Measuring device and measuring method

Abstract

A measuring device 300 includes: a laser device 110, which outputs a frequency-modulated laser beam; a branching component 120, which branches the frequency-modulated laser beam into a reference light and a measuring light; a beat signal generating component 150, which generates a beat signal by mixing the reference light and the reflected light reflected by irradiating the measuring light onto the object to be measured 10; an extraction component 170, which extracts a signal component corresponding to the resonant frequency of the frequency-modulated laser beam; a clock signal generating component 310, which generates a first clock signal based on the signal component; a conversion component 320, which converts the beat signal into a first digital signal using the first clock signal; and a calculation component 180, which calculates the difference in propagation distance between the reference light and the measuring light based on the first digital signal.

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 resonator and outputs a plurality of longitudinal-mode lasers whose oscillation frequency changes linearly with time. In addition, an optical distance meter using such a 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, for example, in design and production sites. FSFLs sometimes cause the measurement accuracy of optical rangefinders to decrease because the length of the resonator may change due to environmental fluctuations such as temperature. In order to prevent the decrease in measurement accuracy, it has generally been considered to reduce environmental fluctuations by installing the FSFL in a constant temperature chamber, observe changes in the resonator length by monitoring the output of the FSFL, and so on. However, such measures have led to an increase in the scale of the device and have caused problems such as increased costs.

[0005] The present invention has been made in view of this problem, and an object of the present invention is to suppress a decrease in accuracy with a simple configuration even when environmental fluctuations occur in an optical distance meter.

[0006] Means of solving the problem

[0007] A first aspect of the present invention provides a measuring device, which includes: a laser device having a laser resonator and outputting a frequency-modulated laser beam having multiple modes; a branching component that branches the frequency-modulated laser beam into (i) a portion of the frequency-modulated laser beam output by the laser device as a reference light, and (ii) at least some of the remaining portion of the frequency-modulated laser beam as a measuring light; a beat signal generating component that generates a beat signal by mixing the reference light and reflected light reflected by irradiating the measuring light onto an object to be measured; an extraction component that extracts a signal component corresponding to the resonance frequency of the laser resonator and superimposed on the frequency-modulated laser beam output from the laser device; a clock signal generating component that generates a first clock signal based on the signal component; a conversion component that converts the beat signal into a first digital signal using the first clock signal; and a calculation component that calculates the difference in propagation distance between the reference light and the measuring light based on the first digital signal.

[0008] The branching component can branch the frequency-modulated laser beam into reference light, measurement 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 frequency of the laser resonator from the electrical signal converted by the photoelectric conversion component.

[0009] The extraction means may further include a filter means that passes a signal component having a resonance frequency of the laser resonator from within the electric signal converted by the photoelectric conversion means.

[0010] The clock signal generating section may include a PLL circuit that uses a frequency of a signal component as a reference frequency and outputs a frequency signal having a frequency that is a multiple of the reference frequency, and the clock signal generating section may output the frequency signal as the first clock signal.

[0011] The conversion section may include an A / D converter that converts the beat signal into the first digital signal in synchronization with the first clock signal.

[0012] The conversion component may further include: an AD converter that converts the beat signal into a second digital signal in synchronization with a second clock signal different from the first clock signal, and a resampling component that resamples the second digital signal using the first clock signal and outputs the first digital signal.

[0013] A second aspect of the present invention provides a measurement method, which includes the following steps: outputting a frequency-modulated laser beam having multiple modes from a laser device having a laser resonator; branching the frequency-modulated laser beam into (i) a portion of the frequency-modulated laser beam as reference light, and (ii) at least some of the remaining portion of the frequency-modulated laser beam as measurement light; generating a beat signal by mixing the reference light and reflected light reflected by irradiating the measurement light onto an object to be measured; extracting a signal component corresponding to the resonance frequency of the laser resonator and superimposed on the frequency-modulated laser beam; generating a first clock signal based on the signal component; converting the beat signal into a first digital signal using the first clock signal; and calculating a difference in propagation distance between the reference light and the measurement light based on the first digital signal.

[0014] Converting the beat signal into a first digital signal may include converting the beat signal into the first digital signal in synchronization with the first clock signal.

[0015] Converting the beat signal into a first digital signal may include converting the beat signal into a second digital signal in synchronization with a second clock signal different from the first clock signal, and resampling the second digital signal using the first clock signal and outputting the first digital signal.

[0016] Effects of the Invention

[0017] According to the present invention, there is an effect that even when environmental fluctuations occur in an optical distance meter, a decrease in accuracy can be suppressed with a simple configuration. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] Figure 1 A configuration example of a measuring device 100 and an object to be measured 10 according to the present embodiment are shown.

[0019] Figure 2 A configuration example of the laser device 110 according to the present embodiment is shown.

[0020] Figure 3 An example of a laser beam output from the laser device 110 according to the present embodiment is shown.

[0021] 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.

[0022] Figure 5 There is shown a configuration example of the beat signal generating section 150 and the detecting section 160 according to the present embodiment.

[0023] Figure 6 An example of an outline of quadrature detection by the beat signal generating section 150 and the detecting section 160 according to the present embodiment is shown.

[0024] Figure 7 A configuration example of the extraction section 170 according to the present embodiment is shown.

[0025] Figure 8 A configuration example of a measuring device 300 and an object to be measured 10 according to the present embodiment are shown.

[0026] Fig. 9 There is shown a configuration example of the beat signal generating section 150 , the extracting section 170 , the clock signal generating section 310 , and the converting section 320 according to the present embodiment.

[0027] Fig.10 There is shown a configuration example of the beat signal generating section 150 , the extracting section 170 , the clock signal generating section 310 , and the converting section 320 provided in a modified example of the measuring apparatus 300 according to the present embodiment. DETAILED DESCRIPTION

[0028] [Configuration Example of Measurement Device 100]

[0029] Figure 1 A configuration example of a measuring device 100 according to the present embodiment and an object to be measured 10 are shown. The measuring device 100 optically measures the distance between the measuring device 100 and the object to be measured 10. In addition, the measuring device 100 can measure the three-dimensional shape of the object to be measured 10 by scanning the position of the laser beam irradiated on the object to be measured 10. The measuring device 100 includes a laser device 110, a branching part 120, an optical circulator 130, an optical head part 140, a beat signal generating part 150, a detecting part 160, an extracting part 170, a calculating part 180, and a display part 190.

[0030] The laser device 110 has a laser resonator and outputs a frequency modulated laser beam having multiple modes. The laser device 110 is provided with a frequency shifter in the resonator and outputs multiple longitudinal mode lasers whose oscillation frequency changes linearly with time. The laser device 110 is, for example, a frequency shift feedback laser (FSFL). The FSFL will be described later.

[0031] 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 and three-output optical 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 and three-output optical coupler, but alternatively, the branch component 120 may be a combination of two one-input and two-output optical couplers.

[0032] 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 An example is shown in which the optical circulator 130 has three input / output ports. In this case, the optical circulator 130 outputs the measurement light provided from the branching part 120 to the optical head part 140. In addition, the optical circulator 130 outputs the light input from the optical head part 140 to the beat signal generating part 150.

[0033] The optical head component 140 irradiates the light input from the optical circulator 130 toward the object 10. The optical head component 140 includes, for example, a collimating lens. In this case, the optical head component 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.

[0034] In addition, the optical head component 140 receives the reflected light of the measuring light irradiated on the object to be measured 10. The optical head component 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 component 140 may include a general collimating lens, and the collimating lens may irradiate the object to be measured 10 with the measuring light and may receive the reflected light from the object to be measured 10. The distance between the optical head component 140 and the object to be measured 10 is defined as d.

[0035] Alternatively, the optical head component 140 may include a condenser lens. In this case, the optical head component 140 focuses the light input from the optical circulator 130 via the optical fiber on the surface of the object to be measured 10. The optical head component 140 receives at least a portion of the reflected light reflected on the surface of the object to be measured 10. The optical head component 140 focuses the received reflected light onto the optical fiber using the condenser lens and provides the light to the optical circulator 130. Also in this case, the optical head component 140 may include a general condenser lens, and the condenser lens may illuminate the object to be measured 10 with the measuring light and receive the reflected light from the object to be measured 10.

[0036] The beat signal generating part 150 receives the reflected light from the optical circulator 130, which is the measuring light irradiated onto and reflected from the object to be measured 10. In addition, the beat signal generating part 150 receives the reference light from the branching part 120. The beat signal generating part 150 mixes the reflected light and the reference light to generate a beat signal. The beat signal generating part 150 includes, for example, a photoelectric conversion element, which converts the beat signal into an electrical signal and outputs the electrical signal.

[0037] Here, since the reflected light travels back and forth over the distance from the optical head unit 140 to the object to be measured 10, a difference in propagation distance corresponding to at least a distance 2d occurs 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 depending on the propagation delay corresponding to the difference in propagation distance occurs between the oscillation frequency of the reference light and the oscillation frequency of the reflected light. The beat signal generating unit 150 generates a beat signal corresponding to this frequency difference.

[0038] The detection unit 160 performs frequency analysis on the beat signal generated by the beat signal generation unit 150 to detect the frequency of the beat signal. Here, the frequency of the beat signal is defined as v B .

[0039] The extraction part 170 extracts a signal component corresponding to the resonance frequency of the laser resonator and superimposed on the frequency modulated laser beam output from the laser device 110. For example, the extraction part 170 extracts the resonance frequency corresponding to the resonator length of the laser device 110 based on the monitoring light. Here, the resonance frequency is defined as v c .

[0040] The calculation part 180 detects the difference in propagation distance between the reference light and the measurement light based on the detection result of the detection part 160 and the extraction result of the extraction part 170. For example, the calculation part 180 detects 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 frequency v c The distance d from the optical head assembly 140 to the object 10 to be measured is calculated.

[0041] The display part 190 displays the calculation result of the calculation part 180. The display part 190 may include a display, etc., and displays the calculation result. In addition, the display part 190 may store the calculation result in a storage unit, etc. The display part 190 may provide the calculation result to an external device via a network, etc.

[0042] The above-mentioned measuring device 100 can measure the distance d between the measuring device 100 and the object 10 to be measured by analyzing the frequency difference between the reflected light of the measuring light irradiated on the object 10 and the reference light. That is, the measuring device 100 can form a non-contact and non-destructive optical distance meter. Next, a more detailed configuration of the measuring device 100 will be described.

[0043] [Configuration Example of Laser Device 110]

[0044] Figure 2 A configuration example of the laser device 110 according to the present embodiment is shown. Figure 2 The laser device 110 of FIG. 1 shows an example of FSFL. The laser device 110 includes a laser resonator, and oscillates a laser beam in the laser resonator. The laser resonator of the laser device 110 includes a laser resonator including a frequency shifter 112, a gain medium 114, a WDM coupler 116, a pump light source 117, and an output coupler 118.

[0045] The frequency shifter 112 shifts the frequency of the input light by approximately a 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 resonator so that for each round, the frequency increases by ν s .

[0046] The gain medium 114 is provided with pump light, and the gain medium 114 amplifies the input light. The 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, thulium, etc. The pump light is provided to the gain medium 114 from the pump light source 117 via the WDM coupler 116. The output coupler 118 outputs a portion of the light that has been laser oscillated in the resonator to an external device.

[0047] That is to say, Figure 2 The laser device 110 shown includes a fiber ring laser having a frequency shifter 112 in a resonator. The laser device 110 preferably further includes an isolator in the resonator. Moreover, the laser device 110 may have an optical bandpass filter that allows light of a predetermined wavelength band in the resonator to pass. The frequency characteristics of the laser beam output from the laser device 110 will be described below.

[0048] Figure 3An example of a laser beam output from the laser device 110 according to the present embodiment is shown. Figure 3 The left side shows the 0 Spectrum of the laser beam output by the laser device 110. In this spectrum, the horizontal axis represents the light intensity and the vertical axis represents the frequency of the light. In addition, 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 resonator, and multiple longitudinal modes travel at 1 / τ RT (=ν c ) are arranged at intervals as shown in the following equation. It should be noted that ν 0 is at time t 0 The initial frequency of the spectrum at .

[0049] [Equation 1]

[0050]

[0051] Figure 3 The right side shows the frequency variation of multiple longitudinal modes output by the laser device 110 over time. Figure 3 On the right side of , the horizontal axis represents time and the vertical axis represents frequency. That is, Figure 3 The right side shows the change in the frequency of the laser beam output from the laser device 110 over time, and the left side shows the change in the frequency of the laser beam at time t 0 The instantaneous frequency at .

[0052] In the laser device 110, each time the light in the resonator propagates around the resonator, the frequency shifter 112 increases the frequency of the light traveling around the resonator by ν s That is, since the frequency of each mode changes every time τ RT Both increase ν s , so the rate of change of frequency dν / dt (i.e. chirp rate) becomes approximately equal to ν s / τ RT Therefore, the plurality of longitudinal modes represented by equation 1 changes as time t passes as shown in the following equation.

[0053] [Equation 2]

[0054]

[0055] [Details of the distance measurement process]

[0056] The measuring device 100 according to the present embodiment measures the distance d between the optical head component 140 and the object to be measured 10 by using the laser device 110 that outputs the frequency element represented 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 reciprocating distance d, and the propagation delay corresponding to the distance 2d is Δt. That is, when the measuring light is reflected at time t and returns from the object to be measured 10, the frequency of the returned reflected light approximately matches the past frequency earlier than time t by time Δt, and can therefore be represented by the following equation.

[0057] [Equation 3]

[0058]

[0059] On the other hand, the reference light at time t can be expressed by the following equation in a manner similar to equation 2, where the reference light is ν q' (t).

[0060] [Equation 4]

[0061]

[0062] 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 v 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 number (=qq′), and Δt=2d / c.

[0063] [Equation 5]

[0064]

[0065] According to Equation 5, the distance d is expressed by the following equation, where 1 / τRT=vc.

[0066] [Equation 6]

[0067]

[0068] 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 v 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.

[0069] 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.

[0070] Figure 4 FIG. 2 shows an example of the relationship between the frequency of the beat signal detected by the measuring device 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 the figure show that for each of the multiple m values, the frequency ν of the beat signal B A graph of (m, d) versus distance d (as shown in Equation 5).

[0071] 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 at approximately the same frequency and are observed as a single-line spectrum.

[0072] 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 in 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.

[0073] As mentioned above, at frequencies 0 and ν c In the observation frequency band between B (m, d) and (ii) image signal ν B (m′,d), image signal ν B The m value of (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 detecting section 160 using orthogonal detection will be described.

[0074] Figure 5 The beat signal generating section 150 and the detecting section 160 according to the present embodiment are shown as configuration examples. The beat signal generating section 150 performs quadrature detection of the reflected light and the reference light. The beat signal generating section 150 includes an optical 90 degree hybrid 152, a first photoelectric conversion section 154, and a second photoelectric conversion section 156.

[0075] 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 the light generated by the other branched reference light passing through a π / 2 wavelength plate.

[0076] 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 may 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 component 154 generates a first beat signal and the second photoelectric conversion component 156 generates a second beat signal. As described above, the beat signal generating component 150 performs orthogonal detection by multiplexing two reference lights and two reflected lights having a phase difference of 90 degrees, respectively, and outputs the two beat signals to the detecting component 160.

[0077] The detection component 160 performs frequency analysis on the two beat signals. Here, an example in which the detection component 160 uses the first beat signal as the I signal and uses the second beat signal as the Q signal to perform frequency analysis will be described. The detection component 160 includes a first filter component 162, a second filter component 164, a first AD converter 202, a second AD converter 204, a clock signal providing component 210, and a frequency analysis component 220.

[0078] 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 is provided to the first AD converter 202. In addition, the second filter component 164 will be c The second beat signal obtained by using the signal component of the frequency of is supplied to the second AD converter 204.

[0079] The first AD converter 202 and the second AD converter 204 convert the analog signal into a digital signal. 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 clock signal providing component 210 provides the clock signal to the first AD converter 202 and the second AD converter 204. By doing so, the first AD converter 202 and the second AD converter 204 convert the analog signal into a digital signal at a sampling rate approximately the same as the clock frequency of the received clock signal.

[0080] Here, when the observation frequency band is from 0 to v c When the frequency of the beat signal is at most the resonant frequency v of the laser resonator c Therefore, the clock signal providing component 210 sets the frequency to be greater than or equal to the resonance frequency v of the laser resonator. c A clock signal twice as large as that of FIG. 2 is provided to the first AD converter 202 and the second AD converter 204, so that a beat signal can be observed.

[0081] 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 the frequency data as the real part, and adds the second beat signal converted into the frequency data as the imaginary part, and eliminates the image signal. It should be noted that after converting the beat signal into a digital signal, the detection 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 detection component 160 will be described below.

[0082] Figure 6 FIG. 2 shows an example of an outline of quadrature detection by the beat signal generating section 150 and the detecting section 160 according to the present embodiment. Figure 6 In FIG. 8 , 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, such as Figure 6 In the I signal and Q signal, for example, at frequencies 0 and v 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 the Q signal, the original beat signal of the image signal -v B (m+1,d) and the beat signal -ν B (m,d) exists at frequencies 0 and -v on the negative side c in the frequency band between .

[0083] 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 and image signals 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 -v on the negative side c In the frequency band between I and V, the beat signal of I B (m, d) and Q signal beat signal -ν B The phases of (m, d) are opposite to each other.

[0084] Therefore, if Figure 6 As shown in the lower part of FIG. 1 , when the frequency analysis unit 220 uses the I signal and the Q signal to calculate I+jQ, at frequencies 0 and v c In the frequency band between B The beat signals of (m, d) reinforce each other, and the frequency is ν B The image signals at (m+1, d) cancel each other. Similarly, at frequencies 0 and -v c In the frequency band between B The beat signals of (m+1,d) reinforce each other, and the frequency is -ν B The beat signals of (m, d) cancel each other.

[0085] According to the frequency analysis result of the frequency analysis component 220, for the frequencies 0 and v c The frequency in the band betweenB (m, d), a beat signal is observed. Since the measuring 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.

[0086] 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 v c and ν s is a frequency determined based on the components used in the laser device 110, so ideally v 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.

[0087] On the other hand, due to v c corresponds to the optical length of the resonator of the laser device 110, and thus it may change due to environmental fluctuations such as temperature. Figure 2 If a fiber ring laser is shown and the resonator is formed by an optical fiber, the resonator length may change by about 10 ppm when the ambient temperature changes by one degree Celsius. It should be noted that even if the laser device 110 is a solid-state laser such as a semiconductor laser, the resonator length may also change due to such environmental fluctuations. Therefore, the extraction component 170 extracts the resonant frequency corresponding to the resonator length in order to monitor such changes in the resonator length. The extraction component 170 will be described below.

[0088] Figure 7 An example of a configuration of the extraction section 170 according to the present embodiment is shown. The extraction section 170 includes a third photoelectric conversion section 172 , a third filter section 174 , a third AD converter 176 , and a resonance frequency output section 178 .

[0089] 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, the multiple longitudinal modes having a frequency modulated laser beam ...c Therefore, when the third photoelectric conversion component 172 performs photoelectric conversion on the frequency modulated laser beam, the output includes the resonant frequency v c The electrical signal.

[0090] The third filter section 174 makes the electric signal converted by the third photoelectric conversion section 172 have the resonance frequency v of the laser resonator. c The third filter component 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.

[0091] The third AD converter 176 converts the input analog signal into a digital signal. 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 analog signal. For example, when a clock signal is received from the clock signal providing part 210, the third AD converter 176 operates.

[0092] The resonance frequency output part 178 converts the digital signal output from the third AD converter 176 into frequency data. As an example, the resonance frequency output part 178 performs a digital Fourier transform (DFT) on the digital signal. The resonance frequency output part 178 analyzes the frequency data and outputs the resonance frequency v c For example, the resonance frequency output component 178 outputs the frequency with the highest signal strength of the frequency data as the resonance frequency v c .

[0093] As mentioned above, Figure 7 The extraction component 170 shown in FIG. 1 extracts the resonant frequency v from the monitoring light. c signal component, and outputs the resonant frequency v c Therefore, even if the resonator length of the laser device 110 changes due to fluctuations in the ambient temperature, the extraction component 170 can extract and output the resonance frequency v corresponding to the change. c Since the calculation unit 180 uses the fixed value v detected in the above manner s ,ν B (m,d) and resonant frequency v c , so the distance d corresponding to the fluctuation of the surrounding temperature can be calculated.

[0094] As described above, even if environmental fluctuations occur, the measuring device 100 can suppress a decrease in measurement accuracy because the measuring device 100 monitors the resonance frequency v corresponding to the environmental fluctuations. cAnd reflect the resonant frequency v 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 .

[0095] However, since the above-mentioned measuring device 100 tends to be a large-scale device, problems such as cost increase, problems related to circuit adjustment, installation area, etc. may occur. Therefore, even if such environmental fluctuations occur, the measuring device according to the present embodiment makes it possible to suppress the decrease in accuracy with a simple configuration. Next, this measuring device will be described.

[0096] [Configuration Example of Measurement Device 300]

[0097] Figure 8 FIG. 1 shows a configuration example of a measuring device 300 and an object to be measured 10 according to the present embodiment. Figure 8 In the measuring device 300 shown, according to Figure 1 The operations of the measuring device 100 of the present embodiment shown are similarly denoted by the same reference numerals, and description thereof is omitted. The measuring device 300 includes a clock signal generating section 310 and a converting section 320 .

[0098] The clock signal generating section 310 generates a first clock signal based on the signal component extracted by the extracting section 170. The clock signal generating section 310 provides the generated first clock signal to the converting section 320. The converting section 320 converts the beat signal generated by the beat signal generating section 150 into a digital signal using the first clock signal. Next, the beat signal generating section 150, the extracting section 170, the clock signal generating section 310, and the converting section 320 provided in the measuring device 300 will be described.

[0099] Fig. 9 2 shows a configuration example of the beat signal generating section 150, the extracting section 170, the clock signal generating section 310, and the converting section 320 according to the present embodiment. Fig. 9 The beat signal generating unit 150, the extracting unit 170 and the converting unit 320 shown in FIG. Figure 5 and Figure 7 Approximately the same operations of the beat signal generating section 150 , the detecting section 160 , and the extracting section 170 of the illustrated embodiment are denoted by the same reference numerals, and description thereof is omitted.

[0100] The extraction component 170 includes a third photoelectric conversion component 172 and a third filter component 174. The third photoelectric conversion component 172 extracts the resonance frequency v of the laser resonator from the converted electrical signal.c The extraction component 170 will have a resonant frequency v through the third filter component 174 c The signal component is provided to the clock signal generating component 310.

[0101] The clock signal generating section 310 generates a signal based on the resonance frequency v of the signal component extracted by the extracting section 170. c Generate a first clock signal. The clock signal generating section 310 includes, for example, a PLL circuit. The PLL circuit uses the frequency of the extracted signal component as a reference frequency and outputs a frequency signal having a frequency that is a multiple of the reference frequency. The PLL circuit includes, for example, a frequency variable oscillator 312, a frequency divider 314, a phase comparator 316, and a loop filter 318.

[0102] The variable frequency oscillator 312 generates a frequency signal corresponding to the control signal. The variable frequency oscillator 312 is, for example, a voltage controlled oscillator, which generates a frequency signal corresponding to the voltage value of the control signal. out frequency signal.

[0103] The frequency divider 314 receives the frequency signal output by the variable frequency oscillator 312 and outputs a frequency-divided signal having a frequency v of the frequency signal. out The frequency divider 314 converts the frequency of the frequency signal to approximately the frequency of the reference frequency signal v c Here, the frequency division ratio of the frequency divider 314 is defined as N.

[0104] The phase comparator 316 compares the phase of the reference frequency signal with the phase of the divided signal output by the frequency divider 314 and outputs the comparison result. The phase comparator 316 outputs, for example, a voltage corresponding to the phase difference between the reference frequency signal and the divided signal as the comparison result.

[0105] The loop filter 318 reduces unnecessary noise components and smoothes and passes the comparison result output from the phase comparator 316. The circuit configuration and circuit constants of the loop filter 318 are determined so that the value of the phase margin in the loop formed by the PLL circuit is within a predetermined range. The loop filter 318 is, for example, a lag lead filter. The loop filter 318 provides the signal passing through the loop filter 318 as a control signal to the frequency variable oscillator 312.

[0106] The above-mentioned PLL circuit adjusts the frequency v of the frequency signal output by the variable frequency oscillator 312. out , so that the frequency of the divided signal output by the frequency divider 314 is equal to the frequency of the reference frequency signal v cWhen the phase of the frequency signal output from the frequency variable oscillator 312 and the phase of the reference frequency signal are synchronized by the PLL circuit, ν out =N·v c As described above, the clock signal generating component 310 outputs a signal having a resonant frequency v c A frequency signal with a frequency N times the frequency of the input signal is used as the first clock signal. The value of N is, for example, an integer equal to or greater than 1. It should be noted that the clock signal generating component 310 may be a component whose output frequency is the resonant frequency v of the input signal. c It is a frequency multiplier of the signal that is N times higher than the PLL circuit.

[0107] The conversion component 320 receives the first clock signal and converts the beat signal into a first digital signal using the first clock signal. Figure 5 As shown, the conversion component 320 includes a first filter component 162, a second filter component 164, a first AD converter 202, a second AD converter 204 and a frequency analysis component 220. Here, the first AD converter 202 and the second AD converter 204 use the first clock signal to convert the analog signal into a digital signal. That is, the conversion component 320 includes the first AD converter 202 and the second AD converter 204, and the first AD converter 202 and the second AD converter 204 convert the beat signal into a first digital signal in synchronization with the first clock signal. Here, the first digital signal is an I signal converted by the first AD converter 202 and a Q signal converted by the second AD converter 204.

[0108] The frequency analysis unit 220 performs frequency analysis on the I signal and the Q signal, and outputs the frequency v of the beat signal. B (m,d). As already referred to Figure 6 The operation of the frequency analysis section 220 is described, and thus a description thereof is omitted.

[0109] As described above, the measurement device 300 according to the present embodiment uses the resonance frequency v extracted from the monitoring light. c The corresponding first clock signal converts the beat signal into a first digital signal. In this case, when the resonator length of the laser device 110 changes due to environmental fluctuations, etc., the clock cycle of the first clock signal also changes according to the change in the resonator length. This change in the first clock signal corresponds to a change in the beat signal associated with the change in the resonator length of the laser device 110.

[0110] In this case, since the conversion part 320 converts the beat signal into a digital signal by sampling the beat signal similarly changed from the constant period using the first clock signal changed from the constant period, the conversion part 320 operates to cancel the change in the resonator length. Therefore, even if the resonator length of the laser device 110 changes, the first digital signal converted by the conversion part 320 becomes a signal approximately equivalent to the digital signal sampled at an approximately constant period.

[0111] The calculation part 180 calculates the difference in propagation distance between the reference light and the measurement light based on the first digital signal. That is, the calculation part 180 uses a fixed resonance frequency v c and ν s and the detected ν B (m, d) to perform calculation as shown in Equation 6. By doing so, even when the ambient temperature or the like fluctuates, the measuring device 300 can measure the distance d to the object to be measured 10 while suppressing a decrease in measurement accuracy.

[0112] As described above, the measuring device 300 can accurately measure the distance d to the object 10 with a simple configuration without using the resonance frequency v c In addition, the measuring device 300 can suppress the reduction of measurement accuracy without using a constant temperature chamber, etc. Therefore, in the measuring device 300 according to the present embodiment, the distance d to the object 10 to be measured can be accurately measured while preventing an increase in equipment scale and cost.

[0113] The measurement device 300 according to the present embodiment and the resonance frequency v extracted from the laser device 110 are described as above. c The example of converting the beat signal as an analog signal into a first digital signal in synchronization with the first clock signal of the measuring device 300 is described, but the present invention is not limited thereto. The measuring device 300 can use the first clock signal to resample the beat signal converted into a digital signal. Next, the beat signal generating section 150, the extracting section 170, the clock signal generating section 310, and the converting section 320 provided in the modified example of the measuring device 300 will be described.

[0114] [Modification Example of Measurement Device 300]

[0115] Fig.10 1 shows a configuration example of the beat signal generating section 150, the extracting section 170, the clock signal generating section 310, and the converting section 320 provided in a modified example of the measuring apparatus 300 according to the present embodiment. Fig.10 The beat signal generating unit 150, the extracting unit 170, the clock signal generating unit 310, and the converting unit 320 shown in FIG. Fig. 9 The operations of the beat signal generating section 150 , the extracting section 170 , the clock signal generating section 310 , and the converting section 320 according to the present embodiment shown are approximately the same as those denoted by the same reference numerals, and description thereof is omitted.

[0116] The conversion component 320 further includes a clock signal providing component 210, and the clock signal providing component 210 provides the second clock signal to the first AD converter 202 and the second AD converter 204. In this case, the first AD converter 202 and the second AD converter 204 convert the beat signal into a second digital signal in synchronization with a second clock signal different from the first clock signal. The frequency analysis component 220 receives the first clock signal from the clock signal generating component 310, and performs a frequency analysis on the beat signal v received from the first AD converter 202 and the second AD converter 204. B (m,d) is resampled.

[0117] That is, the frequency analysis section 220 also functions as a resampling section that resamples the second digital signal using the first clock signal to output the first digital signal. Here, a known algorithm can be used as a processing circuit, algorithm, etc. for the resampling process, and a description thereof is omitted here.

[0118] The frequency analysis section 220 performs frequency conversion on the resampled first digital signal in the above manner, and outputs the frequency v of the beat signal. B (m, d). Therefore, the calculation component 180 can calculate the distance d to the object to be measured 10. As described above, since the first clock signal is used to convert the beat signal into the first digital signal, even if the ambient temperature fluctuates, the measuring device 300 can measure the distance d to the object to be measured 10 while suppressing a decrease in measurement accuracy.

[0119] Preferably, at least a portion of the detection component 160, the calculation component 180, and the conversion component 320 provided in the measurement device 100 and the measurement device 300 according to the present embodiment is formed by an integrated circuit, etc. At least a portion of the detection component 160, the calculation component 180, and the conversion component 320 includes, for example, a field programmable gate array (FPGA), a digital signal processor (DSP), and / or a central processing unit (CPU).

[0120] When at least a part of the detection component 160, the calculation component 180 and the conversion component 320 is formed by a computer or the like, the part 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 implementing the detection component 160, the calculation component 180 and the conversion component 320, and a random access memory (RAM) used as a work area. The storage unit can store an operating system (OS), a program, an application 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).

[0121] The control unit is a processor such as a CPU, and functions as at least a part of the detection section 160, the calculation section 180, and the conversion section 320 by executing a program stored in the storage unit. The control unit may include a graphics processing unit (GPU) or the like.

[0122] 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 unit that is 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 together.

[0123] Description of Reference Numerals

[0124] 10 Objects to be tested

[0125] 100 Measuring devices

[0126] 110 Laser device

[0127] 112 Frequency Shifter

[0128] 114 Gain Medium

[0129] 116 WDM Coupler

[0130] 117 Pump Light Source

[0131] 118 Output Coupler

[0132] 120 Branch components

[0133] 130 Optical Circulator

[0134] 140 Optical head parts

[0135] 150 Beat signal generating unit

[0136] 152 Optical 90 degree mixer

[0137] 154 first photoelectric conversion unit

[0138] 156 second photoelectric conversion unit

[0139] 160 Detection components

[0140] 162 first filter component

[0141] 164 second filter component

[0142] 170 Extraction Parts

[0143] 172 third photoelectric conversion unit

[0144] 174 third filter component

[0145] 176 Third AD converter

[0146] 178 Resonance frequency output component

[0147] 180 Computing components

[0148] 190 Display components

[0149] 202 First AD Converter

[0150] 204 Second AD converter

[0151] 210 clock signal providing component

[0152] 220 Frequency Analysis Components

[0153] 300 Measuring device

[0154] 310 clock signal generating unit

[0155] 312 Variable Frequency Oscillator

[0156] 314 Crossover

[0157] 316 Phase Comparator

[0158] 318 Loop Filter

[0159] 320 Conversion parts

Claims

1. A measuring device, comprising: A laser device having a laser resonator and outputting a frequency modulated laser beam having multiple modes; a branching component that branches the frequency modulated laser beam into (i) a portion of the frequency modulated laser beam output by the laser device as reference light and (ii) at least some of the remaining portion of the frequency modulated laser beam as measurement light; a beat signal generating section that generates a beat signal by mixing the reference light and the reflected light that is reflected by irradiating the measuring light onto the object to be measured; an extraction unit including a filter unit that passes a signal component having a resonance frequency of the laser resonator and superimposed on the frequency modulated laser beam output from the laser device, and extracts the signal component having the resonance frequency of the laser resonator; a clock signal generating means for generating a frequency signal having a frequency N times the resonant frequency as a first clock signal based on the signal component, where N is an integer equal to or greater than 1; a conversion component, converting the beat signal into a first digital signal using the first clock signal; as well as A calculation unit calculates a difference in propagation distance between the reference light and the measurement light based on the first digital signal.

2. 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 section includes a photoelectric conversion section that converts the monitoring light into an electric signal, and extracts a signal component corresponding to the resonance frequency of the laser resonator from the electric signal converted by the photoelectric conversion section.

3. The measuring device according to claim 1 or 2, wherein the calculation means calculates the difference d in propagation distance between the reference light and the measuring light using the following equation, in, v B (m, d) represents the frequency of the beat signal, m represents the interval between the longitudinal modes of the reflected light of the frequency modulated laser beam and the reference light, c is the speed of light, ν s is the frequency shift of the frequency modulated laser beam, ν c is the resonance frequency of the laser resonator.

4. The measuring device according to claim 1 or 2, wherein the clock signal generating means comprises a PLL circuit which uses the frequency of the signal component as a reference frequency and outputs a frequency signal having a frequency which is a multiple of the reference frequency, and The clock signal generating section outputs the frequency signal as the first clock signal. 5 . The measuring device according to claim 1 , wherein the conversion section includes an A / D converter that converts the beat signal into the first digital signal in synchronization with the first clock signal.

6. The measuring device according to claim 1 or 2, wherein the conversion component further comprises: an AD converter that converts the beat signal into a second digital signal in synchronization with a second clock signal different from the first clock signal, and A resampling component resamples the second digital signal using the first clock signal and outputs the first digital signal.

7. A measurement method comprising the following steps: outputting a frequency-modulated laser beam having a plurality of modes from a laser device having a laser resonator; branching the frequency modulated laser beam into (i) a portion of the frequency modulated laser beam as reference light, and (ii) at least some of the remaining portion of the frequency modulated laser beam as measurement 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; extracting the signal component having the resonance frequency of the laser resonator using a filter means for passing the signal component having the resonance frequency of the laser resonator superimposed on the frequency modulated laser beam; generating a frequency signal having a frequency N times the resonant frequency as a first clock signal based on the signal component, N being an integer equal to or greater than 1; Converting the beat signal into a first digital signal using the first clock signal; as well as A difference in propagation distance between the reference light and the measuring light is calculated based on the first digital signal. 8 . The measuring method according to claim 7 , wherein converting the beat signal into the first digital signal comprises converting the beat signal into the first digital signal in synchronization with the first clock signal.

9. The measurement method according to claim 7, wherein converting the beat signal into a first digital signal comprises: converting the beat signal into a second digital signal in synchronization with a second clock signal different from the first clock signal, and The second digital signal is resampled using the first clock signal and the first digital signal is output.

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