Measurement device

Abstract

This measurement device comprises: a first mode-locked laser light source that emits first output light; a second mode-locked laser light source that emits second output light; a first RF oscillator that outputs a first high-frequency signal for controlling the repetition frequency of the first output light; a second RF oscillator that outputs a second high-frequency signal for controlling the repetition frequency of the second output light; a detector that detects interference light generated by the interference of the first output light and the second light output light and outputs a detection signal; and a signal processing circuit 80 that acquires the detection signal using the second high-frequency signal as a trigger or using, as a trigger, a signal generated using the first high-frequency signal and the second high-frequency signal.

Description

Measuring equipment

[0001] The present disclosure relates to a measurement device.

[0002] Patent Document 1 discloses a microscope system equipped with a mode-locked laser. The microscope system disclosed in Patent Document 1 includes a detector that receives intermittently emitted laser light and converts excited phosphors from an object into electrical signals, and an A / D converter that samples the electrical signals at a sampling period synchronized with the intermittent emission period.

[0003] Patent No. 6281193

[0004] The present disclosure provides a measurement device that can improve measurement accuracy with a simple configuration.

[0005] A measurement device according to one aspect of the present disclosure includes a first mode-locked laser light source that emits first output light, a second mode-locked laser light source that emits second output light, a first RF oscillator that outputs a first high-frequency signal for controlling the repetition frequency of the first output light, a second RF oscillator that outputs a second high-frequency signal for controlling the repetition frequency of the second output light, a detector that detects interference light generated by interference between the first output light and the second output light and outputs a detection signal, and a signal processing circuit that acquires the detection signal using the second high-frequency signal as a trigger or a signal generated using the first high-frequency signal and the second high-frequency signal as a trigger.

[0006] According to the present disclosure, it is possible to provide a measurement device that can improve measurement accuracy with a simple configuration.

[0007] FIG. 1A is a diagram schematically illustrating the time change of the electric field of optical comb laser light. FIG. 1B is a diagram schematically illustrating the frequency spectrum of optical comb laser light. FIG. 2 is a diagram schematically illustrating the frequency spectra of two optical comb laser lights and interference light in a dual comb. FIG. 3A is a top view schematically illustrating a laser light source provided in a measurement device according to an embodiment. FIG. 3B is a cross-sectional view of the laser light source shown in FIG. 3A in an xz section. FIG. 4A is a diagram illustrating the frequency spectrum of optical comb laser light. FIG. 4B is a diagram illustrating the frequency spectrum of optical comb laser light when HML (Hybrid Mode Locking) is performed. FIG. 5A is a diagram illustrating the configuration of a measurement device using an internal trigger system. FIG. 5B is a diagram illustrating the relationship between the time waveform of a detection signal output from a detector and an internal trigger. FIG. 6A is a diagram illustrating the configuration of a measurement device using an external trigger system. FIG. 6B is a diagram illustrating the relationship between the time waveform of a detection signal output from a detector and an external trigger. FIG. 7 is a diagram illustrating the configuration of a measurement device according to the first embodiment. FIG. 8 is a diagram showing the configuration of a measurement device according to the second embodiment.

[0008] (Findings that Form the Basis of the Present Disclosure) The present inventors have found that the following problems arise with the conventional measuring devices described in the "Background Art" section.

[0009] When measuring the surface shape of an object or the distance from a measurement device to the object, the timing at which reflected light returns varies depending on the surface shape and position of the object. Missing a signal corresponding to the detected reflected light reduces the measurement accuracy. To prevent missing a signal corresponding to the detected reflected light, it is necessary to adjust the start timing (i.e., trigger) of the signal acquisition period. In Patent Document 1, the sampling period is synchronized with the intermittent light emission period, but the start timing of the signal acquisition period is not adjusted. This can result in missing a signal, leading to a decrease in measurement accuracy.

[0010] There are two main methods for adjusting the start timing of the signal acquisition period: using an internal trigger and using an external trigger. As will be described in detail later, when an internal trigger is used, there is a risk that signals may be missed, reducing measurement accuracy, while when an external trigger is used, there is a problem that the device configuration becomes complicated.

[0011] Therefore, an object of the present disclosure is to provide a measurement device that can improve measurement accuracy with a simple configuration. Specific aspects of the measurement device of the present disclosure are as follows.

[0012] (First Aspect) A measurement device according to a first aspect of the present disclosure includes a first mode-locked laser light source that emits first output light, a second mode-locked laser light source that emits second output light, a first RF oscillator that outputs a first high-frequency signal for controlling the repetition frequency of the first output light, a second RF oscillator that outputs a second high-frequency signal for controlling the repetition frequency of the second output light, a detector that detects interference light generated by interference between the first output light and the second output light and outputs a detection signal, and a signal processing circuit that acquires the detection signal using the second high-frequency signal as a trigger or a signal generated using the first high-frequency signal and the second high-frequency signal as a trigger.

[0013] As a result, since the high-frequency signal from the RF oscillator or a signal generated using the high-frequency signal from the RF oscillator is used as a trigger, no additional configuration is required, and the complexity of the measurement device can be reduced. Furthermore, since the detection signal can be acquired in accordance with the time interval between the pulses of the interference light, failure to capture the detection signal is reduced, and measurement accuracy can be improved. In this way, the measurement device according to this aspect can improve measurement accuracy with a simple configuration.

[0014] (Second Aspect) In the measurement device according to the first aspect of the present disclosure, both the first mode-locked laser light source and the second mode-locked laser light source may be optical frequency comb light sources.

[0015] As a result, the optical frequency comb laser light source emits output light with a highly stable repetition frequency, thereby improving measurement accuracy and long-term measurement reliability.

[0016] (Third Aspect) In the measurement device according to the first or second aspect of the present disclosure, the first mode-locked laser light source and the second mode-locked laser light source may be integrated on the same semiconductor substrate.

[0017] This allows the measurement device to be made smaller.

[0018] (Fourth Aspect) In the measurement device according to the first or second aspect of the present disclosure, the first mode-locked laser light source and the second mode-locked laser light source may be integrated on different semiconductor substrates.

[0019] This allows the measurement device to be made smaller.

[0020] (Fifth Aspect) In the measurement device according to any one of the first to fourth aspects of the present disclosure, the first mode-locked laser light source may include a first saturable absorber, and the first RF oscillator may supply the first high-frequency signal to the first saturable absorber, and the second mode-locked laser light source may include a second saturable absorber, and the second RF oscillator may supply the second high-frequency signal to the second saturable absorber.

[0021] Thus, by adjusting the frequency of at least one of the first and second high-frequency signals, the time interval between the pulses of the interference light can be adjusted. Even if the time interval between the pulses of the interference light changes, the high-frequency signal from the RF oscillator or a signal generated using the high-frequency signal from the RF oscillator is used as a trigger, so that failure to capture the detection signal is suppressed and measurement accuracy can be improved.

[0022] (Sixth Aspect) The measurement device according to the fifth aspect of the present disclosure may further include a mixer that generates a difference frequency signal having a frequency that is the difference between the frequency of the first high-frequency signal and the frequency of the second high-frequency signal, and the signal processing circuit may acquire the detection signal using the difference frequency signal generated by the mixer as the trigger.

[0023] The difference frequency signal generated by the mixer corresponds to the time interval between the pulses of the interference light. Using the difference frequency signal as a trigger can reduce signal loss and improve measurement accuracy. In addition, a small mixer can be used to generate the difference frequency signal, which helps prevent the measurement device from becoming too complicated.

[0024] (Seventh Aspect) The measurement device according to any one of the first to fourth aspects of the present disclosure may further include a mixer that generates a sum frequency signal having a frequency that is the sum of a frequency of the first high frequency signal and a frequency of the second high frequency signal, wherein the first mode-locked laser light source may include a first saturable absorber, the first RF oscillator may supply the first high frequency signal to the first saturable absorber, the second mode-locked laser light source may include a second saturable absorber, and the mixer may supply the sum frequency signal to the second saturable absorber.

[0025] This allows the repetition frequency of the second output light to be adjusted by the sum frequency signal generated by the mixer. Since a small mixer can be used as the mixer for generating the sum frequency signal, it is possible to prevent the configuration of the measurement device from becoming too complicated.

[0026] (Eighth Aspect) In the measurement device according to the seventh aspect of the present disclosure, the signal processing circuit may acquire the detection signal using the second high-frequency signal as the trigger.

[0027] The second high-frequency signal corresponds to the time interval between pulses of the interference light. By using the second high-frequency signal as a trigger, it is possible to prevent signal loss and improve measurement accuracy.

[0028] (Ninth Aspect) In the measurement device according to any one of the first to eighth aspects of the present disclosure, the signal processing circuit may acquire the waveform of the detection signal at a predetermined sampling period, and the period at which the signal processing circuit acquires the detection signal may be different from the sampling period.

[0029] This makes it possible to prevent signals from being missed and improve measurement accuracy.

[0030] (10th Aspect) In a measurement device according to any one of the first to ninth aspects of the present disclosure, the interference light may be interference light generated by interference between the second output light and light of the first output light reflected by an object, and the signal processing circuit may measure the distance from the measurement device to the object based on the detection signal acquired by the signal processing circuit.

[0031] This allows for accurate distance measurement, and for example, allows for accurate measurement of the surface shape of an object.

[0032] Hereinafter, the embodiments will be specifically described with reference to the drawings.

[0033] The embodiments described below are all comprehensive or specific examples. The numerical values, shapes, materials, components, component placement and connection configurations, steps, and step order shown in the following embodiments are merely examples and are not intended to limit the present disclosure. Furthermore, among the components in the following embodiments, components not described in the independent claims are described as optional components.

[0034] Furthermore, each figure is a schematic diagram and is not necessarily an exact illustration. Therefore, for example, the scales of the figures do not necessarily match. Furthermore, in each figure, substantially the same components are given the same reference numerals, and redundant explanations are omitted or simplified.

[0035] Furthermore, in this specification, the numerical ranges are not expressions that express only the strict meaning, but also expressions that include a substantially equivalent range, for example, a difference of about several percent.

[0036] In this specification, the terms "above" and "below" do not refer to the upward direction (vertically upward) and downward direction (vertically downward) in absolute spatial recognition, but are used as terms defined by a relative positional relationship based on the stacking order in a stacked configuration. Furthermore, the terms "above" and "below" are used not only when two components are arranged with a gap between them and another component exists between them, but also when two components are arranged closely together and are in contact with each other.

[0037] In this specification and the drawings, the x-axis, y-axis, and z-axis represent the three axes of a three-dimensional Cartesian coordinate system.

[0038] Furthermore, in this specification, ordinal numbers such as "first" and "second" do not refer to the number or order of components unless otherwise specified, but are used for the purpose of avoiding confusion and distinguishing between components of the same type.

[0039] [Optical Comb Laser] First, the time variation and frequency spectrum of the electric field of optical comb laser light will be described with reference to FIGS. 1A and 1B.

[0040] FIG. 1A is a diagram showing an example of the temporal change in the electric field of an optical comb laser beam. In FIG. 1A, the horizontal axis represents time, and the vertical axis represents the electric field of the optical comb laser beam. The optical comb laser beam is an example of output light emitted by a mode-locked laser light source and is also called an optical frequency comb laser beam. In this specification, the optical comb laser beam may be simply referred to as laser beam.

[0041] As shown in FIG. 1A, the optical comb laser light has a repetition period T ｒｅｐ It is formed from a train of optical pulses generated at a repetition period T ｒｅｐ is, for example, 1 ps or more and 100 ns or less. The full width at half maximum of each optical pulse is represented by Δt. The full width at half maximum of each optical pulse Δt is, for example, 10 fs or more and 100 ps or less.

[0042] In a laser resonator, the envelope of the light pulse propagates at a group velocity v ｇ and the phase velocity v of the waves propagating within the light pulse. ｐThe group velocity v ｇ and the phase velocity v ｐ Due to the difference between the wavelengths of adjacent optical pulses and the wavelength of the laser beam, when two adjacent optical pulses are overlapped so that their envelopes coincide, the phase of the waves in these optical pulses shifts by Δφ, which takes a value between 0 and 2π. The repetition period of the optical pulse train is T ｒｅｐ = L / v ｇ is expressed by

[0043] 1B is a diagram showing a frequency spectrum of the optical comb laser light, where the horizontal axis represents frequency and the vertical axis represents intensity of the optical comb laser light.

[0044] As shown in Figure 1B, the optical comb laser light has a comb-like frequency spectrum formed by a number of discrete equally spaced lines. The frequencies of the discrete equally spaced lines correspond to the resonant frequencies of the longitudinal modes in the laser resonator. The repetition frequency, which corresponds to the spacing between two adjacent equally spaced lines in the optical frequency comb, is f ｒｅｐ = 1 / T ｒｅｐ The repetition frequency f ｒｅｐ is, for example, 10 MHz or more and 1 THz or less. The circumferential length L of the laser resonator is 30 cm, and the group velocity v ｇ is the speed of light in a vacuum (= 3 × 10 ８ m / s), the repetition period T ｒｅｐ becomes 1 ns, and the repetition frequency f ｒｅｐ becomes 1 GHz.

[0045] The full width at half maximum of the optical comb laser light is Δf=1 / Δt. The full width at half maximum Δf of the optical comb laser light is, for example, 10 GHz or more and 100 THz or less. Assuming that the equally spaced lines exist up to near zero frequency, the frequency of the equally spaced line closest to zero frequency is called the carrier envelope offset frequency. The carrier envelope offset frequency is f ＣＥＯ =(Δφ / (2π))f ｒｅｐ The carrier envelope offset frequency f ＣＥＯ is a function of the repetition frequency f ｒｅｐThe carrier envelope offset frequency f ＣＥＯ If we define the 0th mode as f, the nth mode in the optical comb laser is f ｎ = f ＣＥＯ +nf ｒｅｐ The electric field of the optical comb laser light shown in FIG. 1A is expressed by the n-th mode frequency f ｎ The amplitude and phase of the electric field at ｎ and φ ｎ Then, E(t) = ΣnE ｎ exp[-i(2πf ｎ t+φ ｎ ) ].

[0046] The repetition frequency f ｒｅｐ and the carrier envelope offset frequency f ＣＥＯ can change slightly due to disturbances such as vibrations or temperature changes to the optical comb laser source. This is because vibrations can change the circumferential length L of the laser cavity, or temperature changes can change the group velocity v via changes in the refractive index of the laser cavity. ｇ and the phase velocity v ｐ This is because the repetition frequency f ｒｅｐ and the carrier envelope offset frequency f ＣＥＯ are much lower than the frequency of light. Even a slight change in these frequencies can affect the identification of the mode frequencies in the optical comb laser light. For this reason, the optical comb laser source must have a repetition rate of f ｒｅｐ and the carrier envelope offset frequency f ＣＥＯ A modulator element may be incorporated to stabilize the

[0047] The modulation element may include, for example, a piezoelectric element for suppressing vibration, a temperature adjustment element for suppressing temperature changes, or a Peltier element. The modulation element may be provided outside the optical comb laser light source. The repetition frequency f ｒｅｐIn order to stabilize the carrier envelope offset frequency f, for example, a part of the optical comb laser light may be detected, and feedback may be performed based on the detected part using a piezoelectric element and / or a Peltier element so that the circumferential length L of the laser resonator is kept constant. ＣＥＯ In order to stabilize the nonlinearity in the laser resonator, for example, a portion of the optical comb laser light may be detected using a nonlinear optical effect, and feedback may be performed by adjusting the intensity of the excitation light input to the laser resonator based on the detected portion, so that the nonlinearity in the laser resonator remains constant.

[0048] [Dual Comb] Next, the principle of the dual comb will be briefly explained with reference to Fig. 2. The dual comb uses two optical comb laser beams.

[0049] 2 is a diagram showing the frequency spectrum of two optical comb laser beams and interference light in a dual comb. In the first optical comb laser beam, the nth mode frequency f １ｎ is f １ｎ = f ＣＥＯ１ +nf ｒｅｐ１ In addition, the second optical comb laser light has the nth mode frequency f ２ｎ is f ２ｎ = f ＣＥＯ２ +nf ｒｅｐ２ It is expressed by f ＣＥＯ１ is the carrier envelope offset frequency of the first optical comb laser light. ＣＥＯ２ is the carrier envelope offset frequency of the second optical comb laser light. ｒｅｐ１ is the repetition frequency of the first optical comb laser beam. ｒｅｐ２ is the repetition frequency of the second optical comb laser light. ｒｅｐ１ and f ｒｅｐ２ is slightly different, and f ｒｅｐ２ = f ｒｅｐ１ +δf ｒｅｐ The following relationship holds: δf ｒｅｐ is f ｒｅｐ１ Specifically, δf ｒｅｐ is f ｒｅｐ１ δf is 1% or less, but is not limited to this. ｒｅｐ is fｒｅｐ１ It may be 0.5% or less, 0.1% or less, 0.05% or less, or 0.02% or less. ｒｅｐ is, for example, 1 Hz or more and 10 MHz or less.

[0050] In the mode of the first optical comb laser light and the mode of the second optical comb laser light shown in Figure 2, as a result of interference between the nearest modes, a frequency spectrum as shown in Figure 2 is detected as interference light. The detected interference light is a beat generated by the interference between the first optical comb laser light and the second optical comb laser light. The frequency interval of the interference light is δf, which is the difference between the repetition frequency of the first optical comb laser light and the repetition frequency of the second optical comb laser light. ｒｅｐ This becomes:

[0051] The time waveform of the interference light is a pulse waveform similar to that of FIG. 1A. The pulse interval of the interference light is δT ｒｅｐ δT ｒｅｐ = 1 / δf ｒｅｐ Therefore, the time required for one measurement in spectroscopy or distance measurement is the pulse interval δT ｒｅｐ That is, 1 / δf ｒｅｐ Therefore, the number of measurements per second is δf ｒｅｐ Therefore, there is a trade-off between the measurement time and the number of measurements per unit time.

[0052] Furthermore, the longer it takes to perform a single measurement, the more accurate the measurement becomes. Therefore, there is a trade-off between measurement accuracy and the number of measurements per unit time. ｒｅｐ By adjusting the value of the parameter, it is possible to improve the accuracy or increase the number of measurements per unit time.

[0053] [Laser Light Source] Next, an example of the configuration of a mode-locked laser light source will be described with reference to FIGS. 3A and 3B.

[0054] Fig. 3A is a top view schematically showing the laser light source 10 provided in the measurement device according to this embodiment. Fig. 3B is a cross-sectional view schematically showing the laser light source 10 at the position indicated by line IIIB-IIIB in Fig. 3A. For reference, mutually orthogonal x-axis, y-axis, and z-axis are shown schematically, but this is for the sake of convenience and does not limit the orientation during use. Note that Fig. 3B omits some of the diagonal shading representing the cross section.

[0055] The laser light source 10 is an example of a mode-locked laser light source that emits output light 14. Specifically, the laser light source 10 is an optical frequency comb laser light source.

[0056] 3A and 3B, the laser light source 10 includes a resonator 11, a semiconductor substrate 12, and a protective layer 13. In the illustrated example, the surface of the semiconductor substrate 12 is parallel to the xy plane. As shown in FIG. 3B, the semiconductor substrate 12 includes a high refractive index layer 12a made of, for example, Si, and a SiO ２ The protective layer 13 has a laminated structure in which the high refractive index layer 12a and the low refractive index layer 12b such as SiO are laminated in this order in the z-axis direction. The refractive index of the high refractive index layer 12a is higher than the refractive index of the low refractive index layer 12b. The semiconductor substrate 12 does not necessarily have to include the high refractive index layer 12a. The protective layer 13 is made of, for example, SiO ２ or an organic insulating material such as BCB (benzocyclobutene). The protective layer 13 is provided so as to cover the upper surface of the low refractive index layer 12b.

[0057] The resonator 11 is an example of a laser resonator having a predetermined optical path length. As shown in FIG. 3A, the resonator 11 includes a semiconductor layer 11s, an intermediate layer 11i, an optical waveguide 11w, and a first mirror 11m. １ and the second mirror 11m ２ As shown in FIG. 3B, the resonator 11 includes an n-doped layer 11d. １ and p-doped layer 11d ２ and 11d ３ The resonator 11 also includes a gain medium 11g and a saturable absorber 11sa. Parts of the semiconductor layer 11s function as the gain medium 11g and the saturable absorber 11sa, respectively.

[0058] 3A, the planar shape of the semiconductor layer 11s in the resonator 11 is represented by a dotted line. The semiconductor layer 11s is tapered at both ends. The tip of the tapered portion overlaps the intermediate layer 11i in top view. The intermediate layer 11i is also tapered at both ends. The tip of the tapered portion overlaps the optical waveguide 11w in top view. This allows light passing through the semiconductor layer 11s to be efficiently propagated to the optical waveguide 11w via the intermediate layer 11i.

[0059] As shown in FIG. 3B , the optical waveguide 11w in the resonator 11 is embedded in a low-refractive-index layer 12b in the semiconductor substrate 12. The optical waveguide 11w may be provided on the low-refractive-index layer 12b. The optical waveguide 11w may be formed from a high-refractive-index material such as SiN. The refractive index of the optical waveguide 11w is higher than the refractive index of the low-refractive-index layer 12b in the semiconductor substrate 12 and the refractive index of the protective layer 13. This allows light to propagate through the optical waveguide 11w by total internal reflection.

[0060] The intermediate layer 11i is formed of, for example, a-Si (amorphous silicon). As long as the refractive index satisfies the following condition: optical waveguide 11w < intermediate layer 11i < semiconductor layer 11s, the intermediate layer 11i may be formed of other semiconductors. Without the intermediate layer 11i, the refractive index of the semiconductor layer 11s would be higher than the refractive index of the optical waveguide 11w, making it difficult for light that has passed through the semiconductor layer 11s to pass through the optical waveguide 11w.

[0061] First mirror 11m １ and the second mirror 11m ２ The first mirror 11m may be formed of, for example, a distributed Bragg reflector. In a distributed Bragg reflector, light is reflected by Bragg reflection due to a periodic structure of the refractive index. １ The second mirror 11m is provided at the end of the optical waveguide 11w. ２ is the first mirror 11m in the optical waveguide 20w. １ The first mirror 11m is provided at the end opposite to the first mirror 11m. １ and the second mirror 11m ２ The first mirror 11m reflects the light that has propagated through the optical waveguide 11w. １and the second mirror 11m ２ The first mirror 11m may be made of, for example, metal, as long as it has a reflecting function. １ and the second mirror 11m ２ may be a reflective element made of a semiconductor such as a loop mirror.

[0062] Second mirror 11m ２ is the first mirror 11m １ Specifically, the reflectance of the first mirror 11m is lower than that of the first mirror 11m. １ The reflectivity of the second mirror 11m is substantially equal to 100%. ２ The reflectance of the first mirror 11m is equal to or greater than a predetermined value. １ The predetermined value is, for example, 50%, and as an example, ２ The reflectance of the second mirror 11m can be, for example, 70% or 90%. ２ The second mirror 11m reflects most of the light propagating through the optical waveguide 11w, but transmits a portion of the light. ２ The light transmitted through the filter becomes output light 14, which is optical comb laser light.

[0063] As shown in FIG. 3B, the semiconductor layer 11s is an n-doped layer 11d １ and p-doped layer 11d ２ and 11d ３ The n-doped layer 11d is sandwiched between the １ and p-doped layer 11d ２ and 11d ３ The positional relationship may be reversed.

[0064] Semiconductor layer 11s, n-doped layer 11d １ and p-doped layer 11d ２ and 11d ３ is buried in the protective layer 13. １ The bottom surface of the n-doped layer 11d may be in contact with the surface of the semiconductor substrate 12. １ may be in contact with the intermediate layer 11i.

[0065] The semiconductor layer 11s may be formed of, for example, a III-V semiconductor material, which may include, for example, at least one material selected from the group consisting of InGaAlP, InGaAs, GaInAsP, GaInAsSb, InP, GaN, GaAs, AlGaAs, and AlInGaN.

[0066] The semiconductor layer 11s includes a gain medium 11g and a saturable absorber 11sa. The gain medium 11g is a part of the semiconductor layer 11s and is formed by an n-doped layer 11d. １ and p-doped layer 11d ２ The saturable absorber 11sa is a part of the semiconductor layer 11s, and is sandwiched between the n-doped layer 11d. １ and p-doped layer 11d ３ It is the part sandwiched between and.

[0067] n-doped layer 11d １ is an n-type semiconductor layer. １ is formed by doping the same III-V semiconductor material as the semiconductor layer 11s with an n-type impurity. The n-type impurity may be, for example, a tetravalent element such as Si or a hexavalent element such as selenium (Se).

[0068] p-doped layer 11d ２ and 11d ３ is a p-type semiconductor layer. ２ and 11d ３ The p-doped layer 11d is formed by doping a p-type impurity into the same III-V semiconductor material as the semiconductor layer 11s. For example, a divalent element such as zinc (Zn) can be used as the p-type impurity. ２ and p-doped layer 11d ３ and have the same composition, for example.

[0069] p-doped layer 11d ２ and p-doped layer 11d ３ The p-doped layer 11d is separated from the p-doped layer 11d. ２ and 11d ３ Each of the p-doped layers 11d is attached with a different electrode (not shown). ２A current is injected into the p-doped layer 11d via an electrode. ３ The n-doped layer 11d １ By applying this voltage, a reverse bias voltage is applied between the p-doped layer 11d ３ The portion of the saturable absorber 11sa that contacts the first mirror 11m functions as the saturable absorber 11sa. The saturable absorber 11sa may be formed using carbon nanotubes. １ and the second mirror 11m ２ It may be integrated with.

[0070] p-doped layer 11d ２ Similarly, the n-doped layer 11d １ An electrode (not shown) is also attached to the n-doped layer 11d. １ and p-doped layer 11d ２ A part of the semiconductor layer 11s into which electric charges are injected from the electrodes attached to each of the first and second mirrors 11m functions as a gain medium 11g from which light is stimulated and emitted. The stimulated and emitted light is guided to the first mirror 11m via the intermediate layer 11i and the optical waveguide 11w. １ and the second mirror 11m ２ The light is repeatedly reflected between the first mirror 11m and the second mirror 11m. In other words, the light is amplified by passing through the gain medium 11g many times. The amplified light becomes a mode-locked optical pulse train by the saturable absorber 11sa. Only the wavelength corresponding to the optical path length of the resonator 11 (i.e., the resonator length multiplied by the refractive index) is amplified. As a result, the resonator 11 emits optical comb laser light as output light 14. The resonator length of the resonator 11 is determined by the first mirror 11m. １ and the second mirror 11m ２ is the distance between

[0071] [HML (Hybrid Mode Locking)] Next, hybrid mode locking (HML) will be described.

[0072] HML is a technology for stabilizing the repetition frequency of an optical comb laser beam. Specifically, a frequency shifter is used to set the repetition frequency of the optical comb laser beam to a predetermined drive frequency. For example, the frequency shifter includes an RF (Radio Frequency) oscillator that supplies a high-frequency signal. In the case of the laser light source 10 shown in FIGS. 3A and 3B, an RF oscillator (not shown) supplies a high-frequency signal to the saturable absorber 11sa. The frequency of this high-frequency signal is the drive frequency of the frequency shifter.

[0073] FIG. 4A shows the frequency spectrum of the optical comb laser light. Specifically, FIG. 4A shows a graph of the electrical signal output from the detector, observed with an RF spectrum analyzer, after the optical comb laser light is incident on the detector without HML. The peak frequency of approximately 2.9617 GHz in the graph shown in FIG. 4A corresponds to the repetition frequency of the optical comb laser light. The resonator length of the laser light source can vary depending on environmental conditions such as temperature changes and operating conditions. As a result, as shown in FIG. 4A, the peak of the output electrical signal has a wide half-width.

[0074] 4B shows the frequency spectrum of the optical comb laser light when HML is performed. Specifically, FIG. 4B shows a graph of the electrical signal output from the detector, observed with an RF spectrum analyzer, after HML is performed and the optical comb laser light is incident on the detector. In HML, the repetition frequency value when HML is not performed, i.e., the high-frequency signal of approximately 2.9617 GHz shown in FIG. 4A, is supplied to the saturable absorber. Hereinafter, the repetition frequency value when HML is not performed may be referred to as the "repetition frequency reference value."

[0075] As shown in Figure 4B, the peak of the electrical signal output from the detector has a narrow half-width and a steep peak. This indicates that the repetition frequency of the optical comb laser light is stable. Thus, in HML, the repetition frequency can be stabilized by driving the optical frequency comb laser light source at a drive frequency set to the same value as the repetition frequency reference value. A stable repetition frequency can improve measurement accuracy.

[0076] [Measurement Apparatus] Next, a specific configuration of a measurement apparatus according to the present disclosure will be described. Below, a measurement apparatus using an internal trigger method will be described, followed by a measurement apparatus using an external trigger method. After that, a measurement apparatus according to an embodiment of the present disclosure will be described.

[0077] <Internal Trigger Method> First, a measurement device 1x that uses the internal trigger method will be described. As will be described in detail below, the internal trigger method has the problem of reduced measurement accuracy.

[0078] 5A is a diagram showing the configuration of a measurement device 1x using an internal trigger system. First, with reference to FIG. 5A, a basic configuration example common to laser devices according to embodiments of the present disclosure will be described. The measurement device 1x measures the distance from the measurement device 1x to an object 60, i.e., performs distance measurement. Alternatively, the measurement device 1x may inspect the shape of the object 60.

[0079] 5A, the measurement device 1x includes a first laser light source 20, a second laser light source 21, detectors 70 and 71, a signal processing circuit 80x, a first RF oscillator 90, and a second RF oscillator 91. The measurement device 1x also includes couplers 30, 31, 32, and 33, a circulator 40, and a collimator 50 as optical elements for adjusting the optical path.

[0080] The first laser light source 20 is an example of a first mode-locked laser light source that emits first output light. Specifically, the first laser light source 20 is an optical frequency comb light source including a laser resonator. The first laser light source 20 outputs a first optical comb laser light 20L as the first output light. The first optical comb laser light 20L has a repetition rate of f ｒｅｐ１ and the carrier envelope offset frequency is f ＣＥＯ１ It is a laser beam.

[0081] The second laser light source 21 is an example of a second mode-locked laser light source that emits second output light. Specifically, the second laser light source 21 is an optical frequency comb light source including a laser resonator. The second laser light source 21 outputs a second optical comb laser light 21L as the second output light. The repetition frequency of the second optical comb laser light 21L is different from the repetition frequency of the first optical comb laser light 20L. For example, as shown in the middle part of FIG. 2, the second optical comb laser light 21L has a repetition frequency of f ｒｅｐ２ and the carrier envelope offset frequency is f ＣＥＯ２ It is a laser beam.

[0082] The first laser light source 20 and the second laser light source 21 are, for example, the laser light source 10 shown in FIGS. 3A and 3B . That is, the first laser light source 20 and the second laser light source 21 are integrated on different semiconductor substrates. Alternatively, the first laser light source 20 and the second laser light source 21 may be integrated on the same semiconductor substrate. That is, the resonator 11 of the first laser light source 20 may be formed in a first region of one semiconductor substrate 12, and the resonator 11 of the second laser light source 21 may be formed in a second region different from the first region. The resonator length of the resonator 11 of the first laser light source 20 is different from the resonator length of the resonator 11 of the second laser light source 21. As a result, the repetition frequency f ｒｅｐ１ and f ｒｅｐ２ The first laser light source 20 and the second laser light source 21 can be made different from each other. By integrating the first laser light source 20 and the second laser light source 21 on the same semiconductor substrate or on two different semiconductor substrates, the measurement device 1x can be made smaller.

[0083] Each of the couplers 30, 31, 32, and 33 is an optical element that splits or combines light.

[0084] The circulator 40 is an optical element that controls the traveling direction of light.

[0085] The collimator 50 is an optical element that converts light into parallel light and emits the parallel light. A light-collecting element such as a lens may be provided on the light-emitting side of the collimator 50.

[0086] The detectors 70 and 71 are optical elements that convert incident light into electric charges through photoelectric conversion, thereby generating and outputting an electrical signal as a detection signal. The signal level of the detection signal corresponds to the intensity of the incident light. The detectors 70 and 71 are photoelectric conversion elements such as photodiodes and phototransistors.

[0087] Specifically, the detectors 70 and 71 each detect interference light resulting from interference between the first optical comb laser beam 20L and the second optical comb laser beam 21L and output a detection signal. More specifically, the detector 70 detects interference light resulting from interference between light 20Lr, which is part of the first optical comb laser beam 20L, and light 21Lr, which is part of the second optical comb laser beam 21L. The detector 71 also detects interference light resulting from interference between reflected light 20R, which is part of the first optical comb laser beam 20L and reflected by the object 60, and light 21Lt, which is part of the second optical comb laser beam 21L. The detectors 70 and 71 each output a detection signal having a signal level corresponding to the intensity of the detected interference light to the signal processing circuit 80x.

[0088] The signal processing circuit 80x acquires the detection signals output from the detectors 70 and 71, and calculates the distance from the measurement device 1x to the object 60 based on the acquired detection signals. The signal processing circuit 80x may calculate the distance from the measurement device 1x to each portion on the surface of the object 60 based on the acquired detection signals. In this way, the signal processing circuit 80x can obtain information about the surface shape of the object 60.

[0089] The signal processing circuit 80x is realized, for example, by an LSI (Large Scale Integration), which is an integrated circuit (IC). The integrated circuit is not limited to an LSI and may be a dedicated circuit or a general-purpose processor. For example, the signal processing circuit 80x may be a microcontroller. The microcontroller includes, for example, a nonvolatile memory in which a program is stored, a volatile memory that is a temporary storage area for executing the program, input / output ports, and a processor that executes the program. The signal processing circuit 80x may also be a programmable FPGA (Field Programmable Gate Array) or a reconfigurable processor in which the connections and settings of circuit cells within the LSI can be reconfigured. The functions performed by the signal processing circuit 80x may be realized by software or hardware. The signal processing circuit 80x may also be realized by a common hardware configuration.

[0090] The first RF oscillator 90 outputs a first high-frequency signal for controlling the repetition frequency of the first optical comb laser light 20L emitted by the first laser light source 20. Specifically, the first RF oscillator 90 supplies the first high-frequency signal to a saturable absorber 11sa included in the first laser light source 20. This allows the repetition frequency of the first optical comb laser light 20L to be stabilized at the frequency of the first high-frequency signal. The saturable absorber 11sa included in the first laser light source 20 is an example of a first saturable absorber.

[0091] The second RF oscillator 91 outputs a second high-frequency signal for controlling the repetition frequency of the second optical comb laser light 21L emitted by the second laser light source 21. Specifically, the second RF oscillator 91 supplies the second high-frequency signal to a saturable absorber 11sa included in the second laser light source 21. This allows the repetition frequency of the second optical comb laser light 21L to be stabilized at the frequency of the second high-frequency signal. The saturable absorber 11sa included in the second laser light source 21 is an example of a second saturable absorber.

[0092] The frequency of the second high frequency signal is different from the frequency of the first high frequency signal. For example, if the frequency of the first high frequency signal is f ｒｅｐ１ If the frequency of the second high-frequency signal is f ｒｅｐ２ where f ｒｅｐ２ = f ｒｅｐ１ +δf ｒｅｐ , δf ｒｅｐ ≠0 is satisfied.

[0093] Next, the main connections of the above-mentioned components will be described. Specifically, the connections of the components regarding the optical paths of the first optical comb laser beam 20L and the second optical comb laser beam 21L will be described.

[0094] Many of the components of the measurement device 1x are connected by optical fibers indicated by dashed lines in Fig. 5A. Specifically, couplers 30, 31, 32, and 33, a circulator 40, a collimator 50, and detectors 70 and 71 are arranged on the optical fiber path. The first laser light source 20 and the second laser light source 21 are connected to the ends of the optical fibers.

[0095] The first optical comb laser beam 20L is split into two beams, a beam 20Lt and a beam 20Lr, by the coupler 30. The beam 20Lt is a measurement optical comb laser beam and is emitted toward the target 60. The beam 20Lr is a reference optical comb laser beam. The repetition frequency of each of the beams 20Lt and 20Lr is the repetition frequency (f ｒｅｐ１ ) is the same as

[0096] The light 20Lt passes through the circulator 40, is emitted from the collimator 50, and is incident on the object 60. The light 20Lt is then reflected by the object 60. The reflected light 20R reflected by the object 60 is incident on the collimator 50 and then directed by the circulator 40 to the coupler 33. The light 20Lr is directed from the coupler 30 to the coupler 32.

[0097] On the other hand, the second optical comb laser beam 21L is split into two beams, a beam 21Lr and a beam 21Lt, by the coupler 31. The beam 21Lt is an optical comb laser beam for measurement. The beam 21Lr is an optical comb laser beam for reference. The repetition frequency of each of the beams 21Lt and 21Lr is the repetition frequency (f ｒｅｐ２ ) is the same as

[0098] Light 21Lr is combined with light 20Lr by coupler 32 and directed toward detector 70. Light 21Lt is combined with reflected light 20R by coupler 33 and directed toward detector 71. These lights interfere with each other at detector 70 or 71, generating a beat, and the information in the interference light (also called beat light) is converted into a detection signal, which is an electrical signal. The detection signals output from detectors 70 and 71 are input to signal processing circuit 80x.

[0099] The signal processing circuit 80x acquires, based on an internal trigger method, the detection signals output from the detectors 70 and 71. Here, acquiring the detection signals means acquiring them as targets for signal processing.

[0100] 5B is a diagram showing the relationship between the time waveforms of the detection signals output from detectors 70 and 71 and the internal trigger. The reference signal is the detection signal output from detector 70. The measurement signal is the detection signal output from detector 71. The pulse interval of the reference signal and the pulse interval of the measurement signal are both 1 / δf ｒｅｐ is.

[0101] The measurement signal and the reference signal have different optical path lengths until detection, resulting in a time difference in the pulse waveforms. Specifically, the time difference between the pulse waveform of the reference signal and the pulse waveform of the measurement signal depends on the distance from the measurement device 1x to the object 60. Therefore, the distance from the measurement device 1x to the object 60 can be measured by detecting the peak of the pulse waveform and calculating the time difference between the peak positions. In addition, the surface shape of the object 60 can be measured by scanning the position where the light 20Lt is irradiated along the surface of the object 60.

[0102] In order to improve the accuracy of distance measurement, it is necessary to appropriately acquire pulse waveforms for each of the reference signal and the measurement signal. In the internal trigger method, as shown in Fig. 5B, the signal processing circuit 80 sets a threshold value for the reference signal. The signal processing circuit 80 performs a predetermined offset period T from the point when the signal strength of the reference signal exceeds the threshold value. ｏｆｆｓｅｔ The time point at which the signal is acquired is defined as the acquisition period T ｍ is the start point of the acquisition period T ｍ The waveforms of the reference signal and the measurement signal are acquired within an acquisition period T ｍ The sampling period for acquiring the waveform is, for example, f ｒｅｐ１ or f ｒｅｐ２ For example, the sampling period is δf ｒｅｐ For example, δf ｒｅｐ The offset period T ｏｆｆｓｅｔ and acquisition period T ｍ The length of each of the above can be preset to an appropriate length.

[0103] However, in the internal trigger method, fluctuations in the peak intensity of the reference signal can cause a signal (specifically, a pulse waveform) to be missed. For example, in FIG. 5B, the peak intensity of the third pulse of the reference signal does not exceed the threshold, so the acquisition period T ｍ If the threshold is not set, signals will be missed. The number of pulse waveforms that can be acquired will decrease, resulting in a decrease in measurement accuracy. Furthermore, if the pulse waveform is distorted by disturbances such as temperature changes, the position of the peak that exceeds the threshold may shift. This also reduces measurement accuracy.

[0104] <External Trigger Method> Next, a measurement device 1y that uses the external trigger method will be described. As will be described in detail below, the external trigger method has the problem that the configuration of the measurement device 1y becomes complicated.

[0105] 6A is a diagram showing the configuration of a measurement apparatus 1y that uses an external trigger system. The measurement apparatus 1y shown in FIG. 6A differs from the measurement apparatus 1x shown in FIG. 5A in that it includes a signal processing circuit 80y and a function generator 100 instead of the signal processing circuit 80x. The following description will focus on the differences from the measurement apparatus 1x, and will omit or simplify the description of the commonalities.

[0106] The function generator 100 is a circuit that generates a trigger signal. Specifically, as shown in FIG. 6B, the function generator 100 generates a trigger signal δf ｒｅｐ The trigger signal having a frequency of 1 / 2 s is generated and supplied to the signal processing circuit 80y. Note that Fig. 6B is a diagram showing the relationship between the time waveforms of the detection signals output from the detectors 70 and 71 and the external trigger. Fig. 6B shows an example in which the waveform of the trigger signal is a sine wave, but this is not limiting.

[0107] The signal processing circuit 80y corresponds to the signal processing circuit 80x, and differs in that it compares a trigger signal with a threshold instead of comparing a reference signal with a threshold. That is, the signal processing circuit 80y acquires the waveform of the detection signal based on the trigger signal supplied from the function generator 100 during an acquisition period T ｍ The peak position of the trigger signal shown in FIG. 6B coincides with the peak position of the pulse waveform of the reference signal, but this is not limited to this. The peak position of the trigger signal may be different from the peak position of the pulse waveform of the reference signal, and the offset period T ｏｆｆｓｅｔ By adjusting the length of the acquisition period T ｍ can be started at the appropriate time.

[0108] The function generator 100 is less susceptible to the temperature environment than the first laser light source 20 and the second laser light source 21. Therefore, fluctuations in the peak intensity and frequency of the trigger signal are sufficiently small, so that it is possible to prevent the pulse waveform, which is the signal, from being missed and to prevent a decrease in measurement accuracy.

[0109] On the other hand, an additional component such as the function generator 100 is required to generate a stable trigger signal. The additional component for generating a stable trigger signal tends to be large and expensive, which leads to a complicated configuration and high costs for the measurement device 1y.

[0110] As described above, whether the internal trigger method or the external trigger method is used, it is not possible to improve measurement accuracy while simplifying the device configuration. Therefore, the measurement device according to the present disclosure generates a signal that can be used as a substitute for a trigger signal without adding any additional components or by simply adding small components, while suppressing the complexity of the configuration, thereby improving the measurement accuracy of the external trigger method. Specific embodiments of the measurement device according to the present disclosure will be described below.

[0111] First Embodiment First, a measurement device according to a first embodiment will be described with reference to Fig. 7. Fig. 7 is a diagram showing the configuration of a measurement device 1 according to the first embodiment.

[0112] 7, the measurement device 1 differs from the measurement device 1y shown in FIG. 6A in that the measurement device 1 includes a signal processing circuit 80 and a mixer 110 instead of the signal processing circuit 80y. The following description will focus on the differences with the measurement device 1x, and the description of the commonalities will be omitted or simplified.

[0113] The mixer 110 generates a difference frequency signal between the first high frequency signal output from the first RF oscillator 90 and the second high frequency signal output from the second RF oscillator 91. The difference frequency signal has a frequency f ｒｅｐ１ and the frequency f of the second high frequency signal ｒｅｐ２ δf, which is the difference between ｒｅｐ The mixer 110 outputs the generated difference frequency signal to the signal processing circuit 80.

[0114] Specifically, the mixer 110 is an integrated circuit including a first input terminal, a second input terminal, and an output terminal. The first input terminal is connected to the output terminal of the first RF oscillator 90, and outputs a frequency f ｒｅｐ１The second input terminal is connected to the output terminal of the second RF oscillator 91, and a first high frequency signal of frequency f ｒｅｐ２ The output terminal is connected to the signal processing circuit 80 and receives a second high frequency signal of frequency δf ｒｅｐ (=f ｒｅｐ２ -f ｒｅｐ１ ) is supplied to the signal processing circuit 80.

[0115] The signal processing circuit 80 corresponds to the signal processing circuit 80y, and differs in that it uses the difference frequency signal generated by the mixer 110 as a trigger signal. That is, the signal processing circuit 80 acquires a detection signal using the difference frequency signal generated by the mixer 110 as a trigger. The signal processing circuit 80 measures the distance from the measurement device 1 to the object 60 based on the acquired detection signal. Specifically, the signal processing circuit 80 determines the signal acquisition period T based on the point in time when the signal level of the difference frequency signal exceeds a threshold. ｍ The signal processing circuit 80 sets the acquisition period T ｍ The signal processing circuit 80 obtains the pulse waveforms of the reference signal and the measurement signal by sampling each of the reference signal and the measurement signal within the measurement device 1. The signal processing circuit 80 calculates the peak position of each pulse waveform, thereby measuring the distance from the measurement device 1 to the object 60.

[0116] The difference frequency signal output from the mixer 110 is δf ｒｅｐ As a result, the signal processing circuit 80 performs substantially the same processing as the signal processing circuit 80y. In other words, the signal processing circuit 80 performs processing similar to that of the external trigger method, thereby improving measurement accuracy.

[0117] As described above, in the measurement apparatus 1 according to this embodiment, the first RF oscillator 90 and the second RF oscillator 91 for HML, which stabilizes the repetition frequency, are also used to generate trigger signals. The measurement apparatus 1 only needs to include a mixer 110 that is smaller than the function generator 100, which allows for a more compact measurement apparatus 1. Furthermore, the use of an external trigger system allows for improved measurement accuracy. In other words, a measurement apparatus 1 that can improve measurement accuracy with a simple configuration can be realized.

[0118] Second Embodiment Next, a measurement device according to a second embodiment will be described with reference to Fig. 8. Fig. 8 is a diagram showing the configuration of a measurement device 2 according to the second embodiment.

[0119] 8, the measuring device 2 differs from the measuring device 1y shown in Fig. 6A in that the measuring device 2 includes a second RF oscillator 92, a signal processing circuit 82, and a mixer 111 instead of the second RF oscillator 91 and the signal processing circuit 80y. The following description will focus on the differences with the measuring device 1x, and the description of the commonalities will be omitted or simplified.

[0120] The second RF oscillator 92 generates a second high frequency signal for controlling the repetition frequency of the second optical comb laser light 21L emitted by the second laser light source 21. In this embodiment, the second high frequency signal is not directly supplied to the second laser light source 21 but is supplied via a mixer 111. Specifically, the second high frequency signal is δf ｒｅｐ It is a high frequency signal having a frequency of

[0121] The mixer 111 generates a sum frequency signal from the first high frequency signal output from the first RF oscillator 90 and the second high frequency signal output from the second RF oscillator 92. The sum frequency signal has a frequency f ｒｅｐ１ and the frequency δf of the second high frequency signal ｒｅｐ f is the sum of ｒｅｐ２ (=f ｒｅｐ１ +δf ｒｅｐ The mixer 111 supplies the generated sum frequency signal to the second laser light source 21. The second laser light source 21 receives a high-frequency signal having a frequency of f ｒｅｐ２Since a high frequency signal having a frequency f is supplied, similar to the measuring device 1x, ｒｅｐ２ This makes HTML possible.

[0122] Specifically, the mixer 111 is an integrated circuit including a first input terminal, a second input terminal, and an output terminal. The first input terminal is connected to the output terminal of the first RF oscillator 90, and outputs a frequency f ｒｅｐ１ The second input terminal is connected to the output terminal of the second RF oscillator 92, and a first high frequency signal of frequency δf ｒｅｐ The output terminal is connected to the saturable absorber 11sa of the second laser light source 21, and a second high frequency signal of frequency f ｒｅｐ２ (=f ｒｅｐ１ +δf ｒｅｐ ) is supplied to the saturable absorber 11sa of the second laser light source 21.

[0123] In this embodiment, the second RF oscillator 92 outputs a frequency δf ｒｅｐ The signal processing circuit 82 corresponds to the signal processing circuit 80y, and differs in that it uses the second high-frequency signal generated by the second RF oscillator 92 as a trigger signal. In other words, the signal processing circuit 82 acquires a detection signal using the second high-frequency signal generated by the second RF oscillator 92 as a trigger. The signal processing circuit 82 measures the distance from the measuring device 2 to the object 60 based on the acquired detection signal. Specifically, the signal processing circuit 82 determines the signal acquisition period T based on the point in time when the signal level of the second high-frequency signal exceeds a threshold. ｍ The signal processing circuit 82 sets the acquisition period T ｍ The signal processing circuit 82 obtains the pulse waveforms of the reference signal and the measurement signal by sampling each of the reference signal and the measurement signal within the measurement device 2. The signal processing circuit 82 calculates the peak position of each pulse waveform, thereby measuring the distance from the measurement device 2 to the object 60.

[0124] The second RF signal output from the second RF oscillator 92 has a frequency of δf ｒｅｐAs a result, the signal processing circuit 82 performs substantially the same processing as the signal processing circuit 80y. In other words, the signal processing circuit 82 performs processing similar to that of the external trigger method, thereby improving measurement accuracy.

[0125] As described above, in the measurement device 2 according to this embodiment, the second RF oscillator 92 for HML, which stabilizes the repetition frequency, is also used to generate a trigger signal. The measurement device 2 only needs to include a mixer 111 that is smaller than the function generator 100, which allows for a more compact measurement device 2. Furthermore, the use of an external trigger system allows for improved measurement accuracy. In other words, a measurement device 2 that can improve measurement accuracy with a simple configuration can be realized.

[0126] While the measurement device according to one or more aspects has been described above based on the embodiments, the present disclosure is not limited to these embodiments. As long as they do not deviate from the gist of the present disclosure, various modifications conceivable by those skilled in the art to the present embodiments and configurations constructed by combining components of different embodiments are also included within the scope of the present disclosure.

[0127] For example, the frequency of the first high frequency signal, i.e., the repetition frequency f ｒｅｐ１ is the frequency of the second high frequency signal, that is, the repetition frequency f of the second output light ｒｅｐ２ The magnitude relationship is not particularly limited as long as it is different from f ｒｅｐ１ is f ｒｅｐ２ It may be smaller or larger.

[0128] Furthermore, various modifications, substitutions, additions, omissions, etc. can be made to each of the above-described embodiments within the scope of the claims or their equivalents.

[0129] A measurement device according to the present disclosure can be used for various measurement purposes such as distance measurement, displacement measurement, etc. For example, a measurement device according to the present disclosure can be used as a displacement meter, a shape inspection device, etc.

[0130] 1, 1x, 1y, 2 Measuring device 10 Laser light source 11 Resonator 11d１ n-doped layer 11d ２ , 11d ３ p-doped layer 11g gain medium 11i intermediate layer 11m １ First mirror 11m ２ Second mirror 11s Semiconductor layer 11sa Saturable absorber 11w Optical waveguide 12 Semiconductor substrate 12a High refractive index layer 12b Low refractive index layer 13 Protective layer 14 Output light 20 First laser light source 20L First optical comb laser light 20Lr, 20Lt, 21Lr, 21Lt Light 21 Second laser light source 21L Second optical comb laser light 20R Reflected light 30, 31, 32, 33 Coupler 40 Circulator 50 Collimator 60 Object 70, 71 Detector 80, 80x, 80y, 82 Signal processing circuit 90 First RF oscillator 91, 92 Second RF oscillator 100 Function generator 110, 111 Mixer

Claims

1. A measurement device comprising: a first mode-locked laser light source that emits first output light; a second mode-locked laser light source that emits second output light; a first RF oscillator that outputs a first high-frequency signal for controlling the repetition frequency of the first output light; a second RF oscillator that outputs a second high-frequency signal for controlling the repetition frequency of the second output light; a detector that detects interference light generated by interference between the first output light and the second output light and outputs a detection signal; and a signal processing circuit that acquires the detection signal using the second high-frequency signal as a trigger or a signal generated using the first high-frequency signal and the second high-frequency signal as a trigger.

2. The measurement device according to claim 1, wherein the first mode-locked laser light source and the second mode-locked laser light source are both optical frequency comb light sources.

3. The measurement device according to claim 1, wherein the first mode-locked laser light source and the second mode-locked laser light source are integrated on the same semiconductor substrate.

4. The measurement device according to claim 1, wherein the first mode-locked laser light source and the second mode-locked laser light source are integrated on different semiconductor substrates.

5. A measurement device according to any one of claims 1 to 4, wherein the first mode-locked laser light source includes a first saturable absorber, the first RF oscillator supplies the first high-frequency signal to the first saturable absorber, the second mode-locked laser light source includes a second saturable absorber, and the second RF oscillator supplies the second high-frequency signal to the second saturable absorber.

6. The measuring device according to claim 5, further comprising a mixer that generates a difference frequency signal having a frequency that is the difference between the frequency of the first high-frequency signal and the frequency of the second high-frequency signal, and the signal processing circuit acquires the detection signal using the difference frequency signal generated by the mixer as the trigger.

7. A measurement device according to any one of claims 1 to 4, further comprising a mixer that generates a sum frequency signal having a frequency that is the sum of the frequency of the first high frequency signal and the frequency of the second high frequency signal, wherein the first mode-locked laser light source includes a first saturable absorber, the first RF oscillator supplies the first high frequency signal to the first saturable absorber, the second mode-locked laser light source includes a second saturable absorber, and the mixer supplies the sum frequency signal to the second saturable absorber.

8. The measuring device according to claim 7, wherein the signal processing circuit acquires the detection signal using the second high-frequency signal as the trigger.

9. The measuring device according to any one of claims 1 to 4, wherein the signal processing circuit acquires the waveform of the detection signal at a predetermined sampling period, and the period at which the signal processing circuit acquires the detection signal is different from the sampling period.

10. A measuring device as described in any one of claims 1 to 4, wherein the interference light is interference light generated by interference between the second output light and light of the first output light reflected by an object, and the signal processing circuit measures the distance from the measuring device to the object based on the detection signal acquired by the signal processing circuit.

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