Zig-zag-patterned position sensor system

Details Zig-zag-patterned position sensor system Zig-zag-patterned position sensor system

1999-11-12

2002-07-16

Allen, Stephone (Department: 2878)

Radiant energy

Photocells; circuits and apparatus

Photocell controlled circuit

C250S2140RC, C250S559290

Reexamination Certificate

active

06420692

ABSTRACT:

BACKGROUND
The present disclosure relates to determination of a position of an optical spot relative to an optical system.
Optical systems often use position sensing detectors (PSDs) to determine the position of an optical spot that is incident upon the active surface of a device. The optical spot may be a reflected laser beam from the surface of an optical recording medium. The PSD device is constructed using photodetectors, such as photo-diodes or PIN-diodes, in a bi-cell, quadrant or lateral configuration. Signals required for the X and Y displacement of the spot is found by suitably subtracting currents from adjacent cells, followed by normalization to the total intensity of the optical spot. However, with rapid increase in the optical processor speed, the need for faster and more accurate position detectors is desirable.
The PSD device has relatively low output impedance, which often causes offsets when fed to current sensing pre-amplifiers. This may lead to power adjustment problems in a laser beam source during a transition between read and write operations of the optical system. A read operation of an optical system often involves a reflected laser beam modulated with both tracking information and the data stored on the optical recording medium. A write operation involves modulating the laser beam via an optical modulation including beam intensity, phase, and polarization at a laser beam source. Therefore, the transition between these two operations may cause considerable delay in the efficient operation of the optical system.
SUMMARY
An enhanced optical position detector having detector cells is disclosed. The detector cells are connected to each other in a jagged or curved line where segments of the jagged or curved line are interleaved in a saw-tooth shape. The line segments are symmetric about a line drawn through middle of the segments. Each detector cell produces a signal proportional to an amount of light incident on each cell. The signal indicates a location of the optical spot relative to the detector. The saw-tooth shape of the jagged or curved separation line allows the detector to be relatively insensitive to a displacement of the optical spot along a direction of the jagged or curved line.
In another aspect, a differencing element which operates to difference the signals from adjacent detector cells to produce a differencing signal is disclosed. The differencing signal indicates the position of the optical spot.
Other features and advantages will become apparent from the following description and drawings, and from the claims.


REFERENCES:
patent: 6130744 (2000-10-01), Abe et al.
patent: 403108688 (1991-05-01), None

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