Double focal-point magneto-optic pick-up head

Details Double focal-point magneto-optic pick-up head Double focal-point magneto-optic pick-up head

1997-04-16

1998-05-05

Dinh, Tan

Dynamic information storage or retrieval

Storage or retrieval by simultaneous application of diverse...

Magnetic field and light beam

369112, 369109, G11B 700

Patent

active

057485747

ABSTRACT:
A double focal-point magneto-optic pick-up head is provided. This magneto-optic pick-up head reads data from an optical disc by using a diffraction grating to diffract a laser beam into two diffracted beams of equal intensity which are focused on the optical disc at two focal points. One focal point is pinpointed on one groove portion of the optical disc, and the other focal point is pinpointed on one neighboring land portion of the same. This allows the two reflected beams to have a difference in propagation length equal to twice the depth of the land portion. The reflected beams are subsequently diffracted again by the diffraction grating into four beams, two of which are directed to interfere with each other to thereby produce an interference beam representative of a read signal from the optical disc. Since the depth is fixed by manufacture, the difference in propagation length between the two reflected beams from the two focal points on the optical disc can always be maintained at a constant. The interference between the two beams for the read signal is thus precise, allowing the output data from the magneto-optic pick-up head to be reliable.

REFERENCES:
patent: 5270987 (1993-12-01), Kaku et al.
patent: 5570334 (1996-10-01), Kim
patent: 5663940 (1997-09-01), Horimai et al.
patent: 5684762 (1997-11-01), Kubo

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