Optical comb measuring device

Abstract

To reduce the time required to measure multiple types of measurement objects by means of the dual comb spectroscopy.SOLUTION: An optical comb measurement apparatus 1 for measuring an irradiation object body that has multiple types of measurement objects includes: an interference signal acquisition part 16 which acquires an interference signal between the post-irradiation signal comb obtained by irradiating the irradiation object body with the pre-irradiation signal comb and the local comb in which the repetition frequency of the pre-irradiation signal comb is made different by a prescribed difference frequency; and a frequency spectrum measurement part 18 which measures the frequency spectrum of the acquisition result of the interference signal acquisition part 16. The power of the light irradiated to the irradiation object body changes at a prescribed frequency corresponding to each of the measurement objects. One or both of the post-irradiation signal comb and the local comb given to the interference signal acquisition part 16 have only components in multiple required bands including all of the prescribed frequencies. The frequency bands of the interference signals corresponding to each of the multiple required bands do not overlap each other.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present invention relates to dual-comb spectroscopy.

Background Art

[0002] Conventionally, measurements using dual-comb spectroscopy have been known (see, for example, Patent Document 1, Patent Document 2, and Patent Document 3). According to dual-comb spectroscopy, an interference signal (interferogram) obtained by combining a signal comb (before irradiation), which is an optical comb, irradiated onto an irradiated object (after irradiation) and a local comb having a different repetition frequency from the signal comb (before irradiation) is acquired. Further, according to dual-comb spectroscopy, the spectrum of the optical region of the irradiated object is measured by performing a Fourier transform on this interferogram.

[0003] Here, it is assumed that there are a plurality of types (for example, two types) of measurement targets in the irradiated object. In this case, the spectra of the optical regions of these two types of measurement targets must exist within the measurable band of the dual-comb spectroscopy. If the optical frequencies of the spectra of the optical regions of these two types of measurement targets are significantly different, it is necessary to widen the measurable band. In order to widen the measurable band, it is necessary to reduce the difference between the repetition frequency of the signal comb (before irradiation) and the repetition frequency of the local comb.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Patent Document 2

Patent Document 3

Summary of the Invention

Problems to be Solved by the Invention

[0005] However, reducing the difference between the repetition frequency of the signal comb (before irradiation) and the repetition frequency of the local comb increases the measurement time.

[0006] Therefore, the present invention aims to shorten the time required to measure multiple types of objects using dual-comb spectroscopy. [Means for solving the problem]

[0007] The optical comb measuring device according to the present invention is an optical comb measuring device for measuring an irradiated object having multiple types of measurement targets, comprising: an interference signal acquisition unit that acquires an interference signal between a post-irradiation signal comb obtained by irradiating the irradiated object with a pre-irradiation signal comb and a local comb whose repetition frequency is different from that of the pre-irradiation signal comb by a predetermined difference frequency; and a frequency spectrum measuring unit that measures the frequency spectrum of the acquisition result from the interference signal acquisition unit, wherein the pre-irradiation signal comb, the post-irradiation signal comb and the local comb are optical combs, the power of the light irradiated onto the irradiated object changes at a predetermined frequency corresponding to each of the measurement targets, and multiple measurable bands, which are the frequency range of the post-irradiation signal comb to which the frequency of a single post-irradiation signal comb corresponds to the frequency of the interference signal, include one or more of the predetermined frequencies, and either or both of the post-irradiation signal comb and the local comb provided to the interference signal acquisition unit have only components within a plurality of necessary bands that include all of the predetermined frequencies, and the frequency bands of the interference signal corresponding to each of the plurality of necessary bands do not have overlapping regions.

[0008] According to the optical comb measuring device configured as described above, an irradiated object having multiple types of measurement targets is measured. An interference signal acquisition unit acquires an interference signal between a post-irradiation signal comb obtained by irradiating the irradiated object with a pre-irradiation signal comb and a local comb whose repetition frequency is different from that of the pre-irradiation signal comb by a predetermined difference frequency. A frequency spectrum measurement unit measures the frequency spectrum of the result acquired by the interference signal acquisition unit. The pre-irradiation signal comb, the post-irradiation signal comb, and the local comb are optical combs. The power of the light irradiated onto the irradiated object changes at predetermined frequencies corresponding to each of the measurement targets. Multiple measurable bands, which are the frequency domains of the post-irradiation signal comb to which the frequency of a single post-irradiation signal comb corresponds, include one or more of the predetermined frequencies. Either or both of the post-irradiation signal comb and the local comb supplied to the interference signal acquisition unit have only components within a plurality of required bands that include all of the predetermined frequencies. The frequency bands of the interference signal corresponding to each of the plurality of required bands do not have overlapping regions.

[0009] Furthermore, the optical comb measuring device according to the present invention may be equipped with a multi-band pass unit that receives either or both of the pre-irradiation signal comb and the local comb, and passes through multiple components of the required bandwidths.

[0010] Furthermore, the optical comb measuring device according to the present invention may be equipped with a multi-band pass unit that receives either or both of the post-irradiation signal comb and the local comb, and allows a plurality of components of the required bandwidths to pass through.

[0011] Furthermore, in the optical comb measuring device according to the present invention, either or both of the pre-irradiation signal comb and the local comb may have only components within a plurality of required bands that include all of the predetermined frequencies.

[0012] Furthermore, the optical comb measuring device according to the present invention may be configured such that each of the measurable bandwidths includes each of the predetermined frequencies.

[0013] Note that the optical comb measurement device according to the present invention may be configured such that one or more of the measurable bands include a plurality of the predetermined frequencies.

[0014] Note that the optical comb measurement device according to the present invention may be configured such that the irradiated object is a gas.

[0015] Note that the optical comb measurement device according to the present invention may be configured such that the irradiated object is housed in a gas cell.

[0016] Note that the optical comb measurement device according to the present invention may be configured to measure the concentration of the measurement target.

[0017] Note that the optical comb measurement device according to the present invention may be configured such that the irradiated object is a liquid or a solid.

[0018] Note that the optical comb measurement device according to the present invention may be configured to measure the presence or absence of the measurement target.

[0019] Note that the optical comb measurement device according to the present invention may be configured such that the post-irradiation signal comb and the local comb are provided to the interference signal acquisition unit via a polarization-maintaining fiber.

[0020] Note that the optical comb measurement device according to the present invention may be configured such that the interference signal acquisition unit is an optical coupler.

[0021] Note that the optical comb measurement device according to the present invention may be configured such that the interference signal acquisition unit is a power beam splitter.

Brief Description of Drawings

[0022] A diagram showing the configuration of an optical comb measurement device 1 according to an embodiment of the present invention. [Figure 1] [Figure 2] Frequency spectra of a pre-irradiation signal comb (FIG. 2(a)) and a local comb (FIG. 2(b)). [Figure 3] Frequency spectra of the post-irradiation signal comb (before passing through the plurality of bandpass units 14) (FIG. 3(a)), the post-irradiation signal comb (after passing through the plurality of bandpass units 14) (FIG. 3(b)), and the local comb (FIG. 3(c)). [Figure 4] Frequency spectrum of the measurement result of the interference signal by the frequency spectrum measurement unit 18. [Figure 5] It is a diagram showing the correspondence between the frequency of the post-irradiation signal comb and the frequency of the interference signal by the optical comb measurement apparatus 1 according to an embodiment of the present invention. [Figure 6] Diagram showing the absorption spectrum of the measurement target in the irradiated body (FIG. 6(a)), the correspondence between the frequency of the post-irradiation signal comb and the frequency of the interference signal (comparative example) (FIG. 6(b)), and the correspondence between the frequency of the post-irradiation signal comb and the frequency of the interference signal (embodiment) (FIG. 6(c)). [Figure 7] It is a diagram showing the configuration of the optical comb measurement apparatus 1 according to Modification 1 of the embodiment of the present invention. [Figure 8] It is a diagram showing the configuration of the optical comb measurement apparatus 1 according to Modification 2 of the embodiment of the present invention. [Figure 9] It is a diagram showing the configuration of the optical comb measurement apparatus 1 according to Modification 3 of the embodiment of the present invention. [Figure 10] It is a diagram showing the configuration of the optical comb measurement apparatus 1 according to Modification 4 of the embodiment of the present invention. [Figure 11] Frequency spectra of the post-irradiation signal comb (FIG. 11(a)) and the local comb (FIG. 11(b)) when 11fs = 12fL. [Figure 12] Diagram showing the absorption spectrum of the measurement target in the irradiated body (FIG. 12(a)) and the correspondence between the frequency of the post-irradiation signal comb and the frequency of the interference signal (embodiment) (FIG. 12(b)) according to Modification 6 of the embodiment of the present invention. [Figure 13] Diagram showing the absorption spectrum of the measurement target in the irradiated body (FIG. 13(a)) and the correspondence between the frequency of the post-irradiation signal comb and the frequency of the interference signal (embodiment) (FIG.  13(b)) according to Modification 7 of the embodiment of the present invention. [Modes for carrying out the invention]

[0023] Embodiments of the present invention will be described below with reference to the drawings.

[0024] Figure 1 shows the configuration of an optical comb measuring device 1 according to an embodiment of the present invention. The optical comb measuring device 1 according to an embodiment of the present invention measures an irradiated object having multiple types of measurement targets.

[0025] For example, the irradiated object is a gas and is contained in a gas cell (DUT2 in the embodiment of the present invention). More specifically, gas flows into the gas cell and gas is discharged from the gas cell. The gas may have multiple types (for example, two types) of substances to be measured. The optical comb measuring device 1 may also be configured to measure the concentration of the substances to be measured. The method for measuring the concentration of the substances to be measured is well known, so a description will be omitted.

[0026] An optical comb measuring device 1 according to an embodiment of the present invention comprises a signal comb generation unit 12a, a local comb generation unit 12b, a multiple bandpass unit 14, an interference signal acquisition unit 16, and a frequency spectrum measuring unit 18.

[0027] The signal comb generation unit 12a generates a pre-irradiation signal comb (a signal comb before it is irradiated onto the object to be irradiated). The local comb generation unit 12b generates a local comb. The pre-irradiation signal comb and the local comb are optical combs.

[0028] Figure 2 shows the frequency spectra of the pre-irradiation signal comb (Figure 2(a)) and the local comb (Figure 2(b)). The vertical axis represents optical power. Referring to Figure 2(a), the frequencies in the frequency spectrum of the pre-irradiation signal comb are 0, fs, 2fs, ... (repetition frequency fs). Referring to Figure 2(b), the frequencies in the frequency spectrum of the local comb are 0, fL, 2fL, ... (repetition frequency fL). However, the local comb is obtained by changing the repetition frequency fs of the pre-irradiation signal comb by a predetermined difference frequency Δf (=fs-fL). Note that the frequencies of the pre-irradiation signal comb and the local comb are approximately the frequencies of light.

[0029] However, in Figure 2, the minimum frequency of the pre-irradiation signal comb and local comb frequency spectrum is shown as 0 (for illustrative and explanatory purposes), but in reality, these minimum values ​​are mfs (=nfL) (where m and n are positive integers). Therefore, in reality, the frequencies of the pre-irradiation signal comb frequency spectrum are mfs, mfs+fs, mfs+2fs, ... and the frequencies of the local comb frequency spectrum are nfL, nfL+fL, nfL+2fL, ... Note that m is, for example, approximately 4 million.

[0030] When the pre-irradiation signal comb is irradiated onto the object to be irradiated (gas) in the DUT (gas cell) 2, the pre-irradiation signal comb passes through the DUT 2, and a post-irradiation signal comb is obtained. The post-irradiation signal comb is also an optical comb, just like the pre-irradiation signal comb. The post-irradiation signal comb is then supplied to the multi-bandpass section 14, and the components that have passed through are supplied to the interference signal acquisition section 16.

[0031] Figure 3 shows the frequency spectra of the post-irradiation signal comb (before passing through the multi-bandpass section 14) (Figure 3(a)), the post-irradiation signal comb (after passing through the multi-bandpass section 14) (Figure 3(b)), and the local comb (Figure 3(c)). The vertical axis represents optical power. However, Figure 3(c) is the same as Figure 2(b).

[0032] Note that, as with Figure 2, Figure 3 also shows the minimum frequency of the post-irradiation signal comb and local comb frequency spectrum as 0 (for illustrative and explanatory purposes), but in reality, these minimum values ​​are mfs (=nfL).

[0033] In Figure 3, the power of the light irradiated onto the object within DUT2 is assumed to decrease (meaning light absorption) at predetermined frequencies (2fs and 4fs) corresponding to each of the objects being measured. Note that in Figure 3, for the sake of illustration and explanation, the difference between the frequencies at which the power of the light irradiated onto the object decreases (2fs and 4fs) is assumed to be only 2fs, but in reality, the difference between such frequencies is generally much larger (see, for example, Figure 6).

[0034] Referring to Figure 3(a), the post-irradiation signal comb before passing through the multi-bandpass section 14 has low optical power at predetermined frequencies (2fs and 4fs) corresponding to each of the measurement targets among the pre-irradiation signal combs.

[0035] Here, the multi-bandpass section 14 allows signals in the frequency bands near 2fs and 4fs to pass through, but blocks signals in other frequency bands. Then, referring to Figure 3(b), the post-irradiation signal comb after passing through the multi-bandpass section 14 has only components at frequencies 2fs and 4fs.

[0036] The interference signal acquisition unit 16 acquires the interference signal between the post-irradiation signal comb and the local comb. Since the predetermined difference frequency Δf is a relatively small value, a beat is generated between the post-irradiation signal comb and the local comb. The interference signal acquisition unit 16 is, for example, an optical coupler, and the post-irradiation signal comb and the local comb are supplied to the interference signal acquisition unit 16 via a polarization-maintaining fiber and an optical attenuator. The frequency spectrum measurement unit 18 measures the frequency spectrum of the result acquired by the interference signal acquisition unit 16.

[0037] Figure 4 shows the frequency spectrum of the interference signal measured by the frequency spectrum measurement unit 18. Referring to Figures 3(b) and 3(c), the component at frequency 2fs of the post-irradiation signal comb and the component at frequency 2fL of the local comb produce a beat, and the component at frequency 2Δf (=2fs-2fL), which is the difference between the two, is measured (see Figure 4). Furthermore, the component at frequency 4fs of the post-irradiation signal comb and the component at frequency 4fL of the local comb produce a beat, and the component at frequency 4Δf (=4fs-4fL), which is the difference between the two, is measured (see Figure 4).

[0038] While the 2fs and 4fs frequency components of the post-irradiation signal comb are too high-frequency to measure, the 2Δf and 4Δf frequency components of the interference signal are at microwave frequencies and can therefore be measured. This makes it possible to measure the presence and concentration of each of the target substances.

[0039] Furthermore, the frequency components fs, 2fs, 3fs, etc. of the post-irradiation signal comb correspond to the frequency components Δf, 2Δf, 3Δf, etc. of the interference signal. Therefore, by measuring the frequency components Δf, 2Δf, 3Δf, etc. of the interference signal with the frequency spectrum measurement unit 18, the frequency components fs, 2fs, 3fs, etc. of the post-irradiation signal comb can be measured. However, there are limitations to the bandwidth in which the post-irradiation signal comb can be measured.

[0040] Figure 5 is a diagram showing the correspondence between the frequency of the post-irradiation signal comb and the frequency of the interference signal, as illustrated by the optical comb measuring device 1 according to an embodiment of the present invention. However, Figure 5 also shows the measurable bandwidths MB1, MB2, MB3, and MB4. In Figure 5, M is a positive integer, and Mfs = (M+1)fL. Since Mfs = (M+1)fL, MΔf = fL. However, in Figure 5, the minimum value of the post-irradiation signal comb frequency is shown as 0 (for the sake of illustration and explanation), but in reality, the minimum value of the post-irradiation signal comb frequency is mfs (=nfL) (same as in Figure 2).

[0041] Figure 11 shows the frequency spectra of the post-irradiation signal comb (Figure 11(a)) and local comb (Figure 11(b)) when 11fs = 12fL. That is, M = 11. Therefore, 11Δf = fL. However, in Figure 11(a), the absorption of the signal comb is not shown.

[0042] Referring to Figure 11, the frequency components of the signal comb at fs, 2fs, ..., 5fs after irradiation and the frequency components of the local comb at fL, 2fL, ..., 5fL produce a beat, resulting in the frequency components of the interference signal at Δf, 2Δf, ..., 5Δf.

[0043] However, the frequency difference (5Δf) between the 6fs component of the signal comb after irradiation and the 7fL component of the local comb is smaller (6Δf) than the frequency difference (6Δf) between the 6fs component of the local comb and the 7fL component of the local comb. Therefore, the 6fs component of the signal comb after irradiation and the 7fL component of the local comb create a beat, resulting in the 5Δf component of the interference signal. Similarly, the 7fs, 8fs, ..., 11fs components of the signal comb after irradiation and the 8fL, 9fL, ..., 12fL components of the local comb create a beat, resulting in the 4Δf, 3Δf, ..., 0 components of the interference signal.

[0044] Here, the measurable bandwidth MB1 is defined as frequencies from 0 to (1 1 / 2) fs, and the measurable bandwidth MB2 is defined as frequencies from (1 1 / 2) fs to 11 fs. For post-irradiation signal combs within the measurable bandwidth MB1 or MB2, the frequency of a single post-irradiation signal comb corresponds to the frequency of the interference signal.

[0045] On the other hand, it should be noted that in the measurable bandwidths MB1 and MB2, the frequencies of multiple post-irradiation signal combs correspond to the frequencies of the interference signal. For example, the 5Δf component of the interference signal corresponds to the 5fs and 6fs components of the post-irradiation signal comb. In this case, even if the 5Δf component of the interference signal is measured, only the optical power of the sum of the 5fs and 6fs components of the post-irradiation signal comb can be obtained (aliasing occurs).

[0046] Therefore, the measurable bandwidth will be either measurable bandwidth MB1 or measurable bandwidth MB2.

[0047] Referring to Figure 5, in the measurable bandwidth MB1 (post-irradiation signal comb frequency 0 to (1 / 2)Mfs), as the post-irradiation signal comb frequency increases by fs, the interference signal frequency also increases by Δf. The interference signal frequency reaches its maximum value of (1 / 2)MΔf when the post-irradiation signal comb frequency is (1 / 2)Mfs.

[0048] In the measurable bandwidth MB2 (post-irradiation signal comb frequency (1 / 2) Mfs to Mfs), as the post-irradiation signal comb frequency increases by fs, the interference signal frequency decreases by Δf. The interference signal frequency takes its minimum value of 0 when the post-irradiation signal comb frequency is Mfs.

[0049] In the measurable bandwidth MB3 (post-irradiation signal comb frequency Mfs to (3 / 2)Mfs), as the post-irradiation signal comb frequency increases by fs, the interference signal frequency also increases by Δf. The interference signal frequency reaches its maximum value of (1 / 2)MΔf when the post-irradiation signal comb frequency is (3 / 2)Mfs.

[0050] In the measurable bandwidth MB4 (post-irradiation signal comb frequency (3 / 2) Mfs to 2 Mfs), the interference signal frequency decreases by Δf as the post-irradiation signal comb frequency increases by fs. The interference signal frequency takes its minimum value of 0 when the post-irradiation signal comb frequency is 2 Mfs.

[0051] The measurable bandwidths MB1, MB2, MB3, and MB4 are (1 / 2)Mfs.

[0052] Figure 6 shows the absorption spectrum of the object being measured inside the irradiated body (Figure 6(a)), the correspondence between the frequency of the post-irradiation signal comb and the frequency of the interference signal (comparative example) (Figure 6(b)), and the correspondence between the frequency of the post-irradiation signal comb and the frequency of the interference signal (embodiment) (Figure 6(c)).

[0053] Referring to Figure 6(a), the power of the light irradiated onto the object changes at predetermined frequencies S1 and S2 corresponding to each of the objects being measured. Specifically, light is absorbed at predetermined frequencies S1 and S2, resulting in lower transmittance. The difference between frequencies S1 and S2 is a large value, approximately 23 THz.

[0054] Referring to Figure 6(b), the measurement is performed by obtaining an interference signal using a post-irradiation signal comb with frequencies within the measurable bandwidth MB2 (comparative example). In this case, since frequencies S1 and S2 must be included within the measurable bandwidth MB2, the bandwidth of the measurable bandwidth MB2 becomes wider. Here, (bandwidth of measurable bandwidth MB2) = (1 / 2)Mfs, so in order to widen the bandwidth of the measurable bandwidth MB2, M must be increased. Moreover, since MΔf = fL, increasing M makes Δf smaller. The time required for one measurement is the reciprocal of Δf, but since the measurement is repeated many times (for example, 1000 times), if Δf is small, the time required for measurement will be long.

[0055] Therefore, in the embodiment of the present invention, as shown in Figure 6(c), multiple measurable bands MBx and MBy include one or more predetermined frequencies S1 and S2. For example, as shown in Figure 6(c), each of the measurable bands includes one of the predetermined frequencies (measurable band MBx includes predetermined frequency S1, and measurable band MBy includes predetermined frequency S2). Compared to a comparative example (see Figure 6(b)) in which one of the measurable bands (MB2) includes all predetermined frequencies (S1, S2), the embodiment of the present invention (see Figure 6(c)) in which multiple measurable bands MBx and MBy include one or more predetermined frequencies S1 and S2 allows for a narrower bandwidth of the measurable bands MBx and MBy. However, in Figure 6(c), the minimum value of the post-irradiation signal comb frequency is shown as 0 (for the convenience of illustration and explanation), but in reality, the minimum value of the post-irradiation signal comb frequency is mfs (=nfL) (same as in Figure 2).

[0056] The bandwidths of the measurable bandwidths MBx and MBy (see Figure 6(c)) are narrower than the measurable bandwidth MB2 (see Figure 6(b)). Therefore, there is no need to increase M. Moreover, since MΔf = fL, if M does not need to be increased, Δf will not decrease. The time required for one measurement is the reciprocal of Δf, so even if the measurement is repeated many times (for example, 1000 times), the time required for measurement can be shortened as long as Δf does not decrease.

[0057] However, if interference signals are obtained using a post-irradiation signal comb at frequencies within the measurable bandwidths MBx and MBy, and measurements are performed, aliasing will occur.

[0058] Therefore, the measurement is performed by obtaining an interference signal (frequency band B1) corresponding to the component in the required band P1 within the measurable band MBx of the post-irradiation signal comb, and an interference signal (frequency band B2) corresponding to the component in the required band P2 within the measurable band MBy of the post-irradiation signal comb. In order to perform such a measurement, the post-irradiation signal comb only needs to have components within multiple required bands P1 and P2. For example, the multiple band-passing unit 14 can receive the post-irradiation signal comb, pass components of multiple required bands P1 and P2 through it, and provide it to the interference signal acquisition unit 16.

[0059] However, the multiple required bandwidths P1 and P2 include all predetermined frequencies S1 and S2. Moreover, the frequency bandwidths B1 and B2 of the interference signals corresponding to each of the multiple required bandwidths P1 and P2 do not overlap with each other.

[0060] Since the frequency bands B1 and B2 of the interference signal do not overlap, if a component within frequency band B1 of the interference signal is obtained, it can be determined that it is a component within the measurable band MBx of the post-irradiation signal comb. Furthermore, if a component within frequency band B2 of the interference signal is obtained, it can be determined that it is a component within the measurable band MBy of the post-irradiation signal comb. Note that components within the measurable bands MBx and MBy of the post-irradiation signal comb are mixed and not detected (no aliasing occurs).

[0061] Next, the operation of the embodiment of the present invention will be described.

[0062] When the pre-irradiation signal comb (see Figure 2(a)) is irradiated from the signal comb generation unit 12a onto the object to be irradiated (gas) inside the DUT (gas cell) 2, the pre-irradiation signal comb passes through the DUT 2, and a post-irradiation signal comb is obtained.

[0063] After irradiation, the signal comb is fed to the multi-bandpass section 14, and the passed components are fed to the interference signal acquisition section 16. However, the passbands of the multi-bandpass section 14 are the required bands P1 and P2 (see Figure 6(c)).

[0064] Furthermore, a local comb (see Figure 2(b)) is supplied from the local comb generation unit 12b to the interference signal acquisition unit 16.

[0065] The interference signal between the post-irradiation signal comb (components that have passed through the multi-bandpass section 14) and the local comb is acquired by the interference signal acquisition unit 16. The frequency spectrum of the result acquired by the interference signal acquisition unit 16 is measured by the frequency spectrum measurement unit 18.

[0066] According to embodiments of the present invention, the time required to measure multiple types of objects using dual-comb spectroscopy can be reduced.

[0067] In other words, compared to a comparative example (see Figure 6(b)) in which one of the measurable bandwidths (MB2) includes all predetermined frequencies (S1, S2), according to the embodiment of the present invention (see Figure 6(c)) in which the measurable bandwidth MBx includes the predetermined frequency S1 and the measurable bandwidth MBy includes the predetermined frequency S2, the bandwidths of the measurable bandwidths MBx and MBy can be narrowed. Therefore, it is not necessary to increase M. Moreover, since MΔf = fL, if M does not need to be increased, Δf will not decrease. The time required for one measurement is the reciprocal of Δf, so even if the measurement is repeated many times (for example, 1000 times), the time required for measurement can be shortened as long as Δf does not decrease.

[0068] Furthermore, since the multiple bandpass unit 14 receives the post-irradiation signal comb and passes components of multiple required bands P1 and P2 through it before supplying it to the interference signal acquisition unit 16, the frequency bands B1 and B2 of the interference signals do not have any overlapping regions. Therefore, despite measuring interference signals based on multiple measurable bands MBx and Mby, aliasing does not occur.

[0069] Furthermore, various modifications can be considered for the embodiments of the present invention.

[0070] <Example 1> Figure 7 shows the configuration of an optical comb measuring device 1 according to Modification 1 of the embodiment of the present invention. In the optical comb measuring device 1 according to Modification 1, the multiple bandpass unit 14 is placed between the local comb generation unit 12b and the interference signal acquisition unit 16, instead of between the DUT 2 and the interference signal acquisition unit 16.

[0071] The multiple-bandpass unit 14 receives a local comb from the local comb generation unit 12b, passes components of multiple required bands P1 and P2 through it, and provides it to the interference signal acquisition unit 16. In this case, the local comb has only components within the multiple required bands P1 and P2. The rest is the same as in the embodiments of the present invention and will not be described further.

[0072] <Modification 2> Figure 8 shows the configuration of the optical comb measuring device 1 according to Modification 2 of the embodiment of the present invention. In the optical comb measuring device 1 according to Modification 2, a multi-bandpass section is placed both between the DUT2 and the interference signal acquisition unit 16 (multi-bandpass section 14a) and between the local comb generation unit 12b and the interference signal acquisition unit 16 (multi-bandpass section 14b).

[0073] The multiple bandpass section 14a is the same as the multiple bandpass section 14 of the embodiment of the present invention (see Figure 1). The multiple bandpass section 14b is the same as the multiple bandpass section 14 of Modification 1 of the embodiment of the present invention (see Figure 7). In this case, the post-irradiation signal comb and local comb have only components within the multiple required bands P1 and P2. The rest is the same as the embodiment of the present invention and will not be described.

[0074] <Variation 3> Figure 9 shows the configuration of the optical comb measuring device 1 according to Modification 3 of the embodiment of the present invention. In the optical comb measuring device 1 according to Modification 3, the multiple bandpass unit 14 is placed between the signal comb generation unit 12a and the DUT2, instead of between the DUT2 and the interference signal acquisition unit 16.

[0075] The multiple-bandpass unit 14 receives the signal comb from the signal comb generation unit 12a, passes multiple required bands P1 and P2 components through it, and supplies it to the DUT2. The rest is the same as in the embodiments of the present invention and will not be described further.

[0076] <Modification 4> Figure 10 shows the configuration of the optical comb measurement device 1 according to Modification 4 of the embodiment of the present invention. In the optical comb measurement device 1 according to Modification 4, multiple bandpass sections are arranged both between the signal comb generation unit 12a and the DUT2 (multiple bandpass section 14a) and between the local comb generation unit 12b and the interference signal acquisition unit 16 (multiple bandpass section 14b).

[0077] The multiple-band-pass section 14a is the same as the multiple-band-pass section 14 in Modification 3 of the embodiment of the present invention (see Figure 9). The multiple-band-pass section 14b is the same as the multiple-band-pass section 14 in Modification 1 of the embodiment of the present invention (see Figure 7). The rest is the same as in the embodiment of the present invention and will not be described.

[0078] <Modification 5> Modification 5 of the embodiment of the present invention is obtained by removing the multiple bandpass section 14 from the optical comb measuring device 1 of the embodiment of the present invention. However, either or both of the pre-irradiation signal comb and the local comb have only components within a plurality of required bands P1 and P2 that include all predetermined frequencies S1 and S2.

[0079] <Variation 6> Figure 12 shows the absorption spectrum of the object to be measured inside the irradiated body according to a modified example 6 of the embodiment of the present invention (Figure 12(a)), and the correspondence between the frequency of the post-irradiation signal comb and the frequency of the interference signal (embodiment) (Figure 12(b)). However, in Figure 12(b), the minimum value of the post-irradiation signal comb frequency is shown as 0 (for the sake of illustration and explanation), but in reality, the minimum value of the post-irradiation signal comb frequency is mfs (=nfL) (same as in Figure 2).

[0080] Modification 6, referring to Figure 12(a), replaces the embodiment of the present invention (where there are two predetermined frequencies S1 and S2 corresponding to the object to be measured) with three predetermined frequencies S1, S2, and S3 corresponding to the object to be measured. However, referring to Figure 12(b), each of the measurable bandwidths includes each of the predetermined frequencies. That is, the measurable bandwidth MBx and the required bandwidth P1 include the predetermined frequency S1, the measurable bandwidth MBy and the required bandwidth P2 include the predetermined frequency S2, and the measurable bandwidth MBz and the required bandwidth P3 include the predetermined frequency S3. Moreover, the frequency bandwidths B1, B2, and B3 of the interference signals corresponding to each of the multiple required bandwidths P1, P2, and P3 do not have any overlapping regions.

[0081] <Example 7> Figure 13 shows the absorption spectrum of the object to be measured inside the irradiated body according to Modification 7 of the embodiment of the present invention (Figure 13(a)), and the correspondence between the frequency of the post-irradiation signal comb and the frequency of the interference signal (embodiment) (Figure 13(b)). However, in Figure 13(b), the minimum value of the post-irradiation signal comb frequency is shown as 0 (for the convenience of illustration and explanation), but in reality, the minimum value of the post-irradiation signal comb frequency is mfs (=nfL) (same as in Figure 2).

[0082] Modification 7, referring to Figure 13(a), has three predetermined frequencies S1, S2, and S3 corresponding to the object being measured. However, predetermined frequencies S2 and S3 are close together. Therefore, referring to Figure 13(b), one or more of the measurable bandwidths (e.g., MBy) include multiple predetermined frequencies (e.g., S2 and S3). That is, the measurable bandwidth MBx and the required bandwidth P1 include predetermined frequency S1, and the measurable bandwidth MBy and the required bandwidth P2 include predetermined frequencies S2 and S3. Moreover, the frequency bandwidths B1 and B2 of the interference signals corresponding to each of the multiple required bandwidths P1 and P2 do not have any overlapping regions.

[0083] <Differentiation Example 8> Modification 8 of the embodiment of the present invention is a case in which the irradiated object is a liquid or a solid. For example, the presence or absence of the object to be measured is measured. For example, in the case where the irradiated object is a solid, FTIR is used to measure the absorption of OH groups in an optical fiber (1.4 μm band). In the case where the irradiated object is a liquid, FTIR is used to determine whether water is contained, etc., based on the presence or absence of OH group absorption.

[0084] <Modification 9> Modification 9 of the embodiment of the present invention is such that the interference signal acquisition unit 14 is a power beam splitter. The arrangement or non-use of the multiple bandpass units 14, 14a, and 14b is the same as in the embodiment, modification 1, modification 2, modification 3, modification 4, and modification 5 of the present invention.

[0085] The outputs of the signal comb generation unit 12a and the local comb generation unit 12b may be passed through the half-wave plate and the quarter-wave plate. The output of the interference signal acquisition unit 14 may be passed through the optical attenuator and the half-wave plate. [Explanation of Symbols]

[0086] 1. Optical comb measuring device 2 DUT (Gas Cells) 12a Signal comb generation unit 12b Local COM generation unit 14, 14a, 14b Multiple Bandpass Sections 16 Interference signal acquisition unit 18 Frequency spectrum measurement section MB1, MB2, MB3, MB4, MBx, MBy, MBz Measurable bandwidth fs signalcom frequency repetition frequency fL Localcom frequency repetition rate Δf is the difference in repetition frequencies between the local comb and the signal comb. B1, B2, B3 frequency bands P1, P2, P3 Required bandwidth S1, S2, S3 predetermined frequencies

Claims

1. An optical comb measuring device for measuring an irradiated object having multiple types of measurement targets, An interference signal acquisition unit acquires an interference signal between a post-irradiation signal comb obtained by irradiating the object to be irradiated with a pre-irradiation signal comb and a local comb in which the repetition frequency of the pre-irradiation signal comb is differed by a predetermined difference frequency. A frequency spectrum measuring unit that measures the frequency spectrum of the result obtained by the interference signal acquisition unit, Equipped with, The pre-irradiation signal comb, the post-irradiation signal comb, and the local comb are optical combs. The power of the light irradiated onto the object to be irradiated changes at a predetermined frequency corresponding to each of the objects to be measured. Among the measurable bandwidths that are the frequency domains of the post-irradiation signal comb, where the frequency of a single post-irradiation signal comb corresponds to the frequency of the interference signal, there are multiple such bandwidths that include one or more of the predetermined frequencies. Either the post-irradiation signal comb and the local comb, or both, supplied to the interference signal acquisition unit, have only components within a plurality of required bandwidths, including all of the predetermined frequencies. The frequency bands of the interference signals corresponding to each of the aforementioned multiple required bands do not have any overlapping regions. Optical comb measuring device.

2. The optical comb measuring device according to claim 1, An optical comb measuring device comprising a multi-band pass section that receives either or both of the pre-irradiation signal comb and the local comb, and allows a plurality of components of the required frequency bands to pass through.

3. The optical comb measuring device according to claim 1, An optical comb measuring device comprising a multi-band pass section that receives either or both of the post-irradiation signal comb and the local comb, and allows a plurality of components of the required frequency bands to pass through.

4. The optical comb measuring device according to claim 1, An optical comb measuring device in which either or both of the pre-irradiation signal comb and the local comb have components within a plurality of required bands, including all of the predetermined frequencies.

5. The optical comb measuring device according to claim 1, An optical comb measuring device in which each of the measurable bandwidths includes each of the predetermined frequencies.

6. The optical comb measuring device according to claim 1, An optical comb measuring device in which one or more of the measurable bandwidths include a plurality of predetermined frequencies.

7. The optical comb measuring device according to claim 1, The optical comb measuring device wherein the irradiated object is a gas.

8. The optical comb measuring device according to claim 7, An optical comb measuring device in which the irradiated object is housed in a gas cell.

9. The optical comb measuring device according to claim 7, An optical comb measuring device for measuring the concentration of the object to be measured.

10. The optical comb measuring device according to claim 1, An optical comb measuring device in which the irradiated object is a liquid or a solid.

11. An optical comb measuring device according to claim 10, An optical comb measuring device that measures the presence or absence of the aforementioned object to be measured.

12. The optical comb measuring device according to claim 1, An optical comb measuring device in which the post-irradiation signal comb and the local comb are supplied to the interference signal acquisition unit via a polarization-maintaining fiber.

13. The optical comb measuring device according to claim 1, An optical comb measuring device in which the interference signal acquisition unit is an optical coupler.

14. The optical comb measuring device according to claim 1, An optical comb measuring device in which the interference signal acquisition unit is a power beam splitter.

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