Patent ID: 11960110
Assignee: CANON KABUSHIKI KAISHA
Field: Optics (Instruments)
Classification: CPC G | IPC G

Claim 0:
1. An optical filter provided on a substrate, the optical filter comprising in order from a substrate side:
a first layer made of a material whose extinction coefficient at the wavelength of 550 nm is 0.02 or less;
an absorption layer having light absorbency; and
a second layer made of a material whose extinction coefficient at the wavelength of 550 nm is 0.02 or less, the substrate, the first layer, the absorption layer, and the second layer being mutually adjacent,
wherein the following conditions are satisfied:

R2−R1≥10[%], and, 8
   [
   nm
    
   ]
  
  ≤
  
   
    
     ∑
      
    
    
     j
     =
     1
    
    m
   
   ⁢
   kj
   ×
   dj
  
  ≤
  
   13
   ⁢
   
    2
    [
    nm
     
    ]
   
  
 

where R1 [%] represents a reflectance of the optical filter for light whose wavelength is 550 nm and that makes incident on the optical filter from a side opposite to the substrate, and R2 [%] represents a reflectance of the optical filter for light whose wavelength is 550 nm and that makes incident on the optical filter from the substrate side, and
where m represents a number of films constituting the absorption layer, kj represents an extinction coefficient of a j-th film counted from the substrate side among the m films at the wavelength of 550 nm, and dj [nm] represents a physical film thickness of the j-th film.