US 11,914,180 B2
Optical filter, method of producing same, and optical module
Yudai Numata, Osaka (JP); Masato Katsuda, Osaka (JP); and Shoichi Matsuda, Osaka (JP)
Assigned to NITTO DENKO CORPORATION, Osaka (JP)
Appl. No. 17/911,875
Filed by NITTO DENKO CORPORATION, Osaka (JP)
PCT Filed Mar. 15, 2021, PCT No. PCT/JP2021/010416
§ 371(c)(1), (2) Date Sep. 15, 2022,
PCT Pub. No. WO2021/187433, PCT Pub. Date Sep. 23, 2021.
Claims priority of application No. 2020-045671 (JP), filed on Mar. 16, 2020; application No. 2020-163409 (JP), filed on Sep. 29, 2020; and application No. 2020-190208 (JP), filed on Nov. 16, 2020.
Prior Publication US 2023/0116255 A1, Apr. 13, 2023
Int. Cl. G02B 5/08 (2006.01); G02B 5/02 (2006.01); G02B 5/20 (2006.01); G02B 5/26 (2006.01); G02B 5/28 (2006.01)
CPC G02B 5/26 (2013.01) [G02B 5/0242 (2013.01); G02B 5/0284 (2013.01); G02B 5/208 (2013.01)] 20 Claims
OG exemplary drawing
 
1. An optical filter having back-scattering characteristics,
wherein the optical filter has a linear transmittance of 60% or higher for light having a wavelength in at least a part of a wavelength range not shorter than 760 nm and not longer than 2000 nm, and
wherein:
in a case where an incident light has a polar angle of 0° in a direction of incidence, a bidirectional reflectance distribution function value in a direction having an azimuth of 20° from a plane of incidence and having a polar angle of −60° is BRDF (0°; 20°, −60°),
in a case where the incident light has a polar angle of 30° in the direction of incidence, the bidirectional reflectance distribution function value in the direction having an azimuth of 20° from the plane of incidence and having a polar angle of −60° is BRDF (30°; 20°, −60°), and
in a case where the incident light has a polar angle of 60° in the direction of incidence, the bidirectional reflectance distribution function value in the direction having an azimuth of 20° from the plane of incidence and having a polar angle of −60° is BRDF (60°; 20°, −60°),
in a case where the incident light has a wavelength in at least a part of a visible light wavelength range, |BRDF (0°; 20°, −60°)−BRDF (30°; 20°, −60°)|/BRDF (0°; 20°, −60°) is 1.0 or smaller, and |BRDF (0°; 20°, −60°)−BRDF (60°; 20°, −60°)|/BRDF (0°; 20°, −60°) is 1.0 or smaller, and
wherein a transmittance curve of the filter in a visible light wavelength region includes a curved portion where the linear transmittance is decreased monotonously from a longer wavelength to a shorter wavelength side, and the curved portion is shifted toward the longer wavelength as an angle of incidence is increased.