Diffractive optical element and method for manufacturing the same, and imaging apparatus using the diffractive optical element

A method for manufacturing a diffractive optical element, the diffractive optical element including:

• a substrate made of a first resin, the substrate having a surface formed into a diffraction grating pattern;
• and
• a coating film made of a composite material comprising a second a resin and inorganic particles, the coating film being disposed in contact with the diffraction grating pattern portion of the surface,
• the method comprising the steps of:
• forming the substrate having the surface formed in the diffraction grating pattern;
• and
• forming the coating film so that the coating film covers the diffraction grating pattern,
• wherein
• a refractive index of the composite material is greater than a refractive index of the first resin, and
• an Abbe's number of the composite material is greater than an Abbe's number of the first resin.

A diffractive optical element comprising:

• a substrate made of a first resin, the substrate having a surface formed into a diffraction grating pattern;
• and
• a coating film made of a composite material comprising a second resin and inorganic particles, the coating film being disposed in contact with the diffraction grating pattern portion of the surface,
• wherein
• the first resin is at least one selected from a polycarbonate-based resin, a polystyrene-based resin, and a fluorene-based polyester resin,
• the second resin is a cycloolefin-based resin,
• the inorganic particles are made of at least one selected from zirconium oxide, aluminum oxide, and yttrium oxide, and
• the diffraction grating pattern has a groove depth of not more than 20 μm, and a first-order diffraction efficiency of not less than 80% in a wavelength band of 400 nm to 700 nm.

A diffractive optical element comprising:

• a substrate made of a first resin, the substrate having a surface formed into a diffraction grating pattern;
• and;
• a coating film made of a composite material comprising a second resin and inorganic particles, the coating film being disposed in contact with the diffraction grating pattern portion of the surface,
• wherein
• a refractive index of the composite material is greater than a refractive index of the first resin,
• an Abbe's number of the composite material is greater than an Abbe's number of the first resin, and
• the diffraction grating pattern has a groove depth of not more than 20 μm, and a first-order diffraction efficiency of not less than 80% in a wavelength band of 400 nm to 700 nm.