JP6219867B2 - Component concentration measuring device - Google Patents

Description

  The present invention relates to a technique for measuring a component concentration using dielectric spectroscopy.

  As aging progresses, the response to adult diseases has become a major issue. Tests such as blood glucose levels are a heavy burden on patients because they need to collect blood. Therefore, a non-invasive component concentration measuring apparatus that does not collect blood has attracted attention.

  An apparatus using dielectric spectroscopy has been proposed as a noninvasive component concentration measuring apparatus. Dielectric spectroscopy irradiates the skin with electromagnetic waves, absorbs the electromagnetic waves according to the interaction of blood components to be measured, for example, glucose molecules and water, and observes the amplitude and phase with respect to the frequency of the electromagnetic waves. The dielectric relaxation spectrum is calculated from the amplitude and phase with respect to the frequency of the observed electromagnetic wave. In general, the complex dielectric constant is calculated by expressing as a linear combination of relaxation curves based on the Cole-Cole equation.

  As a conventional measurement method, there is a dielectric spectroscopic device using photoelectric conversion (photomixing) in a frequency band from microwave to millimeter wave or more (see Patent Document 1). The dielectric spectroscopic device of Patent Document 1 photoelectrically converts an optical signal in which two continuous light waves having different frequencies are combined to generate an electromagnetic wave, for example, a terahertz wave, irradiates the object to be measured with the generated terahertz wave, The configuration is such that the terahertz wave transmitted through the measurement object is received and the reference light synthesized by modulating the phase of one of the two continuous light waves is input to perform homodyne mixing. For example, a detector that performs homodyne mixing uses a photoconductive antenna, and the conductance between the antennas is modulated by the difference frequency between two continuous light waves included in the reference light by irradiation with the reference light. In the conventional dielectric spectroscopic device, when homodyne detection of electromagnetic waves, it is necessary that the two optical path length differences when the optical signal transmitted through the object to be measured and the reference light are mixed by the detector match. It is. Therefore, the propagation length of the terahertz wave propagating in space, the length of the file through which light propagates, and the like are adjusted.

JP 2013-32933 A

Andrew P. Gregory, and Robert N. Clarke, “A Review of RF and Microwave Techniques for Dielectric Measurements on Polar Liquids”, IEEE Transactions on Dielectrics and Electrical Insulation, August 2006, Vol. 13, No. 4, pp.727- 743 Jae-Young Kim, Ho-Jin Song, Katsuhiro Ajito, Makoto Yaita, and Naoya Kukutsu, “Continuous-Wave THz Homodyne Spectroscopy and Imaging System With Electro-Optical Phase Modulation for High Dynamic Range”, IEEE Transactions on terahertz science and technology, March 2013, Vol. 3, No. 2, pp.158-164

  However, if the refractive index of the fiber fluctuates due to environmental fluctuations such as temperature, and the difference between the two optical path lengths fluctuates, there is a problem that the amplitude and phase of the signal become unstable and measurement reproducibility and measurement accuracy cannot be obtained. .

  The present invention has been made in view of the above, and an object thereof is to ensure measurement reproducibility and measurement accuracy even when the refractive index of a fiber changes due to environmental fluctuations.

  The component concentration measuring apparatus according to the present invention includes a radiator that photoelectrically converts a first optical signal obtained by combining two continuous light waves having different frequencies to generate a first electromagnetic wave of a millimeter wave or a terahertz wave, An optical phase modulator that electrically modulates the phase of one of the two continuous light waves is combined with the continuous light wave that is phase-modulated by the optical phase modulator and the other continuous light wave that is not phase-modulated. A detector that receives the first electromagnetic wave that is irradiated with the waved second optical signal and that is transmitted or reflected by the object to be measured, and that performs homodyne mixing of the first electromagnetic wave and the second optical signal. The delay length of the fiber through which the first optical signal and the second optical signal pass is the same, and is equal to the spatial propagation length of the first electromagnetic wave through the fiber through which the second optical signal passes Characterized by the insertion of a spatial delay line .

  The component concentration measuring apparatus includes an interval adjusting unit that adjusts an interval between the spatial delay lines so that a phase detected by the detector is constant.

  In the component concentration measuring apparatus, a parabolic mirror that reflects the first electromagnetic wave is provided between the radiator and the detector, and the interval adjusting unit adjusts the interval of the parabolic mirror. Features.

  According to the present invention, measurement reproducibility and measurement accuracy can be ensured even when the refractive index of the fiber changes due to environmental fluctuations.

It is a block diagram which shows the structure of the component density | concentration measuring apparatus in this Embodiment. It is a block diagram which shows the structure of another component density | concentration measuring apparatus in this Embodiment. It is a figure which shows the measurement system of a dielectric spectroscopy sensor. It is a figure which shows the measurement system of another dielectric spectroscopy sensor.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings.

  FIG. 1 is a block diagram showing a configuration of a component concentration measuring apparatus according to the present embodiment.

  The component concentration measuring apparatus shown in FIG. 1 includes continuous wave light sources 11A and 11B, splitters 12A and 12B, couplers 13A and 13B, a phase modulator 14, an oscillator 15, a radiator 16, a detector 17, a lock-in amplifier 18, and a monitor 19. And a delay line 20.

  The continuous wave light sources 11A and 11B output continuous light waves having different frequencies. In the following description, the continuous light wave output from the continuous wave light source 11A is referred to as a first optical signal, and the continuous light wave output from the continuous wave light source 11B is referred to as a second optical signal.

  The splitter 12A demultiplexes the first optical signal into two, and the splitter 12B demultiplexes the second optical signal into two.

  The coupler 13A combines the first optical signal demultiplexed by the splitter 12A and the second optical signal demultiplexed by the splitter 12B. The optical signal combined by the coupler 13A is input to the radiator 16 through the fiber.

  The phase modulator 14 is a phase modulator using an electro-optic crystal that can be electrically phase-modulated by a control signal, and is disposed between the splitter 12B and the coupler 13B. The control signal of the single frequency f from the oscillator 15 is applied to the phase modulator 14 to perform serodyne phase modulation, and a frequency shift equivalent to the modulation frequency f is generated in the second optical signal demultiplexed by the splitter 12B. .

  The coupler 13B combines the first optical signal demultiplexed by the splitter 12A and the second optical signal phase-modulated by the phase modulator 14. The reference light combined by the coupler 13B is input to the detector 17 through the delay line 20.

  The radiator 16 photoelectrically converts the optical signal combined by the coupler 13A, and generates an electromagnetic wave (millimeter wave or terahertz wave) having a frequency matching the frequency difference between the first optical signal and the second optical signal. As the radiator 16, for example, a single traveling carrier photodiode (UTC-PD) can be used.

  The detector 17 photoelectrically converts the reference light combined by the coupler 13B to generate an electromagnetic wave, receives the electromagnetic wave radiated from the radiator 16 and transmitted through the sample 100, and performs homodyne mixing to generate an electric frequency f. Output a signal. The detector 17 can be realized by mounting a THz mixer composed of an SBD (Schottky barrier diode) with an antenna, a photomixer composed of an UTC-PD with an antenna, and an optical fiber in the same package. . The detector 17 may be a photoconductive antenna (PCA: Photo-Conductive Antenna). In the photoconductive antenna, the conductance between the antennas is modulated by the difference frequency between two continuous light waves included in the reference light by irradiation of the reference light.

  The lock-in amplifier 18 detects the amplitude and phase by synchronously detecting the electrical signal output from the detector 17, and the monitor 19 processes the amplitude and phase detected by the lock-in amplifier 18.

  In the terahertz wave band, the complex dielectric constant is measured from the transmitted signal by irradiating the sample 100 as a measurement target with a terahertz wave by a free space method using a pseudo optical system using parabolic mirrors 31A and 31B. When the parabolic mirrors 31A and 31B are used, since the multiple reflection in the lens does not occur as compared with the case where the lens is used, the measurement value is stabilized.

  In the conventional dielectric spectroscopic apparatus, when homodyne detection of electromagnetic waves, the length of the fiber through which light propagates is adjusted in advance so that the two optical path length differences at the time of mixing at the detector coincide. In the present embodiment, the fiber from the coupler 13A to the radiator 16 and the fiber from the coupler 13B to the detector 17 have the same delay length, and further, the detection from the radiator 16 is performed between the coupler 13B and the detector 17. A delay line 20 having a length (delay length) equivalent to the spatial propagation length of the terahertz wave emitted to the device 17 is provided. The delay line 20 can be realized with low loss by connecting a lens collimator to the fiber end, making two lenses face each other, and propagating parallel light.

  Here, the effect of the delay line 20 will be described.

The refractive index temperature coefficient dns / dT of the fiber is 6.6 × 10 ⁻⁶ / ° C., and the refractive index temperature coefficient dna / dT of air is −1.4 × 10 ⁻⁷ / ° C. The lengths of the fibers from the coupler 13A to the radiator 16 and from the coupler 13B to the detector 17 are L ₁ and L ₂ . The space propagation length of the terahertz wave and L _3. When the two optical path length differences are combined as the homodyne detection conditions, the respective lengths are as follows.

n _s L ₁ + L ₃ = n _s L ₂
Here, _ns is the refractive index of the fiber core 1.4. The refractive index of air is 1.

  If the temperature change is ΔT, the delay difference ΔL can be expressed by the following equation.

ΔL = (L ₁ −L ₂ ) (dns / dT) ΔT + L ₃ (dna / dT) ΔT

  The delay difference Δτ is as follows.

Δτ = 2πΔL / λ
Here, λ is the wavelength of the terahertz wave. For example, when L1-L2 = 20 cm and L3 = 28 cm and a change of ΔT = 1 ° C. occurs, the wavelength λ of the terahertz wave is λ = 0.3 mm at 1 THz, and therefore the delay difference Δτ = 0. A phase signal variation associated with a temperature of 03 rad = 1.8 degrees occurs.

In this embodiment, the length of the delay line 20 as L _4, together two optical path length difference, and the following respective lengths.

n _s L ₁ + L ₃ = n _s L ₂ + L ₄

That is, by setting L ₁ ≈L ₂ and L ₃ ≈L ₄ , ΔL≈0 can be obtained, and Δτ≈0 can be obtained, so that the fluctuation of the phase signal can be reduced with respect to the temperature fluctuation. Also, when there is a change in the refractive index of air due to humidity, the change can be canceled in the same manner.

  Note that the delay line 20 may be disposed between the coupler 13A and the radiator 16 so as to satisfy the above formula.

  FIG. 2 is a block diagram showing a configuration of another component concentration measuring apparatus in the present embodiment.

  The component concentration measuring apparatus shown in FIG. 2 is provided with a machine moving stage 21 and a controller 22 for adjusting the length of the delay line 20 in addition to the component concentration measuring apparatus of FIG.

  The controller 22 changes the length of the delay line 20 by controlling the machine moving stage 21 so that the phase becomes constant while monitoring the phase signal. Thereby, the minute change by the temperature distribution difference of a fiber can be reduced.

  2 includes two more parabolic mirrors 31A to 31D than the component concentration measuring apparatus of FIG. The terahertz wave radiated from the radiator at a predetermined angle is converted into a parallel beam by the parabolic mirror 31A, and the terahertz wave is parallel between the parabolic mirrors 31A and 31B and the parabolic mirrors 31C and 31D. The distance may be adjusted so that the phase becomes constant. Specifically, the parabolic mirrors 31B and 31C are fixed to the machine moving stage 21, and the controller 22 monitors the phase signal and moves the parabolic mirrors 31B and 31C so that the phase is constant. Adjust the spatial propagation length of terahertz waves. Phase control can be realized with low loss by adjusting the propagation length in the propagation section that becomes a parallel beam. The spatial propagation length of the terahertz wave and the length of the delay line 20 may be adjusted simultaneously.

  Further, a temperature sensor may be connected to the controller 22 to control the machine moving stage 21 based on the measured temperature. The configuration shown in FIG. 2 for monitoring the phase signal is feedback control, whereas the configuration controlled by temperature is feedforward control, so that the delay line 20 can be controlled at high speed.

  Next, a measurement system of a dielectric spectroscopic sensor using a lens will be described.

  FIG. 3 is a diagram showing a measurement system of the dielectric spectroscopic sensor of the present embodiment. In the example of FIG. 3, a transmission type is arranged in the measurement system of the dielectric spectroscopic sensor, and the amplitude and phase of a transmission signal transmitted through a liquid such as an aqueous solution or oil are measured. The terahertz wave radiated from the radiator 16 passes through the lens 51 and enters the sample cell of the dielectric constant measurement cell 53 held by the fixing jig 54. The size of the sample cell is, for example, several millimeters × several millimeters or more as the beam size. The material of the window plate 52 for fixing the sample may be a high resistance Si, Z cut crystal, HDPE, TPX, Tsurupica, etc., and a material having a high transmittance is selected according to the measurement frequency. The terahertz wave that has passed through the sample cell passes through the lens 51 and is received by the detector 17. Note that the sample cell may have a flow cell configuration including an inlet and an outlet. Moreover, you may measure solid.

  FIG. 4 is a diagram showing a measurement system of another dielectric spectroscopic sensor of the present embodiment. In the example of FIG. 4, a sample cell is disposed on the ATR prism 55 made of silicon, and the amplitude and phase of the reflected signal reflected by the sample cell are measured. The terahertz wave radiated from the radiator 16 passes through the lens 51 and the ATR prism 55 and is reflected by the sample cell of the dielectric constant measurement cell 53 held by the fixing jig 54. The sample cell is sealed in the dielectric constant measurement cell 53 by the window plate 52. The terahertz wave reflected by the sample cell passes through the ATR prism 55 and the lens 51 and is received by the detector 17.

  As described above, according to the present embodiment, the fiber from the coupler 13A to the radiator 16 and the fiber from the coupler 13B to the detector 17 have the same delay length, and the gap between the coupler 13B and the detector 17 is set. In addition, by providing the delay line 20 having a length (delay length) equivalent to the spatial propagation length of the terahertz wave emitted from the radiator 16 to the detector 17, the refractive index variation of the optical path length can be made equivalent, and the environment It is possible to suppress phase change due to fluctuations and acquire data with high accuracy.

DESCRIPTION OF SYMBOLS 11A, 11B ... Continuous wave light source 12A, 12B ... Splitter 13A, 13B ... Coupler 14 ... Phase modulator 15 ... Oscillator 16 ... Radiator 17 ... Detector 18 ... Lock-in amplifier 19 ... Monitor 20 ... Delay line 21 ... Machine movement stage DESCRIPTION OF SYMBOLS 22 ... Controller 31A-31D ... Parabolic mirror 51 ... Lens 52 ... Window board 53 ... Cell for dielectric constant measurement 54 ... Fixing jig 55 ... ATR prism 100 ... Sample

Claims (3)

A radiator that photoelectrically converts a first optical signal in which two continuous light waves having different frequencies are combined to generate a first electromagnetic wave of a millimeter wave or a terahertz wave;
An optical phase modulator that electrically modulates the phase of one of the two continuous light waves;
The second optical signal obtained by combining the continuous light wave phase-modulated by the optical phase modulator and the other continuous light wave which is not phase-modulated is irradiated and transmitted or reflected by the object to be measured. A detector that receives the first electromagnetic wave and homodyne mixes the first electromagnetic wave and the second optical signal;
The delay length of the fiber through which the first optical signal and the second optical signal pass is made the same, and a spatial delay line equal to the spatial propagation length of the first electromagnetic wave is inserted into the fiber through which the second optical signal passes. A component concentration measuring apparatus characterized by that.   2. The component concentration measuring apparatus according to claim 1, further comprising interval adjusting means for adjusting an interval between the spatial delay lines so that a phase detected by the detector is constant.   The parabolic mirror that reflects the first electromagnetic wave is provided between the radiator and the detector, and the interval adjusting unit adjusts the interval of the parabolic mirror. Ingredient concentration measuring device.

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