Optical measurement device

Abstract

An optical measurement device comprising: a light source that generates an optical frequency comb; a first optical path that guides an optical pulse train to an object under measurement, the optical pulse train having a pulse interval based on a repetition frequency of the optical frequency comb generated by the light source and a phase difference between pulses based on a carrier envelope offset frequency and the repetition frequency; a second optical path that guides measurement result light obtained from the object under measurement irradiated with the optical pulse train guided by the first optical path; a third optical path that guides delayed light obtained by delaying the optical pulse train by a delay time corresponding to the pulse interval; an interference unit that causes interference between the measurement result light guided by the second optical path and the delayed light guided by the third optical path; and a control unit that variably controls at least one of the carrier envelope offset frequency of the light source and the repetition frequency on the basis of the state of light after the interference caused by the interference unit.

Description

Optical Measurement Device

[0001] The present invention relates to an optical measurement device. This application claims priority to Japanese Patent Application No. 2022-026953, filed on February 24, 2022, the contents of which are incorporated herein by reference.

[0002] An ultrashort pulse train in which a train of optical frequency modes, whose spectral intensities are precisely and evenly spaced like a comb on the frequency axis, are phase-locked with each other and whose absolute values ​​are completely controlled, is called an "optical frequency comb" or simply "optical comb." For example, a mode-locked laser, which is an ultrashort pulse laser, produces a train of numerous equally spaced optical frequency modes on the frequency axis, and each optical frequency mode is phase-locked with each other. When this optical frequency is completely controlled, this light source becomes an optical comb. Because optical frequency can be controlled using extremely accurate clocks such as atomic clocks, it is widely used as a precise ruler for measuring optical frequency and distance (see, for example, Non-Patent Document 1).

[0003] Steven T. Cundiff and Jun Ye “Colloquium: Femtosecond optical frequency combs”, REVIEWS OF MODERN PHYSICS, VOLUME 75, JANUARY (2003).

[0004] As disclosed in the aforementioned non-patent document 1, optical frequency combs have been used as highly stabilized light sources. That is, an optical frequency comb can be considered a low-jitter coherent pulse train in the time domain and an accurately modally decomposed comb-like spectrum in the frequency domain. Conventionally, the carrier-envelope offset frequency and repetition rate (frequency interval) of such an optical frequency comb, as well as the carrier-envelope offset frequency difference and repetition rate difference when two optical frequency combs are used, have been treated as fixed parameters.

[0005] Optical measurement is widely used in fields such as distance measurement, shape measurement, and spectroscopy. The basic measurement method in such optical measurement involves irradiating a measurement object with measurement light and measuring the transmitted and reflected light. However, in such optical measurement, the measurement light may be reflected multiple times by the measurement object, resulting in the generation of extraneous light (background light) other than the light to be measured. For example, when measuring the internal reflection of the measurement object, surface reflected light that is stronger than the internally reflected light may be generated on the surface of the measurement object. Alternatively, when observing a weak nonlinear signal, transmitted light that is stronger than the nonlinear signal may be observed. The presence of such strong background light may obscure the light to be measured.

[0006] Conventionally, in order to remove strong background light, methods have been used to separate the light to be measured from the background light in time by utilizing the delay time difference between the light to be measured and the background light, or to separate the light in space by utilizing the misalignment of the optical axes of the light to be measured and the background light. However, when there is almost no delay time difference or misalignment of the optical axes between the light to be measured and the background light, there is a problem in that the background light cannot be effectively removed by the temporal and spatial separation means.

[0007] The present invention has been made in consideration of the above circumstances, and provides an optical measurement device that can remove background light in optical measurement that utilizes the high controllability of an optical frequency comb.

[0008] an interference unit that causes interference between the measurement result light guided by the second optical path and the delayed light guided by the third optical path; and a control unit that variably controls at least one of the carrier envelope offset frequency and the repetition frequency of the light source based on a state of light after interference by the interference unit.

[0009] Moreover, one embodiment of the present invention is the above-mentioned optical measurement device, further comprising an acquisition unit that acquires at least one of the amplitude and frequency of the light after the interference as the state of the light, and the control unit variably controls at least one of the carrier envelope offset frequency and the repetition frequency of the light source based on the acquisition result of the state of the light by the acquisition unit and information indicating a reference for the state of the light.

[0010] Moreover, in one embodiment of the present invention, in the optical measurement device described above, the control unit changes the pulse interval and the inter-pulse phase difference of the optical pulse train by sweeping and variably controlling at least one of the carrier envelope offset frequency and the repetition frequency of the light source.

[0011] Moreover, in one embodiment of the present invention, in the optical measurement device described above, the control unit changes the pulse interval of the optical pulse train by changing the repetition frequency without changing the ratio between the carrier envelope offset frequency and the repetition frequency.

[0012] Moreover, in one embodiment of the present invention, in the optical measurement device described above, the control unit changes the inter-pulse phase difference of the optical pulse train by changing the ratio between the carrier envelope offset frequency and the repetition frequency.

[0013] Moreover, according to one embodiment of the present invention, the optical measurement device further comprises a measurement unit that measures light after interference by the interference unit as signal light.

[0014] Moreover, one embodiment of the present invention is the above-mentioned optical measurement device, further comprising: a second interference unit that causes interference between a reference light of an optical pulse train based on the optical pulse train and the measurement result light or the light after interference by the interference unit; and a second measurement unit that measures the light interfered by the second interference unit as signal light.

[0015] According to the present invention, background light can be selectively removed in optical measurements using an optical frequency comb.

[0016] FIG. 1 is a diagram showing the correspondence relationship between a waveform in the time domain and a spectral distribution in the frequency domain for an optical frequency comb. FIG. 2 is a diagram showing an example of an ultrashort pulse. FIG. 3 is a diagram showing an example of the configuration of the optical measurement device 1 of this embodiment. FIG. 4 is a diagram showing a first modified example of the configuration of the delay unit of this embodiment. FIG. 5 is a diagram showing a second modified example of the configuration of the delay unit of this embodiment. FIG. 6 is a diagram showing an example of the configuration of the optical measurement device 2 in a modified example of this embodiment. FIG. 7 is a diagram showing an example of the measurement result by the optical measurement device 2 according to the modified example of this embodiment.

[0017] Hereinafter, an embodiment of the optical measurement device according to the present invention will be described with reference to the drawings. Note that the drawings used in the following description are schematic, and the ratios of length, width, thickness, etc. are not necessarily the same as those in the actual devices and can be changed as appropriate.

[0018] [Optical Frequency Comb] Figure 1A shows the correspondence between the waveform in the time domain and the spectral distribution in the frequency domain of an optical frequency comb. The output from a mode-locked laser is a periodic pulse train in the time domain, which can be illustrated by a function of a rapidly oscillating electric field and envelope.

[0019] Generally, an optical comb, which has a group of optical frequency modes spaced equally apart on the frequency axis, can be fully expressed by two frequencies: the repetition frequency (frep) and the carrier envelope frequency (fceo). The repetition frequency represents the spacing between each optical frequency mode, and on the time axis, it represents the interpulse distance of an ultrashort pulse train. Figure 1B shows an example of an ultrashort pulse. On the other hand, the carrier envelope frequency is expressed as the deviation (offset) that occurs when the optical frequency mode train on the frequency axis is repeatedly extended to DC. Considering this on the time axis, it represents the carrier phase difference between each pulse in the pulse train. Here, the carrier phase is referred to as the carrier-envelope offset phase (CEP, also referred to as carrier phase in the following description). Each carrier phase (φn) of a pulse train on the time axis changes by a constant phase amount for each pulse, resulting in a constant period (carrier phase period Tceo). The difference in relative carrier phase between adjacent pulse trains on the time axis is also called inter-pulse phase difference. As shown in equation (1), the reciprocal of the carrier phase period Tceo is the carrier envelope offset frequency fceo on the frequency axis.

[0020] Tceo = 1 / fceo...(1)

[0021] As shown in equation (2), the reciprocal of the pulse repetition period (pulse interval) Trep is the repetition frequency (frequency interval) frep.

[0022] Trep = 1 / frep...(2)

[0023] When observing the output of a mode-locked laser on the frequency axis, the longitudinal modes (optical frequency modes) of the laser are distributed extremely uniformly at intervals of the repetition frequency (frequency interval) frep. The carrier-envelope offset frequency fceo and the repetition frequency frep are related as shown in equation (3) using the inter-pulse phase difference (φn+1-φn).

[0024] φn+1-φn = 2π(fceo / frep)...(3)

[0025] As described above, the repetition frequency frep and the carrier envelope offset frequency fceo in an optical frequency comb are important frequency parameters that indicate the characteristics of a pulse train. In this embodiment, the degree of freedom in controlling the repetition frequency frep and the carrier envelope offset frequency fceo is actively utilized.

[0026] 2 is a diagram showing an example of the configuration of the optical measurement device 1 of this embodiment. The optical measurement device 1 includes a light source 10, a measurement unit 20, a measurement unit 30, and an acquisition unit 40.

[0027] The light source 10 is, for example, a mode-locked laser light source, and generates an optical frequency comb. This optical frequency comb has a predetermined carrier envelope offset frequency fceo relative to zero on the frequency axis, and multiple frequency modes arranged on the frequency axis at intervals of integer multiples of a predetermined repetition frequency frep based on the carrier envelope offset frequency fceo. The light source 10 outputs an optical pulse train L1 based on the generated optical frequency comb to the measurement unit 20. The optical pulse train L1 has a pulse interval Trep based on the repetition frequency frep of the optical frequency comb generated by the light source 10, and an inter-pulse phase difference (φn+1−φn) based on the carrier envelope offset frequency fceo and the repetition frequency frep.

[0028] The measurement unit 20 includes a first optical path 21, a second optical path 22, a third optical path 23, and an interference unit 24. The first optical path 21 guides the optical pulse train L1 to the measurement object 25. The second optical path 22 guides the measurement result light L2 obtained from the measurement object 25 irradiated with the optical pulse train L1 guided by the first optical path 21.

[0029] The third optical path 23 guides delayed light L3 obtained by delaying the optical pulse train L1 by a delay time corresponding to the pulse interval Trep. Specifically, the measurement unit 20 includes a delay unit 230 in the third optical path 23. In one example of this embodiment, the delay unit 230 includes an optical delay circuit using a spatial optical system such as a multi-path cavity (MPC). Note that the delay unit 230 may have any configuration, as shown in, for example, FIGS. 3 and 4, as long as it is possible to adjust the frequency dependency (dispersion) of the delay.

[0030] Fig. 3 is a diagram showing a first modified example of the configuration of the delay unit of this embodiment. A delay unit 232 of the first modified example includes an optical delay circuit using an optical fiber. Fig. 4 is a diagram showing a second modified example of the configuration of the delay unit of this embodiment. A delay unit 233 of the second modified example includes an optical delay circuit using a waveguide (for example, an arrayed waveguide grating; AWG).

[0031] Returning to FIG. 2, the interference unit 24 causes the measurement result light L2 guided by the second optical path 22 and the delayed light L3 guided by the third optical path 23 to interfere with each other.

[0032] The measuring unit 30 measures the light L4 after interference by the interference unit 24 as signal light L5. Here, the signal light L5 is guided to the OSA by an SMF and the spectrum is measured, but other optical systems and measuring devices may be used depending on the object to be measured.

[0033] The acquisition unit 40 acquires at least one of the amplitude and frequency of the post-interference light L4 as the state of the light.

[0034] The light source 10 includes a control unit 100. The control unit 100 variably controls at least one of the carrier envelope offset frequency fceo and the repetition frequency frep of the light source 10 based on the state of the light L4 after interference by the interference unit 24.

[0035] Here, by changing the ratio between two radio frequency parameters (repetition frequency frep and carrier envelope offset frequency fceo) that govern the optical pulse train L1, it is possible to uniformly control the phase of all pulses in the band of the light source 10. Furthermore, as shown in the above-mentioned formula (3), by changing the ratio between the repetition frequency frep and the carrier envelope offset frequency fceo, the phase difference between adjacent pulses in the optical pulse train L1, i.e., the inter-pulse phase difference (φn+1−φn), is controlled. Therefore, by splitting the optical pulse train L1 into two optical paths, the first optical path 21 and the third optical path 23, and imparting a delay to the pulsed light in one optical path (i.e., the third optical path 23), it is possible to generate a pulse pair with a desired phase difference between the pulsed light in the first optical path 21 (i.e., the measurement result light L2) and the pulsed light in the third optical path 23 (i.e., the delayed light L3). By providing the optical pulse train L1 with an inter-pulse phase difference (φn+1−φn) corresponding to the delay time of the third optical path 23 so that the measurement result light L2 in the first optical path 21 and the delayed light L3 in the third optical path 23 are in opposite phase to each other, and causing the measurement result light L2 and the delayed light L3 to interfere, it is possible to remove the background light contained in the measurement result light L2. That is, by changing the ratio between the repetition frequency frep and the carrier envelope offset frequency fceo and controlling the inter-pulse phase difference (φn+1−φn) of the optical pulse train L1, it is possible to remove the background light of the measurement result light L2.

[0036] Furthermore, the control unit 100 may feedback-control at least one of the carrier envelope offset frequency fceo and the repetition frequency frep based on the state of the light L4 after interference. In this case, the frequency ratio between them may be constant, or the absolute frequency may be fixed. When controlling, the frequency ratio between the repetition frequency and the carrier envelope offset frequency may be set to a predetermined frequency ratio using a circuit using a frequency divider, mixer, etc. as shown in the control unit 100. Frequency measurement may also be performed using a microprocessor such as an FPGA. That is, the control unit 100 variably controls at least one of the carrier envelope offset frequency fceo and the repetition frequency frep of the light source 10 based on the light state acquisition result obtained by the acquisition unit 40 and information indicating the reference light state.

[0037] In this embodiment, a case where light transmitted through the measurement object 25 is light to be measured by the measurement unit 30 will be described as an example, but the present invention is not limited to this. Light reflected from the measurement object 25 may also be light to be measured by the measurement unit 30. In other words, the optical measurement device 1 of this embodiment may be a transmission type measurement device that measures transmitted light, or may be a reflection type measurement device that measures reflected light.

[0038] [Example of Control by Control Unit 100] Here, an example of control by the control unit 100 will be described. For example, when it is desired to remove background light due to back surface reflection of the measurement target 25, the background light is dispersed by the measurement target 25. For this reason, there are cases where the background light cannot be sufficiently removed by simply causing the delayed light L3 to interfere with the post-interference light L4.

[0039] (1) Sweep Control of Carrier Envelope Offset Frequency fceo or Repetition Frequency frep Therefore, the control unit 100 of this embodiment sweeps and variably controls the state of the delayed light L3 that interferes with the interfering light L4. The control unit 100 changes the pulse interval Trep and the inter-pulse phase difference (φn+1−φn) of the optical pulse train L1 by sweeping and variably controlling at least one of the carrier envelope offset frequency fceo and repetition frequency frep of the light source 10. The control unit 100 configured in this manner can remove background light that has a dispersive effect of the object to be measured 25. Here, the sweep and variably control of the state of the delayed light L3 can be achieved by variably controlling the parameters of the optical pulse train L1 (the carrier envelope offset frequency fceo and the repetition frequency frep), eliminating the need for variable control using mechanical components. Therefore, the control unit 100 configured in this manner can remove background light that has a dispersive effect of the object to be measured 25 while suppressing control errors due to the mass and precision of mechanical components.

[0040] (2) Sweep Control of Pulse Interval Trep The control unit 100 changes the pulse interval Trep of the optical pulse train L1 by changing the repetition frequency frep without changing the ratio between the carrier envelope offset frequency fceo and the repetition frequency frep. For example, the control unit 100 performs feedback control to cancel the influence of environmental fluctuations by variably controlling the repetition frequency frep in response to changes in the state of the post-interference light L4 due to environmental fluctuations. The control unit 100 configured in this manner can reduce changes in the state of the post-interference light L4 due to environmental fluctuations, thereby highlighting the even smaller signal light L5. In other words, the control unit 100 configured in this manner can realize an optical measurement device 1 that is more robust against environmental fluctuations.

[0041] (3) Sweep Control of Inter-Pulse Phase Difference (φn+1−φn) The control unit 100 changes the ratio between the carrier envelope offset frequency fceo and the repetition frequency frep to change the inter-pulse phase difference (φn+1−φn) of the optical pulse train L1. For example, the control unit 100 variably controls the repetition frequency frep in response to changes in the state of the post-interference light L4 due to environmental fluctuations, thereby changing the ratio between the carrier envelope offset frequency fceo and the repetition frequency frep while performing feedback control to cancel the effects of the environmental fluctuations. The control unit 100 configured in this manner can perform variable sweep control of the inter-pulse phase difference (φn+1−φn) of the optical pulse train L1 while reducing changes in the state of the post-interference light L4 due to environmental fluctuations.

[0042] [Modification of the Configuration of the Optical Measurement Apparatus] Fig. 5 is a diagram showing an example of the configuration of an optical measurement apparatus 2 in a modification of this embodiment. The above-mentioned optical measurement apparatus 1 has been described as an example of an apparatus that performs weak signal detection (non-interferometric measurement) for, for example, optical sensing, optical space communication, cryptographic communication, radio astronomy observation, etc., but is not limited to this. The optical measurement apparatus may also perform interferometric measurement using reference light. The optical measurement apparatus 2 of this modification differs from the above-mentioned optical measurement apparatus 1 in that it includes a second interferometer 50 and a second measurement unit 32. As examples of interferometric measurement, the optical measurement apparatus 2 can be applied to optical coherence tomography (OCT), a Raman spectroscopy apparatus, a thin film measurement apparatus, etc.

[0043] The second interference unit 50 causes interference between reference light L6, which is generated by splitting the optical pulse train L1 using the beam splitter BS1, and light L4 after interference by the interference unit 24. The second measurement unit 32 measures the light interfered by the second interference unit 50 as signal light L5.

[0044] In this modification, the second interference unit 50 is described as causing the reference light L6 to interfere with the interfered light L4, but this is not limiting. The second interference unit 50 may cause the reference light L6 to interfere with the light before interference by the interference unit 24 (i.e., the measurement result light L2). In this case, the interference unit 24 causes the light after interference by the second interference unit 50 to interfere with the delayed light L3. In addition, in this modification, the reference light L6 is described as light generated by splitting the optical pulse train L1 using the beam splitter BS1, but this is not limiting. The reference light L6 does not necessarily have to be light output by the light source 10. For example, light output by a second light source other than the light source 10 may be used as the reference light L6. In this case, the light emitted from the second light source may be an optical pulse train that is coherent with the optical pulse train output by the light source 10. In other words, the reference light L6 may be an optical pulse train based on the optical pulse train L1.

[0045] That is, the second interference section 50 causes interference between the reference light L6 of the optical pulse train based on the optical pulse train L1 and the measurement result light L2 or the light L4 after interference by the interference section 24.

[0046] [Example of Measurement Results] Figure 6 shows an example of measurement results obtained by the optical measurement device 2 according to a modified example of this embodiment. Here, the transmitted light and internally reflected light of a Si substrate are measured, with the strong transmitted light representing the background light and the weak internal reflection representing the measurement target. Figure 6[A] shows an example of measurement results of the signal light L5 when the interference unit 24 does not interfere with the measurement result light L2 and the delayed light L3, i.e., when background light removal, or so-called noise cancellation, is not performed. The signal shown here is a spectral interference fringe of the signal light L5. Figure 6[B] shows an example of measurement results of the signal light L5 when the interference unit 24 interferes with the measurement result light L2 and the delayed light L3, i.e., when noise cancellation is performed. In this example of measurement results, the horizontal axis represents the wavelength of the signal light L5, and the vertical axis represents the intensity of the signal light L5. Two spectral interference fringes are superimposed here: a spectral interference fringe between the high-intensity background light and the reference light L6, and a spectral interference fringe between the weak signal light and the reference light L6. The wavelength λ1 is the lowest interference fringe frequency wavelength of the spectral interference fringes to be observed with the signal light L5. Here, the lowest interference fringe frequency wavelength refers to the wavelength component at which the chirped reference light L6 and the signal light completely overlap on the time axis. When noise cancellation is not performed as shown in FIG. 6[A], the spectral interference fringes of the background light and the reference light L6 appear strongly in a wide band centered on the wavelength λ1 due to the influence of the background light (i.e., noise components). When noise cancellation is performed as shown in FIG. 6[B], the influence of the background light (i.e., noise components) is reduced at wavelength λ1, and the intensity of the spectral interference fringes of the background light and L6 is reduced. As a result, in the case shown in FIG. 6[B], the weak internally reflected light contained in the signal light L5 and the spectral interference fringes of L6 are more apparent than in the case shown in FIG. 6[A].

[0047] [Summary of the Embodiment] As described above, the optical measurement device of this embodiment and the modified example provides the optical pulse train L1 with an inter-pulse phase difference (φn+1-φn) corresponding to the delay time of the third optical path 23 so that the measurement result light L2 in the first optical path 21 and the delayed light L3 in the third optical path 23 are in opposite phase to each other, and causes the measurement result light L2 and the delayed light L3 to interfere with each other, thereby removing background light contained in the measurement result light L2. According to the optical measurement device configured in this manner, noise cancellation of the measurement result light L2 can be performed by changing the ratio between the repetition frequency frep and the carrier envelope offset frequency fceo to control the inter-pulse phase difference (φn+1-φn) of the optical pulse train L1. Note that, although the inter-pulse phase difference of the optical pulse train L1 has been described as the phase difference between adjacent pulses, this is not limited to this. The inter-pulse phase difference of the optical pulse train L1 may be any phase difference between pulses that corresponds to the delay time of the third optical path 23, and the phase difference between every other pulse or every third pulse may be used as the inter-pulse phase difference of the optical pulse train L1 to control the ratio of the repetition frequency frep and the carrier envelope offset frequency fceo.

[0048] Although the embodiments of the present invention have been described in detail above with reference to the drawings, the specific configuration is not limited to this embodiment and can be appropriately modified without departing from the spirit of the present invention. The configurations described in the above-described embodiments may be combined.

[0049] Each unit included in each device in the above-described embodiments may be realized by dedicated hardware, or may be realized by a memory and a microprocessor.

[0050] In addition, each part of each device may be composed of a memory and a CPU (central processing unit), and the functions of each part of each device may be realized by loading a program into memory and executing it.

[0051] In addition, a program for realizing the functions of each unit of each device may be recorded on a computer-readable recording medium, and the program recorded on the recording medium may be read into a computer system and executed to perform processing by each unit of the control unit. Note that the term "computer system" here includes hardware such as an OS and peripheral devices.

[0052] Furthermore, if a WWW system is used, the term "computer system" also includes the homepage provision environment (or display environment). Furthermore, "computer-readable recording medium" refers to portable media such as flexible disks, optical magnetic disks, ROMs, and CD-ROMs, as well as storage devices such as hard disks built into computer systems. Furthermore, "computer-readable recording medium" also includes devices that dynamically store programs for a short period of time, such as communication lines used when transmitting programs over networks like the Internet or over communication lines like telephone lines, and devices that store programs for a fixed period of time, such as volatile memory within the computer systems that serve as servers or clients in such cases. Furthermore, the above-mentioned programs may be those that implement some of the aforementioned functions, or may be those that can realize the aforementioned functions in combination with programs already stored in the computer system.

[0053] REFERENCE SIGNS LIST 1... optical measurement device, 10... light source, 20... measurement unit, 21... first optical path, 22... second optical path, 23... third optical path, 24... interference unit, 30... measurement unit, 40... acquisition unit

Claims

1. a light source that generates an optical frequency comb having a predetermined carrier envelope offset frequency relative to zero on a frequency axis and a plurality of frequency modes arranged on the frequency axis at intervals of an integer multiple of a predetermined repetition frequency based on the carrier envelope offset frequency; a first optical path that guides an optical pulse train, the optical pulse train having a pulse interval based on the repetition frequency of the optical frequency comb generated by the light source and an inter-pulse phase difference based on the carrier envelope offset frequency and the repetition frequency, to an object to be measured; a second optical path that guides measurement result light obtained from the measurement object irradiated with one of the optical pulse train and delayed light obtained by delaying the optical pulse train, which are guided by the first optical path; a third optical path for guiding the other of the optical pulse train and the delayed light; an interference unit that causes interference between the measurement result light guided by the second optical path and the other light guided by the third optical path; a control unit that variably controls at least one of the carrier envelope offset frequency and the repetition frequency of the light source based on the state of the light after interference by the interference unit; An optical measurement device comprising:

2. The delayed light is delayed by a delay time corresponding to the pulse interval. The optical measurement device according to claim 1 .

3. an acquisition unit that acquires at least one of the amplitude and frequency of the light after the interference as the state of the light; Furthermore, The control unit variably controlling at least one of the carrier envelope offset frequency and the repetition frequency of the light source based on the result of the acquisition of the light state by the acquisition unit and information indicating a reference for the light state. The optical measurement device according to claim 1 .

4. The control unit The pulse interval and the inter-pulse phase difference of the optical pulse train are changed by sweeping and variably controlling at least one of the carrier envelope offset frequency and the repetition frequency of the light source. The optical measurement device according to claim 1 .

5. The control unit The pulse interval of the optical pulse train is changed by changing the repetition frequency without changing the ratio between the carrier envelope offset frequency and the repetition frequency. The optical measurement device according to claim 1 .

6. The control unit The inter-pulse phase difference of the optical pulse train is changed by changing the ratio between the carrier envelope offset frequency and the repetition frequency. The optical measurement device according to claim 1 .

7. a measuring section that measures the light after interference by the interference section as signal light; The optical measurement device of claim 1 further comprising:

8. a second interference unit that causes a reference light of an optical pulse train based on the optical pulse train to interfere with the measurement result light or the light after interference by the interference unit; a second measurement unit that measures the light interfered by the second interference unit as signal light; The optical measurement device of claim 1 further comprising: