Measuring device and measuring method

Abstract

A measuring device (100) comprises: a first laser light source (10), which is a mode-locked laser light source having a gain medium, and which emits a first laser beam; a second laser light source (20), which is a mode-locked laser light source having a gain medium, and which emits a second laser beam; a detector (70) that detects at least one of the first laser beam, the second laser beam, and beat light generated by the first laser beam and the second laser beam; and feedback circuits (90, 91) that change the optical spectrum of at least one of the first laser beam and the second laser beam on the basis of the intensity of a signal output from the detector (70).

Description

Measuring device and measuring method

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

[0002] Conventionally, laser light sources known as optical frequency comb lasers or simply optical comb lasers have been known. Specifically, optical frequency comb lasers are light sources that output laser light whose pulse waveforms are evenly spaced on the time axis and whose spectrum is evenly spaced on the frequency axis. This laser light is also called an optical comb.

[0003] For example, Patent Document 1 discloses a carrier envelope offset frequency (f ＣＥＯ A coherent dual scanning laser system is disclosed that controls the difference between the laser power and the laser beam power to stabilize the difference between the laser power and the laser beam power.

[0004] Special Publication No. 2012-519879

[0005] However, as in the above-described conventional technology, simply stabilizing the difference in carrier-envelope offset frequency may not be enough to accurately detect the output light with a detector. A decrease in detection accuracy by the detector leads to a decrease in measurement accuracy by the measurement device.

[0006] Therefore, the present disclosure provides a measurement device and a measurement method that can improve measurement accuracy.

[0007] A measurement device according to one aspect of the present disclosure includes: a first laser light source that is a mode-locked laser light source having a gain medium and emits a first laser light; a second laser light source that is a mode-locked laser light source having a gain medium and emits a second laser light; at least one first detector that detects at least one of the first laser light, the second laser light, and beat light generated by the first laser light and the second laser light; and a feedback circuit that changes the optical spectrum of at least one of the first laser light and the second laser light based on the intensity of a signal output from the at least one first detector.

[0008] A measurement method according to one aspect of the present disclosure includes detecting, with a detector, at least one of a first laser light emitted by a first laser light source that is a mode-locked laser light source having a gain medium, a second laser light emitted by a second laser light source that is a mode-locked laser light source having a gain medium, and beat light generated by the first laser light and the second laser light; and changing an optical spectrum of at least one of the first laser light and the second laser light based on an intensity of a signal output from the detector.

[0009] Furthermore, one aspect of the present disclosure can be realized as a program that causes a computer to execute the measurement method, or as a computer-readable non-transitory recording medium storing the program.

[0010] According to the present disclosure, measurement accuracy can be improved.

[0011] FIG. 1A is a diagram schematically illustrating an example of a time change in the electric field of an optical comb. FIG. 1B is a diagram schematically illustrating the frequency spectrum of the optical comb. FIG. 2 is a diagram illustrating the frequency spectra of the first and second optical combs in a dual comb, and the interference light generated by the interference between these two optical combs. FIG. 3 is a diagram for explaining a problem that may occur in a dual comb. FIG. 4 is a diagram illustrating a configuration of a measurement apparatus according to a first embodiment. FIG. 5 is a flowchart illustrating the operation of the measurement apparatus according to the first embodiment. FIG. 6 is a diagram illustrating a configuration of a measurement apparatus according to a second embodiment. FIG. 7 is a diagram illustrating the relationship between the frequency spectrum of the first optical comb and the frequency spectrum of the second optical comb and the bandpass filter. FIG. 8 is a flowchart illustrating the operation of the measurement apparatus according to the second embodiment. FIG. 9 is a diagram illustrating the configuration of a measurement apparatus according to a modification of the embodiment. FIG. 10 is a diagram illustrating the relationship between the frequency spectrum of the first optical comb and the frequency spectrum of the second optical comb and the bandpass filter. FIG. 11 is a flowchart illustrating the operation of the measurement apparatus according to a modification of the embodiment.

[0012] (Summary of the Present Disclosure) A measurement device according to a first aspect of the present disclosure includes: a first laser light source that is a mode-locked laser light source having a gain medium and emits a first laser light; a second laser light source that is a mode-locked laser light source having a gain medium and emits a second laser light; at least one first detector that detects at least one of the first laser light, the second laser light, and beat light generated by the first laser light and the second laser light; and a feedback circuit that changes the optical spectrum of at least one of the first laser light and the second laser light based on the intensity of a signal output from the at least one first detector.

[0013] This allows the overlap of the frequency bands of the first laser beam and the second laser beam to be increased by changing the optical spectrum of at least one of the first laser beam and the second laser beam. This increases the intensity of the beat light generated by the first laser beam and the second laser beam, thereby improving measurement accuracy. Furthermore, since a spectrometer is not required, the measurement device can be made smaller and the amount of calculation required can be reduced.

[0014] A measurement device according to a second aspect of the present disclosure is the measurement device according to the first aspect, and in the second aspect, the first laser light source and the second laser light source may be integrated on the same semiconductor substrate.

[0015] A measurement device according to a third aspect of the present disclosure is the measurement device according to the first aspect, and in the third aspect, the first laser light source may be arranged on a semiconductor substrate different from the semiconductor substrate on which the second laser light source is arranged.

[0016] The second and third aspects enable the miniaturization of the measurement device. Note that the frequency band of a laser light source integrated on a semiconductor substrate is prone to deviation from a desired value due to process errors and the like. Therefore, the overlap between the frequency bands of the first laser light and the second laser light is likely to be small. Therefore, the effect of improving measurement accuracy by changing the optical spectrum is more effective.

[0017] A measurement device according to a fourth aspect of the present disclosure is the measurement device according to any one of the first to third aspects, and in the fourth aspect, the feedback circuit may change the optical spectrum at a frequency higher than a repetition frequency of at least one of the first laser light and the second laser light.

[0018] This allows the optical spectrum to be changed so that the overlap between the first laser beam and the second laser beam is large even when the frequency bands of the first laser beam and the second laser beam are significantly different from each other, thereby improving measurement accuracy.

[0019] A measurement device according to a fifth aspect of the present disclosure is a measurement device according to any one of the first to fourth aspects, and in the fifth aspect, the intensity of the signal output from the at least one first detector may be a peak intensity of a pulse of light detected by the at least one first detector.

[0020] This makes it possible to realize a measurement device with a simple configuration and high measurement accuracy without using a spectroscope.

[0021] A measurement device according to a sixth aspect of the present disclosure is a measurement device according to any one of the first to fourth aspects, and may further include at least one bandpass filter, and the at least one bandpass filter may be positioned so that light that has passed through the at least one bandpass filter is incident on the at least one first detector, and the intensity of the signal output from the at least one first detector may be the intensity of light that has passed through the at least one bandpass filter.

[0022] This makes it possible to realize a measurement device with a simple configuration and high measurement accuracy without using a spectroscope.

[0023] A measurement device according to a seventh aspect of the present disclosure is the measurement device according to any one of the first to sixth aspects, and in the seventh aspect, the feedback circuit may change the optical spectrum by adjusting the amount of current applied to the gain medium.

[0024] This makes it possible to effectively change the optical spectrum of the laser light emitted by the so-called on-chip comb.

[0025] A measuring device according to an eighth aspect of the present disclosure is a measuring device according to any one of the first to seventh aspects, and may further include a second detector that detects interference light generated by interference between the second laser light and reflected light generated by reflection of the first laser light by an object, and a signal processing unit that calculates the distance from the measuring device to the object based on a signal output from the second detector.

[0026] This allows the distance from the measurement device to be measured, so the measurement device can be used for distance measurement and measurement of the surface shape of the object.

[0027] A measuring device according to a ninth aspect of the present disclosure is a measuring device according to any one of the first to eighth aspects, and may further include a signal processing unit that calculates the distance from the measuring device to an object based on the signal output from the at least one first detector.

[0028] This allows the first detector to be used for both distance measurement and feedback, thereby realizing a miniaturized measurement device according to this aspect.

[0029] A measuring device according to a tenth aspect of the present disclosure may be the measuring device according to the sixth aspect, further comprising: a second detector that detects interference light generated by interference between the second laser light and reflected light generated by reflection of the first laser light by an object; a third detector that detects interference light generated by interference between the first laser light and the second laser light; and a signal processing unit that calculates the distance from the measuring device to the object based on a signal output from the second detector and a signal output from the third detector.

[0030] This allows the distance from the measurement device to be measured, so the measurement device can be used for distance measurement, measuring the surface shape of the object, etc. Furthermore, by providing separate detectors for distance measurement and feedback, it is possible to use detectors suited to each purpose.

[0031] A measurement device according to an eleventh aspect of the present disclosure is the measurement device according to the tenth aspect, wherein in the eleventh aspect, the at least one first detector may include a plurality of first detectors, the at least one bandpass filter may include a plurality of bandpass filters, one of the plurality of first detectors may detect the first laser light that has passed through a corresponding bandpass filter of the plurality of bandpass filters, and another of the plurality of first detectors may detect the second laser light that has passed through a corresponding bandpass filter of the plurality of bandpass filters.

[0032] This makes it possible to obtain the intensities of the component lights of the first laser light and the second laser light that have passed through the bandpass filters, and to easily adjust the optical spectrum.

[0033] A measurement device according to a twelfth aspect of the present disclosure is the measurement device according to the tenth aspect, wherein in the twelfth aspect, the at least one first detector may detect the beat light generated by the first laser light and the second laser light that have passed through the at least one bandpass filter.

[0034] This allows the number of detectors and bandpass filters to be reduced, thereby realizing a miniaturized measurement device.

[0035] A measurement method according to a thirteenth aspect of the present disclosure includes detecting, with a detector, at least one of a first laser light emitted by a first laser light source that is a mode-locked laser light source having a gain medium, a second laser light emitted by a second laser light source that is a mode-locked laser light source having a gain medium, and beat light generated by the first laser light and the second laser light; and changing an optical spectrum of at least one of the first laser light and the second laser light based on an intensity of a signal output from the detector.

[0036] This makes it possible to improve measurement accuracy, similar to the measurement devices according to the above-described aspects.

[0037] Hereinafter, the embodiments will be specifically described with reference to the drawings.

[0038] 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.

[0039] 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.

[0040] 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.

[0041] 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.

[0042] First Embodiment [Optical Comb Laser] First, the basic principle of an optical comb laser will be briefly described with reference to FIGS. 1A and 1B.

[0043] FIG. 1A is a diagram showing an example of the temporal change in the electric field of an optical frequency comb. In FIG. 1A, the horizontal axis represents time, and the vertical axis represents the electric field of the optical frequency comb. Note that the optical frequency comb is also called an optical frequency comb, an optical frequency comb laser light, or an optical frequency comb laser light. In this specification, it may also be simply referred to as laser light.

[0044] As shown in FIG. 1A, the optical frequency comb has a repetition period T ｒｅｐ It is formed from a train of optical pulses generated at a repetition period T ｒｅｐis, 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.

[0045] 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. ｐ The 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

[0046] 1B is a diagram showing a frequency spectrum of an optical frequency comb, in which the horizontal axis represents frequency and the vertical axis represents intensity of the optical frequency comb.

[0047] As shown in Figure 1B, the optical frequency comb has a comb-like frequency spectrum formed from 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.

[0048] If the full width at half maximum of the optical comb is Δf, then Δf = 1 / Δt. The full width at half maximum of the optical comb Δf 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 ｒｅｐ The carrier envelope offset frequency f ＣＥＯ is the 0th mode frequency, the nth mode frequency fn in the optical comb is f ｎ = f ＣＥＯ +nf ｒｅｐ The electric field of the optical comb shown in FIG. 1A is expressed by the nth mode frequency f ｎ The amplitude and phase of the electric field at E ｎ and φ ｎ Then, E(t) = ΣnE ｎ exp[-i(2πf ｎ t+φ ｎ ) ].

[0049] [Dual Comb] Next, the principle of the dual comb will be briefly explained with reference to FIG.

[0050] 2 shows the frequency spectrum of the first and second optical combs in the dual comb, as well as the frequency spectrum of the interference light generated by the interference of these two optical combs. １ｎ is f １ｎ = f ＣＥＯ１ +nf ｒｅｐ１ In the second optical comb, the nth mode frequency f ２ｎ is f ２ｎ = f ＣＥＯ２ +nf ｒｅｐ２ It is represented by f ＣＥＯ１ is the carrier envelope offset frequency of the first optical comb. ＣＥＯ２ is the carrier envelope offset frequency of the second optical comb.ｒｅｐ１ is the repetition frequency of the first optical comb. ｒｅｐ２ is the repetition frequency of the second optical comb. ｒｅｐ１ and f ｒｅｐ２ are different from each other, and f ｒｅｐ２ = f ｒｅｐ１ +δf ｒｅｐ The following relationship holds: δf ｒｅｐ is f ｒｅｐ１ is much smaller than δf ｒｅｐ is, for example, 1 Hz or more and 10 MHz or less.

[0051] Each of the multiple frequency peaks included in the frequency spectrum of the first optical comb interferes with the closest frequency peak among the multiple frequency peaks included in the frequency spectrum of the second optical comb, resulting in detection of interference light having a frequency spectrum as shown in the lower part of Figure 2. The detected interference light is beat light generated by the first optical comb and the second optical comb. This interference light, or beat light, is also called a dual comb signal. The frequency interval of the interference light is 1 / 2 times the repetition frequency f of the first optical comb. ｒｅｐ１ and the repetition frequency f of the second optical comb ｒｅｐ２ δf, which is the difference between ｒｅｐ A typical detector does not have a high enough resolution to detect each individual frequency peak, and therefore the detector detects a spectrum with the shape shown by the dashed line in FIG.

[0052] FIG. 3 is a diagram illustrating potential issues that may occur with dual combs. In the example shown in FIG. 3, unlike the example shown in FIG. 2, there is little overlap between the frequency bands of the spectrum of the first optical comb and the frequency bands of the spectrum of the second optical comb. The frequency band of the spectrum can be considered as the range between the two ends of the dashed line in the figure. When there is little overlap between the frequency bands, there are fewer interfering frequency peaks. This results in a narrower frequency spectrum band and lower intensity of the dual comb signal. The peak intensity of the pulses in the time waveform is also lower.

[0053] Therefore, when measuring a dual comb signal, it is necessary to adjust the optical spectrum of at least one of the first and second optical combs so that the frequency spectrum of the first and second optical combs overlaps greatly. In reality, interference occurs even in non-overlapping regions, but this is difficult to detect with a general detector, leading to a decrease in measurement accuracy.

[0054] As will be described in detail later, a mode-locked laser light source having a gain medium can be used as each light source for the first and second optical combs. By using the same gain medium for each of the two mode-locked laser light sources, the overlap in the frequency bands of the spectra of the two optical combs can be sufficiently large. However, when a laser light source integrated on a semiconductor substrate, known as an on-chip comb, is used as the mode-locked laser light source, it is difficult to form the same gain medium due to process errors, etc. As a result, even if the two on-chip combs are driven under the same driving conditions, the overlap in the frequency bands of the two optical combs may be small.

[0055] In order to check the overlap of optical spectra before measurement, it is necessary to check the spectra using a spectrometer. However, using a spectrometer leads to an increase in the size of the measurement device and an increase in power consumption due to an increase in the amount of calculation. For this reason, there is a demand for a simple means for adjusting the optical spectrum without using a spectrometer. Below, a measurement device according to a first embodiment will be described, which can adjust the optical spectrum without using a spectrometer and improve measurement accuracy.

[0056] [Configuration] Fig. 4 is a diagram showing the configuration of the measurement device 100 according to the first embodiment. First, an example of the basic configuration of the measurement device 100 according to the present embodiment will be described with reference to Fig. 4. The measurement device 100 measures the distance from the measurement device 100 to the object 60, that is, performs distance measurement. Alternatively, the measurement device 100 may inspect the shape of the object 60.

[0057] As shown in FIG. 4 , the measurement device 100 includes a first laser light source 10, a second laser light source 20, detectors 70 and 71, a signal processing unit 80, and feedback circuits 90 and 91. The measurement device 100 also includes couplers 30, 31, 32, and 33, a circulator 40, and a collimator 50 as optical elements for adjusting the optical path. In FIG. 4 , the dashed lines connecting the rectangular or circular blocks representing the components represent optical fibers that transmit light. The solid lines connecting the rectangular blocks representing the components represent signal lines that transmit electrical signals. The signal lines are wired, but may also be wireless. This also applies to FIGS. 6 and 9 , which will be described later.

[0058] The first laser light source 10 is an example of a mode-locked laser light source including a gain medium. The first laser light source 10 outputs a first optical comb 10L as output light. The first optical comb 10L has a repetition frequency of f ｒｅｐ１ and the carrier envelope offset frequency is f ＣＥＯ１ It is a laser beam.

[0059] The second laser light source 20 is an example of a mode-locked laser light source including a gain medium. The second laser light source 20 outputs a second optical comb 20L as output light. The second optical comb 20L has a different repetition frequency from the first optical comb 10L. For example, as shown in the middle part of FIG. 2, the second optical comb 20L has a repetition frequency of f ｒｅｐ２ and the carrier envelope offset frequency is f ＣＥＯ２ It is a laser beam.

[0060] In this embodiment, the first laser light source 10 and the second laser light source 20 are on-chip combs. That is, the first laser light source 10 and the second laser light source 20 are each integrated on a semiconductor substrate. The semiconductor substrate on which the first laser light source 10 is integrated and the semiconductor substrate on which the second laser light source 20 is integrated may be the same or different. In other words, the first laser light source 10 and the second laser light source 20 may be integrated on the same semiconductor substrate, or the first laser light source 10 may be arranged on a semiconductor substrate different from the semiconductor substrate on which the second laser light source 20 is arranged.

[0061] An on-chip comb includes, for example, an optical waveguide with mirrors at both ends and a resonator including a gain medium and a saturable absorber disposed between the mirrors. The gain medium stimulates light emission when an electric charge is supplied. The stimulated emission light is repeatedly reflected between the mirrors at both ends of the optical waveguide. During this repeated reflection, the light is amplified by passing through the gain medium multiple times. The amplified light is then mode-locked by the saturable absorber to form an optical pulse train. One of the two mirrors disposed at both ends of the optical waveguide has a lower reflectivity than the other, and emits a portion of the light from the optical waveguide to the outside as laser light, i.e., an optical comb. Note that this configuration of an on-chip comb is merely an example, and the configuration is not particularly limited as long as it can emit an optical comb.

[0062] Each of the couplers 30, 31, 32, and 33 is an optical element that splits or combines light.

[0063] The circulator 40 is an optical element that controls the traveling direction of light.

[0064] 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.

[0065] The detectors 70 and 71 are optical elements that convert incident light into electric charges to generate and output electrical signals. The signal level of the electrical signals corresponds to the intensity of the incident light. The detectors 70 and 71 are photoelectric conversion elements such as photodiodes and phototransistors.

[0066] The detector 70 is an example of a first detector in the present disclosure and detects at least one of the first laser light emitted by the first laser light source 10, the second laser light emitted by the second laser light source 20, and beat light generated by the first laser light and the second laser light. The term "first laser light" refers not only to light immediately after being emitted from the first laser light source 10 (specifically, the first optical comb 10L), but also to light originating from the first laser light source 10 in general. That is, the term "first laser light" also refers to light after the first optical comb 10L emitted from the first laser light source 10 has undergone optical changes such as demultiplexing, multiplexing, reflection, and focusing (specifically, the light 10Lt and 10Lr, and the reflected light 10R). Similarly, the term "second laser light" not only refers to light immediately after being emitted from the second laser light source 20 (specifically, the second optical comb 20L), but also to light originating from the second laser light source 20 in general. In other words, the second laser light also means the light (specifically, light 20Lt and 20Lr) after the second optical comb 20L emitted from the second laser light source 20 has undergone optical changes such as demultiplexing, multiplexing, reflection, and focusing.

[0067] Detector 70 is also an example of a third detector in the present disclosure, and detects interference light generated by interference between the first laser light and the second laser light. The interference light detected by detector 70 is beat light generated by the first laser light and the second laser light. Specifically, detector 70 detects interference light generated by interference between light 10Lr and light 20Lr.

[0068] The detector 71 is an example of a second detector in the present disclosure, and detects interference light generated by interference between the second laser light and reflected light generated by reflection of the first laser light by the object 60. The interference light detected by the detector 71 is beat light generated by the first laser light and the second laser light. Specifically, the detector 71 detects interference light generated by interference between the reflected light 10R and the light 20Lt.

[0069] The signal processing unit 80 processes signals output from each of the detectors 70 and 71. In this embodiment, a dual comb signal is output from each of the detectors 70 and 71. For example, the signal processing unit 80 calculates the distance from the measurement device to the object 60 based on the dual comb signals output from each of the detectors 70 and 71. The signal processing unit 80 may calculate the distance from the measurement device to each portion on the surface of the object 60. This allows the signal processing unit 80 to obtain information about the surface shape of the object 60.

[0070] The feedback circuit 90 changes the optical spectrum of the first optical comb 10L based on the intensity of the signal output from the detector 70. The feedback circuit 91 changes the optical spectrum of the second optical comb 20L based on the intensity of the signal output from the detector 70. In this embodiment, the intensity of the signal output from the detector 70 is the peak intensity of the pulse of the light detected by the detector 70. Specifically, the intensity of the signal output from the detector 70 is the peak intensity of the pulse of the beat light.

[0071] For example, when the intensity of the signal output from the detector 70 is smaller than a threshold, the feedback circuit 90 changes the center wavelength of the first optical comb 10L by changing the value of the current applied to the gain medium of the first laser light source 10. When the intensity of the signal output from the detector 70 is smaller than a threshold, the feedback circuit 91 changes the center wavelength of the second optical comb 20L by changing the value of the current applied to the gain medium of the second laser light source 20.

[0072] The center wavelength of the first optical comb 10L corresponds to the center frequency of the frequency band of the first optical comb 10L. The center frequency is the midpoint between the high-frequency end and the low-frequency end of the frequency band. Alternatively, the center wavelength of the first optical comb 10L may be considered to correspond to the frequency of the frequency component with the highest intensity among the multiple frequency components included in the first optical comb 10L. The same applies to the center wavelength of the second optical comb 20L.

[0073] The amount of change in the optical spectrum is expressed by the amount of deviation of the center frequency or the amount of deviation of the center wavelength. For example, the feedback circuit 90 adjusts the repetition frequency f ｒｅｐ１ and the repetition frequency f of the second optical comb 20L ｒｅｐ２ The feedback circuit 91 changes the optical spectrum of the first optical comb 10L at a frequency greater than at least one of the repetition frequency f ｒｅｐ１ and the repetition frequency f of the second optical comb 20L ｒｅｐ２ The optical spectrum of the second optical comb 20L is changed at a frequency higher than at least one of the frequencies.

[0074] The measurement device 100 may include only one of the feedback circuits 90 and 91. In other words, the measurement device 100 may include a feedback circuit that changes the optical spectrum of at least one of the first optical comb 10L and the second optical comb 20L based on the intensity of the signal output from the detector 70.

[0075] The signal processing unit 80 and the feedback circuits 90 and 91 are each 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 unit 80 and the feedback circuits 90 and 91 may be a microcontroller. The microcontroller includes, for example, a nonvolatile memory storing a program, a volatile memory serving as a temporary storage area for executing the program, input / output ports, and a processor for executing the program. The signal processing unit 80 and the feedback circuits 90 and 91 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 unit 80 and the feedback circuits 90 and 91 may be realized by software or hardware. The signal processing unit 80 and the feedback circuits 90 and 91 may be realized by a common hardware configuration. The feedback circuits 90 and 91 may include a current source for supplying a current to the gain medium.

[0076] Next, the main connections between the above-mentioned components will be described. Specifically, the connections between the components regarding the optical paths of the first optical comb 10L and the second optical comb will be described.

[0077] Many of the components included in the measurement device 100 are connected by optical fibers indicated by dashed lines in Fig. 4. 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 10 and the second laser light source 20 are connected to the ends of the optical fibers.

[0078] The first optical comb 10L is split into two light beams, light beam 10Lt and light beam 10Lr, by the coupler 30. The light beam 10Lt is an optical comb for measurement and is emitted toward the object 60. The light beam 10Lr is an optical comb for reference.

[0079] The light 10Lt passes through the circulator 40, is emitted from the collimator 50, and is incident on the object 60. The light 10Lt is then reflected by the object 60. The reflected light 10R generated by reflection from the object 60 is incident on the collimator 50 and then directed by the circulator 40 to the coupler 33. The light 10Lr is directed from the coupler 30 to the coupler 32.

[0080] On the other hand, the second optical comb 20L is split into two, light 20Lr and light 20Lt, by the coupler 31. The light 20Lt is an optical comb for measurement, and the light 20Lr is an optical comb for reference.

[0081] Light 20Lr is combined with light 10Lr by coupler 32 and travels toward detector 70. Light 20Lt is combined with reflected light 10R by coupler 33 and travels toward detector 71. These lights interfere with each other at detector 70 or 71, generating beat light, and the light information is converted into an electrical signal. The electrical signals output from detectors 70 and 71 are input to signal processing unit 80. The signal processing unit 80 performs arithmetic processing using the electrical signal output from detector 70 as a reference signal and the electrical signal output from detector 71 as a measurement signal, thereby calculating the distance from measurement device 100 to object 60.

[0082] [Operation] Next, an example of the operation of the measuring device 100 according to this embodiment will be described with reference to Fig. 5. Fig. 5 is a flowchart showing the operation of the measuring device 100 according to this embodiment. The operation shown in Fig. 5 is executed, for example, before measuring the object 60.

[0083] 5, first, the signal processing unit 80 acquires the dual comb signal output from the detector 70 (S10). Specifically, first, the first laser light source 10 emits the first optical comb 10L, and the second laser light source 20 emits the second optical comb 20L. The light 10Lr branched from the first optical comb 10L by the coupler 30 and the light 20Lr branched from the second optical comb 20L by the coupler 31 are each combined at the coupler 32 and enter the detector 70. The detector 70 converts the beat light generated by the incident light 10Lr and light 20Lr into an electrical signal by photoelectric conversion and outputs the electrical signal to the signal processing unit 80 as a dual comb signal.

[0084] Next, the signal processing unit 80 detects peaks of the pulse waveform in the acquired dual-comb signal (S12). Then, the signal processing unit 80 detects the intensity of the detected peaks (S14). The signal processing unit 80 outputs information indicating the peak intensity to the feedback circuits 90 and 91. Note that the detection of the peaks and the peak intensity may be performed by the feedback circuits 90 and 91.

[0085] Next, the feedback circuits 90 and 91 compare the peak intensity with a threshold value (S16). The threshold value is a predetermined value that is the lower limit of the peak intensity required to measure the object 60 with high accuracy. If the peak intensity is equal to or greater than the threshold value (No in S16), the object 60 can be measured, and the process ends. Note that the comparison of the peak intensity with the threshold value may be performed by the signal processing unit 80.

[0086] If the peak intensity is less than the threshold (Yes in S16), at least one of the feedback circuits 90 and 91 changes the optical spectrum of at least one of the first optical comb 10L and the second optical comb 20L (S18). Specifically, the center frequency (or center wavelength) of at least one of the first optical comb 10L and the second optical comb 20L is shifted so that the frequency bands of the first optical comb 10L and the second optical comb 20L overlap more. After changing the optical spectrum, the process from acquiring the dual comb signal (S10 to S18) is repeated until the peak intensity reaches or exceeds the threshold.

[0087] As described above, the measurement device 100 according to this embodiment changes the optical spectrum of at least one of the first optical comb 10L and the second optical comb 20L so that the peak intensity is equal to or greater than the threshold. This allows measurement to be performed in a state where interference light with the intensity required for measurement is obtained, thereby improving measurement accuracy.

[0088] In this embodiment, the feedback circuits 90 and 91 may change the optical spectrum based on the signal output from the detector 71. For example, the detector 71 detects light when a reflector that reflects the light 10Lt is placed between the collimator 50 and the object 60. The detector 71 detects beat light generated by the light 20Lt and the reflected light generated by the reflection of the light 10Lt by the reflector. Then, based on the intensity of the signal output from the detector 71, at least one of the feedback circuits 90 and 91 may change the optical spectrum of at least one of the first optical comb 10L and the second optical comb 20L. As in the case of measuring the object 60, the detector 71 may detect beat light generated by the reflected light 10R from the object 60 and the light 20Lt without placing a reflector.

[0089] Second Embodiment Next, a second embodiment will be described.

[0090] The main difference between the second embodiment and the first embodiment is that the measurement device includes a feedback detector and a bandpass filter arranged on the light incident side of the detector. The following description will focus on the differences from the first embodiment, and the description of the commonalities will be omitted or simplified.

[0091] Fig. 6 is a diagram showing the configuration of a measurement device 200 according to this embodiment. The measurement device 200 shown in Fig. 6 differs from the measurement device 100 shown in Fig. 4 mainly in that it includes couplers 34 and 35, detectors 72 and 73, a signal processing unit 81, and band-pass filters 210 and 211.

[0092] The couplers 34 and 35 are optical elements that split or combine light, respectively.

[0093] The coupler 34 is provided to split the light 10Lr, which is part of the first optical comb 10L emitted from the first laser light source 10. The coupler 34 is connected between the coupler 30 and each of the bandpass filter 210 and the coupler 32. The coupler 34 splits the light 10Lr from the coupler 30 into light 11Lr and light 12Lr. The light 11Lr is directed toward the bandpass filter 210. The light 12Lr is directed toward the coupler 32.

[0094] The location of the coupler 34 is not particularly limited as long as it can direct a portion of the first optical comb 10L to the bandpass filter 210. For example, the coupler 34 may be located between the first laser light source 10 and the coupler 30.

[0095] The coupler 35 is provided to split light 20Lr, which is part of the second optical comb 20L emitted from the second laser light source 20. The coupler 35 is connected between the coupler 31 and each of the bandpass filter 211 and the coupler 32. The coupler 35 splits the light 20Lr from the coupler 31 into light 21Lr and light 22Lr. The light 21Lr is directed toward the bandpass filter 211. The light 22Lr is directed toward the coupler 32. The light 22Lr is combined with light 12Lr at the coupler 32 and directed toward the detector 70.

[0096] The location of the coupler 35 is not particularly limited as long as it can direct a portion of the second optical comb 20L to the bandpass filter 211. For example, the coupler 35 may be located between the second laser light source 20 and the coupler 31.

[0097] The processing performed by the detectors 70 and 71 and the signal processing unit 80 is substantially the same as that in embodiment 1. In this embodiment, the detectors 70 and 71 and the signal processing unit 80 perform processing for measuring the object 60 without performing processing for adjusting the optical spectrum by the feedback circuits 90 and 91.

[0098] The detectors 72 and 73 are optical elements that convert incident light into electric charges to generate and output an electrical signal. The signal level of the electrical signal corresponds to the intensity of the incident light. The detectors 72 and 73 are photoelectric conversion elements such as photodiodes and phototransistors. The detectors 72 and 73 are each an example of a first detector in the present disclosure.

[0099] The detector 72 detects the first laser light that has passed through the corresponding bandpass filter. Specifically, the detector 72 detects the light 11Lr that has passed through the bandpass filter 210.

[0100] The detector 73 detects the second laser light that has passed through the corresponding band-pass filter. Specifically, the detector 73 detects the light 21Lr that has passed through the band-pass filter 211.

[0101] Each of the bandpass filters 210 and 211 has a passband that passes incident light and a stopband that suppresses the passage of incident light. The stopbands are provided on the high-frequency side (shorter wavelength side) and the low-frequency side (longer wavelength side) of the passband.

[0102] 7 shows the relationship between the frequency spectrum of the first optical comb 10L and the frequency spectrum of the second optical comb 20L and the bandpass filter. Specifically, the upper part of FIG. 7 shows the relationship between the light 11Lr, which is part of the first optical comb 10L, and the passband of the bandpass filter 210. The lower part of FIG. 7 shows the relationship between the light 21Lr, which is part of the second optical comb 20L, and the passband of the bandpass filter 211. In this embodiment, the passband of the bandpass filter 210 and the passband of the bandpass filter 211 are equal to each other.

[0103] The bandpass filter 210 is disposed on the light incident side of the detector 72. That is, the bandpass filter 210 is disposed so that light passing through the bandpass filter 210 enters the detector 72. A portion of the first optical comb 10L emitted by the first laser light source 10, specifically, the light 11Lr branched by the coupler 34, enters the bandpass filter 210. The detector 72 detects only the frequency component of the light 11Lr that passes through the bandpass filter 210. When the center frequency of the first optical comb 10L is included in the passband of the bandpass filter 210, the intensity of the light detected by the detector 72 increases. Furthermore, the closer the center frequency of the first optical comb 10L is to the center frequency of the passband of the bandpass filter 210, the stronger the intensity of the light detected by the detector 72 becomes.

[0104] The bandpass filter 211 is disposed on the light incident side of the detector 73. That is, the bandpass filter 211 is disposed so that light passing through the bandpass filter 211 enters the detector 73. A portion of the second optical comb 20L emitted by the second laser light source 20, specifically, the light 21Lr branched by the coupler 35, enters the bandpass filter 211. The detector 73 detects only the light of the frequency component that passes through the bandpass filter 211 from the light 21Lr. When the center frequency of the second optical comb 20L is included in the passband of the bandpass filter 211, the intensity of the light detected by the detector 73 increases. Furthermore, the closer the center frequency of the second optical comb 20L is to the center frequency of the passband of the bandpass filter 211, the stronger the intensity of the light detected by the detector 73 becomes.

[0105] The passband of the bandpass filter 210 is narrower than the frequency band of the spectrum of the first optical comb 10L. The passband of the bandpass filter 211 is narrower than the frequency band of the spectrum of the second optical comb 20L. For example, the passband of the bandpass filter 210 is 50% or less of the frequency band of the spectrum of the first optical comb 10L, but may be 40% or less, 30% or less, or 20% or less. As an example, the passband of the bandpass filter 210 is 10% of the frequency band of the spectrum of the first optical comb 10L. Similarly, the passband of the bandpass filter 211 is 50% or less of the frequency band of the spectrum of the second optical comb 20L, but may be 40% or less, 30% or less, or 20% or less. As an example, the passband of the bandpass filter 211 is 10% of the frequency band of the spectrum of the second optical comb 20L.

[0106] The cutoff shape of the pass band of each of the bandpass filters 210 and 211 is, for example, rectangular, but is not limited to this. The cutoff shape of the pass band of each of the bandpass filters 210 and 211 may be trapezoidal or curved. The pass band of a bandpass filter is the difference between the cutoff frequency on the high frequency side and the cutoff frequency on the low frequency side. The cutoff frequency is the frequency at which the transmittance is 50% of the maximum transmittance within the pass band.

[0107] The signal processing unit 81 processes the signals output from each of the detectors 72 and 73. In this embodiment, the detector 72 outputs a signal corresponding to the intensity of the light 11Lr that has passed through the band-pass filter 210. The detector 73 outputs a signal corresponding to the intensity of the light 21Lr that has passed through the band-pass filter 211. In this embodiment, the signal processing unit 81 calculates the sum (i.e., total value) of the intensity of the signal output from the detector 72 and the intensity of the signal detected by the detector 73. The signal processing unit 81 outputs information representing the calculated sum to each of the feedback circuits 90 and 91.

[0108] The signal processing unit 81 is realized by, for example, an LSI, which is an integrated circuit. The signal processing unit 81 may be realized by a hardware configuration common to the signal processing unit 80.

[0109] In this embodiment, the feedback circuit 90 changes the optical spectrum of the first optical comb 10L based on the intensities of the signals output from the detectors 72 and 73. The feedback circuit 91 changes the optical spectrum of the second optical comb 20L based on the intensities of the signals output from the detectors 72 and 73. The intensity of the signal output from the detector 72 is the intensity of light that has passed through the bandpass filter 210. The intensity of the signal output from the detector 73 is the intensity of light that has passed through the bandpass filter 211.

[0110] For example, the feedback circuits 90 and 91 compare the sum of the intensities of the light beams passing through the bandpass filter 210 or 211 with a threshold value based on information output from the signal processing unit 81. If the sum of the intensities is smaller than the threshold value, the feedback circuit 90 changes the current value applied to the gain medium of the first laser light source 10 to change the center wavelength of the first optical comb 10L. If the sum of the intensities is smaller than the threshold value, the feedback circuit 91 changes the current value applied to the gain medium of the second laser light source 20 to change the center wavelength of the second optical comb 20L.

[0111] [Operation] Next, an example of the operation of the measuring device 200 according to this embodiment will be described with reference to Fig. 8. Fig. 8 is a flowchart showing the operation of the measuring device 200 according to this embodiment. The operation shown in Fig. 8 is executed, for example, before measuring the target object 60.

[0112] 8 , first, the signal processing unit 81 acquires an optical signal that has passed through the bandpass filter 210 or the bandpass filter 211 (S20). Specifically, first, the first laser light source 10 emits the first optical comb 10L, and the second laser light source 20 emits the second optical comb 20L. Of the first optical comb 10L, light 11Lr branched by the couplers 30 and 34 enters the detector 72 via the bandpass filter 210. Of the second optical comb 20L, light 21Lr branched by the couplers 31 and 35 enters the detector 73 via the bandpass filter 211. The detectors 72 and 73 each convert the incident light into an electrical signal and output it to the signal processing unit 81.

[0113] Next, the signal processing unit 81 calculates the sum of the intensities of the two acquired signals (S22). Then, the signal processing unit 81 outputs information representing the sum to the feedback circuits 90 and 91. Note that the calculation of the sum of the intensities may be performed by the feedback circuits 90 and 91.

[0114] Next, the feedback circuits 90 and 91 compare the total intensity value with a threshold value (S24). The threshold value is a predetermined value that is the lower limit of the intensity required to measure the object 60 with high accuracy. If the total intensity value is equal to or greater than the threshold value (No in S24), the object 60 can be measured, and the process ends. Note that the comparison of the total intensity value with the threshold value may be performed by the signal processing unit 81.

[0115] If the sum of the intensities is less than the threshold (Yes in S24), at least one of the feedback circuits 90 and 91 changes the optical spectrum of at least one of the first optical comb 10L and the second optical comb 20L (S26). Specifically, the center frequency (or center wavelength) of at least one of the first optical comb 10L and the second optical comb 20L is shifted so that the center frequency of the first optical comb 10L approaches the center frequency of the passband of the bandpass filter 210 and / or the center frequency of the second optical comb 20L approaches the center frequency of the passband of the bandpass filter 211. After changing the optical spectrum, the process from acquiring the dual comb signal (S20 to S26) is repeated until the sum of the intensities is equal to or greater than the threshold.

[0116] As described above, the measurement device 200 according to this embodiment changes the optical spectrum of at least one of the first optical comb 10L and the second optical comb 20L so that the total intensity is equal to or greater than the threshold value. This allows measurement to be performed in a state where interference light with the intensity required for measurement is obtained, thereby improving measurement accuracy.

[0117] (Modification) Next, a modification of this embodiment will be described.

[0118] This modification differs from embodiment 2 mainly in that there is only one set of a band-pass filter and a detector. This modification also differs from embodiment 1 mainly in that a band-pass filter and a detector are provided. The following description will focus on the differences from embodiments 1 and 2, and will omit or simplify the description of the commonalities between them.

[0119] Fig. 9 is a diagram showing the configuration of a measurement apparatus 300 according to this modification. The measurement apparatus 300 shown in Fig. 9 differs from the measurement apparatus 100 shown in Fig. 4 in that it includes a coupler 36, a detector 74, and a band-pass filter 310. The measurement apparatus 300 also includes a signal processing unit 82 instead of the signal processing unit 80.

[0120] The coupler 36 is an optical element that splits or combines light. The coupler 36 is provided to split the light 10Lr and 20Lr that were combined by the coupler 32. The coupler 36 is connected between the coupler 32 and each of the detector 70 and the bandpass filter 310. The coupler 36 splits the light 10Lr from the coupler 32 into light 11Lr and light 12Lr, and splits the light 20Lr from the coupler 32 into light 21Lr and light 22Lr. The light 11Lr and 21Lr are directed toward the bandpass filter 310. The light 12Lr and 22Lr are directed toward the detector 70.

[0121] The detector 74 is an optical element that converts incident light into an electric charge to generate and output an electrical signal. The signal level of the electrical signal corresponds to the intensity of the incident light. The detector 74 is a photoelectric conversion element such as a photodiode or a phototransistor. The detector 74 is an example of a first detector in the present disclosure. The detector 74 detects the light 11Lr and 21Lr that have passed through the bandpass filter 310.

[0122] The bandpass filter 310 has a passband that passes incident light and a stopband that suppresses the passage of incident light. The stopbands are provided on both the high-frequency side (shorter wavelength side) and the low-frequency side (longer wavelength side) of the passband. The bandpass filter 310 is disposed on the light incident side of the detector 74. In other words, the bandpass filter 310 is disposed so that light that has passed through the bandpass filter 310 enters the detector 74.

[0123] 10 illustrates the relationship between the frequency spectra of the first optical comb 10L and the second optical comb 20L and the bandpass filter. A portion of the first optical comb 10L emitted by the first laser light source 10 and a portion of the second optical comb 20L emitted by the second laser light source 20, specifically, the light 11Lr and the light 21Lr, are incident on the bandpass filter 310. The detector 74 detects interference light generated by interference between the frequency components of the light 11Lr that pass through the bandpass filter 310 and the frequency components of the light 21Lr that pass through the bandpass filter 310. When the center frequency of the first optical comb 10L or the second optical comb 20L is included in the passband of the bandpass filter 310, the intensity of the light detected by the detector 74 increases. Furthermore, the closer the center frequency of the first optical comb 10L or the second optical comb 20L is to the center frequency of the passband of the bandpass filter 310, the stronger the intensity of the light detected by the detector 74 becomes. The closer the center frequency of each of the first optical comb 10L and the second optical comb 20L is to the center frequency of the passband of the bandpass filter 310, the stronger the intensity of the light detected by the detector 74 becomes.

[0124] The passband of the bandpass filter 310 is narrower than both the frequency band of the spectrum of the first optical comb 10L and the frequency band of the spectrum of the second optical comb 20L. For example, the passband of the bandpass filter 310 is 50% or less of the frequency band of the spectrum of each of the first optical comb 10L and the second optical comb 20L, but may be 40% or less, 30% or less, or 20% or less. As an example, the passband of the bandpass filter 310 is 10% of the frequency band of the spectrum of the first optical comb 10L or the second optical comb 20L.

[0125] In addition to calculating the distance, the signal processing unit 82 processes the signal output from the detector 74. In this modification, the detector 74 outputs a signal corresponding to the intensity of beat light generated by the light 11Lr and the light 21Lr that have passed through the band-pass filter 310. In this modification, the signal processing unit 82 outputs information indicating the intensity of the signal output from the detector 74 to each of the feedback circuits 90 and 91.

[0126] In this modification, the feedback circuit 90 changes the optical spectrum of the first optical comb 10L based on the intensity of the signal output from the detector 74. The feedback circuit 91 changes the optical spectrum of the second optical comb 20L based on the intensity of the signal output from the detector 74. Note that the intensity of the signal output from the detector 74 is the intensity of the beat light generated by the first laser light and the second laser light that have passed through the bandpass filter 310.

[0127] For example, the feedback circuits 90 and 91 compare the intensity of the beat light of the light that has passed through the bandpass filter 310 with a threshold value based on information output from the signal processing unit 82. If the intensity is smaller than the threshold value, the feedback circuit 90 changes the value of the current applied to the gain medium of the first laser light source 10 to change the center wavelength of the first optical comb 10L. If the intensity is smaller than the threshold value, the feedback circuit 91 changes the value of the current applied to the gain medium of the second laser light source 20 to change the center wavelength of the second optical comb 20L.

[0128] [Operation] Next, an example of the operation of the measuring device 300 according to this modified example will be described with reference to Fig. 11. Fig. 11 is a flowchart showing the operation of the measuring device 300 according to this modified example. The operation shown in Fig. 11 is executed, for example, before measuring the target object 60.

[0129] 11 , first, the signal processing unit 82 acquires a signal representing the intensity of the beat light of the light that has passed through the bandpass filter 310 (S30). Specifically, the first laser light source 10 emits the first optical comb 10L, and the second laser light source 20 emits the second optical comb 20L. The first optical comb 10L is split by the coupler 30 to form light 10Lr, and the second optical comb 20L is split by the coupler 31 to form light 20Lr. These two light beams are then combined at the coupler 32. The combined light beams 10Lr and 20Lr are then split by the coupler 36 and enter the detector 74 via the bandpass filter 310 as light beams 11Lr and 21Lr. The detector 74 converts the incident light beams into electrical signals and outputs them to the signal processing unit 82.

[0130] Next, the signal processing unit 82 detects the strength of the acquired signal (S32). Then, the signal processing unit 82 outputs information representing the detected signal strength to the feedback circuits 90 and 91. Note that the detection of the signal strength may be performed by the feedback circuits 90 and 91.

[0131] Next, the feedback circuits 90 and 91 compare the signal strength with a threshold value (S34). The threshold value is a predetermined value that is the lower limit of the signal strength required to measure the object 60 with high accuracy. If the signal strength is equal to or greater than the threshold value (No in S34), the object 60 can be measured, and the process ends. Note that the comparison of the signal strength with the threshold value may be performed by the signal processing unit 82.

[0132] If the signal strength is less than the threshold (Yes in S34), at least one of the feedback circuits 90 and 91 changes the optical spectrum of at least one of the first optical comb 10L and the second optical comb 20L (S36). Specifically, the center frequency (or center wavelength) of at least one of the first optical comb 10L and the second optical comb 20L is shifted so that the center frequency of the first optical comb 10L and / or the center frequency of the second optical comb 20L approaches the center frequency of the passband of the bandpass filter 310. After changing the optical spectrum, the process from acquiring the dual comb signal (S30 to S36) is repeated until the signal strength reaches or exceeds the threshold.

[0133] As described above, the measurement device 300 according to this modification changes the optical spectrum of at least one of the first optical comb 10L and the second optical comb 20L so that the signal strength is equal to or greater than the threshold. This allows measurement to be performed in a state where interference light with the intensity required for measurement is obtained, thereby improving measurement accuracy.

[0134] 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.

[0135] For example, in the above embodiment, the first laser light source and the second laser light source are both on-chip combs, but this is not limiting. For example, the first laser light source and the second laser light source may each be a solid-state laser light source. In the case of a solid-state laser light source, the feedback circuit can change the optical spectrum of the laser light by changing the dispersion using an optical element such as a prism pair present in the resonator.

[0136] For example, in the second embodiment and the modification thereof, the pass band of the band pass filter may be swept.

[0137] Furthermore, for example, in the above-described embodiment, the processing performed by a specific processing unit may be performed by another processing unit, the order of multiple processing operations may be changed, or multiple processing operations may be performed in parallel.

[0138] Furthermore, for example, the processing described in the above embodiments may be realized by centralized processing using a single device (or system), or may be realized by distributed processing using multiple devices. Furthermore, the above program may be executed by one processor or multiple processors. In other words, centralized processing or distributed processing may be performed.

[0139] In the above embodiment, all or some of the components such as the signal processing units 80 and 81 may be configured with dedicated hardware, or may be realized by executing a software program suitable for each component. Each component may be realized by a program execution unit such as a CPU (Central Processing Unit) or a processor reading and executing a software program recorded on a recording medium such as an HDD (Hard Disk Drive) or semiconductor memory.

[0140] Furthermore, components such as the signal processing units 80 and 81 may be configured with one or more electronic circuits. Each of the one or more electronic circuits may be a general-purpose circuit or a dedicated circuit.

[0141] The one or more electronic circuits may include, for example, a semiconductor device, an IC, or an LSI. The IC or LSI may be integrated into a single chip or multiple chips. Although the IC or LSI is referred to here as an IC or LSI, the name may vary depending on the degree of integration, and may be called a system LSI, a VLSI (Very Large Scale Integration), or an ULSI (Ultra Large Scale Integration). An FPGA, which is programmed after the LSI is manufactured, can also be used for the same purpose.

[0142] Furthermore, the general or specific aspects of the present disclosure may be realized as a system, an apparatus, a method, an integrated circuit, or a computer program. Alternatively, the general or specific aspects of the present disclosure may be realized as a computer-readable non-transitory recording medium such as an optical disk, a HDD, or a semiconductor memory on which the computer program is stored. Furthermore, the general or specific aspects of the present disclosure may be realized as any combination of a system, an apparatus, a method, an integrated circuit, a computer program, and a recording medium.

[0143] 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.

[0144] The present disclosure can be used in devices, systems, methods, etc. for performing distance measurement or displacement measurement, and can be used in, for example, distance measurement sensors, displacement meters, shape inspection devices, etc.

[0145] REFERENCE SIGNS LIST 10 First laser light source 20 Second laser light source 30, 31, 32, 33, 34, 35, 36 Coupler 40 Circulator 50 Collimator 60 Object 70, 71, 72, 73, 74 Detector 80, 81, 82 Signal processing unit 90, 91 Feedback circuit 100, 200, 300 Measuring device 210, 211, 310 Bandpass filter

Claims

1. A measurement device comprising: a mode-locked laser light source having a gain medium, a first laser light source that emits a first laser beam; a mode-locked laser light source having a gain medium, a second laser light source that emits a second laser beam; at least one first detector that detects at least one of the first laser beam, the second laser beam, and a beat beam generated by the first laser beam and the second laser beam; and a feedback circuit that changes at least one optical spectrum of the first laser beam and the second laser beam based on an intensity of a signal output from the at least one first detector.

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

3. The measurement device according to claim 1, wherein the first laser light source is disposed on a semiconductor substrate different from the semiconductor substrate on which the second laser light source is disposed.

4. The measurement device according to claim 1, wherein the feedback circuit changes the optical spectrum at a frequency higher than at least one of the repetition frequencies of the first laser beam and the second laser beam.

5. The measurement device according to any one of claims 1 to 4, wherein the intensity of the signal output from the at least one first detector is a peak intensity of a pulse of light detected by the at least one first detector.

6. The measurement device according to any one of claims 1 to 4, further comprising at least one band-pass filter, wherein the at least one band-pass filter is disposed such that light passing through the at least one band-pass filter is incident on the at least one first detector, and the intensity of the signal output from the at least one first detector is an intensity of light that has passed through the at least one band-pass filter.

7. The measurement device according to any one of claims 1 to 4, wherein the feedback circuit changes the optical spectrum by adjusting a current amount applied to the gain medium.

8. A second detector that detects interference light generated by interference between the reflected light generated by reflection of the first laser light by the object and the second laser light; and a signal processing unit that calculates the distance from the measuring device to the object based on a signal output from the second detector. The measuring device according to any one of claims 1 to 4, further comprising:

9. The measuring device according to any one of claims 1 to 4, further comprising a signal processing unit that calculates the distance from the measuring device to the object based on the signal output from the at least one first detector.

10. A second detector that detects interference light generated by interference between the reflected light generated by reflection of the first laser light by the object and the second laser light; a third detector that detects interference light generated by interference between the first laser light and the second laser light; and a signal processing unit that calculates the distance from the measuring device to the object based on a signal output from the second detector and a signal output from the third detector. The measuring device according to claim 6, further comprising:

11. The at least one first detector includes a plurality of first detectors, the at least one band-pass filter includes a plurality of band-pass filters, one of the plurality of first detectors detects the first laser light that has passed through the corresponding band-pass filter among the plurality of band-pass filters, and another one of the plurality of first detectors detects the second laser light that has passed through the corresponding band-pass filter among the plurality of band-pass filters. The measuring device according to claim 10.

12. The at least one first detector detects the beat light generated by the first laser light and the second laser light that have passed through the at least one band-pass filter. The measuring device according to claim 10.

13. A measuring method including: a detector detecting at least one of the first laser light emitted by a first laser light source that is a mode-locked laser light source having a gain medium, the second laser light emitted by a second laser light source that is a mode-locked laser light source having a gain medium, and the beat light generated by the first laser light and the second laser light; and changing at least one of the optical spectra of the first laser light and the second laser light based on the intensity of a signal output from the detector.

Images