Canon Patent Application: Diffraction Optical Element

Canon continues to research diffractive optics, as we know, a 600mm DO IS USM has been prototyped and shown off by Canon, so there is little doubt there is more DO lenses coming.  Add to that, the fact that Nikon is happily coming out with PF (their form of DO lenses) at a more rapid pace than Canon is at this time.

This patent deals with the film that exists in between the gratings, that increases the efficiency.  This patent deals with making the film less prone to reflecting light.

It has been known that the diffraction efficiency of a diffractive optical element including a sawblade-like diffraction grating (blazed grating) is improved in a manner in which a film is formed on a grating wall surface to form a waveguide. 

PTL 1 discloses a diffractive optical element having a waveguide. 

PTL 1 also discloses that films are formed on grating wall surfaces, and at this time, films are formed also on grating surfaces to readily obtain the diffractive optical element having the waveguide at a low cost. 

PTL 1: Japanese Patent Laid-Open No. 2011-257689 

However, the diffractive optical element including the films on the grating surfaces carries a risk of an increase in the light reflectance of each grating surface. 

It is an object of the present invention to decrease the reflectance of each grating surface in the diffractive optical element including films between a first diffraction grating and a second diffraction grating. 

US Patent Application 20180284474