Achromatic beam shaping prism
AssigneeFuji Photo Optical Co., Ltd.
InventorToshiaki Katsuma
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Abstract
An achromatic beam shaping prism is disclosed which compensates for a fluctuation in oscillating wavelength of a semiconductor laser source of a recording type optical disc system using a single prism having a diffraction grating with a specified pitch so as to make the beam shaping prism achromatic. Two equations are given for specifying the pitch d or d′ of the diffraction grating, depending on whether the diffraction grating is applied to the output surface or the input surface of the prism, respectively.
Claims1
An achromatic beam-shaping prism, which converts the cross section of a beam incident onto an input surface by a given factor in a specific direction, thereby providing a beam shaping function to a beam output from an output surface of the prism, said achromatic beam shaping prism comprising:
- a single prism in which a diffraction grating having a pitch d′ which satisfies the following Equation (2) is formed on an input surface of the prism
- d′[nλ2 sin {sin−1(sin θ4/nλ2)+α}−nλ1 sin{sin−1(sin θ4/nλ1)+α}]=λ1−λ2 Equation (2)
- where
- d′ is the pitch of the diffraction grating at the input surface of the prism,
- λ1 is the reference wavelength of the incident beam,
- λ2 is the wavelength of the incident beam after the change in wavelength of the light source from the reference wavelength,
- nλ1 is the index of refraction of the prism at wavelength λ1,
- nλ2 is the index of refraction of the prism at wavelength λ2,
- θ4 is the angle the output beam makes with the surface normal to the output surface of the prism, and
- α is the apex angle of the prism.
Dependencies are inferred from the claim text.