Measuring device and measuring method

Abstract

A measurement device 100 includes: a laser device 110 that outputs a frequency-modulated laser beam; a branching member 120 that separates the frequency-modulated laser beam into reference light and measurement light; a beat signal generation member 150 that generates a beat signal by mixing the reference light and reflected light that is reflected by irradiating the measurement light onto an object to be measured 10; a frequency analysis member 160 that performs frequency analysis on the beat signal; a storage member 190 that stores a reference frequency signal that is a frequency signal obtained by converting a reference signal output by the beat signal generation member 150 in a state where the object to be measured 10 is not present; and a calculation member 170 that calculates a difference between propagation distances of the reference light and the measurement light.

Description

TECHNICAL FIELD

[0001] The present disclosure relates to a measuring device and a measuring method. BACKGROUND

[0002] A frequency-shifted feedback laser (FSFL) that is provided with a frequency shifter in a cavity (resonator) and outputs a plurality of longitudinal-mode lasers whose oscillation frequencies linearly change with time is known. Further, an optical range finder using such a FSFL is known (for example, see Patent Literature 1: Japanese Patent No. 3583906, and Non-Patent Literature 1: “Distance Sensing by FSF Laser and Its Application”, Takefumi HARA, Optonews, Vol. 7, No. 3, 2012, pp. 25-31). SUMMARY

[0003] Problem to be Solved by the Invention

[0004] An optical range finder divides a frequency-shifted feedback laser into reference light and measurement light, and generates a beat signal by mixing the reference light and reflected light that is reflected by irradiating the measurement light onto an object to be measured. Then, the optical range finder measures a distance from the optical range finder to the object to be measured by specifying a frequency of the beat signal. In such an optical range finder, reflected light can occur at an exit end that emits the measurement light toward the object to be measured. In a similar manner to the reflected light of the measurement light, the reflected light that occurs at the exit end can be mixed with the reference light to generate the beat signal. This sometimes causes a decrease in measurement accuracy of the optical range finder.

[0005] The present disclosure is made in view of this, and an object thereof is to be able to suppress a decrease in measurement accuracy with a simple configuration even in a case where reflected light occurs at an exit end of a laser beam in an optical range finder.

[0006] Means for Solving the Problem

[0007] A first aspect of the present disclosure provides a measurement device including: a laser device that outputs a frequency-modulated laser beam; a branching member that separates the frequency-modulated laser beam output by the laser device so that a portion of the frequency-modulated laser beam is reference light and at least some of the remaining portion of the frequency-modulated laser beam is measurement light; a beat signal generation member that generates a beat signal by mixing the reference light and reflected light that is reflected by irradiating the measurement light onto an object to be measured; a frequency analysis member that performs frequency analysis on the beat signal; a storage member that stores a reference frequency signal that is a reference signal output by the beat signal generation member in a state in which there is no object to be measured and converted into a frequency signal; and a calculation member that calculates a difference between the propagation distances of the reference light and the measurement light based on the result of the frequency analysis performed by the frequency analysis member on the beat signal, wherein the frequency analysis member subtracts the signal level of the reference frequency signal from the signal level of the frequency signal converted from the beat signal for each frequency, and then specifies the frequency of the beat signal.

[0008] The beat signal generation member can output, as the reference signal, a signal including a reference beat signal that is generated by mixing the reference light and an end surface reflection light that is reflected from an exit end surface that emits the measurement light.

[0009] The beat signal generation member can generate two beat signals that are (i) a first beat signal due to the reflected light of the measurement light and the reference light and (ii) a second beat signal due to the end surface reflection light and the reference light, the frequency analysis member can output, as a distance measurement signal, a signal that is obtained by converting, into a frequency domain signal, a signal in which the two beat signals generated by the beat signal generation member are superimposed, and the frequency analysis member can subtract, from the spectrum of the distance measurement signal, a spectrum of a reference beat signal based on the end surface reflection light by subtracting, from the signal level of the distance measurement signal for each frequency, the signal level of the reference frequency signal.

[0010] The measurement device can further include: a shutter member that is provided between the exit end surface and the object to be measured and that is capable of cutting off the irradiation of the measurement light from the exit end surface to the object to be measured; and a control member that controls the shutter member by opening the shutter member to irradiate the measurement light onto the object to be measured when calculating the difference between the propagation distances of the reference light and the measurement light, and that cuts off the measurement light by closing the shutter member when obtaining the reference frequency signal.

[0011] The control member can close the shutter member to cut off the measurement light in response to a predetermined time elapsing, store the frequency domain signal converted by the frequency analysis member in the storage member, and update the reference frequency signal.

[0012] The measurement device can further include a mirror disposed between the exit end face and the object to be measured, capable of changing an optical path of the measurement light irradiated onto the object to be measured from the exit end face; and a control means that controls the mirror to change a position of the mirror so that the measurement light irradiates the object to be measured when calculating a difference between the propagation distances of the reference light and the measurement light, and changes the position of the mirror so that the optical path of the measurement light is changed when the reference frequency signal is obtained.

[0013] The calculation means can use a frequency v of the beat signal obtained by a frequency analysis means that performs frequency analysis on the beat signal B (m, d) by the following equation,

[0014]

[0015] where c is a speed of light, v s is a frequency shift amount of the frequency-modulated laser beam, v C is 1 / τ RT , τ RT is a time for light to propagate once around a cavity of the laser device, and m is an interval of longitudinal mode numbers of the frequency-modulated laser beam (a difference between a longitudinal mode number of the measurement light and a longitudinal mode number of the reference light).

[0016] A second aspect of the present disclosure provides a measurement method of a measurement device for measuring a distance to an object to be measured, the method including the steps of: outputting a frequency-modulated laser beam; separating the frequency-modulated laser beam so that a portion of the frequency-modulated laser beam is reference light and at least some of the remaining portion of the frequency-modulated laser beam is measurement light; outputting a signal including a reference beat signal as a reference signal, the reference beat signal being obtained by mixing the reference light and an end face reflection light reflected from an exit end face from which the measurement light is emitted in a state in which there is no object to be measured; storing information obtained by converting the reference signal into a frequency signal as a reference frequency signal; generating a plurality of beat signals by mixing the reference light and reflection light reflected by irradiating the measurement light onto the object to be measured; performing frequency analysis on a frequency signal obtained by subtracting a signal level of the reference frequency signal from a signal level of a frequency signal converted from a frequency domain signal converted from the beat signals for each frequency; and calculating a difference between the propagation distances of the reference light and the measurement light based on a result of the frequency analysis.

[0017] Inventive Effects

[0018] According to the present disclosure, there is the following effect: even if reflected light occurs at an exit end of a laser beam in an optical range finder, it is possible to suppress a decrease in measurement accuracy with a simple configuration. BRIEF DESCRIPTION OF DRAWINGS

[0019] Figure 1A configuration example of the measurement device 100 according to the present embodiment and the object to be measured 10 is shown.

[0020] Figure 2 A configuration example of the laser device 110 according to the present embodiment is shown.

[0021] Figure 3 An example of a laser beam output from the laser device 110 according to the present embodiment is shown.

[0022] Figure 4 An example of a relationship between (i) a frequency of a beat signal detected by the measurement device 100 according to the present embodiment and (ii) a distance d between the optical head member 140 and the object to be measured 10 is shown.

[0023] Figure 5 A configuration example of the beat signal generating member 150 and the frequency analysis member 160 according to the present embodiment is shown.

[0024] Figure 6 An example of an outline of quadrature detection performed by the beat signal generating member 150 and the frequency analysis member 160 according to the present embodiment is shown.

[0025] Figure 7 An example of a frequency signal generated by the frequency analysis member 160 according to the present embodiment by converting a beat signal generated by the beat signal generating member 150 into a frequency domain signal is shown.

[0026] Figure 8 An example of a reference frequency signal stored in the storage member 190 according to the present embodiment is shown.

[0027] Figure 9 An example of a result of the frequency analysis member 160 according to the present embodiment subtracting a reference frequency signal from a signal for measuring a distance is shown.

[0028] Figure 10 A variant example of the measurement device 100 according to the present embodiment and the object to be measured 10 is shown. DETAILED DESCRIPTION

[0029] [Configuration example of measurement device 100]

[0030] Figure 1A configuration example of a measurement device 100 according to the present embodiment and an object to be measured 10 are shown. The measurement device 100 optically measures a distance between the measurement device 100 and the object to be measured 10. Further, the measurement device 100 can measure a three-dimensional shape of the object to be measured 10 by scanning a position of a laser beam irradiated onto the object to be measured. The measurement device 100 includes a laser device 110, a branching member 120, an optical circulator 130, an optical head member 140, a beat signal generating member 150, a frequency analysis member 160, a calculation member 170, a display member 180, and a storage member 190.

[0031] The laser device 110 has an optical cavity (laser resonator) and outputs a frequency-modulated laser beam having a plurality of modes. The laser device 110 is provided with a frequency shifter in the cavity (resonator) and outputs a plurality of longitudinal mode lasers whose oscillation frequencies linearly change over time. The laser device 110 is, for example, a frequency-shifted feedback laser (FSFL). The FSFL will be described later.

[0032] The branching member 120 separates the frequency-modulated laser beam output from the laser device 110, a part of which as reference light, and at least some of the remaining part as measurement light. The branching member 120 is, for example, a 1-to-2 optical fiber coupler. In Figure 1 In the example, the branching member 120 supplies the measurement light to the optical circulator 130 and supplies the reference light to the beat signal generating member 150.

[0033] 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 further outputs light input from the next port to the next-but-one port. Figure 1 An example in which the optical circulator 130 has three input / output ports is shown. In this case, the optical circulator 130 outputs the measurement light supplied from the branching member 120 to the optical head member 140. In addition, the optical circulator 130 outputs light input from the optical head member 140 to the beat signal generating member 150.

[0034] The optical head member 140 irradiates light input from the optical circulator 130 toward the object to be measured 10. The optical head member 140 includes, for example, a collimator lens. In this case, the optical head member 140 first adjusts light input from the optical circulator 130 via an optical fiber into a beam shape using the collimator lens and then outputs the light.

[0035] Further, the optical head member 140 receives reflected light of the measurement light irradiated onto the object 10 to be measured. The optical head member 140 focuses the received reflected light onto the optical fiber with a collimator lens, and supplies it to the optical circulator 130. In this case, the optical head member 140 can include one common collimator lens, and the collimator lens can irradiate the object 10 to be measured with the measurement light and receive the reflected light from the object 10 to be measured. The distance between the optical head member 140 and the object 10 to be measured is defined as d.

[0036] Alternatively, the optical head member 140 can include a focusing lens. In this case, the optical head member 140 focuses the light input from the optical circulator 130 via the optical fiber onto the surface of the object 10 to be measured. The optical head member 140 receives at least a part of the reflected light reflected on the surface of the object 10 to be measured. The optical head member 140 focuses the received reflected light onto the optical fiber using the focusing lens, and supplies it to the optical circulator 130. Also in this case, the optical head member 140 can include one common focusing lens, and the focusing lens can irradiate the object 10 to be measured with the measurement light and receive the reflected light from the object 10 to be measured.

[0037] The beat signal generating member 150 receives the reflected light from the optical circulator 130, which is reflected by irradiating the measurement light onto the object 10 to be measured. Further, the beat signal generating member 150 receives the reference light from the branching member 120. The beat signal generating member 150 mixes the reflected light and the reference light to generate a beat signal. For example, the beat signal generating member 150 includes a photoelectric conversion element, which converts the beat signal into an electric signal, and outputs the electric signal.

[0038] Here, since the reflected light travels back and forth over the distance between the optical head member 140 and the object 10 to be measured, a difference in the propagation distance corresponding to at least the 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 the propagation distance occurs between the oscillation frequency of the reference light and the oscillation frequency of the reflected light. The beat signal generating member 150 generates a beat signal corresponding to such a frequency difference.

[0039] The frequency analysis member 160 performs frequency analysis on the beat signal generated by the beat signal generating member 150. For example, the frequency analysis member 160 converts the beat signal into a digital signal, and converts the converted digital signal into a frequency signal. Then, the frequency analysis member 160 detects the frequency of the beat signal by analyzing the frequency signal generated by converting the beat signal into a frequency domain signal. Here, the frequency of the beat signal is defined as v B .

[0040] The calculating section 170 calculates the difference between the propagation distances of the reference light and the measurement light based on the result of the frequency analysis performed by the frequency analysis section 160 on the beat signal. The calculating section 170 calculates the distance d from the optical head section 140 to the object 10 based on the frequency v B The calculating section 170 calculates the difference between the propagation distances of the reference light and the measurement light based on the result of the frequency analysis performed by the frequency analysis section 160 on the beat signal. The calculating section 170 calculates the distance d from the optical head section 140 to the object 10 based on the frequency v

[0041] The display section 180 displays the result of the calculation by the calculating section 170. The display section 180 can include a display or the like and display the result of the calculation. In addition, the display section 180 can store the result of the calculation in the storage section 190 or the like. The display section 180 can provide the result of the calculation to an external device via a network or the like.

[0042] The storage section 190 can store intermediate data, a result of calculation, a set value, a threshold value, a parameter, or the like generated or used in the operation process of the frequency analysis section 160 and the calculating section 170. The storage section 190 can provide the stored data to the source of the request in response to the request from each section of the measurement device 100.

[0043] When a CPU or the like operates as at least a part of the frequency analysis section 160 and the calculating section 170, the storage section 190 can store an operating system (OS) and various information, such as a program that functions as the frequency analysis section 160 and the calculating section 170. In addition, the storage section 190 can store various types of information, including a database to be referred to when the program is executed. For example, a computer functions as the frequency analysis section 160 and the calculating section 170 by executing the program stored in the storage section 190.

[0044] The storage section 190 includes a read-only memory (ROM) that stores, for example, a basic input / output system (BIOS) of a computer or the like and a random access memory (RAM) that functions as a work area. The storage section 190 can include a large-capacity storage device, such as a hard disk drive (HDD) and / or a solid state drive (SSD). In addition, the computer can further include a graphics processing unit (GPU) or the like.

[0045] The measurement device 100 described above can measure the distance d between the measurement device 100 and the object 10 by analyzing the frequency difference between the reflected light of the measurement light irradiated onto the object 10 and the reference light. That is, the measurement device 100 can form a non-contact and non-destructive optical range finder. Next, a more detailed configuration of the measurement device 100 will be described.

[0046] [Configuration example of laser device 110]

[0047] Figure 2 An example configuration of the laser device 110 according to this embodiment is shown. Figure 2 The laser device 110 illustrates an example of an FSFL. The laser device 110 includes an optical cavity in which a laser beam oscillates. The optical cavity of the laser device 110 includes a frequency shifter 112, a gain medium 114, a WDM coupler 116, a pump source 117, and an output coupler 118.

[0048] Frequency shifter 112 shifts the frequency of the input light by an approximately constant frequency. Frequency shifter 112 is, for example, an acousto-optic frequency shifter (AOFS) with an acousto-optic element. Here, the frequency shift amount of frequency shifter 112 is defined as +ν. s That is, frequency shifter 112 shifts the frequency of the light circulating around the cavity so that for each round, the frequency increases by ν. s .

[0049] 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. 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 source 117 via WDM coupler 116. Output coupler 118 outputs a portion of the light already oscillating in the cavity to external devices.

[0050] In other words, Figure 2 The laser device 110 shown includes a fiber ring laser with a frequency shifter 112 in the cavity. The laser device 110 preferably further includes an isolator in the cavity. Furthermore, the laser device 110 may have an optical bandpass filter that allows light of a predetermined wavelength band in the cavity to pass through. The frequency characteristics of the laser beam output from the laser device 110 will be described below.

[0051] Figure 3 An example of a laser beam output from a laser device 110 according to this embodiment is shown. Figure 3 The left side shows the spectrum of the laser beam output from laser device 110 at time t0. In this spectrum, the horizontal axis represents light intensity, and the vertical axis represents light frequency. Furthermore, multiple vertical modes of the spectrum are represented by the number q. The frequencies of the multiple vertical modes are arranged at approximately constant frequency intervals. Assume τ... RT (=1 / ν C ) represents the time it takes for light to travel around the cavity once, with multiple longitudinal modes at 1 / τ.RT (= v C ) are arranged at intervals of v C is the initial frequency of the spectrum at time t0. Furthermore, v C is the cavity frequency (resonator frequency) v

[0052] [Equation 1]

[0053]

[0054] Figure 3 The frequency change of the multiple longitudinal modes output from the laser device 110 over time is shown on the right side. On the right side of the graph, Figure 3 the horizontal axis represents time, and the vertical axis represents frequency. That is, Figure 3 The frequency change of the laser beam output from the laser device 110 over time is shown on the right side, and the instantaneous frequency of the laser beam at time t0 is shown on the left side.

[0055] In the laser device 110, the frequency of the light traveling around the cavity is increased by v s by the frequency shifter 112 each time the light in the cavity propagates around the cavity. That is, since the frequency of each mode is increased by v s every time tRT passes, the rate of change of the frequency dν / dt (i.e., the chirp rate) becomes approximately equal to v s / τRT. Therefore, the multiple longitudinal modes represented by Equation 2 change over time t to be represented by the following equation.

[0056] [Equation 2]

[0057]

[0058] [Details of the distance measurement process]

[0059] The measurement device 100 according to the present embodiment measures the distance d between the optical head member 140 and the object to be measured 10 by using the laser device 110 that outputs the frequency elements represented by Equation 2. It is assumed that the optical path difference between the reference light and the reflected light is only the distance 2d, i.e., the distance d of the round trip, and that the propagation delay corresponding to the distance 2d is At. That is, when the measurement light is reflected and returned from the object to be measured 10 at time t, the frequency of the returned reflected light approximately matches the past frequency at time t - At, and thus can be represented by the following equation.

[0060] [Equation 3]

[0061]

[0062] 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 vq'(t).

[0063] [Equation 4]

[0064]

[0065] Because the beat signal generating part 150 superimposes the reflected light and the reference light, a plurality of beat signals are generated between the plurality of longitudinal modes expressed by Equation 3 and the plurality of longitudinal modes expressed by Equation 4. It is assumed that the frequency of such a beat signal is v B (m, d), v B (m, d) can be expressed by the following equation according to Equation 3 and Equation 4. Note that m is the difference of the longitudinal mode number (= q - q'), Δt = 2d / c, and c is the speed of light.

[0066] [Equation 5]

[0067]

[0068] According to Equation 5, the distance d is expressed by the following equation, where 1 / τRT= v C .

[0069] [Equation 6]

[0070]

[0071] From Equation 6, it can be understood that the distance d can be calculated from the frequency observation result of the beat signal by determining the difference m of the longitudinal mode number. Note that when the amount of frequency shift v s of the laser device 110 is changed, the difference m can be determined by detecting the change of the beat signal. Because such a method of determining the difference m is known as described in Patent Literature 1 and the like, detailed description thereof is omitted.

[0072] Since the observed beat signal is always positive frequency, in the calculation, the beat signal generated on the negative frequency side is folded back on the positive side and observed as an image signal. Next, the generation of such an image signal will be described.

[0073] Figure 4 An example of the relationship between the frequency of the beat signal detected by the measurement device 100 according to the present embodiment and the distance d between the optical head part 140 and the object to be measured 10 is shown. In Figure 4 , the horizontal axis represents the distance d, and the vertical axis represents the frequency v B (m, d) of the beat signal. Figure 4 The plurality of straight lines shown by the solid lines in FIG. 8 are lines showing, for each of a plurality of m values, the frequency v BA graph showing the relationship between (m,d) and distance d (as shown in Equation 6).

[0074] like Figure 4 As shown, multiple beat signals corresponding to the value of m are generated. However, due to the multiple longitudinal modes included in each of the reflected light and the reference light being spaced approximately at a constant frequency ν... C The arrangement is such that multiple beat signals with equal m values ​​are approximately superimposed on the same frequency on the frequency axis. For example, when observing frequencies 0 and ν... C When the frequency bands are between, multiple beat signals are approximately superimposed on the same frequency and observed as a single-line spectrum.

[0075] Additionally, the frequency ν of the beat signal in the negative range is less than 0. B The absolute value of (m,d) is further observed as an image signal. That is, Figure 4 The curve of the region where the vertical axis is less than 0 is folded back with the frequency 0 as the boundary. Figure 4 The folded image signal is illustrated using multiple dashed lines. Since only the positive and negative values ​​of the folded image signal are reversed, the image signal is superimposed on the observed frequency axis at the same absolute value as the frequency before folding. For example, when the observed frequency is between 0 and ν... C When the frequency bands are between ν, the beat signal and the image signal are located at different frequencies, unless the frequencies of the beat signal and the image signal change to ν. C / 2.

[0076] As mentioned above, at frequencies 0 and ν C Two line spectra are generated in the observation frequency band between them, which are (i) beat signal ν B (m,d) and (ii) image signals ν B (m′,d), image signal ν B The value of m in (m′,d) and the beat signal ν B The values ​​of m in (m,d) are different. Here, as an example, m' = m+1. In this case, the beat signal generation unit 150 can eliminate this image signal by using orthogonal detection. Next, the beat signal generation unit 150 and the frequency analysis unit 160 using orthogonal detection will be described.

[0077] Figure 5 An example configuration of the beat signal generation unit 150 and the frequency analysis unit 160 according to this embodiment is shown. The beat signal generation unit 150 performs orthogonal detection on the reflected light and the reference light. The beat signal generation unit 150 includes an optical 90-degree mixer 152, a first photoelectric conversion unit 154, and a second photoelectric conversion unit 156.

[0078] The optical 90-degree hybrid 152 separates each of the input reflected light and the input reference light into two parts. The optical 90-degree hybrid 152 multiplexes one of the separated reflected light and one of the separated reference light using an optical coupler or the like to generate a first beat signal. The optical 90-degree hybrid 152 multiplexes the other separated reflected light and the other separated reference light using an optical coupler or the like to generate a second beat signal. Here, the optical 90-degree hybrid 152 generates the beat signals after generating a phase difference of 90 degrees between the two separated reference lights. For example, the optical 90-degree hybrid 152 multiplexes the separated reflected light and one of the separated reference lights, and multiplexes the separated reflected light and light generated by passing the other separated reference light through a π / 2 wave plate.

[0079] The first photoelectric conversion member 154 and the second photoelectric conversion member 156 receive the multiplexed reflected light and reference light, and convert them into electric signals. Each of the first photoelectric conversion member 154 and the second photoelectric conversion member 156 can be a photodiode or the like. Each of the first photoelectric conversion member 154 and the second photoelectric conversion member 156 is, for example, a balanced photodiode. In Figure 5 In the present embodiment, it is assumed that the first photoelectric conversion member 154 generates the first beat signal, and the second photoelectric conversion member 156 generates the second beat signal. As described above, the beat signal generating member 150 performs quadrature detection by multiplexing two reference lights and two reflected lights, which are different in phase by 90 degrees, respectively, and outputs two beat signals to the frequency analysis member 160.

[0080] The frequency analysis member 160 performs frequency analysis on the two beat signals. Here, an example in which the frequency analysis member 160 performs frequency analysis using the first beat signal as an I signal and the second beat signal as a Q signal will be described. The frequency analysis member 160 includes a first filter member 162, a second filter member 164, a first AD converter 202, a second AD converter 204, a clock signal providing member 210, and a signal processing member 220.

[0081] The first filter member 162 and the second filter member 164 reduce signal components in a frequency band other than a frequency band that a 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 member 162 and the second filter member 164 are, for example, low-pass filters that pass signal components whose frequencies are equal to or less than v C . In this case, the first filter member 162 supplies the first beat signal obtained by reducing signal components having a frequency higher than the frequency v C to the first AD converter 202. Further, the second filter member 164 supplies the second beat signal obtained by reducing signal components having a frequency higher than the frequency v CThe second beat signal obtained by extracting a signal component of a frequency of the second beat signal is supplied to the second AD converter 204.

[0082] 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 supply section 210 supplies a 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.

[0083] Here, when the observation band is from 0 to v C , the frequency of the beat signal is at most the cavity frequency v C of the optical cavity. Therefore, the clock signal supply section 210 supplies a clock signal having a frequency greater than or equal to twice the cavity frequency v C of the optical cavity to the first AD converter 202 and the second AD converter 204, so that the beat signal can be observed.

[0084] The signal processing section 220 converts the first beat signal and the second beat signal into frequency data. As an example, the signal processing section 220 performs a digital Fourier transform (DFT) on the first beat signal and the second beat signal. The signal processing section 220 adds the first beat signal converted into frequency data as a real part, and adds the second beat signal converted into frequency data as an imaginary part, and eliminates the image signal. It should be noted that the signal processing section 220 can be configured using an integrated circuit or the like after the beat signal is converted into a digital signal by the frequency analysis section 160. The following will describe the quadrature detection in the beat signal generation section 150 and the frequency analysis in the frequency analysis section 160.

[0085] Figure 6 An example showing an outline of the quadrature detection of the beat signal generation section 150 and the frequency analysis section 160 according to the present embodiment is shown. In Figure 6 , the horizontal axis represents the frequency of the beat signal, and the vertical axis represents the signal intensity. 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 the upper part of Figure 6 . In the I signal and the Q signal, for example, the beat signal v C (m, d) and the image signal v B (m, d) are observed in the band between the frequencies 0 and v B(m+1,d). In this case, the original beat signal -ν of the image signal in the I and Q signals. B (m+1,d) and beat signal -ν B (m,d) exists at frequencies 0 and -ν on the negative side. C In the frequency bands between.

[0086] Here, since the I and Q signals are signal components orthogonally detected by the beat signal generation unit 150, they contain different phase information even if they have the same spectral shape. For example, at frequencies 0 and ν on the positive side... C In the frequency band between, the image signal ν of the I signal B The image signal ν of (m+1,d) and Q signal B The phases of (m+1,d) are reversed. Similarly, the frequencies 0 and -ν on the negative side are reversed. C In the frequency band between, the beat signal -ν of the I signal B The beat signal -ν of (m,d) and Q signal B The phases of (m,d) are reversed.

[0087] Therefore, as Figure 6 As shown in the lower part, when the signal processing unit 220 calculates I+jQ using the I signal and the Q signal, at frequencies 0 and ν... C In the frequency band between, the frequency is ν B The beat signals of (m,d) reinforce each other, while the frequency ν B Image signals of (m+1,d) cancel each other out. Similarly, at frequencies 0 and -ν... C In the frequency band between -ν B The beat signals of (m+1,d) reinforce each other, while the frequency is -ν B The beat signals of (m,d) cancel each other out.

[0088] Based on the frequency analysis results of the signal processing unit 220, for frequencies 0 and ν C The frequency ν in the frequency band between B (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 (m,d). For example, the signal processing unit 220 uses the frequency with the highest signal strength of the converted frequency domain signal as the frequency ν of the beat signal. B (m,d) Output.

[0089] Here, the distance d measured by the measuring device 100 is represented by Equation 6. It can be seen from Equation 6 that the distance d can be determined by using three frequencies ν. C ν s and νB (m, d) is calculated. It is understood that, among the three frequencies, v B (m, d) can be detected as described above. C and v s are frequencies determined based on components used in the laser device 110, v C and v s can be regarded as fixed values. Therefore, the calculating section 170 calculates the distance d by using the frequency v B (m, d) of the beat signal detected by the frequency analyzing section 160 and the predetermined frequencies v C and v s . As described above, the measuring device 100 can measure the distance d from the optical head section 140 to the object to be measured 10. Further, by adding the offset value corresponding to the reference position to the distance d, the measuring device 100 can calculate and output the distance from the reference position to the object to be measured 10.

[0090] [Measuring device 100 that reduces the influence of end surface reflected light]

[0091] The measuring device 100 described above irradiates the measurement light from the optical head section 140 to the object to be measured 10, and reflected light can occur at the exit end surface of the measurement light emitted from the optical head section 140. For example, when the measurement light is emitted from an optical fiber, the reflected light can occur at the exit end surface of the optical fiber. Further, when the optical head section 140 emits the measurement light using an optical lens such as a collimator lens or a focusing lens, the reflected light can occur at the surface of the lens to which the measurement light is incident. In the present embodiment, such reflected light is end surface reflected light.

[0092] In a similar manner to the reflected light reflected by irradiating the measurement light onto the object to be measured 10, the end surface reflected light can generate a beat signal when mixed with the reference light. In this case, the beat signal generating section 150 generates two beat signals, one of which is due to the reflected light of the measurement light and the reference light, and the other of which is due to the end surface reflected light and the reference light.

[0093] Figure 7 An example of a frequency signal that is a signal generated by the frequency analyzing section 160 according to the present embodiment by converting the beat signal generated by the beat signal generating section 150 into a frequency domain signal is shown. Figure 7 An example in which the beat signal generating section 150 generates two beat signals due to the end surface reflected light is shown. In Figure 7In the diagram, the horizontal axis represents frequency, and the vertical axis represents signal level. In the frequency signal, the spectrum of the beat signal based on the end-face reflected light is superimposed on the spectrum of the beat signal based on the reflected light reflected from the object under test 10. Here, the peak frequency of the beat signal based on the reflected light reflected from the object under test 10 is determined by ν. B This indicates that the peak frequency of the beat signal based on end-face reflected light is determined by ν. B The ' indicates that the frequency signal whose two spectra are superimposed in this way due to the presence of reflected light from the end face is the signal used to measure distance (distance measurement signal).

[0094] When the frequency analysis unit 160 analyzes this distance measurement signal, among the two beat signals, the beat signal ν based on the end-face reflected light... B 'It can be processed into a beat signal to be analyzed. In this case, the distance to be calculated by the calculation unit 170 is different from the distance d from the optical head unit 140 to the object under test 10.'

[0095] In addition, in such Figure 7 In the frequency domain shown, the frequencies of the two beat signals may be close to, for example, the peaks of the two spectra cannot be separated. In this case, even if the frequency analysis unit 160 analyzes such beat signals, based on the frequency ν of the beat signal of the reflected light reflected from the object under test 10, B (m,d) cannot be output accurately either.

[0096] Therefore, even in the event of end-face reflection at the laser beam's emission end, the measuring device 100 according to this embodiment can suppress the decrease in measurement accuracy with a simple configuration. This functionality of the measuring device 100 can be achieved by adding certain operations to be performed by the frequency analysis unit 160 and the storage unit 190, for example, using... Figures 1 to 6 The described operations are used to implement this.

[0097] Here, the measuring device 100 outputs a frequency-modulated laser beam from the optical head component 140 for measuring distance, and uses the signal output by the beat signal generation component 150 in the absence of the object under test 10 as a reference signal. The absence of the object under test 10 includes, for example, the state before the object under test 10 is installed, the state after the object under test 10 is removed, and the state where the frequency-modulated laser beam is irradiated in a direction different from where the object under test 10 is positioned. In other words, the absence of the object under test 10 is a state where the laser device 110 is outputting a frequency-modulated laser beam but the optical head component 140 does not receive reflected light from the object under test 10.

[0098] When the end surface reflected light occurs in this case, the beat signal generating means 150 generates a beat signal by mixing the reference light and the end surface reflected light reflected from the exit end surface of the emitted measurement light even if there is no object 10 to be measured. The beat signal based on this end surface reflected light is used as a reference beat signal. Then, the beat signal generating means 150 outputs a signal including the reference beat signal as a reference signal.

[0099] The storage means 190 stores a reference frequency signal that is the reference signal output by the beat signal generating means 150 in a state where there is no object 10 to be measured and converted into a frequency signal by the frequency analysis means 160. Preferably, the storage means 190 stores the reference frequency signal in advance. Alternatively, the storage means 190 can store the reference frequency signal converted when the reference signal is generated after the distance measuring device 100 performs distance measurement on the object 10 to be measured and the object 10 to be measured is removed.

[0100] Figure 8 An example of the reference frequency signal stored in the storage means 190 according to the present embodiment is shown. In Figure 8 , the horizontal axis indicates the frequency and the vertical axis indicates the signal level. The storage means 190 stores the frequency signal of the reference signal as the reference frequency signal as shown in Figure 8 .

[0101] Then, for each frequency, the frequency analysis means 160 subtracts the signal level of the reference frequency signal from the signal level of the frequency signal converted from the beat signal and then specifies the frequency of the beat signal. For example, the frequency analysis means 160 subtracts the reference frequency signal shown in Figure 7 from the distance measurement signal shown in Figure 8 .

[0102] Figure 9 An example of the result of the frequency analysis means 160 subtracting the reference frequency signal from the distance measurement signal according to the present embodiment is shown. In Figure 9 , the horizontal axis indicates the frequency of light and the vertical axis indicates the signal level. As can be seen from Figure 9 , the frequency spectrum of the reference beat signal based on the end surface reflected light is subtracted from the frequency signal in which two frequency spectra are superimposed. By doing so, the frequency analysis means 160 can analyze the frequency spectrum of the beat signal based on the reflected light reflected on the object 10 to be measured and output the frequency v B (m, d) of the beat signal.

[0103] Then, the calculation means 170 uses the frequency v B(m, d), the difference d between the propagation distances of the reference light and the measurement light is calculated using Equation 6. As described above, since the signal level of the reference frequency signal is subtracted from the signal level of the distance measurement signal output from the beat signal generating section 150, the measurement apparatus 100 according to the present embodiment can reduce the influence of the end surface reflection light present at the exit end of the laser beam on the distance measurement result.

[0104] For example, the distance d from the optical head section 140 to the object to be measured 10 can be measured by reducing the occurrence of the reference beat signal based on the end surface reflection light as the beat signal to be analyzed by the frequency analysis section 160. In addition, even if (i) the peak of the frequency spectrum of the beat signal based on the reflection light reflected on the object to be measured 10 and (ii) the peak of the frequency spectrum of the reference beat signal are superimposed to such an extent that they cannot be separated, the measurement apparatus 100 subtracts the frequency spectrum of the reference beat signal from the superimposed frequency spectrum. By doing so, the measurement apparatus 100 can analyze the frequency spectrum of the beat signal based on the reflection light reflected on the object to be measured 10 and measure the distance d with good accuracy.

[0105] [Variation Example of Measurement Apparatus 100]

[0106] The case where the measurement apparatus 100 according to the present embodiment stores the signal obtained by converting the reference signal output by the beat signal generating section 150 in the state where the object to be measured 10 is not present into a frequency signal as the reference frequency signal has been described above.

[0107] Here, the measurement apparatus 100 can be configured to easily switch between the state where the frequency-modulated laser beam irradiates the object to be measured 10 and the state where the frequency-modulated laser beam does not irradiate the object to be measured 10. Next, such a measurement apparatus 100 will be described.

[0108] Figure 10 A variation example of the measurement apparatus 100 according to the present embodiment and the object to be measured 10 is shown. In the measurement apparatus 100 according to the variation example, the arrangement of the optical system (i.e., the measurement apparatus 100 and the object to be measured 10) is completed by the shutter section 310 and the control section 320. Figure 1 The operation of the measurement apparatus 100 of the present embodiment shown is approximately the same as that of the measurement apparatus 100 of the present embodiment shown in FIG. 1, and the description thereof is omitted. The measurement apparatus 100 of the variation example further includes a shutter section 310 and a control section 320.

[0109] The shutter section 310 is provided between the exit end surface from which the measurement light is emitted and the object to be measured 10 and makes it possible to cut off the irradiation of the measurement light from the exit end surface to the object to be measured 10. For example, when the arrangement of the optical system (i.e., the measurement apparatus 100 and the object to be measured 10) is completed, the measurement light can be irradiated onto the object to be measured 10 when the shutter section 310 is open, whereas the measurement light is cut off and cannot be irradiated onto the object to be measured 10 when the shutter section 310 is closed.

[0110] The shutter member 310 can be provided between the optical head member 140 and the object 10 to be measured, or alternatively can be provided in the optical head member 140. For example, in the shutter member 310, a plate member for cutting off the measurement light is movably provided. In this case, by moving the plate member on the optical axis of the measurement light, the shutter member 310 enters the closed state.

[0111] When calculating the difference d between the propagation distances of the reference light and the measurement light, the control member 320 controls the shutter member 310 to irradiate the measurement light onto the object 10 to be measured by opening the shutter member 310. By doing so, the frequency signal that is the signal output by the beat signal generating member 150 and converted into a frequency domain signal by the frequency analysis member 160 becomes a distance measurement signal when the end face reflection light occurs. Further, when the reference frequency signal is obtained, the control member 320 closes the shutter member 310 to cut off the measurement light. By doing so, the frequency signal that is the signal output by the beat signal generating member 150 and converted into a frequency domain signal by the frequency analysis member 160 becomes a reference frequency signal when the end face reflection light has occurred.

[0112] For example, when the shutter member 310 is closed, the control member 320 controls the frequency analysis member 160 to store the reference frequency signal, which is the reference beat signal subjected to frequency conversion by the frequency analysis member 160, to the storage member 190. Further, for example, when the shutter member 310 is opened, the control member 320 controls the frequency analysis member 160 to read the reference frequency signal from the storage member 190, and then performs frequency analysis on the frequency signal obtained by subtracting the reference frequency signal from the distance measurement signal.

[0113] In this way, the measurement apparatus 100 of the above-described modification example can easily switch between the state in which the measurement light does not irradiate the object 10 to be measured and the state in which the measurement light irradiates the object 10 to be measured, without moving the measurement apparatus 100 or the object 10 to be measured. Therefore, even if the end face reflection light occurs, the measurement apparatus 100 can quickly measure the distance d between the optical head member 140 and the object 10 to be measured.

[0114] For example, the control member 320 includes an FPGA, a DSP, and / or a CPU in a similar manner to the frequency analysis member 160 and the calculation member 170. It should be noted that the frequency analysis member 160, the calculation member 170, and the control member 320 can be configured using one CPU.

[0115] The constants and the like of the individual components forming the measurement device 100 can change according to environmental changes, and can also change over time. For example, the length of the optical fiber, the arrangement of the optical components, the circuit constants of the electronic circuit elements, and the like can change both with the environment and over time. In this case, the frequency of the reference beat signal based on the end face reflected light can change in response to changes in the constants of the internal components of the measurement device 100.

[0116] In this case, the reference frequency signal stored in the storage component 190 is the frequency signal of the reference beat signal before the change. Therefore, there can be a case in which the frequency spectrum shape of the frequency signal obtained by subtracting the signal level of the reference frequency signal stored in the storage component 190 from the signal level of the distance measurement signal is different from the frequency spectrum shape of the beat signal based on the reflected light reflected on the object to be measured 10. In this case, the measurement device 100 cannot accurately measure the distance d between the optical head component 140 and the object to be measured 10.

[0117] Therefore, the control component 320 of the present modification example cuts off the measurement light by closing the shutter component 310 in response to the predetermined time elapsing, stores the frequency domain signal converted by the frequency analysis component 160 in the storage component 190, and updates the reference frequency signal. By doing so, even if the reference frequency signal changes due to environmental changes and / or changes over time, the measurement device 100 can suppress a decrease in measurement accuracy by updating the reference frequency signal stored in the storage component 190.

[0118] It should be noted that the measurement device 100 can also be provided with an acceptance unit for accepting the execution of the update of the reference frequency signal from the user. When the acceptance unit accepts the update of the reference frequency signal, the measurement device 100 updates the reference frequency signal. By doing so, the user can update the reference frequency signal at his / her intended timing, and therefore, even if, for example, a sudden environmental change occurs, a decrease in measurement accuracy can be suppressed.

[0119] In the measurement device 100 of the present modification example described above, the case in which the shutter component 310 is provided so that the measurement light can be cut off has been described, but is not limited thereto. For example, instead of the shutter component 310, a mirror or the like for changing the optical path of the measurement light can be movably provided. Furthermore, a filter or the like for reducing the light intensity of the measurement light can be movably provided.

[0120] The present disclosure is illustrated based on exemplary embodiments. The technical scope of the present disclosure is not limited to the range explained in the above-described embodiments, and various changes and modifications can be made within the scope of the present invention. For example, all or a part of the apparatus can be configured using any unit that is functionally or physically distributed or integrated. Furthermore, new exemplary embodiments generated by any combination thereof are included in the exemplary embodiments of the present disclosure. Furthermore, the effects of the new embodiments brought by the combination also have the effects of the original exemplary embodiments together.

[0121] [Description of reference numerals]

[0122] 10 object to be measured

[0123] 100 measuring apparatus

[0124] 110 laser apparatus

[0125] 112 frequency shifter

[0126] 114 gain medium

[0127] 116 WDM coupler

[0128] 117 pump light source

[0129] 118 output coupler

[0130] 120 branching member

[0131] 130 optical circulator

[0132] 140 optical head member

[0133] 150 beat signal generating member

[0134] 152 optical 90-degree hybrid

[0135] 154 first photoelectric conversion member

[0136] 156 second photoelectric conversion member

[0137] 160 frequency analysis member

[0138] 162 first filter member

[0139] 164 second filter member

[0140] 170 calculation member

[0141] 180 display member

[0142] 190 storage member

[0143] 202 first AD converter

[0144] 204 second AD converter

[0145] 210 clock signal providing means

[0146] 220 signal processing means

[0147] 310 shutter means

[0148] 320 control means

Claims

1. A measurement apparatus comprising: a laser apparatus that outputs a frequency-modulated laser beam; a branching member that separates the frequency-modulated laser beam output by the laser apparatus so that a portion of the frequency-modulated laser beam is reference light and at least some of the remaining portion of the frequency-modulated laser beam is measurement light; a beat signal generating member that generates a beat signal by mixing the reference light and reflected light that is reflected by irradiating the measurement light onto an object to be measured; a frequency analysis member that performs frequency analysis on the beat signal; a storage member that stores a reference frequency signal that is a reference signal output by the beat signal generating member in a state in which there is no object to be measured and that is converted into a frequency signal; and a calculation member that calculates a difference between propagation distances of the reference light and the measurement light based on a result of the frequency analysis performed by the frequency analysis member on the beat signal; a shutter member that is provided between an exit end surface and the object to be measured and that is capable of cutting off irradiation of the measurement light from the exit end surface to the object to be measured; and a control member that controls the shutter member to irradiate the measurement light onto the object to be measured by opening the shutter member when the difference between the propagation distances of the reference light and the measurement light is calculated, and that cuts off the measurement light by closing the shutter member when the reference frequency signal is obtained, wherein the beat signal generating member outputs, as a reference signal, a signal including a reference beat signal that is generated by mixing the reference light and an end surface reflection light that is reflected from the exit end surface from which the measurement light is emitted, and wherein the frequency analysis member subtracts, for each frequency, a signal level of the reference frequency signal from a signal level of a frequency signal converted from the beat signal, and then specifies a frequency of the beat signal.

2. The measurement apparatus according to claim 1, wherein the beat signal generating member generates two beat signals that are (i) a first beat signal due to the reflected light of the measurement light and the reference light, and (ii) a second beat signal due to the end surface reflection light and the reference light, the frequency analysis member outputs, as a distance measurement signal, a signal that is obtained by converting, into a frequency domain signal, a signal in which the two beat signals generated by the beat signal generating member are superimposed, and the frequency analysis member subtracts, from a frequency spectrum of the distance measurement signal, a frequency spectrum of a reference beat signal based on the end surface reflection light by subtracting, for each frequency, a signal level of the reference frequency signal from a signal level of the distance measurement signal.

3. The measurement apparatus according to claim 1, wherein the control member closes the shutter member to cut off the measurement light in response to a predetermined time elapsing, stores a frequency domain signal converted by the frequency analysis member in the storage member, and updates the reference frequency signal. ​ 4. The measuring apparatus according to any one of claims 1 to 3, wherein the calculating means calculates the difference d between the propagation distances of the reference light and the measurement light using the frequency v of the beat signal obtained by the frequency analyzing means that performs frequency analysis on the beat signal B (m, d) by the following equation, where c is the speed of light, v s is the amount of frequency shift of the frequency-modulated laser beam, v C is 1 / τ RT , τ RT is the time for the light to travel once around the cavity of the laser device, and m is the separation of longitudinal mode numbers of the frequency-modulated laser beam, i.e. the difference between the longitudinal mode number of the measurement light and the longitudinal mode number of the reference light.

5. A measurement method of a measurement apparatus for measuring a distance to an object to be measured, the method comprising the steps of: outputting a frequency-modulated laser beam; separating the frequency-modulated laser beam so that a part of the frequency-modulated laser beam is reference light and at least some of the remaining part of the frequency-modulated laser beam is measurement light; outputting a signal including a reference beat signal as a reference signal, the reference beat signal being obtained by mixing the reference light and an end surface reflection light reflected from an exit end surface from which the measurement light is emitted in a state where the object to be measured is not present; storing information obtained by converting the reference signal into a frequency signal as a reference frequency signal; generating a plurality of beat signals by mixing the reference light and reflection light reflected by irradiating the measurement light onto the object to be measured; performing frequency analysis on a frequency signal obtained by subtracting a signal level of the reference frequency signal from a signal level of a frequency signal converted from the beat signals into a frequency domain signal for each frequency; calculating a difference between propagation distances of the reference light and the measurement light based on a result of the frequency analysis; and controlling a shutter member provided between the exit end surface and the object to be measured and capable of cutting off irradiation of the measurement light from the exit end surface to the object to be measured so as to open the shutter member to irradiate the measurement light onto the object to be measured when calculating the difference between the propagation distances of the reference light and the measurement light, and to close the shutter member to cut off the measurement light when obtaining the reference frequency signal.

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