1: Series Structure Sensor

[0034] A cascaded micro-nano fiber multi-parameter sensor based on the Vernier effect in this embodiment, the structural schematic diagram is as Figure 1As shown in the figure, it includes a broadband light source 1, an input optical fiber (2), a micro-nano fiber interferometer for sensing (3), a micro-nano fiber interferometer for reference (4), an output optical fiber (5), and a spectrometer (6). The laser with a continuous wavelength emitted by the broadband light source (1) is transmitted to the micro-nano fiber interferometer for sensing (3) and the micro-nano fiber interferometer for reference (4) after passing through the input optical fiber (2), and is output to the spectrometer (6) after passing through the output optical fiber (5). Multivariate separation and analysis are performed by reading the envelope of the transmission spectrum.

[0035] In this embodiment, the broadband light source 1 uses a superluminescent light-emitting diode (SLED) with a wavelength range of 1250 - 1650 nm and an output power of 10 mW.

[0036] The micro-nano fiber interferometer for sensing (3) and the micro-nano fiber interferometer for reference (4):

[0037] The interferometer for sensing (3) and the interferometer for reference (4) are connected in series by fusion splicing, and the fusion splicing loss is controlled below 0.2 dB. The spectrometer (6) (model: Yokogawa, AQ6370D) is used to collect the output spectrum and extract the envelope of the Vernier effect (as Figure 3 shown).

[0038] Waist diameter: The tapered micro-nano fiber is prepared by the flame stretching method, and the waist diameter is controlled between 4 - 5 μm, and the dispersion turning point is approximately at 1520 nm.

[0039] Waist length: The waist lengths of the micro-nano fiber interferometer for sensing 3 and the micro-nano fiber interferometer for reference 4 are controlled between 7 - 8 mm to ensure that the difference in the free spectral range is approximately between 5 - 10 nm.

[0040] Embodiment 2: Parallel structure sensor

[0041] A cascaded micro-nano fiber multi-parameter sensor based on the Vernier effect in this embodiment has a structural schematic diagram as Figure 2 shown, and includes a broadband light source (1), an input optical fiber coupler (7), a micro-nano fiber interferometer for sensing (3), a micro-nano fiber interferometer for reference (4), an output optical fiber coupler (8), and a spectrometer (6). The laser with a continuous wavelength emitted by the broadband light source (1) is split by the input optical fiber coupler (7) and then transmitted to the micro-nano fiber interferometer for sensing (3) and the micro-nano fiber interferometer for reference (4) respectively, and is combined by the output optical fiber coupler (8) and then output to the spectrometer (6). Multivariate separation and analysis are performed by reading the envelope of the transmission spectrum.

[0042] In this embodiment, the input optical fiber coupler (7) and the output optical fiber coupler (8) use a 50:50 broadband optical fiber coupler (operating wavelength 1300 - 1600 nm, insertion loss ≤ 0.5 dB)

[0043] Micro-nano fiber optic interferometer for sensing (3) and micro-nano fiber optic interferometer for reference (4):

[0044] Waist diameter: The tapered micro-nano optical fiber is prepared by flame stretching method, the waist diameter is controlled between 4 and 5 μm, and the dispersion turning point is approximately at 1520 nm.

[0045] Waist length: The waist length of the sensing micro-nano fiber interferometer 3 and the waist length of the reference micro-nano fiber interferometer 4 are controlled between 7 and 8 mm to ensure that the difference in the free spectrum range is approximately between 5 and 10 nm.

[0046] The analytical equation of the multi-parameter sensor is used to achieve the synchronous decoupling of the temperature, stress, refractive index and other measured parameters (the salinity analysis result in the embodiment is as follows Figure 4 The temperature analysis results are shown in Figure 5 shown).

[0047] The above describes the embodiments of the present invention in conjunction with the accompanying drawings, but the present invention is not limited to the above embodiments. Various changes can be made according to the purpose of the invention. Any changes, modifications, substitutions, combinations or simplifications made according to the spirit and principle of the technical solution of the present invention should be equivalent replacement methods. As long as they meet the purpose of the invention and do not deviate from the technical principles and inventive concepts of the present invention, they belong to the protection scope of the present invention.

Claims

1. A cascaded micro-nano optical fiber multi-parameter sensor based on vernier effect, characterized in that: It comprises a broadband light source (1), an introduction optical fiber (2), a micro-nano optical fiber interferometer for sensing (3), a micro-nano optical fiber interferometer for reference (4), an export optical fiber (5) and a spectrometer (6); The continuous wavelength light emitted by the broadband light source (1) is transmitted to the sensing micro-nano optical fiber interferometer (3) and the reference micro-nano optical fiber interferometer (4) via the introduction optical fiber (2); the output light of the sensing interferometer (3) and the reference interferometer (4) after cascading is transmitted to the spectrometer (6) via the output optical fiber (5), thereby forming an interference spectrum envelope with a vernier effect; The waist diameters of the sensing micro-nano optical fiber interferometer (3) and the reference micro-nano optical fiber interferometer (4) satisfy the existence of several free spectral ranges near the dispersion turning point within the wavelength range of the broadband light source (1), and are used for multi-parameter separation and analysis and vernier effect sensitivity enhancement.

2. The cascaded micro-nano optical fiber multi-parameter sensor based on the vernier effect according to claim 1 is characterized in that: The sensing interferometer (3) and the reference interferometer (4) are cascaded in series or in parallel. When the parallel connection is adopted, an inlet fiber coupler (7) and an outlet fiber coupler (8) are also included. The inlet fiber (2) and the outlet fiber (5) are respectively connected to the inlet fiber coupler (7) and the outlet fiber coupler (8). The inlet fiber coupler (7) transmits the light of the broadband light source (1) to the sensing interferometer (3) and the reference interferometer (4). The outlet fiber coupler (8) combines the two outputs and transmits them to the spectrometer (6).

3. The cascaded micro-nano optical fiber multi-parameter sensor based on the vernier effect according to claim 1, characterized in that: The sensing micro-nano optical fiber interferometer (3) and the reference micro-nano optical fiber interferometer (4) are non-adiabatic tapered micro-nano optical fibers, and their waist diameters satisfy the existence of several free spectral ranges near the dispersion turning point within the wavelength range of the broadband light source (1). The dispersion turning point satisfies Where Δn eff12 HE mode in micro-nano optical fiber 11 and HE 12 The effective refractive index difference.

4. A high-sensitivity micro-nano optical fiber multi-parameter sensor based on vernier effect according to claims 1 and 2, characterized in that The sensing micro-nano optical fiber interferometer (3) and the reference micro-nano optical fiber interferometer (4) are non-adiabatic tapered micro-nano optical fibers, and their waist lengths meet the requirements of the vernier effect, that is, , where FSR is the free spectral range of the tapered micro-nano optical fiber.

5. A high-sensitivity micro-nano optical fiber multi-parameter sensor based on vernier effect according to any one of claims 1 to 4, characterized in that The multi-parameter separation and analysis is performed by shifting the characteristic wavelengths Δλ of the spectral envelope output by the spectrometer (6) k get: Among them, M k is the wavelength λ k The amplification factor of the cursor effect at k =FSR R (λ k ) / [FSR R (λ k )–FSR S (λ k )],S i (λ k ) is λ k Micro-nano fiber optic interferometer is used to measure temperature, refractive index, stress and other parameters. i sensitivity.

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