US-12619016-B2 - Optical filter

US12619016B2US 12619016 B2US12619016 B2US 12619016B2US-12619016-B2

Abstract

The present invention provides an optical filter for its use. In the present invention, it is possible to provide an optical filter that effectively blocks ultraviolet ray and infrared ray and exhibits high transmittance in visible light. Furthermore, it is possible to provide an optical filter where the transmission characteristics are stably maintained even when an incident angle is changed. Moreover, it is possible to provide an optical filter that does not exhibit problems such as ripple or petal flare.

Inventors

Joon Ho Jung
Seon Ho YANG
Sung Min Hwang
Choon Woo JI
Tae Jin SONG

Assignees

LMS CO., LTD.

Dates

Publication Date: 20260505
Application Date: 20230928
Priority Date: 20221006

Claims (20)

1 . An optical filter, comprising: an infrared-absorbing substrate comprising copper; a first dielectric film formed on a first surface of the infrared-absorbing substrate and comprising a structure in which a first sub-layer and a second sub-layer, of which refractive indices are different from each other, are repeatedly stacked; and a second dielectric film formed on a second surface of the infrared-absorbing substrate and comprising a structure in which a third sub-layer and a fourth sub-layer, of which refractive indices are different from each other, are repeatedly stacked, wherein a V value for the first dielectric film in Equation 1 is defined as V 1 and a V value for the second dielectric film in Equation 1 is defined as V 2 ; and V=log [{(R×Cu) 2μ /n 2 +K) 2 }÷{R×Cu) 2p /n 2 −K}] Equation 1 wherein n 1 is a refractive index for a sub-layer having a larger refractive index among the first and second sub-layers or among the third and the fourth sub-layers; n 2 is a refractive index for a sub-layer having a smaller refractive index among the first and the second sub-layers or among the third and the fourth sub-layers; R is a ratio (n 1 /n 2 ) of n 1 relative to n 2 ; Cu is an amount of the copper in the infrared-absorbing substrate; K is a total number of the first sub-layer and the second sub-layer in the first dielectric film or a total number of the third sub-layer and the fourth sub-layer in the second dielectric film; and 2 p is K−1; and wherein a sum of V 1 and V 2 is in a range of 50 to 75; wherein a ratio of V 2 relative to V 1 (V 2 /V 1 ) is in a range of 3 to 7; and wherein a shortest wavelength exhibiting a reflectance of 50% within a wavelength range of 600 nm to 900 nm for the first dielectric film or the second dielectric film is 720 nm or longer or non-existent.
2 . The optical filter of claim 1 , wherein the amount of the copper in the infrared-absorbing substrate is in a range of 7 to 30 weight %.
3 . The optical filter of claim 1 , wherein the infrared-absorbing substrate has a maximum transmittance of 20% or less in a wavelength range of 700 nm to 800 nm and an average transmittance of 5% or less in the wavelength range of 700 nm to 800 nm.
4 . The optical filter of claim 1 , wherein the infrared-absorbing substrate has a maximum transmittance of 2% or less in a wavelength range of 800 nm to 1,000 nm, and an average transmittance of 2% or less in the wavelength range of 800 nm to 1,000 nm.
5 . The optical filter of claim 1 , wherein the infrared-absorbing substrate has a maximum transmittance of 7% or less in a wavelength range of 1,000 nm to 1,200 nm and an average transmittance of 5% or less in the wavelength range of 1,000 nm to 1,200 nm.
6 . The optical filter of claim 1 , wherein the V value for the first dielectric film (V 1 ) according to Equation 1 is in a range of 7 to 20.
7 . The optical filter of claim 1 , wherein a maximum reflectance for the first dielectric film in a wavelength range of 700 nm to 800 nm is 5% or less and an average reflectance for the first dielectric film in the wavelength range of 700 nm to 800 nm is 5% or less.
8 . The optical filter of claim 1 , wherein a maximum reflectance for the first dielectric film in a wavelength range of 800 nm to 1,000 nm is 15% or less and an average reflectance for the first dielectric film in the wavelength range of 800 nm to 1,000 nm is 10% or less.
9 . The optical filter of claim 1 , wherein the V value for the second dielectric film (V 2 ) according to Equation 1 is in a range of 40 to 70.
10 . The optical filter of claim 1 , wherein the second dielectric film has a maximum reflectance of 40% or more within a wavelength range of 700 nm to 800 nm and an average reflectance of 20% or more within the wavelength range of 700 nm to 800 nm.
11 . The optical filter of claim 1 , wherein the second dielectric film has a maximum reflectance of 70% or more within a wavelength range of 800 nm to 1,000 nm and an average reflectance of 70% or more within the wavelength range of 800 nm to 1,000 nm.
12 . The optical filter of claim 1 , wherein the first dielectric film has a thickness within a range of 200 nm to 500 nm.
13 . The optical filter of claim 12 , wherein each of the first sub-layer and the second sub-layer has a thickness in a range of 1 nm to 200 nm and an average value of the thicknesses of the first sub-layer and the second sub-layer is in a range of 10 nm to 100 nm.
14 . The optical filter of claim 1 , wherein the second dielectric film has a thickness within a range of 3,000 nm to 7,000 nm.
15 . The optical filter of claim 14 , wherein each of the third sub-layer and the fourth sub-layer has a thickness in a range of 1 nm to 300 nm and an average value of the thicknesses of the third sub-layer and the fourth sub-layer is in a range of 50 nm to 300 nm.
16 . The optical filter of claim 1 , wherein a maximum transmittance within a wavelength range of 700 nm to 800 nm is 3% or less and an average transmittance within the wavelength range of 700 nm to 800 nm is 2% or less.
17 . The optical filter according to claim 1 , wherein a maximum transmittance within a wavelength range of 800 nm to 1,000 nm is 1% or less and an average transmittance within the wavelength range of 800 nm to 1,000 nm is 1% or less.
18 . The optical filter of claim 1 , wherein a shortest wavelength exhibiting a transmittance of 50% in a wavelength region of 350 nm to 425 nm is in a range of 400 nm to 420 nm.
19 . The optical filter of claim 1 , wherein the longest wavelength exhibiting a transmittance of 50% in a wavelength region of 560 nm to 700 nm is in a range of 590 nm to 650 nm.
20 . An image capturing device comprising the optical filter of claim 1 .

Description

FIELD The present invention relates to an optical filter and an imaging capturing device. BACKGROUND An optical filter is used in an imaging capturing device using a charge-coupled device (CCD) or a complementary metal-oxide-semiconductor (CMOS) image sensor. Such optical filters are used to obtain good color reproducibility and sharp images and are also called as near-infrared cut filters. Thus, various characteristics are required for such an optical filter. The optical filter must transmit visible light with high transmittance while effectively blocking light in the ultraviolet and infrared regions. To achieve such characteristics, rapid and sharp change in transmittance is required at the boundary between ultraviolet light and visible light to be blocked and at the boundary between infrared and visible light. The optical filter needs to maintain the transmission and blocking characteristics as described above even when the incident angle changes. As such wide-angle cameras are developed, these characteristics become more important, and the need for an optical filter maintaining transmission and blocking characteristics even at a wider angle of incidence is bigger. For the optical filter, it is also necessary that a phenomenon called ripple shall be suppressed. The ripple is a phenomenon where a periodic change in transmittance occurs in the visible light region, and a phenomenon where actual transmittance in a predetermined region increases and decreases compared to the average transmittance of the corresponding region is periodically observed. The imaging capturing device senses visible light transmitted through the optical filter by a sensor for each respective RGB (Red, Green, Blue) color. The sensitivity of each sensor of RGB is adjusted in consideration of the average transmittance for each wavelength. When the ripple occurs, fluctuation occurs in the light recognized by the sensor, and thus, color reproducibility is lowered. Such a ripple phenomenon may generate a region (called as a bunk region) where transmittance is momentarily dropped in the visible light region thereby causing a ghost phenomenon. This ghost phenomenon also deteriorates color reproducibility. Recently, a phenomenon—called as a petal flare—has also become a problem. The petal flare phenomenon refers to a phenomenon where a red line is shown in a photograph although it was not observed by naked eyes when the photograph is taken. It is also called as the petal flare because there are many cases where the red line from a light emitting body is shown as a shape of a floral leaf. Because the sensitivity of the sensor included in the imaging capturing device increases and the transmittance of an optical filter is increased to obtain a clearer picture, the occurrence of the petal flare is increasing. As a publicly known optical filter, an optical filter comprising an absorption layer containing an absorbent and/or a reflection layer adapting a dielectric film is known. When a dielectric film is used, light in the ultraviolet and/or infrared region can be blocked. However, the dielectric film has a characteristic that the transmittance curve changes (shifts) depending on the incident angle. Therefore, to compensate for the disadvantages of the dielectric film, an optical filter using an absorption layer containing a near-infrared absorbing dye having a small incident angle dependence of transmittance is also known. An optical filter adapting a so-called infrared absorbing glass (also called as a blue glass) having a near-infrared absorption property as a substrate is also known. An infrared absorbing glass is a glass filter where material such as CuO is added to the glass to selectively absorb light in the near infrared wavelength region. However, since the infrared absorbing glass exhibits absorption characteristics to some extent even in the visible light region, there is a problem where the transmittance of visible light is also reduced. Therefore, it is a difficult problem to obtain an optical filter that exhibits desired blocking and transmission characteristics, does not shift transmission characteristics according to an incident angle, and does not generate ripples and petal flares, etc. SUMMARY An object of the present invention is to provide an optical filter that effectively blocks ultraviolet and infrared rays and exhibits high transmittance in visible light for its use. Another object of the present invention is to provide an optical filter where the transmission characteristics are stably maintained even when an incident angle is changed thereby preventing of showing problems such as ripple or petal flare for its use. According to an embodiment of the invention, there is provided that an optical filter comprising an infrared absorbing substrate containing copper; a first dielectric film formed on a first surface of the infrared absorbing substrate and including a structure where a first sub-layer and a second sub-layer, re