| 摘要 |
PROBLEM TO BE SOLVED: To simply constitute an optical system of a DRAW type optical disk device or a phase transition type optical disk device at a low cost by using two sheets of diffraction grating plates, might dividing luminous flux to data detection light and servo detection light and guiding them to exclusive detectors. SOLUTION: A laser beam 2 reflected from a recording film surface is divided to three pieces of luminous flux by the diffraction grating 21. The luminous flux 2a is a 0-order diffracted light beam, the luminous flux 2b is a +1st-order diffracted light beam and the luminous flux 2c is a -1st-order diffracted light beam, and the luminous flux 2b is equal to the luminous flux 2c in intensity. A bisected diffraction gracing 12 consists of two areas 16 and 17, and the diffraction grating is formed symmetrically for a division line 18. The 0-order diffracted light beam obtained by that the luminous flux 2a passes through the diffraction grating 12 is made incident on the light receiving surfaces a-d of the photodetector 15 through a convex lens 13 and a cylindrical lens 14, and a focus error signal is obtained. Similarly, a track error signal is obtained from the ±1st-order diffracted light beams of the luminous flux 2a. Similarly, a high speed server signal and a high speed information signal are obtained from the 0-order diffracted light beam and the ±1st-order diffracted light beams of the luminous flux 2b and luminous flux 2c through an high speed amplifier 23. |
