Near-infrared cut filter

1. A near-infrared cut filter comprising a transparent substrate and an optical multilayer provided on at least one of principal surfaces of the transparent substrate,

wherein the optical multilayer comprises a repeated layered structure having:

a high-refractive index layer comprising TiO 2 and having a refractive index at a wavelength of 500 nm of 2.0 or higher;

a middle-refractive index layer comprising Ta 2 O 5 and having a refractive index at the wavelength of 500 nm of 1.6 or higher and lower than the refractive index of the high-refractive index layer; and

a low-refractive index layer comprising SiO 2 and having a refractive index at the wavelength of 500 nm of lower than 1.6,

the repeated layered structure being expressed by a repeat of (LMHML)^n (n is a natural number of 1 or more) where the high-refractive index layer is H, the middle-refractive index layer is M, and the low-refractive index layer is L, wherein the optical multilayer comprises

a transmission band where a mean transmittance is 85% or higher in a wavelength range from 400 nm to 700 nm, and

a stopband having a width of 100 nm to 280 nm where a mean transmittance is 10% or lower in a wavelength range from 750 nm to 1100 nm, and

wherein the high-refractive index layer, the middle-refractive index layer, and the low-refractive index layer are stacked so that,

where a QWOT (Quarter-wave Optical Thickness) of the high-refractive index layer of the optical multilayer is T H , a QWOT of the middle-refractive index layer is T M , and a QWOT of the low-refractive index layer is T L ,

in a case where the refractive index of the middle-refractive index layer is equal to or higher than an intermediate value between the refractive index of the high-refractive index layer and the refractive index of the low-refractive index layer,

2T L /(T H +2T M ) falls within a range from 100% to 70% when a maximum value of 2T L /(T H +2T M ) in which there is no part where a transmittance locally decreases by 5% or more in the wavelength range of 400 nm to 700 nm in spectral characteristics under a vertical incident condition is set to 100% and a minimum value thereof is set to 0%, and

in a case where the refractive index of the middle-refractive index layer is lower than the intermediate value between the refractive index of the high-refractive index layer and the refractive index of the low-refractive index layer,

(2T L +2T M )/T H falls within a range from 100% to 70% when a maximum value of (2T L +2T M )/T H in which there is no part where the transmittance locally decreases by 5% or more in the wavelength range of 400 nm to 700 nm in the spectral characteristics under the vertical incident condition is set to 100% and a minimum value thereof is set to 0%,

wherein 2T L /(T H +2T m ) falls within a range of 0.852 to 0.867.

2. A near-infrared cut filter comprising a transparent substrate and an optical multilayer provided on at least one of principal surfaces of the transparent substrate,

wherein the optical multilayer comprises a repeated layered structure having:

a high-refractive index layer comprising TiO 2 and having a refractive index at a wavelength of 500 nm of 2.0 or higher;

a middle-refractive index layer comprising Al 2 O 3 and having a refractive index at the wavelength of 500 nm of 1.6 or higher and lower than the refractive index of the high-refractive index layer; and

a low-refractive index layer comprising SiO 2 and having a refractive index at the wavelength of 500 nm of lower than 1.6,

the repeated layered structure being expressed by a repeat of (LMHML)^n (n is a natural number of 1 or more) where the high-refractive index layer is H, the middle-refractive index layer is M, and the low-refractive index layer is L, wherein the optical multilayer comprises

a transmission band where a mean transmittance is 85% or higher in a wavelength range from 400 nm to 700 nm, and

a stopband having a width of 100 nm to 280 nm where a mean transmittance is 10% or lower in a wavelength range from 750 nm to 1100 nm, and

wherein the high-refractive index layer, the middle-refractive index layer, and the low-refractive index layer are stacked so that,

where a QWOT (Quarter-wave Optical Thickness) of the high-refractive index layer of the optical multilayer is T H , a QWOT of the middle-refractive index layer is T M , and a QWOT of the low-refractive index layer is T L ,

in a case where the refractive index of the middle-refractive index layer is equal to or higher than an intermediate value between the refractive index of the high-refractive index layer and the refractive index of the low-refractive index layer,

2T L /(T H +2T M ) falls within a range from 100% to 70% when a maximum value of 2T L /(T H +2T M ) in which there is no part where a transmittance locally decreases by 5% or more in the wavelength range of 400 nm to 700 nm in spectral characteristics under a vertical incident condition is set to 100% and a minimum value thereof is set to 0%, and

in a case where the refractive index of the middle-refractive index layer is lower than the intermediate value between the refractive index of the high-refractive index layer and the refractive index of the low-refractive index layer,

(2T L +2T M )/T H falls within a range from 100% to 70% when a maximum value of (2T L +2T M )/T H in which there is no part where the transmittance locally decreases by 5% or more in the wavelength range of 400 nm to 700 nm in the spectral characteristics under the vertical incident condition is set to 100% and a minimum value thereof is set to 0%,

wherein (2T L +2T M )/T H falls within a range of 1.167 to 1.218.

3. A near-infrared cut filter comprising a transparent substrate and an optical multilayer provided on at least one of principal surfaces of the transparent substrate,

wherein the optical multilayer comprises a repeated layered structure having:

a high-refractive index layer comprising Nb 2 O 5 and having a refractive index at a wavelength of 500 nm of 2.0 or higher;

a middle-refractive index layer comprising Al 2 O 3 and having a refractive index at the wavelength of 500 nm of 1.6 or higher and lower than the refractive index of the high-refractive index layer; and

a low-refractive index layer comprising SiO 2 and having a refractive index at the wavelength of 500 nm of lower than 1.6,

the repeated layered structure being expressed by a repeat of (LMHML)^n (n is a natural number of 1 or more) where the high-refractive index layer is H, the middle-refractive index layer is M, and the low-refractive index layer is L, wherein the optical multilayer comprises

a transmission band where a mean transmittance is 85% or higher in a wavelength range from 400 nm to 700 nm, and

a stopband having a width of 100 nm to 280 nm where a mean transmittance is 10% or lower in a wavelength range from 750 nm to 1100 nm, and

wherein the high-refractive index layer, the middle-refractive index layer, and the low-refractive index layer are stacked so that,

where a QWOT (Quarter-wave Optical Thickness) of the high-refractive index layer of the optical multilayer is T H , a QWOT of the middle-refractive index layer is T M , and a QWOT of the low-refractive index layer is T L ,

in a case where the refractive index of the middle-refractive index layer is equal to or higher than an intermediate value between the refractive index of the high-refractive index layer and the refractive index of the low-refractive index layer,

2T L /(T H +2T M ) falls within a range from 100% to 70% when a maximum value of 2T L /(T H +2T M ) in which there is no part where a transmittance locally decreases by 5% or more in the wavelength range of 400 nm to 700 nm in spectral characteristics under a vertical incident condition is set to 100% and a minimum value thereof is set to 0%, and

in a case where the refractive index of the middle-refractive index layer is lower than the intermediate value between the refractive index of the high-refractive index layer and the refractive index of the low-refractive index layer,

(2T L +2T M )/T H falls within a range from 100% to 70% when a maximum value of (2T L +2T M )/T H in which there is no part where the transmittance locally decreases by 5% or more in the wavelength range of 400 nm to 700 nm in the spectral characteristics under the vertical incident condition is set to 100% and a minimum value thereof is set to 0%,

wherein (2T L +2T M )/T H falls within a range of 1.191 to 1.234.

4. The near-infrared cut filter according to claim 1 ,

wherein the transmission band has no part where a transmittance locally decreases by 20% in the spectral characteristics under an incident condition of 0° to 45°.

5. The near-infrared cut filter according to claim 1 ,

wherein the near-infrared cut filter comprises at least two or more kinds of the optical multilayers.

6. The near-infrared cut filter according to claim 1 ,

wherein the transparent substrate has optical characteristics having absorption in a near-infrared region.

7. The near-infrared cut filter according to claim 6 ,

wherein the transparent substrate is fluorophosphate-based glass or phosphate-based glass containing Cu 2+ ions as a coloring component.

8. The near-infrared cut filter according to claim 6 ,

wherein the transparent substrate is a resin material containing a pigment absorbing near-infrared light.

9. The near-infrared cut filter according to claim 1 , further comprising:

a near-infrared cut layer provided on the same surface with the optical multilayer or on the other principal surface of the transparent substrate,

wherein the near-infrared cut layer comprises:

two or more of layers different in refractive index and each having a refractive index at a wavelength of 500 nm of 2.0 or higher; and

a layer having a refractive index at the wavelength of 500 nm of lower than 1.6,

wherein the near-infrared cut layer comprises

a transmission band where a mean transmittance is 85% or higher in a wavelength range of 400 nm to 700 nm, and

a stopband where a mean transmittance is 5% or lower on each of an ultraviolet side and a near-infrared side of the transmission band,

wherein a difference between a half-power wavelength on the ultraviolet side and a half-power wavelength on the near-infrared side of the transmission band is 200 nm or more, and

wherein a difference between the half-power wavelengths of the transmission band under a vertical incidence condition and under an incident condition of 30° is less than 10 nm in the half-power wavelength on the ultraviolet side and less than 22 nm in the half-power wavelength on the near-infrared side.

10. The near-infrared cut filter according to claim 2 ,

wherein the transmission band has no part where a transmittance locally decreases by 20% in the spectral characteristics under an incident condition of 0° to 45°.

11. The near-infrared cut filter according to claim 2 ,

wherein the near-infrared cut filter comprises at least two or more kinds of the optical multilayers.

12. The near-infrared cut filter according to claim 2 ,

wherein the transparent substrate has optical characteristics having absorption in a near-infrared region.

13. The near-infrared cut filter according to claim 12 ,

wherein the transparent substrate is fluorophosphate-based glass or phosphate-based glass containing Cu 2+ ions as a coloring component.

14. The near-infrared cut filter according to claim 12 ,

wherein the transparent substrate is a resin material containing a pigment absorbing near-infrared light.

15. The near-infrared cut filter according to claim 2 , further comprising:

a near-infrared cut layer provided on the same surface with the optical multilayer or on the other principal surface of the transparent substrate,

wherein the near-infrared cut layer comprises:

two or more of layers different in refractive index and each having a refractive index at a wavelength of 500 nm of 2.0 or higher; and

a layer having a refractive index at the wavelength of 500 nm of lower than 1.6,

wherein the near-infrared cut layer comprises

a transmission band where a mean transmittance is 85% or higher in a wavelength range of 400 nm to 700 nm, and

a stopband where a mean transmittance is 5% or lower on each of an ultraviolet side and a near-infrared side of the transmission band,

wherein a difference between a half-power wavelength on the ultraviolet side and a half-power wavelength on the near-infrared side of the transmission band is 200 nm or more, and

wherein a difference between the half-power wavelengths of the transmission band under a vertical incidence condition and under an incident condition of 30° is less than 10 nm in the half-power wavelength on the ultraviolet side and less than 22 nm in the half-power wavelength on the near-infrared side.

16. The near-infrared cut filter according to claim 3 ,

wherein the transmission band has no part where a transmittance locally decreases by 20% in the spectral characteristics under an incident condition of 0° to 45°.

17. The near-infrared cut filter according to claim 3 ,

wherein the near-infrared cut filter comprises at least two or more kinds of the optical multilayers.

18. The near-infrared cut filter according to claim 3 ,

wherein the transparent substrate has optical characteristics having absorption in a near-infrared region.

19. The near-infrared cut filter according to claim 18 ,

wherein the transparent substrate is fluorophosphate-based glass or phosphate-based glass containing Cu 2+ ions as a coloring component.

20. The near-infrared cut filter according to claim 18 ,

wherein the transparent substrate is a resin material containing a pigment absorbing near-infrared light.

21. The near-infrared cut filter according to claim 3 , further comprising:

a near-infrared cut layer provided on the same surface with the optical multilayer or on the other principal surface of the transparent substrate,

wherein the near-infrared cut layer comprises:

two or more of layers different in refractive index and each having a refractive index at a wavelength of 500 nm of 2.0 or higher; and

a layer having a refractive index at the wavelength of 500 nm of lower than 1.6,

wherein the near-infrared cut layer comprises

a transmission band where a mean transmittance is 85% or higher in a wavelength range of 400 nm to 700 nm, and

a stopband where a mean transmittance is 5% or lower on each of an ultraviolet side and a near-infrared side of the transmission band,

wherein a difference between a half-power wavelength on the ultraviolet side and a half-power wavelength on the near-infrared side of the transmission band is 200 nm or more, and

wherein a difference between the half-power wavelengths of the transmission band under a vertical incidence condition and under an incident condition of 30° is less than 10 nm in the half-power wavelength on the ultraviolet side and less than 22 nm in the half-power wavelength on the near-infrared side.