Vibration meter and vibration measurement method
The multi-wavelength laser Doppler vibrometer with frequency filters and polarization diversity addresses accuracy issues in long optical fibers by mitigating disturbance vibrations, ensuring flexible and cost-effective measurements.
Patent Information
- Authority / Receiving Office
- JP · JP
- Patent Type
- Patents
- Current Assignee / Owner
- OKI ELECTRIC INDUSTRY CO LTD
- Filing Date
- 2022-07-28
- Publication Date
- 2026-05-15
AI Technical Summary
Existing laser Doppler vibrometers using polarization-maintaining optical fibers face accuracy issues due to polarization crosstalk, which increases with fiber length, especially beyond 100m, negating the flexibility of measurement point adjustment.
A vibration meter utilizing a multi-wavelength laser light source and an interference optical system with frequency filters to separate and process measurement and reference light, employing polarization diversity to mitigate disturbance vibrations independently of fiber length.
The system effectively reduces disturbance vibrations regardless of optical fiber length, maintaining measurement accuracy without relying on expensive polarization-maintaining fibers, allowing flexible measurement locations and reducing costs.
Smart Images
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Abstract
Description
Technical Field
[0001] This invention relates to a vibration meter such as an optical fiber type laser Doppler vibrometer and a vibration measurement method.
Background Art
[0002] When scattered light is generated by irradiating an object in vibration with light, a vibration component due to the Doppler effect is superimposed on the scattered light. Therefore, by receiving the scattered light generated when irradiating an object in vibration with light and demodulating the received scattered light, the phase fluctuation derived from the Doppler effect is detected, and the vibration of the object can be measured.
[0003] As described above, a vibration meter that measures vibration non-contact using the Doppler effect of light is a laser Doppler vibrometer.
[0004] Conventionally, in vibration measurement, contact-type vibration meters have been widely used. Contact-type vibration meters have difficulty in measurement when the measurement object is far away or in measurement under high temperature and high magnetic fields. In addition, contact-type vibration meters have their own natural frequencies. Therefore, vibrations of the order of kHz or higher could not be accurately measured.
[0005] On the other hand, since a laser Doppler vibrometer is a non-contact type vibration meter, it can measure vibrations at a distance, under high temperature, and under high magnetic fields. In addition, a laser Doppler vibrometer can accurately measure vibrations of the order of kHz or higher.
[0006] Laser Doppler vibrometers that can utilize the advantages of non-contact type are expected to be active in predictive maintenance applications of factory and plant equipment and in inspection applications of infrastructure in recent years.
[0007] Referring to FIG. 3, the configuration of a general laser Doppler vibrometer (see, for example, Patent Document 1) will be described. FIG. 3 is a schematic diagram for explaining the configuration of a general laser Doppler vibrometer.
[0008] The laser light source 110 generates linearly polarized continuous light oscillating at the center frequency f0 (= ω0 / 2π) and emits the continuous light. The continuous light emitted from the laser light source 110 is sent to the coupler 121.
[0009] The coupler 121 bifurcates the continuous light. One of the bifurcated lights is used as measurement light for irradiating the measurement object 190, and the other is used as reference light for interfering with the scattered light.
[0010] The measurement light is transmitted through a polarizing beam splitter (PBS) 124 and then sent to a λ / 4 plate 144. The λ / 4 plate 144 converts the measurement light from linearly polarized light to circularly polarized light. The measurement light converted to circularly polarized light propagates through the optical fiber 130, is spatially emitted by the objective lens 150, and irradiates the measurement object 190.
[0011] A part of the scattered light generated by the measurement light irradiating the measurement object 190 is captured by the objective lens 150. The scattered light captured by the objective lens 150 is sent to the λ / 4 plate 144. The λ / 4 plate 144 converts the scattered light from circularly polarized light to linearly polarized light. The scattered light converted to linearly polarized light by the λ / 4 plate 144 is sent to the PBS 124.
[0012] The polarization direction of the scattered light, which is linearly polarized light, sent to the PBS 124 is perpendicular to the polarization direction of the measurement light sent to the PBS 124. Therefore, the scattered light is reflected by the PBS 124 and sent to the optical phase detection circuit 122. The complex signal E of the scattered light at the time of incidence on the optical phase detection circuit 122 SI is given by the following equation (1).
[0013]
Equation
[0014] Here, j is the imaginary unit. Also, ω0 (= 2πf0) is the central angular frequency of the continuous light generated by the laser light source 110. Also A SIθ is the complex amplitude of the reflected light, t is time, and φ(t) is the phase variation component of the light originating from the vibration of the object being measured 190.
[0015] Meanwhile, the reference light obtained by splitting the continuous light into two at the coupler 121 is sent to the frequency shifter 126. The frequency shifter 126 changes the frequency of the input reference light f0 to a frequency f shift (=ω shift A frequency shift of ( / 2π) is applied. With frequency shifter 126, the frequency f shift The reference light, which has undergone a frequency shift, is sent to the optical phase detection circuit 122. The complex signal E of the reference light when incident on the optical phase detection circuit 122 LO This is given by equation (2) below.
[0016]
number
[0017] Here, A LO is the complex amplitude of the reference light.
[0018] Figure 4 is a schematic diagram showing the input and output light spectra of the frequency shifter 126. Figure 4(A) shows the spectrum of the reference light input to the frequency shifter 126, and Figure 4(B) shows the spectrum of the reference light output from the frequency shifter 126.
[0019] The scattered light and reference light sent to the optical phase detection circuit 122 interfere in the optical phase detection circuit 122 to generate interference light. The interference light is sent to the photodetector 172. The photodetector 172 converts the interference light into an electrical current signal, which is an interference electrical signal.
[0020] The interference electrical signal generated by the photodetector 172 is given by the following equation (3).
[0021]
number
[0022] Here, R is the conversion efficiency of the light receiver 172, and P SI and P LO are the intensities of the reflected light and the reference light, respectively. The intensities P SI and P LO of the reflected light and the reference light, and the complex amplitudes A SI and A LO satisfy the relationships given by the following equations (4a) and (4b).
[0023]
Equation
[0024] The interference electrical signal is sent to an analog-to-digital converter (ADC) 174. After being converted into a discrete digital signal in the ADC 174, the interference electrical signal is sent to a signal processing circuit 176. The signal processing circuit 176 calculates the phase fluctuation component of the scattered light resulting from the vibration of the measurement object 190 from the digital signal, and obtains information such as the frequency, displacement, velocity, and acceleration of the vibration.
[0025] Here, in the fiber optic laser Doppler vibrometer using the optical fiber 130 in the optical propagation path between the PBS 124 and the objective lens 150, the position of the objective lens 150 can be flexibly adjusted by using the optical fiber 130. As a result, the versatility of the fiber optic laser Doppler vibrometer as a vibrometer is improved.
[0026] Here, in the general laser Doppler vibrometer described with reference to FIG. 3, the reference light, the measurement light, and the scattered light pass through different paths. Therefore, if external vibrations are applied to the optical fiber 130 before the measurement light and the scattered light reach the optical phase detection circuit 122 from the coupler 121, the phase fluctuation resulting from the vibration of the optical fiber 130 is superimposed on the interference light, and there is a problem that the vibration measurement of the original measurement object 190 becomes inaccurate.
[0027] To solve this problem, a technique has been proposed in which a reference light and a measurement light are propagated through a polarization-maintaining optical fiber, the measurement light is irradiated onto the object to be measured, and the reference light and scattered light are propagated through the same polarization-maintaining optical fiber (see, for example, Patent Document 2). The vibration meter disclosed in Patent Document 2 will be explained with reference to Figure 5. Figure 5 is a schematic diagram for explaining the vibration meter disclosed in Patent Document 2.
[0028] In the technology disclosed in Patent Document 2, laser light is propagated through a polarization-maintaining optical fiber 230 and then separated by a half-mirror 242 located in front of the objective lens 250. The component reflected by the half-mirror 242 becomes the reference light, and the component transmitted through the half-mirror 242 becomes the measurement light. The measurement light is scattered by the object to be measured 290. The scattered light generated by the object to be measured 290 passes through the λ / 4 plate 244 twice, so it passes through the half-mirror 242 with its polarization axis rotated by 90 degrees relative to the measurement light and the reference light. This reference light and scattered light propagate through the same polarization-maintaining optical fiber 230 as the laser light and are sent to the PBS 224.
[0029] Here, since the polarization axis of the scattered light is rotated by 90 degrees relative to the reference light, the scattered light and the reference light can be separated by PBS224. After the separated scattered light and the reference light are frequency-shifted by the frequency shifter 226, one of them is incident on the photodetector 272.
[0030] In the technology disclosed in Patent Document 2, even if disturbance vibrations are applied to the polarization-maintaining optical fiber 230, the same phase shift occurs in the reference light and the measurement light, and the same phase shift also occurs in the reference light and the scattered light. Therefore, between the measurement light and the reference light, and between the scattered light and the reference light, Since the relative phase difference does not change, it is possible to measure the intrinsic vibration of the object being measured. [Prior art documents] [Patent Documents]
[0031] [Patent Document 1] Japanese Patent Publication No. 2001-159560 [Patent Document 2] Japanese Patent Application Publication No. 4-249719 [Overview of the project] [Problems that the invention aims to solve]
[0032] In the technology disclosed in the aforementioned Patent Document 2, the polarization of light is used to mitigate disturbance vibrations. Therefore, if polarization crosstalk occurs, the accuracy of disturbance vibration mitigation deteriorates. Polarization-maintaining optical fibers have the property of maintaining the polarization of the transmitted light, but polarization crosstalk increases as the light propagates, and it is known that polarization crosstalk increases significantly depending on the optical fiber length, especially when the optical fiber length exceeds 100m.
[0033] Therefore, it is thought that the accuracy of disturbance vibration reduction deteriorates as the length of the polarization-maintaining optical fiber increases. If the accuracy of disturbance vibration reduction deteriorates, one of the features of the optical fiber type laser Doppler vibrometer, which is the ability to flexibly adjust the measurement point, becomes negated.
[0034] This invention has been made in view of the above-mentioned problems. The object of this invention is to provide a vibration meter and a vibration measurement method that can mitigate the effects of disturbance vibrations regardless of the length of the optical fiber. [Means for solving the problem]
[0035] To achieve the above-mentioned objectives, the vibration meter of this invention comprises a multi-wavelength laser light source, an optical fiber, an irradiation unit, an interference optical system, and a detection unit. The multi-wavelength laser light source generates continuous light containing at least two frequency components: a first frequency component and a second frequency component.
[0036] The interference optical system splits the continuous light into two, sending one as the measurement light to the irradiation unit via an optical fiber, and the other as the reference light to the detection unit. The irradiation unit splits the measurement light into two, irradiating the object to be measured with one as the first measurement light and the other as the second measurement light to the mirror. The first reflected light, generated when the first measurement light is reflected by the object to be measured, and the second reflected light, generated when the second measurement light is reflected by the mirror, are sent to the detection unit via the irradiation unit, optical fiber, and interference optical system.
[0037] The detection unit comprises a demultiplexer, a first polarizing beam splitter, a second polarizing beam splitter, first and second photodetectors for the first measurement light, first and second photodetectors for the second measurement light, and a signal processing unit. The demultiplexer splits the signal light, which includes the first reflected light, the second reflected light, and the reference light, into two, sending one of the first signal light to the first polarizing beam splitter and the other of the second signal light to the second polarizing beam splitter. The first polarizing beam splitter polarizes the first signal light and sends the separated signal light to the first and second photodetectors for the first measurement light, respectively. The second polarizing beam splitter polarizes the second signal light and sends the separated signal light to the first and second photodetectors for the second measurement light, respectively.
[0038] The signal processing unit acquires vibration information of the object to be measured based on the electrical signals obtained by receiving light from the first and second first measuring light receivers and the first and second second measuring light receivers.
[0039] The system comprises at least one of a first irradiation frequency filter, which is provided in the optical path through which the first measurement light propagates and blocks the second frequency component, and a second irradiation frequency filter, which is provided in the optical path through which the second measurement light propagates and blocks the first frequency component.
[0040] Furthermore, the device includes at least one of a first light-receiving frequency filter provided in the optical path through which the first signal light propagates, which blocks the second frequency component, and a second light-receiving frequency filter provided in the optical path through which the second signal light propagates, which blocks the first frequency component.
[0041] A preferred embodiment of the vibration meter of this invention includes both a first irradiation frequency filter that blocks a second frequency component and is provided in the optical path through which the first measurement light propagates, and a second irradiation frequency filter that blocks a first frequency component and is provided in the optical path through which the second measurement light propagates.
[0042] Furthermore, the system may also include a configuration that provides both a second light-receiving frequency filter for blocking the second frequency component, which is provided in the optical path through which the first signal light propagates, and a second light-receiving frequency filter for blocking the first frequency component, which is provided in the optical path through which the second signal light propagates.
[0043] Furthermore, in order to achieve the above-mentioned objectives, the vibration measurement method of this invention comprises the following steps. First, continuous light containing at least two frequency components, a first frequency component and a second frequency component, is generated. Next, the continuous light is split into two: a measurement light and a reference light. Next, the measurement light propagated through the optical fiber is split into two: one is used as the first measurement light to irradiate the object to be measured, and the other is used as the second measurement light to irradiate the mirror. Next, the first reflected light generated when the first measurement light is reflected by the object to be measured, and the second reflected light generated when the second measurement light is reflected by the mirror, are propagated through the optical fiber. Next, the signal light, which includes the first reflected light, the second reflected light, and the reference light propagated through the optical fiber, is split into two: a first signal light and a second signal light, and then polarization-separated from each. Next, information on the vibration of the object to be measured is obtained based on the electrical signals obtained by photoelectric conversion of the polarization-separated first signal light and the polarization-separated second signal light.
[0044] At this time, at least one of the following is performed: blocking the second frequency component from the first measurement light and blocking the first frequency component from the second measurement light; blocking the second frequency component from the first signal light and blocking the first frequency component from the second signal light.
[0045] According to a preferred embodiment of the vibration measurement method of this invention, both the second frequency component to the first measurement light and the first frequency component to the second measurement light are blocked.
[0046] Furthermore, the system may be configured to perform both the blocking of the second frequency component with respect to the first signal light and the blocking of the first frequency component with respect to the second signal light. [Effects of the Invention]
[0047] According to the vibration meter and vibration measurement method of this invention, it is possible to mitigate disturbance vibrations regardless of the polarization state of the measured light and reflected light, and therefore it is possible to mitigate disturbance vibrations regardless of the length of the optical fiber. [Brief explanation of the drawing]
[0048] [Figure 1] This is a schematic diagram illustrating the first vibration meter. [Figure 2] This is a schematic diagram illustrating the second vibration meter. [Figure 3] This is a schematic diagram (1) illustrating a conventional vibration meter. [Figure 4] This is a schematic diagram illustrating the input and output light of a frequency shifter. [Figure 5] This is a schematic diagram (2) illustrating a conventional vibration meter. [Modes for carrying out the invention]
[0049] The embodiments of this invention will be described below with reference to the figures, but the shapes, sizes, and arrangements of each component are only shown in a general manner to the extent that the invention can be understood. Furthermore, preferred configuration examples of this invention will be described below, but the materials and numerical conditions of each component are merely examples. Therefore, this invention is not limited to the following embodiments. This invention is not intended to be a fixed invention, and many modifications or alterations can be made to achieve the effects of this invention without departing from the scope of its configuration.
[0050] (First vibration meter) Referring to Figure 1, a vibration meter according to the first embodiment of this invention (hereinafter also referred to as the first vibration meter) will be described. Figure 1 is a schematic diagram for illustrating the first vibration meter and shows an example of the configuration of an optical fiber type laser Doppler vibrometer.
[0051] The vibration meter comprises a multi-wavelength laser light source 10, an interference optical system 20, an optical fiber 30, an irradiation unit 40, an objective lens 50, a mirror 52, and a detection unit 60.
[0052] The multi-wavelength laser light source 10 has at least a first frequency f A (=ω A ( / 2π) and the second frequency f B (=ω B It oscillates at two frequencies ( / 2π). The first frequency component f is generated by a multi-wavelength laser light source. A and the second frequency component f B The continuous light containing the signal is sent to the interference optical system 20.
[0053] The interference optical system 20 includes a demultiplexer 22, a beam splitter (BS) 24, a frequency shifter 26, and a multiplexer 28.
[0054] The continuous light generated by the light source unit 10 is split into two by the demultiplexer 22 of the interference optical system 20. One of the two split beams is used as the measurement light that is irradiated onto the object to be measured 90. The measurement light irradiated onto the object to be measured 90 is reflected by the object to be measured 90, producing reflected light. The other of the two split beams is used as a reference light to interfere with the reflected light.
[0055] The measurement light passes through BS24, propagates through the optical fiber 30, and is sent to the irradiation unit 40. Meanwhile, the reference light is f using the frequency shifter 26. shift (=ω shift After undergoing a frequency shift of ( / 2π), it is sent to the multiplexer 28. The complex signal E of the reference light when incident on the multiplexer 28. LO This can be expressed by the following equation (5).
[0056]
number
[0057] Here, A LOA and A LOB These represent the first frequency component f of the optical signal when it is incident on the multiplexer 28. A , and the second frequency component f B This is the complex amplitude.
[0058] The irradiation unit 40 is configured to include a multiplexer / demultiplexer 42, a first irradiation frequency filter (filter A) 44, and a second irradiation frequency filter (filter B) 46.
[0059] The measurement light sent to the irradiation unit 40 is split into a first measurement light and a second measurement light by the multiplexer / demultiplexer 42. The first measurement light is sent to the first irradiation frequency filter 44, and the second measurement light is sent to the second irradiation frequency filter 46. The first irradiation frequency filter 44 filters the first frequency component f A It transmits the second frequency component f B This is a light filter that blocks the second frequency component f. The second irradiation frequency filter 46 blocks the second frequency component f. B It transmits the first frequency component f A It is a light filter that blocks light.
[0060] In the first irradiation frequency filter 44, the second frequency component f B The first measurement light, which has been blocked, passes through the objective lens 50 and is irradiated onto the object to be measured 90. A portion of the reflected light generated is captured by the objective lens 50 and, as first reflected light, is sent to the multiplexer / demultiplexer 42 after passing through the first irradiation frequency filter 44.
[0061] In the second irradiation frequency filter 46, the first frequency component f AThe second measurement light, which has been blocked, is irradiated onto the mirror 52. The reflected light generated by the irradiation of the mirror 52 is sent as the second reflected light, after passing through the second irradiation frequency filter 46, to the multiplexer / demultiplexer 42. The first and second reflected light sent to the multiplexer / demultiplexer 42 propagate through the same optical fiber 30 and are sent to the interference optical system 20. The first and second reflected light sent to the interference optical system 20 are sent to the multiplexer 28 via BS24.
[0062] The complex signals E of the first and second reflected light when incident on the multiplexer 58. SIA and E SIB These are represented by the following equations (6a) and (6b), respectively.
[0063]
number
[0064] Here, A SIA and A SIB These are the complex amplitudes of the first reflected light and the second reflected light, respectively, and φ A disturbance and φ B disturbance These are the phase variation components of the first and second reflected light, respectively, originating from disturbance vibrations applied to the optical fiber 30. A target This is the phase modulation component of light originating from the vibration of the object being measured, 90.
[0065] The first reflected light, the second reflected light, and the reference light sent to the multiplexer 28 are sent to the detection unit 60 as signal light.
[0066] The detection unit 60 is comprised of a demultiplexer 62, a first light-receiving frequency filter (filter A) 64, a second light-receiving frequency filter (filter B) 66, a first polarizing beam splitter (PBS) 68, a second PBS 70, first and second light-receiving receivers 72 and 74 for the first measurement light, first and second light-receiving receivers 76 and 78 for the second measurement light, an analog-to-digital converter (ADC) 80, and a signal processing circuit 82.
[0067] The signal light sent to the detection unit 60 is split into a first signal light and a second signal light by the demultiplexer 62. The first signal light is sent to the first light receiving frequency filter 64, and the second signal light is sent to the second light receiving frequency filter 66.
[0068] The first light-receiving frequency filter 64 detects the first frequency component f of the signal light. A It transmits the second frequency component f B This is an optical filter that blocks the second frequency component f of the signal light. The second light receiving frequency filter 66 blocks the second frequency component f of the signal light. B It transmits the first frequency component f A It is a light filter that blocks light.
[0069] In the first light-receiving frequency filter 64, the second frequency component f B The first signal light, with the first frequency component f blocked, is sent to the first PBS68. In the second light receiving frequency filter66, the first frequency component f A The second signal light, which has been blocked, is sent to the second PBS70.
[0070] The first signal light sent to the first PBS68 is polarization-separated in the first PBS68. The two polarization-separated first signal lights are then sent to the first and second first signal light receivers 72, respectively. The signals are sent to and 74. Similarly, the second signal light sent to the second PBS 70 is polarization-separated in the second PBS 70. The two polarization-separated second signal lights are sent to the first and second second signal light receivers 76 and 78, respectively.
[0071] The demultiplexer 62, the first light-receiving frequency filter 64, and the second light-receiving frequency filter 66 can be configured in the same way as the multiplexer / demultiplexer 42, the first irradiation frequency filter 44, and the second irradiation frequency filter 46 provided in the irradiation unit 40. Furthermore, the first PBS 68 and the second PBS 70 can be configured as any suitable conventionally known polarization beam splitter with mutually orthogonal polarization axes.
[0072] The first and second photodetectors 72 and 74 for the first measuring light, and the first and second photodetectors 76 and 78 for the second measuring light, can be configured using any suitable conventionally known photodetectors that perform photoelectric conversion of the first signal light and the second signal light to obtain a current signal.
[0073] Here, the first PBS68 contains the first frequency component f as the first signal light. A First reflected light and reference light, including the first reflected light and the reference light, are incident. The first and second first measurement light receivers 72 and 74 each obtain current signals from the different polarization components of the interference light obtained by the interference of the first reflected light and the reference light. In addition, the second PBS 70 receives the second signal light, which is the second frequency component f B A second reflected light containing the second reflected light and a reference light are incident on the device. The first and second second measuring light receivers 76 and 78 each obtain current signals from the different polarization components of the interference light obtained by the interference of the second reflected light and the reference light.
[0074] The current signals generated by the first and second first measuring light receivers 72 and 74, and the first and second second measuring light receivers 76 and 78, are sent to the ADC 80. The ADC 80 samples the analog current signals at a predetermined sampling frequency to obtain digital signals. The digital signals generated by the ADC 80 are sent to the signal processing circuit 82.
[0075] The signal processing circuit 82 is comprised of, for example, a personal computer (PC). The signal processing circuit 82 is the part that processes digital signals. In the signal processing circuit 82, for example, the desired function is realized by the execution of a program by the central processing unit (CPU).
[0076] The signal processing circuit 82 performs signal processing on the digital signal obtained from the interference light, which is produced when the reference light and scattered light interfere. When the object to be measured 90 is in a vibrating state, the vibration component of the object to be measured 90 is added to the scattered light due to the Doppler effect. By demodulating the digital signal obtained from the interference light, the signal processing circuit 82 acquires the phase change of the interference light and can calculate the vibration state of the object to be measured 90, such as the vibration frequency, displacement, and velocity, based on this phase change.
[0077] In this configuration example, the detection unit 60 includes a first PBS 68 and a second PBS 70 for polarization separation, and first and second first measurement light receivers 72 and 74, and first and second second measurement light receivers 76 and 78, respectively, for receiving the polarization-separated light. As a result, a receiving system that does not depend on the polarization state of the reflected light, i.e., polarization diversity, becomes possible. Polarization diversity is conventionally known and can be implemented by those skilled in the art, so a detailed explanation is omitted.
[0078] The first frequency component f after polarization diversity processing of the discrete signal obtained with ADC80 A and the second frequency component f B Signal S originating from this signal A [k] and S B [k] is represented by the following equations (7a) and (7b), respectively.
[0079]
number
[0080] Here, k is a discrete-time variable. For the sake of simplification, the constant term is set to 0, and the amplitude of the AC component is normalized to 1.
[0081] By removing the carrier component from equations (7a) and (7b) above and calculating the phase, we obtain the following equations (8a) and (8b).
[0082]
number
[0083] Here, for lasers with different center frequencies, the following relationship holds between the center frequency and the phase originating from disturbance vibrations, given by equation (9).
[0084]
number
[0085] From equations (8b) and (9) above, the following equation (10) is obtained.
[0086]
number
[0087] Furthermore, from equations (8a) and (10) above, we obtain the following equation (11), where the vibration φ of the object being measured is given by A target You can obtain this.
[0088]
number
[0089] This optical fiber type laser Doppler vibrometer performs measurements with polarization diversity processing, enabling the mitigation of disturbance vibrations regardless of the polarization state of the measured and reflected light. As a result, it is possible to mitigate disturbance vibrations regardless of the length of the optical fiber 30. Furthermore, it is possible to mitigate disturbance vibrations without using expensive polarization-maintaining fibers as the optical fiber 30. Therefore, it is possible to provide an optical fiber type laser Doppler vibrometer that is less expensive than conventional models and allows for flexible adjustment of the measurement location.
[0090] (Second vibration meter) Referring to Figure 2, a vibration meter according to the second embodiment of this invention (hereinafter also referred to as the second vibration meter) will be described. Figure 2 is a schematic diagram illustrating the second vibration meter. The second vibration meter differs from the first vibration meter in the configuration of its detection section. Other configurations are the same as those of the first vibration meter, so redundant explanations and illustrations are omitted.
[0091] The detection unit 61 is comprised of a demultiplexer 62, a second light receiving frequency filter 66, a first PBS 68, a second PBS 70, first and second light receivers 72 and 74 for the first measurement light, first and second light receivers 76 and 78 for the second measurement light, an analog-to-digital converter (ADC) 80, and a signal processing circuit 82.
[0092] The signal light sent to the detection unit 61 is split into a first signal light and a second signal light by the demultiplexer 62. First frequency component f A and the second frequency component f B The first signal light, which includes both of the above, is sent to the first PBS68, and the second signal light is sent to the second light-receiving frequency filter66.
[0093] The second light receiving frequency filter 56 detects the second frequency component f of the signal light. B It passes through, and the first frequency component f A This is an optical filter that blocks the first frequency component f. In the second light-receiving frequency filter 66, A The second frequency component f was blocked. B The second signal light, including the above, is sent to the second PBS70.
[0094] The operation of the first PBS68 and second PBS70 to the signal processing device 82 is the same as that of the first vibration meter, so a description will be omitted.
[0095] The first frequency component f after polarization diversity processing of the discrete signal obtained with ADC80 A and the second frequency component f B Signal S originating from this signal AB0 [k] and S B0 [k] is represented by the following equations (12a) and (12b), respectively.
[0096]
number
[0097] By removing the carrier component from equations (12a) and (12b) above and performing complex conjugation, we obtain the following equations (13a) and (13b).
[0098]
number
[0099] Dividing equation (13a) by equation (13b) and removing the constant term yields equation (14).
[0100]
number
[0101] Furthermore, from equations (13b) and (14) above, we obtain the following equation (15), where the vibration φ of the object being measured is given by A target You can obtain this.
[0102]
number
[0103] This second vibration meter achieves the same effect as the first vibration meter. Furthermore, it allows for a reduction in the number of filters, leading to system simplification and cost reduction.
[0104] Here, an example configuration has been described in which the detection unit does not have the first light-receiving frequency filter of the first vibration meter, but instead has a second light-receiving frequency filter; however, the system is not limited to this configuration.
[0105] It is sufficient to have a light-receiving frequency filter in either the optical path between the demultiplexer and the first PBS and the second PBS. Alternatively, the first vibrometer may have a first light-receiving frequency filter but not a second light-receiving frequency filter. Alternatively, the illumination unit may have an illumination frequency filter in either the optical path between the multiplexer / demultiplexer and the objective lens and mirror, but not in the other.
[0106] 10 Multi-wavelength laser light sources 20 Interferometric Optics 22 Duplexer 24 Beam Splitter (BS) 26, 126, 226 frequency shifter 28 Multiplexer 30, 130 optical fibers 40 Irradiation area 42 Multiplexer / demultiplexer 44. First irradiation frequency filter 46. Second irradiation frequency filter 50, 150, 250 objective lenses 52 Mirror 60 Detection unit 62 Duplexer 64. First light-receiving frequency filter 66. Second frequency filter for light reception 68. First Polarizing Beam Splitter (PBS) 70. Second Polarizing Beam Splitter (PBS) 72 First signal light receiver 74. Second receiver for first signal light 76 First receiver for second signal light 78. Second receiver for the second signal light 80, 174, 274 Analog-to-Digital Converters (ADCs) 82, 176, 276 Signal Processing Circuits 90, 190, 290 Objects to be measured 110, 210 laser light source 121 Coupler 122 Optical Phase Detection Circuit 124, 224 Polarizing Beam Splitter (PBS) 144, 244 λ / 4 plate 172, 260 receiver 228 λ / 2 plate 230 Polarization-maintaining optical fiber
Claims
1. It comprises a multi-wavelength laser light source, optical fiber, irradiation unit, interference optical system, and detection unit. The multi-wavelength laser light source generates continuous light containing at least two frequency components: a first frequency component and a second frequency component. The interferometric optical system splits the continuous light into two, sending one as the measurement light to the irradiation unit via the optical fiber, and the other as the reference light to the detection unit. The irradiation unit splits the measurement light into two, irradiating the object to be measured with one as the first measurement light and the other as the second measurement light onto the mirror. The first reflected light generated when the first measurement light is reflected by the object to be measured, and the second reflected light generated when the second measurement light is reflected by the mirror, are sent to the detection unit via the irradiation unit, the optical fiber, and the interference optical system. The detection unit comprises a demultiplexer, a first polarizing beam splitter, a second polarizing beam splitter, first and second photodetectors for first measurement light, first and second photodetectors for second measurement light, and a signal processing unit. The demultiplexer splits the signal light, which includes the first reflected light, the second reflected light, and the reference light, into two, sending one of the first signal light beams to the first polarization beam splitter and the other of the second signal light beams to the second polarization beam splitter. The first polarization beam splitter polarizes the first signal light and sends the separated signal light to the first and second first measurement light receivers, respectively. The second polarization beam splitter polarizes the second signal light and sends the separated signal light to the first and second second measurement light receivers, respectively. The signal processing unit acquires information on the vibration of the object to be measured based on the electrical signals obtained from the first and second first measuring light receivers and the first and second second measuring light receivers. The system comprises at least one of a first irradiation frequency filter provided in the optical path through which the first measurement light propagates, which blocks the second frequency component, and a second irradiation frequency filter provided in the optical path through which the second measurement light propagates, which blocks the first frequency component. The system comprises at least one of the following: a second light-receiving frequency filter provided in the optical path through which the first signal light propagates, which blocks the second frequency component; and a second light-receiving frequency filter provided in the optical path through which the second signal light propagates, which blocks the first frequency component. A vibration meter characterized by the following features.
2. The system comprises a first irradiation frequency filter provided in the optical path through which the first measurement light propagates, which blocks the second frequency component, and a second irradiation frequency filter provided in the optical path through which the second measurement light propagates, which blocks the first frequency component. The vibration meter according to feature 1.
3. The system comprises a second light-receiving frequency filter that blocks a second frequency component and is provided in the optical path through which the first signal light propagates, and a second light-receiving frequency filter that blocks a first frequency component and is provided in the optical path through which the second signal light propagates. The vibration meter according to feature 1 or 2.
4. A process for generating continuous light containing at least two frequency components, a first frequency component and a second frequency component, The process of splitting the aforementioned continuous light into a measurement light and a reference light, The process involves splitting the measurement light propagated through the optical fiber into two, irradiating the object to be measured with one as the first measurement light, and irradiating the mirror with the other as the second measurement light, The process of propagating the optical fiber the first reflected light generated when the first measurement light is reflected by the object to be measured, and the second reflected light generated when the second measurement light is reflected by the mirror, The first reflected light and the second reflected light, and the reference light, propagated through the optical fiber. The process involves splitting the signal light containing into a first signal light and a second signal light, and then polarizing each of them, The process of acquiring vibration information of the object to be measured based on the electrical signals obtained by photoelectric conversion of the polarization-separated first signal light and the polarization-separated second signal light, and Equipped with, At least one of the following is performed: blocking the second frequency component from the first measurement light, and blocking the first frequency component from the second measurement light. At least one of the following is performed: blocking the second frequency component from the first signal light, and blocking the first frequency component from the second signal light. A vibration measurement method characterized by the following features.
5. The process involves blocking the second frequency component from the first measurement light, and blocking the first frequency component from the second measurement light. The vibration measurement method according to feature 4.
6. The process involves both blocking the second frequency component from the first signal light and blocking the first frequency component from the second signal light. The vibration measurement method according to claim 4 or 5.