CN111665220B - Peanut structure-based temperature interference-free M-Z type refractive index sensor - Google Patents

Abstract

The invention discloses a temperature interference-free M-Z type refractive index sensor based on a peanut structure, which comprises a broadband light source, a first single-mode optical fiber, a first peanut structure, a first welding point, a first few-mode optical fiber, a fine core optical fiber, a second few-mode optical fiber, a second peanut structure, a second welding point, a second single-mode optical fiber and a spectrometer, wherein the first single-mode optical fiber is arranged on the first peanut structure; when in use, the broadband light source is connected with the input end of the first single-mode fiber, and the output end of the second single-mode fiber is connected with the spectrometer; by monitoring the position of the resonant wavelength on the spectrometer in real time, high-sensitivity refractive index measurement without temperature interference can be realized. Compared with the prior art, the invention can obviously improve the extinction ratio of the whole sensor, simultaneously can avoid the temperature cross sensitivity problem during refractive index measurement, and has the advantages of high sensitivity, large free spectrum range, simple structure, high mechanical strength and the like.

Description

A M-Z Refractive Index Sensor Based on Peanut Structure Without Temperature Interference

technical field

The invention belongs to the field of optical fiber sensing to measure temperature and refractive index, and specifically relates to a non-temperature interference M-Z type refractive index sensor based on a peanut structure.

Background technique

In the fields of biology, medicine, and chemistry, it is often necessary to measure various parameters of liquids, and the refractive index, as an inherent property of a substance, is one of the important parameters of optics and is the basis for realizing many parameter measurements. Measurement can realize the determination of changes in related parameters such as sugar content, DNA concentration, salinity, pH value, humidity, etc. of substances. However, due to the thermo-optic effect, when the temperature of the external environment changes, the refractive index of the optical fiber itself and the measured substance will change, which will affect the measurement of the external refractive index by the optical fiber M-Z sensor. In order to eliminate the influence of temperature on refractive index sensing, the measured physical quantity and temperature can be distinguished by simultaneous measurement of temperature and refractive index, thereby eliminating the influence of temperature on the refractive index measurement results. Optical fiber M-Z sensors are used to measure temperature, The refractive index has become the research focus of scholars today.

In order to solve this problem, domestic researchers have done a lot of research: Huang Ran et al. (see "Refractometerbased on Mach-Zehnder interferometer with peanut-shape structure[J]. Optics and Interaction of Light with Matter, 2015.") proposed a peanut-structured refractive index sensor, that is, the two ends of a single-mode optical fiber were fused into a peanut structure to form an M-Z sensor, but the cross-sensitivity of temperature to refractive index was not considered; Research on multi-parameter measurement of core fiber M-Z interference sensor. In this paper, a thin core fiber with a high concentration of Ge doped (about 38mol.%) is used to form an M-Z interference sensor. In the temperature range of 30-250 °C, its temperature sensitivity is 70.2pm/ ℃, the sensitivity of the sensors to the refractive index was tested to be -8.12nm/RIU, but the cross-sensitivity of the temperature to the refractive index was not considered; in summary, these sensors were composed of single-mode optical fiber peanut structures. The thin-core fiber constitutes the sensor as the sensing part, but the interference peak has the same response to the refractive index and temperature, which is prone to cross-sensitivity, and the use of single-mode fiber to connect the thin-core fiber has a small free spectral range. Therefore, a method without Cross-sensitive, wide free spectral range and high sensitivity sensors are very necessary.

Contents of the invention

Aiming at the technical problems existing in the above sensors, the present invention proposes an M-Z type refractive index sensor capable of sensing and measuring temperature and refractive index without crossover, so as to overcome the technical problems of cross-sensitivity and small free spectral range existing in the field of temperature and refractive index. .

In order to achieve the above object, the present invention provides a non-temperature interference M-Z type refractive index sensor based on peanut structure, comprising a broadband light source, a first single-mode optical fiber, a first fusion splicing point, a first few-mode optical fiber, a thin-core optical fiber, a second Two few-mode optical fibers, the second fusion splicing point, the second single-mode optical fiber, and a spectrometer;

The output end of the first single-mode optical fiber and the input end of the first few-mode optical fiber are welded into a first peanut structure, and the fusion point is the first fusion point; the first peanut structure and the first fusion point are used to fuse the first single-mode fiber The light transmitted in the mode fiber is evenly coupled into the core and cladding of the first few-mode fiber; the input end of the first single-mode fiber is used for external broadband light source;

The input end of the thin-core fiber is fused to the output end of the first few-mode fiber, and the output end of the thin-core fiber is fused to the input end of the second few-mode fiber;

The output end of the second few-mode fiber and the input end of the second single-mode fiber are fused to form a second peanut structure, and the fusion point is the second fusion point, and the second peanut structure is used to connect the second few-mode fiber core and The light transmitted in the cladding is coupled into the core of the second single-mode fiber; the output end of the second single-mode fiber is externally connected to a spectrometer;

The output end of the first single-mode optical fiber adopts the arc discharge method to melt the ellipsoid, and the input end of the first few-mode optical fiber adopts the arc discharge to melt the ellipsoid to form the first peanut structure, and its fusion point is the first Fusion point; the output end of the first few-mode optical fiber adopts arc discharge to melt the ellipsoid, and the input end of the second single-mode optical fiber adopts arc discharge to melt the ellipsoid to form the second peanut structure, and the fusion point is the second welding point;

The first fusion point is a fusion point formed by fusion of two ellipsoidal structures in the first peanut structure. The difference in the fusion area of the first fusion point makes the cladding mode excited in the first few-mode fiber The numbers are different, and by controlling the fusion area of the fusion point, the light intensity distributed to the core and cladding of the first few-mode optical fiber during the fusion process can be relatively average;

The second fusion point is a fusion point formed by fusion of two ellipsoidal structures in the second peanut structure. The difference in the fusion area of the second fusion point makes the core and cladding of the second few-mode optical fiber The light coupled into the core of the second single-mode optical fiber interferes;

Further, the input end of the spectrometer is connected to the output end of the second single-mode optical fiber; the spectrometer is used to display that the light emitted by the broadband light source passes through the first single-mode optical fiber, the first peanut structure, the first small The interference spectrum of the output light formed by the mode fiber, the thin core fiber, the second few-mode fiber, the second peanut structure, and the second single-mode fiber, thereby obtaining an M-Z type online interference pattern;

Further, the major axis of the first peanut structure is perpendicular to the direction of the optical fiber, the major axis diameter is 200-220 μm, the fiber core diameter is 20-30 μm, the fiber core diameter of the first peanut structure is 20-30 μm, and the major axis diameter is 200-220 μm, the minor axis is parallel to the direction of the fiber, and the diameter of the minor axis is 150-170 μm (this diameter range is selected for the light intensity in the core and cladding of the first few-mode fiber to be relatively average), the second peanut The core diameter of the structure is 20-30 μm, the long-axis diameter is 200-220 μm, and the short-axis diameter is 150-170 μm (this diameter range is selected for the larger range of light intensity in the core and cladding of the second few-mode fiber. interference with the second single-mode fiber core);

Further, the diameter of the first fusion splicing point is 100-120 μm (this diameter range is selected so that the light intensity in the core of the first single-mode fiber can be more evenly distributed to the core and cladding of the first few-mode fiber middle), the diameter of the second fusion splicing point is 100-120 μm (this diameter range is selected for the second few-mode fiber core, the light intensity in the cladding can be in a larger range with the second single-mode fiber core light intensity interferes);

Further, the lengths of the first and second few-mode fibers are both 3 to 5 cm, and few-mode fibers of different lengths will cause interference patterns to form different free spectral ranges; the longer the length of the first and second few-mode fibers, The smaller the free spectral range;

Further, the length of the thin-core fiber is 2 to 2.5 cm, and thin-core fibers of different lengths will cause different extinction ratios in the interference spectrum, and the longer the length of the thin-core fiber, the greater the extinction ratio;

Further, the cladding diameter of the thin-core optical fiber is 70-80 μm, and different cladding diameters make the cladding modes excited in the cladding affected by the external environment in different degrees, thus affecting the final measured temperature and refractive index. Sensitivity, the smaller the cladding diameter, the higher the sensitivity;

Further, the fiber core diameter of the thin-core fiber is 3-4.5 μm, and different core diameters make the optical power of the first few-mode fiber core coupled to the thin-core fiber core different, thereby forming different extinction ratios. interference pattern; the core diameter of the thin-core optical fiber is 3-4.5 μm, and the cladding diameter is 70-80 μm;

In the present invention, the fusion splicing of the first peanut structure is to evenly distribute the optical power transmitted in the first single-mode optical fiber to the core and cladding of the first few-mode optical fiber, so as to obtain a higher extinction ratio The transmission spectrum of the first few-mode fiber and the thin-core fiber are fused to obtain a transmission spectrum with a smaller free spectrum and a larger extinction ratio. The refractive index of the thin-core fiber is 3 times that of the first single-mode fiber, which can improve the sensitivity. Effect. Similarly, the purpose of fusion splicing the thin-core fiber and the second few-mode fiber is to better couple the light in the thin-core fiber to the second few-mode fiber, and finally observe an interference pattern in the interference spectrum.

When the present invention is used for temperature and refractive index measurement, the position of the resonant wavelength that is dominant or has a relatively high extinction ratio generated in the spectrometer is adjusted to the middle of the spectral window; when the external temperature changes, it can be recorded on the spectrum The temperature change can be measured by changing the position of the resonant wavelength; similarly, when the refractive index of the external environment changes, the change of the refractive index can be measured by recording the position change of the resonant wavelength on the spectrum. The temperature and the refractive index are monitored by changing the position of the resonance wavelength, and the two measured parameters do not interfere with each other during the measurement process.

During the temperature measurement process, due to the thermal expansion effect and thermo-optic effect of the fiber itself, the refractive index, diameter, and length of the thin-core fiber will change, and the thermo-optic coefficients of the core and cladding modes of the thin-core fiber are different. Moreover, the thermo-optic coefficients of the two differ by 1 to 2 orders of magnitude, and no light leaks out of the cladding during the temperature measurement process, so the light intensity at the resonant wavelength will not change. Therefore, there will be The intensity of the resonance wavelength does not change, but the position drifts. In the process of measuring the refractive index, since the change of the external refractive index will only affect the effective refractive index of the transmission mode in the cladding, the core refractive index will not be affected, therefore, there will be resonance wavelengths in the process of measuring the refractive index. change, the position drifts.

The peanut structure is to make the light transmitted in the core evenly transmitted in the core and cladding.

Generally speaking, compared with the prior art, the above technical solution conceived by the present invention has the following beneficial effects:

(1) The present invention measures the change of temperature and refractive index by the resonant wavelength produced by the thin-core optical fiber welding peanut structure, and realizes the simultaneous measurement of temperature and refractive index by monitoring the changes of the wavelength positions of different resonant wavelengths of the interference pattern respectively, because Temperature and refractive index have different influences on the interference pattern. The influence of temperature on the interference pattern is very weak and can be ignored, and the refractive index measurement without temperature interference can be realized.

(2) The peanut structure fusion-spliced thin-core optical fiber structure provided by the present invention, because the thin-core optical fiber is more sensitive to the external environment than single-mode and multi-mode optical fibers, it can achieve high sensitivity, large dynamic range, and high-precision optical fiber temperature and refractive index. Measurement; In addition, compared with the traditional dislocation optical fiber interferometer, the M-Z type refractive index sensor based on the peanut structure without temperature interference has the advantages of high mechanical strength and avoiding the influence of the dislocation direction on the interference spectrum.

Description of drawings

Fig. 1 is the structure diagram of a kind of M-Z type refraction index sensor without temperature interference based on peanut structure of embodiment 1 of the present invention;

Fig. 2 is a schematic diagram of a peanut structure fusion-spliced thin-core optical fiber in Embodiment 1 of the present invention;

Fig. 3 is a kind of non-temperature-disturbed M-Z type refraction index sensor test result graph of the spectra obtained by the temperature rise and the wavelength drift based on the peanut structure in Example 1 of the present invention;

Fig. 4 is the fitting curve of a kind of M-Z type refractive index sensor spectrum resonant wavelength changing with temperature based on peanut structure without temperature interference in embodiment 1 of the present invention;

Fig. 5 is a result diagram of the spectrum obtained by testing a non-temperature interference M-Z type refractive index sensor based on the peanut structure in Example 1 of the present invention as the refractive index increases and the wavelength drifts;

Fig. 6 is a fitting curve of the spectral resonance wavelength of a non-temperature interference M-Z type refractive index sensor based on the peanut structure in Example 1 of the present invention as the refractive index changes;

In all the drawings, the same reference numerals are used to represent the same elements or structures, wherein; 1-broadband light source, 2-first single-mode optical fiber, 3-first peanut structure, 4-first fusion point, 5 - the first few-mode fiber, 6 - the thin-core fiber, 7 - the second few-mode fiber, 8 - the second peanut structure, 9 - the second fusion point, 10 - the second single-mode fiber, 11 - the spectrometer.

Detailed ways

In order to make the purpose, constraints and advantages of the present invention clearer, the present invention will be further described in detail below in conjunction with the accompanying drawings and embodiments. It should be understood that the specific embodiments described here are only used to explain the present invention, not to limit the present invention. In addition, the technical features designed in the various embodiments of the present invention described below can be combined with each other as long as there is no conflict with each other.

The present invention provides a non-temperature cross-interference M-Z type refractive index sensor based on peanut structure, including first and second single-mode optical fibers, first and second peanut structures, first and second fusion points, first and second few-mode optical fibers , thin-core optical fiber and spectrometer;

Wherein, the input end of the first single-mode optical fiber is used to connect the output end of the broadband light source, and the output end of the first single-mode optical fiber is used for the welding of the first peanut structure; the output end of the first single-mode optical fiber is melted by arc discharge The ellipsoid is fused with the ellipsoid fused by arc discharge at the input end of the first few-mode fiber to form the first peanut structure, and its fusion point is the first fusion point; the thin-core fiber is connected to the output of the first few-mode fiber end and the input end of the second few-mode fiber; the output end of the second few-mode fiber adopts the ellipsoid fused by arc discharge, and is fused with the ellipsoid fused by arc discharge at the input end of the second single-mode fiber to form the first Two peanut structures, the welding point of which is the second welding point; the output end of the second single-mode optical fiber is connected with the input end of the spectrometer.

A kind of M-Z type refraction index sensor based on peanut structure without temperature interference provided in Example 1, further elaborates the present invention: A kind of M-Z type refraction index sensor test based on peanut structure without temperature cross-interference in Example 1 of the present invention The schematic diagram is shown in Figure 1, including the first single-mode optical fiber 2, the first peanut structure 3, the first fusion splicing point 4, the first few-mode optical fiber 5, the thin-core optical fiber 6, the second few-mode optical fiber 7, and the second peanut structure 8. The second fusion splicing point 9, the second single-mode optical fiber 10, and the spectrometer 11; the broadband light source 1 is connected to the input end of the first single-mode optical fiber 2; , and the input end of the first few-mode optical fiber 5 adopts arc discharge to melt the ellipsoid to form the first peanut structure 3, and its fusion point is the first fusion point 4; the output end of the first few-mode optical fiber 5 adopts arc The ellipsoid fused in the way of electric discharge is fused with the ellipsoid fused by arc discharge at the input end of the second single-mode optical fiber 7 to form the second peanut structure 8, and its fusion point is the second fusion point 9; the second single-mode The output end of the optical fiber 10 is connected to the input end of the spectrometer 11 .

Specifically, in Embodiment 1, the input end of the first single-mode optical fiber 2 and the broadband light source 1 and the output end of the second single-mode optical fiber 10 and the spectrometer 11 are connected through flanges using FC/APC fiber heads.

The working principle of the above-mentioned non-temperature interference M-Z type refractive index sensor based on the peanut structure is described below in conjunction with Example 1:

The broad-spectrum light that broadband light source 1 sends is transmitted to the first splicing point 4 through the first single-mode optical fiber 2; Because the fiber core of the first peanut structure 3 is discontinuous, and because the output end of the first single-mode optical fiber 2, the first less The first input end of the mode fiber 5 is melted into an ellipsoid by arc discharge, and the mode field mismatch phenomenon will appear at the first fusion point 4, so that the core mode transmitted in the first single-mode fiber 2 excites the first few-mode The cladding mode in the optical fiber 5 is transmitted forward, and part of the core mode is coupled to the core of the first few-mode optical fiber 5 and transmitted forward; when the core mode and the cladding mode are transmitted forward to the thin core fiber 6 At the input end, due to the mismatch of core and cladding diameters, the optical signal of the cladding of the first few-mode fiber 5 is partially transmitted to the cladding of the output end of the thin-core fiber 6, and part of it leaks into the air, and the first few-mode The optical signal in the core of the output end of the optical fiber 5 is partially transmitted to the core of the input end of the thin-core optical fiber 6, and partly transmitted to the cladding for forward transmission; when the optical signal reaches the output end of the thin-core optical fiber 6, the optical signal is coupled to the first In the core and cladding of the second few-mode optical fiber 7, the core and cladding modes of the forward transmission are coupled into the core of the second single-mode optical fiber 10 through the second peanut structure 8 to generate interference signals, and finally the interference optical signals enter At the input end of the spectrometer 11, the dominant resonant wavelength produced by the non-temperature interference M-Z type refractive index sensor based on the peanut structure can be observed on the spectrometer 11.

When the refractive index of the external environment changes, the refractive index of the cladding in the thin-core fiber 6 changes, but the refractive index in the core does not change, resulting in a change in the refractive index difference between the core and the cladding. Therefore, in During the refractive index measurement process, there will be a phenomenon that the position of the resonance wavelength will drift; in the spectrometer 11, different resonance wavelengths will drift, but the power intensity of the resonance wavelength will not change, and the wavelength demodulation method can be used to detect the outside world. Changes in the refractive index.

When the temperature of the external environment changes, the length of the thin-core fiber 6 and the refractive index of the cladding will change. Since the thin-core fiber has a characteristic that the thermo-optic coefficients of the core mode and the cladding mode differ greatly, the two The effective refractive index difference will change, resulting in a change in phase; the same change in temperature does not leak light from the cladding to the external environment, so only the resonant wavelength position drifts during the temperature measurement process, which can be used Wavelength demodulation is used to detect changes in the external refractive index.

Fig. 3 is a kind of non-temperature cross-interference-based M-Z type refractive index sensor test spectrum obtained in the embodiment 1 of the peanut structure as the temperature increases, the result graph of the wavelength drift, it can be seen from the figure that when the temperature range When the temperature is from 0 to 120°C, the position of the resonant wavelength hardly changes, that is, the position of the resonant arm length does not drift during the external temperature change process, so when the refractive index is measured, there will be no temperature cross-interference phenomenon.

Fig. 4 is the fitting curve of a kind of non-temperature interference M-Z type refractive index sensor based on peanut structure in embodiment 1 of the present invention. can be ignored, so there will be no temperature cross-interference when performing refractive index measurements.

Fig. 5 is a kind of non-temperature cross-interference M-Z type refractive index sensor test spectrum obtained based on the peanut structure in embodiment 1 of the present invention as the refractive index increases, the result figure of the wavelength drifting, as can be seen from the figure, in the refraction The index ranges from 1.3 to 1.4. With the increase of the refractive index, the interference spectrum moves to the long wavelength direction.

Fig. 6 is the fitting curve of a kind of non-temperature interference M-Z type refractive index sensor based on the peanut structure in the embodiment 1 of the present invention, the spectral resonance wavelength changes with the refractive index. 345.8408nm/RIU.

It is easy for those skilled in the art to understand that the above descriptions are only preferred embodiments of the present invention, and are not intended to limit the present invention. Any modifications, equivalent replacements and improvements made within the spirit and principles of the present invention, All should be included within the protection scope of the present invention.

Claims (7)

1. a kind of no temperature interference M-Z type refractive index sensor based on peanut structure, is characterized in that, comprises broadband light source (1), the first single-mode optical fiber (2), the first peanut structure (3), the first fusion point ( 4), the first few-mode fiber (5), the thin-core fiber (6), the second few-mode fiber (7), the second peanut structure (8), the second fusion point (9), the second single-mode fiber ( 10), spectrometer (11), and connect sequentially; The output end of the first single-mode optical fiber (2) is fused with the input end of the first few-mode optical fiber (5) to form a first peanut structure (3), and its fusion point is the first fusion point (4); the first peanut structure The structure (3) is used to couple the light transmitted in the first single-mode fiber (2) to the core and cladding of the first few-mode fiber (5) more evenly; the input of the first single-mode fiber (2) The end is externally connected with a broadband light source (1); The input end of the thin-core optical fiber (6) is fused to the output end of the first few-mode optical fiber (5), and the output end of the thin-core optical fiber (6) is fused to the input end of the second few-mode optical fiber (7); The output end of the second few-mode optical fiber (7) is fused with the input end of the second single-mode optical fiber (10) to form a second peanut structure (8), and its fusion point is the second fusion point (9); the second peanut structure The structure (8) is used to couple the light transmitted in the core and cladding of the second few-mode optical fiber (7) into the core of the second single-mode optical fiber (10); the second single-mode optical fiber (10) The output end is externally connected with a spectrometer (11); The output end of the first single-mode optical fiber (2) is an ellipsoid fused by arc discharge, and is fused with the ellipsoid fused by arc discharge at the input end of the first few-mode optical fiber (5) to form the first peanut structure (3); the output end of the first few-mode optical fiber (5) is an ellipsoid that adopts the mode of arc discharge fusion, and the input end of the second single-mode optical fiber (7) adopts the ellipsoid phase fusion of the mode of arc discharge to be fused as The second peanut structure (8); the long axis of the first peanut structure (3) is perpendicular to the direction of the fiber, the diameter of the long axis is 200-220 μm, the short axis is parallel to the direction of the fiber, and the diameter of the short axis is 150-170 μm; The long axis of the second peanut structure (8) is perpendicular to the direction of the fiber, the diameter of the long axis is 200-220 μm, the short axis is parallel to the direction of the fiber, and the diameter of the short axis is 150-170 μm; the first welding point (4) is the The two ellipsoidal structures in the first peanut structure (3) are fused and fused to form the fusion joint, and by controlling the fusion area of the first fusion joint, the fibers distributed to the first few-mode optical fiber (5) during the fusion process are The light intensity of the core and cladding is relatively average; The second welding point (9) is a welding point formed by fusion and welding of two ellipsoidal structures in the second peanut structure (8). By controlling the welding area of the second welding point, the second less The light in the core and cladding of the mode fiber (7) is coupled into the core of the second single mode fiber (10) for interference. 2. a kind of non-temperature interference M-Z type refractive index sensor based on peanut structure as claimed in claim 1, is characterized in that, the input end of described spectrometer (11) is connected to the second single-mode optical fiber (10) output end; the spectrometer (11) is used to display that the light emitted by the broadband light source (1) passes through the first single-mode optical fiber (2), the first peanut structure (3), the first few-mode optical fiber (5), the thin The interference spectrum of the output light formed by the core optical fiber (6), the second few-mode optical fiber (7), the second peanut structure (8) and the second single-mode optical fiber (10), thereby obtaining an M-Z type online interference pattern. 3. A kind of non-temperature interference M-Z type refractive index sensor based on peanut structure as claimed in claim 1, characterized in that, the diameter of the first welding point (4) is 100-120 μm, and the diameter of the second welding point (9) has a diameter of 100 to 120 μm. 4. a kind of non-temperature interference M-Z type refractive index sensor based on peanut structure as claimed in claim 1, is characterized in that, the length of the first few-mode fiber (5), the second few-mode fiber (7) is equal to It is 3 ~ 5cm. 5 . The non-temperature interference M-Z type refractive index sensor based on peanut structure according to claim 1 , characterized in that, the length of the thin-core optical fiber ( 6 ) is 2-2.5 cm. 6 . 6 . The M-Z type refractive index sensor based on peanut structure without temperature interference according to claim 1 , characterized in that, the cladding diameter of the thin-core optical fiber ( 6 ) is 70-80 μm. 7 . 7. The M-Z type refractive index sensor based on a peanut structure without temperature interference according to claim 1, characterized in that, the fiber core diameter of the thin-core optical fiber (6) is 3-4.5 μm.

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