JPS6238402A - Optical filter - Google Patents

Abstract

PURPOSE:To obtain the filter having a high transmittance for a visible ray and sufficient absorptance and reflectance for a near infra-red ray by providing the antireflection film and the near infra-red ray reflection film having the high reflectance for a ray of incident light in the near infra-red range on the surface of a transparent body. CONSTITUTION:The antireflection film 2 is prepared by forming a substance layer composed of a magnesium fluoride, an aluminium oxide and a zirconium oxide, etc., as a film on the surface of a cyan type filter glass 1 according to a deposition or a coating method. The antireflection film 2 has preferably a multilayer structure to improve the antireflection effect. The near infra-red ray reflection film 3 has a multiple layer structure obtd. by alternatively laminat ing a silicon dioxide and a titanium dioxide, or obtd. by interposing a condition ing film composed of the aluminium oxide between alternative multiple layer films to reduce a ripple of the transmittivity effect of the obtd. multiple layer film. The near infra-red ray reflection film 3 has preferably >=10 the alternative multiple layers film, since the attenuating amount of the film 3 suddenly occurs in a wavelength of 600-700nm due to the transmittivity effect.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to an optical filter, and particularly to an optical filter suitable for use in sensitivity correction of an image pickup device such as a video camera.

[Prior Art] Imaging with image pickup tubes, COD"'9 solid-state image sensors, etc. (quintuplets generally have sensitivity characteristics as shown in FIG. It also has relatively high sensitivity in the near-infrared light region, which causes deterioration of image characteristics when used in video cameras and the like.

For this reason, there are methods to correct the sensitivity by installing a cyan-colored filter glass that exhibits a high absorption rate for near-infrared light on the front surface of the image sensor, and a method to correct the sensitivity by installing a cyan-colored filter glass that exhibits a high absorption rate for near-infrared light. Improving image characteristics has been attempted by installing an optical filter with a vapor-deposited near-infrared reflective film on the front of the image sensor to correct sensitivity.

[Problems to be Solved by the Invention] However, as shown in Fig. 3, the spectral transmittance of the cyan filter glass is only about 80% in the visible light region, and the spectral transmittance of the cyan filter glass is only about 80% in the visible light region. The slope of the decrease in transmittance of the spectral transmittance curve with respect to wavelength is also small and has the characteristic of slowly attenuating.

For this reason, the conventional sensitivity correction method using a cyan color filter glass has the disadvantage that sufficient visible light sensitivity cannot be obtained and color reproducibility is poor.

In addition, the spectral transmittance characteristics of an optical filter in which a near-infrared light reflection film is deposited on a transparent optical glass are several % for incident light with a wavelength of about 660 nm to 850 nm, as shown by the dashed line 9 in Fig. 3. It has a transmittance of Another drawback was that color reproducibility was poor.

The present invention was made to eliminate the drawbacks of such conventional optical filters, and provides an optical filter that has high visible light transmittance and has 1 minute absorption and reflection rate for near-infrared light. The purpose is to provide.

[Means for Solving the Problems] The optical filter of the present invention has high transmittance for incident light with wavelengths in the visible region, and high absorption for incident light with wavelengths in the infrared region. In an optical filter using a transparent body having a high reflectance, an antireflection film and a near-infrared light reflecting film having a high reflectance for incident light in the near-infrared region are formed on at least one surface of the transparent body. It is characterized by:

That is, as shown in FIG. 1, which is a side view of a typical example of the optical filter of the present invention, it has a high transmittance for incident light with wavelengths in the visible region, and has high transmittance for incident light with wavelengths in the infrared region. An anti-reflection film 2 is formed on one surface of a cyan-colored filter glass l, which is a transparent material with a high absorption rate, and a near-infrared film 2 is formed on the other surface of the cyan color filter glass l, which is a transparent material with a high absorption rate. An infrared light reflecting film 3 is formed.

The optical filter configured in this manner is set in front of the image sensor 4. The incident light beam enters the image sensor 4 through the optical filter.The anti-reflection film 2 is formed by forming a layer of material such as magnesium fluoride, aluminum oxide, or zirconium oxide into a film by vapor deposition or coating. It is formed on one surface of the cyan filter glass 1.

Anti-reflection Ll = Film 2 has a high anti-reflection effect''61''<
It is desirable that i has a multilayer structure.
1. The near-infrared light reflecting film 3 may have a multilayer structure, for example, by alternately depositing silicon dioxide and titanium dioxide, or may have an aluminum oxide adjusting film layer interposed between the alternating multilayer films to reduce ripples in transmittance characteristics. etc. are used.

In terms of transmittance characteristics, the near-infrared light reflecting film 3 is desirably an alternating multilayer film of ten or more layers in order to steepen the amount of attenuation in the wavelength band from flOOn+m to 700n.

In the example explained above, cyan color filter glass was used as the transparent body, but the transparent body is not limited to cyan color filter glass, and even plastic or transparent glass can be used. Any material may be used as long as it has a high transmittance for incident light having a wavelength in the region and a high absorbance for incident light having a wavelength in the near-infrared region.

[Function] 1: As mentioned above, the optical filter of the present invention has high transmittance for incident light with a wavelength in the visible region, and high absorption for incident light with a wavelength in the near-infrared region. The anti-reflection film formed on the transparent body with a 13% reflectance improves the transmittance of light in the visible region, while the near-infrared light reflective film improves the transmittance of light in the visible region.
A transmittance curve showing a steep attenuation for incident light having a wavelength of 0 Or++a to 700 nm is obtained.

[Example] As shown in Figure 1, the length of one side is 10 mm and the thickness is 1.5 m.
A three-layer anti-reflection film 2 made of aluminum oxide, zirconium oxide, and magnesium fluoride is formed on one side of a cyan-colored filter glass 1 by a vapor deposition method, and a total of 16 layers made of silicon difluoride and titanium dioxide are formed on the other surface. A near-infrared light reflecting film 3 consisting of an alternating multilayer film was formed by a vapor deposition method. The optical filter constructed in this manner has the effect of the reflective film +hM2, as shown by the solid line 7 in FIG.

High transmittance of 80% or more is obtained for incident light with wavelengths in the visible range of 400 to 550 nm, and near-infrared light reflection +1
Due to the effect of 723, 600~? Good sharp cut characteristics were obtained in terms of reflection characteristics for wavelengths of OOnm. Further, due to the near-infrared light absorption property of the cyan color filter glass, good light blocking properties against incident light having a wavelength of 700 nm or more were obtained.

[Effects of the Invention] The optical filter of the present invention has a high transmittance (〈) for incident light in the visible wavelength range, and a high absorption rate for incident light in the near-infrared region. 1y] Since an anti-reflection film and a near-infrared light reflecting film are formed on the body, it has an extremely high transmittance for incident light in the visible light range, and has a wavelength of 600 nm.
The transmittance for incident light with a wavelength of 700 nm or more shows a steep attenuation characteristic, and an optical filter having large absorption and reflectance for incident light with a wavelength of 700 nm or more can be obtained, making it extremely suitable for use in sensitivity correction of image pickup devices, etc. This is a method that can give you great effects.

[Brief explanation of the drawing]

FIG. 1 is a side view showing a typical example of the optical filter of the present invention, 2UA is a graph showing an example of the sensitivity characteristics of an image sensor, and FIG. 3 is a spectral transmittance of a conventional cyan color filter glass. 1 is a graph illustrating an example of a comparison between characteristics, spectral transmittance characteristics of an optical filter in which a near-infrared light reflecting film is deposited on transparent glass, and spectral transmittance characteristics of an optical filter of the present invention. 1. Cyan color filter glass 2, antireflection film 3, near-infrared light reflection film 4, image sensor 5, incident light. ]) Figure I F and # (yt) 2nd Sword dyeing 3 Figure

Claims (7)

[Claims] (1) In an optical filter using a transparent body that has high transmittance for incident light with wavelengths in the visible region and high absorbance for incident light with wavelengths in the near-infrared region, the transparent body An optical filter comprising an anti-reflection film and a near-infrared light reflecting film having a high reflectance for incident light in the near-infrared region on at least one surface of the filter. (2) The optical filter according to claim 1, wherein the antireflection film is formed on one surface of the transparent body, and the near-infrared light reflective film is formed on the other surface of the transparent body. (3) The optical filter according to claim 1 or 2, wherein the transparent body is glass. (4) The first claim that the transparent body is plastic
The optical filter according to item 1 or 2. (5) The optical filter according to claim 1 or 2, wherein the antireflection film is a single-layer vapor-deposited film of magnesium fluoride. (6) The antireflection film is a multilayer film in which a vapor-deposited film of aluminum oxide, a vapor-deposited film of zirconium oxide, and a vapor-deposited film of magnesium fluoride are stacked.
Optical filter as described in section. (7) The near-infrared light reflecting film is a multilayer film in which silicon dioxide films and titanium dioxide films are alternately laminated.
The optical filter according to item 1 or 2.