High sensitivity displacement measurement system

Abstract

The application provides a high-sensitivity displacement measurement system, comprising a displacement sensor, a first coupler and a processor, wherein the displacement sensor comprises an optical fiber, a pressing plate and a bottom plate, the pressing plate and the bottom plate are respectively provided with pressing blocks and convex blocks, a first end of the optical fiber inputs a measurement signal, a second end of the optical fiber is laid on the upper surfaces of the convex blocks along the convex blocks, and the second end of the optical fiber is connected with the first coupler after laying a corresponding number of turns; when a to-be-measured object is displaced, each pressing block is synchronously and vertically pressed against each optical fiber segment, so that the optical fiber segment between each two adjacent convex blocks is elongated, the length of each optical fiber segment changes after the elongation, the measurement signal is transmitted to the first coupler through the optical fiber, and the delay of the measurement signal changes; the measurement signal after the delay and a reference signal interfere with each other at the first coupler to generate an interference signal; and the processor determines the displacement of the to-be-measured object according to the interference signal. The application has the advantages of simple structure, low cost and high sensitivity.

Description

TECHNICAL FIELD

[0001] The application belongs to the field of displacement optical fiber sensing, and particularly relates to a high-sensitivity displacement measurement system. BACKGROUND

[0002] In the current optical high-precision displacement sensing system, since the displacement measurement precision is mostly required to be in the micron and nanometer level, most systems adopt a full-space light structure or a fiber structure plus a special probe structure to meet the measurement requirements, and both of the two ways need complex software algorithm assistance in the backend. The commonly used full-space light structure generally utilizes single-frequency or double-frequency laser interference method. Taking the double-frequency laser interference method as an example, there are reference signals and measurement signals in the system, the reference signals are used to monitor the measurement signals, and the phase difference between the two signals is used to obtain the displacement value. The polarization light is transmitted in the full-space light structure, which is easy to be disturbed by the external environment, and the system is large in size and difficult to build. The interference system of the fiber structure plus the special probe is also based on the principle of optical interference. The system structure is relatively simple, and the anti-interference ability is strong due to the fact that most of the structure is optical fiber. However, the probe generally needs special design and processing, so that the overall cost of the system is high. SUMMARY

[0003] The application provides a high-sensitivity displacement measurement system to solve the problems that the current high-precision displacement sensing system is difficult to have both simple structure and low cost, and the backend needs complex algorithm assistance for measurement.

[0004] According to a first aspect of the embodiment of the application, a high-sensitivity displacement measurement system is provided, which comprises a displacement sensor, a first coupler and a processor. The input end of the displacement sensor inputs a measurement signal, and the output end is connected to the first input end of the first coupler. The second input end of the first coupler inputs a reference signal, and the output end is connected to the processor.

[0005] The displacement sensor comprises an optical fiber, a pressing plate and a bottom plate. The pressing plate and the bottom plate are respectively provided with pressing blocks and convex blocks. The pressing blocks and the convex blocks are oppositely arranged, and each pressing block is located between the corresponding adjacent two convex blocks. The first end of the optical fiber is used to input the measurement signal, and the second end is laid on the upper surfaces of the convex blocks facing the pressing plate along the convex blocks. After laying a corresponding number of turns, the second end is connected to the first input end of the first coupler. The two ends of the optical fiber segment between each adjacent two convex blocks are fixedly connected to the adjacent two convex blocks respectively.

[0006] The displacement of the measured object drives the pressing plate to move towards the base plate, and each pressing block vertically presses each optical fiber segment synchronously, so that the optical fiber segment between each two adjacent convex blocks is stretched, and the length of each optical fiber segment changes after stretching, so that the change of the delay of the measurement signal transmitted to the first coupler through the optical fiber occurs; the measurement signal after the delay and the reference signal interfere with each other at the first coupler to generate an interference signal; the processor determines the interference delay difference caused by the displacement change of the measured object according to the interference signal, and determines the length of the optical fiber segment after stretching according to the delay difference, so as to determine the displacement of the measured object; wherein the displacement of the measured object is different, and the delay difference of the interference caused by the displacement of the measured object is different.

[0007] In an optional implementation, the apparatus further comprises a first wavelength single-frequency laser, a second wavelength single-frequency laser, a second coupler, an intensity modulator, and a wavelength division multiplexer, the processor comprises a photodetector and a vector network analyzer (VNA), the output ends of the first wavelength single-frequency laser and the second wavelength single-frequency laser are connected to the corresponding input ends of the second coupler respectively, the output end of the second coupler is connected to the input end of the wavelength division multiplexer through the intensity modulator, the two output ends of the wavelength division multiplexer are connected to the first ends of the optical fibers in the displacement sensor and the second input end of the first coupler respectively, and the VNA is connected to the modulation end of the intensity modulator.

[0008] The second coupler couples and transmits the first wavelength laser and the second wavelength laser provided by the first wavelength single-frequency laser and the second wavelength single-frequency laser to the intensity modulator.

[0009] The intensity modulator performs double-sideband microwave modulation on the first wavelength laser and the second wavelength laser according to the sweep microwave source provided by the VNA, and transmits the optical signal carrying the microwave signal after the double-sideband microwave modulation to the wavelength division multiplexer.

[0010] The wavelength division multiplexer transmits the first wavelength optical signal and the second wavelength optical signal in the optical signal as the measurement signal and the reference signal to the displacement sensor and the first coupler respectively, and the first wavelength optical signal is transmitted to the first coupler after delay processing by the displacement sensor.

[0011] The first wavelength optical signal after time delay and the second wavelength optical signal interfere with each other at the first coupler to generate a microwave interference signal, and the combined light including the microwave interference signal is transmitted to the photodetector; the photodetector converts the combined light into an electrical signal; the VNA recovers the microwave interference signal from the electrical signal, determines the interference time delay difference caused by the displacement change of the object to be measured according to the intensity of the microwave interference signal, and determines the length of the extended optical fiber segment according to the time delay difference, thereby determining the displacement of the object to be measured.

[0012] In another optional implementation, determining the length of the extended optical fiber segment according to the time delay difference, thereby determining the displacement of the object to be measured specifically includes: determining the length ΔL of a single optical fiber segment according to the time delay difference τ, the number of laps m of the optical fiber in the displacement sensor, and the number n of optical fiber segments in each lap.

[0013] According to the length ΔL of a single optical fiber segment, the included angle θ between two segments of the optical fiber segment divided by the pressing point, and the distance a between the inner contact points of the optical fiber segment on the two blocks between the adjacent two blocks, the distance d between the pressing point of the optical fiber segment and the plane where the upper surface of the block is located is determined, and the displacement of the object to be measured is the distance d when the optical fiber segment is in the non-extended state in the initial state; when the optical fiber segment is in the extended state in the initial state, the distance d determined in the initial state is subtracted from the distance d determined in the measurement state, thereby obtaining the displacement of the object to be measured.

[0014] In another optional implementation, the length ΔL of a single optical fiber segment is determined according to the time delay difference τ, the number of laps m of the optical fiber in the displacement sensor, and the number n of optical fiber segments in each lap according to the following formula:

[0015]

[0016] Where n eff represents the effective refractive index of the optical fiber, and c represents the transmission speed of light in vacuum.

[0017] In another optional implementation, the lengths of the optical fiber segments are the same in the initial state and in the measurement state.

[0018] The following equation is established to determine the distance d between the pressing point of the optical fiber segment and the plane where the upper surface of the block is located according to the length ΔL of a single optical fiber segment, the included angle θ between two segments of the optical fiber segment divided by the pressing point, and the distance a between the inner contact points of the optical fiber segment on the two blocks between the adjacent two blocks:

[0019]

[0020]

[0021] In another alternative implementation, the first and second wavelength lasers are represented as:

[0022] E1(t) = A1exp(jω1t);

[0023] E1(t) = A1exp(jω1t);

[0024] where E1(t) and E2(t) represent the intensity of the first and second wavelength lasers respectively, A1and A2represent the amplitude of the first and second wavelength lasers respectively, ω1and ω2represent the angular frequency of the first and second wavelength lasers respectively, and t represents time;

[0025] The double sideband microwave modulated optical signal carrying microwave signal is represented as:

[0026] E M (t) = A1[1 + Mcos(ω M t)]exp(jω1t) + A2[1 + Mcos(ω M t)]exp(jω2t)

[0027] where E M (t) represents the intensity of the optical signal, ω M represents the angular frequency of the microwave modulation, and M represents the modulation coefficient;

[0028] The combined light is represented as:

[0029] E p (t) = αA1{1 + Mcos[ω M (t + τ0+ τ)]}exp[jω1(t + τ0+ τ)] + A2[1 + Mcos(ω M t)]exp(jω2t)

[0030] where E p (t) represents the intensity of the combined light, α represents the output loss during measurement, τ0represents the initial delay difference, and τ represents the delay difference due to displacement change of the object to be measured;

[0031] The electrical signal is represented as:

[0032] i p (t) = ηα 2 A1 2 M 2 cos[ω M (t + τ0+ τ)] + ηA2 2 M 2 cos(ω M t)

[0033] wherein i p (t) represents the current of the electric signal, and η represents the responsivity of the photodetector;

[0034] According to the intensity of the microwave interference signal, the time delay difference τ caused by the displacement of the object to be measured is determined according to the following formula:

[0035] A p (ω M )=η 2 α 4 A1 4 M 4 +η 2 A2 4 M 4 +2η 2 α 2 A1 2 A2 2 M 4 cos(ω M (τ0+τ)) wherein A p (ω M ) represents the intensity of the microwave interference signal.

[0036] In another alternative implementation, a controllable optical attenuator is further included, which is arranged between the wavelength division multiplexer and the second input end of the first coupler.

[0037] In another alternative implementation, each pressing block matches the shape of the space region between two adjacent convex blocks.

[0038] In another alternative implementation, the displacement measurement precision and sensitivity are improved by increasing the laying number m of the optical fiber and / or the number n of optical fiber segments in each circle; as the displacement of the object to be measured increases, the displacement measurement sensitivity gradually decreases.

[0039] In another alternative implementation, the measurement signal and the reference signal are both white light sources, the measurement signal after time delay and the reference signal interfere with each other at the first coupler to generate a white light interference signal; the processor is a spectrometer, which determines the interference time delay difference caused by the displacement of the object to be measured according to the drift of the corresponding wavelength in the white light interference signal, and determines the length of the optical fiber segment after extension according to the time delay difference, thereby determining the displacement of the object to be measured.

[0040] The beneficial effects of the present application are:

[0041] 1、The displacement sensor is innovatively designed in the application, when the displacement of the measured object occurs, the plurality of optical fiber segments in the displacement sensor are stretched, the length of each optical fiber segment after stretching changes, so that the transmission delay of the measurement signal on the measurement arm changes, since there are a plurality of optical fiber segments in the displacement sensor, the transmission delay of the measurement signal on the measurement arm is the sum of the delays caused by each optical fiber segment, and the displacement of the measured object is determined according to the delay difference between the measurement arm and the reference arm, so that the displacement sensor of the application realizes the amplification of the displacement of the measured object, even if the displacement of the measured object is very small, it can also be detected, the displacement measurement sensitivity and accuracy are improved, and the problem of low sensitivity in high-precision displacement measurement such as micrometer and nanometer is solved; compared with the full-space optical structure, the optical fiber measurement form is adopted, the structure is simpler, compared with the special probe, the manufacturing cost of the displacement sensor in the application is lower, so the application can simultaneously have the advantages of simple structure and low cost; in addition, when the displacement of the measured object is determined, only the interference delay difference caused by the displacement of the measured object needs to be determined, the length of the optical fiber segment after stretching is determined according to the delay difference, and the displacement of the measured object can be determined according to the corresponding geometric relationship, the whole rear-end auxiliary measurement algorithm is very simple; the application can even realize nanometer displacement measurement, so as to meet the actual application and facilitate productization;

[0042] 2、Compared with laser interference, the displacement of the measured object is determined based on microwave interference, the measurement result is less affected by the external environment, so that the application has the advantages of good stability and high signal-to-noise ratio, and the measurement data does not need to be denoised, so as to further reduce the complexity of the subsequent measurement auxiliary algorithm; compared with white light interference, the measurement range when the displacement of the measured object is measured based on microwave interference is determined by the coherence length of the microwave source, and is no longer limited by the coherence length of the laser source, so that the possibility of further improving the measurement sensitivity is provided;

[0043] 3、The length of each optical fiber segment is the same in the initial state or in the measurement state, so that the delay caused by the length change of each optical fiber segment is the same when the measured object moves a certain distance, so that the delay difference caused by a single optical fiber segment can be determined in the rear-end measurement auxiliary algorithm, and thus the rear-end measurement auxiliary algorithm can be simplified;

[0044] 4、The application can make the power of the first wavelength optical signal and the second wavelength optical signal transmitted to the first coupler on the measurement arm and the reference arm the same by arranging the controllable optical attenuator on the reference arm, so as to improve the contrast of microwave interference;

[0045] 5、Each pressing block can match the shape of the space region between the adjacent two convex blocks, so that the pressing block can smoothly press the optical fiber segment, and the measurement range can be ensured;

[0046] 6、The present application is based on white light interference, and the displacement sensor is used to measure the displacement of the measured object, so that the measurement sensitivity can be improved, and the present application has the advantages of simple structure, low cost and simple rear-end measurement auxiliary algorithm. BRIEF DESCRIPTION OF DRAWINGS

[0047] Figure 1 is an embodiment of the high-sensitivity displacement measurement system of the present application.

[0048] Figure 2 is a perspective view of the displacement sensor of the present application

[0049] Figure 3 is a partial side view of the displacement sensor of the present application.

[0050] Figure 4 is another embodiment of the high-sensitivity displacement measurement system of the present application. DETAILED DESCRIPTION

[0051] In order to make the person skilled in the art better understand the technical solutions in the embodiments of the present application, and make the above-mentioned purposes, features and advantages of the embodiments of the present application more obvious and easy to understand, the technical solutions in the embodiments of the present application will be further described in detail below with reference to the drawings.

[0052] In the description of the present application, unless otherwise specified and limited, it is necessary to explain that the term "connection" should be understood broadly, for example, it can be mechanical connection or electrical connection, or the communication between two elements, it can be directly connected, or indirectly connected through intermediate medium, and the person skilled in the art can understand the specific meaning of the above-mentioned term according to the specific situation.

[0053] Reference Figure 1 is an embodiment of the high-sensitivity displacement measurement system of the present application. The high-sensitivity displacement measurement system can include a displacement sensor Sensor, a first coupler OC1 and a processor, the input end of the displacement sensor Sensor inputs a measurement signal, the output end is connected to the first input end of the first coupler OC1, the second input end of the first coupler OC1 inputs a reference signal, and the output end is connected to the processor; combined with Figure 2As shown, the displacement sensor Sensor can include an optical fiber 1, a pressing plate 2 and a bottom plate 3, the pressing plate 2 and the bottom plate 3 are respectively provided with pressing blocks 21 and convex blocks 31, the pressing blocks 21 and the convex blocks 31 are oppositely arranged and each pressing block 21 is located between two adjacent convex blocks 31, a first end of the optical fiber 1 is used to input the measurement signal, a second end of the optical fiber 1 is along the convex blocks 31, is laid on the upper surface of each convex block 31 towards the pressing plate 2, and is connected with the first input end of the first coupler OC1 after laying a corresponding number of turns, and the two ends of each optical fiber segment 11 (as shown) between each two adjacent convex blocks 31 are respectively fixedly connected with the two adjacent convex blocks 31. Figure 3 As shown.

[0054] The measured object is connected with the pressing plate 2, when the measured object is displaced, the pressing plate 2 is translated towards the bottom plate 3, each pressing block 21 is synchronously and vertically pressed against each optical fiber segment 11, the optical fiber segment 11 between each two adjacent convex blocks 21 is elongated, the length of each optical fiber segment 11 is changed after elongation, so that the delay of the measurement signal transmitted through the optical fiber 1 to the first coupler OC1 is changed; the measurement signal after the delay and the reference signal interfere at the first coupler OC1 to generate an interference signal; the processor determines the interference delay difference caused by the displacement of the measured object according to the interference signal, determines the length of the optical fiber segment after elongation according to the delay difference, and thus determines the displacement of the measured object; wherein the displacement of the measured object is different, and the interference delay difference caused by the displacement of the measured object is different.

[0055] In the embodiment, the first end of the optical fiber 1 in the displacement sensor is the input end of the displacement sensor, and the second end of the optical fiber 1 is the output end of the displacement sensor; the pressing plate and the bottom plate are parallel to each other and can both be circular plates, the measured object can be arranged in the circular pressing plate or fixedly connected to the upper surface of the circular pressing plate; the pressing block 21 is arranged on the lower surface of the pressing plate 2 facing the bottom plate 3, has the same structure, and can be an isosceles triangular prism, the side edges of the isosceles triangular prism face the bottom plate 3, and the two side surfaces corresponding to the side edges are the same, and each side edge facing the bottom plate 3 is pressed downward at the same position (for example, the middle position) of the corresponding optical fiber segment; the protruding block 31 is arranged on the upper surface of the bottom plate 3 facing the pressing plate 2, has the same structure, and can be an isosceles trapezoidal cube, the upper base surface of the isosceles trapezoidal cube faces upward, the space regions formed between adjacent two isosceles trapezoidal cubes are the same, and match the shape of the isosceles triangular prism. The upper surfaces (i.e., the upper base surfaces of the isosceles trapezoidal cubes) of the protruding blocks 31 facing the upper surface of the pressing plate 2 are on the same horizontal plane. The second end of the optical fiber 1 is laid on the upper surfaces of the protruding blocks 31 facing the upper surface of the pressing plate 2 along the protruding blocks 31, and the closed circles formed by the optical fiber after each laying circle are coaxial with the circular pressing plate and the circular bottom plate. Because the space regions between adjacent two protruding blocks are the same, the structures of the pressing blocks are the same and each is pressed downward at the same position of the optical fiber segment, and the optical fiber is laid along the protruding blocks (for example, each circle of the optical fiber is laid along a circle coaxial with the circular bottom plate), the lengths of each optical fiber segment are the same in the initial state and the measurement state. The present application can ensure that the time delays caused by the length changes of each optical fiber segment are the same when the measured object moves a certain distance, so that the time delay difference caused by a single optical fiber segment can be determined in the rear-end measurement auxiliary algorithm, thereby simplifying the rear-end measurement auxiliary algorithm. It should be noted that the pressing block and the protruding block can also be arranged in other matching shapes, as long as the lengths of each optical fiber segment are the same in the initial state and the measurement state; the optical fiber segment can be fixed on the upper surfaces of the protruding blocks by ultraviolet glue or the like. In addition, each pressing block 21 of the present application can match the shape of the space region between adjacent two protruding blocks 31, so that the pressing block 21 can smoothly press the optical fiber segment, thereby ensuring the measurement range.

[0056] In the embodiment, the present application determines the length of the optical fiber segment after extension according to the time delay difference, thereby determining the displacement of the measured object, which can specifically include: determining the length ΔL of a single optical fiber segment after extension according to the time delay difference τ, the number of laying circles m of the optical fiber in the displacement sensor, and the number n of optical fiber segments in each circle;

[0057] According to the length ΔL of the single fiber segment after extension, the angle θ between the two segments of the fiber segment divided by the pressing point, and the distance a between the inner contact points of the fiber segment on the two adjacent blocks, the distance d between the pressing point of the fiber segment and the plane of the upper surface of the block is determined, and when the fiber segment is in the non-extended state in the initial state (i.e. the parts of the fiber segment are in the same horizontal line), the distance d is the displacement of the object to be measured; when the fiber segment is in the extended state in the initial state (i.e. the pressing point divides the fiber segment into two segments, and there is a certain angle between the two segments in the initial state), the distance d determined in the initial state is subtracted from the distance d determined in the measurement state, so as to obtain the displacement of the object to be measured. After the interference delay difference τ caused by the displacement change of the object to be measured is determined, the length ΔL of the single fiber segment after extension can be determined according to the following formula:

[0058]

[0059] Wherein n eff represents the effective refractive index of the fiber, c represents the transmission speed of light in vacuum, m and n respectively represent the laying number of the fiber in the displacement sensor and the number of fiber segments in each circle.

[0060] The more the laying number m of the fiber and the more the number n of fiber segments in each circle in the present application, the greater the total change of the length of each fiber segment after extension when the object to be measured moves a unit amount, and the higher the amplification degree of the displacement of the object to be measured. Therefore, by increasing the laying number m of the fiber and / or the number n of fiber segments in each circle (i.e. increasing the total number of fiber segments), the displacement measurement precision and sensitivity can be improved.

[0061] After the length ΔL of the single fiber segment after extension is determined, the distance d between the pressing point of the fiber segment and the plane of the upper surface of the block can be determined by combining the distance d between the pressing point of the fiber segment and the plane of the upper surface of the block in the initial state and the distance d between the pressing point of the fiber segment and the plane of the upper surface of the block in the measurement state. Figure 3 The following equation can be established to determine the distance d between the pressing point of the fiber segment and the plane of the upper surface of the block:

[0062]

[0063]

[0064] Wherein θ represents the angle between the two segments of the fiber segment divided by the pressing point, and a represents the distance between the inner contact points of the fiber segment on the two adjacent blocks. As can be seen from the above formula, the length ΔL gradually decreases with the decrease of the angle θ, and with the increase of the displacement of the object to be measured (such as the distance d), the angle θ gradually decreases, and the length of the fiber segment that can continue to extend also gradually decreases, so the displacement measurement sensitivity gradually decreases with the increase of the displacement of the object to be measured.

[0065] As can be seen from the above embodiments, the displacement sensor is innovatively designed, and when the displacement of the measured object occurs, the plurality of optical fiber segments in the displacement sensor are stretched, the lengths of the stretched optical fiber segments are changed, and the transmission delay of the measurement signal on the measurement arm is changed. Since there are a plurality of optical fiber segments in the displacement sensor, the transmission delay of the measurement signal on the measurement arm is the sum of the delays of the optical fiber segments, and the displacement of the measured object is determined according to the delay difference between the measurement arm and the reference arm, so that the displacement sensor of the present application realizes the amplification of the displacement of the measured object. Even if the displacement of the measured object is very small, it can also be detected, thereby improving the displacement measurement sensitivity and accuracy, and solving the problem of low sensitivity in high-precision displacement measurement such as micrometer and nanometer. Compared with the full-space optical structure, the present application adopts the optical fiber measurement form, and the structure is simpler. Compared with the special probe, the manufacturing cost of the displacement sensor in the present application is lower, so the present application can simultaneously have the advantages of simple structure and low cost. In addition, when determining the displacement of the measured object, only the interference delay difference caused by the displacement of the measured object needs to be determined, the length of the stretched optical fiber segment is determined according to the delay difference, and the displacement of the measured object can be determined according to the corresponding geometric relationship. The whole rear-end auxiliary measurement algorithm is very simple. The present application can even realize nanometer displacement measurement, so it can meet the actual application and be easy to realize productization.

[0066] Generally, the optical interference based on optical fiber can be divided into laser interference and white light interference. The laser interference generally measures the displacement of the measured object according to the intensity of the optical interference signal, but the intensity of the optical interference signal is easily affected by the external environment, thereby resulting in low measurement accuracy. The white light interference generally measures the displacement of the measured object according to the wavelength shift. The wavelength shift of the white light interference signal is not easily affected by the external environment, so the measurement accuracy can be guaranteed when measuring the displacement based on the white light interference. Specifically, the measurement signal and the reference signal in the present application can both be white light sources. The delayed measurement signal and the reference signal undergo white light interference at the first coupler to generate a white light interference signal. The processor is a spectrometer. The spectrometer determines the interference delay difference caused by the displacement of the measured object according to the shift of the corresponding wavelength in the white light interference signal, determines the length of the stretched optical fiber segment according to the delay difference, and thereby determines the displacement of the measured object. When the displacement of the measured object is measured based on the white light interference, the present application can improve the measurement sensitivity, and at the same time, the present application has the advantages of simple structure, low cost and simple rear-end measurement auxiliary algorithm.

[0067] Although the displacement of the measured object is measured based on the white light interference, the measurement range is limited by the coherence length of the light source, so the interference mode is designed in the present application. Specifically, as shown in Figure 4 , Figure 4 and Figure 1The embodiment shown is different in that it can further comprise a first single-wavelength laser Laser1, a second single-wavelength laser Laser2, a second coupler OC2, an intensity modulator EOM and a wavelength division multiplexer DWDM, the processor comprises a photodetector PD and a vector network analyzer VNA, the output ends of the first single-wavelength laser Laser1 and the second single-wavelength laser Laser2 are connected to the corresponding input ends of the second coupler OC2 respectively, the output end of the second coupler OC2 is connected to the input end of the wavelength division multiplexer DWDM through the intensity modulator EOM, the two output ends of the wavelength division multiplexer DWDM are connected to the first end of the optical fiber 1 in the displacement sensor Sensor and the second input end of the first coupler OC1 respectively; the VNA (port Port2 thereof) is connected to the modulation end of the intensity modulator EOM.

[0068] The second coupler OC2 couples and transmits the first-wavelength laser and the second-wavelength laser provided by the first single-wavelength laser Laser1 and the second single-wavelength laser Laser2 to the intensity modulator EOM; the intensity modulator EOM performs double-sideband microwave modulation on the first-wavelength laser and the second-wavelength laser according to the swept-frequency microwave source provided by the VNA, and transmits the optical signal carrying the microwave signal after the double-sideband microwave modulation to the wavelength division multiplexer DWDM; the wavelength division multiplexer DWDM transmits the first-wavelength optical signal and the second-wavelength optical signal in the optical signal as the measurement signal and the reference signal respectively, to the displacement sensor Sensor and the first coupler OC1 respectively, and the first-wavelength optical signal is transmitted to the first coupler OC1 after time delay processing by the displacement sensor Sensor. The first-wavelength optical signal after time delay and the second-wavelength optical signal interfere with each other at the first coupler OC1, generate a microwave interference signal, and transmit the combined light including the microwave interference signal to the photodetector; the photodetector PD converts the combined light into an electrical signal; the VNA recovers the microwave interference signal according to the electrical signal, determines the interference time delay difference caused by the displacement change of the object to be measured according to the intensity of the microwave interference signal, and determines the length of the optical fiber section after extension, so as to determine the displacement of the object to be measured.

[0069] In the embodiment, the first wavelength and the second wavelength are different, and the wavelengths of the first-wavelength laser and the second-wavelength laser can be 1550.92 nm and 1550.12 nm respectively, and the two are incoherent light carriers, and the first-wavelength optical signal and the second-wavelength optical signal can both carry microwave signals, and the wavelengths of the two can be 1550.92 nm and 1550.12 nm respectively. The first-wavelength laser and the second-wavelength laser can be represented as:

[0070] E1(t) = A1exp(jω1t);

[0071] E1(t) = A1exp(jω1t);

[0072] wherein E1(t) and E2(t) represent the intensity of the first wavelength laser and the second wavelength laser respectively, A1and A2represent the amplitude of the first wavelength laser and the second wavelength laser respectively, ω1and ω2represent the angular frequency of the first wavelength laser and the second wavelength laser respectively, and t represents time.

[0073] The two incoherent light carriers are coupled to the intensity modulator EOM at the first coupler OC1, and the intensity modulator EOM performs double-sideband microwave modulation on the first wavelength laser and the second wavelength laser according to the swept microwave source provided by the VNA to generate a double-sideband microwave-modulated light signal carrying a microwave signal, which can be expressed as:

[0074] E M (t) = A1[1 + Mcos(ω M t)]exp(jω1t) + A2[1 + Mcos(ω M t)]exp(jω2t)

[0075] wherein E M (t) represents the intensity of the light signal, ω M represents the angular frequency of the microwave modulation, and M represents the modulation coefficient.

[0076] The intensity modulator EOM transmits the double-sideband microwave-modulated light signal carrying a microwave signal to the wavelength division multiplexer DWDM, the wavelength division multiplexer DWDM transmits the first wavelength light signal with a wavelength of 1550.92 nm in the light signal to the displacement sensor Sensor, and the first wavelength light signal is transmitted to the first coupler OC1 after time delay processing by the displacement sensor Sensor, and the wavelength division multiplexer DWDM transmits the second wavelength light signal with a wavelength of 1550.12 nm in the light signal to the first coupler OC1. The first wavelength light signal after time delay processing by the displacement sensor Sensor and the second wavelength light signal are combined at the first coupler OC1 to generate a combined light, which can be expressed as:

[0077] E p (t) = αA1{1 + Mcos[ω M (t + τ0+ τ)]}exp[jω1(t + τ0+ τ)] + A2[1 + Mcos(ω M t)]exp(jω2t)

[0078] wherein E p(t) represents the intensity of the combined light, a represents the output loss at the time of measurement, τ0 represents the initial delay difference, and τ represents the delay difference due to displacement change of the object to be measured.

[0079] The intensity modulator EOM performs double-sideband microwave modulation on the first-wavelength laser and the second-wavelength laser according to the swept microwave source provided by the processor, and the two light signals transmitted to the first coupler, the first-wavelength light signal and the second-wavelength light signal, have an optical path difference, and the two light signals generate a delay difference, so that the first-wavelength light signal and the second-wavelength light signal generate microwave interference at the first coupler OC1 to generate a microwave interference signal.

[0080] After the first coupler OC1 transmits the combined light to the photodetector PD, the photodetector performs photoelectric conversion on the combined light to generate an electrical signal, which can be represented as:

[0081] i p (t) = ηa 2 A1 2 M 2 cos[ω M (t+τ0+τ)]+ηA2 2 M 2 cos(ω M t)

[0082] where i p (t) represents the current of the electrical signal, and η represents the responsivity of the photodetector.

[0083] After the photodetector PD transmits the electrical signal to the processor, the processor recovers the microwave interference signal from the electrical signal, which can be represented as:

[0084] A p (ω M ) = η 2 a 4 A1 4 M 4 +η 2 A2 4 M 4 +2η 2 a 2 A1 2 A2 2 M 4 cos(ω M (τ0+τ))

[0085] where A p (ω M ) represents the intensity of the microwave interference signal. By tracking the frequency of a certain resonant wavelength in the microwave interference signal, the VNA can determine the delay difference τ caused by the displacement of the object to be measured according to the expression of the microwave interference signal.

[0086] In combination Figure 3 As shown in the figure, after determining the time delay difference τ caused by the displacement of the object to be measured, the length of the fiber segment after being stretched is determined according to the time delay difference, so that the displacement of the object to be measured can specifically include: determining the length ΔL of a single fiber segment after being stretched according to the time delay difference τ, the number of laps m of the fiber in the displacement sensor, and the number n of fiber segments in each lap;

[0087] According to the length ΔL of a single fiber segment after being stretched, the included angle θ between the two segments of the fiber segment divided by the pressing point, and the distance a between the inner contact points of the fiber segment on the two blocks between the adjacent two blocks, the distance d between the pressing point of the fiber segment and the plane where the upper surface of the block is located is determined, and when the fiber segment is in a non-stretched state in the initial state, the distance d is the displacement amount of the object to be measured; when the fiber segment is in a stretched state in the initial state, the distance d determined in the initial state is subtracted from the distance d determined in the measurement state, so that the displacement amount of the object to be measured is obtained.

[0088] Wherein, the length ΔL of a single fiber segment after being stretched can be determined according to the time delay difference τ, the number of laps m of the fiber in the displacement sensor, and the number n of fiber segments in each lap according to the following formula:

[0089]

[0090] Wherein n eff The effective refractive index of the fiber, and c represents the transmission speed of light in vacuum.

[0091] Since the length of each fiber segment is the same in the initial state and in the measurement state, the following equation can be established to determine the distance d between the pressing point of the fiber segment and the plane where the upper surface of the block is located according to the length ΔL of a single fiber segment after being stretched, the included angle θ between the two segments of the fiber segment divided by the pressing point, and the distance a between the inner contact points of the fiber segment on the two blocks between the adjacent two blocks:

[0092]

[0093]

[0094] In the embodiment, the wavelength division multiplexer can be a dense wavelength division multiplexer, and the processor can be a vector network analyzer (VNA). Compared with laser interference, the application determines the displacement of the object to be measured based on microwave interference, and the measurement result is less affected by the external environment, so that the application has the advantages of good stability and high signal-to-noise ratio. Therefore, the subsequent measurement auxiliary algorithm is further simplified without the need for noise reduction processing. Compared with white light interference, the measurement range of the displacement of the object to be measured based on microwave interference is determined by the coherence length of the microwave source, and is no longer limited by the coherence length of the laser source. Therefore, the application provides the possibility for further improving the measurement sensitivity.

[0095] In addition, as shown in Figure 4 The high-sensitivity displacement measurement system can further include a controllable optical attenuator (ATT) disposed between the wavelength division multiplexer (DWDM) and the second input end of the first coupler (OC1). The path between the wavelength division multiplexer (DWDM) and the second input end of the first coupler (OC1) is the reference arm, and the path between the first input end of the wavelength division multiplexer (DWDM) and the first coupler (OC1) is the measurement arm. The controllable optical attenuator (ATT) is used to adjust the power of the reference arm, so that the power of the reference arm and the reference arm is the same, thereby improving the contrast of the measured microwave interference. Specifically, a coupler can be disposed on the measurement arm after the displacement sensor, so that the coupler transmits a part of the first wavelength optical signal processed by the displacement sensor to the first coupler (OC1) and another part to the single-chip microcomputer. The single-chip microcomputer monitors the power of the first wavelength optical signal and calculates the power of the first wavelength optical signal transmitted to the first coupler on the measurement arm. Then, according to the calculated power, the controllable optical attenuator is controlled to adjust the power of the second wavelength optical signal transmitted to the first coupler on the reference arm. By disposing the controllable optical attenuator on the reference arm, the application can make the power of the first wavelength optical signal and the second wavelength optical signal transmitted to the first coupler on the measurement arm and the reference arm, respectively, so as to improve the contrast of the microwave interference.

[0096] As can be seen from the above embodiment, the displacement sensor is innovatively designed, multiple fiber segments in the displacement sensor are stretched when the displacement of the measured object, the length of each fiber segment after stretching changes, so that the transmission delay of the measurement signal on the measurement arm changes, since there are multiple fiber segments in the displacement sensor, the transmission delay of the measurement signal on the measurement arm is the sum of the delay of each fiber segment, and the displacement of the measured object is determined according to the delay difference between the measurement arm and the reference arm, so that the displacement sensor of the application realizes the amplification of the displacement of the measured object, even if the displacement of the measured object is very small, it can also be detected, the displacement measurement sensitivity and accuracy are improved, and the problem of low sensitivity of high-precision displacement measurement such as micrometer and nanometer is solved;Compared with the full space light structure, the application adopts the fiber measurement form, the structure is simpler, compared with the special probe, the manufacturing cost of the displacement sensor in the application is lower, so the application can simultaneously have the advantages of simple structure and low cost;In addition, when determining the displacement of the measured object, only the interference delay difference caused by the displacement of the measured object needs to be determined, the length of the fiber segment after stretching is determined according to the delay difference, and the displacement of the measured object can be determined according to the corresponding geometric relationship, the whole rear-end auxiliary measurement algorithm is very simple.

[0097] Those skilled in the art will readily perceive other embodiments of the present application as soon as the nature of the invention becomes apparent from the preceding description. The applicant intends and expects the present application to be practiced otherwise than as specifically described herein. Accordingly, this application includes all modifications and equivalents of the subject matter recited herein as permitted by pertinent law. Neither the description nor the examples limit the scope of the application. It is only the claims that are exhaustive of the scope of the present application.

[0098] It should be understood that the application is not limited to the precise construction that has been described above and illustrated in the accompanying drawings, and that various modifications and changes can be made without departing from the scope thereof. The scope of the application is limited only by the claims that follow.

Claims

1. A high-sensitivity displacement measurement system, characterized in that, It includes a displacement sensor, a first coupler, and a processor. The displacement sensor receives a measurement signal at its input terminal and its output terminal is connected to the first input terminal of the first coupler. The first coupler receives a reference signal at its second input terminal and its output terminal is connected to the processor. The displacement sensor includes an optical fiber, a pressure plate, and a base plate. The pressure plate and the base plate are respectively provided with pressure blocks and protrusions. The pressure blocks and protrusions are arranged opposite to each other, and each pressure block is located between two adjacent protrusions. The first end of the optical fiber is used to input the measurement signal, and the second end is laid along the direction of the protrusion on the upper surface of each protrusion facing the pressure plate. After laying the corresponding number of turns, it is connected to the first input end of the first coupler. The two ends of the optical fiber segment between each pair of adjacent protrusions are fixedly connected to the two adjacent protrusions respectively. When the object under test (DUT) shifts, it causes the pressure plate to move horizontally towards the base plate. Each pressure block presses down vertically on each fiber segment simultaneously, causing the fiber segment between each pair of adjacent protrusions to extend. The change in the length of each fiber segment after extension causes a change in the delay of the measurement signal transmitted through the fiber to the first coupler. The delayed measurement signal interferes with the reference signal at the first coupler, generating an interference signal. The processor determines the interference delay difference caused by the change in the displacement of the DUT based on the interference signal, and determines the length of the extended fiber segment based on the delay difference, thereby determining the displacement of the DUT. The magnitude of the interference delay difference varies depending on the displacement of the DUT.

2. The high-sensitivity displacement measurement system according to claim 1, characterized in that, It also includes a first-wavelength single-frequency laser, a second-wavelength single-frequency laser, a second coupler, an intensity modulator, and a wavelength division multiplexer. The processor includes a photodetector and a vector network analyzer (VNA). The outputs of the first-wavelength single-frequency laser and the second-wavelength single-frequency laser are respectively connected to the corresponding inputs of the second coupler. The output of the second coupler is connected to the input of the wavelength division multiplexer through the intensity modulator. The two outputs of the wavelength division multiplexer are respectively connected to the first end of the optical fiber in the displacement sensor and the second input of the first coupler. The VNA is connected to the modulation end of the intensity modulator. The second coupler couples the first wavelength laser and the second wavelength laser provided by the first wavelength single-frequency laser and the second wavelength single-frequency laser respectively to the intensity modulator. The intensity modulator modulates the first wavelength laser and the second wavelength laser using a swept microwave source provided by the VNA, and transmits the optical signal carrying the microwave signal after double-band microwave modulation to the wavelength division multiplexer. The wavelength division multiplexer uses the first wavelength optical signal and the second wavelength optical signal in the optical signal as the measurement signal and the reference signal, respectively, and transmits them to the displacement sensor and the first coupler accordingly. The first wavelength optical signal is transmitted to the first coupler after being delayed by the displacement sensor. The delayed first-wavelength optical signal and the second-wavelength optical signal undergo microwave interference at the first coupler, generating a microwave interference signal. The combined light including the microwave interference signal is transmitted to the photodetector. The photodetector converts the combined light into an electrical signal. The VNA recovers the microwave interference signal based on the electrical signal. Based on the intensity of the microwave interference signal, it determines the interference delay difference caused by the change in the displacement of the object under test. Based on the delay difference, it determines the length of the extended fiber segment, thereby determining the displacement of the object under test.

3. The high-sensitivity displacement measurement system according to claim 1 or 2, characterized in that, Determining the extended length of the optical fiber segment based on the delay difference, thereby determining the displacement of the object under test, specifically includes: determining the extended length ΔL of a single optical fiber segment based on the delay difference τ, the number of optical fiber loops m in the displacement sensor, and the number of optical fiber segments n in each loop; Based on the extended length ΔL of a single fiber segment, the included angle θ between the two segments divided by the pressure point, and the distance a between the inner contact points of the fiber segments on the two protrusions, the distance d between the pressure point of the fiber segment and the plane containing the upper surface of the protrusion is determined. When the fiber segment is in a non-extended state in the initial state, the distance d is the displacement of the object under test. When the fiber segment is in an extended state in the initial state, the distance d determined in the initial state is subtracted from the distance d determined in the measurement state to obtain the displacement of the object under test.

4. The high-sensitivity displacement measurement system according to claim 3, characterized in that, The extended length ΔL of a single fiber segment is determined according to the following formula, based on the delay difference τ, the number of fiber loops m in the displacement sensor, and the number of fiber segments n in each loop: Where n eff represents the effective refractive index of the optical fiber, and c represents the speed of light in a vacuum.

5. The high-sensitivity displacement measurement system according to claim 3, characterized in that, The lengths of each fiber segment are the same, both in the initial state and in the measurement state. The following equation is established to determine the distance d between the pressure point of the fiber segment and the plane containing the upper surface of the protrusion, based on the extended length ΔL of a single fiber segment, the included angle θ between the two segments divided by the pressure point, and the distance a between the inner contact points of the fiber segments on the two protrusions.

6. The high-sensitivity displacement measurement system according to claim 2, characterized in that, The first wavelength laser and the second wavelength laser are respectively represented as: E1(t) = A1exp(jω1t); E1(t) = A1exp(jω1t); Where E1(t) and E2(t) represent the intensity of the first wavelength laser and the second wavelength laser, respectively; A1 and A2 represent the amplitude of the first wavelength laser and the second wavelength laser, respectively; ω1 and ω2 represent the angular frequencies of the first wavelength laser and the second wavelength laser, respectively; and t represents time. The optical signal carrying the microwave signal after double-sideband microwave modulation is represented as follows: From M (t)=A1[1+Mcos(ω M t)]exp(jω1t)+A2[1+Mcos(ω M t)]exp(jω2t) Where E M (t) represents the intensity of the light signal, ω M The angular frequency of the microwave modulation is represented by M, and the modulation coefficient is represented by M. The combined beam is represented as: E p (t)=αA1{1+Mcos[ω M (t+τ0+τ)]}exp[jω1(t+τ0+τ)]+A2[1+ <cos(ω M t)]exp(jω2t) Where E p (t) represents the intensity of the combined beam, α represents the output loss during measurement, τ0 represents the initial delay difference, and τ represents the delay difference caused by the change in the displacement of the object under test. The electrical signal is represented as: I p (t)=ηα 2 A1 2 M 2 cos[ω M (t+τ0+τ)]+ηA2 2 M 2 cos(ω M t) Where i p (t) represents the current of the electrical signal, and η represents the responsivity of the photodetector; Based on the intensity of the microwave interference signal, the time delay τ caused by the displacement of the object under test is determined according to the following formula: A p (oh M )=η 2 a 4 A1 4 M 4 +n 2 A2 4 M 4 +2nd 2 a 2 A1 2 A2 2 M 4 cos(ω M (τ0+τ)) Where A p (ω M ) represents the intensity of the microwave interference signal.

7. The high-sensitivity displacement measurement system according to claim 2, characterized in that, It also includes a controllable optical attenuator, which is disposed between the wavelength division multiplexer and the second input terminal of the first coupler.

8. The high-sensitivity displacement measurement system according to claim 1 or 2, characterized in that, Each pressure block is shaped to match the space between two adjacent protrusions.

9. The high-sensitivity displacement measurement system according to claim 1, characterized in that, The accuracy and sensitivity of displacement measurement can be improved by increasing the number of fiber layups m and / or the number of fiber segments n per layup; as the displacement of the object under test increases, the displacement measurement sensitivity gradually decreases.

10. The high-sensitivity displacement measurement system according to claim 1, characterized in that, Both the measurement signal and the reference signal are white light sources. After a delay, the measurement signal and the reference signal undergo white light interference at the first coupler to generate a white light interference signal. The processor is a spectrometer. The spectrometer determines the interference delay difference caused by the displacement of the object under test based on the drift of the corresponding wavelength in the white light interference signal. Based on the delay difference, it determines the length of the extended fiber segment, thereby determining the displacement of the object under test.

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