SMS-based spliced ​​tapered resonant ring optical fiber sensor and its preparation method

Abstract

The present application discloses an S-M-S spliced ​​tapered resonant ring optical fiber sensor and its preparation method, which relates to the technical field of optical fiber sensors, including: a first single-mode optical fiber connected to a supercontinuum source, the output end of the first single-mode optical fiber connected to a first seven-core optical fiber, the output end of the first seven-core optical fiber connected to a resonant ring, the resonant ring sleeve is arranged on a low-refractive index UV glue channel, the output end of the resonant ring is connected to a second seven-core optical fiber, the output end of the second seven-core optical fiber is connected to a second single-mode optical fiber, and the output end of the second single-mode optical fiber is connected to a spectrometer. The sensor utilizes the characteristics of single-mode optical fiber and seven-core optical fiber, forms a closed resonant ring structure through tapered technology, realizes the simultaneous measurement of refractive index and temperature, expands the application range of the sensor, and has high sensitivity and good selectivity.

Description

Technical Field

[0001] The present application relates to the technical field of optical fiber sensors, and in particular to an optical fiber sensor based on SMS spliced ​​tapered resonant rings and a preparation method thereof. Background Art

[0002] Fiber optic sensors have been widely used in the detection of various physical quantities due to their unique optical properties, miniaturization, strong anti-electromagnetic interference ability, and remote monitoring. In particular, in the fields of environmental monitoring, biomedicine, petrochemicals, etc., the demand for simultaneous measurement of temperature and refractive index is increasing.

[0003] In recent years, fiber resonant ring sensors have become a hot topic of research due to their unique optical interference effect and high sensitivity. However, most fiber resonant ring sensors can usually only measure a single physical quantity, such as temperature or refractive index, and it is difficult to accurately measure these two parameters at the same time. Traditional refractive index measurement methods, such as refractometers and optical interferometers, usually have problems such as large size, high cost, and difficulty in integration. Temperature measurement often uses thermocouples, thermistors, etc., which also face similar problems.

[0004] Therefore, it is of great practical value to realize a miniaturized, low-cost, and highly sensitive sensor that can simultaneously measure refractive index and temperature. Summary of the invention

[0005] In order to solve the above technical problems, this application proposes the following technical solutions:

[0006] In the first aspect, an embodiment of the present application provides an SMS-spliced ​​tapered resonant ring optical fiber sensor, comprising: a first single-mode optical fiber connected to a supercontinuum source, the output end of the first single-mode optical fiber connected to a first seven-core optical fiber, the output end of the first seven-core optical fiber connected to a resonant ring, the resonant ring is sleeved on a low-refractive index UV glue channel, the output end of the resonant ring is connected to a second seven-core optical fiber, the output end of the second seven-core optical fiber is connected to a second single-mode optical fiber, and the output end of the second single-mode optical fiber is connected to a spectrometer.

[0007] In a possible implementation, a first cone region is formed between the first seven-core optical fiber and the resonant ring, a second cone region is formed between the second seven-core optical fiber and the resonant ring, and the first cone region and the second cone region are formed by tapering the seven-core optical fiber.

[0008] In a possible implementation, the first seven-core optical fiber, the first tapered region, the resonant ring, the second tapered region, and the second seven-core optical fiber are integrated as a whole, and the resonant ring is formed by tapering the seven-core optical fiber and then recycling it.

[0009] In a possible implementation, the resonant ring formed by the seven-core optical fiber after tapering is a micro-nano optical fiber resonant ring. The micro-nano optical fiber has an evanescent field, so part of the light in the resonant ring propagates along the core, and part of the light emerges from the core to interfere with each other.

[0010] In a possible implementation, the formula for light interference in the micro-nano optical fiber resonant ring is:

[0011]

[0012] where Δφ is the phase difference, n eff,SM and n eff,C are the effective refractive indices of single-mode fiber and seven-core fiber respectively, λ is the wavelength of light, m ​​is an integer, and L is the coupling length of the tapered part of the seven-core fiber.

[0013] In a second aspect, an embodiment of the present application provides a method for preparing a SMS spliced ​​tapered resonant ring optical fiber sensor according to any possible implementation of the first aspect, comprising:

[0014] S1, make a UV glue channel through acrylic rods, plastic tubes and UV glue;

[0015] S2, sequentially splicing the first single-mode optical fiber, the seven-core optical fiber, and the second single-mode optical fiber;

[0016] S3, placing the seven-core optical fiber in a taper drawing machine for taper drawing, and after the taper drawing is completed, recovering the optical fiber to automatically form a micro-nano optical fiber resonant ring;

[0017] S4, fixing the UV glue channel with an auxiliary device, and then passing the UV glue channel through the micro-nano optical fiber resonant ring;

[0018] S5, tightening the micro-nano optical fiber resonant ring step by step by adjusting the parameters, and finally observing through a microscope that the resonant ring is completely tightened on the channel, and encapsulating the micro-nano optical fiber resonant ring;

[0019] S6, after the micro-nano optical fiber resonant ring is encapsulated, UV glue is dripped on the un-tapered part of the seven-core optical fiber, and the seven-core optical fiber is fixed on the glass slide by UV light for curing;

[0020] S7, connect one end of the manufactured optical fiber sensor to the supercontinuum light source through a jumper and the other end to the spectrometer for testing.

[0021] In a possible implementation, the method of making a UV glue channel by using an acrylic rod, a plastic tube and UV glue includes:

[0022] Use an acrylic rod to pass through the plastic tube, leaving a small space for dripping low-refractive index UV glue, where: the diameter of the acrylic rod is 1mm;

[0023] Drip the UV glue into the plastic tube, and then wrap it around the acrylic rod along the plastic tube.

[0024] Irradiate with ultraviolet light for more than 20 minutes, and then naturally cure for 4 hours. The friction between the plastic tube and the UV glue can peel off the UV glue to form a UV glue channel with a diameter of about 1mm.

[0025] In a possible implementation, placing the seven-core optical fiber in a taper drawing machine for taper drawing, and recovering the seven-core optical fiber to automatically form a micro-nano optical fiber resonant ring after the taper drawing is completed, includes:

[0026] Set the parameters of the taper machine: hydrogen flow rate 170 SCCM, stretching speed 50 μm / sec, inching speed 35 μm / sec, motor advance delay 3s;

[0027] Turn on the hydrogen ignition to taper the seven-core optical fiber. The taper length is 25000μm and the diameter reaches 2μm.

[0028] Adjust the initial distance of the taper machine, the recovery length is 8000μm, and it will automatically form a ring after recovery.

[0029] In a possible implementation, the micro-nano fiber resonant ring is tightened step by step by adjusting parameters, and finally the resonant ring is completely tightened on the channel by observing through a microscope, and the micro-nano fiber resonant ring is packaged, including:

[0030] At the beginning, the tightening length was 1000 μm each time. Through microscopic observation, the tightening length was 100 μm when it was about to be tightened.

[0031] Finally, observe through a microscope that the resonant ring is completely tightened on the channel, then drop low-refractive index UV glue on it, cure it with a UV lamp for 5-10 minutes, and then encapsulate it.

[0032] In an embodiment of the present application, a single-mode-seven-core-single-mode (SMS) spliced ​​tapered resonant ring optical fiber sensor is proposed. The sensor utilizes the characteristics of single-mode optical fiber and seven-core optical fiber to form a closed resonant ring structure through tapered technology, thereby realizing simultaneous measurement of refractive index and temperature, expanding the application range of the sensor, and having high sensitivity and good selectivity. BRIEF DESCRIPTION OF THE DRAWINGS

[0033] Figure 1 A schematic diagram of the structure of an SMS spliced ​​tapered resonant ring optical fiber sensor provided in an embodiment of the present application;

[0034] Figure 2 A schematic flow chart of a method for preparing an SMS-based spliced ​​tapered resonant ring optical fiber sensor provided in an embodiment of the present application;

[0035] Figure 3 A schematic diagram of a test optical fiber sensor provided in an embodiment of the present application;

[0036] Figure 4 Schematic diagram of the effect of different concentrations of NH4Cl solution on the optical wavelength of the optical fiber sensor;

[0037] Figure 5 Schematic diagram of the effect of different temperatures on the optical wavelength of the optical fiber sensor;

[0038] Figure 1-Figure 5 In the symbol, it is represented as:

[0039] 1-first single-mode optical fiber, 2-first seven-core optical fiber, 3-resonance ring, 4-UV glue channel, 5-second seven-core optical fiber, 6-second single-mode optical fiber, 7-first cone region, 8-second cone region. DETAILED DESCRIPTION

[0040] The present solution is described below in conjunction with the accompanying drawings and specific implementation methods.

[0041] See also Figure 1 The optical fiber sensor based on SMS spliced ​​tapered resonant ring 3 in the embodiment of the present application includes: a first single-mode optical fiber 1 connected to a supercontinuum spectrum source, the output end of the first single-mode optical fiber 1 is connected to a first seven-core optical fiber 2, the output end of the first seven-core optical fiber 2 is connected to a resonant ring 3, the resonant ring 3 is sleeved on a low-refractive index UV glue channel 4, the output end of the resonant ring 3 is connected to a second seven-core optical fiber 5, the output end of the second seven-core optical fiber 5 is connected to a second single-mode optical fiber 6, and the output end of the second single-mode optical fiber 6 is connected to a spectrometer.

[0042] In this embodiment, the seven-core optical fiber model is FIBERCORE SM-7C1500 (6.1 / 125), the single-mode optical fiber model is corning(R) single-mode Optical Fiber, the UV glue is Jane low-refractive index UV glue (PC363), the supercontinuum light source is YSL, SC-5, spectrum range 450-2400nm, and the spectrometer is Yokogawa, AQ6370D, spectral range 600-1700nm.

[0043] The first tapered region 7 is between the first seven-core optical fiber 2 and the resonant ring 3, and the second tapered region 8 is between the second seven-core optical fiber 5 and the resonant ring 3. The first tapered region 7 and the second tapered region 8 are formed by tapering the seven-core optical fiber. The first seven-core optical fiber 2, the first tapered region 7, the resonant ring 3, the second tapered region 8 and the second seven-core optical fiber 5 are integrated, and the resonant ring 3 is formed by tapering the seven-core optical fiber and then recycling it.

[0044] The resonant ring 3 formed by the seven-core optical fiber after tapering is a micro-nano optical fiber resonant ring 3. The micro-nano optical fiber has an evanescent field. Part of the light in the micro-nano optical fiber resonant ring 3 propagates along the core, and part of the light is exposed to the core and interferes with each other.

[0045] Assuming that the propagation constant of the light wave in the resonant ring 3 is β, the formula for the interference of light in the micro-nano optical fiber resonant ring 3 is:

[0046]

[0047] where Δφ is the phase difference, n eff,SM and n eff,C are the effective refractive indices of single-mode fiber and seven-core fiber respectively, λ is the wavelength of light, m ​​is an integer, and L is the coupling length of the tapered part of the seven-core fiber.

[0048] The resonance condition of the sensor is very sensitive to the refractive index and temperature. A change in the refractive index will cause a change in the effective refractive index, which will change the phase difference Δφ. Temperature changes will affect the refractive index of the optical fiber and the wavelength of the light wave, which will in turn affect the resonance condition.

[0049] Sensitivity analysis: By measuring the change in resonant wavelength, the change in refractive index and temperature can be calculated. The sensitivity formula is as follows:

[0050]

[0051]

[0052] Among them, S n and S T are the sensitivities of refractive index and temperature, respectively, Δλ is the change of resonance wavelength, and Δn and ΔT are the changes of refractive index and temperature, respectively.

[0053] Corresponding to the SMS-spliced ​​tapered resonant ring optical fiber sensor provided in the above embodiment, the present application also provides a method for preparing the SMS-spliced ​​tapered resonant ring optical fiber sensor.

[0054] See also Figure 2 The preparation method of the SMS spliced ​​tapered resonant ring optical fiber sensor in this embodiment includes:

[0055] S1, make UV glue channel by using acrylic rod, plastic tube and UV glue.

[0056] To make a UV glue channel, prepare the following materials. Pass the acrylic rod through the plastic tube, leaving a small space for dripping low-refractive index UV glue. The diameter of the acrylic rod is 1mm. Drip the UV glue into the plastic tube. After dripping the UV glue, it will wrap around the acrylic rod along the plastic tube and irradiate with ultraviolet light for more than 20 minutes. The function of the light-shielding box is to form a dark room, so that the curing effect will be improved. Then, after natural curing for 4 hours, the friction between the plastic tube and the UV glue can peel off the UV glue to form a UV glue channel. The diameter of the UV glue channel is about 1mm.

[0057] S2, sequentially splicing the first single-mode optical fiber, the seven-core optical fiber, and the second single-mode optical fiber.

[0058] Two single-mode optical fibers are spliced ​​into a seven-core optical fiber. The length of the seven-core optical fiber is 2cm, and the length of the single-mode optical fiber is arbitrary.

[0059] S3, placing the seven-core optical fiber in a taper drawing machine for taper drawing, and after the taper drawing is completed, recovering it to automatically form a micro-nano optical fiber resonant ring.

[0060] Set the parameters of the taper machine, hydrogen flow rate 170SCCM, stretching speed 50μm / sec, inching speed 35μm / sec, motor advance delay 3s. Turn on the hydrogen ignition to taper, the taper length of the seven-core optical fiber is 25000μm, and the diameter reaches 2μm. Adjust the initial distance of the taper machine, the recovery length is 8000μm, and it will automatically form a loop after recovery.

[0061] S4, fix the UV glue channel with an auxiliary device, and then pass the UV glue channel through the micro-nano optical fiber resonant ring.

[0062] S5, tightening the micro-nano optical fiber resonant ring step by step by adjusting the parameters, and finally observing through a microscope that the resonant ring is completely tightened on the channel, and encapsulating the micro-nano optical fiber resonant ring.

[0063] The resonant ring is tightened step by step by adjusting the parameters. At the beginning, the tightening length is 1000μm each time. Through microscope observation, the tightening length is 100μm when it is about to be tightened. Finally, through microscope observation, the resonant ring is completely tightened on the channel. Then, low-refractive index UV glue is dripped on it, and it is cured with UV lamp for 5-10 minutes to be encapsulated.

[0064] S6, after the micro-nano optical fiber resonant ring is encapsulated, UV glue is dripped on the un-tapered part of the seven-core optical fiber, and the seven-core optical fiber is fixed on the glass slide by UV light for curing.

[0065] S7, connect one end of the manufactured optical fiber sensor to the supercontinuum light source through a jumper and the other end to the spectrometer for testing.

[0066] See also Figure 3When testing the optical fiber sensor, the optical fiber sensor is placed in NH4Cl (ammonium chloride) solutions of different concentrations and tested multiple times to obtain the influence of different NH4Cl solutions on the wavelength of light.

[0067] like Figure 4 As shown in the figure, as the concentration of NH4Cl solution increases, the wavelength shows a red shift phenomenon, that is, the wavelength becomes longer. Figure 4 The data points and fitting curve in the figure show the correlation between wavelength and NH4Cl concentration. The relationship between wavelength and concentration can be approximately regarded as linear, and the equation of the fitting curve is y=52.85714x+1.21429x, where y represents the change in wavelength (which may be a wavelength shift or refractive index change expressed in some units), x represents the concentration percentage of NH4Cl solution, and k value represents the sensitivity, reaching 52.85714nm / %. 2 =0.98032 indicates that the linear fit is very good. 2 The closer the (coefficient of determination) is to 1, the better the prediction effect of the model.

[0068] Of course, in addition to the influence of chemical solutions, temperature changes can also cause wavelength blue shift. Figure 5 As shown, as the temperature decreases, the wavelength becomes shorter, that is, the blue shift phenomenon occurs. This means that the wavelength of light moves toward a shorter wavelength as the temperature decreases. The data points in the figure show the wavelength measurements at different temperatures. The fitting curve is drawn based on the data points to predict the change in wavelength at different temperatures. The equation of the curve is y=-0.45486x+1221.66476, where y represents the wavelength, x represents the temperature (degrees Celsius), and the k value represents the sensitivity, which reaches 454.68pm / %. This equation shows that there is a linear relationship between wavelength and temperature, and the wavelength decreases as the temperature decreases. R 2 =0.98075 indicates that the fitting degree of the fitting curve is very high, R 2 (coefficient of determination) is close to 1, indicating that the model can predict the relationship between wavelength and temperature well. Figure 5 The wavelength values ​​at different temperatures are also marked. For example, the wavelength is 1208nm at -35.0℃, and 1200nm at -40.5℃, showing the specific values ​​of wavelength changes with temperature.

[0069] In the embodiments of the present application, "at least one" refers to one or more, and "plurality" refers to two or more. "And / or" describes the association relationship of associated objects, indicating that three relationships may exist. For example, A and / or B can represent the existence of A alone, the existence of A and B at the same time, and the existence of B alone. Among them, A and B can be singular or plural. The character " / " generally indicates that the previous and subsequent associated objects are in an "or" relationship. "At least one of the following" and similar expressions refer to any combination of these items, including any combination of single or plural items. For example, at least one of a, b and c can be represented by: a, b, c, ab, ac, bc, or abc, where a, b, c can be single or multiple.

[0070] The above is only a specific implementation of the present application. Any person skilled in the art can easily think of changes or substitutions within the technical scope disclosed in the present application, which should be included in the protection scope of the present application. The protection scope of the present application should be based on the protection scope of the claims.

Claims

1. An SMS spliced ​​tapered resonant ring optical fiber sensor, characterized in that: include: A first single-mode optical fiber connected to a supercontinuum source, the output end of the first single-mode optical fiber is connected to a first seven-core optical fiber, the output end of the first seven-core optical fiber is connected to a resonant ring, the resonant ring is sleeved on a low-refractive index UV glue channel, the output end of the resonant ring is connected to a second seven-core optical fiber, the output end of the second seven-core optical fiber is connected to a second single-mode optical fiber, and the output end of the second single-mode optical fiber is connected to a spectrometer; A first cone region is formed between the first seven-core optical fiber and the resonant ring, and a second cone region is formed between the second seven-core optical fiber and the resonant ring. The first cone region and the second cone region are formed by tapering the seven-core optical fiber.

2. The SMS spliced ​​tapered resonant ring optical fiber sensor according to claim 1 is characterized in that: The first seven-core optical fiber, the first tapered region, the resonant ring, the second tapered region and the second seven-core optical fiber are integrated as a whole, and the resonant ring is formed by recycling the tapered seven-core optical fiber.

3. The SMS spliced ​​tapered resonant ring optical fiber sensor according to claim 1 or 2, characterized in that: The resonant ring formed by the seven-core optical fiber after tapering is a micro-nano optical fiber resonant ring. The micro-nano optical fiber has an evanescent field. Part of the light in the micro-nano optical fiber resonant ring propagates along the core, and part of the light is exposed to the core and interferes with each other.

4. The SMS spliced ​​tapered resonant ring optical fiber sensor according to claim 3 is characterized in that: The formula for light interference in the micro-nano optical fiber resonant ring is: where Δφ is the phase difference, n eff,SM and n eff,C are the effective refractive indices of single-mode fiber and seven-core fiber respectively, λ is the wavelength of light, m ​​is an integer, and L is the coupling length of the tapered part of the seven-core fiber.

5. A method for preparing the SMS spliced ​​tapered resonant ring optical fiber sensor according to any one of claims 1 to 4, characterized in that: include: S1, make a UV glue channel through acrylic rods, plastic tubes and UV glue; S2, sequentially splicing the first single-mode optical fiber, the seven-core optical fiber, and the second single-mode optical fiber; S3, placing the seven-core optical fiber in a taper drawing machine for taper drawing, and after the taper drawing is completed, recovering the optical fiber to automatically form a micro-nano optical fiber resonant ring; S4, fixing the UV glue channel with an auxiliary device, and then passing the UV glue channel through the micro-nano optical fiber resonant ring; S5, tightening the micro-nano optical fiber resonant ring step by step by adjusting the parameters, and finally observing through a microscope that the resonant ring is completely tightened on the channel, and encapsulating the micro-nano optical fiber resonant ring; S6, after the micro-nano optical fiber resonant ring is encapsulated, UV glue is dripped on the un-tapered part of the seven-core optical fiber, and the seven-core optical fiber is fixed on the glass slide by UV light for curing; S7, connect one end of the manufactured optical fiber sensor to the supercontinuum light source through a jumper and the other end to the spectrometer for testing.

6. The method according to claim 5, characterized in that The method of making a UV glue channel by using an acrylic rod, a plastic tube and UV glue includes: Use an acrylic rod to pass through the plastic tube, leaving a small space for dripping low-refractive index UV glue, where: the diameter of the acrylic rod is 1mm; Drip the UV glue into the plastic tube, and then wrap it around the acrylic rod along the plastic tube; Irradiate with ultraviolet light for more than 20 minutes, and then naturally cure for 4 hours. The friction between the plastic tube and the UV glue can peel off the UV glue to form a UV glue channel with a diameter of about 1mm.

7. The method according to claim 5, characterized in that The seven-core optical fiber is placed in a taper drawing machine for taper drawing, and after the taper drawing is completed, it is recovered to automatically form a micro-nano optical fiber resonant ring, including: Set the parameters of the taper machine: hydrogen flow rate 170 SCCM, stretching speed 50 μm / sec, inching speed 35 μm / sec, motor advance delay 3s; Turn on the hydrogen ignition to taper the seven-core optical fiber. The taper length is 25000μm and the diameter reaches 2μm. Adjust the initial distance of the taper machine, the recovery length is 8000μm, and it will automatically form a ring after recovery.

8. The method according to claim 5, characterized in that The method of tightening the micro-nano optical fiber resonant ring step by step by adjusting the parameters, and finally observing through a microscope that the resonant ring is completely tightened on the channel, and packaging the micro-nano optical fiber resonant ring, comprises: At the beginning, the tightening length was 1000 μm each time. Through microscopic observation, the tightening length was 100 μm when it was about to be tightened. Finally, observe through a microscope that the resonant ring is completely tightened on the channel, then drop low-refractive index UV glue on it, cure it with a UV lamp for 5-10 minutes, and then encapsulate it.

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