Apparatus and method for measuring scattering medium

Abstract

A scattering medium measuring device and a scattering medium measuring method are provided that can accurately measure a scattering medium using an optical comb. [Solution] The scattering medium measuring device 100 comprises an optical comb generating unit 1 having an optical comb output unit 10 and a wavelength conversion unit 3 that converts the wavelengths of the first and second optical combs L1, L2 output from the optical comb output unit 1 using soliton self-frequency shift, an optical detection unit 6 that detects the first and second optical combs L1, L2 generated by the optical comb generating unit 1, at least one of which has propagated inside the scattering medium S, and an analysis unit 8 that performs analysis related to the measurement of the scattering medium S based on the detection results of the optical detection unit 6.

Description

[Technical Field]

[0001] The present disclosure relates to an apparatus and method for measuring a scattering medium. [Background technology]

[0002] There is known a scattering medium measurement device that measures a scattering medium using an optical comb, which is an ultrashort pulse laser beam having a plurality of frequency modes (longitudinal modes) arranged at equal intervals like a comb on the frequency axis. As this type of technology, for example, Non-Patent Document 1 describes a technology that realizes high-speed spectroscopic measurement by using two optical combs (a first optical comb and a second optical comb). [Prior art documents] [Non-patent literature]

[0003] [Non-Patent Document 1] Sho Okubo, et al, “Ultra-broadband dual-combspectroscopy across 1.0-1.9μm”, Applied Physics Express082402 (2015), published online July 14, 2015, The Japan Society of Applied Physics Summary of the Invention [Problem to be solved by the invention]

[0004] In the above-described techniques, the measurement band is limited, and therefore, in measuring a scattering medium, it is sometimes desirable to broaden the measurement band. However, broadening the measurement band may result in a deterioration in the S / N ratio and a decrease in measurement accuracy. The present disclosure has been made in view of such circumstances, and aims to provide a scattering medium measurement device and a scattering medium measurement method that can accurately measure a scattering medium using an optical comb. [Means for solving the problem]

[0005] The present inventors have conducted extensive research and have found that by varying the wavelengths of the first and second optical combs to generate multiple spectra with different narrow bands, it becomes possible to perform spectroscopic measurement over a wide measurement band without reducing measurement accuracy. They have come to the realization that applying such spectroscopic measurement to the measurement of a scattering medium makes it possible to perform the measurement with high accuracy, and have completed the present disclosure.

[0006] That is, the scattering medium measuring device of the present disclosure is [1] "a scattering medium measuring device for measuring a scattering medium, comprising: an optical comb generator having an optical comb output unit that outputs first and second optical combs having a plurality of frequency modes arranged in a comb shape on the frequency axis; and a wavelength converter that converts the wavelengths of the first and second optical combs output from the optical comb output unit by utilizing soliton self-frequency shift; an optical detection unit that detects the first and second optical combs generated by the optical comb generator, at least either of which has propagated inside the scattering medium; and an analysis unit that performs analysis related to the measurement of the scattering medium based on the detection result of the optical detection unit."

[0007] In this scattering medium measurement device, by using the first and second optical combs that have been wavelength converted using the soliton self-frequency shift, it is possible to perform spectroscopic measurement of the scattering medium over a wide measurement band without reducing the measurement accuracy, as found above. That is, according to the present disclosure, it is possible to measure the scattering medium with high accuracy using the optical comb.

[0008] The scattering medium measuring device of the present disclosure may be [2] "the scattering medium measuring device according to [1], wherein the analysis unit calculates a time waveform and an autocorrelation function based on the detection result of the light detection unit, and calculates internal information of the scattering medium based on the calculated time waveform and autocorrelation function." In this case, the analysis unit can obtain internal information of the scattering medium.

[0009] The scattering medium measuring device of the present disclosure may be [3] "the scattering medium measuring device according to [2], wherein the internal information of the scattering medium includes an absorption coefficient, a scattering coefficient, and a flow index." In this case, it is possible to obtain the absorption coefficient, the scattering coefficient, and the flow index as the internal information of the scattering medium.

[0010] The scattering medium measuring device of the present disclosure may be [4] "the scattering medium measuring device according to any one of [1] to [3], wherein the optical comb output unit is a dual comb laser light source that outputs the first optical comb and the second optical comb whose time interval is different from that of the first optical comb." In this case, it is possible to generate the first and second optical combs using a dual comb laser light source.

[0011] The scattering medium measuring device of the present disclosure may be [5] "the scattering medium measuring device according to any one of [1] to [4], wherein the optical comb generator comprises an optical amplifier that broadens the spectrum of the first and second optical combs output from the optical comb output unit and before wavelength conversion by the wavelength converter." As a result of extensive research, the present inventors have found that multi-soliton generation can be suppressed by broadening the spectrum of the optical comb before wavelength conversion using soliton self-frequency shift. Therefore, according to the present disclosure, it is possible to suppress multi-soliton generation.

[0012] The scattering medium measuring device of the present disclosure may be [6] "the scattering medium measuring device according to [5], in which the optical amplifier broadens the spectrum of the first and second optical combs by similariton amplification." In this case, the optical amplifier can suppress stretching of the first and second optical combs, and can effectively realize wavelength conversion using soliton self-frequency shift.

[0013] The scattering medium measuring device of the present disclosure may be [7] "the scattering medium measuring device according to [5] or [6], in which the optical amplifier controls the intensities of the first and second optical combs." In this case, by controlling the intensities of the first and second optical combs, it is possible to tune the wavelengths of the first and second optical combs.

[0014] The scattering medium measuring device of the present disclosure may be [8] "the scattering medium measuring device according to [1] to [7], wherein the scattering medium is a living body." Living bodies, unlike inorganic materials such as semiconductors, are prone to change state, and therefore high-speed measurement is desired. In this regard, the present disclosure is particularly effective when a living body is the measurement target, as it is capable of high-speed measurement using an optical comb.

[0015] The scattering medium measuring device of the present disclosure may be [9] "the scattering medium measuring device according to [8], wherein the optical comb generator increases the intensities of the first and second optical combs to shift the wavelengths of the first and second optical combs, converted by the wavelength converter using soliton self-frequency shift, to longer wavelengths." In living organisms, there is a tendency that the longer the wavelengths of the first and second optical combs, the higher the damage threshold (the upper threshold of the intensities of the first and second optical combs). In the present disclosure, the optical comb generator is compatible with this tendency, and is particularly effective when a living organism is used as a measurement target, since the wavelengths of the first and second optical combs shift to longer wavelengths as the intensities of the first and second optical combs increase.

[0016] The scattering medium measuring device of the present disclosure may be

[10] "the scattering medium measuring device according to any one of [1] to [9], including a control unit, which is capable of performing a first process of converting the wavelengths of the first and second optical combs to a predetermined wavelength in the wavelength conversion unit, a second process of causing the analysis unit to perform an analysis based on a detection result of the light detection unit when the wavelengths of the first and second optical combs have been converted to the predetermined wavelength by the first process, and a third process of repeatedly performing the first process and the second process by switching the predetermined wavelength among a plurality of different wavelengths." In this case, the process of generating a plurality of different narrowband spectra by varying the wavelengths of the first and second optical combs can be realized by control of the control unit.

[0017] The scattering medium measurement method of the present disclosure is

[11] "a scattering medium measurement method for measuring a scattering medium, comprising: a first step of outputting first and second optical combs having a plurality of frequency modes arranged in a comb-like pattern on a frequency axis and converting the wavelengths of the output first and second optical combs using soliton self-frequency shift; a second step of propagating at least one of the first and second optical combs whose wavelengths have been converted in the first step inside the scattering medium and detecting the first and second optical combs; and an analysis unit that performs analysis related to the measurement of the scattering medium based on the detection result detected in the second step." In this scattering medium measurement method, as with the above-mentioned scattering medium measurement device, the scattering medium can be accurately measured using an optical comb. [Effects of the Invention]

[0018] According to the present disclosure, it is possible to provide an apparatus and a method for measuring a scattering medium that can accurately measure a scattering medium using an optical comb. [Brief explanation of the drawings]

[0019] [Figure 1] FIG. 1 is a diagram showing the configuration of an apparatus for measuring a scattering medium according to an embodiment. [Figure 2] FIG. 2 is a graph showing the first optical comb, the second optical comb, and an interference waveform on the time axis. [Figure 3] FIG. 3 is a diagram illustrating the configuration of the optical comb output unit in FIG. [Figure 4] FIG. 4 is a diagram illustrating the propagation of an optical frequency comb inside a scattering medium. [Figure 5] FIG. 5 is a flowchart showing an example of a scattering medium measuring method according to the embodiment. [Figure 6] Figure 6(a) is a graph showing an example of detected light, and Figure 6(b) is a graph showing an example of detected light after time filtering. [Figure 7]Fig. 7(a) is a diagram showing another configuration around the wavelength selection unit, Fig. 7(b) is a diagram showing yet another configuration around the wavelength selection unit, and Fig. 7(c) is a diagram showing yet another configuration around the wavelength selection unit. DETAILED DESCRIPTION OF THE INVENTION

[0020] Hereinafter, the embodiments will be described in detail with reference to the drawings. In each drawing, the same or corresponding parts are designated by the same reference numerals, and duplicated explanations will be omitted.

[0021] 1, the scattering medium measuring apparatus 100 according to the first embodiment is an apparatus that uses a first optical comb L1 and a second optical comb L2 to measure a scattering medium S. The scattering medium measuring apparatus 100 includes an optical comb generator 1, a wavelength selector 4, a multiplexer 5, a photodetector 6, an analyzer 8, and a controller 9.

[0022] Examples of the scattering medium S include a living body, a suspension, and other scattering mediums. A living body includes a region composed of red blood cells flowing through capillaries or veins and arteries of various diameters, hemoglobin attached to the red blood cells, muscles, fat, water, bones, etc. Examples of the living body include a human, a head, a breast, an organ, a peripheral organ, a blood vessel, a disease, and other living bodies. A suspension is composed of scattering materials with diameters of several nm to several hundred μm and is turbid. Examples of the suspension include materials, pharmaceuticals, and soft matter. Other scattering mediums include snow, glaciers, fog, and clouds.

[0023] The first optical comb L1 and the second optical comb L2 are frequency-controlled ultrashort pulse laser beams (mode-locked laser beams). When viewed on the time axis (time domain), the first optical comb L1 and the second optical comb L2 are represented as ultrashort pulse trains (see Figure 2). By performing a Fourier transform on the ultrashort pulse trains constituting the first optical comb L1 and the second optical comb L2, an optical spectrum with equally spaced frequency modes (longitudinal modes) is obtained. In other words, the first optical comb L1 and the second optical comb L2 are represented as optical spectra with multiple frequency modes arranged in a comb-like pattern on the frequency axis (frequency domain). The first optical comb L1 is represented by two parameters: a repetition frequency frep1 and an offset frequency fCEO1. The second optical comb L2 is represented by two parameters: a repetition frequency frep2 and an offset frequency fCEO2. The second optical comb L2 has a slightly different time interval from the first optical comb L1.

[0024] The scattering medium measuring device 100 includes an optical comb output unit 10 that outputs a first optical comb L1 and a second optical comb L2, an optical amplifier unit 2 that broadens the spectrum of the first optical comb L1 and the second optical comb L2, and a wavelength converter 3 that converts the wavelengths of the first optical comb L1 and the second optical comb L2 by using soliton self-frequency shift.

[0025] As shown in FIG. 3, the optical comb output unit 10 is a bidirectional oscillation dual comb laser light source that outputs a first optical comb L1 and a second optical comb L2. The pulse width of the output first optical comb L1 and second optical comb L2 is, for example, 10 ps or less, and the repetition frequency is, for example, 1 GHz or less. The optical comb output unit 10 outputs the first optical comb L1 oscillating clockwise (CW) and the second optical comb L2 oscillating counterclockwise (CCW). In the optical comb output unit 10, light from a light source 11, such as a laser diode, is sent to a doped fiber 12, such as an erbium-doped fiber or an yttrium-doped fiber, and amplified. The amplified light circulates in a loop optical path 13 in two different directions, clockwise and counterclockwise.

[0026] A nonlinear polarization rotator 15 that changes the polarization state of light to control the intensity and phase of the light, and a semiconductor saturable absorber mirror 16 that is a device for generating optical pulses are provided on the loop optical path 13. A portion of the light circulating clockwise in the loop optical path 13 is extracted by a coupler 17 and output as a first optical comb L1. A portion of the light circulating counterclockwise in the loop optical path 13 is extracted by a coupler 18 and output as a second optical comb L2.

[0027] 1, the optical amplifier 2 broadens the spectrum of the first optical comb L1 and the second optical comb L2 that are output from the optical comb output unit 10 and before their wavelengths are converted by the wavelength converter 3. The optical amplifier 2 includes acousto-optic modulators 21 and 22 and fiber amplifiers 23 and 24.

[0028] The acousto-optic modulators 21 and 22 are devices that perform modulation using the force of acoustics (sound waves) and are called AOMs (Acousto-Optic Modulators). The acousto-optic modulator 21 controls the intensity of the first optical comb L1 for each pulse. The acousto-optic modulator 21 is disposed between the optical comb output unit 10 and the fiber amplifier 23 in the optical path of the first optical comb L1. The acousto-optic modulator 22 controls the intensity of the second optical comb L2 for each pulse. The acousto-optic modulator 22 is disposed between the optical comb output unit 10 and the fiber amplifier 24 in the optical path of the second optical comb L2. The acousto-optic modulators 21 and 22 may be disposed anywhere between the optical comb output unit 10 and the wavelength converter 3.

[0029] The fiber amplifier 23 broadens the spectrum of the first optical comb L1. Specifically, the fiber amplifier 23 broadens the spectrum of the first optical comb L1 and increases the output power of the first optical comb L1 through similariton amplification. The fiber amplifier 23 is disposed between the acousto-optic modulator 21 and the wavelength converter 3 in the optical path of the first optical comb L1. The fiber amplifier 24 broadens the spectrum of the second optical comb L2. Specifically, the fiber amplifier 24 broadens the spectrum of the second optical comb L2 and increases the output power of the second optical comb L2 through similariton amplification. The fiber amplifier 24 is disposed between the acousto-optic modulator 22 and the wavelength converter 3 in the optical path of the second optical comb L2.

[0030] The fiber amplifiers 23, 24 are configured to include a normal dispersion fiber and a pumping light source. The normal dispersion fiber is a double-clad fiber co-doped with erbium and ytterbium. That is, the fiber amplifiers 23, 24 perform amplification while generating a nonlinear effect using the normal dispersion double-clad fiber to prevent stretching, and obtain the first and second optical combs L1, L2 as broadband amplified light. The normal dispersion fiber is a fiber with a negative dispersion parameter D (ps / nm / km). The additive used in the fiber amplifiers 23, 24 is not particularly limited, and various additives may be used. The fiber amplifiers 23, 24 may broaden the spectrum so that the spectral width of the first and second optical combs L1, L2 is 100 nm or more, for example.

[0031] The wavelength conversion unit 3 converts the wavelengths of the first and second optical combs L1 and L2 output from the optical comb output unit 10 by using soliton self-frequency shift. The wavelength conversion unit 3 includes Raman shift fibers 31 and 32.

[0032] The Raman shift fiber 31 tunes the wavelength of the first optical comb L1, which has been spectrum-broadened and output-enhanced by the fiber amplifier 23, to a predetermined wavelength by using soliton self-frequency shift (Raman soliton shift). The Raman shift fiber 31 tunes the wavelength of the first optical comb L1 to generate solitons. The Raman shift fiber 31 is disposed between the fiber amplifier 23 and the wavelength selector 4 in the optical path of the first optical comb L1. The Raman shift fiber 32 tunes the wavelength of the second optical comb L2, which has been spectrum-broadened and output-enhanced by the fiber amplifier 24, by using soliton self-frequency shift. The Raman shift fiber 32 tunes the wavelength of the second optical comb L2 to generate solitons. The Raman shift fiber 32 is disposed between the fiber amplifier 24 and the wavelength selector 4 in the optical path of the second optical comb L2.

[0033] The Raman shift fibers 31 and 32 can be, for example, single-mode anomalous dispersion fibers that exhibit anomalous dispersion in the wavelength bands of the first and second optical combs L1 and L2 generated by the fiber amplifiers 23 and 24. The Raman shift fibers 31 and 32 can output the first and second optical combs L1 and L2 (solitons) in a wavelength band of, for example, 1600 nm to 2200 nm. Note that the first and second optical combs L1 and L2 modulated by the soliton self-frequency shift contain non-soliton components (components that do not become solitons). In this scattering medium measuring device 100, the optical amplifier 2 increases the intensities of the first and second optical combs L1 and L2 output from the optical comb output unit 10, thereby shifting the wavelengths of the first and second optical combs L1 and L2 converted by the wavelength converter 3 using the soliton self-frequency shift to longer wavelengths.

[0034] The wavelength selector 4 transmits the first optical comb L1 and the second optical comb L2 in a predetermined wavelength band. The predetermined band is, for example, 600 nm to 2200 nm. The wavelength selector 4 is arranged between the optical comb generator 1 and the multiplexer 5 in the optical paths of the first optical comb L1 and the second optical comb L2. The wavelength selector 4 includes wavelength filters 41 and 42. The wavelength filter 41 is arranged between the Raman shift fiber 31 and the multiplexer 5 in the optical path of the first optical comb L1. The wavelength filter 42 is arranged between the Raman shift fiber 32 and the multiplexer 5 in the optical path of the second optical comb L2. The wavelength filters 41 and 42 here are long-pass filters.

[0035] The multiplexing unit 5 multiplexes the first optical comb L1 and the second optical comb L2. The multiplexing unit 5 is disposed between the wavelength selection unit 4 and the optical detection unit 6 in the optical paths of the first and second optical combs L1 and L2. In the illustrated example, the multiplexing unit 5 includes mirrors 51 and 52. The mirrors 51 and 52 transmit the first optical comb L1 and reflect the second optical comb L2 so that the first optical comb L1 and the second optical comb L2 are multiplexed on the same optical axis.

[0036] The optical detection unit 6 detects the first and second optical combs L1 and L2 combined by the multiplexing unit 5. The optical detection unit 6 is configured with, for example, a photodetector. The optical detection unit 6 detects the first and second optical combs L1 and L2 combined by the multiplexing unit 5, thereby acquiring detection light having an interference waveform of the first and second optical combs L1 and L2 (hereinafter simply referred to as "interference waveform") (see FIG. 2). The optical detection unit 6 outputs the acquired detection light to the analysis unit 8.

[0037] The analysis unit 8 performs analysis related to spectroscopic measurement based on the detection results of the light detection unit 6. The analysis unit 8 is physically configured to include memories such as RAM and ROM, a processor (arithmetic circuit) such as a CPU, a communication interface, and a storage unit such as a hard disk. Examples of the analysis unit 8 include a personal computer, a cloud server, and a smart device (smartphone, tablet terminal, etc.). The analysis unit 8 functions by executing a program stored in the memory on the CPU or GPU of the computer system.

[0038] The analysis unit 8 performs analysis relating to the measurement of the scattering medium S based on the detected light detected by the light detection unit 6 (the detection result of the light detection unit 6). The analysis unit 8 calculates a time waveform and an autocorrelation function based on the detected detected light, and calculates internal information of the scattering medium S based on the calculated time waveform and autocorrelation function. The internal information of the scattering medium S includes information on the substance to be measured inside the scattering medium S and information related to the substance to be measured. For example, if the scattering medium S is a living body, the substance to be measured is at least one of red blood cells, hemoglobin, fat, water, blood flow, etc. The internal information of the scattering medium S includes, for example, an absorption coefficient, a scattering coefficient, and a flow index. The calculations of the analysis unit 8 will be described in detail later.

[0039] The control unit 9 controls various operations of the scattering medium measuring apparatus 100. The control unit 9 is physically configured in the same manner as the analysis unit 8. The control unit 9 may be formed integrally with the analysis unit 8 or may be formed separately. The control unit 9 controls the output of the first optical comb L1 and the second optical comb L2 in the optical comb output unit 10.

[0040] The control unit 9 is capable of performing a first process of controlling the acousto-optic modulators 21, 22 to adjust the intensity of the first and second optical combs L1, L2 (i.e., adjusting the excitation laser output of the optical amplification unit 2) and converting the wavelengths of the first and second optical combs L1, L2 to a predetermined wavelength in the wavelength conversion unit 3; a second process of causing the analysis unit 8 to perform analysis based on the detected light when the wavelengths of the first and second optical combs L1, L2 and L2 have been converted to the predetermined wavelength by the first process; and a third process of repeatedly performing the first and second processes by switching the predetermined wavelength between multiple wavelengths that are different from each other.

[0041] In the third process, the control unit 9 converts the wavelengths of the first and second optical combs L1 and L2 by a time interval of 1 / Δfrep. Δfrep is the measurement time, which is the difference between the repetition frequency frep1 of the first optical comb L1 and the repetition frequency frep2 of the second optical comb L2 (Δfrep = frep1 - frep2). More preferably, the control unit 9 may switch the wavelengths when 1 / (2 × Δfrep) has elapsed from the peak of the interference waveform. Note that since the measurement bandwidth Δν can be expressed as (frep1 × frep2) / (2 × Δfrep), Δfrep may be calculated from the measurement bandwidth Δν.

[0042] As shown in FIG. 1, in the scattering medium measurement device 100, a scattering medium S can be placed on the optical path of the first optical comb L1 before being multiplexed in the multiplexing unit 5. In this case, in the scattering medium measurement device 100, as shown in FIG. 4, the first optical comb L1 of a predetermined band generated by the optical comb generator 1 and transmitted through the wavelength selector 4 is propagated, for example, by optical fiber or spatial propagation, and then incident on the scattering medium S (a human in the illustrated example). The first optical comb L1 propagates inside the scattering medium S, exits the scattering medium S, and propagates again by optical fiber or spatial propagation. At this time, scattering particles (red blood cells in the illustrated example) h inside the scattering medium S move in random directions at various speeds, generating various amounts of Doppler shift of light. The lights interfere with each other in multiple ways, generating a speckle pattern SP on the surface of the scattering medium S, and this speckle pattern SP changes over time. This change over time appears as the decay of the autocorrelation function; if the decay is fast, the scattering particles h are moving fast, and if the decay is slow, the scattering particles h are moving slowly. At the same time, the scattering particles h are absorbed and scattered by hemoglobin, water, fat, etc. inside the scattering medium S. The degree of absorption and scattering is respectively reflected in the shape of the time waveform. After that, the first optical comb L1 is multiplexed with the second optical comb in the multiplexing unit 5, and these first and second optical combs L1 and L2 are detected by the optical detection unit 6. That is, in this embodiment, the optical detection unit 6 detects the first optical comb L1 that has propagated inside the scattering medium S and the second optical comb L2 that has not propagated inside the scattering medium S.

[0043] Next, an example of a scattering medium measuring method carried out by the scattering medium measuring device 100 will be described with reference to the flowchart of FIG.

[0044] First, the control unit 9 controls the optical comb output unit 10 to output the first optical comb L1 and the second optical comb L2 from the optical comb output unit 10 and input them to the optical amplifier unit 2. The acousto-optic modulators 21 and 22 adjust the intensities of the first optical comb L1 and the second optical comb L2, and the fiber amplifiers 23 and 24 broaden the spectra of the first optical comb L1 and the second optical comb L2. Then, the wavelength converter 3 converts the wavelengths of the first optical comb L1 and the second optical comb L2 using soliton self-frequency shift (step S1). In step S1, the control unit 9 controls the acousto-optic modulators 21 and 22 to adjust the intensities of the first optical comb L1 and the second optical comb L2 so that the wavelength converter 3 converts the wavelengths of the first optical comb L1 and the second optical comb L2 to predetermined wavelengths.

[0045] The predetermined wavelength is, for example, a wavelength in the range of 1600 to 2000 nm, and is 1600 nm here. For example, if the substance to be measured is blood flow, the predetermined wavelength may be 600 to 1600 nm or 700 to 1100 nm, or a single wavelength of 1064 nm here. For example, if the substance to be measured is hemoglobin, the predetermined wavelength may be 600 to 1600 nm or 700 to 1100 nm, or multiple wavelengths near 760 nm, 805 nm, 830 nm, 915 nm, 940 nm, and 980 nm here. In step S1, the wavelength selector 4 transmits the first optical comb L1 and the second optical comb L2 with wavelengths in the predetermined band and extracts the first optical comb L1 and the second optical comb L2 with wavelengths in the predetermined band.

[0046] The first optical comb L1 that has passed through the wavelength selection unit 4 is made incident on the scattering medium S, and the first optical comb L1 is propagated inside the scattering medium S (step S2). The first optical comb L1 and the second optical comb L2 that has passed through the wavelength selection unit 4 but has not propagated through the scattering medium S are multiplexed by the multiplexing unit 5. The multiplexed first and second optical combs L1 and L2 are detected by the optical detection unit 6, and a detection light F having an interference waveform shown in FIG. 6(a), for example, is generated.i (t) is acquired (step S3). i is wavelength and t is time. tr in the figure is the timing at which the first and second optical combs L1 and L2 enter the light detection unit 6, and may be obtained using a trigger signal acquired by a trigger signal acquisition unit (not shown). The analysis unit 8 acquires the acquired detected light F i Based on (t), a time waveform and an autocorrelation function are calculated (step S4). A specific example of step S4 will be described below.

[0047] In step S4, the detected light F i Since (t) contains two pieces of information, the information obtained can be selected by adjusting the time scale to be analyzed. The envelope is extracted, and the data range to be analyzed is selected by filtering the time after the light is incident. The detected light F after the time filtering is i,j (t) is obtained (see, for example, Figure 6(b)). This allows information with adjusted depth sensitivity to be obtained. j indicates that the depth sensitivity can be adjusted. In the figure, the waveform within the dashed-dotted line frame corresponds to j=0, the waveform within the broken-dashed line frame corresponds to j=1, and the waveform within the two-dot-dash line frame corresponds to j=2.

[0048] According to the following formula (1), the time waveform (probability distribution of light intensity) H i,j (u) is calculated. In order to improve the signal-to-noise ratio, the detected light F is calculated based on tr. i (t) or the detected light F after time filtering i,j (t) integrated f i,j (t) can be used. u can be calculated by u=t / (frep / Δfrep). The autocorrelation function g1 i,j (s) is calculated by the autocorrelation function g1 according to the following equation (2): i,j (s) is calculated. γ is g2 in the vicinity of s = 10 ns to 10 μs. i,j (s), where s is the lag time and <> is the average. H i (u)=f i (t),H i,j (u)=f i,j (t) (1) g2 i,j (s)= <fi,j (t)f i,j (t+s)> / <f i,j (t)> 2 , g2 i,j (s)=1+γ×g1 i,j (s) (2)

[0049] Next, the analysis unit 8 calculates the time waveform H i,j (u) and autocorrelation function g1 i,j Based on (s), the internal information of the scattering medium S is calculated (step S5). A specific example of step S5 will be described below.

[0050] In step S5, the absorption coefficient μa i,j [cm -1 ], scattering coefficient μs i,j [cm -1 ] and the reduced scattering coefficient μsp i,j [cm -1 For example, the light diffusion equation or the light transport equation and the time waveform H i,j (u) and the absorption coefficient μa i,j , scattering coefficient μs i,j and the reduced scattering coefficient μsp i,j In this case, a method using a lookup table obtained in advance by numerical calculation of each equation, a method using analytical solutions or approximate solutions of each equation, a method using deep learning, or the like may be used. As an example, the absorption coefficient μa i,j , scattering coefficient μs i,j and the reduced scattering coefficient μsp i,j The value of may be found.

number

[0051] The symbol with an × inside a circle indicates convolution, y is the analytical solution of each equation, an approximate solution, or a solution created using a lookup table, n is the order, τ is a hyperparameter, and R is the regularization term. i,j(u) is the time waveform for calibration. Time waveform for calibration Hc i,j (u) can be obtained by previously carrying out the above-mentioned steps S1 to S4 on a scattering medium for calibration.

[0052] In step S5, a calculation may be performed to estimate the second internal information B. For example, the second internal information B may be calculated by using a diffusion correlation equation or a light transport diffusion equation and an autocorrelation function g1 i,j (s) is used to obtain an optimal solution for the second internal information B. At this time, a method using a lookup table obtained in advance by numerically calculating each equation, a method using analytical solutions or approximate solutions for each equation, a method using deep learning, or the like may be used. As an example, the value of the second internal information B that minimizes ψ in the following equation (4) may be found.

number

[0053] The second internal information B is the flow index B i,j [cm 2 / s]. Flow Index B i,j Specifically, the Brownian diffusion coefficient [cm] represents the speed or blood flow of red blood cells flowing through capillaries or arterial veins of various sizes. 2 / s] and is the mean square displacement. Flow index B i,j is ideally a value that is independent of wavelength. In reality, the flow index B i,j Since the values ​​of the scattering medium S vary depending on the wavelength, their average values, expected values, median values, variations, etc. may be used as representative values. When the scattering medium S is a human, the flow index is also called a blood flow index.

[0054] In step S5, the first internal information A is obtained by using the time waveform H i,j Feature value α of (u) i,j and calculate the autocorrelation function g1 as the second internal information B. i,j Feature value β of (s) i,j The feature amount α i,j and feature value β i,j An example of this is as follows:

[0055] (1) Time waveform H i,j (u) and autocorrelation function g1 i,j (s) itself. (2) Time waveform H i,j (u) and autocorrelation function g1 i,j The Mellin Laplace transform value M of (s) (see the following formula (5)). For example, the area (p=0, q=0) represents the amount of light transmitted through the scattering medium S, and reflects the concentration, composition ratio, and position of the substance to be measured.

number

[0056] However, p=0,0.1,…,100, q=0,0.1,…,100, t1,t2: Time waveform H i,j (u) 0 to 100 ns, autocorrelation function g1 i,j (s) is any time between 100ns and 10s.

[0057] (3) Time waveform H i,j (u) and autocorrelation function g1 i,j The Mellin Laplace transform value M of (s) (see equation (6) below). For example, the center of gravity (p=1, q=0) is the mean optical path length, which reflects the concentration, composition ratio, and position of the substance to be measured.

number

[0058] However, p=0,0.1,…,100, q=0,0.1,…,100, t1,t2,t3,t4: Time waveform H i,j (u) 0 to 100 ns, autocorrelation function g1 i,j (s) is any time between 10ns and 100s

[0059] (4) Time waveform H i,j (u) and autocorrelation function g1 i,jRise time, fall time, mean value, median value, standard deviation, interquartile range, x% value (= (maximum value - minimum value) / 100 x x + minimum value, minimum value when x = 0, maximum value when X = 100) of (s), and the width of x% value if there are multiple values ​​(time waveform H i,j (u) time width, 50% value full width at half maximum), decay constant

[0060] (5) Absorption coefficient μa i,j , scattering coefficient μs i,j , reduced scattering coefficient μsp i,j and flow index B i,j A series of coefficients that approximate the change in depth and / or wavelength of μsp using an n-th order equation (n=0, 1, . . . , 10) or a curve (spline, Bayesian, etc.). i,j m0 and m1 are the wavelength changes when approximated by m0 × (wavelength / wavelength standard)^m1. They depend on the size and number density of the scattering center, and the wavelength standard related to the state or fluctuation of the measured material is an arbitrary value. In addition, the absorption coefficient μa i,j The wavelength change indicates the absorption spectrum, and the depth change indicates the spatial distribution of the absorbing substance. It is possible to estimate the constituent ratio of the measured substance and indicators such as blood sugar, blood pressure, and heart rate. The scattering coefficient μs i,j The wavelength change indicates the scattering characteristics of the object being measured, and the depth change indicates the spatial distribution of the scattering material. i,j The wavelength change indicates the wavelength fluctuation of the object being measured, and the depth change indicates the spatial distribution of the flow. (6) A value obtained by combining at least any one of the above (1) to (5) and performing arithmetic operations. This value can be a parameter that specifically indicates a certain disease or condition.

[0061] In step S5, after obtaining the first internal information A, if the number of wavelengths is sufficient to obtain the third internal information C, the third internal information C may be estimated using at least one of the following (i) and (ii). (i) The optimal solution of the simultaneous equations LXc=μa-Z is found to obtain the third internal information C and Xc. The values ​​of each term are expressed in the following equation (7).

number

[0062] L: Molar absorption coefficient [cm -1 μM] or extinction coefficient [cm -1 ], Z: offset (used to subtract absorption due to another element), K: number of third internal information C, M: absorption coefficient μa i,j The number of wavelengths. (ii) Absorption coefficient μa for each wavelength i,j An absorption spectrum arranged by wavelength, or its first derivative absorption spectrum.

[0063] The third internal information C is the concentration [μmol / L], content [%], density [mg / cm 3 The third internal information C includes information on at least one of the following: oxygenated hemoglobin, deoxygenated hemoglobin, fat, water, methemoglobin, fetal hemoglobin, carboxyhemoglobin, carbaminohemoglobin, myoglobin, collagen, melanin, bilirubin, lactic acid, oxygenated cytochrome oxidase, and reduced cytochrome. Furthermore, based on the third internal information C, total hemoglobin, tissue oxygen saturation, total cytochrome oxidase, oxygenation ratio of cytochrome oxidase, venous blood oxygen saturation, bound water and free water separated from the water ratio using spectroscopic information, blood volume, relative cerebral perfusion pressure, and relative intracranial pressure can also be calculated.

[0064] In step S5, after the second and third internal information B and C are obtained, a calculation may be performed to estimate the fourth internal information D. The fourth internal information D includes, for example, information on oxygen consumption, oxygen intake and its change, particle size [μm], and viscosity coefficient [Pa×s]. The fourth internal information D includes information on quantities obtained by arithmetic operations combining a plurality of the first to third internal information A to C. In step S5, the fourth internal information D may be estimated by the following calculation. Oxygen consumption = Flow index B i,j × Total hemoglobin concentration × 1.34 × (arterial blood oxygen saturation – venous blood oxygen saturation) However, arterial blood oxygen saturation can be substituted with pulse oximeter measurements. Venous blood oxygen saturation can be calculated using the following formula: StO2 = (1 - fv)SaO2 + fv × SvO2 StO2: tissue oxygen saturation, SvO2: venous blood oxygen saturation, fv = 0.75 (0.4 to 0.8) assumed Oxygen intake = 1 - venous oxygen saturation / arterial oxygen saturation The particle size and viscosity coefficient are the flow index B i,j These include particle size and viscosity coefficients calculated by relating the above to the Einstein-Stokes relation. When calculating one of these, values ​​assuming the other are used. Arithmetic operations combining multiple pieces of internal information A, B, and C (1st to 3rd)

[0065] In step S5, after obtaining the fourth internal information D, a calculation may be performed to estimate the fifth internal information E. The fifth internal information E includes, for example, feature quantities calculated from the temporal changes, spatial changes, and other changes of the first to fourth internal information A to D. The temporal changes are, for example, changes before and after multiple events such as surgery or drug treatment, or changes over time. The temporal changes are, for example, changes over several seconds, several minutes, several hours, several days, several months, or several years. The temporal changes are, for example, pulse rate, heart rate, and respiratory rate obtained by interpreting pulsation data obtained by arranging the third internal information C in the order of milliseconds. The spatial changes are, for example, changes at a measurement position relative to a symmetrical position such as a normal area. The spatial changes are, for example, an image in which the results of the first to fifth internal information at multiple measurement positions are arranged in two dimensions. The spatial changes are, for example, a three-dimensional image obtained by image reconstruction. The other changes are, for example, changes between generations (relatives and others) and changes in other groups such as a normal group. In step S5, in order to obtain the fifth internal information E, a calculation for arranging in the time direction or the space direction and image reconstruction may be performed.

[0066] Next, the analysis unit 8 determines whether or not measurement in the desired spectral band has been completed (step S6). In step S6, for example, it is determined whether or not a predetermined number of detected lights have already been acquired across the desired spectral band. The desired spectral band is, for example, 600 nm to 1600 nm. If the answer is NO in step S6, the amount of wavelength shift is changed (for example, increased by 100 nm) with respect to the predetermined wavelength that is the target wavelength for wavelength conversion in step S1, and the process returns to step S1. If the answer is YES in step S6, it is determined that a wideband spectrum has been obtained and the process ends.

[0067] Next, the effects of the present disclosure will be described. Through extensive research, the present inventors have discovered that by varying the wavelengths of the first and second optical combs L1 and L2 to generate multiple spectra with different narrow bands, spectroscopic measurement over a wide measurement band is possible without degrading the S / N ratio or reducing measurement accuracy. The inventors have realized that applying such spectroscopic measurement to the measurement of a scattering medium S would enable the measurement to be performed with high accuracy, and have completed the scattering medium measurement device 100. That is, the scattering medium measurement device 100 uses the first and second optical combs L1 and L2 that have been wavelength-converted using soliton self-frequency shift, and as discovered above, it is possible to perform spectroscopic measurement of the scattering medium S over a wide measurement band without degrading the S / N ratio or reducing measurement accuracy. The scattering medium S can be measured with high accuracy using the first and second optical combs L1 and L2.

[0068] Furthermore, in dual comb spectroscopy measurement using the first optical comb L1 and the second optical comb L2, there is a trade-off between the measurement time (difference in repetition frequency) and the measurement band (Nyquist spectrum band). If the measurement time is shortened, the measurement band becomes narrower. Furthermore, if the measurement band is changed, multiple bandpass filters are required. If the measurement band is widened, stabilization control is also required to prevent degradation of the S / N ratio. In this regard, the scattering medium measuring device 100 can tune the wavelength while maintaining a narrow spectrum (bandwidth of up to 10 nm), thereby enabling high-speed and wide-band measurement of the scattering medium S.

[0069] In the scattering medium measuring device 100, the analyzing section 8 generates a time waveform H i,j (u) and autocorrelation function g1 i,j (s) and calculate the time waveform H i,j (u) and autocorrelation function g1 i,j Based on (s), the internal information of the scattering medium S is calculated. In this case, the internal information of the scattering medium S can be obtained by the analysis unit 8.

[0070] In the scattering medium measuring device 100, the internal information of the scattering medium S is obtained by the absorption coefficient μa i,j , scattering coefficient μs i,j and flow index B i,j In this case, the internal information of the scattering medium S includes the absorption coefficient μa i,j , scattering coefficient μs i,j and flow index B i,j In particular, in the scattering medium measuring device 100, the absorption coefficient μa i,j , scattering coefficient μs i,j and flow index B i,j It is possible to measure these simultaneously.

[0071] In the scattering medium measuring apparatus 100, the optical comb output section 10 is a dual comb laser light source. In this case, the first and second optical combs L1 and L2 can be generated using the dual comb laser light source.

[0072] In the scattering medium measuring device 100, the optical comb generator 1 includes an optical amplifier 2 that broadens the spectrum of the first and second optical combs L1, L2 that are output from the optical comb output unit 10 and before their wavelengths are converted by the wavelength converter 3. As a result of extensive research, the present inventors have found that multi-soliton generation can be suppressed by broadening the spectrum of the first and second optical combs L1, L2 before wavelength conversion using soliton self-frequency shift is performed. Therefore, the scattering medium measuring device 100 makes it possible to suppress multi-soliton generation.

[0073] In the scattering medium measuring apparatus 100, the optical amplifier 2 broadens the spectrum of the first and second optical combs L1 and L2 by similariton amplification. In this case, the optical amplifier 2 can suppress stretching of the first and second optical combs L1 and L2, and can effectively realize wavelength conversion using soliton self-frequency shift.

[0074] In the scattering medium measuring apparatus 100, the optical amplifier 2 controls the intensities of the first and second optical combs L1 and L2. In this case, by controlling the intensities of the first and second optical combs L1 and L2, it becomes possible to tune the wavelengths of the first and second optical combs L1 and L2.

[0075] The scattering medium S is a living organism. Unlike inorganic materials such as semiconductors, the state of a living organism is easily changed, and therefore high-speed measurement (measurement at a speed at which the state does not change) is desired. In this regard, the scattering medium measuring device 100 is capable of high-speed measurement using the first and second optical combs L1 and L2, and therefore can measure the living organism before its state changes, which is particularly effective when the living organism is the measurement target.

[0076] In living organisms, the longer the wavelengths of the first and second optical combs L1 and L2, the higher the damage threshold (the upper threshold of the intensity of the first and second optical combs L1 and L2). For example, the following thresholds are preferable for the intensity (average power) of the first and second optical combs L1 and L2 depending on the wavelength to prevent damage and alteration of the living organism. Irradiation area is 1mm 2 in the case of, Average power <3mW, wavelength λ=800nm Average power <10mW, wavelength λ=1064nm

[0077] In this regard, the optical comb generator 1 increases the intensity of the first and second optical combs L1 and L2, thereby shifting the wavelengths of the first and second optical combs L1 and L2, which are converted using the soliton self-frequency shift in the wavelength converter 3, to longer wavelengths. Therefore, when the scattering medium S is a living body, the optical comb generator 1 is compatible with this tendency, and the scattering medium measurement device 100 is particularly effective when a living body is used as the measurement target. In other words, this embodiment, in which the wavelength shifts to longer wavelengths as the intensity increases, has the advantage of being compatible with living bodies, which have a higher damage threshold as the wavelength increases.

[0078] In the scattering medium measuring device 100, the control unit 9 can execute the following steps: a first process in which the wavelength converter 3 converts the wavelengths of the first and second optical combs L1, L2 to a predetermined wavelength; a second process in which the analyzer 8 performs an analysis based on the detection result of the light detector 6 when the wavelengths of the first and second optical combs L1, L2 have been converted to the predetermined wavelengths by the first process; and a third process in which the first and second processes are repeatedly executed by switching the predetermined wavelength among a plurality of different wavelengths. In this case, the process of generating a plurality of different narrowband spectra by varying the wavelengths of the first and second optical combs L1, L2 can be realized by the control of the control unit 9.

[0079] The scattering medium measurement method includes step S1 of outputting first and second optical combs L1, L2 and converting the wavelengths of the output first and second optical combs L1, L2 by using soliton self-frequency shift, steps S2 and S3 of propagating the first optical comb L1, whose wavelength has been converted in step S1, inside the scattering medium S and detecting the first and second optical combs L1, L2, and steps S4 to S6 of performing analysis related to measurement of the scattering medium S based on the detection result detected in step S3. The scattering medium measurement method also makes it possible to accurately measure the scattering medium S using the first and second optical combs L1, L2. In the above, step S1 constitutes a first step, steps S2 and S3 constitute a second step, and steps S4 to S6 constitute a third step.

[0080] The scattering medium measuring device 100 can be applied to the following fields, for example. Disease: Early detection of various diseases, prognosis prediction, evaluation of drug and treatment effectiveness, prevention, condition assessment, condition prediction, Brain function elucidation: cognitive function elucidation, relationship with human emotions, Suspension: Determine if it is in the right condition Other: Detecting objects inside or behind scattering media, collision avoidance, situational awareness in security fields,

[0081] Furthermore, in dual-comb spectroscopy using the first optical comb L1 and the second optical comb L2, there is a trade-off between the measurement time (difference in repetition frequency) and the measurement bandwidth (Nyquist spectrum bandwidth). If the measurement time is shortened, the measurement bandwidth becomes narrower. Furthermore, if the measurement bandwidth is changed, multiple bandpass filters are required. If the measurement bandwidth is widened, stabilization control is also required to prevent degradation of the S / N ratio. In this regard, in this embodiment, the wavelength can be tuned while maintaining a narrow spectrum (bandwidth of up to 10 nm), thereby realizing high-speed, wide-band dual-comb spectroscopy.

[0082] As described above, one aspect of the present disclosure is not limited to the above embodiment.

[0083] In the above embodiment, the scattering medium S is arranged on the optical path of the first optical comb L1 before being combined in the multiplexing unit 5, but the scattering medium S may also be arranged on the optical paths of the first and second optical combs L1, L2 after being combined in the multiplexing unit 5, or the scattering medium S may be arranged on the optical path of the second optical comb L2 before being combined in the multiplexing unit 5. In other words, the optical detection unit 6 may detect the first and second optical combs L1, L2 generated by the optical comb generation unit 1, at least one of which has propagated inside the scattering medium S.

[0084] In the above embodiment, as shown in FIG. 7A, a nonlinear optical crystal (second harmonic crystal) 340 may be disposed downstream of the wavelength filter 41. The nonlinear optical crystal 340 includes BBO (Beta Barium Borate), PPLN (Periodically Poled Lithium Niobate), and KTP (Potassium Titanyl Phosphate). In this case, for example, the first optical comb L1 having a wavelength of 1600 to 2000 nm is further transmitted through the nonlinear optical crystal 340 and wavelength-converted (optical parametrically generated) to the first optical comb L1 having a wavelength of 800 to 1000 nm. This allows the wavelength band of the first optical comb L1 to be controlled toward shorter wavelengths. Note that this wavelength band control also applies to the second optical comb L2.

[0085] As shown in FIG. 7(b), the above embodiment may include a wavelength filter 341, which is a short-pass filter, to utilize anti-Stokes instead of the wavelength filter 41 (see FIG. 1). In this case, the wavelength filter 341 transmits the first optical comb L1, for example, with a wavelength of 800 to 1000 nm. This allows the wavelength band of the first optical comb L1 to be controlled toward the shorter wavelength side. Note that this wavelength band control also applies to the second optical comb L2.

[0086] In the above embodiment, as shown in FIG. 7(c), a nonlinear optical crystal 350, such as a GaSe crystal, may be disposed downstream of the wavelength filter 341. In this case, for example, the first optical comb L1 having a wavelength of 800 nm is further transmitted through the nonlinear optical crystal 350 and wavelength-converted (optical parametric generation) to the first optical comb L1 having a wavelength of 10 μm. This allows the wavelength band of the first optical comb L1 to be controlled toward the higher wavelength side, enabling, for example, mid-infrared light to be generated. Note that this wavelength band control is similarly applied to the second optical comb L2.

[0087] In the above embodiment, the nonlinear polarization rotator 15 (see FIG. 2) is used as the mode locking technique in the optical comb output unit 10, but this is not limited to this. For example, a nonreciprocal phase shifter, a nonlinear loop mirror, or a saturable absorber that absorbs only continuous light and has high transmittance for pulsed light may be used as the mode locking technique. Preferably, a nonreciprocal phase shifter or a saturable absorber using a polarization-maintaining fiber that is robust against external disturbances may be used as the mode locking technique. The gain medium of the laser light in the optical comb output unit 10 is not particularly limited and may be, for example, any of erbium, ytterbium, thulium, and niodymium.

[0088] In the above embodiment, a bidirectional oscillation type dual comb laser light source is used as the optical comb output unit 10. However, the optical comb output unit 10 is not particularly limited in configuration or type as long as it can output the first optical comb L1 and the second optical comb L2. For example, the optical comb output unit 10 may be a dual-comb laser light source synchronized with two lasers. In this case, noise can be suppressed. For example, the technology described in the following document 1 may be used as a dual-comb laser light source synchronized with two lasers. Reference 1: Sho Okubo, et al, “Ultra-broadband dual-comb spectroscopy across 1.0-1.9μm”, Applied Physics Express 8, 082402 (2015), publishedonline July 14, 2015, The Japan Society of AppliedPhysics, pp.082402-1-82402-05

[0089] Furthermore, for example, the optical comb output unit 10 may be a dual comb laser light source of a shared mechanical type. As a dual comb laser light source of a shared mechanical type, for example, the technology described in the following document 2 may be adopted. Reference 2: TAKUMI YUMOTO, et al, “All-polarization-maintaining dual-comb fiber laser with mechanically shared cavity configuration and micro-optic component”, OpticsContinuum, Vol. 2, No. 8 / 15, Aug2023, pp.1867-1874

[0090] Furthermore, for example, the optical comb output unit may be a multi-polarization type dual comb laser light source. As a multi-polarization type dual comb laser light source, for example, the technology described in the following document 3 may be adopted. Document 3: YOSHIAKI NAKAJIMA, etal, “All-polarization-maintaining, polarization-multiplexed, dual-comb fiber laser with a nonlinear amplifying loop mirror”, OPTICS EXPRESS, Vol.27, No. 10, 13 May 2019, pp.14648-14656

[0091] Furthermore, for example, the optical comb output unit may be a microcomb-type dual comb laser light source. As a microcomb-type dual comb laser light source, for example, the technology described in the following document 4 may be adopted. Document 4: Nikita Yu. Dmitriev, et al, “A hybrid integrated dual-microcomb source”, physics.optics, arXiv:2112.07398v1, 14 December, 2021, pp.1-5

[0092] In the above embodiment, fiber amplifiers using double-clad normal dispersion fiber are used as the fiber amplifiers 23 and 24. However, fiber amplifiers using single-clad normal dispersion fiber (e.g., erbium-doped) may be used instead. Even in this case, it is possible to broaden the spectrum of the first optical comb L1 and the second optical comb L2.

[0093] In the above embodiment, the optical amplifier 2 may use an electro-optic modulator instead of the acousto-optic modulators 21 and 22, or may modulate the intensity through current modulation of the pump laser. In the above embodiment, the wavelength converter 3 may use anti-Stokes to change the wavelengths of the first optical comb L1 and the second optical comb L2.

[0094] The respective components in the above-described embodiment and modified examples are not limited to the materials and shapes described above, and various materials and shapes can be applied. Furthermore, the respective components in the above-described embodiment and modified examples can be arbitrarily applied to the respective components in other embodiments or modified examples. [Explanation of symbols]

[0095] 1...optical comb generation unit, 2...optical amplification unit, 3...wavelength conversion unit, 6...optical detection unit, 8...analysis unit, 9...control unit, 10...optical comb output unit, 100...scattering absorber measurement device, L1...first optical comb, L2...second optical comb, S...scattering absorber.

Claims

1. A scattering medium measuring device for measuring a scattering medium, an optical comb generator including: an optical comb output unit that outputs first and second optical combs having a plurality of frequency modes arranged in a comb shape on a frequency axis; and a wavelength converter that converts the wavelengths of the first and second optical combs output from the optical comb output unit by utilizing soliton self-frequency shift; an optical detector that detects the first and second optical combs generated by the optical comb generator, at least one of which has propagated through the scattering medium; an analysis section that performs analysis relating to measurement of the scattering medium based on the detection result of the light detection section.

2. The analysis unit calculating a time waveform and an autocorrelation function based on the detection result of the light detection unit; 2. The scattering medium measuring device according to claim 1, wherein internal information of said scattering medium is calculated based on said calculated time waveform and said autocorrelation function.

3. The scattering medium measuring device according to claim 2 , wherein the internal information of the scattering medium includes an absorption coefficient, a scattering coefficient, and a flow index.

4. 2. The scattering medium measuring device according to claim 1, wherein the optical comb output unit is a dual comb laser light source that outputs the first optical comb and the second optical comb having a time interval different from that of the first optical comb.

5. 2. The scattering medium measuring device according to claim 1, wherein the optical comb generating unit includes an optical amplifier that broadens the spectrum of the first and second optical combs output from the optical comb output unit and before their wavelengths are converted by the wavelength converting unit.

6. 6. The scattering medium measuring device according to claim 5, wherein the optical amplifier broadens the spectrum of the first and second optical combs by similariton amplification.

7. 7. The scattering medium measuring device according to claim 5, wherein the optical amplifier controls the intensities of the first and second optical combs.

8. 3. The scattering medium measuring apparatus according to claim 1, wherein the scattering medium is a living body.

9. 9. The scattering medium measuring device according to claim 8, wherein the optical comb generating unit increases the intensities of the first and second optical combs, thereby shifting the wavelengths of the first and second optical combs, which are converted by utilizing soliton self-frequency shift in the wavelength converting unit, to the longer wavelength side.

10. A control unit is provided, The control unit a first process for converting the wavelengths of the first and second optical combs to predetermined wavelengths in the wavelength conversion unit; a second process of causing the analyzer to perform analysis based on a detection result of the optical detector when the wavelengths of the first and second optical combs are converted to the predetermined wavelength by the first process; 3. The scattering medium measuring device according to claim 1, further comprising: a third process for repeatedly performing the first process and the second process by switching the predetermined wavelength among a plurality of different wavelengths.

11. A scattering medium measurement method for measuring a scattering medium, comprising: a first step of outputting first and second optical combs having a plurality of frequency modes arranged in a comb-like pattern on a frequency axis and converting the wavelengths of the output first and second optical combs by utilizing soliton self-frequency shift; a second step of propagating at least one of the first and second optical combs whose wavelengths have been converted in the first step inside the scattering medium and detecting the first and second optical combs; an analysis unit that performs an analysis relating to the measurement of the scattering medium based on the detection result detected in the second step.

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