| 摘要 |
PURPOSE: To enlarge the grating constant of a hologram element and facilitate manufacture of hologram element by using a narrow reflection type diffraction grating on a laser beam dividing, utilizing a hologram element with a trick lens function as a diffraction device of reflected light and reducing a diffraction angle of primary diffracted light. CONSTITUTION: A laser beam generated from a laser diode 1 is divided into three beams, which are reflected by an optical disk 5. And a narrow width reflection type diffraction grating 2 is provided at a fixed position on a same line with the laser diode 1, and a six-divided beam photo-detector 6 is provided on the right bottom end of the reflection type diffraction grating. On the other hand, in the optical path of the laser beam reflected from the optical disk 5, a hologram element 3 having a toric lens function is provided between the objective lens 4 and the reflection type diffraction grating 2. In this case, a diffraction angle α of a positive primary diffracted light 7 is very small due to the narrow width of the reflection type diffraction grating 2. Consequently, a grating constant of the hologram element 3 can be enlarged and the manufacture of the element is facilitated. |
