Process for detecting a focal point in an optical head

Details Process for detecting a focal point in an optical head Process for detecting a focal point in an optical head

1988-10-13

1990-09-04

Nelms, David C.

Radiant energy

Photocells; circuits and apparatus

Photocell controls its own optical systems

369 45, G01J 120

Patent

active

049547020

ABSTRACT:
A method for detecting a focal point uses an optical system which includes a laser diode light source, a beam-splitter prism having three surfaces with one surface perpendicular to luminous flux emanating from a recording medium and another surface inclined relative to the first, an objective lens between the prism and the recording medium, a photodetector, and an apparatus capable of moving the objective lens perpendicular to the recording surface. The method using this apparatus includes the steps of placing the prism so that the incident angle of the flux through the objective lens is less than the emergent angle of the flux from the prism to the photodetector, detecting the intensity of the light, and driving the objective lens in response to an electrical signal.

REFERENCES:
patent: 4482803 (1984-11-01), Lacotte et al.
patent: 4716283 (1987-12-01), Ando
patent: 4778984 (1988-10-01), Nakamura

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