Laser device, measuring device and measuring method

Abstract

Provided are a laser device 110, a measuring device 100, and a measuring method, in which the laser device 110 outputs a frequency-modulated laser beam having a plurality of modes and includes: an optical cavity having a gain medium 114 for amplifying light to be input, and an optical SSB modulator 30 for shifting the frequency of light amplified by the gain medium; and a control section 50 that controls the optical SSB modulator 30 to shift the frequency of light to be input to the optical SSB modulator 30.

Description

TECHNICAL FIELD

[0001] The present application relates to a laser device, a measuring device, and a measuring method. BACKGROUND

[0002] A frequency-shifted feedback laser (FSFL) is known in which a frequency shifter is provided in a cavity (resonator), and a plurality of longitudinal-mode lasers whose output oscillation frequency varies linearly with time. Further, an optical range finder using such a FSFL is known (for example, see Patent Literature 1: Japanese Patent No. 3583906, and Non-Patent Literature 1: "Distance Sensing by FSF Laser and Its Application", Takefumi HARA, Optonews, Vol. 7, No. 3, 2012, pp. 25-31). In addition, an optical single-sideband (SSB) modulator as a frequency shifter is also known (for example, see Patent Literature 2: Japanese Patent No. 3867148, and Patent Literature 3: Japanese Patent No. 4524482). SUMMARY

[0003] PROBLEMS TO BE SOLVED BY THE INVENTION

[0004] As such a FSFL, a configuration is known in which a frequency shifter using an acousto-optic element is provided in a cavity. The acousto-optic element is an element that, when light is input to a region in which an ultrasonic signal propagates in the element, the frequency of the output diffracted light is shifted from the frequency of the input light by the frequency of the ultrasonic signal. Such an acousto-optic element is not easy to change (i) the frequency to be shifted and (ii) the sign of the frequency. Therefore, the FSFL using such an acousto-optic element cannot easily change the amount of frequency shift and the direction of frequency shift.

[0005] The present application focuses on this point, and the object of the present application is to easily change the amount of shift and / or the direction of the frequency applied to the FSFL.

[0006] MEANS FOR SOLVING THE PROBLEMS

[0007] A first aspect of the present application provides a laser device for outputting a frequency-modulated laser beam having a plurality of modes, the laser device comprising: an optical cavity having a gain medium for amplifying light to be input, and an optical SSB modulator for shifting the frequency of the light amplified by the gain medium; and a control means that controls the optical SSB modulator to shift the frequency of the light to be input to the optical SSB modulator.

[0008] The control part can set the frequency shift amount of the optical SSB modulator.

[0009] The optical SSB modulator can have a substrate, a main Mach-Zehnder waveguide provided on the substrate and having a first arm waveguide and a second arm waveguide, a first sub Mach-Zehnder waveguide provided on the first arm waveguide, and a second sub Mach-Zehnder waveguide provided on the second arm waveguide, and the control part can provide a DC voltage of a predetermined value and an RF signal to electrodes provided on the substrate and corresponding to the main Mach-Zehnder waveguide, the first sub Mach-Zehnder waveguide, and the second sub Mach-Zehnder waveguide, and can set the frequency shift amount by changing the frequency of the RF signal.

[0010] The control part can set the frequency shift direction of the optical SSB modulator.

[0011] The optical SSB modulator can have a substrate, a main Mach-Zehnder waveguide provided on the substrate and having a first arm waveguide and a second arm waveguide, a first sub Mach-Zehnder waveguide provided on the first arm waveguide, and a second sub Mach-Zehnder waveguide provided on the second arm waveguide, and the control part can switch the frequency shift direction by providing a DC voltage of a predetermined value to electrodes provided on the substrate and corresponding to the main Mach-Zehnder waveguide, the first sub Mach-Zehnder waveguide, and the second sub Mach-Zehnder waveguide.

[0012] The optical SSB modulator can have a substrate, a main Mach-Zehnder waveguide provided on the substrate and having a first arm waveguide and a second arm waveguide, a first sub Mach-Zehnder waveguide provided on the first arm waveguide, and a second sub Mach-Zehnder waveguide provided on the second arm waveguide, and the control part can invert the phase of an RF signal to be provided to electrodes provided on the substrate and corresponding to the main Mach-Zehnder waveguide, the first sub Mach-Zehnder waveguide, and the second sub Mach-Zehnder waveguide, and can switch the frequency shift direction.

[0013] The main Mach-Zehnder waveguide can be a waveguide that branches light input to the optical SSB modulator to the first arm waveguide and the second arm waveguide, and multiplexes the branched light to output the multiplexed light, the first sub Mach-Zehnder waveguide can be a waveguide that branches light input to the first arm waveguide to the first sub arm waveguide and the second sub arm waveguide, and multiplexes the branched light to output the multiplexed light to the first arm waveguide, the second sub Mach-Zehnder waveguide can be a waveguide that branches light input to the second arm waveguide to the third sub arm waveguide and the fourth sub arm waveguide, and multiplexes the branched light to output the multiplexed light to the second arm waveguide, the electrodes can have a main DC electrode provided between the first arm waveguide and the second arm waveguide of the main Mach-Zehnder waveguide, a first sub DC electrode and a first RF electrode provided between the first sub arm waveguide and the second sub arm waveguide of the first sub Mach-Zehnder waveguide, a second sub DC electrode and a second RF electrode provided between the third sub arm waveguide and the fourth sub arm waveguide of the second sub Mach-Zehnder waveguide, and the control means can supply a predetermined DC voltage to the main DC electrode, the first sub DC electrode, and the second sub DC electrode, and can supply a predetermined RF signal to the first RF electrode and the second RF electrode.

[0014] A second aspect of the present application provides a measuring apparatus including: a laser apparatus according to the first aspect of the present application; a branching means that branches a part of a frequency-modulated light beam output by the laser apparatus as reference light and branches at least some of the remaining part of the frequency-modulated light beam as measurement light; a beat signal generating means that generates a beat signal by mixing the reference light and reflected light that is reflected by irradiating the measurement light onto an object to be measured; and a detecting means that detects a difference in propagation distance between the reference light and the measurement light by frequency-analyzing the beat signal.

[0015] A third aspect of the present application provides a measurement apparatus including the laser apparatus according to the first aspect of the present application, wherein, in the laser apparatus, a control means sets a frequency shift amount of the optical SSB modulator; a branching means branches a part of a frequency-modulated laser beam outputted by the laser apparatus as reference light and branches at least some of the remaining part of the frequency-modulated laser beam as measurement light; a beat signal generating means generates a beat signal by mixing the reference light and reflected light reflected by irradiating the measurement light onto an object to be measured; and a detection means detects a difference in propagation distance between the reference light and the measurement light by frequency-analyzing the beat signal, wherein the control means sets the frequency shift amount of the optical SSB modulator to one of a first frequency or a second frequency larger than the first frequency, then causes the detection means to frequency-analyze the beat signal, and the detection means detects the difference in propagation distance between the reference light and the measurement light based on the results of frequency-analyzing (i) an order number determining beat signal when the frequency shift amount of the optical SSB modulator is set to the first frequency, and (ii) a distance measuring beat signal when the frequency shift amount of the optical SSB modulator is set to the second frequency.

[0016] A fourth aspect of the present application provides a measurement apparatus including the laser apparatus according to the first aspect of the present application, wherein, in the laser apparatus, a control means sets a frequency shift direction of the optical SSB modulator; a branching means branches a part of a frequency-modulated laser beam outputted by the laser apparatus as reference light and branches at least some of the remaining part of the frequency-modulated laser beam as measurement light; a beat signal generating means generates a beat signal by mixing the reference light and reflected light reflected by irradiating the measurement light onto an object to be measured; and a detection means detects a difference in propagation distance between the reference light and the measurement light by frequency-analyzing the beat signal, wherein the control means switches the frequency shift direction of the optical SSB modulator to one of a positive side or a negative side, then causes the detection means to frequency-analyze the beat signal, and the detection means detects the difference in propagation distance between the reference light and the measurement light based on the results of frequency-analyzing (i) a positive side beat signal generated when the frequency shift direction of the optical SSB modulator is the positive side, and (ii) a negative side beat signal generated when the frequency shift direction of the optical SSB modulator is the negative side.

[0017] The detection means can calculate the difference d in propagation distance between the reference light and the measurement light by the following equation:

[0018]

[0019] The frequency v of the beat signal obtained by frequency-analyzing the beat signal B (m, d), where c is the speed of light, v s is the frequency shift amount of the frequency-modulated laser beam, v c = 1 / τRT , τ RT It is the time it takes for light to travel around the optical cavity of the laser device (110), and m is the interval of the longitudinal modes of the frequency-modulated laser beam (the difference between the longitudinal modes of the measured light and the longitudinal modes of the reference light).

[0020] The beat signal generation unit can perform orthogonal detection of the reflected light and the reference light.

[0021] A fifth aspect of the present invention provides a measurement method comprising the steps of: setting the frequency shift amount and frequency shift direction of an optical SSB modulator; outputting a frequency-modulated laser beam having multiple modes from a laser device, the laser device including an optical cavity having a gain medium and the optical SSB modulator; branching a portion of the frequency-modulated laser beam output from the laser device as a reference light and at least some of the remaining portion of the frequency-modulated laser beam as measurement light; generating a first beat signal by mixing the reference light and reflected light reflected by illuminating the measurement light onto an object under test; and detecting the difference in propagation distance between the reference light and the measurement light based on a frequency analysis result of the first beat signal.

[0022] After generating the first beat signal, the following steps can be performed: generating a second beat signal by switching the frequency shift direction of the optical SSB modulator; and detecting the difference in propagation distance between the reference light and the measurement light based on the frequency analysis results of the first and second beat signals.

[0023] The setup may include setting the frequency shift of the optical SSB modulator to a first frequency; and after generating the first beat signal, the following steps may be performed: generating the distance measurement beat signal by switching the frequency shift of the optical SSB modulator to a second frequency greater than the first frequency; and detecting the difference in propagation distance between the reference light and the measurement light based on the frequency analysis results of the first beat signal and the distance measurement beat signal.

[0024] The settings may include setting the frequency shift of the optical SSB modulator (30) to a first frequency; the following steps may be performed after generating the first beat signal: generating a third beat signal by switching the frequency shift of the optical SSB modulator to a second frequency greater than the first frequency; generating a fourth beat signal by switching the frequency shift direction to the opposite direction while keeping the frequency shift of the optical SSB modulator at the second frequency; and detecting the difference in propagation distance between the reference light and the measurement light based on the frequency analysis results of the first beat signal, the third beat signal and the fourth beat signal.

[0025] The effects of the invention

[0026] According to the present invention, it has the effect of easily changing the shift amount and / or direction of the frequency applied to the FSFL. Attached Figure Description

[0027] Figure 1 A configuration example of the laser device 110 according to the present embodiment is shown.

[0028] Figure 2 A configuration example of an acousto-optic frequency shifter (AOFS) 20 is shown.

[0029] Figure 3 A configuration example of the optical SSB modulator 30 and the control component 50 according to the present embodiment is shown.

[0030] Figure 4 An example of a laser beam output from the laser device 110 according to the present embodiment is shown.

[0031] Figure 5 A configuration example of the measurement device 100 according to the present embodiment and the object 10 to be measured are shown.

[0032] Figure 6 An example of a relationship between (i) the frequency of the beat signal detected by the measurement device 100 according to the present embodiment and (ii) the distance d between the optical head component 140 and the object 10 to be measured is shown.

[0033] Figure 7 A configuration example of the beat signal generation component 150 and the detection component 160 according to the present embodiment is shown.

[0034] Figure 8 An example of an outline of the quadrature detection performed by the beat signal generation component 150 and the detection component 160 according to the present embodiment is shown.

[0035] Figure 9 A first example of the operation flow of the measurement device 100 according to the present embodiment is shown.

[0036] Figure 10 A concept of (i) the optical frequencies of the reference light and the measurement light and (ii) the frequency of the beat signal to be observed of the measurement device 100 according to the present embodiment is shown.

[0037] Figure 11 A second example of the operation flow of the measurement device 100 according to the present embodiment is shown.

[0038] Figure 12 A configuration example of the laser device 110 according to the present embodiment is shown. s A concept of a relationship between the frequency shift amount v

[0039] Figure 13A third example of an operation flow of the measurement device 100 according to the present embodiment is shown.

[0040] Figure 14 A variant example of the control section 50 and an optical SSB modulator according to the present embodiment are shown. DETAILED DESCRIPTION

[0041] [Configuration example of laser device 110]

[0042] Figure 1 A configuration example of the laser device 110 according to the present embodiment is shown. Figure 1 The laser device 110 shown shows an example of a frequency-shifted feedback laser (FSFL) that outputs a frequency-modulated laser beam having a plurality of modes. The laser device 110 has an optical cavity (laser resonator) and oscillates a laser beam within the optical cavity. The optical cavity of the laser device 110 includes a frequency shifter 112, a gain medium 114, a WDM coupler 116, a pump light source 117, and an output coupler 118.

[0043] The frequency shifter 112 shifts the frequency of light to be input by an approximately constant frequency. Here, the frequency shift amount of the frequency shifter 112 is defined as +ν s or ν s . For example, the frequency shifter 112 shifts the frequency of light circulating around the cavity so that the frequency increases ν s for each round.

[0044] The gain medium 114 is provided with pump light and amplifies input light. The gain medium 114 is, for example, an optical fiber doped with impurities. The impurities are, for example, rare earth elements such as erbium, neodymium, ytterbium, terbium, thulium, and the like. Pump light is supplied to the gain medium 114 from the pump light source 117 via the WDM coupler 116. The output coupler 118 outputs a portion of light that has been laser-oscillated in the cavity to an external device.

[0045] That is, Figure 1 The laser device 110 shown contains a fiber ring laser having the frequency shifter 112 in the cavity. The laser device 110 preferably further includes an isolator in the cavity. Furthermore, the laser device 110 can have an optical bandpass filter that passes light of a predetermined wavelength band in the cavity.

[0046] An acousto-optic frequency shifter (AOFS) having an acousto-optic element is referred to as the frequency shifter 112 for the laser device 110. The AOFS will be described next.

[0047] [Configuration example of AOFS 20]

[0048] Figure 2 A configuration example of the AOFS 20 is shown. The AOFS 20 includes an optical crystal 21, an ultrasonic transducer 22, an ultrasonic absorber 23, and an oscillator 24. The optical crystal 21 is a crystal that transmits light, such as TeO2, PbMoO4, a dense flint glass, or the like.

[0049] The ultrasonic transducer 22 is provided on a first end surface of the optical crystal 21 and generates an ultrasonic wave in accordance with an electric signal of a frequency ω1provided from the oscillator 24. The ultrasonic transducer 22, for example, propagates the ultrasonic wave generated from the first end surface of the optical crystal 21 to a second end surface opposite to the first end surface. In Figure 2 In the drawing, an example of a propagation direction of the ultrasonic wave is indicated by an arrow. It should be noted that the ultrasonic absorber 23 is provided on the second end surface opposite to the first end surface of the ultrasonic transducer 22 of the optical crystal 21.

[0050] Due to the propagation of the ultrasonic wave, a refractive index modulation occurs inside the optical crystal 21. When light is incident on such an optical crystal 21, the incident light is diffracted by Raman-Nath diffraction. Due to the Doppler effect caused by the propagation of the ultrasonic wave, the frequency of the diffracted light is shifted from the frequency ω0of the incident light by the frequency ω1of the ultrasonic wave. Since the frequency of the diffracted light is shifted in this way based on the Doppler effect, the sign of the frequency to be shifted is determined in accordance with the propagation direction of the ultrasonic wave and the incident direction of the incident light. Figure 2 An example is shown in which the direction of the frequency shift is positive, and the frequency of the diffracted light is ω0+ ω1.

[0051] For example, in order to generate strong diffracted light, the refractive index grating interval d achieved by the ultrasonic wave, the wavelength λ of the light wave, the incident angle θ1of the light wave, the diffraction angle θ0, and the h-th order of the diffraction must satisfy the relationship d (sin θ1- sin θ0) = h λ, where h = 0, ±1, ±2, and the like. When h is positive, the frequency shift becomes positive; when h is negative, the frequency shift becomes negative; and when h is zero, no frequency shift occurs. Usually, λ and θ1are fixed, and θ0is adjusted to take out the diffracted light of h = +1 or h = -1.

[0052] Therefore, for example, in order to switch the sign of the frequency to be shifted in the AOFS 20, it is necessary to switch the propagation direction of the ultrasonic wave to the opposite direction, or it is necessary to change the incident angle of the light. Since the propagation direction of the ultrasonic wave and the incident angle of the light cannot be easily changed by an electric signal or the like, in a conventional laser device 110 using such an AOFS 20, it is difficult to switch the direction of the frequency shift.

[0053] Further, because the ultrasonic transducer 22 has a cavity frequency (resonator frequency) that depends on the material, the ultrasonic transducer 22 cannot generate ultrasonic waves having a frequency largely deviated from the cavity frequency. Further, a diffraction angle of light diffracted by the optical crystal 21 is an angle corresponding to the frequency of the ultrasonic wave. When the diffraction angle changes according to the amount of frequency shift, coupling loss to the optical system on the output side occurs. Therefore, it is difficult to freely change the amount of shift of the frequency to be shifted in the AOFS 20. Therefore, the laser device 110 according to the present embodiment makes it possible to easily switch the amount of shift and / or the direction of application to the frequency by using an optical single sideband (SSB) modulator as the frequency shifter 112. Such an optical SSB modulator will be described below.

[0054] [Configuration example of optical SSB modulator 30]

[0055] Figure 3 A configuration example of the optical SSB modulator 30 and the control section 50 according to the present embodiment is shown. The optical SSB modulator 30 includes a substrate 31, a main Mach-Zehnder waveguide 32, a first sub-Mach-Zehnder waveguide 33, a second sub-Mach-Zehnder waveguide 34, a main DC electrode 35, a first sub-DC electrode 36, a second sub-DC electrode 37, a first RF electrode 38, and a second RF electrode 39.

[0056] The substrate 31 is a substrate at least partially formed of an electro-optic crystal, and includes, for example, a LiNbO3 crystal. A waveguide and a substrate are formed on a surface of such a substrate 31. The main Mach-Zehnder waveguide 32 branches light input to the optical SSB modulator 30 into two beams, and outputs the branched light after multiplexing the branched light. The main Mach-Zehnder waveguide 32 has a first arm waveguide 41 through which one of the branched light passes and a second arm waveguide 42 through which the other branched light passes.

[0057] The first arm waveguide 41 includes the first sub-Mach-Zehnder waveguide 33. The first sub-Mach-Zehnder waveguide 33 branches the light passing through the first arm waveguide 41 into two beams, and outputs to the first arm waveguide 41 after multiplexing the branched light. The first sub-Mach-Zehnder waveguide 33 has a first sub-arm waveguide 43 through which the input light passes and a second sub-arm waveguide 44.

[0058] The second arm waveguide 42 includes the second sub-Mach-Zehnder waveguide 34. The second sub-Mach-Zehnder waveguide 34 branches the light passing through the second arm waveguide 42 into two beams, and outputs to the second arm waveguide 42 after multiplexing the branched light. The second sub-Mach-Zehnder waveguide 34 has a third sub-arm waveguide 45 through which the input light passes and a fourth sub-arm waveguide 46.

[0059] As an example, the main DC electrode 35 is disposed at a position approximately the same distance from each of the first arm waveguide 41 and the second arm waveguide 42 of the main Mach-Zehnder waveguide 32. A DC voltage is supplied from the control member 50 to the main DC electrode 35.

[0060] As an example, the first sub DC electrode 36 and the first RF electrode 38 are disposed at a position approximately the same distance from each of the first sub arm waveguide 43 and the second sub arm waveguide 44 of the first sub Mach-Zehnder waveguide 33. The first sub DC electrode 36 and the first RF electrode 38 can be separate electrodes or can be one common electrode.

[0061] Similarly, as an example, the second sub DC electrode 37 and the second RF electrode 39 are disposed at a position approximately the same distance from each of the third sub arm waveguide 45 and the fourth sub arm waveguide 46 of the second sub Mach-Zehnder waveguide 34. The second sub DC electrode 37 and the second RF electrode 39 can be separate electrodes or can be one common electrode.

[0062] A DC voltage is supplied from the control member 50 to the first sub DC electrode 36 and the second sub DC electrode 37. An RF signal is supplied from the control member 50 to each of the first RF electrode 38 and the second RF electrode 39. The RF signal is, for example, a high frequency signal of several GHz to several tens of GHz.

[0063] Therefore, when a voltage is applied to an electrode disposed in the vicinity of a waveguide through which input light passes, an electro-optic effect (Pockels effect) that changes the refractive index of the waveguide occurs. The amplitude intensity level and the phase of light passing through the waveguide in which the electro-optic effect has occurred undergo modulation, shift, and the like corresponding to the applied voltage. Since the refractive index change due to this electro-optic effect corresponds to the direction of application of the electric field, for example, the direction of change of the phase can be switched simply by changing the sign of the voltage applied to the electrode.

[0064] The control member 50 adjusts the phase of light passing through the waveguide by supplying a DC voltage and an RF signal to the plurality of electrodes of the optical SSB modulator 30. The control member 50 has a DC voltage generation member 52 and an RF signal generation member 54. The DC voltage generation member 52 generates a DC voltage and supplies the DC voltage to the main DC electrode 35, the first sub DC electrode 36, and the second sub DC electrode 37. The RF signal generation member 54 generates an RF signal and supplies the RF signal to the first RF electrode 38 and the second RF electrode 39.

[0065] The control section 50 controls the DC voltage generating section 52 and the RF signal generating section 54 to supply the DC voltage and the RF signal to the optical SSB modulator 30, and adjusts the frequency shift direction and the frequency shift amount. For example, the control section 50 shifts the frequency of the light input to the optical SSB modulator 30 by the frequency of the RF signal. The control section 50 can further set the frequency shift amount of the optical SSB modulator 30 by changing the frequency of the RF signal.

[0066] In addition, the control section 50 switches the frequency shift direction by supplying the DC voltage of a predetermined value to the main DC electrode 35, the first sub DC electrode 36, and the second sub DC electrode 37, which are provided on the substrate 31 and correspond to the main Mach-Zehnder waveguide 32, the first sub Mach-Zehnder waveguide 33, and the second sub Mach-Zehnder waveguide 34. Since such switching of the frequency shift and shift direction of the optical SSB modulator 30 is described in the known patent documents 2 and 3, detailed description thereof is omitted here.

[0067] As described above, the laser device 110 according to the present embodiment uses the optical SSB modulator 30 shown in FIG. 2 as the frequency shifter 112. The control section 50 sets the frequency of the RF signal supplied to the optical SSB modulator 30, thereby enabling setting of the frequency shift amount of the optical SSB modulator 30. In addition, the control section 50 switches the voltage supplied to the optical SSB modulator 30, thereby enabling switching of the frequency shift direction of the optical SSB modulator 30 to one of the positive side or the negative side. By doing so, it is possible to easily set (i) the shift amount and (ii) the positive or negative direction for the shift of the frequency of the laser device 110. The frequency characteristics of the laser beam output from such a laser device 110 will be described below. Figure 3

[0068] Figure 4 An example of the laser beam output from the laser device 110 according to the present embodiment is shown. Figure 4 The spectrum of the laser beam output at time t0 by the laser device 110 is shown on the left. In the spectrum, the horizontal axis represents the light intensity, and the vertical axis represents the frequency of the light. In addition, a plurality of longitudinal modes of the spectrum are represented by the number q. The frequencies of the plurality of longitudinal modes are arranged at an approximately constant frequency interval. Assume that τ RT (=1 / ν c ) represents the time for the light to travel around the cavity, the plurality of longitudinal modes are arranged at an interval of 1 / τ RT (=ν c ), as shown in the following equation. Note that v0 is the initial frequency of the spectrum at time t0.

[0069] [Equation 1]

[0070]

[0071] ​Figure 4 The frequency change of the multiple longitudinal modes output from the laser device 110 over time is shown on the right side. In Figure 4 the right side, the horizontal axis represents time, and the vertical axis represents frequency. That is, Figure 4 The frequency change of the laser beam output from the laser device 110 over time is shown on the right side, and the instantaneous frequency of the laser beam at time t0 is shown on the left side.

[0072] In the laser device 110, as an example, the shift amount of the frequency shifter 112 is set to +v s Every time the light in the cavity travels around the resonator, the frequency shifter 112 increases the frequency of the light traveling around the cavity by v s . That is, since the frequency of each mode increases by v RT every time t s passes, the rate of change of the frequency dν / dt (i.e., the chirp rate) becomes approximately equal to v s / t RT . Therefore, the multiple longitudinal modes represented by Equation 1 change over time t as shown in the following equation.

[0073] [Equation 2]

[0074]

[0075] It should be noted that in Equation 2, the shift of the frequency is in the positive direction (positive direction). In Figure 4 the right side, an example of the change in the frequency of the laser beam over time in the time period between time t0 and time t1 is shown when the shift direction of the frequency is the positive direction. Alternatively, if the shift direction of the frequency is the negative direction (negative direction), the sign of v s in v RT · t / t s as the second term of Equation 2 is negative. In Figure 4 the right side, an example of the change in the frequency of the laser beam over time in the time period between time t2 and time t3 is shown when the shift direction of the frequency is the negative direction.

[0076] As described above, the laser device 110 using the optical SSB modulator 30 as the frequency shifter 112 can switch the shift direction of the frequency in one of the positive direction or the negative direction. Furthermore, the laser device 110 can easily change the frequency shift amount. Therefore, the optical SSB modulator 30 can perform the change of the frequency shift amount and the frequency shift direction without changing the output angle. That is, the laser device 110 can easily change the frequency shift amount and the frequency shift direction with almost no change in the output power. When such a laser device 110 is used in an optical range finder or the like, the improvement in the accuracy of distance measurement, the improvement in the function, or the like can be easily achieved. Next, an optical range finder including the laser device 110 according to the present embodiment is described.

[0077] [Configuration example of measurement device 100]

[0078] Figure 5 A configuration example of a measurement device 100 according to the present embodiment and an object to be measured 10 are shown. The measurement device 100 optically measures the distance between the measurement device 100 and the object to be measured 10. Furthermore, the measurement device 100 can measure the three-dimensional geometry of the object to be measured 10 by scanning the position of the laser beam irradiated onto the object to be measured 10. The measurement device 100 includes a control section 50, a laser device 110, a branching section 120, an optical circulator 130, an optical head section 140, a beat signal generation section 150, a detection section 160, and a display section 170.

[0079] The control section 50 supplies a DC voltage and an RF signal for controlling the laser device 110. The laser device 110 is a frequency-shifted feedback laser having an optical SSB modulator 30. Since the control section 50 and the laser device 110 have been described, they will not be described here.

[0080] The branching section 120 branches a part of the frequency-modulated laser beam output from the laser device 110 as reference light and branches at least some of the remaining part thereof as measurement light. For example, the branching section 120 is a fiber coupler. In the example shown in FIG. 1, the branching section 120 branches the measurement light to the optical circulator 130 and branches the reference light to the beat signal generation section 150. Figure 5

[0081] The optical circulator 130 has a plurality of input / output ports. For example, the optical circulator 130 outputs light input from one port to the next port and outputs light input from the next port to the next-but-one port. Figure 5 An example in which the optical circulator 130 has three input / output ports is shown. In this case, the optical circulator 130 outputs the measurement light supplied from the branching section 120 to the optical head section 140. In addition, the optical circulator 130 outputs light input from the optical head section 140 to the beat signal generation section 150.​

[0082] The optical head member 140 irradiates the light input from the optical circulator 130 toward the measurement target 10. The optical head member 140 includes, for example, a collimator lens. In this case, the optical head member 140 first adjusts the light input from the optical circulator 130 via the optical fiber into a light beam shape using the collimator lens, and then outputs the light.

[0083] Further, the optical head member 140 receives the reflected light of the measurement light irradiated onto the measurement target 10. The optical head member 140 focuses the received reflected light onto the optical fiber with the collimator lens, and provides it to the optical circulator 130. In this case, the optical head member 140 can include one common collimator lens, and the collimator lens can irradiate the measurement target 10 with the measurement light, and can receive the reflected light from the measurement target 10. The distance between the optical head member 140 and the measurement target 10 is defined as d.

[0084] Alternatively, the optical head member 140 can include a condenser lens. In this case, the optical head member 140 focuses the light input from the optical circulator 130 via the optical fiber on the surface of the measurement target 10. The optical head member 140 receives at least a part of the reflected light reflected on the surface of the measurement target 10. The optical head member 140 focuses the received reflected light onto the optical fiber using the condenser lens, and provides the light to the optical circulator 130. Also in this case, the optical head member 140 can include one common condenser lens, and the condenser lens can irradiate the measurement target 10 with the measurement light and receive the reflected light from the measurement target 10.

[0085] The beat signal generating member 150 receives the reflected light, which is the measurement light irradiated onto the measurement target 10 and reflected therefrom, from the optical circulator 130. Further, the beat signal generating member 150 receives the reference light from the branching member 120. The beat signal generating member 150 mixes the reflected light and the reference light to generate a beat signal. The beat signal generating member 150 includes, for example, a photoelectric conversion element, which converts the beat signal into an electric signal, and outputs the electric signal.

[0086] Here, since the reflected light travels back and forth over the distance between the optical head member 140 and the measurement target 10, a difference in the propagation distance corresponding to at least the distance 2d occurs compared to the reference light. Since the oscillation frequency of the light output from the laser device 110 changes linearly over time, between the oscillation frequency of the reference light and the oscillation frequency of the reflected light, a frequency difference depending on the propagation delay corresponding to the difference in the propagation distance occurs. The beat signal generating member 150 generates a beat signal corresponding to such a frequency difference.

[0087] The detection section 160 detects the difference in the propagation distance between the reference light and the measurement light by frequency-analyzing the beat signal generated by the beat signal generation section 150. The frequency analysis by the detection section 160 will be described below.

[0088] The display section 170 displays the analysis result by the detection section 160. The display section 170 can include a display or the like and display the detection result. In addition, the display section 170 can store the analysis result in a storage unit or the like.

[0089] The measurement apparatus 100 described above can measure the distance between the measurement apparatus 100 and the object 10 to be measured by analyzing the frequency difference between the reflected light of the measurement light irradiated onto the object 10 to be measured and the reference light. That is, the measurement apparatus 100 can form a non-contact and non-destructive optical range finder.

[0090] [Details of the distance measurement process]

[0091] The measurement apparatus 100 according to the present embodiment measures the distance d between the optical head section 140 and the object 10 to be measured by using the laser apparatus 110 that outputs the frequency element represented by Equation 2. It is assumed that the optical path difference between the reference light and the reflected light is only the distance 2d, that is, the distance d of the reciprocation, and that the propagation delay corresponding to the distance 2d is Δt. That is, when the measurement light is reflected at the time t and returns from the object 10 to be measured, the frequency of the returned reflected light approximately matches the past frequency at the time Δt earlier than the time t, and thus can be represented by the following equation.

[0092] [Equation 3]

[0093]

[0094] On the other hand, the reference light at the time t can be represented by the following equation in a similar manner to Equation 2, where the reference light is v q′ (t).

[0095] [Equation 4]

[0096]

[0097] Since the beat signal generation section 150 superimposes the reflected light and the reference light, a plurality of beat signals are generated between the plurality of longitudinal modes represented by Equation 3 and the plurality of longitudinal modes represented by Equation 4. It is assumed that the frequency of such a beat signal is v B (m, d), v B (m, d) can be represented by the following equation according to Equation 3 and Equation 4, where m is the interval of the longitudinal mode number (= q - q'), and Δt = 2d / c.

[0098] [Equation 5]

[0099]

[0100] According to Equation 5, the distance d is expressed by the following equation, where 1 / τ RT =ν c .

[0101] [Equation 6]

[0102]

[0103] According to Equation 6, it can be understood that the distance d can be calculated based on the frequency observation results of the beat signal by determining the interval m of the longitudinal modulus. It should be noted that when the frequency shift ν of the laser device 110... s When the signal changes, the interval m, known as the order m of the beat signal, can be determined by detecting the change in the beat signal. Since such a method for determining the order m is known, as described in Patent Document 1, etc., its detailed description is omitted.

[0104] Since the observed beat signal is always at a positive frequency, in the calculation, the beat signal generated on the negative frequency side is reflected back to the positive side and observed as the image signal. The generation of this image signal will be described next.

[0105] Figure 6 An example is shown illustrating the relationship between the frequency of the beat signal detected by the measuring device 100 according to this embodiment and the distance d between the optical head component 140 and the object under test 10. Figure 6 In the diagram, the horizontal axis represents distance d, and the vertical axis represents the frequency ν of the beat signal. B (m,d). Figure 6 The solid lines in the diagram represent the frequency ν of the beat signal for each of several values ​​of the order m. B A graph showing the relationship between (m,d) and distance d (as shown in Equation 5).

[0106] like Figure 6 As shown, multiple beat signals corresponding to the value of m are generated. However, due to the multiple longitudinal modes included in each of the reflected light and the reference light being spaced at approximately constant frequencies ν... c The arrangement is such that multiple beat signals with equal m values ​​are superimposed on approximately the same frequency on the frequency axis. For example, when observing frequencies 0 and ν... c When the frequency bands are between, multiple beat signals are superimposed on approximately the same frequency and observed as a single-line spectrum.

[0107] Additionally, the frequency ν of the beat signal in the negative range is less than 0. B The absolute value of (m,d) is further observed as an image signal. That is, Figure 6The graph of the region where the longitudinal axis of the beat signal is smaller than 0 is folded back with frequency 0 as a boundary. Figure 6 The folded image signal is shown by a plurality of dotted lines. Since only the sign of the folded image signal is inverted, the image signal is superimposed on the observed frequency axis at the same absolute value of the frequency before folding. For example, when the observation frequency is in the frequency band between 0 and v c , the beat signal and the image signal are located at different frequencies, unless the frequencies of the beat signal and the image signal become v c / 2.

[0108] As described above, in the observation frequency band between frequency 0 and v c , two line spectra are generated, which are (i) the beat signal v B (m, d) and (ii) the image signal v B (m', d), the m value of the image signal v B (m', d) is different from the m value of the beat signal v B (m, d). Here, as an example, m' = m + 1. In this case, the beat signal generating section 150 can eliminate such an image signal by using quadrature detection. Next, the beat signal generating section 150 and the detection section 160 using quadrature detection will be described.

[0109] [Configuration example of the beat signal generating section 150 and the detection section 160]

[0110] Figure 7 A configuration example of the beat signal generating section 150 and the detection section 160 according to the present embodiment is shown. The beat signal generating section 150 quadrature detects the reflected light and the reference light. The beat signal generating section 150 includes an optical 90-degree hybrid 152 and two photoelectric conversion sections 154.

[0111] The optical 90-degree hybrid 152 branches the input reflected light and the input reference light into two parts, respectively. The optical 90-degree hybrid 152 multiplexes one of the branched reflected light and one of the branched reference light by using an optical coupler or the like to generate a first beat signal. The optical 90-degree hybrid 152 multiplexes the other branched reflected light and the other branched reference light by using an optical coupler or the like to generate a second beat signal. Here, the optical 90-degree hybrid 152 generates the beat signal after generating a phase difference of 90 degrees between the two branched reference lights. For example, the optical 90-degree hybrid 152 multiplexes the branched reflected light and one of the branched reference lights, and multiplexes the branched reflected light and light generated by passing the other branched reference light through a π / 2 wavelength plate.

[0112] The photoelectric conversion parts 154 receive the multiplexed reflected light and reference light and convert them into electric signals. The photoelectric conversion parts 154 can each be, for example, a photodiode or the like. The photoelectric conversion parts 154 are each, for example, a balanced photodiode. In Figure 7 the present embodiment, it is assumed that one of the photoelectric conversion parts 154 generates a first beat signal, and the other photoelectric conversion part 154 generates a second beat signal. As described above, the beat signal generating part 150 performs quadrature detection by multiplexing two reference lights and two reflected lights, which are 90 degrees out of phase, respectively, and outputs two beat signals to the detection part 160.

[0113] The detection part 160 performs frequency analysis on the two beat signals. Here, an example in which the detection part 160 performs frequency analysis using the first beat signal as an I signal and the second beat signal as a Q signal will be described. The detection part 160 includes a first filter part 162, a second filter part 164, a first AD conversion part 202, a second AD conversion part 204, a clock signal providing part 210, and a frequency analysis part 220.

[0114] The first filter part 162 and the second filter part 164 reduce signal components in frequency bands other than a frequency band that a user or the like wants to analyze. Here, the frequency band that the user or the like wants to analyze is set to 0 to v c . The first filter part 162 and the second filter part 164 are, for example, low-pass filters that pass signal components whose frequencies are equal to or less than v c . In this case, the first filter part 162 supplies the first beat signal obtained by reducing signal components having frequencies higher than the frequency v c to the first AD conversion part 202. Further, the second filter part 164 supplies the second beat signal obtained by reducing signal components having frequencies higher than the frequency v c to the second AD conversion part 204.

[0115] The first AD conversion part 202 and the second AD conversion part 204 convert input analog signals into digital signals. For example, the first AD conversion part 202 converts the first beat signal into a digital signal, and the second AD conversion part 204 converts the second beat signal into a digital signal. The clock signal providing part 210 supplies a clock signal to the first AD conversion part 202 and the second AD conversion part 204. By doing so, the first AD conversion part 202 and the second AD conversion part 204 convert analog signals into digital signals at a sampling rate that is approximately the same as a clock frequency of the received clock signal.

[0116] Here, when the observation band is from 0 to v c , the frequency of the beat signal is at most the cavity frequency vc Therefore, the clock signal providing section 210 provides a clock signal having a frequency greater than or equal to twice the cavity frequency v c of the optical cavity to the first AD conversion section 202 and the second AD conversion section 204, so that a beat signal can be observed. Here, the frequency twice or more than twice the cavity frequency v c of the optical cavity should be the sampling frequency. In this way, the detection section 160 performs frequency analysis on the first beat signal and the second beat signal (as first sampling data) generated by sampling the beat signal at the sampling frequency.

[0117] The frequency analysis section 220 converts the first beat signal and the second beat signal into frequency data. As an example, the frequency analysis section 220 performs a digital Fourier transform (DFT) on the first beat signal and the second beat signal. The frequency analysis section 220 adds the first beat signal converted into frequency data as a real part and adds the second beat signal converted into frequency data as an imaginary part, and eliminates an image signal. The above operation of the detection section 160 is controlled by the control section 50, for example.

[0118] At least a part of such a control section 50 and detection section 160 includes, for example, an integrated circuit or the like. In this case, at least a part of the detection section 160 includes an integrated circuit or the like after converting the beat signal into a digital signal. For example, the control section 50 and the detection section 160 include a field programmable gate array (FPGA), a digital signal processor (DSP), and / or a central processing unit (CPU).

[0119] When at least a part of the control section 50 and the detection section 160 is formed of a computer or the like, the control section 50 and the detection section 160 include a storage unit. The storage unit includes, for example, a read only memory (ROM) that stores a basic input output system (BIOS) or the like of the computer or the like to operate the control section 50 and the frequency analysis section 220, and a random access memory (RAM) used as a work area. Furthermore, the storage unit can include an operating system (OS) and various information including an application program and / or a database to be referred to when executing the application program. That is, the storage unit can include a large-capacity storage device such as a hard disk drive (HDD) and / or a solid state drive (SSD).

[0120] The computer or the like includes a processor such as a CPU and functions as the control section 50 and the frequency analysis section 220 by executing a program stored in the storage unit. The computer or the like can include a graphics processing unit (GPU) or the like.

[0121] [Quadrature Detection Overview]

[0122] Figure 8 An example summarizing the orthogonal detection performed by the beat signal generation unit 150 and the detection unit 160 according to this embodiment is given. Figure 8 In the diagram, the horizontal axis represents the frequency of the beat signal, and the vertical axis represents the signal strength. Figure 8 The spectrum of one of the I and Q signals is shown. The spectra of both the I and Q signals have approximately the same spectral shape, as shown... Figure 8 The upper part is shown. In the I and Q signals, for example, at frequencies 0 and v... c Beat signal ν was observed in the frequency band between B (m,d) and image signal ν B (m+1,d). In this case, the beat signal -ν of the image signal in the I and Q signals. B (m,d) and the original beat signal -ν B (m+1,d) exists at frequencies 0 and -v on the negative side. c In the frequency bands between.

[0123] Here, since the I and Q signals are signal components orthogonally detected by the beat signal generation unit 150, they contain different phase information even if they have the same spectral shape. For example, at frequencies 0 and q on the positive side... c In the frequency band between, the image signal ν of the I signal B The image signal ν of (m+1,d) and Q signal B The phases of (m+1,d) are reversed. Similarly, the frequencies 0 and -v on the negative side are reversed. c In the frequency band between, the beat signal ν of the I signal B The beat signal -ν of (m,d) and Q signal B The phases of (m,d) are reversed.

[0124] Therefore, as Figure 8 As shown in the lower part, when the frequency analysis unit 220 calculates I+jQ using the I and Q signals, at frequencies 0 and v c In the frequency band between, the frequency is ν B The beat signals of (m,d) reinforce each other, while the frequency ν B The image signals of (m+1,d) cancel each other out. Similarly, at 0 and -v c In the frequency band between -ν B The two beat signals of (m+1,d) reinforce each other, and the frequency is -ν. B The two beat signals of (m,d) cancel each other out.

[0125] Based on the frequency analysis results of the frequency analysis unit 220, for frequencies 0 and v c The frequency ν in the frequency band betweenB (m, d), a beat signal is observed. Since the measuring device 100 can eliminate the image signal in this way, it is possible to measure the distance d between the optical head member 140 and the object 10 to be measured.

[0126] As described above, according to the measuring device 100 of the present embodiment, it is possible to measure the distance d between the measuring device 100 and the object 10 to be measured in a non-destructive and non-contact manner. Such a measuring device 100 that measures the distance d to the object 10 to be measured in a non-contact manner is generally placed independently of the object 10 to be measured. Therefore, when at least one of the measuring device 100 or the object 10 to be measured oscillates or moves, a relative velocity is generated between the measuring device 100 and the object 10 to be measured. Such a relative velocity can affect the measurement result of the measuring device 100 as an error.

[0127] For example, when a component of the relative velocity in a direction parallel to the direction of the optical axis of the measurement light of the measuring device 100 has a finite value, a frequency shift corresponding to the component of the relative velocity occurs in the reflected light of the object 10 to be measured due to the Doppler effect. The frequency shift of the reflected light causes an error in the measurement result of the measuring device 100 because the frequency shift of the reflected light fluctuates the frequency of the beat signal generated by the beat signal generation member 150.

[0128] Therefore, in order to reduce such an error due to the Doppler effect, the measuring device 100 according to the present embodiment changes the frequency shift direction of the laser device 110, and performs frequency analysis on the beat signal before and after the shift direction is changed. Next, the measurement operation of the measuring device 100 will be described.

[0129] [First example of operation flow of measuring device 100]

[0130] Figure 9 A first example of the operation flow of the measuring device 100 according to the present embodiment is shown. The measuring device 100 measures the distance d between the optical head member 140 and the object 10 to be measured by performing the operations of S1010 to S1060 of Figure 9 .

[0131] First, in S1010, the control member 50 sets the frequency shift direction of the optical SSB modulator 30 to one of the positive side or the negative side. For example, the control member 50 sets the frequency shift direction of the optical SSB modulator 30 to the positive side. In addition, the control member 50 can also set the frequency shift amount v s .

[0132] Next, in S1020, the control section 50 controls the laser device 110 having the gain medium 114 and the optical SSB modulator 30 in the optical cavity to output a frequency-modulated laser beam having a plurality of modes. Then, the branching section 120 branches a part of the frequency-modulated laser beam output from the laser device 110 as reference light and at least some of the remaining part thereof as measurement light. The optical head section 140 irradiates the measurement light to the object to be measured 10. Then, the optical head section 140 receives reflected light reflected from the object to be measured 10. The beat signal generation section 150 mixes the reflected light and the reference light to generate a positive-side beat signal.

[0133] Next, in S1030, the control section 50 controls the detection section 160 to cause the detection section 160 to perform frequency analysis on the positive-side beat signal. The detection section 160, for example, samples the positive-side beat signal at a sampling frequency greater than or equal to twice the cavity frequency of the optical cavity to generate sampling data. The frequency analysis section 220 calculates I + jQ by performing frequency conversion on I and Q signals of the sampling data. The frequency analysis section 220 calculates a positive-side frequency Fl at which the positive-side beat signal is generated.

[0134] Next, in S1040, the control section 50 switches the frequency shift direction of the optical SSB modulator 30 to the opposite direction. For example, the control section 50 switches the frequency shift direction of the optical SSB modulator 30 from the positive side to the negative side. The branching section 120 branches a part of the frequency-modulated laser beam whose frequency shift direction has been switched as reference light and at least some of the remaining part thereof as measurement light. The optical head section 140 irradiates the measurement light to the object to be measured 10. The optical head section 140 receives reflected light reflected from the object to be measured 10. The beat signal generation section 150 mixes the reflected light and the reference light to generate a negative-side beat signal.

[0135] Next, in S1050, the control section 50 switches the frequency shift direction of the optical SSB modulator 30 and then controls the detection section 160 to perform frequency analysis on the negative-side beat signal. For example, the detection section 160 calculates a negative-side frequency F2 at which the negative-side beat signal is generated in a similar manner to the positive-side beat signal.

[0136] Next, in S1060, the frequency analysis section 220 detects the difference in the propagation distance between the reference light and the measurement light, i.e., the distance d, based on the results of the frequency analysis of the positive-side beat signal and the negative-side beat signal. Here, if the Doppler effect corresponding to the relative velocity between the measurement device 100 and the object to be measured 10 occurs, the frequency analysis results of the positive-side beat signal and the negative-side beat signal will include an error.

[0137] For example, assume that a frequency error ΔF due to the Doppler effect occurs. In this case, the positive side frequency F1 of the positive side beat signal can be expressed as F0- ΔF. Here, F0 is the frequency of the positive side beat signal observed when the Doppler effect does not occur. Further, because the frequency shift direction of the optical SSB modulator 30 is switched to the opposite side, the sign of the error due to the Doppler effect is reversed, and thus the negative side frequency F2 of the negative side beat signal can be expressed as F0+ ΔF. The concept of such a positive side frequency F1 and a negative side frequency F2 will be described with reference to Figure 10 the upper part of FIG. 6.

[0138] Figure 10 The concept of (i) the optical frequencies of the reference light and the measurement light and (ii) the frequencies of the observed beat signals of the measurement apparatus 100 according to the present embodiment is shown. In Figure 10 the upper part of FIG. 6, the horizontal axis represents time, and the vertical axis represents the optical frequencies of the reference light and the measurement light. In Figure 10 the lower part of FIG. 6, the horizontal axis represents time, and the vertical axis represents the frequencies of the beat signals. Figure 10 An example in which the control means 50 repeatedly switches the frequency shift direction of the optical SSB modulator 30 at a constant period T is shown.

[0139] For example, the reference light that reaches the beat signal generation means 150 during the time period from time t n to time t n+1 is a portion of the laser beam output from the laser apparatus 110 during the time period in which the frequency shift direction of the optical SSB modulator 30 is set to the positive side. Further, the measurement light branched during the time period in which the frequency shift direction of the optical SSB modulator 30 is set to the positive side reaches the beat signal generation means 150 during the time period from time t m delayed by a certain amount of time to time t m+1 .

[0140] If there is no influence from the Doppler effect, the delay time of the measurement light with respect to the reference light corresponds to the distance d to the object to be measured 10, and the frequency of the beat signal generated by the beat signal generation means 150 is F0. Figure 10 An example in which an error ΔF due to the Doppler effect occurs and the positive side frequency F1 of the positive side beat signal generated by the beat signal generation means 150 during the time period from time t m to time t n+1 is expressed as F0- ΔF is shown.

[0141] Similarly, the negative side frequency F2 of the negative side beat signal generated by the beat signal generation means 150 during the time period from time t n+1 to time t n+2The reference light arriving at the beat signal generation unit 150 during the time period is a portion of the laser beam output from the laser device 110 during the time period when the frequency shift direction of the optical SSB modulator 30 is set to the negative side. Furthermore, the measurement light, branched during the time period when the frequency shift direction of the optical SSB modulator 30 is set to the negative side, from time t... m+1 Delay a certain amount of time until time t m+2 The beat signal generation unit 150 arrives during the time period.

[0142] Here, the frequency of the measurement light is shifted due to errors caused by the Doppler effect. Figure 10 In the upper part, the waveform of the measuring light is shifted in the vertical direction. In this case, the delay time of the measuring light relative to the reference light varies depending on the direction of the shift. For example, from time t... m+1 By time t n+2 During the time period, the negative side frequency F2 of the negative side beat signal generated by the beat signal generation unit 150 is F0+ΔF.

[0143] Therefore, as an example, if the frequency analysis unit 220 ideally calculates the average of the positive side frequency F1 and the negative side frequency F2, the value of the frequency F0 of the beat signal generated without the influence of the Doppler effect can be obtained. By doing so, the frequency analysis unit 220 can calculate the distance d between the optical head unit 140 and the object under test 10 using Equation 6. The display unit 170 displays the calculated value of the distance d.

[0144] As described above, the detection unit 160 can detect the difference in propagation distance between the reference light and the measurement light when the influence of the Doppler effect is reduced, based on the results of frequency analysis of the following: (i) the positive side beat signal generated when the frequency shift direction of the optical SSB modulator 30 is set to the positive side, and (ii) the negative side beat signal generated when the frequency shift direction of the optical SSB modulator 30 is set to the negative side. It should be noted that the measurement device 100 can change the position of the frequency-modulated laser beam illuminating the object under test 10 and repeat... Figure 9 The operation procedure shown is used to measure the geometry of the object to be measured 10.

[0145] The measuring device 100 according to this embodiment, as described above, can reduce the influence of the Doppler effect and accurately measure the distance d to the object 10 under test by using a laser device 110 with an optical SSB modulator 30. Here, according to Equation 6, ν s and ν c The larger the value, the higher the signal frequency ν of the beat signal. B The smaller the impact of (m,d) on the measurement accuracy of distance d, the greater the influence of ν. The accuracy of ν can be increased by shortening the cavity length of the laser device 110. cbut the value of v cannot be easily increased because of limitations on the length of the gain medium 114 required for laser oscillation, the length of the processing fiber required, and the like. c

[0146] When the AOFS 20 is used as the frequency shifter 112, the maximum value of the frequency shift amount of the optical crystal 21 is about 1.5 GHz, and the shift amount is usually about several hundred MHz in terms of efficiency and the like. In addition, because the ultrasonic transducer 22 has a cavity frequency, there are limitations on making the frequency shift amount variable and using it.

[0147] In contrast, because the optical SSB modulator 30 is used in the measurement apparatus 100 according to the present embodiment, the frequency shift amount v s can be set to be several tens of times larger than in the case of using the AOFS 20. Therefore, the measurement apparatus 100 can increase the sensitivity of the beat frequency to the change in the distance d to several tens of times that of the past, and can measure the distance d of the object to be measured 10 with high accuracy.

[0148] In addition, for example, because the measurement apparatus 100 according to the present embodiment can change the frequency shift amount of the FSFL, the order m of the beat signal can be easily determined. As described in Equation 6, the order m can be determined by detecting the change in the beat signal when the frequency shift amount v s of the laser device 110 is changed.

[0149] Such a method of determining the order m is known as a method of detecting the beat signal for each different frequency shift amount, simultaneously formulating the relational expression of Equation 5, and calculating the order m as a solution of the simultaneous equations, as described in Patent Literature 1 and the like. The measurement apparatus 100 can determine the order m using this method by changing the frequency shift amount of the FSFL.

[0150] Note that when the order m changes according to the change in the frequency shift amount, the number of solutions of the equations to be simultaneously formulated increases, and the number of equations to be simultaneously formulated must increase accordingly. The value of the order m can be expressed as a quotient of the distance d divided by the absolute length measurement range, with the following equation. Here, the absolute length measurement range is a range in which the distance d can be continuously measured without changing the value of the order m, and is the distance traveled by light in the reciprocal of the shift frequency v s . Furthermore, c / 2v s is the distance traveled by light back and forth in the time of the reciprocal of the shift frequency v s . Furthermore, floor() is the truncation of any decimal fraction.

[0151] [Equation 7]

[0152]

[0153] Here, by making the frequency shift amount v s variable, the order m of the beat signal can be determined.s Taking the differential of Equation 7, the following equation is obtained.

[0154] [Equation 8]

[0155]

[0156] According to Equation 8, it can be seen that the larger the value of the distance d is, the larger the change in the value of the order m with respect to the change in the frequency shift amount v s . This means that the farther the distance d from the laser device 110 to the object 10 to be measured is, the more the order m changes due to the frequency shift. Furthermore, when the frequency shift amount v s is increased in the above-described manner, on the one hand, the measurement accuracy of the distance d is improved, but on the other hand, the absolute length measurement range is narrowed and the order m is easily changed. Therefore, there can be cases where it is difficult to accurately measure the object 10 to be measured at a farther distance using the measurement device 100 because the value of m changes more and the simultaneous equations become complicated.

[0157] Therefore, the measurement device 100 according to the present embodiment is able to measure the distance d at a greater distance with higher sensitivity by making the frequency shift amount for determining the order m different from the frequency shift amount for measuring the distance d. Next, the measurement operation of such a measurement device 100 will be described.

[0158] [Second Example of the Operation Flow of the Measurement Device 100]

[0159] Figure 11 A second example of the operation flow of the measurement device 100 according to the present embodiment is shown. In the operation flow of the second example, the description of some of the operations that have been described in the operation flow of the first example is omitted.

[0160] First, in S1110, the control component 50 sets the frequency shift amount v s of the optical SSB modulator 30 to a first frequency v s1 . The first frequency v s1 is a frequency shift amount for determining the order m, and is smaller than the frequency shift amount for measuring the distance d. The first frequency v s1 is preferably a low frequency for expanding the absolute length measurement range for measuring the distance d to a range of about several times or more. In addition, it is more preferable that the first frequency v s1 be a frequency corresponding to the distance d, as will be described below. The first frequency v s1 is, for example, a frequency of about several tens of MHz to several GHz. The control component 50 can further set the direction of the frequency shift of the optical SSB modulator 30.

[0161] Next, in S1120, the control unit 50 controls the laser device 110, which has a gain medium 114 in the optical cavity and an optical SSB modulator 30, to output a frequency-modulated laser beam with multiple modes. The branching unit 120 branches a portion of the frequency-modulated laser beam output from the laser device 110 as a reference beam and at least some of the remaining portion as a measurement beam. The optical head unit 140 illuminates the object under test 10 with the measurement beam. Then, the optical head unit 140 receives the reflected light reflected from the object under test 10. The beat signal generation unit 150 mixes the reflected light and the reference light to generate a beat signal with a determined order.

[0162] Next, in S1130, the control unit 50 controls the detection unit 160 to perform frequency analysis on the order determination beat signal. The frequency analysis unit 220 calculates the frequency F3 used for order determination, at which the order determination beat signal is generated.

[0163] Next, in S1140, the frequency analysis unit 220 uses the frequency F3 used for order determination and Equation 5 to determine the order m. The frequency analysis unit 220 determines the order m within the absolute length measurement range used to determine the distance d. (Refer to...) Figure 12 Describing the frequency shift ν s The relationship between absolute length measurement range and absolute length measurement range.

[0164] Figure 12 The frequency shift ν of the laser device 110 according to this embodiment is shown. s The concept of the relationship between absolute length measurement range and the absolute length measurement range. Figure 12 The horizontal axis represents the distance d to the object 10 under test, and the vertical axis represents the frequency of the beat signal. Figure 12 The solid lines in the diagram represent the frequency ν of the beat signal for each of the multiple m. B The relationship between (m,d) and distance d (e.g.) Figure 6 The graph described above. That is, the multiple straight lines shown by the solid lines represent the frequency shift ν set by the control unit 50 for the laser device 110 to measure the distance d. s2 Distance d and frequency ν at time B The relationship between (m,d). In this case, the frequency shift ν s2 Set to the second frequency. The absolute length measurement range is calculated as c / 2ν. s =c / 2ν s2 .

[0165] Depend on Figure 12 The dashed line represents a straight line indicating when the frequency shift ν is... s Set to the first frequency ν s1 Distance d and frequency ν at time BThe relationship between (m,d). Figure 12 The first frequency ν is shown. s1 It is ν s2 / 5 is an example. It can be seen that the range of absolute length measurements has been extended to 5c / 2ν. s2 Therefore, when the frequency shift ν is passed... s Set to the first frequency ν s1 Determine from 0 to ν c When determining the order of a beat signal within a frequency range, the frequency F3 corresponding to the distance d for order determination can be detected while keeping the order m constant.

[0166] As an example, suppose the detection unit 160 detects the beat signal whose order is determined and performs frequency analysis on it to calculate the frequency F3. In this case, since the frequency of the beat signal whose order is determined is within the range of absolute length measurements, the distance d3 corresponding to the frequency F3 can be calculated. Then, based on the calculated distance d3, it is possible to determine when the frequency shift is set to the second frequency ν. s The order m at which time. For example, from the... Figure 12 As shown by the solid lines in the diagram, the absolute length of the distance d3 can be measured within the range of order m=3, and the beat signals represented by lines of other orders are duplicates. As mentioned above, this can be achieved by using the first frequency ν... s1 A lower frequency is used to extend the absolute length measurement range in order to determine the order m when measuring distance d. First frequency ν s1 Preferably, the frequency is set such that the frequency corresponding to the distance d to the object 10 being measured is included in the extended range of absolute length measurements.

[0167] Next, in S1150, the control unit 50 adjusts the frequency shift ν of the optical SSB modulator 30. s Switch to a frequency greater than the first frequency ν s1 The second frequency ν s2 As mentioned above, the second frequency ν s2 This is the frequency shift used to measure distance d. The branching component 120 branches a portion of the frequency-modulated laser beam, whose frequency shift has been switched, as a reference beam and at least some of the remaining portion as the measurement beam. The optical head component 140 illuminates the object under test 10 with the measurement beam. The optical head component 140 receives the reflected light from the object under test 10. The beat signal generation component 150 mixes the reflected light and the reference light to generate a distance measurement beat signal.

[0168] Next, in S1160, the control unit 50 switches the frequency shift of the optical SSB modulator 30, and then controls the detection unit 160 to perform frequency analysis on the distance measurement beat signal. The frequency analysis unit 220 calculates the frequency F4 used for distance measurement, at which the distance measurement beat signal is generated.

[0169] Next, in S1170, the frequency analysis unit 220 detects the difference in propagation distance between the reference light and the measurement light based on the results of frequency analysis of the beat signal used to determine the order and the beat signal used to determine the distance. For example, the frequency analysis unit 220 calculates the distance d by substituting the order m and the frequency F4 used for distance determination into Equation 6. The display unit 170 displays the calculated value of the distance d.

[0170] As described above, the measuring device 100 can easily determine the order m by reducing the frequency shift amount to achieve a resolution sufficient to at least determine the order m. Then, the measuring device 100 measures the distance d after improving measurement accuracy by switching the frequency shift amount to a higher frequency. This allows the measuring device 100 to measure the distance d at a greater distance with greater sensitivity.

[0171] exist Figure 11 The operation procedure has already described an example in which the measuring device 100 detects the distance measurement beat signal after the beat signal is determined by the order of detection; however, this embodiment is not limited to this. The measuring device 100 can detect the distance measurement beat signal before the beat signal is determined by the order of detection. In this way, the control unit 50 can set the frequency shift of the optical SSB modulator 30 to a first frequency ν. s1 or greater than the first frequency ν s1 The second frequency ν s2 One of them, and then the detection unit 160 performs frequency analysis on the beat signal. The detection unit 160 detects the difference in propagation distance between the reference light and the measurement light based on the results of the frequency analysis of the following: (i) when the frequency shift of the optical SSB modulator 30 is set to the first frequency ν. s1 The order of the generated beat signal is determined, and (ii) when the frequency shift of the optical SSB modulator 30 is set to the second frequency ν. s2 The distance measurement beat signal generated at that time.

[0172] In the measurement apparatus 100 according to this embodiment described above, the operations for reducing the influence of the Doppler effect and determining the order m have been described respectively, but this embodiment is not limited thereto. The measurement apparatus 100 can determine the order m while reducing the influence of the Doppler effect. Next, the operation of this measurement apparatus 100 will be described.

[0173] [Third example of the operation procedure of measuring device 100]

[0174] Figure 13 A third example of the operation flow of the measurement device 100 according to the present embodiment is shown. In the operation flow of the third example, the description of some operations that have been described in the operation flow of the first example and the operation flow of the second example is omitted.

[0175] First, in S1210, the control section 50 sets the frequency shift amount of the optical SSB modulator 30 to a first frequency v s1 / 5 and sets the frequency shift direction to one of the positive side or the negative side. For example, the control section 50 sets the first frequency to v s / 5 and sets the frequency shift direction to positive.

[0176] Next, in S1220, the control section 50 controls the laser device 110 and outputs the frequency-modulated laser beam having a plurality of modes. The branching section 120 branches a part of the frequency-modulated laser beam output from the laser device 110 as the reference light and branches at least some of the remaining part thereof as the measurement light. The optical head section 140 irradiates the measurement light to the object to be measured 10. Then, the optical head section 140 receives the reflected light reflected from the object to be measured 10. The beat signal generation section 150 mixes the reflected light and the reference light to generate the order-determining beat signal.

[0177] Next, in S1230, the control section 50 controls the detection section 160 to cause the detection section 160 to perform frequency analysis on the order-determining beat signal. The frequency analysis section 220 calculates the frequency F0 for order determination at which the order-determining beat signal is generated.

[0178] Next, in S1240, the frequency analysis section 220 determines the order m using the frequency F0 for order determination and Equation 5. At this stage, the frequency F0 calculated based on the order-determining beat signal can contain an error due to the influence of the Doppler effect. However, the error due to the influence of the Doppler effect is a very small error, the degree of which has little influence on the determination of the order m, so it is not a problem here.

[0179] Next, in S1250, the control section 50 switches the frequency shift amount of the optical SSB modulator 30 to a second frequency greater than the first frequency to generate the positive-side beat signal. Here, the control section 50 does not change the frequency shift direction of the optical SSB modulator 30.

[0180] Next, in S1260, the control section 50 controls the detection section 160 to perform frequency analysis on the positive-side beat signal. The frequency analysis section 220 calculates the positive-side frequency F1 at which the positive-side beat signal is generated by using the frequency analysis result. Also at this stage, the positive-side frequency F1 calculated based on the positive-side beat signal can include an error due to the influence of the Doppler effect.

[0181] Next, in S1270, the control section 50 switches the frequency shift direction to the opposite reverse while keeping the frequency shift amount of the optical SSB modulator 30 at the second frequency to generate a negative-side beat signal. For example, the control section 50 switches the frequency shift direction of the optical SSB modulator 30 from the positive side to the negative side. The branching section 120 branches at least some of the remaining portion of the frequency-modulated laser beam whose frequency shift direction has been switched as the measurement light from the portion of the frequency-modulated laser beam as the reference light. The optical head section 140 irradiates the measurement light to the object 10 to be measured. The optical head section 140 receives the reflected light reflected from the object 10 to be measured. The beat signal generation section 150 mixes the reflected light and the reference light to generate the negative-side beat signal.

[0182] Next, in S1280, the control section 50 controls the detection section 160 to perform frequency analysis on the negative-side beat signal. The frequency analysis section 220 calculates the negative-side frequency F2 at which the negative-side beat signal is generated by using the frequency analysis result. Also at this stage, the negative-side frequency F2 calculated based on the negative-side beat signal can include an error due to the influence of the Doppler effect. In this case, the error included in the negative-side frequency F2 has approximately the same value as the error included in the positive-side frequency F1, with the sign being reversed.

[0183] Next, in S1290, the frequency analysis section 220 detects the difference in the propagation distance between the reference light and the measurement light based on the results of the frequency analysis of (i) the order number determination beat signal, (ii) the positive-side beat signal, and (iii) the negative-side beat signal. The frequency analysis section 220, for example, calculates the average value of the positive frequency F1 and the negative frequency F2. By doing so, the frequency analysis section 220 calculates the distance d between the optical head section 140 and the object 10 to be measured by substituting the average value and the order number m into Equation 6. The display section 170 displays the value of the calculated distance d.

[0184] As described above, since the measurement apparatus 100 according to the present embodiment is provided with the laser device 110 whose frequency shift amount and frequency shift direction can be easily changed, the measurement apparatus 100 can highly accurately measure the distance d to the object 10 to be measured by determining the order number m while reducing the influence of the Doppler effect.

[0185] [Variant Example of Control Section 50]

[0186] In the measurement apparatus 100 according to the present embodiment described above, an example has been described in which the laser apparatus 110 has the optical SSB modulator 30, and the direction of frequency shift of the optical SSB modulator 30 can be switched by switching the voltage supplied to the optical SSB modulator 30, but the present embodiment is not limited to this. For example, the measurement apparatus 100 can switch the direction of frequency shift of the optical SSB modulator 30 by inverting the phase of the RF signal that drives the optical SSB modulator 30. Next, the optical SSB modulator 30 and the control means 50 of such a measurement apparatus 100 will be described.

[0187] Figure 14 A variant example of the control means 50 and the optical SSB modulator 30 according to the present embodiment are shown. In the control means 50 of the variant example, Figure 14 In the control means 50 of the optical SSB modulator 30 shown, for the operation of the optical SSB modulator 30 according to the present embodiment, Figure 3 The operation of the optical SSB modulator 30 and the control means 50 of the present embodiment shown is approximately the same as the operation of the optical SSB modulator 30 and the control means 50 of the present embodiment shown, and the description thereof is omitted. The control means 50 of the variant example further includes a phase difference generation means 310 and a switching means 320.

[0188] In the control means 50 of the variant example, the RF signal generation means 54 generates a plurality of RF signals. For example, the RF signal generation means 54 generates two RF signals whose phases and frequencies approximately match. For example, the RF signal generation means 54 can branch one RF signal into two parts. The RF signal generation means 54 supplies the plurality of generated RF signals to the phase difference generation means 310.

[0189] The phase difference generation means 310 causes the phases of the plurality of input RF signals to differ and outputs a plurality of RF signals, each two of the output RF signals having a predetermined phase difference. For example, the phase difference generation means 310 outputs two input RF signals that are in phase as three RF signals, each of the RF signals having a phase difference of approximately 90 degrees. For example, when the phase of a first RF signal among the three RF signals output from the phase difference generation means 310 is 0 degrees, the phase of a second RF signal differs from the phase of the first RF signal by approximately 90 degrees, and the phase of a third RF signal differs from the phase of the first RF signal by approximately 180 degrees.

[0190] The phase difference generating section 310, for example, makes the phase of one of the two input RF signals differ by 90 degrees. In addition, the phase difference generating section 310 generates an RF signal whose phase differs by 180 degrees with respect to the other of the two input RF signals. In other words, the phase difference generating section 310 generates three RF signals including one RF signal (e.g., the second RF signal described above) and two RF signals (e.g., the first and third RF signals described above) whose phases differ by ±90 degrees with respect to the one RF signal.

[0191] Alternatively, the RF signal generating section 54 can generate three RF signals whose phases and frequencies approximately match each other, and supply them to the phase difference generating section 310. In this case, the phase difference generating section 310 can make the phase of one of the three input RF signals differ by 90 degrees, and can make the phase of one of the remaining two RF signals differ by 180 degrees.

[0192] The phase difference generating section 310 supplies one of the three RF signals, whose phase differs by 90 degrees with respect to each of the other two RF signals, to the first RF electrode 38 or the second RF electrode 39. Then, the phase difference generating section 310 supplies the remaining two RF signals to the switching section 320. Figure 14 An example is shown in which the phase difference generating section 310 supplies the second RF signal to the first RF electrode 38, and supplies the first RF signal and the third RF signal to the switching section 320.

[0193] The switching section 320 supplies one of the two input RF signals to either of the first RF electrode 38 and the second RF electrode 39 to which the phase difference generating section 310 does not supply an RF signal. Figure 14 An example is shown in which one of the two RF signals to be input to the switching section 320 is input to the second RF electrode 39.

[0194] By doing so, the phase difference between the two RF signals supplied to the first RF electrode 38 and the second RF electrode 39, respectively, becomes +90 degrees or -90 degrees. In addition, the phase difference between the two RF signals can be switched by the control section 50 controlling the switching section 320. The control section 50 reverses the sign of the phase difference of the RF signals supplied to the first RF electrode 38 and the second RF electrode 39 in this way, and thus the direction of frequency shift of the optical SSB modulator 30 can be switched. That is, the control section 50 can switch the direction of frequency shift of the optical SSB modulator 30 by switching the phases of the RF signals supplied to the optical SSB modulator 30.

[0195] As described above, the switching of the RF signal supplied to the optical SSB modulator 30 can be achieved by a simple circuit configuration such as a switch. Since the control section 50 of such a modification example can be a simple circuit configuration, it is possible to switch the frequency shift direction at low cost, stably, and at high speed.

[0196] The present application has been described based on example embodiments. The technical scope of the present application is not limited to the scope described in the above embodiments, and various changes and modifications can be made within the scope of the present application. For example, all or a part of the device can be configured using any unit that is functionally or physically distributed or integrated. Furthermore, new example embodiments generated by any combination thereof are included in the example embodiments of the present application. In addition, the effects of the new embodiments brought by the combination also have the effects of the original example embodiments together.

[0197] [Legend of Reference Numerals]

[0198] 10 object to be measured

[0199] 20 AOFS

[0200] 21 optical crystal

[0201] 22 ultrasonic transducer

[0202] 23 ultrasonic absorber

[0203] 24 oscillator

[0204] 30 optical SSB modulator

[0205] 31 substrate

[0206] 32 main Mach-Zehnder waveguide

[0207] 33 first sub Mach-Zehnder waveguide 34 second sub Mach-Zehnder waveguide 35 main DC electrode

[0208] 36 first sub DC electrode

[0209] 37 second sub DC electrode

[0210] 38 first RF electrode

[0211] 39 second RF electrode

[0212] 41 first arm waveguide

[0213] 42 second arm waveguide

[0214] 43 first sub arm waveguide

[0215] 44 second sub arm waveguide

[0216] 45 third sub-arm waveguide

[0217] 46 fourth sub-arm waveguide

[0218] 50 control section

[0219] 52 DC voltage generating section

[0220] 54 RF signal generating section

[0221] 100 measuring device

[0222] 110 laser device

[0223] 112 frequency shifter

[0224] 114 gain medium

[0225] 116 WDM coupler

[0226] 117 pump light source

[0227] 118 output coupler

[0228] 120 branching section

[0229] 130 optical circulator

[0230] 140 optical head section

[0231] 150 beat signal generating section

[0232] 152 optical 90-degree hybrid

[0233] 154 photoelectric conversion section

[0234] 160 detecting section

[0235] 162 first filter section

[0236] 164 second filter section

[0237] 170 display section

[0238] 202 first AD conversion section

[0239] 204 second AD conversion section

[0240] 210 clock signal providing section

[0241] 220 frequency analyzing section

[0242] 310 phase difference generating section

[0243] 320 switching section

Claims

1. A measurement apparatus comprising: a laser device for outputting a frequency-modulated laser beam having a plurality of modes; a branching member that branches a part of the frequency-modulated laser beam output by the laser device into reference light and branches at least some of the remaining part of the frequency-modulated laser beam into measurement light; a beat signal generating member that generates a beat signal by mixing the reference light and reflected light that is reflected by irradiating the measurement light onto an object to be measured; and a detecting member that detects a difference in propagation distance between the reference light and the measurement light by frequency-analyzing the beat signal, wherein the laser device includes: an optical cavity having a gain medium for amplifying light to be input, and an optical SSB modulator for shifting the frequency of light amplified by the gain medium; and a control member that controls the optical SSB modulator to shift the frequency of light input to the optical SSB modulator.

2. The measurement apparatus according to claim 1, wherein the detecting member calculates the difference d in propagation distance between the reference light and the measurement light by the following equation: its use by frequency analysis of the beat signal B (m, d), where c is the speed of light, v s is the frequency shift of the frequency-modulated laser beam, v c = 1 / τ RT , τ RT is the time of the light traveling around the optical cavity of the laser device, and m is the separation of longitudinal mode numbers of the frequency-modulated laser beam (the difference between the longitudinal mode number of the measurement light and the longitudinal mode number of the reference light).

3. The measurement apparatus according to claim 1 or 2, wherein the beat signal generating member quadrature-detects the reflected light and the reference light.

4. A measurement apparatus comprising: a laser device for outputting a frequency-modulated laser beam having a plurality of modes; a branching member that branches a part of the frequency-modulated laser beam output by the laser device into reference light and branches at least some of the remaining part of the frequency-modulated laser beam into measurement light; a beat signal generating member that generates a beat signal by mixing the reference light and reflected light that is reflected by irradiating the measurement light onto an object to be measured; and a detecting member that detects a difference in propagation distance between the reference light and the measurement light by frequency-analyzing the beat signal, wherein the laser device includes: an optical cavity having a gain medium for amplifying light to be input, and an optical SSB modulator for shifting the frequency of light amplified by the gain medium; and a control member that controls the optical SSB modulator to shift the frequency of light input to the optical SSB modulator, wherein the control member sets the amount of frequency shift of the optical SSB modulator, the control member sets the amount of frequency shift of the optical SSB modulator to one of a first frequency or a second frequency that is larger than the first frequency, then causes the detecting member to frequency-analyze the beat signal, and the detecting member detects the difference in propagation distance of the reference light and the measurement light based on the results of frequency analysis of (i) an order number determining beat signal when the amount of frequency shift of the optical SSB modulator is set to the first frequency, and (ii) a distance measurement beat signal when the amount of frequency shift of the optical SSB modulator is set to the second frequency.

5. The measurement apparatus according to claim 4, wherein the optical SSB modulator has: a substrate, a main Mach-Zehnder waveguide provided on the substrate and having a first arm waveguide and a second arm waveguide, a first sub-Mach-Zehnder waveguide provided on the first arm waveguide, and a second sub-Mach-Zehnder waveguide provided on the second arm waveguide; and the control means provides a predetermined DC voltage and an RF signal to electrodes provided on the substrate and corresponding to the main Mach-Zehnder waveguide, the first sub-Mach-Zehnder waveguide, and the second sub-Mach-Zehnder waveguide, and sets the amount of frequency shift by changing the frequency of the RF signal.

6. The measuring apparatus according to claim 5, wherein the main Mach-Zehnder waveguide is a waveguide that branches light input to the optical SSB modulator to the first arm waveguide and the second arm waveguide, and multiplexes the branched light to output the multiplexed light, the first sub-Mach-Zehnder waveguide is a waveguide that branches light input to the first arm waveguide to a first sub-arm waveguide and a second sub-arm waveguide, and multiplexes the branched light to output the multiplexed light to the first arm waveguide, the second sub-Mach-Zehnder waveguide is a waveguide that branches light input to the second arm waveguide to a third sub-arm waveguide and a fourth sub-arm waveguide, and multiplexes the branched light to output the multiplexed light to the second arm waveguide, the electrodes have: a main DC electrode provided between the first arm waveguide and the second arm waveguide of the main Mach-Zehnder waveguide, a first sub-DC electrode and a first RF electrode provided between the first sub-arm waveguide and the second sub-arm waveguide of the first sub-Mach-Zehnder waveguide, a second sub-DC electrode and a second RF electrode provided between the third sub-arm waveguide and the fourth sub-arm waveguide of the second sub-Mach-Zehnder waveguide, and the control means provides a predetermined DC voltage to the main DC electrode, the first sub-DC electrode, and the second sub-DC electrode, and provides a predetermined RF signal to the first RF electrode and the second RF electrode.

7. The measuring apparatus according to any one of claims 4 to 6, wherein the detection means calculates the difference d in the propagation distance between the reference light and the measurement light by the following equation: its use by frequency analysis of the beat signal yields a frequency v B (m, d), where c is the speed of light, v s is the frequency shift of the frequency-modulated laser beam, v c = 1 / τ RT , τ RT is the time of flight of the light around the optical cavity of the laser device, and m is the separation of longitudinal mode numbers of the frequency-modulated laser beam (the difference between the longitudinal mode number of the measurement light and the longitudinal mode number of the reference light).

8. The measuring apparatus according to any one of claims 4 to 6, wherein the beat signal generation means quadrature detects the reflected light and the reference light.

9. A measuring apparatus comprising: a laser device for outputting a frequency-modulated laser beam having a plurality of modes; a branching means that branches a portion of the frequency-modulated laser beam output by the laser device as reference light and at least some of the remaining portion of the frequency-modulated laser beam as measurement light; a beat signal generation means that generates a beat signal by mixing the reference light and reflected light that is reflected by irradiating the measurement light onto an object to be measured; and a detection means that detects a difference in the propagation distance between the reference light and the measurement light by frequency-analyzing the beat signal, wherein the laser device includes: an optical cavity having a gain medium for amplifying light to be input, and an optical SSB modulator for shifting the frequency of light amplified by the gain medium; and the control means provides a predetermined DC voltage and an RF signal to electrodes provided on the substrate and corresponding to the main Mach-Zehnder waveguide, the first sub-Mach-Zehnder waveguide, and the second sub-Mach-Zehnder waveguide, and sets the amount of frequency shift by changing the frequency of the RF signal.

6. The measuring apparatus according to claim 5, wherein the main Mach-Zehnder waveguide is a waveguide that branches light input to the optical SSB modulator to the first arm waveguide and the second arm waveguide, and multiplexes the branched light to output the multiplexed light, the first sub-Mach-Zehnder waveguide is a waveguide that branches light input to the first arm waveguide to a first sub-arm waveguide and a second sub-arm waveguide, and multiplexes the branched light to output the multiplexed light to the first arm waveguide, the second sub-Mach-Zehnder waveguide is a waveguide that branches light input to the second arm waveguide to a third sub-arm waveguide and a fourth sub-arm waveguide, and multiplexes the branched light to output the multiplexed light to the second arm waveguide, the electrodes have: a main DC electrode provided between the first arm waveguide and the second arm waveguide of the main Mach-Zehnder waveguide, a first sub-DC electrode and a first RF electrode provided between the first sub-arm waveguide and the second sub-arm waveguide of the first sub-Mach-Zehnder waveguide, a second sub-DC electrode and a second RF electrode provided between the third sub-arm waveguide and the fourth sub-arm waveguide of the second sub-Mach-Zehnder waveguide, and the control means provides a predetermined DC voltage to the main DC electrode, the first sub-DC electrode, and the second sub-DC electrode, and provides a predetermined RF signal to the first RF electrode and the second RF electrode.

7. The measuring apparatus according to any one of claims 4 to 6, wherein the detection means calculates the difference d in the propagation distance between the reference light and the measurement light by the following equation:

8. The measuring apparatus according to any one of claims 4 to 6, wherein the beat signal generation means quadrature detects the reflected light and the reference light.

9. A measuring apparatus comprising: a laser device for outputting a frequency-modulated laser beam having a plurality of modes; a branching means that branches a portion of the frequency-modulated laser beam output by the laser device as reference light and at least some of the remaining portion of the frequency-modulated laser beam as measurement light; a beat signal generation means that generates a beat signal by mixing the reference light and reflected light that is reflected by irradiating the measurement light onto an object to be measured; and a detection means that detects a difference in the propagation distance between the reference light and the measurement light by frequency-analyzing the beat signal, wherein the laser device includes: an optical cavity having a gain medium for amplifying light to be input, and an optical SSB modulator for shifting the frequency of light amplified by the gain medium; and the control means provides a predetermined DC voltage and an RF signal to electrodes provided on the substrate and corresponding to the main Mach-Zehnder waveguide, the first sub-Mach-Zehnder waveguide, and the second sub-Mach-Zehnder waveguide, and sets the amount of frequency shift by changing the frequency of the RF signal. a control section that controls the optical SSB modulator to shift a frequency of light input to the optical SSB modulator, wherein the control section sets a direction of frequency shift of the optical SSB modulator, wherein the control section switches the direction of frequency shift of the optical SSB modulator to one of a positive side or a negative side, and then causes the detection section to perform frequency analysis on the beat signal, and the detection section detects a difference in propagation distance between the reference light and the measurement light based on frequency analysis results of (i) a positive-side beat signal generated when the direction of frequency shift of the optical SSB modulator is the positive side, and (ii) a negative-side beat signal generated when the direction of frequency shift of the optical SSB modulator is the negative side.

10. The measurement apparatus according to claim 9, wherein the optical SSB modulator has: a substrate, a main Mach-Zehnder waveguide provided on the substrate and having a first arm waveguide and a second arm waveguide, a first sub-Mach-Zehnder waveguide provided on the first arm waveguide, and a second sub-Mach-Zehnder waveguide provided on the second arm waveguide; and the control section switches the direction of frequency shift by providing a DC voltage of a predetermined value to electrodes provided on the substrate and corresponding to the main Mach-Zehnder waveguide, the first sub-Mach-Zehnder waveguide, and the second sub-Mach-Zehnder waveguide.

11. The measurement apparatus according to claim 9, wherein the optical SSB modulator has: a substrate, a main Mach-Zehnder waveguide provided on the substrate and having a first arm waveguide and a second arm waveguide, a first sub-Mach-Zehnder waveguide provided on the first arm waveguide, and a second sub-Mach-Zehnder waveguide provided on the second arm waveguide; and the control section inverts a phase of an RF signal to be provided to electrodes provided on the substrate and corresponding to the main Mach-Zehnder waveguide, the first sub-Mach-Zehnder waveguide, and the second sub-Mach-Zehnder waveguide, and switches the direction of frequency shift.

12. The measurement apparatus according to any one of claims 9 to 11, wherein the detection section calculates a difference d in propagation distance between the reference light and the measurement light by the following equation: its use by frequency analysis of the beat signal B (m, d), where c is the speed of light, v s is the frequency shift of the frequency-modulated laser beam, v c = 1 / τ RT , τ RT is the time of the light traveling around the optical cavity of the laser device, m is the spacing of the longitudinal mode numbers of the frequency-modulated laser beam (the difference between the longitudinal mode number of the measurement light and the longitudinal mode number of the reference light).

13. The measurement apparatus according to any one of claims 9 to 11, wherein the beat signal generation section performs quadrature detection on the reflected light and the reference light.

14. A measurement method comprising the steps of: setting an amount of frequency shift and a direction of frequency shift of an optical SSB modulator; outputting a frequency-modulated light beam including a plurality of modes from a laser device including an optical cavity having a gain medium and the optical SSB modulator; branching a portion of the frequency-modulated light beam output by the laser device as reference light and branching at least some of the remaining portion of the frequency-modulated light beam as measurement light; generating a first beat signal by mixing the reference light and reflected light that is reflected by irradiating the measurement light onto an object to be measured; and detecting a difference in propagation distance between the reference light and the measurement light based on a frequency analysis result of the first beat signal.

15. The measurement method according to claim 14, wherein ​ performing the following steps after generating the first beat signal: generating a second beat signal by switching a frequency shift direction of the optical SSB modulator; and detecting a difference in the propagation distance between the reference light and the measurement light based on frequency analysis results of the first beat signal and the second beat signal.

16. The measurement method according to claim 14, wherein the setting includes setting a frequency shift amount of the optical SSB modulator to a first frequency; and performing the following steps after generating the first beat signal: generating a distance measurement beat signal by switching the frequency shift amount of the optical SSB modulator to a second frequency that is larger than the first frequency; and detecting a difference in the propagation distance between the reference light and the measurement light based on frequency analysis results of the first beat signal and the distance measurement beat signal.

17. The measurement method according to claim 14, wherein the setting includes setting a frequency shift amount of the optical SSB modulator to a first frequency in the setting; and performing the following steps after generating the first beat signal: generating a third beat signal by switching the amount of frequency shift of the optical SSB modulator to a second frequency that is greater than the first frequency; and generating a fourth beat signal by switching the frequency shift direction to an opposite direction while keeping the frequency shift amount of the optical SSB modulator at the second frequency; and detecting a difference in the propagation distance between the reference light and the measurement light based on frequency analysis results of the first beat signal, the third beat signal, and the fourth beat signal.

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