TW202134607A - Linearity correction method of optical measuring device, optical measuring method and optical measuring device - Google Patents

Abstract

High-precision linear correction of optical measurement devices using CMOS linear image sensors. Provided is a linear correction method for an optical measurement device with a CMOS linear image sensor, which includes the following steps: an exposure step, changing the exposure time, so that reference light of constant intensity is sequentially incident on the focused light-receiving element of the CMOS linear image sensor ; The measurement value obtaining step is to sequentially obtain the measurement value of the light-receiving element of interest; the actual linear error calculation step is to sequentially calculate the difference between the linear value obtained based on the exposure time corresponding to the measurement value and the measurement value An actual linearity error; and a fitting step, for each of the actual linearity errors, a fitting of a first function indicating the first linearity error is performed.

Description

Linear correction method of optical measuring device, optical measuring method and optical measuring device

The invention relates to a linear correction method of an optical measuring device, an optical measuring method and an optical measuring device.

CCD (Charged-coupled devices) linear image sensors can be used in optical measurement equipment (such as multi-channel spectrometers, etc.). The specific wavelength portion of the measurement light dispersed by the diffraction grating is incident on each light receiving element arranged in the CCD linear image sensor, and an electric signal corresponding to the light intensity is output from these light receiving elements. However, although the CCD linear image sensor generally has the advantage of high sensitivity, its structure tends to be complicated and expensive. [Patent Literature]

[Patent Document 1] Japanese Patent Laid-open No. 5-15628

CMOS (Complementary Metal Oxide Semiconductor) linear image sensors are also called electronic parts with the same functions as CCD linear image sensors. The CMOS linear image sensor has the advantages of extremely simple structure, low cost, low power consumption, and easy speed improvement.

However, the CMOS linear image sensor has the disadvantage that the linearity is lower than that of the CCD linear image sensor. That is, there is a disadvantage that even if light having an intensity of α times is incident on each light receiving element arranged in the CMOS linear image sensor, a measurement value of α times is not necessarily obtained. Therefore, there is a problem that the intensity of the light to be measured cannot be determined immediately based on the original output value of the CMOS linear image sensor. Therefore, when a CMOS linear image sensor is used as an optical measurement device, high-precision linear correction is required.

The present invention was invented in view of the above-mentioned problems, and its purpose is to provide a linear correction method capable of linearly correcting an optical measurement device using a CMOS linear image sensor with high precision, an optical measurement method using the method, and Optical measuring device.

In order to solve the above problems, the linear correction method according to the present invention is a linear correction method for an optical measuring device, which is characterized by a CMOS linear image sensor, and includes the following steps: In the exposure step, the exposure time is changed so that the reference light of constant intensity is incident on the focused light-receiving element of the CMOS linear image sensor in sequence; The measurement value obtaining step is to sequentially obtain the measurement value of the concerned light-receiving element; The actual linear error calculation step sequentially calculates the actual linear error indicating the difference between the linear value obtained based on the exposure time corresponding to the measured value and the measured value; and In a fitting step, for each of the actual linear errors, fitting of a first function indicating the first linear error is performed.

Here, the first function may be a quadratic function.

In addition, the fitting step may determine the variable parameter of the first function by using a least square method of the objective function indicating the total amount of the difference between each actual linear error and the first linear error. The objective function may include a term indicating the difference between the first linear error and the actual linear error corresponding to each of the measured values. These terms can be weighted by the amount of deviation that indicates the deviation of each of the measured values.

In addition, it may further include an exposure time correction step of performing exposure time correction on the measured value corrected by the first function.

In addition, the exposure time correction step may apply a second function approaching a predetermined value as the exposure time becomes longer to the measured value corrected by the first function to perform the exposure time correction.

Here, the second function can be a fractional function.

In addition, the measurement value may be obtained based on the difference between the first output value of the light-receiving element of interest when the reference light is incident and the second output value of the light-receiving element of interest when the reference light is not incident.

In addition, the fitting step may perform the fitting using the measurement value obtained based on the first output value above a predetermined threshold.

In addition, the CMOS linear image sensor may include a non-attention light-receiving element, and the non-attention light-receiving element has no light incident during the time when the reference light is incident on the attention light-receiving element. At this time, the linear correction method may further include a basic correction value calculation step that calculates the basic value that makes the measured value of the non-attention light-receiving element close to zero when the reference light is incident on the light-receiving element of interest. Correction value. The measurement value obtaining step may sequentially obtain the measurement value corrected by the basic correction value.

According to the optical measurement method of the present invention, the linear correction method of the optical measurement device described in any one of the above is used. When the measurement light is incident on the light-receiving element of interest, the measured value of the light-receiving element of interest is corrected based on the first function .

There are a plurality of light-receiving elements of interest. In addition, when the measurement light is incident on each light-receiving element of interest, the measurement value of the light-receiving element of interest can be corrected based on a function representing the first function obtainable for each of the light-receiving elements of interest.

The optical measuring device according to the present invention includes: A memory device, which memorizes the correction parameter corresponding to the first function obtained by the linear correction method described in any one of the above; and a correction device, which uses the correction parameter when the measuring light is incident on the light-receiving element of interest To correct the measured value of the light-receiving element of interest.

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

Fig. 1 shows a structural diagram of an optical measuring device according to an embodiment of the present invention. The optical measuring device 10 measures the light intensity of each wavelength, that is, the spectrum, by dispersing light emitted from a sample such as the light source 11. The spectrum can be directly used as the optical characteristic information of the light source 11, for example. In addition, when the sample is a thin film, the spectrum of the reflected light from the thin film can be used, for example, to calculate the thickness of the thin film.

The light emitted from the sample such as the light source 11 is applied to the slit 12 provided in the optical measuring device 10. The slit 12 has, for example, an elongated rectangular opening. The cut-off filter 13 is provided on the back surface of the slit 12 as necessary. The cut-off filter 13 blocks light whose wavelength is outside the measurement range. The measurement light that has passed through the cut-off filter 13 reaches the collimator lens 14. The collimator lens 14 is, for example, a concave mirror with a constant curvature, which reflects and converts the measurement light passing through the slit 12 into parallel light, and irradiates the diffraction grating 15 with the parallel light.

The diffraction grating 15 diffracts each wavelength component of the light emitted from the collimator lens 14 in a direction corresponding to the wavelength. The diffraction grating 15 is, for example, a reflection type diffraction grating, and a plurality of grooves may be provided on the reflective surface, and the plurality of grooves extend in the same direction as the opening of the slit 12. As a result, the diffraction grating 15 reflects each wavelength component of the light emitted from the collimator lens 14 so that its intensity increases in a direction corresponding to the wavelength.

The focusing mirror 16, for example, a concave mirror having a constant curvature, reflects the light of each wavelength component diffracted by the diffraction grating 15 and concentrates it on each light receiving element arranged in the CCD linear image sensor 17. As shown schematically in FIG. 2, the CCD linear image sensor 17 includes a plurality of (here, 1024) light receiving elements 17-0 to 17-1023, which are spaced at equal intervals in the diffraction direction of the diffraction grating 15 Configuration. Each light-receiving element 17-i includes a photodiode that stores electric charge that increases with the intensity and time of the received light, and outputs a value corresponding to the amount of stored electric charge. Each light receiving element 17-i is assigned a wavelength according to its arrangement order, and outputs the intensity of the optical component to which the wavelength is assigned. Here, the subscript i represents the wavelength channel (0~1023).

The output value of each light receiving element 17-i is input to the calculation unit 18 mainly composed of a computer. The calculation section 18 applies various corrections such as linear correction to each output value to obtain a measurement value of the light intensity of each wavelength component.

The CMOS linear image sensor 17 has the disadvantage of poor linearity as described above. Therefore, in the optical measurement device 10, various corrections are made to the original output value of the light receiving element 17-i of the CMOS linear image sensor 17 to achieve linearity. That is, the conversion based on the correction parameter is applied to the original output value of each light receiving element 17-i, and is used as a measurement value. The measured value thus obtained has the so-called linearity, when the light intensity increases by α times, it also increases by α times.

Figures 3 and 4 show the flow chart of the method of calculating the linear correction parameters. Here, the correction of the measurement value performed by the CMOS linear image sensor 17 includes the following three corrections: 1) the first correction to prevent the measurement value from becoming less than zero in the short wavelength region; 2) in the region with high light intensity Realize the linear second correction in the middle; 3) Realize the three linear third corrections in the area with low light intensity. In order to sequentially apply these three corrections to the original output value of each light receiving element 17-i. The processing shown in FIGS. 3 and 4 is executed by a computer such as the calculation unit 18.

In order to obtain the correction parameters for the first correction, the second correction, and the third correction, first, in the optical measuring device 10, each light receiving element 17 of the CMOS linear image sensor 17 is in a position where no light enters from the slit 12 In the state in the device, the original output value Ai0 of each light receiving element 17-i of the CMOS linear image sensor 17 is obtained (S101).

Next, a reference light having a constant light intensity such as white light from a halogen lamp is incident from the slit 12 into the inside of the device, and while increasing the exposure time t from 0 to tmax, a CMOS linear image sensor 17 is obtained. The original output value Ai of each light receiving element 17-i (S102). When the exposure time t changes from ts to ts to tmax, the output value Ai of each wavelength channel i contains the value of tmax/ts (here tmax=10000).

Next, a measurement value Si is calculated, which is a value obtained by subtracting the output value Ai0 from the output value Ai (S103). When the exposure time t changes from ts to ts to tmax, the measured value Si of each wavelength channel i includes the tmax/ts value.

Fig. 5 is a spectrogram showing the measured value Si. The horizontal axis corresponds to the wavelength channel i, and the vertical axis corresponds to the measured value Si. Here, four spectra corresponding to the exposure time t=100, 3000, 6000, and 10000 are displayed. As shown in the figure, the measured value Si increases from close to zero near the wavelength channel i=200, and decreases to close to zero near the wavelength channel i=600. Fig. 6 is an enlarged view showing the part of the wavelength channel i=0 to 150 in Fig. 5. As shown in FIG. 6, in a region where the wavelength channel i is small (ie, short wavelength), the measured value Si may be less than zero. Therefore, here, for each exposure time t, the average value of the measured value Si is calculated for a predetermined number of wavelength channels i (here i = 0 to 9), where the measured value Si is initially regarded as zero, and the value Set to b (S104). That is, when the exposure time t changes from ts to ts to tmax, the correction parameter b (basic correction value) includes the tmax/t value. The first corrected measurement value Si′ is obtained by subtracting the correction parameter b from the measurement value Si for each combination of the exposure time t and the wavelength channel i (S105). In addition, as described later, here, in order to obtain the statistical change of the first corrected measurement value Si′, the processing of S102 to S105 is repeated multiple times (for example, 100 times) under the same conditions.

Secondly, the measured value Si' is converted into the actual linear error ei'. FIG. 7 is a graph showing the change of the measured value Si′ after the first correction with respect to the increase in the exposure time t compared with the ideal straight line Li. In this figure, a plane with a horizontal axis indicating the exposure time t and a vertical axis indicating the first corrected measurement value Si′ is shown. The ideal straight line Li is based on a straight line. The straight line consists of the point (tmax, Si'max) formed by the maximum exposure time t = tmax and the value of the first corrected measurement value Si' at that time (this value is called Si' max) and The origin (0,0) is connected (S106). The actual linear error ei', as shown in the following mathematical formula (1), shows the ratio of the difference between the ideal straight line Li and the first corrected measurement value Si' to the first corrected measurement value Si'.

[Math 1]

FIG. 8 is a graph showing the relationship between the first corrected output value Si' and the actual linearity error ei'. Here, take the case of i=456 as an example. As shown in the figure, as the output value Si' becomes larger after the first correction, the actual linear error ei' becomes smaller. In addition, in the area where the measured value Si′ after the first correction is small, the actual linear error ei′ fluctuates greatly, and in the area where the measured value Si′ after the first correction is large, the actual linear error ei′ fluctuates very little. Therefore, in the second calibration, the area where the measured value Si′ is large after the first calibration, that is, the value of the exposure time t falls in the large area, improves the linearity of the measured value of the CMOS linear image sensor 17.

Therefore, first, the error Δei' of the actual linearity error ei' is calculated using the following mathematical formula (2) (S108). Mathematical formula (2) is derived from the well-known law of propagtion of error. The error Δei' is calculated for each combination of the exposure time t and the first corrected measurement value Si'. In the mathematical formula (2), ΔSi' and ΔSi'max represent the sample standard deviations of the measured values Si' and Si'max after the first calibration. As shown in FIG. 8, when the value of the exposure time t and the first corrected measurement value Si′ is small, the error Δei′ increases, and when the value is large, the error Δei′ decreases. The error Δei' is an example of the amount of change indicating the change of the measured value Si', and the amount of change can be obtained through another calculation formula.

[Math 2]

Next, each wavelength channel i provides a quadratic function f(Si')=C2×Si'2+C1×Si'+C0, which is useful to show the linear error, and in each wavelength channel i, f(Si' ') Fit to the actual linear error ei' (S109). The least square method is used for fitting. As a result, the coefficients C0, C1, and C2 are determined. Here, a quadratic function is adopted as an example of the first function of the present invention, but it goes without saying that it may be another function.

In addition, the fitting in S109 may be performed only for the wavelength channel i whose output value Ai at the exposure time t=tmax is above the predetermined threshold. In this case, the coefficients C0, C1, and C2 will be determined only for this wavelength channel i.

Fig. 9 is a graph showing the fit of the quadratic function f(Si') and the actual linear error ei'. Similarly, take the case of i=456 as an example. The horizontal axis represents the measured value Si', and the vertical axis represents the actual linear error ei'. The black dot in the figure represents the measurement point (Si', ei') composed of the measured value Si' and the actual linear error ei'. The curve sloping to the lower right shows the shape of the quadratic function f that fits these measurement points. In addition, the vertical line segment running through each black dot indicates the error Δei'. As shown in the figure, in an area where the measured value Si′ is small (that is, an area where the exposure time t is short), the error Δei′ is relatively large. Then, in the area where the error Δei' is large as described above, the degree of fitting of the quadratic function f to the measurement point is reduced. On the contrary, in the area where the error Δei' is small, the fitting of the quadratic function f to the measurement point is increased. degree. Therefore, the objective function in the least square method is the weighted total of the difference between the quadratic function f(Si′) and the actual linear error ei′, and the reciprocal of the error Δei′ is used as the weight. As a result, in a region where the value of the exposure time t and the measured value Si′ after the first correction is large, the quadratic function f(Si′) is fitted by the actual linear error ei′.

Next, using the coefficients C0, C1, and C2 determined in S109, the second corrected measurement value Si" is calculated using the following mathematical formula (3) (S110).

[Math 3]

In addition, in S109, the coefficients C0, C1, and C2 are determined for each wavelength channel i. Therefore, when calculating the second corrected measurement value Si″, the coefficients C0, C1, and C2 determined for the same wavelength channel i are used.

For the sake of simplicity, calculate the average value (representative value) of C0, C1, and C2, and in the mathematical formula (3), these representative values (that is, a quadratic function represents a plurality of Quadratic function) can be used in common in all wavelength channels i. In particular, when the fitting of S109 is performed only on the wavelength channels whose first corrected measured value Si' at the exposure time t=tmax is above the predetermined threshold, for the wavelength channels for which the fitting of S109 has not been performed, C0 can be used. The average value of, C1 and C2 appropriately calculates the second corrected measured value Si''.

Next, for each wavelength channel i, the second corrected measurement value Si" is converted into an actual linear error ei" (S111). The actual linear error ei'' can also be calculated through the same equation as the above mathematical equation (1).

FIG. 10 shows the relationship between the measured value Si" after the second correction using the function f and the actual linear error ei". Similarly, take the case of i=456 as an example. As shown in the figure, the actual linearity error ei" is a sufficiently small value in the region where the measured value Si" is 0.2 or more, and linearity can be sufficiently achieved in this region. However, in the area where the measured value Si" is less than 0.2, that is, in the area where the exposure time is short, the linearity is insufficient. Therefore, in this embodiment, the exposure time correction is performed as the third correction. The exposure time correction is a correction that increases the measured value Si″ in the area of the short exposure time based on the short exposure time. Specifically, the third corrected measurement value Si′″ is defined by the following mathematical formula (4). That is, the third corrected measurement value Si″′ is obtained by multiplying the second corrected measurement value Si″ by the fractional function t/(dt) as an example of the second function of the present invention. Here, d is the corrected exposure time. The larger the d, the larger the correction amount. However, in an area where the exposure time t is large, the correction amount will become smaller, and the difference between the second corrected measured value Si" and the third corrected measured value Si"' will become smaller. In addition, the second function is not limited to the above-mentioned score function. It approaches a predetermined value (here, 1) as the exposure time t increases, and is a function that increases as the exposure time approaches 0. As long as the shape is changed by a variable parameter, Any function can be used.

[Math 4]

Next, as shown in the following mathematical formula (5), it is assumed that the third corrected measured value Si″′ is proportional to the exposure time t.

[Math 5]

Using mathematical formulas (4) and (5), the actual linear error ei" corresponding to the second corrected measurement value Si" is shown in the following mathematical formula (6), which is expressed as the exposure time t with the correction parameter d The function g(t).

[Math 6]

Next, using the result of S111, fit the function g(t) to the measurement point (t, ei") (S112). As a result, the correction parameter d is determined. Figure 11 is a graph showing this fit. Similarly, take the case of i = 456 as an example.

Then, using the determined parameter d, the second corrected measurement value Si″ is converted into the third corrected measurement value Si″′ using mathematical formula (4) (S113 ). In addition, a correction parameter d is determined for each wavelength channel i in S112. Therefore, for each wavelength channel i, the correction parameter d corresponding to the wavelength channel i can be used and the third corrected measurement value Si"' can be calculated by the mathematical formula (4). Alternatively, the average value of the correction parameter d can be calculated, and the average value can be used in all wavelength channels i, and the third corrected measurement value Si"' can be calculated by the mathematical formula (4).

FIG. 12 is a diagram showing the relationship between the third corrected measured value Si'" and the actual linear error ei"' calculated from the third corrected measured value Si"'. Similarly, take the case of i=456 as an example. As shown in the figure, through the first to third corrections, the linearity error ei"' is within a sufficiently small value in the entire area of Si"', so it can be known that sufficient linearity is achieved in all areas.

Finally, each wavelength channel Ai0 obtained in S101, the correction parameters C0, C1, and C2 obtained in S109, and the correction parameter d obtained in S112 are stored in a memory or the like (S114). These correction parameters are used for optical measurement of samples.

FIG. 13 is a flowchart for performing optical measurement using the correction parameters saved as described above. First, light emitted from a sample such as the light source 11 is irradiated to the slit 12, and the output value Ai (i=0 to 1023) of the CMOS linear image sensor 17 is obtained by the calculation section 18 (S201). The exposure time ta of the measurement light to the CMOS linear image sensor 17 at this time can be set, and ta can be a value below tmax, and can be set to a sufficiently large value.

Next, the calculation section 18 obtains the measurement value Si (i=0 to 1023) by subtracting the correction parameter Ai0 from the Ai obtained in S201 (S202). In addition, the average value of the measured value Si is calculated for the wavelength channel i = 0~9, and it is set as b (S203). Then, by subtracting the correction parameter b from the measurement value Si, the first corrected measurement value Si′ is obtained (S204).

The calculation part 18 also applies the above-mentioned mathematical formula (3) to the first corrected measured value Si′, and obtains the second corrected measured value Si″ (i=0-1023) (S205). At this time, as the correction parameters C0, C1, and C2, the correction parameters corresponding to the same wavelength channel i are used, as long as they are stored for each wavelength channel i. If a common value (average value) is stored for all wavelength channels, this value is used.

The calculation unit 18 uses the exposure time ta and the correction parameter d, and calculates the third corrected measurement value Si″′ from the second corrected measurement value Si″ according to the above-mentioned mathematical formula (4) (S206). Here, as the correction parameter d, if the correction parameter is saved for each wavelength channel i, the correction parameter corresponding to the same wavelength channel i is used. If a common value (average value) is stored for all wavelength channels, that value is used.

After that, the calculation unit 18 displays the third corrected measurement value Si″' calculated in S205 (S207), and also outputs it by printing, communication, or the like (S207). When the sample is a thin film, the calculation unit 18 may use the second corrected measurement value Si″ calculated in S206 to calculate the film thickness. A conventional algorithm can be used to calculate the film thickness.

According to the linear correction method of the optical measuring device 10 described above, the first to third corrections are performed on the output value Si of the CMOS linear image sensor 17 to obtain a measurement value Si'' with sufficient linearity and obtain high Precision of the spectrum. In addition, using this spectrum, the film thickness of the sample or the like can be calculated with high precision.

The present invention is not limited to the above-mentioned embodiments, and various modifications can be made. Of course, such modifications are also included in the scope of the present invention.

10: Optical measuring device 11: Light source (sample) 12: gap 13: Cut-off filter 14: Collimating lens 15: Diffraction grating 16: Focusing lens 17: CMOS linear image sensor 17-i (i = 0~1023): light receiving element 18: Computing Department

Fig. 1 shows an overall structure diagram of an optical measuring device according to an embodiment of the present invention. Figure 2 shows a schematic diagram of a CMOS linear image sensor. Figure 3 shows a flow chart of the method of calculating the correction parameters. Figure 4 shows a flow chart of the method of calculating the correction parameters. Figure 5 shows the spectrum of the measured value Si. Fig. 6 shows a partial enlarged view of Fig. 5. FIG. 7 shows the change graph of the increase in the measured value Si′ with respect to the exposure time t after the first correction compared with the ideal straight line Li. Figure 8 shows the relationship between the measured value Si' and the actual linear error ei' after the first correction. Figure 9 shows the fitting graph of the function f(Si') to the actual linear error ei'. FIG. 10 shows the relationship between the measured value Si" after the second correction using the function f and the actual linear error ei". Fig. 11 shows the variation of the actual linear error ei″ with respect to the increase in the exposure time t. Figure 12 shows the relationship between the measured value Si''' after the third correction and the actual linear error ei''''. Figure 13 shows a flowchart of an optical measurement method using correction parameters.

Claims (12)

A linear correction method, equipped with a CMOS linear image sensor and used in an optical measuring device, is characterized by the following steps: In the exposure step, the exposure time is changed, and the reference light of constant intensity is sequentially incident on the focused light-receiving element of the CMOS linear image sensor; The measurement value obtaining step is to sequentially obtain the measurement value of the concerned light-receiving element; The actual linear error calculation step sequentially calculates the actual linear error indicating the difference between the linear value obtained based on the exposure time corresponding to the measured value and the measured value; and In a fitting step, for each of the actual linear errors, fitting of a first function indicating the first linear error is performed. Such as the linear correction method of claim 1, wherein the first function is a linear correction method of a CMOS linear image sensor with a quadratic function. For example, the linear correction method of claim 1 or 2, wherein the fitting step uses the least square method of the objective function indicating the total amount of the difference between the actual linear error and the first linear error to determine the first linear error A variable parameter of a function, The objective function includes terms indicating the difference between the first linear error and the actual linear error corresponding to each of the measured values, and these terms are weighted by the amount of deviation indicating the deviation of each of the measured values. Such as the linear correction method of claim 3, which further includes an exposure time correction step of performing exposure time correction on the measured value corrected by the first function. Such as the linear correction method of claim 4, wherein the exposure time correction step is to apply a second function close to a predetermined value as the exposure time becomes longer to the measurement value corrected by the first function to perform the exposure time correction . For example, the linear correction method of claim 5, wherein the second function is a fractional function. The linear correction method of any one of claims 1 to 6, wherein the measurement value is based on the first output value of the light receiving element of interest when the reference light is incident and the light receiving of interest when the reference light is not incident The difference between the second output value of the element is obtained. For example, the linear correction method of claim 7, characterized in that the linear correction method of a CMOS linear image sensor, wherein the fitting step uses the measurement value obtained based on the first output value above a predetermined threshold to perform the fitting . The linear calibration method of any one of claims 1 to 8, wherein the CMOS linear image sensor includes a non-focused light-receiving element, and the focused light-receiving element has no light incident during the time when the reference light is incident on the focused light-receiving element; The linear correction method further includes a basic correction value calculation step that calculates a basic correction value that makes the measured value of the non-attention light receiving element close to zero when the reference light is incident on the attention light receiving element; The measurement value obtaining step is to sequentially obtain the measurement value corrected by the basic correction value. An optical measurement method using any one of claims 1 to 9 of the linear correction method, When the measurement light is incident on the light-receiving element of interest, the measurement value of the light-receiving element of interest is corrected based on the first function. Such as the optical measurement method of claim 10, where: There are multiple light-receiving elements of interest, When the measurement light is incident on each light-receiving element of interest, the measurement value of the light-receiving element of interest is corrected based on a function representing the first function obtainable for each of the light-receiving elements of interest. An optical measuring device, which features: A memory device, which memorizes the calibration parameters corresponding to the first function obtained by the linear calibration method of any one of claim items 1 to 9; and The correction device uses the correction parameter to correct the measured value of the light-receiving element of interest when the measurement light is incident on the light-receiving element of interest.

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