A primary pressure metering system and optical pressure gauge

Abstract

The application provides a pressure primary metering system and an optical pressure gauge, and relates to the technical field of pressure gauges. The system comprises a vacuum sealed cavity, a laser output module, a double-channel resonant cavity and a processing module. The double-channel resonant cavity is located in the vacuum sealed cavity and comprises a vacuum reference resonant cavity and an open measurement resonant cavity formed based on the same substrate, so that the cavity deformation of the two can offset each other. The reference resonant cavity forms a first transmitted light signal based on a first laser beam, and the measurement resonant cavity forms a second transmitted light signal based on a second laser beam. The processing module comprises a frequency shift unit and a processing unit. The frequency shift unit shifts the frequency of the second laser beam before and after the vacuum sealed cavity is filled with gas, respectively, and transmits the second laser beam to the measurement resonant cavity. The processing unit obtains the frequency of the second laser beam based on the second transmitted light signal, and obtains the internal pressure of the vacuum sealed cavity based on the frequency difference between the first laser beam and the second laser beam, thereby avoiding the introduction of a complex frequency-locked optical path and an electronic feedback control system.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of pressure gauges, in particular to a pressure primary measurement system, a measurement method and a measurement device. BACKGROUND

[0002] Traditional gas pressure reference measurement methods mainly rely on mercury height gauges and static expansion methods, etc. However, such methods have obvious limitations. Mercury is highly toxic and is easily affected by mechanical vibration and chemical corrosion, resulting in insufficient long-term stability and reliability. With the development of the international system of units towards quantumization and natural constant traceability, optical interference methods have gradually become the mainstream technology for replacing traditional physical references. This method establishes a direct link between gas pressure and its microscopic properties, and has higher reproducibility and potential for promotion.

[0003] A gas refractive index pressure gauge based on the principle of optical interference is a high-performance pressure measurement technology. Its core principle is to correlate macroscopic gas pressure with microscopic polarizability of atoms or molecules. According to the gas state equation and the Lorentz-Lorenz formula, pressure measurement is converted into accurate measurement of gas refractive index. The refractive index is closely related to the longitudinal mode frequency of the optical resonant cavity, so accurate gas pressure values can be obtained by high-precision laser frequency measurement, which not only avoids the inherent defects of physical references, but also realizes high-precision traceability of pressure values.

[0004] The principle of an optical pressure gauge is to use a fixed-length resonant cavity to measure the refractive index of the working gas to obtain the gas density, and to obtain the gas pressure by combining the temperature value. The formula for measuring the optical pressure gauge can be expressed as:

[0005] ;

[0006] ;

[0007] where k B is the Boltzmann constant, N A is the Avogadro constant, p is the pressure, T is the temperature, n is the gas refractive index, A ε is the molar polarizability of the gas molecule, B T is the second virial coefficient, B ε is the second dielectric virial coefficient, B is the high-order small coefficient obtained based on the molar polarizability A ε of the gas molecule, the second virial coefficient B T , and the second dielectric virial coefficient B ε .

[0008] Based on the above, the pressure primary metrology technology mainly relies on the laser and optical resonant cavity system, and is established on the basic principle of light and gas interaction. At present, a gas refractive index pressure metrology standard device based on nitrogen has been successfully developed, and the measurement uncertainty reaches 8.8ppm and 23ppm respectively, which is comparable to the performance of the traditional measurement method.

[0009] However, the deformation of the resonant cavity body of the optical resonant cavity in the optical pressure gauge due to thermal expansion effect cannot be ignored for the measurement inaccuracy of the pressure primary metrology. Therefore, how to suppress the deformation of the resonant cavity body of the optical resonant cavity has become the research focus of the technical personnel in the field. SUMMARY

[0010] Therefore, the present application provides a pressure primary metrology system, method and device, and the scheme is as follows:

[0011] A pressure primary metrology system comprises a vacuum sealed cavity and a pressure metrology structure, wherein the pressure metrology structure comprises:

[0012] A double-channel resonant cavity is located in the vacuum sealed cavity and comprises a reference resonant cavity and a measurement resonant cavity formed on the same substrate, wherein the reference resonant cavity is a sealed vacuum resonant cavity, and the measurement resonant cavity is an open resonant cavity with an opening;

[0013] A laser output module outputs a first laser beam and a second laser beam, wherein the double-channel resonant cavity is located on the transmission path of the first laser beam and the second laser beam, the reference resonant cavity forms a first transmitted light signal based on the first laser beam coupled into the resonant cavity body, and the measurement resonant cavity forms a second transmitted light signal based on the second laser beam coupled into the resonant cavity body;

[0014] A processing module comprises a frequency shift unit and a processing unit, wherein the frequency shift unit respectively shifts the frequency of the second laser beam when the vacuum sealed cavity is in a vacuum state and after being filled with gas, and transmits the frequency-shifted second laser beam to the measurement resonant cavity; the processing unit is located on the transmission path of the first transmitted light signal and the second transmitted light signal, detects the second transmitted light signal when the vacuum sealed cavity is in a vacuum state and after being filled with gas, and obtains the frequency of the second laser beam based on the second transmitted light signal; and the processing unit also obtains the internal pressure of the vacuum sealed cavity based on the frequency difference between the first laser beam and the second laser beam.

[0015] The frequency difference comprises the frequency difference when the vacuum sealed cavity is in a vacuum state and the frequency difference after being filled with gas.

[0016] Optionally, the double-channel resonant cavity comprises the substrate, the substrate comprises a first region and a second region arranged along a first direction, the first region is formed with a first resonant cavity, the second region is formed with a second resonant cavity, the first resonant cavity and the second resonant cavity are arranged along the first direction; wherein the first resonant cavity is a through-hole type resonant cavity penetrating through the substrate along a second direction; the second resonant cavity penetrates through the substrate along the second direction, and the second resonant cavity comprises an opening extending along the second direction; the first direction and the second direction are parallel to the plane where the substrate is located, and the first direction and the second direction intersect.

[0017] The double-channel resonant cavity further comprises a first mirror and a second mirror, the reference resonant cavity comprises the first resonant cavity and the first mirror located on the opposite sides of the first resonant cavity along the second direction, and the measurement resonant cavity comprises the second resonant cavity and the second mirror located on the opposite sides of the second resonant cavity along the second direction.

[0018] Optionally, the material of the substrate is quartz glass or ULE glass.

[0019] Optionally, the frequency shift unit comprises a radio frequency source and an electro-optical modulator;

[0020] The radio frequency source provides a radio frequency signal, and the electro-optical modulator adjusts the frequency of the second laser beam under the control of the radio frequency signal, and transmits the frequency-shifted second laser beam to the measurement resonant cavity, and the frequency of the radio frequency signal is the frequency shift value of the second laser beam;

[0021] Wherein, the radio frequency source provides a series of radio frequency signals according to a preset step size, and the electro-optical modulator adjusts the frequency of the second laser beam according to the preset step size under the control of the series of radio frequency signals, generates a plurality of second laser beams with different frequencies, and transmits them to the measurement resonant cavity in turn.

[0022] Optionally, the processing unit comprises a photoelectric detector and a processor;

[0023] The photoelectric detector detects the second transmitted light signal, the processor obtains the frequency of the second laser beam based on the second transmitted light signal, and obtains the internal pressure of the vacuum sealed cavity based on the frequency difference between the first laser beam and the second laser beam; wherein the second transmitted light signal is formed based on the second laser beam with at least one frequency coupled into the measurement resonant cavity from the second laser beams with different frequencies, and the frequency of the second laser beam is the center frequency of the second transmitted light signal.

[0024] Optionally, the laser output module comprises a laser source and a split optical fiber;

[0025] The laser source outputs a laser beam, the laser beam is split into the first laser beam and the second laser beam through the beam splitting fiber, the first laser beam is transmitted to the reference cavity through the beam splitting fiber, and the second laser beam is transmitted to the frequency shift unit through the beam splitting fiber.

[0026] Before the second laser beam is frequency shifted through the frequency shift unit, the frequencies of the first laser beam and the second laser beam are the same.

[0027] Optionally, the laser is a near-infrared distributed feedback laser.

[0028] Optionally, the laser source is a narrow linewidth laser, and the linewidths of the first laser beam and the second laser beam are less than a preset value.

[0029] Optionally, the metrology system further comprises a constant temperature cavity.

[0030] The vacuum sealed cavity is placed in the constant temperature cavity together with the double-channel cavity.

[0031] An optical pressure gauge comprises the pressure primary metrology system.

[0032] Compared with the related art, the technical scheme has the following beneficial effects:

[0033] The system comprises a vacuum sealed cavity and a pressure metrology structure, and the pressure metrology structure comprises a laser output module, a double-channel cavity and a processing module. The double-channel cavity is located in the vacuum sealed cavity and comprises a vacuum reference cavity and an open measurement cavity formed on the basis of the same substrate. The reference cavity forms a first transmitted light signal based on a first laser beam, and the measurement cavity forms a second transmitted light signal based on a second laser beam. The processing module comprises a frequency shift unit and a processing unit. The frequency shift unit frequency shifts the second laser beam before and after the vacuum sealed cavity is inflated and transmits the second laser beam to the measurement cavity. The processing unit detects the second transmitted light signal, obtains the frequency of the second laser beam based on the second transmitted light signal, and obtains the internal pressure of the vacuum sealed cavity based on the frequency difference between the first laser beam and the second laser beam. Since the double-channel cavity 300 is formed on the basis of the same substrate, the cavity deformation is offset, the influence of thermal expansion on pressure measurement can be effectively suppressed, and it is not necessary to deliberately use ultra-low expansion glass (ULE) as the substrate material of the cavity and design a multi-layer temperature control structure, thereby greatly reducing the structural complexity and process preparation difficulty of the pressure primary metrology system. In addition, the processing unit can obtain the internal pressure of the vacuum sealed cavity based on the frequency difference between the first laser beam and the second laser beam before and after the vacuum sealed cavity is inflated, thereby avoiding the introduction of a complex frequency locking optical path and an electronic feedback control system, and the operation is simple and the reliability is high. BRIEF DESCRIPTION OF DRAWINGS

[0034] In order to more clearly illustrate the technical solutions in the embodiments of the present application or the related art, the accompanying drawings needed to be used in the embodiments or the prior art description will be briefly introduced. Obviously, the accompanying drawings in the following description are only part of the embodiments of the present application, and for those skilled in the art, other drawings can be obtained without creative labor on the basis of the provided drawings.

[0035] The structures, proportions, sizes, etc. shown in the drawings of the present specification are only used to cooperate with the content disclosed in the present specification, to be understood and read by those skilled in the art, and do not have technical significance, so any modification of the structure, change of the proportional relationship or adjustment of the size, without affecting the effects and purposes that can be achieved by the present application, should still fall within the scope of the technical content disclosed by the present application.

[0036] Figure 1 A structural schematic diagram of a pressure primary metering system provided by the present application is shown in the following figure:

[0037] Figure 2 A structural schematic diagram of a vacuum sealed cavity is shown in the following figure:

[0038] Figure 3 A structural schematic diagram of a double-channel resonant cavity is shown in the following figure:

[0039] Figure 4 A frequency drift comparison curve of the double-channel resonant cavity is shown in the following figure:

[0040] Figure 5 A structural schematic diagram of a constant temperature cavity is shown in the following figure:

[0041] Figure 6 A pressure measurement comparison diagram of an optical pressure gauge provided by the present application is shown in the following figure. DETAILED DESCRIPTION

[0042] The embodiments in the present application will be described clearly and completely in the following with reference to the drawings in the embodiments of the present application. Obviously, the described embodiments are only part of the embodiments of the present application, but not all the embodiments. Based on the embodiments in the present application, all other embodiments obtained by those skilled in the art without creative labor fall within the scope of the present application.

[0043] In order to make the above-mentioned purposes, features and advantages of the present application more obvious and easy to understand, the present application will be further described in detail with reference to the drawings and specific embodiments.

[0044] As described in the background section, optical pressure gauges rely on laser and optical resonant cavity systems, based on the fundamental principle of light-gas interaction. Accurate gas pressure values ​​can be obtained by inverting the measurement through high-precision laser frequency. However, the deformation of the optical resonant cavity significantly affects its frequency. Therefore, in optical pressure gauges, the deformation of the optical resonant cavity has a non-negligible impact on the accuracy of pressure measurement.

[0045] For example, current optical pressure gauges use ultra-low expansion glass (ULE) to minimize cavity deformation caused by temperature changes and incorporate a multi-layered active temperature control structure. However, this significantly increases manufacturing costs. Furthermore, to isolate external mechanical disturbances, the cavity is suspended, and it integrates complex optical path designs and electronic control modules, resulting in a large and heavy overall structure that is difficult to port or deploy in the field. Moreover, it is very expensive, hindering large-scale promotion and mass production applications.

[0046] Based on the above, this application provides a pressure primary stage metering system, which includes a vacuum-sealed cavity 100 and a pressure metering structure. For example... Figure 1 and Figure 2 As shown, Figure 1 This is a schematic diagram of the pressure metering structure in a pressure primary metering system provided in this application. Figure 2 This is a schematic diagram of the vacuum-sealed cavity 100. The pressure measurement structure includes a laser output module 200, a dual-channel resonant cavity 300, and a processing module 400. The dual-channel resonant cavity 300 is located within the vacuum-sealed cavity 100. The cavity base of the vacuum-sealed cavity 100 can be made of aluminum alloy; slots are cut on both sides to accommodate windows (to allow the laser beam to pass through), and these are sealed with zero-turn seals; the top is a stainless steel cover plate, with a welded vacuum connector and gas path connector. The cover plate and base are sealed with zero-turn seals; the cavity dimensions can be approximately 10cm × 10cm × 10cm. It should be noted that the aforementioned vacuum-sealed cavity 100 refers to a vacuum state before gas is filled, i.e., a vacuum state in a non-working state where pressure measurement is not being performed.

[0047] like Figure 3 As shown, Figure 3A structural schematic diagram of a double-channel resonant cavity 300 in a pressure primary standard measurement system provided by the present application is shown in FIG. 1. The double-channel resonant cavity 300 includes a reference resonant cavity 320 and a measurement resonant cavity 340. The reference resonant cavity 320 is a vacuum resonant cavity, and the measurement resonant cavity 340 is an open resonant cavity with an opening. That is, the reference resonant cavity 320 and the measurement resonant cavity 340 are both located inside the vacuum sealed cavity 100, but the reference resonant cavity 320 is a closed vacuum resonant cavity that is isolated from the internal environment of the vacuum sealed cavity 100. The resonant frequency (the longitudinal mode frequency) of the reference resonant cavity 320 is not affected by the internal environment of the vacuum sealed cavity 100, so the longitudinal mode frequency of the reference resonant cavity 320 can be used as a reference for measuring the frequency change of the measurement resonant cavity 340. That is, the longitudinal mode frequency of the reference resonant cavity 320 can be used as a frequency reference, and the frequency change of the measurement resonant cavity 340 before and after the vacuum sealed cavity 100 is filled with gas can be obtained based on the frequency change of the longitudinal mode frequency of the measurement resonant cavity 340 relative to the longitudinal mode frequency of the reference resonant cavity 320 before and after the vacuum sealed cavity 100 is filled with gas. The measurement resonant cavity 340 is in communication with the internal environment of the vacuum sealed cavity 100 through the opening, and the resonant frequency (the longitudinal mode frequency) of the measurement resonant cavity 340 is related to the gas pressure in the vacuum sealed cavity 100, so the internal pressure of the vacuum sealed cavity 100 can be obtained based on the frequency change of the measurement resonant cavity 340 before and after the vacuum sealed cavity 100 is filled with gas.

[0048] In particular, in the pressure primary standard measurement system provided by the present application, the resonant cavity bodies of the reference resonant cavity 320 and the measurement resonant cavity 340 in the double-channel resonant cavity 300 are formed on the same substrate, that is, the cavity body of the reference resonant cavity 320 and the cavity body of the measurement resonant cavity 340 are integrally formed based on the same substrate.

[0049] The laser output module 200 outputs a first laser beam and a second laser beam, and the double-channel resonant cavity 300 is located on the transmission path of the first laser beam and the second laser beam, that is, the laser output module 200 is located at the input end of the double-channel resonant cavity 300 and transmits the first laser beam and the second laser beam to the reference resonant cavity 320 and the measurement resonant cavity 340, respectively. The reference resonant cavity 320 forms a first transmitted light signal based on the first laser beam coupled into the resonant cavity body thereof, and the measurement resonant cavity 340 forms a second transmitted light signal based on the second laser beam coupled into the resonant cavity body thereof.

[0050] The processing module 400 comprises a frequency shift unit 420 and a processing unit 440. The frequency shift unit 420 is located between the laser output module 200 and the double-channel resonant cavity 300. When the vacuum sealed cavity 100 is in a vacuum state and after being filled with gas, the frequency shift unit 420 respectively shifts the frequency of the second laser beam and transmits the frequency-shifted second laser beam to the measurement resonant cavity 340. Specifically, before the vacuum sealed cavity 100 is filled with gas, i.e. when the vacuum sealed cavity 100 is in a vacuum state, the frequency shift unit 420 shifts the frequency of the second laser beam and transmits the frequency-shifted second laser beam to the measurement resonant cavity 340. After the vacuum sealed cavity 100 is filled with gas, the frequency shift unit 420 also shifts the frequency of the second laser beam and transmits the frequency-shifted second laser beam to the measurement resonant cavity 340.

[0051] The processing unit 440 is located on the transmission path of the first transmitted light signal and the second transmitted light signal, i.e. the processing unit 440 is located at the output end of the double-channel resonant cavity 300. When the vacuum sealed cavity 100 is in a vacuum state and after being filled with gas, i.e. before and after the vacuum sealed cavity 100 is filled with gas, the processing unit 440 respectively detects the second transmitted light signal and obtains the frequency of the second laser beam based on the second transmitted light signal. The processing unit 440 also obtains the internal pressure of the vacuum sealed cavity 100 based on the frequency difference between the first laser beam and the second laser beam. The frequency difference between the first laser beam and the second laser beam includes the frequency difference between the first laser beam and the second laser beam when the vacuum sealed cavity 100 is in a vacuum state, and the frequency difference between the first laser beam and the second laser beam after the vacuum sealed cavity 100 is filled with gas. It should be noted that the processing unit 440 can also obtain the internal pressure of the vacuum sealed cavity 100 based on the frequency difference between the first laser beam and the second laser beam and the internal absolute temperature data of the vacuum sealed cavity 100, depending on the specific situation.

[0052] It should be noted that since the reference resonant cavity 320 is a vacuum sealed resonant cavity, its resonant cavity body is isolated from the external environment, so the cavity mode of the reference resonant cavity 320 remains stable in frequency, i.e. the longitudinal mode frequency is fixed. Since the measurement resonant cavity 340 is an open resonant cavity and is in communication with the internal environment of the vacuum sealed cavity 100, the longitudinal mode frequency of the measurement resonant cavity 340 changes before and after the vacuum sealed cavity 100 is filled with gas, i.e. the longitudinal mode frequency of the measurement resonant cavity 340 is related to the internal pressure of the vacuum sealed cavity 100. Therefore, based on the frequency change of the measurement resonant cavity 340 in the double-channel resonant cavity 300 relative to the reference resonant cavity 320 before and after the vacuum sealed cavity 100 is filled with gas, the pressure of the internal environment of the vacuum sealed cavity 100 can be known, and the pressure measurement of the vacuum sealed cavity 100 can be realized.

[0053] Specifically, the relationship between the gas refractive index n in the vacuum sealed cavity 100 and the frequency change Δv (the frequency difference between the first laser beam and the second laser beam described above) of the measurement resonant cavity 340 before and after the vacuum sealed cavity 100 is filled with gas is as follows:

[0054] ;

[0055] wherein v f is the absolute frequency of the second laser beam coupled into the measurement resonator cavity 340, K ref is the bulk modulus of the cavity material of the reference resonator cavity 320, K mea is the bulk modulus of the cavity material of the measurement resonator cavity 340, d is the pressure deformation correction coefficient of the cavity mirror (first mirror 324 and second mirror 344 described below), and d ref and d mea are the pressure deformation correction coefficients of the cavity mirrors of the reference resonator cavity 320 and the measurement resonator cavity 340, respectively, and Δp is the rough pressure value before and after the vacuum sealed cavity 100 is inflated, which is used to calibrate the influence of pressure change. Since the cavity of the reference resonator cavity 320 and the cavity of the measurement resonator cavity 340 are integrally formed on the same substrate, that is, the cavity of the reference resonator cavity 320 and the cavity of the measurement resonator cavity 340 are designed in a double-channel design on the same substrate, so that the cavity deformation and the deformation of the mirrors at both ends of the cavity of the reference resonator cavity 320 and the measurement resonator cavity 340 due to thermal expansion effect can be the same to a certain extent, and then in the process of obtaining the internal pressure of the vacuum sealed cavity 100 based on the frequency difference between the reference resonator cavity 320 and the measurement resonator cavity 340, the cavity deformation and the mirror deformation of the measurement resonator cavity 340 and the reference resonator cavity 320 can be offset to a certain extent. That is, in the process of measuring the pressure of the vacuum sealed cavity 100, the bulk modulus of the cavity and the deformation coefficient of the mirror of the measurement resonator cavity 340 and the reference resonator cavity 320 can be greatly offset to each other.

[0056] It is defined that , , then the relationship between the frequency change Δv and the gas pressure p of the vacuum sealed cavity 100 can be obtained as follows according to the above formula

[0057] ;

[0058] ;

[0059] wherein K' represents the relative change between the bulk modulus of the reference resonator cavity 320 and the measurement resonator cavity 340, d' represents the relative change between the pressure deformation correction coefficients of the cavity mirrors of the reference resonator cavity 320 and the measurement resonator cavity 340, and A is based on the Avogadro constant N A , the molar polarizability of the gas molecules A ε , and the second virial coefficient B T ​The first-order coefficient is obtained. As described above, the primary pressure measurement system can obtain the internal pressure of the vacuum sealed cavity 100 based on the double-channel resonant cavity 300 in the vacuum sealed cavity 100. The resonant cavities of the reference resonant cavity 320 and the measurement resonant cavity 340 in the double-channel resonant cavity 300 of the primary pressure measurement system are formed on the same substrate, so that the cavity deformation and mirror deformation of the reference resonant cavity 320 and the measurement resonant cavity 340 can be mutually offset in a common mode, and the equivalent thermal expansion coefficient of the cavity deformation after offsetting can reach a level comparable to ultra-low expansion glass (ULE). As shown in Figure 4 , Figure 4 , the frequency drift of the independent resonant cavity as the reference resonant cavity 320 (as shown in a graph of Figure 4 ) and the frequency drift of the independent resonant cavity as the measurement resonant cavity 340 (as shown in a graph of Figure 4 ), and the frequency drift of the double-channel resonant cavity 300 described in the present application (as shown in a graph of Figure 4 ) are obtained, and the specific Figure 4 , the frequency f (unit: MHz) of the ULE ultra-stable optical resonant cavity changes with temperature in the graphs a and b of Figure 4 , the frequency changes with temperature T (unit: K) in the graph a of Figure 4 , the frequency changes with temperature in the graph b of Figure 4 , the frequency of the reference resonant cavity 320 and the measurement resonant cavity 340 changes with temperature in the graph c of Figure 4 , according to the graphs a and b of Figure 3 , the frequency drift k caused by thermal expansion effect is about 100 MHz / K when the independent optical resonant cavity is used as the reference resonant cavity and the measurement resonant cavity, and the frequency drift is large, which has a great influence on pressure measurement, resulting in high inaccuracy. According to the graph c of ,

[0060] Therefore, the pressure primary metrology system can effectively suppress the influence of thermal expansion effect on pressure measurement by the double-channel resonant cavity 300 formed based on the same substrate, and effectively reduce the inaccuracy of the optical pressure gauge. Moreover, the double-channel resonant cavity 300 is designed only by the double-channel design based on the same substrate, without deliberately using ultra-low expansion glass (ULE) as the substrate material of the cavity and designing a multi-layer temperature control structure, thereby greatly reducing the structural complexity and process preparation difficulty of the pressure primary metrology system, greatly reducing the cost of the optical pressure gauge, and providing help for the large-scale promotion and mass production of the optical pressure gauge.

[0061] In addition, according to the above, it can also be known that the processing unit 440 obtains the frequency of the second laser beam based on the second transmission light signals before and after the vacuum sealed cavity 100 is inflated, and obtains the internal pressure of the vacuum sealed cavity 100 based on the frequency difference between the first laser beam and the second laser beam before and after the vacuum sealed cavity 100 is inflated, thereby realizing pressure measurement without additional operation on the measurement resonant cavity 340. In the related art, the Pound-Drever-Hall (PDH) frequency locking technology is usually used, which needs to introduce a complex frequency locking optical path and an electronic feedback control system. However, the frequency locking strategy is prone to lose lock when subjected to external interference, thereby adversely affecting the measurement accuracy. Therefore, the pressure primary metrology system provided in the present application can simplify the optical design of the optical pressure gauge, and also eliminate the risk of losing lock that may be caused by the frequency locking link, and has higher reliability.

[0062] In an embodiment of the present application, as shown in Figure 3 The double-channel resonant cavity 300 includes a substrate, the substrate includes a first region and a second region along a first direction (not shown in the figure), the first region is formed with a first resonant cavity body 322, and the second region is formed with a second resonant cavity body 342, and the first resonant cavity body 322 and the second resonant cavity body 342 are arranged along the first direction. The first resonant cavity body 322 is a through-hole type resonant cavity body penetrating through the substrate along a second direction, that is, the first resonant cavity body 322 is a through hole extending along the second direction and penetrating through the substrate. The second resonant cavity body 342 penetrates through the substrate along the second direction, and the second resonant cavity body 342 includes an opening extending along the second direction, that is, the second resonant cavity body 342 is a groove extending along the second direction and penetrating through the substrate. The first direction and the second direction are parallel to the plane where the substrate is located, and the first direction and the second direction intersect, for example Figure 1 As shown in the figure, the first direction and the second direction are perpendicular.

[0063] The double-channel resonant cavity 300 further comprises a first mirror 324 arranged in pairs and a second mirror 344 arranged in pairs, the reference resonant cavity 320 comprises a first resonant cavity body 322 and the first mirror 324 arranged on opposite sides of the first resonant cavity body 322 along the second direction, and the measurement resonant cavity 340 comprises a second resonant cavity body 342 and the second mirror 344 arranged on opposite sides of the second resonant cavity body 342 along the second direction. The first mirror 324 arranged at both ends of the first resonant cavity body 322 and the second mirror 344 arranged at both ends of the second resonant cavity body 342 can be firmly connected to the resonant cavity body by a precise bonding process.

[0064] As can be seen from the above, the reference resonant cavity 320 of the double-channel resonant cavity 300 is a vacuum resonant cavity composed of the through hole penetrating through the substrate and the first mirror 324 tightly fitted at both ends, and the measurement resonant cavity 340 is an open resonant cavity composed of the groove penetrating through the substrate and the second mirror 344 tightly fitted at both ends, so that the reference resonant cavity 320 and the measurement resonant cavity 340 are both placed inside the vacuum sealed cavity 100, but the reference resonant cavity 320 is isolated from the internal environment of the vacuum sealed cavity 100, and the measurement resonant cavity 340 is in communication with the internal environment of the vacuum sealed cavity 100. It should be noted that since the reference resonant cavity 320 is a vacuum resonant cavity, in order to achieve the vacuum state of the reference resonant cavity 320, an exhaust hole 326 is arranged on the first resonant cavity body 322, so as to achieve the vacuum state of the reference resonant cavity 320 based on the exhaust hole 326, and the exhaust hole 326 can be sealed.

[0065] In an embodiment of the present application, the material of the substrate can be quartz glass or ULE glass, etc. However, the present application is not limited thereto, and the specific material can be determined as appropriate.

[0066] In an embodiment of the present application, as shown in FIG. 4, the frequency shift unit 420 comprises a radio frequency source 422 and an electro-optical modulator 424. The radio frequency source 422 is configured to provide a radio frequency signal, and the electro-optical modulator 424 is configured to adjust the frequency of the second laser beam under the control of the radio frequency signal, i.e., to frequency shift the second laser beam, and the electro-optical modulator 424 is further configured to transmit the frequency-shifted second laser beam to the measurement resonant cavity 340. The frequency of the radio frequency signal is the frequency shift value of the second laser beam. Figure 1 Specifically, the radio frequency source 422 can provide a series of radio frequency signals at a predetermined step size, and the electro-optical modulator 424 adjusts the frequency of the second laser beam at a predetermined step size under the control of the series of radio frequency signals to generate a plurality of second laser beams with different frequencies, and sequentially transmits them to the measurement resonant cavity 340.

[0067]

[0068] ​It should be noted that the optical resonator generally only allows laser beams matching the resonant frequency of the optical resonator to enter the resonator body, so the frequency of the laser beam that can enter the resonator body of the optical resonator can be considered to be the resonant frequency of the optical resonator, or it can be considered that the frequency of the laser beam that can enter the resonator body of the optical resonator is the same as the resonant frequency of a certain mode of the optical resonator. Therefore, the electro-optical modulator 424 generates a second laser beam with a different frequency under the control of a series of radio frequency signals provided by the radio frequency source 422, so that the frequency-shifted second laser beam can be coupled into the measurement resonator 340, thereby obtaining the resonant frequency of the measurement resonator 340, that is, the frequency of the measurement resonator 340 before and after the vacuum sealed cavity 100 is filled with gas. It should be noted that it should be understood that the second laser beam with a different frequency is obtained by frequency-shifting the second laser beam output by the laser output module by the radio frequency source, that is, the second laser beam with a different frequency is obtained by frequency-adjusting a basic second laser beam.

[0069] In an embodiment of the present application, as shown in Figure 5 The photodetector 442 is configured to detect the second transmitted light signal and obtain the intensity of the second transmitted light signal. The processor 444 is configured to obtain the frequency of the second laser beam based on the second transmitted light signal, specifically based on the intensity of the second transmitted light signal, and obtain the frequency of the second laser beam that can be coupled into the measurement resonator 340. The second transmitted light signal is formed by the second laser beam with at least one frequency that can be coupled into the measurement resonator 340 in the second laser beam with a different frequency, and the frequency of the second laser beam is equal to the center frequency of the second transmitted light signal. It should be noted that the optical resonator can increase the intensity of the laser beam coupled into it, but generally the frequency of the laser beam does not change, so the frequency of the second laser beam is equal to the center frequency of the second transmitted light signal.

[0070] The known optical resonant cavity generally only allows laser beams matching the resonant frequency thereof to enter the resonant cavity, so when the photodetector 442 can detect the second transmitted light signal, it indicates that the second laser beam can match the resonant frequency of the measurement resonant cavity 340 at this time. Since the frequency of the laser beam that can be coupled into the optical resonant cavity can be considered to be the same as the resonant frequency of a certain mode of the optical resonant cavity, at least one second laser beam that can be coupled into the measurement resonant cavity 340 can represent the resonant frequency of the measurement resonant cavity 340, so the processing unit 440 can obtain the frequency of the second laser beam before and after the vacuum sealed cavity 100 is inflated based on the second transmitted light signal, that is, the resonant frequency of the measurement resonant cavity 340, and then obtain the internal pressure of the vacuum sealed cavity 100 based on the frequency difference between the first laser beam and the second laser beam. Wherein, the processor 444 obtains the resonant frequency of the measurement resonant cavity 340 based on the second laser beam, specifically, the frequency center of the second laser beam is the resonant frequency of the measurement resonant cavity 340.

[0071] It should be noted that although the electro-optic modulator 424 can generate a plurality of second laser beams with different frequencies under the control of a series of radio frequency signals provided by the radio frequency source 422, during pressure measurement, the frequency of the second laser beam coupled into the measurement resonant cavity 340 is generally defined as the resonant frequency of the measurement resonant cavity 340. Specifically, before the vacuum sealed cavity 100 is inflated, the resonant frequency of the measurement resonant cavity 340 is determined by one of the plurality of second laser beams with different frequencies, which can be referred to as the first frequency. After the vacuum sealed cavity 100 is inflated, the second laser beam can be frequency-shifted with the first frequency as the initial value, and when the photodetector 442 can detect the second transmitted light signal, the frequency of the second laser beam at this time is defined as the resonant frequency of the measurement resonant cavity 340 after the vacuum sealed cavity 100 is inflated.

[0072] It should also be noted that the reference resonant cavity 320 is an optical resonant cavity with a fixed longitudinal mode frequency, and the resonant frequency thereof can be a known value, which can be used as the resonant frequency of the reference resonant cavity 320 during pressure measurement. However, the present application does not limit this, and the resonant frequency of the reference resonant cavity 320 can also be obtained according to the above method for obtaining the resonant frequency of the measurement resonant cavity 340, and the obtained resonant frequency of the reference resonant cavity 320 can be used as the resonant frequency of the reference resonant cavity 320 during pressure measurement.

[0073] In an embodiment of the present application, the laser output module 200 can include a laser source and a beam splitter optical fiber, the laser source outputs a laser beam, the laser beam is split by the beam splitter optical fiber to form a first laser beam and a second laser beam. The first laser beam is transmitted to the reference cavity 320 through the beam splitter optical fiber, and the second laser beam is transmitted to the frequency shift unit 420 through the beam splitter optical fiber. Wherein, before the second laser beam is frequency shifted by the frequency shift unit 420, the frequencies of the first laser beam and the second laser beam are the same.

[0074] As can be seen from the above, the first laser beam and the second laser beam are split by the beam splitter optical fiber, so before the second laser beam is frequency shifted, the frequencies of the first laser beam and the second laser beam are the same. Therefore, before the vacuum sealed cavity 100 is inflated, the frequency shift value of the second laser beam that can be coupled into the measurement cavity 340 is the frequency of the measurement cavity 340 and the reference cavity 320. After the vacuum sealed cavity 100 is inflated, the frequency shift value of the second laser beam that can be coupled into the measurement cavity 340 is the frequency of the measurement cavity 340 and the reference cavity 320. Therefore, based on the difference between the frequency shift values of the second laser beam before and after the inflation of the vacuum sealed cavity 100, the frequency change of the measurement cavity 340 relative to the reference cavity 320 before and after the inflation of the vacuum sealed cavity 100 can be obtained, which greatly simplifies the pressure measurement process.

[0075] In an embodiment of the present application, the laser source is a narrow linewidth laser, and the linewidths of the first laser beam and the second laser beam are less than a preset value, so that the error between the frequencies of the first laser beam and the second laser beam and the resonance frequencies of the corresponding optical cavities is small, which helps to improve the inaccuracy of pressure measurement.

[0076] In order to further suppress the influence of thermal expansion effect, in an embodiment of the present application, the pressure primary metrology system further includes a constant temperature cavity 500, the vacuum sealed cavity 100 is placed in the constant temperature cavity 500 together with the double-channel cavity, that is, the double-channel cavity 300 is located in the vacuum sealed cavity 100, and the vacuum sealed cavity 100 is located in the constant temperature cavity 500. As shown in Figure 5 Figure 5 Fig. a in the drawings is a schematic diagram of the overall structure of the constant temperature cavity 500, Figure 6 Fig. b in the drawings is an exploded view, the constant temperature cavity 500 can use an aluminum alloy panel as a support layer, a vacuum cavity is placed in the middle part thereof, a silicon rubber heating element is wrapped outside the shell, and the outermost layer is wrapped with thermal insulation cotton for heat insulation. The front panel and the upper panel are perforated to pass through the optical fiber assembly and the high-purity gas path. The constant temperature cavity 500 can stabilize the temperature of the vacuum cavity thereof at 25°C, and control the temperature fluctuation to be less than 20mK.

[0077] The present application also provides an optical pressure gauge, which includes the pressure primary metrology system of any of the above embodiments.

[0078] ​The optical pressure gauge provided in this application can be used directly for pressure measurement or for in-situ calibration of various commercial pressure gauges. During operation, the device is first connected to the instrument being calibrated via a gas path. After confirming good airtightness, a vacuum pump is used to evacuate the entire gas path to a vacuum. The constant temperature chamber is then activated, stabilizing the temperature at 25°C and controlling temperature fluctuations to be less than 20 mK. Once the gas path and temperature have stabilized, the laser output module 200 is activated. The laser source in this module can be a near-infrared distributed feedback laser (DFB), and its tuning range should be greater than the free spectral range of the dual-channel resonant cavity (e.g., 3 GHz). After the laser source is preheated and stabilized, a laser beam is output and transmitted via a near-infrared fiber to a splitting fiber, splitting into a first laser beam and a second laser beam. The first laser beam is directly incident on the reference resonant cavity 320, and the photodetector 442 at the rear end can observe the transmission peak of the complete first transmitted light signal. The second laser beam is first frequency-shifted by the frequency shifting unit 420 before being coupled to the measurement resonant cavity 340. A precision radio frequency source 422 accurately controls the electro-optic modulator 424 and records the radio frequency value in real time. Before the vacuum-sealed cavity 100 is filled with gas, the radio frequency value is the frequency difference f0 between the measurement resonant cavity 340 and the reference resonant cavity 320 under vacuum conditions. Subsequently, a preset gas is filled into the vacuum-sealed cavity 100 through a high-purity gas source (such as high-purity argon or nitrogen), and the above frequency shifting process is repeated to obtain the frequency difference f between the measurement resonant cavity 340 and the reference resonant cavity 320 after filling. Based on the change in frequency difference before and after filling (Δf = f – f0), and combined with the real-time acquired internal absolute temperature data of the vacuum-sealed cavity 100, the processor 444 (embedded system or PC) can automatically calculate and output the corresponding real-time absolute pressure value, thereby obtaining the internal pressure of the vacuum-sealed cavity 100, thus achieving pressure measurement or calibration of commercial pressure gauges.

[0079] like Figure 6 As shown, Figure 6 Figure a in the figure shows the relationship between the measured values ​​(vertical axis) of the optical pressure gauge provided in this application and the reading values ​​(horizontal axis) of a commercial thin-film pressure gauge. Figure 6 Figure b in the figure is based on Figure 6 Figure a shows the residual (in Pa) distribution between the measured values ​​of the optical pressure gauge and the readings of a commercial pressure gauge, with a measurement repeatability of 50 ppm. The establishment of... Figure 6 The relationship curve shown in Figure a is specifically constructed by selecting multiple pressure points within an atmospheric pressure range, simultaneously recording the measured values ​​of the optical pressure gauge provided in this application and the reading values ​​of a commercial pressure gauge, and establishing the curve based on the acquired measured and reading values. Figure 6It can be seen that the pressure value measured by the optical pressure gauge provided by the present application is equivalent to the reading value of the commercial pressure gauge, which indicates that the optical pressure gauge has a measurement capability comparable to the commercial thin-film pressure gauge, has commercial prospects and value, and can also be used to calibrate the commercial thin-film pressure gauge. It should be noted that when calibrating the commercial thin-film pressure gauge using the optical pressure gauge, the process is the same as the process shown in the above ​ The process is the same as the process shown in the above

[0080] In summary, the present application provides a pressure primary metrology system and an optical pressure gauge. The system includes a vacuum sealed cavity and a pressure metrology structure. The pressure metrology structure includes a laser output module, a dual-channel resonant cavity, and a processing module. The dual-channel resonant cavity is located in the vacuum sealed cavity and includes a vacuum reference resonant cavity and an open measurement resonant cavity formed based on the same substrate. The reference resonant cavity forms a first transmitted light signal based on a first laser beam, and the measurement resonant cavity forms a second transmitted light signal based on a second laser beam. The processing module includes a frequency shift unit and a processing unit. The frequency shift unit shifts the frequency of the second laser beam before and after the vacuum sealed cavity is inflated, respectively, and transmits it to the measurement resonant cavity. The processing unit detects the second transmitted light signal, respectively, obtains the frequency of the second laser beam based on the second transmitted light signal, and obtains the internal pressure of the vacuum sealed cavity based on the frequency difference between the first laser beam and the second laser beam. Since the dual-channel resonant cavity 300 is formed based on the same substrate, the cavity deformation is offset, which can effectively suppress the influence of thermal expansion effect on pressure measurement, and it is not necessary to deliberately use ultra-low expansion glass (ULE) as the substrate material of the cavity and design a multi-layer temperature control structure, which greatly reduces the structural complexity and process preparation difficulty of the pressure primary metrology system. In addition, the processing unit can obtain the internal pressure of the vacuum sealed cavity based on the frequency difference between the first laser beam and the second laser beam before and after the vacuum sealed cavity is inflated, which is simple to operate and has high reliability.

[0081] The various embodiments in the specification are described in a progressive, or parallel, or progressive and parallel combination manner, and each embodiment focuses on the difference from other embodiments. The same or similar parts between various embodiments can be referred to each other. For the device disclosed in the embodiments, since it corresponds to the method disclosed in the embodiments, the description is relatively simple, and the related parts can be referred to the method part.

[0082] It should be noted that, in the description of the present application, it is to be understood that the terms "upper", "lower", "top", "bottom", "inner", "outer", and the like are terms of reference and are made only for the purpose of facilitating the description of the present application and simplifying the description, and do not indicate or imply that the device or element referred to must have a particular orientation, be constructed and operated in a particular orientation, and therefore should not be understood as limiting the present application. When a component is considered to be "connected" to another component, it can be directly connected to the other component or there can be a component disposed therebetween.

[0083] It should also be noted that, in this document, the terms of relationship such as first and second are only used to distinguish one entity or operation from another entity or operation, and do not necessarily require or imply any such actual relationship or order between the entities or operations. Moreover, the terms "include", "contain" or any other variant thereof are intended to cover non-exclusive inclusion, so that the article or device including a series of elements not only includes those elements, but also includes other elements not explicitly listed or inherent to such article or device. Without more limitation, the element defined by the statement "including a" does not exclude the presence of additional identical elements in the article or device including the above-mentioned element.

[0084] The above description of the disclosed embodiments enables a person skilled in the art to implement or use the present application. Various modifications to these embodiments will be apparent to those skilled in the art, and the general principles defined herein can be implemented in other embodiments without departing from the spirit or scope of the present application. Therefore, the present application will not be limited to the embodiments shown herein, but will conform to the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. A primary pressure metering system, characterized in that, include: A vacuum-sealed cavity and a pressure metering structure, wherein the pressure metering structure includes: A dual-channel resonant cavity, located in the vacuum-sealed cavity, includes a reference resonant cavity and a measurement resonant cavity formed on the same substrate. The reference resonant cavity is a sealed vacuum resonant cavity, and the measurement resonant cavity is an open resonant cavity with an opening. A laser output module outputs a first laser beam and a second laser beam. The dual-channel resonant cavity is located on the transmission path of the first laser beam and the second laser beam. The reference resonant cavity forms a first transmitted light signal based on the first laser beam coupled into its resonant cavity. The measurement resonant cavity forms a second transmitted light signal based on the second laser beam coupled into its resonant cavity. The processing module includes a frequency shifting unit and a processing unit. After the vacuum-sealed cavity is in a vacuum state and after it is filled with gas, the frequency shifting unit shifts the frequency of the second laser beam and transmits the frequency-shifted second laser beam to the measurement resonant cavity. The processing unit is located on the transmission paths of the first transmitted light signal and the second transmitted light signal. After the vacuum-sealed cavity is in a vacuum state and after it is filled with gas, the processing unit detects the second transmitted light signal and obtains the frequency of the second laser beam based on the second transmitted light signal. The processing unit also obtains the internal pressure of the vacuum-sealed cavity based on the frequency difference between the first laser beam and the second laser beam. The frequency difference includes the frequency difference when the vacuum-sealed cavity is in a vacuum state, and the frequency difference after being filled with gas.

2. The primary pressure standard system of claim 1, wherein, The dual-channel resonant cavity includes the substrate, which includes a first region and a second region arranged along a first direction. A first resonant cavity is formed in the first region, and a second resonant cavity is formed in the second region. The first and second resonant cavities are arranged along the first direction. The first resonant cavity is a through-hole type resonant cavity that penetrates the substrate along a second direction. The second resonant cavity penetrates the substrate along the second direction and includes an opening extending along the second direction. The first and second directions are parallel to the plane of the substrate and intersect each other. The dual-channel resonant cavity further includes a first reflector and a second reflector. The reference resonant cavity includes the first resonant cavity body and the first reflector located on opposite sides of the first resonant cavity body along the second direction. The measurement resonant cavity includes the second resonant cavity body and the second reflector located on opposite sides of the second resonant cavity body along the second direction.

3. The primary pressure standard system of claim 2, wherein, The substrate is made of quartz glass or ULE glass.

4. The primary pressure standard system of claim 1, wherein, The frequency shift unit includes a radio frequency source and an electro-optic modulator; The radio frequency source provides a radio frequency signal, and the electro-optic modulator, under the control of the radio frequency signal, adjusts the frequency of the second laser beam and transmits the frequency-shifted second laser beam to the measurement resonant cavity. The frequency of the radio frequency signal is the frequency shift value of the second laser beam. The radio frequency source provides a series of radio frequency signals according to a preset step, and the electro-optical modulator adjusts the frequency of the second laser beam according to the preset step under the control of the series of radio frequency signals, generates a plurality of second laser beams with different frequencies, and sequentially transmits them to the measurement resonant cavity.

5. The primary pressure standard system of claim 4, wherein, The processing unit includes a photodetector and a processor; The photodetector detects the second transmitted light signal, and the processor obtains the frequency of the second laser beam based on the second transmitted light signal, and obtains the internal pressure of the vacuum sealed cavity based on the frequency difference between the first laser beam and the second laser beam; wherein the second transmitted light signal is formed based on the second laser beam with at least one frequency coupled into the measurement resonant cavity from the second laser beams with different frequencies, and the frequency of the second laser beam is the center frequency of the second transmitted light signal.

6. The primary pressure standard system of claim 1, wherein, The laser output module includes a laser source and a beam splitter fiber; The laser source outputs a laser beam, and the laser beam is split by the beam splitter fiber to form the first laser beam and the second laser beam, the first laser beam is transmitted to the reference resonant cavity through the beam splitter fiber, and the second laser beam is transmitted to the frequency shift unit through the beam splitter fiber. Before the second laser beam is frequency shifted by the frequency shift unit, the frequencies of the first laser beam and the second laser beam are the same.

7. The primary pressure standard system of claim 6, wherein, The laser source is a near-infrared distributed feedback laser.

8. The primary pressure standard system of claim 6, wherein, The laser source is a narrow linewidth laser, and the linewidths of the first laser beam and the second laser beam are less than a preset value.

9. The primary pressure standard system of claim 1, wherein, The metrology system further includes a constant temperature cavity; The vacuum sealed cavity is placed in the constant temperature cavity together with the double-channel resonant cavity.

10. An optical pressure gauge characterized by, The pressure primary metrology system includes any one of claims 1-9. The laser source is a near-infrared distributed feedback laser. The laser source is a narrow linewidth laser, and the linewidths of the first laser beam and the second laser beam are less than a preset value. The metrology system further includes a constant temperature cavity; The vacuum sealed cavity is placed in the constant temperature cavity together with the double-channel resonant cavity. The pressure primary metrology system includes any one of claims 1-9.

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