A single optical fiber in-situ refractive index measurement device and its application

Abstract

The present invention provides a single-fiber in-situ refractive index measuring device and its application, which belongs to the photosensitive measurement technology, and includes a fiber optic branching system, which is respectively connected to a detection fiber, a light source fiber and a receiving fiber through optical path coupling; the light source fiber is provided with a light source at one end, which is used to transmit the light signal emitted by the light source to the fiber optic branching system; the detection fiber transmits the light signal from the fiber optic branching system to the surface of the sample to be measured through the fiber end face, and transmits the light signal reflected by the sample back to the fiber optic branching system; the receiving fiber is connected with a detector at one end, which is used to receive the reflected light signal from the fiber optic branching system, and transmit it to the detector for measurement and analysis. The device does not require complex optical elements and high-cost detectors, has low manufacturing costs, and simple assembly and debugging processes.

Description

Technical Field

[0001] The present application belongs to the technical field of light sensitivity measurement, and specifically relates to a single optical fiber in-situ refractive index measurement device and its application. Background Art

[0002] With the rapid development of science and technology, refractive index testing technology plays an important role in optics, materials science, communications and other fields, and is increasingly attracting people's attention. The following are the applications of refractive index testing technology in some fields:

[0003] i. Fiber optic communication: Fiber optic communication is one of the important applications of refractive index testing technology. By accurately measuring the refractive index of optical fiber, the transmission performance of optical fiber can be improved, achieving faster and longer-distance data transmission.

[0004] ii. New material research: In new material research, refractive index testing technology can be used to analyze the optical properties of materials, providing an important basis for optimizing material structure and improving material performance.

[0005] iii. Optical devices: Refractive index testing technology is crucial in the manufacturing process of optical devices; by testing the refractive index of optical components, the imaging quality of the optical system can be guaranteed and the performance of optical equipment can be improved.

[0006] iv. Biomedicine: In the biomedical field, refractive index testing technology can be used to detect the refractive index of biological tissues, thereby achieving non-destructive testing and diagnosis; in addition, refractive index testing technology is also widely used in drug delivery, cell culture and other fields.

[0007] v. Environmental monitoring: Refractive index testing technology also plays an important role in the field of environmental monitoring; by measuring the refractive index of the atmosphere and water bodies, we can understand the environmental conditions in real time and provide a scientific basis for environmental protection.

[0008] vi. Scientific research field: In the field of scientific research, refractive index testing technology is widely used in physics, chemistry, biology and other disciplines, providing an important means to reveal the laws of nature and explore unknown areas.

[0009] vii. Inspection and quarantine: Rapidly detect samples by correlating the refractive index with the purity, concentration, dispersion, thermo-optical coefficient and other parameters of the liquid.

[0010] Among them, in-situ, miniaturized probes are increasingly meeting the needs of the fields of chemistry, life sciences, and medicine.

[0011] At present, the refractive index measurement method usually relies on prisms and CCD detection systems. The principle is that when light enters from one medium into another medium, refraction, reflection and total reflection will occur. For example, when light passes through the surface of a prism and reaches the contact interface between the prism and the sample to be tested, different incident angles will cause part of the light to be refracted into the sample to be tested, while other light will be reflected back into the prism and eventually reach the CCD detector. As a result, light and dark areas will be formed on the CCD, and the ratio of these areas will change with the change of solution concentration; the CCD detector converts the optical signal into an electrical signal, and after data processing, the refractive index information of the material can be obtained.

[0012] For example, the invention patent CN101221284A discloses an optical path design of an automatic Abbe refractometer, including an LED light source group and a high-refractive-index refractive prism. Along the propagation direction of the light wave emitted by the LED light source group, the plane light wave sequentially passes through a condensing lens group, a trapezoidal high-refractive-index refractive prism with one waist perpendicular to the main optical axis of the condensing lens group, an imaging lens group with the main optical axis perpendicular to the other waist of the trapezoidal high-refractive-index refractive prism 5, and a linear array CCD receiving surface located at the focal plane of the imaging lens group. The optical elements in this method are complex, the assembly accuracy of the instrument is high, the debugging method is cumbersome and expensive.

[0013] For example, the invention patent CN113030021A liquid refractive index in-situ sensor uses a prism with a V-groove on the prism. The liquid to be tested must be placed in the V-groove. The FP cavity is set to receive the laser signal after being refracted by the liquid to be tested in the V-groove; a light intensity detection device is provided to detect the light intensity of the laser signal emitted by the FP cavity and send it to the controller, and the controller calculates the refractive index of the liquid to be tested based on the light intensity. And the invention patent CN118583819A, a high-precision measurement method of liquid refractive index based on optical self-collimation, which designs a liquid-loaded reflector with trapezoidal slope cavity structural characteristics. When measuring, the liquid to be tested needs to be placed in the cavity and integrated with the self-collimation angle measurement optical path structure. The deflection angle of the collimated light beam can be used to measure the change in the refractive index of the solution in the reflector cavity. These designs and detection principles cannot enable the device to achieve true in-situ and miniaturization, and the use scenarios are limited. Summary of the invention

[0014] In order to solve the above problems, the present invention proposes a single-fiber in-situ refractive index measurement device and its application. By measuring the intensity of reflected light at the end face of the optical fiber, the refractive index of the unknown substance is calculated using a linear fitting relationship. The device has a simple structure and avoids the use of complex optical components and high-cost detectors. It not only reduces manufacturing and maintenance costs, but also simplifies the assembly and debugging process, greatly improving the economy and operability of the equipment.

[0015] The specific scheme of the present invention is as follows:

[0016] A single optical fiber in-situ refractive index measurement device, characterized in that it includes an optical fiber branching system, which is respectively connected to a detection optical fiber, a light source optical fiber and a receiving optical fiber by optical path coupling; and is arranged as follows:

[0017] The light source optical fiber has a light source at one end thereof, which is used to transmit the optical signal emitted by the light source to the optical fiber branching system;

[0018] The detection optical fiber transmits the optical signal from the optical fiber branching system to the sample to be tested through its optical fiber end face, and transmits the reflected light signal of the sample to be tested back to the optical fiber branching system;

[0019] The receiving optical fiber has one end connected to a detector for receiving the reflected light signal of the sample from the optical fiber branching system 3 and transmitting it to the detector for measurement and analysis;

[0020] The above arrangement enables: the light source is transmitted through the light source optical fiber to the optical fiber branching system and then reaches the optical fiber end face of the detection optical fiber. When the optical fiber end face contacts the sample to be tested, end face reflection occurs. Based on the difference in refractive index between the sample to be tested and the optical fiber end face, different samples to be tested have different reflected light intensities. The reflected light of the sample to be tested is transmitted to the detector via the detection optical fiber, the optical fiber branching system and the receiving optical fiber for measurement.

[0021] Preferably, the optical fiber end face of the detection optical fiber is provided with an optical window piece for protecting the optical fiber body.

[0022] Preferably, the optical fiber branching system may be: an optical fiber beam splitter, an optical fiber splitter, a wavelength division multiplexer, an optical switch, an optical isolator or an optical fiber circulator.

[0023] Preferably, the detector may be a photodiode, an avalanche photodiode or a complementary metal oxide semiconductor sensor.

[0024] Preferably, the light source comprises one or more of the following components: LED, SLD, fiber coupled halogen lamp, xenon lamp and low power level laser.

[0025] The present invention also provides a method for measuring the refractive index of an unknown substance using any of the above-mentioned measuring devices, characterized in that it comprises the following steps:

[0026] Step 1: adjust the light source type and power of the device, the size of the end face of the detection fiber, and the sensitivity and sampling rate of the detector, and insert the detection fiber into the sample to be tested, and obtain the reflected light intensity of the contact surface between the optical window and the substance to be tested through the detector;

[0027] Step, according to the known refractive index of the standard substance, establish a curve fitting formula between the reflected light intensity and the refractive index, and determine the refractive fitting parameters;

[0028] The curve fitting formula is a polynomial fitting;

[0029] For example, in most embodiments, the standard substances can be water and 1-bromonaphthalene, wherein the refractive index of water is 1.33 and the refractive index of 1-bromonaphthalene is 1.6576;

[0030] Step 3: Substitute the reflected light intensity of the sample to be tested into the curve fitting formula in step 2 to calculate and obtain the refractive index of the sample to be tested.

[0031] The above method preferably further comprises: step 4, test result verification; measuring the refractive index of the standard substance, and comparing the measured value with its known refractive index;

[0032] When the two are the same, the measured refractive index value of the sample to be tested is output as the final result, and the device status is confirmed to be normal;

[0033] When the measured refractive index of the standard material is different from its known refractive index, return to step 1 to adjust the light source type, power, detection fiber end face size, and detector sensitivity and sampling rate; then go to step 2 to readjust the fitting curve and calculate the refractive index of the sample to be measured again;

[0034] The re-adjustment of the fitting curve refers to: re-selecting the fitting model, recalculating the fitting parameters, and adding refractive index data samples of known standard substances.

[0035] Another aspect of the present invention further provides a method for measuring the concentration of a substance using any of the above-mentioned measuring devices, characterized in that it comprises the following steps:

[0036] Step 1: Mix at least two known standard substances in different proportions to prepare at least two mixed samples with different concentrations, and record the actual concentration data of each substance in each sample;

[0037] Step 2: Adjust the light source type and power of the device, the size of the detection fiber end face, and the sensitivity and sampling rate of the detector;

[0038] Insert the detection optical fiber into the known standard substance and the mixed sample respectively, and measure and record the reflected light intensity between the contact surface of the optical window and these substances by the detector 7;

[0039] According to the known refractive index of the standard substance, a curve fitting formula between the reflected light intensity and the refractive index is established, and the refractive fitting parameters are determined. Then, the reflected light intensity of the mixed sample is substituted into the formula to calculate the refractive index of each sample.

[0040] For example, in most embodiments, the standard substances are water and 1-bromonaphthalene, wherein the refractive index of water is 1.33 and the refractive index of 1-bromonaphthalene is 1.6576;

[0041] Step 3: Based on the known concentration data and the corresponding refractive index of the sample, a curve fitting relationship between the concentration and the refractive index is established, and the concentration fitting parameters are calculated;

[0042] Step 4, measure the reflected light intensity of the sample of unknown concentration, and enter it into the fitting formula established in step 2 to calculate its refractive index;

[0043] Subsequently, the refractive index is substituted into the concentration curve fitting relationship established in step 3, and finally the actual concentration of each substance in the sample is obtained.

[0044] The method preferably further comprises testing result verification:

[0045] Compare the measured refractive index of the standard substance with its known refractive index;

[0046] When the two are the same, it can be confirmed that the device status is normal;

[0047] When the measured refractive index is different from the known refractive index, return to step 1 to adjust the light source type, power, detection fiber end face size, and detector sensitivity and sampling rate; then go to step 3 to readjust the fitting curve and calculate the refractive index of the sample to be measured again.

[0048] Another aspect of the present invention provides a method for measuring material properties using any of the above-mentioned measuring devices, characterized in that it includes: establishing a curve fitting formula between the material properties and refractive index of a known standard substance, and then substituting the refractive index of the sample to be measured into the formula to obtain the material properties of the sample to be measured;

[0049] The material properties include: purity, temperature, pressure, composition ratio, wavelength dispersion characteristics, crystallinity, impurity content, concentration, photothermal coefficient, phase change state and electromagnetic wave response characteristics.

[0050] In another aspect of the present invention, protection is sought for the application of any of the above-mentioned measuring devices in optical fiber communication research and development, new material research and development, optical device manufacturing, biological research, medical research, environmental monitoring, and inspection and quarantine.

[0051] The connection of the optical components in the present invention adopts the method of optical path coupling, that is, the optical signal is effectively transmitted from one optical fiber to another optical fiber through the optical component to achieve the distribution, merging or switching of the optical signal.

[0052] This application has at least the following technical effects:

[0053] The present invention establishes a simple and feasible method, which utilizes the phenomenon of end face reflection at the end face of the optical fiber (the contact surface between the optical fiber surface and the material) when the light in a single optical fiber passes through the end face of the optical fiber. Due to the difference in refractive index between the contact material and the end face of the optical fiber, different samples to be tested have specific different reflected light intensities. The reflected light of the sample to be tested is transmitted to the detector through the detection optical fiber, the optical fiber branching system and the receiving optical fiber for measurement. Based on the method of measuring the reflected light intensity, the present invention establishes the corresponding relationship between the reflected light intensity of the contact material and the refractive index, performs linear fitting, and calculates the refractive index of the unknown material with the fitting curve.

[0054] The present invention adopts the principle of single optical fiber combined with end face reflection measurement to avoid the use of complex optical elements (such as prisms, beam splitters, etc.) and high-cost detectors (such as CCD), so that the device has a simple structure, low cost, and is easy to manufacture and maintain.

[0055] The present invention adopts a single optical fiber design, and only detects the contact between the optical fiber end face and the sample to be measured. Therefore, the device is not only highly sensitive and portable, but also light and compact, and realizes probe and miniaturization, which is particularly suitable for measurement on site, in situ or in dynamic environment;

[0056] The application of the reflective measurement method means that the present invention does not require multi-fiber alignment or complex calibration, which simplifies the assembly and debugging process. It can achieve high-precision refractive index measurement in a variety of scenarios such as microfluidic environments, field detection, and medical diagnosis, significantly improving the practicality and adaptability of the equipment.

[0057] By using the above-mentioned measuring device, by combining the measurement of the intensity of the reflected light at the end face of the optical fiber with the linear fitting method, it not only supports fast and accurate refractive index detection, but also does not require complicated data processing or multi-parameter calibration, making the measurement process simpler and faster. Therefore, the present invention is particularly suitable for application scenarios that require real-time analysis and rapid detection, and significantly improves work efficiency.

[0058] In summary, the measuring device of the present invention not only reduces the manufacturing and maintenance costs, but also simplifies the assembly and debugging process, greatly improving the economy and operability of the equipment. It can be widely used in the fields of optical fiber communication research and development, new material research and development, optical device manufacturing, biological research, medical research, environmental monitoring, inspection and quarantine, etc. BRIEF DESCRIPTION OF THE DRAWINGS

[0059] Figure 1 It is a connection schematic diagram of the single optical fiber in-situ refractive index measurement device of the present application;

[0060] Among them: 1-optical window, 2-detection optical fiber, 3-optical fiber branching system, 4, light source optical fiber, 5-receiving optical fiber, 6-light source, 7-detector. DETAILED DESCRIPTION

[0061] In order to make the purpose, technical scheme and advantages of the implementation of the present application clearer, the technical scheme in the embodiment of the present application will be described in more detail below in conjunction with the drawings in the embodiment of the present application. In the drawings, the same or similar reference numerals throughout represent the same or similar elements or elements with the same or similar functions. The described embodiments are part of the embodiments of the present application, rather than all of the embodiments, and these embodiments are exemplary and are intended to be used to explain the present application, and cannot be understood as limiting the present application.

[0062] The following is combined with Figure 1 The single optical fiber in-situ refractive index measurement device of the present application is further described in detail.

[0063] The present application discloses a single optical fiber in-situ refractive index measuring device, comprising an optical fiber branching system 3, a detection optical fiber 2, a light source optical fiber 4, a receiving optical fiber 5, a light source 6 and a detector 7.

[0064] The optical fiber splitting system 3 is connected to the detection optical fiber 2, the light source optical fiber 4 and the receiving optical fiber 5 respectively through optical path coupling. Unless otherwise specified, the optical path coupling known in the present invention is the general meaning in this field, that is, the process of effectively transmitting the optical signal from one optical fiber to another optical fiber through optical components to achieve the distribution, merging or switching of the optical signal.

[0065] Furthermore, the optical components of the optical fiber branching system 3 can be flexibly selected according to needs, such as: optical fiber beam splitter (Coupler), optical fiber splitter (Splitter), wavelength division multiplexer (WDM, Wavelength Division Multiplexer), optical switch (Optical Switch), optical isolator (Optical Isolator), optical circulator (Optical Circulator).

[0066] One end of the light source optical fiber 4 is connected to the light source 6, and the optical signal emitted by the light source 6 is transmitted to the optical fiber branching system 3 through the light source optical fiber 4, and then transmitted to the detection optical fiber 2 through the optical fiber branching system 3. The detection optical fiber 2 transmits the light to the optical window 1; the optical window 1 contacts the sample to be tested, and transmits the reflected light of the contact surface to the optical fiber branching system 3 through the detection optical fiber 2; the optical fiber branching system 3 transmits the light to the detector 7 through the receiving optical fiber 5.

[0067] Furthermore, the light source 6 can select different types of light source components, including light emitting diodes (LEDs), super luminescent diodes (SLDs), halogen lamps with fiber coupling, xenon lamps (Xe Lamp) or low-power lasers (i.e., class 1, class 2, class 3R lasers) to meet requirements of different light intensities and wavelengths.

[0068] One end of the receiving optical fiber 5 is connected to the detector 7 for receiving the reflected light signal from the optical fiber branching system 3 .

[0069] The detector 7 measures and analyzes the received optical signal to determine the optical properties of the sample to be measured, such as the refractive index. In the measuring device of the present invention, the detector 7 can use different types of sensors, such as a photodiode (PD), an avalanche photodiode (APD), or a complementary metal oxide semiconductor (CMOS) sensor.

[0070] The detection optical fiber 2, the light source optical fiber 4 and the receiving optical fiber 5 can select different types of optical fibers according to the requirements. In the embodiment of the present invention, the above three preferably use polarization-maintaining optical fibers. In addition, the optical fiber end face of the detection optical fiber 2 can also be installed with an optical window 1 or coated, or no protective components can be set to ensure the safety of the optical fiber body and the effective transmission of the optical signal.

[0071] It is understandable that, on the basis of the existing structure, various housing devices such as tubular housing, box-shaped housing, waterproof housing, explosion-proof housing, heat-insulating housing, electromagnetic shielding housing, shockproof housing and portable housing, etc., should also be included in the protection scope of this application. Furthermore, these housings can provide functions such as physical protection, environmental isolation, electromagnetic shielding and portability according to different application scenarios and environmental requirements, thereby enhancing the durability, stability and applicability of the equipment.

[0072] Application Example 1. Using the measuring device provided by the present invention to measure the refractive index of an unknown substance

[0073] Step 1: Device setup and data collection

[0074] Before starting the measurement, the measuring device is set up and adjusted. According to the properties of the object to be measured, the appropriate type of light source 6 is selected, and its power output is adjusted to ensure stable light source intensity. At the same time, the fiber end face of the detection optical fiber 2 is processed, such as installing an optical window or performing a coating treatment, and adjusting the distance between the fiber end face and the surface of the sample to be measured to optimize the transmission and reflection effect of the optical signal.

[0075] For example, a test of a standard substance is provided to determine whether the device is set correctly (e.g., step 4 below), specifically, comparing the measured refractive index of the standard substance with its known refractive index;

[0076] When the two are the same, it means that the device parameters (light source, detection fiber end face, and distance range between the fiber end face and the sample to be measured) are appropriately selected; when the measured refractive index value is different from the known refractive index, adjust the light source type, power, detection fiber end face size, and detector sensitivity and sampling rate.

[0077] Then, configure the detector 7, select the appropriate type and adjust its sensitivity and sampling rate to ensure that it can accurately capture the changes in the reflected light signal. After completing the above settings, start the light source and guide the light beam to the surface of the sample to be tested or the known standard material through the optical fiber system. The detector 7 collects the light intensity data reflected back by the contact material and records the reflected light intensity value for subsequent analysis and calculation.

[0078] Please see the table below for details on the properties of the standard substances and the setting parameters of the device.

[0079] Setting reference table (example)

[0080]

[0081] Step 2: Establish a curve fitting relationship between reflected light intensity and refractive index

[0082] Based on the analysis of the experimental measurement data of water and 1-bromonaphthalene in the above table, and using the end face reflection phenomenon occurring at the end face of a single optical fiber (the contact surface between the optical fiber surface and the material) when light in the fiber passes through the end face, it is found that under this condition, the intensity of the reflected light and the refractive index show a good linear correlation.

[0083] After completing the data collection in step 1, a linear fitting formula between the reflected light intensity and the refractive index is established based on the collected reflected light intensity and corresponding refractive index data of the known standard substance.

[0084] Subsequently, the fitting formula is calculated using the least squares method to obtain the parameters of the refractive index linear fitting. Through these fitting parameters, a linear formula that can reflect the relationship between the reflected light intensity and the refractive index is formed, providing a basis for the subsequent calculation of the refractive index of unknown substances.

[0085] It is understandable that the user can also adopt other fitting methods, such as binary curve fitting (including binary linear fitting and binary polynomial fitting), by adding data samples of the refractive index of standard substances, and these methods should also be included in the above protection scope.

[0086] Step 3: Calculate the refractive index of the unknown substance

[0087] According to the refractive index fitting parameters obtained in step 2, substitute them into the corresponding fitting formula. Then, input the reflected light intensity data of the unknown substance into the formula to calculate the refractive index of the unknown substance. In order to improve the accuracy of the calculation results, multiple measurements or averaging of the results can be performed to reduce experimental errors. This belongs to conventional methods in the art.

[0088] Step 4: Test the refractive index of a known substance

[0089] The above device is used to measure and calculate the refractive index of a known standard substance, and the measured value is compared with its known refractive index; when the two are the same, the refractive index of the sample to be tested is output as the final result, and the device state is confirmed to be normal. For this embodiment, the experimenter can directly measure the refractive index of water and 1-bromonaphthalene and compare them with their known refractive index.

[0090] Step 4.1. Error correction

[0091] When the measured refractive index of the standard substance is different from its known value, return to step 1 to adjust the device and repeat step 2 to readjust the fitting curve;

[0092] The readjustment method includes: adding the refractive index data sample of the standard substance, reselecting the fitting model, and recalculating the fitting parameters. Then, executing step 3, bringing the new fitting parameters into the model for calculation. Finally, executing step 4, repeating the test process until the measured value of the standard substance is the same as its known refractive index.

[0093] Application Example 2. Measuring the concentration of a solution using the measuring device provided by the present invention

[0094] Step 1: Mix at least two known standard substances in different proportions to prepare at least two mixed samples with different concentrations, and record the actual concentration data of each substance in each sample.

[0095] In this experiment, water and 1-bromonaphthalene can be mixed to prepare mixed samples with 1-bromonaphthalene accounting for 10%, 30%, 50%, and 70%.

[0096] Step 2: After preparing the type and power of the light source 6 of the device, the end face size of the detection optical fiber 2, and determining the sensitivity and sampling rate of the detector 7, the detection optical fiber 2 is inserted into water and 1-bromonaphthalene respectively, and the detector 7 measures and records the reflected light intensity between the contact surface of the optical window 1 and the two media.

[0097] It is known that the refractive index of water is 1.33 and the refractive index of 1-bromonaphthalene is 1.6576. A curve fitting formula between the reflected light intensity and the refractive index is established, and the fitting parameters are determined.

[0098] Then, the detection optical fiber 2 is inserted into the mixed liquid sample to measure the intensity of its reflected light, and the data is substituted into the curve fitting formula to calculate the refractive index of each mixed sample.

[0099] Step 3: Based on the known sample concentration data and the corresponding refractive index, a curve fitting relationship between concentration and refractive index is established, and the concentration fitting parameters are calculated.

[0100] Step 4: Measure the reflected light intensity of the unknown concentration sample and calculate its refractive index using the fitting formula established in step 2. Substitute the calculated refractive index into the concentration curve fitting relationship established in step 3 to obtain the actual concentration data of each substance in the unknown concentration sample.

[0101] The above is only a specific implementation of the present application, and the protection scope of the present application is not limited thereto. For example, a method for deriving the material properties of a sample to be tested based on the fitting relationship between the refractive index of a known substance and material properties (such as purity, temperature, pressure, component ratio, wavelength dispersion properties, crystallinity, impurity content, concentration gradient, phase change state, and electromagnetic wave response properties, etc.) should also be included in the protection scope of the present application.

Claims

1. A method for measuring the refractive index of an unknown substance, characterized in that: The single optical fiber in-situ refractive index measurement device is used for measurement. The single-fiber in-situ refractive index measuring device comprises an optical fiber branching system, which is respectively connected to a detection optical fiber, a light source optical fiber and a receiving optical fiber through optical path coupling; and is configured as follows: The light source optical fiber has a light source at one end thereof, which is used to transmit the optical signal emitted by the light source to the optical fiber branching system; The detection optical fiber transmits the optical signal from the light source optical fiber from the optical fiber branching system to the sample to be tested through its optical fiber end face, and transmits the reflected light signal of the sample to be tested back to the optical fiber branching system; the end face of the detection optical fiber is provided with an optical window; The receiving optical fiber has one end connected to a detector for receiving the reflected light signal of the sample from the optical fiber branching system and transmitting it to the detector for measurement and analysis; The above arrangement enables: the light source is transmitted to the optical fiber branching system through the light source optical fiber and reaches the optical fiber end face of the detection optical fiber. When the optical fiber end face contacts the sample to be tested, end face reflection occurs. Based on the difference in refractive index between the sample to be tested and the optical fiber end face, different samples to be tested have different reflected light intensities. The reflected light of the sample to be tested is sequentially transmitted to the detector through the detection optical fiber, the optical fiber branching system and the receiving optical fiber for measurement. The following steps are involved: Step 1: insert the detection optical fiber into the known standard substance and the sample to be tested respectively, and measure and record the reflected light intensity between the contact surface of the optical window and these substances through the detector; Step 2: According to the known refractive index of the standard substance, a curve fitting formula between the reflected light intensity and the refractive index is established, and the fitting parameters are determined; Step 3: Substitute the reflected light intensity of the sample to be tested into the curve fitting formula in step 2 to calculate and obtain the refractive index of the sample to be tested.

2. The method according to claim 1, characterized in that Also includes: Step 4, test result verification: measure the refractive index of the standard substance and compare the measured value with its known refractive index; When the two are the same, the measured refractive index value of the sample to be tested is output as the final result, and the status of the device is confirmed to be normal; When the measured refractive index of the standard material is different from its known refractive index, return to step 1 to adjust the light source type, power, detection fiber end face size, and detector sensitivity and sampling rate; then go to step 2 to readjust the fitting curve and calculate the refractive index of the sample to be measured again; The re-adjustment of the fitting curve refers to: re-selecting the fitting model, recalculating the fitting parameters, and adding refractive index data samples of known standard substances.

3. A method for measuring the concentration of a substance, characterized in that: The single optical fiber in-situ refractive index measurement device is used for measurement. The single-fiber in-situ refractive index measuring device comprises an optical fiber branching system, which is respectively connected to a detection optical fiber, a light source optical fiber and a receiving optical fiber through optical path coupling; and is configured as follows: The light source optical fiber has a light source at one end thereof, which is used to transmit the optical signal emitted by the light source to the optical fiber branching system; The detection optical fiber transmits the optical signal from the light source optical fiber from the optical fiber branching system to the sample to be tested through its optical fiber end face, and transmits the reflected light signal of the sample to be tested back to the optical fiber branching system; the end face of the detection optical fiber is provided with an optical window; The receiving optical fiber has one end connected to a detector for receiving the reflected light signal of the sample from the optical fiber branching system and transmitting it to the detector for measurement and analysis; The above arrangement enables: the light source is transmitted to the optical fiber branching system through the light source optical fiber and reaches the optical fiber end face of the detection optical fiber. When the optical fiber end face contacts the sample to be tested, end face reflection occurs. Based on the difference in refractive index between the sample to be tested and the optical fiber end face, different samples to be tested have different reflected light intensities. The reflected light of the sample to be tested is sequentially transmitted to the detector through the detection optical fiber, the optical fiber branching system and the receiving optical fiber for measurement. The following steps are involved: Step 1: Mix at least two known standard substances in different proportions to prepare at least two mixed samples with different concentrations, and record the actual concentration data of each substance in each sample; Step 2, insert the detection optical fiber into the known standard substance and the mixed sample respectively, and measure and record the reflected light intensity of the contact surface between the optical window and these substances through the detector; According to the known refractive index of the standard substance, a curve fitting formula between the reflected light intensity and the refractive index is established, and the refractive fitting parameters are determined. Then, the reflected light intensity of the mixed sample is substituted into the formula to calculate the refractive index of each sample. Step 3: Based on the known concentration data and the corresponding refractive index of the sample, a curve fitting relationship between the concentration and the refractive index is established, and the concentration fitting parameters are calculated; Step 4: Measure the reflected light intensity of the sample of unknown concentration and substitute it into the fitting formula established in step 2 to calculate its refractive index. Substitute the refractive index into the concentration curve fitting relationship established in step 3 to finally obtain the actual concentration of each substance in the sample.

4. The method according to claim 3, characterized in that: Also includes: Verification of test results; comparison of the measured refractive index of the standard substance with its known refractive index; When the two are the same, confirm that the status of the device is normal; When the measured refractive index is different from the known refractive index, return to step 1 to adjust the light source type, power, detection fiber end face size, and detector sensitivity and sampling rate; then go to step 3 to readjust the fitting curve and calculate the refractive index of the sample to be measured again.

5. The method according to any one of claims 1 to 4, characterized in that: The optical window piece is: sapphire, diamond, optical fiber end face coating, optical fiber end face lens or optical fiber collimating lens.

6. The method according to any one of claims 1 to 4, characterized in that: The optical fiber branching system is an optical fiber beam splitter, an optical fiber splitter, a wavelength division multiplexer, an optical switch, an optical isolator or an optical fiber circulator.

7. The method according to any one of claims 1 to 4, characterized in that: The detector is a photodiode, an avalanche photodiode or a complementary metal oxide semiconductor sensor.

8. The method according to any one of claims 1 to 4, characterized in that: The light source is an LED, an SLD, a fiber-coupled halogen lamp, a xenon lamp or a low-power laser.

9. The method according to any one of claims 1 to 4, characterized in that: One or more of the detection optical fiber, the light source optical fiber and the receiving optical fiber are polarization-maintaining optical fibers.

10. A single optical fiber in-situ refractive index measurement device, characterized in that: It includes an optical fiber splitting system, which is connected to the detection optical fiber, the light source optical fiber and the receiving optical fiber respectively through optical path coupling; and is configured as follows: The light source optical fiber has a light source at one end thereof, which is used to transmit the optical signal emitted by the light source to the optical fiber branching system; The detection optical fiber transmits the optical signal from the light source optical fiber from the optical fiber branching system to the sample to be tested through its optical fiber end face, and transmits the reflected light signal of the sample to be tested back to the optical fiber branching system; the end face of the detection optical fiber is provided with an optical window; The receiving optical fiber has one end connected to a detector for receiving the reflected light signal of the sample from the optical fiber branching system and transmitting it to the detector for measurement and analysis; The above arrangement enables: the light source is transmitted through the light source optical fiber to the optical fiber branching system and then reaches the optical fiber end face of the detection optical fiber. When the optical fiber end face contacts the sample to be tested, end face reflection occurs. Based on the difference in refractive index between the sample to be tested and the optical fiber end face, different samples to be tested have different reflected light intensities. The reflected light of the sample to be tested is sequentially transmitted through the detection optical fiber, the optical fiber branching system and the receiving optical fiber to the detector for measurement.

11. The measuring device according to claim 10, characterized in that The optical window piece is: sapphire, diamond, optical fiber end face coating, optical fiber end face lens or optical fiber collimating lens.

12. The measuring device according to claim 10, characterized in that The optical fiber branching system is an optical fiber beam splitter, an optical fiber splitter, a wavelength division multiplexer, an optical switch, an optical isolator or an optical fiber circulator.

13. The measuring device according to claim 10, characterized in that The detector is a photodiode, an avalanche photodiode or a complementary metal oxide semiconductor sensor.

14. The measuring device according to claim 10, characterized in that The light source is an LED, an SLD, a fiber-coupled halogen lamp, a xenon lamp or a low-power laser.

15. The measuring device according to any one of claims 10 to 14, characterized in that: One or more of the detection optical fiber, the light source optical fiber and the receiving optical fiber is a flat-preserving optical fiber.

Images