Focus error detection using an equal path length lateral shearin

Details Focus error detection using an equal path length lateral shearin Focus error detection using an equal path length lateral shearin

1992-11-06

1995-08-29

Psitos, Aristotelis

Dynamic information storage or retrieval

With servo positioning of transducer assembly over track...

Optical servo system

369112, 359638, G11B 700

Patent

active

054467101

ABSTRACT:
This invention provides an equal path length lateral shearing interferometer and its implementation in focus detection devices, particularly for optical data storage devices. The interferometer comprises a beamsplitter and two abutting roof prisms. Shifting the placement of a roof prism along an axis orthogonal to the direction of light propagation and to the peak of the roof creates a lateral shear between the two output beams. Rotation a roof prism about this axis produces a tilt between the two output beams. This creates an interference pattern with a rotational orientation which is a function of the focus of the beam impinging on the optical storage medium. A pattern sensor is provided to adjust the focus of the beam in an accurate and dynamic manner.

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Cohen (1987) "Lateral Shearing Interferometer (LSI)" Analysis of Methods For Detecting Focus Error in Optical Data Storage Systems pp. 153-185 (Graduate College-Univ. of Ariz.).
Murty (1978) "Lateral Shearing Interferometers" Optical Shop Testing (Wiley Series in Pure and Applied Optics) pp. 105-148.
Kelsall (1959) "Optical Frequency Response Characteristics in the presence of Spherical Aberration measured by an automatically recording Interferometric Instrument" Proc. Phys. Soc. LXXXIII, 3:465-479.
Saunders (1967) "A Simple, Inexpensive Wavefront Shearing Interferometer" Applied Optics 6(9):1581-1583.
Wyant and Smith (1975) "Interferometer for measuring power distribution of ophthalmic lenses" Applied Optics 14(7):1607-1612.

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