JP6433000B2 - Measuring apparatus and measuring method - Google Patents

Description

  The present invention relates to a technical field of a measurement apparatus and a measurement method for measuring, for example, information related to movement of a measurement target using light scattered in the measurement target.

  In a semiconductor laser used in this type of measuring apparatus, the band gap changes due to an increase in the temperature of the laser, so that the oscillation wavelength gradually changes to a long wavelength as the temperature increases. When the temperature continues to rise, the oscillation wavelength suddenly jumps to the wavelength having the maximum gain on the long wavelength side at a certain timing. This phenomenon is called mode hopping, and is known to cause a measurement error in a measuring apparatus using optical Doppler, for example.

  Patent Document 1 proposes a technique of controlling the temperature of a laser light source using a Peltier element in order to suppress the occurrence of the mode hop described above.

JP 2001-120509 A

  In the technique described in Patent Document 1 described above, a Peltier element that is a heat absorbing means is always operated. However, since the Peltier element consumes a large amount of power, it is not preferable to always operate it from the viewpoint of power saving. Moreover, since battery driving becomes difficult when the power consumption is large, there is a technical problem that an increase in cost and an increase in the size of the apparatus cannot be avoided.

  Examples of problems to be solved by the present invention include the above. It is an object of the present invention to provide a measurement apparatus and a measurement method that can suitably suppress the occurrence of mode hops.

  A first measuring apparatus for solving the above-described problems includes an irradiation unit that irradiates a laser beam to the measurement target, a light receiving unit that receives the laser beam scattered by the measurement target, and a mode of the irradiation unit Detection means for detecting a hop, and suppression means for suppressing the mode hop based on the output of the detection means.

  A second measuring apparatus for solving the above problems includes an irradiating means for irradiating a measurement target with laser light, a light receiving means for receiving the laser light scattered by the measurement target, and an output of the light receiving means. Comparing means for comparing the signal with a predetermined threshold, and control means for controlling the irradiation of the laser beam by the irradiating means based on the output of the comparing means.

  A first measurement method for solving the above problems includes an irradiation step of irradiating a measurement target with laser light, a light receiving step of receiving the laser light scattered by the measurement target, and a mode in the irradiation step A detection step of detecting a hop; and a suppression step of suppressing the mode hop based on an output in the detection step.

  A second measurement method for solving the above problems includes an irradiation step of irradiating a measurement target with laser light, a light reception step of receiving the laser light scattered by the measurement target, and an output in the light reception step. A comparison step of comparing the signal with a predetermined threshold value, and a control step of controlling the irradiation of the laser beam in the irradiation step based on the output in the comparison step.

It is a block diagram which shows the whole structure of the measuring apparatus which concerns on 1st Example. It is a circuit diagram which shows the specific structure of a light receiving element and an I-∨ converter. It is a block diagram which shows the specific structure of a mode hop determination part. It is a block diagram which shows the specific structure of the mode hop determination part which concerns on a 1st modification. It is a block diagram which shows the specific structure of the mode hop determination part which concerns on a 2nd modification. It is a conceptual diagram which shows the determination method in the mode hop determination part which concerns on a 2nd modification. It is a wave form diagram which shows the detection voltage at the time of mode hop generation | occurrence | production. It is a wave form diagram which shows the detection voltage after superimposing an AC component on a drive current. It is a block diagram which shows the whole structure of the measuring apparatus which concerns on 2nd Example. It is a block diagram which shows the whole structure of the measuring apparatus which concerns on 3rd Example.

<1>
The first measurement apparatus according to the present embodiment includes an irradiation unit that irradiates a measurement target with laser light, a light reception unit that receives the laser light scattered by the measurement target, and a mode hop of the irradiation unit. Detection means for detecting, and suppression means for suppressing the mode hop based on the output of the detection means.

  According to the first measuring apparatus according to the present embodiment, the laser beam is irradiated from the irradiation unit to the measurement target during the operation. The irradiation means is configured to include, for example, a semiconductor laser element or the like, and is disposed at a position where the measurement target can be efficiently irradiated with light when used. The measurement target is a fluid such as blood of a living body. However, the measurement target is not particularly limited, and may be other than fluid (for example, an individual) as long as it moves.

  The laser light emitted from the irradiating means is scattered (specifically reflected and transmitted) in the object to be measured and then received by the light receiving means. The light receiving means includes, for example, a photodiode and outputs an output signal corresponding to the received light. The output signal is used, for example, to calculate the moving speed of the measurement target. Specifically, for example, the moving speed of the object to be measured can be calculated based on a beat signal resulting from the Doppler shift of the laser light included in the output signal of the light receiving means.

  As described above, when the laser beam is irradiated and received, the detection unit detects the mode hop of the irradiation unit. In other words, the detection means monitors whether or not a mode hop has occurred in the irradiation means. The specific method of detecting the mode hop is not particularly limited, but can be detected using, for example, the intensity of the output signal.

  Here, in this embodiment, in particular, the mode hop of the irradiation unit is suppressed by the suppression unit. Note that the suppression unit does not execute the process for suppressing the mode hop at all times, but suppresses the mode hop based on the output of the detection unit. More specifically, the suppression unit executes a process for suppressing the mode hop when the detection unit detects a mode hop. Therefore, mode hops can be suppressed extremely efficiently.

  By the way, the method of suppressing the mode hop is not particularly limited, and the mode hop occurrence state or the state where the mode hop is likely to occur is escaped or the frequency of the mode hop occurring is determined. What is necessary is just to perform the various processes for reducing suitably.

  As described above, according to the measuring apparatus according to the present embodiment, it is possible to suitably perform measurement while suppressing mode hops.

<2>
In one aspect of the first measurement apparatus according to the present embodiment, the detection unit detects the mode hop when the intensity of the output signal of the light receiving unit exceeds a predetermined threshold.

  According to this aspect, it is only necessary to compare the output signal with the predetermined threshold value, so that the mode hop can be detected easily and accurately. The “predetermined threshold value” is a value for discriminating the strength of the output signal when the mode hop is occurring and the strength of the output signal when the mode hop is not occurring. It can be determined by simulation or the like.

<3>
In the aspect in which the mode hop is detected using the predetermined threshold described above, the detection unit may change the predetermined threshold according to the intensity of the output signal in the past.

  In this case, since the predetermined threshold is changed according to the intensity of the past output signal (in other words, a normal output signal in which no mode hop has occurred), the mode hop can be detected more accurately.

  For example, the predetermined threshold value may be changed greatly when the intensity of the past output signal is relatively large, and may be changed small when the intensity of the past output signal is relatively small.

<4>
In another aspect of the measuring apparatus according to this embodiment, the suppression unit suppresses the mode hop by changing a drive current of the irradiation unit.

  According to this aspect, it is possible to reliably suppress the mode hop by changing the driving current of the irradiating means so that the mode hop is suppressed. Note that an AC component may be placed on the driving current of the irradiation unit so that a single mode hop is generated with a long period that does not easily affect the measurement result.

<5>
In another aspect of the measuring apparatus according to this embodiment, the suppression unit suppresses the mode hop by changing the temperature of the irradiation unit.

  According to this aspect, it is possible to reliably suppress mode hops by changing the temperature of the irradiation means using a Peltier element or the like, for example.

<6>
In another aspect of the measuring apparatus according to this embodiment, the suppression unit suppresses the mode hop by changing a refractive index of a liquid crystal window provided between the irradiation unit and the measurement target. .

  According to this aspect, by changing the refractive index of the liquid crystal window, it is possible to suppress the return light from the measurement target from entering the irradiation unit. Therefore, the occurrence of mode hops due to the incident return light can be reliably suppressed.

<7>
In another aspect of the measuring apparatus according to the present embodiment, the suppression unit suppresses the mode hop when the mode hop is continuously detected for a predetermined time or more.

  According to this aspect, when the mode hop is not continuously detected for a predetermined time or more, the mode hop is not suppressed. Therefore, it is possible to prevent the suppression process from being executed even for mode hops that need not be suppressed. It should be noted that the “predetermined time” according to this aspect may be set as a time that affects the measurement result due to the continuous generation of mode hops.

<8>
In another aspect of the measuring apparatus according to this embodiment, the suppression unit suppresses the mode hop when the number of occurrences of the mode hop within a predetermined period is equal to or greater than a predetermined number.

  According to this aspect, the mode hop is not suppressed when the mode hop has not occurred a predetermined number of times within the predetermined period. Therefore, it is possible to prevent the suppression process from being executed even for mode hops that need not be suppressed. The “predetermined period” and “predetermined number of times” according to this aspect may be set as values corresponding to the frequency of occurrence of mode hops that affect the measurement result.

<9>
In another aspect of the measuring apparatus according to the present embodiment, an output unit that processes and outputs an output signal of the light receiving unit, and an output before the mode hop is detected when the mode hop is detected. Output maintaining means for controlling the output means to maintain.

  According to this aspect, when the mode hop is detected, the output before the mode hop is detected is maintained in the output means. For this reason, even if the output of the output means becomes an inappropriate value due to the mode hop, it is possible to continue outputting an appropriate value. Note that the output maintenance of the output unit may be canceled when the mode hop is no longer detected by the suppression process by the suppression unit, for example.

<10>
In another aspect of the measuring apparatus according to the present embodiment, the light receiving means includes a plurality of light receiving elements.

  According to this aspect, high sensitivity can be realized by the plurality of light receiving elements, but the measurement result may still be affected by a change in the intensity of light incident on each of the plurality of light receiving elements due to the mode hop. For this reason, also in this aspect, the effect of eliminating the influence on the measurement result is obtained by suppressing the mode hop, which is very advantageous in practice.

<11>
The second measuring apparatus according to the present embodiment includes an irradiating unit that irradiates a measurement target with laser light, a light receiving unit that receives the laser light scattered by the measurement target, and an output signal of the light receiving unit. Comparing means for comparing with a predetermined threshold value, and control means for controlling the irradiation of the laser beam by the irradiating means based on the output of the comparing means.

  According to the second measuring apparatus of the present embodiment, during the operation, the comparison means compares the output signal of the light receiving means with a predetermined threshold value. The “predetermined threshold value” here distinguishes between an output signal in a state where a phenomenon (typically mode hop) that may affect the measurement result has occurred and an output signal in a state where it has not occurred. For example, it can be determined by a prior simulation or the like.

  Here, when the laser beam is irradiated by the irradiation unit described above, the irradiation is controlled by the control unit. Specifically, the control unit controls the irradiation of the laser beam by the irradiation unit based on the output of the comparison unit. Here, “controlling the laser beam irradiation” includes directly controlling the operation of the laser beam irradiation unit (for example, driving current control), and the laser beam irradiation state is This is a broad concept including indirect control that changes (for example, temperature control of the irradiation means, control of an optical member that guides laser light, and the like). By performing such control, it becomes possible to irradiate laser light in an appropriate state.

  As described above, according to the second measurement apparatus according to the present embodiment, even when a phenomenon that may affect the measurement result occurs in the irradiation unit, such as a mode hop, the occurrence occurs. It is possible to perform measurement while suitably suppressing the above.

  Note that the second measurement apparatus according to the present embodiment can also adopt various aspects similar to the various aspects of the first measurement apparatus according to the present embodiment described above.

<12>
The first measurement method according to the present embodiment includes an irradiation step of irradiating a measurement target with laser light, a light reception step of receiving the laser light scattered by the measurement target, and a mode hop in the irradiation step. A detecting step for detecting, and a suppressing step for suppressing the mode hop based on an output in the detecting step.

  According to the first measurement method of the present embodiment, it is possible to suitably perform the measurement while suppressing the mode hop, similarly to the first measurement apparatus according to the present embodiment described above.

  In addition, also in the 1st measuring method which concerns on this embodiment, it is possible to take the various aspects similar to the various aspects in the 1st measuring apparatus which concerns on this embodiment mentioned above.

<13>
The second measurement method according to the present embodiment includes an irradiation step of irradiating a measurement target with laser light, a light reception step of receiving the laser light scattered by the measurement target, and an output signal in the light reception step. A comparison step for comparing with a predetermined threshold value, and a control step for controlling the laser beam irradiation in the irradiation step based on the output in the comparison step.

  According to the second measurement method of the present embodiment, similar to the second measurement apparatus according to the present embodiment described above, a phenomenon that may affect the measurement result occurs in the irradiator means. However, it is possible to perform measurement while suitably suppressing the occurrence.

  In the second measurement method according to the present embodiment, it is possible to adopt various aspects similar to the various aspects in the second measurement apparatus according to the present embodiment described above.

  The operation and other gains of the measuring apparatus and measuring method according to the present embodiment will be described in more detail in the following examples.

  Hereinafter, embodiments of the measuring apparatus and the measuring method will be described in detail with reference to the drawings. In the following, a case where the measurement device according to the present invention is configured as a blood flow measurement device that measures blood flow will be described as an example.

<First embodiment>
A measuring apparatus according to the first embodiment will be described with reference to FIGS.

<Overall configuration>
First, the overall configuration of the measuring apparatus according to the first embodiment will be described with reference to FIG. FIG. 1 is a block diagram showing the overall configuration of the measuring apparatus according to the first embodiment.

  In FIG. 1, the measuring apparatus according to the present embodiment includes a laser driving unit 110, a semiconductor laser 120, a light receiving element 130, an IV conversion unit 140, a signal processing unit 150, a mode hop determination unit 160, The mode hop suppression processing unit 170 is provided.

  The laser driver 110 generates a current for driving the semiconductor laser 120.

  The semiconductor laser 120 is a specific example of “irradiation means”, and irradiates the measurement target 200 (for example, skin of a living body) with laser light corresponding to the drive current generated in the laser drive unit 110. .

  The light receiving element 130 is a specific example of “light receiving means”, and receives scattered light scattered by the blood 200 out of the laser light emitted from the semiconductor laser 120. The light receiving element 130 outputs a detection current according to the intensity of the received scattered light.

  The IV converter 140 converts the detection current output from the light receiving element 130 into a voltage and outputs a detection voltage.

  The signal processing unit 150 includes, for example, an amplifier, an A / D converter, a calculation unit, and the like. The signal processing unit 150 performs various types of signal processing on the detected voltage and outputs information related to the blood flow that is the measurement target 200 (for example, blood flow velocity and blood flow rate).

  The mode hop determination unit 160 is a specific example of “detection means”. Based on the input detection voltage, it is determined whether or not a mode hop has occurred in the semiconductor laser 120. In addition, when the mode hop determination unit 160 determines that a mode hop has occurred, the mode hop determination unit 160 outputs a signal permitting execution of the processing in the mode hop suppression processing unit 170 and also sends a previous value hold signal to the signal processing unit 150. (That is, a command for maintaining the immediately preceding output). The specific configuration of the mode hop determination unit 160 will be described in detail later.

  The mode hop suppression processing unit 170 is a specific example of “suppression unit”, and executes suppression processing for suppressing mode hops according to the determination result in the mode hop determination unit 160. The suppression process will be described in detail later.

<Description of operation>
Below, operation | movement of the measuring apparatus mentioned above is demonstrated in detail with reference to FIG.

  In FIG. 1, during the operation of the measuring apparatus according to the present embodiment, first, the laser driving unit 110 generates a specified operating current that is equal to or higher than the threshold current of the semiconductor laser 120 and supplies it to the semiconductor laser 120. Thereby, the semiconductor laser 120 oscillates.

  The semiconductor laser 120 is fixed to the measurement target 200 with a clip or the like (not shown) so as to emit laser light to the measurement target 200. When the measurement target 200 is living body skin, the irradiated laser light becomes scattered light scattered by a skin tissue that is a fixed object and scattered light scattered by red blood cells in a capillary that is a moving object, Both of them are received by the light receiving element 130.

  Here, the scattered light scattered by the skin tissue is the reference light, and the scattered light scattered by the red blood cells is scattered light that has caused an optical Doppler shift corresponding to the moving speed of the red blood cells. These two scattered lights cause interference due to the coherence of the laser light. The light receiving element 130 generates a detection current corresponding to the intensity of the optical beat signal as a result of this interference.

  Similar to the semiconductor laser 120, the light receiving element 130 is fixed to the measurement target 200 with a clip or the like (not shown) so as to receive scattered light from the measurement target 200. The detection current corresponding to the optical beat signal detected by the light receiving element 130 is converted into a current voltage by the IV converter 140 and output as a detection voltage.

  Hereinafter, specific configurations and operations of the light receiving element 130 and the IV converter 140 will be described with reference to FIG. FIG. 2 is a circuit diagram showing a specific configuration of the light receiving element and the I-Ｉ converter.

  In FIG. 2, the light receiving element 130 according to the present embodiment includes two light receiving elements 130a and 130b. The light receiving elements 130a and 130b are configured as, for example, photodetectors using PIN type semiconductors. The light receiving elements 130a and 130b have cathodes connected to each other and are connected in series in opposite directions. If comprised in this way, DC component can be suppressed and AC component which is a signal component can be detected efficiently.

  Specifically, a current component corresponding to a steady light component included in the input light (hereinafter appropriately referred to as a “DC (direct current) component”) among currents output from each of the light receiving elements 130a and 130b is reduced or removed. Thus, a current mainly including a current component corresponding to the signal light component included in the input light (hereinafter appropriately referred to as “AC (alternate current) component”) can be output as the detection current. That is, the DC component of the output current of the light receiving element 130a and the DC component of the current output of the light receiving element 130b can be canceled, and a detection current mainly including an AC component corresponding to the signal light component included in the input light is obtained. Can be output.

  For example, if the detection current of the light receiving element 130a is Id1 and the detection current of the light receiving element 130b is Id2, the polarity is reversed and the series connection is made.

Idt = Id2-Id1 (1)
Further, since the scattered light received by the light receiving element 130a and the scattered light received by the light receiving element 130b are different from each other, if the wavelength of the light is used as a reference length, the signal is approximately uncorrelated. Therefore, the intensity of the optical beat signal, which is a signal component, is multiplied by √2 by subtraction.

  On the other hand, since the DC current is canceled out by subtraction, saturation can be prevented even when the detection sensitivity of the transimpedance amplifiers Amp1 and Amp2 is set high. Specifically, the resistance values of the feedback resistors Rf1 and Rf2 can be set high, and the current-voltage conversion sensitivity is improved. As a result, a high detection S / N (Signal-to-Noise ratio) is obtained.

  The non-inverting input terminals of Amp1 and Amp2 are grounded. Due to the negative feedback action of the feedback resistors Rf1 and Rf2 of Amp1 and Amp2, the non-inversion terminal and the inversion terminal are in an imaginary shoot state and have approximately the same potential. Therefore, the anode of the light receiving element 130a and the anode of the light receiving element 130b are at the same potential, and the P light receiving element 130a and the light receiving element 130b operate in a so-called power generation mode. With this power generation mode, dark current is suppressed, and noise increase due to dark current fluctuation can be suppressed.

  The detection voltage Vd1 of Amp1 and the detection voltage Vd2 of Amp2 are as shown in the following equations (2) and (3).

Vd1 = Rf1 · Idt (2)
Vd2 = Rf2 · (−Idt) (3)
Amp3 differentially amplifies the detection voltage of Amp1 and Amp2 and outputs it as Vout. This differential amplification removes common mode noise such as power supply noise and hum.

  Here, when the resistance value is set such that Ra1 = Ra2 = Ra and Rb1 = Rb2 = Rb, Vout is expressed by the following formula (4).

Vout = (Rb / Ra) (Vd1-Vd2) (4)
From the above mathematical formulas (2), (3), and (4), when the resistance value is set so that Rf1 = Rf2 = Rf, Vout is represented by the following mathematical formula (5).

Vout = 2Rf (Rb / Ra) Idt (5)
From the above equation (5), it can be seen that the detection voltage Vout corresponding to the intensity of the optical beat signal as the signal component can be obtained.

  Returning to FIG. 1, the detection voltage output from the IV converter 140 is input to the signal processing unit 150 and subjected to various signal processing. For example, the detection voltage is amplified by an amplifier and quantized by an A / D converter to become digital data. Then, frequency analysis processing such as FFT (Fast Fourier Transform) is executed on the data, and information on blood flow is output as a result.

  On the other hand, the detected voltage output from the IV converter 140 is also input to the mode hop determination unit 160. Hereinafter, a specific configuration and operation of the mode hop determination unit 160 will be described in detail with reference to FIG. FIG. 3 is a block diagram showing a specific configuration of the mode hop determination unit.

  As shown in FIG. 3, the mode hop determination unit 160 includes a comparator 161 and a control unit 162.

  The comparator 161 compares the detected voltage with the predetermined upper threshold value and lower threshold value input from the control unit 162, and outputs the comparison result to the control unit 162. The upper threshold value and the lower threshold value are set as values corresponding to the upper limit value and the lower limit value of the detected power when no mode hop occurs, for example.

  The control unit 162 determines that a mode hop has occurred when it is determined that the detected voltage is greater than the upper threshold or when it is determined that the detected voltage is smaller than the lower threshold. When determining that a mode hop has occurred, the control unit 162 outputs a suppression process permission signal to the mode hop suppression processing unit 170. Thereby, the mode hop suppression processing unit 170 executes a suppression process for suppressing the mode hop.

  When it is determined that a mode hop has occurred, the control unit 162 outputs a previous value hold signal to the signal processing unit 150. For this reason, even when the output of the signal processing unit 150 becomes an inappropriate value due to the mode hop, an appropriate value (that is, a value before the mode hop occurs) is continuously output. be able to.

  Note that the configuration of the mode hop determination unit 160 described above is merely an example, and various modes can be adopted as long as the occurrence of the mode hop can be determined.

  Below, the modification of the mode hop determination part 160 is demonstrated with reference to FIGS. 4-6. FIG. 4 is a block diagram showing a specific configuration of the mode hop determination unit according to the first modification. FIG. 5 is a block diagram illustrating a specific configuration of the mode hop determination unit according to the second modification, and FIG. 6 is a conceptual diagram illustrating a determination method in the mode hop determination unit according to the second modification. .

  As illustrated in FIG. 4, the mode hop determination unit 160b according to the first modification includes an A / D converter 163, a memory 164, and a threshold value calculation unit 165 in addition to the comparator 161 and the control unit 162. Configured.

  The detection voltage input to the mode hop determination unit 160b is first digitally converted by the A / D converter 163 and output to the comparator 161 and the memory 164, respectively.

  The memory 164 is configured to be able to store a detection voltage for a preset period, and outputs the stored detection voltage value to the threshold value calculation unit 165.

  The threshold output unit 165 calculates the upper threshold and the lower threshold based on the value of the immediately preceding detection voltage stored in the memory 164 (that is, the value in the state where no mode hop has occurred). Thus, if the threshold value is changed based on the value of the past detection voltage, the occurrence of the mode hop can be determined more appropriately.

  As shown in FIG. 5, the mode hop determination unit 160 c according to the second modified example includes an envelope detector 166 and an LPF unit 167 in addition to the comparator 161 and the control unit 162.

  The detection voltage input to the mode hop determination unit 160 c is first input to the envelope detector 166 and then input to the comparator 161 via the LPF unit 167.

  In FIG. 6, it is assumed that a detection voltage that causes a mode hop with a high frequency is input to the mode hop determination unit 160c, for example, as in the left waveform in the figure. In this case, the output of the envelope detector 166 continues to take a relatively high value, and the output of the LPF unit 167 temporarily exceeds the upper threshold value. Therefore, in the example shown by the left waveform in the figure, it is determined that the period in which the output of the LPF unit 167 exceeds the upper threshold is the period in which the mode hop occurs.

  On the other hand, it is assumed that a detection voltage in which mode hops are generated at a low frequency as shown in the right waveform in FIG. In this case, the output of the envelope detector 166 is sufficiently small between the mode hops, and the output of the LPF unit 167 does not exceed the upper threshold. Therefore, in the example shown by the waveform on the right side in the figure, it is determined that there is no period in which the mode hop occurs.

  Here, if mode hops occur at a high frequency, it is highly likely that the measurement results will be adversely affected.If mode hops occur at a low frequency, the effect on the measurement results may also be affected. It is small and may not be a problem. On the other hand, according to the mode hop determination unit 160c using the envelope detector 166 described above, it is determined that a mode hop is generated only when the mode hop occurs frequently enough to cause inconvenience. Is done. Therefore, it is possible to avoid that the suppression process is executed even for mode hops that do not need to be suppressed.

  Next, the mode hop suppression processing by the mode hop suppression processing unit 170 will be described with reference to FIGS. FIG. 7 is a waveform diagram showing the detected voltage when the mode hop occurs. FIG. 8 is a waveform diagram showing the detected voltage after the AC component is superimposed on the drive current.

  As shown in FIG. 7, it is assumed that mode hops occur frequently and noise is generated intensively in the detected voltage. In such a case, the suppression processing permission signal is input to the mode hop suppression processing unit 170 from the mode hop determination unit 160. Then, the mode hop suppression processing unit 170 that has received the suppression process permission signal outputs a drive current control signal to the laser drive unit 110. That is, the driving current for outputting the laser light is controlled to suppress the occurrence of mode hops. Specifically, the mode hop suppression processing unit 170 performs control so as to superimpose an AC component of a predetermined period on the drive current (for example, superimpose a 100 m∨ signal at 10 Hz).

  As shown in FIG. 8, when an AC component is superimposed on the drive current, noise in the detection voltage is also generated at a relatively long and stable period. That is, mode hops that have occurred intensively occur with a long period corresponding to the superimposed AC component. Mode hops are likely to adversely affect the measurement when they occur intensively. However, when the mode hops occur in a stable state as in the example shown in the figure, the influence on the measurement is small. Therefore, by superimposing the AC component on the drive current, it is possible to realize a suitable measurement in which the influence of the mode hop is suppressed.

  As described above, according to the measurement apparatus of the first embodiment, it is possible to suppress the occurrence of mode hopping of the semiconductor laser 120 and perform more accurate blood flow measurement. In addition, in the measurement apparatus according to the present embodiment, since the suppression process is executed only when a mode hop occurs, the mode hop can be suppressed extremely efficiently.

<Second embodiment>
Next, a measuring apparatus according to the second embodiment will be described with reference to FIG. FIG. 9 is a block diagram showing the overall configuration of the measuring apparatus according to the second embodiment.

  The second embodiment is different from the first embodiment described above only in part of the configuration and operation, and many parts are the same as the first embodiment. For this reason, below, a different part from 1st Example is demonstrated in detail, and description is abbreviate | omitted suitably about the overlapping part.

  In FIG. 9, in the measuring apparatus according to the second example, the laser driving unit 110 is provided with a Peltier element 300 for controlling the temperature. And the mode hop suppression process part 170b which concerns on 2nd Example suppresses generation | occurrence | production of a mode hop by controlling the Peltier device 300. FIG.

  Specifically, the mode hop suppression processing unit 170b receives the Peltier element control signal when the suppression processing permission signal is input from the mode hop determination unit 160 (that is, when it is determined that a mode hop has occurred). And the heat absorption of the laser driving unit 110 by the Peltier device 300 is performed. In this way, the temperature of the laser driving unit 110 decreases, and mode hops that have occurred due to the temperature increase are suppressed.

  As described above, according to the measuring apparatus according to the second embodiment, the generation of mode hops in the semiconductor laser 120 can be suppressed and more accurate blood flow measurement can be performed as in the first embodiment. Is possible.

<Third embodiment>
Next, a measuring apparatus according to the third embodiment will be described with reference to FIG. FIG. 10 is a block diagram showing the overall configuration of the measuring apparatus according to the third embodiment.

  Note that the third embodiment differs from the first and second embodiments described above only in part of the configuration and operation, and many parts are the same as in the first and second embodiments. For this reason, below, a different part from 1st and 2nd Example is demonstrated in detail, and description shall be abbreviate | omitted suitably about the overlapping part.

  In FIG. 10, in the measuring apparatus according to the third example, a liquid crystal 400 is provided between the semiconductor laser 120 and the measurement target 200. The mode hop suppression processing unit 170c according to the third embodiment controls the liquid crystal 400 to suppress the occurrence of mode hops.

  Specifically, the mode hop suppression processing unit 170c outputs a liquid crystal control signal when a suppression processing permission signal is input from the mode hop determination unit 160 (that is, when it is determined that a mode hop has occurred). Thus, the refractive index of the liquid crystal 400 is changed to realize an environment in which the return light from the measurement target 200 does not enter the semiconductor laser 120. In this way, the mode hop that has occurred due to the return light entering the semiconductor laser 120 is suppressed.

  As described above, according to the measurement apparatus of the third embodiment, as in the first and second embodiments, the generation of mode hops in the semiconductor laser 120 is suppressed and more accurate blood flow measurement is performed. Is possible.

  The present invention is not limited to the above-described embodiment, and can be appropriately changed without departing from the spirit or idea of the invention that can be read from the claims and the entire specification. The method is also included in the technical scope of the present invention.

DESCRIPTION OF SYMBOLS 110 Laser drive part 120 Semiconductor laser 130 Light receiving element 140 IV conversion part 150 Signal processing part 160 Mode hop determination part 161 Comparator 162 Control part 163 A / D converter 164 Memory 165 Threshold calculation part 166 Envelope detector 167 LPF part 170 Mode Hop Suppression Processing Unit 200 Measurement Object 300 Peltier Element 400 Liquid Crystal

Claims (10)

Irradiating means for irradiating the measurement target with laser light;
A light receiving means for receiving the laser light scattered by the measurement object;
Detecting means for detecting a mode hop of the irradiation means;
Suppression means for suppressing the mode hop when the mode hop is detected by the detection means , and
The measuring device detects the mode hop when the intensity of the output signal of the light receiving unit exceeds a predetermined threshold . The measurement apparatus according to claim 1 , wherein the detection unit changes the predetermined threshold according to the intensity of the output signal in the past. The suppressing means, by changing the drive current of the illumination means, the measuring device according to claim 1 or 2, characterized in that to suppress the mode hopping. Irradiating means for irradiating the measurement target with laser light;
A light receiving means for receiving the laser light scattered by the measurement object;
Detecting means for detecting a mode hop of the irradiation means;
Suppression means for suppressing the mode hop when the mode hop is detected by the detection means;
With
The suppressing means, by varying the temperature of the irradiation unit, measurement unit you characterized by inhibiting the mode hopping. Irradiating means for irradiating the measurement target with laser light;
A light receiving means for receiving the laser light scattered by the measurement object;
Detecting means for detecting a mode hop of the irradiation means;
Suppression means for suppressing the mode hop when the mode hop is detected by the detection means;
With
The suppressing means, said irradiation means by varying the refractive index of the liquid crystal window provided between the object to be measured, measurement apparatus you characterized by inhibiting the mode hopping. Irradiating means for irradiating the measurement target with laser light;
A light receiving means for receiving the laser light scattered by the measurement object;
Detecting means for detecting a mode hop of the irradiation means;
Suppression means for suppressing the mode hop when the mode hop is detected by the detection means;
With
The suppressing means, when the mode hopping has been continuously detected for a predetermined time or more, measurement equipment you characterized by inhibiting the mode hopping. Irradiating means for irradiating the measurement target with laser light;
A light receiving means for receiving the laser light scattered by the measurement object;
Detecting means for detecting a mode hop of the irradiation means;
Suppression means for suppressing the mode hop when the mode hop is detected by the detection means;
With
The suppressing means, when the number of occurrences of the mode hopping in the predetermined time period is not less than a predetermined number of times, measurement device you characterized by inhibiting the mode hopping. Irradiating means for irradiating the measurement target with laser light;
A light receiving means for receiving the laser light scattered by the measurement object;
And a control unit that superimposes an AC component on the drive current of the irradiating unit when the output signal of the light receiving unit is higher than a predetermined threshold value. Irradiating means for irradiating the measurement target with laser light;
A light receiving means for receiving the laser light scattered by the measurement object;
Detecting means for detecting a mode hop of the irradiation means;
Suppression means for suppressing the mode hop based on the output of the detection means;
An output means for processing and outputting the output signal of the light receiving means so as to maintain the output before the mode hop is detected when the mode hop is detected by the detecting means;
A measuring apparatus comprising: An irradiation step of irradiating a measurement target with laser light;
A light receiving step for receiving the laser light scattered by the measurement object;
A detection step of detecting a mode hop in the irradiation step;
A step of suppressing the mode hop when the mode hop is detected by the detection step , and
In the measuring step, the mode hop is detected when the intensity of the output signal of the light receiving means exceeds a predetermined threshold .

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