Dual optical frequency comb generator and measurement system

Abstract

This dual optical frequency comb generation device (201) comprises a semiconductor substrate (14), a first optical frequency comb laser light source (20) including a first resonator, a second optical frequency comb laser light source (21) that includes a second resonator and that has a different optical pulse repetition frequency than the first optical frequency comb laser light source, two or more output units including output units (50, 51), an optical waveguide (20w) for connecting the first optical frequency comb laser light source (20) and the output unit (50), an optical waveguide (21w) for connecting the second optical frequency comb laser light source (21) and the output unit (51), and an optical waveguide (40) that branches from the optical waveguide (20w) and that is coupled to the optical waveguide (21w). The first optical frequency comb laser light source (20), the second optical frequency comb laser light source (21), the two or more output units, and the optical waveguides (20w, 21w, 40) are integrated on the semiconductor substrate (14).

Description

[Technical field]

[0001] The present disclosure relates to a dual optical frequency comb generator and metrology apparatus. [Background technology]

[0002] By irradiating an object with light and obtaining the frequency spectrum of the light that has passed through the object or the light that has been reflected by the object, the characteristics of the object's optical frequency can be investigated. Conventionally, in order to obtain the frequency spectrum of high-frequency light, a light source with fluctuating intensity and a diffraction grating or prism were used for spectroscopy. This limited the accuracy of the frequency spectrum that could be obtained.

[0003] However, optical frequency comb technology has made it possible to obtain a precise frequency spectrum of light. An optical frequency comb is a comb-like frequency spectrum formed from multiple discrete, equally spaced longitudinal modes. In this specification, laser light having an optical frequency comb is called "optical frequency comb laser light."

[0004] In recent years, dual comb spectroscopy, which uses two optical frequency comb laser beams with slightly different longitudinal mode intervals (repetition frequencies) of the optical frequency comb, has made it easier to obtain the frequency spectrum of light (see, for example, Non-Patent Documents 1 to 3). In dual comb spectroscopy, an object is irradiated with interference light obtained by superimposing these two optical frequency comb laser beams, and the characteristics of the optical frequency of the object can be investigated by obtaining the beat frequency spectrum of the interference light that has passed through the object or that has been reflected by the object. [Prior art documents] [Non-patent literature]

[0005] [Non-Patent Document 1] N. Picque et al., “Frequency comb spectroscopy”, Nature Photonics, 2019, Vol. 13, pp. 146-157 [Non-Patent Document 2] I. Coddington et al., “Dual-comb spectroscopy”, Optica, 2016, Vol. 3, No. 4, pp. 414-426 [Non-Patent Document 3] AL Gaeta et al., “Photonic-chip-based frequency combs”, Nature Photonics, 2019, Vol. 13, pp. 158-169 [Non-Patent Document 4] S. Keyvaninia et al., “Narrow-linewidth short-pulse III-V-on- silicon mode-locked lasers based on a linear and ring cavity geometry”, Optics Express, 2015, Vol. 23, Issue 3, pp. 3221-3229. Summary of the Invention [Problem to be solved by the invention]

[0006] Conventional dual-comb spectroscopy uses two optical frequency combs with different repetition rates as well as various optical elements. This results in a complex and large-sized optical system overall. In recent years, the development of optical frequency combs integrated on a substrate (see Non-Patent Document 4) has made the overall size relatively small. However, this does not change the fact that the system remains very complex, and further miniaturization is expected.

[0007] In addition, optical frequency combs have the problem of being vulnerable to external disturbances such as vibrations. In addition, optical frequency combs are expected to be used for various purposes other than obtaining frequency spectra, and therefore are expected to be highly versatile.

[0008] Therefore, the present disclosure provides a dual optical frequency comb generator and measurement device that is small, resistant to external disturbances, and highly versatile. [Means for solving the problem]

[0009] A dual optical frequency comb generator according to an embodiment of the present disclosure includes a semiconductor substrate, a first optical frequency comb laser source including a first resonator, a second optical frequency comb laser source including a second resonator and having a different optical pulse repetition frequency from the first optical frequency comb laser source, two or more output units including a first output unit and a second output unit, a first optical waveguide connecting the first optical frequency comb laser source and the first output unit, a second optical waveguide connecting the second optical frequency comb laser source and the second output unit, and a third optical waveguide branching from the first optical waveguide and coupled to the second optical waveguide. The first optical frequency comb laser source, the second optical frequency comb laser source, the two or more output units, the first optical waveguide, the second optical waveguide, and the third optical waveguide are integrated on the semiconductor substrate.

[0010] A measurement device according to one embodiment of the present disclosure includes the dual optical frequency comb generator described above, a first optical fiber having one end connected to the first output unit, a second optical fiber having one end connected to the second output unit, a circulator connected to the other end of the first optical fiber, a third optical fiber and a fourth optical fiber, each having one end connected to the circulator, a collimator connected to the other end of the third optical fiber, a coupler that combines and outputs light propagated through each of the third optical fiber and the fourth optical fiber, and a detector that detects light output from the coupler. Effect of the Invention

[0011] According to the present disclosure, it is possible to provide a dual optical frequency comb generator that is small, resistant to external disturbances, and highly versatile. [Brief description of the drawings]

[0012] [Figure 1A] FIG. 1A is a diagram showing a schematic diagram of the change over time in the electric field of optical frequency comb laser light. [Figure 1B] FIG. 1B is a diagram illustrating a frequency spectrum of optical frequency comb laser light. [Diagram 2] FIG. 2 is a schematic diagram of an optical frequency comb laser source having a ring resonator integrated on a semiconductor substrate. [Figure 3A] FIG. 3A is a top view diagram illustrating a schematic of an optical frequency comb laser source having a resonator including a gain medium integrated on a semiconductor substrate. [Figure 3B] FIG. 3B is a cross-sectional view showing a schematic diagram of the optical frequency comb laser source at the position shown by the line IIIB-IIIB in FIG. 3A. [Figure 4] FIG. 4 is a diagram illustrating a schematic diagram of an optical system in dual-comb spectroscopy. [Diagram 5] FIG. 5 is a diagram for explaining the principle of obtaining a frequency spectrum of light in dual-comb spectroscopy. [Figure 6] FIG. 6 is a diagram illustrating a schematic configuration of a dual optical frequency comb generator and a measurement device according to the first embodiment. [Figure 7] FIG. 7 is a diagram showing an example of an electrical signal generated by the detector. [Figure 8] FIG. 8 is a diagram illustrating a schematic configuration of a dual optical frequency comb generator and a measurement device according to a first modification of the first embodiment. In FIG. [Figure 9] FIG. 9 is a diagram illustrating a schematic configuration of a dual optical frequency comb generator and a measurement device according to the second modification of the first embodiment. In FIG. [Figure 10] FIG. 10 is a diagram illustrating a schematic configuration of a dual optical frequency comb generator and a measurement device according to the second embodiment. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0013] (Summary of the Disclosure) A dual optical frequency comb generator according to an embodiment of the present disclosure includes a semiconductor substrate, a first optical frequency comb laser source including a first resonator, a second optical frequency comb laser source including a second resonator and having a different optical pulse repetition frequency from the first optical frequency comb laser source, two or more output units including a first output unit and a second output unit, a first optical waveguide connecting the first optical frequency comb laser source and the first output unit, a second optical waveguide connecting the second optical frequency comb laser source and the second output unit, and a third optical waveguide branching from the first optical waveguide and coupled to the second optical waveguide. The first optical frequency comb laser source, the second optical frequency comb laser source, the two or more output units, the first optical waveguide, the second optical waveguide, and the third optical waveguide are integrated on the semiconductor substrate.

[0014] In this way, not only is the optical frequency comb laser light source integrated on the semiconductor substrate, but two or more output sections and three optical waveguides are also integrated. This integration makes it possible to make the optical system for dual-comb spectroscopy compact and simple. In addition, the increased integration of components makes the system more resistant to external disturbances such as vibrations.

[0015] On the other hand, if all of the optical system is integrated on a semiconductor substrate, dual comb spectroscopy cannot be performed if an error occurs in the semiconductor process of some of the elements. In contrast, according to this aspect, by limiting the integration target to the output section, it is possible to reduce manufacturing errors, and the optical system subsequent to the output section can be freely rearranged. This expands the application options of the dual optical frequency comb generator, and improves its versatility. In this way, according to this aspect, it is possible to provide a dual optical frequency comb generator that is small, resistant to external disturbances, and highly versatile.

[0016] Furthermore, for example, when the semiconductor substrate is viewed in a plan view, the first output portion and the second output portion may be located on different sides of the semiconductor substrate.

[0017] This allows the two output sections to be separated, making it easy to physically connect optical fibers to each of the two output sections.

[0018] Furthermore, for example, each of the first resonator and the second resonator may include a gain medium located on the optical path.

[0019] This eliminates the need to provide a laser light source outside the optical path of the resonator, allowing the resonator to be made more compact.

[0020] Also, for example, the two or more outputs may include a coupling to an optical fiber.

[0021] This allows the optical frequency comb laser light output from the output section to be input into an optical fiber.

[0022] Also, for example, the two or more output sections may include a third output section, and the second optical waveguide may include a fourth optical waveguide branching off from a path connecting the second optical frequency comb laser light source and the second output section and coupled to the third output section.

[0023] This allows the signal light and the reference light to be detected separately. Even if the pulses of the signal light and the reference light overlap, they can be detected separately. In other words, it is possible to eliminate the dead zone where detection is impossible due to the overlap of the pulses of the signal light and the reference light.

[0024] Moreover, a measurement device according to one embodiment of the present disclosure includes the above-mentioned dual optical frequency comb generator, a first optical fiber having one end connected to the first output unit, a second optical fiber having one end connected to the second output unit, a circulator connected to the other end of the first optical fiber, a third optical fiber and a fourth optical fiber, each having one end connected to the circulator, a collimator connected to the other end of the third optical fiber, a coupler that combines and outputs light propagated through each of the third optical fiber and the fourth optical fiber, and a detector that detects light output from the coupler.

[0025] This makes it possible to realize a measurement device that is small, resistant to external disturbances, and highly versatile, similar to the dual optical frequency comb generator described above.

[0026] For example, a measurement device according to an embodiment of the present disclosure may include the dual optical frequency comb generator, a first optical fiber having one end connected to the first output unit, a second optical fiber having one end connected to one of the second output unit and the third output unit, a circulator connected to the other end of the first optical fiber, a third optical fiber and a fourth optical fiber each having one end connected to the circulator, a collimator connected to the other end of the third optical fiber, a coupler that couples the third optical fiber and the fourth optical fiber, a coupler that couples and outputs light propagated through each of the third optical fiber and the fourth optical fiber, and a detector. The detector may include a first detector that detects light output from the coupler and a second detector that detects light output from the other of the second output unit and the third output unit.

[0027] This allows the signal light and the reference light to be detected separately. Even if the pulses of the signal light and the reference light overlap, they can be detected separately. In other words, it is possible to eliminate the dead zone where detection is impossible due to the overlap of the pulses of the signal light and the reference light.

[0028] Furthermore, for example, the measurement device according to one aspect of the present disclosure may further include a sweeping mechanism that sweeps the light emitted from the collimator.

[0029] This makes it possible to change the position on the object where the laser light is irradiated, thereby making it possible to obtain two-dimensional or three-dimensional information about the object.

[0030] Furthermore, for example, the measurement device according to one aspect of the present disclosure may include a signal processing circuit that measures the spectrum of an object based on the detection result by the detector.

[0031] This makes it possible to measure the color of an object, etc. For example, since it is possible to measure gas floating in space, the measurement device can be used as a gas sensor.

[0032] Also, for example, a measurement device according to one aspect of the present disclosure may include a signal processing circuit that measures the distance to an object based on a detection result by the detector.

[0033] This allows the measurement device to be used as a distance measuring device.

[0034] Hereinafter, the embodiment will be specifically described with reference to the drawings.

[0035] The embodiments described below are all comprehensive or specific examples. The numerical values, shapes, materials, components, component arrangements and connection forms, steps, and order of steps 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 that are not described in the independent claims are described as optional components.

[0036] In addition, each figure is a schematic diagram and is not necessarily illustrated precisely. Therefore, for example, the scales in each figure do not necessarily match. In addition, in each figure, substantially the same configurations are given the same reference numerals, and duplicated explanations are omitted or simplified.

[0037] Furthermore, in this specification, terms indicating the relationship between elements, such as parallel or coincident, terms indicating the shape of an element, such as rectangle, and numerical ranges are not expressions that only express a strict meaning, but are expressions that include a substantially equivalent range, for example, a difference of about a few percent.

[0038] In this specification, the terms "upper" and "lower" do not refer to the upper direction (vertically upward) and lower direction (vertically downward) in absolute spatial recognition, but are used as terms defined by a relative positional relationship based on the stacking order in a stacked configuration. The terms "upper" and "lower" are applied not only to the case where two components are arranged with a gap between them and another component exists between the two components, but also to the case where two components are arranged closely together and are in contact with each other.

[0039] (Optical Frequency Comb Laser Light and Dual Comb Spectroscopy) Before describing specific embodiments of the present disclosure, the basic principles of optical frequency comb laser light and dual-comb spectroscopy will be briefly described below.

[0040] First, the time variation and frequency spectrum of the electric field of the optical frequency comb laser light will be described with reference to FIGS. 1A and 1B.

[0041] 1A is a diagram showing an example of a change in the electric field of an optical frequency comb laser beam over time, where the horizontal axis represents time and the vertical axis represents the electric field of the laser beam.

[0042] As shown in FIG. 1A, the optical frequency comb laser light has a repetition period T rep It is composed of a train of optical pulses generated at a repetition period of T repis, 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 of each optical pulse Δt is, for example, 10 fs or more and 1 ps or less.

[0043] The optical frequency comb laser source includes a laser resonator that generates an optical frequency comb laser light by inputting excitation light or by injecting electric charges. The laser resonator will be described in detail later. In the laser resonator, the envelope of the optical pulse propagates at a group velocity v g and the phase velocity v of the waves in the light pulse. p The group velocity v may differ. g and phase velocity v p Due to the difference between the envelopes of two adjacent optical pulses, when they are overlapped so that their envelopes coincide, the phase of the waves in these optical pulses shifts by Δφ, which is smaller than 2π. The repetition period of an optical pulse train is T rep =L / v g It is represented by:

[0044] 1B is a diagram showing a frequency spectrum of an optical frequency comb laser beam, where the horizontal axis represents the frequency and the vertical axis represents the intensity of the laser beam.

[0045] As shown in FIG. 1B, the optical frequency comb laser light has a comb-like frequency spectrum formed by multiple discrete equally spaced lines. The frequencies of the multiple 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 10 GHz or less. The optical path 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 1ns, and the repetition frequency f rep will be 1GHz.

[0046] If the full width at half maximum of the optical frequency comb is Δf, then Δf=1 / Δt. The full width at half maximum of the optical frequency comb Δf is, for example, 1 THz to 100 THz. If we assume that the equidistant lines exist up to near zero frequency, the frequency of the equidistant lines 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 the repetition frequency f rep Lower than the carrier envelope offset frequency f CEO is the 0th mode frequency, then the nth mode frequency in the optical frequency comb, f n f n =f CEO +nf rep The electric field E(t) of the optical frequency comb laser light shown in FIG. 1A has the amplitude and phase of the electric field at the n-th mode frequency fn, respectively, as E n and φ n Then, E(t) = ΣnE n exp[-i(2πf n t+φ n )].

[0047] Next, with reference to FIGS. 2, 3A and 3B, two types of optical frequency comb laser sources integrated on a semiconductor substrate will be briefly described.

[0048] 2 is a diagram showing an optical frequency comb laser source having an external light source and a ring resonator. As shown in FIG. 2, the optical frequency comb laser source includes an optical waveguide 3w, a ring resonator 3, and a semiconductor substrate 4. The optical waveguide 3w and the ring resonator 3 are integrated in the semiconductor substrate 4. The CW laser source 1 is not integrated in the semiconductor substrate 4.

[0049] The CW laser light source 1 emits a laser light 2. However, the laser light 2 has a single longitudinal mode and is adjusted to the resonance frequency of the ring resonator 3. The CW laser light source 1 emits the laser light 2 toward a semiconductor substrate 4.

[0050] When the laser light 2 is input to the ring resonator 3 via the optical waveguide 3w integrated in the semiconductor substrate 4, four-wave mixing, which is a nonlinear optical effect, occurs in the ring resonator 3. As a result, the optical frequency comb laser light 5 is generated from the semiconductor substrate 4. At this time, f rep is equal to the speed of light divided by the optical path length of the ring resonator 3. The optical path length of the ring resonator 3 is the resonator length of the ring resonator 3 multiplied by the refractive index. The resonator length is the circumferential length of the ring-shaped optical path.

[0051] Fig. 3A is a top view of an optical frequency comb laser source having a resonator including a gain medium integrated on a semiconductor substrate. Fig. 3B is a cross-sectional view of the optical frequency comb laser source at the position indicated by line IIIB-IIIB in Fig. 3A. For reference, mutually orthogonal X-axis, Y-axis, and Z-axis are shown in schematic form for the sake of convenience of explanation, but are not intended to limit the orientation during use.

[0052] 3A and 3B, the optical frequency comb laser source 10 includes a resonator 13, a semiconductor substrate 14, and a protective layer 16. In the illustrated example, the surface of the semiconductor substrate 14 is parallel to the XY plane. As shown in FIG. 3B, the semiconductor substrate 14 includes a high refractive index layer 14a, such as Si, and a SiO 2 The protective layer 16 has a laminated structure in which the high refractive index layer 14a and the low refractive index layer 14b such as SiO are laminated in this order in the Z-axis direction. The refractive index of the high refractive index layer 14a is higher than that of the low refractive index layer 14b. The semiconductor substrate 14 does not necessarily have to include the high refractive index layer 14a. The protective layer 16 is, for example, made of SiO 2 or 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.

[0053] The resonator 13 is an example of a laser resonator having a predetermined optical path length. As shown in FIG. 3A, the resonator 13 includes a semiconductor layer 13s, optical waveguides 13w1 and 13w2, and mirrors 13m1 and 13m2. As shown in FIG. 3B, the resonator 13 includes an n-doped layer 13d1, and p-doped layers 13d2 and 13d3. The resonator 13 also includes a gain medium 13g and a saturable absorber 13sa. Parts of the semiconductor layer 13s function as the gain medium 13g and the saturable absorber 13sa, respectively.

[0054] In Fig. 3A, the planar shape of the semiconductor layer 13s in the resonator 13 is represented by a dotted line. The semiconductor layer 13s is tapered at both ends. The tips of the tapers overlap with the optical waveguides 13w1 and 13w2 in a top view. This allows light passing through the semiconductor layer 13s to be efficiently propagated to the optical waveguides 13w1 and 13w2.

[0055] As shown in FIG. 3B, the optical waveguide 13w1 in the resonator 13 is embedded in the low refractive index layer 14b in the semiconductor substrate 14. The optical waveguide 13w1 may be provided on the low refractive index layer 14b. The optical waveguide 13w1 may be formed of at least one high refractive index material selected from the group consisting of Si and SiN. The refractive index of the optical waveguide 13w1 is higher than the refractive index of the low refractive index layer 14b in the semiconductor substrate 14 and the refractive index of the protective layer 16. This allows light to propagate through the optical waveguide 13w1 by total reflection. The same applies to the optical waveguide 13w2.

[0056] The mirror 13m1 may be formed, for example, from a distributed Bragg reflector. In a distributed Bragg reflector, light is reflected by Bragg reflection caused by a periodic structure of the refractive index. The mirror 13m1 is provided at the end of the optical waveguide 13w1. The mirror 13m1 reflects the light propagated through the optical waveguide 13w1. The mirror 13m1 may be formed, for example, from a metal as long as it has a reflecting function. The same applies to the mirror 13m2. The mirror 13m2 is provided at the end of the optical waveguide 13w2. The mirror 13m2 reflects the light propagated through the optical waveguide 13w2.

[0057] Mirror 13m2 has a lower reflectance than mirror 13m1. Specifically, mirror 13m1 has a reflectance substantially equal to 100%, whereas mirror 13m2 has a reflectance of, for example, 90%. Mirror 13m2 reflects most of the light propagating through optical waveguide 13w2, but transmits a portion of the light. The light transmitted through mirror 13m2 becomes optical frequency comb laser light 5.

[0058] 3B, the semiconductor layer 13s is sandwiched between an n-doped layer 13d1 and p-doped layers 13d2 and 13d3. The positional relationship between the n-doped layer 13d1 and the p-doped layers 13d2 and 13d3 may be reversed.

[0059] The semiconductor layer 13s, the n-doped layer 13d1, and the p-doped layers 13d2 and 13d3 are buried in a protective layer 16. The bottom surface of the n-doped layer 13d1 may be in contact with the surface of the semiconductor substrate 14. Both ends of the n-doped layer 13d1 may be in contact with the optical waveguides 13w1 and 13w2, respectively.

[0060] The semiconductor layer 13s may be formed of, for example, a III-V group semiconductor material, which may include, for example, at least one material selected from the group consisting of ZnSe, InGaAlP, InGaAs, GaInAsP, GaInAsSb, InP, GaN, GaAs, InGaAs, AlGaAs, and AlInGaN.

[0061] The semiconductor layer 13s includes a gain medium 13g and a saturable absorber 13sa. The gain medium 13g is a part of the semiconductor layer 13s and is sandwiched between the n-doped layer 13d1 and the p-doped layer 13d2. The saturable absorber 13sa is a part of the semiconductor layer 13s and is sandwiched between the n-doped layer 13d1 and the p-doped layer 13d3.

[0062] The n-doped layer 13d1 is an n-type semiconductor layer. The n-doped layer 13d1 is formed by doping an n-type impurity into a III-V semiconductor material, which is the same as the semiconductor layer 13s. As the n-type impurity, for example, a tetravalent element such as Si or a hexavalent element such as selenium (Se) can be used.

[0063] The p-doped layers 13d2 and 13d3 are p-type semiconductor layers. The p-doped layers 13d2 and 13d3 are formed by doping the same III-V group semiconductor material as the semiconductor layer 13s with a p-type impurity. For example, a divalent element such as zinc (Zn) can be used as the p-type impurity. The p-doped layers 13d2 and 13d3 have, for example, the same composition.

[0064] The p-doped layer 13d2 and the p-doped layer 13d3 are separated from each other. Different electrodes (not shown) are attached to the p-doped layers 13d2 and 13d3. A current is injected into the p-doped layer 13d2 via the electrodes. A reverse bias voltage is applied between the p-doped layer 13d3 and the n-doped layer 13d1. With this voltage application, a part of the semiconductor layer 13s that is in contact with the p-doped layer 13d3 functions as a saturable absorber 13sa. The saturable absorber 13sa may be formed using carbon nanotubes. The saturable absorber 13sa may be integrated with the mirrors 13m1 and 13m2.

[0065] Similarly to the p-doped layer 13d2, an electrode (not shown) is attached to the n-doped layer 13d1. A part of the semiconductor layer 13s into which charges are injected from the electrodes attached to each of the n-doped layer 13d1 and the p-doped layer 13d2 functions as a gain medium 13g from which light is stimulated and emitted. This stimulated and emitted light is repeatedly reflected between the mirror 13m1 and the mirror 13m2 via the optical waveguide 13w2. That is, the light is amplified by passing through the gain medium 13g many times. The amplified light becomes an optical pulse train mode-locked by the saturable absorber 13sa. Only the wavelength corresponding to the optical path length of the resonator 13, that is, the resonator length multiplied by the refractive index, is amplified. As a result, the optical frequency comb laser light 5 is emitted from the resonator 13. The optical path length of the resonator 13 is the optical path length between the mirror 13m1 and the mirror 13m2.

[0066] Next, the principle of dual-comb spectroscopy will be briefly described with reference to FIGS.

[0067] Fig. 4 is a schematic diagram of an optical system in dual-comb spectroscopy. The measurement device 100 shown in Fig. 4 includes a first optical frequency comb laser source 20, a second optical frequency comb laser source 21, an optical fiber 30, couplers 31a, 31b, and 31c, a circulator 32, a collimator 33, and a detector 35. In Fig. 4, the path of the optical fiber 30 is indicated by a dashed line.

[0068] The first optical frequency comb laser light source 20 includes a first laser resonator (not shown) that emits a first optical frequency comb laser light 20L. The second optical frequency comb laser light source 21 includes a second laser resonator (not shown) that emits a second optical frequency comb laser light 21L. The optical path lengths of the first laser resonator and the second laser resonator are different from each other.

[0069] The first optical frequency comb laser light 20L has an n-th mode frequency f 1n But, f 1n =f CEO1 +nf rep1 The second optical frequency comb laser light 21L has an n-th mode frequency f2n But, f 2n =f CEO2 +nf rep2 and a second optical frequency comb represented by f CEO1 and f CEO2 are the carrier envelope offset frequencies of the first and second optical frequency combs, respectively. f rep1 and f rep2 are the repetition rates of the first and second optical frequency combs, respectively. f rep1 and f rep2 is slightly different, f rep2 =f rep1 +δ f The following relationship holds: δ f f rep1 Much smaller than δ f For example, f rep1 1 / 10 3 From 1 / 10 9 For example, it is greater than 0 Hz and equal to or less than 10 MHz.

[0070] 4, the components of the measurement device 100 are connected by an optical fiber 30. That is, optical elements such as couplers 31a, 31b, and 31c, a circulator 32, a collimator 33, and a detector 35 are arranged on the path of the optical fiber 30. The first optical frequency comb laser source 20 and the second optical frequency comb laser source 21 are connected to the ends of the optical fiber 30.

[0071] The couplers 31a, 31b, and 31c are optical elements that split or combine light. The circulator 32 is an optical element that controls the traveling direction of light. The collimator 33 is an optical element that converts light into parallel light and emits it. The detector 35 is an optical element that generates and outputs an electrical signal by photoelectrically converting the incident light. The signal level of the electrical signal corresponds to the intensity of the incident light. The detector 35 is a photoelectric conversion element such as a photodiode or a phototransistor.

[0072] The first optical frequency comb laser light 20L is split into two, light 20Lt and light 20Lr, by the coupler 31a. The light 20Lt passes through the circulator 32, is emitted from the collimator 33, and is incident on the object 34. Then, the light 20Lt is reflected by the object 34. The reflected light 20R is incident on the collimator 33 and then directed to the coupler 31c by the circulator 32. On the other hand, the light 20Lr goes from the coupler 31a to the coupler 31b, where it is combined with the second optical frequency comb laser light 21L and directed to the coupler 31c. Then, in the coupler 31c, the reflected light 20R, the light 20Lr, and the second optical frequency comb laser light 21L are combined and directed to the detector 35. These lights interfere with each other in the detector 35, generating a beat.

[0073] FIG. 5 is a diagram for explaining the principle of obtaining a frequency spectrum of light in dual comb spectroscopy. FIG. 5(a) shows a schematic diagram of the spectrum of the first optical frequency comb and the second optical frequency comb. The solid line represents the first optical frequency comb, and the dashed line represents the second optical frequency comb. FIG. 5(b) shows a schematic diagram of the beat frequency spectrum of the interference light. The difference between the closest mode frequencies of the first optical frequency comb and the second optical frequency comb corresponds to the beat frequency.

[0074] From the beat frequency spectrum, the optical frequency characteristics of the object 34 can be investigated. For example, it is possible to investigate which frequency of light is absorbed by the object 34 and how much of it. If one of the multiple mode frequencies in the first optical frequency comb matches one of the multiple mode frequencies in the second optical frequency comb, a beat frequency of zero appears. This makes it easy to investigate the optical frequency characteristics of the object 34 using the matching mode frequency as a reference.

[0075] The advantage of dual-comb spectroscopy is that it can obtain information from high-frequency light on the order of terahertz (THz) by down-converting it to radio frequencies on the order of megahertz (MHz). The time waveform of signal waves with frequencies on the order of gigahertz (GHz) or less can be detected by a general detector.

[0076] However, it is difficult to detect the time waveform of a signal wave with a frequency on the order of THz or higher using a general detector. For this reason, signal waves with frequencies on the order of THz or higher have traditionally been detected by splitting them into individual frequencies using a spectrometer such as a diffraction grating or prism. This frequency sweep takes time, so the frequency spectrum of light cannot be obtained in a short time.

[0077] In dual-comb spectroscopy, the time waveform of the radio frequency beat can be detected by a general detector. By performing a Fourier transform on the time waveform of the beat, the beat frequency spectrum shown in Figure 5(b) can be obtained in a short time. This makes it possible to obtain the frequency spectrum of high-frequency light with high accuracy in a short time.

[0078] The inventors have conceived of a simple dual optical frequency comb generator that can be realized by integrating some of the optical elements arranged on the path of the optical fiber 30 shown in Fig. 4 on the same semiconductor substrate as the first optical frequency comb laser source 20 and the second optical frequency comb laser source 21. Specific embodiments will be described below.

[0079] (Embodiment 1) First, a configuration example of a dual optical frequency comb generator and a measurement device according to the first embodiment will be described with reference to Fig. 6. Fig. 6 is a diagram showing a schematic configuration of a dual optical frequency comb generator and a measurement device according to the present embodiment.

[0080] The measurement device 200 includes a dual optical frequency comb generator 201, a plurality of optical fibers 30a, 30b, 30c, 30d and 30e, a coupler 31c, a circulator 32, a collimator 33, a detector 35, and a signal processing circuit .

[0081] The dual optical frequency comb generator 201 includes a first optical frequency comb laser source 20, a second optical frequency comb laser source 21, two output sections 50 and 51, an optical waveguide 20w, an optical waveguide 21w, and an optical waveguide 40. All of these are integrated on the same semiconductor substrate 4 or 14. In the following description, the first optical frequency comb laser source 20 will be simply referred to as the "first laser source 20" and the second optical frequency comb laser source 21 will be simply referred to as the "second laser source 21".

[0082] The first laser light source 20 includes a first laser resonator having a first optical path length. The optical path length corresponds to the product of the actual distance and the refractive index. The second laser light source 21 includes a second laser resonator having a second optical path length. The first laser light source 20 and the second laser light source 21 here respectively refer to two types of optical frequency comb laser light sources that can be integrated on a semiconductor substrate as described in FIG. 2 or FIG. 3A and FIG. 3B. The first laser light source 20 and the second laser light source 21 are, for example, of the same type.

[0083] 2, the ring resonator 3 and optical waveguide 3w of the first laser light source 20, the ring resonator 3 and optical waveguide 3w of the second laser light source 21, the optical waveguides 20w, 21w and 40, and the output sections 50 and 51 are formed. The optical path length of the ring resonator 3 of the first laser light source 20 and the optical path length of the ring resonator 3 of the second laser light source 21 are different from each other. The CW laser light source 1 may or may not be integrated into the semiconductor substrate 4.

[0084] Alternatively, the resonator 13 of the first laser light source 20, the resonator 13 of the second laser light source 21, the optical waveguides 20w, 21w, and 40, and the output sections 50 and 51 are formed on the semiconductor substrate 14 shown in Fig. 3B. The optical path length of the resonator 13 of the first laser light source 20 and the optical path length of the resonator 13 of the second laser light source 21 are different from each other. For example, the distance between the mirrors 13m1 and 13m2 of the first laser light source 20 and the distance between the mirrors 13m1 and 13m2 of the second laser light source 21 are different from each other.

[0085] The optical waveguide 20w is an example of a first optical waveguide that connects the first laser light source 20 and the output section 50. The optical waveguide 21w is an example of a second optical waveguide that connects the second laser light source 21 and the output section 51.

[0086] The optical waveguide 40 is an example of a third optical waveguide that branches from the optical waveguide 20w and couples with the optical waveguide 21w. That is, the optical waveguide 40 serves as a branching device in the optical waveguide 20w and as a coupler in the optical waveguide 21w. The optical waveguide 40 serves as the coupler 31a and the coupler 31b in FIG. 4. The optical waveguide 40 has a structure that utilizes evanescent coupling, but is not limited to this. The optical waveguide 40 may be, for example, a Y-shaped waveguide, as long as it has the functions of branching and coupling.

[0087] The optical waveguides 20w, 21w, and 40 are formed in the semiconductor substrate 4 or 14, respectively. For example, like the optical waveguides 13w1 and 13w2 shown in Fig. 3B, the optical waveguides 20w, 21w, and 40 are formed by being embedded in the low-refractive-index layer 14b using a material having a refractive index higher than that of the low-refractive-index layer 14b. For example, the optical waveguides 20w, 21w, and 40 are formed using a material such as Si or SiN.

[0088] The output unit 50 is an example of a first output unit, and outputs the laser light emitted from the first laser light source 20. Specifically, the first optical frequency comb laser light 20L emitted from the first laser light source 20 is separated into light 20Lt propagating through the optical waveguide 20w and light 20Lr propagating through the optical waveguide 40. Of these, the output unit 50 outputs the light 20Lt.

[0089] The output unit 51 is an example of a second output unit, and outputs a light obtained by combining the laser light emitted from the first laser light source 20 and the laser light emitted from the second laser light source 21. Specifically, the output unit 51 outputs the second optical frequency comb laser light 21L emitted from the second laser light source 21 and the light 20Lr propagated through the optical waveguide 40.

[0090] Each of the output sections 50 and 51 includes a coupling section for an optical fiber. Each of the output sections 50 and 51 is, for example, a grating coupler, but is not limited to this. The output sections 50 and 51 may be, for example, an output by edge coupling, as long as they can output the light in the optical waveguide.

[0091] The optical fiber 30a is an example of a first optical fiber, and one end is connected to the output unit 50 and the other end is connected to the circulator 32. The optical fiber 30a propagates the light 20Lt emitted by the first laser light source 20 and emitted from the output unit 50 through the optical waveguide 20w to the circulator 32.

[0092] The optical fiber 30b is an example of a second optical fiber, and one end is connected to the output unit 51 and the other end is connected to the coupler 31c. The optical fiber 30b propagates, to the coupler 31c, the light 20Lr emitted by the first laser light source 20, which passes through the optical waveguide 40 and is output from the output unit 51, and the second optical frequency comb laser light 21L (hereinafter simply referred to as "light 21L") emitted by the second laser light source 21, which passes through the optical waveguide 21w and is output from the output unit 51.

[0093] The optical fiber 30c is an example of a third optical fiber, and one end is connected to the circulator 32 and the other end is connected to the collimator 33. The optical fiber 30c propagates the light 20Lt that has been propagated through the optical fiber 30a and passed through the circulator 32 to the collimator 33. The optical fiber 30c also propagates the reflected light 20R from the object 34 that has entered the collimator 33 to the circulator 32. The circulator 32 is configured so that the light 20Lt does not enter the optical fiber 30d.

[0094] The optical fiber 30d is an example of a fourth optical fiber, and has one end connected to the circulator 32 and the other end connected to the coupler 31c. The optical fiber 30d propagates the reflected light 20R that has been propagated through the optical fiber 30c and passed through the circulator 32 to the coupler 31c. The circulator 32 is configured to prevent the reflected light 20R from entering the optical fiber 30a.

[0095] The optical fiber 30e is an example of a fifth optical fiber, and has one end connected to the coupler 31c and the other end connected to the detector 35. The optical fiber 30e propagates, to the detector 35, the reflected light 20R propagated through the optical fiber 30d and the light 20Lr and light 21L propagated through the optical fiber 30b.

[0096] In the detector 35, beats are generated by the interference between the reflected light 20R and the light 21L, and by the interference between the light 20Lr and the light 21L. The beat based on the interference between the reflected light 20R and the light 21L is a signal light according to the characteristics of the object 34. The beat based on the interference between the light 20Lr and the light 21L is a reference light.

[0097] The detector 35 photoelectrically converts each beat to generate an electrical signal, for example, as shown in Fig. 7. Fig. 7 is a diagram showing an example of an electrical signal generated by the detector. As shown in Fig. 7, the electrical signal includes a detection signal corresponding to the signal light and a reference signal corresponding to the reference light.

[0098] The signal processing circuit 36 ​​measures the spectrum of the object 34 based on the detection result by the detector 35. Specifically, the signal processing circuit 36 ​​performs a Fourier transform on the detection signal and the reference signal, respectively. As a result, beat frequency spectra as shown in FIG. 5(b) are obtained for each of the detection signal and the reference signal. The signal processing circuit 36 ​​can determine frequency components absorbed by the object 34 by comparing the beat frequency spectrum of the detection signal with the beat frequency spectrum of the reference signal. In this way, the spectrum of the object 34 can be measured.

[0099] Furthermore, the signal processing circuit 36 ​​may measure the distance to the object 34 based on the detection result by the detector 35. Specifically, the signal processing circuit 36 ​​measures the time difference between the detection signal and the reference signal, and measures the distance to the object 34 based on a ToF (Time of Flight) method. Alternatively, the signal processing circuit 36 ​​may perform a Fourier transform on the time waveforms of the detection signal and the reference signal, thereby acquiring phase information of the detection signal and the reference signal, and measure the distance to the object 34 based on the difference between the two pieces of acquired phase information.

[0100] As described above, in the measurement device 200 according to the present embodiment, the number of optical elements integrated on the semiconductor substrate 4 or 14 is increased compared to the conventional optical system of dual comb spectroscopy. Therefore, the measurement device 200 is smaller and more resistant to disturbances than the conventional one, and can be used simply as a dual comb spectroscopy. spectroscopy This can be done.

[0101] In addition, the number and arrangement of the coupler 31c, the circulator 32, the collimator 33, and the optical fibers can be freely changed in design. This improves the versatility of the measurement device 200. In addition, compared to the case where the coupler 31c, the circulator 32, and the collimator 33 are all integrated on a semiconductor substrate, the risk of failure in the semiconductor process is lower, so that the optical loss on the semiconductor substrate can be reduced. This improves the yield during manufacture. Furthermore, the reflected light 20R reaches the detector 35 without passing through the output units 50 and 51 including the coupling parts between the optical fibers and the waveguides on the semiconductor substrate, so it is not affected by the optical loss due to the coupling parts. This allows the measurement device 200 to be miniaturized without reducing the detection sensitivity.

[0102] <Variation 1> Next, a modification of the first embodiment will be described with reference to Fig. 8. Fig. 8 is a diagram illustrating a schematic configuration of a dual optical frequency comb generator and a measurement device according to a modification of the first embodiment.

[0103] As shown in FIG. 8, the measurement device 300 includes a dual optical frequency comb generator 301 instead of the dual optical frequency comb generator 201 compared to the measurement device 200 shown in FIG. 6. The only difference between the dual optical frequency comb generator 301 and the dual optical frequency comb generator 201 is the positional relationship between the two output units 50 and the output unit 51. In the case of the dual optical frequency comb generator 201 shown in FIG. 6, the two output units 50 and 51 are both located on the same side of the semiconductor substrate 4 or 14. In contrast, in this modification, the output units 50 and 51 are located on different sides of the semiconductor substrate 4 or 14. For example, when the semiconductor substrate 4 or 14 has a rectangular shape in plan view, the side on which the output unit 50 is provided and the side on which the output unit 51 is provided are opposite sides to each other. As a result, the output direction of light from the output unit 50 is opposite to the output direction of light from the output unit 51.

[0104] In reality, one side of the semiconductor substrate 4 or 14 may only have a length of a few centimeters. Therefore, when the two output units 50 and 51 are close to each other, it is physically difficult to connect them to the optical fibers. In contrast, according to this modification, the distance between the two output units 50 and 51 can be increased. This makes it easy to connect the two output units 50 and 51 to the optical fibers 30a and 30b, respectively.

[0105] <Variation 2> Next, a second modification of the first embodiment will be described with reference to Fig. 9. Fig. 9 is a diagram illustrating a schematic configuration of a dual optical frequency comb generator and a measurement device according to the second modification of the first embodiment.

[0106] As shown in FIG. 9, the measurement device 400 is different from the measurement device 200 shown in FIG. 6 in that it newly includes a scan mechanism 60. The scan mechanism 60 is an example of a sweep mechanism that sweeps the light 20Lt emitted from the collimator 33. The scan mechanism 60 is, for example, a galvano scanner. However, the scan mechanism 60 may be another optical element as long as it can sweep the light 20Lt two-dimensionally. For example, the scan mechanism 60 may be a stepping motor that changes the position and attitude of the collimator 33. According to this modification, the scan mechanism 60 is provided, so that two-dimensional or three-dimensional information of the object 34 can be obtained.

[0107] (Embodiment 2) Next, a second embodiment will be described.

[0108] The main difference between the second embodiment and the first embodiment is that the number of output units in the dual optical frequency comb generator is three. In the following, the differences from the first embodiment will be mainly described, and the description of the commonalities will be omitted or simplified.

[0109] Fig. 10 is a diagram showing the configuration of a dual optical frequency comb generator and a measurement device according to this embodiment. As shown in Fig. 10, the measurement device 500 includes a dual optical frequency comb generator 501 instead of the dual optical frequency comb generator 201 of the measurement device 200 shown in Fig. 6. Furthermore, the measurement device 500 includes two detectors 35a and 35b instead of the detector 35, and an optical fiber 30f.

[0110] Compared to the dual optical frequency comb generator 201 , the dual optical frequency comb generator 501 further comprises an optical waveguide 41 and an output section 52 .

[0111] The optical waveguide 41 is an example of a fourth optical waveguide that branches off from a path connecting the second laser light source 21 and the output unit 51 and is coupled to the output unit 52. The optical waveguide 41 has a structure that utilizes, for example, evanescent coupling, similar to the optical waveguide 40, but is not limited thereto.

[0112] The output unit 52 is an example of a third output unit, and outputs the laser light emitted from the second laser light source 21. Specifically, the second optical frequency comb laser light 21L emitted from the second laser light source 21 is separated into light 21Lr propagating through the optical waveguide 21w and light 21Lt propagating through the optical waveguide 41. The output unit 52 outputs the light 21Lt. The output unit 52 is, for example, a grating coupler, similar to the output units 50 and 51, but is not limited thereto.

[0113] In this way, in the dual optical frequency comb generator 501, not only the first optical frequency comb laser light 20L emitted by the first laser light source 20, but also the second optical frequency comb laser light 21L emitted by the second laser light source 21 is separated into two lights 21Lt and 21Lr, and each can be extracted from a different output section.

[0114] 10, an optical fiber 30f is connected to an output unit 51 that outputs light 20Lr and light 21Lr. The optical fiber 30f is an example of a sixth optical fiber, and one end is connected to the output unit 51 and the other end is connected to the detector 35b. The optical fiber 30f propagates the light 20Lr and light 21Lr to the detector 35b.

[0115] In the detector 35b, a beat is generated as a reference light by interference between the light 20Lr and the light 21Lr. The detector 35b is an example of a second detector, and is a detector dedicated to detecting the reference light.

[0116] An optical fiber 30b is connected to an output unit 52 that outputs the light 21Lt. The light 21Lt propagated through the optical fiber 30b is coupled with the reflected light 20R propagating through the optical fiber 30d by a coupler 31c, passes through an optical fiber 30e, and is detected by a detector 35a.

[0117] In the detector 35a, a beat is generated as a signal light due to interference between the reflected light 20R and the light 21Lt. The detector 35a is a dedicated detector for detecting the signal light.

[0118] In this manner, in the present embodiment, the detectors 35a and 35b, which are an example of the first detector and are dedicated to detecting the reference light and the signal light, respectively, are provided. Note that the detectors 35a and 35b are each a photoelectric conversion element such as a photodiode, similar to the detector 35.

[0119] For example, the pulses of the reference light and the signal light shown in Fig. 7 may overlap. When the pulses overlap, a single detector cannot distinguish between the reference light and the signal light. In contrast, in this embodiment, even when the reference light and the signal light overlap, they can be detected individually.

[0120] In the present embodiment, similarly to the first modification of the first embodiment, the three output units 50, 51, and 52 may be provided on different sides of the semiconductor substrate 4 or 14. In other words, one output unit may be provided on each of the three sides of the semiconductor substrate 4 or 14.

[0121] (Other embodiments) Although the dual optical frequency comb generator and the measurement device according to one or more aspects have been described based on the embodiments, the present disclosure is not limited to these embodiments. As long as it does not deviate from the gist of the present disclosure, various modifications conceivable by those skilled in the art to the present embodiments and forms constructed by combining components of different embodiments are also included in the scope of the present disclosure.

[0122] For example, in each of the above embodiments and variants, an example has been shown in which the reflected light 20R from the object 34 is detected by the detector 35 or 35a, but the detector 35 or 35a may also detect transmitted light that has passed through the object 34.

[0123] Also, for example, in the second embodiment, the optical waveguide 40 may be coupled to the optical waveguide 41 and then coupled to the output unit 52. In this case, the output unit 52 outputs the light 20Lr and the light 21Lr, and is therefore connected to a detector 35b for detecting the reference light via an optical fiber 30f. The output unit 51 outputs the light 21Lt, and is therefore connected to a detector 35a for detecting the signal light via an optical fiber 30b, a coupler 31c, and an optical fiber 30e.

[0124] For example, the first laser light source 20 and the second laser light source 21 may be different types of optical frequency comb light sources. For example, one of the first laser light source 20 and the second laser light source 21 includes the ring resonator 3 and the optical waveguide 3w shown in FIG. 2, and the first laser light source 20 and the second laser light source 21 The other of these may include a resonator 13 as shown in FIG. 3A.

[0125] Furthermore, each of the above embodiments can be modified, substituted, added, omitted, and the like in various ways within the scope of the claims or their equivalents. [Industrial Applicability]

[0126] The present disclosure can be used as a dual optical frequency comb generator that is small, resistant to external disturbances, and highly versatile, and can be used, for example, in object analysis devices and distance measuring devices. [Explanation of symbols]

[0127] 1 CW laser light source 2. Laser light 3. Ring resonator 3w, 13w1, 13w2, 20w, 21w, 40, 41 optical waveguide 4, 14 Semiconductor substrate 5. Optical frequency comb laser light 10 Optical Frequency Comb Laser Source 13 Resonator 13d1 n-doped layer 13d2, 13d3 p-doped layers 13g Gain medium 13m1, 13m2 mirror 13s Semiconductor layer 13sa Saturable absorber 14a High refractive index layer 14b Low refractive index layer 16 Protective layer 20. First Optical Frequency Comb Laser Source 20L 1st optical frequency comb laser light 20Lr, 20Lt, 21Lr, 21Lt light 20R Reflected Light 21 Second optical frequency comb laser source 21L 2nd optical frequency comb laser light 30, 30a, 30b, 30c, 30d, 30e, 30f Optical fiber 31a, 31b, 31c couplers 32 Circulator 33 Collimator 34 Object 35, 35a, 35b Detectors 36 Signal Processing Circuit 50, 51, 52 Output section 60 Scanning Mechanism 100, 200, 300, 400, 500 Measuring device 201, 301, 501 Dual optical frequency comb generator

Claims

1. A semiconductor substrate; a first optical frequency comb laser source including a first resonator; a second optical frequency comb laser source including a second resonator and having a different optical pulse repetition frequency from the first optical frequency comb laser source; two or more outputs including a first output and a second output; a first optical waveguide connecting the first optical frequency comb laser light source and the first output section; a second optical waveguide connecting the second optical frequency comb laser light source and the second output section; a third optical waveguide branched from the first optical waveguide and coupled to the second optical waveguide; Equipped with the first optical frequency comb laser source, the second optical frequency comb laser source, the two or more outputs, the first optical waveguide, the second optical waveguide, and the third optical waveguide are integrated on the semiconductor substrate; the first output section outputs the guided light of the first optical waveguide to an outside of the semiconductor substrate; the second output section outputs the guided light of the second optical waveguide to an outside of the semiconductor substrate. Dual optical frequency comb generator.

2. When the semiconductor substrate is viewed in a plan view, the first output unit and the second output unit are located on different sides of the semiconductor substrate.

2. The dual optical frequency comb generator of claim 1.

3. each of the first resonator and the second resonator includes a gain medium located on an optical path; 3. A dual optical frequency comb generator according to claim 1 or 2.

4. the two or more outputs include a coupling to an optical fiber; A dual optical frequency comb generator according to any one of claims 1 to 3.

5. the two or more outputs include a third output; the second optical waveguide includes a fourth optical waveguide branching off from a path connecting the second optical frequency comb laser light source and the second output section and coupled to the third output section; A dual optical frequency comb generator according to any one of claims 1 to 4.

6. A dual optical frequency comb generator according to any one of claims 1 to 4; a first optical fiber having one end connected to the first output; a second optical fiber having one end connected to the second output; a circulator connected to the other end of the first optical fiber; a third optical fiber and a fourth optical fiber, each having one end connected to the circulator; a collimator connected to the other end of the third optical fiber; a coupler that couples and outputs the light propagated through the second optical fiber and the fourth optical fiber; a detector for detecting light output from the coupler; Measuring equipment.

7. A dual optical frequency comb generator according to claim 5; a first optical fiber having one end connected to the first output; a second optical fiber having one end connected to one of the second output portion and the third output portion; a circulator connected to the other end of the first optical fiber; a third optical fiber and a fourth optical fiber, each having one end connected to the circulator; a collimator connected to the other end of the third optical fiber; a coupler that couples and outputs the light propagated through the second optical fiber and the fourth optical fiber; A detector; Equipped with The detector comprises: a first detector for detecting light output from the coupler; a second detector that detects light output from the other of the second output section and the third output section; Measuring equipment.

8. Further, a sweeping mechanism for sweeping the light emitted from the collimator is provided. The measuring device according to claim 6 or 7.

9. A signal processing circuit is provided for measuring a distance to an object based on a detection result by the detector. The measuring device according to any one of claims 6 to 8.

10. A signal processing circuit is provided for measuring a spectrum of an object based on a detection result by the detector. The measuring device according to any one of claims 6 to 9.

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