Optical head chromatically optimized for self-focusing

Details Optical head chromatically optimized for self-focusing Optical head chromatically optimized for self-focusing

1989-11-03

1990-11-27

Nelms, David C.

Radiant energy

Photocells; circuits and apparatus

Photocell controls its own optical systems

369 4424, G01J 120

Patent

active

049738321

ABSTRACT:
A self-focusing optical head of the type used in magneto-optical and optical recording systems for directing a focused laser beam onto a moving recording surface uses a non-achromatized optical path between the laser and recording surface and the laser wavelength (mode) shifts induced by optically coupling reflected laser energy back to the laser cavity to automatically maintain the beam in sharp focus (i.e., self-focus) on the recording surface. A focus servo system including a photodetector positioned in the path of reflected laser energy serves to coarsely position a focusing lens relative to the recording surface. A field lens, used to concentrate reflected laser energy onto the photodetector, is achromatized to compensate for the chromatic aberration between laser and photodetector. Such achromatization allows the focus servo to operate independently of the wavelength (mode) shifts required to achieve self-focusing of the laser beam on the recording surface.

REFERENCES:
patent: 4725721 (1988-02-01), Nakamura et al.
patent: 4815058 (1989-03-01), Nakamura et al.
patent: 4900910 (1990-02-01), Doi

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