Measuring device and measuring method

Abstract

To make it possible to easily switch a performance of an optical range-finder.SOLUTION: A measurement device is provided that comprises: a laser device having a plurality of frequency shifters, and outputting frequency modulation laser light; a control unit switching a chirp rate of the frequency modulation laser light to be outputted from the laser device by controlling the plurality of frequency shifters; a branch unit causing the frequency modulation laser light the laser device outputs to be branched to reference light and measurement light; a beat signal generation unit mixing reflection light reflected by irradiating a measurement object with the measurement light with the reference light to generate a beat signal; a frequency analysis unit performing a frequency analysis of the beat signal; and a calculation unit calculating a difference in a propagation distance between the reference light and the measurement light on the basis of a result of performing the frequency analysis of the beat signal.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present invention relates to a measurement device and a measurement method. [Background technology]

[0002] A frequency shifted feedback laser (FSFL) is known, which has a frequency shifter in a resonator and outputs multiple longitudinal mode lasers whose oscillation frequency changes linearly over time. Also, an optical range finder using such a frequency shifted feedback laser is known (see, for example, Patent Document 1 and Non-Patent Document 1). [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Patent No. 3583906 specification [Non-patent literature]

[0004] [Non-Patent Document 1] Takefumi Hara, "Distance sensing using FSF laser and its applications", Optnews, Vol. 7, No. 3, 2012, pp. 25-31 Summary of the Invention [Problem to be solved by the invention]

[0005] The optical range finder splits a frequency-shifted feedback laser into a reference light and a measurement light, irradiates the measurement light on a measurement object, and mixes the reflected light with the reference light to generate a beat signal. The optical range finder measures the distance from the optical range finder to the measurement object by identifying the frequency of the beat signal. Such an optical range finder is sometimes required to measure longer distances easily, and sometimes required to measure with higher accuracy and higher resolution. However, it is not easy to switch the performance of the optical range finder.

[0006] The present invention has been made in consideration of these points, and has an object to make it possible to easily switch the performance of an optical rangefinder. [Means for solving the problem]

[0007] In a first aspect of the present invention, there is provided a laser device having a plurality of frequency shifters and outputting a frequency-modulated laser beam; a control unit that controls the plurality of frequency shifters to switch a chirp rate based on a rate of change per unit time of the frequency of the frequency-modulated laser beam outputted from the laser device; a branching unit that branches the frequency-modulated laser beam outputted from the laser device into a reference beam which is a part of the frequency-modulated laser beam and at least a part of a measurement beam which is the remaining frequency-modulated laser beam; a beat signal generating unit that generates a beat signal by mixing a reflected beam reflected by irradiating a measurement object with the measurement beam and the reference beam; and a frequency analyzing unit that performs a frequency analysis on the beat signal. The present invention provides a measurement apparatus including a calculation unit that calculates a difference in propagation distance between the reference light and the measurement light based on a result of frequency analysis of the beat signal by the frequency analysis unit.

[0008] The control unit may be configured to lower the chirp rate of the frequency-modulated laser light output from the laser device when a distance from the measurement device to the object to be measured is longer.

[0009] The control unit may increase the chirp rate of the frequency-modulated laser light output from the laser device when measuring the distance from the measurement device to the measurement object with higher accuracy.

[0010] The laser device may include a laser resonator that oscillates laser light, the laser resonator having a first frequency shifter that shifts the frequency of input light by a first shift amount, a second frequency shifter that shifts the frequency of the input light by a second shift amount larger than the first shift amount, an input switching unit that inputs light circulating in the laser resonator to one of the first frequency shifter and the second frequency shifter, and an optical coupler including a first port to which light output by the first frequency shifter is input, a second port to which light output by the second frequency shifter is input, and a third port to which a portion of the light input to the first port and the second port is output, and the control unit may control the input switching unit to switch the chirp rate of the frequency-modulated laser light output from the laser device.

[0011] The laser device includes a laser resonator that oscillates laser light, the laser resonator having a first frequency shifter that shifts a frequency of input light by a first shift amount, a second frequency shifter that shifts a frequency of zero-order diffracted light output by the first frequency shifter by a second shift amount different from the first shift amount, and an optical coupler including a first port to which first-order diffracted light output by the first frequency shifter is input, a second port to which first-order diffracted light output by the second frequency shifter is input, and a third port to output a portion of the light input to the first port and the second port, and the control unit may switch the chirp rate of the frequency-modulated laser light output from the laser device based on switching whether or not to operate the first frequency shifter.

[0012] The laser device includes a laser resonator that oscillates laser light, the laser resonator having a first frequency shifter that shifts a frequency of input light by a first shift amount, a second frequency shifter that shifts a frequency of first-order diffracted light output by the first frequency shifter by a second shift amount, and an optical coupler including a first port to which the zeroth-order diffracted light output by the second frequency shifter is input, a second port to which the first-order diffracted light output by the second frequency shifter is input, and a third port to which a portion of the light input to the first port and the second port is output, and the control unit may switch the chirp rate of the frequency-modulated laser light output from the laser device based on switching whether or not to operate the second frequency shifter.

[0013] The laser device includes a laser resonator that oscillates laser light, the laser resonator having a first frequency shifter that shifts a frequency of input light by a first shift amount, a second frequency shifter that shifts a frequency of first-order diffracted light output by the first frequency shifter by a second shift amount, a third frequency shifter that shifts a frequency of zero-order diffracted light output by the second frequency shifter by a third shift amount different from the second shift amount, and an optical coupler including a first port to which the first-order diffracted light output by the second frequency shifter is input, a second port to which the first-order diffracted light output by the third frequency shifter is input, and a third port to which a portion of the light input to the first port and the second port is output, and the control unit may switch the chirp rate of the frequency-modulated laser light output from the laser device based on switching whether or not to operate the second frequency shifter.

[0014] The laser device includes a laser resonator that oscillates laser light, the laser resonator having a first frequency shifter that shifts a frequency of input light by a first shift amount, a second frequency shifter that shifts a frequency of zero-order diffracted light output by the first frequency shifter by a second shift amount, a third frequency shifter that shifts a frequency of first-order diffracted light output by the first frequency shifter by a third shift amount, and an optical coupler including a first port to which the first-order diffracted light output by the second frequency shifter is input, a second port to which the first-order diffracted light output by the third frequency shifter is input, and a third port to which a portion of the light input to the first port and the second port is output, and the control unit may switch the chirp rate of the frequency-modulated laser light output from the laser device based on switching whether or not to operate the first frequency shifter.

[0015] The second shift amount of the second frequency shifter may have a positive or negative sign different from that of the third shift amount of the third frequency shifter.

[0016] The control unit may switch the sign of the chirp rate of the frequency-modulated laser light output from the laser device between positive and negative when a distance from the measurement device to the object to be measured changes relatively.

[0017] The laser device may include a laser resonator that oscillates laser light, the laser resonator having a first frequency shifter that shifts the frequency of input light by a first shift amount, a second frequency shifter that shifts the frequency of the input light by a second shift amount that is different in sign from the first shift amount, an input switching unit that inputs light circulating in the laser resonator to one of the first frequency shifter and the second frequency shifter, and an optical coupler including a first port to which light output by the first frequency shifter is input, a second port to which light output by the second frequency shifter is input, and a third port to which a portion of the light input to the first port and the second port is output, and the control unit may control the input switching unit to switch the chirp rate of the frequency-modulated laser light output from the laser device.

[0018] The laser device includes a laser resonator that oscillates laser light, the laser resonator having a first frequency shifter that shifts a frequency of input light by a first shift amount, a second frequency shifter that shifts a frequency of zero-order diffracted light output by the first frequency shifter by a second shift amount having a positive or negative sign different from the first shift amount, and an optical coupler including a first port to which first-order diffracted light output by the first frequency shifter is input, a second port to which first-order diffracted light output by the second frequency shifter is input, and a third port to which a portion of the light input to the first port and the second port is output, and the control unit may switch the chirp rate of the frequency-modulated laser light output from the laser device based on switching whether or not to operate the first frequency shifter.

[0019] The laser device may include a first laser resonator that oscillates laser light, a second laser resonator that oscillates laser light, a first port to which a first frequency-modulated laser light output from the first laser resonator is input, a second port to which a second frequency-modulated laser light output from the second laser resonator is input, and a third port to output at least a part of the laser light input to the first port and the second port, wherein the first laser resonator has a first frequency shifter that shifts the frequency of the input light by a first shift amount, and the second laser resonator has a second frequency shifter that shifts the frequency of the input light by a second shift amount that is different in sign from the first shift amount.

[0020] The laser device includes a laser resonator that oscillates laser light, the laser resonator having a first frequency shifter that shifts the frequency of input light by a first shift amount, a second frequency shifter that shifts the frequency of the input light by a second shift amount that is different in sign from the first shift amount, an optical coupler that inputs light circulating in the laser resonator to the first frequency shifter and the second frequency shifter, and an optical multiplexing unit including a first port to which light output by the first frequency shifter is input, a second port to which light output by the second frequency shifter is input, and a third port to which at least a portion of the light input to the first port and the second port is output, and the control unit may switch the chirp rate of the frequency-modulated laser light output from the laser device based on switching operations of the first frequency shifter and the second frequency shifter.

[0021] The control unit may switch the chirp rate of the frequency-modulated laser beam to either a first chirp rate or a second chirp rate, the first chirp rate being equal to a multiplication result of a first resonator frequency corresponding to a resonator length of the laser resonator through which the first-order diffracted light output by the first frequency shifter circulates, and the first shift amount, the second chirp rate being equal to a multiplication result of a second resonator frequency corresponding to a resonator length of the laser resonator through which the first-order diffracted light output by the second frequency shifter circulates, the absolute value of the first chirp rate being equal to the absolute value of the second chirp rate, and a positive / negative sign of the first chirp rate being different from a positive / negative sign of the second chirp rate.

[0022] In a second aspect of the present invention, a measurement method of a measurement device for measuring a distance to a measurement object includes the steps of: outputting a frequency-modulated laser beam having a chirp rate based on a rate of change of frequency per unit time set to a first chirp rate; branching the frequency-modulated laser beam into a reference beam which is a part of the frequency-modulated laser beam and a measurement beam which is at least a part of the remaining frequency-modulated laser beam; irradiating the measurement beam onto the measurement object and mixing the reflected beam with the reference beam to generate a beat signal; frequency-analyzing the beat signal; calculating a difference in propagation distance between the reference beam and the measurement beam based on a result of the frequency analysis under a first calculation condition corresponding to the first chirp rate; the step of specifying a second calculation condition corresponding to a second chirp rate higher than the first chirp rate of the frequency-modulated laser beam based on the difference in propagation distance calculated under the first calculation condition, the second calculation condition being used when calculating with a higher measurement accuracy than the measurement accuracy when calculating with a first chirp rate condition, the second calculation condition corresponding to a second chirp rate higher than the first chirp rate of the frequency-modulated laser beam based on the difference in propagation distance calculated under the first calculation condition, the step of switching the chirp rate of the frequency-modulated laser beam from the first chirp rate to the second chirp rate, and after switching the chirp rate, performing steps from the branching step to the frequency analyzing step, and the step of calculating the difference in propagation distance between the reference beam and the measurement beam under the second calculation condition based on a result of the frequency analysis after switching the chirp rate.

[0023] In a third aspect of the present invention, there is provided a measurement method for a measurement device that measures a distance to a measurement object, the method including the steps of: outputting a frequency-modulated laser beam with a chirp rate based on a rate of change of frequency per unit time set to a first chirp rate; branching the frequency-modulated laser beam into a reference beam that is a part of the frequency-modulated laser beam and a measurement beam that is at least a part of the remaining frequency-modulated laser beam; irradiating the measurement beam onto the measurement object and mixing the reflected light with the reference beam to generate a beat signal; frequency-analyzing the beat signal; calculating a difference in propagation distance between the reference beam and the measurement beam based on a result of the frequency analysis under a first calculation condition corresponding to the first chirp rate; and calculating the chirp rate of the frequency-modulated laser beam based on the first chirp rate. a step of switching from a first chirp rate to a second chirp rate; a step of performing steps from the branching step to the frequency analysis step after switching the chirp rate; a step of calculating a difference in propagation distance between the reference light and the measurement light under second calculation conditions corresponding to the second chirp rate based on a result of the frequency analysis after switching the chirp rate; and a step of calculating a distance from the measurement device to the object to be measured based on the difference in propagation distance calculated under the first calculation conditions and the difference in propagation distance calculated under the second calculation conditions, wherein an absolute value of the first chirp rate is equal to an absolute value of the second chirp rate and a positive / negative sign of the first chirp rate is different from a positive / negative sign of the second chirp rate. Effect of the Invention

[0024] According to the present invention, it is possible to easily switch the performance of the optical rangefinder. [Brief description of the drawings]

[0025] [Figure 1] An example of the configuration of a measurement device 100 according to this embodiment is shown together with a measurement object 10. [Diagram 2] 1 shows an example of the configuration of a laser device 110 according to this embodiment. [Diagram 3]1 shows an example of a laser beam outputted by the laser device 110 according to this embodiment. [Figure 4] 1 shows 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 section 140 and the measurement object 10. [Diagram 5] 1 shows an example of the configuration of a beat signal generating section 150 and a frequency analyzing section 160 according to the present embodiment. [Figure 6] 1 shows an example of an outline of quadrature detection by the beat signal generating section 150 and the frequency analyzing section 160 according to this embodiment. [Figure 7] 1 shows a first configuration example of a laser device 300 according to the present embodiment. [Figure 8] 2 shows a second configuration example of the laser device 300 according to the present embodiment. [Figure 9] 1 shows a third configuration example of a laser device 300 according to the present embodiment. [Figure 10] 13 shows a fourth configuration example of the laser device 300 according to the present embodiment. [Figure 11] 5 shows a fifth configuration example of the laser device 300 according to the present embodiment. [Figure 12] 1 shows an example of an operation flow of the measurement device 100 according to the present embodiment. [Figure 13] 13 shows a sixth configuration example of the laser device 300 according to the present embodiment. [Figure 14] 13 shows a seventh configuration example of the laser device 300 according to the present embodiment. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0026] [Configuration example of measuring device 100] 1 is a diagram showing an example of the configuration of a measuring device 100 according to this embodiment together with a measurement object 10. The measuring device 100 optically measures the distance between the measuring device 100 and the measurement object 10. The measuring device 100 may also measure the three-dimensional shape of the measurement object 10 by scanning the position of a laser beam irradiated on the measurement object 10. The measuring device 100 includes a laser device 110, a branching unit 120, an optical circulator 130, an optical head unit 140, a beat signal generating unit 150, a frequency analyzing unit 160, a calculating unit 170, a display unit 180, and a control unit 190.

[0027] The laser device 110 has a laser resonator and outputs frequency-modulated laser light of multiple modes. The laser device 110 has a frequency shifter provided in the resonator and outputs multiple longitudinal mode lasers whose oscillation frequency changes linearly over time. As an example, the laser device 110 is a frequency-shifted feedback laser. The frequency-shifted feedback laser will be described later.

[0028] The branching unit 120 branches the frequency-modulated laser light output by the laser device 110 into a reference light which is a part of the frequency-modulated laser light and a measurement light which is at least a part of the remaining frequency-modulated laser light. As an example, the branching unit 120 is a one-input, two-output optical fiber type optical coupler. In the example of FIG. 1, the branching unit 120 supplies the measurement light to the optical circulator 130 and supplies the reference light to the beat signal generating unit 150.

[0029] The optical circulator 130 has a plurality of input / output ports. For example, the optical circulator 130 outputs light input to one port from the next port, and outputs light input from the next port from the next port. FIG. 1 shows an example in which the optical circulator 130 has three input / output ports. In this case, the optical circulator 130 outputs the measurement light supplied from the branching unit 120 to the optical head unit 140. The optical circulator 130 also outputs the light input from the optical head unit 140 to the beat signal generating unit 150.

[0030] The optical head unit 140 irradiates the light input from the optical circulator 130 toward the measurement target 10. The optical head unit 140 has a collimator lens, for example. In this case, the optical head unit 140 adjusts the light input from the optical circulator 130 via an optical fiber into a beam shape using the collimator lens, and then outputs the light.

[0031] Furthermore, the optical head unit 140 receives reflected light of the measurement light irradiated to the measurement object 10. The optical head unit 140 collects the received reflected light into an optical fiber using a collimator lens and supplies it to the optical circulator 130. In this case, the optical head unit 140 may have one common collimator lens, which is used to irradiate the measurement light to the measurement object 10 and receive the reflected light from the measurement object 10. Note that the distance between the optical head unit 140 and the measurement object 10 is denoted as d.

[0032] Alternatively, the optical head unit 140 may have a condensing lens. In this case, the optical head unit 140 condenses the light input from the optical circulator 130 via the optical fiber onto the surface of the measurement object 10. Then, the optical head unit 140 receives at least a part of the reflected light reflected on the surface of the measurement object 10. The optical head unit 140 condenses the received reflected light into the optical fiber using the condensing lens and supplies it to the optical circulator 130. Even in this case, the optical head unit 140 may have one common condensing lens, and may irradiate the measurement light onto the measurement object 10 and receive the reflected light from the measurement object 10 using the condensing lens.

[0033] The beat signal generating unit 150 receives the reflected light from the optical circulator 130, which is generated by irradiating the measurement light on the measurement object 10. The beat signal generating unit 150 also receives the reference light from the branching unit 120. The beat signal generating unit 150 mixes the reflected light and the reference light to generate a beat signal. The beat signal generating unit 150 has, for example, a photoelectric conversion element, and converts the beat signal into an electrical signal and outputs it.

[0034] Here, since the reflected light travels back and forth over the distance from the optical head unit 140 to the measurement object 10, a difference in propagation distance occurs between the reference light and the reflected light that corresponds to at least the distance 2d. Since the oscillation frequency of the light output by the laser device 110 changes linearly over time, a frequency difference occurs between the oscillation frequencies of the reference light and the reflected light that corresponds to a propagation delay corresponding to the difference in the propagation distance. The beat signal generating unit 150 generates a beat signal that corresponds to such a frequency difference.

[0035] The frequency analysis section 160 performs frequency analysis on the beat signal generated by the beat signal generating section 150. For example, the frequency analysis section 160 converts the beat signal into a digital signal, and converts the converted digital signal into a frequency signal. The frequency analysis section 160 then analyzes the frequency-converted frequency signal to detect the frequency of the beat signal. Here, the frequency of the beat signal is expressed as v B Let us assume that.

[0036] The calculation unit 170 detects the difference in the propagation distance between the reference light and the measurement light based on the result of frequency analysis of the beat signal by the frequency analysis unit 160. The calculation unit 170 calculates the frequency v B Based on this, the distance d from the optical head unit 140 to the measurement object 10 is calculated.

[0037] The display unit 180 displays the calculation result of the calculation unit 170. The display unit 180 may have a display or the like and display the calculation result. The display unit 180 may also store the calculation result in a storage unit or the like. The display unit 180 may supply the calculation result to the outside via a network or the like.

[0038] The control unit 190 controls each unit in the measurement device 100. For example, the control unit 190 controls the laser device 110 to output a frequency-modulated laser beam. The control unit 190 also controls the frequency analysis unit 160 and the calculation unit 170 to calculate the distance d from the optical head unit 140 to the measurement object 10. The control unit 190 may control the display unit 180 to display the calculation result of the distance d.

[0039] At least a part of the frequency analysis unit 160, the calculation unit 170, and the control unit 190 is preferably configured with an integrated circuit or the like. At least a part of the frequency analysis unit 160, the calculation unit 170, and the control unit 190 includes, for example, a field programmable gate array (FPGA), a digital signal processor (DSP), and / or a central processing unit (CPU). The frequency analysis unit 160, the calculation unit 170, and the control unit 190 may be integrally formed. Such a control unit 190 has a storage unit.

[0040] The storage unit may store intermediate data, calculation results, setting values, thresholds, parameters, and the like that are generated or used in the course of operation by the frequency analysis unit 160, the calculation unit 170, and the control unit 190. In response to a request from each unit in the measurement device 100, the storage unit may supply the stored data to a request source.

[0041] When a CPU or the like operates as at least a part of the frequency analysis unit 160, the calculation unit 170, and the control unit 190, the storage unit may store information on an OS (Operating System) and a program that function as the frequency analysis unit 160, the calculation unit 170, and the control unit 190. The storage unit may also store various information including a database that is referenced when the program is executed. For example, a computer functions as the frequency analysis unit 160, the calculation unit 170, and the control unit 190 by executing a program stored in the storage unit.

[0042] The storage unit includes, for example, a read only memory (ROM) that stores a basic input output system (BIOS) of a computer or the like, and a random access memory (RAM) that serves as a working area. The storage unit may also include a large-capacity storage device such as a hard disk drive (HDD) and / or a solid state drive (SSD). The computer may further include a graphics processing unit (GPU) or the like.

[0043] The above-described measuring device 100 is capable of measuring the distance d between the measuring device 100 and the measuring object 10 by analyzing the frequency difference between the reflected light of the measuring light irradiated on the measuring object 10 and the reference light. That is, the measuring device 100 can constitute a non-contact and non-destructive optical distance meter. A more detailed configuration of the measuring device 100 will be described next.

[0044] [Configuration example of laser device 110] Fig. 2 shows a configuration example of a laser device 110 according to this embodiment. The laser device 110 in Fig. 2 shows an example of a frequency-shifted feedback laser. The laser device 110 has a laser resonator, and oscillates laser light within the laser resonator. The laser resonator of the laser device 110 has a laser resonator including a frequency shifter 112, an amplification 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 a substantially constant frequency. As an example, the frequency shifter 112 is an AOFS (Acousto-Optic Frequency Shifter) having an acousto-optic element. Here, the amount of frequency shift by the frequency shifter 112 is +ν s That is, the frequency shifter 112 changes the frequency of the light circulating around the resonator by v s The frequency is shifted upwards by

[0046] The amplification medium 114 is supplied with pump light and amplifies the input light. As an example, the amplification medium 114 is an optical fiber doped with an impurity. The impurity is, for example, a rare earth element such as erbium, neodymium, ytterbium, terbium, or thulium. The amplification medium 114 is also supplied with pump light from a pump light source 117 via a WDM coupler 116. An output coupler 118 outputs a part of the light oscillated by the laser in the resonator to the outside.

[0047] That is, the laser device 110 shown in Fig. 2 constitutes a fiber ring laser having a frequency shifter 112 in a resonator. It is preferable that the laser device 110 further has an isolator in the resonator. The laser device 110 may also have an optical bandpass filter in the resonator that passes light in a predetermined wavelength band. The frequency characteristics of the laser light output by such a laser device 110 will be described below.

[0048] FIG. 3 shows an example of laser light output by the laser device 110 according to this embodiment. On the left side of FIG. 3, the optical spectrum of the laser light output by the laser device 110 at time t0 is shown. In this optical spectrum, the horizontal axis indicates the light intensity, and the vertical axis indicates the light frequency. Furthermore, multiple longitudinal modes of the optical spectrum are indicated by the number q. The frequencies of the multiple longitudinal modes are arranged at approximately constant frequency intervals. Here, the time it takes for light to make one revolution around the resonator is defined as τ RT (=1 / ν c ), then multiple longitudinal modes are expressed as 1 / τ RT (=ν c ) interval. Note that ν0 is the initial frequency of the optical spectrum at time t0. c is the resonant frequency ν of the laser resonator c It is.

number

[0049] Fig. 3 shows the change over time in frequency of multiple longitudinal modes output by laser device 110 on the right side. On the right side of Fig. 3, the horizontal axis shows time and the vertical axis shows frequency. That is, Fig. 3 shows the change over time in frequency of the laser light output by laser device 110 on the right side, and the instantaneous frequency of the laser light at time t0 on the left side.

[0050] In the laser device 110, every time the light in the resonator makes one revolution around the resonator, the frequency shifter 112 changes the frequency of the circulating light by v s In other words, the time is increased by τ RT With each lapse, the frequency of each mode is ν s Since the frequency increases by dν / dt, the time change in frequency is ν s / τ RT Therefore, the multiple longitudinal modes shown in equation (1) change as time t passes, as shown in the following equation:

number

[0051] [Distance measurement process details] The measurement device 100 according to this embodiment measures the distance d between the optical head unit 140 and the measurement object 10 using a laser device 110 that outputs a frequency component as shown in Equation 2. Here, the optical path difference between the reference light and the reflected light is only the distance 2d traveled back and forth over the distance d, and the propagation delay corresponding to the distance 2d is Δt. That is, when the measurement light is reflected back from the measurement object 10 at time t, the reflected light that has returned approximately matches the frequency of the past by a time Δt before time t, and can be expressed by the following equation.

number

[0052] On the other hand, the reference light at time t can be expressed by the following equation, similar to equation (2). Here, the reference light is v q’ The result was (t).

number

[0053] The beat signal generating section 150 superimposes the reflected light and the reference light, so that a plurality of beat signals are generated between the plurality of longitudinal modes shown in the formula (3) and the plurality of longitudinal modes shown in the formula (4). The frequency of such beat signals is defined as ν B If (m, d), then ν B (m, d) can be expressed by the following formula from (3) and (4). Note that m is the interval between longitudinal mode numbers (=q-q'), Δt=2d / c, 1 / τ RT =ν c It was decided.

number

[0054] From equation (5), the distance d is expressed as follows:

number

[0055] From equation (6), it can be seen that if the interval m between the longitudinal mode numbers is determined, the distance d can be calculated from the frequency observation results of the beat signal. Note that the interval m is determined by the frequency shift amount v s This can be determined by detecting a change in the beat signal when m is changed. Such a method for determining the interval m is known, as described in Patent Document 1, etc., and therefore a detailed description thereof will be omitted here.

[0056] Since the observed beat signal is always a positive frequency, a beat signal that is mathematically generated on the negative frequency side is folded back to the positive frequency side and observed as an image signal. The generation of such an image signal will be explained next.

[0057] 4 shows an example of the relationship between the frequency of the beat signal detected by the measurement device 100 according to this embodiment and the distance d between the optical head unit 140 and the measurement target 10. The horizontal axis of FIG. 4 shows the distance d, and the vertical axis shows the frequency ν B(m, d). The solid straight lines in FIG. 4 represent the frequency ν B This is a graph showing the relationship between (m, d) for multiple m's.

[0058] As shown in FIG. 4, multiple beat signals are generated according to the value of m. However, multiple longitudinal modes included in the reflected light and the reference light have a substantially constant frequency interval v c Therefore, multiple beat signals with the same value of m are superimposed on approximately the same frequency on the frequency axis. For example, from frequency 0 to c When the frequency band between these is observed, multiple beat signals are superimposed at approximately the same frequency and are observed as a single line spectrum.

[0059] In addition, the frequency of the beat signal in the negative region less than 0, ν B The absolute value of the frequency of (m,d) is further observed as an image signal. That is, the graph of the region in FIG. 4 where the vertical axis is smaller than 0 is folded over at frequency 0 as the boundary. FIG. 4 shows the folded over image signals with multiple dotted lines. The folded over image signals are simply inverted in sign, so on the observed frequency axis they are superimposed on the same frequency as the absolute value of the frequency before folding. For example, from frequency 0 to ν c When observing the frequency band between ν c Unless they are equal to / 2, they will be located at different frequencies.

[0060] Thus, from frequency 0 to ν c In the observation band between B (m,d) and the beat signal ν B (m,d) is an image signal ν with a different m value BTwo line spectra (m', d) are generated. Here, as an example, m'=m+1. In this case, the beat signal generating section 150 can cancel such an image signal by using quadrature detection. Next, the beat signal generating section 150 and the frequency analyzing section 160 using quadrature detection will be described.

[0061] 5 shows an example of the configuration of the beat signal generating section 150 and the frequency analyzing section 160 according to this embodiment. The beat signal generating section 150 performs quadrature detection of the reflected light and the reference light. The beat signal generating section 150 has an optical 90-degree hybrid 152, a first opto-electrical conversion section 154, and a second opto-electrical conversion section 156.

[0062] The optical 90-degree hybrid 152 splits the input reflected light and reference light into two. The optical 90-degree hybrid 152 multiplexes one of the split reflected light and one of the split reference light using an optical coupler or the like to generate a first beat signal. The optical 90-degree hybrid 152 also multiplexes the other of the split reflected light and the other of the split 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 split reference lights. For example, the optical 90-degree hybrid 152 multiplexes one of the two split reference lights with the reflected light via a π / 2 wavelength plate.

[0063] The first photoelectric conversion unit 154 and the second photoelectric conversion unit 156 receive the combined reflected light and reference light and convert them into an electrical signal. Each of the first photoelectric conversion unit 154 and the second photoelectric conversion unit 156 may be a photodiode or the like. As an example, each of the first photoelectric conversion unit 154 and the second photoelectric conversion unit 156 is a balanced photodiode. In FIG. 5, the first photoelectric conversion unit 154 generates a first beat signal, and the second photoelectric conversion unit 156 generates a second beat signal. As described above, the beat signal generating unit 150 combines two reference lights and a reflected light whose phases are different by 90 degrees, performs quadrature detection, and outputs two beat signals to the frequency analyzing unit 160.

[0064] The frequency analysis unit 160 performs frequency analysis on the two beat signals. Here, an example will be described in which the frequency analysis unit 160 performs frequency analysis on the first beat signal as an I signal and the second beat signal as a Q signal. The frequency analysis unit 160 has a first filter unit 162, a second filter unit 164, a first AD converter 202, a second AD converter 204, a clock signal supply unit 210, and a signal processing unit 220.

[0065] The first filter unit 162 and the second filter unit 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 a value ranging from 0 to v c The first filter section 162 and the second filter section 164 are, for example, c In this case, the first filter unit 162 is a low-pass filter that passes the signal components of the frequency v c The second filter section 164 supplies the first beat signal, in which the signal components of frequencies higher than the frequency v c The second beat signal, in which signal components at frequencies higher than the first beat signal have been reduced, is supplied to the second AD converter 204.

[0066] The first AD converter 202 and the second AD converter 204 convert the input 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 supplying unit 210 supplies a clock signal to the first AD converter 202 and the second AD converter 204. As a result, the first AD converter 202 and the second AD converter 204 convert the analog signal into a digital signal at a sampling rate substantially equal to the clock frequency of the received clock signal.

[0067] Here, the observation band is set from 0 to ν c Then, the frequency of the beat signal is at most the resonator frequency ν c Therefore, the clock signal supply unit 210 generates the resonator frequency vc By supplying a clock signal having a frequency at least twice that of the first AD converter 202 and the second AD converter 204, the beat signal can be observed.

[0068] The signal processing unit 220 converts the first beat signal and the second beat signal into frequency data. As an example, the signal processing unit 220 performs a digital Fourier transform (DFT) on each of the first beat signal and the second beat signal. The signal processing unit 220 adds the first beat signal converted into frequency data as a real part and the second beat signal converted into frequency data as an imaginary part, and cancels out the image signal. After the beat signal is converted into a digital signal, the frequency analysis unit 160 may be configured as an integrated circuit or the like. The above-mentioned quadrature detection in the beat signal generating unit 150 and the frequency analysis in the frequency analysis unit 160 will be described next.

[0069] Fig. 6 shows an example of an outline of the quadrature detection of the beat signal generating section 150 and frequency analyzing section 160 according to this embodiment. The horizontal axis of Fig. 6 shows the frequency of the beat signal, and the vertical axis shows the signal intensity. Fig. 6 shows the frequency spectrum of either the I signal or the Q signal. As shown in the upper part of Fig. 6, the frequency spectra of both the I signal and the Q signal have approximately the same spectral shape. The I signal and the Q signal have, for example, a frequency range from 0 to v c In the frequency band between B (m,d) and the image signal ν B (m+1,d) is observed. In this case, the I and Q signals are in the negative frequency range from 0 to -ν c In the frequency band between B (m,d) and the original beat signal of the image signal -ν B There exists (m+1,d).

[0070] Here, the I signal and the Q signal are signal components that have been quadrature-detected by the beat signal generating section 150, so even if they have the same spectrum shape, they contain different phase information. c In the frequency band between B(m+1,d) and the image signal ν of the Q signal B (m+1,d) have the opposite phase. Similarly, the negative frequencies 0 to -ν c In the frequency band between B (m,d) and the beat signal of the Q signal -ν B (m,d) have opposite phases to each other.

[0071] Therefore, as shown in the lower part of FIG. 6, when the signal processing unit 220 calculates I+jQ using the I signal and the Q signal, the frequency from 0 to v c In the frequency band between B The (m,d) beat signals reinforce each other, and the frequency ν B The image signal of (m+1,d) is canceled. Similarly, the image signal of frequencies 0 to -ν c In the frequency band between B The (m+1,d) beat signals reinforce each other, resulting in a frequency of -ν B The beat signals of (m,d) are cancelled out.

[0072] As a result of the frequency analysis by the signal processing unit 220, the frequency from 0 to v c There is one beat signal at frequency ν B In this way, the measurement device 100 can cancel the image signal, so that the beat signal frequency v B For example, the signal processing unit 220 may detect the frequency at which the converted frequency signal has the highest signal strength as the frequency v B Output as (m,d).

[0073] Here, the distance d measured by the measuring device 100 is expressed by the following equation (6). From the equation (6), v c , v s , and v B It can be seen that the calculation unit 170 can calculate the distance d by using the three frequencies (m, d). BAs described above, (m, d) can be detected by frequency analysis in the signal processing unit 220. c and ν s is a frequency determined by the material of the laser device 110, and can be treated as a fixed value. B (m,d) and a predetermined ν c and ν s As described above, the measurement apparatus 100 can measure the distance d from the optical head unit 140 to the measurement object 10. The measurement apparatus 100 may also add an offset value corresponding to the reference position to the distance d to calculate and output the distance from the reference position to the measurement object 10.

[0074] From equation (6), the signal frequency of the beat signal, ν B The effect of the measurement accuracy of (m,d) on the measurement accuracy of distance d is ν s and ν c It can be seen that the larger the value of , the smaller the s and ν c The product ν s ν c is called the chirp rate. The chirp rate is a parameter based on the rate of change of frequency per unit time. In other words, by increasing the chirp rate, the measurement accuracy and resolution of the measurement device 100 can be improved.

[0075] The frequency shift amount ν of the frequency shifter 112 s can be increased to several hundreds of MHz by selecting an acousto-optical element. As shown in FIG. 4, for example, the distance d is in the range of 0 to v c Since the analysis is performed at frequency intervals up to s Distance d measurable with the same order m for max is expressed as follows:

number

[0076] From equation (7), the frequency shift amount ν s If we increase the distance d that can be measured with the same order m, max It can be seen that the measurable distance d max Since the value of the order m changes when m becomes smaller, for example, when measuring different distances, the frequency of identifying different orders m increases. The above-mentioned known methods of identifying the order m are laborious and time-consuming, which may result in a long measurement time.

[0077] On the other hand, the frequency shift amount v s By reducing the measurable distance d max Increasing m reduces the measurement accuracy as described above, but it is possible to extend the distance that can be measured with the lowest order (m=0), for example. In this case, even if multiple different distances are measured, the frequency at which measurements can be made without calculating the order m increases. In addition, the frequency at which measurements can be made using the same order m increases, so the frequency at which different orders m need to be specified decreases, and the measurement time can be shortened.

[0078] As described above, the measurement device 100 has a performance based on the chirp rate of the frequency-modulated laser light. Such a measurement device 100 can adjust the measurable distance d max Large long range low accuracy measurement and measurable distance d max It is desirable to be able to switch between different device performances, such as short-range, high-precision measurement with small chirp. Therefore, it is conceivable to provide a plurality of laser devices 110 with different chirp rates in the measurement device 100, and to switch between the laser devices 110 with chirp rates appropriate for the application.

[0079] In this case, the control unit 190 switches the laser device 110 in response to a user input or the like. The control unit 190 may execute a program stored in the storage unit to switch the laser device 110. Although such a measuring device 100 can easily switch the performance of the device, the laser device 110 is expensive, which may increase the cost of the device and the size of the device.

[0080] Therefore, the measurement device 100 according to the present embodiment uses a laser device capable of changing the chirp rate in response to a control signal instead of the laser device 110, thereby preventing the device from becoming large in size and enabling the device performance to be switched easily and at low cost. An example of the configuration of such a laser device will be described below.

[0081] [First Configuration Example of Laser Device 300] 7 shows a first configuration example of a laser device 300 according to this embodiment. In the laser device 300 shown in FIG. 7, the components that operate substantially the same as those in the laser device 110 according to this embodiment shown in FIG. 2 are given the same reference numerals, and duplicated explanations will be omitted. The laser device 300 includes a laser resonator that oscillates laser light. The laser resonator includes an amplification medium 114, a WDM coupler 116, a pump light source 117, an output coupler 118, a first frequency shifter 310, a second frequency shifter 320, an input switching unit 330, and an optical coupler 340.

[0082] The first frequency shifter 310 shifts the frequency of the input light by a first shift amount. For example, the frequency of the light input to the first frequency shifter 310 is set to ν0, and the first shift amount is set to +ν s1 Then, the first frequency shifter 310 is s1 The first frequency shifter 310 operates in response to a control signal from an external device such as the control unit 190.

[0083] The second frequency shifter 320 shifts the frequency of the input light by a second shift amount that is greater than the first shift amount. For example, the frequency of the light input to the first frequency shifter 310 is set to ν0, and the second shift amount is set to +νs2 Then, the first frequency shifter 310 is s2 It outputs light of frequency (ν s2 >ν s1 The second frequency shifter 320 operates in response to a control signal from an external source such as the control unit 190.

[0084] The input switching unit 330 inputs the light circulating in the laser resonator to either the first frequency shifter 310 or the second frequency shifter 320. The input switching unit 330 is, for example, a one-input, two-output optical switch. The input switching unit 330 outputs the input light to either the first frequency shifter 310 or the second frequency shifter 320 in response to a control signal from an external device such as the control unit 190.

[0085] The optical coupler 340 has a first port 341, a second port 342, and a third port 343. The first port 341 receives the light output from the first frequency shifter 310. The second port 342 receives the light output from the second frequency shifter 320. The third port 343 outputs a part of the light input to the first port 341 and the second port 342. For example, the optical coupler 340 outputs light from the third port 343 with approximately half the intensity of the light input to the first port 341, and outputs light from the third port 343 with approximately half the intensity of the light input to the second port 342.

[0086] The laser device 300 of the first configuration example described above changes the chirp rate to v s1 ν c and ν s2 ν c or the like. Therefore, the control unit 190 can switch the chirp rate of the frequency-modulated laser light output from the laser device 300 by controlling the input switching unit 330. The measurement device 100 equipped with the laser device 300 of the first configuration example can perform long-range low-precision measurement by using the first frequency shifter 310, and can perform short-range high-precision measurement by using the second frequency shifter 320, for example.

[0087] The laser device 300 of the first configuration example shown in FIG. 7 is just an example, and is not limited to a configuration in which two frequency shifters are switched. The laser device 300 may be configured to switch three or more frequency shifters. In this case, the input switching unit 330 is, for example, a 1-input, n-output optical switch. The input switching unit 330 may function as a 1-input, n-output optical switch by combining a plurality of optical switches. In this way, the laser device 300 of the first configuration example can change the chirp rate to v s1 ν c , v s2 ν c , v s3 ν c , , and ν sn ν c It can be switched to either of the above.

[0088] [Second Configuration Example of Laser Device 300] 8 shows a second configuration example of the laser device 300 according to this embodiment. In the laser device 300 shown in FIG. 8, the same reference numerals are used for the components that are substantially the same as those of the laser device 110 and the laser device 300 according to this embodiment shown in FIG. 2 and FIG. 7, and the duplicated description will be omitted. The laser device 300 includes a laser resonator that oscillates a laser beam. The laser resonator includes an amplification medium 114, a WDM coupler 116, a pump light source 117, an output coupler 118, a first frequency shifter 310, a second frequency shifter 320, and an optical coupler 340.

[0089] The first frequency shifter 310 shifts the frequency of the input light by a first shift amount. The first shift amount of the first frequency shifter 310 is +ν s1 The first frequency shifter 310 includes an input port 311, a first output port 312, and a second output port 313. For example, light with a frequency ν0 is input to the input port 311.

[0090] When the first frequency shifter 310 is operating in response to a control signal from an external device such as the control unit 190, the frequency of the light input to the input port 311 is shifted by a first shift amount to ν0+ν s1 From first output port 312, light having the same frequency as the frequency of the light input to input port 311 is output. The light output from first output port 312 in this manner is called 1st order diffracted light. Furthermore, when first frequency shifter 310 is not operating in response to an external control signal, it outputs from second output port 313 light having the same frequency as the frequency of the light input to input port 311. The light output from second output port 313 in this manner is called 0th order diffracted light.

[0091] The second frequency shifter 320 shifts the frequency of the input light by a second shift amount. The second shift amount of the second frequency shifter 320 is +ν s2 The second frequency shifter 320 includes an input port 321 and a first output port 322. The input port 321 receives the zeroth order diffracted light output from the second output port 313 of the first frequency shifter 310.

[0092] The second frequency shifter 320 operates in response to a control signal from an external device such as the control unit 190, and shifts the frequency of the zero-order diffracted light output by the first frequency shifter 310 by a second shift amount different from the first shift amount. The second shift amount may be larger than the first shift amount, or may be smaller than the first shift amount. The second frequency shifter 320 shifts the frequency of the zero-order diffracted light by, for example, ν0+ν s2 The light having this frequency is output from the first output port 322 as the first-order diffracted light.

[0093] The first port 341 of the optical coupler 340 receives the first-order diffracted light output from the first output port 312 of the first frequency shifter 310. The second port 342 receives the first-order diffracted light output from the first output port 322 of the second frequency shifter 320. The third port 343 outputs a portion of the light input to the first port 341 and the second port 342.

[0094] For example, the control unit 190 operates the first frequency shifter 310 to output the first-order diffracted light from the first output port 312 of the first frequency shifter 310 and output the first-order diffracted light of ν0+ν from the third port 343 of the optical coupler 340. s1 In addition, the control unit 190 can stop the operation of the first frequency shifter 310 while keeping the second frequency shifter 320 in operation, thereby outputting the first-order diffracted light from the first output port 322 of the second frequency shifter 320 and outputting the light of the frequency of ν0+ν from the third port 343 of the optical coupler 340. s2 It is possible to output light of a frequency of 1000 MHz.

[0095] As described above, the laser device 300 of the second configuration example, like the laser device 300 of the first configuration example, can change the chirp rate to v s1 ν c and ν s2 ν c or the like. When the measurement device 100 is equipped with the laser device 300 of the second configuration example, the control unit 190 can switch the chirp rate of the frequency-modulated laser light output from the laser device 300 by switching whether or not to operate the first frequency shifter 310. This allows the measurement device 100 to switch between long-range low-precision measurement and short-range high-precision measurement.

[0096] The laser device 300 of the second configuration example shown in Fig. 8 is just an example, and is not limited to a configuration in which the operation of two frequency shifters is switched. The laser device 300 may be configured to switch the operation of n number of frequency shifters, which is three or more. In this case, for example, the zero-order diffracted light of the second frequency shifter 320 is input to the next third frequency shifter.

[0097] In this way, the nth frequency shifter receives the zero-order diffracted light of the (n-1)th frequency shifter, and shifts the frequency of the input light by a frequency shift amount different from the frequency shift amounts of the other frequency shifters. In this case, the optical coupler 340 is, for example, an n-input, 1-output optical coupler. As a result, the laser device 300 of the second configuration example can reduce the chirp rate by ν s1 ν c , v s2 ν c , v s3 ν c , , and ν sn ν c It can be switched to either of the above.

[0098] [Third Configuration Example of Laser Device 300] 9 shows a third configuration example of the laser device 300 according to this embodiment. In the laser device 300 shown in FIG. 9, the same reference numerals are used for the components that are substantially the same as those of the laser device 110 and the laser device 300 according to this embodiment shown in FIG. 2, FIG. 7, and FIG. 8, and the duplicated description will be omitted. The laser device 300 includes a laser resonator that oscillates a laser beam. The laser resonator includes an amplification medium 114, a WDM coupler 116, a pump light source 117, an output coupler 118, a first frequency shifter 310, a second frequency shifter 320, and an optical coupler 340.

[0099] The first frequency shifter 310 shifts the frequency of the input light by a first shift amount. The first shift amount of the first frequency shifter 310 is +ν s1 The first frequency shifter 310 includes an input port 311 and a first output port 312. The first frequency shifter 310, for example, changes the frequency of light of frequency ν0 input to the input port 311 to +ν s1 ν0+ν shifted by s1 The light having this frequency is output from the first output port 312 as the first-order diffracted light.

[0100] The second frequency shifter 320 shifts the frequency of the input light by a second shift amount. The second shift amount of the second frequency shifter 320 is +ν s2The second frequency shifter 320 includes an input port 321, a first output port 322, and a second output port 323. The input port 321 receives the first-order diffracted light output from the first output port 312 of the first frequency shifter 310.

[0101] The second frequency shifter 320 operates in response to a control signal from an external device such as the control unit 190, and shifts the frequency of the first-order diffracted light output by the first frequency shifter 310 by a second shift amount. The second shift amount may be the same as the first shift amount, or may be a shift amount different from the first shift amount. The second frequency shifter 320 shifts the frequency of the first-order diffracted light by, for example, ν0+ν s1 +ν s2 The light having this frequency is output from the first output port 322 as the first-order diffracted light.

[0102] When the second frequency shifter 320 is not operating in response to an external control signal, it outputs light having the same frequency as the light input to the input port 321 as 0th-order diffracted light from the second output port 323. Note that since the light input to the input port 321 is the 1st-order diffracted light of the first frequency shifter 310, the 0th-order diffracted light output from the second output port 323 is ν0+ν s1 The light becomes of this frequency.

[0103] The optical coupler 340 has a first port 341, a second port 342, and a third port 343. The first port 341 receives the zeroth-order diffracted light output from the second output port 323 of the second frequency shifter 320. The second port 342 receives the first-order diffracted light output from the first output port 322 of the second frequency shifter 320. The third port 343 outputs a part of the light input to the first port 341 and the second port 342.

[0104] For example, the control unit 190 operates the second frequency shifter 320 while keeping the first frequency shifter 310 in operation, thereby outputting the first-order diffracted light from the first output port 322 of the second frequency shifter 320 and outputting ν0+ν from the third port 343 of the optical coupler 340. s1 +ν s2In addition, the control unit 190 stops the operation of the second frequency shifter 320 while keeping the first frequency shifter 310 in operation, thereby outputting the zeroth-order diffracted light from the second output port 323 of the second frequency shifter 320 and outputting the light of the frequency of v0+v1 from the third port 343 of the optical coupler 340. s1 It is possible to output light of a frequency of 1000 MHz.

[0105] As described above, the laser device 300 of the third configuration example changes the chirp rate by v s1 ν c and (ν s1 +ν s2 )ν c or the like. When the measurement device 100 is equipped with the laser device 300 of the third configuration example, the control unit 190 can switch the chirp rate of the frequency-modulated laser light output from the laser device 300 by switching whether or not to operate the second frequency shifter 320. This allows the measurement device 100 to switch between long-range low-precision measurement and short-range high-precision measurement.

[0106] [Fourth Configuration Example of Laser Apparatus 300] 10 shows a fourth configuration example of the laser device 300 according to this embodiment. In the laser device 300 shown in FIG. 10, the same reference numerals are used for the components that are substantially the same as those of the laser device 110 and the laser device 300 according to this embodiment shown in FIG. 2, FIG. 7 to FIG. 9, and the duplicated description will be omitted. The laser device 300 includes a laser resonator that oscillates a laser beam. The laser resonator includes an amplification medium 114, a WDM coupler 116, a pump light source 117, an output coupler 118, a first frequency shifter 310, a second frequency shifter 320, an optical coupler 340, and a third frequency shifter 350.

[0107] The laser device 300 of the fourth configuration example is configured such that the laser device 300 of the third configuration example is further provided with a third frequency shifter 350. Therefore, redundant explanations of the first frequency shifter 310 and the second frequency shifter 320 will be omitted.

[0108] The third frequency shifter 350 shifts the frequency of the input light by a third shift amount. The third shift amount of the third frequency shifter 350 is +ν s3 The third frequency shifter 350 shifts the frequency of the zeroth-order diffracted light output by the second frequency shifter 320 by a third shift amount different from the second shift amount. The third frequency shifter 350 includes an input port 351 and an output port 352.

[0109] For example, the input port 351 of the third frequency shifter 350 receives the ν0+ν s1 The third frequency shifter 350 outputs light of frequency ν0+ν from the output port 352. s1 +ν s3 The light of this frequency is output as the first-order diffracted light.

[0110] In this case, the first-order diffracted light output by the second frequency shifter 320 is input to a first port 341 of the optical coupler 340. The first-order diffracted light output by the third frequency shifter 350 is input to a second port 342 of the optical coupler 340. Then, a third port 343 of the optical coupler 340 outputs a part of the light input to the first port 341 and the second port 342.

[0111] For example, by operating the second frequency shifter 320 while keeping the first frequency shifter 310 in operation, the first-order diffracted light is output from the first output port 322 of the second frequency shifter 320, and the first-order diffracted light is output from the third port 343 of the optical coupler 340. s1 +ν s2 In addition, by stopping the operation of the second frequency shifter 320 while keeping the first frequency shifter 310 and the third frequency shifter 350 in operation, the first-order diffracted light is output from the output port 352 of the third frequency shifter 350, and the light of the frequency of ν0+ν0 is output from the third port 343 of the optical coupler 340. s1 +ν s3 It is possible to output light of a frequency of 1000 MHz.

[0112] As described above, the laser device 300 of the fourth configuration example can change the chirp rate (ν s1 +ν s2 )ν c and (ν s1 +ν s3 )ν c or the like. When the measurement device 100 is equipped with the laser device 300 of the fourth configuration example, the control unit 190 can switch the chirp rate of the frequency-modulated laser light output from the laser device 300 by switching whether or not to operate the second frequency shifter 320. This allows the measurement device 100 to switch between long-range low-precision measurement and short-range high-precision measurement.

[0113] In some cases, it may be more desirable to increase the range of change in the chirp rate, since this can expand the range of performance that can be switched by the measurement device 100. For example, in the case of the laser device 300 of the fourth configuration example, it is desirable to increase the difference between the second shift amount of the second frequency shifter 320 and the third shift amount of the third frequency shifter 350.

[0114] For example, it is more preferable that the second shift amount of the second frequency shifter 320 is different in sign from the third shift amount of the third frequency shifter 350. s2 In this case, the laser device 300 changes the chirp rate (ν s1 -ν s2 )ν c and (ν s1 +ν s3 )ν c When the measurement device 100 is equipped with the laser device 300 of the fourth configuration example, the control unit 190 can switch the chirp rate of the frequency-modulated laser light output from the laser device 300 by switching whether or not to operate the second frequency shifter 320.

[0115] [Fifth Configuration Example of Laser Apparatus 300] 11 shows a fifth configuration example of the laser device 300 according to this embodiment. In the laser device 300 shown in FIG. 11, the same reference numerals are used for the components that are substantially the same as those of the laser device 110 and the laser device 300 according to this embodiment shown in FIG. 2, FIG. 7 to FIG. 10, and the duplicated description will be omitted. The laser device 300 includes a laser resonator that oscillates a laser beam. The laser resonator includes an amplification medium 114, a WDM coupler 116, a pump light source 117, an output coupler 118, a first frequency shifter 310, a second frequency shifter 320, an optical coupler 340, and a third frequency shifter 350.

[0116] The laser device 300 of the fifth configuration example is a modified example of the laser device 300 of the fourth configuration example. In the laser device 300 of the fifth configuration example, the second frequency shifter 320 shifts the frequency of the zero-order diffracted light output by the first frequency shifter 310 by a second shift amount. For example, light with a frequency of ν0 output from the second output port 313 of the first frequency shifter 310 is input to the input port 321 of the second frequency shifter 320. Then, the second frequency shifter 320 outputs a frequency of ν0+ν s2 Alternatively, the second frequency shifter 320 outputs light of frequency ν0-ν1 from the first output port 322 as the first-order diffracted light. s2 The light having the frequency of 1.0 may be output as the first-order diffracted light.

[0117] Moreover, the third frequency shifter 350 shifts the frequency of the first-order diffracted light output from the first frequency shifter 310 by a third shift amount. For example, the input port 351 of the third frequency shifter 350 receives the ν0+ν s1 The third frequency shifter 350 outputs light of frequency ν0+ν from the output port 352. s1 +ν s3 The light of this frequency is output as the first-order diffracted light.

[0118] For example, the control unit 190 operates the first frequency shifter 310 while keeping the third frequency shifter 350 in operation, thereby outputting the first-order diffracted light from the output port 352 of the third frequency shifter 350 and outputting ν0+ν from the third port 343 of the optical coupler 340. s1 +ν s3 In addition, the control unit 190 stops the operation of the first frequency shifter 310 while keeping the second frequency shifter 320 in operation, thereby outputting the first-order diffracted light from the first output port 322 of the second frequency shifter 320 and outputting the light of the frequency of ν0+ν from the third port 343 of the optical coupler 340. s2 It is possible to output light of a frequency of 1000 MHz.

[0119] As described above, the laser device 300 of the fifth configuration example changes the chirp rate (ν s1 +ν s3 )ν c and ν s2 ν c When the measurement device 100 is equipped with the laser device 300 of the fifth configuration example, the control unit 190 can switch the chirp rate of the frequency-modulated laser light output from the laser device 300 by switching whether or not to operate the first frequency shifter 310.

[0120] In the laser device 300 of the fifth configuration example, the second frequency shifter 320 outputs ν0-ν s2 The frequency shifter can output light of frequency |-ν as the first-order diffracted light, even if the frequency shift direction is negative. s2 Therefore, even if the shift direction of the second frequency shifter 320 is changed, the laser device 300 does not change the chirp rate by (ν s1 +ν s3 )ν c and ν s2 ν c It is still a device that switches between one of the two.

[0121] As described above, the measurement apparatus 100 according to this embodiment includes the laser apparatus 300 having a plurality of frequency shifters, instead of the laser apparatus 110 described in Fig. 2. The control unit 190 controls the plurality of frequency shifters to switch the chirp rate of the frequency-modulated laser light output by the laser apparatus 300.

[0122] This allows the measurement device 100 to easily switch performance. In the case of the laser device 300 described in Fig. 8 to Fig. 11, the chirp rate can be easily switched to switch the performance of the measurement device 100 simply by controlling the frequency shifter, without switching the optical path using an optical switch or the like. Furthermore, the measurement device 100 may switch the chirp rate of the laser device 300 to switch to the corresponding performance in response to the measurement distance range, measurement accuracy, resolution, and the like input by the user operating the measurement device 100.

[0123] For example, when the distance from the measurement device 100 to the measurement object 10 is longer, the control unit 190 reduces the chirp rate of the frequency-modulated laser light output from the laser device 300. In this manner, the measurement device 100 can quickly measure the distance between the measurement device 100 and the measurement object 10 at a low order such as the zeroth order by switching to the long-range low-precision measurement.

[0124] Furthermore, when measuring the distance from the measurement device 100 to the object 10 with higher accuracy and higher resolution, the control unit 190 increases the chirp rate of the frequency-modulated laser light output from the laser device 300. Furthermore, the measurement device 100 may perform a long-range low-accuracy measurement, and then switch to a short-range high-accuracy measurement to measure the distance between the measurement device 100 and the object 10. The operation of such a measurement device 100 will now be described.

[0125] [Operation flow of the measuring device 100] Fig. 12 shows an example of an operation flow of the measurement device 100 according to this embodiment. The measurement device 100 performs operations from S510 to S570 in Fig. 12, thereby quickly performing long-range and highly accurate measurement.

[0126] First, the control unit 190 controls the laser device 300 to output a frequency-modulated laser beam with a chirp rate set to a first chirp rate from the laser device 300 (S510). The first chirp rate is a lower rate. The first chirp rate is desirably the lowest rate among the rates that can be set. In other words, the control unit 190 switches the measurement device 100 to a measurement range with a longer measurable distance or a measurement range with the longest measurable distance, making it possible to measure the distance between the measurement device 100 and the measurement object 10 in the lowest order.

[0127] Next, the measuring device 100 measures the distance between the measuring device 100 and the measurement object 10 by long-range low-precision measurement. For example, the branching unit 120 branches the frequency-modulated laser light into a reference light that is a part of the frequency-modulated laser light and a measurement light that is at least a part of the remaining frequency-modulated laser light. The beat signal generating unit 150 generates a beat signal by mixing the reflected light that is reflected by irradiating the measurement light on the measurement object 10 with the reference light. Then, the frequency analyzing unit 160 performs frequency analysis on the beat signal generated by the beat signal generating unit 150 (S520).

[0128] Next, the calculation unit 170 calculates the difference in propagation distance between the reference light and the measurement light under a first calculation condition corresponding to the first chirp rate based on the result of the frequency analysis performed by the frequency analysis unit 160 (S530). The calculation unit 170 calculates the distance d by, for example, applying the lowest order condition of m=0 to the formula (6). In this embodiment, the lowest order condition corresponding to the first chirp rate used by the calculation unit 170 is set as the first calculation condition. In this way, the measurement device 100 quickly measures the distance d by expanding the measurement range without determining the interval m between the longitudinal mode numbers by another method.

[0129] Next, the calculation unit 170 specifies a second calculation condition based on the difference in propagation distance between the reference light and the measurement light (S540). The second calculation condition is used when calculating the difference in propagation distance with a higher measurement accuracy than the measurement accuracy when calculating with the first calculation condition, and is a condition corresponding to a second chirp rate higher than the first chirp rate of the frequency-modulated laser light. The second calculation condition is a value of the order m corresponding to the second chirp rate used by the calculation unit 170.

[0130] Since the calculation unit 170 has already calculated the difference in the propagation distance between the reference light and the measurement light, it can calculate the value of the order m when the measurement range is switched to measure the distance between the same measurement object 10 and the measurement device 100. Note that although the calculation result of the distance d by the calculation unit 170 has a lower measurement accuracy by the amount that the measurement range is expanded, it goes without saying that the measurement accuracy is sufficient to calculate the value of m.

[0131] Next, the control unit 190 switches the chirp rate of the frequency-modulated laser beam of the laser device 300 from the first chirp rate to the second chirp rate (S550). In other words, the control unit 190 switches the measurement range to one in which the measurement distance of the measurement device 100 can be measured is shorter.

[0132] Next, the measuring device 100 measures the distance between the measuring device 100 and the measurement object 10 by short-range high-precision measurement. For example, the branching unit 120 branches the frequency-modulated laser light into a reference light that is a part of the frequency-modulated laser light and a measurement light that is at least a part of the remaining frequency-modulated laser light. The beat signal generating unit 150 generates a beat signal by mixing the reflected light that is reflected by irradiating the measurement light on the measurement object 10 with the reference light. Then, the frequency analyzing unit 160 performs frequency analysis on the beat signal generated by the beat signal generating unit 150 (S560).

[0133] Next, the calculation unit 170 calculates the difference in the propagation distance between the reference light and the measurement light under the second calculation condition based on the result of the frequency analysis after switching the chirp rate (S570). The calculation unit 170 applies the value of the order m specified as the second calculation condition in S540 to Equation 6 to calculate the distance d. This allows the measurement device 100 to output the result of measuring the distance between the measurement device 100 and the measurement object 10 by short-range high-precision measurement.

[0134] As described above, the measurement device 100 identifies the value of the order m used to measure the distance between the measurement device 100 and the measurement object 10 by short-range, high-precision measurement from the measurement results of the long-range, low-precision measurement. Therefore, the measurement device 100 can quickly measure the distance d with high precision without identifying the order m by another method.

[0135] The above description has been given of an example in which the measurement device 100 performs a long-range low-precision measurement, specifies the value of the order m, and then performs a short-range high-precision measurement, but the present invention is not limited to this example. Since the calculation section 170 can calculate the distance d after the measurement of the beat signal, the measurement device 100 may perform a long-range low-precision measurement and a short-range high-precision measurement, and then specify the value of the order m to calculate the distance d. That is, the calculation section 170 may perform the process of S540 between S550 and S570. Furthermore, the measurement device 100 may perform a long-range low-precision measurement after a short-range high-precision measurement.

[0136] [Example of reducing errors caused by Doppler shift] The measuring device 100 according to the present embodiment described above is an example in which a measurement is performed by switching between a long-range low-precision measurement and a short-range high-precision measurement, but the present invention is not limited to this. For example, the measuring device 100 may measure a moving object 10. Also, the measuring device 100 may measure the object 10 while moving. In this case, the distance between the measuring device 100 and the object 10 may change relatively, and an error due to a Doppler frequency shift (hereinafter, Doppler shift) may occur in the measurement result of the measuring device 100. The measuring device 100 may switch the chirp rate to reduce such an error due to the Doppler shift.

[0137] For example, when the measurement device 100 and the measurement target 10 are moving at a relative moving speed V on the optical axis of the measurement light, the frequency ν B (m,d) is the error Δν due to the Doppler shift as follows: R Frequency ν including B (m,d)1. Here, the error Δν R1 is a value greater than or equal to 0 and becomes 0 when V=0.

number

[0138] Even if the measurement device 100 inverts the positive and negative sign of the chirp rate while keeping the absolute value of the chirp rate approximately constant for the same measurement target 10, the measurement results of the measurement device 100 will include an error Δν R2 However, since the frequency sweep direction of the laser device 110 is reversed, the frequency v B (m,d)2 reverses the sign of the error term as shown in the following equation. Here, the error Δν R2 is the error Δν R1 Similarly, it is assumed that the value is 0 or greater and becomes 0 when V=0.

number

[0139] In addition, when the absolute value of the chirp rate is approximately constant before and after the sign of the chirp rate is inverted, the error Δν R1 and error Δν R2 Therefore, when the calculation unit 170 of the measurement device 100 calculates the beat signal frequency measurement result v B (m,d)1 and ν B It can be seen that the error caused by the Doppler shift can be reduced by calculating 1 / 2 the sum of (m, d)2.

[0140] In this way, the measurement device 100 that reduces the error caused by the Doppler shift includes, for example, a laser device 300 as shown in Fig. 7. The configuration of the laser device 300 has been described in Fig. 7, so a duplicated description will be omitted here.

[0141] The first frequency shifter 310 shifts the frequency of the input light by a first shift amount +ν s1 The second frequency shifter 320 shifts the frequency of the input light by the first shift amount + v s1 The second shift amount -ν s2 The frequency of the frequency-modulated laser beam is shifted by 100 Hz. Here, it is desirable that the absolute value of the first shift amount is approximately equal to the absolute value of the second shift amount. For such a laser device 300, the control unit 190 can switch the sign of the chirp rate of the frequency-modulated laser beam output from the laser device 300 between positive and negative by controlling the input switching unit 330.

[0142] The chirp rate of frequency-modulated laser light is determined by the frequency shift amount ν s and the resonator frequency ν c The product ν s ν c In other words, the first chirp rate of the frequency-modulated laser light output from the laser device 300 when the first frequency shifter 310 is used is a first resonator frequency v c1 and the first shift amount ν s1 It is equal to the result of multiplication with .

[0143] In addition, when the second frequency shifter 320 is used, the second chirp rate of the frequency-modulated laser light output from the laser device 300 is a second resonator frequency v c2 and the second shift amount -ν s2 Therefore, it is desirable that the laser device 300 is manufactured so that the resonator length of the optical path passing through the first frequency shifter 310 and the resonator length of the optical path passing through the second frequency shifter 320 are substantially equal to each other.

[0144] This allows the absolute value of the first chirp rate to be approximately equal to the absolute value of the second chirp rate. Then, the control unit 190 can switch the chirp rate of the frequency-modulated laser beam to either the first chirp rate or the second chirp rate by controlling the input switching unit 330.

[0145] Alternatively or in addition, the control unit 190 may adjust the first shift amount of the first frequency shifter 310 and the second shift amount of the second frequency shifter 320. For example, the control unit 190 may adjust the first shift amount of the first frequency shifter 310 to +ν s1 The first frequency shifter 310 is set to a frequency v s1 The control unit 190 also controls the second frequency shifter 320 to supply a drive signal of −ν s2 The second frequency shifter 320 is set to a frequency v s2 The drive signal is supplied to the

[0146] Here, the frequency ν s1 and ν s2 It is desirable to adjust the first resonator frequency v c1 and the second resonator frequency ν c2 is assumed to be measured in advance.

number

[0147] For example, the resonator length of the laser resonator through which the first-order diffracted light output from the first frequency shifter 310 circulates may differ from the resonator length of the laser resonator through which the first-order diffracted light output from the second frequency shifter 320 circulates. In this case, the first resonator frequency v c1 and the second resonator frequency ν c2 However, when the control unit 190 receives the driving signal v s1 to the first frequency shifter 310, and the drive signal v s2 to the second frequency shifter 320, the absolute value of the first chirp rate can be easily made equal to the absolute value of the second chirp rate. Therefore, the laser device 300 can be manufactured without precise adjustment of the cavity length.

[0148] An example of the laser device 300 provided in the measurement device 100 capable of reducing errors caused by the Doppler shift has been described above with the configuration shown in FIG. 7, but the present invention is not limited to this. The laser device 300 may have the configuration shown in FIG. 8. In this case, the first frequency shifter 310 shifts the frequency of the input light by a first shift amount +v s1 The second frequency shifter 320 shifts the frequency of the zero-order diffracted light output by the first frequency shifter 310 by a second shift amount −ν s1 Shift only.

[0149] In this case, too, it is desirable that the absolute value of the first shift amount is approximately equal to the absolute value of the second shift amount. It is also desirable that the laser device 300 is manufactured so that the resonator length of the optical path passing through the first frequency shifter 310 and the resonator length of the optical path passing through the second frequency shifter 320 are approximately equal to each other. Alternatively or in addition to this, the control unit 190 controls the frequency v s1 and ν s2 It is more preferable to supply the drive signal to the first frequency shifter 310 and the second frequency shifter 320.

[0150] Thus, the control unit 190 can easily switch the positive / negative sign of the chirp rate of the frequency-modulated laser light output from the laser device 300 by switching whether to operate the first frequency shifter 310. Then, the measurement device 100 can reduce errors caused by the Doppler shift by using the measurement result of the beat signal frequency due to the first chirp rate and the measurement result of the beat signal frequency due to the second chirp rate.

[0151] As described above, the configuration example of the laser device 300 shown in Fig. 7 and Fig. 8 can be used to switch between long-range low-accuracy measurement and short-range high-accuracy measurement, and can also be used to reduce errors caused by Doppler shift. Therefore, the measurement device 100 equipped with such a laser device 300 can realize switching between long-range low-accuracy measurement and short-range high-accuracy measurement, or measurement that reduces errors caused by Doppler shift.

[0152] For example, in the configuration example of the laser device 300 shown in FIG. 7, it has been described that three or more frequency shifters may be switched. Therefore, the laser device 300 has a frequency shift amount of +ν s1 and a first frequency shifter 310 having a frequency shift amount of −ν s2 In addition to the second frequency shifter 320, the frequency shift amount is +ν s3 In this case, the input switching unit 330 inputs the light circulating in the laser resonator to one of the three frequency shifters.

[0153] As a result, the laser device 300 can output, for example, a frequency-modulated laser beam with a chirp rate using the third frequency shifter in the case of long-range low-precision measurement, a frequency-modulated laser beam with a chirp rate using the first frequency shifter 310 in the case of short-range high-precision measurement, and switch between and output frequency-modulated laser beams with two chirp rates using the first frequency shifter 310 and the second frequency shifter 320 in the case of reducing errors caused by Doppler shift. The configuration example of the laser device 300 shown in FIG. 8 may also be configured to switch between three or more frequency shifters, and can be configured to have the same function.

[0154] In the above, an example has been described in which the control unit 190 according to this embodiment switches the sign of the chirp rate of the frequency-modulated laser light output from the laser device 300 between positive and negative when the distance from the measurement device 100 to the measurement target object 10 changes relatively, but the configuration of the laser device 300 is not limited to the configurations in Figs. 7 and 8. The laser device 300 may have two independent laser resonators. Such a laser device 300 will be described next.

[0155] [Sixth Configuration Example of Laser Apparatus 300] 13 shows a sixth configuration example of the laser device 300 according to this embodiment. In the laser device 300 shown in FIG. 13, the same reference numerals are used for the components that operate substantially the same as those of the laser device 110 and the laser device 300 according to this embodiment shown in FIG. 2, FIG. 7 to FIG. 11, and duplicated explanations will be omitted. The laser device 300 includes a first laser resonator 301, a second laser resonator 302, and an optical multiplexing section 360.

[0156] The first laser resonator 301 includes an amplification medium 114, a WDM coupler 116, a pump light source 117, an output coupler 118, and a first frequency shifter 310. The first frequency shifter 310 shifts the frequency of the input light by a first shift amount +ν s1 This causes the first laser cavity 301 to output a first frequency-modulated laser beam with a first chirp rate.

[0157] The second laser resonator 302 includes an amplification medium 114, a WDM coupler 116, a pump light source 117, an output coupler 118, and a second frequency shifter 320. The second frequency shifter 320 shifts the frequency of the input light by a second shift amount −ν s1 As a result, the second laser cavity 302 outputs a second frequency-modulated laser beam with a second chirp rate.

[0158] The optical multiplexer 360 has a first port 361, a second port 362, and a third port 363. The first frequency-modulated laser light output from the first laser resonator 301 is input to the first port 361. The second frequency-modulated laser light output from the second laser resonator 302 is input to the second port 362. The third port 363 outputs at least a part of the laser light input to the first port 361 and the second port 362.

[0159] For such a laser device 300, the control unit 190 can operate the first frequency shifter 310 to cause the laser device 300 to output a frequency-modulated laser beam with a first chirp rate. Also, the control unit 190 can operate the second frequency shifter 320 to cause the laser device 300 to output a frequency-modulated laser beam with a second chirp rate.

[0160] Even in this case, it is desirable that the absolute value of the first shift amount is approximately equal to the absolute value of the second shift amount. Also, it is desirable that the laser device 300 is manufactured so that the cavity length of the first laser cavity 301 and the cavity length of the second laser cavity 302 are approximately equal to each other. Alternatively or in addition to this, the control unit 190 controls the frequency v s1 and ν s2 It is more preferable to supply the drive signal to the first frequency shifter 310 and the second frequency shifter 320.

[0161] 13, the optical multiplexer 360 may be an optical switch. The controller 190 can control the optical switch to output either the first frequency-modulated laser beam or the second frequency-modulated laser beam.

[0162] The above embodiment of the laser device 300 is described as being configured to be able to switch the chirp rate of the frequency-modulated laser light, but is not limited to this. When the measurement device 100 reduces the error caused by the Doppler shift, the laser device 300 may output two frequency-modulated laser lights with chirp rates that have the same absolute value but different positive and negative values.

[0163] For example, in the laser device 300 of the sixth configuration example shown in Fig. 13, the first frequency-modulated laser light output from the first laser resonator 301 is input to the optical multiplexer 360 via the polarization-maintaining fiber. Here, the polarization direction of the first frequency-modulated laser light is adjusted so as to substantially coincide with the direction of the fast axis or the direction of the slow axis of the polarization-maintaining fiber. Note that, in order to adjust the polarization direction of the first frequency-modulated laser light, a λ / 2 wave plate that is rotatable around the optical axis on a plane perpendicular to the optical axis direction may be further provided between the first laser resonator 301 and the optical multiplexer 360.

[0164] In the laser device 300 of the sixth configuration example, the second frequency-modulated laser light output from the second laser resonator 302 is input to the optical multiplexer 360 via a polarization-maintaining fiber. The polarization direction of the second frequency-modulated laser light is adjusted to be substantially the same as the polarization direction of the first frequency-modulated laser light, that is, the polarization direction of the second frequency-modulated laser light is adjusted to be substantially the same as the polarization direction of the fast axis or the slow axis of the polarization-maintaining fiber. Then, the second frequency-modulated laser light is input to the optical multiplexer 360 so that the polarization direction of the first frequency-modulated laser light and the polarization direction of the second frequency-modulated laser light are orthogonal to each other. The optical fibers constituting the first laser resonator 301 and the second laser resonator 302 may be polarization-maintaining fibers.

[0165] The optical multiplexer 360 has a polarizing beam splitter and multiplexes the first frequency-modulated laser light and the second frequency-modulated laser light. The optical multiplexer 360 outputs the multiplexed first frequency-modulated laser light and the second frequency-modulated laser light to a polarization-maintaining fiber. The optical multiplexer 360 outputs the multiplexed light such that, for example, the polarization direction of the first frequency-modulated laser light substantially coincides with the direction of the fast axis of the polarization-maintaining fiber, and the polarization direction of the second frequency-modulated laser light substantially coincides with the direction of the slow axis of the polarization-maintaining fiber.

[0166] As described above, the laser device 300 and the optical multiplexer 360 can transmit the first frequency-modulated laser light and the second frequency-modulated laser light, whose polarization directions are orthogonal to each other, using one polarization-maintaining fiber. In this case, the optical system of the measuring device 100 described in FIG. 1 can also use a polarization-maintaining fiber to split the first frequency-modulated laser light and the second frequency-modulated laser light into a measurement light and a reference light, respectively. Then, the two split measurement lights are irradiated onto the measurement target 10, and the two reflected lights are transmitted to the beat signal generating unit 150 using one polarization-maintaining fiber. Similarly, the two split reference lights can be transmitted to the beat signal generating unit 150 using one polarization-maintaining fiber.

[0167] Here, when the reflected light transmitted through one polarization-maintaining fiber is input to a polarizing beam splitter, the polarizing beam splitter can split the reflected light into the first frequency-modulated laser light and the second frequency-modulated laser light. Similarly, when the reference light transmitted through one polarization-maintaining fiber is input to the polarizing beam splitter, the polarizing beam splitter can split the reference light into the first frequency-modulated laser light and the second frequency-modulated laser light.

[0168] Therefore, the beat signal generating section 150 has a polarizing beam splitter at each of the output ends of the polarization-maintaining fibers that transmit the two reflected beams and the output ends of the polarization-maintaining fibers that transmit the two reference beams. The beat signal generating section 150 mixes the reflected beam of the first frequency-modulated laser beam with the reference beam to generate a beat signal. The beat signal generating section 150 may perform quadrature detection of the reflected beam of the first frequency-modulated laser beam and the reference beam. Based on the beat signal thus generated, the measuring apparatus 100 calculates the frequency ν B (m,d)1 can be measured.

[0169] Furthermore, the beat signal generating section 150 generates a beat signal by mixing the reflected light of the second frequency-modulated laser beam with the reference beam. The beat signal generating section 150 may perform quadrature detection of the reflected light of the second frequency-modulated laser beam and the reference beam. Based on the beat signal thus generated, the measuring apparatus 100 calculates the frequency v B (m,d)2 can be measured.

[0170] Therefore, the measurement apparatus 100 measures the beat signal frequency v B (m,d)1 and ν B By calculating 1 / 2 of the sum of (m, d)2, the error caused by the Doppler shift can be reduced. In this way, by transmitting frequency-modulated laser light with chirp rates of different positive and negative signs so that their polarization directions are orthogonal, beat signals based on the respective frequency-modulated laser lights can be generated and measured. Therefore, for example, the laser device 300 may output two frequency-modulated laser lights simultaneously, and in this case, the measuring device 100 can reduce the measurement time while reducing the error caused by the Doppler shift.

[0171] The above laser device 300 has been described as an example in which two independent resonators are used to output two frequency-modulated laser beams with different chirp rates, but the present invention is not limited to this. The laser device 300 may output a first frequency-modulated laser beam and a second frequency-modulated laser beam with different polarization directions using a single resonator.

[0172] [Seventh Configuration Example of Laser Apparatus 300] Fig. 14 shows a seventh configuration example of the laser device 300 according to this embodiment. In the laser device 300 shown in Fig. 14, the same reference numerals are used for the parts that are substantially the same as those of the laser device 110 and the laser device 300 according to this embodiment shown in Fig. 2, Fig. 7 to Fig. 11, and the duplicated explanation will be omitted. The laser device 300 has an amplification medium 114, a WDM coupler 116, a pump light source 117, an output coupler 118, a first frequency shifter 310, a second frequency shifter 320, an optical multiplexer 360, and an optical brancher 370.

[0173] The optical fiber constituting the resonator of the laser device 300 of the seventh configuration example is preferably a polarization maintaining fiber. The optical branching unit 370 has a polarizing beam splitter and branches the input light into two directions, to the first frequency shifter 310 and the second frequency shifter 320. For example, the optical branching unit 370 outputs the input light having a polarization direction that approximately matches the direction of the fast axis to the first frequency shifter 310. In this case, the optical branching unit 370 outputs the input light having a polarization direction that approximately matches the direction of the slow axis to the second frequency shifter 320.

[0174] The first frequency shifter 310 shifts the frequency of the input light by a first shift amount. The second frequency shifter 320 shifts the frequency of the input light by a second shift amount, which is opposite in sign to the first shift amount. The optical multiplexer 360 has a polarizing beam splitter and multiplexes the light output by the first frequency shifter 310 and the light output by the second frequency shifter 320.

[0175] The optical multiplexing unit 360 outputs the light frequency-shifted by the first frequency shifter 310 as light having a polarization direction that approximately matches the direction of the fast axis. In this case, the optical multiplexing unit 360 outputs the light frequency-shifted by the second frequency shifter 320 as light having a polarization direction that approximately matches the direction of the slow axis.

[0176] Such a laser device 300 can generate a first frequency-modulated laser beam by circulating the light having passed through the first frequency shifter 310 in such a way that the polarization direction of the light is aligned with the fast axis of the polarization-maintaining fiber in the resonator. Then, the control unit 190 drives the first frequency shifter 310 to cause the laser device 300 to generate the first frequency-modulated laser beam. The laser device 300 outputs the generated first frequency-modulated laser beam from the output coupler 118. The output coupler 118 is a polarization-maintaining coupler, and outputs the first frequency-modulated laser beam in such a way that the polarization direction of the first frequency-modulated laser beam is aligned with the direction of the fast axis of the polarization-maintaining fiber of the output port.

[0177] Moreover, the laser device 300 can generate a second frequency-modulated laser beam by circulating the light having passed through the second frequency shifter 320 in such a way that the polarization direction of the light is aligned with the slow axis of the polarization-maintaining fiber in the resonator. Then, the control unit 190 drives the second frequency shifter 320 to cause the laser device 300 to generate the second frequency-modulated laser beam. The laser device 300 outputs the generated second frequency-modulated laser beam from the output coupler 118. The output coupler 118 outputs the second frequency-modulated laser beam in such a way that the polarization direction of the second frequency-modulated laser beam is aligned with the direction of the slow axis of the polarization-maintaining fiber of the output port.

[0178] The laser device 300 of the seventh configuration example described above can output one frequency-modulated laser beam with the first chirp rate or the second chirp rate corresponding to the drive signal in response to receiving a drive signal for driving the first frequency shifter 310 or the second frequency shifter 320 from the control unit 190. Also, the laser device 300 can output two frequency-modulated laser beams with the first chirp rate and the second chirp rate whose polarization directions are orthogonal to each other in response to receiving a drive signal for driving the first frequency shifter 310 and the second frequency shifter 320 from the control unit 190.

[0179] Therefore, the measurement device 100 equipped with the laser device 300 of the seventh configuration example can reduce errors caused by the Doppler shift, similar to the measurement device 100 equipped with the laser device 300 of the sixth configuration example. Moreover, the measurement device 100 can shorten the measurement time while reducing errors caused by the Doppler shift.

[0180] Although the present invention has been described above using the embodiments, the technical scope of the present invention is not limited to the scope described in the above embodiments, and various modifications and changes are possible within the scope of the gist of the present invention. For example, all or part of the device can be configured by distributing or integrating functionally or physically in any unit. In addition, new embodiments resulting from any combination of multiple embodiments are also included in the embodiments of the present invention. The effect of the new embodiment resulting from the combination combines the effect of the original embodiment. [Explanation of symbols]

[0181] 10 Measurement Object 100 Measuring Equipment 110 Laser device 112 Frequency Shifter 114 Amplification medium 116 WDM Coupler 117 Pump Light Source 118 Output Coupler 120 Branch 130 Optical Circulator 140 Optical head unit 150 Beat signal generator 152 Optical 90 degree hybrid 154 First photoelectric conversion unit 156 Second photoelectric conversion unit 160 Frequency Analysis Section 162 First filter section 164 Second filter section 170 Calculation section 180 Display section 190 Control section 202 First AD converter 204 Second AD converter 210 Clock signal supply unit 220 Signal Processing Unit 300 Laser device 301 First Laser Cavity 302 Second Laser Cavity 310 First Frequency Shifter 311 Input port 312 1st output port 313 Second output port 320 Second Frequency Shifter 321 input port 322 1st output port 323 Second output port 330 Input switching unit 340 Optical Coupler 341 Port 1 342 Second Port 343 Port 3 350 3rd Frequency Shifter 351 input port 352 output ports 360 Optical multiplexing section 361 Port 1 362 Port 2 363 Port 3 370 Optical Branching Unit

Claims

1. a laser device having a plurality of frequency shifters and outputting a frequency-modulated laser beam; a control unit that controls the frequency shifters to switch a chirp rate based on a rate of change per unit time of the frequency of the frequency-modulated laser light output from the laser device; a branching unit that branches the frequency-modulated laser light output from the laser device into a reference light that is a part of the frequency-modulated laser light and a measurement light that is at least a part of the remaining frequency-modulated laser light; a beat signal generating unit that generates a beat signal by mixing the reference light with light reflected from a measurement object that is irradiated with the measurement light; a frequency analysis unit that performs frequency analysis on the beat signal; a calculation unit that calculates a difference in propagation distance between the reference light and the measurement light based on a result of the frequency analysis of the beat signal by the frequency analysis unit; A measuring device comprising:

2. The measurement device according to claim 1 , wherein the control unit reduces the chirp rate of the frequency-modulated laser light output from the laser device when a distance from the measurement device to the measurement object is longer.

3. 3. The measurement device according to claim 1, wherein the control unit increases the chirp rate of the frequency-modulated laser light output from the laser device when measuring the distance from the measurement device to the measurement object with higher accuracy.

4. The laser device includes a laser resonator that oscillates laser light, The laser resonator comprises: a first frequency shifter that shifts the frequency of input light by a first shift amount; a second frequency shifter that shifts the frequency of the input light by a second shift amount that is greater than the first shift amount; an input switching unit for inputting light circulating through the laser resonator to either the first frequency shifter or the second frequency shifter; an optical coupler including a first port to which the light output from the first frequency shifter is input, a second port to which the light output from the second frequency shifter is input, and a third port to output a part of the light input to the first port and the second port; having The measurement device according to claim 1 , wherein the control unit controls the input switching unit to switch the chirp rate of the frequency-modulated laser light output from the laser device.

5. The laser device includes a laser resonator that oscillates laser light, The laser resonator comprises: a first frequency shifter that shifts the frequency of input light by a first shift amount; a second frequency shifter that shifts the frequency of the zero-order diffracted light output by the first frequency shifter by a second shift amount different from the first shift amount; an optical coupler including a first port to which the first-order diffracted light output from the first frequency shifter is input, a second port to which the first-order diffracted light output from the second frequency shifter is input, and a third port to output a part of the light input to the first port and the second port; having 4. The measurement device according to claim 1, wherein the control unit switches the chirp rate of the frequency-modulated laser light output from the laser device based on switching whether or not to operate the first frequency shifter.

6. The laser device includes a laser resonator that oscillates laser light, The laser resonator comprises: a first frequency shifter that shifts the frequency of input light by a first shift amount; a second frequency shifter that shifts the frequency of the first-order diffracted light output by the first frequency shifter by a second shift amount; an optical coupler including a first port to which the zero-order diffracted light output from the second frequency shifter is input, a second port to which the first-order diffracted light output from the second frequency shifter is input, and a third port to output a part of the light input to the first port and the second port; having 4. The measurement device according to claim 1, wherein the control unit switches the chirp rate of the frequency-modulated laser light output from the laser device based on switching whether or not to operate the second frequency shifter.

7. The laser device includes a laser resonator that oscillates laser light, The laser resonator comprises: a first frequency shifter that shifts the frequency of input light by a first shift amount; a second frequency shifter that shifts the frequency of the first-order diffracted light output by the first frequency shifter by a second shift amount; a third frequency shifter that shifts the frequency of the zero-order diffracted light output by the second frequency shifter by a third shift amount different from the second shift amount; an optical coupler including a first port to which the first-order diffracted light output from the second frequency shifter is input, a second port to which the first-order diffracted light output from the third frequency shifter is input, and a third port to output a part of the light input to the first port and the second port; having 4. The measurement device according to claim 1, wherein the control unit switches the chirp rate of the frequency-modulated laser light output from the laser device based on switching whether or not to operate the second frequency shifter.

8. The laser device includes a laser resonator that oscillates laser light, The laser resonator comprises: a first frequency shifter that shifts the frequency of input light by a first shift amount; a second frequency shifter that shifts the frequency of the zero-order diffracted light output by the first frequency shifter by a second shift amount; a third frequency shifter that shifts the frequency of the first-order diffracted light output by the first frequency shifter by a third shift amount; an optical coupler including a first port to which the first-order diffracted light output from the second frequency shifter is input, a second port to which the first-order diffracted light output from the third frequency shifter is input, and a third port to output a part of the light input to the first port and the second port; having 4. The measurement device according to claim 1, wherein the control unit switches the chirp rate of the frequency-modulated laser light output from the laser device based on switching whether or not to operate the first frequency shifter.

9. 9. The measurement apparatus according to claim 7, wherein the second shift amount of the second frequency shifter is different in sign from the third shift amount of the third frequency shifter.

10. 2. The measurement device according to claim 1, wherein the control unit switches the positive / negative sign of the chirp rate of the frequency-modulated laser light output from the laser device when a distance from the measurement device to the measurement object changes relatively.

11. The laser device includes a laser resonator that oscillates laser light, The laser resonator comprises: a first frequency shifter that shifts the frequency of input light by a first shift amount; a second frequency shifter that shifts the frequency of the input light by a second shift amount, the second shift amount having a positive and negative opposite relationship to the first shift amount; an input switching unit for inputting light circulating through the laser resonator to either the first frequency shifter or the second frequency shifter; an optical coupler including a first port to which light output from the first frequency shifter is input, a second port to which light output from the second frequency shifter is input, and a third port to output a part of the light input to the first port and the second port; having The measurement apparatus according to claim 10 , wherein the control unit controls the input switching unit to switch the chirp rate of the frequency-modulated laser light output from the laser device.

12. The laser device includes a laser resonator that oscillates laser light, The laser resonator comprises: a first frequency shifter that shifts the frequency of input light by a first shift amount; a second frequency shifter that shifts the frequency of the zero-order diffracted light output by the first frequency shifter by a second shift amount, the second shift amount having a positive and negative sign different from the first shift amount; an optical coupler including a first port to which the first-order diffracted light output from the first frequency shifter is input, a second port to which the first-order diffracted light output from the second frequency shifter is input, and a third port to output a part of the light input to the first port and the second port; having The measurement apparatus according to claim 10 , wherein the control unit switches the chirp rate of the frequency-modulated laser light output from the laser device based on switching whether or not to operate the first frequency shifter.

13. The laser device includes: a first laser resonator for oscillating a laser beam; a second laser resonator for oscillating a laser beam; an optical multiplexing unit including a first port to which the first frequency-modulated laser light output from the first laser resonator is input, a second port to which the second frequency-modulated laser light output from the second laser resonator is input, and a third port to output at least a part of the laser light input to the first port and the second port; Equipped with the first laser resonator has a first frequency shifter that shifts the frequency of input light by a first shift amount; the second laser resonator has a second frequency shifter that shifts the frequency of the input light by a second shift amount, the second shift amount having a positive and negative sign different from the first shift amount; 11. The measuring device according to claim 10.

14. The laser device includes a laser resonator that oscillates laser light, The laser resonator comprises: a first frequency shifter that shifts the frequency of input light by a first shift amount; a second frequency shifter that shifts the frequency of the input light by a second shift amount, the second shift amount having a positive and negative opposite relationship to the first shift amount; an optical coupler for inputting light circulating through the laser resonator to the first frequency shifter and the second frequency shifter; an optical multiplexing unit including a first port to which the light output from the first frequency shifter is input, a second port to which the light output from the second frequency shifter is input, and a third port to which at least a part of the light input to the first port and the second port is output; having The control unit switches the chirp rate of the frequency-modulated laser light output from the laser device based on switching the operation of the first frequency shifter and the second frequency shifter.

11. The measuring device according to claim 10.

15. the control unit switches the chirp rate of the frequency-modulated laser beam to one of a first chirp rate and a second chirp rate, the first chirp rate is equal to a product of a first resonator frequency corresponding to a resonator length of a resonator through which the first-order diffracted light output from the first frequency shifter circulates and the first shift amount; the second chirp rate is equal to a product of a second resonator frequency corresponding to a resonator length of a resonator through which the first-order diffracted light outputted from the second frequency shifter circulates and the second shift amount; the absolute value of the first chirp rate is equal to the absolute value of the second chirp rate, and the sign of the first chirp rate is different from the sign of the second chirp rate; 15. A measuring device according to any one of claims 11 to 14.

16. A method for measuring a distance to a measurement object using a laser device having a plurality of frequency shifters and outputting a frequency-modulated laser beam, comprising the steps of: outputting the frequency-modulated laser light with a chirp rate based on a rate of change of frequency per unit time set to a first chirp rate; splitting the frequency-modulated laser light into a reference light which is a part of the frequency-modulated laser light and a measurement light which is at least a part of the remaining frequency-modulated laser light; a step of irradiating the measurement light onto the measurement object and mixing the reflected light with the reference light to generate a beat signal; performing a frequency analysis on the beat signal; calculating a difference in propagation distance between the reference light and the measurement light under a first calculation condition corresponding to the first chirp rate based on a result of the frequency analysis; determining a second calculation condition corresponding to a second chirp rate higher than the first chirp rate of the frequency-modulated laser beam, the second calculation condition being used when calculating the difference in propagation distance with a measurement accuracy higher than the measurement accuracy when calculating the difference in propagation distance with the first calculation condition, based on the difference in propagation distance calculated with the first calculation condition; controlling the plurality of frequency shifters to switch the chirp rate based on a rate of change per unit time of the frequency of the frequency-modulated laser light output from the laser device from the first chirp rate to the second chirp rate; a step of performing steps from the branching step to the frequency analysis step after switching the chirp rate; calculating a difference in the propagation distance between the reference light and the measurement light under the second calculation condition based on a result of the frequency analysis performed after switching the chirp rate; The measuring method according to claim 1,

17. A method for measuring a distance to a measurement object using a laser device having a plurality of frequency shifters and outputting a frequency-modulated laser beam, comprising the steps of: outputting the frequency-modulated laser light with a chirp rate based on a rate of change of frequency per unit time set to a first chirp rate; splitting the frequency-modulated laser light into a reference light which is a part of the frequency-modulated laser light and a measurement light which is at least a part of the remaining frequency-modulated laser light; a step of irradiating the measurement light onto the measurement object and mixing the reflected light with the reference light to generate a beat signal; performing a frequency analysis on the beat signal; calculating a difference in propagation distance between the reference light and the measurement light under a first calculation condition corresponding to the first chirp rate based on a result of the frequency analysis; controlling the plurality of frequency shifters to switch the chirp rate based on a rate of change per unit time of the frequency of the frequency-modulated laser light output from the laser device from the first chirp rate to a second chirp rate; a step of performing steps from the branching step to the frequency analysis step after switching the chirp rate; calculating a difference in propagation distance between the reference light and the measurement light under a second calculation condition corresponding to the second chirp rate based on a result of frequency analysis performed after switching the chirp rate; calculating a distance from the measurement device to the object to be measured based on a difference in the propagation distance calculated under the first calculation condition and a difference in the propagation distance calculated under the second calculation condition; having the absolute value of the first chirp rate is equal to the absolute value of the second chirp rate, and the sign of the first chirp rate is different from the sign of the second chirp rate; Measurement method.

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