JP2008077741A - Diffraction grating measurement apparatus and diffraction grating measurement method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a diffraction grating measurement apparatus which has simple and compact constitution and nonetheless can accurately measure a diffraction angle and an intensity branching ratio in a diffraction grating and even when diffraction beams in the diffraction grating come close to and overlap with each other, can quickly separate the diffraction beams into several distribution functions by a simple method, and to provide a diffraction grating measurement method. <P>SOLUTION: The diffraction grating measurement apparatus is provided with: an imaging means 3 acquiring two-dimensional luminance distribution information on a luminous flux passing through the diffraction grating 1; a means 4 separating a luminance distribution in a diffraction direction by the diffraction grating 1 and a luminance distribution in a direction orthogonal to the diffraction direction from each other based on the two-dimensional luminance distribution information obtained by the imaging means 3 and determining parameters for luminous flux widths of respective beams diffracted by the diffraction grating by using the luminance distribution in the direction orthogonal to the diffraction direction; and the means 4 separating respective diffracted beam components diffracted by the diffraction grating 1 based on the luminance distribution in the diffraction direction and the determined parameters. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a diffraction grating measuring apparatus and a diffraction grating measuring method for measuring a diffraction angle and an intensity branching ratio in a diffraction grating used in an optical pickup device, various optical measuring instruments, and the like.

  In recent years, diffraction gratings have become an indispensable component in optical pickup devices and various optical measuring instruments that are remarkably increased in density and accuracy. A diffraction grating often used as a functional optical element is required to have high accuracy with respect to optical characteristics such as a diffraction angle and an intensity branching ratio. Therefore, at the manufacturing stage of the diffraction grating, it is required to measure and confirm optical characteristics such as diffraction angle and intensity branching ratio with high accuracy and speed.

  Conventionally, as shown in FIG. 9, the diffraction angle and intensity branching ratio in a diffraction grating are measured by projecting diffracted light that has passed through the diffraction grating onto a screen, separating the light spots of each diffracted light, and the light of each light spot. This is done by measuring the intensity and the distance between each light spot.

That is, in this measurement method, parallel light from a laser light source molded in a circular shape using an aperture and a collimator lens (not shown) is incident on the diffraction grating 101, diffracted, and projected onto the screen 102. Then, the intensity and relative position of the light spot 103 of 0th order light and the light spot 104 of ± 1st order diffracted light projected on the screen 102 are measured. The distance from the diffraction grating 101 to the screen 102 is L, the distance between the zeroth-order light spot 103 and the first-order diffracted light spot 104 is d, the zero-order light spot 103, and the intensity of the first-order diffracted light spot 104. When the the P _0, P _1, respectively, the diffraction angle theta, expressed in the following equation (1), the intensity branching ratio T is expressed by the following equation (2).
θ = tan ⁻¹ (d / L) ≈d / L (Formula 1)
T = P ₁ / P ₀ (Equation 2)

The light intensity is measured using a photodetector, a CCD camera, or the like. In the measurement by the photodetector, the light intensity at the light spot of each diffracted light is individually measured for each coordinate, and the diffraction angle and the intensity branching ratio are calculated using (Expression 1) and (Expression 2). In the measurement by the CCD camera, as shown in FIG. 10, luminance distribution information of the light spot of each diffracted light is obtained. From this luminance distribution information, the distance d between each light spot and the light intensity (luminance) P ₀ , P ₁ of each light spot are obtained, and the diffraction angle and intensity branching are obtained using (Expression 1) and (Expression 2). Calculate the ratio.

On the other hand, Non-Patent Document 1 describes a waveform analysis method for separating waveform data such as a spectrum into several distribution functions (for example, Gaussian distribution). In this method, first, the peak value and the number of peaks are estimated from the third derivative of the original waveform. Next, the calculation is repeated while correcting the value of each parameter by the simplex method so that the square residual E shown in the following (Equation 3) is minimized. Here, Q _i is a measurement value, P (x _i ) is a fitting function, and N is the number of measurement samples. The distribution function has three parameters: width, peak intensity, and relative position. If the number of peaks to be separated is n, the number of parameters to be optimized is 3n.
^{_{E = Σ N i = 1 {}} Q i -P (x i)} 2 ··· ( Equation 3)

FIG. 11 is a flowchart showing a procedure for separating the luminance distribution information obtained by the CCD camera into three waveforms of 0th order light and ± 1st order diffracted light by this method. In this method, first, it is determined whether or not the original waveform obtained by measurement is noisy (F101). If the original waveform is noisy, the original waveform is smoothed (F102). The third order differentiation is performed by the method (F103). When there is little noise in the original waveform, the original waveform is used as it is, and the third order differentiation is performed by the spline method (F103).
Next, the point at which the value of the third derivative becomes 0 is detected, and the number of peaks and the initial value of the peak position are determined (F104). Then, the initial half-width and height of each peak are obtained by automatic calculation (F105). Next, each parameter is optimized by the simplex method so that the square residual E is minimized (F106). In this case, although it is separated into three peaks, since the position of the central peak is 0, in effect, eight parameters are optimized. Finally, it is confirmed whether the optimization is appropriate (F107), and if it is appropriate, the fitting is finished (F109). When checking whether optimization is appropriate or not, such as when it does not converge to the solution or when the value of E is large, the peak parameter is corrected, and fitting is repeated (F108), and the check is performed again. (F107).

  According to this method, as shown in FIG. 12, in the luminance distribution information obtained by the measurement by the CCD camera, as shown in FIG. 13, the 0th order light and the ± 1st order diffracted light approach each other and overlap, Even if the peak of the luminance distribution is difficult to see, the measured luminance distribution is separated into, for example, three different Gaussian distributions, and the zero-order light spot and the ± first-order diffracted light spot are separated. The light intensity and position can be estimated. Therefore, by using this method, it is possible to measure the diffraction angle and the intensity branching ratio in the diffraction grating.

J. Chem. Softwere, Vol. 6, No. 2, p. 55-p. 66 (2000)

  By the way, the conventional diffraction grating measuring apparatus described above has the following problems. In other words, when measuring the light intensity using a photodetector in a conventional diffraction grating measurement device, it is necessary to clearly separate the diffracted light of each order, so that the diffraction grating and the detector are not separated. Needs to be sufficiently large, and the total length of the measuring apparatus becomes large. Further, in this measuring apparatus, it is difficult to accurately measure the positional relationship between the light spots of the diffracted lights of the respective orders.

  In a conventional diffraction grating measuring apparatus, if the light intensity is measured using a CCD camera, the position information and luminance distribution information of each light spot can be taken in as one image information. The distance between can be shortened. In this case, the positional relationship of the light spots of the diffracted lights of the respective orders can be accurately known by collating with the luminance distribution information. Even when the zero-order light and the first-order diffracted light overlap and the peak of the luminance distribution approaches as shown in FIG. 13, as described above, the method of separating the original waveform data into several distribution functions Can be separated into components of diffracted light of each order.

  However, the method of separating the original waveform data into several distribution functions has the following problems. That is, in this method, as shown in FIG. 11, the number of parameters to be optimized is large, and there are many steps that require high-level calculations. Therefore, a high-speed computer is required to execute this method. There is a problem that it takes a long time to calculate.

  Therefore, the present invention has been proposed in view of the above circumstances, and can measure the diffraction angle and the intensity branching ratio in the diffraction grating accurately while having a simple and compact configuration. Even when the diffracted lights in the diffraction grating are close and overlapping, it is possible to detect the intensity peak value and coordinates of each diffracted light by separating them into several distribution functions quickly by a simple method. An object of the present invention is to provide a diffraction grating measuring device and a diffraction grating measuring method.

  In order to solve the above-described problems and achieve the above object, a diffraction grating measuring apparatus according to the present invention has any one of the following configurations.

[Configuration 1]
A diffraction grating measuring apparatus for measuring a diffraction angle and an intensity branching ratio in a diffraction grating, an imaging unit for acquiring two-dimensional luminance distribution information of a light beam that has passed through the diffraction grating, and two-dimensional luminance distribution information obtained by the imaging unit Based on the above, the luminance distribution in the diffraction direction by the diffraction grating and the luminance distribution in the direction orthogonal to the diffraction direction are separated, and the parameter relating to the beam width of each diffracted light by the diffraction grating is determined by the luminance distribution in the direction orthogonal to the diffraction direction And means for separating each diffracted light component by the diffraction grating according to the luminance distribution in the diffraction direction and the parameters.

[Configuration 2]
A diffraction grating measuring apparatus for measuring a diffraction angle and an intensity branching ratio in a diffraction grating, an imaging unit for acquiring two-dimensional luminance distribution information of a light beam that has passed through the diffraction grating, and two-dimensional luminance distribution information obtained by the imaging unit The luminance distribution in the diffraction direction by the diffraction grating and the luminance distribution in the direction orthogonal to the diffraction direction are separated based on the luminance and the luminance in the direction orthogonal to the diffraction direction passing through the center of the diffracted light having the highest luminance from the luminance distribution in the diffraction direction. And a means for separating each diffracted light component by the diffraction grating by subtracting the distribution.

  The diffraction grating measuring method according to the present invention has any one of the following configurations.

[Configuration 3]
A diffraction grating measuring method for measuring a diffraction angle and an intensity branching ratio in a diffraction grating, wherein two-dimensional luminance distribution information of a light beam that has passed through the diffraction grating is obtained, and a diffraction direction of the diffraction grating is determined based on the two-dimensional luminance distribution information. The brightness distribution and the brightness distribution in the direction orthogonal to the diffraction direction are separated, and the parameter related to the beam width of each diffracted light by the diffraction grating is determined by the brightness distribution in the direction orthogonal to the diffraction direction. The diffracted light components by the diffraction grating are separated by the above.

[Configuration 4]
A diffraction grating measuring method for measuring a diffraction angle and an intensity branching ratio in a diffraction grating, wherein two-dimensional luminance distribution information of a light beam that has passed through the diffraction grating is obtained, and a diffraction direction of the diffraction grating is determined based on the two-dimensional luminance distribution information. Separate the luminance distribution and the luminance distribution in the direction perpendicular to the diffraction direction, and subtract the luminance distribution in the direction orthogonal to the diffraction direction passing through the center of the diffracted light with the highest luminance from the luminance distribution in the diffraction direction. The diffracted light component is separated.

  In the diffraction grating measuring apparatus according to the present invention having the configuration 1, the luminance distribution in the diffraction direction by the diffraction grating and the luminance distribution in the direction orthogonal to the diffraction direction are obtained based on the two-dimensional luminance distribution information obtained by the imaging means. Means for determining a parameter relating to the beam width of each diffracted light beam by the diffraction grating based on the luminance distribution in a direction orthogonal to the diffraction direction; and means for separating each diffracted light component by the diffraction grating based on the luminance distribution and parameter in the diffraction direction; Because there is no need to completely separate the light spots of adjacent orders of diffracted light, the length of the measurement optical system can be shortened, and diffraction gratings with a small diffraction angle can also be measured. Is possible. The present invention is applicable to a large number of light spots as long as the diffraction direction in the diffraction grating is a one-dimensional direction.

  Further, in the diffraction grating measuring apparatus according to the present invention having the configuration 2, the luminance distribution in the diffraction direction by the diffraction grating and the luminance distribution in the direction orthogonal to the diffraction direction based on the two-dimensional luminance distribution information obtained by the imaging means. And a means for separating each diffracted light component by the diffraction grating by subtracting the brightness distribution in the direction orthogonal to the diffraction direction passing through the center of the diffracted light with the highest brightness from the brightness distribution in the diffraction direction. Even if it is difficult to detect the peak position of high-order diffracted light in the brightness distribution, the brightness distribution in the direction orthogonal to the diffraction direction passing through the center of the diffracted light with the highest brightness can be Peaks can be separated. Therefore, in this diffraction grating measuring apparatus, it is possible to improve the resolution of measurable diffraction angles and to reduce the size of the measuring optical system.

  In the method for measuring a diffraction grating according to the present invention having the configuration 3, the luminance distribution in the diffraction direction by the diffraction grating and the luminance distribution in the direction orthogonal to the diffraction direction are obtained based on the two-dimensional luminance distribution information of the light beam that has passed through the diffraction grating. The parameters relating to the beam width of each diffracted light beam by the diffraction grating are determined by the luminance distribution in the direction orthogonal to the diffraction direction, and each diffracted light component by the diffraction grating is separated by the luminance distribution and parameter in the diffraction direction. It is not necessary to completely separate the light spots of the diffracted light of the order, the length of the measuring optical system can be shortened, and a diffraction grating having a small diffraction angle can be measured. The present invention is applicable to a large number of light spots as long as the diffraction direction in the diffraction grating is a one-dimensional direction.

  In the method for measuring a diffraction grating according to the present invention having the configuration 4, the luminance distribution in the diffraction direction by the diffraction grating and the luminance distribution in the direction orthogonal to the diffraction direction are obtained based on the two-dimensional luminance distribution information of the light beam that has passed through the diffraction grating. Separates each diffracted light component by the diffraction grating by subtracting the brightness distribution in the direction orthogonal to the diffraction direction passing through the center of the diffracted light with the highest brightness from the brightness distribution in the diffraction direction. Even if it is difficult to detect the peak position of the next diffracted light, the peak of each diffracted light can be separated by a simple method using the luminance distribution in the direction perpendicular to the diffraction direction passing through the center of the diffracted light with the highest luminance. . Therefore, by using this diffraction grating measurement method, it is possible to improve the resolution of measurable diffraction angles and to reduce the size of the measurement optical system.

  That is, the present invention can accurately measure the diffraction angle and the intensity branching ratio in the diffraction grating while having a simple and small configuration, and each diffracted light in the diffraction grating approaches and overlaps. Even so, a diffraction grating measuring device and a diffraction grating measuring method capable of detecting the intensity peak value and coordinates of each diffracted light by quickly separating them into several distribution functions by a simple method are provided. Is something that can be done.

  Hereinafter, the configuration of the diffraction grating measurement apparatus and the diffraction grating measurement method according to the present invention will be described in detail. The diffraction grating measuring method according to the present invention is executed in the diffraction grating measuring apparatus according to the present invention described below.

[First Embodiment]
FIG. 1 is a plan view showing a configuration of a diffraction grating measuring apparatus according to a first embodiment of the present invention.

  This diffraction grating measuring device has, for example, a semiconductor laser having an emission wavelength of 405 nm as a light source. Light from this light source is isotropically beam-shaped, and then has a circular cross section by an aperture and a collimator lens. As shown in FIG. 1, the light beam is made into a parallel light beam and is incident on the diffraction grating 1 to be measured.

  In this diffraction grating measuring apparatus, the diffraction grating 1 is supported by a movable stage in the X-axis, Y-axis, and Z-axis directions and a tilt stage around the X-axis and the Y-axis via a jig (not shown). A light beam from the light source is incident at a desired incident angle.

  The light beam that has passed through the diffraction grating 1 passes through the ND filter 2 and is received and imaged by the CCD camera 3 serving as an imaging means. The ND filter 2 is for adjusting the amount of transmitted light and appropriately adjusting the luminance of an image captured by the CCD camera 3. The CCD camera 3 can adjust the input gain level so that the dynamic range of the luminance range that can be imaged can be utilized to the maximum.

  In addition, each stage that supports the diffraction grating 1 has a memory function so that the distance between the diffraction grating 1 and the CCD camera 3 can always be accurately measured.

  An image signal output from the CCD camera 3 is sent to the computer 4 as two-dimensional luminance distribution information. As will be described later, the computer 4 separates the luminance distribution in the diffraction direction by the diffraction grating 1 and the luminance distribution in the direction perpendicular to the diffraction direction based on the two-dimensional luminance distribution information obtained by the CCD camera 3, and performs diffraction. As a means for determining a parameter relating to the beam width of each diffracted light beam by the diffraction grating 1 by the luminance distribution in the direction orthogonal to the direction, each diffracted light component by the diffraction grating 1 is separated by the luminance distribution and parameter in the diffraction direction. As a means, image analysis based on the image signal sent from the CCD camera 3 is performed. In the image signal analyzed by the computer 4, for example, each pixel has a dynamic range of luminance from 0 to 1023. The image signal output from the CCD camera 3 is displayed as an image on the computer 4 by the monitor.

  In the diffraction grating 1 to be measured in this embodiment, when the wavelength of incident light is 405 nm, the diffraction angle of ± 1st order diffracted light with respect to 0th order light is, for example, 0.015 °, and 0th order light. This is a diffractive element manufactured with a design value in which the intensity branching ratio of + 1st order diffracted light is 50% and the intensity branching ratio of −1st order diffracted light is 30%. In this embodiment, high-order diffracted light of ± 2nd order or higher is not considered, but the present invention can also be applied to high-order diffracted light if the following methods are sequentially applied.

  FIG. 2 is a front view showing an image (a) imaged by a CCD camera and an image (b) divided into 0th-order light and ± 1st-order diffracted light.

  In this diffraction grating measuring apparatus, as shown in FIG. 2A, elliptical two-dimensional luminance distribution information extending in the diffraction direction of the diffraction grating, that is, in the direction in which ± first-order diffracted light appears is obtained. . In this diffraction grating measuring apparatus, based on the obtained two-dimensional luminance distribution information, as shown in (b) of FIG. Divided into components of the first-order diffracted light.

First, instead of the diffraction grating 1, a reference scale is imaged by the CCD camera 3, and image analysis is performed to calculate a length corresponding to one pixel in the CCD. Further, when the distance between the CCD camera 3 and the diffraction grating 1 (reference scale) is measured and an angle corresponding to one pixel is obtained from these results, 4.3 × 10 ⁻⁴ [deg / pix] is obtained. became. This value is used in the following embodiments.

  Then, the diffraction grating 1 is installed instead of the reference scale, and the light spot is picked up by the CCD camera 3 to obtain two-dimensional luminance distribution information as shown in FIG.

  In this analysis method, for the obtained two-dimensional luminance distribution information, an X axis that is a diffraction direction in the diffraction grating 1 and a Y axis that is a direction orthogonal to the diffraction direction are determined. As a method for determining each axis, for example, first, the output of the light source is increased, or the ND filter 2 is replaced with one having a high transmittance, or the sensitivity of the CCD camera 3 is increased, so that the diffracted light of the second or higher order is obtained. Also be displayed on the image. Then, using the higher-order diffracted light, first, the X axis that is the diffraction direction can be determined, and then the Y axis can be determined as an axis that passes through the center of the light spot and is perpendicular to the X axis. However, how to determine each axis is not limited to such a method.

  FIG. 3 is a graph showing luminance distribution information in the X-axis direction and the Y-axis direction.

  Then, after determining the X axis and the Y axis, as shown in FIG. 3, luminance distribution information on the X axis and luminance distribution information on the Y axis are obtained. In this luminance distribution information, the luminance distribution is wider in the X-axis direction than in the Y-axis direction.

Next, the luminance distribution in the X-axis direction is decomposed into three components and separated into zero-order light and ± first-order diffracted light. Here, all the components can be regarded as an isotropic Gaussian distribution. The obtained entire luminance distribution information is P (x, y), and the 0th and ± 1st order diffracted lights are P ₀ (x, y), P ₊₁ (x, y), and P ₋₁ (x, y), respectively. And the following (Expression 4), (Expression 5-1), (Expression 5-2) and (Expression 5-3).
P (x, y) = P ₋₁ (x, y) + P ₀ (x, y) + P ₊₁ (x, y) (Equation 4)
P ₋₁ (x, y) = A · t ₋₁ · exp [−a {(x + X ₋ ) ² + y ² }] (Equation 5-1)
P ₀ (x, y) = A · exp {−a (x ² + y ² )} (Equation 5-2)
P ₊₁ (x, y) = A · t _{+ 1} · exp [−a {(x + X ₊ ) ² + y ² }] (Equation 5-3)

Here, A is a parameter representing amplitude, t _{± 1} is an intensity ratio of ± 1st order diffracted light with respect to 0th order light, a is a parameter representing the spread of distribution, and X _± is 0 respectively. The position coordinates of ± 1st order diffracted light with respect to the next light are shown. At this time, it is easy to understand when the peak position of the zero-order light is zero. Note that the width a of the Gaussian distribution is the same in the 0th order and ± 1st order diffracted light.

For the measured light spot, the luminance distribution Py (X = 0) on the Y-axis can be expressed as in the following (Equation 6).
Py (y) = P (0, y) = P ₀ (0, y) + P ₋₁ (0, y) + P ₊₁ (0, y)
... (Formula 6)

Here, since all the peak positions of the three Gaussian distributions are in the center (Y = 0), Py can be fitted using only two parameters of amplitude A and width a. In the Gaussian distribution, the amplitude and width parameters are weak parameters that are related to each other, so the parameters can be determined immediately. Therefore, in this embodiment, first, the luminance distribution in the Y-axis direction is fitted to Py. Further, at the time of fitting, each parameter is optimized so that the square residual Ey shown in the following (Equation 7) is minimized. Qy _i is an actual measurement value of the luminance distribution in the Y-axis direction.
^{_{Ey = Σ N i = 1 {}} Qy i -Py (y i)} 2 ··· ( Equation 7)

Next, the luminance distribution Px (Y = 0) on the X-axis can be expressed as (Equation 8) below.
Px (x) = P (x, 0) = P ₀ (x, 0) + P ₋₁ (x, 0) + P ₊₁ (x, 0)
... (Formula 8)

Here, Px is determined by all parameters of the amplitude A, the width a, the position X _±, and the intensity ratio t _±. However, since a is determined at the time of fitting on the Y axis, when fitting Px There are five parameters to be optimized. Since the amplitude A is related to the position X _± and the intensity ratio t _± , it cannot be determined only by fitting Py. Further, at the time of fitting, the parameters are optimized so that the square residual Ex shown in the following (Equation 9) is minimized. Qx _i is an actual measurement value of the luminance distribution in the X-axis direction.
^{_{Ex = Σ N i = 1 {}} Qx i -Px (x i)} 2 ··· ( Equation 9)

  FIG. 4 is a flowchart showing a fitting procedure in the diffraction grating measuring apparatus.

  That is, in this diffraction grating measuring apparatus, as shown in FIG. 4, first, when the measured waveform is noisy, smoothing is performed (F01, F02), and then the amplitude A and the initial value are set as initial values. An appropriate value is substituted for the width a (F10).

  Then, the luminance distribution on the Y axis is fitted to a Gaussian distribution. Specifically, the amplitude A and the width a are changed to minimize the square residual Ey shown in (Expression 7) (F11, F12). The width a is determined at this point, and the amplitude A is changed again in fitting the luminance distribution on the X axis.

Next, initial values of parameters relating to ± first-order diffracted light are set. If the position X _± and the intensity ratio t _± can be determined in advance by design values, etc., the values are substituted as initial values. Otherwise, the luminance distribution on the X-axis and the luminance on the Y-axis The half widths of the respective half values are obtained from the measured values of the distribution, and the difference between them is taken and substituted for the position X _± (F13).

If the initial value of the parameter is set, the luminance distribution on the X axis is fitted to the sum of three Gaussian distributions. The luminance distribution on the X axis is shown in (Equation 8), and the parameters are the width a, the amplitude A, the position X _±, and the intensity ratio t _±. Among these, the width a is the luminance on the Y axis. Since it is determined by distribution fitting, there are five parameters. After the initial values are substituted, the amplitude A, the position X _±, and the intensity ratio t _± are sequentially changed to minimize the square residual Ex shown in (Equation 9) (F14). Similar to the fitting of the luminance distribution on the Y axis, this is repeated until the square residual Ex does not change (F15), and the fitting is completed (F16).

  FIG. 5 is a graph showing a fitting result (a) about the X axis and a fitting result (b) about the Y axis in this diffraction grating measuring apparatus.

  By the above-described procedure, the luminance distribution on the X axis is fitted as shown in (a) of FIG. 5, and the luminance distribution on the Y axis is fitted as shown in (b) of FIG. The

  FIG. 6 is a graph showing the result (a) of decomposition into three components for the X axis and the result (b) of decomposition into three components for the Y axis in this diffraction grating measurement apparatus.

  In the fitting result, as shown in (a) of FIG. 6, for the + 1st order diffracted light, the peak position is +41 pixels, the diffraction angle is 0.018 deg, the intensity is 61% with respect to the 0th order light, −1 For the next-order diffracted light, the peak position was −44 pixels, the diffraction angle was 0.019 deg, and the intensity was 56% with respect to the 0th-order light. The results are shown in [Table 1] below.

[Second Embodiment]
In the diffraction grating measuring apparatus according to the present invention, the diffraction angle of ± 1st order diffracted light is large to some extent, observed away from the 0th order light spot, and the intensity of ± 1st order diffracted light at the center of the 0th order light spot is In the case where it can be ignored, the following second embodiment can be applied.

  In this embodiment, based on the two-dimensional luminance distribution information obtained by the CCD camera 3, the luminance distribution in the diffraction direction (X axis) by the diffraction grating 1 and the luminance distribution in the direction orthogonal to the diffraction direction (Y axis). And the luminance distribution on the Y axis passing through the center of the diffracted light with the highest luminance are subtracted from the luminance distribution on the X axis to separate each diffracted light component by the diffraction grating 1.

That is, in this case, since the intensity of the ± 1st order diffracted light at the center of the 0th order light spot is negligible, the luminance distribution Py on the Y axis eliminates the ± 1st order diffracted light term of (Equation 6). And can be expressed as (Equation 10) below.
Py (y) = P (0, y) ≈P ₀ (0, y) = P ₀ (y, 0) (Equation 10)

Looking at this (Equation 10), the profile on the Y axis, which is the direction orthogonal to the diffraction direction, is the luminance distribution itself of the 0th-order light. Further, by subtracting the luminance distribution on the Y axis from the luminance distribution on the X axis by substituting (Equation 10) into (Equation 8), only ± first-order diffracted light is obtained as shown in the following (Equation 11). It is possible to take out.
P ₋₁ (x, 0) + P ₊₁ (x, 0) = Px (x, 0) −Py (x, 0) (Equation 11)

  FIG. 7 is a flowchart showing a fitting procedure in the diffraction grating measuring apparatus according to the second embodiment.

  In this embodiment, as shown in FIG. 7, first, as in the first embodiment described above, when the measured waveform is noisy, smoothing is performed (F01, F02), and on the X axis. Are fitted (F10, F11, F12).

Next, the luminance distribution on the Y-axis is subtracted from the luminance distribution on the X-axis, and the resulting luminance distribution information of the two spots is taken as the ± first-order diffracted light peak (F17), and the four parameters (position X _± and intensity ratio t _± ) are optimized (F18, F19), the light spot of ± first-order diffracted light is determined, and the fitting is finished (F20).

Then, the diffraction angle and the intensity branching ratio are calculated by comparing the intensity and coordinates of the peak of ± 1st order diffracted light with that of 0th order light. At this time, X ₊ and t _{+ correspond} to the + 1st order diffracted light, and X ₋ and t ₋ correspond to the −1st order diffracted light.

  FIG. 8 is a graph showing a fitting result (a) about the X axis and a fitting result (b) about the Y axis in the second embodiment of the diffraction grating measuring apparatus.

  As a result of the fitting and analysis as described above, as shown in FIG. 8, the distance between the 0th order light and the + 1st order diffracted light was 38 pixels, and the distance between the 0th order light and the −1st order diffracted light was 42 pixels. . When the pixel was converted into a diffraction angle, the diffraction angle of the + 1st order diffracted light was 0.016 deg, and the diffraction angle of the −1st order diffracted light was 0.018 deg. The intensity ratio with respect to the 0th order light was 50% for both ± 1st order diffracted lights. The results are shown in [Table 2] below.

  In the diffraction grating measuring apparatus and measuring method according to the present invention, first, the analysis method in the second embodiment is executed, so that ± 1st order diffracted light approaches the light spot of 0th order light, and 0th order light. If the intensity of the ± 1st order diffracted light at the center of the light cannot be ignored and this analysis cannot be performed, the analysis method in the first embodiment described above may be used.

It is a top view which shows the structure in 1st Embodiment of the measuring apparatus of the diffraction grating which concerns on this invention. FIG. 4 is a front view showing an image (a) imaged by a CCD camera and an image (b) divided into 0th-order light and ± 1st-order diffracted light in the diffraction grating measurement apparatus according to the present invention. It is a graph which shows the luminance distribution information of the X-axis direction and Y-axis direction obtained in the measuring apparatus of the diffraction grating which concerns on this invention. It is a flowchart which shows the procedure of the fitting in 1st Embodiment of the measuring device of the diffraction grating which concerns on this invention. It is a graph which shows the fitting result (a) about the X-axis and the fitting result (b) about the Y-axis in the diffraction grating measuring apparatus according to the present invention. It is a graph which shows the result (b) decomposed | disassembled into three components about the X-axis about the X-axis in the measuring apparatus of the diffraction grating which concerns on this invention, and the three components about the Y-axis. It is a flowchart which shows the procedure of the fitting in 2nd Embodiment of the measuring apparatus of the diffraction grating which concerns on this invention. It is a graph which shows the fitting result (a) about the X-axis in the 2nd Embodiment of the measuring apparatus of the diffraction grating which concerns on this invention, and the fitting result (b) about the Y-axis. It is a side view which shows the structure of the measuring apparatus of the conventional diffraction grating. It is a graph which shows the luminance distribution of the light spot of each diffracted light obtained by a CCD camera. It is a flowchart which shows the measuring method of the conventional diffraction grating which isolate | separates from the luminance distribution information obtained with the CCD camera into three waveforms of 0th order light and +/- 1st order diffracted light. It is a side view which shows the state which 0th order light and +/- 1st order diffracted light overlapped. It is a graph which shows the luminance distribution in the state where the 0th-order light and the ± 1st-order diffracted light overlap and the peak of the light spot of each diffracted light becomes difficult to see.

Explanation of symbols

1 Diffraction grating 2 ND filter 3 CCD camera 4 Computer

Claims (4)

A diffraction grating measuring apparatus for measuring a diffraction angle and an intensity branching ratio in a diffraction grating,
Imaging means for acquiring two-dimensional luminance distribution information of a light beam that has passed through the diffraction grating;
Based on the two-dimensional luminance distribution information obtained by the imaging means, the luminance distribution in the diffraction direction by the diffraction grating and the luminance distribution in the direction orthogonal to the diffraction direction are separated, and in the direction orthogonal to the diffraction direction. Means for determining a parameter relating to the beam width of each diffracted light by the diffraction grating, according to the luminance distribution;
A diffraction grating measuring apparatus comprising: means for separating each diffracted light component by the diffraction grating based on the luminance distribution in the diffraction direction and the parameter. A diffraction grating measuring apparatus for measuring a diffraction angle and an intensity branching ratio in a diffraction grating,
Imaging means for acquiring two-dimensional luminance distribution information of a light beam that has passed through the diffraction grating;
Based on the two-dimensional luminance distribution information obtained by the imaging means, the luminance distribution in the diffraction direction by the diffraction grating and the luminance distribution in the direction orthogonal to the diffraction direction are separated, and from the luminance distribution in the diffraction direction. Means for separating each diffracted light component by the diffraction grating by subtracting the brightness distribution in the direction orthogonal to the diffraction direction passing through the center of the diffracted light having the highest brightness. measuring device. A method of measuring a diffraction grating for measuring a diffraction angle and an intensity branching ratio in the diffraction grating,
Obtaining two-dimensional luminance distribution information of the light beam that has passed through the diffraction grating,
Based on the two-dimensional luminance distribution information, the luminance distribution in the diffraction direction by the diffraction grating and the luminance distribution in the direction orthogonal to the diffraction direction are separated,
A parameter relating to a beam width of each diffracted light by the diffraction grating is determined by a luminance distribution in a direction orthogonal to the diffraction direction,
Each diffraction light component by the said diffraction grating is isolate | separated by the luminance distribution of the said diffraction direction, and the said parameter. The measuring method of the diffraction grating characterized by the above-mentioned. A method of measuring a diffraction grating for measuring a diffraction angle and an intensity branching ratio in the diffraction grating,
Obtaining two-dimensional luminance distribution information of the light beam that has passed through the diffraction grating,
Based on the two-dimensional luminance distribution information, the luminance distribution in the diffraction direction by the diffraction grating and the luminance distribution in the direction orthogonal to the diffraction direction are separated,
Each diffraction light component by the diffraction grating is separated by subtracting the brightness distribution in the direction perpendicular to the diffraction direction passing through the center of the diffracted light with the highest brightness from the brightness distribution in the diffraction direction. How to measure the lattice.

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