Optical fiber sensing type nanometer level instrument

Abstract

The application provides a fiber sensing type nanometer level meter, which comprises, in sequence along the direction of light beam transmission, a broadband light source, a fiber coupler, a fiber sensing probe, a spectrometer and a demodulation module, the fiber coupler being connected with the broadband light source, the fiber sensing probe and the spectrometer; the fiber sensing probe comprises a sealed box, a plurality of single-mode optical fibers and a liquid, the liquid being located in the sealed box, a plurality of through holes being arranged on the upper surface of the sealed box, the single-mode optical fibers corresponding to the through holes one by one, the light input end of the single-mode optical fiber penetrating through the through hole, the light output end being located in the sealed box and outputting light to free space, the liquid surface of the liquid being used for reflecting the optical signal, the light output end, the liquid surface of the liquid and air forming an FP optical interference cavity, when the optical signal is transmitted to the light input end surface, part of the light is reflected, and the other part of the light is transmitted to the liquid surface of the liquid and is reflected again, the two beams of reflected light meet in space and generate interference spectrum. The application can realize detection of the size and position of two-dimensional horizontal inclination.

Description

Technical Field

[0001] This invention relates to the field of fiber optic sensing, and more particularly to a fiber optic sensing nanoscale level. Background Technology

[0002] A level is a precision measuring instrument used to determine horizontal baselines and check levelness. It plays an important role in the leveling of precision instruments and equipment, leveling in building construction, and in instrumentation. Currently, the main types of levels on the market include bubble levels, electronic levels, and laser levels.

[0003] Bubble levels seal liquid and bubbles within a glass cavity. The change in gravity due to the tilted liquid surface causes the bubbles to move upwards, and the levelness is determined by reading the deviation of the bubble from the center of the scale. However, the human eye reading method is prone to random errors and has low measurement efficiency. To improve calibration accuracy, an article titled "Research on Bubble Level Reading Recognition Algorithm Based on Image Processing" was published in the 49th issue of Metrology and Testing Technology in 2022, proposing an algorithm for recognizing scale lines and bubbles based on image processing. However, limited by the reading and measurement principles of bubbles and scale lines, this method still struggles to meet the requirements of high-precision level testing applications. Furthermore, bubble levels are prone to leakage after prolonged use, further restricting the application of this method.

[0004] Electronic levels come in two types: inductive and capacitive. Their basic working principle involves tilting the instrument to move a pendulum, causing a change in the inductance or capacitance of an induction coil or electrode plate. This change is then converted into a corresponding change in voltage or current, thus detecting the levelness of the instrument. However, electronic levels are susceptible to external electromagnetic interference, limiting their application environment and detection accuracy.

[0005] Laser levels utilize a well-collimated laser beam as a horizontal reference line and employ photoelectric detection elements to verify levelness. For example, the Bosch GLL8-40E laser level has an accuracy of 0.1 mm / m and is commonly used for benchmark leveling in engineering and construction. However, for leveling precision equipment such as interferometric optical devices, millimeter-level accuracy is insufficient.

[0006] Currently, most measurement methods can only detect one-dimensional levelness, which brings great difficulties to related research and applications. Summary of the Invention

[0007] To address the shortcomings of existing technologies, this invention provides a fiber optic sensing nanoscale level that can detect the magnitude and position of two-dimensional horizontal tilt.

[0008] The present invention achieves the above-mentioned technical objectives through the following technical means.

[0009] A fiber optic sensing nanoscale level includes, in sequence along the beam transmission direction: a broadband light source, a fiber optic coupler, a fiber optic sensing probe, a spectrometer, and a demodulation module, wherein the fiber optic coupler connects the broadband light source, the fiber optic sensing probe, and the spectrometer.

[0010] The fiber optic sensing probe includes a sealed box, several single-mode optical fibers, and a liquid. The liquid is located inside the sealed box, and several through holes are provided on the upper surface of the sealed box. Each single-mode optical fiber corresponds to one of the through holes. The light-incident end of the single-mode optical fiber passes through the through holes, and the light-exiting end is located inside the sealed box, outputting light into free space. The surface of the liquid is used to reflect optical signals. The light-exiting end, the surface of the liquid, and the air form an FP optical interference cavity. When the optical signal is transmitted to the light-incident end, part of the light is reflected, and the other part of the light is transmitted to the surface of the liquid and reflected again. The two reflected beams meet in space and generate an interference spectrum.

[0011] Furthermore, several single-mode optical fibers form a first interference cavity group and a second interference cavity group. The first interference cavity group includes a first FP optical interference cavity and a second FP optical interference cavity, and the second interference cavity group includes a third FP optical interference cavity and a fourth FP optical interference cavity. The first interference cavity group and the second interference cavity group are orthogonally distributed.

[0012] Furthermore, the liquid is a liquid with reflectivity and fluidity.

[0013] Furthermore, the liquid is water or mercury.

[0014] Furthermore, the broadband light source has a center wavelength of 1550nm and is used to provide an optical signal for levelness detection.

[0015] Furthermore, the spectrometer has a wavelength range of 600–1700 nm and is used to detect reflectance spectral signals.

[0016] Furthermore, the demodulation module demodulates the acquired spectral signal to obtain the magnitude and position information of the tilt.

[0017] Furthermore, the distance between the light-emitting end of the single-mode optical fiber and the liquid surface is adjustable.

[0018] Furthermore, the interference spectral intensity I of the FP optical interference cavity is:

[0019]

[0020] Where I0 is the incident light intensity, R is the end face reflectivity, λ is the wavelength, and L is the length of the FP optical interference cavity.

[0021] Furthermore, the free spectral range (FSR) of the FP optical interferometer cavity is:

[0022]

[0023] n is the refractive index of the FP optical interferometer material.

[0024] The beneficial effects of this invention are:

[0025] This invention enables the detection of two-dimensional horizontal tilt magnitude and position by setting up orthogonally distributed interference cavities. This invention has advantages such as high integration and high measurement accuracy, solving the problems of low measurement accuracy, susceptibility to external electromagnetic interference, and limited measurement dimensions of current levels. Attached Figure Description

[0026] Figure 1 This is a schematic diagram of the structure of a fiber optic sensing nanoscale level according to an embodiment of the present invention.

[0027] Figure 2 This is a schematic diagram of the structure of the fiber optic sensing probe according to an embodiment of the present invention;

[0028] Figure 3 This is a top view of the fiber optic sensing probe according to an embodiment of the present invention;

[0029] Figure 4 This is the vernier spectral envelope generated by the level instrument in this embodiment of the invention;

[0030] Figure 5 This is a graph showing the drift of the vernier spectral envelope of the level as a function of levelness in an embodiment of the present invention.

[0031] Figure 6 This is a sensitivity diagram of the fiber optic level in the horizontal and vertical directions of an embodiment of the present invention.

[0032] Figure 7 This is a schematic diagram of vector superposition for detecting two-dimensional levelness using a fiber optic sensing nanoscale level instrument proposed in this invention.

[0033] Figure label:

[0034] 1. Broadband light source; 2. Fiber optic coupler; 3. Fiber optic sensing probe; 31. Sealed box; 32. Single-mode fiber; 33. Liquid; 34. First interference cavity group; 35. Second interference cavity group; 321. First FP optical interference cavity; 322. Second FP optical interference cavity; 323. Third FP optical interference cavity; 324. Fourth FP optical interference cavity; 4. Spectrometer; 5. Demodulation module. Detailed Implementation

[0035] To make the above-mentioned objects, features, and advantages of the present invention more apparent and understandable, specific embodiments of the present invention will be described in detail below with reference to the accompanying drawings. Many specific details are set forth in the following description to provide a thorough understanding of the present invention. However, the present invention can be practiced in many other ways different from those described herein, and those skilled in the art can make similar modifications without departing from the spirit of the invention. Therefore, the present invention is not limited to the specific embodiments disclosed below.

[0036] Please see Figures 1 to 3 According to an embodiment of the present invention, a fiber optic sensing nanoscale level includes, in sequence along the optical path transmission direction, a broadband light source 1, a fiber optic coupler 2, a fiber optic sensing probe 3, a spectrometer 4, and a demodulation module 5.

[0037] Specifically, the broadband light source 1 has a center wavelength of 1550 nm, providing an optical signal for levelness detection. The fiber optic coupler 2 has 2×4 ports, used to connect the broadband light source 1, the fiber optic detection probe 3, and the spectrometer 4. The demodulation module 5 is connected to the spectrometer 4. The spectrometer 4 has a wavelength range of 600–1700 nm and is used to detect the reflected spectral signal. The demodulation module 5 is used to demodulate the drift and direction of the vernier spectral envelope to obtain the magnitude and position information of the levelness in the x and y directions. The demodulated magnitude and position of the levelness in the x and y directions are then vector-superimposed to obtain the two-dimensional levelness measurement result.

[0038] Fiber optic sensor probe 3 is used to detect levelness. For example... Figure 2 As shown in Figure a, the fiber optic sensing probe 3 includes a sealed box 31, several single-mode optical fibers 32, and a liquid 33. The liquid 33 is located inside the sealed box 31 and is a liquid with reflectivity and fluidity, such as water or mercury. Several through holes are provided on the upper surface of the sealed box 31; in this embodiment, the number of through holes is four. Each single-mode optical fiber 32 corresponds to one of the through holes. The light-input end of the single-mode optical fiber 32 passes through the through hole, and the light-output end is located inside the sealed box 31, outputting light into free space. The surface of the liquid 33 is used to reflect the optical signal. The light-output end, the surface of the liquid 33, and the air form a Photonic Interference Cavity (FP). When the optical signal is transmitted to the input end face, part of the light is reflected to form a reflected beam, and another part of the light is transmitted to the surface of the liquid 33 and reflected again to form another reflected beam. The two reflected beams meet in space and generate an interference spectrum. The interference spectrum intensity I of the FP optical interference cavity is:

[0039]

[0040] Where I0 is the incident light intensity, R is the end face reflectivity, λ is the wavelength, and L is the length of the FP optical interference cavity.

[0041] The free spectral range (FSR) of the FP optical interferometer is:

[0042]

[0043] n is the refractive index of the FP optical interferometer material.

[0044] Single-mode fiber 32 forms a first interference cavity group 34 and a second interference cavity group 35. The first interference cavity group 34 includes a first FP optical interference cavity 321 and a second FP optical interference cavity 322, located in the horizontal x-direction. The second interference cavity group 35 includes a third FP optical interference cavity 323 and a fourth FP optical interference cavity 324, located in the vertical y-direction. Figure 3 As shown, the first interference cavity group 34 and the second interference cavity group 35 are orthogonally arranged in the x and y directions. The optical signal interference coupling produces a vernier effect, resulting in two sets of vernier spectral signals.

[0045] The free spectral ranges of the reflection spectra of the first FP optical interference cavity 321, the second FP optical interference cavity 322, the third FP optical interference cavity 323, and the fourth FP optical interference cavity 324 are close. The coupled interference generates two sets of vernier spectral signals, which are used for tilt sensing in the x and y directions, respectively.

[0046] Furthermore, the distance between the light-emitting end face of the single-mode fiber 32 and the liquid surface of the liquid 33 is adjusted using a microscope and a precision displacement stage. In this embodiment, the cavity lengths L of the first FP optical interference cavity 321, the second FP optical interference cavity 322, the third FP optical interference cavity 323 and the fourth FP optical interference cavity 324 are set to L1 = 240 μm, L2 = 300 μm, L3 = 400 μm and L4 = 460 μm, respectively, and are fixed to the upper surface of the sealing box 31 with UV adhesive.

[0047] The period of the vernier spectral envelope can be expressed as:

[0048]

[0049] Compared to a single FP optical interferometer, the spectral shift based on the vernier effect is effectively amplified.

[0050] The multiple is:

[0051]

[0052] Among them, FSR s FSR r This represents the free spectral range of the sensing and reference interferometer cavities in the two FP interferometer cavities, which directly affects the period and amplification factor of the vernier envelope signal.

[0053] When the liquid level of liquid 33 changes with the tilt of the tilt, the cavity lengths of the two FP optical interference cavities in the x or y direction increase one and decrease the other, further increasing the drift of the vernier spectral envelope and producing an enhanced vernier effect. For example... Figure 2As shown in b, taking the third FP optical interference cavity 323 and the fourth FP optical interference cavity 324 located in the vertical y direction as an example, the tilt of the liquid causes the cavity length of the two FP optical interference cavities to increase one and decrease the other.

[0054] Furthermore, environmental disturbances such as temperature have the same effect on the length of the FP optical interference cavity; they either increase or decrease simultaneously, resulting in a weakened vernier effect.

[0055] Taking the lengths of the two FP optical interference cavities (L3, L4) = (400 μm, 460 μm) and the horizontal tilt change of 1 μm as an example, the vernier spectral signal drift is calculated. Figure 4 'a' is a standard vernier. Two FP optical interference cavities are used, one as a sensing cavity and the other as a reference cavity, i.e., cavity lengths (L3, L4) = (399μm, 460μm) or (401μm, 460μm) or (400μm, 461μm) or (400μm, 459μm).

[0056] Furthermore, both FP interferometer cavities are used as sensing cavities. Figure 4 b is a positive enhancement vernier with cavity length (L3, L4) = (399 μm, 461 μm); Figure 4 c represents the reduction of the vernier, with cavity lengths (L3, L4) = (399 μm, 459 μm), corresponding to the effect of environmental disturbances such as temperature on the cavity length of the FP optical interference. Figure 4 d is a negative enhancement vernier, and the cavity length (L3,L4) = (401μm,459μm).

[0057] Depend on Figure 4 As shown in the spectral drift diagrams of the ordinary, enhanced, and weakened vernier signals, for the same change in FP optical interferometer cavity length, the enhanced vernier exhibits a larger spectral envelope drift than the ordinary vernier, while the weakened vernier shows almost no spectral envelope drift. Therefore, the fiber optic sensing nanoscale level according to an embodiment of the present invention demonstrates good environmental stability. Furthermore, by utilizing the drift directions of the spectral envelopes of the forward and reverse enhanced verniers, tilt measurements of levelness in different directions can be achieved.

[0058] like Figure 5 As shown, when the change in horizontal tilt causes the FP optical interference cavity length to change by 10 nm and 20 nm, the drift diagram of the vernier spectral envelope as a function of horizontal tilt is calculated according to formulas (1)-(4). It can be seen from the figure that as the horizontal tilt increases, the wavelength of the vernier envelope spectrum shifts significantly, indicating that the theoretical resolution of the fiber optic sensing nanoscale two-dimensional level proposed in this invention can reach 10 nm and 20 nm.

[0059] like Figure 6As shown, the lengths (L1, L2) of the first FP optical interference cavity 321 and the second FP optical interference cavity 322 in the first interference cavity group in the x-direction are (240μm, 300μm), and the lengths (L3, L4) of the third FP optical interference cavity 323 and the fourth FP optical interference cavity 324 in the second interference cavity group in the y-direction are (400μm, 460μm). When the lengths are changed by 0.5μm, 1.0μm, 1.5μm, and 2.0μm respectively, the corresponding vernier spectral envelope wavelength shift is calculated. Furthermore, the sensitivities in the horizontal and vertical directions are -0.04886 and -0.04771, respectively.

[0060] like Figure 7 As shown, the horizontality Δh in the x and y directions is obtained by independently demodulating two sets of orthogonally distributed vernier spectra. x and Δh y By superimposing vectors, the magnitude and position information of the levelness Δh on the two-dimensional plane can be obtained.

[0061] The above embodiments merely illustrate several implementation methods of the present invention, and their descriptions are relatively specific and detailed, but they should not be construed as limiting the scope of the present invention. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of the present invention, and these all fall within the protection scope of the present invention. Therefore, the protection scope of this patent should be determined by the appended claims.

Claims

1. A fiber optic sensing nanoscale level, characterized in that, The beam transmission direction includes, in sequence: a broadband light source (1), an optical fiber coupler (2), an optical fiber sensing probe (3), a spectrometer (4), and a demodulation module (5). The optical fiber coupler (2) connects the broadband light source (1), the optical fiber sensing probe (3), and the spectrometer (4). The fiber optic sensing probe (3) includes a sealed box (31), several single-mode optical fibers (32), and a liquid (33). The liquid (33) is located inside the sealed box (31). Several through holes are provided on the upper surface of the sealed box (31). Each single-mode optical fiber (32) corresponds to one of the through holes. The light-input end of the single-mode optical fiber (32) passes through the through hole, and the light-output end is located inside the sealed box (31), outputting light into free space. The surface of the liquid (33) is used to reflect optical signals. The light-output end, the surface of the liquid (33), and the air form an FP optical interference cavity. When the optical signal is transmitted to the light-input end face, a Part of the light is reflected, and the other part of the light is transmitted to the surface of the liquid (33) and reflected again. The two reflected beams meet in space and produce an interference spectrum. Several single-mode optical fibers (32) form a first interference cavity group (34) and a second interference cavity group (35). The first interference cavity group (34) includes a first FP optical interference cavity (321) and a second FP optical interference cavity (322). The second interference cavity group (35) includes a third FP optical interference cavity (323) and a fourth FP optical interference cavity (324). The first interference cavity group (34) and the second interference cavity group (35) are orthogonally distributed. Two FP optical interference cavities within the same interference cavity group... The free spectral ranges of the optical interference cavities are close, and the optical signal interference coupling generates a vernier spectral signal; when the level is tilted, the cavity lengths of the two FP optical interference cavities in the same interference cavity group increase one and decrease the other, resulting in an enhanced vernier effect; when the temperature and other environmental disturbances occur, the cavity lengths of the two FP optical interference cavities in the same interference cavity group increase or decrease simultaneously, resulting in a weakened vernier effect and achieving temperature self-compensation; the demodulation module (5) demodulates the collected vernier spectral signal, obtains the tilt amount in the x and y directions respectively, and obtains the magnitude and position information of the two-dimensional level after vector superposition.

2. The fiber optic sensing nanoscale level according to claim 1, characterized in that, The liquid (33) is a liquid with reflectivity and fluidity.

3. The fiber optic sensing nanoscale level according to claim 2, characterized in that, The liquid (33) is water or mercury.

4. The fiber optic sensing nanoscale level according to claim 1, characterized in that, The broadband light source (1) has a center wavelength of 1550 nm and is used to provide a light signal for level detection.

5. The fiber optic sensing nanoscale level according to claim 1, characterized in that, The wavelength range of the spectrometer (4) is 600~1700 nm, and it is used to detect reflectance spectral signals.

6. The fiber optic sensing nanoscale level according to claim 1, characterized in that, The demodulation module (5) demodulates the acquired spectral signal to obtain the magnitude and position information of the tilt.

7. The fiber optic sensing nanoscale level according to claim 1, characterized in that, The distance between the light-emitting end of the single-mode optical fiber and the surface of the liquid (33) is adjustable.

8. The fiber optic sensing nanoscale level according to claim 1, characterized in that, The interference spectral intensity I of the FP optical interference cavity is: (1) Where I0 is the incident light intensity, R is the end face reflectivity, λ is the wavelength, and L is the length of the FP optical interference cavity.

9. The fiber optic sensing nanoscale level according to claim 8, characterized in that, The free spectral range (FSR) of the FP optical interferometer cavity is: (2) n is the refractive index of the FP optical interferometer material.

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