JP2006195373A - Visibility correcting near infrared cut filter, and optical low pass filter and visibility correcting element using the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a visibility correcting near infrared cut filter which has a sufficient visibility correcting performance and is capable of realizing a thin and low-cost optical low pass filter. <P>SOLUTION: The visibility correcting near infrared cut filter of a coating type is provided. The visibility correcting near infrared cut filter has the maximum transmittance in the region of wavelength 450 to 550 nm, and has such a spectral characteristic as to exhibit transmittance of 80% or less of the maximum value at wavelength 400 nm, transmittance of 90% or less of the maximum value at wavelength 600 nm and transmittance of 80% or less of the maximum value at wavelength 650 nm. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a visibility correction near-infrared cut filter that can be used in a solid-state imaging device and can perform sufficient visibility correction, and an optical low-pass filter and a visibility correction device using the same.

  Solid-state imaging devices such as CCD (Charge Coupled Device) and CMOS (Complementary Metal-Oxide Semiconductor) are used in digital still cameras and digital video cameras. However, since the spectral sensitivity of the solid-state imaging device is different from the sensitivity (visual sensitivity) of the human eye, correction is necessary.

  FIG. 5 shows the spectral sensitivity of the solid-state imaging device, and FIG. 6 shows the standard relative luminous sensitivity of the human eye. Comparing the spectral sensitivity of the solid-state imaging device and the standard relative luminous efficiency of the human eye, the sensitivity difference in the visible region (wavelength 400 to 700 nm) is a white balance difference, and infrared (hereinafter referred to as “IR”) having a wavelength of 700 nm or more. In the (abbreviated) area, invisible objects such as near-infrared light from the remote controller are photographed or exposure difference is caused.

Therefore, conventionally, by using the visibility correction glass, correction of spectral sensitivity in the visible region and absorption (blocking) of near-infrared light have been performed. In addition, an IR cut coat may be used in combination to improve near-infrared light blocking characteristics, or only an IR cut coat may be used (see, for example, Patent Document 1). FIG. 7 shows the spectral characteristics of the visibility correction glass, and FIG. 8 shows the spectral characteristics of the IR cut coat. These are usually combined with a spatial filter for preventing moire and used as an optical low-pass filter. FIG. 9 shows an example of a conventional optical low-pass filter. As shown in FIG. 8, the conventional optical low-pass filter 9 includes a spatial filter 5 including a depolarizing plate 2 and first and second birefringent plates 3 and 4 provided on both surfaces thereof, and a first complex filter. The refracting plate 3 is composed of a visibility correction glass 10 bonded to the surface opposite to the surface on which the depolarization plate 2 is provided.
JP 2003-279726 A

  However, the IR cut coat alone has a large difference from the visibility. For example, in the case of the one disclosed in Patent Document 1, the transmittance is lowered gradually from the wavelength 550 nm to the wavelength 650 nm. However, the transmittance is almost 100% in the wavelength region of 550 nm or less (see FIG. 3 of Patent Document 1), and some correction means is necessary. Therefore, when an IR cut coat is used for the optical low-pass filter, the thickness can be reduced, but the visibility correction is incomplete.

  The visibility correction glass needs to be as thick as several hundred μm in order to perform sufficient visibility correction. Therefore, when the visibility correction glass is used for the optical low-pass filter, since adhesion is also required, it is not possible to reduce the size of the solid-state imaging device, and thus the digital still camera on which it is mounted.

  The present invention has been made to solve the above-mentioned problems in the prior art, and has a sufficient visibility correction performance and can realize a thin and low-cost optical low-pass filter and a visibility correction element. An object is to provide a sensitivity-corrected near-infrared cut filter, an optical low-pass filter using the same, and a visibility correction element.

  In order to achieve the above object, the configuration of the visibility-corrected near-infrared cut filter according to the present invention is a coating-type visibility-corrected near-infrared cut filter having a maximum transmittance in a wavelength region of 450 to 550 nm, And having a spectral characteristic of a transmittance of 80% or less of the maximum value at a wavelength of 400 nm, a transmittance of 90% or less of the maximum value at a wavelength of 600 nm, and a transmittance of 80% or less of the maximum value at a wavelength of 650 nm. To do.

  In addition, the configuration of the optical low-pass filter according to the present invention includes a spatial filter, and the visibility-corrected near-infrared cut filter according to the present invention coated on any surface of the spatial filter. .

  In addition, the configuration of the visibility correction element according to the present invention includes a transparent substrate and the visibility correction near-infrared cut filter according to the present invention coated on any surface of the transparent substrate. To do.

  ADVANTAGE OF THE INVENTION According to this invention, the coating type which has the spectral characteristic equivalent to the spectral characteristic of the visibility correction | amendment glass, ie, a thin visibility correction | amendment near-infrared cut filter, can be provided. As a result, it is possible to realize a thin and low-cost optical low-pass filter and a visibility correction element having sufficient visibility correction performance.

  Hereinafter, the present invention will be described more specifically using embodiments.

[First Embodiment]
FIG. 1 is a perspective view showing the configuration of an optical low-pass filter including a visibility-corrected near-infrared cut filter according to the first embodiment of the present invention.

  As shown in FIG. 1, the optical low-pass filter 1 of the present embodiment includes a spatial filter 5 including a depolarizing plate 2 and first and second birefringent plates 3 and 4 provided on both surfaces thereof, The birefringent plate 3 is composed of a near-infrared cut filter 6 with a corrected visibility coated on the surface opposite to the surface on which the depolarizing plate 2 is provided. Here, the depolarizing plate is an element for converting polarized light into non-polarized light, and the birefringent plate is an element for separating incident light into ordinary rays and extraordinary rays.

  The visibility-corrected near-infrared cut filter 6 has a maximum transmittance in the wavelength region of 450 to 550 nm, a transmittance of 80% or less of the maximum value at a wavelength of 400 nm, and a transmittance of 90% or less of the maximum value at a wavelength of 600 nm. , And has a spectral characteristic of a transmittance of 80% or less of the maximum value at a wavelength of 650 nm. This spectral characteristic is equivalent to the spectral characteristic of the visibility correction glass shown in FIG. 7, and sufficient visibility correction can be realized.

The visibility-corrected near-infrared cut filter 6 is formed by alternately laminating a transparent thin film made of titanium dioxide (TiO ₂ ) as a high refractive index material and a transparent thin film made of silicon dioxide (SiO ₂ ) as a low refractive index material. It has a layered structure. That is, the visibility correction near infrared cut filter 6 is a coating type, that is, a thin visibility correction near infrared cut filter. The visibility-corrected near-infrared cut filter 6 includes a transparent thin film made of a high refractive index material and a low refractive index material on the surface of the first birefringent plate 3 opposite to the surface on which the depolarization plate 2 is provided. The transparent thin film to be obtained is obtained, for example, by alternately forming using a known vacuum deposition method. In addition to TiO ₂ , tantalum pentoxide (Ta ₂ O ₅ ), niobium pentoxide (Nb ₂ O ₅ ), etc. can be used as the high refractive index material, and SiO ₂ can be used as the low refractive index material. _In addition to ₂ , magnesium fluoride (MgF ₂ ) or the like can be used.

  The following (Table 1) to (Table 3) show layer configuration examples of the visibility-corrected near-infrared cut filter 6 of the present embodiment. The following (Table 1) is a layer configuration example when the total number of layers is 38 layers, and the following (Table 2) is a layer configuration example when the total number of layers is 30 layers. ) Is an example of a layer structure when the total number of layers is 28 layers. In addition, “thickness” in each table means an optical thickness (n · d).

  FIG. 2 shows spectral characteristics of the visibility-corrected near-infrared cut filter having the layer configuration shown in (Table 1) to (Table 3). As shown in FIG. 2, when the total number of layers is 30 and 38, the above-described spectral characteristics are obtained. That is, when the total number of layers is 30, the maximum transmittance is 99.6% at a wavelength of 492.6 nm, the maximum transmittance is 5.4% at a wavelength of 400 nm, and the maximum value is at a wavelength of 600 nm. It has a spectral characteristic of 81% transmittance and a maximum transmittance of 45% at a wavelength of 650 nm. When the total number of layers is 38, the maximum transmittance is 98.5% at a wavelength of 503.7 nm, the maximum transmittance is 5.4% at a wavelength of 400 nm, and the maximum value is at a wavelength of 600 nm. It has a spectral characteristic of 81.5% transmittance and a maximum transmittance of 45% at a wavelength of 650 nm. On the other hand, when the total number of layers is 28, it deviates from the spectral characteristics described above. However, an AR (Anti Reflection) film having a reflectance of 10% or more at a wavelength of 400 nm and a wavelength of 650 nm is coated on the surface opposite to the coating surface of the visibility correction near-infrared cut filter 6. For example, the above-described spectral characteristics can be obtained. In this case, a combination of the visibility corrected near-infrared cut filter 6 and the AR film is the “visibility corrected near-infrared cut filter” according to the present invention. The following (Table 4) shows a layer configuration example in the case where the total number of layers is four as an AR film having a reflectance of 10% or more at a wavelength of 400 nm and a wavelength of 650 nm. In the following (Table 4), “thickness” means optical thickness (n · d).

  3 shows the spectral characteristics of the visibility corrected near-infrared cut filter 6 having the layer configuration (28 layers) shown in (Table 3) above, the visibility corrected near-infrared cut filter, and the above (Table 4). Spectral characteristics when combined with an AR film having the layer structure shown in FIG. Note that FIG. 3 also includes the reflectance characteristics of the AR film.

  As described above, according to the present embodiment, it is possible to provide a coating-type, that is, a thin, visibility-corrected near-infrared cut filter having spectral characteristics equivalent to the spectral characteristics of the visibility-corrected glass. . As a result, the first birefringent plate 3 of the spatial filter 5 is coated with the visibility corrected near-infrared cut filter 6 (by coating the second birefringent plate 4 with an AR film as necessary). Therefore, it is possible to realize a thin and low-cost optical low-pass filter 1 having sufficient visibility correction performance.

  Note that the visibility-corrected near-infrared cut filter has a maximum transmittance in the wavelength region of 450 to 550 nm, a transmittance of 80% or less of the maximum value at the wavelength of 400 nm, and a transmittance of 90% or less of the maximum value at the wavelength of 600 nm. As long as it can be configured to have a spectral characteristic having a transmittance of 80% or less of the maximum value at a wavelength of 650 nm, it is not limited to those having the layer configurations shown in the above (Table 1) to (Table 4).

  In the present embodiment, the visibility correction near-infrared cut filter 6 is coated on the surface of the first birefringent plate 3 opposite to the surface on which the depolarization plate 2 is provided. The configuration is not necessarily limited to this. For example, the visibility-corrected near-infrared cut filter 6 may be coated on the adhesion surface of the spatial filter 5 between the depolarization plate 2 and the first or second birefringence plates 3 and 4 and includes the adhesion surface. The spatial filter 5 may be divided and coated on two surfaces.

  In the present embodiment, the spatial filter 5 including the depolarizing plate 2 and the first and second birefringent plates 3 and 4 provided on both sides thereof is described as an example. The configuration is not necessarily limited to this. As the spatial filter, for example, one having a configuration of one or three or more birefringent plates or a configuration not using a depolarizing plate may be used.

[Second Embodiment]
FIG. 3 is a perspective view showing a visibility correction element equipped with a visibility correction near-infrared cut filter according to the second embodiment of the present invention.

  As shown in FIG. 3, the visibility correction element 7 of the present embodiment includes a parallel plate optical glass 8 as a transparent substrate, and a visibility correction near-infrared cut filter coated on one surface of the optical glass 8. 6. Here, the visibility correction near-infrared cut filter 6 has the same configuration as that described in the first embodiment, and the AR described in the first embodiment as necessary. Used in combination with a membrane.

  In order to perform sufficient visibility correction, the visibility correction glass needs to be as thick as several hundred μm. However, the surface of the optical glass 8 having a small thickness is coated with the visibility correction near-infrared cut filter 6. As a result, it is possible to realize a thin and low-cost visibility correction element 7 having sufficient visibility correction performance.

  In the present embodiment, the visibility-corrected near-infrared cut filter 6 is coated on one surface of the optical glass 8, but it is not necessarily limited to this configuration. For example, the visibility correction near-infrared cut filter 6 may be divided and coated on both sides of the optical glass 8.

  In the present embodiment, the optical glass 8 is described as an example of the transparent substrate, but the transparent substrate is not necessarily limited to the optical glass 8. Even if, for example, transparent resin, quartz, ceramic, or the like is used as the transparent substrate, the same effect as described above can be obtained.

  The visibility correction near-infrared cut filter of the present invention is a coating type having a spectral characteristic equivalent to the spectral characteristic of the visibility correction glass, that is, a thin visibility correction near-infrared cut filter. And is useful for high-performance digital still cameras and video cameras that require downsizing.

The perspective view which shows the structure of the optical low-pass filter carrying the visibility correction | amendment near-infrared cut filter in the 1st Embodiment of this invention. The figure which shows the spectral characteristic of the visibility correction | amendment near infrared cut filter in the 1st Embodiment of this invention The figure which shows the spectral characteristic of the visibility correction | amendment near-infrared cut filter including AR film | membrane in the 1st Embodiment of this invention The perspective view which shows the visibility correction element which mounts the visibility correction near-infrared cut filter in the 2nd Embodiment of this invention. Diagram showing spectral sensitivity of solid-state image sensor Diagram showing the standard relative luminous efficiency of the human eye Diagram showing spectral characteristics of visibility correction glass Diagram showing spectral characteristics of IR cut coat A perspective view showing an example of a conventional optical low-pass filter

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Optical low-pass filter 2 Depolarization plate 3 1st birefringent plate 4 2nd birefringent plate 5 Spatial filter 6 Visibility correction near-infrared cut filter 7 Visibility correction element 8 Optical glass

Claims (3)

This is a coating-type visible-sensitivity corrected near-infrared cut filter that has a maximum transmittance in the wavelength region of 450 to 550 nm, a transmittance of 80% or less of the maximum value at a wavelength of 400 nm, and a maximum value of 90% at a wavelength of 600 nm. A visibility-corrected near-infrared cut filter having the following transmittance and spectral characteristics having a transmittance of 80% or less of the maximum value at a wavelength of 650 nm. An optical low-pass filter comprising: a spatial filter; and the visibility-corrected near-infrared cut filter according to claim 1 coated on any surface of the spatial filter. The visibility correction | amendment element provided with the transparent substrate and the visibility correction | amendment near-infrared cut filter of Claim 1 coated in any surface of the said transparent substrate.

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