JP2005308643A - Imaging device, and using method therefor - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an imaging device analyzing a spectral image, using a wavelength-variable filter based on a principle not affected greatly by working precision. <P>SOLUTION: This imaging device 50 for re-image-focusing an image of an object by light from the object is provided with an imaging element 4 for re-image-focusing the object, and the wavelength-variable filter 10. The filter is positioned in front of the imaging element, and has the first and second diffraction gratings 5, 6, and a space regulating mechanism for changing a space between the first and second diffraction gratings. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to an imaging apparatus and a method for using the same.

  A conventional spectral image analysis apparatus using a wavelength tunable filter typically uses a Fabry-Perot interference filter as a wavelength tunable filter, and makes the wavelength variable by precisely controlling the interval between two reflective layers ( For example, see Patent Documents 1-4). The Fabry-Perot type interference filter supported by the precise control of the reflective layer spacing as described above is suitable for identifying a slight spectral difference.

In addition to the above-mentioned document, there is also disclosed a configuration for identifying a specific wavelength with high resolution by connecting two sets of interference filters in series (Patent Document 5). For example, in a system for discriminating between a wavelength of 500 nm and a wavelength of 555 nm, in order to extract 500 nm, a configuration in which the spacing between the reflective layers constituting one interference filter is 1500 nm and the spacing between the reflective layers of the other interference filter is 1750 nm. It is disclosed.
JP-A-8-285688 Japanese Patent Laid-Open No. 11-304588 JP 2000-162044 A JP 2001-165775 A Japanese Patent Laid-Open No. 11-304582

  When the interference filter configured as described above is used in a spectral image analysis apparatus, it is necessary to control the distance between the interference filters on the order of several hundred nm with respect to a lens diameter of a centimeter order such as an imaging lens. For example, Patent Document 1 discloses a mechanism for precisely controlling the distance on the order of several tens of nanometers using a piezoelectric element for the distance control. For this reason, extremely high processing accuracy is required for the flatness of a thin film such as a reflective layer constituting an interference filter.

  An object of the present invention is to provide an imaging apparatus capable of performing spectral image analysis using a wavelength tunable filter based on a principle that is not greatly affected by processing accuracy, and a method of using the imaging apparatus.

  The imaging device of the present invention is an imaging device for re-imaging an image of an object with light from the object. This imaging apparatus is located in front of the imaging element that re-images an object, and changes the distance between the first and second diffraction gratings and the first diffraction grating and the second diffraction grating. And a wavelength tunable filter having an interval adjusting mechanism.

  In the above configuration, the wavelength tunable filter uses two diffraction gratings having the same pitch, creates interference fringes with the first diffraction grating, and adjusts the distance from the second diffraction grating to thereby transmit the transmittance in a desired wavelength band. Can be changed. In this method, the interval between the diffraction gratings is about 1000 times as large as the wavelength range to be selected, and the change in transmittance of each wavelength with respect to the change in the interval is relatively gradual. The influence of the accuracy of the degree and the grating interval is small. Accordingly, a motor-type or solenoid-type linear motion can be used for the linear motion for adjusting the interval of the diffraction grating.

  In addition, the wavelength tunable filter in the image pickup apparatus of the present invention is effective in any wavelength band as long as it is an electromagnetic wave, and can change the wavelength even in an X-ray region in which the reflectance from a substance is close to zero.

  The method of using the imaging apparatus of the present invention is a method of using the imaging apparatus in which the first and second diffraction gratings are arranged in the optical system and an image of an object is re-imaged on the imaging element. In this usage method, for each of the first measurement wavelength region and the second measurement wavelength region, the first image is re-imaged on the image sensor with the interval between the first and second diffraction gratings as the first interval. An image forming step and a second image forming step of re-imaging the object image on the imaging device are performed with the interval between the first and second diffraction gratings being a second interval different from the first interval. And obtaining the intensity of light in the first and second measurement wavelength regions based on the output of the imaging device in the first and second imaging steps.

  By such a method, high resolution spectral image analysis can be performed quickly and easily.

Next, embodiments of the present invention will be described with reference to the drawings.
(Embodiment 1)
FIG. 1 is a diagram showing a spectral image device (imaging device) 50 according to Embodiment 1 of the present invention. In FIG. 1, light 7 emitted from an object image 1 reaches an image sensor 4 having a plurality of pixels via a first lens 2 and a second lens 3. A wavelength tunable filter 10 including a first diffraction grating 5 and a second diffraction grating 6 is disposed between the first lens 2 and the second lens 3. The first diffraction grating 5 and the second diffraction grating 6 are provided with a distance adjusting mechanism that can change the distance between them. By controlling the distance between the two diffraction gratings 5 and 6 using this distance adjusting mechanism, the wavelength to be extracted can be changed and function as a wavelength variable filter. Various charge-coupled devices (CCD: Charge Coupled Devices) can be used as the imaging device 4. The dimension R of the image sensor represents the length of one side, and here is the length of the long side.

  In FIG. 1, L1 is the distance from the object image 1 to the first lens 2, L2 is the distance from the first lens 2 to the first diffraction grating 5, and L3 is the second diffraction grating 6 to the second lens. 3 is a distance from the second lens 3 to the image sensor 4. The optical system is disposed so as to have a main optical axis 11.

  FIG. 2 is an operation principle diagram of the wavelength tunable filter 10. Incident light 12 enters the wavelength tunable filter 10. Both the opening pitches of the first and second diffraction gratings 5 and 6 are d, the distance (interval) between the first diffraction grating 5 and the second diffraction grating 6 is z, and the direction of the opening pitch is the x direction. And The intensity distribution in the x direction of the light of wavelength λ emitted from the first diffraction grating is expressed by the following equation (1). In equation (1), k represents the wave number, h represents the order of the Fourier component, and Fh represents the Fourier coefficient. Σ means taking the sum from 0 to infinity (∞) for the order h of the Fourier component.

u (x) = exp (-ikz) ΣF _h exp (iπλh ² z / d ² ) cos (2πhx / d) (1)
Here, the following specific distance is considered as the distance z between the two diffraction gratings.

z = nd ² / λ (n = 1,2, ...) (2)
When n is an even number (n = 2m: m integer), the exponent part of exp in the equation (1) is i2πmh ² . Since N = mh ² is an integer, exp (iπλh ² z / d ² ) = 1 in equation (1). Therefore, equation (1) becomes the following equation (3).

u (x) = exp (-ikz) ΣF _h cos (2πhx / d) (3)
According to the above equation (3), the area under the opening of the first diffraction grating is bright and the area under the opening is dark.

  When n is an odd number, the exponent part of the equation (1) can be expressed as (2N + 1) π, and the following equation (4) is obtained.

u (x) = exp (-ikz) ΣF _h cos ((2πh / d) (x ± d / 2)) (4)
The above equation (4) is obtained by shifting the period of each Fourier component by ½ pitch in the x direction. According to the equation (4), an inverted image of the image represented by the equation (3) is formed in which the area under the opening is dark and the area under the opening is bright.

  Due to the above property, by providing an interval adjusting mechanism that makes the interval between the two diffraction gratings variable, the distance between the two diffraction gratings is changed, and a reverse image is formed on the second diffraction grating only for a specific wavelength. be able to. When a material that absorbs or reflects light is used for the second diffraction grating 6, the specific wavelength is cut.

  As an interval adjusting mechanism for changing the interval between two diffraction gratings, linear motion using a motor system or an electromagnetic solenoid system is known. Further, when the moving range is 100 μm or less, a bulk actuator or a spring type actuator may be used.

  In order to operate on the principle as described above, the first angle is such that the angle formed by the light from the first lens 2 to the first diffraction grating 5 with the main optical axis 12 is substantially zero, that is, substantially parallel. It is desirable to select the focal length of the lens 2. In some cases, an optical system may be provided in the previous stage of the present system to adjust the incident angle of light reaching the first diffraction grating. Specifically, it is preferable that the incident angle θ of the light transmitted through the first lens satisfies the following relationship.

θ ≦ tan ^-1 (d / z) (5)
In addition, the light that has passed through the second diffraction grating 6 also diffracts, generating a ghost pattern with a period of (dL4 / λ). In this case, when the dimension of the light receiving (imaging) element 4 is R, the following inequality may be satisfied.

(DL4 / λ) ≦ R (6)
As an example, application to an infrared image sensor having sensitivity in a wavelength range of 3 μm to 5 μm will be described. As the first and second lenses, plano-convex lenses having the same focal length of 24 mm are used. However, the lens need not be limited to a plano-convex lens, and may be a convex lens having focal points on the front and rear sides. L1 and L4 are made to coincide with the focal lengths of the first and second lenses, respectively.

  The pitch d of the first and second diffraction gratings is 80 μm, and the material is made of a material that does not transmit light, such as metal, ceramics, and polymer materials. The positions where these diffraction gratings are placed are in the vicinity of the focal position of the first lens. However, if the light from the first lens 2 is parallel light, high positional accuracy is not required.

  FIG. 3 is a diagram showing the wavelength band characteristics of light observed on the image sensor 4, that is, the wavelength dependency of the transmittance when configured as described above. In the same figure, the case where the space | interval of the two diffraction gratings 5 and 6 is changed by the 800 micrometer step from 800 micrometers to 3600 micrometers is shown. The figure shows that the transmittance depends on the transmittance even if the position due to the linear motion is shifted by several μm because the wavelength dependency of the transmittance is gentle and the fluctuation width of the grating interval is two digits or more larger than the wavelength. It turns out that there is almost no influence.

  Next, how to capture a spectral image will be described. First, determine the range of the wavelength band to be examined and the number of divisions of the wavelength band to be examined. Here, for example, a case where a spectrum image obtained by dividing a wavelength range of 3 μm to 5 μm into 8 is obtained will be described. In this case, an image of 8 steps may be taken every 400 μm from the interval of two diffraction gratings from 800 μm to 3600 μm. The transmittance of each wavelength when the distance between the two diffraction gratings is changed can be obtained from FIG. 3 and is a known amount.

Each wavelength λ _1, λ _2, ···, and lambda _8, to the intensity I _1, I _2, and · · · I _8. Further, T _ij is the transmittance of light of each wavelength at a predetermined interval of the diffraction grating. FIG. 4 is a diagram for explaining a method of determining each wavelength λ _i and the transmittance T _ij at that wavelength from a graph showing the wavelength dependence of the transmittance at a certain diffraction grating interval. T _ij is represented by an average transmittance within the divided wavelength band. When the distance between the two diffraction gratings is 800 μm (first step), the transmittance for each wavelength is T ₁₁ , T ₁₂ ,..., T _18, and the output of the image sensor at this time is S _1. The simultaneous linear equation (7) for the variable I _i is established.

I ₁ T ₁₁ + I ₂ T ₁₂ + .... + I ₈ T ₁₈ = S ₁ (7)
Similarly, when the distance between two diffraction gratings is 1200 μm (second step), the following simultaneous equations (8) are established for Ii.

I ₁ T ₂₁ + I ₂ T ₂₂ + .... + I ₈ T ₂₈ = S ₂ (8)
The following simultaneous equations (9) can be obtained by measuring all 8 steps including the above formulas (7) and (8) while further increasing the distance between the two diffraction gratings by 400 μm. .

上記（９）式にまとめられた８行８列の連立方程式をＩiについて解くことにより、各波長の強度を知ることができる。

The intensity of each wavelength can be known by solving the 8-by-8 simultaneous equations summarized in the above equation (9) for Ii.

  In the above example, an example in which the measurement is performed eight times is given. However, at least, the first image in the imaging element measured by dividing the wavelength band of light into two and measuring the interval between the two diffraction gratings as the first interval. A spectrum analysis image can be obtained by inputting the output and the second image output of the image sensor measured with the interval as the second interval, and calculating the dispersed image.

  FIG. 5 shows a configuration example of the imaging apparatus. The wavelength tunable filter 30 has a configuration in which two diffraction gratings 5 and 6 are integrally incorporated in the interval adjusting mechanism 13. The data for adjusting the interval by the interval adjusting mechanism 13 and the output data from each pixel from the image sensor 4 are introduced into the computer 21 where necessary calculations and instructions for the next step are issued. After the series of measurements is completed, the spectrum image is displayed on the screen of the image display device 22.

(Embodiment 2)
Embodiment 2 of the present invention is characterized in that the first diffraction grating is made of a material that is substantially transparent to the wavelength to be measured. For example, when an infrared imaging device having a wavelength of 3 μm to 5 μm is used for the imaging device 4, a groove having a depth of 1 μm can be engraved on the ZnSe plate to form a phase shift type diffraction grating.

  FIG. 6 is a diagram showing the wavelength dependence of the transmittance of light observed on the image sensor 4 when a diffraction grating in which a groove of 1 μm depth is carved in a ZnSe plate is used as the first diffraction grating. It can be seen that the maximum light transmittance is increased by a factor of about 2 compared to the transmittance shown in FIG. On the other hand, since the minimum transmittance is almost the same, the dynamic range of the light intensity due to the filter effect is approximately doubled.

(Embodiment 3)
Embodiment 3 of the present invention is characterized in that correction is performed by giving a specific transmittance Tij to the image element at each position of the image sensor. In the first embodiment of the present invention, a restriction is imposed on the angle of light incident on the first diffraction grating. However, when a large aperture ratio is required, the incident angle is θ = tan ⁻¹ (d / z) or more. In such a case, depending on the interval z between the first and second diffraction gratings, interference fringes appear on the image sensor 4 with a period of {d (L3 + L4) / z}. Since the position and intensity at which this interference fringe appears is known, correction can be applied by giving a specific transmittance Tij to each position of the image sensor, that is, each image element (pixel) as described above.

  The correction is performed so that the correction coefficient shown in FIG. 7 is added to the output of the image sensor. For this correction, a filter for giving the correction coefficient may be arranged in front of the image sensor, or the correction coefficient may be taken into account by data pre-installed in the computer 21 in FIG. .

(Embodiment 4)
Embodiment 4 of the present invention is characterized in that a two-dimensional grating is used as the diffraction grating. That is, in the first embodiment described above, a one-dimensional grating is used as the diffraction grating. However, as shown in FIG. 8, a rectangular pattern such as a two-dimensional grating or a checkered pattern may be used for the diffraction grating.

  Next, a modified example of the embodiment of the present invention will be enumerated including the embodiment of the present invention.

  A first lens for receiving light from the object; and a second lens for rearranging the object image on the image sensor, the image sensor being located behind the first lens. The wavelength tunable filter is located behind the second lens and may be located between the first and second lenses.

  With this configuration, an optical system including a condenser lens and an imaging lens can be obtained with a very simple structure.

  The light from the object includes first and second bands, and the first image output in the image sensor obtained by using the first gap as the first gap is the first image output. The second image output of the image sensor obtained by setting the interval between the first diffraction grating and the second diffraction grating as the second interval is input and obtained by calculating the images dispersed in the first and second bands. A calculation unit can be provided.

  By providing such a calculation unit, high-resolution spectral image analysis can be performed quickly and easily.

  Further, the first diffraction grating constituting the wavelength tunable filter may be translucent, and a diffraction pattern may be generated by the phase of light.

  With this configuration, a good spectral image can be obtained even with a dark object image.

The angle θ formed by the light from the first lens and the main optical axis, the aperture pitch d of the diffraction grating constituting the wavelength tunable filter, and the distance z between the first diffraction grating and the second diffraction grating, It can be configured to satisfy θ ≦ tan ⁻¹ (d / z).

  With this configuration, it is possible to obtain spectral image data without generating interference fringes on the image sensor.

  Further, in the arrangement of the distance L3 between the second diffraction grating and the second lens and the distance L4 between the second lens and the image sensor, the light generated on the image sensor side at a cycle of {d (L3 + L4) / z}. Corresponding to the intensity interference fringes, the light intensity correction can be performed in the pixels of the opposing image sensor.

As a result, the influence of the interference fringes can be eliminated while increasing the aperture ratio. In the above configuration, the angle θ formed by the light from the first lens and the main optical axis, the pitch d of the diffraction grating that constitutes the wavelength tunable filter, and the first diffraction grating and the second diffraction grating This is particularly effective when the distance z is in a relation of θ> tan ⁻¹ (d / z).

  The aperture pitch d of the first and second diffraction gratings constituting the wavelength tunable filter, the distance L4 from the second lens to the image sensor, the dimension R of the image sensor, and the wavelength λ of the spectral object are as follows: The relationship dL4 / λ ≦ R may be satisfied.

  With this configuration, only the 0th order light can be captured on the image sensor.

  The openings of the first and second diffraction gratings can be arranged two-dimensionally.

  With the above configuration, by setting an appropriate ratio between the period of the grating in the X direction and the period of the grating in the Y direction, only a narrower band wavelength can be transmitted.

  Although the embodiments of the present invention have been described above, the embodiments of the present invention disclosed above are merely examples, and the scope of the present invention is not limited to these embodiments. The scope of the present invention is indicated by the description of the scope of claims, and further includes meanings equivalent to the description of the scope of claims and all modifications within the scope.

  ADVANTAGE OF THE INVENTION According to this invention, the imaging device which can perform a spectrum image analysis, and its usage method can be obtained, without being received to the influence of processing precision largely. Further, since the transmittance can be made to exceed 50% by using a transmission type diffraction grating, a good image can be obtained even with a dark object image. In addition, it may be limited to paraxial rays so as not to receive interference fringes from the diffraction grating. If the aperture ratio is large and it is unavoidable that the interference fringes are incident on the image sensor, it corresponds to the interference fringes. The output of the pixel to be corrected can be corrected. Since it has the above advantages, it is expected to be widely used in the field of spectral image analysis in the future.

  The embodiment disclosed this time should be considered as illustrative in all points and not restrictive. The scope of the present invention is defined by the terms of the claims, rather than the description above, and is intended to include any modifications within the scope and meaning equivalent to the terms of the claims.

It is a figure explaining the spectrum image apparatus in Embodiment 1 of this invention. It is a figure which shows the principle of operation of the wavelength variable filter in the spectrum image apparatus shown in FIG. It is a figure which shows the wavelength band characteristic of the spectrum image apparatus in Embodiment 1 of this invention. It is a figure which shows the data acquisition method of the spectrum image apparatus in Embodiment 1 of this invention. It is a figure which shows the structural example of the imaging device of Embodiment 1 of this invention. It is a figure which shows the wavelength band characteristic of the spectrum image apparatus in Embodiment 2 of this invention. It is a figure which shows how to apply the correction of the image pick-up element in the image pick-up device of Embodiment 3 of this invention. It is a figure which shows the opening pattern of the diffraction grating in the imaging device of Embodiment 4 of this invention.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 1 Object image, 1st lens, 3rd lens, 4 Image pick-up element (imaging element), 4a pixel, 5 1st diffraction grating, 6 2nd diffraction grating, 7 light, 10 Wavelength variable filter, 11 Main optical axis of optical system, 12 incident light, 13 interval adjustment mechanism, 20 integrated tunable filter, 21 computer, 22 display device, 50 imaging device, d, d1, d2 aperture pitch, z interval between two diffraction gratings, L1 Distance between the object image and the first lens, L2 Distance between the first lens and the first diffraction grating, L3 Distance between the second diffraction grating and the second lens, L4 Second lens and the imaging element And R, the dimensions of the image sensor (opening diameter).

Claims (9)

An imaging device for re-imaging an image of an object with light from the object,
An image sensor for re-imaging the object;
An image pickup comprising a first and second diffraction gratings and a wavelength tunable filter having a distance adjusting mechanism for changing a distance between the first diffraction grating and the second diffraction grating, which is located in front of the image pickup element. apparatus.   A first lens for receiving light from the object; and a second lens positioned rearward of the first lens for re-imaging the object image on the imaging device, The imaging device according to claim 1, wherein the imaging element is located behind the second lens, and the wavelength tunable filter is located between the first and second lenses.   The light from the object includes first and second bands, and the first image output in the imaging device obtained as the first distance between the first diffraction grating and the second diffraction grating; The second image output from the image sensor obtained by setting the distance between the first diffraction grating and the second diffraction grating as the second distance is input, and the light intensity dispersed in the first and second bands is calculated. The imaging device according to claim 1, further comprising an arithmetic unit for obtaining the imaging device.   The imaging device according to claim 1, wherein the first diffraction grating constituting the wavelength tunable filter is made translucent, and a diffraction pattern is generated by a phase of light. An angle θ formed by the light from the first lens with the main optical axis, an aperture pitch d of the diffraction grating constituting the wavelength tunable filter, and a distance z between the first diffraction grating and the second diffraction grating. The imaging device according to claim 2, wherein the imaging device is configured to satisfy θ ≦ tan ⁻¹ (d / z).   In the arrangement of the distance L3 between the second diffraction grating and the second lens and the distance L4 between the second lens and the image sensor, the image is generated on the image sensor side at a period of {d (L3 + L4) / z}. The imaging apparatus according to any one of claims 1 to 4, wherein light intensity correction is performed in pixels of an opposing imaging device in correspondence with interference fringes of light intensity.   The aperture pitch d of the first and second diffraction gratings constituting the wavelength tunable filter, the distance L4 from the second lens to the image sensor, the dimension R of the image sensor, and the wavelength λ of the spectral object The imaging device according to claim 1, wherein d satisfies a relationship of dL4 / λ ≦ R.   The imaging device according to claim 1, wherein openings of the first and second diffraction gratings are two-dimensionally arranged. A method of using an imaging apparatus in which first and second diffraction gratings are arranged in an optical system and an image of an object is re-imaged on an imaging device,
For each of the first measurement wavelength range and the second measurement wavelength range,
A first imaging step of re-imaging an object image on the imaging device, with the interval between the first and second diffraction gratings being a first interval;
A second imaging step of re-imaging an object image on the image sensor with a second interval different from the first interval as an interval between the first and second diffraction gratings;
Using the imaging device in the first and second imaging steps, and determining the intensity of light in the first and second measurement wavelength regions.

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