Diffractive optical element

Abstract

A diffractive optical element includes a first diffractive optical part having a phase type diffractive grating, and a second diffractive optical part having a phase type diffractive grating formed of a material differing from that of the first diffractive optical part. The first diffractive optical part and the second diffractive optical part are disposed in proximity to each other with an air layer. Each of the first diffractive optical part and the second diffractive optical part has a mark for aligning them with the optical effective areas thereof.

1 - 9 . (canceled)  
   
   
       10 . A diffractive optical element comprising: 
 a diffractive optical part having a phase-type diffractive grating,    said diffractive optical part having a mark for aligning with another member, said mark being in an area where the diffractive grating is provided,    wherein the depth or height of said mark is 10% or less of the depth or height of the diffractive grating of said diffractive optical part.    
   
   
       11 . The diffractive optical element of  claim 10 , wherein the diffractive grating of said diffractive optical part is a diffractive grating formed into a concentric circular shape, and said mark has a size of 0.1% or less of a projection area of a first diffractive grating area as counted from the center.  
   
   
       12 . The diffractive optical element of  claim 11 , wherein the influence of said mark upon the optical performance of said diffractive optical element is smaller than the reduction of optical performance caused by manufacturing imperfections.  
   
   
       13 . An optical system provided with the diffractive optical element of  claim 10 .  
   
   
       14 . A diffractive optical element comprising: 
 a diffractive optical part having a phase-type diffractive grating,    said diffractive optical part having an alignment mark,    said mark being in an area where the diffractive grating is provided,    wherein the depth or height of said mark is 10% or less of the depth or height of the diffractive grating of said diffractive optical part.    
   
   
       15 . An optical system provided with the diffractive optical element of  claim 14.