JP6254543B2 - Dielectric spectrometer - Google Patents

Description

  The present invention relates to a technique for non-invasively measuring the concentration of a component to be measured, and more particularly to a technique 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. In the measurement of biological components, for example, the complex dielectric constant has a correlation with the amount of blood components such as glucose and cholesterol contained in blood, and is measured as an electrical signal (amplitude, phase) corresponding to the change. A calibration model is constructed by measuring the correlation between the complex dielectric constant change and the component concentration in advance, and the component concentration is calibrated from the measured change in the dielectric relaxation spectrum.

  As a conventional measurement method, there is a dielectric spectroscopic device using photoelectric conversion in a frequency band from microwave to millimeter wave or more (see Patent Document 1 and Non-Patent Document 1). The dielectric spectroscopic device disclosed in Patent Document 1 combines two continuous light waves output from two continuous wave light sources with different frequencies, photoelectrically converts the combined optical signal, and generates an electromagnetic wave (for example, terahertz wave). The target electromagnetic wave is irradiated to the object to be measured, the electromagnetic wave transmitted through the object to be measured is received, and the reference light synthesized by modulating one phase of two continuous light waves is input and homodyne mixing is performed. It is. The detector for homodyne mixing is realized by, for example, using a photoconductive antenna and modulating the conductance between the antennas with the reference light by the difference frequency between two continuous light waves included in 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.

  There is also known a dielectric spectroscopic device in which two continuous wave light sources are realized by one dual mode light source using an acoustooptic device that oscillates continuously (see Non-Patent Document 2).

JP 2013-32933 A

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 Steven Jones, JaeYoung Kim, Yoshiyuki Doi, Takashi Yamada, Nobutatsu Koshobu, and Hiroyoshi Togo, “Ultra-Wideband Tunable Dual-Mode Laser for Continuous Wave Teraherts Generation”, Journal of Lightwave Technology, 2014, Vol. 32, Issue 20, pp .3461-3467 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

  However, homodyne detection using two continuous wave light sources has a problem that the S / N ratio is limited because amplitude noise is generated during terahertz wave photomixing due to the phase noise of the two continuous wave light sources.

  Compared with the case where two continuous wave light sources are used, the dielectric spectroscopic device using the dual mode light source can reduce the phase noise and can simplify the system. However, in the dual mode light source, when the two frequencies are close to 1 THz or less, the third oscillation peak occurs at a frequency intermediate between the two frequencies, and in addition to the difference frequency beat signal by the combination of the two desired frequencies. However, there is a problem that a difference frequency beat signal is generated and a continuous spectrum cannot be obtained in the frequency band.

  The present invention has been made in view of the above, and an object of the present invention is to generate a difference frequency beat signal at a desired frequency and obtain a spectrum with a high S / N ratio.

A dielectric spectroscopic device according to the present invention includes a light source that outputs light of a predetermined frequency, a light source that outputs light of a predetermined frequency, a splitter that branches the light into two, and one of the light branched by the splitter. A phase modulation means for phase-modulating the light to shift the frequency, a coupler for multiplexing the light phase-modulated by the phase modulation means and the other light branched by the splitter, and the light multiplexed by the coupler Measuring means for generating an electromagnetic wave by photoelectric conversion, receiving the electromagnetic wave transmitted or reflected by the object to be measured, and measuring the amplitude of the electromagnetic wave, and the measuring means includes the combined light An amplitude modulator that modulates the amplitude at a predetermined frequency, a radiator that photoelectrically converts the amplitude-modulated light to generate an electromagnetic wave, and the electromagnetic wave that has been transmitted or reflected by the object to be measured is received, and envelope detection is performed. The electric power of the predetermined frequency And having a detector for outputting a signal.

  In the dielectric spectroscopic apparatus, the phase modulation means includes a plurality of phase modulators connected in multiple stages.

  The dielectric spectroscopic apparatus includes a second phase modulation means for phase-modulating the other of the lights branched by the splitter and shifting the frequency in the reverse direction.

  According to the present invention, a difference frequency beat signal can be generated at a desired frequency, and a spectrum with a high S / N ratio can be obtained.

It is a functional block diagram which shows the structure of the dielectric spectroscopy apparatus in 1st Embodiment. It is a figure for demonstrating control of the phase modulator of the said dielectric spectroscopy apparatus. It is a functional block diagram which shows the structure of the dielectric spectroscopy apparatus in 2nd Embodiment. It is a functional block diagram which shows the structure of another dielectric spectroscopy apparatus in 2nd Embodiment. It is a functional block diagram which shows the structure of the dielectric spectroscopy apparatus in 3rd Embodiment. It is a figure which shows the measurement system of the dielectric spectroscopy sensor using a lens. It is a figure which shows the measurement system of another dielectric spectroscopy sensor using a lens.

[First Embodiment]
FIG. 1 is a functional block diagram showing the configuration of the dielectric spectroscopic apparatus according to the first embodiment.

  The dielectric spectroscopic device shown in FIG. 1 includes a laser 11, a splitter 12, phase modulators 13A and 13B, an oscillator 14, a coupler 15, a radiator 16, a detector 17, a lock-in amplifier 18, and a monitor 19.

  The laser 11 is a continuous wave light source that generates a continuous light wave having a predetermined frequency F1.

  The splitter 12 has a function of branching the optical power of input light into two at a predetermined ratio. For example, the center frequency of the operating band is 193.125 THz, and the optical power ratio is 50:50.

  One light branched by the splitter 12 is phase-modulated by the phase modulators 13A and 13B using the electro-optic effect. A sawtooth waveform signal having a single frequency w (for example, 1 GHz) from the oscillator 14 is applied to the phase modulators 13A and 13B to perform serodyne phase modulation, and a frequency shift equivalent to the modulation frequency w is generated in the light. , Outputs light of frequency F2 (= F1 + 2w). For the phase modulators 13A and 13B, an electro-optic crystal that can be electrically phase-modulated by a control signal is used. The control voltage of the phase modulators 13A and 13B can be expressed as Vm (t) = N2Vπwt by the product of an integer N and 2Vπ (Vπ is a control voltage whose phase changes by π).

  When there is one phase modulator, a frequency transition 2N times the frequency w of the control voltage occurs, and the frequency of the signal detected by the detector 17 is 2N times the frequency of the control voltage (see Non-Patent Document 1). ). The frequency that can be swept is limited by the modulation band of the phase modulator. Therefore, in the present embodiment, the frequency shift region is doubled by configuring the phase modulators 13A and 13B in two stages. Note that the phase modulator may have three or more stages. In order to compensate the insertion loss due to the multistage phase modulator, an optical amplifier may be appropriately inserted.

  The coupler 15 combines the light having the frequency F1 branched by the splitter 12 and the light having the frequency F2 phase-modulated by the phase modulators 13A and 13B, branches the light, and emits light having two different frequencies F1 and F2. To the detector 16 and the detector 17.

  FIG. 2 is a diagram for explaining the control of the phase modulators 13A and 13B. In the present embodiment, the control voltage is controlled, the frequency of light input to the phase modulators 13A and 13B is linearly changed, and the frequency of the F2-F1 difference frequency beat signal input to the radiator 16 is changed. Sweep linearly. If the center frequency of the operating band of the splitter 12 is 193.125 THz, for example, in order to generate an electromagnetic wave of 0.6 THz, F1 = 193.125 THz and F2 = 193.725 THz. By shifting the frequency of one light branched by the splitter 12 linearly with respect to the frequency of the other light, a continuous spectrum can be obtained by changing the frequency of the difference frequency beat signal.

  The radiator 16 generates an electromagnetic wave (millimeter wave or terahertz wave) having a frequency difference of an optical signal obtained by combining two light beams having different frequencies. As the radiator 16, for example, a single traveling carrier photodiode (UTC-PD) can be used.

  The detector 17 receives the transmission signal output from the radiator 16 and transmitted through the sample 100, and outputs an electrical signal having a frequency of 2w by homodyne detection. The detector 17 can be realized by mounting a THz mixer composed of an SBD with an antenna and a photomixer composed of an UTC-PD with an antenna in the same package as the optical fiber. Further, as the detector 17, a photoconductive antenna (PCA: Photo-Conductive Antenna) may be used. 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. When homodyne detection is performed on the electromagnetic wave, the length of the fiber through which the light propagates is adjusted in advance so that the two optical path length differences at the time of mixing by the detector 17 coincide.

  The electrical signal output from the detector 17 is synchronously detected by the lock-in amplifier 18 to detect the amplitude and phase, and processed by the monitor 19. The intensity of the terahertz wave may be modulated by modulating the bias of the UTC-PD that is the radiator 16.

  In the terahertz wave band, the sample 100, which is a measurement target, is irradiated with a terahertz wave by a free space method using a pseudo optical system using parabolic mirrors 41A to 41D, and the amplitude and phase of a transmission signal and a reflection signal are measured. A complex dielectric constant of 100 is calculated (see Non-Patent Document 3).

  As described above, according to the present embodiment, the laser 11 that generates light of the predetermined frequency F1, the splitter 12 that splits the light generated by the laser 11 into two, and the light that is split by the splitter 12 The phase modulators 13A and 13B that phase-modulate one of them to cause a frequency shift equivalent to the frequency w of the control voltage, and the light phase-modulated by the phase modulators 13A and 13B and the other light branched by the splitter 12 are combined. A coupler 15 that swells, a radiator 16 that generates an electromagnetic wave having a frequency difference of the light combined by the coupler 15 and irradiates the sample 100, a light that is combined by the coupler 15, and is irradiated with the sample 100. By including a detector 17 that receives the transmitted or reflected electromagnetic wave and detects homodyne, photomixing with light from one light source generates a differential frequency beat signal. Since, it is possible to obtain the spectrum of the high SN ratio because it is not affected by the deterioration of the SN ratio due to phase noise. Moreover, since it is realized by a single light source, the cost is low.

[Second Embodiment]
FIG. 3 is a functional block diagram showing the configuration of the dielectric spectroscopic device according to the second embodiment.

  3 includes a laser 11, a splitter 12, phase modulators 13A and 13B, an optical amplifier 21, an oscillator 14, a coupler 15, an amplitude modulator 22, a radiator 16, a detector 17, a lock-in amplifier 18, And a monitor 19.

  Similarly to the first embodiment, the splitter 12 branches the light of the frequency F1 output from the laser 11, and the phase modulators 13A and 13B convert one of the branched lights to a single frequency from the oscillator 14. A sawtooth waveform signal is applied by applying a w (for example, 1 GHz) sawtooth waveform signal, and the coupler 15 performs the light of the frequency F1 branched by the splitter 12 and the frequency F2 phase-modulated by the phase modulators 13A and 13B. Combine light. In the dielectric spectroscopic device of FIG. 3, an optical amplifier 21 is provided after the phase modulator 13A to compensate for insertion loss.

  The light combined by the coupler 15 is amplitude-modulated at a frequency f (for example, 100 kHz) from the oscillator 14 by the Mach-Zehnder type amplitude modulator 22 using the electro-optic effect in order to detect the electromagnetic wave by diode detection.

  The radiator 16 receives the light amplitude-modulated by the amplitude modulator 22 and generates an electromagnetic wave (millimeter wave or terahertz wave) having a frequency difference of light obtained by combining two continuous light waves having different frequencies. As the radiator 16, for example, a single traveling carrier photodiode (UTC-PD) can be used.

  An electromagnetic wave transmitted through the sample 100 is received by an SBD (Schottky barrier diode) with an antenna which is the detector 17. In SBD, an electric signal having a frequency f is output by envelope detection. The electric signal is synchronously detected, the amplitude is detected by the lock-in amplifier 18 and processed by the monitor 19.

  The bias of the UTC-PD that is the radiator 16 may be modulated, and the terahertz wave may be amplitude-modulated with a chopper or the like.

  FIG. 4 is a functional block diagram showing the configuration of another dielectric spectroscopic apparatus according to the second embodiment.

  The dielectric spectroscopic apparatus of FIG. 4 has a configuration in which phase modulators 13C and 13D are further added to another branch destination of the splitter 12 of the dielectric spectroscopic apparatus of FIG.

  The phase modulators 13C and 13D perform serodyne phase modulation on the other branched light by applying a signal having an inverted sawtooth waveform having a single frequency w (for example, 1 GHz) from the oscillator 14, and performing phase modulation 13A, The frequency of light is shifted in the frequency direction opposite to 13B. In addition to doubling the frequency shift amount by a two-stage phase modulator, phase splitters 13 </ b> A to 13 </ b> D are provided at each branch destination of the splitter 12, and signals having sawtooth waveforms that are inverted from each other are applied. With this configuration, a total of four times the frequency shift can be generated.

  Also in the first embodiment, the same effect can be produced by providing a phase modulator at each branch destination of the splitter 12 and performing serodyne phase modulation with mutually inverted sawtooth waveform signals.

[Third Embodiment]
FIG. 5 is a functional block diagram showing the configuration of the dielectric spectroscopic apparatus in the third embodiment.

  The dielectric spectroscopic apparatus shown in FIG. 5 includes a laser 11, a splitter 12, a multistage phase modulator 31, an oscillator 14, splitters 32A and 32B, couplers 33A and 33B, a phase modulator 34, a radiator 16, a detector 17, and a lock-in amplifier. 18 and a monitor 19. The dielectric spectroscopic apparatus of FIG. 5 is a dielectric spectroscopic apparatus in which the two continuous wave light sources of the dielectric spectroscopic apparatus described in Patent Document 1 are replaced with one laser 11, a splitter 12, and a multistage phase modulator 31.

  Similarly to the first embodiment, the splitter 12 branches the light having the frequency F1 output from the laser 11, and the multistage phase modulator 31 converts the branched light to the single frequency w from the oscillator 14. A signal having a sawtooth waveform (for example, 1 GHz) is applied to perform serodyne phase modulation, and light having a frequency F2 (F1 + nw) is output.

  The splitter 32A demultiplexes the light with the frequency F1 into two, and the splitter 32B demultiplexes the light with the frequency F2 into two.

  The coupler 33A combines the light having the frequency F1 demultiplexed by the splitter 32A and the light having the frequency F2 demultiplexed by the splitter 32B, and inputs them to the radiator 16.

  The phase modulator 34 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 32B and the coupler 33B. A control signal having a single frequency w from the oscillator 14 is applied to the phase modulator 34 to perform serodyne phase modulation, and a frequency shift equivalent to the modulation frequency w is generated in the light having the frequency F2 demultiplexed by the splitter 32B. .

  The coupler 33B combines the light having the frequency F1 demultiplexed by the splitter 32A and the light having the frequency F2 + w phase-modulated by the phase modulator 34 and inputs the light to the detector 17.

  The radiator 16 photoelectrically converts the light combined by the coupler 33A and generates an electromagnetic wave (millimeter wave or terahertz wave) having a frequency that matches the frequency difference between the frequencies F1 and F2.

  The detector 17 is irradiated with the light combined by the coupler 33B, receives the electromagnetic wave emitted from the radiator 16 and transmitted through the sample 100, and performs homodyne mixing between the received electromagnetic wave and the irradiated 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.

  The homodyne detection of the third embodiment can have a higher S / N ratio than the envelope detection by the diode of the second embodiment.

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

  FIG. 6 is a diagram showing a measurement system of a dielectric spectroscopic sensor using a lens. In the example of FIG. 6, the amplitude and phase of a transmission signal transmitted through a liquid such as an aqueous solution or oil are measured by arranging a transmission type in the measurement system of the dielectric spectroscopic sensor. 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. 7 is a diagram showing a measurement system of another dielectric spectroscopic sensor using a lens. In the example of FIG. 7, a sample cell is arranged 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.

DESCRIPTION OF SYMBOLS 11 ... Laser 12 ... Splitter 13A-13D ... Phase modulator 14 ... Oscillator 15 ... Coupler 16 ... Radiator 17 ... Detector 18 ... Lock-in amplifier 19 ... Monitor 21 ... Optical amplifier 22 ... Amplitude modulator 31 ... Multistage phase modulator 32A, 32B ... Splitter 33A, 33B ... Coupler 34 ... Phase modulator 41A-41D ... Parabolic mirror 51 ... Lens 52 ... Window plate 53 ... Cell for measuring dielectric constant 54 ... Fixing jig 55 ... ATR prism 100 ... Sample

Claims (3)

A light source that outputs light of a predetermined frequency;
A splitter for splitting the light into two;
Phase modulation means for phase-modulating one of the lights branched by the splitter and shifting the frequency;
A coupler that combines the light phase-modulated by the phase modulation means and the other light branched by the splitter;
Measurement means for photoelectrically converting the light combined by the coupler to generate an electromagnetic wave, receiving the electromagnetic wave transmitted or reflected by the object to be measured, and measuring the amplitude of the electromagnetic wave ;
The measurement means includes an amplitude modulator that amplitude-modulates the combined light at a predetermined frequency, a radiator that photoelectrically converts the amplitude-modulated light to generate an electromagnetic wave, and transmits or reflects the object to be measured. And a detector that receives the electromagnetic wave and outputs an electric signal of the predetermined frequency by envelope detection . The dielectric spectroscopic apparatus according to claim 1, wherein the phase modulation unit includes a plurality of phase modulators connected in multiple stages. 3. The dielectric spectroscopic apparatus according to claim 1, further comprising: a second phase modulation unit configured to phase-modulate the other of the lights branched by the splitter and shift a frequency in a reverse direction.

Images