Optical frequency comb device and measurement device

Abstract

An optical frequency comb device includes: an optical waveguide; a first mirror disposed at a first position of the optical waveguide; a second mirror disposed at a second position of the optical waveguide different from the first position; a gain medium and a saturable absorber disposed between the first mirror and the second mirror; and a control unit that fixes one of a repetition frequency and a carrier envelope offset frequency of an optical frequency comb output from an end of the optical waveguide and changes the other.

Description

TECHNICAL FIELD

[0001] The present application relates to an optical frequency comb device and a measurement device. BACKGROUND

[0002] By irradiating light to an object and obtaining a spectrum of light that has transmitted through the object or light that has been reflected by the object, it is possible to investigate the characteristics of the optical frequency of the object. In the past, in order to obtain a spectrum of light of a higher frequency, a light source with intensity fluctuations and a diffraction grating or a prism or the like were used for spectroscopy. Therefore, the precision of the obtained spectrum was limited.

[0003] However, by optical frequency comb technology, it is possible to precisely obtain a spectrum of light. By optical frequency comb, it means a comb-shaped spectrum formed by a plurality of discrete equidistant longitudinal modes. In this specification, a laser having an optical frequency comb will be referred to as "optical frequency comb laser" or simply "optical frequency comb". In Non-Patent Literatures 1 to 3, optical frequency comb devices that generate an optical frequency comb are disclosed.

[0004] PRIOR ART DOCUMENTS

[0005] NON-PATENT LITERATURES

[0006] Non-Patent Literature 1: A. L. Gaeta et al., "Photonic-chip-based frequency combs", Nature Photonics, 2019, Vol. 13, pp. 158-169

[0007] Non-Patent Literature 2: J. Riemensberger et al., "Massively parallel coherent laser ranging using a soliton microcomb", Nature, 2020, Vol. 581, pp. 164-170

[0008] Non-Patent Literature 3: Z. Wang et al., "A III-V-on-Si ultra-dense comb laser", Light: Science & Applications, 2017, Vol. 6, e16260 SUMMARY

[0009] PROBLEMS TO BE SOLVED BY THE INVENTION

[0010] In order to apply an optical frequency comb to a variety of uses, it is required to be able to change the frequency with good precision.

[0011] The present application provides an optical frequency comb device and the like that can change the frequency with good precision.

[0012] Means for solving the problem

[0013] The optical frequency comb device of one aspect of the present application includes: an optical waveguide; a first mirror disposed at a first position of the optical waveguide; a second mirror disposed at a second position of the optical waveguide different from the first position; a gain medium and a saturable absorber disposed between the first mirror and the second mirror; and a control unit that fixes one of a repetition frequency and a carrier envelope offset frequency of an optical frequency comb output from an end portion of the optical waveguide and changes the other.

[0014] Further, the optical frequency comb device of one aspect of the present application includes: an optical waveguide; a first mirror disposed at a first position of the optical waveguide; a second mirror disposed at a second position of the optical waveguide different from the first position; a gain medium and a saturable absorber disposed between the first mirror and the second mirror; and a signal generator that supplies a high-frequency signal to the saturable absorber; the signal generator changes a repetition frequency of an optical frequency comb output from an end portion of the optical waveguide by changing a frequency of the high-frequency signal.

[0015] The measurement device of one aspect of the present application includes: the optical frequency comb device of one aspect of the present application; an emission unit that emits the optical frequency comb toward an object; a light detection unit that receives reflected light of the optical frequency comb from the object; and a calculation unit that calculates a distance to the object or a speed of the object based on a detection result obtained by the light detection unit.

[0016] Effects of the invention

[0017] The optical frequency comb device and the like according to one aspect of the present application can change a frequency with good precision. BRIEF DESCRIPTION OF DRAWINGS

[0018] Figure 1A is a graph schematically showing a time change of an electric field of an optical frequency comb laser.

[0019] Figure 1B is a graph schematically showing a spectrum of an optical frequency comb laser.

[0020] Figure 2A is a plan view schematically showing an optical frequency comb laser source composed of a resonator including a gain medium integrated on a semiconductor substrate.

[0021] Figure 2B is a cross-sectional view schematically showing the optical frequency comb laser source at a position indicated by a line IIB-IIB of Figure 2A

[0022] Figure 2C is a graph schematically showing​Figure 2B Cross-sectional view of a transmission path of light in the cross-section shown.

[0023] Figure 3 FIG. 1 is a diagram showing the principle of distance measurement by FMCW.

[0024] Figure 4 FIG. 2 is a diagram showing optical frequency combs on a frequency axis before and after modulation of a carrier envelope offset frequency.

[0025] Figure 5 FIG. 3 is a diagram showing optical frequency combs on a frequency axis before and after modulation of a repetition frequency.

[0026] Figure 6 FIG. 4 is a diagram schematically showing an example of an optical frequency comb device of Embodiment 1.

[0027] Figure 7 FIG. 5 is a diagram schematically showing an example of an optical frequency comb device of Embodiment 2.

[0028] Figure 8 FIG. 6 is a diagram schematically showing an example of an optical frequency comb device of Embodiment 3.

[0029] Figure 9 FIG. 7 is a diagram schematically showing an example of an optical frequency comb device of a modification of Embodiment.

[0030] Figure 10 FIG. 8 is a diagram schematically showing the structure of a measurement device of Embodiment 4.

[0031] Figure 11 FIG. 9 is a diagram schematically showing the structure of a detection section of the measurement device of Embodiment 4. DETAILED DESCRIPTION

[0032] (SUMMARY OF THE INVENTION)

[0033] The optical frequency comb device of the technical solution of the present application has: an optical waveguide; a first mirror provided at a first position of the optical waveguide; a second mirror provided at a second position of the optical waveguide different from the first position; a gain medium and a saturable absorber provided between the first mirror and the second mirror; and a control section that fixes one of a repetition frequency and a carrier envelope offset frequency of an optical frequency comb output from an end of the optical waveguide and changes the other.

[0034] Thus, both the repetition frequency and the carrier envelope offset frequency are not changed at the same time, so the frequency precision of the optical frequency comb can be changed to a desired frequency with good precision. In addition, as an example of a change in frequency, frequency modulation can be performed.

[0035] Further, for example, the control section can include a current source that supplies a current to the gain medium, and a signal generator that supplies a high-frequency signal to the saturable absorber.

[0036] Thus, the carrier envelope offset frequency can be fixed or varied depending on the magnitude of the current supplied to the gain medium. Further, the repetition frequency can be fixed or varied depending on the frequency of the high-frequency signal supplied to the saturable absorber.

[0037] Further, for example, the current source can vary the carrier envelope offset frequency by varying the magnitude of the current, and the signal generator can fix the frequency of the high-frequency signal.

[0038] Thus, by varying the carrier envelope offset frequency, the plurality of modes (i.e., frequency components) of the optical frequency comb can be easily varied. Further, since the repetition frequency can be fixed, the separation of the modes in the detector can be easily performed. Therefore, distance measurement based on FMCW (Frequency-modulated Continuous-wave) can be easily performed.

[0039] Further, for example, the current source can fix the magnitude of the current, and the signal generator can vary the repetition frequency by varying the frequency of the high-frequency signal.

[0040] Thus, distance measurement based on FMCW can be performed even when the repetition frequency is varied.

[0041] Further, for example, the optical frequency comb device of one aspect of the present application can further include a phase modulator provided between the first mirror and the second mirror, and the control section can further include a voltage source that supplies a voltage to the phase modulator, the voltage source can vary the carrier envelope offset frequency by varying the magnitude of the voltage, and the signal generator can fix the frequency of the high-frequency signal.

[0042] Thus, by varying the carrier envelope offset frequency, the plurality of modes (i.e., frequency components) of the optical frequency comb can be easily varied. Further, since the repetition frequency can be fixed, the separation of the modes in the detector can be easily performed. Therefore, distance measurement based on FMCW can be easily performed.

[0043] Further, for example, the optical frequency comb device of one aspect of the present application can further include a semiconductor substrate, and the optical waveguide, the first mirror, the second mirror, the gain medium, and the saturable absorber can be integrated in the semiconductor substrate.

[0044] Thus, the optical frequency comb device can be miniaturized. Further, compared with a case where a CW laser source and a micro resonator that generates an optical frequency comb by resonating laser emitted from the CW laser source are provided, the frequency can be easily changed. That is, in a case where the frequency of laser from the CW laser source is changed, an optical frequency comb whose repetition frequency or carrier envelope offset frequency is changed can be obtained in theory. However, it is difficult to continuously obtain the resonance of the CW laser source and the micro resonator while changing the frequency of laser from the CW laser source, and the precision of the frequency change cannot be maintained. In contrast, in the on-chip optical frequency comb device including a gain medium, like the optical frequency comb device of one aspect of the present application, the frequency precision of the optical frequency comb can be changed to a desired frequency by the control unit.

[0045] Further, for example, the control unit can be integrated with the semiconductor substrate.

[0046] Thus, the optical frequency comb device can be further miniaturized.

[0047] Further, the optical frequency comb device of one aspect of the present application includes: an optical waveguide; a first mirror provided at a first position of the optical waveguide; a second mirror provided at a second position of the optical waveguide different from the first position; a gain medium and a saturable absorber provided between the first mirror and the second mirror; and a signal generator that supplies a high-frequency signal to the saturable absorber, and the signal generator changes the repetition frequency of an optical frequency comb output from an end of the optical waveguide by changing the frequency of the high-frequency signal.

[0048] Thus, the repetition frequency can be changed with good precision according to the change in the frequency of the high-frequency signal.

[0049] Further, for example, the optical frequency comb device of another aspect of the present application can further include a current source that supplies a current to the gain medium, and the current source fixes the magnitude of the current.

[0050] Thus, the repetition frequency and the carrier envelope offset frequency are not changed at the same time, and thus the frequency precision of the optical frequency comb can be changed to a desired frequency with good precision.

[0051] Further, the measurement device of one aspect of the present application includes: the optical frequency comb device of each aspect; an emission unit that emits the optical frequency comb toward an object; a light detection unit that receives reflected light of the optical frequency comb from the object; and a calculation unit that calculates the distance to the object or the speed of the object based on a detection result obtained by the light detection unit.

[0052] Thus, one of the carrier envelope offset frequency and the repetition frequency can be fixed, and the other can be varied, so that distance measurement based on FMCW can be easily performed.

[0053] Further, for example, the light detection section can also be configured to receive the optical frequency comb. The operation section can calculate the distance or the speed based on beat signals generated by interference between the reflected light and the optical frequency comb in the light detection section.

[0054] Thus, by using the beat signals, the speed can be easily calculated in addition to the distance.

[0055] Further, for example, the light detection section can include a splitter configured to separate the incident light by frequency, and a plurality of light receivers configured to receive the light of each frequency after the separation.

[0056] Thus, detection based on a wavelength division multiplexing (WDM) scheme or the like can be performed. Since a plurality of modes can be separately detected, the modulation range of each mode can be ensured to be large.

[0057] Further, for example, the light emission section can be configured to emit the optical frequency comb in different directions according to the frequency.

[0058] Thus, the distance and / or the speed at a plurality of points can be simultaneously measured.

[0059] Hereinafter, embodiments will be specifically described with reference to the drawings.

[0060] In addition, the embodiments described below are examples of general or specific application. The numerical values, shapes, materials, component configurations, component arrangement positions and connection modes, steps, order of steps, and the like indicated in the embodiments below are examples and are not intended to limit the present application. In addition, regarding the components in the embodiments below, components not described in the independent claims are arbitrary components.

[0061] Further, each drawing is a schematic view and is not necessarily strictly illustrated. Thus, for example, the scale and the like are not necessarily consistent in each drawing. In addition, in each drawing, the same reference numerals are assigned to substantially the same structures, and repeated descriptions or simplifications are omitted.

[0062] Further, in the present specification, terms indicating the relationship between elements, such as parallel or consistent, terms indicating the shape of an element, such as a rectangle, and numerical ranges are not only expressions in a strict sense, but also expressions in a substantially equivalent range, for example, including a difference of several percent or the like.

[0063] Further, in the present specification, the terms "above" and "below" do not refer to the absolute spatial recognition of above (vertically upward) and below (vertically downward), but are used as terms defined by the relative positional relationship based on the stacking order in the stacked structure. Further, the terms "above" and "below" are applicable not only to the case where two constituent elements are arranged apart from each other with a space and there is another constituent element between the two constituent elements, but also to the case where two constituent elements are arranged in close contact with each other so that the two constituent elements are in contact with each other.

[0064] Further, in the present specification, ordinal numbers "1st", "2nd", and the like do not refer to the number or order of constituent elements unless specifically stated, but are used for the purpose of avoiding confusion with the same constituent elements and making distinction.

[0065] (Optical frequency comb)

[0066] First, referring to Figure 1A and Figure 1B , the temporal variation of the electric field of the optical frequency comb (i.e., the optical frequency comb laser) and the spectrum are described.

[0067] Figure 1A is a diagram schematically showing an example of the temporal variation of the electric field of the optical frequency comb laser. In Figure 1A , the horizontal axis represents time, and the vertical axis represents the electric field of the laser.

[0068] As shown in Figure 1A , the optical frequency comb laser is formed of a train of optical pulses generated with a repetition period T rep . The repetition period T rep is, for example, 100 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 Δt of each optical pulse is, for example, 10 fs or more and 1 ps or less.

[0069] The optical frequency comb laser source includes a laser resonator that generates the optical frequency comb laser by excitation of input light or charge injection. Details of the laser resonator are described later. With respect to the laser resonator, there is a case where the group velocity v g of the envelope line of the optical pulse is different from the phase velocity v p of the wave propagation within the optical pulse. Due to the difference between the group velocity v g and the phase velocity v p , if two adjacent optical pulses are overlapped in a manner that the envelope lines coincide with each other, the phase of the wave within these optical pulses is shifted by less than 2π. Assuming that the round-trip length of the laser resonator is L, the repetition period of the train of optical pulses is represented by T rep = L / v g .

[0070] Figure 1B is a graph schematically showing the spectrum of the optical frequency comb laser. In Figure 1B , the horizontal axis represents frequency, and the vertical axis represents the intensity of the laser light.

[0071] As shown in Figure 1B , the optical frequency comb laser has a comb-shaped spectrum formed of a plurality of discrete equi-spaced lines. The frequencies of the plurality of discrete equi-spaced lines correspond to the resonance frequencies of the longitudinal modes of the laser resonator. The repetition frequency corresponding to the interval of the adjacent two equi-spaced lines of the optical frequency comb is represented by f rep = 1 / T rep . The repetition frequency f rep is, for example, 10 MHz or more and 10 GHz or less. In the case where the optical path length L of the laser resonator is 30 cm, and the group velocity v g is substantially equal to the speed of light in vacuum (= 3 x 10 8 m / s), the repetition period T rep becomes 1 ns, and the repetition frequency f rep becomes 1 GHz.

[0072] In the case where the full width at half maximum of the optical frequency comb is Δf, Δf = 1 / Δt. The full width at half maximum Δf of the optical frequency comb is, for example, 1 THz or more and 100 THz or less. The frequency of the nearest equi-spaced line to the zero frequency in the case where the equi-spaced lines exist up to the vicinity of the zero frequency is called the carrier envelope offset frequency. The carrier envelope offset frequency is represented by . The carrier envelope offset frequency f CEO is lower than the repetition frequency f rep . If the carrier envelope offset frequency f CEO is set as the 0th mode frequency, the nth mode frequency f n of the optical frequency comb is represented by f n = f CEO + nf rep . The amplitude and the phase of the electric field at the nth mode frequency fnare set as E n and Figure 1A The electric field E(t) of the optical frequency comb laser shown in is represented by

[0073] (Optical frequency comb device)

[0074] Next, the optical frequency comb device of the type integrated on a semiconductor substrate, i.e., the on-chip optical frequency comb device, will be briefly described with reference to Figure 2A and Figure 2B . The optical frequency comb device is also called an optical frequency comb laser source.

[0075] Figure 2A is a plan view schematically showing an optical frequency comb laser source having a resonator including a gain medium integrated on a semiconductor substrate. Figure 2B is a plan view schematically showing an optical frequency comb laser source having a resonator including a gain medium integrated on a semiconductor substrate. Figure 2A is a sectional view of the optical frequency comb laser source schematically showing a position shown by a line IIB-IIB. For reference, X, Y and Z axes orthogonal to each other are schematically shown for convenience of explanation and do not limit an orientation in use. Further, in Figure 2B in the drawing, no hatching is given to the n-doped layer 13d1, the p-doped layers 13d2 and 13d3, the low refractive index layer 14b and the protective layer 16.

[0076] As shown in Figure 2A and Figure 2B , the optical frequency comb laser source 10 includes a resonator 13, a semiconductor substrate 14 and a protective layer 16. The surface of the semiconductor substrate 14 in the illustrated example is parallel to the XY plane. As shown in Figure 2B , the semiconductor substrate 14 has, for example, a stacked structure in which a high refractive index layer 14a of Si or the like and a low refractive index layer 14b of SiO2or the like are stacked in this order in the Z-axis direction. The refractive index of the high refractive index layer 14a is higher than the refractive index of the low refractive index layer 14b. The semiconductor substrate 14 can not include the high refractive index layer 14a. The protective layer 16 is formed using, for example, an inorganic insulating material such as SiO2or an organic insulating material such as BCB (benzocyclobutene). The protective layer 16 is provided so as to cover the upper surface of the low refractive index layer 14b.

[0077] The resonator 13 is an example of a laser resonator having a prescribed optical path length. As shown in Figure 2A , the resonator 13 includes a semiconductor layer 13s, an intermediate layer 13i, an optical waveguide 13w and mirrors 13m1 and 13m2. Further, as shown in Figure 2B , the resonator 13 includes an n-doped layer 13d1 and p-doped layers 13d2 and 13d3. Further, the resonator 13 includes a gain medium 13g and a saturable absorber 13sa. A part of the semiconductor layer 13s functions as the gain medium 13g and the saturable absorber 13sa, respectively.

[0078] In Figure 2AIn the diagram, the planar shape of the semiconductor layer 13s of the resonator 13 is represented by dashed lines. The semiconductor layer 13s has tapered portions at both ends. The leading edges of the tapered portions overlap with the intermediate layer 13i when viewed from above. Furthermore, the intermediate layer 13i also has tapered portions at both ends. The leading edges of the tapered portions overlap with the optical waveguide 13w when viewed from above. Thus, light passing through the semiconductor layer 13s is efficiently transmitted to the optical waveguide 13w via the intermediate layer 13i. That is, in the optical frequency comb laser source 10, the optical waveguide 13w, the intermediate layer 13i, and the semiconductor layer 13s each function as a path for light to pass through.

[0079] like Figure 2B As shown, the optical waveguide 13w of the resonator 13 is embedded in the low-refractive-index layer 14b of the semiconductor substrate 14. The optical waveguide 13w can also be disposed on the low-refractive-index layer 14b. The optical waveguide 13w can, for example, be formed from at least one high-refractive-index material selected from the group consisting of SiN and Si. The refractive index of the optical waveguide 13w is higher than the refractive index of the low-refractive-index layer 14b of the semiconductor substrate 14 and the refractive index of the protective layer 16. Therefore, light can propagate within the optical waveguide 13w via total internal reflection.

[0080] An intermediate layer 13i is disposed between the optical waveguide 13w and the semiconductor layer 13s. The intermediate layer 13i is formed, for example, of a-Si (amorphous silicon). The refractive index of the intermediate layer 13i is higher than that of the optical waveguide 13w and lower than that of the semiconductor layer 13s. Furthermore, regarding the intermediate layer 13i, it can be formed of other semiconductors as long as the refractive index satisfies the condition: optical waveguide 13w < intermediate layer 13i < semiconductor layer 13s. If the intermediate layer 13i is not disposed, the large difference between the refractive index of the semiconductor layer 13s and the optical waveguide 13w makes it difficult for light to propagate from the semiconductor layer 13s (with a higher refractive index) to the optical waveguide 13w (with a lower refractive index). Therefore, the light transmission loss between the semiconductor layer 13s and the optical waveguide 13w increases. By providing the intermediate layer 13i, the refractive index difference between the layers can be reduced. Therefore, by providing the intermediate layer 13i, such as… Figure 2C As shown, this enables light to transmit from semiconductor layer 13s to optical waveguide 13w with low loss. Furthermore, Figure 2C It is a schematic representation Figure 2B The cross-sectional view shown shows the light transmission path. The intermediate layer 13i can be omitted if the difference between the refractive index of the semiconductor layer 13s and the refractive index of the optical waveguide 13w is relatively small.

[0081] like Figure 2CAs shown, in the optical waveguide 13w, the first part 13w1, which is closer to the reflector 13m1, and the second part 13w2, which is closer to the reflector 13m2, function as light transmission paths. The first part 13w1 is the portion of the optical waveguide 13w between the gain medium 13g, the saturable absorber 13sa, and the reflector 13m1. The second part 13w2 is the portion of the optical waveguide 13w between the gain medium 13g, the saturable absorber 13sa, and the reflector 13m2.

[0082] Reflector 13m1 is positioned at the first location of optical waveguide 13w. Specifically, reflector 13m1 is located at the end of optical waveguide 13w. Reflector 13m1 can be formed, for example, by a distributed Bragg reflector. In a distributed Bragg reflector, light is reflected by Bragg reflection, which is caused by the periodic structure of the refractive index. Reflector 13m1 reflects the light transmitted in optical waveguide 13w. Reflector 13m1 can also be formed of metal, for example, as long as it has a reflective function. Furthermore, reflector 13m1 can also be a reflective element formed of semiconductor, such as a loop mirror. The same applies to reflector 13m2. Reflector 13m2 is positioned at a second location of optical waveguide 13w, different from the first location. Specifically, reflector 13m2 is located at the end of optical waveguide 13w opposite to reflector 13m1.

[0083] Compared to mirror 13m1, mirror 13m2 has a lower reflectivity. Specifically, mirror 13m1 has a reflectivity of approximately 100%, while mirror 13m2 has a reflectivity of, for example, between 70% and 90%. Although mirror 13m2 reflects most of the light transmitted in the optical waveguide 13w, it allows a portion to pass through uninterruptedly. The light that passes through mirror 13m2 becomes the optical frequency comb laser 5.

[0084] like Figure 2B As shown, semiconductor layer 13s is sandwiched between n-doped layer 13d1 and p-doped layers 13d2 and 13d3. The arrangement of n-doped layer 13d1 and p-doped layers 13d2 and 13d3 can also be reversed.

[0085] Semiconductor layer 13s, n-doped layer 13d1, and p-doped layers 13d2 and 13d3 are embedded in protective layer 16. Additionally, the lower surface of n-doped layer 13d1 can also contact the surface of semiconductor substrate 14. n-doped layer 13d1 can also contact intermediate layer 13i.

[0086] The semiconductor layer 13s can be formed of a Group III-V semiconductor material, for example. The Group III-V semiconductor material can include at least one material selected from the group consisting of ZnSe, InGaAlP, InGaAs, GaInAsP, GaInAsSb, InP, GaN, GaAs, InGaAs, AlGaAs, AlInGaN, for example.

[0087] The semiconductor layer 13s includes a gain medium 13g and a saturable absorber 13sa. The gain medium 13g and the saturable absorber 13sa are provided between the mirror 13ml and the mirror 13m2. Specifically, the gain medium 13g and the saturable absorber 13sa are provided on the transmission path of light between the mirror 13ml and the mirror 13m2.

[0088] The gain medium 13g is a part of the semiconductor layer 13s, which is sandwiched by an n-doped layer 13dl and a p-doped layer 13d2. The saturable absorber 13sa is a part of the semiconductor layer 13s, which is sandwiched by the n-doped layer 13dl and a p-doped layer 13d3.

[0089] The n-doped layer 13dl is an n-type semiconductor layer. The n-doped layer 13dl is formed by doping an n-type impurity in the same Group III-V semiconductor material as the semiconductor layer 13s. As the n-type impurity, a tetravalent element such as Si, or a hexavalent element such as selenium (Se), or the like can be used, for example.

[0090] The p-doped layers 13d2 and 13d3 are p-type semiconductor layers. The p-doped layers 13d2 and 13d3 are formed by doping a p-type impurity in the same Group III-V semiconductor material as the semiconductor layer 13s. As the p-type impurity, a divalent element such as zinc (Zn) can be used, for example. The p-doped layer 13d2 and the p-doped layer 13d3 have the same composition, for example.

[0091] The p-doped layers 13d2 and 13d3 are separated from each other. To the p-doped layers 13d2 and 13d3, mutually different electrodes (not shown) are attached, respectively. To the p-doped layer 13d2, a current is injected via the electrode. To the p-doped layer 13d3, a reverse bias voltage is applied between the n-doped layer 13dl. By this voltage application, a part of the semiconductor layer 13s that contacts the p-doped layer 13d3 functions as the saturable absorber 13sa. The saturable absorber 13sa can also be formed using carbon nanotubes. The saturable absorber 13sa can also be integrated with the mirrors 13ml and 13m2.

[0092] As with the p-doped layer 13d2, an electrode not shown is also installed for the n-doped layer 13dl. A part of the semiconductor layer 13s, which is subjected to charge injection from the electrodes installed in the n-doped layer 13dl and the p-doped layer 13d2, respectively, functions as a gain medium 13g that emits light by stimulated emission. The light emitted by stimulated emission is repeatedly reflected between the mirror 13ml and the mirror 13m2 via the intermediate layer 13i and the optical waveguide 13w. That is, the light emitted by stimulated emission is amplified by passing through the gain medium 13g multiple times. The light amplified by this is made into a pulse train of light that is mode-locked using the saturable absorber 13sa. Only the wavelength corresponding to the optical path length of the resonator 13, that is, the value obtained by multiplying the resonator length by the refractive index, is amplified. Thus, the optical frequency comb laser 5 is emitted from the resonator 13. Note that the optical path length of the resonator 13 is the optical path length between the mirror 13ml and the mirror 13m2.

[0093] (FMCW)

[0094] The optical frequency comb device of the embodiment can be used for FMCW. Hereinafter, the FMCW will be described using the optical frequency comb device of the embodiment. Figure 3 The principle of FMCW will be described. Figure 3 is a graph showing the principle of distance measurement by FMCW. In Figure 3 , the horizontal axis represents time, and the vertical axis represents the frequency of laser light.

[0095] With FMCW, the laser light emitted from the CW light source is subjected to time-dependent frequency modulation. In the case of Figure 3 , frequency modulation of ΔF is performed during a time width T. The frequency modulation here is linear modulation. That is, the rate of change of the frequency is constant.

[0096] In the case of distance measurement to an object, the laser light subjected to frequency modulation is branched into two, one of which is used as a reference light (solid line in Figure 3 ) and the other as a measurement light, which is irradiated to the object. The reflected light (long dashed line in Figure 3 ) returned by reflection at the object is detected by a light receiver. At this time, there is a frequency difference Δf between the reference light and the measurement light, that is, the reflected light. This is derived from the time difference of the measurement light to and from the object. Thus, by multiplying the frequency difference Δf by cT / 2ΔF, the distance to the object can be measured. That is, the distance is represented by the following formula (1).

[0097] (1) Distance = Δf x c x T / (2 x ΔF)

[0098] Here, c represents the speed of light. For example, if T = 40 μs, ΔF = 4 GHz, and Δf = 4 MHz are assumed, the distance to the object can be calculated as 6 m by the above formula (1).

[0099] (Two methods of frequency modulation of optical frequency comb)

[0100] In the measuring device of the present invention, the ranging method based on the FMCW is applied to the optical frequency comb device.

[0101] As already stated, in an optical frequency comb, there exists a repetition frequency f. rep and carrier envelope offset frequency f CEO These two frequency parameters. Therefore, as long as one of them can be modulated, ranging can be performed in the same way as FMCW.

[0102] First, use Figure 4 This indicates that only the carrier envelope offset frequency f is considered. CEO Modulation conditions. Figure 4 This indicates that the carrier envelope is offset by the frequency f. CEO A diagram of the optical frequency comb on the frequency axis before and after modulation. Specifically, Figure 4 (a) represents the optical frequency comb before modulation, and (b) represents the optical frequency comb after modulation. In each of (a) and (b), the horizontal axis represents the frequency of light, and the vertical axis represents the intensity of light.

[0103] Let the value of the carrier envelope offset frequency before modulation be f. CEO In this case, at a certain moment, the carrier envelope offset frequency becomes f CEO +δf CEO The value of . Subsequently, the frequency f of the nth modulus. n Can be represented as f n =(f CEO +δf CEO )+nf rep Furthermore, by treating each mode (specifically, the light of each frequency component) as a laser from a CW source, many FMCWs can be performed simultaneously.

[0104] Next, use Figure 5 The explanation only considers the repetition frequency f rep Modulation conditions. Figure 5 This indicates that the repetition frequency f rep A diagram of the optical frequency comb on the frequency axis before and after modulation. Figure 5 (a) represents the optical frequency comb before modulation, and (b) represents the optical frequency comb after modulation. In each of (a) and (b), the horizontal axis represents the frequency of light, and the vertical axis represents the intensity of light.

[0105] Let the repetition frequency before modulation be f. rep In this case, at a certain moment, the repetition frequency becomes f. rep +δf rep The value of . Subsequently, the frequency f of the nth modulus. n Can be represented as f n =f CEO +n(frep + δf rep ). In this case as well, many FMCW can be performed at the same time by regarding one by one the modes as lasers from a CW light source. Figure 4

[0106] In addition, as a method of performing modulation of frequency, there are EOM (electro-optical modulation) and modulation of resonator length based on temperature adjustment, and the like. However, in the on-chip light frequency comb device with a gain medium built in, even if the amount of current applied to the gain medium is modulated or the resonator length is modulated by temperature adjustment, both of the repetition frequency f rep and the carrier envelope offset frequency f CEO change. Therefore, it is difficult to cause the light frequency comb device to function as an FMCW.

[0107] Therefore, in the present application, in the light frequency comb device, a modulation section that modulates one of the repetition frequency f rep and the carrier envelope offset frequency f CEO and fixes the other is incorporated. Hereinafter, the specific structure of the light frequency comb device of the embodiment of the present application will be described.

[0108] (Embodiment 1)

[0109] First, the structure example of the light frequency comb device of Embodiment 1 of the present application will be described with reference to Figure 6 Figure 6 is a diagram that schematically shows the light frequency comb device 10A of the present embodiment. The basic configuration of the light frequency comb device 10A is the same as that of the light frequency comb laser source 10 shown in Figure 2A and Figure 2B Hereinafter, the description will be made focusing on the points of difference from the light frequency comb laser source 10 shown in Figure 2A and Figure 2B , and the description of the common points will be omitted or simplified.

[0110] As the point of difference, as shown in Figure 6 , the light frequency comb device 10A newly has a modulation section 21A. The modulation section 21A is an example of the control section, and has a modulation current source 17m and a fixed RF signal generator 18.

[0111] The modulation current source 17m is connected to the gain medium 13g, and supplies a current whose magnitude is modulated (hereinafter referred to as a modulation current) to the gain medium 13g. Specifically, the modulation current source 17m is connected to the p-doped layer 13d2 and the n-doped layer 13dl, and a modulation current flows from the p-doped layer 13d2 to the n-doped layer 13dl. Thereby, the modulation current is supplied to the gain medium 13g sandwiched by the p-doped layer 13d2 and the n-doped layer 13dl.

[0112] ​​The fixed RF signal generator 18 is connected to the saturable absorber 13sa, and supplies a high-frequency signal (hereinafter referred to as a fixed RF signal) having a fixed frequency to the saturable absorber 13sa. Specifically, the fixed RF signal generator 18 is connected to the p-doped layer 13d3 and the n-doped layer 13d1, and supplies a high-frequency voltage signal having a fixed frequency as the fixed RF signal to between the p-doped layer 13d3 and the n-doped layer 13d1. Thereby, the fixed RF signal is supplied to the saturable absorber 13sa sandwiched by the p-doped layer 13d3 and the n-doped layer 13d1.

[0113] The modulation current source 17m modulates the carrier envelope offset frequency by modulating the magnitude of the current supplied to the gain medium 13g. At this time, by modulating the magnitude of the current, not only the carrier envelope offset frequency is modulated, but also the repetition frequency is modulated.

[0114] In contrast to this, the fixed RF signal generator 18 fixes the repetition frequency by fixing the frequency of the high-frequency signal. This is derived from the fact that, by the fixed RF signal, the saturable absorber 13sa has a function as a shutter, and controls the pulse interval in the resonator.

[0115] By the above, the optical frequency comb device 10A in which only the carrier envelope offset frequency is modulated is realized, so that the distance measurement based on FMCW can be performed. More specifically, the optical frequency comb device 10A can simultaneously perform the distance measurement at multiple points. The specific distance measurement will be described later.

[0116] (Embodiment 2)

[0117] Next, the structure of the optical frequency comb device according to Embodiment 2 of the present application will be described with reference to Figure 7 The structure of the optical frequency comb device according to Embodiment 2 of the present application will be described with reference to Figure 7 is a diagram schematically showing the optical frequency comb device 10B according to the present embodiment. The basic configuration of the optical frequency comb device 10B is the same as that of the optical frequency comb laser source 10 shown in Figure 2A and Figure 2B . Hereinafter, the description will be made focusing on the difference from the optical frequency comb laser source 10 shown in Figure 2A and Figure 2B , and the common parts will be omitted or simplified.

[0118] As the difference, the optical frequency comb device 10B newly has a phase modulator 20 and a modulation section 21B as shown in Figure 7

[0119] The phase modulator 20 is inserted in the optical waveguide 13w. The phase modulator 20 is provided between the mirror 13m1 and the mirror 13m2. In the present embodiment, two phase modulators 20 are respectively inserted in the first portion 13w1 and the second portion 13w2.​

[0120] The modulation section 21B is an example of a control section, and includes the fixed current source 17, the fixed RF signal generator 18, and the modulation voltage source 19m.

[0121] The fixed current source 17 is connected to the gain medium 13g, and supplies a fixed current (hereinafter referred to as a fixed current) to the gain medium 13g. Specifically, the fixed current source 17 is connected to the p-doped layer 13d2 and the n-doped layer 13dl, and a fixed current flows from the p-doped layer 13d2 to the n-doped layer 13dl. Thus, the fixed current is supplied to the gain medium 13g sandwiched by the p-doped layer 13d2 and the n-doped layer 13dl.

[0122] The fixed RF signal generator 18 is connected to the saturable absorber 13sa, and supplies an RF signal to the saturable absorber 13sa. The fixed RF signal generator 18 is connected specifically in the same manner as in Embodiment 1. The modulation voltage source 19m is connected to the phase modulator 20, and supplies a voltage to the phase modulator 20.

[0123] The fixed current source 17 fixes the carrier envelope offset frequency by fixing the magnitude of the current supplied to the gain medium 13g. In addition, the fixed RF signal generator 18 fixes the repetition frequency by fixing the frequency of the RF signal. Thus, no frequency modulation occurs in this state.

[0124] In contrast, the modulation voltage source 19m modulates the carrier envelope offset frequency by modulating the magnitude of the voltage. Specifically, the phase modulator 20 changes the refractive index in accordance with the supplied voltage. Since the phase modulator 20 is present in the optical waveguide 13w, the phase of the optical frequency comb is modulated. Thus, the carrier envelope offset frequency of the optical frequency comb is modulated. At this time, not only the carrier envelope offset frequency is modulated, but also the repetition frequency is modulated, but since the frequency of the RF signal is fixed, the repetition frequency is fixed.

[0125] By the above, the optical frequency comb device 10B in which only the carrier envelope offset frequency is modulated is realized, so that distance measurement based on FMCW can be performed simultaneously.

[0126] Alternatively, the optical frequency comb device 10B can replace the phase modulator 20 by having a temperature regulating mechanism similar to a heater. This temperature regulating mechanism can change the temperature of the optical waveguide 13w according to the voltage. The optical waveguide 13w expands or contracts with temperature changes, thereby changing its refractive index. That is, like the phase modulator 20, the temperature regulating mechanism can change the refractive index of the optical waveguide 13w. Therefore, by connecting the temperature regulating mechanism to the modulation voltage source 19m and supplying a modulated voltage, the same situation as described above can be achieved. Furthermore, the temperature regulating mechanism can simply apply heat to the optical waveguide 13w, or it may not need to be located within the optical waveguide 13w.

[0127] In this embodiment, since the current supplied to the gain medium 13g is fixed, the intensity of the optical frequency comb is not easily modulated. Therefore, the optical frequency comb device 10B can also be used for applications requiring a certain intensity of optical frequency comb, thus improving its versatility.

[0128] (Implementation Method 3)

[0129] Next, refer to Figure 8 The following describes a structural example of the optical frequency comb device according to Embodiment 3 of the present invention. Figure 8 This diagram schematically illustrates the optical frequency comb device 10C according to this embodiment. The basic structure of the optical frequency comb device 10C is similar to... Figure 2A and Figure 2B The optical frequency comb laser source 10 shown is the same. Hereinafter, it will be used in conjunction with... Figure 2A and Figure 2B The explanation focuses on the differences of the optical frequency comb laser source 10 shown, while the explanation of the common points is omitted or simplified.

[0130] like Figure 8 As shown, the optical frequency comb device 10C is newly equipped with a modulation unit 21C. The modulation unit 21C is an example of a control unit, and includes a fixed current source 17 and a modulated RF signal generator 18m.

[0131] A fixed current source 17 is connected to a gain medium 13g, supplying a fixed current to the gain medium 13g. The specific connection of the fixed current source 17 is the same as in embodiment 2.

[0132] A modulated RF signal generator 18m is connected to a saturable absorber 13sa, supplying a frequency-modulated RF signal (hereinafter referred to as the modulated RF signal) to the saturable absorber 13sa. Specifically, the modulated RF signal generator 18m is connected to the p-doped layer 13d3 and the n-doped layer 13d1, supplying a frequency-modulated high-frequency voltage signal as the modulated RF signal between the p-doped layer 13d3 and the n-doped layer 13d1. Thus, a modulated RF signal is supplied to the saturable absorber 13sa sandwiched between the p-doped layer 13d3 and the n-doped layer 13d1.

[0133] The fixed current source 17 fixes the carrier envelope offset frequency by fixing the magnitude of the current supplied to the gain medium 13g. On the other hand, the modulated RF signal generator 18m modulates the repetition frequency by modulating the frequency of the RF signal.

[0134] Through the above, an optical frequency comb device 10C was realized that modulates only the repetition frequency, thus enabling distance measurement based on FMCW.

[0135] Furthermore, in the above embodiments, the modulation of the current magnitude, the frequency of the RF signal, and the voltage magnitude is... Figure 3 The situation shown is similarly repeated through linear modulation. When modulating the carrier envelope offset frequency, the frequency difference of the nth mode is δf. CEO This becomes a value independent of n. Therefore, by detecting multiple modes separately using wavelength division multiplexing (WDM) or similar methods, distance measurement based on FMCW can be performed for each mode. That is, distance and / or velocity at multiple locations can be measured simultaneously. In this way, when detecting multiple modes separately, since the overlap of the modulation ranges of each mode does not need to be considered, a large modulation range can be ensured. Detection based on wavelength division multiplexing can be implemented, for example, using a demultiplexer that separates the incident light by frequency, and multiple photodetectors that receive the separated light at each frequency.

[0136] On the other hand, when the repetition frequency is modulated, the frequency difference of the nth mode is n×δf rep This becomes dependent on the value of n. Therefore, even without separating the modes for illumination, it is possible to distinguish each mode. Furthermore, in this case, the modulation ranges of the multiple modes contained in the optical frequency comb are within non-overlapping ranges.

[0137] The fixed current source 17, the modulated current source 17m, the fixed RF signal generator 18, the modulated RF signal generator 18m, and the modulated voltage source 19m are each implemented by an electronic circuit including at least one of a resistor, an inductor, a capacitor, a transformer, a diode, a transistor, etc. The electronic circuit can be implemented by integrated circuit (IC) components.

[0138] In each embodiment, the optical waveguide 13w, reflectors 13m1 and 13m2, gain medium 13g, and saturable absorber 13sa are integrated on the same semiconductor substrate 14. That is, the optical frequency comb devices 10A, 10B, and 10C are so-called on-chip optical frequency comb devices. This enables the miniaturization of the optical frequency comb devices 10A, 10B, and 10C.

[0139] At this time, in each embodiment, the modulation sections 21A, 21B, and 21C are configured separately from the semiconductor substrate 14, but are not limited thereto. For example, as shown in FIG. 10, the modulation section 21A can also be integrated in the semiconductor substrate 14. Figure 9 Figure 9 is a diagram schematically showing an optical frequency comb device 10D of a modification example of the embodiment. In Figure 9 , it is a modification example of the optical frequency comb device 10A shown in Figure 6 , but the modulation section 21B or 21C can also be integrated in the semiconductor substrate 14 in the optical frequency comb device 10B or 10C shown in Figure 7 or Figure 8

[0140] (Embodiment 4)

[0141] Next, a measurement device provided with the optical frequency comb device will be described. Figure 10

[0142] Figure 10 is a diagram schematically showing a structure of a measurement device 100 of Embodiment 4. Figure 10 The measurement device 100 shown in FIG. 11 measures a distance to an object 101 and / or a moving speed of the object 101. The measurement device 100 is provided with the optical frequency comb device 10A, couplers 111 and 112, a circulator 113, an emission section 120, a detector 130, and a signal processing circuit 140. In addition, the measurement device 100 can be provided with the optical frequency comb device 10B, 10C, or 10D instead of the optical frequency comb device 10A.

[0143] The couplers 111 and 112 and the circulator 113 are connected to an optical fiber that guides the optical frequency comb laser 5 emitted from the optical frequency comb device 10A. The optical fiber is configured to connect the output section 15 of the optical frequency comb device 10A to the emission section 120, from the circulator 113 to the detector 130, and from the coupler 111 to the coupler 112, respectively.

[0144] In addition, the output section 15 is provided at an end portion of the optical waveguide 13w as shown in Figure 6 . Specifically, the output section 15 is located outside the mirror 13m2 and outputs the optical frequency comb laser 5 that has passed through the mirror 13m2 to the outside. The output section 15 includes, for example, a coupling section to an optical fiber. Specifically, the output section 15 is a grating coupler, but is not limited thereto. The output section 15 can also be output by edge coupling.

[0145] ​​​The coupler 111 branches the optical frequency comb laser 5 into the measurement light 5a and the reference light 5b. In addition, the coupler 111 is an element that branches light at a prescribed intensity ratio, and the frequency and wavelength of the light do not change after branching. That is, the measurement light 5a and the reference light 5b are both optical frequency combs having the same carrier envelope offset frequency and repetition frequency. The intensity ratio of the measurement light 5a and the reference light 5b is, for example, 9:1, but can also be 1:1. The measurement light 5a is emitted from the emission section 120 toward the object 101 via the circulator 113. The reference light 5b is incident on the detector 130 via the coupler 112.

[0146] The emission section 120 is an optical element that emits the measurement light 5a toward the object 101. The emission section 120 is, for example, a prism or a diffraction grating. The emission section 120 emits the measurement light 5a in a direction that differs depending on the frequency. In the present embodiment, the emission section 120 emits the measurement light 5a in a direction that is different for each frequency component included in the measurement light 5a. The emission section 120 is not limited to a prism or a diffraction grating, and can be an optical element that emits light in a direction that differs depending on the frequency. Figure 10 In the present embodiment, the multiple solid arrows extending from the emission section 120 toward the object 101 represent light of each frequency component included in the measurement light 5a. Each of the lights is reflected by a different part of the object 101. The reflected light 5c that is generated by this reflection returns to the emission section 120 and is guided by the circulator 113 toward the coupler 112. In addition, the circulator 113 is an optical element that restricts the direction of travel of light, and suppresses the reflected light 5c guided from the emission section 120 from returning to the coupler 111.

[0147] The coupler 112 couples the reference light 5b and the reflected light 5c and causes them to be incident on the detector 130. The coupling ratio is, for example, 1:1, but is not limited thereto.

[0148] The detector 130 is an example of a light detection section, and the reference light 5b and the reflected light 5c are incident thereon, and an electric signal corresponding to the intensity of the incident light is generated and output. In the detector 130, the reference light 5b and the reflected light 5c interfere with each other and a beat signal is generated. The detector 130 outputs an electric signal that represents the time waveform of the beat signal. In addition, the detector 130 is, for example, a photoelectric conversion element such as a photodiode.

[0149] The signal processing circuit 140 is an example of an arithmetic section, and calculates the distance to the object 101 and / or the speed of the object 101 on the basis of the detection result of the detector 130. Specifically, the signal processing circuit 140 calculates the distance and / or the speed on the basis of the beat signal. The method of calculating the distance performed by the signal processing circuit 140 is as described using the block diagram of FIG. 6, for example. In addition, with respect to the distance, it is also possible to calculate on the basis of the method of the general FMCW. Figure 3

[0150] ​In the present embodiment, since both the reference light 5b and the reflected light 5c are optical frequency combs, the distance to the portion irradiated with light of the corresponding frequency and / or the moving speed of the portion can be calculated by performing the operation by frequency. Thus, the distance and / or the speed of a plurality of portions of the object 101 can be measured at the same time. That is, the measuring device 100 can perform the FMCW-based multi-point simultaneous measurement.

[0151] In addition, the detector 130 can also include, as shown in Figure 11 , a separator 131 that separates the incident light by frequency and a plurality of light receivers 132 that receive the light of each frequency after the separation. The plurality of light receivers 132 are established in one-to-one correspondence with the plurality of frequencies after the separation. In this way, by separating and receiving the signal by frequency, the light of each frequency component can be received with good accuracy, and the accuracy of the distance measurement and the speed measurement can be improved.

[0152] (Other Embodiments)

[0153] The above describes the optical frequency comb device and the measuring device in one or more forms based on the embodiments, but the present application is not limited to these embodiments. As long as the gist of the present application is not deviated from, various modified forms thought by those skilled in the art after the present embodiments, and forms constructed by combining the constituent elements of different embodiments are also included in the scope of the present application.

[0154] For example, the modulation section can not have the modulation current source or the fixed current source. That is, for the gain medium, the stimulated emission can be performed not by electrical excitation but by optical excitation. For example, the modulation section can have a laser source instead of the modulation current source or the fixed current source. The laser source irradiates laser light to the gain medium as excitation light for the gain medium. The laser source can modulate the intensity of the laser light to modulate the carrier envelope offset frequency f CEO . In addition, the laser source can fix the intensity of the laser source to fix the carrier envelope offset frequency f CEO .

[0155] In addition, for example, the modulation section can switch the frequency that is fixed and the frequency that is modulated in the repetition frequency f rep and the carrier envelope offset frequency f CEO . That is, the frequency that is fixed and the frequency that is modulated can not always be the same, and the modulation section can switch the frequency that is fixed and the frequency that is modulated depending on the situation.

[0156] Specifically, the modulation section can include two operation modes including a first mode and a second mode, the first mode fixes the repetition frequency f rep and modulates the carrier envelope offset frequency f CEOThe modulation is performed, and the repetition frequency f is changed in the second mode rep The modulation is performed, and the carrier envelope offset frequency f is changed in the second mode CEO The modulation is performed, and the carrier envelope offset frequency f is changed in the second mode

[0157] In addition, for example, the change in frequency performed by the control section can not be the modulation of the frequency. For example, the control section can also change one of the repetition frequency and the carrier envelope offset frequency between two prescribed values.

[0158] In addition, each of the embodiments described above can be variously changed, replaced, added, omitted, and the like, within the scope of the claims or an equivalent scope thereof.

[0159] Industrial Applicability

[0160] The present application can be utilized as an optical frequency comb device or the like that can change a frequency with good precision, and can be used, for example, for a detection, analysis, and distance measuring device for an object or the like.

[0161] Explanation of Reference Signs

[0162] 5 Optical frequency comb laser

[0163] 5a Measuring light

[0164] 5b Reference light

[0165] 5c Reflected light

[0166] 10 Optical frequency comb laser source

[0167] 10A, 10B, 10C, 10D Optical frequency comb device

[0168] 13 Resonator

[0169] 13d1 n-doped layer

[0170] 13d2, 13d3 p-doped layer

[0171] 13i Intermediate layer

[0172] 13g Gain medium

[0173] 13m1, 13m2 Mirror

[0174] 13s Semiconductor layer

[0175] 13sa Saturable absorber

[0176] 13w Optical waveguide

[0177] 13w1 First portion

[0178] 13w2 Second portion

[0179] 14 semiconductor substrate

[0180] 14a high refractive index layer

[0181] 14b low refractive index layer

[0182] 15 output section

[0183] 16 protective layer

[0184] 17 fixed current source

[0185] 17m modulated current source

[0186] 18 fixed RF signal generator

[0187] 18m modulated RF signal generator

[0188] 19m modulated voltage source

[0189] 20 phase modulator

[0190] 21A, 21B, 21C modulation section

[0191] 100 measurement device

[0192] 101 object

[0193] 111, 112 coupler

[0194] 113 circulator

[0195] 120 emission section

[0196] 130 detector

[0197] 131 splitter

[0198] 132 light receiver

[0199] 140 signal processing circuit

Claims

1. An optical frequency comb device characterized by comprising: an optical waveguide; a first mirror disposed at a first position of the optical waveguide; a second mirror disposed at a second position of the optical waveguide different from the first position; a gain medium and a saturable absorber disposed between the first mirror and the second mirror; and a control section that fixes one of a repetition frequency and a carrier envelope offset frequency of an optical frequency comb output from an end of the optical waveguide and changes the other.

2. The optical frequency comb device according to claim 1, characterized in that the control section includes: a current source that supplies a current to the gain medium; and a signal generator that supplies a high-frequency signal to the saturable absorber.

3. The optical frequency comb device according to claim 1, characterized in that the control section includes: a current source that supplies a current to the gain medium; and a signal generator that supplies a high-frequency signal to the saturable absorber.

4. The optical frequency comb device according to claim 1, characterized in that the control section further includes a voltage source that supplies a voltage to a phase modulator disposed between the first mirror and the second mirror.

5. The optical frequency comb device according to any one of claims 1 to 4, characterized in that the optical waveguide, the first mirror, the second mirror, the gain medium, and the saturable absorber are integrated in a semiconductor substrate.

6. The optical frequency comb device according to claim 5, characterized in that the control section is integrated in the semiconductor substrate.

7. A measurement device characterized by comprising: the optical frequency comb device according to any one of claims 1 to 6; an emission section that emits the optical frequency comb toward an object; a light detection section that receives reflected light of the optical frequency comb from the object; and a calculation section that calculates a distance to the object or a speed of the object based on a detection result obtained by the light detection section.

8. The measurement device according to claim 7, characterized in that the light detection section further receives the optical frequency comb; and the calculation section calculates the distance or the speed based on a beat signal generated by interference between the reflected light and the optical frequency comb in the light detection section.

9. The measurement device according to claim 7 or 8, characterized in that the light detection section includes: a splitter that separates incident light by frequency; and a plurality of light receivers that receive light of each frequency after the separation. ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ 10. The measuring device according to claim 7 or 8, wherein ​

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