An ultra-high-precision fiber FPI sensor based on a cavity optomechanical effect and a preparation method thereof

Abstract

This invention discloses an ultra-high precision fiber optic FPI sensor based on cavity optomechanical effect, comprising a transmission fiber, an optical microcavity, and a sensitive thin film connected in sequence. The sensitive thin film has a two-dimensional photonic crystal structure formed by a periodic arrangement of multiple nanopores, and the photonic bandgap of the two-dimensional photonic crystal structure covers the operating wavelength of the ultra-high precision fiber optic FPI sensor. This ultra-high precision fiber optic FPI sensor effectively reduces the Young's modulus of the sensitive thin film while improving its reflectivity. This invention also discloses a method for fabricating the above-mentioned ultra-high precision fiber optic FPI sensor.

Description

Technical Field

[0001] This invention relates to the field of fiber optic FPI sensing, and in particular to an ultra-high precision fiber optic FPI sensor based on cavity optomechanical effect and its fabrication method. Background Technology

[0002] The fiber optic FPI sensor is a fiber optic sensor that operates based on the Fabry-Perot interferometry principle. It consists of a transmission fiber, an optical microcavity, and a sensitive thin film connected sequentially. One end face of the transmission fiber and the sensitive thin film form two parallel reflecting surfaces of the optical microcavity. When a light beam is incident on the optical microcavity, the incident beam undergoes multiple reflections between the two reflecting surfaces. The reflected beams interfere with each other, forming an interference light signal. This interference light signal carries the vibration information of the sensitive thin film. When the measured physical quantity (such as temperature, pressure, strain, refractive index, displacement, sound wave, acceleration, etc.) acts on the sensitive thin film, it causes stress changes, deformation, or energy dissipation, thereby altering the resonant frequency of the sensitive thin film. By demodulating the frequency response curve of the interference light signal, the frequency change of the sensitive thin film can be obtained, and the magnitude of the measured physical quantity can be calculated.

[0003] The reflectivity of the sensitive film directly affects the interference contrast and the fineness of the interference spectrum of the fiber optic FPI sensor. As the fineness of the interference spectrum increases, the light intensity response sensitivity of the fiber optic FPI sensor improves, the minimum measurement threshold decreases, and the overall sensitivity increases.

[0004] To improve the reflectivity of the sensitive film, existing technologies typically deposit a metal film on its surface. However, the metal film increases the effective thickness and Young's modulus of the sensitive film. Under the same measured physical quantity, the frequency change of the sensitive film decreases, which in turn reduces the sensitivity of the fiber optic FPI sensor and increases its minimum measurement threshold. Summary of the Invention

[0005] To address the shortcomings of the prior art, this invention provides an ultra-high precision fiber optic FPI sensor based on cavity optomechanical effect, which effectively reduces the Young's modulus of the sensitive film while improving the reflectivity of the sensitive film.

[0006] The present invention also provides a method for fabricating the above-mentioned ultra-high precision fiber optic FPI sensor.

[0007] The technical problem to be solved by the present invention is achieved through the following technical solution:

[0008] An ultra-high precision fiber optic FPI sensor based on cavity optomechanical effect includes a transmission fiber, an optical microcavity, and a sensitive thin film connected in sequence. The sensitive thin film has a two-dimensional photonic crystal structure formed by a periodic arrangement of multiple nanopores. The photonic bandgap of the two-dimensional photonic crystal structure covers the operating wavelength of the ultra-high precision fiber optic FPI sensor.

[0009] Furthermore, the duty cycle of the two-dimensional photonic crystal structure is 30% to 50%.

[0010] Furthermore, the transmission optical fiber has a chirped fiber grating on one end near the optical microcavity. The reflection wavelength of the chirped fiber grating covers the operating wavelength of the ultra-high precision fiber optic FPI sensor, and the end face of this end coincides with the last grating of the chirped fiber grating.

[0011] Furthermore, the chirped fiber grating is also used to sense ambient temperature, thereby using a temperature compensation algorithm to compensate for the frequency drift of the sensitive thin film caused by ambient temperature.

[0012] Furthermore, the ultra-high precision fiber optic FPI sensor also includes a vacuum-sealed tube, one end of which is open and the other end is closed; the vacuum-sealed tube is sleeved outside the optical microcavity and the sensitive film, and its open end is sealed to the transmission optical fiber.

[0013] Furthermore, the two-dimensional photonic crystal structure adopts a square lattice or a hexagonal lattice.

[0014] A method for fabricating an ultra-high precision fiber optic FPI sensor based on cavity optomechanical effect, used to fabricate the aforementioned ultra-high precision fiber optic FPI sensor; the fabrication method includes the following steps:

[0015] Step 100: Initially determine the required operating wavelength, and perform simulation calculations on the optical parameters of the two-dimensional photonic crystal structure through simulation experiments;

[0016] Step 200: Fabricate the ultra-high precision fiber optic FPI sensor based on the optical parameters of the two-dimensional photonic crystal structure;

[0017] Step 300: Test the actual fabricated ultra-high precision fiber optic FPI sensor to determine its actual operating wavelength based on its reflection spectrum.

[0018] Furthermore, the optical parameters of the two-dimensional photonic crystal structure include the arrangement period and single-pore area of ​​each nanopore, and the arrangement period 'a' of each nanopore satisfies the following formula:

[0019]

[0020] n eff =n m *(1-f)+n0*f

[0021] If the two-dimensional photonic crystal structure adopts a square lattice, then the single pore area S of each nanopore satisfies the following formula:

[0022] S = f * a 2

[0023] If the two-dimensional photonic crystal structure adopts a regular hexagonal lattice, then the single pore area S of each nanopore satisfies the following formula:

[0024]

[0025] Where, n eff n is the effective refractive index of the two-dimensional photonic crystal structure, n0 is the refractive index of the medium within the nanopore, and n m λ is the refractive index of the sensitive thin film material, λ0 is the initially determined operating wavelength, and f is the duty cycle of the two-dimensional photonic crystal structure.

[0026] Furthermore, if the transmission optical fiber is also provided with the chirped fiber grating to improve the end face reflectivity of the transmission optical fiber, then in step 100, the optical parameters of the chirped fiber grating are simulated and calculated through simulation experiments, and in step 200, the ultra-high precision fiber optic FPI sensor is fabricated based on the optical parameters of the chirped fiber grating.

[0027] Furthermore, the steps for simulating and calculating the optical parameters of the chirped fiber grating through simulation experiments are as follows:

[0028] First, determine the required fineness of the interference spectrum, and then calculate the required reflectivity of the chirped fiber grating;

[0029] Next, using the required operating wavelength as the center wavelength of the chirped fiber grating, and combining it with the required reflectivity of the chirped fiber grating, other optical parameters of the chirped fiber grating are obtained through simulation experiments.

[0030] The present invention has the following beneficial effects: The ultra-high precision fiber optic FPI sensor of the present invention creates multiple periodically arranged nanopores on the sensitive film, so that the medium inside the pores and the thin film medium are periodically and alternately distributed in a two-dimensional direction on the sensitive film, thereby forming a two-dimensional photonic crystal structure with periodically changing refractive index. When the photonic bandgap of the two-dimensional photonic crystal structure covers the operating wavelength of the ultra-high precision fiber optic FPI sensor, the two-dimensional photonic crystal structure can strongly reflect the probe light using the operating wavelength, which greatly improves the reflectivity of the sensitive film. At the same time, due to the presence of the nanopores, the Young's modulus of the sensitive film is also reduced, which can generate a large frequency change under the action of a small measured physical quantity, thereby improving the sensitivity of the ultra-high precision fiber optic FPI sensor and reducing the minimum measurement threshold of the ultra-high precision fiber optic FPI sensor. Attached Figure Description

[0031] Figure 1 This is a schematic diagram of the structure of the ultra-high precision fiber optic FPI sensor provided by the present invention.

[0032] Figure 2 This is a schematic diagram of the two-dimensional photonic crystal structure in the ultra-high precision fiber optic FPI sensor provided by the present invention.

[0033] Figure 3 This is a schematic diagram of the two-dimensional photonic crystal structure in another ultra-high precision fiber optic FPI sensor provided by the present invention.

[0034] Figure 4 This is a schematic diagram of another ultra-high precision fiber optic FPI sensor provided by the present invention.

[0035] Figure 5 This is a schematic diagram of the demodulation optical path of the ultra-high precision fiber optic FPI sensor provided by the present invention.

[0036] Figure 6 A schematic diagram illustrating the steps of the fabrication method for the ultra-high precision fiber optic FPI sensor provided by this invention. Detailed Implementation

[0037] The present invention will now be described in detail with reference to the accompanying drawings and embodiments, examples of which are shown in the drawings, wherein the same or similar reference numerals denote the same or similar elements or elements having the same or similar functions throughout. The embodiments described below with reference to the accompanying drawings are exemplary and intended to explain the present invention, and should not be construed as limiting the present invention.

[0038] In the description of this invention, it should be understood that the terms "length", "width", "upper", "lower", "front", "rear", "left", "right", "vertical", "horizontal", "top", "bottom", "inner", "outer", etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. They are only for the convenience of describing this invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limitations on this invention.

[0039] Furthermore, the terms "first," "second," and "third" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of technical features indicated. Thus, a feature defined as "first," "second," or "third" may explicitly or implicitly include one or more of that feature. In the description of this invention, "multiple" means two or more, unless otherwise explicitly specified.

[0040] In this invention, unless otherwise explicitly specified and limited, the terms "installation," "connection," "linking," "fixing," and "setting," etc., should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral part; they can refer to a mechanical connection or an electrical connection; they can refer to a direct connection or an indirect connection through an intermediate medium; and they can refer to the internal communication of two components or the interaction between two components. Those skilled in the art can understand the specific meaning of the above terms in this invention according to the specific circumstances.

[0041] Example 1

[0042] like Figure 1 As shown, an ultra-high precision fiber optic FPI sensor based on cavity optomechanical effect includes a transmission fiber 1, an optical microcavity 22 and a sensitive film 3 connected in sequence. The sensitive film 3 has a two-dimensional photonic crystal structure 30 formed by a periodic arrangement of multiple nanopores 301. The photonic bandgap of the two-dimensional photonic crystal structure 30 covers the operating wavelength of the ultra-high precision fiber optic FPI sensor.

[0043] The two-dimensional photonic crystal structure 30 refers to a periodic structure formed by the regular arrangement of at least two optical media in a two-dimensional direction in a planar space. This periodic structure will have a "modulation effect" on the propagation of the light beam, so that when the light beam propagates in the two-dimensional photonic crystal structure 30, its wave behavior will be constrained by the periodic potential field (periodic change of refractive index), thereby generating a "photonic bandgap (PBG)", that is, the light beam in a specific wavelength range cannot propagate forward and is reflected, while the light beam in other wavelength ranges can continue to propagate forward.

[0044] The ultra-high precision fiber optic FPI sensor of the present invention creates multiple periodically arranged nanopores 301 on the sensitive thin film 3, so that the medium inside the pores and the thin film medium are periodically alternating in a two-dimensional direction on the sensitive thin film 3, thereby forming a two-dimensional photonic crystal structure 30 with periodically changing refractive index. When the photonic bandgap of the two-dimensional photonic crystal structure 30 covers the operating wavelength of the ultra-high precision fiber optic FPI sensor, the two-dimensional photonic crystal structure 30 can strongly reflect the probe light using the operating wavelength, which greatly improves the reflectivity of the sensitive thin film 3. At the same time, due to the presence of the nanopores 301, the Young's modulus of the sensitive thin film 3 is also reduced, which can generate a large frequency change under the action of a small measured physical quantity, thereby improving the sensitivity of the ultra-high precision fiber optic FPI sensor and reducing the minimum measurement threshold of the ultra-high precision fiber optic FPI sensor.

[0045] The operating wavelength refers to the light wavelength that, when incident on the ultra-high precision fiber optic FPI sensor, can effectively generate a stable interference signal and achieve the sensing function. It is usually consistent with the wavelength of the probe light used to achieve the sensing.

[0046] During measurement, modulated excitation light and probe light are coupled together into the ultra-high precision fiber optic FPI sensor. The excitation light and probe light have different wavelengths, and the frequency range of the modulated excitation light covers the resonant frequency of the sensitive film 3 within the range of influence of the measured physical quantity. The wavelength of the probe light is consistent with the operating wavelength of the ultra-high precision fiber optic FPI sensor. After the modulated excitation light reaches the sensitive film 3, it drives the sensitive film 3 to generate forced vibration. The probe light wavelength is usually selected as the wavelength value at -3dB of the reflection spectrum of the ultra-high precision fiber optic FPI sensor. The light beam undergoes a first reflection when it passes through the transmission optical fiber 1 and approaches the end face of the optical microcavity 22, and a second reflection when it reaches the sensitive film 3. The two reflected beams interfere with each other to form an interference light signal. When the sensitive film 3 is not subjected to the measured physical quantity, it can generate different resonant responses under the drive of excitation light at different frequencies. At this time, by demodulating the intensity of the interference light signal, the corresponding frequency response curve can be plotted to obtain the resonant frequency of the sensitive film 3 at the initial position. When the sensitive film 3 is subjected to the measured physical quantity, the resonant frequency of the sensitive film 3 in the frequency response curve drifts. The larger the measured physical quantity, the greater the frequency change of the sensitive film 3, and the greater the frequency drift in the frequency response curve. Therefore, the magnitude of the measured physical quantity acting on the sensitive film 3 can be calculated based on the relationship curve or mathematical model between the frequency drift and the measured physical quantity.

[0047] Preferably, the wavelength of the excitation light is also within the photonic bandgap of the two-dimensional photonic crystal structure 30, so that the two-dimensional photonic crystal structure 30 also strongly reflects the excitation light.

[0048] In this embodiment, as Figure 2 and 3 As shown, the two-dimensional photonic crystal structure 30 can adopt a square lattice or a regular hexagonal lattice, that is, the two-dimensional photonic crystal structure 30 can be equally divided into multiple square regions or hexagonal regions connected sequentially along the two-dimensional direction, and each nanopore 301 is located at the center of the corresponding square region or hexagonal region; the nanopore 301 can be, but is not limited to, a circular hole, a square hole, or a regular hexagonal hole, etc.

[0049] Preferably, the duty cycle of the two-dimensional photonic crystal structure 30 is 30% to 50% to ensure the contrast of the periodic refractive index distribution and enhance the bandgap effect.

[0050] The duty cycle refers to the area ratio of all nanopores 301 within the two-dimensional photonic crystal structure 30.

[0051] The sensing optical fiber 1 includes an optical fiber core 11 and an optical fiber cladding 12, with the optical fiber cladding 12 surrounding the outer peripheral sidewall of the optical fiber core 11; the two-dimensional photonic crystal structure 30 is aligned with the optical fiber core 11, so that the probe light propagating in the optical fiber core 11 can reach the two-dimensional photonic crystal structure 30 in the largest possible amount.

[0052] The optical microcavity 22 can be directly etched on one end face of the transmission optical fiber 1, and the fiber cladding 12 of the transmission optical fiber 1 serves as the cavity wall 21 of the optical microcavity 22; the peripheral region of the sensitive film 3 is attached to the fiber cladding 12 of the transmission optical fiber 1 with the optical microcavity 22 on one end face.

[0053] In this embodiment, the ultra-high precision fiber optic FPI sensor further includes a straight tube device 2. One end face of the transmission fiber 1 is connected to one end of the straight tube device 2, and the sensitive film 3 is disposed on the other end of the straight tube device 2. The cavity inside the straight tube device 2 forms the optical microcavity 22. The straight tube device 2 may be, but is not limited to, a hollow glass tube, a quartz capillary, a hollow optical fiber, or a ceramic tube.

[0054] The specific material of the sensitive film 31 depends on the physical quantity being measured. It can be a graphene film or a quartz film that is sensitive to temperature, pressure and strain. The graphene film is also sensitive to humidity, electric field and gas molecule concentration, while the quartz film is also sensitive to environmental refractive index. It can also be a target metal film that is sensitive to hydrogen, a magnetic film that is sensitive to magnetic field, or a biofilm that is sensitive to specific biomolecules, etc.

[0055] The graphene film, target metal film, and magnetic film can be attached to the cavity wall 21 of the optical microcavity 22 by wet transfer. The quartz film can be attached to the cavity wall 21 of the optical microcavity 22 by bonding or welding. The biofilm can be attached to the cavity wall 21 of the optical microcavity 22 by electrophoresis. Then, the sensitive film 3 is processed and etched with a focused ion beam to form the two-dimensional photonic crystal structure 30.

[0056] The precision of the interference spectrum of the ultra-high precision fiber optic FPI sensor is related not only to the reflectivity of the sensitive thin film 3, but also to the reflectivity of the end face of the transmission fiber 1.

[0057] Therefore, the preferred option is, such as Figure 4 As shown, the transmission optical fiber 1 has a chirped fiber grating 10 on one end near the optical microcavity 22. The reflection wavelength of the chirped fiber grating 10 covers the operating wavelength of the ultra-high precision fiber optic FPI sensor, and the end face of this end coincides with the last grating of the chirped fiber grating 10.

[0058] The ultra-high precision fiber optic FPI sensor of the present invention uses a chirped fiber grating 10 fabricated in the end of the transmission fiber 1 near the optical microcavity 22. The chirped fiber grating 10 replaces the end face of that end face to reflect the probe light, which is equivalent to increasing the reflectivity of that end face, thereby further improving the precision of the interference spectrum.

[0059] Compared to traditional Bragg fiber gratings, the chirped fiber grating 10 has a wider reflection peak width, making it easier to match the reflectivity of the sensitive thin film 3, thereby forming an optical microcavity 22 with ultra-high precision. The ultra-high precision fiber optic FPI sensor exhibits high precision in its interference spectrum. R1 and R2 are the reflectivities of the chirped fiber grating 10 and the sensitive thin film 3, respectively.

[0060] In addition, since most materials have the property of thermal expansion and contraction, the ambient temperature will also cause the frequency of the sensitive film 3 to change, thereby causing measurement interference to the measured physical quantity other than temperature.

[0061] Therefore, the preferred option is, such as Figure 4 As shown, the ultra-high precision fiber optic FPI sensor also includes a vacuum-sealed tube 4, one end of which is an open end and the other end is a closed end; the vacuum-sealed tube 4 is sleeved outside the optical microcavity 22 and the sensitive film 3, and its open end is sealed to the transmission optical fiber 1.

[0062] The vacuum-sealed tube 4 allows the optical microcavity 22 and the sensitive film 3 to be placed in a vacuum environment. This high vacuum environment specifically reduces the interference of ambient temperature's heat conduction and convection on the sensitive film 3, decreases the frequency of heat transfer through molecular collisions, and eliminates the conditions for heat transport by macroscopic fluid flow. This makes it difficult for these two strong heat transfer paths to continuously affect the sensitive film 3, significantly weakening the influence of ambient temperature on the measurement of the sensitive film 3. Simultaneously, the high vacuum seal can improve the Q value (quality factor) of the sensitive film 3, thereby increasing sensor sensitivity and lowering the detection limit.

[0063] In addition, the chirped fiber grating 10 is also used to sense temperature, thereby using a temperature compensation algorithm to compensate for the frequency drift caused by ambient temperature, so as to reduce the impact of ambient temperature on measurement accuracy.

[0064] like Figure 5As shown, the demodulation optical path of the ultra-high precision fiber optic FPI sensor of the present invention includes an excitation light source 51, a probe light source 52, a broadband light source 53, an electro-optic modulator 54, a first coupler 55, a second coupler 56, a circulator 57, a beam splitter 58, a first bandpass filter 59, a second bandpass filter 510, a photodetector 511, a spectrum analyzer 512, a spectrometer 513, an arbitrary waveform generator 514, and a host computer 515. The excitation light source 51 is connected to the first input terminal of the first coupler 55 through the electro-optic modulator 54. The probe light source 52 is connected to the second input terminal of the first coupler 55. The output terminal of the first coupler 55 is connected to the first input terminal of the second coupler 56. The broadband light source 53 is connected to the... The second input terminal of the second coupler 56 and the output terminal of the second coupler 56 are connected to the first port of the circulator 57. The transmission fiber 1 of the ultra-high precision fiber optic FPI sensor is connected to the second port of the circulator 57. The third port of the circulator 57 is connected to the input terminal of the beam splitter 58. The first output terminal of the beam splitter 58 is connected to the input terminal of the spectrum analyzer 512 in sequence through the first bandpass filter 59 and the photodetector 511. The second output terminal of the beam splitter 58 is connected to the input terminal of the spectrometer 513 through the second bandpass filter 510. The host computer 515 is connected to control the spectrum analyzer 512 and the spectrometer 513. The arbitrary waveform generator 514 is connected to control the electro-optic modulator 54.

[0065] The working principle is as follows: The electro-optic modulator 54 generates a frequency comb or sweep signal (generally, the frequency comb acts directly, while the sweep signal acts frequency by frequency, resulting in faster detection speed), to modulate the excitation light emitted by the excitation light source 51 under the control of the arbitrary waveform generator 514; the probe light emitted by the probe light source 52 is mixed with the excitation light in the first coupler 55 to output a first mixed light with a mixing ratio of 10:90; the broadband light emitted by the broadband light source 53 is mixed with the first mixed light in the second coupler 56 to output a second mixed light with a mixing ratio of... The ratio is also 10:90; the second mixed light enters the transmission fiber 1 of the ultra-high precision fiber optic FPI sensor through the circulator 57, wherein the excitation light in the second mixed light, after reaching the optical microcavity 22, acts on the sensitive film 3 through optical force or photothermal effect, thereby driving the sensitive film 3 to generate forced vibration; the detection light in the second mixed light generates a first reflection when passing through the chirped fiber grating 10, and a second reflection when reaching the sensitive film 3; the broadband light in the second mixed light is reflected when passing through the chirped fiber grating 10; All reflected light is output through the circulator 57 to the beam splitter 58 for beam splitting processing, with a splitting ratio of 50:50. One beam passes through the first bandpass filter 59, where the broadband and excitation light are filtered out, providing only the probe light to the photodetector 511 for acquisition. The spectrum analyzer 512 then demodulates the light intensity data output by the photodetector 511 to obtain the frequency response curve of the interference light signal. The other beam passes through the second bandpass filter 510, where the excitation and probe light are filtered out, providing only the broadband light to the spectrometer 513. The system collects data to obtain the reflection spectrum of the chirped fiber grating 10. The host computer 515 first calculates the ambient temperature sensed by the chirped fiber grating 10 based on the wavelength drift of the broadband light collected by the spectrometer 513, and then calculates the total frequency change of the sensitive film 3 based on the resonant frequency drift of the interference light signal collected by the spectrum analyzer 512. Next, it compensates for the total frequency change of the sensitive film 3 based on the ambient temperature, thereby obtaining the frequency change component caused by the physical quantity to be measured in the total frequency change. Finally, it calculates the physical quantity to be measured based on the frequency change component.

[0066] Example 2

[0067] like Figure 6 As shown, a method for fabricating an ultra-high precision fiber optic FPI sensor based on cavity optomechanical effect is provided for fabricating the ultra-high precision fiber optic FPI sensor described in Example 1; the fabrication method includes the following steps:

[0068] Step 100: Initially determine the required operating wavelength, and perform simulation calculations on the optical parameters of the two-dimensional photonic crystal structure through simulation experiments.

[0069] In step 100, the required operating wavelength refers to the wavelength corresponding to the selected probe light. In this embodiment, the probe light wavelength is 1550nm, which is suitable for long-distance sensing. Depending on the transmission distance, other wavelengths of probe light can also be selected, such as probe light with a wavelength of 1310nm, which is suitable for medium-distance sensing, or probe light with wavelengths of 850nm / 890nm, which is suitable for short-distance sensing.

[0070] The optical parameters of the two-dimensional photonic crystal structure include the arrangement period and single-pore area of ​​each nanopore, and the arrangement period 'a' of each nanopore satisfies the following formula:

[0071]

[0072] n eff =n m *(1-f)+n0*f

[0073] Where, n eff n is the effective refractive index of the two-dimensional photonic crystal structure, n0 is the refractive index of the medium within the nanopore, and n m λ is the refractive index of the sensitive thin film material, λ0 is the initially determined operating wavelength, and f is the duty cycle of the two-dimensional photonic crystal structure.

[0074] The arrangement period refers to the distance between the center positions of two adjacent nanopores 301.

[0075] If the two-dimensional photonic crystal structure adopts a square lattice, that is, the two-dimensional photonic crystal structure is divided into multiple square regions, and each square region has a nanopore, then the single pore area S of each nanopore satisfies the following formula:

[0076] S = f * a 2

[0077] If the two-dimensional photonic crystal structure adopts a regular hexagonal lattice, that is, the resonant region of the sensitive thin film is divided into multiple regular hexagonal regions, and each regular hexagonal region has a nanopore, then the single pore area S of each nanopore satisfies the following formula:

[0078]

[0079] Where f is the duty cycle of the two-dimensional photonic crystal structure, and a is the arrangement period of each nanopore.

[0080] Then, the optical parameters of the two-dimensional photonic crystal structure were optimized through simulation experiments. The simulation software mainly performed RCWA (rigid coupled-wave analysis) and FDTD (finite-difference time-domain method). The duty cycle f and the arrangement period a of each nanopore were adjusted through simulation experiments to ensure that the reflectivity of the two-dimensional photonic crystal structure and the interference contrast of the ultra-high precision fiber optic FPI sensor both reached ideal values.

[0081] Step 200: Fabricate the ultra-high precision fiber optic FPI sensor based on the optical parameters of the two-dimensional photonic crystal structure.

[0082] Step 300: Test the actual fabricated ultra-high precision fiber optic FPI sensor to determine its actual operating wavelength based on its reflection spectrum.

[0083] In step 300, the actual operating wavelength of the ultra-high precision fiber optic FPI sensor is compared with the required operating wavelength to determine whether the error value between the two is within the allowable error range. If it exceeds the allowable error range, the ultra-high precision fiber optic FPI sensor actually manufactured is determined to be a defective product and needs to be remanufactured. If it is within the allowable error range, the ultra-high precision fiber optic FPI sensor actually manufactured is determined to be a qualified product.

[0084] Preferably, if the transmission optical fiber is further provided with the chirped fiber grating to improve the end face reflectivity of the transmission optical fiber, then in step 100, the optical parameters of the chirped fiber grating are also simulated and calculated through simulation experiments.

[0085] Specifically, first determine the required fineness of the interferometric spectrum, and then apply the formula for fineness of the interferometric spectrum. The required reflectivity R1 of the chirped fiber grating is calculated, while the reflectivity R2 of the sensitive film is determined in the above calculation and simulation process. Then, the required operating wavelength λ0 is used as the center wavelength of the chirped fiber grating. Combined with the required reflectivity R1 of the chirped fiber grating, other optical parameters of the chirped fiber grating (such as refractive index modulation depth, grating length, average grating period, chirp coefficient, initial period, and termination period) are obtained through simulation experiments.

[0086] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the embodiments of the present invention and not to limit them. Although the embodiments of the present invention have been described in detail with reference to preferred embodiments, those skilled in the art should understand that modifications or equivalent substitutions can still be made to the technical solutions of the embodiments of the present invention, and these modifications or equivalent substitutions cannot cause the modified technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A method for preparing an ultra-high-fineness optical fiber FPI sensor based on a cavity optomechanical effect, characterized in that, The ultra-high precision fiber optic FPI sensor includes a transmission fiber, an optical microcavity, and a sensitive thin film connected in sequence. A two-dimensional photonic crystal structure, formed by a periodic arrangement of multiple nanopores, is formed on the sensitive thin film. Each nanopore causes the medium within the pore and the thin film medium to be periodically alternating in a two-dimensional direction on the sensitive thin film, thereby causing a periodic change in the refractive index of the two-dimensional photonic crystal structure, resulting in a photonic bandgap. The photonic bandgap of the two-dimensional photonic crystal structure covers the operating wavelength of the ultra-high precision fiber optic FPI sensor. The preparation method includes the following steps: Step 100: Initially determine the required operating wavelength, and perform simulation calculations on the optical parameters of the two-dimensional photonic crystal structure through simulation experiments; Step 200: Fabricate the ultra-high precision fiber optic FPI sensor based on the optical parameters of the two-dimensional photonic crystal structure; Step 300: Test the actual fabricated ultra-high precision fiber optic FPI sensor to determine its actual operating wavelength based on its reflection spectrum.

2. The production method according to claim 1, characterized by, The duty cycle of the two-dimensional photonic crystal structure is 30% to 50%.

3. The preparation method according to claim 1, characterized in that, The transmission optical fiber has a chirped fiber grating on one end near the optical microcavity. The reflected wavelength of the chirped fiber grating covers the operating wavelength of the ultra-high precision fiber optic FPI sensor, and the end face of this end coincides with the last grating of the chirped fiber grating.

4. The production method according to claim 3, characterized by, The chirped fiber grating is also used to sense ambient temperature, thereby using a temperature compensation algorithm to compensate for the frequency drift of the sensitive thin film caused by ambient temperature.

5. The preparation method according to claim 1, characterized in that, The ultra-high precision fiber optic FPI sensor also includes a vacuum-sealed tube, one end of which is open and the other end is closed. The vacuum-sealed tube is sleeved outside the optical microcavity and the sensitive film, and its open end is sealed to the transmission optical fiber.

6. The method of claim 1, wherein, The two-dimensional photonic crystal structure adopts a square lattice or a hexagonal lattice.

7. The preparation method according to claim 1, characterized in that, The optical parameters of the two-dimensional photonic crystal structure include the arrangement period of each nanopore and the area of ​​a single pore. Satisfy the following formula: If the two-dimensional photonic crystal structure adopts a square lattice, then the single pore area S of each nanopore satisfies the following formula: If the two-dimensional photonic crystal structure adopts a regular hexagonal lattice, then the single pore area S of each nanopore satisfies the following formula: in, The effective refractive index of the two-dimensional photonic crystal structure is... The refractive index of the medium within the nanopore is given. The refractive index of the sensitive thin film is given. To initially determine the required operating wavelength, is the duty cycle of the two-dimensional photonic crystal structure.

8. The preparation method according to claim 1, characterized in that, If a chirped fiber grating is provided inside the transmission fiber to improve the end face reflectivity of the transmission fiber, then in step 100, the optical parameters of the chirped fiber grating are simulated and calculated through simulation experiments. In step 200, the ultra-high precision fiber optic FPI sensor is fabricated based on the optical parameters of the chirped fiber grating.

9. The preparation method according to claim 8, characterized in that, The steps for simulating and calculating the optical parameters of the chirped fiber grating through simulation experiments are as follows: First, determine the required fineness of the interference spectrum, and then calculate the required reflectivity of the chirped fiber grating; Next, using the required operating wavelength as the center wavelength of the chirped fiber grating, and combining it with the required reflectivity of the chirped fiber grating, other optical parameters of the chirped fiber grating are obtained through simulation experiments.

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