JP2008157809A - Laser output control device and optical measuring unit - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To improve measurement accuracy of a laser output control device and an optical measuring unit, and to miniaturize the device. <P>SOLUTION: In this laser output control device (part) 10 for optically measuring a portion to be measured, a correction plate 33 is provided in the laser output control device (part) 10 and laser light 21 is transmitted, and a laser output is controlled based on an absorptivity of the laser light 21 by the correction plate 33. Since a laser driver 63 is controlled by negatively adding a signal wherein an effect of an absorptivity of water is corrected to a signal for keeping a conventional laser output constant, by forming the correction plate 33 from a material having a similar absorption characteristic to pure water, the laser light 21 can be emitted with an output wherein the absorptivity by water is corrected. By measuring with the corrected laser light 21, a measured value can be acquired as a direct value of a specific component of the portion to be measured. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a laser output control device and an optical measurement unit, and more particularly, to a laser output control device and an optical measurement unit that achieve miniaturization and high accuracy.

  There are invasive methods and non-invasive methods as methods for detecting the sugar content inside the measurement site.

  As an example of detecting the sugar content, a blood collection method (invasive method) and a non-blood collection method (non-invasive method) are methods for measuring a blood glucose level in a living body. As a blood sampling method, a method is generally used in which the collected blood is reacted with a reagent usually by glucose oxidase method, and a blood glucose level is obtained from the reaction color using a colorimetric method. Various methods have been reported for the bloodless method, and for example, a method for optical measurement is known.

  The method of optically measuring the blood glucose level is expected because it has the least load and high convenience for non-measurers. In the measurement of an optical blood glucose level, light absorption (absorption rate) by glucose is generally performed based on the measurement. However, it is very difficult to measure the blood sugar level from the absorbance because the sensitivity is low because of the low absorbance of glucose as a measurement target and the wavelength used for analysis. As a method for improving the measurement, a measurement method based on a statistical method based on spectrum analysis and second-order differential processing has been proposed (see, for example, Patent Document 1).

Also, calibration reference for blood glucose measurement aimed at improving the measurement accuracy of non-invasive blood glucose measurement with high accuracy by dealing with environmental conditions changes when obtaining blood glucose level by infrared light analysis A body, a blood glucose level measuring method and a blood glucose level measuring apparatus using the body, and a blood glucose level measuring apparatus have been proposed (see, for example, Patent Document 2).
Japanese Patent Laid-Open No. 5-176717 (pages 3-7 and 2-6) Japanese Unexamined Patent Publication No. 2000-258344 (pages 1, 3 and 1-7)

  However, these secondary differential processing methods are called qualitative analysis amounts in the process. Therefore, in order to obtain a quantitative analysis amount, a measurement object (reference object) to be referred to is necessary. By comparing (calculating) the measurement result of the reference object and the measurement value of the object to be measured, As a quantitative value, it can be obtained.

  For example, there is a method in which a reference object and an object to be measured are measured simultaneously, and quantitative analysis is performed from the measurement results.

  In this method, a beam emitted from a light source such as a halogen lamp is guided to a measurement site by a fiber through a heat shielding plate, a pinhole, and a lens. The transmitted light of the beam irradiated to the object to be measured is collected by a mirror, and signal processing is performed as an absorptivity at the light receiving unit. In addition, the reference body is also measured in the same time series, and the actual measurement value of the object to be measured is corrected using the transmitted light detected by the light receiving unit as the standard absorbance (none of which is shown).

  In this method, it is possible to minimize the measurement error by measuring the reference object and the object to be measured in the same time series. However, in such a method, it is necessary to arrange a reference body (for example, a predetermined volume of pure water) in the measurement system, and the measurement apparatus itself tends to be enlarged.

  In addition, in the case where such a reference object does not exist in the measuring apparatus, the same measurement is performed with the reference object (pure water) before measuring the actual object to be measured, and the measurement result is obtained. A method of using it internally as reference data is conceivable. However, in this case, since the measurement is not performed in the same time series, the error factor becomes large.

  In general, a method based on spectral analysis needs to be a light source having a broad and flat spectral characteristic as a light source. However, in reality, there are no light sources having a wide range of characteristics, and when measuring by the above method, it is necessary to maintain the uniformity of the light quantity in the spectrum.

  In any case, measuring the reference object at the same time or before the measurement is an tedious action, and there are problems associated with an increase in the size of the apparatus and an increase in measurement time. Further, since the extinction coefficient is the output irradiated to the object to be measured versus the received light, it is desirable to make the output of the light source uniform even if the spectral characteristics are corrected flat by the reference body.

  In addition to the above, when a specific component inside a measurement site is optically measured, a method using a so-called spectroscopic analysis or spectral analysis (FTIR) or a statistical method has been proposed. However, for qualitative analysis, measurement with a reference material is required. In addition, it is necessary to measure the reference body in order to correct the non-uniformity of the light source. In addition, a spectroscope used for spectrum analysis needs to secure a certain optical path length, and there is a limit to downsizing the measuring apparatus. Also, the method using the FTIR analyzer cannot be miniaturized because of the presence of movable parts such as an optical path and a mirror, and there is a problem that miniaturization of the apparatus using these does not progress.

  An object of this invention is to provide the laser output control apparatus and optical measurement unit which can improve a measurement precision in view of an above-described point.

  The present invention has been made in view of the various circumstances described above. First, a laser output control device that controls the output of near-infrared laser beams having a plurality of different emission wavelengths emitted from a light source, A photodetector that receives a part of the near-infrared laser light emitted from a light source, and a first laser output control circuit that controls the output of the near-infrared laser light to be constant according to a light reception result of the photodetector; A correction plate having a different amount of light absorption depending on the emission wavelength, and the near-infrared laser emitted from the light source based on the absorption amount when a part of the near-infrared laser light is transmitted through the correction plate. This is solved by providing a second laser output control circuit for correcting the output of light.

  Second, an optical measurement unit that optically measures the sugar content at the site to be measured, and the near-infrared laser light having emission wavelengths of the first wavelength, the second wavelength, and the third wavelength, respectively, with respect to the site to be measured Each of which detects a reflected light of the near-infrared laser light reflected from the measurement site, and a light-emitting unit having a light source that individually outputs a light source, a light detector that receives a part of the near-infrared laser light A light receiving unit; a first laser output control circuit that holds the output of the near infrared laser light constant according to a light reception result of the photodetector; a correction plate having a different amount of light absorption depending on the emission wavelength; and the correction plate And a second laser output control circuit that corrects the output of the near-infrared laser beam based on the amount of absorption when a part of the near-infrared laser beam is transmitted. .

  According to the present invention, for example, in a laser output driving device (laser output control device) suitably used for a non-invasive and small optical measurement unit, it is possible to perform laser output that improves measurement accuracy.

  First, the laser output is kept constant by the first laser output control circuit, and a part of the near-infrared laser light is transmitted through a correction plate having light absorption characteristics equivalent to that of pure water. The control circuit adds the wavelength variation based on the light absorption rate of the water as a correction signal, and negatively adds it to the signal generated by the first laser output control circuit to make the laser output constant. By measuring an object to be measured using this laser light, a value automatically corrected by the amount of light absorbed by pure water is obtained as the measured value. Therefore, measurement accuracy can be improved when employed in an optical measurement unit.

  In the present invention, a small gypsum board is used as the correction plate, the correction plate is held in a laser output control device, and the laser output is controlled by hardware based on the amount of light absorbed by the correction plate. Therefore, for example, the apparatus can be reduced in size as compared with the conventional structure in which pure water having a predetermined volume is held in the measurement system as a reference body and the measurement value is corrected by software based on the reference body. Therefore, when the laser output control device (/ laser output control circuit / laser output control circuit unit) of the present invention is employed in the optical measurement unit, the size can be reduced. Further, since three single wavelengths are used as the laser light to be irradiated, the apparatus can be downsized and the measurement time can be shortened as compared with the spectrum analysis method. In addition, since the measurement is performed in the same time series, the error factor can be reduced, and high accuracy of the optical measurement unit can be realized.

  Second, it is possible to realize an optical measurement unit including a laser output driving unit (/ laser output control circuit / device) that can automatically correct the laser output based on the absorbance of pure water. The optical measurement unit calculates the absorptance of the laser light of three wavelengths and performs the calculation as the amount of change based on these secondary differential values. Therefore, the sugar content can be calculated without using a spectral analysis method or the like. Miniaturization is realized. Further, since the absorbance at the site to be measured is measured with laser light whose output is corrected by the absorbance of pure water, the actual measurement value can be directly used as the absorbance of the sugar content. Furthermore, since the secondary differential value is used, fluctuations such as fluctuation can be absorbed, so that the measurement error can be reduced.

  The optical measurement unit of the present invention is suitable for use in, for example, a blood glucose level measurement device, a fruit fructose measurement device, and the like, and is small and non-invasive, thus reducing the burden on the subject (measurement object). In addition, the measurement accuracy can be further improved.

  Hereinafter, an exemplary embodiment of the present invention will be described in detail with reference to FIGS. 1 to 7. First, a laser output control device will be described as a first embodiment of the present invention with reference to FIGS. 1 and 2.

  FIG. 1 is a circuit block diagram showing an outline of the configuration of the laser output control apparatus of the present embodiment.

  The laser output control device 10 of this embodiment includes a light source 111, a photodetector 112, a first laser output control circuit 31, a second laser output control circuit 32, and a correction plate 33. A plurality of near infrared laser beams having different emission wavelengths are output from the light source 111. A plurality of near-infrared laser beams having different emission wavelengths are used, for example, in order to quantitatively measure a component of the object to be measured. Specifically, the laser output control device 10 is preferably used by being installed in an optical measurement unit that measures sugar content in a measurement site of a living body in a non-invasive manner, which will be described later.

  The light source 111 is a plurality of semiconductor laser diodes LD that individually output near-infrared laser beams (hereinafter referred to as laser beams) 21 having different wavelengths. Here, as an example, the laser output control apparatus 10 provided with three semiconductor laser diodes LD that individually output the laser light 21 of the first wavelength λ1, the second wavelength λ2, and the third wavelength λ3 will be described as an example. The number of semiconductor laser diodes LD may be, for example, singular or plural, and is not limited to three.

  The photodetector 112 is, for example, a photodiode (hereinafter referred to as a first photodetector 112) that receives part of the laser light 21 emitted from the light source 111. The first photodetector 112 is a photodetector for back monitoring that detects part of the laser beam 21 emitted behind the light source 111.

  The first laser output control circuit 31 includes a first differential amplifier 311 and a reference voltage setting circuit 312 so that the output of the laser light 21 at each wavelength is constant according to the light reception result of the first photodetector 112. A control signal for the laser driving circuit 63 is output.

  The correction plate 33 has a different amount of absorption (hereinafter referred to as “absorbance”) for each of the laser light 21 of the first wavelength λ1, the second wavelength λ2, and the third wavelength λ3, and the correction plate 33 itself is equivalent to pure water. For example, gypsum board or quartz plate.

  The second laser output control circuit 32 includes a second differential amplifier 321 and another photodetector (hereinafter referred to as a second photodetector) 322. The second photodetector 322 receives the laser beam 21 that has passed through the correction plate 33, and a signal based on the amount of absorption (absorbance) of the laser beam 21 by the correction plate 33 and the first laser output control circuit 31 output the signal. The control signal of the laser driving circuit 63 is negatively added by the second differential amplifier 321, thereby controlling the laser driving circuit 63 and correcting the output of the laser light 21 emitted from the light source 111.

  Part of the laser beam 21 output from the light source 111 is received by the first photodetector 112. The first laser output control circuit 31 uses the first differential amplifier 311 to calculate the difference between the light reception voltage based on the amount of light received by the first photodetector 112 and the reference voltage generated by the reference voltage setting circuit 312. In the loop of the first laser output control circuit 31, a control signal for the laser driver 63 is generated in order to keep the laser output constant at a plurality of wavelengths (first wavelength λ1, second wavelength λ2, and third wavelength λ3).

  At the same time, part of the laser light 21 output from the light source 111 is split by the half mirror 15. The divided laser light 21 passes through the correction plate 33 and is received by the second photodetector 322. Based on the received light quantity, the absorption amount of the laser light 21 due to absorption by the correction plate 33, that is, the absorbance of the laser light 21 by pure water can be detected. The absorbance of the laser beam 21 by the correction plate 33 (pure water) varies depending on the wavelength. That is, in the loop of the second laser output control circuit 32, since the absorbance varies depending on the first wavelength λ1, the second wavelength λ2, and the third wavelength λ3, the laser driver 63 is controlled by the correction signal corresponding to the change. The laser output will change.

  FIG. 2 is a diagram for explaining the first laser output control circuit 31 and the second laser output control circuit 32. FIG. 2A is a diagram showing the absorptivity characteristics of the correction plate 33 with respect to the wavelength of the laser light 21, and FIG. 2B is a diagram showing laser output with respect to the wavelength of the laser light 21.

  When the correction plate 33 is irradiated with laser light and the absorbance at each wavelength of the correction plate 33 is shown as the characteristic shown in FIG. 2A, the final laser output is shown in FIG. Controlled as shown.

  In FIG. 2B, a broken line indicates a constant output at each wavelength controlled by the first laser output driving circuit 31, and a solid line indicates the first laser output driving circuit 31 and the second laser output driving circuit 32. The final laser output corrected by the above is shown. That is, the solid line indicates the laser output in which the amount of change in the laser beam 21 due to transmission through the correction plate 33 (water) is corrected.

  When using this laser beam 21 to measure a specific component of the object to be measured (measurement site), if the output of the laser beam 21 irradiating the object to be measured is considered to be constant, it is transmitted or reflected by the object to be measured. The received light quantity itself becomes the light absorption rate of the object to be measured. Therefore, a laser beam having a light absorption characteristic (pure water) in a state in which the measurement plate of the object to be measured does not contain the measurement molecule (pure water) is selected, and the laser output based on the light absorption rate of the correction plate 33 is selected. By irradiating the object to be measured with the laser beam 21 in a state where the amount of change is corrected, the amount of received light can be used as it is as the absorbance of the object to be measured.

  Conventionally, when other components (for example, moisture) are included in addition to a specific component to be measured, it is necessary to hold a reference body for correcting an actual measurement value in the measurement device. Moreover, when not holding a reference body, the process of measuring an absorptivity with a reference body separately was needed at the time of a measurement, and there existed a problem which took the whole measurement time and time. However, according to the present embodiment, as a result, an absolute absorbance can be automatically obtained.

  In addition, according to the present embodiment, it is not necessary to measure the reference body, the measurement system can be downsized, and the data is measured in the same time series, so that the error factor can be reduced. .

  Next, a second embodiment of the present invention will be described with reference to FIGS.

  In the second embodiment, the absorbance of each glucose is measured using a single three-wavelength near-infrared laser, and the glucose concentration is calculated from the second derivative of the measured three absorbances. This is an optical measurement unit 1. Since the optical measurement unit 1 is preferably used for the blood glucose level measuring apparatus 100, for example, this case will be described below as an example.

  The optical measurement unit 1 includes the laser output control unit as in the first embodiment. First, the principle of blood glucose measurement using the optical measurement unit 1 of the present embodiment will be described with reference to FIG. Will be described with reference to FIG.

  FIG. 3 is a diagram showing an example of a blood glucose level measuring apparatus 100 equipped with the optical measurement unit 1 of the present embodiment. FIG. 3 (A) is an external view, and FIG. 3 (B) is a diagram in FIG. 3 (A). Aa line sectional drawing and Drawing 3 (C) (D) are the top views inside.

  As shown in FIGS. 3A and 3B, for example, a power switch 4, a measurement start / stop button 5, a display unit 2, and the like are provided on one main surface of the external housing 8 of the blood glucose level measuring apparatus 100. An attachment 3 serving as a contact portion with the measurement site is provided on the upper portion of the external housing 8. The attachment 3 is provided continuously with the optical measurement unit 1. The attachment 3 shown as an example of this embodiment has a shape (for example, a cylindrical shape) and a material so that light output from the light emitting unit in the optical measurement unit 1 and light received by the light receiving unit do not leak to the outside. A part of the external housing of the optical measurement unit 1 is configured.

  As shown in FIG. 3C, the optical measurement unit 1 includes a light emitting unit, a light receiving unit (both not shown here), and a control unit 6. The control unit 6 is configured by, for example, a semiconductor integrated circuit integrated on a printed circuit board, and includes an arithmetic processing unit.

  3D, in the internal structure of the optical measurement apparatus 100, the display unit 2 is connected to a display driver that is a part of the control unit 6. The display unit 2 is, for example, an LCD (Liquid Crystal Display) panel, an organic EL (Electronic Luminescent) display panel, etc., and displays a blood glucose level and other measurement information (for example, notification of measurement error, date and time) so that the measurer can recognize it. Anything can be used. A power supply unit 7 connected to the control unit 6 is provided. The power source is charging by an AC adapter, a battery, or a combination thereof.

  FIG. 4 is a schematic diagram showing the measurement site 25 where the blood glucose level is measured. 4A is a diagram showing the blood glucose level measuring device 100 and the site to be measured 25, and FIG. 4B is a schematic cross-sectional view of the site to be measured 25.

  As shown in FIG. 4A, the blood glucose level is measured by attaching the attachment 3 of the blood glucose level measuring apparatus 100 to the inside of the arm or wrist. When the blood glucose level is measured by applying the attachment 3 of the blood glucose level measuring device 100 to the measurement site 25 such as the inner side of the arm or wrist, the dermal layer 252 of the living body is used as the measurement site 25 as shown in FIG. Use. A dermis layer 252 is present in the lower layer (inside) of the epidermis 251 of the living body, and a subcutaneous tissue 253 is present in the lower layer.

  In the present embodiment, the laser light 21 emitted from the optical measurement unit 1 is diffusely reflected by the dermis layer 252. More specifically, the laser light 21 is output from the light emitting unit at an irradiation angle θ at which the laser light 21 incident from the skin 251 is diffusely reflected by the dermis layer 252.

  In order to measure the blood glucose level, it is efficient to detect the blood glucose concentration. In addition, when measuring blood sugar levels non-invasively (without blood sampling), light in a wavelength band that is transparent to the human body is used. In the case of glucose, some spectra of near-infrared light are used. It is known to have light absorption characteristics. When measuring a blood glucose level using a conventional optical blood glucose level measuring device, the blood glucose level is measured by transmitting near-infrared rays through the blood vessel and detecting the absorption rate by glucose.

  However, in addition to glucose, there are various substances in the blood, and the absorbance of glucose is very small. In particular, in the case of transmitted light, there is a problem that the blood glucose level cannot be accurately measured as a result of the strong influence of hemoglobin, which is a component in blood, to change the amount of light.

  Therefore, in the present embodiment, glucose in the dermis layer 252 is measured so as not to be affected by blood components (hemoglobin). Since the dermis layer 252 is located at a relatively shallow position from the outside of the living body (skin 251), the aperture angle (eg, the lens numerical aperture NA is set to an appropriate value) and the irradiation angle of the laser light 21 are appropriately selected. Thus, it is possible to obtain reflected light sufficient for calculating the blood sugar level. In addition, measurement using reflected light is more advantageous than using transmitted light because light does not pass through the subcutaneous tissue 253 and measurement errors due to components other than glucose can be avoided.

  5A and 5B are diagrams illustrating the optical measurement unit 1, in which FIG. 5A is a top view and FIG. 5B is a cross-sectional view taken along the line bb of FIG. 5A.

  The optical measurement unit 1 includes a light emitting unit 11 and a light receiving unit 12. The light emitting unit 11 includes a light source (not shown), a light detector (hereinafter referred to as a first light detector) that receives a part of the laser light 21 output from the light source, and a condensing lens 11a. The light source is a semiconductor laser diode LD that individually outputs near-infrared laser beams having emission wavelengths of the first wavelength λ1, the second wavelength λ2, and the third wavelength λ3, respectively, to the measurement site. The laser beam 21 is condensed by the condensing lens 11a having a lens numerical aperture NA, and is irradiated to the measurement site with a small spot (FIG. 5A). As shown in FIG. 5B, two condenser lenses 11a are provided on the light emitting unit 11 side of the optical measurement unit 1, but the number of condenser lenses 11a is not limited to this number.

  Here, the first wavelength λ1, the second wavelength λ2, and the third wavelength λ3 are near-infrared lights having wavelengths in the vicinity, and the wavelengths become longer in this order (λ1 <λ2 <λ3). The third wavelength λ3 is a wavelength at which the absorbance by pure water is very large and only the absorbance by pure water can be measured, the second wavelength λ2 is a wavelength at which the absorbance by glucose is large, and the first wavelength λ1 is , The wavelength at which the absorbance due to glucose is small. The reason for selecting these wavelengths will be described later.

  The light receiving unit 12 includes a photodetector (for example, a photodiode) PD and a condensing lens 12a, and the reflected light 22 of the laser light 21 reflected by the measurement site 25 is reflected by the condensing lens 12a having a lens numerical aperture NA ′. Each is condensed and detected by the photodetector PD.

  Since it is desirable to collect as much reflected light 22 as possible on the light receiving unit 12, the spot diameter at the light receiving unit 12 is set larger than that of the light emitting unit 11 (FIG. 5A).

  The light emitting unit 11 and the light receiving unit 12 are arranged adjacent to each other with a light shielding plate 17 interposed therebetween. For example, as shown in FIG. 5B, the light emitting unit 11 and the light receiving unit 12 are arranged in the same housing (a part of the attachment 3 in this embodiment), and the light shielding plate 17 is arranged in the center. The light shielding plate 17 is provided at substantially the same height as at least the outer periphery of the attachment 3. When the attachment 3 is brought into contact with the measurement site 25 and the measurement site 25 is irradiated with the laser beam 21, a part of the laser beam 21 is reflected by the skin 251. In order to prevent such directly reflected light from reaching the light receiving unit 12, a light shielding plate 17 is provided. The light-emitting unit 11 and the light-receiving unit 12 are arranged in separate spaces by the light-shielding plate 17.

  The light shielding plate 17 is, for example, a material that has a black surface and absorbs near-infrared without transmitting or reflecting.

  More specifically, for example, a metal plate whose surface is coated, specifically, a metal plate whose surface is coated with a black brushed painted material may be mentioned. Examples of the light shielding plate 17 include a resin plate formed by using a resin material containing at least one resin selected from the group consisting of acrylic and polycarbonate resins. In that case, in order to improve light-shielding properties, it is preferable to use a resin plate in which at least one black filler selected from the group consisting of carbon fiber and graphite is contained in the resin material. Further, as the light shielding plate 17, for example, a black polarizing plate may be used. In that case, it is preferable to use the board | substrate which used glass as a base material as a polarizing plate, for example. Further, as the light shielding plate 17, for example, a stone material or the like may be used.

  The laser light 21 is affected by the return light, but the light shielding plate 17 can reduce the influence. Therefore, the laser beam 21 can be stably oscillated, and measurement noise can be reduced.

  Furthermore, since the light receiving unit 12 is also used in a space partitioned by the light shielding plate 17, it can be made less susceptible to the influence of electrical noise.

  The light shielding plate 17 may function as a contact detection sensor. More specifically, the light shielding plate 17 is movable and movable in the vertical direction, and protrudes from the surrounding attachment 3 when not measured. On the other hand, when the attachment 3 is brought into contact with the measurement site 25 at the time of measurement, the light shielding plate 17 comes into contact with the measurement site 25 with a certain degree of tension and is pressed into the optical measurement unit 1, and below the light shielding plate 17. The switch 18 is operated. In other words, the switch 18 can detect that the attachment 3 has normally contacted the measurement site, and can cause the optical measurement device 100 to start the measurement process in a normal state (in a state where external light is shielded).

  Further, when the light shielding plate 17 functions as a contact detection sensor and the measurement apparatus is operated after detecting normal contact, the light shielding plate 17 may be provided at a position lower than the attachment 3. For example, the attachment 3 side is movable, a contact sensor with a contacted part is provided at the upper end of the light shielding plate 17, and is connected to the switch 18 via wiring in the light shielding plate 17. By making contact with the measurement site 25 with a predetermined tension, the attachment 3 is pushed down, and the heights of the light shielding plate 17 and the peripheral wall portion of the attachment 3 become substantially equal. In this state, if the contact sensor on the upper part of the light shielding plate 17 detects contact and the switch 18 for operating the measuring device is turned on, the measuring device can be operated in a state where the outside light is shielded.

  Further, when a contact sensor is provided at the upper end of the light shielding plate 17, the heights of the peripheral wall portions of the light shielding plate 17 and the attachment 3 may be the same, and both may be fixed.

  In order to avoid the intrusion of external light, the attachment 3 is also selected from a material having a light shielding property. Further, although the laser spot from the light emitting unit 11 is very small and the laser spot of the light receiving unit 12 is also large, the spread of the diffuse reflected light is about 1 mm (for example, 0.1 mm to 0.00 mm on the photodiode surface). About 5 mm). In order to improve the measurement accuracy, it is desirable to avoid the intrusion of outside light. If a sufficient opening for the laser light 21 and the reflected light 22 to pass through is secured, the upper surface of the attachment 3 is continuous from the side surface without a gap. And it is preferable to make it the shape which covers an inside as much as possible.

  Moreover, the optical measurement unit 1 may have a temperature detection part (for example, temperature sensor). The temperature sensor measures the temperature of the measurement site 25 (or in addition to the outside air temperature). The light absorption characteristics of glucose vary with temperature. Therefore, the temperature is measured by the temperature sensor before measuring the blood glucose level, and the wavelength of the laser beam 21 is corrected within a minute range from the measurement result. Specifically, since the laser light 21 has a characteristic that the oscillation wavelength changes depending on the current or temperature, the temperature or driving current of the laser light 21 is controlled based on the temperature dependence of the glucose absorption characteristic measured in advance. For example, when controlling by the drive current of the laser beam 21, the laser drive amount is calculated and fed back to the laser driver. As a result, the first wavelength λ1 to the third wavelength λ3 are selected as the most efficient wavelengths within the range satisfying the wavelength condition of the present embodiment according to the temperature of the measurement site 25, and are shifted by, for example, several nm. The Thereby, an accurate blood glucose level can be measured.

  The laser beam 21 emitted from the light emitting unit 11 is focused by an appropriate lens numerical aperture NA, and is irradiated to the measurement site 25 (dermis layer 252) at an angle θ. This angle θ is an angle formed by the center line in the vertical direction (up and down in the drawing) of the light shielding plate 17 and the optical axis of the laser light 21, and is set to an angle most suitable for measuring the glucose concentration of the dermis layer 252. The position of the focus point of the beam is set by focusing on the position where the reflected light (diffuse reflected light) from glucose of the dermis layer 252 can be obtained most efficiently.

  Here, the focus point is connected at a predetermined depth D from the surface of the epidermis 251 and is connected as one point in the dermis layer 252 suitable for glucose measurement. The depth D is a numerical value indicating how much the focus point is connected from the surface of the skin 251. Further, the focus point is connected as one point separated from the substantially central part of the thickness of the light shielding plate 1 by a predetermined distance W. The distance W is a numerical value indicating how far the focus point is from the center or end of the thickness of the light shielding plate 17 at the depth D position from the surface of the skin 251 into the dermis layer 252.

  Another reason for making the laser beam 21 incident at a predetermined angle θ is to prevent the reflected beam 22 from returning as much as possible to the laser oscillation point.

  On the other hand, the angle θ ′ of the laser light on the light receiving unit 12 side is the angle θ ′ at which the reflected light 22 is efficiently acquired. The angle θ ′ is an angle formed by the vertical center line of the light shielding plate 17 and the optical axis of the reflected light 22, and the focus points are the depth D ′ from the skin 251 and the thickness of the light shielding plate 17, respectively. It is connected to a distance W ′ from the approximate center or end.

  Since the diffusely reflected beam is basically reflected light from all layers, the reflected light from the dermis layer 252 is selectively selected by the angle θ ′, the focus points D ′, W ′, and the lens numerical aperture NA ′. The position, angle, and the like of the light receiving unit 12 are set so as to collect light.

  The optical measurement unit 1 is an example. Although illustration is omitted, as a configuration of the light emitting unit 11 and the light receiving unit 12, for example, a mirror may be provided and light may be collected by the mirror. As described above, when the light is condensed by the condensing lenses 11a and 12a, the amount of light is attenuated by the transmittance of the lens. By condensing with a mirror, attenuation of the light amount can be suppressed, and depending on the focal length, it may be easier to design by reflecting with a mirror.

  The optical measurement unit 1 of the present embodiment does not require an optical path length required by a spectroscopic analyzer, an FTIR analyzer, or the like, or a movable part such as a mirror. Further, even when the mirror is employed as described above, it is not necessary to operate it, and the miniaturization can be maintained. In addition, since the reflected light of a single wavelength laser is received, it is not necessary to split the light with a diffraction grating or the like, and the light receiving side can be composed of, for example, a lens and a photodetector. Therefore, the optical measuring device 100 can be reduced in size and weight, and the portability can be greatly improved. The size is small enough to fit in the palm of the hand and can be carried and operated with one hand.

  Next, the principle of blood glucose level measurement using the optical measurement unit 1 of the present embodiment will be described with reference to FIG. The horizontal axis in FIG. 6 is the laser emission wavelength λ, and the vertical axis is the absorbance I.

  In the present embodiment, the laser beam 21 is used for measuring the blood sugar level (glucose). The spectrum of the laser beam 21 is very narrow and is almost a single wavelength light. Then, the laser beam having at least three different wavelengths (λ1, λ2, λ3) is individually irradiated to measure the absorbance I (first absorbance I1, second absorbance I2, and third absorbance I3) for each wavelength. Then, these secondary differential values are obtained from the three absorbances corresponding to the three wavelengths.

  The absorptance I can be obtained from the irradiation amount of the laser light irradiated from the light emitting unit and the received light amount of the reflected light reflected from the dermis layer. The light absorption rate I will be described in detail. If the intensity of the light having the wavelength λ incident on the measurement site is L0 (λ) and the intensity of the reflected light having the received wavelength λ is L (λ), the measurement site 25 The light absorption rate I (λ) is obtained by ln (L (λ) / L0 (λ)) (in the case where the incident light is constant, the received light intensity itself is equivalent to the light absorption rate).

  However, as described above, the absorbance due to glucose is very small, and the blood glucose level is about 100 mg / dl. Therefore, it is not known whether the actual blood glucose level fluctuates or is a measurement error. There is a case.

  Therefore, a secondary differential value is used. The second-order differential value of the present embodiment uses the fact that light absorption by glucose varies depending on the wavelength of light, and selects three adjacent wavelengths including a wavelength region where the variation due to this wavelength appears as large as possible. It is defined as a value corresponding to the derivative of the second derivative of the rate I and the wavelength λ.

  Obtaining the second order differential value of the three points of data means obtaining the amount of change in data from the three points of wavelengths λ1, λ2, and λ3 to the center point (second data: λ2). That is, the amount of change from the absorbance at the two surrounding points (λ1, λ3) (first absorbance I1, third absorbance I3) with the absorbance at the center wavelength λ2 (second absorbance I2) as the apex. Therefore, the calculation sensitivity can be improved as compared with the calculation based on the actual measurement value of the irradiation light amount versus the received light amount.

  In addition, since the secondary differential value is obtained as a change amount, it is possible to absorb fluctuations such as fluctuations (fluctuation). Therefore, the same result as that obtained when the blood glucose level is measured by the spectrum analysis method can be obtained.

  Furthermore, in the present embodiment, only the absorption spectrum of glucose is measured and unnecessary spectrum is not measured, so that the measurement time can be shortened.

  The procedure for obtaining the absorptance will be described. First, the laser is driven at the first wavelength λ1, the laser beam having the first wavelength λ1 is irradiated to the measurement site, and the first absorptance I1 is measured from the reflected light. Next, the laser is driven at the second wavelength λ2, the laser beam having the second wavelength λ2 is irradiated to the measurement site, and the second absorbance I2 is measured from the reflected light. Similarly, the third absorbance I3 is measured for the third wavelength λ3. The laser is driven at the third wavelength λ3, the laser beam having the third wavelength λ3 is irradiated to the measurement site, and the third absorbance I3 is measured from the reflected light. Here, if the light emission output of the laser is constant, these secondary differential values can be calculated as discrete differential processing from the first extinction coefficient I1, the second extinction coefficient I2, and the third extinction coefficient I3.

  As described above, glucose has absorption characteristics for several spectra with respect to near-infrared light. In the case of pure water, it has been found that there is very strong absorption for wavelengths near 2000 nm.

  In FIG. 6, the spectrum spectrum curve of pure water measured in advance is indicated by a solid line and the spectrum spectrum curve of a mixture of pure water and glucose measured in advance is indicated by a broken line as a reference.

  From these spectral curves, it can be said that a wavelength having a larger light absorption rate I than a solid line is a wavelength at which the light absorption rate of glucose is high.

  When the wavelength λ is around 2000 nm, the absorption by pure water is very large, and the solid line and the broken line are superimposed. Therefore, in this wavelength band, there are almost no molecules or substances that absorb light other than pure water. Only the absorbance due to can be measured. In addition, since the extinction coefficient in this wavelength band is very high, even if there is absorption of other molecules and substances, it becomes relatively very small and can be ignored.

  In the present embodiment, the wavelength closest to 2000 nm at which the absorbance by pure water is the highest and the wavelength at which the absorbance by glucose is increased is the approximate center of the laser oscillation wavelength, that is, the second wavelength λ2. As an example, the second wavelength λ2 is 1870 nm. The wavelengths before and after (λ1, λ3), that is, the first wavelength λ1 and the third wavelength λ shown in FIG. 6 are selected as follows.

  The third wavelength λ3 is a wavelength away from the second wavelength λ2 in a region where the light absorption by pure water is high and no light absorption of glucose. The first wavelength λ1 is a wavelength lower than the second wavelength λ2, and a wavelength that does not absorb light by glucose is selected.

  Here, assuming that the absorbance measured at the first wavelength λ1, the second wavelength λ2, and the third wavelength λ3 are the first absorbance I1, the second absorbance I2, and the third absorbance I3, respectively, the series S Is as follows.

      S = {I1, I2, I3}

  And the secondary differential value i by these discrete differential processes is expressed by the following equation.

i = Δ ² S / (Δ ² Λ) = 2 × I 2 − (I 1 + I 3)

  The value of the secondary differential value i corresponds to the amount of change. For this reason, a reference value for identifying the amount of change is required, and a quantitative numerical value is obtained from this reference value. The reference values are the first absorbance I1, the second absorbance I2, and the third absorbance I3 at each wavelength. And a blood glucose level is calculated | required with the blood glucose level conversion function which uses these as a parameter.

  Here, since the site to be measured 25 contains a component (for example, moisture) other than glucose, the absorbance of glucose itself is measured even when the laser beam 21 is irradiated and reflected by a known method. It will not be. In other words, before performing the differentiation process described above, an arithmetic process or the like that corrects the difference caused by including water by software is required.

  However, in the present embodiment, the laser output control unit obtains values obtained by absorbing the laser light 21 having the first wavelength λ1, the second wavelength λ2, and the third wavelength λ3 by the correction plate (pure water) 33, respectively. The laser output is corrected by hardware by feeding back a correction value signal based on the above to the laser driver.

  Therefore, the laser light 21 having the first wavelength λ1, the second wavelength λ2, and the third wavelength λ3 that is finally irradiated to the measurement site 25 is output after the difference due to the amount of absorption (absorbance) of water is corrected. Therefore, the first absorbance I1, the second absorbance I2, and the third absorbance I3 obtained by actual measurement with these can be directly used for differential processing as the absorbance of glucose itself.

  FIG. 7 is an example of a circuit block diagram illustrating an outline of the optical measurement unit 1.

  The optical measurement unit 1 includes a light emitting unit 11 having a light source 111 and a first light detector 112, a light receiving unit 12, a laser output control unit 10, and a control unit 6. The laser output control unit 10 includes: The first laser output control circuit 31, the second laser output control circuit 32, and the correction plate 33 are included. The control unit 6 that performs various controls of the optical measurement unit 1 includes a DSP (Digital signal processor) 61, an A / D conversion circuit 62, a laser driver 63, an arithmetic processing unit 65, and the like. Although not shown, the control unit 6 includes a display driver for outputting data such as measurement results to the display unit, a desired circuit necessary for other controls, and the like.

  Note that the basic configuration of the laser output control unit 10 is the same as that of the laser output control device of the first embodiment, and the same components are denoted by the same reference numerals.

  The light emitting unit 11 includes a light source 111 and a first photodetector 112. The light source 111 is, for example, a laser diode LD, and is provided in the light-emitting unit 11. The laser light 21 has emission wavelengths of the first wavelength λ 1, the second wavelength λ 2, and the third wavelength λ 3 with respect to the measurement site 25. Are output individually. The first photodetector 112 receives a part of the laser light 21.

  The laser beam 21 emitted from the light emitting unit 11 is divided by the half mirror 15, a part of the light is reflected by the measurement site 25, and the other part is transmitted through the correction plate 33.

  The light receiving unit 12 includes a photodetector PD such as an InGaAs (indium gallium arsenide) photodiode, for example, and the reflected light of the laser light 21 reflected from the measurement site 25 is absorbed by each wavelength (first). Absorbance I1, second absorbance I2, and third absorbance I3) are detected.

  The correction plate 33 is made of a material having a light absorption coefficient that differs depending on the emission wavelength and has light absorption characteristics equivalent to that of pure water, such as a gypsum board or a quartz plate. The laser beam 21 that has passed through the correction plate 33 is detected by another photodetector (second photodetector) 322 of the second laser output control circuit 32.

  The first laser output control circuit 31 includes a first differential amplifier 311, a first front monitor diode (hereinafter referred to as FMD) 313, and a reference voltage setting circuit 312. A control signal for controlling the laser driving circuit 63 is generated so that the output of the laser light 21 at the wavelength of becomes constant.

  The light quantity of the laser beam 21 (for example, the first wavelength λ1) received by the first photodetector 112 is converted into a voltage signal (light reception voltage) by a current-voltage conversion circuit (not shown) as a light reception current, and then the first FMD 313. To the first differential amplifier 311. The first differential amplifier 311 generates a differential voltage (first differential voltage) corresponding to the difference between the received light voltage and the reference voltage generated from the reference voltage setting circuit 312. The first laser output control circuit 31 outputs the first differential voltage so as to control the laser output of each diode LD constituting the light source 111 to a constant light amount.

  The second laser output control circuit 32 includes a second differential amplifier 321, a second photodetector 322, and a second FMD 323. The second photodetector 322 detects the laser light 21 that has passed through the correction plate 33, and the correction plate. A correction signal for correcting the output of the laser beam 21 is generated on the basis of the amount of absorption by 33. Further, in the second differential amplifier 321, the first differential voltage output from the first laser output control circuit 31 and the correction signal (voltage) are negatively added, thereby controlling the laser driver 63.

  Further, the second laser output control circuit 32 calculates the difference from the absorbance at other emission wavelengths in the second FMD 323 with reference to the absorbance of the laser light 21 at any one of the emission wavelengths transmitted through the correction plate 33. The output of the laser light having other emission wavelength is corrected.

  Hereinafter, the reference wavelength will be described as a first wavelength as an example, and will be described more specifically.

  In the present embodiment, by arranging the correction plate 33 in the laser output control unit 10, when the laser wavelength is changed, the final output light (irradiates the object to be measured) according to the absorbance of pure water at that wavelength. Light) can be corrected. That is, when output is performed at each wavelength and the absorbance at a measurement object (for example, glucose) is measured, the difference in absorbance in pure water due to the difference in wavelength at that time is corrected. By directly performing a second derivative process on this measured value, the amount of change in absorbance due to glucose, that is, the glucose concentration can be measured.

  The second laser output circuit 32 cuts off the connection of the second FMD 323 of the second laser output circuit 32 only for the first time, and the absorbance (first reference absorbance) Ir1 by the correction plate 33 with respect to the first wavelength λ1. It is held in the second laser output control circuit 32.

  The second laser output control circuit 32 causes the second FMD 323 to generate a second differential voltage based on the first reference absorbance Ir1. The second differential voltage is an absorbance (second wavelength) between the first absorbance I1 of the reference first wavelength λ1 and the other wavelengths (second wavelength λ2, third wavelength λ3) at the three wavelengths sequentially received. The difference between the reference absorbance I2 and the third reference absorbance I3) is converted into a voltage. In the case of the first laser beam 21 having the first wavelength λ1, the value obtained by voltage-converting the first reference absorbance Ir1. It is.

  The second differential voltage is negatively added to the first differential voltage output from the first laser output control circuit 31 by the second differential amplifier 321 and output as a drive signal for driving the laser diode LD.

  This signal is generated by the second laser output control circuit 32 as a signal for constantly maintaining the output of the laser light 21 having the first wavelength λ1 generated by the first laser output control circuit 31, and the first wavelength. This is a correction signal obtained by negatively adding a correction signal based on the amount of fluctuation caused by the absorption of the laser light 21 of λ1 by the correction plate 33. By controlling the laser driver 63 with this correction signal, the laser light 21 having the first wavelength λ 1 emitted from the laser diode LD with a predetermined output is transmitted to the next first wavelength by the laser light 21 transmitted through the correction plate 33. The output of λ1 is corrected.

  That is, by selecting a correction plate 33 having an absorption characteristic equivalent to that of pure water (for example, gypsum board), the laser beam 21 can be emitted with an output corrected by the absorption ratio of pure water.

  Since the measurement site 25 includes components other than glucose (for example, moisture), components other than glucose (water) are also included when receiving light reflected by irradiating laser light using a conventional method. It becomes a measured value.

  However, in the present embodiment, the measurement site 25 is irradiated with the laser beam 21 with an output corrected by the absorbance of pure water. That is, the laser light 21 having the first wavelength λ1, the second wavelength λ2, and the third wavelength λ3 that is finally irradiated on the measurement site 25 is output after the difference due to the water absorption rate is corrected. The measured values (first absorbance I1, second absorbance I2, and third absorbance I3) that are reflected by the portion 25 and received by the light receiving unit 12 are directly differentiated as the absorbance of glucose itself. Can be used for processing.

  Further, since the laser output is corrected by the water absorptivity at that time in the same time series as the output of the laser light 21, correction according to the situation such as the outside air temperature and humidity is also possible.

  Next, for example, when the laser beam 21 having the second wavelength λ2 output after the first wavelength λ1 passes through the correction plate 33, the second laser output control circuit 32 receives the amount of light received by the second photodetector 322. The (second reference absorbance Ir2) is converted into a received light voltage.

  The second laser output control circuit 32 calculates the difference between the received light voltages based on the held first reference absorbance Ir1 and second reference absorbance Ir2 in the second FMD, and generates a second difference voltage.

  In addition, a first differential voltage is generated in part of the laser light 21 having the second wavelength λ2 by the first laser output control circuit 31 so as to maintain a constant value. The first differential voltage and the second differential voltage are negatively added and output to the laser driver 63 as a drive signal for driving the laser diode LD. As a result, the laser output of the second wavelength λ2 output next time is corrected.

  The same applies to the laser light 21 having the third wavelength λ3. The difference between the first reference absorbance Ir1 and the third reference absorbance Ir3 is calculated based on the laser light having the first wavelength λ1, and the laser light having the third wavelength λ3 is calculated. The first differential voltage generated so as to make 21 constant and the second differential voltage for performing correction based on the absorbance of pure water are negatively added and output to the laser driver 63. As a result, the laser output of the third wavelength λ3 output next time is corrected.

  In this manner, the output of the laser light 21 having the first wavelength λ1, the second wavelength λ2, and the third wavelength λ3 and the correction thereof are repeated for a predetermined time.

  Note that the output order of the laser light 21 of each wavelength is not limited to that described here, and the reference wavelength is not limited to the above.

  The laser beam 21 is irradiated to the measurement site 25 at a predetermined irradiation angle and a beam aperture angle (for example, the lens numerical aperture NA is set to an appropriate value).

  The light receiving unit 12 receives the reflected light 22 from the dermis layer 252 of the measurement site 25 (first absorbance I1, second absorbance I2, and third absorbance I3) and converts them into an electrical signal. The electric signal is proportional to the intensity of the received light, is amplified by the amplifier 14, and is output to the A / D converter 62 of the control unit 6.

  As described above, in the present embodiment, the correction plate 33 having the same light absorption characteristics as pure water is selected. As a result, a laser output according to the light absorption rate of the correction plate 33 is obtained according to the wavelength. With this corrected laser output, the laser beam 21 is irradiated onto the measurement site 25 and the reflected light at that time is received. At this time, since the amount of light received is corrected by the absorbance of pure water, the amount of received light (the first absorbance I1, the second absorbance I2, and the third absorbance I3) is the absolute glucose absorbance. As required.

  Since the laser light 21 is output by switching the respective wavelengths in sequence, the absorption rate at that time is sampled. The control unit 6 performs differential processing on the basis of the signals based on the first absorbance I1, the second absorbance I2, and the third absorbance I3 output from the A / D conversion circuit 62 by the arithmetic processing unit 65, and performs the second derivative. The blood sugar level is calculated by a blood sugar level conversion function using these values as parameters.

  According to the optical measuring unit 1, since it is not necessary to have a correction plate as in the conventional system, the overall size can be reduced. Moreover, since the measurement is performed in the same time series, the error factor can be reduced, and as a result, the optical measurement unit 1 that measures the blood glucose level with high accuracy is realized.

  The optical measurement unit 1 of the present embodiment corrects the laser output by hardware in the laser output control unit 10. In the case of correction by calculation in terms of software, in order to absorb variations in the output of the laser diode LD, etc., the variation state is measured and recorded in production, or the output is the same value. It is necessary to make adjustments and so on.

  On the other hand, if the laser output is automatically adjusted by hardware, it is possible to save the trouble of measuring or adjusting the state of variation in advance.

The optical measurement unit 1 for measuring the blood sugar level has been described above as an example. However, the present invention is not limited to this. For example, the optical measurement unit that detects the fructose of a fruit can be implemented in the same manner, and similar effects can be obtained.

It is a circuit block diagram for demonstrating this invention. (A) The characteristic view which shows the relationship between a wavelength and an absorptivity for demonstrating this invention, (B) The characteristic view which shows the relationship between a wavelength and a laser output. It is (A) external view, (B) sectional drawing, (C) top view, (D) top view for demonstrating this invention. It is (A) schematic diagram for demonstrating the to-be-measured site | part of this invention, (B) It is sectional drawing. It is (A) top view and (B) sectional view for explaining the present invention. It is a characteristic view which shows the relationship between the wavelength and light absorption factor for demonstrating this invention. It is a circuit block diagram for demonstrating this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Optical measurement unit 2 Display part 3 Attachment 4 Power switch 5 Measurement start / stop button 6 Control part 7 Power supply part 8 External housing 10 Laser output control apparatus (laser output control part)
DESCRIPTION OF SYMBOLS 11 Light emission part 11a Condensing lens 12 Light receiving part 12a Condensing lens 14 Amplifier 17 Light-shielding plate 18 Switch 21 Laser light 22 Reflected light 25 Measured part 31 1st laser output control circuit 32 2nd laser output control circuit 33 Correction board 61 DSP
62 A / D conversion circuit 63 Laser driver (laser drive circuit)
65 Arithmetic Processing Unit 100 Blood Glucose Level Measuring Device 111 Light Source 112 First Photodetector (Photodetector)
251 Epidermis 252 Dermis layer 253 Subcutaneous tissue 311 First differential amplifier 312 Reference voltage setting circuit 313 First FMD
321 second differential amplifier 322 second photodetector (other photodetector)
323 2nd FMD
λ1 first wavelength λ2 second wavelength λ3 third wavelength I1 first absorbance I2 second absorbance I3 third absorbance i second derivative

Claims (10)

A laser output control device that controls the output of near-infrared laser light having a plurality of different emission wavelengths emitted from a light source,
A photodetector for receiving a part of the near-infrared laser light emitted from the light source;
A first laser output control circuit for controlling the output of the near-infrared laser light to be constant according to a light reception result of the photodetector;
A correction plate having a different amount of light absorption depending on the emission wavelength;
A second laser output control circuit for correcting the output of the near infrared laser light emitted from the light source based on the amount of absorption when a part of the near infrared laser light is transmitted through the correction plate;
A laser output control device comprising:   The second laser output control circuit includes another photodetector that receives the near-infrared laser light that has passed through the correction plate, and a signal from the other photodetector is received by the first laser output control circuit. The laser output control device according to claim 1, wherein a negative addition is performed on the laser output control device.   The second laser output control circuit is based on a difference between the absorption amount of the near infrared laser light at any one of the emission wavelengths transmitted through the correction plate and the absorption amount at the other emission wavelengths. The laser output control apparatus according to claim 1, wherein an output of the near-infrared laser light having the other emission wavelength is corrected.   The laser output control apparatus according to claim 1, wherein the correction plate has light absorption characteristics equivalent to pure water. An optical measurement unit that optically measures the sugar content at a measurement site,
A light source that individually outputs near-infrared laser light having an emission wavelength of the first wavelength, the second wavelength, and the third wavelength, respectively, and light detection that receives a part of the near-infrared laser light. A light-emitting unit having a device;
A light receiving unit for detecting the reflected light of the near-infrared laser beam reflected by the measurement site;
A first laser output control circuit that holds the output of the near-infrared laser light constant according to a light reception result of the photodetector;
A correction plate having a different amount of light absorption depending on the emission wavelength;
A second laser output control circuit that corrects the output of the near infrared laser light based on the amount of absorption when a part of the near infrared laser light is transmitted through the correction plate;
An optical measurement unit comprising:   The second laser output control circuit includes another photodetector that receives the near-infrared laser light that has passed through the correction plate, and a signal from the other photodetector is received by the first laser output control circuit. The optical measurement unit according to claim 5, wherein a negative addition is performed on the optical measurement unit.   The second laser output control circuit is based on a difference between the absorption amount of the near infrared laser light at any one of the emission wavelengths transmitted through the correction plate and the absorption amount at the other emission wavelengths. The optical measurement unit according to claim 5, wherein the output of the near-infrared laser light having the other emission wavelength is corrected.   An arithmetic processing unit that performs arithmetic processing, the arithmetic processing unit calculates a second differential value of the first absorbance, the second absorbance, and the third absorbance based on the reflected light received by the light receiving unit; 6. The optical measurement unit according to claim 5, wherein a sugar content at the measurement site is calculated from the second-order differential value and the first, second, and third absorbances.   The first wavelength, the second wavelength, and the third wavelength are wavelengths in the vicinity of each other, and the wavelengths become longer in this order. The third wavelength has a very large absorbance by pure water and almost only absorption by pure water. 6. The wavelength according to claim 5, wherein the second wavelength is a wavelength having a large absorbance due to the sugar, and the first wavelength is a wavelength having a small absorbance due to the sugar. Optical measurement unit.   6. The optical measurement unit according to claim 5, wherein the correction plate has light absorption characteristics equivalent to pure water.

Images