DIFFRACTION ELEMENT FOR THREE WAVELENGTH, DIFFRACTION ELEMENT FOR THREE WAVELENGTH WITH TOPOLOGY PLATE AND OPTICAL HEAD APPARATUS

摘要

PROBLEM TO BE SOLVED: To obtain a diffraction element capable of obtaining diffraction efficiency and a diffraction direction suitable to a laser beam having three wavelength bands used for an optical head apparatus and to attain miniaturization and lightweight of the optical head apparatus though the element is mounted on the optical head apparatus and the function of the element is maintained.

SOLUTION: The diffraction element in which light having three wavelengths λ1, λ2and λ3is made incident comprises two diffraction gratings wherein two different resins come in contact with each other to form periodic projecting and recessed shapes, protrusions 4 and 5 are made of a birefringent resin and recesses 6 and 7 are made of an optically isotropic resin. The diffraction element is mounted on the optical head apparatus as an element wherein a first diffraction grating diffracts light having the wavelength λ1and transmits light having the wavelengths λ2and λ3and a second diffraction grating transmits light having the wavelength λ1and diffracts light having the wavelength λ3.

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