Measuring device and measuring method

Abstract

A measuring device (300) comprises: a laser device (110); a branching component (120) for branching a frequency-modulated laser beam output by the laser device (110) into reference light and measuring light; a beat signal generating component (150) for generating a beat signal by mixing reflected light and reference light; a conversion component (160) for converting the beat signal into a digital signal at a first sampling rate and performing frequency analysis on the digital signal; an extraction component (170) for extracting a signal component corresponding to a resonant cavity frequency from the frequency-modulated laser beam; a digital filter (310) for digitally filtering the extracted signal component at a second sampling rate; and a calculation component (180) for calculating a difference in propagation distance between the reference light and the measuring light.

Description

Technical Field

[0001] The invention relates to a measuring device and a measuring method. Background Art

[0002] A frequency-shifted feedback laser (FSFL) is known that has a frequency shifter in a resonant cavity (resonator) and outputs multiple longitudinal-mode laser beams whose oscillation frequency changes linearly with time. Furthermore, an optical rangefinder using such an FSFL is known (for example, see Patent Document 1: Specification of Japanese Patent No. 3583906, and Non-Patent Document 1: “Distance Sensing by FSF Laser and Its Application,” Takefumi HARA, Optonews, Vol. 7, No. 3, 2012, pp. 25-31). Summary of the Invention

[0003] Problems to be solved by the present invention

[0004] Optical rangefinders using frequency-shifted feedback lasers (FSFLs) can acquire a large amount of three-dimensional information in a non-contact manner and have been used in design and production sites, for example. FSFLs sometimes lead to a reduction in the measurement accuracy of optical rangefinders because the resonant cavity length (resonator length) may vary due to environmental fluctuations such as temperature. To prevent the reduction in measurement accuracy, it has generally been considered to reduce environmental fluctuations by installing the FSFL in a constant-temperature chamber, observing changes in the resonant cavity length by monitoring the output of the FSFL, and so on. However, when the observed changes in the resonant cavity length are used for distance measurement, the observed changes in the resonant cavity length are superimposed on the changes in the distance measurement, which leads to an increase in the variation in the distance measurement.

[0005] The present invention has been made in view of this problem, and an object of the present invention is to enable an optical rangefinder to measure distance with high accuracy while suppressing an increase in cost.

[0006] Means of solving the problem

[0007] A first aspect of the present invention provides a measuring device for measuring the distance to an object to be measured, the measuring device comprising: a laser device having an optical resonant cavity (laser resonator) and outputting a frequency-modulated laser beam having multiple modes; a branching component that branches a portion of the frequency-modulated laser beam output by the laser device into reference light, and branches at least some of the remaining portion of the frequency-modulated laser beam into measurement light; a beat signal generating component that generates a beat signal by mixing the reference light and reflected light reflected by irradiating the measurement light onto the object to be measured; a conversion component that converts the beat signal into a digital signal at a first sampling rate and then performs frequency analysis on the digital signal; an extraction component that extracts a signal component that corresponds to the resonant cavity frequency (resonance frequency) of the optical resonant cavity and is superimposed on the frequency-modulated laser beam output from the laser device; a digital filter that digitally filters the extracted signal component at a second sampling rate; and a calculation component that calculates the difference in propagation distance between the reference light and the measurement light based on the result of the frequency analysis of the beat signal and the digitally filtered signal component.

[0008] The digital filter may digitally filter the extracted signal component at a second sampling rate slower than the first sampling rate. The branching component may branch the frequency modulated laser beam into reference light, measuring light, and monitoring light, and the extraction component may include a photoelectric conversion component that converts the monitoring light into an electrical signal, and extracts a signal component corresponding to the resonant cavity frequency of the optical resonant cavity from the electrical signal converted by the photoelectric conversion component.

[0009] The extraction component may also include: a filter component that allows a signal component having a resonance cavity frequency of the optical resonance cavity from within the electrical signal converted by the photoelectric conversion component to pass through; and a resonance cavity frequency output component that performs frequency analysis on the signal component that has passed through the filter component and outputs the resonance cavity frequency of the optical resonance cavity.

[0010] The calculation means may further include: a change rate calculation means that calculates a change rate per unit time of the digitally filtered signal component; and a determination means that determines stability of measurement of the measurement device based on the change rate per unit time.

[0011] The determination section may determine that the measurement device is stable when the calculated value of the rate of change is equal to or greater than a first threshold value and equal to or less than a second threshold value.

[0012] A second aspect of the present invention provides a measurement method for measuring the distance to an object to be measured, the measurement method comprising the following steps: outputting a frequency-modulated laser beam having multiple modes from a laser device having an optical resonant cavity; branching a portion of the frequency-modulated laser beam into reference light, and branching at least some of the remaining portion into measurement light; generating a beat signal by mixing the reference light and reflected light reflected by irradiating the measurement light onto the object to be measured; converting the beat signal into a digital signal at a first sampling rate, and then performing frequency analysis on the digital signal; extracting a signal component corresponding to the resonant cavity frequency of the optical resonant cavity and superimposed on the frequency-modulated laser beam; digitally filtering the signal component at a second sampling rate; and calculating the difference in propagation distance between the reference light and the measurement light based on the result of the frequency analysis of the beat signal and the digitally filtered signal component.

[0013] The measurement method may further comprise the steps of: calculating a rate of change per unit time of the digitally filtered signal component; and determining stability of the measurement based on the rate of change per unit time.

[0014] Effects of the Invention

[0015] According to the present invention, there is an effect of enabling an optical distance meter to measure distance with high accuracy while suppressing an increase in cost. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] Figure 1 A configuration example of the measuring device 100 and the object to be measured 10 according to the present embodiment are shown.

[0017] Figure 2 A configuration example of the laser device 110 according to the present embodiment is shown.

[0018] Figure 3 An example of a laser beam output from the laser device 110 according to the present embodiment is shown.

[0019] Figure 4 An example of the relationship between (i) the frequency of the beat signal detected by the measuring apparatus 100 according to the present embodiment and (ii) the distance d between the optical head section 140 and the object to be measured 10 is shown.

[0020] Figure 5 A configuration example of the beat signal generating section 150 and the converting section 160 according to the present embodiment is shown.

[0021] Figure 6 An example of an outline of quadrature detection by the beat signal generating section 150 and the converting section 160 according to the present embodiment is shown.

[0022] Figure 7A configuration example of the extraction section 170 according to the present embodiment is shown.

[0023] Figure 8 A configuration example of the measuring device 300 and the object to be measured 10 according to the present embodiment are shown.

[0024] Figure 9 shows the resonant cavity frequency v output by the extraction component 170 according to this embodiment. C .

[0025] Figure 10 shows the resonant cavity frequency ν filtered and output by the digital filter 310 according to this embodiment. C .

[0026] Figure 11 Modified examples of the measuring device 300 and the object to be measured 10 according to the present embodiment are shown. DETAILED DESCRIPTION

[0027] [Configuration Example of Measurement Device 100]

[0028] Figure 1 The present invention shows an example configuration of a measuring device 100 according to this embodiment and an object to be measured 10. The measuring device 100 optically measures the distance between the measuring device 100 and the object to be measured 10. Furthermore, the measuring device 100 can measure the three-dimensional shape of the object to be measured 10 by scanning the position of a laser beam irradiated onto the object to be measured 10. The measuring device 100 includes a laser device 110, a branching unit 120, an optical circulator 130, an optical head unit 140, a beat signal generating unit 150, a conversion unit 160, an extraction unit 170, a calculation unit 180, and a display unit 190.

[0029] Laser device 110 includes an optical resonant cavity (laser resonator) and outputs frequency-modulated laser beams in multiple modes. Laser device 110 includes a frequency shifter in the resonant cavity (resonator) and outputs multiple longitudinal-mode laser beams whose oscillation frequency varies linearly over time. Laser device 110 is, for example, a frequency-shifted feedback laser (FSFL). FSFLs will be described later.

[0030] The branching component 120 branches the frequency modulated laser beam output from the laser device 110, with a portion of the beam serving as reference light and at least some of the remaining portion serving as measurement light. For example, the branching component 120 branches the frequency modulated laser beam output from the laser device 110 into reference light, measurement light, and monitoring light. The branching component 120 is, for example, a one-input, three-output fiber coupler. Figure 1 In the example of FIG. 1 , the branching component 120 provides the measuring light to the optical circulator 130 , provides the reference light to the beat signal generating component 150 , and provides the monitoring light to the extracting component 170 . Figure 1 An example is shown in which the branch component 120 is a one-input, three-output optical coupler, but alternatively, the branch component 120 may be a combination of two one-input, two-output optical couplers.

[0031] The optical circulator 130 has a plurality of input / output ports. For example, the optical circulator 130 outputs light input from one port to the next port, and outputs light input from the next port to the next port. Figure 1 The optical circulator 130 is shown as having three input / output ports. In this case, the optical circulator 130 outputs the measurement light provided from the branching unit 120 to the optical head unit 140. In addition, the optical circulator 130 outputs the light input from the optical head unit 140 to the beat signal generating unit 150.

[0032] The optical head 140 irradiates the light input from the optical circulator 130 toward the object 10. The optical head 140 includes, for example, a collimating lens. In this case, the optical head 140 first adjusts the light input from the optical circulator 130 via the optical fiber into a beam shape using the collimating lens, and then outputs the light.

[0033] In addition, the optical head assembly 140 receives the reflected light of the measurement light irradiated on the object to be measured 10. The optical head assembly 140 focuses the received reflected light onto the optical fiber using a collimating lens and provides it to the optical circulator 130. In this case, the optical head assembly 140 can include a general collimating lens, and the collimating lens can illuminate the object to be measured 10 with the measurement light and can receive the reflected light from the object to be measured 10. The distance between the optical head assembly 140 and the object to be measured 10 is defined as d.

[0034] Alternatively, the optical head assembly 140 may include a focusing lens. In this case, the optical head assembly 140 focuses the light input from the optical circulator 130 via the optical fiber onto the surface of the object to be measured 10. The optical head assembly 140 receives at least a portion of the reflected light reflected from the surface of the object to be measured 10. The optical head assembly 140 uses the focusing lens to focus the received reflected light onto the optical fiber and provides the light to the optical circulator 130. In this case as well, the optical head assembly 140 may include a general-purpose focusing lens, and the focusing lens may illuminate the object to be measured 10 with the measurement light and receive the reflected light from the object to be measured 10.

[0035] The beat signal generating unit 150 receives reflected light from the optical circulator 130, which is measurement light that is irradiated onto and reflected from the object to be measured 10. Furthermore, the beat signal generating unit 150 receives reference light from the branching unit 120. The beat signal generating unit 150 mixes the reflected light and the reference light to generate a beat signal. The beat signal generating unit 150 includes, for example, a photoelectric conversion element that converts the beat signal into an electrical signal and outputs the electrical signal.

[0036] Here, because the reflected light travels back and forth across the distance from the optical head assembly 140 to the object 10, it experiences a propagation distance difference corresponding to at least a distance 2d compared to the reference light. Since the oscillation frequency of the light output from the laser device 110 changes linearly over time, a frequency difference occurs between the oscillation frequency of the reference light and the oscillation frequency of the reflected light, depending on the propagation delay corresponding to the difference in propagation distance. The beat signal generating assembly 150 generates a beat signal corresponding to this frequency difference.

[0037] The conversion section 160 performs frequency analysis on the beat signal generated by the beat signal generating section 150 to detect the frequency of the beat signal. Here, the frequency of the beat signal is defined as ν B .

[0038] The extraction unit 170 extracts a signal component corresponding to the resonant cavity frequency (resonant frequency) of the optical resonant cavity and superimposed on the frequency-modulated laser beam output from the laser device 110. For example, the extraction unit 170 extracts a signal component having a frequency equal to the resonant cavity frequency corresponding to the resonant cavity length (resonator length) of the laser device 110 from the signal components included in the frequency-modulated laser beam based on the monitoring light. Here, the resonant cavity frequency is defined as ν C .

[0039] The calculation unit 180 calculates the difference in propagation distance between the reference light and the measurement light based on the detection result of the conversion unit 160 and the extraction result of the extraction unit 170. For example, the calculation unit 180 calculates the difference in propagation distance between the reference light and the measurement light based on the frequency v of the beat signal. B and the resonant cavity frequency ν C The distance d from the optical head assembly 140 to the object to be measured 10 is calculated.

[0040] The display unit 190 displays the calculation results of the calculation unit 180. The display unit 190 may include a display, etc., and displays the calculation results. In addition, the display unit 190 may store the calculation results in a storage unit, etc. The display unit 190 may provide the calculation results to an external device via a network, etc.

[0041] The measuring device 100 described above can measure the distance d between the measuring device 100 and the object 10 by analyzing the frequency difference between the reflected light of the measuring light irradiated on the object 10 and the reference light. In other words, the measuring device 100 can form a non-contact and non-destructive optical distance meter. Next, the configuration of the measuring device 100 will be described in more detail.

[0042] [Configuration Example of Laser Device 110]

[0043] Figure 2 A configuration example of the laser device 110 according to the present embodiment is shown. Figure 2 An example of a FSFL is shown in FIG. The laser device 110 includes an optical resonant cavity, and oscillates a laser beam in the optical resonant cavity. The optical resonant cavity of the laser device 110 includes an optical resonant cavity including a frequency shifter 112, a gain medium 114, a WDM coupler 116, a pump light source 117, and an output coupler 118.

[0044] The frequency shifter 112 shifts the frequency of the input light by an approximately constant frequency. The frequency shifter 112 is, for example, an acousto-optic frequency shifter (AOFS) having an acousto-optic element. Here, the frequency shift amount of the frequency shifter 112 is defined as +ν s That is, the frequency shifter 112 shifts the frequency of the light circulating around the resonant cavity so that for each round, the frequency increases by ν s .

[0045] Gain medium 114 is supplied with pump light, and amplifies the input light. Gain medium 114 is, for example, an optical fiber doped with impurities. The impurities are, for example, rare earth elements such as erbium, neodymium, ytterbium, terbium, and thulium. Pump light is supplied to gain medium 114 from pump light source 117 via WDM coupler 116. Output coupler 118 outputs a portion of the light that has been laser-oscillated in the resonant cavity to an external device.

[0046] That is to say, Figure 2 The illustrated laser device 110 includes a fiber ring laser with a frequency shifter 112 in a resonant cavity. The laser device 110 preferably further includes an isolator in the resonant cavity. Furthermore, the laser device 110 may include an optical bandpass filter that allows light within a predetermined wavelength band in the resonant cavity to pass through. The frequency characteristics of the laser beam output from the laser device 110 will be described below.

[0047] Figure 3An example of a laser beam output from the laser device 110 according to the present embodiment is shown. Figure 3 The spectrum of the laser beam output by the laser device 110 at time t0 is shown on the left. In this spectrum, the horizontal axis represents the light intensity and the vertical axis represents the frequency of the light. In addition, the multiple longitudinal modes of the spectrum are represented by the number q. The frequencies of the multiple longitudinal modes are arranged at approximately constant frequency intervals. Assuming τ RT (=1 / ν c ) represents the time it takes for light to propagate around the resonant cavity, and multiple longitudinal modes are transmitted at 1 / τ RT (=ν c ) are arranged at intervals as shown in the following equation. It should be noted that ν0 is the initial frequency of the spectrum at time t0.

[0048] [Equation 1]

[0049]

[0050] Figure 3 On the right side, the frequency changes of the multiple longitudinal modes output by the laser device 110 over time are shown. Figure 3 On the right side, the horizontal axis represents time and the vertical axis represents frequency. Figure 3 The change in the frequency of the laser beam output from the laser device 110 over time is shown on the right, and the instantaneous frequency of the laser beam at time t0 is shown on the left.

[0051] In the laser device 110, each time the light in the resonant cavity propagates around the resonant cavity, the frequency shifter 112 increases the frequency of the light traveling around the resonant cavity by ν. s That is, since the frequency of each mode changes every time τ RT Both increase ν s , so the frequency change rate dν / dt (i.e. chirp rate) becomes approximately equal to ν s / τ RT Therefore, the plurality of longitudinal modes expressed by Equation 1 changes as time t passes as shown in the following equation.

[0052] [Equation 2]

[0053]

[0054] [Details of the distance measurement process]

[0055] The measuring device 100 according to this embodiment measures the distance d between the optical head assembly 140 and the object 10 to be measured by using the laser device 110 that outputs the frequency element expressed by Equation 2. Assume that the optical path difference between the reference light and the reflected light is only the distance 2d, that is, the round-trip distance d, and that the propagation delay corresponding to the distance 2d is Δt. That is, when the measuring light is reflected and returns from the object 10 to be measured at time t, the frequency of the returned reflected light approximately matches the frequency of the past by time Δt before time t, and can therefore be expressed by the following equation.

[0056] [Equation 3]

[0057]

[0058] On the other hand, the reference light at time t can be expressed by the following equation in a similar manner to Equation 2, where the reference light is ν q' (t).

[0059] [Equation 4]

[0060]

[0061] Since the beat signal generating section 150 superimposes the reflected light and the reference light, a plurality of beat signals are generated between the plurality of longitudinal modes represented by Equation 3 and the plurality of longitudinal modes represented by Equation 4. Assuming that the frequency of such a beat signal is ν B (m,d),ν B (m, d) can be expressed by the following equation according to Equation 3 and Equation 4, where m is the interval of the longitudinal mode (=qq′), and Δt=2d / c.

[0062] [Equation 5]

[0063]

[0064] According to Equation 5, the distance d is expressed by the following equation, where 1 / τ RT =ν C .

[0065] [Equation 6]

[0066]

[0067] As can be understood from Equation 6, the distance d can be calculated from the frequency observation result of the beat signal by determining the interval m of the longitudinal mode. It should be noted that when the frequency shift amount ν of the laser device 110 is changed s When the interval m is detected, the interval m can be determined by detecting the change in the beat signal. Since such a method of determining the interval m is known, as described in Patent Document 1, etc., its detailed description is omitted.

[0068] Since the observed beat signal is always a positive frequency, in the calculation, the beat signal generated on the negative frequency side is folded back to the positive side and observed as an image signal. Next, the generation of such an image signal will be described.

[0069] Figure 4 FIG. 1 shows an example of the relationship between the frequency of the beat signal detected by the measuring apparatus 100 according to the present embodiment and the distance d between the optical head unit 140 and the object to be measured 10. Figure 4 In the figure, the horizontal axis represents the distance d and the vertical axis represents the frequency ν of the beat signal. B (m,d). Figure 4 The solid lines in FIG. 1 are lines showing the frequency ν of the beat signal for each of the multiple m values. B A plot of (m, d) versus distance d (as shown in Equation 5).

[0070] like Figure 4 As shown, a plurality of beat signals corresponding to the value of m are generated. However, since a plurality of longitudinal modes included in each of the reflected light and the reference light are spaced at approximately constant frequency intervals ν C Arrange so that multiple beat signals with equal m values ​​are superimposed on approximately the same frequency on the frequency axis. For example, when observing frequencies 0 and ν C When the frequency band is between , multiple beat signals are superimposed on approximately the same frequency and are observed as a single line spectrum.

[0071] In addition, the frequency ν of the beat signal in the negative range less than 0 B The absolute value of (m, d) is further observed as an image signal. That is, Figure 4 The graph of the region where the vertical axis is less than 0 is folded back with frequency 0 as the boundary. Figure 4 The image signal after folding is shown by multiple dotted lines. Since only the positive and negative of the image signal after folding are reversed, the image signal is superimposed on the observed frequency axis with the same absolute value of the frequency before folding. For example, when the observed frequency is between 0 and ν C When the frequency band is between ν and ν, the beat signal and the image signal are located at different frequencies, unless the frequencies of the beat signal and the image signal become ν C / 2.

[0072] As mentioned above, at frequencies 0 and ν C In the observation frequency band between , two line spectra are generated, which are (i) the beat signal ν B (m, d) and (ii) image signal ν B (m′,d), image signal ν B The value of m in (m′,d) and the beat signal ν BThe m value of (m, d) is different. Here, as an example, m'=m+1. In this case, the beat signal generating section 150 can eliminate such an image signal by using orthogonal detection. Next, the beat signal generating section 150 and the conversion section 160 using orthogonal detection will be described.

[0073] Figure 5 The configuration example of the beat signal generating unit 150 and the conversion unit 160 according to this embodiment is shown. The beat signal generating unit 150 performs quadrature detection on the reflected light and the reference light. The beat signal generating unit 150 includes an optical 90-degree hybrid 152, a first photoelectric conversion unit 154, and a second photoelectric conversion unit 156.

[0074] The optical 90-degree hybrid 152 branches the input reflected light and the input reference light into two parts respectively. The optical 90-degree hybrid 152 multiplexes one of the branched reflected lights with one of the branched reference lights using an optical coupler or the like to generate a first beat signal. The optical 90-degree hybrid 152 multiplexes the other branched reflected light with the other branched reference light using an optical coupler or the like to generate a second beat signal. Here, the optical 90-degree hybrid 152 generates a beat signal after generating a phase difference of 90 degrees between the two branched reference lights. For example, the optical 90-degree hybrid 152 multiplexes the branched reflected light with one of the branched reference lights, and multiplexes the branched reflected light with light generated by the other branched reference light passing through a π / 2 wavelength plate.

[0075] The first photoelectric conversion unit 154 and the second photoelectric conversion unit 156 receive the multiplexed reflected light and reference light and convert them into electrical signals. Each of the first photoelectric conversion unit 154 and the second photoelectric conversion unit 156 can be a photodiode or the like. Each of the first photoelectric conversion unit 154 and the second photoelectric conversion unit 156 is, for example, a balanced photodiode. Figure 5 , it is assumed that the first photoelectric conversion unit 154 generates a first beat signal and the second photoelectric conversion unit 156 generates a second beat signal. As described above, the beat signal generation unit 150 performs quadrature detection by multiplexing two reference lights and two reflected lights that differ in phase by 90 degrees, and outputs the two beat signals to the conversion unit 160.

[0076] The conversion component 160 performs frequency analysis on the two beat signals. Here, an example in which the conversion component 160 performs frequency analysis using the first beat signal as the I signal and the second beat signal as the Q signal will be described. The conversion component 160 includes a first filter component 162, a second filter component 164, a first AD converter 202, a second AD converter 204, a first clock signal supply component 210, and a frequency analysis component 220.

[0077] The first filter section 162 and the second filter section 164 reduce signal components in a frequency band different from the frequency band that the user or the like wants to analyze. Here, the frequency band that the user or the like wants to analyze is set to 0 to v C The first filter element 162 and the second filter element 164 are, for example, such that the frequency is equal to or less than ν C In this case, the first filter component 162 will reduce the signal component with a frequency greater than ν by C The first beat signal obtained by reducing the signal component with a high frequency than the frequency v is provided to the first AD converter 202. C The second beat signal obtained by using the signal component of the frequency of φ is supplied to the second AD converter 204.

[0078] The first AD converter 202 and the second AD converter 204 convert analog signals into digital signals. For example, the first AD converter 202 converts the first beat signal into a digital signal, and the second AD converter 204 converts the second beat signal into a digital signal. The first clock signal providing component 210 provides the first clock signal to the first AD converter 202 and the second AD converter 204. In doing so, the first AD converter 202 and the second AD converter 204 convert the analog signals into digital signals at a first sampling rate that is approximately the same as the clock frequency of the received first clock signal.

[0079] Here, when the observation frequency band is from 0 to ν C When the beat signal frequency is at most the resonant cavity frequency ν of the optical resonant cavity C Therefore, the first clock signal providing component 210 provides a frequency greater than or equal to the resonant cavity frequency ν of the optical resonant cavity. C The first clock signal, which is twice the value of the first clock signal, is provided to the first AD converter 202 and the second AD converter 204, so that a beat signal can be observed.

[0080] The frequency analysis component 220 converts the first beat signal and the second beat signal into frequency data. As an example, the frequency analysis component 220 performs a digital Fourier transform (DFT) on the first beat signal and the second beat signal. The frequency analysis component 220 adds the first beat signal converted into frequency data as the real part, and adds the second beat signal converted into frequency data as the imaginary part, and eliminates the image signal. As described above, the conversion component 160 converts the beat signal into a digital signal at a first sampling rate, and then performs frequency analysis on the digital signal. It should be noted that after converting the beat signal into a digital signal, the conversion component 160 can configure the frequency analysis component 220 using an integrated circuit or the like. The orthogonal detection in the beat signal generating component 150 and the frequency analysis in the conversion component 160 will be described below.

[0081] Figure 6 An example of an outline of quadrature detection by the beat signal generating section 150 and the converting section 160 according to the present embodiment is shown. Figure 6 In FIG, the horizontal axis represents the frequency of the beat signal, and the vertical axis represents the signal strength. Figure 6 The spectrum of one of the I signal and the Q signal is shown. The spectrum of both the I signal and the Q signal has approximately the same spectrum shape, as shown in FIG. Figure 6 In the I signal and Q signal, for example, at frequencies 0 and ν C The beat signal ν is observed in the frequency band between B (m, d) and image signal ν B (m+1, d). In this case, in the I signal and Q signal, the original beat signal of the image signal -ν B (m+1,d) and the beat signal -ν B (m,d) exists at frequencies 0 and -ν on the negative side C in the frequency band between .

[0082] Here, since the I signal and the Q signal are signal components detected orthogonally by the beat signal generating section 150, they contain different phase information even if the spectrum shapes are the same. C In the frequency band between I signal and image signal ν B (m+1,d) and the image signal ν of the Q signal B The phases of (m+1, d) are opposite to each other. Similarly, the frequencies 0 and -ν on the negative side C In the frequency band between the I signal and the B (m, d) and Q signal beat signal -ν B The phases of (m, d) are opposite to each other.

[0083] Therefore, if Figure 6 As shown in the lower part of FIG, when the frequency analysis unit 220 calculates I+jQ using the I signal and the Q signal, at frequencies 0 and ν C In the frequency band between B The beat signals of (m, d) enhance each other, and the frequency is ν B The image signals at (m+1, d) cancel each other. Similarly, at frequencies 0 and -ν C In the frequency band between B The beat signals of (m+1,d) enhance each other, and the frequency is -ν B The beat signals of (m, d) cancel each other.

[0084] According to the frequency analysis result of the frequency analysis unit 220, for the frequencies 0 and ν C The frequency in the band between B (m, d), a beat signal is observed. Since the measurement device 100 can cancel the image signal in this way, the frequency ν of the beat signal can be detected B For example, the frequency analysis unit 220 uses the frequency with the highest signal strength of the converted frequency signal as the frequency v of the beat signal. B (m,d) output.

[0085] Here, the distance d measured by the measuring device 100 is expressed by Equation 6. As can be seen from Equation 6, the distance d can be measured by using three frequencies v C 、ν s and ν B (m, d) calculates the distance d. In the three frequencies, ν can be detected as described above B (m,d). In addition, due to ν C and ν s is a frequency determined based on the components used in the laser device 110, so ideally ν C and ν s should be a fixed value. Here, due to ν s is the frequency shift amount of the frequency shifter 112, so by using a device having a stable frequency shift amount as the frequency shifter 112, ν s Basically considered as a fixed value.

[0086] On the other hand, due to ν C corresponds to the optical length of the resonant cavity of the laser device 110, and thus it may change due to environmental fluctuations such as temperature. For example, if the laser device 110 is Figure 2In the example shown, a fiber ring laser with an optical fiber resonant cavity can vary by approximately 10 ppm for every one degree Celsius change in ambient temperature. It should be noted that even if laser device 110 is a solid-state laser such as a semiconductor laser, the resonant cavity length may vary due to such environmental fluctuations. Therefore, extraction component 170 extracts the resonant cavity frequency corresponding to the resonant cavity length in order to monitor such changes in the resonant cavity length. Extraction component 170 will be described below.

[0087] Figure 7 The following figure shows an example configuration of extraction section 170 according to this embodiment. Extraction section 170 includes a photoelectric conversion section and extracts a signal component corresponding to the resonant cavity frequency of the optical resonant cavity from the electrical signal converted by the photoelectric conversion section. Extraction section 170 includes a third photoelectric conversion section 172, a third filter section 174, a third AD converter 176, and a resonant cavity frequency output section 178.

[0088] The third photoelectric conversion component 172 converts the monitoring light into an electrical signal. The third photoelectric conversion component 172 may be a photodiode or the like. Figure 4 As shown, the laser device 110 outputs a frequency modulated laser beam having multiple longitudinal modes with a frequency that is consistent with the resonant cavity frequency ν. C Therefore, when the third photoelectric conversion component 172 performs photoelectric conversion on the frequency modulated laser beam, the output includes the resonant cavity frequency ν C electrical signal.

[0089] The third filter section 174 allows the electrical signal converted by the third photoelectric conversion section 172 to have a resonance cavity frequency v of the optical resonance cavity. C The third filter section 174 has, for example, at least one of a high-pass filter, a low-pass filter, a band-pass filter, and a band-stop filter. Figure 7 An example is shown in which the third filter component 174 is a bandpass filter.

[0090] The third AD converter 176 converts the input analog signal into a digital signal. C The analog signal is converted into a digital signal in synchronization with a clock signal having a frequency twice that of the first clock signal providing unit 210. For example, when the third AD converter 176 receives the clock signal from the first clock signal providing unit 210, it operates.

[0091] The resonant cavity frequency output component 178 performs frequency analysis on the signal component that has passed through the third filter component 174. The resonant cavity frequency output component 178 first converts the digital signal output from the third AD converter 176 into frequency data. As an example, the resonant cavity frequency output component 178 performs a digital Fourier transform (DFT) on the digital signal. The resonant cavity frequency output component 178 performs frequency analysis on the frequency data and outputs the resonant cavity frequency v C For example, the resonant cavity frequency output component 178 outputs the frequency data with the highest signal strength as the resonant cavity frequency v C .

[0092] As mentioned above, Figure 7 The extraction component 170 shown in FIG extracts the resonant cavity frequency ν from the monitoring light C signal component and output the resonant cavity frequency ν C Therefore, even if the cavity length of the laser device 110 changes due to fluctuations in the ambient temperature, the extraction component 170 can extract and output the cavity frequency ν corresponding to the change. C Since the calculation unit 180 uses the fixed value ν detected in the above manner s 、ν B (m,d) and the resonant cavity frequency ν C , so the distance d corresponding to the fluctuation of the surrounding temperature can be calculated.

[0093] As described above, even if environmental fluctuations occur, the measurement apparatus 100 can suppress a decrease in measurement accuracy because the measurement apparatus 100 monitors the resonant cavity frequency ν corresponding to the environmental fluctuations. C And the cavity frequency ν is reflected in the calculation of the distance d C Alternatively or additionally, the laser device 110 may be placed in a temperature-stable controlled room such as a constant temperature room to reduce the influence of environmental fluctuations and suppress a decrease in the measurement accuracy of the measurement device 100 .

[0094] However, since the above-mentioned measuring device 100 tends to be a large device, problems such as increased cost, problems related to circuit adjustment, installation area, etc. may arise. In addition, when the observed change in the resonant cavity length is used for distance measurement, the observed change in the resonant cavity length is superimposed on the change in the distance measurement, which causes the change in the distance measurement to increase. Here, it is assumed that the change in the distance measurement is Δd and the change in the measurement of the beat signal is Δν. B , and the measured change in the resonant cavity frequency is Δν C , the change in distance measurement Δd is expressed by the following formula.

[0095] [Equation 7]

[0096]

[0097] As shown in Equation 7, by using the measurement results of the resonant cavity frequency, it can be understood that the change in distance measurement Δd is increased by the measurement change Δν including the resonant cavity frequency. C Therefore, the measurement device according to this embodiment can reduce the measurement change Δν of the resonant cavity frequency by C Next, this measuring device will be described.

[0098] [Configuration Example of Measurement Device 300]

[0099] Figure 8 FIG. 1 shows a configuration example of a measuring device 300 and an object to be measured 10 according to this embodiment. Figure 8 In the measuring device 300 shown, Figure 1 The operations substantially the same as those of the illustrated measurement apparatus 100 according to the present embodiment are denoted by the same reference numerals, and description thereof is omitted. The measurement apparatus 300 further includes a digital filter 310 and a second clock signal supply section 320 .

[0100] The digital filter 310 digitally filters the signal component extracted by the extraction component 170. The digital filter 310 digitally filters the resonant cavity frequency ν extracted from the monitoring light by the extraction component 170. C Filter and reduce the resonant cavity frequency ν C The measured change Δν C The digital filter 310 is, for example, a Kalman filter, a Gaussian filter, a moving average filter, etc. In addition, the digital filter 310 may further include a sparse filter, a high-pass filter, a low-pass filter, a band-pass filter, and / or a band-stop filter, etc.

[0101] The second clock signal providing component 320 provides a second clock signal to the digital filter 310. The second clock signal providing component 320 may also provide the second clock signal to the extraction component 170. The clock frequency of the second clock signal is, for example, substantially the same as the clock frequency of the first clock signal. Alternatively, the clock frequency of the second clock signal may be a frequency lower than the clock frequency of the first clock signal.

[0102] Due to the resonant cavity frequency ν performed by the extraction component 170 C The extraction and filtering process performed by the digital filter 310 is used to measure the resonant cavity frequency ν caused by the ambient temperature, etc. CBecause the second clock signal used by the extraction component 170 and the digital filter 310 may have a lower clock frequency than the first clock signal used to measure the beat signal used to measure the difference in propagation distance between the reference light and the measurement light, the clock frequency used for these processing operations may be relatively low. For example, the second clock signal used by the extraction component 170 and the digital filter 310 may have a lower clock frequency than the first clock signal used to measure the beat signal used to measure the difference in propagation distance between the reference light and the measurement light.

[0103] Therefore, the second clock signal providing component 320 provides a second clock signal having a lower clock frequency than the first clock signal to the digital filter 310. By doing so, the digital filter 310 performs digital filtering on the signal components extracted by the extraction component 170 at a second sampling rate slower than the first sampling rate. The third AD converter 176 can also receive the second clock signal from the second clock signal providing component 320 and convert the analog signal input at the second sampling rate into a digital signal. This allows, for example, an AD converter that is slower and more economical than the first AD converter 202 and the second AD converter 204 to be used as the third AD converter 176.

[0104] Figure 9 shows the resonant cavity frequency ν output by the extraction component 170 according to this embodiment. C . Figure 9 The horizontal axis represents time, and the vertical axis represents frequency. The resonant cavity frequency ν output by the extraction component 170 C becomes, for example, a signal waveform on which (i) the resonant cavity frequency ν is superimposed C The measured change Δν C and (ii) the measured change Δν caused by ambient temperature, etc. C Slow fluctuations.

[0105] Figure 10 The resonant cavity frequency ν is filtered and output by the digital filter 310 according to this embodiment. C Example. Figure 10 In, with Figure 9 In a similar way, the horizontal axis represents time and the vertical axis represents frequency. Figure 10 As shown, the digital filter 310 output has a reduced measurement variation Δν superimposed on the signal waveform. C The resonant cavity frequency ν C This filtering process of the digital filter 310 can be implemented by a known algorithm, etc., without providing a special device, etc. In addition, since the operation of the digital filter 310 may be slower than that of the conversion section 160, this digital filter can be configured using a simple configuration, which is low in cost and consumes little power.

[0106] The calculation unit 180 calculates the difference in propagation distance between the reference light and the measurement light based on the frequency analysis result of the beat signal and the digitally filtered signal component. s 、ν B (m, d) and the resonant cavity frequency ν C , so the distance d corresponding to the fluctuation of the ambient temperature can be calculated. As described above, since the measuring device 300 uses the measurement change Δν C The resonant cavity frequency ν is reduced by the digital filter 310 C , so the distance d to the object to be measured 10 can be measured with high accuracy while suppressing an increase in cost.

[0107] like Figure 10 As shown, the calculation component 180 can obtain the frequency ν of the resonant cavity from the digital filter 310. C Observed changes with decreasing Δν C Therefore, the calculation component 180 can also observe the changes in the resonant cavity frequency ν caused by the activation of the measuring device 300, the rapid change of the ambient temperature, the instantaneous voltage drop of the power supply, the short-term power supply stop (instantaneous stop, short interruption), etc. C Significant fluctuations.

[0108] As described above, the calculation component 180 may take into account the resonant cavity frequency v C The distance d to the object 10 to be measured can be calculated based on the fluctuation of the resonance cavity frequency ν. However, it is possible to avoid performing accurate measurements when the environmental fluctuation occurs rapidly. C The stability of the measurement of the measuring device 300 is determined based on the fluctuation of the value ...

[0109] [Modification Example of Measuring Device 300]

[0110] Figure 11 FIG. 1 shows a modified example of the measuring device 300 and the object to be measured 10 according to the present embodiment. Figure 11 In the measuring device 300 shown, Figure 8 The operations of the measurement device 300 according to the present embodiment shown are substantially the same as those denoted by the same reference numerals, and description thereof is omitted. In the measurement device 300 according to the modified example, the calculation section 180 further includes a change rate calculation section 330 , a determination section 340 , and an output control section 350 .

[0111] The rate of change calculation unit 330 calculates the rate of change per unit time of the digitally filtered signal component. The rate of change calculation unit 330 is, for example, responsive to a predetermined number of resonant cavity frequencies v obtained from the digital filter 310. C The rate of change calculation unit 330 may calculate the rate of change per unit time for each predetermined time period.

[0112] Determination unit 340 determines the stability of measurement by measurement device 300 based on the rate of change per unit time. Determination unit 340 pre-stores, for example, a rate of change range within which the measurement results of measurement device 300 are stable. Then, in response to the rate of change calculation result of rate of change calculation unit 330 being within the stored rate of change range, determination unit 340 determines that measurement device 300 can perform stable measurement. In this case, when the calculated value of the rate of change is equal to or greater than a first threshold value and equal to or less than a second threshold value, determination unit 340 determines that measurement device 300 is stable.

[0113] Output control section 350 provides the calculation result of distance d to display section 190 based on the determination result of measuring device 300. For example, when measuring device 300 can stably perform measurement, output control section 350 provides the calculation result of distance d to display section 190. Furthermore, when measuring device 300 cannot stably perform measurement, output control section 350 does not need to provide the calculation result of distance d to display section 190. In this way, display section 190 can only output the results of measuring device 300 that stably measured distance d. This enables users of measuring device 300, etc., to use only measurement results obtained by measuring device 300 in a stable operating environment.

[0114] Alternatively, when the measurement device 300 cannot stably perform measurement, the output control unit 350 provides the calculation result of the distance d to the display unit 190 and notifies the display unit 190 that the measurement environment is unstable. In this case, the display unit 190 displays the calculation result of the distance d along with, for example, "reference value," "measurement environment fluctuates," and the like. This allows the user of the measurement device 300, etc., to easily understand whether the measurement device 300 has performed measurement in a stable environment and effectively use the measurement results.

[0115] Although the measurement device 300 according to this embodiment includes the second clock signal providing component 320 and provides the second clock signal to the digital filter 310, the present invention is not limited thereto. For example, the first clock signal providing component 210 may provide the first clock signal to the digital filter 310. In this case, it is desirable that the digital filter 310 include a conversion circuit, a filter, etc., and perform filtering using a clock signal obtained by converting the first clock signal to a lower frequency. Alternatively, the first clock signal providing component 210 may provide the first clock signal to the extraction component 170, and in this case, the second clock signal providing component 320 may not be provided.

[0116] Preferably, at least a portion of the conversion component 160, the extraction component 170, and the calculation component 180 provided in the measurement device 100 and the measurement device 300 according to this embodiment is formed by an integrated circuit, etc. At least a portion of the conversion component 160, the extraction component 170, and the calculation component 180 includes, for example, a field programmable gate array (FPGA), a digital signal processor (DSP), and / or a central processing unit (CPU).

[0117] When at least a portion of the conversion component 160, the extraction component 170, and the calculation component 180 is configured by a computer or the like, the portion includes a storage unit and a control unit. The storage unit includes, for example, a read-only memory (ROM) for storing a basic input / output system (BIOS) of a computer or the like that implements the conversion component 160, the extraction component 170, and the calculation component 180, and a random access memory (RAM) used as a work area. The storage unit can store an operating system (OS), programs, applications, and / or various information. The storage unit can also include a large-capacity device such as a hard disk drive (HDD) and / or a solid-state drive (SSD).

[0118] The control unit is a processor such as a CPU and functions as at least part of the conversion unit 160, the extraction unit 170, and the calculation unit 180 by executing a program stored in the storage unit. The control unit may include a graphics processing unit (GPU) or the like.

[0119] The present invention has been described based on exemplary embodiments. The technical scope of the present invention is not limited to the scope described in the above embodiments, and various changes and modifications can be made within the scope of the present invention. For example, all or part of the device can be configured using any units that are functionally or physically distributed or integrated. In addition, new exemplary embodiments generated by any combination of them are included in the exemplary embodiments of the present invention. In addition, the effects of the new embodiments brought about by the combination also have the effects of the original exemplary embodiments.

[0120] [Explanation of Reference Numerals]

[0121] 10 Objects to be tested

[0122] 100 Measuring device

[0123] 110 Laser device

[0124] 112 Frequency Shifter

[0125] 114 Gain Medium

[0126] 116 WDM coupler

[0127] 117 Pump Light Source

[0128] 118 Output Coupler

[0129] 120 branch components

[0130] 130 Optical Circulator

[0131] 140 optical head components

[0132] 150 Beat signal generating component

[0133] 152 Optical 90 degree mixer

[0134] 154 first photoelectric conversion unit

[0135] 156 second photoelectric conversion unit

[0136] 160 conversion parts

[0137] 162 first filter component

[0138] 164 second filter component

[0139] 170 Extraction Parts

[0140] 172 third photoelectric conversion component

[0141] 174 third filter component

[0142] 176 Third AD Converter

[0143] 178 Resonance Cavity Frequency Output Component

[0144] 180 computing components

[0145] 190 Display Components

[0146] 202 First AD Converter

[0147] 204 Second AD converter

[0148] 210 first clock signal providing component

[0149] 220 frequency analysis unit

[0150] 300 measuring devices

[0151] 310 Digital Filter

[0152] 320 second clock signal providing component

[0153] 330 Change rate calculation component

[0154] 340 Determine the components

[0155] 350 Output control components

Claims

1. A measuring device for measuring the distance to an object to be measured, the measuring device comprising: A laser device having an optical resonant cavity and outputting a frequency-modulated laser beam having multiple modes; a branching component that branches a portion of the frequency-modulated laser beam output by the laser device into reference light and branches at least some of the remaining portion of the frequency-modulated laser beam into measuring light; a beat signal generating section that generates a beat signal by mixing the reference light and reflected light that is reflected by irradiating the measuring light onto the object to be measured; A conversion component converts the beat signal into a digital signal at a first sampling rate, and then outputs the frequency v of the beat signal by frequency analysis of the digital signal. B (m,d); Extraction component, extracting the resonance cavity frequency ν of the optical resonance cavity C and a signal component superimposed on the frequency modulated laser beam output from the laser device; a digital filter for digitally filtering the extracted signal component at a second sampling rate; as well as The calculation component calculates the frequency ν of the beat signal by B (m, d) and the resonant cavity frequency ν of the digitally filtered optical resonant cavity C Substitute the following equation to calculate the difference in propagation distance between the reference light and the measurement light: where m is the separation between the longitudinal modes of the reflected beam of the frequency modulated laser and the reference beam, c is the speed of light, and ν s is the frequency shift of the frequency modulated laser beam.

2. The measuring device according to claim 1, wherein The digital filter digitally filters the extracted signal components at the second sampling rate that is slower than the first sampling rate.

3. The measuring device according to claim 1, wherein The branching component branches the frequency modulated laser beam into the reference light, the measuring light, and the monitoring light, and The extraction unit includes a photoelectric conversion unit that converts the monitoring light into an electric signal, and extracts a signal component corresponding to the resonant cavity frequency of the optical resonant cavity from the electric signal converted by the photoelectric conversion unit.

4. The measuring device according to claim 3, wherein The extraction component also includes: a filter section that passes a signal component having a resonant cavity frequency of the optical resonant cavity from among the electrical signal converted by the photoelectric conversion section; and A resonant cavity frequency output section performs frequency analysis on the signal component having passed through the filter section and outputs a resonant cavity frequency of the optical resonant cavity.

5. The measuring device according to claim 4, wherein The extraction section further includes an AD converter that converts the signal component that has passed through the filter section into a digital signal at the second sampling rate, and The resonant cavity frequency output component converts the digital signal output from the AD converter into frequency data and performs frequency analysis on the frequency data.

6. The measuring device according to any one of claims 1 to 5, wherein: The computing component further comprises: a rate-of-change calculation unit that calculates a rate of change per unit time of the digitally filtered signal component; and A determining component determines the stability of the measurement of the measuring device based on the rate of change per unit time.

7. The measuring device according to claim 6, wherein The determination section determines that the measurement device is stable when the calculated value of the change rate is equal to or greater than a first threshold value and equal to or less than a second threshold value.

8. The measuring device according to claim 7, wherein The calculation section further includes a display section that displays a calculation result of the calculation section, and provides the calculation result to the display section based on a determination result of the determination section.

9. A method for measuring the distance to an object to be measured, the method comprising the following steps: Outputting frequency-modulated laser beams having multiple modes from a laser device having an optical resonant cavity; branching a portion of the frequency-modulated laser beam into reference light and branching at least some of the remaining portion into measuring light; generating a beat signal by mixing the reference light and reflected light reflected by irradiating the measuring light onto the object to be measured; The beat signal is converted into a digital signal at a first sampling rate, and then the frequency v of the beat signal is output by frequency analysis of the digital signal. B (m,d); Extract the resonant cavity frequency ν of the optical resonant cavity C and a signal component superimposed on the frequency modulated laser beam; digitally filtering the signal component at a second sampling rate; as well as By setting the frequency ν of the beat signal B (m, d) and the resonant cavity frequency ν of the digitally filtered optical resonant cavity C Substitute the following equation to calculate the difference in propagation distance between the reference light and the measurement light: where m is the separation between the longitudinal modes of the reflected beam of the frequency modulated laser and the reference beam, c is the speed of light, and ν s is the frequency shift of the frequency modulated laser beam.

10. The measuring method according to claim 9, further comprising the following steps: calculating a rate of change per unit time of the digitally filtered signal component; as well as The stability of the measurement is determined based on the rate of change per unit time.

Images